Sulfur Conversion of Mixed Coal and Gangue during Combustion in a CFB Boiler

The construction of a power plant using a 660 MWe supercritical circulating fluidized bed (CFB) boiler with co-combustion of coal and gangue has been proposed in China. Therefore, this study simulated the distribution law and transformation mechanism of sulfur-containing phases using three low-calorific samples of gangue and coal mixtures under different conditions, based on the thermodynamic simulation software HSC Chemistry. The results showed that sulfur low in calorific value coal is mainly converted into gas phase SO2, solid phase alkali metal sulfate (Na2SO4 and K2SO4), and alkaline earth metal sulfate (CaSO4 and MgSO4) in an oxidizing atmosphere. Under a reductive atmosphere, sulfur in coal is mainly converted into gaseous H2S, COS (Carbon oxysulfide), and solid FeSx. With an increase in the O/C ratio, the distribution curve of sulfur-containing substances contracted to lower temperatures. It was established that the sulfur fixation capacity of coal ash depends on the relative amounts of basic oxides and sulfur present in it. Relevant conclusions were also verified and compared to those of the laboratory small-fluidized bed test bench and the 3 MWth CFB combustion test bench.