Multi Stage Evaporator

I. What is a MultiStageEvaporator?

A MultiStageEvaporator (commonly referred to as "Multi-Effect Evaporator" or MEE in China) is an energy-saving evaporation device that reuses steam multiple times.  It uses 2 to 8 stages in series, progressively reducing pressure and boiling point. The secondary steam generated in the previous stage becomes the heating source for the next stage, ultimately evaporating a large amount of water from the solution with extremely low fresh steam consumption, producing concentrated liquid or directly producing reusable distilled water.

II. Working Principle – "Step-by-Step Energy Utilization" allows 1 ton of steam ≈ 4-7 tons of evaporation

1. First stage: External fresh steam (≈105℃) heats the material, generating the first secondary steam.

2. Second stage: Using the secondary steam from the first stage as a heat source, evaporation continues at a lower boiling point of only 85-90℃ due to reduced pressure.

3. Third stage and beyond: The above process is repeated until the last stage evaporates at a low temperature of 45-60℃.

4. Terminal vacuum condensation: The remaining steam is condensed by a surface condenser or cooling tower, maintaining an absolute pressure of 20-30 kPa in the system.

Result: Evaporating 1 ton of water consumes only 0.15-0.3 tons of fresh steam, saving more than 60% energy compared to single-effect evaporation.

III. Core Components – The "Four Modules" Owners Need to Focus On

1. Evaporator body: Tube/plate falling film or rising film structure, made of 304/316L/duplex stainless steel/titanium, capable of withstanding chloride ions ≤20000 mg/L.

2. Hot and cold side separators: Ensure efficient vapor-liquid separation, with mist entrainment ≤50 ppm, preventing "carryover".

3. Vacuum and condensation module: Water ring pump + surface condenser, automatically maintaining the design vacuum; cooling water consumption ≤5 t/t-evaporation.

4. Intelligent control: PLC + HMI, real-time display of temperature, pressure, concentration, and conductivity, one-button start and stop, supports communication with the owner's DCS.

IV. Which Owner Scenarios are Suitable? 

Zero Liquid Discharge of High-Salinity Wastewater: Power plant desulfurization wastewater, coal chemical concentrated brine, electroplating/dyeing wastewater, with TDS up to 150,000 mg/L.

Chemical/Pharmaceutical Industry: Mother liquor recovery, solvent recovery, concentration of heat-sensitive products (vitamins, antibiotics, glucose).

Food and Fermentation: Low-temperature concentration of fruit juice, whey, starch sugar, and yeast extract, preserving color, aroma, and taste.

Resource Recovery: Integrated "evaporation → crystallization → drying" of inorganic salts such as Na₂SO₄, NaCl, and (NH₄)₂SO₄, producing by-product salts meeting industrial-grade standards.

V. Six Major Values for Owners

1. Low operating costs: Compared to single-effect systems, steam savings of 60% to 75%. Based on an evaporation capacity of 10 t/h, 7200 hours of operation per year, and a steam cost of 220 yuan/t, annual steam cost savings are ≥ 6 million yuan.

2. Small footprint and lower investment: Three-effect integrated frame structure, occupying ≤ 1.3 times the area of a single-effect system, eliminating the need for large-span factory buildings.

3. High degree of automation: Requires only one operator, with automatic system cleaning and online CIP, reducing labor by 50%.

4. High-quality effluent: Distilled water with COD ≤ 30 mg/L and conductivity ≤ 100 μS/cm, which can be directly reused in boilers or circulating cooling systems.

5. Low-temperature evaporation, less corrosion: The final effect operates at 45-60°C, extending equipment life by more than 30% compared to 110°C single-effect evaporation.

6. Policy-friendly: Included in the "National Catalogue of Encouraged Industrial Water-Saving Technologies," with 10% to 30% investment subsidies available in some provinces.

VI. Three-Step Selection Method for Owners

1. Water quality assessment: Provide annual water quality fluctuations (TDS, COD, Cl⁻, Ca²⁺/Mg²⁺, SiO₂, hardness) to determine materials and scaling risks.

2. Energy balance calculation: Based on steam pressure, cooling water temperature, and electricity price, select the number of effects (3/4/5/6) and whether to add MVR mechanical vapor recompression, with the lowest overall operating cost being the optimal choice. 3. Site and Utilities: Confirm steam pipe diameter, cooling water volume, power load, and effluent discharge direction; integrated skid-mounted or separate layout can be determined accordingly.

VII. Operation and Maintenance Key Points – Ensuring Equipment Remains Up-to-Date for 20 Years

Startup: First evacuate to -0.085 MPa, then feed the material to prevent scaling caused by "dry wall" conditions.

Cleaning: Circulate with 60°C, 2%-3% NaOH for 30 minutes per shift; passivate with 1% nitric acid on weekends; annual shutdown scaling thickness ≤0.5mm.

Corrosion Prevention: When Cl⁻ > 8000 mg/L, select 2205/2507 duplex stainless steel or titanium for heat exchange tubes, and rubber lining for the end caps, doubling the lifespan.

Vacuum Leakage Rate: Monthly detection ≤0.5 kPa/h; replace mechanical seals and gaskets promptly if exceeded to maintain energy consumption targets.

VIII. Typical Cases (for Owner Reference)

A pharmaceutical company in East China: Triple-effect falling film + forced circulation crystallization, processing 8 t/h of high-salt mother liquor, evaporation rate 6.5 t/h, steam consumption 0.22 t/t-water, saving 5.2 million RMB in steam costs annually, with a return on investment in 18 months.

A printing and dyeing park in South China: Quadruple-effect + MVR, 20 t/h evaporation rate, water reuse rate 92%, solid mixed salt water content ≤5%, meeting the "Standard for Industrial Wastewater Reuse" GB/T19923-2005.

IX. Conclusion

The Multi-Stage Evaporator is not simply an "evaporator," but a system engineering solution that brings three-fold value to owners: "energy saving + emission reduction + resource recovery." As long as you have steam ≥0.3 MPa or waste heat above 85°C on site, plus high-salt or high-COD wastewater, or materials requiring concentration/crystallization, multi-effect evaporators are almost always the solution with the lowest life cycle cost and the most policy support. Welcome to contact us with your water quality report and steam parameters to obtain a free energy balance and return on investment calculation, allowing every ton of steam to create more than four tons of "evaporation benefits"!