Characteristics and kinetics of the gas releasing during oil shale pyrolysis in a micro fluidized bed reactor

Abstract

This paper presents a comprehensive study on characteristics and kinetics of the gas component (H2, CH4, CO, CO2) releasing during oil shale (OS) pyrolysis. Firstly, the thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TGA-FTIR) was used to determine the decomposition regions of OS. The results showed that the OS undergoes two pyrolysis regions: first stage (400∼600 °C) and second stage (600∼800 °C). The isothermal pyrolysis of OS was carried out in a micro-fluidized bed reaction analyzer (MFBRA). The evolved temperature and time span of each gas product are different in both sections. Reaction kinetics were investigated with respect to the formation of individual gas component and gas mixture. The kinetics of gas components and gas mixture were calculated by model fitting method. The activation energy (Ea) calculated by the three models for H2, CH4 and CO2 were in the range of 51.05∼60.15, 6.84∼9.65 and 13.21∼14.10 kJ/mol, respectively, while the values varied significantly in high temperature zone. In particular, the resulting Ea values for H2 decreased to 38.88∼40.57 kJ/mol, while that for CH4 and CO2 increased to 25.16∼27.61and 26.12∼35.12 kJ/mol, respectively. However, compared with other three gases, CO only appears in the high temperature zone, and the activation energy of CO is in the range of 32.98∼34.82 kJ/mol. The Ea of the stage 2 is higher than that of the stage 1. The result indicated that the control step gradually transits from the surface chemical reaction control to the joint control of reaction and diffusion with increasing temperature.