Environmental Protection

King County Taps Methane Gas for Renewable Energy

King County, Puget Sound Energy, and Bio Energy-Washington, a company that specializes in building landfill gas-to-energy systems, are joining forces to turn the public’s garbage into natural gas. The collaboration should generate enough electricity to power an estimated 24,000 homes.

This project will use methane gas generated from decomposing garbage buried at the county’s Cedar Hills Regional Landfill in Maple Valley, about 20 miles southeast of Seattle. Methane will be collected, processed, and piped to Puget Sound Energy’s natural gas-fired power plants.

“By partnering with Puget Sound Energy and Bio Energy-Washington, King County is fulfilling our commitment to a cleaner, greener future,” said King County Executive Ron Sims on April 6. “We are reducing carbon dioxide emissions roughly equal to taking 22,000 average passenger cars off the road each year, and we’re creating a valuable commodity from what was previously considered a useless byproduct.”

Kimberly Harris, executive vice president and chief resource officer for PSE, said, “We’re going to use the landfill gas to light people’s homes. This waste-to-energy project is an example of how we, as a society, can transform long-held practices into more environmentally sustainable actions.”

There are more than 100 landfill-gas power projects today in the United States. The power PSE produces from Cedar Hills’ methane—equivalent to the output of a modern, efficient 35-megawatt gas-fired power plant—will make Cedar Hills the third-largest landfill-gas energy project in the nation.

Because the converted methane gas from the landfill replaces an equal amount of nonrenewable natural gas, the landfill gas-to-energy project will result in an overall reduction of emissions, including greenhouse-gas (GHG) emissions. This project translates into an estimated 63 percent reduction in the carbon footprint of the landfill.

A connecting line that runs between the landfill and the adjacent Northwest Pipeline will transport the methane gas to PSE natural gas-fired power plants. PSE will use the methane, the primary component of commercial-grade natural gas, to generate an estimated 287,000 megawatt-hours of electricity annually, on average.

Bio Energy-Washington, a subsidiary of Richmond, Va.-based INGENCO, is building and operating the gas-to-energy facility at Cedar Hills, which includes the quarter-mile pipeline for shipping the processed landfill gas to Northwest Pipeline and on to PSE’s natural gas-fired power plants.

The gas-processing plant includes a series of sequential steps that remove contaminants found in landfill gas. The end result is gas cleaner than natural gas recovered from conventional gas wells.

In addition to installing the equipment necessary to clean up the landfill gas, Bio Energy has installed proprietary equipment manufactured by INGENCO to make use of gas that would otherwise be waste for some of the facility’s power needs.

Bio Energy-Washington estimates that it will process and deliver to PSE at least 4.5 million cubic feet of methane daily from the county landfill. Deliveries are expected to average about 5.5 million cubic feet per day over 20 years.

Bio Energy-Washington expects to start delivery of the pipeline-quality gas to PSE by the end of April. PSE will purchase the gas from Bio Energy-Washington at a competitive price commensurate with regional wholesale prices.

PSE has partnerships in other waste-to-energy projects in the Puget Sound region, including a landfill-gas power-production facility near Puyallup and King County’s wastewater treatment plant in Renton, which delivers captured methane to PSE’s natural gas system.

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