Study On The Emission Characteristic Of Thiophenes Organosulfurs During Coal Pyrolysis

Thiophenes organosulfurs may be released during coal gasification,carbonization and combustion. The research found that thiophenes organosulfurs are hard to degrade in environment and much more carcinogenic than polycyclic aromatic hydrocarbons and nitrogenous compounds. Due to pyrolysis is an important stage of the coal conversion, it is very important for clean coal utilization to study on the principle of thiophenes organosulfurs released during the coal pyrolysis.In order to find the emission principle of thiophenes organosulfurs during the coal pyrolysis, discuss the formation mechanism of thiophenes organosulfurs, and provide theoretical guidance for clean coal utilization to reduce the amount of organic pollution emitted from coal, the pyrolysis device (CDS-5250) and GC-MS (Focus GC-DSQII) were used to quantify and qualitify benzothiophene and dibenzothiophene produced during the coal pyrolysis in situ. They are two important compounds of thiophenes organosulfurs, to study their formation mechanism can make sense for understanding release behaivor of thiophenes organosulfurs during the coal pyrolysis.Seven coals with diffierent coal rank were choosed as experiment samples. This study focuses on the factors that have influence on the yield of thiophenes organosulfurs produced during the coal pyrolysis, which include the internal factors (degree of coalification, elemental composition) and external factors (pyrolysis temperature, heating rate). Besides that the experiment also discusses the formation mechanism of the thiophenes organosulfurs during the coal pyrolysis. Some primary conclusions have been gotten from the experiment:1. The degree of coalification has an important effect on pyrolysis of coal. With the increase of coal rank, the yield of thiophenes organosulfurs produced during the coal pyrolysis increases first and then decreases. The reason is explained by coal property. The yield of thiophenes organosulfurs increases with the increase of the organic sulfur content, it has positive correlation with the organic sulfur content in coal, but has no immediate connection with the inorganic sulfur content.2. During low pyrolysis temperature, the yield of thiophenes organosulfurs is low, and the yield of thiophenes organosulfurs increases with temperature up, and achieves the maximum value at 800℃. The thiophenes organosulfurs mainly come from the decomposition of the macromolecular and the condensation of the micromolecular. As the temperature is higher than 1200℃, the yield of thiophenes organosulfurs increases again, that's because the higher temperature could offer enough energy to the system, some organosulfurs staying in coal are released again. The results indicate that the yield of thiophenes organosulfurs may have difference owing to the different heating rates, and achieves the maximum value at the optimalizing heating rate of 12℃/ms. The results also show the yield of thiophenes organosulfurs produced during the rapid pyrolysis is much more than medium pyrolysis.3. This paper also confers the possible mechanism of thiophenes organosulfurs produced during the coal pyrolysis. When the temperature is low, thiophenes organosulfurs may come from the decomposition of the macromolecular, the condensation of the micromolecular and release from free state thiophenes organosulfurs in coal. Some of them may be decomposed into micromolecular compounds or sulfur radicals at a higher temperature. Others may react with micromolecular compounds or sulfur radicals and form sulfocompounds with higher degree of polycondensation, bigger molecular weight and higher stability. The research presents the yield of thiophenes organosulfurs and PAHs produced during the coal pyrolysis have the same trend with the temperature, they both increase with the increase of temperature and achieve to the maximum value at 800℃. It indicates that the formation paths and chemical reactions of thiophenes organosulfurs and PAHs are similar during the coal pyrolysis and they may be interconvertible to a certain extent.