Abstract
In the salt-manufacturing process in Japan and desalination, scale formation and its prevention are the most important problem. This study has been carried out in an attempt to solve this problem.
On the scale formation, following studies were made:
1) The relationship between concentrating method of sea water and behavior of scale components of sea water or compositions of adhered scale.
2) Proceeding of scale formation of NS triple salt-A in the salt manufacturing process from the brine obtained by salt-field method.
3) Proceeding of scale formation of di-sodium pentacalcium sulfate in the salt manufacturing process from the brine obtained by ion-exchange membrane method.
4) Rate of dissolution and crystallization of calcium sulfate in the brine during transition stage.
5) Formation of alkaline scale in heating the brine obtained by ion-exchange membrane method.
6) Decomposition of condensed sodium phosphate in heating the brine obtained by ion-exchange membrane method.
On the scale prevention, following studies were made:
1) Effect of various additives on the formation of alkaline and calcium sulfate scale.
2) Effect of various seeds on the formation of alkaline and calcium sulfate scale.
3) Application of sodium hexametaphosphate to prevention of scale formation of brine-preheater.
4) Development of a new, preventing method of scale formation in salt manufacturing process by using sodium hexametaphosphate together, with hydrochloric acid.
5) Development of a preventing method of scale formation in multi-flash evaporater by using seeds (CaCO3+Mg (OH)2, CaSO4·anh) together with slaked lime.
Bench and plant scale tests of the developed methods such as 3), 4) and 5) above mentioned were made in salt-manufacturing factories and desalination factories of 6-stage flash evaporator. And satisfactory results were obtained. Then, the methods of 3) and 4) have been applied successfully to salt-manufacturing factories.
