Gas-pressurized torrefaction of biomass wastes: The effect of varied pressure on pyrolysis kinetics and mechanism of torrefied biomass

Abstract

A novel gas-pressurized (GP) torrefaction of biomass waste was proposed in our recent work to deeply upgrade the biomass under the pressure of 5 MPa prior to their subsequent use in thermo-conversion technologies such as pyrolysis, combustion and gasification. However, the effect of varying pressure on the GP torrefaction process and the thermochemical behaviour of the torrefied biomass were not clear. In this work, the effect of varying torrefaction pressure on the pyrolysis kinetics and mechanism of GP torrefied biomass was studied in detail. It was revealed that the activation energy (Ea) of the GP torrefied biomass ranged from 195 to 198 kJ mol−1 increasing with torrefaction pressure, and their activation energy distributions were invariably wider compared to raw and torrefied biomass produced by atmospheric pressure torrefaction. The carbon and fixed carbon content, aromaticity, and crystallinity of the GP torrefied biomass were promoted by increasing the torrefaction pressure. On the other hand, the porosity of the GP torrefied biomass was reduced by elevated pressure. These are the reasons for the Ea increase of the GP torrefied biomass under elevated pressure. The presented kinetics and mechanism study provide a deep understanding of the novel GP torrefaction method.