Solution of Tasks of Energy Efficiency of the Process of Drying Raw Plant Materials by Methods of Mathematical Modeling

Abstract

Beet pulp has a high feed value, but after pressing it has a sufficiently high humidity, which leads to rapid spoilage. One of the ways to stabilize the quality of beet pulp is drying with superheated steam of reduced pressure. Mathematical modeling of heat transfer during convective drying of beet pulp is proposed. A feature of the model is the description of the drying process, which ensures its high intensity due to high heat and mass transfer ratios and preserves the quality of the finished product as a result of the process at a reduced pressure of transfer medium. In the period of a constant drying speed, dehydration of macroscopic pores topologically related to the sample surface, which are characterized by a relatively low binding energy of water molecules with the liquid phase, is taken into account. According to experimental data, the proportion of water content in these pores is 60…70% of the total moisture content. In the final stage of this period, an increase in the binding energy occurs due to the removal of water from microcapillaries, which is explained by the formation of structured clusters in thin wetting films of water molecules. The change in steam temperature as a result of passing through the product layer was 8 … 10 K, and the relative temperature change was 5 … 10%. The parameters of the models were identified in the following range of parameters: superheated steam temperature 393 … 453 K; speed of superheated steam 3 … 5 m/s; the pressure inside the drying chamber is 40 … 100 kPa; the specific load of the product on the grate is 8 … 24 kg/m2. The interpretation of the simulation results is presented by the dependences of the temperature difference between beet pulp and heat carrier T on the temperature of superheated steam Ts at various pressures P: 1 - 100 kPa; 2 - 80 kPa; 3 - 60 kPa; 4 - 40 kPa; υ = 4 m/s; at various specific loads of beet pulp on the gas distribution grid qsp: 1 - 8 kg/m2; 2 - 16 kg/m2; 3 - 24 kg/m2; υ = 4 m/s; P = 60 kPa and various speeds of superheated steam υ: 1 - 5 m/s; 2 - 4 m/s; 3 - 3 m/s. A sufficient convergence of the results was ensured, in which the deviation of the calculated data from the experimental data did not exceed 12, 5% in absolute value. The obtained results of the simulation can be used in the operational control of the technological parameters of the process of drying beet pulp with superheated steam of reduced pressure with a restriction on the temperature mode due to the receipt of a high quality product.