Novel concept for efficient and clean power production from natural gas

At present, slightly over 80% of the total energy demand is satisfied by fossil fuels. With more stringent policies and increasing global awareness of the effects of excessive CO₂ emissions, this is subject to decrease. Steps to reduce CO₂ emissions involve increasing energy efficiency, switching to less carbon-intensive fuels like natural gas, adopting green energy systems like renewables and nuclear, and the deployment of CO₂ capture and sequestration (CCS) technologies.

CO₂ capture methods are broadly classified into three types: pre-, post-, and oxy-combustion. A more efficient application of oxy-combustion is currently being investigated: gas switching technology. It is based on the principle of chemical looping, which is gaining momentum particularly due to its ability to inherently separate CO₂ with no direct energy penalty. To this end, two types of chemical looping systems have been reported, namely: chemical looping combustion (CLC) and chemical looping reforming (CLR). Gas switching technologies differ from chemical looping in that, instead of circulating an oxygen carrier material between two reactors, the oxygen carrier kept in a single reactor and the gas feed to the reactor is switched. This allows easier scale-up and pressurization of these reactors, the latter being a requirement for high process efficiencies. When CLR is applied using the gas switching principle, it can be configured for efficient pure hydrogen production, which can be exported or combusted in a power plant called the gas switching reforming combined cycle (GSR-CC) plant.

In this context, Norwegian University of Science and Technology scientists: Dr. Shareq Mohd Nazir, Dr. Shahriar Amini and Dr. Jan Hendrik Cloete, in collaboration with Dr. Schalk Cloete atSINTEF Industry, presented a study where they optimized the GSR-CC plant. The study focused on evaluating the different process integration options that could reduce the efficiency penalty and simplify the GSR-CC process layout to make it more suitable for flexible power or hydrogen production. Their work was recently published in the research journal, Energy.

In brief, the research approach presented five cases, in which a systematic approach was adopted to improve the net electrical efficiency of the GSR-CC process. Two cases focused on reducing the number of unit operations and the other three cases focused on heat integration. In addition, an improved gas turbine configuration was proposed for the direct injection of the hot N₂-rich stream from the GSR reactors into the combustion chamber, where it could aid in controlling the lean pre-mixed combustion – a known problem area in hydrogen turbines.

In summary, the study by Dr. Shareq Mohd Nazir and his colleagues successfully presented a means to improve the GSR-CC process, which comprises of a novel gas switching reforming (GSR) process for hydrogen production with integrated CO₂ capture linked to a combined cycle to generate electricity from the produced hydrogen gas. The net electrical efficiency of the GSR-CC process could be improved, while simultaneously improving plant flexibility and offering a potential solution to premixed combustion of hydrogen. This flexible GSR-CC plant offers a promising solution for the ongoing global energy transition because it can integrate higher shares of fluctuating wind and solar power and supply clean hydrogen for decarbonizing transport and industry.

This work is part of “GaSTech” project under the Horizon 2020 programme, ACT Grant Agreement No 691712. GaSTech aims at demonstrating gas switching technology for accelerated scale-up of pressurized chemical looping applications.