Advances on resource utilization of semi-dry desulfurization ash by thermal decomposition: a high-efficiency and low-temperature method for large-scale processing

The semi-dry flue gas desulfurization ash (SFGDA) is an industrial waste generated by the semi-dry desulfurization process, and its resources have been continuously attracted attention. Through the method of heat decomposition, the SFGDA decomposed into CaO and SO2 has emerged as a prominent research topic. This paper summarizes various of research workers, who revealed that the decomposition temperature of CaSO4 in SFGDA is greater than 1678 K and 1603 K in the air atmosphere and N2 atmosphere, respectively, presenting challenges such as high energy consumption and limited economic feasibility. On the one hand, the effects of CO and C regulating the pyrolysis atmosphere on reducing the pyrolysis temperature were reviewed. On the other hand, the impact of additives such as Fe2O3 and FeS2 was considered. Ultimately, the joint effects of regulating atmosphere and additives were discussed, and an efficient and low-temperature decomposition route was obtained; adding solid C source and Fe2O3 for pyrolysis reaction, the decomposition temperature of CaSO4 can be reduced by at least 230 K and desulfurization efficiency exceeds 95% under the condition of micro-oxidizing atmosphere. Moreover, the CaO resulting from SFGDA decomposition can be further synthesized into calcium ferrite, while the enriched SO2 can be utilized for the production of industrial sulfuric acid, which holds promising prospects for large-scale industrial applications.