IN THE LAB: NREL researcher Guido Bender works in the gas manifold corridor for cell testing in the Fuel Cell Test and Development Laboratory at NREL.
Biogas-powered fuel cells hold great promise for their ability to transform waste streams directly into electricity, with zero emissions. Far from new technology, dating back to 1839, fuel cells are becoming one of the popular methods of generating cleaner energy not only for automobiles and space craft, but also for residential, commercial and industrial sites. Today, companies such as AT&T, Coca-Cola Co., Apple and The Kroger Co. are utilizing biogas-powered fuel cells to generate energy for television studios, data hubs, distribution centers and administration offices.
Tony Leo, vice president of application engineering and new technology development of FuelCell Energy, says the top benefit of biogas-powered fuel cells is the ability to transform a waste stream directly into electricity to offset grid purchases. Even for facilities that are flaring biogas for electricity or powering a combustion-engine generator, fuel cells produce more electricity per unit of biogas with zero emissions, he says.
In addition to utilizing waste for energy, Leo says other benefits include heat generation and self-sufficiency. The exhaust of a fuel cell is roughly 750 degrees Fahrenheit, and can be fed back into a digester to maintain heat or support faster material breakdown. Additionally, the heat may be used for hot water systems, absorption chilling systems or sold to neighboring facilities. Fuel cells enable a facility to become energy self-sufficient, Leo says. “We like to describe this as building one’s own micro-grid, where in instances the grid goes down, you can keep your facility operational.”
How It Works
A fuel cell is basically electrolyte material, sandwiched between positive and negative electrodes, that utilizes chemical reactions, rather than combustion, to produce energy. To generate electricity, outside air flows through piping. Upon contact with a negatively charged cathode, oxygen atoms acquire extra electrons, thus becoming ions that diffuse through the electrolyte material. The oxygen ions travel to the positively charged anode, where they react with the hydrogen in the fuel, shedding extra electrons that travel out of the fuel cell as electricity.
To provide an idea of how much gaseous fuel is utilized in one of these fuel cells, Leo says when its DFC3000 unit is running at full capacity, the fuel cell consumes roughly 565 cubic feet of biogas per minute. If the fuel cell ran at full capacity 24 hours a day, seven days a week, it will utilize nearly 300 million cubic feet of biogas over the course of a year.
Biogas Sources
As more fuel cells come on line, a growing demand for sustainable fuel will stimulate growth in biogas utilization. Leo explains in the near term, wastewater treatment facilities represent the largest market potential in biogas because the anaerobic digesters already exist at many sites. One such biogas project is in Fountain Valley, Calif., where a fuel cell is powered by digester gas from a wastewater treatment facility. This system produces roughly 300 kilowatts (kW) of electricity and also pipes the exhaust through a catalyst, which results in a hydrogen stream that can be used to fuel vehicles powered by hydrogen fuel cells.
In the long term, however, wastewater applications will be in the minority. “If you look at how much of this resource is available, it’s actually a fairly small amount per capita,” says Mike Penev, senior chemical engineer at the National Renewable Energy Laboratory. Considering the number of people and the amount of wastewater flowing into the facility, he says, “how much energy is generated is actually not a very large amount.” Other sources of biogas have more plentiful supplies, such as dairy farms and landfills, he adds.
Landfills are a third source of biogas that can be purified to power fuel cells. Penev explains the methane in landfill gas can be purified by removing sulfur, hydrogen sulfide and siloxanes to produce fuel that may be utilized within a fuel cell. “I know there are some landfill-to-energy projects, though I don’t think any of them are running fuel cells,” says Genevieve Saur, engineer and hydrogen systems analyst from NREL. “I think they’re generally combusting the landfill gas.”
Another source for biogas fuel may lie within the food and beverage processing industry. Leo indicates the food and beverage processing plants are a promising short-term market, but only on a small scale. Instead of feeding off biogas from the waste of an entire city, these projects get their biogas from a single factory, he adds, but the cost and energy self-sufficientcy gains to be had by these factories are materially significant to the bottom line.
Growing Market
Fuel cell deployments have been steadily rising, especially in the U.S. and overseas, in places where air pollution and fuel access are larger concerns, such as Los Angeles, Penev says. “They have so much pollution per capita that they don’t allow additional power generation to be put online unless the quality of the exhaust basically contains no pollution.” He adds fuel cells, in general, have practically zero criteria pollutants, such as carbon monoxide and particulate matter. This has made fuel cells more popular in heavily population areas in California and the Northeast, where more of the nonattainment areas exist.
Internationally, Penev says most of the fuel cell utilization that he knows of is occurring in South Korea. “As I understand it, they don’t have a native natural gas supply and they end up importing all their natural gas,” he explains. “And, for the natural gas they ship into the country, they want to get every last Btu out of it.” To accomplish that, he adds, South Korea has invested in very efficient technologies that can utilize natural gas to produce electricity.
Future Possibilities
In terms of project size, multimegawatt fuel cell projects running on natural gas currently represent the biggest growth spot for stationary fuel cells, Leo notes, adding that the biomass and biogas markets stand to benefit from these types of projects, since higher volume production of fuel cells will continue to drive down the project cost of smaller-scale installations.
By building bridges with fuel cell users, biogas producers may help strengthen the market. Leo says, by working with trade organizations such as the National Fuel Cell Research Center, biogas producers can help build relationships with fuel cell users and producers. He recommends interested biogas producers seek out and speak with facilities that currently operate fuel cells.
Biogas producers may want to look into the costs of upgrading the biogas into hydrogen fuel for automobiles. “Most of the large auto manufacturers are coming out with hydrogen fuel cells within a 2015 to 2017 timeframe,” Penev explains. “There’s a least half a dozen manufacturers coming out with hydrogen cars.” There are currently two ways to produce hydrogen fuel, he says, one of which is accomplished from natural gas. Some states, like California, require certain portions of it to be derived from renewable resources.
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