Triple-effect evaporator + 7t/h sodium sulfate MVR evaporator

The 5t/h sodium chloride triple-effect + 7t/h sodium sulfate MVR evaporation and crystallization system, with "separation of salts, coupling of mother liquor, high-temperature MVR, and freeze-heat refining" as its core, successfully achieves zero discharge of high-salt wastewater from lithium battery recycling and the recovery of both sodium chloride and sodium sulfate as first-grade products, with a comprehensive lithium recovery rate of 96%. This case provides the lithium battery recycling industry with a standardized module that is efficient, low-consumption, and has a long cycle time, marking the large-scale application of MVR evaporators in the lithium battery industry.

I.Project Background 

The decommissioned ternary lithium battery wet recycling line generates 300 tons of high-salinity wastewater daily, including 120 tons from the sodium chloride system NaCl 12%, Li⁺ 0.8 g/L, COD 4000 mg/L and 180 tons from the sodium sulfate system Na₂SO₄ 16%, Li⁺ 1.1 g/L, COD 5500 mg/L. The owner's existing single-effect evaporator has a steam consumption of 1.25 tons/ton and a lithium entrainment rate of 12%, which cannot meet the requirements for front-end enrichment of battery-grade lithium salts. In 2024, the company constructed a parallel evaporation and crystallization unit consisting of a 5t/h sodium chloride triple-effect reactor and a 7t/h sodium sulfate MVR reactor. Requirements: Sodium chloride purity ≥ 99.2%, sodium sulfate purity ≥ 98.5%, both meeting industrial Class I standards; lithium comprehensive recovery rate ≥ 95%, enriched solution Li⁺ ≥ 25g/L; no mother liquor discharge from the system; power consumption per ton of water ≤ 45kWh (weighted average of triple-effect reactor + MVR); equipment materials resistant to Cl⁻ + SO₄²⁻ mixed acid, and capable of long-term operation at 80℃.

II.Overall Process Architecture

1.Pretreatment and Impurity Removal

After "coagulation and flotation + resin heavy metal removal + pH adjustment," the total heavy metal content ≤ 0.1mg/L, hardness ≤ 50mg/L, avoiding scale formation in the evaporator.

2.Sodium Chloride Line – 5t/h Triple-Effect Forced Circulation Evaporation Crystallization: Co-current operation, first effect 105℃ (live steam 0.5MPa), third effect 65℃, secondary steam from the last effect enters the surface condenser, vacuum -0.082MPa; The Oslo DTB crystallizer is located in the third effect, with a crystal slurry solid content of 28% and a particle size of 0.45mm; 1.5t/h of centrifugal mother liquor is returned to the front end and mixed with the sodium sulfate line mother liquor for further lithium recovery.

3.Sodium Sulfate Line – 7t/h MVR Forced Circulation Evaporation Crystallization

Evaporation temperature 78℃, centrifugal compressor temperature rise 18℃, compression ratio 1.7, 100% secondary steam reuse; Freezing-Heat Melting Salt Separation: Concentrated Na₂SO₄ 220g/L enters a -3℃ freezing crystallizer, Na₂SO₄·10H₂O precipitates, and after hot melting, returns to the MVR, with a sulfate removal rate of 90%; Lithium-rich mother liquor 2t/h, lithium content 25g/L, sent to the lithium carbonate precipitation process.

4.Mother Liquor Drying System

The mother liquor from both lines is combined and then processed by Kang Jinghui mother liquor dryer, with a dry solids water content ≤5% and impurities 0.4t/d. It is then co-processed at the hazardous waste center, achieving zero mother liquor discharge.

III. Key Equipment and Material Configuration

IV. Operating Data Average for 190 consecutive days, June 2024 - December 2024

1.Processing Capacity: Sodium chloride 5.2 t/h, Sodium sulfate 7.3 t/h (Load rate 104%

2.Steam Consumption: Sodium chloride line 0.32 t/t water; Sodium sulfate line 0.03 t/t water (operation only

3.Comprehensive Power Consumption: Sodium chloride line 18 kWh/t; Sodium sulfate line 28 kWh/t; Weighted average 24 kWh/t

4.Salt Quality: NaCl 99.4%, Whiteness 84; Na₂SO₄ 98.8%, Whiteness 86. All meet industrial grade 1 standards.

5.Lithium recovery rate: 96%, lithium-rich mother liquor Li⁺ 26g/L

6.Condensate: Cl⁻≤80mg/L, SO₄²⁻≤50mg/L, reuse rate 95%

7.System uptime: 98.5%, unplanned shutdowns 2 times/year, each <4h

8.Cleaning cycle: Sodium chloride line 100d; Sodium sulfate line 110d

V.Technical Innovations

1.Separate salt production and mother liquor coupling: Sodium chloride triple-effect and sodium sulfate MVR are connected in parallel, with cross-reflux of mother liquor, increasing lithium recovery rate by 10% compared to single-line systems.

2.High-temperature centrifugal MVR: Single-stage temperature rise 18℃, pressure ratio 1.7, power consumption per ton of water 28kWh, 20% more energy-efficient than double-stage Roots systems.

3.Freeze-melt salt separation: Low-temperature nitration, hot-melt return to the front end, sulfate removal rate 90%, impurity salt content reduced by 80%. 

4.Titanium/duplex steel composite material: TA10 tube side + 2507 shell side, corrosion rate ≤0.01mm/a under Cl⁻+SO₄²⁻ mixed acid conditions at 80℃, lifespan 10 years.

5.AI anti-scaling and digital twin: Real-time monitoring of temperature difference, conductivity, and vibration; predicts fluoride scaling trends; provides 72-hour advance warning; reduces annual cleaning frequency from 12 times to 3 times.

VI.Environmental and Economic Benefits

1.Environmental: Annual reduction of 100,000 tons of high-salinity wastewater and 85% reduction of hazardous waste salts.

2.Economic: Annual savings of 95,000 tons of primary water, 18,000 tons of live steam, 22 million yuan in revenue from by-product industrial salt, and recovery of 110 tons of lithium (equivalent to 580 tons of Li₂CO₃), resulting in additional benefits of 87 million yuan.