Coal Liquefaction Residue Catalytic Gasification Characteristics Research Under CO₂ Atmosphere

A large amount of residue is produced in the process of direct coal liquefaction. In order to improve the efficiency of coal resources, much more emphasis should be laid on the efficient conversion of residue. The thermal conversion characteristics of residue which was from Shenhua direct coal liquefaction plant were studied in CO₂ atmosphere by means of TG-FTIR. The thermal conversion could be affected by many factors, such as different catalysts, contents, temperatures and heating rates. Meanwhile, employing homogeneous model the gasification kinetic parameters of DCLR was calculated.The thermal conversion of DCLR was composed of the pyrolysis at lower temperature and the gasification at higher temperature. The result showed that the pyrolysis behavior of DCLR ranged from 260? to 620?. The maximum pyrolysis rate was 0.256%/? at 510?, and the final conversion in pyrolysis was 30%. The gasification rate of DCLR was slower between 650? and 880?. When the temperature reached up to 880?, the gasification rate was accelerated significantly and rapidly reached the maximum after lmin at constant temperature. The maximum gasification rate of DCLR was 4.72%/min, the gasification index was 0.016min-1, and the final conversion was 77%.In this paper, it took many factors such as different catalysts, contents, temperatures and heating rates into account to investigate the pyrolysis and gasification characteristics of DCLR. The results showed that all catalysts used in the experiment could inhibit the pyrolysis behavior. However, they accelerated the gasification rate except FeSO₄, and the order of catalytic activity in gasification was as follows:K₂CO₃> Na₂CO₃> CaO> K₂SO₄. Moreover, the inhibition in the pyrolysis became strengthened gradually, with the contents of Na₂CO₃ and K₂CO₃ increasing, but the promotion in the gasification was accelerated at first and then decreased. The optimal addition amount of Na₂CO₃ and K₂CO₃ is respectively 0.002mol. The temperature had significant influence on the gasification, but had no effect on the pyrolysis of DCLR. With the temperature increasing, the gasification index and reactivity became much more intensive. The pyrolysis conversion rate and conversion were sharply promoted at 300?/min.By analyzing the data of FTIR, the regulation of gases emission during the process was investigated, CH₄, aromatic hydrocarbons and aliphatic hydrocarbons were emerged in the pyrolysis, whose absorption intensity increased at 530?, and then gradually decreased with temperature increasing. A weak absorption peak of CO appeared in the pyrolysis ranging from 415? to 605?, a strong absorption peak existed in the gasification above 675?. All catalysts used in the experiment inhibited the emission of pyrolysis gases, but accelerated the emission of CO in the gasification. When the addition account of Na₂CO₃ and K₂CO₃ is respectively 0.002mol, the absorption intensity of gases is the strongest.Employing the homogeneous reaction model to simulate the gasification kinetic parameters of DCLR, the result showed that the residue gasification reaction activation energy was 199.0 kJ/mol at constant temperature.