A comprehensive study on fuel property, pyrolysis kinetic and product characteristic of torrefied biomass for high-value utilization

Torrefaction is regarded as a promising way to improve the pyrolysis behavior of biomass. This work studied the effect of torrefaction on the physicochemical and pyrolytic properties of biomass, focusing on the typical agricultural residues of rice straw and corn stalk. The torrefaction experiments were conducted through a horizontal fixed-bed reactor at 200–290 °C. The results demonstrated that torrefaction resulted in the loss of a considerable number of oxygen-containing functional groups from biomass. The particle surface of sample exhibited a transformation from a loose state to a dense one, and was subsequently cracked with the temperature increasing. In addition, the pyrolysis kinetics were determined to be a one-stage reaction level model combining with TG-DSC-FTIR. The activation energy and pre-exponential factor firstly increased and then decreased with the increased temperature, showing good integrated pyrolysis characteristics. The release of gas products mainly occurred at 250–500 °C, and the peak values of small molecule gas products as well as the oxygen-containing organics significantly reduced, indicating that the kinds of organic species were simplified. After torrefaction, the char yield increased while the pyrolysis bio-oil decreased, and the pyrolysis syngas also showed a decrease trend due to the combined effects of decreased volatile content and the breaking of chemical bonds. The cross-linking reactions during torrefaction led to an increase in the as-built solids yield. The results obtained in this work may provide some fundamental information and progressive guidance for upgradation of bioenergy properties and sustainable agriculture thermal conversion to a good extent.