Integrated Process Of Coal Pyrolysis With Steam Reforming Of Ethane For Tar Production

Low-and-medium temperature pyrolysis of low rank coal to obtain high quality tar with high yield is an effective way to use coal cleanly and efficiently.Focused on the influence of ethane steam reforming on coal pyrolysis,aimed for improving tar yield,the main research content of this dissertation is to investigate the effect of reaction temperature and catalysts on the integrated process of coal pyrolysis with steam reforming of ethane for tar production.Meanwhile,the coal tar obtained was characterized and analyzed.The main results are summarized as follows:(1)Commercial Ni/Al2O3 catalysts was modified by addition of Ce promoter with different content(3,6,12 wt.%).The influence of catalysts on steam reforming of ethane(SRE)and integrated process of coal pyrolysis with steam reforming of ethane(CP-SRE)under the condition of 550 oC,molar steam to carbon ratio 1 were studied and the catalysts were characterized by XRD,H2-TPR.The results show that the higher ethane conversion and tar yield can be achieved over the Ce-Ni/Al2O3 catalyst with 3 wt.% Ce calcinated at 650 oC than that over the other catalysts.The high catalytic activity with addition of Ce is attributed to the high dispersion on catalyst support and smaller particle size of the metal active species Ni.The Ce-Ni/Al2O3 catalyst with 3 wt.% Ce showed the best resistance of carbon deposition in SRE,and the carbon deposition of the catalyst was only 0.5 wt.% after 485 min reaction under the condition of 550 oC and molar steam to carbon ratio 1.However,Ce-Ni/Al2O3 catalyst with 12 wt.% Ce showed the worst catalytic activity and resistance of carbon deposition possibly owing to the decrease of metal Ni dispersion due to agglomeration of metal Ni.The highest tar yield can be obtained in an integrated process of coal pyrolysis with steam reforming of ethane(CP-SRE)when the Ce-Ni/Al2O3 catalyst with 3 wt.% Ce due to the fact that the best catalytic activity and resistance of carbon deposition lead to more active species participate in the coal pyrolysis.(2)Both of CP-SRE and integrated process of coal pyrolysis with steam reforming of methane and ethane mixture(CP-SRME)are conducive to promote the tar yield.The tar yield of CP-SRE and CP-SRME at the reaction temperature 500-700 oC and molar steam to carbon ratio 1 is 1.25-1.46 times and 1.24-1.40 times as that in coal pyrolysis under nitrogen atmosphere,respectively.The highest tar yield 14.60 wt.% was obtained from CP-SRE at 550 oC,which is 1.46 times and 1.26 times as that in coal pyrolysis under nitrogen and hydrogen atmosphere,respectively.Above 550 oC,tar yield from CP-SRME decreases more slowly than that from CP-SRE.When reaction temperature is 700 oC,tar yield from CP-SRME is 13.17 wt.%,which is only 0.70 wt.% lower than the highest tar yield from CP-SRME at 550 oC.Due to the promoting effect of methane on ethane conversion in steam reforming of methane and ethane mixture(SRME)and higher methane conversion at 600-700 oC,more tar yield can be obtained from CP-SRME than that from CP-SRE.(3)The analyses of coal tar indicated that light oil content in tar from CP-SRE and CP-SRME is higher than that from coal pyrolysis under nitrogen at 500-700 oC.The tar obtained from CP-SRE at 550 oC has higher light oil and phenol oil content,but lower pitch content than those at other reaction temperature.The benzenes,naphthalenes and condensed aromatics content in the tar from CP-SRE and CP-SRME are 1.89 and 1.40 times,1.30 and 1.28 times,1.86 and 1.54 times as those in the tar from coal pyrolysis under N2 atmosphere,respectively.