Evaporation is a unit operation for concentration of solution. Generally, the solvent can be volatilized, while the vapor pressure of most solutes tends to zero and cannot be volatilized. Under the boiling condition, the process of removing part of the solvent by vaporization to make it concentrated is called evaporation. In most cases, the water vapor of the evaporator is used as the heating medium (usually called heating steam, primary steam or fresh steam) to indirectly heat transfer the solution through the metal wall. After the solution is heated, the solvent boils and vaporizes. The generated steam (in most cases, it is also water vapor) is called secondary steam.

Falling film evaporator is a distributor for feeding liquid from the top. The material liquid distributor evenly distributes the material liquid into each heating tube and makes it flow down the inner wall of the tube in a film shape. The liquid film is vaporized by the heat transmitted from the tube wall. When the heat transfer temperature difference is small, the vaporization occurs on the inner surface of the strongly disturbed film, rather than on the interface between the heating tube and the liquid film (that is, the inner surface of the heating tube), so it is not easy to scale. The steam produced usually flows down in parallel with the liquid film. Because the vaporization surface is very large, the entrainment of liquid foam in the steam is less, and the material liquid flows in a film shape on the inner wall of the pipe, which does not fill the whole cross section of the pipe, so the material liquid passing through can be very small.

Falling film evaporator:

The material liquid distributor is the key part of the falling film evaporator. The heat exchange strength and production capacity of the falling film evaporator depend on the uniformity of the material liquid distribution along the heat exchange tube. The so-called uniform distribution not only means that the liquid should be evenly distributed in each pipe, but also along all the periphery of each pipe, and maintain its uniformity in the length of the whole pipe. When the material liquid can't wet the inner surface of all the heating pipes evenly, the surface with lack of liquid or less liquid may be scaling due to evaporation, and the scaling surface in turn blocks the flow of the liquid film and further worsens the heat transfer conditions in the adjacent areas.

Characteristics of falling film evaporation system:

1) The feed liquid of falling film evaporator is added from the top of the evaporator, falling down the tube wall in the form of film under the action of gravity, and in the process of evaporation and concentration, the concentrated liquid is obtained at the bottom. Falling film evaporator can evaporate materials with high concentration and viscosity.

2) Due to the film flow of solution in one-way evaporator, the heat transfer coefficient is high.

3) It has a short residence time and is not easy to cause material deterioration, so it is suitable for the treatment of heat sensitive materials.

4) The falling film evaporator can operate quickly according to the change of energy supply, vacuum degree, feed quantity and concentration. Near constant

5) Because the process fluid only flows under the action of gravity, rather than driven by high temperature difference, low temperature difference evaporation can be used.

6) falling film evaporator is suitable for evaporating and concentrating foaming materials. As the material liquid evaporates in the heating tube, vapor-liquid separation is formed, and at the bottom of the effective body, most of the liquid material is removed. Only a small amount of liquid and all two steam enters the separator to strengthen separation. The process of liquid material formation does not cause too much impact, thus avoiding the formation of foam.