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Zero discharge of desulfurization wastewater and salt recycling system in coal-fired power plant

Limestone gypsum wet desulfurization process is mostly used in coal-fired power plants. The quality of desulfurization wastewater is complex and fluctuates greatly. The zero discharge treatment system is very easy to scale. Because the hardness in wastewater is very high, the operation cost of softening unit is very high. The crystalline salt of the zero discharge system is difficult to be used as a resource because of its low purity.
The zero discharge system of desulfurization wastewater developed by the company has low operation cost and high purity of crystalline salt. It can be used as raw materials for chlor alkali and other industries.


System flow

According to the different quality and quantity of desulfurization wastewater in the power plant, the company can provide two zero emission salt making processes, namely "membrane concentration and salt separation + crystallization" (membrane process) and "crystal seed evaporation + crystal seed crystallization" (crystal seed process).


Membrane process

After chemical softening and resin softening, the membrane process intercepts sodium sulfate through the nanofiltration membrane. Sodium chloride is further concentrated by reverse osmosis, and the concentrated solution enters the crystallizer to prepare high-quality sodium chloride. Nanofiltration concentrated water is returned to the pretreatment system.


Seed process

The crystal seed process adopts regulation softening, that is, the system does not add sodium carbonate to remove calcium ions, and there is no need for filtration and ion exchange. Instead, two cheap agents of lime and sodium sulfate are added to adjust the wastewater to two inorganic salt solutions of sodium chloride and calcium sulfate. After clarification, it directly enters the crystal seed evaporator to prevent calcium sulfate from scaling in the evaporator. The concentrated water from the evaporator enters the salt crystallizer for seed production. The gypsum seed is separated from sodium chloride in the crystallizer to prepare high-purity sodium chloride. The gypsum seed is returned to the pretreatment system for dehydration. The operation cost of crystal seed process is greatly reduced, which is very suitable for systems with high hardness and large water volume (above 10m3 / h).

system composition

High density clarifier unit

     It is specially designed for high salt content water quality, with good hardness removal effect, high sedimentation efficiency and strong resistance to load impact.

Filter unit

      Variable pore filter or multi-media filter is often used after softening and clarification.

Resin softening unit

      Designed for efficient removal of permanent hardness in high TDS environment, the effluent hardness can be less than 0.1ppm (calculated by CaCO3).

Decarburizer

     The residual alkalinity is removed by decarbonization tower and decarbonization fan to reduce the scaling risk of subsequent systems.

Reverse osmosis unit

     Ensure the energy-saving, safe and stable operation of the system according to the requirements of customer recovery rate and desalination rate.

Technical advantages

The system allows a certain amount of hardness to enter ro. Through the precise hardware removal unit, it has high operation safety, regular high pH water flushing, control organic pollution, microbial pollution and silicon scaling. The ion exchanger has a long regeneration cycle and high ammonia nitrogen removal rate.

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