Drastic SOx Removal and Influences of Various Factors in O2/CO2 Pulverized Coal Combustion System

Coal combustion with O 2 /CO 2 is promising because of its easy CO 2 recovery, extremely low NO x emission, and high desulfurization efficiency. However, there exist many unknowns concerning in-furnace desulfurization in O 2 /CO 2 pulverized coal combustion, which is much different from that in conventional coal combustion. Research on CaSO 4 decomposition aimed at desulfurization in O 2 /CO 2 pulverized coal combustion is also necessary to investigate the desulfurization behaviors. The kinetics of desulfurization and CaSO 4 decomposition were examined in atmospheres of high CO 2 and SO 2 concentrations. The characteristics and mechanisms of desulfurization in an O 2 /CO 2 pulverized coal combustion system were clarified by combining experimental results and modeling with the kinetics obtained by us. The effects of sorbent type, residence time, and so on were investigated. It has been identified that the system desulfurization efficiency in O 2 /CO 2 pulverized coal combustion is increased to about four to six times as high as that of conventional pulverized coal combustion mainly attributed to the following: (1) practical residence time of SO 2 is extended and SO 2 is enriched inside furnace owing to flue gas recirculation; (2) CaSO 4 decomposition is inhibited because of a high SO 2 concentration. Their contributions were quantitatively clarified as follows: below 1450 K, the former contributes above two-thirds, whereas above 1500 K, the latter contributes above two-thirds to the overall increase in desulfurization efficiency. The system desulfurization efficiency in O 2 /CO 2 pulverized coal combustion maintains a high value in a wide range of temperature and particle residence time. These results of a high system desulfurization efficiency, in addition to an extremely low conversion ratio from fuel-N to exhausted NO and an easy CO 2 recovery without CO 2 separation process, make simultaneous control of CO 2 /NO x /SO x possible in O 2 /CO 2 pulverized coal combustion. It can be concluded that O 2 /CO 2 pulverized coal combustion is a promising advanced coal combustion technology for the protection of global environment.

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