Reaction pathway and kinetics study on supercritical water gasification of oily sludge

Abstract

Supercritical water gasification of oily sludge is a clean technology for waste disposal and energy recovery. In this work, gaseous productions from supercritical water gasification (SCWG) of oily sludge in a batch reactor under different temperatures (550–650 °C) and residence times (1–40 min) was studied. Then, a quantitative kinetic model was employed to study the reaction mechanism and optimize the H2 and CH4 productions. The H2 yield was promoted with the increase in temperature and residence time. The CH4 yield and carbon gasification efficiency (CE) increased with the prolongation of residence time, but reached the maximum when the temperature was 600 °C. The liquid products were mainly composed of alkene, acetone, benzene, toluene, ethylbenzene and xylene, phenolic substances and polycyclic aromatic hydrocarbons (PAHs). Higher temperatures promoted the formation of phenol and PAHs in liquid products, which were hard for gasification. The results of kinetic model indicated that higher temperatures accelerated the reaction rate and intermediates formation, but the effect on gas formation was limited. Reaction rate analysis at 650 °C indicated that H2 was mainly produced from pyrolysis rather than steam reforming. CH4 was produced mostly from pyrolysis and methanation reaction can be neglected.