Falling film triple-effect evaporator

1. Working Principle of Falling Film Triple-Effect Evaporator

The core of falling film evaporation lies in forming a uniform liquid film on the inner wall of the heating tubes, which then flows downwards under gravity. The extremely thin liquid film results in revolutionary heat transfer efficiency.

2. Countercurrent Falling Film Triple-Effect Evaporator

Film Distribution - Key Step: The pretreated liquid is evenly distributed to the top of each evaporator heating tube by a top distributor. The design of the distributor e.g., sieve plate, nozzle, or guide tube type is crucial; it must ensure that a continuous, uniform, and stable liquid film forms on the inner wall of each tube, preventing dry-wall phenomena.

Falling Film Evaporation: Under the influence of gravity, the liquid flows downwards in a film along the inner wall of the heating tubes. Simultaneously, the heating steam outside the tubes (shell side) condenses and releases latent heat, which is transferred to the liquid film inside the tubes through the tube wall. The liquid film boils instantaneously and evaporates, producing secondary steam that flows downwards at high speed along with the liquid.

Vapor-Liquid Separation: The vapor-liquid mixture enters the separation chamber at the bottom of the evaporator. Due to the reduced flow rate and the action of separators such as baffles and wire mesh demisters, the concentrated liquid and secondary steam are completely separated.

Multi-effect operation: The separated secondary steam is introduced into the heating chamber of the next effect as a heat source (the secondary steam of the first effect is the heat source of the second effect, and so on). The concentrated liquid is pumped to the previous effect due to the counter-current flow, the concentrated liquid of the second effect enters the first effect, opposite to the steam flow direction for further concentration, or the concentrated liquid of the last effect is discharged after reaching a predetermined concentration.

Condensation and vacuum system: The secondary steam generated in the last effect enters a mixing or surface condenser for complete condensation, and a vacuum pump system maintains a high vacuum in the entire system especially the last effect, thereby lowering the boiling point of each effect, especially the last effect.

3. Features and Advantages of Falling Film Triple-Effect Evaporation Technology

Ultra-high heat transfer efficiency: The liquid film is extremely thin, with high turbulence and low thermal resistance, resulting in a heat transfer coefficient far exceeding that of flooded evaporators. This means that for the same throughput, a smaller heat transfer area is required, potentially leading to a more cost-effective equipment investment.

Low residence time, suitable for heat-sensitive materials: The material passes rapidly through the heating tubes in thin film form, with the entire evaporation process taking only tens of seconds. This ultra-short residence time, combined with low-temperature evaporation under vacuum, makes it ideal for processing heat-sensitive materials such as antibiotics, fruit juices, vitamins, and natural extracts, which are easily decomposed or polymerized by heat, maximizing product activity and quality.

Low static head effect, minimal temperature difference loss: Because the liquid does not accumulate within the heating tubes, there is no boiling point rise caused by liquid column static pressure. This maximizes the utilization of the effective heat transfer temperature difference, making it particularly suitable for multi-effect evaporation designs under small temperature difference conditions.

Low energy consumption: Inheriting the inherent energy-saving advantages of multi-effect evaporation, it boasts high steam economy theoretical steam consumption can be as low as 0.3-0.4 kg steam/kg water.

High operational flexibility: By adjusting the feed rate and heating steam volume, it can adapt to changes in different processing loads over a wide range.

4. Typical Application Areas:

Food and Juice Industry: Milk concentration, juice concentration (orange juice, apple juice), sugar solution concentration.

Pharmaceutical and Bioengineering: Low-temperature concentration of antibiotics, glucose, vitamins, and plant extracts.

Chemical Industry: Concentration of clean inorganic salt solutions such as NaOH, NaCl, and organic acid salts.

Environmental Protection Industry: Volume reduction treatment of RO concentrate and landfill leachate pretreatment is required to control scaling.

Seawater Desalination: As a pre-concentration unit in seawater desalination.