Fluidized Bed Combustion Boiler Technology For Cogeneration

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					Technical Study Report on
B    I   O     M     A      S   S        F     I    R    E     D

Fluidized Bed Combustion Boiler Technology
                                          For Cogeneration

 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 II

 About the Technical Study Report

Cleaner Production (CP) and Energy Efficiency (EE) are established and powerful strategies
helping enterprises throughout the world to reduce costs, generate profits by reducing
waste and mitigate climate change. Integration of CP and EE provides synergies that broaden
the scope of their individual application and give more effective results both environmental
and economic.
Implementing CP-EE projects in industries also requires efficient and environment-friendly
technology interventions. Co-generation through fluidized bed combustion (FBC) boiler
using biomass (such as rice husk, straw etc.) is one such proven technology which could help
in mitigation of green house gases emissions.
UNEP-DTIE's Energy Branch is planning to develop a series of technical study reports
covering various specific technologies that can be adopted by the industries all over the
world as a part of their CP-EE initiatives.
This is first such technical study report that documents the various techno-economical and
managerial aspects of biomass-based FBC technology for practical use by the industries in
the regions where large amounts of biomass are available.
The study report provides an overview of FBC technology, co-generation system and
practical aspects of implementing such a system in an industry. A detailed case study
provides insights to the technical specifications of the various equipments, systems and cost
economics. It also provides list of technology providers and suppliers worldwide.
All in all, this technical report is a comprehensive and complete documentation for
implementation of biomass based FBC boiler for co-generation. The technical study report is
targeted to the decision makers, technical personnel in the industry, academia, consultants
as well as government agencies. Specifically, it is very useful for the technical managers in the
industries who would like to implement biomass based co-generation systems in their

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
   Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                                                                                               III


About the Technical Report ..........................................................................................................ii


        List of Tables.................................................................................................................................................................................v

        List of Figures...............................................................................................................................................................................vi

        Abbreviations and Acronyms Used....................................................................................................................................vii

1.0 Introduction ................................................................................................................................ 8

        1.1 Cleaner Production & Energy Efficiency......................................................................................................................8

        1.2 Biomass as a Fuel..................................................................................................................................................................9

        1.3 Biomass Energy Conversion Technologies..............................................................................................................13

2.0 FBC Boiler & Cogeneration Systems................................................................................18

        2.1 FBC Boilers .........................................................................................................................................................................18

        2.2 Cogeneration (Combined Heat & Power)..............................................................................................................26

3.0 Biomass-based FBC and Co-generation Technology ..................................................30

        3.1 Overview of the Technology........................................................................................................................................30

        3.2 Areas of Application ........................................................................................................................................................31

        3.3 Issues in Implementation of Biomass-based Cogeneration Systems ..............................................................32

        3.4 Environmental Benefits of Biomass based cogeneration Systems...................................................................39

        3.5 Social Benefits of Biomass based cogeneration Systems.....................................................................................39

4.0 Implementing Biomass Cogeneration Technology.......................................................41

        4.1 Raw material, Energy Resource requirement.........................................................................................................41

        4.2 Infrastructure Requirement ..........................................................................................................................................43

        4.3 Supporting Technologies................................................................................................................................................44

        4.2 Waste Disposal..................................................................................................................................................................46

        4.5 Human Resources Demand..........................................................................................................................................46

        4.6 Equipment Suppliers.........................................................................................................................................................47

5.0 Case Study.................................................................................................................................49

        5.1 Introduction........................................................................................................................................................................49

   UNEP-DTIE Energy Branch                                                                                                                                     http://www.unep.fr/energy
   Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                                                                              IV

       5.2 Manufacturing Process ....................................................................................................................................................49

       5.3 Baseline Energy Scenario................................................................................................................................................50

       5.4 Implementation of Rice Husk based Cogeneration System..............................................................................51

6.0 Further Suggestions ................................................................................................................58

       6.1 Power Generation using bio-mass in FBC Boiler..................................................................................................58

       6.2 Power Generation through Biomass Gasifier ........................................................................................................59

Annex 1 Block Diagram of Kraft Paper...................................................................................61

Annex 2: Block Diagram of White Duplux Board...............................................................62

Annex 3: Technical Specification of Key Equipment/Components ................................64

   UNEP-DTIE Energy Branch                                                                                                                        http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                                               V

List of Tables

               Table 1 Global Biomass-fuel based Electricity Generation Capacity, 2004                                                       9

               Table 2 Crop Residue from 4 Major Crops in EJ (1987)..........11

               Table 3 : Global Bagasse Residues.........................................................12

               Table 4 Comparison of Different Types of Biomass Conversion Technologies 16

               Table 5: Heat to Power ratios and other parameters of cogeneration systems31

               Table 6 : Typical heat to Power ratio for Certain Energy intensive Industries 32

               Table 7 : Fuels and their typical calorific values............................43

               Table 8 : External Infrastructure Requirements..........................43

               Table 9 : Area requirements for different components of a typical cogeneration

               Table 10 : Supporting Technologies for Cogeneration Systems                                                     44

               Table 11 : Waste Generated in Cogeneration Plant.................46

               Table 12 : Suppliers for Steam Turbine and FBC Boiler........47

               Table 13 : Specifications of the DG sets installed for captive power generative50

               Table 14 : (A) Preliminary & Preoperative Expenses...............53

               Table 15: (B) Cost Involved for procuring Land & Site Development 53

               Table 16 (C): Cost of Civil Works Required...................................53

               Table 17 : (D) Cost of Plant & Machinery Required ..................54

               Table 18: (E.)Repair & Maintenance Cost for Building, Plant & Machinery                                                       54

               Table 19: (F) Additional Manpower required for Co-generation project                                                          54

               Table 20 : Summary of Costs (From A to E) .................................55

               Table 21: Cost Analysis Before and After Implementation of Cogeneration
                  Scheme ..........................................................................................................55

               Table 22 : Greenhouse Gases Emissions Reduction due to Cogeneration 2004-05

 UNEP-DTIE Energy Branch                                                                                             http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                                              VI

List of Figures

               Figure 1: Electricity Generation by Source .....................................10

               Figure 2 Regional Distribution of various Sources of Biomass & its use in EJ /

               Figure 3 Global Agricultural Residues, 1987...................................11

               Figure 4 : Principles of Fluidization .......................................................19

               Figure 5 A View of AFBC Boiler.............................................................20

               Figure 6 : A Detailed View of Different Components of AFBC Boiler 21

               Figure 7 : A CFBC Boiler.............................................................................23

               Figure 8 : Energy Balance of a Typical Thermal Power Plant in India 26

               Figure 9: Configurations of different types of turbine systems27

               Figure 10: Different Configurations of Back Pressure Turbine28

               Figure 11: Configuration of Extraction cum condensing turbine                                                     28

               Figure 12 : Elements of a Biomass Based Cogeneration System using FBC Boiler

               Figure 13: Chipping Machine for Cajurina branches & coconut fronds at Varam
                   Power, India................................................................................................36

               Figure 14 : Collection & Baling Machine for sugarcane trash at GMR technologies,

               Figure 15 : Example on estimation of fuel requirement for co-generation                                                       42

               Figure 16 Annual Production Trend....................................................49

               Figure 17 : Electrical Power requirements trends- Baseline values                                                 51

               Figure 18: Steam requirements trends- Baseline values ........51

               Figure 19: Electrical Power Requirements after Installing the Cogeneration

               Figure 20: Steam Requirements after Installing the Cogeneration System                                                        52

               Figure 21 : Schematics of the Cogeneration System................53

               Figure 22 : Various Biomasses based power plants and their numbers in India 59

               Figure 23 : Biomass Gassifier in Operation .....................................59

 UNEP-DTIE Energy Branch                                                                                                 http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                VII

Abbreviations and Acronyms Used

BBCS                            Biomass based Cogeneration System

CHP                             Combined Heat & Power

CP                              Cleaner Production

CPEE                            Cleaner Production Energy Efficiency

DG sets                         Diesel Generator Set

EJ                               Exa-Jourles (IEJ = 1 x 1018 Joules)

ESP                             Electro static Precipitators

FBC                             Fluidized Bed Combustion

GWh                             Giga Watt hour

H.T.                            High Tension

KVA                             Kilo Volt Ampere

KWth                            Kilo Watts Thermal

KWe                             Kilo Watts electrical

MNRE                            Ministry of New & Renewable Energy, India

MW                              Mega Watt

0C                              Degree Centigrade

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                              8

 1.0 Introduction

1.1 Cleaner Production & Energy Efficiency

For decades UNEP has been championing the concepts and practices of Cleaner
Production (CP) and Energy Efficiency (EE) in a systematic manner. Recognizing the
immense benefits that can be realized by the end-users, UNEP has recently developed
guidelines for integration of CP and EE.
The idea of this integrated approach is to incorporate the energy management principles
into the resource efficiency approach that lies at the heart of CP.
These guidelines have been presented in a form of a manual popularly known as the CP-EE
Manual. This guidance manual is primarily used by facility personnel for conducting in-house
assessments as well as by external consultants.
While managers gain insights into the role they can play in instigating and supporting an
ongoing, cost-effective process for continual improvement leading to both economic and
environmental advantages, CP professionals and consultants (who may not necessarily be
energy specialists) find such guidance on incorporating energy issues into their CP
assessments at industrial or other facilities immensely valuable.
The integrated methodology is derived from the
basic principles of the Deming’s Cycle of Plan
Do      Check       Act – popularly acronymed as
PDCA Cycle. Moreover, it addresses eight
different categories for identifying the options for
resource conservation:
    1. Good housekeeping
    2. Process Optimization
    3. Operation Practices/management
    4. Raw Material Substitutions
    5. New technology
    6. New product design
    7. Onsite recycle and reuse
    8. Recovery of useful by products
As seen from the list above, “New Technology” is one of the most important categories
amongst the CP-EE options. For this, rapid technological advancements in the current times
require the professionals to remain updated about the new technologies that are
continuously evolving in response to the various environmental challenges.
Global warming and Climate change is one of the most pressing and burning issues that
needs urgent global action at all levels. The key to address this problem is by mitigation of
carbon dioxide and other “greenhouse gases” produced by combustion of various fuels (both
fossil and non fossil). Various new technological solutions are being tried and tested around
the world to address this serious problem for the humankind.
This study report highlights the use of one such proven technology viz. “Biomass based
Fluidized Bed Combustion Boilers for Combined Heat and Power Applications” which
could possibly help in addressing the issue of global warming and climate change.

 UNEP-DTIE Energy Branch                                                  http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                      9

1.2 Biomass as a Fuel1

Biomass, the oldest form of renewable energy, has been used for thousands of years.
However, with the emergence of fossil fuels, its relative share of use has declined over past
years. Currently some 13% of the world’s primary energy supply is from biomass, though
there are strong regional differences. Developed countries source around 3% of their energy
from biomass while, in Africa it ranges between 70-90%.
With adverse environmental effects on the environment such as climate change coming to
the forefront, people everywhere are rediscovering the advantages of biomass.
Potential benefits of biomass:
    Reducing carbon emissions if managed (produced, transported, used) in a sustainable
    Enhancing energy security by diversifying energy sources & utilizing local resources
    Reduced problem of biomass waste management
    Possible additional revenues for the agricultural and forestry sectors
Until the industrial revolution, humankind relied almost exclusively on biomass for their
energy needs. Most of the biomass is burnt to provide heat for cooking or warmth. Some is
used for small industrial applications (For instance, Charcoal is used in steelmaking in countries
like Brazil, which have no major coal reserves). A small percentage of biomass is also used to
generate electricity.
    Total biomass consumption at the beginning of the twenty-first century was 55 exa-
    Joules or 55EJ2 out of total global energy consumption of around 400EJ.
    Estimates of the total quantities of biomass available vary widely but could represent up
    to 100EJ of energy.
Biomass energy accounts for around 14% of total primary energy consumption. This bold
figure hides a major disparity between the developed and the developing world. Estimates of
the amount of energy that can be supplied from biomass too vary widely, but according to
some estimates, by 2050 it could provide as much as 50% of global primary energy supply.
Generating electricity from biomass is perhaps one very attractive and easy option to make
use of this valuable resource. It uses exactly the same technology that has become common
in the power generation industry - furnaces to burn coal, boilers to raise steam from the
heat produced and steam turbines to turn the steam into electricity. Table 1 represents the
electricity generation capacity of the world using biomass as fuel.
             Table 1 Global Biomass-fuel based Electricity Generation Capacity, 2004

                                Region             Approx. Installed Capacity (MW)
                                Europe                           8000
                                US                                   7000
                                ASEAN region                         2000
                                Australia                            300
                                Indonesia                            300
                                Philippines                          20
                                Thailand                             1200

                   Biomass, Issue Brief Energy and Climate Change, World Business Council for Sustainable Development
                   1EJ = 1x1018 Joules

 UNEP-DTIE Energy Branch                                                                         http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                           10

In 2000, biomass was the largest renewable energy source for electricity generation - other
than hydro - generating around 1% of the world’s electricity or 167 TWh. However, its
share is and will remain small in comparison to fossil-based sources (see Figure 1).

                                   Figure 1: Electricity Generation by Source

Biomass as a Carbon Neutral Fuel
Use of biomass as a fuel is considered to be carbon neutral because plants and trees remove
carbon dioxide (CO2) from the atmosphere and store it while they grow. Burning biomass in
homes, industrial processes, energy generation, or for transport activities returns this
sequestered CO2 to the atmosphere. At the same time, new plant or tree growth keeps the
atmosphere’s carbon cycle in balance by recapturing CO2.
This net-zero or carbon neutral cycle can be repeated indefinitely, as long as biomass is re-
grown in the next management cycle and harvested for use. The sustainable management
of the biomass source is thus critical to ensuring that the carbon cycle is not interrupted.
In contrast to biomass, fossil fuels such as gas, oil and coal are not regarded as carbon
neutral because they release CO2 which has been stored for millions of years, and do not
have any storage or sequestration capacity.

1.2.1 Sources of Biomass as fuel3

There are a variety of biomass residues available around the world. The most important of
these are crop residues but there are significant quantities of forestry residues and livestock
residues as well, which can also be used for energy production.
Most of the world's crops generate biomass residues that can be used for energy production.
    Wheat, barley and oats all produce copious amounts of straw, which have traditionally
    been burned (approx. 1 - 2 Billion T of crop residues may be burned annually).
    Rice produces both straw in the fields and rice husks at the processing plant which can
    be conveniently and easily converted into energy. (Recent legislation has made straw
    burning illegal in some parts of the world. Since the straw must still be removed from fields,
    such legislation could make it cost effective to convert these residues into energy. )
    When Maize is harvested significant quantities of biomass remain in the field. Much of
    this needs to be returned to the soil but when the harvested maize is stripped from its
    cob the latter remains, more biomass which can easily be converted into energy on-site.

                 Business Insights, The Future of Global Biomass Power Generation: The technology, economics and impact of
               biomass power generation By Paul Breeze, 2004

 UNEP-DTIE Energy Branch                                                                               http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                         11

    Sugar cane harvesting leaves harvest 'trash' in the fields while processing produces
    fibrous bagasse. The latter is a valuable source of energy.
    Harvesting and processing of coconuts produces quantities of shell and fibre that can be
    Peanuts leave shells, which is a great source of biomass energy.

     Figure 2 Regional Distribution of various Sources of Biomass & its use in EJ / annum

                                  Figure 3 Global Agricultural Residues, 1987

Putting figures on the quantities of each of these crops is rather difficult. One estimate is
shown in Table 2 where the total residue from the four major crops listed is equivalent to
32EJ. Another estimate puts the total of crop residues at 65EJ7 while yet another, from 1993,
suggested that utilizing only 25% of the waste from the world's main agricultural crops could
generate 38EJ.
                           Table 2 Crop Residue from 4 Major Crops in EJ (1987)

   REGION             MAIZE STRAW              WHEAT STRAW           RICE STRAW   BAGASSE      TOTAL
   Africa             0.48                     0.25                  0.20         0.54         1.47
   US & Canada        2.95                     1.93                  0.13         0.19         5.20
   Latin America      0.71                     0.38                  0.29         3.58         4.94
   Asia               1.74                     3.65                  8.96         3.19         17.54
   Europe             0.61                     2.39                  0.04         0.00         3.04
   Oceania            0.23                     2.26                  0.06         0.22         2.77
   Total              6.72                     10.86                 9.68         7.72         31.98

 UNEP-DTIE Energy Branch                                                             http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                     12

Varying Estimates
A major problem when estimating the quantity of residues that might be used for energy
production is to determine how much of each is required for other purposes. At least, part
of many crop residues must be returned to the soil to maintain soil quality. Similarly,
livestock residues need to be returned to pastures as manure.
Taking this into account, a recent exercise carried out by US Department of Agriculture
concluded that crop residues alone could provide electricity equivalent to 5% of US
consumption in 2003. Though local factors make direct comparisons with other regions
difficult, a similar contribution might be expected in other parts of the developed world.
Given the high per capita electricity use in the US, developing countries might expect to be
able to find a greater proportion of their electricity in this way.
The figures in Table 2 also suggest that Asia produces the largest quantities of agricultural
residues and there is potential across all the continents. However, mere availability of the
residue does not guarantee its use.
From the perspective of electricity generation, the cost of collection of the residue becomes
the key factor in determining its viability. Wheat straw can be baled, making collection more
efficient. Several European projects have demonstrated that power plants based on straw
can become cost effective when the straw cannot be burned in the fields where it is cut.
Another aspect to consider is the seasonal nature of the harvest, which necessitates the
plants to either have a large storage facility or alternative sources of fuel. Fuels such as rice
husks and maize cobs are produced during processing of these crops. This takes place after
harvesting of the crop, so the waste is already concentrated at a point and is an easily
exploitable source of energy - particularly if it can be utilized on site to provide heat and
Sugar cane bagasse is another valuable source of fuel and one that can be exploited easily
because it, too, is generated during the processing of the cane. Table 3 provides a
breakdown of global bagasse potential from the World Energy Council.
                                         Table 3 : Global Bagasse Residues

                            REGION               QUNATITY OF BAGASSE (,000 MT)
                            Africa                          26025
                            North America                   55279
                            South America                   88881
                            Asia                            131197
                            Europe                            502
                            Middle east                       914
                            Oceania                          19358
                            Total                          322156

The bagasse figures in Table 3 represent only part of the biomass generated during sugar
cane farming. The 'trash' which is left in the fields represents about 55% of the total, and this
is often burned. With efficient collection methods, this could provide a further rich source
of energy, provided minimum required amount is returned to the soil to maintain fertility.
Sugar processing plants have traditionally burned this fuel, generally inefficiently, to generate
process heat which is all used on-site. Modern combined heat and power plants can produce
more energy than is required by the plant itself. According to one estimate, the amount of
surplus electricity that sugar processing plants could generate and export to their local grids
could, by 2025, account for 15%- 20% of the total demand in the developing countries.

 UNEP-DTIE Energy Branch                                                         http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                           13

 Biomass Availability in India and Potential for Co-generation
 Biomass is the traditional fuel in India, used for cooking, and even today, most
 households, in rural India, use it as cooking fuel. This biomass, mostly consists of
 agricultural farm residues (e.g. paddy straw, sugar cane trash etc), agro-industrial
 residues (e.g. paddy husk, coffee husk etc), forests & social forests residues and energy
 plantations, which (i.e. energy plantation) is just picking up. The following Table, provides
 the different types of biomass, that are presently being used in India
                        Biomass varieties presently used in India for Co-generation

        Agro and farm Biomass              Agro-Industrial Biomass   Forest Residues & plantations
        Babul Stems                        Coffee Husk               Fire Wood
        Chilly stalks                      Bagasse                   Forest residues
        Coconut husk                       De oiled bran             Julie Flora
        Coconut Pith                       Ground nut husk           Other woody biomass chips
        Corn cobs                          Ground nut shells
        Cotton Stalk                       Rice Husk
        Maize Stems                        Saw dust
        Mango residues
        Mustard Stalk
        Palm leaf
        Rai Stems
        Sugar Cane Trash
        Tamarind husk
        Til stems
        Casurina branches & fruit

 Indian Ministry of New and Renewable Energy’s Annual Report for 2005-06 indicates
 surplus agro & forest residues of 60 Million MT available for power generation. Further,
 the report also projected an availability of 40 million MT of woody biomass annually,
 from energy plantation, on 4 million hectares of wasteland. Considering plant load factor
 of 70%, the estimated potential for power generation in India alone is 13,000 MW from
 various biomass based sources.

1.3 Biomass Energy Conversion Technologies

There are a number of ways for converting biomass into electricity.
    The simplest approach is to burn the biomass in a furnace, exploiting the heat generated
    to produce steam in a boiler, which is then used to drive a steam turbine. This approach,
    often called direct firing, is the most widespread means of deriving heat and electricity
    from biomass today. It is also generally rather inefficient, though new technologies will
    be able to improve efficiency significantly.
    A simple, direct-fired biomass power plant can either produce electricity alone or it can
    operate as a combined heat and power unit, producing both electricity and heat. This
    latter is common in the textile, food processing, chemical and paper industries where
    the heat is used in the processing plant. The electricity generated is used by the plant

 UNEP-DTIE Energy Branch                                                               http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                   14

    too, with any surplus exported to the grid. Simplicity is the key feature of direct firing
    type of application.
    A more advanced approach is biomass gasification. This employs a partial combustion
    process to convert biomass into a combustible gas. The gas has a lower energy content
    than natural gas. Nevertheless, it can be used in the same way as natural gas. In
    particular it can provide fuel for gas turbines and fuel cells. Biomass gasification is still in
    the development stage but it promises high efficiency and may offer the best option for
    future biomass-based generation.
    An intermediate option for exploiting biomass is to mix it with coal and burn it in a
    coal fired power station. In the short term this may offer the cheapest and most efficient
    means of exploiting biomass. Finally there are number of specialized methods of turning
    biomass wastes into energy. These include digesters, which can convert dairy farm waste
    into a useful fuel gas, and power stations that utilize chicken farm litter, which they burn
    to generate electricity.
In terms of conversion technologies, following technologies are commonly used:
    1. Pile Combustion
    2. Stoker Combustion
    3. Suspension Combustion
    4. Fluidized Bed Combustion
1.3.1 Pile Combustion

The simplest form of direct firing involves a pile burner. This type of burner has a furnace,
which contains a fixed grate inside a combustion chamber. Wood is fed (piled) onto the
grate where it is burned in air, which passes up through the grate (called under-fire air). The
grate of a pile burner is within what is known as the primary combustion chamber where
the bulk of the combustion process takes place.
Combustion at this stage is normally incomplete - there may be significant quantities of both
unburned carbon and combustible carbon monoxide remaining - so further air (called over-
fire air) is introduced into a secondary combustion chamber above the first - where
combustion is completed.
The boiler for raising steam is positioned above this second combustion chamber so that it
can absorb the heat generated during combustion. The heat warms, and eventually boils
water in the boiler tubes, providing steam to drive a steam turbine. From the steam turbine
the steam is condensed and then returned to the boiler so that it can be cycled through the
system again. (In a combined heat and power system, steam will be taken from the steam
turbine outlet to provide heat energy first.)
Wood fuel is normally introduced from above the grate, though sometimes there is a more
complicated arrangement, which feeds fuel from under the grate. The pile burner is capable
of handling wet and dirty fuels but it is extremely inefficient. Boiler efficiencies are typically
There is no means to remove the ash from a pile burner except by shutting down the
furnace. Thus the power plant cannot be operated continuously. Pile burners are also
considered difficult to control and they are slow to respond to changes in energy input. This
means that electricity output cannot easily be changed in response to changes in demand.
Power generation in a pile-burner based power station will usually involve a single pass
steam turbine generator operating at a relatively low steam temperature and pressure. This
adds to the relatively low efficiency of the power plant, which can operate, with an overall
efficiency as low as 20%.

 UNEP-DTIE Energy Branch                                                       http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 15

1.3.2 Stoker Combustion

The pile burner represents the traditional method of burning wood. However, its basic
operation can be improved by introducing a moving grate or stoker. This allows continuous
removal of ash so that the plant can be operated continuously. Fuel can also be spread more
thinly on the grate, encouraging more efficient combustion.
The first US stoker grate for wood combustion was introduced by the Detroit Stoker Co. in
the 1940s. In this type of furnace, combustion air still enters below the grate of a stoker
burner. This flow of air into the combustion chamber helps cool the grate. The air flow and
consequent grate temperature determines the maximum operating temperature of the
combustor. This, in turn, determines the maximum moisture content allowable in the wood
fuel if combustion is to proceed spontaneously.
There are refinements of the basic stoker grate such as inclined grates and water-cooled
grates, both of which can help improve overall performance and make the operation less
sensitive to fuel moisture. Nevertheless stoker combustors are still relatively inefficient, with
boiler efficiencies of 65%-75% and overall efficiencies of 20%-25%.
1.3.3 Suspension Combustion

Most modern coal-fired power stations burn pulverized coal, which is blown into the
combustion chamber of a power plant through a specially designed burner. The burner
mixes air with the powdered coal, which then burns in a flame in the body of the
combustion chamber. This is suspension combustion and in this type of plant there is no
grate. Finely ground wood, rice husk, bagasse, or sawdust can be burned in a similar way.
Suspension firing requires a special furnace. The size and moisture content of the biomass
(wood) must also be carefully controlled. Moisture content should be below 15% and the
biomass particle size has to be less than 15mm. Suspension firing results in boiler efficiency
of up to 80% and allows a smaller sized furnace for a given heat output.
However it also requires extensive biomass drying and processing facilities to ensure that
the fuel is of the right consistency. It also demands special furnace burners. A small number
of plants designed to burn biomass in this way have been built. The technology is also of
great interest as the basis for the co-firing of wood or other biomass with coal in pulverized
coal plants.
1.3.4 Fluidized Bed Combustion

Aside from suspension firing of wood, the most efficient method of directly burning biomass
is in a fluidized bed combustor (FBC). This is also the most versatile since the system can
cope with a wide range of fuels and a range of moisture contents.
The basis for a FBC system is a bed of an inert mineral such as sand or limestone through
which air is blown from below. The air is pumped through the bed in sufficient volume and
at a high enough pressure to entrain the small particles of the bed material so that they
behave much like a fluid.
The combustion chamber of a fluidized bed plant is shaped so that above a certain height the
air velocity drops below that necessary to entrain the particles. This helps retain the bulk of
the entrained bed material towards the bottom of the chamber. Once the bed becomes hot,
combustible material introduced into it will burn, generating heat as in a more conventional
furnace. The proportion of combustible material such as biomass within the bed is normally
only around 5%.
There are different designs of FBC system which involve variations around this principle. The
most common for biomass combustion is the circulating fluidized bed which incorporates a

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                          16

cyclone filter to separate solid material from the hot flue gases which leave the exhaust of
the furnace. The solids from the filter are re-circulated into the bed, hence the name.
The fluidized bed has two distinct advantages for biomass combustion: First, it is the ability
to burn a variety of different fuels without affecting performance. Second is the ability to
introduce chemical reactants into the fluidized bed to remove possible pollutants. In FBC
plants burning coal, for example, limestone can be added to capture sulphur and prevent its
release to the atmosphere as sulphur dioxide. Biomass tends to contain less sulphur than
coal so this strategy may not be necessary in a biomass plant.
A fluidized bed boiler can burn wood with up to 55% moisture. One specialized application
is in plants designed to burn chicken litter, the refuse from the intensive farming of poultry.
Power stations have been built that are devoted specifically to this fuel source and these
plants use FBCs.
Of the four different types of combustion technologies discussed above, the FBC technology
is best suited for a range of small and medium scale operation for combined heat and power.
With technological advancements the FBC boilers give efficiency of as high as 80-82% and
can be used for a wide variety of fuels.
1.3.4 Comparison of Different Types of Biomass Conversion Technologies

Table 4 below compiles a quick Comparison of Different Types of Biomass Conversion
Technologies commonly used worldwide.
            Table 4 Comparison of Different Types of Biomass Conversion Technologies

Parameter         Pile Combustion               Stoker Combustion         Suspension                   Fluidized Bed
                                                                          Combustion                   Combustion
Grate             Fixed / Stationary Grate      Fixed or moving grate     No grate or moving           No grate
Fuel Size         Uniform size of the fuel      Uneven fuel size can be   Preferable for high %        Uniform size fuel in
                  in the range of range 60      used                      of fins in the fuel          the range of 1 to 10
                  to 75 mm is desired &                                                                mm.
                  % fines should not be
                  more than 20%
Combustion        Difficult to maintain         The combustion is         It is similar to stoker      Best combustion takes
                  good combustion due           better & an improved      combustion, but since        place in comparison
                  to :                          version of pile           the fuel sizes is small &    with the other types
                     Air fuel mixing is not     combustion. Since         even the combustion          since the fuel particles
                     proper                     most of the fuel is       efficiency is improved       are in fluidized state &
                     Bed height is in           burnt in suspension the   as maximum amount            there is adequate
                     stationary condition       heavier size mass falls   of fuel is combusted         mixing of fuel & air.
                     resulting in clinker       on the grate. If the      during suspension.
                     formation                  system has a moving
                     Difficult to avoid air     grate the ash is
                     channeling                 removed on a
                     Due to intermittent        continuous basis &
                     ash removal system it      therefore the chances
                     is difficult to maintain   of clinker formation
                     good combustion            are less.
Bed               1250- 1350 ºC                 1000- 1200 ºC             1250- 1350 ºC                800- 850 ºC
Moisture          High moisture leads to        Combustion condition      Same as Stoker               It can handle fuels with
                  bed choking & difficult       not very much             Combustion                   high moisture
                  combustion conditions         disturbed with 4-5 %                                   condition up to 45-
                                                increase in moisture                                   50% but high moisture
                                                                                                       in the fuels is not
                                                                                                       desirable, & adequate
                                                                                                       precautions are to be
                                                                                                       taken up in the design
                                                                                                       stage itself.

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                     17

Parameter         Pile Combustion               Stoker Combustion        Suspension               Fluidized Bed
                                                                         Combustion               Combustion
Draft             Natural Draft / Forced        Forced Draft / Balance   Balance draft            Balance draft
Conditions        Draft/ Balance Draft          draft
Maintenance       Not much maintenance          Frequent problems        Variation in fines in    Erosion of boiler tubes
                  problems                      due to moving grate      fuel leads to delayed    embedded in the bed
                                                                         combustion thereby       is quite often
                                                                         affecting the boiler

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                    18

 2.0 FBC Boiler & Cogeneration Systems

2.1 FBC Boilers4

2.1.1 Introduction to FBC Boilers

The traditional grate fuel firing systems have several limitations and hence are techno-
economically unviable to meet the challenges of the future. FBC has emerged as a viable
alternative as it has significant advantages over conventional firing system.
FBC offers multiple benefits, such as: compact boiler design, flexibility with fuel used, higher
combustion efficiency and reduced emissions of noxious pollutants such as SOx and NOx.
The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse and other
agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over
100 T/hr.
2.1.2 Mechanism of Fluidized Bed Combustion

When an evenly distributed air or gas is passed upward through a finely divided bed of solid
particles such as sand supported on a fine mesh, the particles remain undisturbed at low
velocities. As the air velocity is gradually increased, a stage is reached when the individual
particles are suspended in the air stream and the bed is called “fluidized”.
With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid
mixing and formation of dense defined bed surface. The bed of solid particles exhibits the
properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”.
At higher velocities, bubbles disappear, and particles are blown out of the bed. Therefore,
some amounts of particles have to be re-circulated to maintain a stable system and is called
as “circulating fluidized bed". This principle of fluidization is illustrated in Figure 4.
Fluidization depends largely on the particle size and the air velocity. The mean solids velocity
increases at a slower rate than does the gas velocity. The difference between the mean solid
velocity and mean gas velocity is called as slip velocity. Maximum slip velocity between the
solids and the gas is desirable for good heat transfer and intimate contact. If sand particles in
fluidized state are heated to the ignition temperatures of fuel (rice husk, coal or bagasse),
and fuel is injected continuously into the bed, the fuel will burn rapidly and the bed attains a
uniform temperature.
The fluidized bed combustion (FBC) takes place at about 840°C to 950°C. Since this
temperature is much below the ash fusion temperature, melting of ash and associated
problems are avoided. The lower combustion temperature is achieved because of high
coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of
heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity
is maintained between minimum fluidization velocity and particle entrainment velocity. This
ensures a stable operation of the bed and avoids particle entrainment in the gas stream.

                Energy Efficiency in Thermal Utilities, A Guide Book for Energy Managers and Auditors, Bureau of Energy
               Efficiency, Ministry of Power, Government of India, 2005

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                           19

 Fixing, Bubbling & Fast Fluidized Beds: As the velocity of a gas flowing through a bed of particles
 increases, a value is reaches when the bed fluidizes and bubbles form as in a boiling liquid. At higher
 velocities the bubbles disappear; and the solids are rapidly blown out of the bed and must be recycled to
 maintain a stable system.
                                         Figure 4 : Principles of Fluidization

Any combustion process requires three “T”s - that is Time, Temperature and Turbulence. In
FBC, turbulence is promoted by fluidization. Improved mixing generates evenly distributed
heat at lower temperature. Residence time is many times higher than conventional grate
firing. Thus an FBC system releases heat more efficiently at lower temperatures. Since
limestone can also be used as particle bed (in case the fuel with sulphur content is used),
control of SOx and NOx emissions in the combustion chamber is achieved without any
additional control equipment. This is one of the major advantages over conventional boilers.
2.1.3 Types of Fluidized Bed Combustion Boilers

There are three basic types of fluidized bed combustion boilers:
1. Atmospheric Fluidized Bed Combustion System (AFBC)
2. Atmospheric circulating (fast) Fluidized Bed Combustion system (CFBC)
3. Pressurized Fluidized Bed Combustion System (PFBC).

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                20 AFBC / Bubbling Bed
AFBC is one of the most important types of FBC boilers as it can be used for variety of fuels
- such as agricultural residues like rice husk or bagasse and even low quality coal. This type
of boiler find use in industries where there is a possibility of having a combined heat and
power generation application.
In AFBC boilers the fuel is sized depending on the type of fuel (in case of coal, the coal is
crushed to a size of 1 – 10 mm depending on the grade of coal) and the type of fuel feeding
system and is fed into the combustion chamber.
The atmospheric air, which acts as both the fluidization air and combustion air, is delivered
at a pressure and flows through the bed after being preheated by the exhaust flue gases. The
velocity of fluidizing air is in the range of 1.2 to 3.7 m /sec. The rate at which air is blown
through the bed determines the amount of fuel that can be reacted.
Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubes in the bed of limestone,
sand and fuel for extracting the heat from the bed to maintain the bed temperature. The bed
depth is usually 0.9 m to 1.5 m deep and the pressure drop averages about 1 inch of water
per inch of bed depth. Very little material leaves the bubbling bed – only about 2 to 4 kg of
solids is recycled per ton of fuel burned. Typical fluidized bed combustors of this type are
shown in Figures 5 and 6.

                                           Figure 5 A View of AFBC Boiler

The combustion gases pass over the super heater sections of the boiler, flow past the
economizer, the dust collectors and the air pre-heaters before being exhausted to
atmosphere. The main special feature of atmospheric fluidized bed combustion is the
constraint imposed by the relatively narrow temperature range within which the bed must
be operated. With coal, there is risk of clinker formation in the bed if the temperature
exceeds 950°C and loss of combustion efficiency if the temperature falls below 800°C. For
efficient sulphur retention, the temperature should be in the range of 800°C to 850°C.
General Arrangements of AFBC Boiler
AFBC boilers comprise of following systems:
    Fuel feeding system
    Air distributor

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                              21

    Bed & In-bed heat transfer surface
    Ash handling system.
Many of these are common to all types of FBC boilers.

                Figure 6 : A Detailed View of Different Components of AFBC Boiler

a) Fuel Feeding System
For feeding fuel and adsorbents like limestone or dolomite, usually two methods are
followed: under bed pneumatic feeding and over-bed feeding.
    Under Bed Pneumatic Feeding
    If the fuel is coal, it is crushed to 1–6 mm size and pneumatically transported from feed
    hopper to the combustor through a feed pipe piercing the distributor. Based on the
    capacity of the boiler, the number of feed points is increased, as it is necessary to
    distribute the fuel into the bed uniformly.
    Over-Bed Feeding
    The crushed coal, 6–10 mm size is conveyed from coal bunker to a spreader by a screw
    conveyor. The spreader distributes the coal over the surface of the bed uniformly. This
    type of fuel feeding system accepts over size fuel also and eliminates transport lines,
    when compared to under-bed feeding system. Now a days for rise husk and other
    agricultural residues Over bed feeding system is quite prominent and economical. Some
    of the boilers are so designed that they have both types of feeding systems.
b) Air Distributor
The purpose of the distributor is to introduce the fluidizing air evenly through the bed cross
section thereby keeping the solid particles in constant motion, and preventing the formation
of de-fluidization zones within the bed. The distributor, which forms the furnace floor, is

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                22

normally constructed from metal plate with a number of perforations in a definite geometric
pattern. The perforations may be located in simple nozzles or nozzles with bubble caps,
which serve to prevent solid particles from flowing back into the space below the distributor.
The distributor plate is protected from high temperature of the furnace by:
          Refractory Lining
          A Static Layer of the Bed Material or
          Water Cooled Tubes.
c) Bed & In-Bed Heat Transfer Surface:
    The bed material can be sand, ash, crushed refractory or limestone, with an average size
    of about 1 mm. Depending on the bed height these are of two types: shallow bed and
    deep bed. At the same fluidizing velocity, the two ends fluidize differently, thus affecting
    the heat transfer to an immersed heat transfer surfaces. A shallow bed offers a lower
    bed resistance and hence a lower pressure drop and lower fan power consumption. In
    the case of deep bed, the pressure drop is more and this increases the effective gas
    velocity and also the fan power.
    In-Bed Heat Transfer Surface
    In a fluidized in-bed heat transfer process, it is necessary to transfer heat between the
    bed material and an immersed surface, which could be that of a tube bundle, or a coil.
    The heat exchanger orientation can be horizontal, vertical or inclined. From a pressure
    drop point of view, a horizontal bundle in a shallow bed is more attractive than a vertical
    bundle in a deep bed. Also, the heat transfer in the bed depends on number of
    parameters like (i) bed pressure (ii) bed temperature (iii) superficial gas velocity (iv)
    particle size (v) Heat exchanger design and (vi) gas distributor plate design.
d) Ash Handling System
    i) Bottom Ash Removal
    In the FBC boilers, the bottom ash constitutes roughly 30 – 40 % of the total ash, the
    rest being the fly ash. The bed ash is removed by continuous over flow to maintain bed
    height and also by intermittent flow from the bottom to remove over size particles,
    avoid accumulation and consequent defluidization. While firing high ash coal such as
    washery rejects, the bed ash overflow drain quantity is considerable so special care has
    to be taken.
    ii) Fly Ash Removal
    The amount of fly ash to be handled in FBC boiler is relatively very high, compared to
    conventional boilers. This is due to elutriation of particles at high velocities. Fly ash
    carried away by the flue gas is removed in number of stages; firstly in convection section,
    then from the bottom of air pre-heater/economizer and finally a major portion is
    removed in dust collectors.
    The types of dust collectors used are cyclone, bag filters, electrostatic precipitators
    (ESP’s) or some combination of all of these. To increase the combustion efficiency,
    recycling of fly ash is practiced in some units. Circulating Fluidized Bed Combustion (CFBC)

Circulating Fluidized Bed Combustion (CFBC) technology has evolved from conventional
bubbling bed combustion as a means to overcome some of the drawbacks associated with
conventional bubbling bed combustion (see Figure 7).

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                               23

                                                Figure 7 : A CFBC Boiler

CFBC technology utilizes the fluidized bed principle in which crushed (6 –12 mm size) fuel
and limestone are injected into the furnace or combustor. The particles are suspended in a
stream of upwardly flowing air (60-70% of the total air), which enters the bottom of the
furnace through air distribution nozzles. The fluidizing velocity in circulating beds ranges
from 3.7 to 9 m/sec. The balance of combustion air is admitted above the bottom of the
furnace as secondary air. The combustion takes place at 840-900 °C, and the fine particles
(<450 microns) are elutriated out of the furnace with flue gas velocity of 4–6 m/s.
The particles are then collected by the solids separators and circulated back into the furnace.
Solid recycle is about 50 to 100 kg per kg of fuel burnt. There are no steam generation tubes
immersed in the bed. The circulating bed is designed to move a lot more solids out of the
furnace area and to achieve most of the heat transfer outside the combustion zone –
convection section, water walls, and at the exit of the riser. Some circulating bed units even
have external heat exchanges. The particles circulation provides efficient heat transfer to the
furnace walls and longer residence time for carbon and limestone utilization.
The controlling parameters in the CFB combustion process are temperature, residence time
and turbulence. For large units, the taller furnace characteristics of CFBC boiler offers
better space utilization, greater fuel particle and adsorbent residence time for efficient
combustion and SO2 capture, and easier application of staged combustion techniques for
NOx control than AFBC generators.

 UNEP-DTIE Energy Branch                                                   http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                    24

CFBC boilers are said to achieve better calcium to sulphur utilization – 1.5 to 1 vs. 3.2 to 1
for the AFBC boilers, although the furnace temperatures are almost the same.
CFBC requires huge mechanical cyclones to capture and recycle the large amount of bed
material, which requires a tall boiler. A CFBC could be good choice if the following
conditions are met.
          Capacity of boiler is large to medium
          Sulphur emission and NOx control is important
          The boiler is required to fire low-grade fuel or fuel with highly fluctuating fuel quality.
Major performance features of the CFBC system are as follows:
          It has a high processing capacity because of the high gas velocity through the system.
          The temperature of about 870°C is reasonably constant throughout the process
          because of the high turbulence and circulation of solids. The low combustion
          temperature also results in minimal NOx formation.
          Sulphur present in the fuel is retained in the circulating solids in the form of calcium
          sulphate and removed in solid form. The use of limestone or dolomite adsorbents
          allows a higher sulfur retention rate, and limestone requirements have been
          demonstrated to be substantially less than with bubbling bed combustor.
          The combustion air is supplied at 1.5 to 2 psig (pounds per square inch gauge) rather
          than 3–5 psig as required by bubbling bed combustors.
          It has high combustion efficiency.
          It has a better turndown ratio than bubbling bed systems.
          Erosion of the heat transfer surface in the combustion chamber is reduced, since the
          surface is parallel to the flow. In a bubbling bed system, the surface generally is
          perpendicular to the flow.
CFBC boilers are generally claimed to be more economical than AFBC boilers
for industrial application requiring more than 75 - 100 T/hr of steam, therefore
this type of boilers is beyond the scope of the document. Pressurized Fluid Bed Combustion Boiler

Pressurized Fluidized Bed Combustion (PFBC) is a variation of FBC technology that is meant
for large-scale coal burning applications. In PFBC, the bed vessel is operated at pressure up
to 16 ata ( 16 kg/cm2). The off-gas from the FBC drives the gas turbine. The steam turbine is
driven by steam raised in tubes immersed in the fluidized bed. The condensate from the
steam turbine is pre-heated using waste heat from gas turbine exhaust and is then taken as
feed water for steam generation.
The PFBC system can be used for cogeneration or combined cycle power generation. By
combining the gas and steam turbines in this way, electricity is generated more efficiently
than in conventional system. The overall conversion efficiency is higher by 5% to 8%.
PFBC Boiler is beyond the scope of this document

2.1.4 Advantages of FBC Boilers

1. High Efficiency: FBC boilers can burn fuel with a combustion efficiency of over 95%
   irrespective of ash content. FBC boilers can operate with overall efficiency of 84% (±2%).
2. Reduction in Boiler Size: High heat transfer rate over a small heat transfer area
   immersed in the bed results in overall size reduction for the boiler.

 UNEP-DTIE Energy Branch                                                        http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                25

3. Fuel Flexibility: FBC boilers can be operated efficiently with a variety of fuels. Even
   fuels like flotation slimes, washer rejects, agro waste can be burnt efficiently. These can
   be fed either independently or in combination with coal into the same furnace.
4. Ability to Burn Low Grade Fuel: FBC boilers would give the rated output even with
   an inferior quality fuel. The boilers can fire coals with ash content as high as 62% and
   having calorific value as low as 2,500 kCal/kg. Even carbon content of only 1% by weight
   can sustain the fluidized bed combustion.
5. Ability to Burn Fines: Coal containing fines below 6 mm can be burnt efficiently in
   FBC boiler, which is very difficult to achieve in conventional firing system.
6. Pollution Control: SO2 formation can be greatly minimized by addition of limestone
   or dolomite for high sulphur coals (3% limestone is required for every 1% sulphur in the
   coal feed). Low combustion temperature eliminates NOx formation.
7. Low Corrosion and Erosion: The corrosion and erosion effects are less due to lower
   combustion temperature, softness of ash and low particle velocity (around 1 m/sec).
8. Easier Ash Removal – No Clinker Formation: Since the temperature of the
   furnace is in the range of 750 – 900 °C in FBC boilers, even coal of low ash fusion
   temperature can be burnt without clinker formation. Ash removal is easier as the ash
   flows like liquid from the combustion chamber. Hence less manpower is required for ash
9. Less Excess Air – Higher CO2 in Flue Gas: The CO2 in the flue gases will be of the
   order of 14 – 15% at full load. Hence, the FBC boiler can operate at low excess air -
   only 20 - 25%.
10. Simple Operation, Quick Start-Up: High turbulence of the bed facilitates quick
    start up and shut down. Full automation of start up and operation using reliable
    equipment is possible.
11. Fast Response to Load Fluctuations: Inherent high thermal storage characteristics
    can easily absorb fluctuation in fuel feed rates. Response to changing load is comparable
    to that of oil fired boilers.
12. No Slagging in the Furnace – No Soot Blowing: In FBC boilers, volatilization of
    alkali components in ash does not take place and the ash is non sticky. This means that
    there is no slagging or soot blowing.
13. Provisions of Automatic Coal and Ash Handling System: Automatic systems for
    coal and ash handling can be incorporated, making the plant easy to operate comparable
    to oil or gas fired installations.
14. Provision of Automatic Ignition System: Control systems using micro-processors
    and automatic ignition equipment give excellent control with minimum supervision.
15. High Reliability: The absence of moving parts in the combustion zone results in a high
    degree of reliability and low maintenance costs.
16. Reduced Maintenance: Routine overhauls are infrequent and high efficiency is
    maintained for long periods.
17. Quick Responses to Changing Demand: FBC can respond to changing heat
    demands more easily than stoker fired systems. This makes it very suitable for
    applications such as thermal fluid heaters, which require rapid responses.
18. High Efficiency of Power Generation: By operating the fluidized bed at elevated
    pressures, it can be used to generate hot pressurized gases to power a gas turbine. This can
    be combined with a conventional steam turbine to improve the efficiency of electricity
    generation resulting in a potential fuel savings of at least 4%.

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                26

2.2 Cogeneration (Combined Heat & Power)

Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation
of two different forms of useful energy - typically mechanical energy and thermal energy -
from a single primary energy source.
Mechanical energy may be used to drive an alternator for producing electricity, or rotating
equipment such as motor, compressor, pump or fan for delivering various services. Thermal
energy can be used either for direct process applications or for indirectly producing steam,
hot water, hot air for dryer or chilled water for process cooling.
Cogeneration provides a wide range of technologies for application in various domains of
economic activities. The overall efficiency of energy use in cogeneration mode can be up to
85 per cent - and even above in some cases. Along with the saving of fossil fuels,
cogeneration also helps reducing the emissions of greenhouse gases (particularly CO2
2.2.1 Need for Cogeneration

Thermal power plants are a major source of electricity worldwide. The conventional
method of power generation and supply to the customer is wasteful in the sense that only
about a third of the primary energy fed into the power plant is actually made available to the
user in the form of electricity (Figure 8).

                 Figure 8 : Energy Balance of a Typical Thermal Power Plant in India

The major source of loss in the conversion process is the heat rejected to the surrounding water
or air due to the inherent constraints of the different thermodynamic cycles employed in power
generation. Also further losses of around 10–15% are associated with the transmission and

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                        27

distribution of electricity in the electrical grid. In cogeneration, the production of electricity being
on-site, the burden on the utility network is reduced and the transmission line losses eliminated.
Cogeneration therefore makes sense from both macro and micro perspectives. At the
macro level, it allows a part of the financial burden of the national power utility to be shared
by the private sector; in addition, indigenous energy sources are conserved. At the micro
level, the overall energy bill of the users can be reduced, particularly when there is a
simultaneous need for both power and heat at the site, and a rational energy tariff can be
practiced in the country.

2.2.2 Steam Turbines

Steam turbines are the most commonly employed prime movers for cogeneration
applications. In the steam turbine, the incoming high pressure steam is expanded to a lower
pressure level, converting the thermal energy of high pressure steam to kinetic energy
through nozzles and then to mechanical power through rotating blades. The different types
of steam turbine include extraction cum condensing type and back pressure steam turbines.




     Fuel                                                            Boiler                                 Condenser

        Boiler                                                                 Process

                          Process                                                                             Cooling Water

                  (i) Back-Pressure Turbine                                      (ii) Extraction -Condensing Turbine

                      Figure 9: Configurations of different types of turbine systems Back Pressure Turbine
In this type of turbines, steam enters the turbine chamber at high pressure and expands to
low or medium pressure. Enthalpy difference is used for generating power/work. Depending
on the pressure (or temperature) levels at which process steam is required, backpressure
steam turbines can have different configurations as shown in Figure 10.
In extraction and double extraction backpressure turbines, some amount of steam is
extracted from the turbine after being expanded to a certain pressure level. The extracted
steam meets the heat demands at pressure levels higher than the exhaust pressure of the
steam turbine.
The efficiency of a backpressure steam turbine cogeneration system is the highest. In cases
where 100 per cent backpressure exhaust steam is used, the only inefficiencies are gear
drive and electric generator losses, and the inefficiency of steam generation. Therefore, with
an efficient boiler, the overall thermal efficiency of the system could reach as much as 90 per

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                28

               High Pressure Steam                        Extracted Steam              Exhaust Steam

 (I) Simple Back Pressure                    (II) Extaction Back Pressure              (III) Double Extraction
                                                                                            Back Pressure

                      Figure 10: Different Configurations of Back Pressure Turbine Extraction Condensing Turbine
In this type, steam entering at high / medium pressure is extracted at an intermediate
pressure in the turbine for process use while the remaining steam continues to expand and
condenses in a surface condenser and work is done till it reaches the condensing pressure
In extraction-cum-condensing steam turbine as shown in figure 11, high pressure steam
enters the turbine and passes out from the turbine chamber in stages. In the process of two-
stage extraction cum condensing turbine MP steam and LP steam pass out to meet the
process needs. Balance quantity condenses in the surface condenser. The energy difference
is used for generating power. This configuration meets the heat-power requirement of the

                               Steam                         Steam
                              Generator                      Turbine        G


                                        Feed Water                              Condenser

                    Figure 11: Configuration of Extraction cum condensing turbine

The extraction condensing turbines have higher power to heat ratio in comparison with
back pressure turbines. Although condensing systems need more auxiliary equipment such
as the condenser and cooling towers, better matching of electrical power and heat demand
can be obtained where electricity demand is much higher than the steam demand and the
load patterns are highly fluctuating.
The overall thermal efficiency of an extraction condensing turbine cogeneration system is
lower than that of back pressure turbine system, basically because the exhaust heat cannot
be utilized (it is normally lost in the cooling water circuit). However, extraction condensing
cogeneration systems have higher electricity generation efficiencies.

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                29

2.2.3 Factors Influencing Cogeneration Choice

The selection and operating scheme of a cogeneration system is very much site-specific and
depends on several factors, as described below: Base Electrical Load Matching

In this configuration, the cogeneration plant is sized to meet the minimum electricity demand
of the site based on the historical demand curve. The rest of the needed power is purchased
from the utility grid. The thermal energy requirement of the site could be met by the
cogeneration system alone or by additional boilers. If the thermal energy generated with the
base electrical load exceeds the plant’s demand and if the situation permits, excess thermal
energy can be exported to neighboring customers. Base Thermal Load Matching

Here, the cogeneration system is sized to supply the minimum thermal energy requirement
of the site. Stand-by boilers or burners are operated during periods when the demand for
heat is higher. The prime mover installed operates at full load at all times. If the electricity
demand of the site exceeds that which can be provided by the prime mover, then the
remaining amount can be purchased from the grid. Likewise, if local laws permit, the excess
electricity can be sold to the power utility. Electrical Load Matching

In this operating scheme, the facility is totally independent of the power utility grid. All the
power requirements of the site, including the reserves needed during scheduled and
unscheduled maintenance, are to be taken into account while sizing the system. This is also
referred to as a “stand-alone” system. If the thermal energy demand of the site is higher than
that generated by the cogeneration system, auxiliary boilers are used. On the other hand,
when the thermal energy demand is low, some thermal energy is wasted. If there is a
possibility, excess thermal energy can be exported to neighboring facilities. Thermal Load Matching

The cogeneration system is designed to meet the thermal energy requirement of the site at
any time. The prime movers are operated following the thermal demand. During the period
when the electricity demand exceeds the generation capacity, the deficit can be
compensated by power purchased from the grid. Similarly, if the local legislation permits,
electricity produced in excess at any time may be sold to the utility.

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
     Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                              30

     3.0 Biomass-based FBC and Co-generation Technology

This technical study report is on the use of rice husk as a fuel in an FBC boiler to
generate medium to high pressure steam and using this steam to generate electricity by a
steam turbine and also use part of the steam in the manufacturing process in the industry.
In the preceding sections different types of FBC boilers, steam turbines and their
configurations have been discussed in detail to develop a thorough understanding of the
equipments used in the process. The contexts in the other sections are with reference to
this specific technology only. Although numerous configurations are possible, but for small
and medium scale of operations the following four are the main configurations
i)      Steam generation using FBC boiler and no electricity generation
ii) Steam generation using FBC boiler and electricity generation using Backpressure type of
iii) Steam generation using FBC boiler and electricity generation using Extraction cum
     condensing type of turbine
iv) Steam generation using FBC boiler and electricity generation using condensing type of
    turbine with no steam used in process
The fourth case is rarely used by the industries and is more applicable to the thermal power
plants which use biomass as a fuel and FBC boilers for steam generation. The configurations
of system and the design of the boiler and the turbine are wholly dependent on the site
specific requirements and a detailed feasibility analysis needs to be conducted to determine
the correct configuration and the design parameters. Beside this, the choice is also governed
by other factors like, economic feasibility, fuel availability, electricity availability, etc. For
example if the cost and availability of the grid electricity supply is satisfactory, industries
rarely go for co-generation systems and just settle for steam generation by a FBC boiler
(Case i).
The most important parameters which helps us to determine the choice of technology
implementation between Case ii and iii are, the steam quantity and steam pressure
requirements in the process house. Beside this a choice has to be made as per section 2.2.3
3.1 Overview of the Technology

The overall working of the technology with major process steps and equipments with inputs
and outputs is depicted in Figure 12. The process steps may vary from site to site depending
on the nature and quality of Biomass, the type of system and the local environmental

     UNEP-DTIE Energy Branch                                                  http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                     31

                     Biomass                       Baling of               Storage of                Sizing of
                       from                       Biomass at               Biomass at               Biomass if
                       Field                         Site                     Site                   required

                     Raw Water                       Water
                                                  Treatment                                         Mixing of

                                                  Plant (DM)                                        Biomass if
          Condensate to Boiler                                                                       required

                                                               High           FBC
                                                                                                      Bottom Ash
                                                             Pressure        BOILER

                             TURBINE                     G
    Low Pressure Steam                                                              ESP                  Fly Ash

     Pressure Steam                                                     Clean Flue Gases to
       to Process                                                            Chimney

        Figure 12 : Elements of a Biomass Based Cogeneration System using FBC Boiler

3.2 Areas of Application

The cogeneration technology can be adopted in various industrial sectors such as textile,
pulp and paper, brewery, food processing etc.). The first and basic requirement for
implementation of cogeneration system is that the industry must require both steam and
electrical power in its operations.
The ratio of the heat value of the steam required to the electricity required is known as
heat to power ratio and is one of the most important factor which helps to decide the type
and configuration of the cogeneration systems to be installed.
Heat to Power Ratio is defined as the ratio of thermal energy to electricity required by the
energy consuming facility. It can be expressed in different units such as Btu/kWh, kcal/kWh,
lb./hr/kW, etc. The heat-to-power ratio of a facility should match with the characteristics of
the cogeneration system to be installed. Basic heat-to-power ratios of the different
cogeneration systems are shown in Table 5 along with other technical parameters. The
steam turbine cogeneration system can offer a large range of heat-to- power ratios.
          Table 5: Heat to Power ratios and other parameters of cogeneration systems

            Cogeneration System            Heat-to-power ratio          Power output (as per        Overall efficiency
                                                (kWth / kWe)              cent of fuel input)             (per cent)
           Back-pressure steam                     4.0-14.3                     14 - 28                    84 – 92
           Extraction- Condensing                  2.0- 10.0                   22 – 40                     60 - 80

Cogeneration is likely to be most attractive under the following circumstances:
          The demand for both steam and power is balanced i.e. consistent with the range of
          steam: power output ratios that can be obtained from a suitable cogeneration plant.

 UNEP-DTIE Energy Branch                                                                         http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                             32

          A single plant or group of plants has sufficient demand for steam and power to
          permit economies of scale to be achieved.
          Peaks and troughs in demand can be managed or, in the case of electricity, adequate
          backup supplies can be obtained from the utility company.
The ratio of heat to power required by a site may vary during different times of the day and
seasons of the year. Importing power from the grid can make up a shortfall in electrical
output from the cogeneration unit and firing standby boilers can satisfy additional heat
demand. Many large cogeneration units utilize supplementary or boost firing of the exhaust
gases in order to modify the Heat to Power Ratio of the system to match site loads.
The proportions of heat and power needed (heat: power ratio) vary from site to site, so the
type of plant must be selected carefully and appropriate operating schemes must be
established to match demands as closely as possible. The plant may therefore be set up to
supply part or all of the site heat and electricity loads, or an excess of either may be
exported if a suitable customer is available. The following Table 6 shows typical heat: power
ratios for certain energy intensive industries:
          Table 6 : Typical heat to Power ratio for Certain Energy intensive Industries

                                  Industry          Minimum          Maximum   Average
                              Breweries                  1.1           4.5       3.1
                              Pharmaceuticals            1.5           2.5       2.0
                              Fertilizers                0.8           3.0       2.0
                              Food                       0.8           2.5       1.2
                              Paper                      1.5           2.5       1.9

3.3 Issues in Implementation of Biomass-based Cogeneration Systems

The key issues in implementation of a biomass based cogeneration systems (BBCS) are
broadly classified as: technical and economical, environmental and social issues and are
discussed in the following sections.
3.3.1 Technical Issues and Barriers

Biomass based cogeneration is faced with some technical barriers, which not only have a
direct impact on day-to-day operations, but also on overall viability of the project. These
issues are sometimes stand-alone issues and some are more complex and interrelated. In the
following sections, these issues and problems have been discussed in detail.
It may be noted that, some of the issues/problems are interconnected and complement each
other and thus add to the complexities in the overall scenario. However, for reasons of
clarity, these problems have been presented as stand - alone issues. Technology Sourcing for Bio- Mass Power Generation

In a typical thermal power station, the basic fuel is prepared to the specific size, according to
the technical requirements of the boiler furnace in order to ensure efficient combustion. In
such cases, the boiler furnaces are specifically designed to suit the characteristics and
parameters of the fuel (say, coal or gas) on which the system is proposed to run. The
availability of this specific fuel is ensured by the user well in advance through techno-legal
agreements with fuel suppliers, for guaranteed supply of the fuel in the specified quality and

 UNEP-DTIE Energy Branch                                                                 http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 33

Ironically, in case of biomass projects, no such agreements exist as biomass fuel market is
unorganized and rural based. The supply position of any particular type of fuel is never
assured, and the biomass based projects are forced to fend for themselves in the best way
they can against the whims, fancies and the vagaries of the biomass supply chain.
Making the right technology choice for biomass-based FBC boiler therefore is a key element
for the success of such projects. Viable Availability of Biomass Fuel

There have been innumerable instances, where the supplier have taken undue advantage of
demand –supply gap and wrested very high prices from reluctant but helpless biomass based
cogeneration projects.
Even assuming that the biomass based cogeneration project is lucky enough to strike a
cordial deal with the suppliers, more critical issue of the wide variation in the sizes of the
biomass as it is received, poses another bottleneck. This calls for an additional process of
appropriate sizing of the bio mass.
If it were the case of a particular biomass, the situation would perhaps have been
comparatively simple. But considering the wide variation and seasonality in the availability of
the bio mass, and their basic characteristics, (size, shape, texture, moisture content, volatile
matter, Calorific Values, etc.) make effective preparation of biomass to suit the boiler
technical requirements, a very complex exercise.
It is but natural that the efficiencies of the boilers would be low as compared to a boiler
operating with a single fuel, for which the basic operating parameters can be set once & for
all, needing only periodic adjustments. This is very difficult with multi-fuels scenario with
frequently changing mix.
Apparently, this seems to be one of the reasons, for several biomass based cogeneration
projects, to have opted for higher heating surface area, compared to the well established
fossil fuel based power plants (of equivalent rating).
Following is a summary of various factors related to the availability of biomass, which can
greatly affect the viability of the cogeneration projects;
A) Types of biomass used in biomass based cogeneration projects
    In any country there could be several varieties of biomass which are in use, depending
    upon the geographic regions, geo-climatic conditions, agricultural practices, growing
    patterns, season and their commercial availability. Considering wide variety of biomass
    being used, with different moisture content, volatiles, unknown chemical composition
    and external impurities’ like mud, clay, sand etc. It is easy to appreciate the technical
    difficulties of collecting, preparing and combusting them in an efficient manner.
B) Availability of Biomass:
    It is a well known fact that, biomass availability is highly influenced by crop patterns of a
    region, climate, weather and seasons, added to these factors is the diffused availability of
    biomass, which makes the collection and transport logistics a difficult and costly task.
    These factors impose constrains on the total quantity of biomass that can be made
    economically available at the project site.
C) Fuel Collection & Logistics:
    When biomass power generation was conceived in the mid 1990’s in India and
    entrepreneurs came up with project proposals with rice husk as biomass, the early
    biomass plants did not face any problems in collecting their main biomass fuel (i.e., rice
    husk), since rice husk was available in plenty at rice mills. In fact, the rice millers were
    more than happy to give away the rice husk at very nominal rates (some times free of
    cost) since that would solve their disposal problem. The plants only had to engage
    transporters to bring in the rice husk from rice mills.

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 34

    However, with installation of more and more biomass based cogeneration plants, the
    situation changed, to an extent that, today, biomass based cogeneration plants are
    looking for any agro or forest residue (woody biomass) that could be burned in their
    Accordingly, the spectrum of biomass fuels broadened from one or two main fuels to 5
    to 10 different types of biomass being used in a single cogeneration plant. This has led to
    several technical and financial problems for these plants:
          More number of biomass types necessitated different types of collection and
          handling equipment. Since most of these biomass fuels, such as Cajurina branches,
          cotton stalks, husks of different pulses, sugar cane trash, spent coffee waste, coconut
          fronts & shells, jute waste, marind husk, red chilly waste etc., were new to these
          plants, there were no readily available equipment/machines to suit the new
          requirements. Hence, all biomass cogeneration plants were forced to spend a sizable
          amount of money in sourcing such equipment from domestic / international vendors
          or developing these machines indigenously. There are also cases of in-house design
          & development to manufacture collection equipment resulting additional capital
          investment and operating cost.
          Many of the agro residues need to be collected manually, baled and transported to
          cogeneration plants. Since this is a highly labor intensive activity and biomass is
          available in distributed quantities, some small and some large, the fuel contractors
          would only be interested to supply biomass that is available in large quantities at a
          single location. Thus biomass available in smaller lots would be ignored.
          The transport of biomass from rice mills / other places of availability is effected by
          transport contractors. Sometimes, transport contractors also become fuel supply
          contractors. Depending on type, biomass is transported in lorries/trucks, tractor
          trolleys, bullock carts etc.,
          The major problem is, the high bulk density of biomass fuels, which results in lower
          tonnage per vehicle, spillage due to light weight when transported in open trucks,
          and thus higher transportation cost. The transportation cost (including loading and
          unloading cost) constitutes a significant portion of the landed cost of the biomass.
          For example, rice husk in India costs around INR800 (US $ 20) to INR1,000 (US $
          25) per ton at the rice mill, whereas transportation costs are an additional INR300
          (US $8) to INR400 (US $10) per ton. For biomass fuels which have to be collected
          directly from the fields (such as sugar cane trash, coconut fronds, forest residues
          etc), and which do not have a centralized collection point, the cost of logistics
          (collection, loading, transport and unloading) further increases. Fuel Pricing

The biomass fuel, presently an unregulated commodity and available in the open market,
makes its price very dynamic and varies extensively from region to region. The price is
influenced by several factors; such as: supply-demand gap (fierce competition among
entrepreneurs), seasonality, distance to be transported, quantities available in single lots etc.
Depending on the price, the cost of fuel constitutes a major portion in total generation cost.
The cost of fuel ranges between 50 to 70% of electricity generation cost, in case only
electricity is produced. Fuel Storage Handling and Preparation

A) Problems in biomass storage
    It is observed that many of the cogeneration plants have no sheltered storage space
    wherein different types of (degradable) biomass could be safely stored, protected from
    the vagaries of the weather. The propensity of biomass fuel to decay/decompose with

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                   35

    time, when exposed in open yards, puts a limit on the fuel inventory that a biomass
    based cogeneration plant can have (to take care of availability).
    This also means that these plants have to put a sustained effort to procure biomass for
    their plant, on a regular basis, as they cannot store large amounts of biomass.
    It would be beneficial to build sheltered storage yards, where loss of biomass due to
    decay can be reduced. Storage sheds need to be built with bay arrangements and
    necessary tools for stacking and reclaiming.
B) Need for Multiple Preparation & Handling Equipment
    Biomass power projects, can no longer afford the luxury of depending on a single fuel,
    for sustained operations. It has become quite normal that, multi biomass fuel is the way
    to go. This has imposed, the necessity to introduce various types of fuel preparation
    options, to suit the various fuels, in the way and sizes, they have to be fed to the boiler.
    This makes it very difficult for any single unit to invest in many different kinds of fuel
    preparation equipment.
    More so, there is a dearth of such equipment, and most of those in use, have been
    indigenously developed, by individual plants. In India, some of the plants have designed
    and developed equipment for fuel preparation on their own (with a little help from
    others and not necessarily very efficient), which range from basic cutters and chippers to
    bailing, drying, and feeding systems. Some of the equipments are listed below:
          Sizing equipment (Chopping) for woody biomass
          Saw cutter and wood chipper for woody biomass like Juliflora etc,
          Chippers for making palm bunches into fibrous material for ease in firing
          Chippers for making coconut fronds, into smaller pieces & powder
          Rotary shredding machinery for bushy biomass like Jute Stick, Cotton stalk, Casurina
          branches etc.
          De Oiled Bran Crusher
          Briquette making (yet to be tried out)
          Sieving machines for coir pith
          Dryers for moisture removal by air drying,
          Drying - natural (solar) drying
          Conveying equipment (Belt, drag chain, bucket, pneumatic)
    Other problems associated with storage and handling of biomass include:
          Many biomass are collected directly from fields, which adds complications of
          external impurities like mud, sand and unknown chemical compositions. It has been
          observed that typically the moisture content ranges between 25% to 38%.
          While sun drying is a simpler option, it has its own constraints, e.g.
          •    Large floor area requirement where the bio mass can be spread to provide
               maximum exposed surface area.
          •    There is unfortunate situation that when there is bright sun there is no bio mass
               and the reverse.

 UNEP-DTIE Energy Branch                                                       http://www.unep.fr/energy
Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                  36

         •    Enormous labor requirement for handling and transporting, stacking, etc., which
              pushes up the cost of the fuel beyond the capacity of the unit. Most of the
              biomasses have a typical and peculiar characteristic that only about the top 2
              inches thick material dries up but the inner mass do not get dried.This calls for
              periodic restacking/disturbing of the heaps of the bio mass, calling for extra
              labor and other costs.

        Figure 13: Chipping Machine for Cajurina branches & coconut fronds at Varam
                                        Power, India

      Figure 14 : Collection & Baling Machine for sugarcane trash at GMR technologies,

         While some of the units use the waste gases for this preliminary drying, they had
         faced the problem of huge capital investment for the appropriate equipment.
         Since the cogeneration plants are using variety of biomass fuels, separate conveying
         and handling systems are required for each (or group of similar) biomass fuels. For
         example, separate conveyers have to be used for rice husk & woody biomass
         (juliflora chips) as they have to be fed at different locations/ways. Another example is

UNEP-DTIE Energy Branch                                                      http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                  37

          screw feeders used for conveying rice husk cannot be used for sugar cane trash as
          the trash would roll around and jam the screw.
          Further, to meet the demand several fuels (of similar nature) such as rice husk, pulse
          husks are mixed and fed to the boiler. All these factors contribute additional capital
          and operation and maintenance (labour, energy etc.) costs for industries. Issues in Use of Supplementary Fuels

The poor quality of biomass in terms of high moisture content, low calorific value and low
bulk density, often results in low heat generation in the boiler, which can not sustain power
generation at the rated capacity. This problem gets further aggravated during the rainy
season. Also, unavailability of sufficient biomass, due to seasonal constraints, necessitates co-
firing of fossil fuels such as coal, to maintain the required steam parameters and/or power
While use of coal as a supplementary fuel is allowed, care should be taken with regards to
the quality of the coal, and it should be of a low quality or it would result in high bed
temperature and subsequently choking of the bed due to ash fusion. Other Technical Problems in BPP Operations

A) High heat rate of Biomass based FBC boilers
    Compared to coal based power plants, biomass based cogeneration plants operate with
    higher heat rate (low efficiency) due to poor fuel quality (high moisture and low GCV),
    lack of optimization of boiler parameters and the turbine parameters (such as
    optimization of excess air and steam parameters).
    It is natural, that the efficiencies of these boilers would be low in comparison with
    boilers operating with a single fuel, for which the basic operating parameter can be set
    once for all, needing only periodic adjustments. This is very difficult with multi-fuels, with
    frequently changing mix. This is one of the reasons for high heat rate or low boiler and
    system efficiency.
    To circumvent this problem the cogeneration plants opted for higher heating surface
    area in the FBC boiler, compared to the well established fossil fuel based power plants
    (of equivalent rating), giving them operational flexibility.
    Another rationale for opting for higher heat transfer area is fouling of heat transfer area
    due to unavoidable dust loading in the boiler furnace (due to inherent biomass
    properties). The overall heat transfer coefficient, especially in closely packed convective
    zone, would deteriorate gradually with time and spare heat transfer area in these
    situations, would help maintain required heat transfer.
    On the down side, the additional heat transfer provided, would impose part loading on
    the boiler, when the tubes are relatively clean. To sum up, the much talked about low
    efficiency (with a wide variation) of power generation cycle in the biomass based
    cogeneration systems is on account of the following factors:
          Problems in technology adequacy
          Varying multi fuel mixes and improper sizing
          Technology is not yet fully matured & optimized (for smooth & efficient operations)
B) Others
    Some of the troublesome operational problems being faced by biomass based
    cogeneration plants are highlighted below:

          Uneven spreading of biomass fuel on boiler grate is leading to secondary combustion
          at super heater zone, resulting in over heating of super heater tubes and also

 UNEP-DTIE Energy Branch                                                      http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                38

          fluctuations in steam pressure. Due to troublesome flow characteristics of biomass
          in bunkers, some plants feed the biomass directly from the top of the boiler with
          conveyors, leading to uneven distribution. Also, since the bunkers (which serve as
          reserve capacity to smoothen the variations in flow from the conveying system), are
          bypassed, furnace loading and combustion are not uniform, resulting in fluctuating
          steam parameters and generator output.
          Corrosive constituents in biomass badly effect boiler internals, especially the super-
          heater tubes. Chloride content in some biomass (8-9% for cotton stalks) combined
          with sodium and potassium at high temperatures can cause much damage. Frequent
          erosion of super-heater & economizer coils also results due to high silica content in
          the biomass.
          High extraneous matter in biomass (sand and mud) causes boiler tube fouling and
          also requires fluidized bed to be drained more frequently with resultant heat loss.
          Carbon and dust coating of boiler tubes resulting in lowering of steam temperatures,
          especially during soot blowing.
          Pesticides used during cropping add to tube failure frequencies - especially the
          content of potassium.
          Corrosion of heating surfaces (coils) is a big issue. Such is the uncertainty of their
          well being that, many plants are compelled to stock at least one bundle, as spare, at
          all times. There are instances where the super heater coil bundle was replaced at
          least once a year.
2.4.2 Financial Issues / Barriers

The first and the foremost barrier in implementation of the biomass based cogeneration
plant is the capital investment. The capital investment cannot be ascertained off-hand as it
depends on various configurations of the boiler and the steam turbine system, and these two
equipments are strictly site specific.
It would be grave mistake to follow a same type of approach and design for two process
houses even though they are of similar nature. As a rule of thumb the capital cost for Indian
condition is approximately US 300,000 per MW. This includes the FBC boiler, turbine, and
all other accessories. This capital cost is somewhat high for the small and medium
enterprises to invest, more so in the absence of government subsidies or an encouraging
The second biggest financial risk in implementation of the biomass based cogeneration plants
is the uncertainty in the prices of the biomass. The cost of the biomass is highly variable and
depends on the market demand. Therefore there is always a degree of uncertainty with
regards to the profitability of the project. This is more so in the absence of government
interference in the biomass pricing as compared to the regular fossil fuel pricing.
It sometimes so happen that in order to make the complete project viable the industry
chooses a configuration so as to export the surplus electricity or steam generated (most of
the times it is the export of electricity rather than steam) to another industry close by or to
the local electricity service company through the grid. In such a case there is always a power
tariff agreement between the supplier and the receiver with regards to the minimum
quantity of electricity supplied and the cost at which the electricity is supplied. In lieu of
increased biomass prices the supplier is not able to increase the tariff of the electricity
exported, whereas it has to necessarily keep on supplying the minimum quantity of
electricity as agreed upon during the time of contract. This makes the project financially

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                   39

3.4 Environmental Benefits of Biomass based cogeneration Systems

The benefits of biomass use as a source of fuel in cogeneration systems, besides energy
security & independence of the industries, include several environmental benefits, mainly in
terms of GHG reduction.
          Biomass Power generation, is considered to be CO2 neutral, since only the amount
          of carbon fixed during the growth of a crop/tree, is emitted during its combustion.
          Biomass is traditionally used as cooking fuel in households in many countries,
          especially in rural areas, which is the cause of indoor air pollution and health
          impacts, such as asthma, bronchitis, respiratory infections etc. on women & children,
          leading to morbidity & mortality. Governments in various countries provide clean
          fuels such as LPG & kerosene, at subsidized prices, to reduce & disengage firewood/
          biomass as a cooking fuel. Hence power generation through biomass, is a good
          alternative, not only in the use of surplus agro & woody residues but also because, it
          brings in efficiency.
          The surplus biomass is burnt in the fields, by farmers, to get rid of it and at the same
          time to retain some nutrients in the fields. This open burning in the fields, have
          environmental & health impacts which can be alleviated due to efficient utilization
          and burning process in the FBC boilers.
          Open burning and cooking cause a high level of particulate matter problems, which
          are addressed effectively, with electrostatic precipitators (ESP) in cogeneration
          It reduces the transmission losses which otherwise would have incurred when the
          electricity is supplied to an industry. This in turn leads to less fuel usage to produce
          electricity by an equivalent amount.
3.5 Social Benefits of Biomass based cogeneration Systems

Biomass power generation undoubtedly leads to several social benefits as below:
          Biomass power plants monetize the heat value of biomass, which brings in additional
          income to various players in the biomass supply chain (farmers, traders, agro
          processing industries such rice mills etc).
          It creates additional employment in collection and transportation of biomass, as well
          as additional employment in power generation.
          It brings additional economic and income generation activity into rural areas –
          especially for women - thereby contributing to local & regional development.
          It would diversify the rural economy, which generally rely entirely on food crops, by
          introducing energy plantations. This is all the more important, since most energy
          plantations are grown on so called “wasteland” which have, no/minimal access to
          irrigation. This is a significant aspect in water stressed areas.
          In countries like India the employment generation, in fuel collection and logistics,
          have excellent gender mix in favor of women, which, is lacking in many employment
          generation schemes of the government and in other sectors such as infrastructure
          building (roads, highways etc.).
          It brings additional skills to rural areas and can raise the income levels of farmers and
          laborers, which in turn improves the standard of living. The creation of employment
          opportunities in rural areas would reduce the government spending on employment
          generation and at the same time would bring in additional tax revenues to the

 UNEP-DTIE Energy Branch                                                       http://www.unep.fr/energy
Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                              40

         It would reduce the equivalent fossil fuel import bill of the government & thereby
         improve the balance of payment position.
         Biomass based cogeneration projects have given impetus to technology
         development, by encouraging use of different agro and woody biomass in plants. It
         would also give impetus to technology development at the farm level, by introducing
         farm level machinery, to facilitate collection and baling.
         The success of biomass power plants using combustion route, has led to increased
         efforts in power generation through other routes, like gasification.

UNEP-DTIE Energy Branch                                                  http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 41

 4.0 Implementing Biomass Cogeneration Technology

After understanding the basics of the FBC based biomass cogeneration technology, it is
important to know the various practical requirements in order to effectively implement and
ensure smooth and trouble free operation of the technology. Of course, these requirements
can not be elaborated to the last detail - as a lot depends on many site specific factors.
Broadly, the various requirements of the technology implementation can be divided into the
          Raw material and energy resources requirement
          Waste & its disposal
          Infrastructure requirement including land
          Supporting technologies
          Human Resource Requirement
          Technology suppliers
4.1 Raw material, Energy Resource requirement

FBC boilers can be used to burn many grades and types of solid fuels like rise husk, bagasse,
etc. In fact, depending on the available fuel, the boiler suppliers design and supply the boiler.
In case of rice husk, with a calorific value in the range of 3,000-3,100 kcal/kg, and boiler
efficiency of 80%, 0.25 tons of fuel (rice husk) is required to produce 1 ton of saturated
steam at a pressure of 26 kg/cm2. But the amount of rice husk consumption would be
increased if the steam is in superheated condition.
For cogeneration plant with a capacity of electricity generation of 1 MW and above, the
degree of superheat is in the range of 220 to 290 ºC. It means the temperature of steam is
in the range of 390ºC to 460ºC. The amount of fuel required is totally dependent on the
quantity and pressure of steam required and the degree of superheat at that pressure.
This in turn is dependent on the on-site requirements. Therefore, the primary data required
to estimate the total fuel required is
    -     the pressure at which steam needs to be generated and the degree of superheated
          steam required
    -     the quantity of steam required
    -    the amount of electricity needs to be generated.

The quantity of fuel required can be worked out by back calculation after having determined
the steam requirements in the process house and electricity to be generated and the steam
to the condenser. Thereafter an energy balance could be performed. Let us consider a case
as in Figure 15:

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                           42

                  Steam (saturated) = x tons/hr
                  Temperature = 450 oC
                  Pressure = 26 kg/cm2

                                                                              Electricity Output
                                                                              = y (known)

                 Steam (to process) = z tons/hr
                                                                     Steam (to condenser)
                 Temperature = 250 oC
                                                                     Pressure = 0.10 kg/cm2
                 Pressure = 10 kg/cm2

             Figure 15 : Example on estimation of fuel requirement for co-generation

Making a Material & Energy Balance

a) Input
  Enthalpy of steam (kcal/hr)              = [Quantity of steam input to turbine (x)] X [Enthalpy of
                                           steam at 26 kg/cm2 & 450ºC temperature (from steam table)]
b) Output
  i) Electrical Energy                     = [Electricity produced in watts (y) X 860] / [Efficiency of
                                           Turbo generator & Steam Turbine i. e. 81%]
                                           = [y x 860] / [0.81] kcal/hr

  ii) Enthalpy of steam to process (kcal/hr)
                                           = [Quantity of steam (z)] X [Enthalpy of steam at 10 kg/cm2
                                           & 250ºC temperature (from steam table)]
  iii) Enthalpy of steam to condensate
                                = (x-z) X enthalpy of steam at 0.1 kg/cm2 i.e. vacuum

Since; Energy Input = Energy Output, the only variable unknown is x i.e. quantity of
steam required which can be calculated using: a) = b(i) + b(ii) + b(iii)

The quantity of fuel can be determined as:
       Fuel quantity (kg/hr)    = [Enthalpy of steam at inlet to turbine] / [Boiler efficiency
                                X GCV of fuel]

It can be observed from the above calculations than the quantity of fuel used is totally
dependent on the electricity to be generated and the steam requirement in the process
However it must be noted that the steam demand in the process house and the electricity
requirements are never constant in an industry. Therefore the actual fuel requirement can
be estimated only over a period of time after the system is in place. It is a general practice to
maintain at least 7 days inventory of the fuel required.
Another aspect to keep in mind while estimating the fuel requirement is the peak load
period. If the system is designed to operate optimally at the time of peak loads then, it is
going to perform at low efficiency during the average or low load period. In order to
remove this anomaly the FBC boilers are generally designed to handle different type of fuels

 UNEP-DTIE Energy Branch                                                               http://www.unep.fr/energy
    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                      43

and there is also a provision of co-firing using solid fossil fuel like coal (of a very low quality);
since even a low quality coal do have higher energy contents than the rice husk.
Therefore in order to meet the peak load demands either the rice husk is mixed with coal
or there is a separate coal feeding system from which coal is fed and combusted in the boiler
in parallel to the rice husk. Table 7 lists the various fuels and there calorific value which can
be used in a FBC boiler for steam generation.
                                   Table 7 : Fuels and their typical calorific values

              No.     Fuel               Calorific Value (Kcal/Kg)        Moisture Content ( % )          Ash (%)
              1       Rice Husk                        3100                           8.92                  19.40
              2       Bagasse                          3550                           10.53                 7.03
              3       Straw                            3050                            15                     4
              4       Nuts and Shells                  4100                            10                     6
              5       Wood                             4400                           9.83                  3.14

In addition to the fuel in the boiler, another very important input into the co-generation
system is the electricity required by the various equipments in the cogeneration system.
These include: boiler feed water pumps, air supply fans, (induced & force drafts) compressed
air, ESP, water treatment plant, ash handling system, cooling towers for condenser etc.
The total electricity consumed by these auxiliaries is named as auxiliary power consumption.
Primarily all the auxiliary power consumed is drawn from the electricity product by the
turbo generator there the turbine. As a rule of thumb, the auxiliary power consumption is in
the range of 12-15% of the total power generated. This however varies with the type of
turbine system configuration and the fuel mix used for the boiler. Therefore when estimating
the power requirements of the industry an addition sum amounting least 15% may be added
on to the average demand.
4.2 Infrastructure Requirement

                    Infrastructure requirement for a biomass based cogeneration plants can be
                    broadly divided into two categories (i) External Infrastructure i.e. outside the
                    industry premises (ii) Internal Infrastructure i.e. within the industry premises.

       •      External infrastructure: Although the industry which is setting up a cogeneration
              system does not have control one the conditions outside, but still during conducting
              detailed feasibility analysis external factors should be taken into consideration. Table
              9 lists the important parameters to look out for.
                                   Table 8 : External Infrastructure Requirements

No                Parameters                                                Remarks
                                      Wide metalled roads to cater to the need of fuel transports in large quantities by
1          Road connecting
                                      truck all through the year
           Close to bio mass
2                                     To ensure perennial supply of bio-mass
3          Water availability         Either ground water or municipal supply.
4          Ash disposal               Facilities for ash disposal in landfill or road construction material etc.
5          Electrical Grid            To upload the excess power generated to the grid.

    UNEP-DTIE Energy Branch                                                                          http://www.unep.fr/energy
    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                   44

       •     Internal Infrastructure: One of the most important infrastructure requirements in
             case of implementation of the biomass fired co-generation system is the availability
             of land area. Large space is required to set up the boiler house, the turbine house,
             the electrical distribution system etc. The land/area required for each of the
             component would be different and would depend on the configuration and size of
             the cogeneration system. In absence of space availability it would be not possible to
             set up the described technology. The following table lists the area and other
             infrastructure requirements to be analysed before starting the project. The data in
             the table 10 is for a typical cogeneration plant generating 3-5 MW of electricity and
             high pressure steam generation of about 25 tons/hr.
            Table 9 : Area requirements for different components of a typical cogeneration

                                       Approx. Area & Other
No.            Equipment                                                                  Comments
1          Boiler house              5000 sq. ft                         Industrial type shed with a height of a plant 50
2          Biomass storage and       Open space/ shed of about           Depends on the climate of the region
           handling                  10,000 sq ft to maintain 7
                                     days inventory of fuel
3          Water treatment           1000 sq. ft
4          Turbine house             7000 sq ft                          The turbine house is a permanent concrete
                                                                         structure with typically two floors. The same
                                                                         structure houses the electricity load monitoring
                                                                         & distribution panel.
5          Electrical load
           monitoring &
           distribution panels
6          Water storage tank        20,000 m3 of water storage
                                     tank, preferably overhead
7          Laboratory, store &       1000 sq ft
4.3 Supporting Technologies

In implementation of new technologies it is imminent that some additional and supporting
technologies are required along with the new technology implemented. Although in
implementation of a biomass fired boiler and cogeneration system the additional
technologies are part of the system and generally the supplier of the system do install and
commission all the other technologies as a package rather than just the boiler, or the turbine.
Nevertheless it is important for the industries to know about the additional technologies as
it helps them identify the new work areas they have to handle & maintain at a later stage.
The additional technologies required for a cogeneration plan are listed in table 11.
                        Table 10 : Supporting Technologies for Cogeneration Systems

No.           Equipments/Technologies                                             Remarks
1          Water treatment plant                      The input TDS should be less than 10 mg/l for high pressure boiler
2          Fuel preparation & handling system         Needed in case of multi fuel use
3          ESP/Bag filters/multi cycle                Choice depends on the norms of the country
4          Ash handling system                        Depends on volume of ash to be handled & disposal pattern.
5          Fuel drying system                         Dependent on the type of fuel to be used
6          Cooling Towers                             Size and choice depends on the climatic condition of the area

    UNEP-DTIE Energy Branch                                                                       http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 45

The capacity & design of these additional technologies will depend on the size of the boiler &
the co-generation system.
4.4.1 Water Treatment Plant: Typically the water treatment plant consists of a Reverse
Osmosis plant followed by an ion exchange plant. For a high pressure boiler, typically the
TDS of the water being fed into the boiler should be less than 10 mg/l. These two
technologies do have limited environmental impact. The rejects from the RO plant and the
waste water generated from the ion exchange plant is neutralized in a tank and can be used
for sundry purposes like floor washing, gardening etc.
4.4.2 Fuel Preparation & Handling: Generally the biomass like straw etc. is just picked up
from the agricultural field and brought to the industry. These types of fuels need to be sized
so as to be used in the boiler. Therefore there is a need for a shredding machine which
would size the fuel to be used. In many cases the fuel brought to the industry is in form of
bales. These bales are de-baled by a de-baling machine before it could be fed to the FBC
boiler. Further since the industry maintains an inventory of about 7 days the fuel is stored
over a large area. To collect this spread over fuel and bring it to the fuel feeding system
requires either manual work by workers or loaders and pushers operated by their drivers.
Although there is no direct and major environmental pressure associated with these
technologies but the use of the various equipment increase the auxiliary power consumption.
4.4.3 Suspended Particulate Matter (SPM) Control: In any case of a solid fuel fired FBC
boiler the control of particulate matter is a necessity. The amount of fly ash depends on the
type of the fuel used. In case of bagasse the amount of fly ash is quite less where as for rice
husk it is more. Therefore the choice of SPM control technology is also dependent on the
nature of fuel being used. But since FBC boilers are designed to combust multiple fuels the
most prominent technology for particulate control is Electrostatic Precipitators (ESP) or bag
filters. The capital cost of ESP is more than the bag filter, although its operation cost is less
than that of a bag filter. These technologies themselves do not have any negative
environmental impacts. The choice is also governed by the local laws and regulation with
respect to the limits of the SPM in the flue gases.
4.4.4 Ash Handling System: Ash is generated as bottom ash from the boiler furnace and
is also collected as fly ash from the ESP or any pollution control device. The ash handling
system depends on what is the end use of the ash generated. In case the ash is to be used
for cement manufacture or bricks making or as a subgrade material in road construction etc.
The ash is handled in dry form. It is pneumatically conveyed through pipes by help of
compressed air, but this is a very costly type of system and is used only in case of large
amount of ash to be handled. For a small cogeneration plant of 3-5 MW capacity this type of
system is not economically feasible. In such plants the ash is handled manually using loaders,
excavators and trucks or tractors/ trolley. The loaders load the ash to the trucks and
trolleys which are then transported to the desired site. Another method to handle ash is to
form slurry by mixing with water and this slurry is then pumped to the ash dyke (a huge pit).
In the ash dyke the water is drained and the wet ash is deposited. The drained water can be
recycled back for slurry preparation.
4.4.5 Fuel Drying System: Some of the biomass fuel like bagasse, have high inherent
moisture content. Therefore these types of fuel need to be dried before being fed into the
boiler. High moisture in the fuel could lead to problems in the fluidization of the fuel. The
high moisture will also increase the stickiness and would cause deposition on the boiler
tubes; it would also lead to formation of black smoke from the chimney and choking of the
bed. A very common method of fuel drying is by spreading it over a large area and sun
drying it. But in some cases where the quantity of fuel to be dried is large, special fuel drying
system is installed, where in the fuel is dried by the waste heat from the flue gases. In such
system addition environmental pollution control system to control the particulate matter
are generally installed.

 UNEP-DTIE Energy Branch                                                     http://www.unep.fr/energy
    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                  46

4.4.6 Cooling Towers: Cooling towers are part of the boiler-turbine system. The type and
the size of the cooling tower is dependent on the climatic condition of the region where it is
installed. The cooling tower by itself does not have any negative environmental impact. The
amount of water evaporated in the cooling tower is about 5-7 % of the total cooling water
used in the circuit.
4.2 Waste Disposal

Both solid and liquid wastes are generated from different areas of a cogeneration plant.
Although the wastes generated are not hazardous, but need good practices to mange them
so that they may not result in any additional environmental impacts. The major wastes
generated from the cogeneration system are listed in table 8.
                                Table 11 : Waste Generated in Cogeneration Plant

                                                                                                  Frequency of
No.      Waste                                          Area
1        Used lube oil                                  Turbo generator, turbine etc.             Once in 6 months
2        Cooling water                                  Turbine being cooling etc.                Continuous
3        Reverse Osmosis (RO) Reject Water              Water Treatment Plant                     Continuous
         and DM plant wash water
4        Ash                                            Boiler bottom ash from boiler furnace,    Continuous
                                                        fly ash from ESP or bag filter

The most significant waste that is produced is the ash. The quantity of ash varies according
to the fuel mix used. In case only rice husk is used as a fuel, the total quantity of ash
generated from the process is about 28-30% of the rice husk used by weight considering that
the rice husk has a moisture content of about 10% only.
If we analyse the composition of fuels like rice husk and bagasses as in Table 7, we observe
that the quantity of ash content in the fuel is only 19.4% and 7.03% respectively. However,
when these fuels are burned in a boiler there is some unburnt carbon particles. This
unburned carbon comes out mixed with ash.
The quantity of unburnts in FBC boilers is dependent on many factors, the most prominent
one being the mode of firing & type of distribution system to spread the fuel inside the
boiler furnace.
The quantity of ash generated in case of use of bagasse as a fuel is in the range of 10-12% of
the total fuel used. Therefore in comparison to the rice husk it is a better fuel in terms of
quality of solid waste generated. The ash generated from the ESP and the boiler is collected
and is disposed off in landfills. However, there are certain more ways of effectively using the
fly ash generated namely
             Use as sub-grade material in road construction.
             Used for making fly ash bricks
             Partial use in cement manufacturing
The other wastes like spent lube oil, cooling water, R.O. rejects water are not of much
environmental consequence as their quantities are quite low in comparison. The lube oil is
recycled back to the company which provides it. The cooling water is in a closed circuit and
the losses in the circuit are only evaporation losses through the cooling towers. The rejects
from the R.O. plant/DM Plant are neutralized and used in gardening and other purposes like
floor washing etc.
4.5 Human Resources Demand

A trouble free operation of implemented technology is very much dependent on the way it
is handled and operated. Therefore the role of both trained and untrained manpower at

    UNEP-DTIE Energy Branch                                                                      http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                  47

supervisory level and operations level are of utmost importance. In most of the cases and
especially in case of biomass fired cogeneration plant it is very difficult to assign the number
of people which would be optimum for the purpose of plant operation and maintenance,
since the manpower requirement is more or less a function of the size of the plant.
However, for a plant size of 3-5 MW about 30-35 personnel’s are required. This includes
managers, supervisors and operators.
4.6 Equipment Suppliers

The main equipments in case of a biomass based cogeneration plant are : Atmospheric
Bubbling Fluidized Bed Combustion Boiler and a Extraction cum condensing Steam Turbine.
The FBC technology for the use of rice husk as a fuel is quite matured in India. There are
more than 200 cogeneration plants using the FBC boilers in operation in the country. Table
12 lists the various suppliers of steam turbine and the biomass fired FBC boilers. All the
other auxiliary equipments like cooling tower, water treatment plants, ESP, ash handling
plant etc are supplied by the boiler manufacture as a part of the package.
                          Table 12 : Suppliers for Steam Turbine and FBC Boiler

Disclaimer : The addresses provided in the table above are only representative and in no way it is implied
           that the product are being endorsed by DTIE, UNEP
 Components             Supplier          Country                    Address               Phone              Fax
Steam Turbine       Triveni               India         12A,Peenya Industrial Area,     +91-80-2839      + 91 80
                    Engineering &                       Bangalore, Karnataka India      1624             2839
                    Industries Ltd                      560058                                           5945
Steam Turbine       Turbo                 India         2/C/1, Picnic Garden 3Rd        +91-33- 2343
                    Engineers                           Lane, Kolkata, WB, India        4948
Steam Turbine       UES                   India         A-302,2nd floor, Vikashpuri,    +91-98101-
                                                        New Delhi, India 110018         39601
Steam Turbine       Citation              USA           27275 Haggerty Road/Suite       +1-248-761-        +1-248-
                    Corporation                         420,NoviMichigan USA 48822      1805               522-4577
Steam Turbine       Skinner Power         USA           8214 Edinboro Road, Erie,       +1-887-868-        +1-814-
                    Systems LLC                         Pennsylvania USA 16509          8577               868-5299
Steam Turbine       Canton Drop           USA           4575 Southway St. SW,           +1-330-477-
                    Forge                               Canton, OHIO USA 44706          4511
Steam Turbine       eTurbines Inc.        USA           3030 Greens Road, Houston       +1-281-442-        +1-281-
                                                        TX USA 77032                    2700               590-2233
Steam Turbine       National              USA           800 King Avenue, Columbus,      +1-614-488-        +1-614-
                    Electric Coil                       Ohio USA 43212                  1151               488-8892
Steam Turbine       Solar Thermal         USA           2736 N. Palmer, Milwaukee,      +1-414-372-
                    & Biomass                           Wiscosin USA 53212              7097
                    Power Plant
Steam Turbine       Turbosteam            USA           161 Industrial Blvd., Turners   +1-413-863-        +1-413-
                                                        Falls, Massachusetts USA        3500               863-3157
Steam Turbine       HPG Limited           Canada        2240 Speers Rd, Oakville,Ont    +1-905-825-        +1-905-
                                                        Canada L6L 2X8                  1218               825-1220
Steam Turbine       CITIC Heavy           China         206 Jianshe Road Luoyang City   +86-379-           +86-379-
                    Machinery                           Henan China 471039              4218067            4218509/
                    Company Ltd.                                                        +86-379-           +86-379-
                                                                                        4218711-5455       4218067
Steam Turbine       HI Efficiency         India         # B-143A/1,3rd Cross, 1st       +91-80-4117-       +91-80-
                    Turbo-                              Peenya Industrial Estate,       8394               4117-
                    machinery PVT.                      Bangalore 560058 Karnataka      +91-               9394
                    LTD                                 India                           9945699051
Steam Turbine       Mitsubishi            Japan         Environmental Systems           +81-3-3212-        +81-3-
                    Heavy                               Division,2-5-1,                 3111               3212-
                    industries, Ltd.                    Marunouchi,Chiyoda-ku,100                          9800
                                                        Tokyo, Japan

 UNEP-DTIE Energy Branch                                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                    48

 Components             Supplier          Country                    Address                 Phone              Fax
Steam Turbine       Peter                 UK            Werrinton Parkway,                +44-1733           +44-
                    Brotherhood                         Peterborough, UK,PE4 5 HG         292200             1733-
                    Ltd                                                                                      292300
Steam Turbine       Solar                 Germany       Margarethenstraβe 25,             +49-2234-          +49-
                    International                       Frechen B. Koln, Nrw              4356886            2234-
                    Energy Ltd.                         Germany 50226                                        4356887
Steam Turbine       Spilling Energie      Germany       Werftstrasse 5, Hamburg,          +49-40-789         +49-40-
                    Systeme Gmbh                        Germany 20457                     1750               7892836
FBC BOILER          Thermax               India         9, Community Centre, Basant       +91-11-2614        +91-11-
(Biomass Fired)     Limited                             Lok, Near Priya Cinema, New       5326 /2614-        2614
                                                        Delhi - 110 057                   5319               5311/
FBC BOILER          Babcock &             USA           20 S. Van Buren Avenue            +1- 330-753-       +1-330-
(Biomass Fired)     Wilcox                              Barberton, OH, U.S.A 44203-       4511               860-1886
FBC BOILER          Wartsila              Finland       Wärtsilä Corporation              +358-10-709-       +358-10-
(Biomass Fired)     Biomass Power                       John Stenbergin ranta 2           0000               709-5700
                                                        FI-00530 Helsinki /
                                                        P.O. Box 196 FI-00531
FBC BOILER          Indtex Boilers        India         Mr. B. K. Gupta                   +91-11-2767-
(Biomass Fired)     Pvt Ltd.                            204, Amber Tower, B/H,            6771 / 2767-
                                                        Akash Cinema, Badlapur, New       7137
                                                        Delhi - 110033 India              +91-98111-
                                                                                          34966 /
FBC BOILER          Fluidcon Boilers      India         208, Vikas Surya Arcade, Plot     +91-11-4277-       +91-11-
(Biomass Fired)     Equipments Pvt.                     No. 8, Sector 11, Dwarka,         3736 / 3091-       2508-
                    Ltd.                                New Delhi - 110 001, India        1908               3509
FBC BOILER          A.V.U.                India         Survey No. 53, Bahadurpally       +91-40-2309-       +91-40-
(Biomass Fired)     Engineers Pvt.                      Village, Qutubullapur (M),        2343               2309-
                    Ltd.                                Ranga Reddy, Hyderabad,                              3235
                                                        Andhra Pradesh - 500 043,

FBC BOILER          Mega Retro            India         192, Banjara Hills, Raod No. 3,   +91-40-2309-       +91-40-
(Biomass Fired)     Thermal                             Plot No. 4, Hyderabad, Andhra     2343               2309-
                    Equipments                          Pradesh - 500 034, India                             3235

 UNEP-DTIE Energy Branch                                                                       http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                49

  5.0 Case Study

This case study is an illustration of how a biomass (rice husk) fired cogeneration technology
using an FBC boiler is implemented and operated in a techno-economically feasible manner
in a small/medium scale pulp and paper industry in India.
The project feasibility studies were conducted in the year 2002-03 and the project was
commissioned in 2004-05. Most of the data in the case are taken from the project, however
to simplify the case for easy understanding, some of the values/data has been modified.
5.1 Introduction

Bindlas Duplex Limited (BDL) an ISO 14001 company belongs to the Bindal Group, which
has three companies viz. Neeraj Paper Marketing Limited, Bindlas Duplex Limited and Tehri
Pulp & Paper Limited. The annual group turnover is about 1,000 million rupees (23.8 Million
US $).
The project was initiated in the year 1991 with the installation of a high quality Kraft paper
manufacturing unit, with an installed capacity of 5,000 TPA, which was later enhanced to
6,600 TPA. In the year 1997, the company initiated another project for manufacturing duplex
board with an installed capacity of 13,200 TPA. Later, in year 2000, the duplex board unit
was modernized to produce coated duplex board. Presently, the industry has two
production lines: Unit 1 for Kraft paper and Unit 2 for duplex board.
The management of BDL is highly committed towards growth. The unit has shown growth
since its inception and in the year 2002-03 achieved 100 % capacity utilization. The
management in year 2003-04 had a planning for capacity addition and production of Kraft
Paper & Coated Duplex Board to increase gradually over the next few years. The Figure 16
below gives the projects annual production trend.

                                        Figure 16 Annual Production Trend

5.2 Manufacturing Process

In the industry/factory Kraft Paper-manufacturing line is referred to as Unit # 1 and the
Duplex Board manufacturing line is referred to as Unit # 2. The present capacity of the
Units # 1 & 2 are 6,600 & 13,200 tons per annum (TPA) respectively
5.2.1 Kraft Paper Manufacturing Process

          The raw material used for Kraft paper manufacturing is a mix of agriculture residue
          (60%) such as bagasse, wheat straw, etc. & waste paper (40%). A rotating spherical

 UNEP-DTIE Energy Branch                                                    http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                  50

          digester is used for cooking agro based raw material along with caustic. After
          cooking, the pulp is passed through mechanical devices such as refiners, and the
          ratio of agro based pulp & waste paper pulp is maintained as the per requirement.
          Again this stock is passed out through the refiners. In the blending chest, the
          chemicals & colors are added as per requirement, after which the pulp is fed to
          machine chest & to subsequent machine sections. The Unit #1 is installed with a
          four dryer machine with Machine Glazed (MG) & 16 dryer’s cylinder for producing
          Kraft paper. Steam supply to digester for cooking and dryers is provided by help of
          boilers installed in the utilities section of the industry. The process flow diagram is
          illustrated in Annexure 1.
5.2.2 Duplex Board Manufacturing process

          The raw material used for Duplex board manufacturing is entirely waste paper. In
          Unit # 2, the Duplex board (coated) manufactured is prepared in four layers. The
          1st layer is white, the 2nd layer is for protection purposes, the 3rd layer is the filler
          and the 4th layer is the back layer. For the 1st & 2nd layers, de-inking & bleaching is
          carried out for improving whiteness. Steam supply to the process is supplied by the
          boilers installed in the utility section. The process flow diagram is illustrated in
          Annexure 2.
5.3 Baseline Energy Scenario

The present electrical load of the plant is 1.875 MW and the steam requirement is around
10 TPH. The management has already initiated measures for modernization, which would
increase the production as well as quality. After the modernization i.e., by the end of
financial year 2003-04, the production is expected to increase to 8250 TPA of Kraft paper &
16500 TPA of Duplex board. Simultaneously the power & steam requirement are also
expected to raise to 2.38 MW & 12.32 TPH respectively
5.3.1 Electrical Energy

The industry had its own captive power generation through the Diesel generating sets
because of the fact that the utility power company namely Uttar Pradesh State Electricity
Board (UPSEB) power supply has been erratic and unreliable, the management of BDL was
compelled to discontinue use of UPSEB power and install its own captive power generation
plant. This consists of a battery of DG sets, with a combined aggregate capacity of 5.7 MVA.
The ratings of the four DG sets are presented in the table 13:
          Table 13 : Specifications of the DG sets installed for captive power generative

                             No.     Make                 Rating KVA   Fuel Used
                             1       Plistic (Marine)     2500         Furnace Oil
                             2       Kirloskar            750          HSD
                             3       Skoda                1450         Light Distillate Oil
                             4       Kirloskar            1000         HSD
Under normal circumstances, the 2500 KVA DG set (Plistic make) and 750 KVA DG Set
(Kirloskar make) are put online while the other two remain as standby. At times, however,
the 1000 KVA DG set (Kirloskar make) is also put into service, for short duration. The
Skoda make generator is hardly used and is just kept for emergency purposes. The annual
fuel oil consumption by the DG sets during the year 2002-03 is 3248.8 kilo litre furnace oil
(FO) and 1272.8 high speed diesel (HSD). The overall annual fuel oil bill (energy) for power
generation through DG sets is around 68.6 million rupees (1.6 Million US $). The average
specific generation (kWh / litre) for each of the DG sets is 3.2 kW/litre for Plistic 2500 KVA
DG set and 3.5 kW for Kirloskar 750 KVA and 1000 KVA DG sets. The existing and
projected electrical power requirements of the industry is depicted in figure 17

 UNEP-DTIE Energy Branch                                                                      http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                           51

                    Power Requirement Trend- baseline values in MW
                               (With Existing Setup)
        3                               2.38                  2.57         2.72
               2002 - 03             2003 - 04            2004 - 05    2005 - 06      2006 - 07

                   Figure 17 : Electrical Power requirements trends- Baseline values

5.3.2 Thermal Energy - Steam

Towards meeting plant process steam requirements, two boilers (Industrial Boilers Ltd - IBL
make & Thermax make) have been installed. The IBL & Thermax boilers cater to the steam
demand of Unit # 1 and Unit # 2 respectively. Fuel used in IBL and Thermax boilers is low
grade coal. The rated capacity of both the boilers is 10 tons per hour (TPH) and saturated
steam is generated at a pressure of 9.6-10 kg/ cm2(g).
As the maximum steam pressure requirement by the process is 4 kg/cm2(g), the boiler steam
pressure is regulated through pressure reducing valves and subsequently distributed in the
industry. The total annual fuel consumption in 2002-03 by the boilers was 14100 tons
amounting to Rs 32.4 million (US $0.7 million). The existing and projected steam
requirements of the industry is depicted in figure 18

                                     Steam Requirement Trend- baseline
            Steam (T/hr)                                l
                                           (With Existing Setup)
             20                                                                      15.28
                                                               13.31      14.3
             15                             12.32
                      2002 - 03          2003 - 04         2004 - 05   2005 - 06   2006 - 07

                           Figure 18: Steam requirements trends- Baseline values

5.4 Implementation of Rice Husk based Cogeneration System

After analysis of the various system configurations it was concluded that an extraction cum
condensing turbine type of system would be the best option for implementation. The steam
to this turbine would be supplied from a new Fluidized bed combustion boiler in place of the
two existing boilers. In this scheme, steam is generated in a high-pressure boiler at a high
pressure & is expanded through a extraction cum condensing turbine. A part of steam (60%-
65%) is extracted to meet the process requirement and the rest is condensed. The

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                               52

advantage with this scheme is that the entire process steam & power requirement of the
unit would be met through the project.
Since the installation of a new FBC boiler and steam turbine system would require additional
electrical power and steam requirements, the projected steam and electrical demands were
revised and the system was designed for revised demands. Further, the start of the project
was taken to be in the year 2004-05 as it takes at least 6-9 months to erect and commission
the system. Till the time the new system comes up the old system continued to be in
operation. The revised electrical power and steam demands are depicted in figure 19 and 20.

                                 kWh & MW Requirement (After Co-generation)

                                 25                                             24.23          3.2
                   h illions)

                                 24                           22.66                     3.06   3

                                          21.38                         2.86
                 kW (M

                                 22                                                            2.8

                                 21                2.7
                                 19                                                            2.4
                                         2004-05            2005-06            2006-07
                                                              Year                      kWh (Millions)
     Figure 19: Electrical Power Requirements after Installing the Cogeneration System

                                     Steam Requirement (After Co-generation)

                                25                                                    24.11

                                22        21.2
                                         2004-05                2005-06              2006-07

             Figure 20: Steam Requirements after Installing the Cogeneration System

5.4.1 Details about the suggested scheme

Considering the steam & power requirement of the plant, it is suggested that the plant may
install a co-generation system with the following configuration.
          Type:                                  Extraction-cum-condensing turbine
          Alternator rating:                     5 MVA
          Steam turbine rating:                  4 MW
          FBC Boiler:                            30 TPH(64 kg/cm2 and 4850C)
The schematic diagram of the suggested system along with the envisaged steam & power
generation potential is given in figure 21.

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    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                        53

                      64 kg/cm2 (a),
                                                                              BASE YEAR – 2004-05
                      485 0C, 21.2 T/hr

                                      Turbine                             2.7 MW

                                                                              To condenser 7.5 MT/ hr
                                                                              0.1 kg/cm2

                                                                              To process 12.45 MT/ hr
                                                                              5 kg/cm2 (a) & 2300C
                                                                               To de-aerator 1.25 MT/ hr
                                                                               5 kg/cm2(a)

                                 Figure 21 : Schematics of the Cogeneration System

The technical specifications of the various equipments and accessories are enclosed in
Annexure 3.
5.4.2 Investment details (investment break up of cogeneration project)

A total investment of Rs.103.3 million (US $ 2.46 million) was made for implementation of
this project. The break up of investment for the different heads is detailed in Table 14-20.
The cost economics of the scheme has been worked out keeping the base line year as 2004-
                                 Table 14 : (A) Preliminary & Preoperative Expenses

                  No.       Particulars                                 Amount (Rs.-Million)   Amount (US $)
                  1         Processing legal & professional Fees        0.7                    16,666.67
                  2         Final Run Expenses                          0.1                    2,380.95
                  3         Miscellaneous Expenses                      0.1                    2,380.95
                            TOTAL                                       0.9                    21,428.57

                      Table 15: (B) Cost Involved for procuring Land & Site Development

                        No.     Particulars                       Amount (Rs-Millions)     Amount (US $)
                        1       Cost of Land                      Rs.0.8 millions          95,238.09
                        2       Cost of Site Development          Rs.0.275 millions        32,738.09
                                Total Cost                        Rs.1.075 millions        127,976.18


                                      Table 16 (C): Cost of Civil Works Required

No.      Particulars                               Proposed         Type of Construction          Amount           Amount
                                                   Area                                           (Mil Rs.)        (US $)
1        Shed for Turbine & D.M.Plant              7000 sq. ft.     A.C. Sheet roofing over       2.8              333,333.33
                                                                    steel column (@Rs.400/-

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    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                         54

2        Shed for high pressure Boiler             5000 sq. ft.        A.C. Sheet roofing over       2.00          238,095.2
                                                                       steel column with tubular
                                                                       steel braces
3        Over head tank of 40 T capacity                               RCC                           0.3           35,714.3
4        Lab/Store/Godown shed for fuel                                                              0.7           83,333.33
         Electrification & other                                                                     0.58          69,047.6
         miscellaneous expenses (@ 10%
         of civil works)
                                                   TOTAL                                             6.38          759,523.8

                                 Table 17 : (D) Cost of Plant & Machinery Required

Reference                                                         Amount (Mil. Rs.)                Amount (US $)
Turbine (Capacity 4 MW)                                           29                               690,476.19
Air compressor for Turbine                                        0.312                            7,428.57
Cooling Towers for Turbine                                        0.676                            16,095.238
High Pressure Boilers (30TPH)                                     21.522                           512,428.57
Boilers chimneys structure Insulation, Refractory &               10.00                            238,095.24
fuel handling system & others miscellaneous
R.O. Plant                                                        2.450                            58,333.33
Pressure Reducing Station                                         1.05                             25,000.00
Safety valves & others valves                                     1.70                             40,476.19
Steam pipe line & pump                                            4.5                              107,142.86
Crane                                                             0.650                            15,476.19
Electrical cable, panel, motors                                   5.00                             119,047.62
Transformer                                                       1.45                             34,523.81
Sub Total                                                         78.31                            1,864,523.81
Trade Tax 4.00%                                                   3.13                             74,523.81
Sub Total                                                         81.44                            1,939,047.62
Freight 10%                                                       8.14                             193,809.52
Total                                                             89.58                            2,132,857.14

                Table 18: (E.)Repair & Maintenance Cost for Building, Plant & Machinery

                        Year       Cost (Million Rupees)                        Amount (US $)
                       2003-04                  2.9                                  69,047.62
                       2004-05                 3.35                                  79,761.90
                       2005-06                 3.85                                  91,666.67

                 Table 19: (F) Additional Manpower required for Co-generation project

                                          No.     Designation                    Number
                                          1       Maintenance Engineer           1
                                          2       Shift Supervisor               3

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     Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                          55

                                           3          Turbine Supervisor       3
                                           4          Boiler Supervisor        3
                                           5          Skilled Workers          9
                                           6          Semiskilled workers      15
                                                      Total                    34 Nos.
                        Annual Salary bill for the above personnel is Rs.1.75 million (US $ 208,333.33)

                                      Table 20 : Summary of Costs (From A to E)

      No.    Particulars                                                            Amount (Mil. Rs.)    Amount       (US $)
      A      Preliminary & Preoperative Expenses                                    0.9                  21,428.57
      B      Cost Involved for procuring Land & Site Development                    1.075                25,595.24
      C      Cost of Civil Works Required                                           6.38                 151,904.76
      D      Cost of Proposed Plant & Machinery Required                            89.58                2,132,857.14
      E      Repair & Maintenance Cost for Building, Plant & Machinery              2.90                 69,047.62
             Contingencies                                                          2.50                 59,523.81
             TOTAL                                                                  103.335              2,460,357.14

   The industry paid an advance of 10 % for initiating the project and 60 % of the payment was
   made after receipt of the machinery & accessories at the industry premises. After the
   successful erection and commissioning of the equipment the unit paid 20% of the total cost
   and the balance 10 % was made after the warranty period of equipment (Year-2005). The
   order was placed in July 2003 and erection and commissioning of the boiler and turbine was
   completed by the end of March 2004.
   5.4.3 Cost benefit of the scheme

   The cost benefit analysis of the scheme was worked out on actual basis taking all the cost.
   The complete analysis is depicted in Table 21
          Table 21: Cost Analysis Before and After Implementation of Cogeneration Scheme

ITEM                   DETAILS                 2002-03             2003-04                 2004-05      2005-06          2006-07
ANNUAL PAPER           THOUSAND                19.80               24.75                   26.73        28.71            30.69
COST OF STEAM          Quantity of             9.79                12.32                   13.31        14.30            15.28
(with existing set     Steam T/hr
up)                    Quantity of             77,536.80           97,574.40               105,415.20   113,256.00       121,017.60
                       Steam T/yr
                       Quantity of Coal        1.78                2.24                    2.42         2.60             2.78
                       Quantity of Coal        14,097.60           17,740.80               19,166.40    20,592.00        22,003.20
                       Rate of Coal            2,300.00            2,300.00                2,300.00     2,300.00         2,300.00
                       TOTAL                   32.42               40.80                   44.08        47.36            50.61
                       COST OF
                       STEAM (Mil. Rs.)

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     Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                             56

ITEM                   DETAILS                2002-03              2003-04     2004-05     2005-06          2006-07
                       TOTAL                  0.772                0.972       1.050       1.128            1.205
                       COST OF
                       STEAM (US
COST OF                Units of               1,312.50             1,662.50    1,795.50    1,903.13         2,034.38
ELECTRICITY            electricity
PRODUCED               produced kW/hr
(with existing         from DG set 1
setup)                 Quantity of            410.16               519.53      561.09      594.73           635.74
                       Quantity of FO(        3,248.44             4,114.69    4,443.86    4,710.25         5,035.09
                       Rate of FO             13,500.00            14,000.00   16,000.00   18,000.00        18,000.00
                       Annual Cost            43.85                57.61       71.10       84.78            90.63
                       (Mil. Rs.)
                       Units of               562.50               712.50      769.50      815.63           871.88
                       produced in
                       kW/hr from DG
                       set 2
                       Quantity of            160.71               203.57      219.86      233.04           249.11
                       Quantity of            1,272.86             1,612.29    1,741.27    1,845.65         1,972.94
                       Rate of                19,500.00            21,000.00   24,000.00   28,000.00        28,000.00
                       Annual Cost            24.82                33.86       41.79       51.68            55.24
                       (Mil. Rs.)
                       Annual                 6.87                 8.70        9.39        9.96             10.60
                       Cost of DG
                       sets(Mil. Rs.)
                       Total Annual           1.88                 2.38        2.57        2.72             2.91
                       MW electricity
                       TOTAL                  75.54                100.16      122.28      146.42           156.47
                       COST OF
                       (Mil. Rs.)
                       TOTAL                  1.80                 2.38        2.91        3.49             3.73
                       COST OF
                       (US $)
TOTAL COST OF          Mil. Rs./year          107.97               140.97      166.36      193.78           207.08
STEAM AND              Million US $           2.57                 3.36        3.96        4.61             4.93

TOTAL COST OF          Quantity of                                             21.20       22.55            24.11
STEAM AND              Steam(T/hr)
ELECTRICITY IN         Quantity of Rice                                        7.07        7.52             8.04
CASE OF                husk (T/hr)
COGENERATION           Quantity of Rice                                        55,968.00   59,532.00        63,650.40
                       husk (T/yr)
                       Rate of Rice           1,600.00             1,700.00    1,800.00    1,900.00         2,000.00
                       Husk (Rs/T)
                       Total Cost of                                           100.74      113.11           127.30
                       Rice Husk (Mil.

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    Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                 57

ITEM                  DETAILS                2002-03              2003-04           2004-05   2005-06          2006-07
                      Total Annual                                                  2.70      2.86             3.06
                      MW electricity
                      Additional                                                    1.75      1.85             1.95
                      annual Cost of
                      manpower (Mil.
                      TOTAL                                                         102.49    114.96           129.25
                      COST OF
                      STEAM AND
                      (Mil. Rs.)
                      (Million US $)                                                2.44      2.74             3.08
PROFITS DUE TO        (Mil. Rs.)                                                    63.87     78.82            77.83
SAVINGS IN FUEL       Million US $                                                  1.52      1.88             1.85

  It can be clearly seen from table 21 that the total investment of 2.46 Million US $ would be
  recovered in just 18 months after the cogeneration plant comes into operation. However in
  reality, due to various other miscellaneous expenditures like price variations, disposal cost of
  ash generated etc. the total cost was recovered after 24 months.
  In addition to the tremendous cost benefits, the adoption of co-generation could
  substantially reduce the energy related GHG emissions by the industry as the furnace oil,
  LDO/HSD & coal used for steam & power generation could be avoided. The direct GHG
  reduction possible for the unit for the year 2004-05 will be 47,322 Tons (The GHG emission
  for Diesel: 2.68 Tons/KL, Furnace Oil: 3Tonnes/KL; Coal 1.53 T/T). This will increase further in
  the following years due to expected increase in production. An illustration is depicted in
  Table 22.
           Table 22 : Greenhouse Gases Emissions Reduction due to Cogeneration 2004-05

                              Fuel                         Quantity     GHG emission in ton
                                                BEFORE COGENERATION
                              Coal (T)                     191,66.40    29324.59
                              Furnace Oil (FO) (KL)        4,443.86     13331.58
                              LDO (KL)                     1,741.27     4666.6036
                              TOTAL GHG                                 47,322.77
                                                 AFTER COGENERATION
                              Rice Husk                    55,968.0     ZERO

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                   58

 6.0 Further Suggestions

The technology described in the earlier sections would fit into the system and process only
if certain specific criteria’s are met and this varies from place to place. Therefore detailed
project feasibility should be undertaken on the guidelines of the case study in section 5 and
then one should go for implementation.
While conducting a detailed feasibility study latest prices should be obtained from various
suppliers. Generally it is a practice to involve the local technology supplier in undertaking
such a detailed feasibility study.
There could be places where the technology would have to be adapted to be used according
to local conditions. Description of such adaptations is beyond the scope of the document.
The technology as described in the earlier sections is for the industries with both steam and
electrical power requirements. However the biomass like rice husk, wood chips etc can be
also used for generating electrical power only. Especially, in areas where electric power is
not available through the grid supply (e.g. in remote villages and inaccessible areas) biomass
based technologies are put to use to generate power. Few of the technologies which have
been successfully demonstrated for rural electrification/application are as follows:
    •     Power generation through direct burning of bio-mass in fluidized bed boiler.
    •     Power generation through bio-mass gasifier.
6.1 Power Generation using bio-mass in FBC Boiler

This is exactly the same technology as described in earlier sections. The only difference is
that in place of an extraction cum condensing turbine, the system has a condensing turbine
only. All the other equipments remain the same. However the sizes of condensers and
cooling towers may slightly increase.
Sometimes, it so happens that the power generated from such power plants are also
supplied to the grid (existing network of electrical power distribution cables). Grid
connected bio-mass power projects, based on direct combustion, have started to pick up in
most of the countries. Compared to the conventional power plants, the biomass operated
power plants have higher heat rate or low efficiency because of high moisture content in fuel
and low gross calorific value. This affects the operating parameters of boilers & turbine.
Normally coal based power plants operate at a heat rate of 2300-2400 kCal/kWh whereas
rice husk fired power generation system the heat rate is in the vicinity of 4500 kCal/kWh.
In India there are several power plants which are in operation using various kinds of biomass.
Figure 225 depicts the number of biomass based power plants and the various fuels used.

                 Based on survey done by National Productivity Council for “An evaluation study on impact of MNRE
               incentive for biomass power generation /cogeneration program”.Nov 2006, by A. K. Asthana and team.

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                    59

          Figure 22 : Various Biomasses based power plants and their numbers in India

6.2 Power Generation through Biomass Gasifier

Biomass fuels available for gasification include charcoal, wood, wood waste agriculture
residues such as coconut shells, rice husks, maize cobs, cereal straws etc. The biomass fuels
differ greatly in their chemical, physical properties; they make different demands on the
method of gasification and require different gasification technology.
The range of different gasifier design includes updraft, downdraft, fluidized bed etc. (Figure
23). All systems show relative advantages and disadvantages with respect to type of fuel. The
followings fuel properties have direct bearing on performance of gasifier.
          Energy content
          Moisture content
          Volatile matter
          Ash content & ash composition
          Bulk density
          Charring properties

                                   Figure 23 : Biomass Gassifier in Operation

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                 60

Before choosing a gasifier for any individual fuel, it is important to ensure that the fuel meets
the requirements of the gasifier. Practical tests are needed if the fuel has not previously been
successfully gasified.
For smooth operation of internal combustion engine for power generation the gas as a fuel
requires a fairly clean gas. The gas to be dust and tar free and during the process it is cooled
down. The biomass gas used for power generation must be virtually tar and dust free in
order to minimize engine wear, and should be as cool as possible in order to maximize the
engine's gas intake and power out put. Biomass gasification for power generation is the befit
technology to meet the power requirement for rural electrification.
For small power generating units say (50 kW - 500 kW) the overall efficiency level varies
from 12-18%, whereas for circulating fluidized bed gasifiers can be used for higher capacity
say 4-4 MW - 10 MW with an efficiency of 23-28%. The capital investment for bio-mass
gasifier power generation system varies from US$ 800-1000 /kWh.

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Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                   61

Annex 1 Block Diagram of Kraft Paper


                        PULPER                                      DIGESTER

                        PULPER                                       BLOW
                          KIT                                        TANK

                       DECKER                                       TDR/SDR




                                                     M/C CHEST

                                               CENTRI CLEANER


                                                    HEAD BOX






                                                     PAPER ROLL

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Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                        62

Annex 2: Block Diagram of White Duplux Board

                      T/L PULPER

                      PULPER PIT                                               P/L PULPER
                                                                               PULPER PIT

                       CHEST 01                                                   H.D

                            H.D                                                3F SCREEN
                     F.N. SCREEN                                    SCREEN


                                                                               M/C CHEST

                                                                               HEAD BOX
                       M/C CHEST

                       HEAD BOX

                        B/L PULPER

                        PULPER PIT


                        TURBO - 500
                          TURBO          -                                                PRIMARY
                          300                                                              CC PIT

                                                                                           CC PIT
SCREEN                                                 DECKER
                                                                                        CC PIT

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Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                       63





   M/C CHEST                                                        M/C CHEST

                                                                    HEAD BOX


                                                                    PRE COATING

PRESS SECTION                                                       CALANDER

  PRE DRYERS                                                        TOP COATING

       M.G                                                             BACK

                                                                    PAPER ROLL


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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                     64

 Annex 3: Technical Specification of Key

A.          BOILERS (MCR)

Steam flow at super heater outlet           30,000 kg/hr
Steam pressure at super heater              65 kg/cm2 (g)
Steam temp. at super heater outlet          485+/-5 Deg.C.
Super heater turndown                       70-100%
Feed water temp. Entering Deaerator 55 Deg.C.
Feed water temp. Leaving Deaerator          105 Deg.C.
Peak load                                   5% of MCR (for half an hour per shift)

Boiler turndown                             1:3
Deaeration steam requirement                Approx. 3000 Kg/hr at 4.0 kg/cm2g & 230 Deg.C. Pr. Control station

     •      GENERAL

                               Type of combustion system             FBC
                               Type of Boiler                        Bi-drum
                               Type of feeding system                Overbed firing
                               Type of water circulation             Natural
                               Type of support/installation          Bottom supported/Indoor
                               No. of Boilers                        One


                      Total number of beds                    Two
                      Expanded bed height                     700-800 mm (approx)
                      Distributor plate section
                      - Top plate thickness                   12 mm
                      - Plate material specification          IS 2062
                      - Material of construction              Alloy C1
                      Inbed tubes
                      - Tube size mm x mm                     Dia 50.8 x 6.35 Thk.
                      - Tube material specification           BS 3059 Part 1 Gr. 320 seasmless
                      - Inbed headers
                      - Material specification                SA 106 Gr. B
                      - Header dia                            219.1 mm OD

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Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                      65

                     Type of fluidized bed wall cons.        Refractory Brick lined (by customer)
                     Combustor Refractory Material
                     Upto 1500 mm above ADP                  IS 8 (50% Alumuina)
                     Above 1500 mm top of ADP
                                                             IS 8 (40% Alumina insulation bricks
                     Outer Layer
                                                             (IS 2042 Gr.II)


                               FUEL FEEDERS (Rice Husk)
                               *    Type of feeders                 Screw Feeder
                               *    No. of feeders                  Four (Total)
                               *    From drive arrangement          CGD/ECV
                               FUEL FEEDERS (Bagasse)
                               *    Type of feeders                 Rotary feeder
                               *    No. of feeders                  Two (Total)
                               *    From drive arrangement          Constant speed motor


                   Location                             Between Boiler Bank and Air preheater
                   Tube size mm                         Dia 38.1 x 3.66 Thk
                   Arrangement and type                 Horizontal in line tubes, counter flow
                   Tube material specification          BS 3059 Part 1 Gr. 320 ERW
                   Headers size                         Dia 168.3 mm
                   Headers material specification       SA 106 Gr. B
                   Casing material                      IS 2062./4 mm thick
                   Tube protection                      Dummy tubes at inlet anti-chanelling baffles

   •     AIR HEATER

                   Arrangement and type                Staggered tubes
                   Tube size                           Dia 63.5 x 2.34 Thk
                   Tube material Specification         BS 6323 ERW
                   Flow medium
                   - Inside tube                       GAS
                   - Outside tube                      AIR
                   Casing material specification       4 mm Thi IS 2062
                   Erosion protection                  Extended tube length of 150 mm at the inlet

   •     Ducting

                                     Air ducting thickness             3.15 mm Thk
                                     Flue gas ducting thickness        4.00 mm Thk
                                     Plate material specification      IS 2062 Gr. A

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  Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                     66


                                      Item reference                  FD FAN      ID FAN
                                      Design Volume, m3/min           400         1300
                                      Design head, mmwg               700         370
                                      Medium                          Air         Flue gas
                                      Temperature Deg.C               40          150


                              Design flow                    38 m3/hr
                              Pressure head                  840 mtc
                              Feed water temperature         105 Deg. C
                              Quantity                       2 nos (one working one standby)
                              Connected load                 160 KW (Approx.)


                Design code                                           As per IS 2825/ASME Sec. VIII
                Design Pressure & Temp                                1.5 kscg. 150 Deg C.
                Source of deaerator steam                             Turbine bleed
                Design capacity                                       36 m 3/ hr
                Capacity of deaeraeted water tank                     10 m3
                Condensate temp. at deaerator inlet                   55 Deg. C
                Steam required at deaerator inlet (Approx.)           3 TPH @ 4 kg/cm2g and 240 Deg. C.
                Material of construction of shell                     IS 2062
                Nozzle/Stubs                                          IS 1239 C Class
                Flanges                                               IS 2062
                Spray Nozzles                                         SS 304
                Trays                                                 SS 304

     •     Feed water

Hardness, max                                                                           ppm                    Nil
PH at 25 Deg.C                                                                                                 8.8 – 9.2
Oxygen, max                                                                             ppm                    0.007
Total iron max.                                                                         ppm                    0.01
Total copper max.                                                                       ppm                    0.01
Silica, Max                                                                             ppm                    0.02
TDS max                                                                                 ppm                    0.1
Conductivity at 25 Deg.C measured max. us/cm after cation exch. In H+ from and after CO2                       0.2
Hydrazine residual                                                                      ppm                    0.02        –

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 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                                                  67

                                       Composition          Rice Husk     Bagasse
                                       Carbon               36.70         23.50
                                       Hydrogen             3.00          3.25
                                       Nitrogen             0.40          0.00
                                       Sulphur              0.08          0.00
                                       Moisture             10.00         50.00
                                       Ash                  18.80         1.50
                                       Oxygen               31.02         21.75
                                       GCV Kcal/Kg          3100          2350

               Type                                   : Multistage, extraction cum condensing Horizontal, Impulse

               Inlet steam conditions                 : 63 kg/cm2G, 485+ 5 Deg. C.

               Extraction pressure                    : 4 kg/cm2G

               Inlet steam flow                       : 26 tph

               Extraction flow                        : 23 tph

               Exhaust flow to condenser               : 6 tph

               Power developed                         : 4000 KW

               Gearbox out speed                       : 1500 rpm

               Alternator                              : 4000 rpm

               Voltage                                 : 11 KV

               Cooling water inlet                     : 32 Deg. C.
               Cooling water outlet temp.              : 40 Deg. C

               Rating                                  : 4000 kW, 5000 kVA

               Type                                   : Brushless Excitation

               Generation Voltage                      11000 Volts

               Frequency                              : 50 Hz

               Speed                                  : 1500 rpm

               Cooling                                : CACW

               Tube material                          : Admiralty Brass

               Cleanliness factor                     : 0.85

               Cooling water inlet temp.              : 32 Deg. C

               Cooling water outlet temp.             : 40 Deg. C

               Cooling Water Flow                     : 556 Cu.m/hr

The steam turbine with speed reduction gearing shall comprise of the following equipment.

 UNEP-DTIE Energy Branch                                                                     http://www.unep.fr/energy
 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration                               68

     1.        One Number Horizontal spindle, two bearing, multistage, impulse type,
               extraction cum condensing steam turbine, capable of generating electrical power
               at generator terminals.
     2.        One Number Set of hardened and ground speed reducing gears, capable of
               transmitting continuously the power generated by above turbine. The gear
               output speed will be 1500 RPM.
     3.        One Number High speed coupling (non-lubricated, flexible type) between the
               turbine and gearbox and low speed coupling (non-lubricated, flexible type)
               between gearbox and alternator.
The A.C. Generator and its control switchgear will be consisting of the following:
     1. One Number - 5000 KVA, 4000 kW, 11000 Volts, 50 Hz, 0.8 p.f.1500 RPM,
        revolving field, double pedestal horizontal alternator.
     2. The alternator will be complete with excitation, automatic voltage regulator and is
        of brush less excitation type.

H.        HT PANEL
     1. One Number H.T. Panel, sheet metal clad, cubicle type for controlling the generator
        output. The panel shall be totally enclosed, self-supporting, floor mounting type for
        indoor installation. It shall be complete with following equipment:
     2. Vacuum circuit breaker of suitable rating.

 UNEP-DTIE Energy Branch                                                   http://www.unep.fr/energy