Taking into account convective heat and mass exchange in autoclave reactors when scaling hydrothermal and hydrometallurgical processes

Abstract

The article presents the procedure of scaling the processes of hydrothermal synthesis for various dispersed inorganic materials and selection of an optimal technological mode for a given autoclave reactor on the base of a reaction kinetics experimental study with applying in situ heat flux calorimetry and developing the reaction mathematical model to simulate temperature and conversion fields inside a chosen apparatus for the selected mode. Natural convection is shown to be the main driving force for heat exchange and mass exchange in autoclave reactors without mechanical mixing and heating with a jacket. This may lead to a considerable non-homogeneity of temperature and concentration fields inside the reactor and be the reason of phase composition and particle size variations as well as real crystal structure of reaction products non-reproducibility. Applying an optimal heating mode with temperature linear programming on the wall results in forming stationary fields of temperature and concentrations inside the reactor and makes it possible to monitor the current conversion along the apparatus cross-section and minimize corresponding gradients in the final point. It is also possible to evaluate overheating of the reaction mixture for a hydrometallurgical process in the batch stirred reactor or continuous flow reactor. The proposed procedure makes it possible to select an optimal technological mode for producing a definite product in a definite apparatus on the base of a hydrothermal or hydrometallurgical reaction kinetic model with heat generation or heat absorbtion. The author would like to thank the leadership of the Saint Petersburg Mining University for their extensive support of the basic studies into hydrothermal synthesis of dispersed inorganic materials and that of mathematical modelling work.