Preparation Of Carbon-based Filter Material And Its In-situ Adjustment Of Coal Pyrolysis Tar Quality

Aiming at the problems of high content of asphalt,serious carbon deposition,difficulty in online separation of oil-dust,and easy clogging of pipelines during the operation of pulverized coal pyrolysis process,this paper explores the influence of filter mediums on the reaction behavior of volatiles.The distribution and composition of pyrolysis products under different filter mediums such as quartz bead(QB),expanded perlite(EP),ceramic ball(CB),?-Al₂O₃,coal-based activated carbon(AC-1)and coconut shell activated carbon(AC-2)were analyzed.On that basis,Through the way of blending coking with bio-char and coal,the high abrasion-resistant multi-stage porous carbon-based filter mediums and Fe and Ni modified carbon-based filter mediums suitable for particle bed filtration dust removal are prepared,in order to regulate the distribution of pyrolysis products,achieve in-situ lightening of tar,and achieve the purpose of online filtering and dust removal.The Specific work and results of this article reads as follows:1.Effects of different filter mediums on the reaction of coal pyrolysis volatilesThe filter medium significantly affects the reaction of volatiles and ultimately affects the coal pyrolysis product distribution and carbon deposition behavior.Compared with the absence of filter medium,the residence time of volatiles in the heat flow field and increase the reaction of volatiles under QB filter medium,resulting in the change of three-phase yields.The three-phase yields under QB,EP and CB filter media are not much different.Under EP and CB filter medium,the yield of pitch is increased,which is not conducive to improving the quality of tar.Under the?-Al₂O₃,AC-1 and AC-2 filter medium with catalytic cracking activity,the yield of tar is greatly reduced,while the yield of pyrolysis gas and carbon deposition is increased.These three filter mediums crack heavy tar(boiling point<360 ?)while crack light tar(boiling point>360 ?),and the reduction ratio of heavy tar is larger than that of light tar.Activated carbon has advantages in reducing carbon deposits in tar,but its microporous structure inhibits the diffusion of macromolecular compounds in tar,resulting in the formation of large amounts of carbon deposits on the surface of the filter medium during the reaction of volatiles.When the filter medium is AC-1,as the feed time decreases,the relative content of aliphatic hydrocarbons and oxygenates decreases.The formation of coke may be related to the cracking of aliphatic hydrocarbons and oxygenates.2.The effect of carbon-based filter medium on the catalytic upgrading of volatilesThe amount of biomass char in the carbon-based filter medium have significant effects on the distribution of pyrolysis products and tar composition.Carbon-based filter medium including a biomass char blending amount of 10-30wt.%of Coke(BC:BC-1,BC-2,and BC-3)and activated coke(BHC:BHC-1,BHC-2,and BHC-3).The highest tar yield is 12.85 wt.%under the BC-2 filter medium,2.88%higher than that QB filter medium.20%BC and 30%BC as filter medium are conducive to cracking the pitch of tar and increase the yield of light oil(boiling point<170 ?).Compared with BC filter medium,the yield of carbon depositions of BHC filter medium increases rapidly,and the existence of micropore intensifies the formation of carbon depositions.BHC has more carbon crystal structure defects than BC,which is more conducive to cracking heavy tar fractions.Compared with BC filter medium,the yield of asphalt is reduced by50.31%and 55.50%,respectively.The yield of pitch decreases by 50.31%and55.50%under BHC-2 and BHC-3 filter mediums,respectively.The content of aromatic hydrocarbon compounds,oxygen-containing compounds,heterocyclic compounds containing N and S in tar are reduced,while the content of phenolic compounds are increased under carbon-based filter mediums.It may promote the occurrence of hydrogen transfer reactions in volatiles and have better selectivity for the formation of phenolic compounds.3.Effect of Fe and Ni modified carbon-based filter medium on the catalytic upgrading of volatilesFe and Ni modified coke(Fe-BC,Ni-BC),activated coke(Fe-BHC,Ni-BHC),commercial coal-based activated carbon(Fe-AC-1,Ni-AC-1),and commercial coconut shell activated carbon(Fe-AC-2,Ni-AC-2)obviously affect the distribution of pyrolysis products.Compared with QB filter medium,the tar yield increased by 9.15%and 4.58%under the action of Fe-BC and Ni-BC filter medium,respectively.The carbon-based filter medium modified by Fe and Ni both increase the yield of H₂ and CO,and reduce the yield of CO₂and CH₄.Compared with carbon-based filter medium,Fe and Ni modified carbon-based filter medium can increase the yield of light tar and have a positive impact on improving the quality of tar.The yield of light oil can be increased by 38.35%and 48.19%under Fe-BC and Ni-BC filler medium,respectively.The increase in tar yield and light tar yield may be related to the free radicals in H·and CH_x·produced by the reforming of CH₄ and CO₂.These hydrogen donors can be used in the volatile reaction process to stabilize free radicals in tar.Compared with Fe-BC and Ni-BC filter medium,Fe-BHC and Ni-BHC is more conducive to cracking heavy components of asphalt.Compared with QB filter medium,the yield of asphalt is reduced by 41.01%and 42.59%respectively,and the yield of tar is also reduced.From the above,Fe-BC and Ni-BC filter medium have higher yield of tar and light tar,more suitable as particle bed filter medium.Compared with QB filter medium,both Ni and Fe modified coke and activated coke reduce the content of oxygen compounds and heterocyclic compounds containing N and S in tar,and increase the content of aliphatics and aromatics.The presence of Fe and Ni promoted the dehydroxylation reaction,showing higher catalytic activity and enhancing the selectivity to aromatic compounds.Compared with Fe-AC-1,Fe-AC-2,Ni-AC-1,and Ni-AC-2 filter mediums,it can be seen that Fe-BHC and Ni-BHC have higher tar yield and lower coke yield,and have more advantages as particle bed filter medium.