Study On The (Catalytic) Co-pyrolysis Of Shendong Coal And Coal Tar And Its Gasification Performance Of Char

Coal pyrolysis technology has enriched the way of coal replacing oil and provided good basic raw materials for the downstream extension of coal chemical industry.However,it still has some problems to be solved,such as low tar yield,difficult separation between tar and dust and high content of heavy components in the coal tar.The(in-situ catalytic)co-pyrolysis of coal with hydrogen-rich substances is an effective way to improve the yield and quality of coal tar,and also an effective control means to enhance the reaction efficiency of coal pyrolysis,improve the yield of liquid/gas products,and directionally regulate the composition of products.In this paper,Shendong coal(SD)and low temperature heavy coal tar(HCT)were used as raw materials,metal salts(ferric nitrate,copper nitrate,nickel nitrate and ammonium molybdate)and hematite(CTK),chalcopyrite(HTK),laterite nickel(HTNK)and molybdenite(HMK)were used as catalysts.The effects of coal-tar ratio,different coal tar fractions,catalyst type and addition amount on the pyrolysis characteristics and product distribution were investigated by thermogravimetric analyzer(TG),pyrolysis-gas chromatography/mass spectrometer(Py-GC/MS)and fixed bed rapid pyrolysis device.Response surface design and artificial neural network were introduced to optimize the catalyst ratios(combination of natural minerals),and the mechanism of coal-tar(catalytic)co-pyrolysis was proposed.The main results are as follows:(1)TG studies showed that the volatiles from coal-tar co-pyrolysis escaped in advance,and the total weight loss rate of pyrolysis decreased with the increase of coal-tar ratios,when the coal-tar ratio was 6:4,it was 54.76 wt%.Compared with the theoretical value,the co-pyrolysis reduced the initial and termination temperatures of volatiles,and the maximum weight loss rate of coal increased by more than 10%.The apparent activation energy of coal in the main pyrolysis stage was reduced by at least 49 k J/mol.(2)Py-GC/MS experiment results showed that coal-tar co-pyrolysis was favorable to the generation of oxygen-containing compounds,but unfavorable to the generation of aromatics.Compared with the non-catalytic condition,ferric nitrate significantly increased the relative contents of aromatics and aliphatics by 26.45%and 27.79%,respectively,while oxygen-containing compounds decreased by 23.65%,which effectively inhibited the formation of oxygen-containing compounds such as phenol,cresol and xylenol.The four natural minerals with an addition of 3 wt%were beneficial to the production of oxygen-containing compounds including phenol,cresol and xylenol,but not to the production of aliphatics,monocyclic and tricyclic aromatics.(3)The results of fixed bed pyrolysis showed that when the coal-tar ratio was 5:5(S5H5),the tar yield increased by 2.61 wt%compared with the theoretical value.Coal-tar co-pyrolysis significantly increased the relative content of aliphatics and oxygen-containing compounds,promoted the generation of xylenol,and significantly reduced the aromatics,which was not conducive to the generation of phenol and cresol.The studies on gasification performance of char from coal-tar co-pyrolysis showed that the gasification time decreased with the increase of coal-tar ratios,and the gasification effect of char decreased.The tar yield of fraction<210 ~oC co-pyrolysis with SD increased by 52.87 wt%compared with the theoretical value,and the relative content of light component of tar reached 85.97%.(4)In the catalytic pyrolysis of metal salts and natural minerals with the addition amount of3 wt%,the yields of char and gas increased,while the yield of tar decreased.Metal salts inhibited the formation of phenol,but the content of light components in tar catalyzed by ammonium molybdate increased.For the natural minerals,the content of light components is related to the type,addition amount and particle size of natural minerals.When the addition amount of HMK was 3 wt%,the lightening effect is the best.Compared with S5H5,the relative content of oxygen-containing compounds in natural mineral pyrolysis products with the addition of 0.5 wt%was reduced,which was conducive to the generation of phenol and monocyclic aromatics,but not conducive to the generation of xylenol.(5)During the process of coal-tar co-pyrolysis,the violent pyrolysis of HCT produced more H’,which timely stabilized the free radical fragments generated from SD pyrolysis and avoided their interaction to generate semicoke,thus forming more tar,resulting in an increase in tar yield.The metal elements in natural minerals promoted the cracking of tar,which caused the heavy components of volatiles from coal-tar slurry pyrolysis to break into light components,and caused the hydroxyl groups in phenolic compounds to fall off from aromatic rings to form light aromatics.The oxygen-containing heterocyclic compounds deoxidized and decomposed into aliphatics,or further transform into aromatics.(6)The ratio of catalyst was optimized by artificial neural network.The results showed that when the ratio of HTNK was high,the compound catalysts were beneficial to improve the yield of tar.When the ratio of HTK was relatively high and the ratio of HMK and HTNK was low,the content of light components was higher.When the ratio of HMK to HTNK was close and HTK was higher,the product of tar yield and light component content(product value)was higher.The tar yield,light component content and product value can reach 50.49wt%,46.14%and 21.14 wt%after verification of optimization results,respectively.