King County fuel cell demonstration project

King County's Wastewater Treatment Division, FuelCell Energy Inc., and the Office of Wastewater Management of the U.S. Environmental Protection Agency worked together to sponsor the world's largest demonstration project of a molten carbonate (MCFC or "Direct") fuel cell using digester gas (methane) as fuel. With the help of federal grant funding, the demonstration project aimed at testing the technology and the claims of high energy conversion efficiencies and low air emissions for fuel cells.

Located at King County's South Treatment Plant in Renton, Washington, the power plant was demonstrated for two years beginning in summer 2004 and ending summer 2006.

King County wastewater treatment plants in Seattle and Renton use gas generated during treatment operations in two ways. At the South Treatment Plant, gas is scrubbed to pipeline quality and sold to Puget Sound Energy. At the West Point Treatment Plant in Seattle, gas is used to power the influent pumps.

A market and economic feasibility study of fuel cells for the wastewater industry, which included King County's South Plant, was completed by the engineering firm of CH2M Hill in May 1997. The study revealed that fuel cell power plants could be cost competitive with engine driven and turbine power plants to recover energy from digester gas.

One megawatt fuel cell power plant

Potential Benefits

Fuel cells can operate on a range of fuel, including methane, and thus offer enormous potential for the wastewater treatment industry. By generating electrical power from digester gas, significant electrical operating cost savings can be realized. Sufficient gas to produce 1 megawatt of electricity can be generated by a wastewater plant treating 30 million gallons per day (and using anaerobic digesters to heat wastewater solids). That is enough energy to supply electricity to 1,000 households.

Other pluses of fuel cells include few moving parts, modular design, negligible emission of pollutants, and the ability to provide electricity without adding transmission lines and substations. If the demonstration project is successful, full-scale fuels cells could be a cost-effective way of providing a portion of the electricity used at the South Treatment Plant.

For fuel cells to be competitive in the power generation market, the cost of manufacturing must be reduced. Fuel cell makers often cite a commercial entry price of about $1,200 per kilowatt as the price point where fuel cells could compete successfully with other small power generators (for example, micro turbines and engine/generators). Current fuel cell costs are roughly double that entry estimate, but manufacturing techniques and volume of production are driving costs down rapidly.