A prediction of arsenic and selenium emission during the process of bituminous and lignite coal co-combustion

摘要

Coal blending has been extensively applied in coal-fired power plant. The emission of trace elements was greatly affected by the change of combustion characteristic in the blended coal. Based on thermodynamic calculation and combustion experiments, the distribution of arsenic and selenium in the process of SH bituminous and HLH lignite co-combustion were investigated at a wide temperature range (500-1500 °C). The result of thermodynamic calculation displayed that the main existing forms of arsenic were considered as Ca_3(AsO_4)_2(s), As_4O_6(g), and As2O3(g). At temperatures below 1000 °C, As_4O_6 was deemed the dominant gas-phase species of arsenic. Moreover, the form of selenium was predicted to be SeO2(g) which accounted for almost 100% of the selenium species at 500-1100 °C. When the temperature was increased to 1200 °C, gaseous-phase SeO begun to appear. The result of co-combustion experiments suggested that the retention ratio of arsenic and selenium in ash was decreased obviously at 500-900 °C with the increasing of temperature, which was consistent with the result of the calculation. SH coal had more effective arsenic and selenium retention capacity than HLH coal at 500-900 °C. The retention ratio of arsenic in 3SH:1HLH coal was fluctuated between 6.20 and 18.04%, and that of 1SH:3HLH coal was 3.29-7.08%. The retention ratio of selenium in the ash of mixed coals combusted at different temperature was lower than 7%, especially at 800 and 900 °C; nearly all of the selenium species were volatilized.