Tubular falling film evaporator

Working Principle

1. Liquid Distribution and Film Formation: The feed liquid enters the liquid distributor  from the top of the evaporator and is evenly distributed to the tops of each heating tube.

Under the influence of gravity, vacuum induction, and airflow, the liquid flows downwards along the inner wall of the heating tubes in a film-like manner, forming a thin liquid film.

2. Evaporation and Heat Transfer: The heating medium  flows outside the tubes, transferring heat to the liquid film through the tube walls, causing the solvent in the liquid film to rapidly evaporate and vaporize.

The secondary steam generated by evaporation, along with some unevaporated liquid, enters the gas-liquid separation chamber.

3. Gas-Liquid Separation and Condensation: In the separation chamber, steam and liquid are physically separated . The steam enters the condenser for condensation and recovery, while the concentrated liquid is discharged from the bottom of the separation chamber.

4. Multi-Effect Operation: By connecting multiple-effect evaporators in series, the secondary steam from the previous effect can be used as the heating medium for the next effect, achieving multi-stage energy utilization and significantly reducing energy consumption.

Core Structure and Components

1. Heating Tube Bundle: Composed of multiple vertical or inclined heating tubes, with the inner wall serving as the evaporation surface. Materials include carbon steel, stainless steel, or corrosion-resistant alloys.

2. Liquid Distributor: A critical component ensuring uniform liquid distribution to the top of each heating tube, forming a stable liquid film.

3. Gas-Liquid Separation Chamber: Located at the bottom of the evaporator, used to separate steam and concentrate. An internal demister prevents liquid entrainment.

4. Heating Evaporation Chamber: Includes the shell, tube sheet, baffles, etc. The shell can be designed as an atmospheric pressure or vacuum container depending on the pressure.

5. Condensation System: Typically a shell-and-tube or plate condenser, used to condense secondary steam and recover solvent or heat energy.

6. Circulation System: Includes built-in circulation pipes or pumps for preheating the liquid or maintaining stable fluid dynamics within the tubes.

Key Features and Advantages

1. High Heat Transfer Efficiency: The thin and turbulent liquid film flow results in low thermal resistance and a significantly higher overall heat transfer coefficient than traditional evaporators.

No boiling point elevation due to static liquid pressure, resulting in high effective temperature difference utilization.

2. Suitable for heat-sensitive materials: Short material residence time avoids decomposition or deterioration caused by prolonged high-temperature residence.

3. Strong anti-scaling properties: Rapid liquid film flow reduces the tendency for scaling on the pipe wall, and maintenance can be achieved through mechanical, chemical, or high-pressure water cleaning.

4. High operational flexibility: Adaptable to different flow rates and concentrations of feed, with flexible control of the concentration ratio by adjusting parameters such as feed rate and temperature.

5. Energy saving and consumption reduction: Multi-effect operation significantly reduces steam consumption, and some designs can recover condensate or waste heat.

6. Compact structure and reliability: Small equipment size, small footprint; robust tubular structure, strong pressure resistance, and low maintenance costs.

Application Areas

1. Chemical Industry: Solution concentration , solvent recovery, distillation purification.

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

3. Pharmaceutical Field: Concentration and separation of heat-sensitive drug extracts.

4. Seawater Desalination and Wastewater Treatment: Desalination and concentration of seawater or high-salinity wastewater, recovery of crystalline salts.

5. Papermaking and Alumina Production: Evaporation and concentration of black liquor in papermaking to recover alkali; Concentration of mother liquor and wastewater treatment in alumina production, crystallization to precipitate salt impurities.

6. Petroleum and Petrochemical: Separation and purification of crude oil components.

Key Design and Operating Parameters

1. Heating Tube Parameters: Tube diameter, length, and quantity must be designed based on material characteristics and evaporation load.

2. Liquid Flow Rate and Distribution: Ensure uniform film formation and avoid excessively thick dry walls or liquid films.

3. Evaporation Temperature and Pressure: Control vacuum or heating medium temperature to adjust the evaporation rate.

4. Condensing Medium Temperature: Affects heat transfer temperature difference and condensation efficiency.

5. Cleaning Cycle: Develop a cleaning plan based on the material's scaling tendency to maintain heat transfer performance.

Challenges and Precautions

1. Design and Commissioning Complexity: Optimal parameters must be determined through process calculations and experiments to avoid uneven distribution or incomplete evaporation.

2. Initial Investment Cost: High-precision distributors and multi-effect systems may increase equipment costs.

3. Operation and Maintenance Requirements: Regular monitoring of heat transfer efficiency is necessary, and scaling or blockage must be addressed promptly.

Development Trends

With advancements in materials science and process optimization, future tubular falling film evaporators will develop towards faster, more modular, and more intelligent directions. For example:

• Applying new corrosion-resistant materials to extend lifespan;

• Combining with automated control to achieve real-time parameter optimization;

• Developing more compact multi-effect integrated equipment to reduce energy consumption.

Summary

Tubular falling film evaporators, with their rapid heat transfer, short residence time, and anti-scaling characteristics, have become an ideal choice for processing heat-sensitive materials and high-concentration solutions. Through reasonable design and operational optimization, they can meet the energy-saving and high-quality evaporation and concentration needs in various industries, making them an important component of modern industrial evaporation technology.