Crystal‐size distribution in mixed suspensions

Abstract

Abstract Although vacuum crystallizers are used widely, crystal‐size–control methods have not been adequately analyzed. This paper supplies in part the deficiency of technical information on this problem. Industrial crystallizers may have inherent nucleation rates in excess of or below the seed‐crystal requirement for the desired product‐crystal size. This paper deals specifically with means of crystal‐size control by removal of excess nuclei from mixed circulating suspensions as encountered in vacuum crystallizers. It is shown that under certain conditions the cumulative size distribution in the suspension varies as the fourth power of the size. Therefore, it may also be shown that the key to effective size‐control procedures is the segregation time of nuclei in the fines‐removal system. Procedures based mainly on crystal‐size classification by hydraulic elutriation can hardly be effective unless they are also designed to meet the segregation‐time requirements.