Kinetic, volatile release modeling and optimization of torrefaction

Abstract

Torrefaction is a thermal pretreatment of biomass process carried out in the temperature range of 473–573K under inert atmosphere to enhance fuel properties. In the present study, different biomass are analyzed through numerical simulations and optimized parameters are reported. Kinetic, volatile release and solid composition models are coupled & simulated. Results of the kinetic model are verified by comparing with experimental results. Then, compositional coefficients for volatiles of different biomass are found by volatile release model. Further, volatile release model used to calculate composition of releasing volatiles. By means of mass conservation, composition of remaining solid product is estimated. Effect of torrefaction temperature, residence time and nature of biomass on moisture content of biomass, volatiles release, hydrogen to carbon (H/C) & oxygen to carbon (O/C) molar ratios, energy densification and elemental compositions are given. It is found that during mild torrefaction regime 508–548K; water removal and energy densification increases more rapidly as compared to light 473–508K and severe 548–573K regimes. Further, H/C and O/C molar ratios are found to be decreasing linearly in mild regime. In light and severe torrefaction; moisture removal and energy densification are increasing slowly. So, mild torrefaction was found to be optimum regime of torrefaction for practical applications. In mild torrefaction regime energy densification ratio was 1.05-1.52 for different biomasses studied.