Fuel cells are similar to rechargeable batteries, which are discharged and then recharged, except fuel cells require a constant fuel source (i.e., constant recharging) and continuously generate electricity. Methane, from either natural gas or digester gas, enters the fuel processing stage. The fuel is preheated, partially reformed, and then flows to the anode. The reforming reaction (hydrogen formation) is completed in the fuel cell stack. Air flows through the cathode. Hydrogen splits into electrons and protons at the anode, and the electrons leave the fuel cell. The electrons return at the cathode, react with oxygen, and form water.
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.
It was thought at the start of the demonstration project that if the technology proved successful, King County would consider continuing its operation. From experience gained during the project, the county decided not to continue operating the test configuration. The costs for repair and upgrades, coupled with the fact that FuelCell Energy has substantially improved its newest power plant designs, made total plant replacement a more viable option. The county also considered an alternative of replacing the existing 1-MW power plant with a 300-kW plant. The relatively low cost of electricity in the Pacific NW and cost of equipment replacement ultimately led to a final decision to decommission the fuel cell.
View Final Report (PDF, 9.6MB), issued April 2009 and submitted to the U.S. Environmental Protection Agency.
- King County Fuel Cell Demonstration Project, Project Summary, (PDF, 390KB), March 2008
- View a poop powered power plant (, external link), an interview with John Phillips, King County Staff.
Faircompanies, sustainable news, Dec. 14, 2007
- Lessons Learned from the World's Largest Digester Gas Fuel Cell, (PDF, 1.2 MB) Washington State Recycling Association - Spokane, May, 2006.
Presented by Greg Bush - King County
- Poster (PDF, 1.3 MB). Sustainable On-Site Power Generation using a 1 MW Fuel Cell and Digester Gas, Jaimie Hennessy, Eleanor Allen, Greg Bush, Dave Hennessy, WEF Technology 2005, Second Joint Specialty Conference for Sustainable Management of Water Quality Systems for the 21st Century, San Francisco, California, August 2005.
- King County Carbonate Fuel Cell Demonstration Project -- Case Study of a 1-MW Fuel Cell Power Plant Fueled by Digester Gas, (PDF, 765 KB), Interim Report, February 2005, Dan Rastler, Electric Power Research Institute (EPRI)