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New Avenues for Electrochemistry PUBLIC ACCESS

Fuel Cell Systems are Being Designed for Service at Coal Mines, Private Homes, and Tomorrow's Battlefields.

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Mechanical Engineering 123(02), 46-51 (Feb 01, 2001) (6 pages) doi:10.1115/1.2001-FEB-2

Manufacturers of fuel cells are working to improve the economics of electrochemical devices to make them more competitive with conventional fossil fuel power systems for industrial plants and vehicles. FuelCell Energy of Danbury, Connecticut, is designing a system to convert polluting coal mine methane into electricity. General Electric MicroGen of Latham, New York, plans to introduce a residential fuel cell system by the end of the year to provide remote homes with backup current and heat. Another residential system is being developed by International Fuel Cells of South Windsor, Connecticut. The Department of Energy’s National Energy Technology Laboratory in Morgantown, West Virginia, is sponsoring a program to determine the feasibility of feeding coal mine methane to fuel cells. The program involves building a 250-kilowatt fuel cell system at the Nelms mining complex operated by Harrison Mining Corp. in Cadiz, Ohio. A fuel cell system planned for the Nelms complex will assist these automotive engines in consuming methane emissions while generating electricity.

Manufacturers of fuel cells are working to improve the economics of these electrochemical devices to make them more competitive with conventional fossil fuel power systems for industrial plants and vehicles. They are also using fuel cells' strengths-energy efficiency, virtually emission-free operation, and scalability-to open distributed power generation uses for their products beyond vehicular and factory applications.

In one Department of Energy project, FuelCell Energy of Danbury, Conn., is designing a system to convert polluting coal mine methane into electricity. General Electric MicroGen of Latham, N.Y, plans to introduce a residential fuel cell system by the end of the year to provide remote homes with backup current and heat. Another residential system is being developed by International Fuel Cells of South Windsor, Conn.

Future soldiers may thank their lucky stars for the miniature fuel processors being developed by Pacific Northwest National Laboratory of Richland, Wash. The processors will produce hydrogen for fuel cells, which will power portable electronics gear.

Fuel cells have always been considered environmentally friendly, and would burnish their ecological credentials by capturing the methane emissions produced by coal mining, and using it to generate electricity. Methane is stored in the microscopic pores in coal. The pores create a large internal surface area that can store up to 10 times as much methane as rock. When miners remove water from a coal bed, they relieve pressure and permit the methane to escape into the min e. If sufficient methane is present in such a confined space, it can explode. To minimize the risk, mining companies open vents into coal seams to release the gas into the air prior to the start of mining operations.

Methane is believed to be a greenhouse gas. The U.S. DOE sponsors a Coalbed Methane Outreach Program to encourage coal mines to recover and use or sell methane as a fuel Approximately 43 billion cubic feet of coal bed methane was used in the United States in 1998, according to the DOE.

Because the methane from a coal seam is often mixed with air, it is typically unsuitable as a pipeline gas, which requires a concentration of about 94 percent. Oxygen and nitrogen dilute the coal bed gas until it is less than 50 percent methane. Dilution also occurs over time in coal seams where the methane is initially quite rich, but declines in Btu value over time.

Fuel cells can convert hydrocarbons into energy when they are too diluted for standard combustion.

The DOE's National Energy Technology Laboratory in Morgantown, W.Va., is sponsoring a program to determine the feasibility of feeding coal mine methane to fuel cells. The program involves building a 2S0-kilowatt fuel cell system at the Nelms mining complex operated by Harrison Mining Corp. in Cadiz, Ohio.

The DOE awarded FuelCell Energy of Danbury, Conn., a contract for the project, and North West Fuel Development Inc. of Lake Oswego, Ore., will be the site manager under a subcontract. The DOE and FuelCell Energy will share equally the $5.4 million cost of the Cadiz project.

Coal bed methane gas fuels this GM 454 engine to generate electricity at an Ohio mine. A DOE project is planning another installation that will use fuel cells.

Grahic Jump LocationCoal bed methane gas fuels this GM 454 engine to generate electricity at an Ohio mine. A DOE project is planning another installation that will use fuel cells.

Converting a pollutant into power: Vents that coal miners drill to release methane gas into the atmosphere become a source of energy for NorthWest Fuel Development.

Grahic Jump LocationConverting a pollutant into power: Vents that coal miners drill to release methane gas into the atmosphere become a source of energy for NorthWest Fuel Development.

North West Fuel Development will contribute its technique of extracting methane gas from active or abandoned coal mines and burning it as fuel. The company developed this expertise over the last 20 years with projects at Island Creek Coal Co.'s mines in Virginia, and Bethenergy mines in Pennsylvania.

North West Fuel Development also is designing a coal mine methane power system for Sumitomo Coal Mining Ltd. In Japan.

"We typically use any well or vent that the coal miners have drilled," said Peet Soot, a chemical engineer and president of North West Fuel Development. "One type is the gob vent holes that mining companies drill in advance of mining, from the surface into the strata just ahead of the mine's working face , to release methane gas from the coal seam."

As the mine advances, the overburden falls and the gas is vented through the gob wells.

Soot's company connects pipes to the wells and, if pressure is sufficient, collects the methane emitted. If the pressure is ambient, NorthWest Fuel Development will use a vacuum blower to draw the gas to the surface.

NorthWest Fuel Development built a coal methane power system in 1994 at Nelms Vent No. 5. It uses approximately 100,000 cubic feet of coal bed gas, with a methane content of70 percent, to run four internal combustion engines that generate 300 kW The power drives mine equipment, and excess is sold to American Electric Power.

"The methane is sent to modules made up of l00-horsepower (75-kW) automotive engines, which are directly attached to our proprietary electrical gen era to r," Soot said. "The fuel is burned in the engines, which turn the generator, and it produces hundreds of kilowatts of electricity for the mine and, occasionally, excess electricity for the local utility."

The extraction system will supply the fuel to cells to be designed by FuelCell Energy.

Fuel Cell Energy will contribute its patented carbonate fuel cell technology for the N elms project. The FuelCell Energy technology uses a lithium and potassium carbonate electrolyte. Carbonate fuel cells are suited to large-scale power applications.

Gas is sent to a stack of cells, which operate at 1,200°F, converting the gas internally into a hydrogen- rich fuel without the need for a fuel processor.

FuelCell Energy built and operated a fuel cell power plant as a demonstration in Santa Clara, Calif. During 1996 and 1997, 256 standard cubic feet per minute of natural gas were sent to 16 stacks of fuel cells that generated 2 megawatts of electricity at 44 percent efficiency.

"We used a supplemental burner for the test plant, but future plants will not be equipped with this burner and will achieve 49 percent electrical efficiency. We also did not recover heat at the Santa Clara demonstration, which would have raised the system's overall efficiency to more than 50 percent ," said George Steinfeld , a chemical engineer and manager of systems development at FuelCell Energy.

Steinfeld said he and his colleagues were also confident that their power system could handle the less-than-pipeline-clean coal bed methane.

Fuel Cell Energy became interested in tapping coal mine methane for its energy systems based on a market study conducted by NorthWest Fuel Development. " The study showed that potential power generation from U.S. coal mine methane is 317 MW from active and inactive mines," Steinfeld said.

Initial design work for the Nelms project involves site preparation to supply utilities, including water, start-up power, and connections for the energy the fuel cells produce. The power plant equipment will compress, pre heat, and pipe the Nelms coal bed gas to a contaminant removal system where zinc oxides will remove sulfur, a

solid sorbent material will absorb halogens, and a platinum catalyst will combust a small amount of the gas to remove oxygen.

The cleaned fuel will be mixed with steam and sent to a pre-reformer that will remove higher hydrocarbons, trace compounds such as ethanes, propanes, and butanes. The gas will be heated to the 1,200°F operating temperature of the fuel cell stack.

Once in the stack, the methane and steam mixture is internally reformed into hydrogen and carbon monoxide. The carbon monoxide is shifted chemically with the water vapor, forming additional hydrogen and carbon dioxide. Roughly three-quarters of the hydrogen reacts electrochemically with the carbonate ions in the fuel cell anode, producing direct current electricity that is inverted to ac power and can be sent to the local utility grid.

The remaining 25 percent of the fuel, containing hydrogen, carbon monoxide, carbon dioxide, and water, leaves the anode and is sent to the catalytic oxidizer, where air is added. Combusting the fuel and air produces carbon dioxide and water vapor.

The carbon dioxide is directed to the cathode where it reacts with oxygen in the air to form carbonate ions that migrate across the fuel cell electrolyte from the cathode to the anode. These ions react electrochemically with the hydrogen ions produced in the anode, forming water, carbon dioxide, and the electrons for electricity.

"The heat produced by the cathode is more than sufficient for the reforming process that occurs within the fuel cell stack ," noted Steinfeld. "We will direct the cathode exhaust-around 1,250°F- to heat exchangers that will preheat the fuel, and create process steam in a boiler."

Steinfeld and his colleagues considered different power plant sizes for the Nelms project and chose a single fuel cell stack to generate 250 kW Because Harrison Mining Corp. requires 1 MW for its baseload demand, and an additional megawatt for peaking service, the 250-kW fuel cell plant could operate at base load to assist the internal combustion engines in reducing peak electrical demand. This plant would have rated power output of 268 kW net ac.

FuelCell Energy predicts that early production models of coal gas power systems will have 49 percent electrical efficiency, while more advanced units will have 54 percent efficiency.

power plant would consist of a fuel processor, fuel cell stack, power conditioner, controls, thermal management system, and deionized water management system.

Engineers expect the Nelms power plant to be 10.5 feet wide, 11.5 feet tall , and 23 feet long.

A larger design would suit bigger coal mining operations. It would mean building two Separate fuel cell stack modules in a 2.85-MW power plant with its associated balance of plant equipment. The fuel cell module can deliver about 1,450 kW at 57 percent efficiency.

"The technology for utilizing the coal bed methane fuel cell systems is available," Steinfeld said. "Ironically, the challenge to large- scale commercialization of the technology is that it can produce more electricity than most mines need."

He suggested that mining companies could become independent power producers and arrange to sell power to other consumers, such as industrial parks or utilities.

A fuel cell system planned for the Nelms complex will assist these automotive engines in consuming methane emissions while generating electricity.

Grahic Jump LocationA fuel cell system planned for the Nelms complex will assist these automotive engines in consuming methane emissions while generating electricity.

FuelCell Energy converts hydrocarbon fuels into hydrogen directly in the fuel cell stack to eliminate the need for a separate processor.

Grahic Jump LocationFuelCell Energy converts hydrocarbon fuels into hydrogen directly in the fuel cell stack to eliminate the need for a separate processor.

This generic 1.5-MW FuelCell Energy system includes the fuel cell stack, a dc to ac inverter, heat exchangers, pumps, and piping.

Grahic Jump LocationThis generic 1.5-MW FuelCell Energy system includes the fuel cell stack, a dc to ac inverter, heat exchangers, pumps, and piping.

FuelCell Energy practiced what it preaches by operating a 2S0-kW fuel cell system at its headquarters for 18 months during 1999 and 2000.

Grahic Jump LocationFuelCell Energy practiced what it preaches by operating a 2S0-kW fuel cell system at its headquarters for 18 months during 1999 and 2000.

Proton exchange membrane fuel cells separate hydrogen into protons and electrons, merge the protons with oxygen to form water, and send electrons to the power conditioner to create ac power.

Grahic Jump LocationProton exchange membrane fuel cells separate hydrogen into protons and electrons, merge the protons with oxygen to form water, and send electrons to the power conditioner to create ac power.

GE MicroGen, a subsidiary of the General Electric Co., formed the joint venture company GE Fuel Cell Systems with Plug Power two years ago to sell residential fuel cell systems. The strongest markets the company sees for its products are homes built in remote locations where utility backup power is unavailable, or in areas completely off the power grid.

One residential fuel cell system, called Home Gen 7000, is being developed to offer reliable electricity in case utility service suffers power shortages like those in the summer or complete outages. Power failures, though only a second or less in duration, can wreak havoc on personal computers and video recorders

The design of the HomeGen 7000 has three major subsystems: a processor that extracts hydrogen from natural gas or propane, a fuel cell to convert the hydrogen into electricity, and a power conditioner that converts the fuel cell's output into 7 kW of household- quality alternating current.

A standard residential connection delivers natural gas to the fuel processor. The processor uses a catalyst to reduce the fuel into a hydrogen- rich gas that is sent to a stack of proton exchange membrane fuel cells. PEM fuel cells are particularly suited to small-scale power applications, and consist of a polymer membrane sandwiched between an anode and a cathode.

When hydrogen contacts the anode, it is separated into its constituent protons and electrons. The protons p ass freely through the membrane, while the electrons travel around the membrane to generate electricity. The pro tons and electrons link up at the cathode and combine with oxygen in the air, producing water, heat, and carbon dioxide.

A connection with the plumbing removes the water and heat, which can be used for space heating or for hot tap water to improve fuel efficiency. Carbon dioxide emissions per kilowatt-hour are virtually the same as those from a home furnace.

Plug Power engineers designed the HomeGen 7000 so it can be installed within a day. The energy system, measuring 75 inches long, 35 inches wide, and 55 inches deep-about the size of a refrigerator- is placed on a precast concrete pad. Installers will attach its fuel and water connections to the residence's gas and water lines, and its output cable to the service panel.

Once installed, the fuel cell system runs continuously and will provide up to 7 kW free of grid power interruptions. Plug Power has indicated that the first HomeGen 7000s should become commercially available early

next year, and are intended for installations where grid power is available. A year later, Plug Power will introduce a grid-independent, LPG-fueled system for use in stand-alone applications.

The independent systems can be pitched to utilities as economical alternatives to new power lines to take electricity to a few distant homes.

Another company banking on a residential market is International Fuel Cells in South Windsor, Conn., a division of United Technologies Corp. [Fe has manufactured the fuel cells for manned U.S. space flights since 1966.

The company is now designing a proton exchange membrane fuel cell for private homes and small businesses. It hopes to put the cell to a beta test in the second half of this year and introduce it commercially next year.

The IFC system consists of a fuel processor that will use a catalyst and steam to extract hydrogen-rich fuel from natural gas or propane to feed the PEM fuel cell stack. A platinum catalyst in the stack refines the fuel further.

IFC is designing its residential fuel cells to provide between 5 and 10 kW of electricity, which can be used parallel to, or independent from, the local grid.

"Cost and reliability will drive the use of the system," said Guy Hatch, an engineer and director of residential business at International Fuel Cell s. "Cost meaning places where the price of natural gas is cheap enough, and electricity is expensive enough, to consider purchasing the system. Reliability refers to homes or businesses, such as computer processing centers, that cannot afford power interruptions lasting even a few seconds."

The IFC system will measure less than 40 inches long, 24 inches wide, and 40 inches tall, enabling it to be installed inside basements or attics, as well as in yards.

In addition, the fuel cell system can heat water to between 120 and 160°F [Fe has designed its system to operate at the noise level of a furnace or air conditioner

The PEM fuel cells within the GE HomeGen 7000 will provide homes with as much as 7 kW of electricity and hot water as a byproduct to improve its fuel efficiency

Grahic Jump LocationThe PEM fuel cells within the GE HomeGen 7000 will provide homes with as much as 7 kW of electricity and hot water as a byproduct to improve its fuel efficiency

Microchannels enable Pacific Northwest National Lab to keep its fuel processor under 2 inches square to fit a soldier's pack.

Grahic Jump LocationMicrochannels enable Pacific Northwest National Lab to keep its fuel processor under 2 inches square to fit a soldier's pack.

Fuel cells may find a place on battlefields, providing a highly mobile power source for soldiers manning sophisticated electronic equipment, including communications gear and perhaps helmets with image displays.

Battelle researchers at the Department of Energy's Pacific Northwest National Laboratory are working on a small fuel cell system, about the size of a soda can, that tomorrow's infantry can carry in their backpacks. The miniature fuel cell development is funded by the U.S. Army Communications and Electronics Command at Fort Monmouth, N.J., and represents the first year of a scheduled four-year project.

The fuel cell system supports the Army's Land Warrior program that is developing a variety of equipment, including a helmet-mounted digital display, a global positioning system, night vision optics, and a laser-sighted rifle with an integrated video camera.

The PNNL researchers' work involves developing a fuel processor and integrating it with a proton exchange membrane fuel cell to be provided by another company, yet to be chosen by the Army.

"We are looking at PEM fuel cells because of their advanced stage of development, their suitability for small-scale applications, and the fact that the Army has chosen them for other portable power source projects," said Ed Baker, a chemical engineer and technical group manager for chemical process development at PNNL.

Baker and his colleagues are working to develop a miniature fuel processor to use methanol, diesel, or other easily available military fuels as sources of hydrogen for the fuel cells. The challenge is scaling down catalytic steam reforming technology to less than 2 inches in any dimension. Because this is impractical with conventional steam reforming equipment, PNNL is using micro channel components originally intended for an automobile. The lab developed the components for a compact fuel processor to produce hydrogen for a 50-kW automotive fuel cell.

"We use microchannels to eliminate the heat and mass transfer resistance in chemical reactions and significantly speed up the catalytic reactions," Baker explained.

A portion of hydrocarbon fuel will be sent to a small combustor to provide heat for the fuel processor. Fuel and water are sent to the micro channel vaporizer that is heated by hot combustion gases. The heated mixture is then sent through the microchannel steam-reforming reactor, creating hydrogen, carbon dioxide, and carbon monoxide.

"We are considering sending these gases through a hydrogen permeable membrane, or through a water gas shift reactor to convert the CO into CO2 and additional water. In either case, the hydrogen will be sent to the fuel cells to generate electricity," noted Baker. The PNNL design team expects to integrate all the fuel processor's components into a unit measuring 1.5 by 1 by 0.5 inches.

The man-portable system is scheduled for testing in 2003. Its success could give warriors the edge they need in battles yet to come.

Copyright © 2001 by ASME
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