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One of West Point's cogeneration engines

Cogeneration (combined heat and power) is the concurrent production of power and heat from the same source.

Cogeneration of power and heat can be produced using any number of methods. King County currently uses two cogeneration systems: internal combustion cogeneration and gas turbine cogeneration, described below. Additionally, a  fuel cell (a non-combustion method of cogeneration) was built and tested in 2004 as a two-year demonstration project. For more information on the fuel cell demo and other research and demonstration projects, visit our project library.

Internal combustion engines

Internal combustion cogeneration systems use an engine similar to an automobile engine. In this case, renewable digester gas is used as the energy source instead of gasoline, and the output of the engine runs a generator. At the West Point Treatment Plant , two internal combustion engines fueled by digester gas provide power to generators that produce electricity. The exhaust heat from these engines also boils water, which is then sent to heat the plant's digesters and occupied spaces. This new system is expected to produce 17,500MWh of electricity each year.

 

Gas turbines

The South Treatment Plant in Renton, WA currently operates this gas turbine cogeneration. Two gas turbines combust digester gas and turn fan blades, creating heat. This recovered exhaust heat is then used to boil water and create steam. The steam is used to heat the digester tanks and other places in the plant. The steam is also used to generate electricity in a steam turbine.

This system was designed to provide standby power at the treatment plant, but can also operate during months of high energy use to reduce peak load charges. If the total system were called into action, it would generate 8 megawatts of electricity under normal conditions, enough power to operate the plant most days of the year.

For more information about resource recovery, please contact us at: