Effects of syngas from semi-coke in-situ gasification on yield and quality of tar from pyrolysis of Naomaohu coal

Pyrolysis atmosphere has significant effect on yield and composition of coal tar. A pyrolysis and gasification integrated reactor in laboratory was used to investigate effects of gasification syngas on yield and composition of coal tar. The results show that tar yield of Naomaohu coal reaches the maximum at 600 ℃, and gasification syngas (G-gas) is more beneficial to improve the tar yield at low temperature (550–600 ℃). Especially, 550 ℃ tar yield increases by 4.4% compared with that under N₂. With the introduction of G-gas, the yield of tar obtained at high temperature (650–800 ℃) decreases, but the quality of tar obtained at 650–700 ℃ is improved obviously due to the increase of light components. The cracking reaction of aliphatic hydrocarbons and oxygen-containing compounds in volatiles from pyrolysis at 550 and 600 ℃ is intensified by G-gas, thus substituted benzene and naphthalene compounds in coal tar increase. For the volatiles obtained above 650 ℃, the secondary cracking reaction of phenolic compounds is enhanced with the introduction of G-gas, which results in a decrease of phenolic compounds in tar. G-gas is also favorable for the secondary cracking reaction of polycyclic aromatic hydrocarbons in volatiles from pyrolysis at 800 ℃, but more favorable for generation of which in the tar obtained below 700 ℃.