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4.7 | Installing Cogeneration |
CHARACTERISTICS
Cogeneration is the joint production of electricity and heat from a single combustion process. A typical cogeneration system consists of an engine, steam turbine, or combustion turbine that drives an electrical generator. A waste heat exchanger recovers waste heat from the engine and/or exhaust gas to produce hot water or steam. Cogeneration produces a given amount of electric power and process heat with 10% to 30% less fuel than it takes to produce the electricity and process heat separately.
Cogeneration can be used wherever there is a need for both electricity and steam. Wherever on-site electric generation is required, thermal energy can also be created; conversely, thermal energy users can also generate electricity.
By offering significantly higher efficiencies than conventional power generating technologies (when used with combined cycle applications, cogeneration can achieve up to 90% efficiency), cogeneration is an excellent means of increasing overall energy efficiency in the generation mix. The amount of useful energy obtained per amount of greenhouse gases emitted increases and where low-carbon fuels (i.e., biomass) are used, emissions are reduced even more.
SIZE:
Steam turbines (extraction-condensing type): 30-300 MWe; back pressure type: 20-200 MWe.
Combustion gas turbines: 10-100 MWe.
Indirectly fired gas turbines: open-cycle: 10-85 MWe; closed-cycle: 5-350 MWe.
Diesel engines: 0.05-25 MWe.
FEATURES:
Can be used wherever there is a need for both electricity and steam, and whenever on-site electric generation is required or thermal energy users are in close proximity. When used with combined cycle applications, can achieve up to 90% efficiency.
COST:
$1000/kW combined output for industrial engine.
Cogeneration is the cheapest form of thermal power generation.
CURRENT USAGE:
Currently, manufacturers use 90% of all cogeneration systems. Another large-scale application of cogeneration is for district heating.
POTENTIAL USAGE:
Several initiatives are underway to actively promote increased use of cogeneration. Industrial customers with steam demands are ideal candidates for cogeneration, but commercial establishments can also cogenerate electricity from the energy they use for space conditioning and water heating. Another potential deployment opportunity can be as a substitute for heat-only boilers used for district heating. Smaller systems are being developed for residential uses. Small-scale (20-650 kW and up to 5 MW) packaged or "modular" systems that produce electricity and hot water from engine waste heat are being manufactured for commercial and light industrial applications. However, small-scale cogeneration has not been widely used in the United States due to the initial costs associated with buying and installing the system.
ISSUES ASSOCIATED WITH IMPLEMENTING ACTION
- Design of cogeneration applications are site-specific making system replications (or standardization) difficult or impossible.
- Time-of-use characteristics of electrical generation and thermal host needs must be conducive to economic operation of both.
- It can be difficult to set tariffs for grid sales and purchase of complementary power.
CLIMATE CHANGE IMPACT
EMISSION EFFECT:
CONDITIONS FOR EMISSIONS MITIGATION:
- Because of high operating efficiency, carbon emissions will be much less than with conventional power systems.4
EMISSION ESTIMATE:
Carbon emissions will be significantly less than from conventional systems because of the much higher efficiencies of cogeneration systems.
COST-EFFECTIVENESS:
Where located close to industrial facilities that demand the steam and electricity, cogeneration is a highly cost-effective way to reduce GHG emissions.
SECONDARY EFFECTS:
SO2: Produces no emissions from natural gas, but other fossil fuels will produce some emissions.
NOx: Emissions will vary according to the turbine design/boiler/combustion chamber type/fuel.
Particulates: No particulates when natural gas is combusted; amounts for solid fuels will depend on the type of control technology.
Hydrocarbons: Varies according to operating conditions and type of fuel.
RESOURCES
- DOE Office of Industrial Technologies demonstrations of improved steam and gas turbine systems. This same office also sponsors the Combined Heat and Power Challenge, working with states to promote dialogue and innovation to increase the use of CHP. http://www.oit.doe.gov/chpchallenge/#addresses
- Wilkinson, B.W., and R.W. Barnes. 1980. Cogeneration of Electricity and Useful Heat, CRC Press, Inc., Boca Raton, FL (US).
- Brown, Michael, 1996, Industrial Cogeneration: Towards a New Vision for Electricity Production, COGEN Europe (October), Belgium.
- NERAC, Inc., 1996, Cogeneration: Economic and Technical Analysis, (Latest citations from the INSPEC database), National Technical Information Service.
CONTACTS
Association of Energy Engineers
Atlanta, GA
Tel: (770) 447-5083
Fax: (770) 446-3969
http://www.aeecenter.org
Electric Power Research Institute
Palo Alto, CA
Tel: (650) 855-2000
http://www.epri.com
International District Energy Association
Washington, DC
Tel: (202) 429-5111
Fax: (202) 429-5113
U.S. Department of Energy
Office of Industrial Technologies
Combined Heat and Power Challenge
Patricia Hoffman
Washington, DC
Tel: (202) 586-6074
Patricia.Hoffman@hq.doe.gov
http://www.doe.gov
U.S. Environmental Protection Agency
Washington, DC
Skip Laitner
Tel: (202) 564-9833
laitner.skip@epa.gov
http://www.epa.gov
4One project, in Decin, Czech Republic expects to achieve 20,000 tons/year C avoided from retiring coal boilers and adding two gas turbines and a cogeneration systems to its approximately 20 MW system (6,000 tons/year C reduction will result from fuel-switching). Cost of these reductions is estimated to be US $5.56 tons of CO2 per year. This project also virtually eliminates SO2 and ash.
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