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Power Generation at the JWPCP
The JWPCP is self-reliant with respect to power generation. All of the power and heating steam requirements for the plant are provided by three digester gas fired turbines and one steam turbine. Utility power is available whenever the on-site power plant is out of service.
DIGESTER GAS PRETREATMENT
Digester gas from Primary Treatment is dewatered and scrubbed of particulate matter to protect the compressors from excessive wear. Digester gas is first scrubbed of particulate matter using two venturi scrubbers and non-potable water. Particulate matter is removed and regularly blown-down from the scrubber storage tanks. Two mist eliminators, downstream of the venturi scrubbers, remove water droplets from the gas stream. The digester gas is further treated using two chillers that condense water vapor. Water vapor is removed to prevent deterioration of the compressor lubrication oil. From there, the digester gas is directed to a surge tank to remove surges from the low-pressure digester gas supply and act as a mixing chamber for natural gas prior to compression. Natural gas is used to supplement digester gas during periods of low digester gas production.
FUEL GAS COMPRESSORS
Three compressors are used to compress digester gas approximately 10 inches of water to 350 pounds per square inch (psig). Compression is accomplished in three stages. Each compressor has two first stage cylinder pistons that compress the low-pressure digester gas to approximately 50 psig. A single second stage cylinder piston compresses the gas further to roughly 150 psig. The third and final stage cylinder piston achieves a pressure of 350 psig. Prior to combustion in the gas turbines, the high-pressure digester gas is chilled to 40 degrees Fahrenheit to condense most of the remaining water vapor. Chilling is accomplished using a refrigeration system.
The gas turbine driven generator system is the normal source of power for the JWPCP. Three Solar Mars 90 digester gas-fired turbines provide the necessary power. Each turbine package is equipped with a 9.9 MW electric generator. Typically, two gas turbines are in operation with the third acting in standby. Emissions control is achieved using water injection to reduce oxides of nitrogen. De-ionized water is used for injection eliminate turbine blade damage. The water treatment system includes a water softener unit for the removal of hardness, a reverse osmosis unit to remove dissolved solids, and a set of demineralizers to provide additional dissolved solids removal. During periods when the gas turbines are not operational, the digester gas can be burned at two different flare stations. The South Flare Station consists of five waste gas flares and the North Flare Station consists of seven waste gas flares.
Gas turbine exhaust gas is used to heat water, thereby, producing steam. Steam is produced through the use of heat recovery steam generators (HRSGs) and directed to a Steam Turbine for power production and digester heating steam.
When the steam system is not operational, digester heating steam is provided by means of four digester gas-fired boilers. An additional natural gas-fired boiler is available for emergencies.