Pyrolysis Of Xinjiang Hefeng Coal And Catalytic Cracking Of The Produced Tar

Pyrolysis for high-quality tar and gas is the core technology for value-added cascade utilization of coal. The critical problem that causes the difficulty in industrial applications of coal pyrolysis technology is the formation of too many heavy species in coal tar. Addressing this problem, to improve the tar quality, pyrolysis and catalytic pyrolysis of Hefeng coal were carried out in a fixed bed reactor, and then catalytic cracking behaviors of produced tar was studied with two fixed-bed reactors in series.The major research results are as follows.(1) Pyrolysis performance of Hefeng coal. With the increase of pyrolysis temperature from 500 ℃ to 750 ℃in N2 atmosphere, char yield declined while the gas yield increased. Tar yield and light tar fraction reached the maximum value of 15.0 wt. %, and 55.7% at 600 ℃, respectively. When coal was pyrolyzed in different atmosphere at 600 ℃, water yield increased in both N2+H2 and N2+CH4 atmosphere compared with that in N2 atmosphere. Simulating pyrolysis gas(SPG) had little effect on tar yield, but increased the fraction of light tar slightly, thus increased the yield of light tar.(2) Catalytic pyrolysis performance of Hefeng coal. Hefeng coal was pyrolyzed at600 ℃ in SPG atmosphere at the presence of Ni, Mo, Co and W catalyst using HZSM-5(38) as carrier. The results showed that tar yield all decreased, while light tar fraction increased in varing degrees. Light tar fraction reached its maximum value of 79.4% when Ni/HZSM-5(38) was added into the reactor, though the tar yield was only 11.0 wt. %. At the presence of Mo/HZSM-5(38), the light tar fraction decreased 11.6 percent compared that of Ni based catalyst. The acidity of Ni-Mo/HZSM-5(38) catalyst increased when loaded Ni active component on Mo based catalyst, leading to the increase of light tar fraction from 67.8% to 77.9%, while the tar yield decreased a little, about 0.3 percent, thus the light tar yield increased about 10.8% than that without catalyst.(3) Coal pyrolysis coupled with tar catalytic cracking process. Effect of carriers on tar catalytic cracking performance was studied. Ni/USY catalyst which possessed the highest specific surface area and acidity facilitated the conversion of pitch into light tar, so the light fraction in tar increased to 71.9%.