Exxon Mobil, with partner Fuel Cell Energy, is advancing technology with the aim of improving CCS efficiency, effectiveness, and affordability for large natural gas-fired power plants.
Carbon capture and sequestration (CCS) is a process by which carbon dioxide that would otherwise be released into the atmosphere is captured, compressed and injected into underground geologic formations for permanent storage. Exxon Mobil applies CCS applications with all of its component technologies, including participation in several carbon dioxide injection projects. Exxon claims that the they captured 6.9 million metric tons of carbon dioxide for sequestration in 2015.
Exxon Mobil’s scientists have been pursuing new technology that could reduce the costs associated with current CCS processes by increasing the amount of electricity a power plant produces while simultaneously delivering significant reductions in carbon dioxide emissions. At the center of Exxon Mobil’s technology is a carbonate fuel cell.
According to the company, laboratory tests have demonstrated that the unique integration of carbonate fuel cells and natural gas power generation captures carbon dioxide more efficiently than current, conventional capture technology. During the conventional capture process, a chemical reacts with the carbon dioxide, extracting it from power plant exhaust. Steam is then used to release the carbon dioxide from the chemical – steam that would otherwise be used to move a turbine, thus decreasing the amount of power the turbine can generate.
Using fuel cells to capture carbon dioxide from power plants results in a more efficient separation of carbon dioxide from power plant exhaust, but with an increased output of electricity. Power plant exhaust is directed to the fuel cell, replacing air that is normally used in combination with natural gas during the fuel cell power generation process. As the fuel cell generates power, the carbon dioxide becomes more concentrated, allowing it to be more easily and affordably captured from the cell’s exhaust and stored. Exxon Mobil’s research indicates that a typical 500 megawatt (MW) power plant using a carbonate fuel cell may be able to generate up to an additional 120 MW of power while current CCS technology consumes about 50 MW of power.
ExxonMobil’s research indicates that by applying this technology, more than 90 % of a natural gas power plant’s carbon dioxide emissions could be captured. Natural gas is already the least carbon-intensive of the major energy sources.
In addition, carbonate fuel-cell technology has the potential to generate significant volumes of hydrogen. Simulations suggest that the new technology can produce up to 150 million cubic feet per day of hydrogen while capturing carbon dioxide from a 500 MW power plant. To put that in perspective, a world-scale steam methane reforming hydrogen plant produces around 125 million cubic feet per day. In addition, synthesis gas, or syngas, composed of hydrogen and carbon monoxide, can be produced that can be upgraded to other useful products such as methanol, olefins, or higher molecular weight hydrocarbons for transportation fuels or lubricants.
Next steps in development
Exxon Mobil has been assessing a number of carbon capture technologies for many years and believes that carbonate fuel-cell technology offers great potential. The technology’s capability has been demonstrated in the laboratory, and data from those simulations is currently under analysis. Further development will involve a more detailed examination of each component of the system, and optimization of the system as a whole.
The scope of the agreement between Exxon Mobil and Fuel Cell Energy will focus on better understanding the fundamental science behind carbonate fuel cells and how to increase efficiency in separating and concentrating carbon dioxide from the exhaust of natural gas-fueled power turbines. The technology will be more comprehensively tested in a small-scale pilot test prior to integration at a larger-scale pilot facility, which is currently being evaluated.