Molten carbonate fuel cells for simultaneous CO2 capture, power generation, and H2 generation

The global energy demand has steadily grown over the last few century due to a surge in the global population and increased economic productivity. With the increasing awareness of climate change and global warming and the stringent measures to reduce the emissions of greenhouse gases (GHG), the energy industry has focused on providing an affordable and reliable energy supply. Most importantly, the energy supply needs to be sustainable and with minimal impacts on the environment. While affordable and clean energy is listed among the seventeen UN sustainable development goals, the energy industry will also play a critical role in achieving the other goals.

Several technologies have been developed to stabilize global GHG emissions. Among them, carbon capture and sequestration technology have attracted significant research attention as a potential solution for the challenges facing the energy industry today. To date, different CO₂-reducing technologies have been successfully deployed in natural gas processing. Unfortunately, most of these technologies are not suitable for combustion fuel gas which accounts for a larger proportion of global CO₂ emissions. On the other hand, hydrogen has also been considered a viable technology though achieving desired production efficiency is costly and still in the early development stages.

The simultaneous generation of steam and electricity, also known as cogeneration, offers opportunities for reducing CO₂ emissions and enhancing efficiency and has been used widely by industry. However, CO₂ capture from cogeneration units remains highly underexplored. The current best technology for CO₂ capture uses liquid amine units, which are effective for removing CO₂ from combustion flue gas. However, amine units consume significant amounts of power and steam, which reduce the overall efficiency of the system. Thus, developing alternative and more efficient technologies is highly desirable.

Now scientists from ExxonMobil Research and Engineering, Tim Barckholtz and Sundar Narayanan, together with Stephen Jolly and Hossein Ghezel-Ayagh from FuelCell Energy and Kevin Taylor from AECOM, presented a novel technology for reducing GHG emissions from cogeneration units. The technology was based on molten carbonate fuel cell (MCFC) for H₂ generation and CO₂ capture. MCFC facilitated the transfer of CO₂ from cathode to anode. At the anode, H₂O and CH₄ were converted into H₂ and CO₂, respectively. Their work is currently published in the journal, Applied Energy.

The researchers reported that the newly proposed technology could simultaneously and effectively capture CO₂ from flue gas sources and generate a large volume of low-carbon hydrogen gas at high efficiency and negligible energy penalty. The efficiency of the MCFC was also attributed to the generation of additional power during electrochemical oxidation and CO₂ capturing. After separation, the resulting CO₂ could be sequestered, while H₂ could be used as a chemical reagent in separate process/independent combustion units or recycled as fuel.

For all the studied cases, the MCFC efficiency was remarkably higher than that of amines. It also avoided more CO₂ than amine-based technology. For instance, using amine for cogeneration of power and hydrogen could avid up to 87.6% of CO₂, which required additional 4.91 MJ/kg additional primary energy. On the other hand, MCFCs could avoid 89.4% of CO₂ at only 1.37 MJ/kg of additional primary energy. The experimental data demonstrated the versatility of the proposed approach as it was applicable to wide range CO₂ sources, including cement, gas turbines, heat and power generation sector, cogeneration units and steam boilers.

In summary, the study demonstrated the applicability and efficiency of using MCFCs to capture CO₂ from a wide range of flue gas sources. The new innovative technology facilitated simultaneous CO₂ capture and generation of power and H₂ with high efficiency. The unique features and capability of MCFC make it a promising technology for facilitating the creation of a low-carbon energy economy.