Pressurized entrained-flow pyrolysis of lignite for enhanced production of hydrogen-rich gas and chemical raw materials

Abstract

This paper reports the enhanced production of H2 and polyaromatics during lignite pyrolysis under pressurized entrained-flow conditions. The pyrolysis temperature and pressure ranged between 600−900 °C and 0.1–4.0 MPa, respectively, and were found to greatly influence the yield and composition of pyrolysis products. The results showed that the concentration of H2 in the light gas fraction increased drastically with pyrolysis temperature and pressure, reaching 91.69 vol% at 900 °C and 4.0 MPa, which corresponded to H2 generation of 0.27 m3/kg coal. The yield of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, biphenylene, fluorene, phenanthrene, pyrene, and fluoranthene was also promoted at elevated pyrolysis temperatures and pressures. The highest PAHs concentration of 90.4 area% in the pyrolysis oil was obtained at 900 °C and 4.0 MPa. It was also found that the changes in the hydrogen distribution under pressurized entrained-flow conditions mainly took place during the secondary pyrolysis reactions. It was postulated that hydrogen was formed via aromatization, condensation, aromatic ring growth mechanism, and direct cleavage reactions. The findings of this study showed that lignite could be efficiently converted to H2-rich gas, PAHs as chemical raw materials, and energy-dense lignite char via a novel poly-generation system based on pressurized entrained-flow pyrolysis.