An Experimental Study on SO2 Emission and Ash Deposition Characteristics of High Alkali Red Mud under Large Proportional Co-Combustion Conditions in Fluidized Bed

As an industrial solid waste, the discharge of a large amount of red mud (RM) causes serious environmental problems; thus, a large proportion of RM co-combustion has been proposed to solve the consumption problem. In this paper, an experiment with various proportions of RM co-combustion was conducted on a 0.2 t/h circulating fluidized bed (CFB) boiler. Desulfurization performance, combustion characteristics, and ash deposition characteristics were analyzed, especially under the large proportional co-combustion conditions. As the study results showed, the desulfurization efficiency was positively correlated with the RM co-combustion proportion. When the RM co-combustion proportion reached 50%, the desulfurization efficiency was over 94%. After a period of cyclic combustion, the highest desulfurization efficiency exceeded 99.5%. The smaller size of RM was beneficial to improve the combustion efficiency and the combustion stability. However, a large area of sintering formed on the top of the heating surface in the furnace, which was lighter than the sintering of high alkali fuels such as Zhundong coal. Meanwhile, the content of sulfates, such as Na2SO4 and CaSO4, in the ash increased, which clearly proves that RM has the desulfurization effect. Therefore, a large proportion of co-combustion could meet the requirements of in-situ desulfurization and realize the resource utilization of RM.