Wastewater is the fuel

FuelCell Energy and King County, Washington have signed an agreement to install and operate a 1MW Direct FuelCell (DFC) power plant at the County's South Wastewater Treatment Facility in Renton, Washington using municipal wastewater digester gas as the fuel.

The cost of the two year demonstration project will be shared equally by FuelCell Energy and King County, through a cooperative grant to the County from the US Environmental Protection Agency (EPA). The total value of the contract is $18.8 million. Operations are expected to commence during the third quarter of 2002.

'This megawatt-class commercial field trial of the DFC power plant represents the first advanced wastewater digester project for FuelCell Energy', said Jerry Leitman, president and CEO of FuelCell Energy. 'This project will demonstrate the versatility of fuel use with the Direct FuelCell, as well as its capability to produce more electricity than other technologies using the same quantity of fuel.

In operation, a wastewater treatment system that uses an anaerobic digester process to stabilise solids and reduce pathogenic microorganisms produces a methane-rich gas that can be fed to the DFC power plant. According to industry sources, a 30 mgd wastewater treatment plant generates sufficient digester gas to fuel a one megawatt fuel cell power plant using carbonate technology.

FuelCell Energy's field trials are precursors to the commercial market entry of the DFC. Current field trials in operation or scheduled for 2001 include 250 kW DFC power plants at the University of Bielefeld and the Rhone Klinikum Hospital in Germany, at the headquarters of the Los Angeles Department of Water and Power, a 250 kW system in Japan for Marubeni and a 250 kW unit slated for the spring of 2001 at Mercedes-Benz US International in Tuscaloosa, Alabama.

Also slated for 2001 is a 3 kW DFC unit for the US Coast Guard at the Cape Henry Lighthouse in Virginia which aims to demonstrate the capabilities of the fuel cell at remote sites.

Fuel Cell Energy's hybrid concept combines the Direct FuelCell and an unfired gas turbine. This hybrid system uses a network of heat exchangers to transfer waste heat from the DFC system to the turbine, which converts a portion of the waste heat to mechanical energy and then electricity.

The system adds 10 to 15 percentage points to the efficiency of the DFC. For large systems in the long term, unsurpassed net electric efficiency of close to 80% is possible. In the nearer term, it is believed that cost effective small MW class hybrid systems can be configured with efficiencies of 70% or better.

What distinguishes this hybrid concept from many other proposed hybrid systems is the approach of integrating the turbine with an atmospheric pressure fuel cell and recovery of the waste heat in a Brayton cycle.

The fuel cell does not need to operate at the turbine pressure, instead it operates at the preferred ambient pressure and is independent of gas turbine cycle pressure ratio. The system works efficiently with a wide range of turbine compression ratios (3 to 15). This means that, in principle, the concept can be applied from the multi-MW scale (with industrial size turbines operating at 9 to 16 pressure ratios), to smaller systems using microturbines at a lower pressure ratio.