Technological bases of multistage convective drying in small-sized devices with utilization and heat recovery units

Abstract

The following new scientific results were obtained during the research: 1. The model of calculation of hydrodynamic indicators of movement of streams in the multistage shelf dryer is created. 2. A model for calculating the kinetics of changes in temperature and humidity parameters of the dispersed phase and the drying agent at the stage of the dryer is created. 3. Theoretical data and data of experimental researches concerning the description of processes of heat and mass transfer during drying are received. 4. The main hydrodynamic modes of operation of shelf dryers are determined. 5. Data on the mechanisms of motion control of the dispersed phase in the dryer in different hydrodynamic modes are obtained. 6. The fields of gas flow velocity in the working space of the gravity shelf dryer are obtained. The limits of existence of each of the hydrodynamic modes of operation of the device are shown experimentally. 7. Temperature-humidity characteristics of interacting flows and values of efficiency of stages of the dryer depending on the design of shelves and the organization of movement of the drying agent are received. It is shown that the most significant influence on the change of temperature and humidity characteristics has the time of the material on the step, which is due to the angle of the shelves and their length. 8. Under different conditions of the experiment, the range of efficiencies of individual stages of the dryer in the range of 0.12-0.47 was determined. The amount of moisture removed from the material may be from 4 to 8% of the mass. The initial value of the moisture content of the dispersed material of 13% of the mass. 9. It is shown that by changing the design of the shelf and the organization of the drying agent (in particular, in the case of its bypass), it is possible to control the drying time of the material and the efficiency of the steps of the dryer. The angle of the shelf can have a minimum value that corresponds to the angle of the natural slope of the material. The practical significance of the obtained results. Based on the received data, the technique of engineering calculation of shelf dryers with vertical sectioning of working space, and also a technique of an estimation of energy efficiency of convective dryers is created. An improved design of a multistage shelf dryer is proposed, which allows controlling the residence time of the dispersed phase in the volume of the apparatus, ensures uniform contact of the drying agent and dispersed material in the suspended layer mode, avoids unwanted changes in the properties of dispersed material (overheating, abrasion, cracking reduces the probability of removal of the commodity fraction of the dispersed material from the boundaries of the inclined perforated contact shelf. Experimental samples of porous ammonium nitrate were obtained, which passed the final drying stage in a gravity shelf dryer and are characterized by a developed porous surface. The obtained scientific results are prepared for implementation in the implementation of economic agreements. A project proposal for participation in the competition of joint Ukrainian-Czech research projects for implementation in 2021 - 2022. Together with representatives of Alexander Dubcek University of Trencin (Slovakia), as well as the University of Pardubice and J.E. Purkyne University in Usti nad Labem (Czech Republic) based on the obtained theoretical and experimental data is the development of a software package for calculating the technological parameters of the gravity shelf dryer and its design dimensions.