Paper mill uses combined cycle CHP with landfill gas

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					                                                                                         RESULT 93
                                                                                         UK 90.005/2C.H01
                                                                                         CHP at a paper mill
                                     energy efficiency

      Paper mill uses combined
     cycle CHP with landfill gas

Summary                           turbine driven - and
                                  modifying the existing              Highlights
                                  water-tube boiler,
At Purfleet Board Mills paper     approximately 80% of the         • 2.8 years payback
mill, an increasing power-to-     paper mills’ electrical power      period
heat ratio meant that the         requirements have been met.
original steam turbine-based      Landfill gas had already
CHP system was out of             been shown to be a suitable      • Multi-fuel including
balance with site needs. As a     fuel for the water-tube boiler     LFG
result, efficiencies were poor.   and was adopted as one of
By installing two new             the main fuels for the gas       • High steam load
generators - one gas turbine      turbine. Significant energy
driven, the other steam           cost savings were made.

The steam turbine.

Centre for the Analysis and Dissemination of Demonstrated Energy Technologies
Aim of the project                                   psig). This meant that, by 1985,     retain the boiler in the new
                                                     the turbine was operating at         scheme, modifying it as
                                                     approximately 55% of its             required. Landfill gas was also
Purfleet Board Mills paper mill                      design steam throughput and          chosen as the primary fuel for
manufactures multi-ply paper                         generating only 3.7 MWe of           the new gas turbine. Purfleet
boards from recycled waste                           the 7.64 MWe required by the         Board Mills applied to the
paper. The process requires                          mill. Large quantities of power      Energy Efficiency Office
between 8.4 to 8.8 MWe of                            therefore had to be imported         (EEO) for assistance under the
electricity and manufacturing is                     from the grid to meet the            Energy Efficiency Demonstra-
carried out 24 hours/day, seven                      demand of the site. A new CHP        tion Scheme because the
days/week throughout the year.                       system was therefore                 project was both novel in being
Approximately 140,000 tonnes                         developed to reduce energy           the first gas-turbine-based CHP
of paper is produced annually.                       costs.                               system to use landfill gas as a
Originally, the site was served                                                           primary fuel, and it offered
by a CHP plant comprising a                                                               energy efficiency benefits.
high-pressure Babcock water-                         The Principle
tube boiler capable of
producing 90,000 kg/hour                             The company decided to adopt         The Situation
(200,000 lb/hour) of steam at                        a scheme incorporating a new
4.2 MP (600 psig), and a single                      steam turbine designed for           The new plant is based on a
steam turbine with a design                          present steam conditions in          Ruston TB5000 two-shaft gas
rating of 10 MWe.                                    conjunction with a gas turbine       turbine, an Allen multistage
                                                     to give a combined cycle CHP         steam turbine, and the original
A change in manufacturing                            system with a high power to          water-tube boiler, modified to
practices reduced the amount                         heat ratio closely matching the      allow the high temperature
of process steam required on                         mill loads. Figure 1 shows the       exhaust from the gas turbine to
site. As a result, the boiler                        main features.                       be used as pre-heated
output was reduced to                                                                     combustion air. The gas turbine
63,500 kg/hour (140,000 lb/                          The boiler had been shown to         is operated on either landfill
hour) and the pass-out pressure                      operate satisfactorily on landfill   gas or natural gas (with
was increased to 653 kP (80                          gas and the company wished to        distillate fuel oil as the stand-
                                                                                          by fuel), while the main boiler
                                                                                          is fired by natural gas and
Figure 1: The CHP Scheme
                                                                                          heavy fuel oil; provision
                                                                                          remains for the boiler to fire

                                                                                          landfill gas on two of the

                                      vent                          Boiler stack          burners. A pair of multistage
                                                                                          Belliss & Morcom compressors
                                   FD fan                                                 raise respectively the pressures
                                                                                          of the natural gas and landfill
                           Gas                                                            gas supplies to the level
                         turbine                                                          required by the gas turbine.
                                                Boiler and   fan
                                               economiser            Steam                The nominal output of the two
                                                         BFW         turbine
                                                                                          generators is:
                   M                                                       20 PSIG
                   M                                 Gas oil                              • 3.7 MWe for the gas turbine;
   mill 11kV

                                                                           80 PSIG

                                                     Natural gas                          • 7.6 MWe for the steam
                                                     Landfill gas                            turbine.
                                                                           200 PSIG
                   Landfill gas     Natural gas                                           On average the power output
                   compressor       compressor
                                                                                          meets approximately 80% of
                                                                                          the mill’s requirements. Any
                    Landfill         Natural         Heavy           Gas              Electricity(MWh)
                     gas(TJ)         gas(TJ)       fuel(TJ)       oil(TJ)        bought              sold

  Unit price         1.27/GJ         1.57/GJ        1.65/GJ      3.23/GJ                        0.0247/kWh

  cycle CHP

  Boiler              257             210            780             -
  Gas turbine         204             244              -           6.4
  Electricity                                                                     12,376             765
  Total               462             454            780           6.4            12,376             765

  cycle CHP

  Boiler              462             454            661             -
  Electricity                                                                     48,867                -
  Total               462             454            661             -            48,867                -


  Boiler              462             454            463             -
  Electricity                                                                     73,108                -
  Total               462             454            463             -            73,108                -

  Total costs:   GBP 3.90 for combined cycle CHP
                 GBP 3.44 for steam cycle CHP
                 GBP 3.39 for shell boilers

Table 1: Energy Consumption of New CHP System Compared with Old Steam Cycle CHP System and
System based on Shell Boilers and Purchased Electricity.

imbalance between supply and             extended periods on both           for the whole of 1988. During
demand is accommodated by                natural and landfill gas and       that time, the Powerhouse
either importing or exporting            power has been generated in        operated for 8,100 hours - 300
electricity to or from the grid as       accordance with expectations.      hours less than normal because
required. This aspect of                 Normally, there is a power         of the installation and
operation has presented no               generation deficit of              commissioning of new
problems.                                approximately 1.4 MWe, and         equipment within the mill.
                                         this is balanced by importing      Consumption figures were
The overall availability of the          electricity from the grid.         therefore modified to consider a
steam turbine and gas turbine is                                            typical year of 8,400 hours
in excess of 96% and the                                                    operation.
efficiency of the CHP system at
full load is approximately 77%                                              Table 1 summarizes the energy
gross (83% net). The gas                 The energy consumption of          consumption of the new
turbine has operated for                 the new system was measured        combined cycle CHP system,
and compares it with the                 Taking additional maintenance
energy which would have been             costs into account, cost savings           Host Company
consumed over the same period            are GBP 971,000 for steam                  Purfleet Board Mills
by the old steam cycle CHP               cycle CHP replacement and                  London Road
system and by a system based             GBP 1,444,600 for shell boiler             Purfleet
on shell boilers and purchased           replacement.                               Essex RM16 1RE
electricity.                                                                        United Kingdom
                                         The total capital cost of the
The energy costs for the three           modifications to the system at             Engineering
systems are:                             Purfleet was GBP 2,704,000                 Contractor
                                         giving a simple payback period             Thermal Developments Ltd.
Combined cycle CHP:                      of 2.8 years for the project. If           The Whins
GBP 3,071,400                            the CHP system is used to                  North End Sedgefield
                                         replace shell boilers, the capital         Stockton-on-Tees
Steam cycle CHP:                         cost would be greater, probably            Cleveland TS21 2AZ
GBP 4,074,400                            of the order of GBP 4,700,000.             United Kingdom
                                         In this case, the simple payback           Tel.: +44-740-21614
Shell boilers:                           period would be approximately              Contact: Dr R. Nicholson
GBP 4,548,000.                           3.3 years.

Please write to the address below if you require more information.
                                                                                                                           IEA *
                                                                                            energy efficiency

                                                                                   Swentiboldstraat 21,
                                                                                   6137 AE Sittard,
                                                                                   P.O. Box 17, 6130 AA Sittard,
                                                                                   The Netherlands,
                                                                                   Telephone: +31-(0)46-595-224,
                                                                                   Telefax: +31-(0)46-510-389.

                                                                                   * IEA:   International Energy Agency
                                                                                   OECD:    Organisation for Economic
                                                                                            Co-operation and Development

IEA                                      The Scheme
The IEA was established in 1974 within   CADDET functions as the IEA Centre        Neither CADDET, nor any person
the framework of the OECD to             for Analysis and Dissemination            acting on their behalf:
implement an International Energy        Demonstrated Energy Technologies for
Programme. A basic aim of the IEA is     all IEA CADDET member countries.          (a)   makes any warranty or
to foster co-operation among the                                                         representation, express or
twenty-one IEA Participating Countries   This project can now be repeated in             implied, with respect to the
to increase energy security through      CADDET member countries. Parties                information contained in this
energy conservation, development of      interested in adopting this process can         brochure; or
alternative energy sources and energy    contact their National Team or
research development and                 CADDET. Demonstrations are a vital        (b)   assumes any liabilities with
demonstration (RD&D). This is            link between R&D or pilot studies and           respect to the use of this
achieved, in part, through a programme   the end-use market.                             information.
of collaborative RD&D, consisting of
forty-two Implementing Agreements,       Projects are published as a CADDET        It is permissible to make a copy of this
containing a total of over eighty        ‘Demo’ or ‘Result’ respectively, for      publication as long as the source is
separate energy RD&D projects.           on-going and finalised projects.          acknowledged.

                                                                                                                  March 1992

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