Energy efficiency reserves convective drying dispersed materials under variable conditions

Abstract

At present, methods of drying dispersed materials in variable regimes, when not only the temperature and speed of the drying agent varies with time, but also the state of the material layer undergoes changes, due to controlled hydrodynamics in the working volume of the drying plant. Variable modes are used for drying in oscillating modes, with stepped hydrodynamic and temperature modes, and also when drying in an isothermal cycle. If oscillating drying with alternation of heating and cooling zones of the material and drying of the material in stepwise modes, first of all, is aimed at preserving the quality of the target product, then isothermal drying consists in preheating the material to the maximum permissible temperature with subsequent drying without reducing it during the whole process with a maximum rate of moisture removal. Reduction of heat energy costs in drying processes with variable heat supply is achieved due to the maximum heat recovery in closed thermodynamic cycles for the heat carrier, including using heat pump technology. Using the example of a multi-zone drum dryer, equipped with a two-stage steam compression heat pump, the possibility of a significant saving of heat energy costs during the drying of dispersed material without additional calorific heating. From the analysis of the drying process in the I-d diagram it follows that the utilization and heat recovery in a closed thermodynamic cycle by the heat carrier can reduce the specific energy consumption. An algorithm for controlling technological parameters in the field of permissible technological properties of the dried material is proposed.