Abstract
Models for gas–solid reactions in porous particles typically consist of a set of mass and energy balances in the form of conservation equations. For spherical or close to spherical particles, these equations are formulated in 1D spherical coordinates. In the case where accumulation of gas inside the particle is significant, the balance equations contain convective terms. The present work presents a simple numerical scheme based on flux limited finite volume methods for discretizing conservation equations for convective and diffusive transport of mass and energy in radial direction in a porous sphere. The velocity is governed by Darcy’s law coupled to an equation of state. The proposed scheme is applied to a series of test problems that admit full or partial analytical solutions. For the cases where only partial analytical solutions are available, a Comsol model is adopted for comparison. It is found that the scheme is able to resolve step gradients without generating oscillations and that it properly handles changes in the sign of the convective velocity. Applying the scheme for solving a common model for biomass pyrolysis reveals the importance of convective gas transport in the pyrolysis of thermally thick biomass particles.
Highlights
Gas−solid reactions in porous particles play a significant role in the thermochemical conversion of solid fuels and in catalytic processes.[1]
The transport of gaseous products out of the particle is relevant in the case of pyrolysis and gasification processes where large amounts of gaseous products are formed
In a gasification process, the solid fuel reacts with a substoichiometric amount of O2 to form CO and H2 whose combined volume exceeds the volume of O2 brought into the particle
Summary
Gas−solid reactions in porous particles play a significant role in the thermochemical conversion of solid fuels and in catalytic processes.[1]. We show data obtained from the finite volume scheme using the Min-Mod flux limiter (symbols) together with the analytical solution for the stationary distributions (dashed lines).
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