Modelling and simulation of intra-particle heat transfer during biomass torrefaction in a fixed-bed reactor

Abstract

A two-dimensional, transient and single particle model was developed for biomass torrefaction. A wood cylinder $(\rho =700\mathrm{ }\mathrm{kg}/{\mathrm{m}}^3,\mathrm{ }28\text{ mm in diameter and }100\text{ mm long})$ was modeled as a porous solid. The transport, energy conservation and intra-particle pressure evolution equations were discretized by the finite volume method. The resulting linear algebraic equations were solved using the tridiagonal matrix algorithm. Intra-particle flow velocity was estimated by Darcy’s law. Simulation results for intra-particle temperature profile and mass loss history showed good agreement with experimental data from the literature. Thermal flux, drying and torrefaction fronts advanced into the interior of the particle in semi-ellipsoidal form. Water vapor is the main volatile released. The reduction in mass yield is higher than the reduction in energy yield due to loss of water and carbon dioxide. This model can be used in a wide range of process conditions and as an important tool in biomass thermal pretreatment.

Keywords:

• Biomass torrefaction
• particle dynamics
• energy yield
• intra-particle gradient functions
• 2D transient model

Funding

There was no funding for this study.

Disclosure statement

There is no potential conflict of interest.

Data availability statement

The data that support the findings of this study are available from the author upon reasonable request.