Review of pressurized chemical looping processes for power generation and chemical production with integrated CO2 capture

Chemical looping has great potential for reducing the energy penalty and associated costs of CO2 capture from fossil fuel-based power and chemical production while maintaining high efficiency. However, pressurized operation is a prerequisite for maximizing energy efficiency in most proposed chemical looping configurations, introducing significant complexities related to system design, operation and scale-up. Understanding the effects of pressurization on chemical looping systems is therefore important for realizing the expected cost reduction of CO2 capture and speed up the industrial deployment of this promising class of technologies. This paper reviews studies that investigated three key aspects associated with pressurized operation of chemical looping processes. First, the effect of pressure on the kinetics of the various reactions involved in these processes was discussed. Second, the different reactor configurations proposed for chemical looping were discussed in detail, focusing on their suitability for pressurized operation and highlighting potential technical challenges that may hinder successful operation and scale-up. Third, techno-economic assessment studies for these systems were reviewed, identifying the process configuration and integration options that maximize the energy efficiency and minimize the costs of CO2 avoidance. Prominent conclusions from the review include the following. First, the frequently reported negative effect of pressure on reaction kinetics appears to be overstated, implying that pressurization is an effective way to intensify chemical looping processes. Second, no clear winner could be identified from the six pressurized chemical looping reactor configurations reviewed. Further information on elements such as oxygen carrier durability, technical feasibility of downstream high-temperature valves and filters, and scale-up challenges will be required to select the best configuration. Third, the maximum reactor temperature imposes a major constraint for combined cycle power production applications, requiring an extra combustor after the reactor. Hydrogen production applications do not face such constraints and can approach the techno-economic performance of unabated benchmarks. Flexible power and hydrogen chemical looping plants appear promising for integrating renewable energy. Based on these findings, pressurized chemical looping remains a promising decarbonization pathway and further development is recommended.