Industrial Falling Film Evaporator

According to the characteristics of the materials, some raw materials require a falling film evaporator for concentration treatment . Wuxi Hongdinghua Chemical Equipment Co., Ltd. has many years of experience in designing and manufacturing falling film evaporators.

Industrial Falling Film Evaporator is a device that can achieve evaporation and concentration through heating with hot water, steam, and heat transfer oil.

The material in falling film evaporator flows downwards in the form of a thin film, so it is named "falling film" to distinguish it from the process where the raw material liquid flows upwards. Its main function is to evaporate water and gas from the raw material, thereby increasing the dry matter content of the material, hence the name "evaporator".

Principle of Process

The raw material to be evaporated enters the falling film evaporator from the falling film evaporator top through the feeding pump, passing a liquid distributor which is installed at the falling film Evaporator top and a falling-film tube equipped to each piece of heat exchange tube inside, so that the raw material liquid can be formed a film. The raw material liquid passes through the evaporation tube (tube side) and is distributed in a film like shape into the heat exchange tube. When the raw material flows downward into the tube cavity by its own gravity , it is heated by the steam outside the tube and evaporates when it reaches the evaporation temperature. The raw material, along with the secondary steam, flows down from the tube and evaporates in the form of a film. The secondary steam is sucked in by the steam jet heat pump through the Venturi effect and mixed with external fresh steam, which is sent to the shell side of the falling film evaporator’s heating chamber as heating steam. The shell side of the falling film heating chamber has plates to guide secondary steam, condense and discharge non condensable gases. During the process, the heat energy is transferred from the outside through the tube wall to the material evaporated inside the tube. After heat exchange, the secondary steam is condensed into water by the condenser and discharged from the falling film evaporator.

Advantages of falling film evaporator

1. The retention time of the liquid mixture is short, and it will not cause degradation damage to heat sensitive substances; 

2. Due to its thin film status and high liquid flow rate, the heat transfer coefficient of primary evaporation crystallization is correspondingly high; 

3. The pressure drop is small, and the pressure and temperature measured by the heat exchanger process are almost constant, so sensible heat can be avoided or minimized; 

4. Since the raw material fluid only flows under the effect of gravity, rather than being driven by the high temperature difference, it is allowed to adopt a more economical low temperature difference; 

5. The amount of liquid holding in the equipment is relatively small, which can avoid small-scale liquid retention and continuous high temperature; 

6. Boiling is convective boiling, so the surface condition of the tube has a relatively small impact on boiling.

Falling film evaporators are widely used for the evaporation and concentration of water or solvent solutions in industries such as medicine, food, chemical, and light industry. Falling film evaporators can also be widely used for waste liquid treatment in these industries. Especially suitable for heat sensitive materials, this equipment operates continuously under vacuum and low temperature conditions, with high evaporation capacity, energy saving and consumption reduction, low operating costs, and can ensure the invariance of materials during the evaporation process.

Detail of falling film evaporators:

In a falling film evaporator, the liquid to be evaporated enters from the falling film evaporator top and passes through the liquid distributor. The liquid flows downward along the pipe wall in a film shape. The reason why falling film flow can improve the heat transfer coefficient is that the flow area of the film flow is far more less than the actual cross-sectional area of the tube, so the Reynolds number of the flow is greatly increased, making the heat transfer coefficient significantly higher than that of ordinary equipment filled with liquid. The falling film and rising film are both due to the film flow, which significantly increases the heat transfer coefficient, but their film forming principle are different. Rising film is due to the high airflow velocity, which causes the liquid to form a film and rise along the pipe wall; Falling film is caused by gravity and the wetting force of the liquid on the pipe wall, which causes the liquid to flow downwards along the pipe wall in a film shape. 

Therefore,some of the falling film evaporator’ characteristics are different from that of the rising film evaporator:

There is no static pressure column in the falling film evaporator, which will not cause the boiling point rising. At the same time, the heat transfer coefficient has nothing to do with the temperature difference. This means that the heat transfer coefficient can be very high at a low heat transfer temperature difference, so falling film is more suitable than rising film for the evaporation of heat sensitive substances.

The falling film is different from the rising film, and the film transmission coefficient does not depend on the speed of the vapor in the tube, so it is suitable for occasions with small evaporation. For example, some Two effect evaporator often uses rising film evaporation during the first stage evaporation, while falling film evaporation is used in the second stage evaporation.

Because the film flow of falling film evaporation relies on the affection of gravity, under the affection of gravity, the liquid passes through the falling film distributor, forming a film shape and evenly distributed to each heat exchange tube. When installing the falling film distributor, it must be ensured to be horizontal to avoid uneven distribution of liquid flow, which may affect the film formation and flow rate required for falling film evaporation. Before HDH designing and manufacturing a falling film evaporator, technical person will communicate in detail with the customers about follwing:

The composition and specifications of the raw material liquid mixture - this can determine the accurate material selection to build the evaporator

Concentration rate of raw material (Liquid Mixture)

Concentration requirements for completion

Processing capacity(Volume)

In this way, HDH can design according to the data and requirements you provide, determine the appropriate materials for equipment building, and determine which evaporation form to use, whether it is a rising film evaporator or a falling film evaporator.

Falling film Evaporator（hydraulic testing）