IN 1996, THE NEW York State Energy Research & Development Authority, New York Power Authority (NYPA), Department of Energy, and EPRI funded the application of an experimental 200-kW phosphoric acid fuel cell (PAFC). The fuel cell uses about 50 percent of the excess anaerobic digester gas (ADG) from the Yonkers Joint Wastewater Treatment Plant in Westchester County, New York. The installation is a joint attempt to evaluate the use of ADG in PAFCs.
The ADG from municipal waste treatment plants has a methane concentration of approximately 60 percent and is frequently burned in boilers to heat the digesters or in engines to generate power. Otherwise, the methane must be flared, which still causes greenhouse emissions without creating a useful product.
ADG contains about 60 percent CH4, 37 percent CO2 and about 500 ppmv H2S. The H2S is a poison to the fuel cell system and must be removed to less than 4 ppm. For
the Yonkers installation, H2S is absorbed in an activated carbon bed. The cleanup system has performed satisfactorily since April 1997, according to EPRI reports.
The system consists of a blower, a coalescing filer to remove entrained moisture, and two activated carbon charcoal filters set up to operate individually, in parallel, or in series. The filters must be replaced about every four months.
Broad variations of methane concentrations cause power fluctuations between 85 percent and 100 percent. The fuel cell electric efficiency is 40 percent. Operations and maintenance costs run between $0.015/kWh and $0.02/kWh. All emissions are running at or below predicted levels with NOx at less than 0.37 ppm, SOx at less than 1 ppm, and VOCs and particulates at 0 ppm.
“This innovative use of fuel cell technology not only provides real benefit to our customer, Westchester County, but also helps illustrate the commercial potential of this application,” said Carol Garcia of the NYPA.
DIESEL DG BUMPS COMED’S CAPACITY
THE SUMMER OF 1998 brought with it an acute power shortage that adversely affected the upper Midwest. As a result, Chicago’s Commonwealth Edison (ComEd) contracted Aggreko to provide 20 MW of temporary diesel generators to supplement the utility’s capacity. The project was deemed such a success that this April, Aggreko was again contracted, this time to supply 60 MW for distributed generation (DG).
Two Chicago area substations were supplied with 1,250 kW generators totaling 30 MW each. The sites are manned by Aggreko technicians for the duration of the project.
When needed, each generator synchronizes with the grid and is base loaded to 1,000 kW. The GreenPower generators have been running six to eight hours daily, based on area grid demands.
The generators are set up in groups of two and are connected to one 2,500 kVA transformer. A 2,300-gallon EnviroTank fuel tank allows approximately 15 hours of continuous run time if needed. More than 24,000 feet of low voltage cable was used to set up the peaking diesels.
The project has been running all summer and will be demobilized this month.