抄録
Naruto Engyo Co., Ltd., has been making food salts sea water by using electrodialyzers (using ion-exchange membranes) and three effective vacuum evaporators.
In recent years, crystal size control operation has become an important problem because salt users require various sizes of salt crystals.
We tested crystal size control operation by using a so-called 3-B pan, which is the 2nd effective vacuum evaporator, with outside heat exchanger 400 m2 and forced reverse circulation. The 3-B pan operating condition was kept around 15% of crystal content in saturated brine and varied inlet supplysteam from 6 to 20 t/h.
Output crystal size was measured and we applied Toyokura's crystallization theory. Correlation between these obtained data, crystal size, production rate, crystal growth speed, and nucleation rate were investigated.
And also data of No.3 pan and No.4 pan, under commercial running, was plotted on Rosin-Rammler diagram and operation diagram.
Results: (1) when we changed supply steam from 6 to 20 t/h and maintained 15% slurry, we obtained the same size of crystals; (2) when we incleased production rate, correlation between crystal growth speed and nucleation rate was a direct proportion line.
