The analysis of crystallization of sodium chloride from the solution in vacuum crystallizer with the recirculation of the suspension

摘要

Crystallization from a solution most often is the final stage of many technological processes, and has a major role in bulk chemical industry. Basic requirements which stand before the process of crystallization are as follows: providing a minimum energy use-up together with a maximum specific capacity of the crystallizer, as well as with obtaining a product with the necessary degree of purity. These demands are successfully fulfilled by vacuum crystallizers with recirculation of suspension, which are the most promising apparatus for the crystallization of inorganic salts from solutions in bulk production. Vacuum crystallizers, like other chemical apparatuses, are described as a sum of physical and chemical phenomena which together create a unit process of crystallization of NaCl from water solutions. The term apparatus process unit (APU) was introduced and a vacuum crystallizer is described as the sum of APU and shown in a structural scheme. The analysis of the vacuum crystallizer was performed based on its APU component, using theoretical assumptions, the results published as well as the results of researches on models. A particular focus was given to the description of the mass and heat transfer, as well as to the hydrodynamics of fluids in the area where the starting solution and the recircular suspension are mixed, in the circulation channel and the central pipe, as well as in the area of vaporization. This study gives the conclusions made based on the investigation of vacuum crystallizers. .