Sodium chloride-trisodium phosphate evaporation salt MVR system, Kang Jinghui evaporator and talk about sodium chloride-trisodium phosphate evaporation salt MVR system.
1. Solubility characteristics of sodium chloride-trisodium phosphate
In the actual production process of sodium chloride and trisodium phosphate, sodium chloride can be obtained by high-temperature evaporation crystallization, and then the mother liquor can be cooled and crystallized to prepare trisodium phosphate to realize the separation of sodium chloride and trisodium phosphate.
The solubility curves of trisodium phosphate and sodium chloride are very different, the solubility of trisodium phosphate is very large, and it increases significantly with the change of temperature, and the solubility curve of sodium chloride is flat, so the mixed salt solution of trisodium phosphate and sodium chloride can be separated and purified by MVR evaporator and continuous cooling crystallization at different temperatures.
It can be seen from the ternary phase diagram of trisodium phosphate and sodium chloride that the high concentration of sodium chloride in the cosaturated solution of (100) sodium chloride and trisodium phosphate is only 10% at high temperature, and as high as 25 at low temperature3%。The solubility of trisodium phosphate can decrease rapidly with the decrease of temperature, which brings convenient conditions for the crystallization and purification of the two.
2. The principle of sodium chloride-trisodium phosphate salt separation
In the actual production process, sodium chloride can be taken out by high-temperature evaporation crystallization, and trisodium phosphate can be prepared by cooling and crystallization of the mother liquor, so as to realize the separation and purification of two mixed salts. Because the trisodium phosphate product has 12 crystal waters, during the cooling and crystallization process, due to the precipitation of the crystal water with the trisodium phosphate, the solution has a partial concentration effect, and the range of Na3PO4 12H2O phase region becomes smaller. Therefore, the product obtained when the sodium chloride mother liquor is cooled and crystallized is a mixed salt of trisodium phosphate dodecahydrate and sodium chloride, and appropriate blending measures need to be taken in the process production to avoid it.
IIISodium chloride-trisodium phosphate salt MVR system
Sodium chloride-trisodium phosphate is a saltThe high-temperature evaporation section adopts MVR evaporator, and the functional area is set up to produce and enrich the mother liquor. The oslo cooling crystallizer can be used to obtain a lower crystallization temperature and reduce the amount of mother liquor exchange between the high and low temperature sections in the process of mass crystallization.
DTB vacuum crystallizer can also be used, although the crystallization temperature is slightly higher, and the amount of mother liquor exchange in the high and low temperature section becomes larger, but the vacuum crystallizer has no heat exchange surface of the material, and there is no trouble of scarring and scaling, which can optimize the continuity of the sodium phosphate trisodium chloride separation and purification crystallization system, and the operation convenience is better.
The separation and purification system of trisodium phosphate and sodium chloride applies different temperature operation points, and the two temperature sections have the mother liquor circulation exchange, so when the low-temperature mother liquor is sent to the MVR evaporator in the high-temperature section, additional steam needs to be added to maintain the heat balance of the system, and the replenishment amount is proportional to the output of trisodium phosphate in the system.