Multi-effect vacuum evaporator

I. Technical Principle of Multi-Effect Vacuum Evaporator

Multi-effect vacuum evaporators achieve tiered utilization of thermal energy by connecting two or more evaporators in series. The core of this technology lies in the recycling of secondary steam.

Working Principle

1. Steam Progression: Live steam (fresh steam) is used only in the first-effect heating chamber; the secondary steam generated in the previous effect serves as the heating source for the next effect.

2. Pressure Decrease: The operating pressure of each effect in the system decreases progressively, forming a vacuum gradient (the vacuum level of the final effect can reach below -0.098 MPa).

3. Boiling Point Reduction: The boiling point of the feed liquid decreases under vacuum conditions, achieving low-temperature evaporation and protecting heat-sensitive components.

4. Heat Circulation: The thermal energy carried by the secondary steam is repeatedly utilized as the number of effects increases.

Energy Saving Mechanism

Under ideal conditions (processing pure water, no heat loss), 1 pound of heating steam can evaporate 6-7 pounds of water (six-effect system). In practical applications, due to factors such as heat of solution concentration and heat loss, the energy saving efficiency is approximately 1/6 to 1/7 of that of single-effect evaporation. A typical five-effect system can reduce steam consumption by approximately 80% compared to a single-effect system.

II. System Structure

The multi-effect vacuum evaporator consists of multiple independent evaporation units connected in series. Each unit includes:

Core Components

Heating Chamber: Transfers heat from the steam to the feed liquid via heat exchange tubes.

Separation Chamber: Performs gas-liquid separation to ensure steam purity.

Distributor: Ensures uniform film formation of the feed liquid on the heating tube wall (falling film evaporator).

Auxiliary Systems

Vacuum System: Vacuum pump + condenser, maintaining a negative pressure environment in the system.

Material System: Feed pump, discharge pump, circulation pump.

Condensation System: Condenses the steam from the last effect and recovers condensate.

Control System: PID controller achieves precise control of temperature, pressure, and liquid level.

Common Configurations (by...) Number of Efficiencies: Two to five effects are most common; large-scale production can reach six or even twelve effects.

By Process Flow: Parallel flow, counter-flow, horizontal flow

By Evaporation Method: Falling film, rising film, forced circulation

III. Main Features

Advantages

Significant Energy Savings: Steam consumption decreases significantly with increasing number of effects.

Low Temperature Operation: Boiling point decreases under vacuum, suitable for heat-sensitive materials.

High Automation: Operating parameters can be automatically adjusted.

Large Processing Capacity: Suitable for large-scale continuous production.

Limitations

High Investment Costs: Increased number of effects leads to a significant increase in equipment investment.

Large Footprint: Requires a large heat transfer area.

Scaling Issues: Some materials are prone to scaling on heat exchange tubes. Scaling on the walls affects heat transfer efficiency.

Unsuitable for small-scale production: Poor economic efficiency for small-capacity scenarios.

IV. Operating Parameters

Temperature Range: 75°C to 40°C (Dairy Products) (Further details omitted for brevity)

Pressure gradient: Gradually decreases to create a vacuum environment

Concentration ratio: Can reach over 10:1 depending on material characteristics

V. Application Scenarios

1. Salt Industry

Brine concentration and purification using a five-effect evaporation process (I-II effects positive pressure, III-V effects negative pressure)

Produced salt with a purity of over 98%, sodium chloride content up to 99%

2. Food Industry

Dairy products: Milk powder, condensed milk, whey concentrate production (operating temperature 75-40°C to prevent protein denaturation)

Sugar industry: Sugar juice concentration (increasing dry matter content from 15% to over 68%)

Fruit juice: High-viscosity fruit juice concentration

3. Pharmaceutical Industry

Low-temperature concentration of heat-sensitive materials such as antibiotics and enzyme preparations

Low-temperature vacuum evaporation (≤55℃) meets GMP standards, with an effective ingredient retention rate of 98%.

4. Environmental Protection Sector

High-Salinity Wastewater Treatment: Achieving Zero Discharge (ZLD)

Heavy Metal Recovery: Nickel and Cobalt Recovery Rates Exceed 95%, Cost Reduction by 40%

Lithium Battery Wastewater: Daily Treatment of 300 Tons, Nickel Recovery Rate 98%

5. Chemical Industry

Chemical Product Concentration

Solvent Recovery

Electroplating Wastewater Treatment: Achieving Zero Discharge of Heavy Metals, Annual Cost Savings Exceeding 5 Million Yuan

VI. Typical Cases

Case 1: Triple-Effect Evaporator in an Electroplating Industrial Park

Scale: 500 tons of wastewater treated per day

Results: Achieved zero discharge of heavy metals, saving over 5 million yuan annually in hazardous waste treatment costs

Operation: Stable operation for over 5 years

Case 2: High-Salinity Wastewater Treatment in Coal Chemical Industry

Scale: 500,000 tons of wastewater treated annually

Technology: Nanofiltration + MVR crystallization process

Results: Sodium chloride and sodium sulfate separation purity >99%, by-product industrial salt revenue covers equipment costs

Multi-effect vacuum evaporators, as a mature energy-saving technology, achieve highly efficient concentration with steam consumption only 1/6 that of single-effect evaporators, making them particularly suitable for heat-sensitive material processing and large-scale industrial production. With the integration of new technologies such as MVR, intelligent control, and anti-scaling materials, their economic and environmental benefits will be further enhanced.