Decarbonizing power and fuels production by chemical looping processes: Systematic review and future perspectives

The decarbonization of power and fuels production is a crucial element of the energy transition. Among several available technologies, chemical looping processes promise to be a feasible solution to support the decarbonization of large-scale industrial sectors. They involve a solid material, commonly called an oxygen carrier, that circulates between two or more reactors according to a redox process. In the reduction step, the oxygen carrier loses some its oxygen atoms by reaction with a fuel. In the oxidation step, it is oxidized back to the initial phase by an oxidizing agent such as air, steam and/or CO2. The flexibility of this process enables it to be used in diverse applications, such as: (1) fuel combustion; (2) hydrocarbon reforming; (3) solid fuels gasification, with limited energy penalties for CO2 separation and possibility of autothermal operation within the cycle. Therefore, this technology has a significant potential to contribute to the sustainable transition. This review paper aims at shedding light on a range of chemical looping progresses and to explore open questions in this field. The discussion is divided into three main chemical looping variants: combustion, reforming, and gasification. For each of these, recent progresses and challenges are highlighted by considering two scales of analysis: lab-scale and system scale. At the lab-scale, advances in materials development and process performance are discussed, while at the system scale, technical, environmental and economic analyses are presented in comparison with benchmark alternative technologies. Materials development and testing represents a crucial element hampering chemical looping development. Combination of costly and often toxic synthetic materials with natural ores is considered a promising solution that can reduce cost, increase stability and environmental compatibility. Iron oxides have several decontaminating properties and due to their low cost, large availability and high stability and appear as promising oxygen carriers. The synergistic mixing of metal oxides is also a solution to optimizing oxygen carrier properties. Different reactor configurations have been proposed with circulating fluidized beds being the most mature in terms of operational hours. Nevertheless, pressurized operation has been mainly conducted with fixed bed reactors. Techno-economic analyses indicate that chemical looping reforming can approach competitiveness with the unabated benchmark, while in power production the limit in the maximum reactor temperature is a significant drawback. An interesting application with still limited experimental and modelling research is the application of chemical looping for energy storage applications.