Fuel Cells Finally Find a Killer App: Carbon Capture

At an Alabama power plant, FuelCell Energy and ExxonMobil aim to capture 90 percent of CO2

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At the 2.7-gigawatt James M. Barry Electric Generating Plant, in Bucks, Ala., an experiment is under way that could one day usher in a new era of nearly emissions-free fossil-fuel-powered electricity. This year, technicians and engineers will begin installing a pair of boxy white containers in the shadow of the main power plant. The containers house a novel type of fuel cell, designed not only to generate power but also to capture and concentrate up to 90 percent of the carbon dioxide coming from the main plant, which burns coal as well as natural gas. If implemented at scale, that level of carbon capture would give the Barry plant an emissions profile more like a geothermal plant’s and without the intermittency of wind and solar power.

The technology comes from the Danbury, Conn., firm FuelCell Energy, which is partnering with oil-and-gas heavyweight ExxonMobil, as well as Southern Co., whose subsidiary owns and operates the Barry plant. The project is intended to demonstrate how newer, more efficient approaches to carbon capture could allow countries that rely heavily on fossil fuels for electricity—most of the world, in other words—to meet their targets for cutting greenhouse gas emissions. It’s also a showcase for fuel cells, which have struggled to reach commercial readiness despite 180 years of R&D and countless false starts.

In 1839, the British lawyer and amateur scientist William Robert Grove demonstrated that platinum foil could catalyze a reaction between hydrogen and oxygen that yielded electricity and a little water. Ever since, researchers, industrialists, and environmentalists have been captivated by the hydrogen fuel cell’s potential as a clean, efficient source of power.

The technology, though, has proved extraordinarily difficult to perfect. Costly materials, durability problems, and the difficulty of securing a steady supply of hydrogen have derailed many a fuel cell project. Meanwhile, commercial applications have been slow to materialize. The U.S. auto industry’s attempt in the early 2000s to position the fuel cell as the ultimate power source for electric vehicles fizzled when it became clear that the technology was far from ready. Nevertheless, many automakers continue to research fuel cells, giving hope to the promoters of a hydrogen economy; see, for example, “The Automotive Future Belongs to Fuel Cells,” IEEE Spectrum, February 2017.

And in southern Alabama, fuel cell technology is squarely in the spotlight. Unlike the devices being developed for cars, which use pure hydrogen as a fuel, FuelCell Energy’s molten carbonate fuel cells use the hydrogen bound up in natural gas or biogas. They’re also much bigger, they’re stationary, and they operate at a higher temperature, around 650 °C. The high temperature makes them less susceptible to poisons like carbon monoxide (created by processing carbonaceous fuels), which can damage the innards of lower-temperature fuel cells.

In a molten carbonate fuel cell, carbon is an integral part of the equation. At the cathode—also known as the air electrode—carbon dioxide and oxygen are fed to the cell, and they react to form charge-carrying carbonate ions suspended in a molten salt electrolyte. The ions migrate through the electrolyte to the anode—or fuel electrode—where they react with hydrogen (which is formed from a hydrocarbon fuel like natural gas or biogas) to produce water, CO2, and electrons. The electrons then go into an external circuit to do useful work before returning to the cathode, while the carbon dioxide produced in the reaction gets recycled back to the cathode.

This power-source technology has another use. “As a molten carbonate fuel cell makes electricity, it pumps carbon dioxide electrochemically through the system,” explains Tony Leo, FuelCell Energy’s vice president of advanced applications and technology development. “It was something that we did not think too much about until we started to see that people were interested in capturing carbon dioxide.” Against the backdrop of climate change, the company’s engineers realized that the fuel cell’s pumping action could be used to concentrate and collect carbon dioxide at the anode. To replenish the carbon dioxide needed to keep the fuel cell running, they could use pollution—industrial exhaust, that is.

At the Barry plant, the fuel cells will use the flue gas coming from the thermoelectric plant as their carbon source. The exhaust from a steel or cement plant could also work; worldwide, these sources each contribute about 5 percent of CO2 emissions. The concentrated CO2 can be stored deep underground or used as an industrial feedstock. Unlike the conventional amine-based method of carbon capture, which consumes electricity, the fuel cells will generate their own electricity to drive the process.

This latest incarnation of the molten carbonate fuel cell was years in the making, Leo says. Researchers who first investigated the technology in the 1950s were impressed by its apparent flexibility. The system’s high operating temperature means that the catalyst can be made from cheap nickel rather than pricey platinum, and practically any hydrocarbon can be used as a fuel source, at least in principle. What’s more, the heat it generates can also be captured and put to use. In the 1960s, the U.S. Army envisioned using molten carbonate fuel cells anywhere its troops were deployed, allowing soldiers to process whatever fuel was available. Natural-gas utilities wanted to integrate the technology into their pipeline grids, forming decentralized power systems that would compete with the electric utilities. But such efforts were stymied by the corrosive nature of molten carbonate, which led most sponsors to shelve the technology at a relatively early stage.

The energy crisis and environmental movement of the 1970s brought renewed interest in all kinds of clean power, including the carbonate fuel cell. It was in this ferment that FuelCell Energy, then known as Energy Research Corp., was founded. “What we thought made the most sense was a power generation system that could run on pipeline-volume natural gas, and high-temperature fuel cells like carbonate did that,” Leo says.

One of the salient facts about advanced power sources is that new products typically take decades to enter the marketplace. As more than one observer has noted, there is no Moore’s Law for batteries. Sustained government support is thus crucial. With help from the U.S. Department of Energy, FuelCell Energy was able to focus on the thankless task of improving the efficiency, cost, and durability of its molten carbonate fuel cells. After years of research and development, the company demonstrated a 2-megawatt plant in Santa Clara, Calif., which operated from 1996 to 1997. In 2003, FuelCell Energy shipped its first commercial unit. To date, it has installed several hundred megawatts of capacity in 50 locations around the world, most notably a 59-MW combined heat-and-power plant in South Korea. Today, the company is the leading provider of molten carbonate technology.

Having nurtured FuelCell Energy in its fledgling years, the U.S. government also played a key role in getting the company into carbon capture. The Department of Energy had long supported research into so-called clean coal, and by the late 1990s it was pushing carbon capture and combined cycles as means to this end. In the early 2000s, with energy policy increasingly emphasizing sustainability, says Leo, FuelCell Energy started thinking about using its fuel cells as a carbon filter.

“We were a bunch of guys drawing stuff on napkins and just realized that, conceptually, it made sense,” he recalls.

Assisted by the Environmental Protection Agency, FuelCell Energy studied how its fuel cells might operate on a simulated coal exhaust stream. Molten carbonate fuel cells don’t tolerate some of the contaminants found in coal, such as sulfur, so the engineers figured out a way to extract those poisons from the exhaust stream. Along the way, they made a serendipitous discovery: The reaction process destroys 70 percent of the exhaust stream’s nitrogen oxides, thus reducing conventional air pollutants.

But most battles on the fuel cell front are not so easily won. In September 2015, FuelCell Energy announced a US $23.7 million cost-shared project with the Department of Energy to demonstrate that its technology could capture 90 percent of the CO2 from a small stream of coal exhaust and concentrate it to 95 percent purity. In the first phase of the project, a modified version of its commercially available 2.8-MW SureSource 3000 fuel cell system will capture 54 metric tons of carbon dioxide per day at the Barry plant.

That’s just a small fraction of the CO2 emitted by the facility. To put things in perspective, a typical 500-MW coal plant emits [PDF] about 3.3 million metric tons of carbon dioxide per year—which works out to about 9,000 metric tons per day—and so capturing 90 percent of those emissions would require about 400 MW of fuel cell capacity.

That’s a lot of fuel cells. In terms of capital investment, fuel cell power is three to four times as expensive as conventional coal power. With a carbonate fuel cell, the cogenerated heat and electricity could boost the host plant’s power output by 80 percent. Advocates point out [PDF] that when full life-cycle costs are taken into account, along with the difficult-to-quantify environmental benefits, the balance begins to favor such a combined cycle.

At the moment, though, the partners on the Barry project are a long way from building such a system. For starters, in order to integrate carbon-capturing fuel cells with a coal-fired plant, you need a way to fuel the fuel cells. Regular coal isn’t suitable, so you'd have to gasify it first, which adds complexity and cost.

So, paradoxically, FuelCell Energy’s coal exhaust experiment will be fueled by natural gas, which is one of the reasons that the Barry plant was selected as the host site. A hybrid coal/natural gas facility, the plant is itself a bellwether of U.S. energy trends. As built in 1954, the station was an all-coal operation, and by 1971 its original two generators had been joined by three more coal-fired units. Then, in 2000, Southern installed five natural-gas-fired units, and in succeeding years, it moved to phase out coal, shutting down one coal unit in 2015 and converting two others to gas.

Another attraction of the Barry plant is that it’s already hosted a demonstration of carbon capture and sequestration [PDF]. In partnership with the DOE, Southern used Mitsubishi Heavy Industries’ amine process to chemically fix the carbon from coal-fired exhaust and then pipe it for storage in an oil field 19 kilometers away. The project, which ran from August 2012 to September 2014, sequestered about 104,000 metric tons of CO2. (Another coal plant, operated by Southern in Kemper, Miss., was supposed to showcase a different method of carbon capture, but last year the company announced that the site would simply switch to natural gas without capturing any of the emissions.)

In a second phase of the project involving ExxonMobil, FuelCell Energy will adapt its technology to decarbonize natural gas exhaust. That will entail a somewhat different process, which the energy giant will help sort out. Tim Barckholtz, an ExxonMobil senior science advisor, says that when his company first heard about FuelCell Energy’s pioneering work in carbon capture, it proposed a collaboration, which began in 2014.

In principle, it’s simpler to capture carbon from natural gas exhaust than from coal exhaust, Barckholtz says. “Gas turbines have half as much CO2 per electron as a coal-fired power plant does, so your job is half as big.”

In practice, though, integrating the fuel cells with any type of power plant brings surprises. “In the stand-alone mode, the carbonate fuel cell is operating in ideal conditions,” Barckholtz explains. “But when you couple it to a big power plant, it’s kind of the tail wagging the dog.” A delicate “balance of plant” must be maintained when working with combined cycles like this. Otherwise, the plant can trip off. Ironing out such issues will occupy ExxonMobil scientists and engineers in the months to come.

In the meantime, says FuelCell Energy’s Leo, his company is focused on building the coal exhaust portion of the experiment. When ready for operation in early 2019, the fuel cell system will run for about six months before switching to natural-gas exhaust. If history is any guide, expect incremental developments instead of breakthroughs.

That such a project is taking place at all, though, testifies to a shifting view of electricity that sees climate change and greenhouse gas emissions as unacceptable consequences of business as usual. And that shift is driving interdisciplinary collaborations at the frontier of industrial research.

“When I got into this [project], I had to spend the first six months reteaching myself a whole lot of electrochemistry,” admits Barckholtz, who holds a doctorate in inorganic chemistry. FuelCell Energy and ExxonMobil are each experts in their own fields and accustomed to operating at very different scales. “So putting the two together has really led to some interesting ideas of how to improve and optimize our systems.”

And for companies like FuelCell Energy that have struggled for decades to challenge the cheap-energy-at-all-costs paradigm, that is progress.

This article appears in the June 2018 print issue as “The Carbon-Eating Fuel Cell.”

About the Author

Matthew N. Eisler is a Strathclyde Chancellor’s Fellow and lecturer in history at the University of Strathclyde, in Glasgow. His 2012 book Overpotential: Fuel Cells, Futurism, and the Making of a Power Panacea (Rutgers) explored the long road to commercialize the fuel cell.

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