Sodium Hydroxide Flakes Production

The process under analysis comprises two major sections: (1) Evaporation; and (2) Flaker.

Evaporation. Sodium Hydroxide solution (50 wt%) is evaporated in three evaporation stages until molten Sodium Hydroxide is obtained. Initially, food grade sugar is dissolved with water to form a 5 wt% solution. This aqueous solution is mixed with the caustic soda solution before it is fed to the first stage. This Preconcentrator operates at mild temperatures (about 90 °C) under vacuum - a steam ejector is used to produce vacuum conditions. Steam generated in the Final Evaporator is used as heating medium. A caustic solution with 55-60% concentration is obtained and pumped to the Rising Film Evaporator, where it is evaporated to 75-85%. This evaporator operates under lower vacuum and higher temperatures (about 160 °C). The water vapors from the first two stages are condensed and discarded. The concentrated caustic solution is transferred to the final falling film evaporator, where 99% molten caustic. It operates at ambient pressure and very high temperature. Molten salt is used as heating medium.

Flaker. The hot liquid film of molten caustic is brought into contact with the cold surface of a horizontal rotating drum. As the drum rotates, the liquid film is cooled to below it melting point and solidifies. The solid caustic is removed from the drum surface by a knife, which is mounted in front of and across the whole length of the drum. The solid caustic is broken into flakes and packed.