Final Report, King County Fuel Cell Demonstration Project

Issued April 2009

Executive Summary

Increasing energy costs, more stringent air emission regulations, and an interest in exploring emerging energy technologies prompted King County, Washington, to search for new and innovative ways to provide electricity for its wastewater treatment plants. In June 2004, the county began a two-year demonstration of a fuel cell power plant to be fueled by gas produced through anaerobic digestion of solids produced at its South Treatment Plant. The project was the first application in the country to use digester gas to fuel a molten carbonate fuel cell.

Molten carbonate is one of the most efficient of the fuel cell technologies under development. Fuel cells produce electric power directly through electrochemical reactions. By avoiding the two-step process of conventional combustion technology, where fuel is first burned and then heat is used to produce power, fuel cells are more energy efficient.

The demonstration project was conceived and implemented through a strong public-private partnership. FuelCell Energy, Inc., provided the power plant and oversaw its operation and maintenance. King County hosted the site, managed the project, and supported operation and maintenance. The U.S. Environmental Protection Agency (EPA) identified a funding source via annual cooperative agreements from the EPA Office of Water.

King County’s fuel cell power plant was sized to produce 1 megawatt (MW) of electricity and was designed to capture waste heat from the fuel cell exhaust and return it to the treatment plant. Two project goals were established:

• Demonstrate that the molten carbonate fuel cell technology can be adapted to use anaerobic digester gas as a fuel source.
• Achieve a nominal plant power output target of 1 MW using either digester gas or natural gas.

Both goals were achieved during the two‑year demonstration period. A number of secondary objectives (performance goals) were also met. The following table summarizes the performance of the fuel cell power plant.

Testing the digester gas–fueled molten carbonate fuel cell gave FuelCell Energy and King County many opportunities to learn about what is needed to make such applications work well. Power plant shutdowns and their causes provided an environment for highly accelerated life and stress testing at the total system level that will benefit next-generation fuel cell applications, designs, and operations.

Challenges encountered during the demonstration period led to a variety of improvements to the design and operation of the fuel cell plant. FuelCell Energy has incorporated some of these improvements into subsequent fuel cell designs. The challenges centered on mechanical and fuel quality issues. Although the fuel cell module was replaced three times, no issues were identified that would indicate problems with using digester gas to produce energy from molten carbonate technology. The failure of one of the fuel cell module stacks that occurred just after completion of the two-year demonstration and that shut down the plant has been addressed in the vendor manufacturing process, quality inspections, and design specifications.

Problems with digester gas quality, which prevented use of digester gas as a fuel source in the second year of the project, stemmed from the routes and equipment used to convey the gas to the power plant. Modifications were identified and implemented; the last modification was installed at the end of the project before it could be put to use.

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 current configuration. The costs for repair and upgrades, coupled with the fact that FuelCell Energy has substantially improved its newest power plant designs, make total plant replacement a more viable option. The county is considering an alternative that would replace the existing 1-MW power plant with a 300-kW plant. This smaller fuel cell plant would scale better with available digester gas at the South Treatment Plant and would be more portable for possible transfer to other treatment plants.