20IEEE power & energy magazine november/december 2003© KPT POWER PHOTOS,HSC SOFTWAREAn Innovative Emission-OffsetProject That Utilizes AnaerobicDigester Gas-Powered FuelCells to Produce ElectricityYan Kishinevsky and Shalom ZelingherFFUEL CELLS, UNTIL RECENTLY A CURIOSITY LARGELY CONFINED TO THE SPACEprogram, are emerging as a valuable clean and efficient generator of electricity. A number ofcompanies are developing fuel cells for use in stationary applications. Most of the current appli-cations for fuel cells utilize natural gas as a fuel. In certain states, such as New York and Con-necticut, fuel cells operating on natural gas are recognized by the state as a renewable energysource. Recently, however, fuel cells, mostly phosphoric acid, have been shown to operate wellon renewable biogas fuels, such as anaerobic digester gas (ADG) produced at wastewater treat-ment plants as well as landfill gas (LFG) and gas produced at beer breweries. While the present cost of a stationary fuel cell is high, there are certain “niche” applicationsfor which that higher price is justified. These niche applications offer utilities opportunities toprovide additional value and better serve their customers, and they provide new business oppor-tunities. Three very good examples of such high-value applications by the New York PowerAuthority (NYPA), working together with its customers, include:✔ use of eight fuel cells at four New York City Department of Environmental Protection (NYCDEP) wastewater treatment facilities (WWTFs) to offset emissions from conventional smallpower plants (combustion turbines previously installed by NYPA in New York City)✔ use of a fuel cell at Westchester County’s Yonkers Joint Wastewater Treatment Plant to avoidflaring emissions✔ use of a fuel cell at the New York City Central Park Police Precinct Building (Figure 1) toupgrade the building’s electrical system and defer costly infrastructure improvements in anenvironmentally friendly way. This fuel cell supplied electricity to the precinct throughoutthe August 2003 blackout.1540-7977/03/$17.00©2003 IEEEnovember/december 2003 IEEE power & energy magazineWWTFs represent a growing niche for distributed generation.Many WWTFs in the United States and abroad utilize aprocess called anaerobic decomposition to purify water priorto discharging it into a river or bay. According to U.S. Envi-ronmental Protection Agency statistics, there are over 16,000WWTFs in the United States, of which about 3,400 (21%)use anaerobic decomposition as part of their process. Lessthan 2% (about 260 facilities) use digester gas for energy pro-duction. While the process of anaerobic decomposition isvery effective in reducing water pollution, many WWTFsflare off the gas produced during the digester process, whichincreases air pollution and contributes to the greenhousewarming effect.NYPA, the nation’s largest state-owned electric utility,pioneered an innovative emission offset project by installingfuel cells powered by ADG at WWTFs in New York City toachieve zero-emissions impact from conventional gas turbinepower plants. As can be seen from Table 1, NYPA currentlyowns 2.4 MW of fuel cell capacity and operates 12 fuel cellsat eight sites. Nine of the 12 fuel cells are powered by ADG.Most of these units supply both electricity and heat to thehost facility with virtually no emissions.In the early 1990s, NYPA recognized the potential benefi-cial impact of utilizing ADG produced at WWTFs as anuntapped “free” renewable fuel resource for distributed gen-eration. NYPA has since been a national leader in advancingthis technology and installed the world’s first commercialfuel cell (manufactured by UTC Fuel Cells) powered byADG at Westchester County’s Yonkers WWTF. This projectis currently supplying electricity and heat to the host facilitywhile dramatically reducing air emissions.Wastewater Treatment FacilitiesAnaerobic decomposition involves microorganisms thatderive energy from metabolizing organic materials to decom-pose organic waste at WWTFs. In the absence of oxygen, thebyproducts of their metabolism are carbon dioxide (CO2) andmethane (CH4) plus trace quantities of other compounds,such as hydrogen sulfide (H2S) and organic halides (mostlychlorides). ADG is primarily a mixture of these gases (60%methane and 40% carbon dioxide). A simplified diagram ofthe wastewater treatment process is shown in Figure 2. ADG is generally collected and either used as fuel in boil-ers to keep anaerobic digesters warm, flared off, or, in somecases, used in internal combustion engines to produce elec-tricity. At many WWTFs, ADG is being utilized inefficiently,or not at all. For example, many facilities are located in tem-perate climates in which the requirement for heat in the sum-mer is minimal. If ADG is released uncombusted, it significantly con-tributes to the greenhouse effect. This occurs principallythrough emissions of methane, which traps at least tentimes as much heat as carbon dioxide. For this reason andfor odor control, excess ADG is typically flared (burned)in flame towers, a process that eliminates methane emis-sions. However, flaring is only a partial solution, sinceADG combustion generates photoreactive ozone precur-sors, such as nitrogen oxides and volatile organic com-pounds. As a result, all large WWTFs in the United Statesare regulated as stationary sources of air pollution underthe federal Clean Air Act. All 14 WWTFs in New YorkCity are designated and regulated as major pollutionsources. This designation necessitates installation of con-trol and monitoring technologies, which can be very cost-ly. Fuel cells provide the most effective solution to theseproblems. They efficiently generate premium quality elec-tricity and much needed thermal energy, while consumingADG and emitting negligible amounts of regulated pollu-tants. In addition, they permit significant reductions in car-bon dioxide emissions compared to flaring. As a result,WWTFs are primary candidates for clean distributed gen-eration and for win-win partnerships between the WWTFoperators and utilities. Yonkers Fuel Cell: A Pioneering Project In 1996, NYPA joined forces with International Fuel Cells(now UTC Fuel Cells), EPRI, the New York State EnergyResearch and Development Authority (NYSERDA), U.S.Department of Energy (DOE), and Westchester County at theYonkers Joint Wastewater Treatment Plant to develop anddemonstrate the first fuel cell in the Western Hemispherepowered