Development of tailor-made oxygen carriers and reactors for chemical looping processes at Huazhong University of Science & Technology

For the concerns of global warming, there is an urgent need of green, low-cost, and sustainable ways for the conversion and utilization of fossil energy. Holding the merit of inherent CO2 separation during carbonaceous fuel conversion, chemical looping technique is emerging as a perfect alternative to conventional fossil fuel conversion processes. Central to this technique is the design of high-performance oxygen carriers and suitable reactors that can efficiently realize the cyclic redox loop involved. To date, plenty kinds of (over 1200) oxygen carriers have been screened, synthesized and investigated by different research groups worldwide. Dozens of chemical looping reactors with thermal power ranged from kW(th) to MWth were also constructed and successfully operated. All these help to support the commercial demonstration and even industrial application of this innovative fuel conversion and carbon capture technique. The chemical looping related research at Huazhong University of Science & Technology (HUST) has experienced rapid development during the past 10 years, from rational synthesis of oxygen carrier to inter-connected fluidized bed reactor design and operation. In this article, the development of tailor-made oxygen carriers and active design of reactors at HUST is comprehensively reviewed and appraised, including the screening and optimization of oxygen carriers, reduction kinetics of oxygen carriers with gaseous fuels, microcosmic level understanding of the reaction mechanism in chemical looping via density functional theory (DFT) calculation, rational design and controllable synthesis of a hierarchically-structured oxygen carrier, and negative effects of pollutants (like sulfur and chlorides) on oxygen carriers. Moreover, experience gained from the design, macro simulation and modeling as well as continuous operation of inter-connected fluidized bed reactors is also provided. Overall, more than 100 different oxygen carriers based on Fe-, Cu-, Mn-, Ni-, as well as mixed oxides and natural ores, are systematically reviewed in terms of different chemical looping processes. The rational design route of a representative CuO@TiO2-Al2O3 oxygen carrier is proposed from the bottom up, on the basis of DFT calculation, molecular dynamic (MD) simulation, and detailed kinetics analysis. Over 300 h of continuous operation experience of the inter-connected fluidized bed reactor contributes to the demonstration of this technique. Numerical simulation via commercial computational fluid dynamics (CFD) software further helped the design, optimization, and scale-up of the reactor. In general, this review paper outlines the research route of chemical looping at HUST in details, which is expected to provide useful reference and guidance for the relevant readers.