Study Of The Occurrence Of Sulfur In Coal From Huainan-Huaibei Areas And Its Migration Characteristics In Pyrolysis

The ocurrence and migration of sulfur is the theoretical basis for the clean and efficient utilization of coal,but it is also the key for desulfurization technics.In this paper,six kinds of coal from Huainan-Huaibei areas were selected to study the composition and distribution of various sulfur.The solvent extraction of Panbei-Mine(PBK)and Taoyuan-Mine(TYK)were carried out.The ocurrence of organic sulfur in the extractives of PBK were investigated by GC/MS.Then,the migration and distribution of different sulfur forms in PBK,TYK and their deashed coal were studied during pyrolysis under N2 atmosphere in different temperatures ranging from 300 ? to 900 ?.The ocurrence and migration of sulfur in coal tar,gaseous products and(semi)coke by pyrolysis were examined.In addition,the effects of deash pretreatment on the pyrolysis characteristics of coal and the migration of various sulfur forms were studied.Finaly,sulfur removal and release behaviors during pyrolysis of sulfur-containing model compounds were investigated by TPD-MS connected with Py-GC/MS.The researches indicate that the distribution of different sulfur forms in coal is related to the coal-forming environment.Among the six kinds of coal,the contents of sulfur in PBK and TYK are relatively higher,and the major forms of sulfur are pyritic and organic sulfur.The results of GC/MS showed that the major organic sulfur compounds determined in extractives of PBK are thioethers,thiophenol and thiophene.The results of sulfur migration during pyrolysis indicate that the migration characteristics of PBK are largely consistent with TYK.In the range of 300-500 °C,the decomposition of organic sulfur and transformation to pyrite occured,releasing H2 S,CH3SH,SO2,and COS,which resulting in the increase of sulfur content in tar.In the range of 500-600 °C,the decomposition of pyrite and the transformation to organic sulfur occurred,releasing H2 S,SO2,and COS.In the range of 600-900 °C,the release of sulfur-containing gas compounds and the content of organic sulfur in coke and in tar all decreased.However,the sulfate contents slightly increased and the pyrite contents stayed largely constant.The migration of different sulfur forms during pyrolysis of deashed coal is different from the results of the raw coals.Compared with raw coals,the decomposition of organic sulfur in(semi)coke and the content of sulfur in tar were both decreased,but pyrite was obviously decomposed,with the release of sulfur-containing gas compounds increased in range of 300-500 °C.In the range of 500-900 °C,the content of organic sulfur is lower than that of raw coal in tar.The results indicated that the coal ash minerals can affect the interaction between inorganic sulfur and organic sulfur during coal pyrolysis.Meanwhile,the ash can improve the release of sulfur-containing gas compounds and decrease the content of sulfur in tar.The study of sulfur-containing model compounds by TPD-MS and Py-GC/MS shows that the broken of C–S bond is the key for sulfur-containing model compounds conversion,and the indigenous hydrogen or oxygen can react with sulfur radicals to form H2 S,CH3SH or SO2.With the temperature increasing,unstable organic sulfur easily converts to thiophene sulfur.Combining the pyrolysis characteristics of PBK,TYK and the deashed coal and the pyrolysis of model compounds,it is speculated that the migration characteristics of different sulfur forms in pyrolysis process are as follows: the C–S bond can be broken in pyrolysis of coal to form Sn and sulfur-containing radicals,and the indigenous hydrogen and indigenous oxygen can react with sulfur radicals to form H2 S or SO2 in the temperature ranging from 300 °C to 500 °C.In addition,Sn and sulfur-containing radicals can react with organic or inorganic compounds in coal to form organic sulfur or pyrite.The transformation of the volatile organic sulfur to tar leads to the increase of sulfur content,while the non-volatile organic sulfur retains in(semi)coke.In the temperature of 500-600 °C,with the temperature increasing the iron sulfide may decompose to sulfur radicals,which can react with the indigenous hydrogen or oxygen to form H2 S or SO2.Meanwhile,the sulfur radicals can react with organic or inorganic compounds in coal to form non-volatile and volatile organic sulfur,and the non-volatile organic sulfur retains in char and the volatile organic sulfur transforms to tar.The non-volatile organic sulfur converts to thiophene sulfur over 600 °C.At the temperature of 600-900 °C,thiophene sulfur can slightly decompose and portions of the decomposer convert to sulfate,others convert to the sulfur-containing gas compounds.