With a little extra engineering work, some researchers believe fuel cells could become one of the most affordable ways for coal plants to keep their doors open as pollution regulations tighten.
The Department of Energy selected FuelCell Energy Inc. (FCE) last week as one of eight funding recipients to pilot low-cost carbon dioxide capture and compression technologies. The $23.7 million project (with $15 million coming from the DOE and $8.7 million from FCE) will see a 2-megawatt fuel cell deployed at a coal-fired power plant designed to capture about 60 tons of CO2 per day, while simultaneously producing about 40,000 kilowatt-hours of electricity per day.
This first-of-its-kind application is a modification to FCE’s existing Direct FuelCell technology, which the company says has already generated more than 4 billion kilowatt-hours of electricity. Researchers have been exploring the use of fuel cells for carbon capture since the early 1990s, but only recently has the technology declined enough in cost to be seriously considered as a solution.
Carbon capture only works with a molten carbonate fuel cell, a chemistry that relies on CO2 to operate. Flue gas from a coal plant contains 5 percent to 15 percent CO2, with the remainder made up largely of nitrogen, as well as other gases. In FCE’s application, the flue gas is routed into the fuel cell at one electrode, where the cell selectively takes up the CO2 and releases it in a concentrated stream at the other electrode. During this process, approximately 70 percent of the smog-producing nitrogen oxide is destroyed.
Once the CO2 is captured, it’s cooled and compressed utilizing standard refrigeration equipment. The purified carbon can then be sequestered or used for enhanced oil recovery.
Today’s commercially available carbon-capture technology has proven to be extremely expensive and energy-intensive, nearly doubling the cost of electricity from a coal-fired power plant. FCE’s technology also increases the cost of electricity from coal-fired power plants, but the DOE believes that increase could be one-third or less.
“At an estimated cost of $40 per metric ton of carbon dioxide, these second generation technologies are showing they could potentially achieve a 30 percent increase in the cost of electricity, which is a significant drop compared to today’s commercially available technologies,” said José Figueroa, senior carbon capture project manager at the DOE, in an interview.
“The challenge of emissions reduction has always been to find a proven technology that’s affordable, and that’s reasonable to deploy, as opposed to spending billions,” said Arthur Bottone, CEO of FCE. “We’ve met that challenge with our solution.”
As states act to meet their compliance obligations under the EPA’s Clean Power Plan, several stakeholders will seek new technologies to clean up their coal plants. FCE has only tested its carbon-capture technology in the lab to date, but the application is already the attracting interest from the power industry and legislators in states with a high reliance on coal, said Bottone.
Questions about efficiency, scale, climate impact and cost
FCE is currently evaluating multiple sites for the DOE-supported pilot with interested utility and independent power producers, and it expects to announce the site selection this fall.
One of the selection criteria is that there needs to be a nearby supply of natural gas to power the fuel cell. Molten carbonate fuel cells take in CO2, but still need a fuel source to operate.
The chiller used to condense CO2 also needs a power source. To meet that demand, the system is outfitted with a 2.8-megawatt fuel cell, which the chiller brings down to around 2 megawatts of actual power output.
Even with these extra steps, Bottone said the fuel cell application is much more efficient than other carbon-capture technologies. Rather than drain productivity at the power plant, FCE’s technology generates additional power — and revenue — in exchange for the energy it consumes.
“This is a power generation device that concentrates CO2 at the same time. It’s a completely different thought process, versus a device that’s doing nothing but capturing CO2,” he said. “We’re multitasking on the same asset as compared to a different way of doing it, which would only be a cost and not necessarily a benefit.”
This dual use makes the project easily financeable by private capital, because the electricity generated by the fuel cell creates a reliable revenue stream, Bottone added. Selling the purified CO2 for use in other applications like enhanced oil recovery would create additional revenue, although FCE didn’t factor those sales into its financial modeling.
Another benefit is that the technology is modular, so it can be scaled up incrementally as funding becomes available.
FCE sees the DOE-supported pilot as the first phase of a much larger project. In the second phase, once the application engineering is established, FCE will seek private capital to install 11 additional fuel-cell power plants. This 25-megawatt system is expected to capture a total of 700 tons of carbon dioxide per day, while generating about 648,000 kilowatt-hours of electricity per day.
At a 500-megawatt coal plant, 25 megawatts of fuel cells would reduce emissions by between 5 percent and 6 percent, said Bottone. Under the Clean Power Plan, emissions have to fall by roughly 3 percent over a 10-year period. So by installing FCE’s technology in phases, a coal-plant operator could meet the 32 percent overall emissions reduction target in a few years, while adding about 100 megawatts of power generation to its site.
“On paper, it’s a massive market opportunity,” said Bottone. “The question is how fast we can go.”
“We think that given the significant assurance of the technology we’ve developed for other businesses, we can go pretty quick, not to mention the fact that some of these utility customers and others are already our customers,” he added. “So the business model, and the confidence in us, frankly, is already there.”
But several questions remain. For one thing, while the system captures CO2 from the natural gas fed into the fuel cell, as well as from the coal plant itself, there are still concerns about the net climate benefit because of the emissions associated with natural gas production.
There are similar concerns with enhanced oil recovery. Pumping CO2 underground could help unlock new oil resources, and the CO2 could then be sequestered underground once the reservoir is depleted. But the net benefit is unclear, since the carbon sequestration would be offset by the continued use of oil. Plus, there’s the added complexity of getting the CO2 to the oil well to begin with.
Another issue is that flue gas from a coal plant contains pollutants, such as sulfur and chlorine, that could degrade the fuel-cell stack over time. How much FCE’s application ultimately costs will depend on how much the coal plant exhaust has to be cleaned up before it enters the cell.
“A coal-fired power plant has a lot of environmental control systems to meet environmental regulations, so those emissions are very low. But fuel cells are still sensitive to many contaminants, and so the flue gas would have to go through a polishing step to get it to even lower contaminant levels before getting to the fuel cell,” said Figueroa.
Lab tests to date show that the fuel cell sees little degradation using a simulated polished gas, but more testing is needed to see how the fuel cell performs in real world conditions.
“Understand this technology is still at a small scale,” said Figueroa. “Conceptual cost estimates, versus what it will look like at a 500-megawatt scale, with all of the flue gas that needs to be processed at that level, can differ.”
“There’s a lot that can still happen as you scale up and that’s why they’re performing more research, and that takes time,” he said.