1、 Pre processing stage: Remove impurities and protect subsequent equipment

Pre treatment is the foundation for ensuring the stable operation of the entire system, mainly solving the problem of impurity interference in high salt wastewater.

Filtering treatment: Solid impurities such as suspended particles and sediment in wastewater are removed through equipment such as quartz sand filters and precision filters to avoid clogging the heat exchange tubes or nozzles of the evaporator.

Softening/hardness removal: If the calcium and magnesium ion content in the wastewater is high (i.e. high hardness), softening agents (such as sodium carbonate) or ion exchange resins need to be added to prevent calcium and magnesium ions from forming scale during evaporation and adhering to the heat exchange surface, which affects heat transfer efficiency.

Removing organic matter (optional): If the wastewater contains high concentrations of organic matter, it is necessary to reduce the organic matter content through processes such as activated carbon adsorption and advanced oxidation to avoid organic matter condensing into fresh water during evaporation or contaminating salt products during crystallization.

2、 Low temperature evaporation stage: achieving water vaporization in a vacuum environment

This stage is the core process, which uses vacuum to lower the boiling point of wastewater and completes the preliminary separation of water and salt at low temperatures.

Wastewater preheating: The pre treated wastewater enters the preheater and is heated using the waste heat generated in the subsequent condensation process to increase the wastewater temperature (usually to 30-40 ℃) and reduce the energy consumption of the main evaporator.

Vacuum evaporation: Preheated wastewater enters the main evaporator (such as plate evaporator, tube evaporator), and the system uses a vacuum pump to reduce the pressure inside the evaporator to negative pressure (usually vacuum degree>-0.09MPa), reducing the boiling point of the wastewater to 40-60 ℃, and rapidly vaporizing at low temperatures to form secondary steam containing a small amount of impurities.

Salt concentration: After the water evaporates, the remaining wastewater will gradually concentrate, and the salt concentration will continue to increase, forming a high concentration of "concentrated salt water", which is temporarily stored in the concentrated salt water storage tank and waiting for subsequent crystallization treatment.

3、 Condensation recovery stage: secondary steam is converted into fresh water

The secondary steam generated by vaporization needs to be treated and converted into freshwater that can be reused or discharged in compliance with standards.

Steam purification: The secondary steam first enters the vapor-liquid separator to separate the entrained droplets (to prevent salt from entering fresh water with the droplets). Some systems also add defoggers to further improve steam purity.

Low temperature condensation: The purified secondary steam enters the condenser and exchanges heat with cooling water (or refrigerant). The steam liquefies into fresh water when cooled and is collected in a fresh water storage tank.

Freshwater reuse/discharge: If the quality of freshwater meets the requirements (such as conductivity<100 μ S/cm), it can be directly reused in the production workshop (such as cleaning, cooling); If discharge is required, it is necessary to test whether it meets the local wastewater discharge standards, and after meeting the standards, it can be discharged.

4、 Crystallization separation stage: concentrated salt water is converted into solid salt

The concentrated brine (close to or reaching saturation) needs to be separated by crystallization to convert the salt into a solid state, achieving "zero discharge" or reduction of wastewater.

Forced circulation crystallization: Concentrated salt water enters the crystallizer (commonly used forced circulation crystallizer), and the system circulates the concentrated salt water at high speed in the crystallizer through a circulation pump, while slightly heating or maintaining low temperature to gradually precipitate salt and form crystals.

Solid liquid separation: The "crystal slurry" containing crystals enters a centrifuge or filter, and the salt crystals are separated from the mother liquor by centrifugal force or pressure to obtain wet salt.

Salt drying/disposal: The separated wet salt can enter a drying machine (such as a hot air drying machine) to remove surface moisture and form dry salt; Several salt purity standards are met (such as industrial grade sodium chloride), which can be recycled and reused; If the purity does not meet the standard (such as containing heavy metals or mixed salts), it will be treated as hazardous waste and handed over to professional institutions for disposal. The remaining mother liquor can be refluxed to the evaporator for reprocessing, forming a closed loop.