Study On Co-pyrolysis Characteristics And Mechanism Of Low-rank Pulverized Coal In Northern Shaanxi

In this paper,the co-pyrolysis of low-rank pulverized coal(SJC)in northern Shaanxi was carried out with the adding of heavy oil(HS),coking coal(JM),direct coal liquefaction residue(DCLR),respectively.The distribution of functional groups of solid coke,composition of tar and the precipitation of gas products were characterized by Fourier transformed infrared spectrometry(FTIR),gas chromatography-mass spectrometry(GC-MS)and thermogravimetric Fourier transform infrared analyzer(TGFTIR).The process and technical parameters of co-pyrolysis process were investigated,and the synergistic mechanism between SJC and HS,JM and DCLR during pyrolysis was discussed in detail.The results showed that the co-pyrolysis process of SJC and HS,JM and DCLR could be divided into three stages.The first stage was the precipitation of surface water,adsorbed gas in coal and the fragmentation of weak chemical bonds.Depolymerization and decomposition of SJC and HS,JM and DCLR occured mainly at the second stage with gas and tar precipitation and then turn coal into char.Char condensated into coke with the precipitation of carbon monoxide and hydrogen gas during the third step of polycondensation reaction,meanwhile the weight loss curves decreased slowly.The synergetic effect existed in the process of co-pyrolysis,and mainly occured in the second stage,which was represented by the transfer and transformation of [H] mainly in SJC.The hydrogen radicals produced by the co-pyrolysis process were free to bind to other free radical fragments,and the hydrogenation reaction produceed more tar and gas,resulting in a significant reduction of H2 content and a significant change of main components content in tar.The production of tar and gas was obviously promoted by HS,and the oil and gas yield increased by 12.18% and 7.26% respectively after co-pyrolysis of SJC+HS.JM would inhibit the secondary cracking of tar,resulting in tar yield increased by 7.40%,while the gas yield decreased by 6.24%.JM and DCLR could effectively promote the production of fatty hydrocarbon,and the secondary cracking and conversion of aromatic hydrocarbons,causing fat hydrocarbon content increased by 29.33% and 16.25% respectively,aromatic hydrocarbon content was reduced 15.07% and 11.88% respectively.Co-pyrolysis process could get relatively high-value tar and high-calorific gas under the conditions of heating rate of 7?/min,pyrolysis temperature 800?,holding time 4h,HS 20%,and the additions of JM,asphalt(LQ)and SJC were 15%,5% and 60%,respectively.Long holding time and fast heating rate will increase the possibility of secondary cracking of gaseous products,resulting in reduced yield of tar.With the increase of pyrolysis temperature,the yield of coke tends to decrease first and then increase,while the yield of tar and gas is reversed.The calorific value of gas increased with the increase of pyrolysis temperature,and the content of H2 in gas increased gradually,while the contents of CO and CH4 increase first and then decrease.the CO and CH4 contents reached the maximum of 12.77% and 33.16% at 800?,and the H2 content was 19.61% at this time.The solid coke yield continued to decrease with the increase of HS addition,while the yield of tar increased first and then decreased.When the amount of HS was 20%,the yield of tar was 33.40%,and the content of alkanes and phenols in the tar were 7.71% and 21.85%,respectively.