A novel insight into biomass pyrolysis – The process analysis by identifying timescales of heat diffusion, heating rate and reaction rate

Abstract

The complex nature of pyrolysis that involves coupled physical and chemical sub-processes is a bottleneck for its in-depth recognition. This is also due to physical-chemical parameters, which appear insufficiently identified, particularly for biomass. This study is motivated by the inconsistencies in the description of wood pyrolysis processes and primarily refers to the uncertainties in terms of kinetics of reaction. A new approach to analyze the biomass devolatilization was discussed. A strong emphasis was placed on the crucial role of thermal transport processes and their impact on the kinetics of pyrolysis of a single sample. Characteristic timescales influencing each other, namely: heating rate, heat transfer and reaction rates, were considered. The theoretical research was conducted with a use of a simple two-equation model. A standard heat transfer equation for the sample and a mass conservation equation with slightly different approach were implemented. Mass loss curves and temperature profiles were presented for very low heating rate (1.7K/min) and high heating rate (170K/min) for samples of size ranging from 0.49 mm to 15.4 mm, while assuming different reaction rates. Based on the calculation results, the possible role of the process timescales in analysing the kinetics of pyrolysis was outlined.