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IPCL Vadodara Steam Traps

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					    Energy Audit of Fuel Fired
 Combustion Furnaces/ Kilns/ Dryers
(covering refractories & insulation aspects)
              & Case Study
                      By
             Debashis Pramanik
               TERI-New Delhi

                 September 13, 2010
    Energy Audit (EA) of Combustion Furnaces,
             Kilns, Dryers & ovens

•    Thermal Systems EA is a part of the Energy Audit, which is
     meant for performing systematic thermal energy systems
     study in a plant. It covers all the systems in the plant which
     involves thermal energy.
•    Type of thermal heating systems (E.g.: Furnaces, Kilns, Dryers,
     Ovens etc.) and refractory/ insulation materials
•    Assessment of furnaces/ kilns/ dryers/ ovens
•    Energy efficiency opportunities
    Energy Audit/ Conservation Opportunities in
             Furnaces/ Kilns/ Dryers
•   Combustion furnace (exclude metals melting)
     – Heating/ baking, Change moisture level (mostly without deforming
       shape) & properties and heat treatment, etc.
•   Type of fuel important
     – Mostly liquid/ gaseous fuel
•   Low efficiencies due to
     – High operating temperature
     – Emission of hot exhaust gases
•   Identify conservation opportunities typical findings include:
          Missing insulation
          Leaking systems
          Equipment running when not required
          Optimization of thermal loading pattern
          Scope for waste heat recovery
          Improperly adjusted or malfunctioning control systems
          System/ Equipment which require diagnostic or special energy audit study.
                            Methodology
For each system:
        a) Identify and check operation of instrumentation associated with
           process and energy.
        b) Identify energy reporting procedure
        c) Check control systems.
        d) Identify and measure all the energy related parameters.
Basic thermal energy/ related parameters measured to work out energy/
heat balance:
        i.   Thermal energy/ fuel flow rate/ pressure
        ii.  Raw materials intake/ products exit quantity/ rate & temperature (raw
             material would include moisture, volatiles, etc)
        iii. Surface temperature
        iv. Flue gas composition (O2, CO percentage & temperature at chamber
             exit for oil/ gas fired systems)
        v. Process section temperature and ambient/ air temperature and
             humidity
        vi. Steam leakage (for steam heating dryers) and steam trap
             performance indices.
                   Test procedure

•   Plan / inform the concerned dept.
•   All the Instrument should be calibrated
•   Ensure fuel/ energy and raw material availability (for
    peak load operation)
•   Test at maximum, steady load condition
•   Conduct 8 hrs minimum (1/2 or 1 hr frequently)
•   Raw material flow level in the system chamber should
    be steady at start & end of test
•   Gas Sampling point should be proper
Furnace/Kiln/Dryer/Oven Components (The Carbon Trust, 1993)

                                                    Chimney: remove            Burners: raise or
                                                    combustion gases           maintain chamber
                                                                                 temperature



Furnace chamber: constructed of
      insulating materials



 Hearth: support or carry the
 steel. Consists of refractory
          materials




                                  Charging & discharging doors for loading &
                                               unloading stock
                       Combustion

• It is an oxidation process in which the constituents
  of fuel combine with oxygen and release heat
• 3 important “T”s of combustion-
   – Time (air/fuel mixing, combustion, residence time)
   – Turbulence (air/fuel mixing)
   – Temperature (adequate to initiate reaction)
Air/Fuel Ratio (Combustion Efficiency Theory/
   Practice) - Excess air introduced to prevent
             incomplete combustion



AIR (O2 & N2)                  EXCESS O2
                 PERFECT
                COMBUSTION
 FUEL (C2H)                      EXHAUST
                               (CO2, H2O & N2)


  Left over oxygen carries heat away from
   furnace/ kiln/ dryer/ oven
       Combustion characteristics & ambient
                   condition
Flue gas consists of
   –   CO2
   –   SO2
   –   CO
   –   N2
   –   H2O ( vapors)
   –   O2 / air (unreacted and infiltrated)

Ambient condition
• Temperatures
   – Dry bulb
   – Wet bulb
• Absolute humidity

• These are beyond the control of system operators
 Furnace/ kiln/ dryer/ oven efficiency
           and heat losses
                    Efficiency evaluation


    Direct method                  Indirect method


- Easy & quick                    - Heat loss method
- Few parameters
                                  - Calculate all losses
- Few instrumentation
                                  - Efficiency = 100 - losses
- Accurate measurement
                                  - Needs more parameters
- Chances of large error
- No clue on low efficiency       - Needs more instruments
- No clue on losses               - More accurate
   Heat distribution/ losses in the furnace/ kiln/
                    dryer/ oven

• Heat absorbed in endothermic process/ heat discharged in
  exothermic process
• Dry flue gas loss (due to high EA and FGT)
• Loss due to CO in flue gas (%CO in FG)
• Loss due to hydrogen and moisture in fuel (moist. & H2 in fuel and
  FGT)
• Loss due to moisture in air (abs. humidity, EA and FGT)
• Heat absorbed by the dry raw material constituents
• Surface heat loss (surface temp.)
• Heat loss in removal of moisture (if any)
• Heat retained with thermally processed product, moisture (if any)
  in the product
      Approach for energy efficient operation of
                 thermal systems
•   Complete combustion with minimum excess air (15-30% for Fuel oil & 5-10%
    for Natural Gas ) and control air infiltration
•   To avoid infiltration/ ex-filtration, slight positive pressure should be maintained
    inside the furnace/ kiln/ dryer. oven
•   Proper heat distribution
•   Operation at the optimum temperature of combustion chamber in furnace/ kiln/
    dryer/ oven
•   Reducing heat losses from chamber openings
•   Maintaining correct amount of system draft
•   Optimum capacity utilization
•   Waste heat recovery from the flue gases
•   Minimize furnace/ kiln/ dryer/ oven skin losses
•   Improving the performance of refractories/ insulations
  Energy efficiency/ conservation opportunities
EFFECTS OF EXCESS AIR
• Every fuel has the need of stoichiometric air for combustion
• It is not sufficient to burn the fuel completely
• Excess air
    – depends on type of fuel, age and type of thermal systems
    – needed to complete combustion
• Optimum combustion air = increased efficiency
    – Too much air = decrease flame/ comb. chamber temperature and increase the
        losses (excess heat loss in stack)
    – Too little air = render the combustion incomplete and more CO will be formed
        resulting into the fuel loss and more pollution (wasted fuel)
• CAUSES OF EXCESS STACK TEMPS.:
    – Excess air
    – Fouled raw material/ product side surfaces
    – Overfiring
    – Insufficient heat transfer surface
    – High product temperature
              Optimum capacity utilization

• Optimum load (low/ high)
   – Underloading: lower efficiency
   – Overloading: load not heated to right temp
• Optimum load arrangement
   – Load receives maximum radiation
   – Hot gases are efficiently circulated
   – Stock not placed in burner path, blocking flue system, close to
     openings
• Optimum residence time
   – Planning at design and installation stage
   – Coordination between personnel
       Waste heat recovery from flue gases
• Only insufficient heat transfer surface or high flue gas
  temperature (> 200OC) indicates potential for recovery of waste
  heat and justify a recovery system:
   –   Excess air - adjust air/ fuel ratio
   –   Fouled surfaces - can be detected by visual inspection
   –   Over-firing
   –   FG temp must be at least 35-40°C (practical range) over the minimum
       allowable
• Charge/ load pre-heating
   – Reduced fuel needed to heat them in furnace/ kiln/ dryer/ oven
• Pre-heating of combustion air
   – Applied to compact industrial furnaces/ kilns/ dryers/ ovens
   – Equipment used: recuperator/ air pre-heater, self-recuperative burner
   – Up to 25% energy savings
• Heat source for other processes
   – Install waste heat boiler to produce steam/ hot water
   – Heating in other equipment (with care)
    Broad Classification Insulation Materials

• Material with low heat conductivity: keeps furnace surface
  temperature low
• Classification into four groups
   – Insulating bricks
   – Insulating castables and concrete
   – Ceramic fiber
   – Calcium silicate
                         Refractories

• Materials that
   – Withstand high temperatures and sudden changes
   – Withstand action of molten slag, glass, hot gases etc
   – Withstand load at service conditions
   – Withstand abrasive forces
   – Conserve heat
   – Have low coefficient of thermal expansion
   – Will not contaminate the load
           Classification of refractories
Classification method                      Examples

Chemical composition
ACID, which readily combines with          Silica, Semisilica, Aluminosilicate
  bases
BASIC, which consists mainly of            Magnesite, Chrome-magnesite,
  metallic oxides that resist the action   Magnesite-chromite, Dolomite
  of bases
NEUTRAL, which does not combine            Fireclay bricks, Chrome, Pure Alumina
  with acids nor bases
Special                                    Carbon, Silicon Carbide, Zirconia

End use                                    Blast furnace casting pit

Method of manufacture                      Dry press process, fused cast, hand
                                           moulded, formed normal, fired or
                                           chemically bonded, unformed (monolithics,
                                           plastics, ramming mass, gunning castable,
                                           spraying)
            Refractories Walls/ Linings
• Refractory lining of a furnace arc




• Refractory walls of a furnace
  interior with burner blocks
• (BEE India, 2005)
            Major properties of refractories
• Melting point (Temp. at which a „test pyramid‟/ cone fails to support its
  own weight)
• Size
    – Affects stability of furnace structure
• Bulk density (kg/m3), high (high volume stability, heat capacity and
  resistance)
• Porosity (open pores as % of total refractory volume)
• Thermal conductivity
    – Depends on composition and silica content
    – Increases with rising temperature
• Low thermal conductivity:
    – Heat conservation required (insulating refractories)
    – E.g. heat treatment furnaces
• High thermal conductivity:
    – Heat transfer through brickwork required
    – E.g. recuperators/ regenerators
• Volume stability, expansion & shrinkage
    – Permanent changes during refractory service life
    – Occurs at high temperatures
                  Ceramic fibres

• Thermal mass insulation materials
• Blended alumina & silica are the raw materials
• Bulk wool to make insulation products
   – Blankets, strips, paper, ropes, wet felt etc
• Produced in two temperature grades
Economic reasons for Thermal insulation in
               industry

• Reduces fuel
  consumption, and hence     • Day-to-day economy
  overall operational cost     benefits
• Reduces capacity
  requirements for heating   • Savings in Capital costs
  systems
        Thermal Insulation In Industry

• The basic criterion for thermal insulation is
  Economics
• However, this is not the sole criterion
                Thermal Insulation



Insulation, by virtue of its features, should resist the
transfer of heat by:
- Radiation
- Convection
- Conduction
        Remarkable properties and benefits

•   Low thermal conductivity   •   Lightweight furnace
•   Light weight               •   Simple steel fabrication work
•   Lower heat storage         •   Low down time
•   Thermal shock resistant
                               •   Increased productivity
•   Chemical resistance
•   Mechanical resilience      •   Additional capacity
•   Low installation costs     •   Low maintenance costs
•   Ease of maintenance        •   Longer service life
•   Ease of handling           •   High thermal efficiency
•   Thermal efficiency
                               •   Faster response
          Hot Surface Thermal Insulation

Is a provision made to retard flow of heat
- from a hot surface to a cold environment

When chosen properly and installed well, thermal insulation is
like the ideal wife
- non-complaining
- maintenance-free
- patient workhorse
                  Hot Surface Insulation

Other benefits
- Prevent heat loss
- Reduces energy consumption
- Control process temperatures
- Protection to personnel
- Provides fire protection to equipment
- Absorbs vibration

Lack of insulation  unnecessary heat loss
Wet insulation  heat loss
        Energy loss from hot surfaces

 Difference between Heat loss kcal/ m2-hr
 ambient and surface
 temperature°C

            25                        340
            40                        600
            100                       1910
            150                       3225
            225                       5330
From a metallic surface at 30°C ambient temperature and
wind velocity 3m/sec
                                Economic Thickness



                                                          TOTAL
COST PER YEAR, RS




                                                          COST




                        INSUL                                           MINIMUM
                                                      LOST              COST
                        ATION
                                                      HEAT
                        COST
                                                      COST




                    0   1   2     3   4   5   6   7   8      9    10   11

                                INSULATION THICKNESS, INCHES
  Process Control reasons for Hot Thermal
                insulation



• Reduce temperature drop of fluid in a heated system
• Reduce boil off rate in volatile liquid storage systems.
• Assist in maintaining thermal balance in reaction
  systems
                   Types of insulation

• Mass-type insulation
  -   Based on interposing a mass of material with a built-in
      capacity to retard heat flow.
• Reflective insulation
  -    Based on providing a series of reflective surface with the
       intervening spaces evacuated.
• Microporous Insulation
  -   Based on a combination of Mass & Reflective
      technologies.
                   Physical properties

Significant physical parameters of thermal insulating materials
can be divided into

-   Thermal Properties (temp. resistance, thermal
    conductivity, thermal diffusivity, thermal shock
    resistance)
-   Mechanical Properties (strength, abrasion
    resistance, coefficient of expansion/contraction,
    ability to withstand vibration and noise)
-   Chemical Properties (resistance to metal and
     moisture, chemicals, fire, etc)
-   Commercial Factors
                   Fibrous Materials

They are easily available in various usable forms:
a)     Rigid slabs, matts & preformed pipe sections
b)     Blankets / mattress
c)     Felts
d)     Loose fill
e)     Sprayable solid surface coating
f)     Cement type formulations
                              Commonly used hot insulation

                        0.1

                       0.08
Thermal Conductivity
     in W/mk




                       0.06                                         Cal. Silicate
                                                                    Rockwool
                       0.04

                       0.02

                         0
                              165   265   365   465     565   665
                                          Temp. in °C



                                    -Rockwool,
                                    -Calcium silicate
                                    -Ceramic fiber
          Protective Covering/Cladding


A covering is required over the insulation for-
-    protection against mechanical damage, weather, and
     chemical attacks
-    retardation of flame spread in case of fire
-    physical protection
-    an easy-to-clean surface
-    identification of pipelines, and
-    external appearance.
          Protective Covering/Cladding

The various types of protective coverings used in the complex
are:

- metal sheets (aluminum and galvanized iron sheets, tainless
  steel)
- finishing cement, and
- bituminous materials with wire netting (tar)
             Energy audit of insulation

•   Identify/Categorize all major hot segments
•   Measure surface temperature at regular intervals
•   Measure the wind velocity and ambient temperature
•   Mark damaged portion / bare surfaces
•   Replace damaged insulation or provide insulation to the bare
    surfaces
             Energy audit of insulation

A walk-through survey of the hot surfaces should be carried
out once every six months. This would help in identifying the
status of insulation and any degraded or bare surface for
necessary action. Such a survey also helps in reducing the
problems of temperature drop along hot surfaces.
Typical format for insulation data collection

• Measured data
A) Furnace walls
  Table – I-1

    Location    Type of insulation   Surface            Ambient
                & comments           temperature (0C)   temperature (0C)




B) Doors/ covers, valves & flanges (hot segment surroundings)
  Table – I-2

    Location    Type of insulation   Surface            Ambient
                & comments           temperature (0C)   temperature (0C)
Typical efficiencies for industrial furnaces/ kilns/ dryers

                         Furnace type     Thermal efficiency (%)
1) Low Temperature furnaces
a. 540 – 980 oC (Batch type)                       20-30

b. 540 – 980 oC (Continous type)                   15-25

c. Coil Anneal (Bell) radiant type                  5-7

d. Strip Anneal Muffle                             7-12

2) High temperature furnaces
a. Pusher, Rotary                                  7-15

b. Batch forge                                     5-10

3) Continuous Kilns/ dryers
a. Hoffman                                         25-90

b. Tunnel                                          20-80

4) Ovens
a. Indirect fired ovens (20 oC –370 oC)            35-40

b. Direct fired ovens (20 oC –370 oC)              35-40
                        Energy saving tips
•   Recover and utilize waste heat from furnace flue gases for preheating of
    combustion air. Every 21OC rise in combustion air temperature results in
    1% fuel oil savings.
•   Control excess air in furnaces. A 10% drop in excess air amounts to 1%
    saving of fuel in furnaces. For an annual consumption of 3000 KL of
    furnace oil means a saving of Rs 3 lakhs, (cost of furnace oil-Rs. 10 per
    liter).
•   Reduce heat losses through furnace openings. Observations show that a
    furnace operating at a temperature of 1000OC having an open door
    (1500mm × 750mm) results in a fuel loss of 10 lit/hr. For a 4000 hrs
    furnace operation, this translates into a loss of approx. Rs. 4 lakhs per
    year.
•   Improve insulation if the surface temperature exceeds 20OC above
    ambient. Studies have revealed that heat loss form a furnace wall 115mm
    thick at 650OC amounting to 2650 kcal/m2/hr can be cut down to 850
    kcal/m2hr by using 65 mm thick insulation on the 115 mm wall.
   Case Study - LPG Fired Ovens in
        Engineering Industry

• Taikisha
  – Dry-off oven
  – Bake oven
• ABS
• OMT
  – Dry-off oven
  – Bake oven
• Haden
                         Important Data

                            Taikisha             ABS              OMT          Haden
                                                           Dry-
                         Dry-off       Bake                Off      Bake

                        Frame         Fuel     Visor /     Fuel Frame          Fuel
Material processed      body          tank     Fenders     Tank body           Tank
Material processed
(kg/hr)                     4882        2667        409 3080            4421     3080
Oven Temperature (OC)        130         138         76 152              147      135
LPG consumption
(m3/hr)                         7.2                  1.4          7.6             5.2
                                     Heat Balance

                          Taikisha                ABS                 OMT                 Haden

                      kcal/hr    %          kcal/hr     %       kcal/hr     %       kcal/hr       %

Heat Input
LPG                   146127.2   100.0      28893.3     100.0 154148.0      100.0 106421.6        100.0

Heat Output
Exhaust Air            58517.0       40.0    7944.1      27.5   51747.5      33.6   20481.2           19.2
Material               49518.3       33.9    5011.7      17.3   69716.5      45.2   29752.8           28.0
Surface Losses         12066.7        8.3    6766.9      23.4    7751.3       5.0   11138.1           10.5
Conveyor               14519.8        9.9    3541.9      12.3   17708.5      11.5   10867.5           10.2
Unaccounted Lossess    11505.4        7.9    5628.7      19.5    7224.2       4.7   34182.0           32.1
                           Savings

• The temperature can be reduced by bringing down the hot
  air inlet temperature by about 200C.
• Rs 32,000/- per annum

Parameter                         Unit
Present air inlet temperature     o
                                      C           183
Proposed hot air inlet            o
                                      C           163
temperature
Quantity of air                      3            372
                                 m /hr
Reduction in heat requirement   kC al/hr         2207
Equivalent fuel                  Kg/hr           0.19
Monthly fuel saving               kg              76
                               Savings

•   Fuel savings by reducing exhaust temperature in OMToven
     – by enhancing heat exchange area
•   Rs 3.46 lacs per annum


    Parameter                            Unit

    Present air inlet temperature               o
                                                    C         334
    Proposed exhaust flue gas                   o
                                                    C         180
    temperature
    Quantity of air                                           450
                                            m3 /hr
    Reduction in heat requirement          kC al/hr           2207
    Equivalent fuel                         Kg/hr             1.9
    Monthly fuel saving                         kg            886
Thank you !

 debashis@teri.res.in
   www.teriin.org

				
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