Seawater desalination and concentrated brine evaporation treatment
Seawater desalination plants produce large amounts of concentrated brine (typically with a TDS of 60,000–80,000 mg/L) while generating fresh water. Direct discharge into the sea poses a threat to nearshore ecosystems, and an increasing number of inland desalination projects face the requirement of "zero discharge." Evaporation and crystallization are key pathways to achieve the resource utilization and harmless treatment of concentrated brine.
Wastewater characteristics
● High salinity: TDS 60,000～120,000 mg/L, mainly NaCl, MgSO₄, CaSO₄;
● Large water volume: The concentrated brine volume of a single desalination unit can reach 50% to 100% of the water production capacity;
● High hardness: High Ca²⁺/Mg²⁺ concentration, easily forming carbonate and sulfate scale;
● Highly corrosive: High-chlorine environments place stringent requirements on metal equipment (titanium or duplex steel is required).
Processing flow
| Seawater desalination concentrated brine treatment process Concentrated brine stock solution → Pretreatment (softening/scale inhibition/filtration) → Multi-effect evaporation/MVR concentration (TDS increased to 50,000~100,000 mg/L) → Forced circulation evaporator crystallizer → Solid-liquid separation (centrifuge) → Drying and packaging Products: Industrial sodium chloride (≥97%), magnesium sulfate, magnesium chloride and other mixed salts Condensate: Reuse or discharge in compliance with standards |
Key Processes
● Softening and hardening: Pre-removal of Ca²⁺/Mg²⁺ to prevent excessive scaling during evaporation. This is usually achieved using the lime-soda ash method or nanofiltration for salt separation.
● Multi-effect + MVR combination: For large water volume applications, multi-effect evaporation is preferred to reduce steam consumption, while MVR is used at the end for deep concentration, balancing economy and stability.
● Salt crystallization: By controlling the evaporation temperature and concentration window, NaCl and Na₂SO₄ are precipitated in steps, realizing the resource utilization of salt.
● Material Selection: The evaporator heating tube and shell are made of titanium, which is resistant to chlorine corrosion.
