Pressurized Gas Switching Combustion in a Pre-Pilot Scale Reactor Cluster

CO₂ capture and storage (CCS) is increasingly seen as a vital cost-effective tool for bridging to a sustainable low carbon economy, especially given the importance of limiting global warming to 1.5 °C, as highlighted in the recently released IPCC special report [1]. CCS implementation is, however, still a far-reaching goal, requiring the development of high efficiency CO₂ capture processes, since energy penalty is the primary economic and environmental concern hampering current CCS technology.

Gas Switching Combustion, GSC, is an emerging technology for power production with integrated CO₂ capture, that incorporates the high energy efficiency of chemical looping combustion (CLC) and the design simplicity and practicality of a standalone dense fluidized bed [2]. This configuration avoids external solids circulation taking place in conventional chemical looping that uses interconnected fluidized beds, thereby avoiding many of the operational challenges, especially at high pressures. In the GSC concept, gas feeds are alternated into a bed of oxygen carrier, initially placed in a single reactor, to complete the redox cycle: the oxygen carrier is first reduced by a gaseous fuel in the fuel stage then oxidized by the oxygen from the air feed in the air stage. In this way, contact between air and fuel is avoided, resulting in inherent CO₂ and N₂ separation.

The GSC concept was demonstrated in a single reactor using different oxygen carriers (Ni-based, ilmenite and CaMnO_3-δ-based) and fuels (CO, H₂ and CH₄), under atmospheric and pressurized conditions [2-4]. In these studies, the GSC has shown very attractive features, such as ease of operation and control under pressurized conditions, in addition to sufficiently high CO₂ purity and capture efficiency.

Because of the dynamic nature of the gas switching concept, GSC requires a cluster of reactors operating in a coordinated manner to ensure a steady supply of hot gasses to a downstream power cycle. In this study, the standalone GSC reactor operated in previous studies [2-4], is scale up from 5 to 10 cm ID, then a cluster of three such reactors is constructed. The system is designed to operate at pressures up to 20 bar and temperatures up to 1100 °C. The CaMnO_3-δ-based oxygen carrier previously tested in the GSC reactor, was selected for this first of a kind GSC cluster testing, given its good performance with both syngas and methane, in addition to its exothermic reduction reaction that minimizes temperature variation across the GSC cycle.

[1] "IPCC, Global Warming of 1.5 °C (2018). Intergovernmental Panel on Climate Change."

[2] A. Zaabout, S. Cloete, S. T. Johansen, M. v. S. Annaland, F. Gallucci, and S. Amini, "Experimental Demonstration of a Novel Gas Switching Combustion Reactor for Power Production with Integrated CO2 Capture," Industrial & Engineering Chemistry Research, vol. 52, no. 39, pp. 14241-14250, Oct 2 2013.

[3] A. Zaabout, S. Cloete, and S. Amini, "Autothermal operation of a pressurized Gas Switching Combustion with ilmenite ore," International Journal of Greenhouse Gas Control, vol. 63, pp. 175-183, 2017/08/01/ 2017.

[4] A. Zaabout, S. Cloete, J. R. Tolchard, and S. Amini, "A pressurized Gas Switching Combustion reactor: Autothermal operation with a CaMnO3−δ-based oxygen carrier," Chemical Engineering Research and Design, vol. 137, pp. 20-32, 2018/09/01/ 2018.