Abstract
A salt-making facility A in the U.S.A. produces common salt (>99.85%) and pure salt (estimated>99.99%), which are made from brine obtained by solution mining from a bed of rock salt. Onthe other hand, salt is produced by eight facilities in Japan. Seven of them use the brine concentrated sea water by ion-exchange membrane electrodialysis method and one uses the brine dissolved solar salt. In this paper, we made the flow sheet of the salt-making process of facility A based on someoperating data, and attemped to clear some differences of producing techniques, compositions ofthe brine and the bittern and efficiencies of production among facility A, domestic reproductivefacility (facility B) and four dometic facilities with quardruple-effects system. The results wereas follows.
1) The method of using the waste heat is different between facility A and domestic facilities.
2) The apparatuses for dehydrating and drying products are different.
3) The operation of crystallization process is controlled under the standard according to the composition of brine, because it changes by the method of producing the brine and the grade ofpurifying it.
4) Facility A produces common salt on low concentration of impurities in the mother liquid. On the other hand, facility B produces the same grade salt as refined salt with purification ofbrine.
5) In the comparison of the energy cost of crystallization, from least to most expensive in orderwere facility B, facility A and then the domestic facilities of quadruple-effects system. Thisis greatly affected by the number of effects and the concentration of brine.
6) When the energy cost was calculated by taking the number of effects and the concentration ofthe brine into consideration, the result was different. From least to most expensive in orderwere the domestic facilities of quadruple-effects system, facility A and then facility B. How ever there was little difference in cost among the facilities.
