Some network models related to heat and mass transfer during thermal conversion of biomass

The paper deals with a porous network model based simulation of effects of microwave pre-treatment of biomass pellets. Different heating regimes – rapid and slow – are compared; it is shown that rapid heating regime results in pressure build-up reaching values that cause breakage of the biomass material. Slow heating regime results in much lower maximum pressure values. As a second stage, ignition of pre-treated and non pretreated granules is compared. It is demonstrated that the pre-treated granule ignites considerably faster. The simulation considers intra-particle processes. The pellet is modelled as a porous material. The transport of volatiles is calculated using a nonlinear porous media equation. Thermal decomposition of the pellet is modelled using Arrhenius kinetics for three principal components of the biomass. An exponential rule for calculating the permeability of the material as a function of conversion rate is implemented. The model has been implemented in Octave. The result is a numerically cheap model that can be implemented and used to control the biomass gasification process. The model is versatile and can be extended to incorporate other physical and chemical processes.