Influence of Operating Conditions on Crystal Growth Rate of Salt Particles in a Semibatch-type, Stirred Evaporation Crystallizer Fitted with a Draft Tube

Abstract

The influence of operating conditions on the crystal growth rate of salt particles was investigated to realize both a high suspension density and a high crystal growth rate, for in order to improve the efficiency of the salt crystallization process in an evaporation crystallizer. A semibatch-type, stirred vessel fitted with a draft tube was used as the crystallizer. First, a method of direct heating with a coil-heater set around the outer side of the draft tube was investigated in order to attain a high evaporation rate in the vessel. Subsequently, operating conditions, such as heating rate, γ_e, and the amount of initial injection of the seed crystals, M₀, were investigated in order to attain both a high suspension density and a high crystal growth rate. It was clarified, as a result, that a crystal growth rate higher than 300μm/hr on the basis of D₉₀ and a suspension density higher than 30 vol% ca n be maintained under the conditions of γ_e=804kg/hr, and M₀=0.05 to 0.10kg. Thus, the feasibility of greatly improving the efficiency of the salt crystallization process in an industrial evaporation crystallizer was verified by these investigations.