Study On Pyrolysis Of HLL Coal To Improve Tar Quality And Increase Tar Yield

Pyrolysis is one of the important ways to realize efficient clean utilization of low rank coal.Aiming at the problem of low tar yield and poor quality in traditional coal pyrolysis,this work using the Hongliulin bituminous(HLL)coal with high volatile content and low ash content as the sample,the effects of modified HZSM-5 catalysts on the in-situ catalytic cracking of coal pyrolysis gaseous tar and integrated process of Coal Pyrolysis with Steam Reforming of Methanol(CP-SRM)on the distribution of pyrolysis products were explored.The results have certain theoretical guiding significance for the breakthrough of pyrolysis technology of low rank coal in northern Shaanxi.(1)In-situ catalytic cracking of HLL coal pyrolysis gaseous tar on a fixed bed.The HZSM-5 catalyst was modified by P and metal loading(Fe?Co?Ni?Mo)by equal volume impregnation,and the catalysts were characterized by N2 adsorption-desorption,XRD,NH3-TPD,and thermogravimetry.The effects of HZSM-5 and its modified catalysts on the in-situ catalytic cracking of coal pyrolysis gaseous tar were studied on the fixed bed.The results show that different catalysts have different effects on tar yield after in-situ catalytic cracking of gaseous tar.The order of tar yield is:Ytar(N2)>Ytar(HZSM-5)>Ytar(P/HZSM-5))Ytar(Mo-P/HZSM-5)>Ytar(Fe-P/HZSM-5)>Ytar(Co-P/HZSM-5)>Ytar(Ni-P/HZSM-5).After in-situ catalytic cracking of gaseous tar,the tar yield is reduced.Among them,the P-modified catalyst reduces the tar yield to the greatest extent.The tar quality after in-situ catalytic cracking was significantly improved,and the heavy components in tar decreased from 67.2%(No cat)to 60.8%(Mo-P/HZSM-5).(2)The coke-resistant property of catalysts applied in catalytic cracking of gaseous tar.The amount of carbon deposited on the catalyst after the reaction was compared by TG.The results show that the P-modified catalyst is beneficial to improve the coke-resistant property.The amount of coke deposition of Mo-P/HZSM-5 and Ni-P/HZSM-5 is about 54%lower than that of HZSM-5.The introduction of P modulates the surface acid strength and acid center distribution of the catalyst,and P interacts with the surface of HZSM-5 to enhance the Al-O bond and enhance the coke-resistant property of the catalysts.(3)The integrated process of coal pyrolysis and steam reforming of methanol(CP-SRM)on a fixed bed.Four commercial hydrocarbon conversion catalysts Z111,Z205,FFT-1B and FHUDS-6 were selected for SRM reaction,and their structure and performance were characterized.The effect of different catalysts on the distribution of pyrolysis products during the CP-SRM process were studied on the fixed bed.It was found that the CP-SRM process can not only improve the tar yield,but also improve its quality.The catalytic performance and carbon deposition resistance of Ni-based catalysts Z111 and Z205 are significantly better than those of Ni-Mo catalysts FFT-1B and FHUDS-6 in CP-SRM process.Under the action of Z111,the tar yield of the CP-SRM process is up to 15.2%,which is 1.4 times than that obtained under the N2 atmosphere and 1.2 times than that under the H2 atmosphere.The tar simulated distillation results further showed that the asphaltene heavy content in tar decreased from 46.2%to 41.3%through CP-SRM process,and the tar quality was greatly improved.(4)Isotope tracing study on mechanism of CP-SRM process.CP-SRM(CD3OD)process was carried out by using CD3OD instead of common methanol.The R value(D/H abundance ratio)of hydrogen in representative compounds such as phenols and naphthalenes in tar obtained from CP-SRM(CD3OD)process over Z205 catalyst was studied by GC-Py-IRMS.The results showed that the R value of hydrogen in tar obtained during the isotope tracer process was much higher than that under N2 atmosphere.It is indicated that H2 and H·,·CH3,·OCH3 and other free radicals generated during SRM process participated in the coal pyrolysis process,which stabilized the free radical fragments generated by coal pyrolysis and inhibited the polycondensation between coal macromolecules.Therefore,the purpose of improving the yield of tar and improving the quality of tar is attained.