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Currently, CO2 conversion and utilization have become a key to mitigate the global warming. In this study, a novel separate-type autothermal dry reforming of methane (S-ATDRM) system is proposed and simulated, in which the methane dry reforming combined with methane partial oxidation is performed in a circulating fluidized bed with exergy recuperation to eliminate the negative effect of the products of CH4 partial oxidation on the DRM reaction and further improve the CO2 conversion efficiency. The results demonstrate that this S-ATDRM system can achieve an exergy efficiency of 84.7 %, and about 1055.7 kW of exergy can be recuperated from the process for crude syngas cooling and reapplied for pre-heating of feedstocks of CO2, O2 and CH4. It is found that the largest exergy destruction in this system occurs in the partial oxidation reactor, which occupies ca. 45.6 % of the whole exergy loss. Comparing with the conventional ATDRM system, although the exergy of S-ATDRM system is decreased by approximately 0.3 %, the CO2 conversion is substantially increased by about 11.3 %.

A transport bed flash calcination (TBFC) process applied to magnesite is systematically investigated through process simulation to optimize the energy-saving strategy. The high-temperature calciner flue gas is used to preheat the fed magnesite, while the sensible heat with the caustic calcined magnesia (CCM) product is cooled by air sent to the calciner. Pre-decomposition of magnesite during preheating is considered on basis of the kinetics measured using a micro fluidized bed reaction analyzer that allows the minimized effect of external diffusion on reaction. With staged fuel gas supply the TBFC process allows the equivalence ratios around 1.2 for combustion. The preferred arrangement of stages for magnesite preheating and CCM cooling are respectively 4 and 2, leading to the energy consumption of 4100 kJ/kg-CCM and the energy efficiency of 66.8%, which is almost doubly higher than the 33.9% of the conventional reverberatory furnaces (RF). The pre-decomposition occurs mainly in the 1st-stage preheater, and the maximal conversion is about 13%. Varying the stages of preheating appears more influential on the energy saving than varying the cooling stages, while residence time above 1 s in the preheaters has limited effect.