Kinetics and thermodynamics evaluation of carbon dioxide enhanced oil shale pyrolysis

Shuai Zhao,Xiaoshu Lü,Youhong Sun,Qiang Li

doi:10.1038/s41598-020-80205-4

Abstract

The pyrolysis process of oil shale is significantly affected by atmospheric conditions. In this paper, the pyrolysis experiments of oil shale under non-isothermal conditions are carried out using nitrogen and carbon dioxide as heat-carrying fluids. The results show that the activation energy of the second stage of oil shale pyrolysis under carbon dioxide is less than that under nitrogen. The thermodynamic analysis of the second stage of oil shale pyrolysis shows that Gibbs free energy, activation enthalpy and activation entropy are higher under carbon dioxide than those under nitrogen, which obeys the law of carbon dioxide promoting oil shale pyrolysis. In addition, the volatile release characteristics of oil shale in the second stage of pyrolysis were analyzed, which proves that the volatile release characteristics of oil shale under carbon dioxide are higher than that under nitrogen. Therefore, carbon dioxide is helpful to promote the pyrolysis of oil shale and increases the release of volatile substances during pyrolysis.

Highlights

CO2 can promote the transformation of semi-coke in coal and oil shale
Huadian oil shale is taken as a sample to study the pyrolysis kinetics, thermodynamic law and volatile release characteristic index of oil shale in pure C O2
KAS and FWO methods are used to calculate the kinetic parameters of the second stage of Huadian oil shale pyrolysis under the two atmospheric conditions

Summary

Introduction

CO2 can promote the transformation of semi-coke in coal and oil shale. For deep buried oil shale, C O2 can be used as heat-carrying fluid and displacement fluid to realize underground burial of CO2, which plays a positive role in reducing the greenhouse effect of the earth. KAS and FWO methods are used to calculate the kinetic parameters of the second stage of Huadian oil shale pyrolysis under the two atmospheric conditions. The process curves of activation energy calculated by the two methods show that under N 2, the conversion rate of oil shale pyrolysis concentration ranges from 25 to 90%, and the corresponding temperature ranges from 700 to 774 K when the heating rate is low.

Results

Conclusion