Study On Catalytic Upgrading Of Coal Low Temperture Pyrolysis Tar Over Bio-char

China's coal resources are relatively rich,of which the low rank coal reserves account for about 55%.The coal pyrolysis-based staged conversion technology is an important method to realize a clean and efficient utilization of low rank coal.However,the tar yield of coal pyrolysis is low and the content of heavy tar fractions obtained from the current pyrolysis unit is usually high.Heavy components in tar not only deteriorate tar quality making it difficult for further utilization,but also condense easily resulting in blockage of subsequent pipelines and affecting the stable operation of the pyrolysis system.The low H/C of coal itself is the essential reason for the coal pyrolysis tar with high content of heavy fractions.There are two effective ways to upgrade the coal tar.One is to introduce hydrogen-rich materials for co-pyrolysis with coal,in which hydrogen is supplied to coal volatiles to obtain lighter tar by influencing the formation of volatiles.The other is to introduce the catalytic material to catalytically crack coal pyrolysis volatiles to improve tar quality through controlling secondary reactions.The co-pyrolysis system of coal and biomass have the above two characteristics.Biomass is a kind of hydrogen-rich resource compared with coal and the bio-char obtained from pyrolysis has certain catalytic effect on coal volatiles.Based on the previous work of the research group,this paper mainly studies the catalytic cracking ability of bio-char on coal pyrolysis volatiles using isolation method.Hulunbuir lignite was used as the pyrolysis material,and two representative biomass was selected as char-making raw materials.The comparative study of coal pyrolysis alone and coal pyrolysis with the bio-char was carried out.The change of tar yield and fractions distribution of tar,element distribution,the content of light tar and distribution of pyrolysis products were investigated.And the physicochemical properties of the fresh and spent bio-chars were analyzed,which can reveal the catalytic cracking mechanism and influence factors of coal pyrolysis with bio-char.The main results of this paper are as follows:1.Bio-chars?rice straw char and pine sawdust char?have obvious catalytic upgrading effect on coal pyrolysis volatiles,making the content of light tar and the yield of pyrolysis gas increase significantly.The experimental results of bio-chars'dosage?RSCR-650 as an example?showed that the optimal amount of RSCR-650 was 20 wt.%and the yield of the light component reached the maximum value?5.08 wt.%,d?.2.After tar upgrading with rice straw char,the content of N and S in tar decreased and the H/C ratio increased.The catalytic upgrading effect of RSCR-700 is the most obvious?compared with quartz sand?.The H/C mole ratio of tar increased by 22.06%,while the content of N and S elements reduced by 27.88%and 25.00%.The upgrading effect is mainly due to the catalytic cracking of heavy components to light components and gases.The content of PAHs decreased and that of mono cyclic aromatic hydrocarbons increased accordingly in the upgraded tar.3.Bio-char prepared by fast pyrolysis has larger specific surface area and more defective active sites,so the catalytic cracking effect is better than that of slow pyrolysis prepared char.The content of light component using RSCR-650 was 79.94 wt.%,which was higher than that of 66.23 wt.%corresponding to RSCS-650.4.Pine sawdust char?PSCR?and Co/PSCR can reduce the yield of pyrolysis water and increase the content of phenolic compounds in tar.The amount of CO,CO₂ and H₂ increased and that of CH₄ decreased with cobalt supported bio-char.5.The large specific surface and abundant pore structure?precondition?,alkali?earth?metal and oxygen-containing functional groups?active sites?are the main factors of catalytic upgrading.