Mathematical Model and Method for Calculating the Dynamics of Drying Biomass at the Production of Pellets

Ключові біомаса, сушка, Abstract. All types of biomass (straw, stalks of corn, sunflower, wood shavings, energy willow, sorghum, miscantus) are colloidal capillary-porous bodies, drying of which is carried out in a high-temperature drying agent and involves the pas-sage of transfer processes due to diffusion, filtration and phase transformations. A mathematical model and a numerical method for calculating the dynamics of heat and mass transfer, phase transformations and shrinkage during the drying of colloidal capillary-porous cylindrical bodies under conditions of uniform cooling by a coolant are developed. The mathematical model was built on the basis of the differential equation of substance transfer (energy, mass, momentum) in de-formable systems. It includes the equations diffusion-filtration transfer of energy for the system as a whole, and the mass transfer of the liquid, vapour and air phases in the pores of the body. Formulas are presented for finding the diffusion coefficients in the liquid and gas phases, for the evaporation rate on the surfaces and in the pores of the particles. Experi-mental studies of the kinetics of dehydration of energy willow particles in the air flow were carried out to verify the mathematical model. Comparison of the results of numerical and physical experiments testify to the adequacy of the mathematical model and the effectiveness of the method for its implementation. On their basis, it is possible to conduct a study of the dynamics of heat and mass transfer during drying of particles of various types of shredded biomass; determine the time to achieve an equilibrium moisture content depending on the properties of the material and the drying agent. It has been established that the small sizes of biomass particles and high heat transfer coefficients at high temperature drying cause their intensive dehydration, and when the material reaches an equilibrium moisture content, the temperature at the outer boundaries of the particles does not reach the temperature of the drying agent. On the basis of these data it is possible to select the process parameters that are optimal from the point of view of energy and quality preservation of the dried product.