On the kinetic rate of biomass particle decomposition - Experimental and numerical analysis

• Published in: Energy (Oxford) 2021-03, Vol.219, p.119575, Article 119575
• Main Authors: Kardaś, Dariusz, Hercel, Paulina, Wardach-Świȩcicka, Izabela, Polesek-Karczewska, Sylwia
• Format: Article
• Language: English
• Subjects: Biomass; Chemical properties; Chemical reactions; Conservation equations; Damköhler number; Decomposition; Diffusion; Energy conservation; Heat transfer; Low temperature; Mathematical models; Numerical analysis; Particle size; Physicochemical properties; Pyrolysis; Pyrolysis time; Reaction rate; Reaction time; Single particle; TGA; Thermal decomposition; Thermo-chemical properties
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2020.119575

A simple two-equation model including both, mass and energy conservation equations, is considered to describe the pyrolysis of a single biomass particle. The model is used to numerically investigate thermal decomposition of a single cylindrical wood particle of 5 mm diameter, accounting for variable physico-chemical properties. The aim of the study is to estimate the contribution of heat transfer and chemical processes occurring during pyrolysis by estimating and comparing their characteristic times. The reaction rate of pyrolysis and kinetic constant values for biomass found in the literature were discussed, and a new approach for determination of reaction rate was proposed. Chemical reaction time based on Arrhenius equation as well as the heat diffusion time were evaluated for particle diameter ranging from 1 to 10 mm. Analysis and comparison of the obtained times in various temperature scopes between 300 K and 900 K was performed. It was estimated that chemical reaction time drops down over three orders of magnitude within 500 K and 800 K, while the heat diffusion time differs slightly. The carried out study showed that at low temperatures (below 600 K) the time of chemical reaction is much longer than the time of thermal transfer for each investigated case. •A two-equation coupled model of single particle pyrolysis was applied.•Variable physico-chemical properties of the decomposing sample were adopted.•Biomass pyrolysis kinetics was discussed based on a novel approach.•Timescales for processes of heat diffusion and chemical reaction were analysed.•Pyrolysis process analysis by means of Damkhöler number was carried out.