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Thermophysical processes in dry granulation of metallurgical slags
Mathematical model for theoretical analysis of thermophysical processes of melt drops solidification is examined during their motion inside cooling gas, applying to granulation task. The heat exchange equations during granulation, taking into account convection, heat conductivity in solid phase and Stefan conditions on the boundary of phase transition, are presented. The relationships characterizing correlation of the power exchange parameters in dispersed medium are obtained in the conditions of phase transition in melt drops inside gas phase flow. Analytical relationships allow to consider correlation of the parameters which characterize granulation process, to provide directions of efficient conduction of the processes for achieving the preset aims and to reveal the conditions for optimal technological parameters of the process. Speed of the power exchange processes determines the size of an installation and allows to make preliminary assessment during designing. Different motion modes for particles and gas are investigated. The variants for calculation of gas dynamic parameters of straight flying trajectory for a slag melt particle are suggested; they are based on solving the problem of particle motion in the gas medium, taking into account particle size, medium resistance, initial particle speed. Used relationships allow to assess the particle flying time, which is corresponded to the required time of particle cooling during its flying, and to choose programming conditions for motion of dispersed jet of slag melt. These conditions guarantee forming of solid crust on the cooled particle and possibility of size determination for a granulation system. Possible scheme of slag heat realization, allowing to utilize maximally the exergy of secondary power resources, is considered. The obtained results can be used for improvement of the existing installations fir dry granulation and for designing of the new ones, as well as for optimization of operating modes of granulators, for their efficiency rise and increase of power saving possibilities for a granulation system.