Desulfurization of coal through pyrolysis in a fluidized-bed reactor under nitrogen and 0.6% O2–N2 atmosphere

The raw Yima (YM) and Datong (DT) coal, their demineralized (YM-ash, DT-ash) and de-pyrite (YM-p, DT-p) coals were pyrolyzed in a fluidized-bed reactor to examine the sulfur removal efficiency. The effect of process parameters such as temperature, residence time and atmosphere were investigated. The results show that there is an optimal temperature and residence time for the maximum desulfurization, varying with type of coal and the thermal stability of organic sulfur. The alkaline-earth mineral in the raw coal plays an important role for the fixation of sulfur and makes desulfurization decrease. The interaction of pyrite with the organic matrix of coal is the dominant reason that leads to organic sulfur accumulation in char. YM has higher desulfurization of organic sulfur than DT due to more aliphatic sulfur in the raw coal. YM and DT were pyrolyzed in 0.6%O2–N2 mixed atmosphere, aiming at examining the effect of reactive gas on the sulfur removal during pyrolysis. The results show that sulfur removal is improved without great decrease in char yield. This indicates that small amount of O2 in inert atmosphere can improve desulfurization efficiency. In addition, TG-MS runs in 0.6%O2–Ar and Ar were carried out to check the sulfur-containing compounds in pyrolysis gas and further understand the desulfurization process.