Sulfur transformation during the pyrolysis of coal mixed with coal ash in a fixed bed reactor

• The coal ash could capture H2S at low temperatures, but promote H2S at high temperatures.
• The coal ash could enhance COS evolution at high temperature.
• The release of H2S and COS seemed to be less affected by the ash which was prepared under 1000 °C than that under 800 °C and 900 °C.
• The evolution of H2S and COS under pyrolyzed atmosphere followed the same general trend with that under N2 atmosphere.

The Xiaolongtan coal with different blend ratios (ash/coal) of ash was pyrolyzed in a fixed bed reactor to study sulfur transformation during the pyrolysis of the mixture of coal and coal ash. The addition of coal ash inhibited H2S evolution at low temperatures, and this was because H2S was captured by Fe2O3 of the coal ash. However, the coal ash promoted H2S evolution at high temperatures, which should be due to the reaction 4H2 + CaSO4 → CaO + 3H2O + H2S. More COS was evolved with the addition of coal ash at 700–800 °C, and the possible reason was that COS could be produced through the reactions 4CO+CaSO4→CaO+3CO2+COS4CO+CaSO4→CaO+3CO2+COS and 2C+CaSO4→CaO+CO2+COS2C+CaSO4→CaO+CO2+COS. The addition of coal ash reduced tar sulfur. The effects of the conditions (temperature of ash preparation and atmosphere) on the sulfur containing gas were also discussed. The evolution of H2S and COS were less affected by the ash prepared under 1000 °C than that under 800 °C and 900 °C. The possible reason was that the reactions among the volatile matters and coal ash were unfavorable due to the sintering of the ash under 1000 °C. The effect of coal ash on H2S and COS under simulated pyrolyzed gas atmosphere was similar to that under N2 atmosphere, but higher H2S and COS yields were obtained under simulated pyrolyzed gas atmosphere.