NUMERICAL INVESTIGATION OF THE INFLUENCE OF VARIOUS PARAMETERS ON THE THERMOCHEMICAL PROCESSING OF THE COKE-ASH STRAW PARTICLE IN THE FIXED BED

Abstract

Equations describing the rate of carbon conversion in the range of surface and bulk reactions are obtained taking into account the kinetics of heterogeneous reactions for the diffusion, kinetic and transition regions of the reaction. Deriving the equations, it was assumed that in the zone with a high carbon concentration (<<) reaction proceeds on the surface of the particle according to the model of a compressible combustible core, so that diameter of the particles decreases. In the second zone (≤) reaction proceeds in the volume with the same particle size. Here we use the model of a strong ash frame when the reaction proceeds throughout the volume of the particle. On the basis of the constructed equations, a model for thermochemical processing of the solid fuel coke-ash particle in a fixed bed is developed, taking into account the radiative and conductive-convective heat transfer between the bed and the particle and the heat release of chemical heterogeneous reactions. Numerical studies have been carried out in the intervals of surface and volumetric reacting in order to obtain detailed information on the geometric, aerodynamic, thermal, and physicochemical parameters of the combustion and gasification of a particle of straw in a fixed bed. It is shown that: a) with a decrease in the size of the coke-ash biomass particle, the time intervals for warming up and burning out are narrowed; b) expansion of the range of the volumetric reacting promotes an increase in the burnout time of the particle; d) As the concentration of oxygen in the gas mixture decreases, the rate of conversion of carbon and the temperature of the particle decrease, so that the time for the thermochemical treatment of the coke-ash straw particle increases.