?EFFECTS OF AGITATION AND BITTERN QUALITY ON RECOVERY OF MAGNESIUM SULPHATE

Abstract

Experiments have been conducted in an externally cooled batch chiller (crystallizer) to study the effects of (i) agitation level,
(ii) stirrer design and (iii) quality of sea bittern, on the recovery of magnesium sulphate and other variables like heat flow
rate, heatof crystallization and heat transfer coefficient. The studies indicate that the linearity of temp-time plot and its slope
are neither affected by the agitation level nor by quality of sea bittern (excepting spent sea bittern). Recovery/crystallization
patterns (or cone-temp relationships) have been found critically dependent on agitation level, degree of turbulence, stirrer
design and bittern quality. Three straight blades stirrer is found to be more suitable whereas, 6 curved blades stirrer causes
greater turbulence thereby resulting into reduced recovery. The optimum level of agitation is found to be around 165 r p m
(tip velocity 62.5 m rnin' and Reynolds number 13000), around which incidently, both, (a) percent recovery against
temperature and (b) energy consumed in stirring, Kj rnin' Vs Reynolds number behave linearly, the recovery is at its optimal,
and the energy consumption is minimum. Beyond the optimallimitof(165 rm p) 62.54 m min' tip velocity, thepcrform-
ance parameters become independent of agitation rate, however, under such situation they are influenced by the quality of
sea bittern and hence found to change unpredictably. Normal sea bittern is found to be asuitable raw material, whereas any
pretreatment of normal bittern renders it unsuitable and at times an uneconomical raw material.