Fuel cells are a rapidly expanding option for distributed generation, with fuel cell–based power plants now being deployed in capacities into tens of megawatts (see “59-MW Fuel Cell Park Opening Heralds Robust Global Technology Future” in the May 2014 issue). But as the technology improves and costs begin to scale, opportunities for other applications are being explored.
One such application may even go beyond power generation. Danbury, Conn.–based FuelCell Energy (FCE), one of the largest suppliers of fuel cells worldwide, and ExxonMobil in May announced a partnership to explore the possibilities for using fuel cells for carbon capture.
According to Kurt Goddard, FCE’s vice president of investor relations, the application will depart from the traditional method of powering the fuel cells with ambient air and methane. Instead of air, it uses coal- or gas-plant flue gas.
Normally in FCE’s carbonate fuel cells, methane is reformed in the cell anode to create CO2 and H2, which is then used to generate electricity by combining with oxygen from ambient air to create an electric current and exhaust streams of water vapor and CO2 (Figure 6). The carbon-capture fuel cell will still be powered by methane, but by using flue gas instead of ambient air, the chemical reactions in the cell can concentrate up to 90% of the incoming CO2, which flows with the CO2 generated in the reforming process into the normal exhaust stream, where it can easily be separated from the water vapor.
6. Game changer? Fuel cells powered by natural gas could potentially function as carbon capture technology by using power plant flue gas instead of ambient air. Courtesy: FuelCell Energy
A critical difference—and bonus—in this process is that rather than being a parasitic drain on the plant, it actually generates additional power. In addition, the process destroys roughly two-thirds of the NOx in the flue gas.
How much CO2 can be captured depends on how many fuel cells are employed. A typical 500-MW combined cycle plant would need around 120 MW of fuel cells to achieve 90% capture, Goddard said, while an equivalent coal plant might need around 400 MW of fuel cells because of its lower efficiency and higher CO2 emissions. Commercial deployment is still years away, but representatives from both companies are optimistic about the potential.
The possibilities of employing fuel cells to reduce power plant emissions for both coal plants and natural gas combined cycle plants, and potentially capture CO2, have drawn research attention in recent years, though applications have typically involved placing the fuel cells in front of the turbines or replacing typical combustion processes altogether. The FCE-ExxonMobil initiative is among the first to look at placing the fuel cells after combustion.
ExxonMobil began working with FCE on this project several years ago, Goddard said, beginning with informal discussions that led to more formal testing. With the potential now clear, the two companies have gone public with the initiative. The partnership will focus initially on how to further increase efficiency in separation and concentration of the CO2 from gas turbine exhaust. That is expected to take one to two years.
FCE and ExxonMobil scientists will be working to better understand the chemical processes that are taking place and how they respond to different compositions of flue gas. Assuming success, the second phase will move to a small-scale pilot project for additional testing, then integration into a larger-scale pilot facility.
—Thomas W. Overton, JD, POWER associate editor.