Landfill Gas Capture and Utilization
These are two enclosed methane flares at the I-95 Landfill.
What is Landfill Gas?
Landfill gas is essentially an equal mixture of methane and carbon dioxide, and is a by-product of the decomposition of organic matter buried in sanitary landfills.
In the past, it was common practice to vent or flare the gas once it was collected. Thanks to several technological advancements, it is now possible for landfill gas to be collected and conditioned in order to be used as a valuable resource for heating fuel - as an alternative to natural gas and propane - and energy production.
Landfill Gas Utilization: Process Overview
Landfill gas utilization began in Fairfax County in 1990. From that point on, landfill gas has been used as a fuel source for the incineration of bio-solids at the Noman M. Cole Pollution Control Plant, as an alternative source of heating fuel and to produce electricity.
- Collection. Landfill gas is recovered from each of the county's sanitary landfills through several hundred gas wells which are drilled into the landfill and connected by a network of pipes to the blower station. A high-powered vacuum system draws the gas from the gas wells and delivers it to the compression and treatment system.
- Conditioning. This stage of the process is essential for removing moisture and particulates from the landfill gas. The conditioning process involves the cooling of landfill gas to about 34 to 40 degrees. At that point, moisture is removed from the landfill gas in the form of condensation and is collected in a separate reservoir and drained out of the system. This results in the removal of 99 percent of condensed moisture from the landfill gas. The conditioning system also includes filters to remove particulate matter sized 1/2 micron or larger.
Saving Money by Using Landfill Gas
- Energy Production: Approximately 2,000 cubic feet/minute (cfm) of landfill gas is extracted from the I-95 Landfill. Approximately 1,600 cfm of that gas is used to power up to eight Caterpillar 3516 gas engines. These generators produce 4.9 megawatts of electricity - enough to power approximately 3,100 homes in Fairfax County. The power is sold to our local utility, Dominion Virginia Power. The revenues from the sale of the electricity help to keep the Solid Waste Management Program as a self-funded agency. This landfill gas to energy project has been operating since 1990.
- Noman M. Cole Pollution Control Plant: A three-mile pipeline transmits landfill gas from the I-95 Landfill to the nearby Noman M. Cole Pollution Control Plant at a rate of up to 700 cfm. The landfill gas supports the incineration process to destroy bio-solids and fuels afterburners which reduce hydrocarbon emissions. Landfill gas utilization in this process saves Fairfax County approximately $100,000 a year.
- Heating Fuel: In 2009, standard natural gas infrared heaters were retrofitted to utilize landfill gas and installed in the maintenance building, truck wash of the I-66 landfill complex, and a 10-bay vehicle garage nearby. The total savings from these projects is estimated at approximately $105,000 annually.
Quick Facts About Landfill Gas Utilization
- More than 200 methane extraction system wells are used to collect landfill gas. Captured gas is used to generate almost five megawatts of electricity - enough for about 3,100 homes. The gas is also sent to the nearby Noman M. Cole Wastewater Treatment Plant where it is used as a medium BTU fuel in the sludge combustion process. Seven standby flares are available if needed.
- Gas-to-energy project: Two methane-to-electricity utilization plants have been operational since 1990, through a public/private partnership with Michigan Cogeneration Systems (MCS). The plants can produce three megawatts of electricity each and have a net possible output of six megawatts. Although due to the age of the landfill with waning gas production, only about five mwmegawatts are currently being generated.
- This is the largest wellfield and landfill/electrical generation network in the State of Virginia.
- Over 30 landfill gas monitoring wells surround the landfill in order to protect from off-site gas migration. To date, no off-site gas migration has been detected in any of the monitoring wells.