Two-dimensional model of a single biomass particle pyrolysis including moisture evaporation and gas pressure

In many pyrolysis studies, the role of energy is reduced to the heating rate. This underestimates the role of thermal energy that initiates and governs the processes. This work presents a two-dimensional transient model of biomass particle pyrolysis. Explicit numerical methods are used to compromise the high computing power requirements. The model includes solid mass conservation equation in a standard form for pyrolysis, with the reaction rate constant described with Arrhenius equation. Additionally, mass balance equation for water was implemented. The energy balance equation includes conductive heat transfer and source terms describing the released gasses. The non-homogeneous structure of wood is considered with the use of two different thermal conductivity coefficients, depending on the direction. Moreover, the pressure of released pyrolysis gas and steam were calculated. The simulation was performed using an in-house code. Simulations were performed for two fiber orientations. Different initial moisture contents were also considered. The results showed a sequence of temperature rise leading to decomposition, followed by increases in gas pressure from mass loss and steam pressure from evaporation. The dynamics of decomposition was dependent on assumed fiber orientation. Moisture content significantly increased the total time of decomposition from 110 s (dry) up to 200 s (10% moisture).