Waste water evaporation and fractional crystallization system

Wastewater usually contains high organic pollutants and scaling components, so the evaporative crystallization unit is easy to scale, resulting in reduced evaporation, frequent shutdown and cleaning, easy mist entrainment, blockage and poor water production quality. The crystalline salt in the zero emission system has high organic content and low purity, which is difficult to be used as a resource.
Inorganic scale can be avoided by adopting high-efficiency membrane concentration process to reduce the hardness of concentrated water, or by using crystal seed evaporator. In addition to efficient pretreatment, the rational design of evaporative crystallization unit is also very important to reduce organic pollution and mist entrainment. The wastewater evaporation and fractional crystallization system developed by the company adopts different process routes and equipment according to different water quality to ensure long-term stable operation and prepare high-purity crystalline salt.

System flow

According to different water quality characteristics, membrane salt separation or thermal salt separation process can be selected. When sodium chloride or sodium sulfate accounts for the vast majority of wastewater, it can be considered to extract most of the dominant salt components, and the remaining components can be extracted from mixed salt and miscellaneous salt. The wastewater after membrane concentration first enters the evaporator for further concentration and reduction, and then enters the pure salt crystallizer to extract most of the sodium chloride or sodium sulfate, and the remaining part extracts the mixed salt. A very small amount of mother liquor is crystallized or dried to form mixed salt.

When the proportion of sodium chloride and sodium sulfate in wastewater is not much different, the method of fractional crystallization of sodium sulfate and sodium chloride can be adopted. The concentrated water of evaporator crystallizes sodium sulfate first, and the mother liquor further crystallizes sodium sulfate decahydrate through freezing. Sodium chloride accounts for the vast majority in the drainage of freezing crystallizer. Sodium chloride is prepared through sodium chloride crystallizer, and a small amount of mother liquor is crystallized or dried to form mixed salt.

When the proportion of sodium chloride in wastewater is dominant, the membrane process can also be used to intercept sodium sulfate through nanofiltration. After the nanofiltration produced water is further evaporated and concentrated, sodium chloride is crystallized. After the nanofiltration concentrated water is evaporated and concentrated, sodium sulfate is crystallized first, and then sodium sulfate decahydrate is frozen and crystallized. A small amount of mother liquor is crystallized or dried to form miscellaneous salts.

The thermal method has the advantages of simple process flow, reliable operation and better economy. The organic content of sodium sulfate crystallized by mass is lower, but the organic content of sodium chloride is higher than that of membrane method. It is suitable for occasions with high purity requirements of sodium sulfate. The sodium chloride purity is more guaranteed due to the low content of organic matter in the nanofiltration produced water of the membrane salt separation route, but the purity of sodium sulfate is low and the process is longer than that of the thermal process. When the relative proportion of sodium chloride is high and the purity of sodium chloride is required, the membrane process can be selected.

In order to reduce the organic content in crystalline salt, the crystallizer adopts a proprietary crystallizer with salt purification device, which can greatly reduce the organic content in crystalline salt.

system composition

Nanofiltration salt separation unit

    Effectively intercept sulfate and most organic pollutants, so that most of the water production side is sodium chloride.

Vertical falling film evaporation unit

    The system can be designed as multi effect or MVR evaporation. The vertical falling film evaporator has the advantages of large evaporation area, high heat exchange efficiency and low energy consumption.

Freeze crystallization unit

   The freezing crystallization unit separates most of sodium sulfate in water at low temperature according to the characteristics of sudden drop of solubility of Na2SO4 at low temperature. Purified salt crystallizer

   The crystallizer with a proprietary salt purification device is adopted. The elutriation brine (influent) enters from the lower part of the salt purification device and rises along the leg wall to wash against the crystalline salt, so as to remove the organic matter and other impurities in the crystalline salt and reduce the heat loss of salt discharge.

Technical advantages

Customized by users, relying on rich design and operation experience, it provides users with targeted process system, introduces advanced purification and salt making crystallization technology, and greatly improves the purity and resource utilization rate of crystalline salt. Through impurity removal pretreatment and washing of crystalline salt dehydrator, the quality of crystalline salt can be further improved. Through system design and evaporator device design, it can eliminate frequent scaling, mist entrainment, etc.