Fuel Cells: Garbage In, Electricity Out

Bill Siuru

Landfills produce more than one-third of U.S. manmade methane gas emissions, a significant contributor to global warming. Though pricey, a new fuel cell concept which converts landfill gas (LFG)-to-electricity can offer an alternative.

As part of an 18-month demonstration project, the first commercial fuel cell converting LFG-to-electricity has been operating at a landfill in Groton, Conn., for a little more than a year. Connected to the Connecticut Light and Power grid, the fuel cell plant's 1.6 million kilowatt-hours output will be sufficient to supply approximately 100 homes with electricity during the project. It also could supply electricity and heat to an individual facility such as a factory or processing plant.

A fuel cell is similar to a battery in that it too uses an electrochemical process to directly convert fuel into electricity as well as heat and water. Like batteries, fuel cells have electrodes, an electrolyte and positive and negative terminals. Neither have rotating parts or polluting combustion processes (see chart).

A series of individual cells, whether in a battery or fuel cell, are connected in a cell stack to produce a usable direct current voltage and power output. However, unlike batteries which run down if they are not recharged, fuel cells will continue to produce energy as long as they are supplied with fuel and air.

The IFC 200-kilowatt, 20-ton PC25 phosperic acid fuel cell installed at the 42-acre Groton site receives approximately 20 percent of the facility's gas. It is relatively quiet - at 30 feet the noise level is below 60dBA or about as loud as the typical room air conditioner - and does not produce any harmful air emissions. In fact, fuel cells are so clean that they are do not require air quality permits in Los Angeles, San Francisco and Massachusetts.

Before the LFG enters the fuel cell, a gas clean-up system removes chlorinated compounds, sulfur compounds and contaminants. The process begins when carbon pellets absorb hydrogen sulfide. Next, the gas is chilled to liquify the other impurities so they can be drained off. The methane then goes to a reformer which turns it into the hydrogen rich gas used by the fuel cell. Heat from the fuel cell is used by the reformer. Finally, a power conditioner converts the DC electricity produced by the fuel cell into AC electricity.

A study prepared for the U.S. Environmental Protection Agency (EPA), Washington, D.C., showed that as many as 1,700 landfills in the United States are ideally suited for fuel cell-based LFG-to-electricity. This could generate more than 1,000 megawatts of electric energy, enough to provide electricity to nearly a half million homes. Additionally, fuel cells can operate on methane gases produced by sewage treatment plants and, indeed, several are already in operation.

The limiting factor for widespread use of LFG fuel cells, however, is their current high cost. Systems like the one in Groton which includes the extensive clean-up equipment costs approximately $1 million to $1.5 million.

The demonstration project is a partnership between the town of Groton; Northeast Utilities Service Company's subsidiary, The Connecticut Light and Power Company (CL&P); International Fuel Cells Corporation and EPA. CL&P operates and maintains the facility allowing Groton to avoid pollution control expenses.