Grobovenko Y. The process of drying a fine paste of titanium dioxide

The dissertation is aimed at solving an important scientific and technical task – increasing the efficiency of the process of drying a fine paste of titanium dioxide in the vortex flow of coolant with the use of fluidization and continuous grinding of the material. It is theoretically substantiated and experimentally proved that the use of active hydrodynamic mode of vortex flows of the coolant in combination with continuous grinding of the material significantly increases the intensity of heat and mass transfer processes while maintaining the stable kinetics of the process of drying the dioxide paste. The method of combining the processes of drying and grinding of TiO2 paste and drying of fine particles of titanium dioxide in one vortex type drying apparatus has been substantiated and experimentally confirmed. It is established that the vortex flows of the coolant are characterized by 2 velocity vectors: the axial velocity vector, which has the largest values in the center of the chamber and the vector of the tangential velocity, the largest values of which are concentrated around the periphery of the drying chamber. The ratio of the tangential velocity to the axial velocity in the cross section of the drying chamber determines the degree of swirling of the vortex flow of the coolant. The physical and mathematical models of the processes of drying and drying of the fine paste of titanium dioxide in the vortex flows of the coolant are scientifically substantiated. It is determined that the internal resistance of the mass conductivity of the particles of the material does not affect the intensity of the drying process, the speed of which depends entirely on the rate of diffusion of moisture in the outer region. That is, the mass transfer coefficient in the gas and gas phase is equal to the mass transfer coefficient K = β, and the mass transfer equation in the gas and gas phase is replaced by the mass transfer equation. In this case, the equilibrium parameters correspond to the parameters of the saturated vapor near the surface of the dried particles. The kinetic regularities and basic parameters of the process of drying of titanium dioxide paste necessary for the design of industrial drying plants were obtained. The effect of continuous grinding of particles of material in the fluidized bed on the drying rate of titanium dioxide paste was experimentally determined. The fields of tangential and axial velocities and vortex pressures of the coolant are theoretically determined. The physical model of separation of fine TiO2 particles in the vortex flow of the coolant formed in the developed drying apparatus is formulated. The most rational parameters of the process of drying the paste and drying of fine particles of the material to a residual moisture content of 0,3 % were determined. During the drying process, surface water evaporates which connects and holds TiO2 crystals within the paste agglomerates. The dried crystals and the individual wet agglomerates are separated from the dried particles of the paste and carried by the vortex flow of the coolant to the separation zone. Under the action of centrifugal forces back to the fluidized vortex layer for further grinding and drying. The values of the coefficient of grinding of the titanium paste agglomerates Kz and the coefficients of the hydraulic resistance of the dispersant ξ1 and the tangential input of the coolant into the drying zone ξ2 were obtained experimentally, which made it possible to calculate a mathematical model of the process of drying the titanium dioxide paste. The design and technological parameters of the drying cone chamber, which provide the conditions for the creation of vortex flows of the fluid and the separation of particles of material TiO2. According to the results of the study, a methodology was developed and an algorithm and program for the calculation of an industrial drying apparatus, with a capacity of 500 kg/h on evaporated moisture, were developed for drying TiO2 paste in the vortex flow of a coolant. Keywords: drying, fluidization, titanium dioxide, grinding, vortex flows, coolant, moisture content.