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.
Barckholtz, T. A., Taylor, K. M., Narayanan, S., Jolly, S., & Ghezel-Ayagh, H. (2022). Molten carbonate fuel cells for simultaneous CO2 capture, Power Generation, and H2 generation. Applied Energy, 313, 118553.