Exelon taps into landfill gases to create electricity.
Ben Armstrong - EXELON GENERATION - June 2006
Gas collection tanks at a Landfill Gas power generation facility.
Exelon Power’s Fairless Hills Generating Station is a two-unit, 60-megawatt plant purchased in 1997 from USX Corporation, also known as U.S. Steel that has been configured to burn captured landfill gas.
The plant, which began commercial operation in 1952, was originally designed to burn oil, natural gas and waste gases from the adjacent USX steel plant.
Soon after purchasing the plant, Exelon, which was PECO at the time, retrofitted two of the plant’s boilers to burn landfill gas. The landfill gas is generated at the adjacent GROWS and Tulleytown landfills, which are owned and operated by Waste Management, Inc.
Most of the waste generated in the United States is disposed of in landfills. Inside a landfill, waste breaks down and produces gas. The main components of landfill gas are methane and carbon dioxide (CO2).
Exelon is reducing overall greenhouse gas emissions by supporting the use of landfill gas for electricity production. This results in less emissions than burning fossil fuels, and has the added benefit of capturing an energy source that otherwise would have gone to waste. CO2 from landfill methane gas is considered biogenic, or part of the natural carbon cycle, as contrasted with CO2 from the burning of fossil fuel, which is considered anthropogenic, or arising from human activity. Thus, when the landfill gas displaces fossil fuel, it helps reduce human-caused greenhouse gas emissions into the atmosphere.
As waste in a landfill continues to decay, it produces more gas. Most landfills collect the gas in some way to control its release into the environment. In many cases, this collected gas is used as a fuel to create electricity, including at Fairless Hills.
In 2004, Exelon Power began a two-phase project to make the updates needed to take advantage of additional landfill gas being captured at the landfills.
Phase one of the project included the refurbishment of the two operating boilers and one of the turbine generators, TGB, to its original design condition. These upgrades were performed to improve efficiency and increase the output when operating on landfill gas.
In December 2004, $4.2 million was invested to upgrade the number 4 and 5 boilers and the “B” turbine generator. About 25 percent of the super heater tubing has been replaced in the boilers. Employees also replaced the steam separator tubes, which limit the amount of sodium carryover into the turbine, according to Eric Schwalm, senior project manager for Exelon Power’s Peaking Division. “Sodium from the steam is deposited on the turbine components, which causes a loss in turbine efficiency and corrosion of those components”, he said.
Additional repairs to the boilers include the replacement of refractory, which protects the outside of the boiler from the high temperature inside, and the replacement of steam stop valves, which allow workers to sectionalize areas of the boiler for work.
On the “B” turbine, repairs included the replacement of 50 percent of the turbine rotating blading, extensive repairs to the stationary blading and seals. Additionally, employees replaced turbine supervisory instrumentation to allow the operators and engineers to better analyze turbine vibration and bearing temperature problems.
Exelon Power recently completed phase two of this upgrade project. The TGA turbine was opened and approximately 80 percent of the rotating and stationary blading has been replaced.
As a result of this project, Fairless Hills Generating Station has become the second largest landfill gas station in the United States, second only to Puente Hills landfill gas project in Los Angeles, Calif.
While Exelon has worked to improve the capabilities at Fairless Hills, Waste Management has been working to ensure the landfill gas continues to flow. Waste Management has been increasing the size of the landfills and installing new wells to make more gas available.
Prior to the work, Fairless Hills utilized about 10,641 standard cubic feet per minute (scfm), which was about as much fuel as Waste Management could provide. This was due to the system that transports the gas from the near by landfills to the station.
Much like moving natural gas, landfill gas is transported through a piping system. Waste Management uses a compressor at Tulleytown to push the landfill gas to Pennsbury, another Exelon owned landfill gas generating station. At Pennsbury, Exelon operates three high-speed compressors (22,000 rpm) to pull the gas from the GROWS and Tulleytown landfills and “push” it to the boilers at Fairless Hills.
Waste Management has been able to improve its ability to provide landfill gas by both rehabbing and installing new equipment at Tulleytown and Exelon’s compressor station at Pennsbury. Currently Fairless Hills is receiving 15,000 scfm of landfill gas and generating 32 megawatts of electricity. It is projected that by 2013 Waste Management will have the ability to provide 22,997 scfm per day to Fairless Hills, more than doubling the landfill gas previously provided.
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