Sodium Sulfate MVR Single-Effect Evaporator

I. Process Positioning

The sodium sulfate MVR single-effect evaporator is an energy-saving integrated concentration/crystallization unit specifically designed for solutions containing Na₂SO₄. It adopts a core route of "single-stage forced circulation + mechanical vapor recompression (MVR)," producing ≤18kg of steam per ton of water and consuming ≤32kWh of electricity per ton of water. Compared to traditional triple-effect evaporators, its overall operating cost is reduced by more than 45%, making it the preferred technology for the resource utilization of sodium sulfate from sodium sulfate, dye intermediates, high-salt wastewater from coal chemical industry, and lithium battery cathode byproducts.

II. Process Principle

1. Feed Preheating: The sodium sulfate solution (3–15%wt) is heated to 80–85℃ by recovering the sensible heat of the condensate from a multi-stage plate preheater.

2. Forced Circulation Evaporation: The circulation pump maintains a flow velocity of 2–4m/s within the pipes, and the membrane shear force inhibits crystal adhesion to the walls; the evaporation temperature is controlled at 85–95℃, effectively avoiding the Na₂SO₄·10H₂O phase transition zone and preventing pipe blockage. 

3. Mechanical Vapor Recompression: Secondary steam (80℃, saturated) is adiabatically compressed to 105–110℃ by a centrifugal/Roots compressor, with a temperature rise ΔT = 22–28℃, a compression ratio of 1.6–1.8, and a motor power reduction of over 12%.

4. Gas-Liquid Separation: High-efficiency wire mesh demister + two-stage baffle separation, mist entrainment ≤30ppm, ensuring long-term liquid-slugging-free compressor operation.

5. Crystallization and Discharge: Oslo-type OSLO crystallizer for staged crystal growth, average particle size 0.4–0.8mm, product moisture content ≤3% after centrifugation; mother liquor reflux ratio 30–50%, ensuring continuous and stable system operation.

III. System Composition

1.Main Evaporator: Titanium alloy or 2205 duplex steel heat exchange tubes, design pressure 0.2MPa, design temperature 150℃, heat transfer coefficient ≥3500W·m⁻²·K⁻¹.

2.MVR Compressor: High-efficiency three-dimensional flow impeller, isentropic efficiency 82–85%, frequency conversion range 30–110%, noise ≤82dB(A).

3.Forced Circulation Pump: Axial flow type, impeller with wear-resistant alloy coating, service life ≥25000h, mechanical seal adopts double-end face cartridge type, circulation flow rate 1000–12000m³·h⁻¹.

4.Vacuum System: Two-stage steam injection + water ring pump combination, ultimate vacuum 6kPa(a), automatic discharge of non-condensable gases.

5.Automation: PLC + touch screen, online monitoring of key parameters (temperature, pressure, liquid level, shaft vibration, current), supports remote 4G/5G cloud operation and maintenance, one-button start/stop, achieving "unattended operation".

IV. Technical Highlights

1. Extreme Energy Saving: Secondary steam heat recovery rate ≥90%, only a small amount of live steam is required for start-up, "zero live steam, zero cooling water" during normal operation, electricity consumption per ton of water 28–35kWh, steam consumption ≤0.02t.

2. Anti-scaling design: High-speed turbulent flow + low evaporation temperature difference (≤5℃) reduces scaling rate by 70%; built-in CIP automatic cleaning nozzle completes online acid/alkali cleaning in 4 hours.

3. High crystal quality: OSLO graded crystallization, uniform particle size, purity ≥99.2%, meeting GB/T6009-Class I Grade 1 standard, can be directly sold as commercial sodium sulfate.

4. Modular delivery: Skid-mounted unit, only requiring on-site connection of inlet and outlet pipes and cables, shortening construction time by 40%; supports parallel operation of multiple units within the range of 1–100t·h⁻¹, flexible capacity expansion.

5. Green and low-carbon: No waste gas, full recirculation of high-salt mother liquor, carbon emission intensity reduced by 55% compared to traditional multi-effect refrigerators, helping enterprises improve their ESG rating.

V. Typical Applications

1.Coal chemical high-salinity wastewater: TDS 45000 mg·L⁻¹ → 250000 mg·L⁻¹, sodium sulfate recovery rate 92%, impurity salt rate <5%.

2.Lithium battery by-product sodium sulfate recovery: impurity Li⁺ level 10 ppm, after evaporation and crystallization, Na₂SO₄ purity 99.5%, meeting battery-grade reuse requirements.

3.Dye intermediate mother liquor: COD 20000 mg·L⁻¹, after concentration, it is sent for incineration to achieve "zero emission".