Effects of different co-pyrolysis ways on sulfur transformation of coals under different atmospheres

In this study, the effects of different co-pyrolysis ways (direct mixed co-pyrolysis and indirect layer-separated co-pyrolysis) on sulfur transformation behavior of Yangquan raw, deashed and depyrited coals were investigated during their co-pyrolysis with biomass (corn-cob) in Ar and CO2 atmospheres. Under the same pyrolysis way, the desulfurization ratios of these coals under CO2 atmosphere are all higher than those under Ar atmosphere, while their char yields lower than those under Ar atmosphere. During the same atmosphere, the char yields of the same kind of coal are almost similar during single pyrolysis and indirect layer-separated co-pyrolysis. However, the char yields (Y-mix) during the direct mixed pyrolysis are higher than those (Y-3) during the indirect layer-separated co-pyrolysis. Under CO2 atmosphere, the main sulfur-containing gases are composed by H2S and COS, while only H2S in Ar atmosphere, no obvious SO2 emission was detected. During the same co-pyrolysis way, the calorific values of YQ chars under Ar atmosphere are higher than those under CO2 atmosphere. The trend of total release amount of sulfur-containing gases is: indirect layer-separated co-pyrolysis > direct mixed co-pyrolysis > single-pyrolysis. This indicates that H-2, CO, CH4 or a small amount of hydrocarbons resulting from biomass decomposition can promote more sulfurs to decompose. But, biomass oil or black carbon from biomass pyrolysis can prohibit the release of sulfur-containing gases. Thus, this study can provide the detailed information about the effects of different co-pyrolysis ways on sulfur transformation of coals under different atmospheres.