Behavior Of Coal And Sulfur Removal During Pyrolysis

Ten Chinese coals were used in this study. Thermal gravimetric analysis (TGA) was used to investigate coal pyrolysis, and kinetic parameters of coal pyrolysis were determined by Distributed Activation Energy Model (DAEM); the effect of pyrolysis conditions and coal properties on coal pyrolysis and sulfur transformation was studied in fixed-bed; the effect of pyrolysis atmosphere on the evolution of sulfur containing gases during coal pyrolysis was carried out in a micro-fixed bed combined with a TPD detector; the effect of various gas pretreatment on sulfur removal during hydropyrolysis was also touched in this study.1. The TGA study indicates that both coal properties and pyrolysis conditions have great influence on coal pyrolysis. The character temperature of coal pyrolysis increases with increasing rank, and the total weight loss decreases. The influence of atmosphere on coal pyrolysis is not pronounced at low temperature, while CH4 increases char yield and CO2 decreases char yield at high temperature, and FTIR was used to investigate coal pyrolysis. The result of DAEM indicates the activation energy of coal pyrolysis was focus in the range of 200-300kJ/mol.2. The fixed bed study indicates that coal properties and pyrolysis conditions are effect product distribution and sulfur transformation. Compared with N2, H2 promotes sulfur removal; CO shows similar effect on sulfur removal as H2 does at temperature below 450℃, at high temperature, no more sulfur is removed in CO; CH4 promotes sulfur removal slightly. The decomposition of pyrite is almost complete at 550℃ in H2 and CO, and at 650℃ in N2 and CH4; organic sulfur content change in char is the net effect of decomposition of organic sulfur species with low thermal stability and formation of new ones with high thermal stability by the reaction of hydrogen sulfide and/or nascent sulfur with organic matrix. The AP-TPR also shows similar result. Increase H2 flow rate, enhance H2 pressure, and prolong residence time in H2, resulting sulfur removal increase. Although sulfur form in coal affect sulfur content in char, it is difficult to predict sulfur content in char, for many coal properties influence sulfur transformation. It seems that the S/C on the surface and in bulk of coal affects sulfur removal.3. Gas pretreatment influence product distribution and sulfur removal during coal hydropyrolysis, hydrogen pretreatment increases tar yield and decreases water yield, meanwhile, promotes sulfur remova; CO2 pretreatment promotes sulfur removal; N2 shows no effect of sulfur removal; coal properties also affect the effect of pretreatment on sulfur removal.4. The evolution of sulfur containing gases is affected by pyrolysis atmosphere. H2 promotes the evolution of H2S and prohibits the evolution of other sulfur containing gases; CO and CO2 promotes the formation of COS; no evidence proves CH4 is necessary on the formation of CS2. Coal properties affect the evolution of sulfur containing gases, and the evolution of H2S reflects the distribution of sulfur in coal. And the evolution of H2S in hydropyrolysis indicates more stable organic sulfur in high rank coal and more non-stable organic sulfur in low rank coal.