MVR tubular falling film evaporator

Working Principle

1. Falling Film Evaporation Process: The feed liquid enters the liquid distributor from the top of the evaporator and is evenly distributed onto the inner wall of the heating tubes (usually a vertical tube bundle), forming a thin liquid film.

Heating steam (initially external steam is required, but compressed secondary steam is used after stable operation) condenses and releases heat outside the tubes, causing the solvent in the liquid film to evaporate rapidly, generating secondary steam.

The concentrated liquid flows downward along the tube wall and enters the gas-liquid separator along with the secondary steam. The separated concentrated liquid is discharged, and the secondary steam enters the compressor.

2. MVR Cycle Process: The compressor (such as a centrifugal compressor or Roots blower) compresses the secondary steam, increasing its temperature and pressure (usually by 520℃).

The compressed steam is reintroduced as the heating medium outside the evaporator tubes, replacing the fresh steam and forming a closed-loop cycle.

The system maintains stable evaporation temperature and pressure by adjusting the compressor speed or steam flow rate, achieving continuous operation.

3. Energy Recovery Mechanism: By replacing a large amount of fresh steam consumption with the mechanical work of the compressor, only a small amount of electrical energy is required, significantly reducing energy consumption.

The system can be configured with a preheater to further recover heat using condensate or a low-temperature heat source, improving overall thermal efficiency.

Core Structure and Components

1. Tubular Falling Film Evaporation Unit:

• Heating Tube Bundle: Arranged vertically or inclined, forming a liquid film evaporation surface on the inner wall.

• Liquid Distributor: Ensures uniform film distribution, avoiding dry walls or uneven liquid film.

• Gas-Liquid Separator: Separates steam and concentrate, with a built-in demister to prevent entrainment.

2. MVR System Components:

• Steam Compressor: Core component, providing steam compression energy (selection required based on evaporation capacity).

• Preheater: Preheats the feed liquid using condensate or low-temperature steam, reducing the heat load on the evaporation section.

• Control System: Integrates temperature, pressure, and flow sensors, automatically adjusting parameters such as compressor speed, liquid level, and valve opening.

• Vacuum System: Maintains a low-pressure environment within the evaporator, lowering the boiling point and adapting to heat-sensitive materials.

Significant Advantages

1. Extreme Energy Saving: No need for large amounts of fresh steam; energy consumption is only 30%-50% of traditional multi-effect evaporators, resulting in low operating costs.

Electricity replaces heat energy, making it particularly suitable for scenarios with high steam prices or limited supply.

2. Environmentally Friendly: Closed-loop circulation reduces wastewater and exhaust emissions, meeting low-carbon production requirements.

3. Rapid Heat Transfer and Short Residence Time: Falling film evaporation ensures short material residence time (seconds), avoiding thermal decomposition, suitable for heat-sensitive materials (such as pharmaceuticals and food).

4. Flexible Operation and Automation: PLC control system enables fully automatic operation, allowing adjustment of parameters such as concentration ratio and evaporation temperature to adapt to different operating conditions.

5. Compact Structure and Small Footprint: Integrated design saves space, suitable for retrofit projects or site-constrained scenarios.

Application Areas

1. High-Salinity Wastewater Treatment: Concentration and crystallization salt recovery from high-salinity wastewater in industries such as chemical, pharmaceutical, and electroplating.

2. Food and Beverage: High-concentration concentration of fruit juices, dairy products, and syrups, preserving nutrients and flavor.

3. Chemicals and Pharmaceuticals: Organic solvent recovery, concentration and purification of heat-sensitive intermediates.

4. New Energy Materials: Concentration of lithium battery electrolytes, separation of rare earth elements.

5. Seawater Desalination: Replacing traditional multi-stage flash evaporation with low-energy seawater concentration.

Key Design and Operation Points

1. Compressor Selection: The compressor type (centrifugal or positive displacement) must be matched according to the evaporation rate, vapor pressure rise, and material characteristics.

2. Scale Prevention and Cleaning: Regular online cleaning or application of anti-scale coatings, monitoring changes in heat transfer efficiency.

3. Evaporation Temperature Control: Maintaining a stable temperature difference by adjusting compressor speed and feed flow rate.

4. System Sealing: Ensuring a leak-free vacuum system to prevent air from entering and affecting evaporation efficiency.

Challenges and Precautions

1. High Initial Investment: The cost of the compressor and control system is higher than that of traditional evaporators; cost recovery requires long-term energy savings. 

2. Material Adaptability: High-viscosity, easily crystallizing, or corrosive materials require special design (e.g., wide flow channel tube bundles, corrosion-resistant materials).

3. Operational Stability: The compressor requires regular maintenance to avoid mechanical failures affecting continuous production.

Development Trends

The future of MVR tubular falling film evaporators will focus on the following directions:

Intelligent Control: AI algorithms optimize operating parameters to achieve adaptive adjustment.

Material Innovation: High-performance corrosion-resistant alloys or ceramic coatings extend equipment lifespan.

Multi-Effect Coupling: Combining with heat pump technology and membrane separation technology further improves energy utilization.

Summary

MVR tubular falling film evaporators, by integrating mechanical vapor recompression and falling film evaporation technologies, achieve a synergy of rapid energy saving, environmental protection, and high product quality, making them particularly suitable for high-energy-consumption evaporation scenarios. Their core value lies in reducing operating costs and carbon emissions, representing an important development direction in the field of evaporation and concentration.