Effects of steam and CO₂ on gasification tar composition and evolution of aromatic compounds

The removal of tar is conducive to improving the energy efficiency of downstream equipment and reducing the damage caused to it. In this study, a two-stage continuous feeding apparatus was developed to explore the yield and characteristics of tar produced from the co-gasification of microcrystalline cellulose (MCC) and polyethylene (PE) under separate and mixed atmospheres of steam and CO₂. The tar yield can effectively reduce to 2.27 % when the steam and feedstock mass ratio (S/F) is 0.8. CO₂ can partially substitute the steam in the gasification process, which can effectively promote a decrease in benzofuran. Furthermore, Gaussian software was employed to analyze the evolution mechanism of aromatic compounds. When the temperature is more than 800 °C, hydrogen consumption in the benzene cracking process is reduced, which is instrumental in improving the quality of syngas. Naphthalene is prone to form through the recombination of two cyclopentadienyls. Controlling the cyclization of cyclopentadienyls is a critical step in reducing the formation of polycyclic aromatic hydrocarbons. H and OH radicals are critical in phenol and benzofuran cracking, respectively. Although radicals act differently on specific aromatic compounds, the gasification effect of CO₂ is less than that of steam because steam can provide both H and OH radicals, whereas CO₂ needs to consume H radicals to generate OH radicals. The results provide beneficial guidance for controlling tar formation.