|Landfill Gas Generation
Landfill gas forms when organic matter and moisture are trapped underground. Because the landfill is maintained under a vacuum, some air is drawn into the "bed," but ideally, the amount is minimal and the process for the most part takes place in the absence of oxygen or anaerobically. Anaerobic organisms digest the organic matter and give off a bio-gas that, when drawn out of the landfill, contains a mixture of approximately 50% methane, 40% carbon dioxide, 9% nitrogen and 1% oxygen that is saturated with water vapor. The mixture includes trace amounts of gas made up of compounds of sulfur and nitrogen which give it a strong odor.
|Green Knight Energy Center
Prior to the establishment of the Green Knight Energy Center, landfill gas was extracted from the landfill by exhauster blowers and delivered to large flares that burned the methane to eliminate any fire or explosion hazard. Flaring the gas also destructs the odorous trace gases. At the Green Knight Energy Center, landfill gas now is diverted away from flares, and goes through multiple stages of filtering, compression, cooling and drying before reaching the three turbine engines for use as fuel. Each turbine engine drives its own electric generator, which produces electricity at 4,160 volts. A high-voltage transformer raises the voltage to 34,500 volts to match that in the wires of the local delivery company (Metropolitan Edison) for transmission to the main distribution grid.
|Power to Distribution Grid
The Green Knight Energy Center is capable of generating approximately 10 megawatts of 4,180 volt electric power. It uses approximately 19% of that to drive the landfill gas compressors and operate the station. Electricity going to market must first be transformed to 34,500 volts to match the voltage on the lines of the local electric utility company that transmits it to the North Bangor substation. At the substation, the voltage is increased to 110,000 volts for transmission on the PJM (Pennsylvania-New Jersey-Maryland) grid. From the grid, the electricity goes to a power purchaser (Exelon) for sale as "green" (or renewable) power.
Gas Turbine Overview
Environmental Protection Agency’s Landfill Methane Outreach Program
Landfill Methane Outreach Program in Pennsylvania
Waste Management Educational Resources, includes factsheets about methane gas extraction wells and landfill gas-to-energy
Tour of the Grand Central Sanitary Landfill