Vacuum Salt Plants
Vacuum salt production process can be vary depending on the raw material and utilities available. Mainly following three production schemas can be used;
1) Multiple Effect Evaporation / Crystallization with Thermal Vapor Recompression (TVR)
If raw material is brine and low pressure steam is available with low cost, then this technology can be advised. It is the classical process to produce vacuum salt. Increasing the number of effects will decrease the live steam consumption. On the other hand, investment cost will increase. Optimum design depends on the relation between operation costs and investment costs. Preheating of the feed solution plays an important role in order to decrease specific steam consumption.
2) Mechanical Vapor Recompression (MVR)
If raw material is brine and electrical power is available with low cost, then this technology can be advised. Evaporated water vapor of the crystallizer is reused in the main heater of the system by increasing the pressure of vapor with a radial turbo compressor or industrial blowers connected in series. Main advanteges of MVR are as follows;
- Since all evaporated vapor is reused by recompression, almost no steam is consumed. Only at start-up, small amount of steam is required.
- No cooling water is required.
- Low structural costs due to the compact design of the plant
- Easy operation and start-up
3) Recrystallization (Multiple Effect Flash Evaporation with Thermal Vapor Recompression and Direct-Contact type heat exchangers)
If raw material is rock salt or solar salt, then this technology can be advised. Evaporation load is reduced compared to other two options described above. So, specific steam consumption is reduced. High recirculation rate of mother brine is required since evaporation is obtained by flash. Solubility of salt does not change much with increasing temperature. But, since the recirculation rate is high, significant amount of salt is produced by temperature change. So, this causes less evaporation rates. Main advantages are noted below,
- Low specific steam consumption
- Very high product purity is achieved
- Scaling is not a serious problem because direct contact type preheaters are used
- Plant capacities are low compared to other two options. (Max. 200,000 tons/year)
Multiple Effect with TVR