Evaporation is a unit operation for concentrating a solution. Usually, the solvent can be volatilized, but the vapor pressure of most solutes is close to zero and cannot be volatilized. The process of evaporating a solution under boiling conditions to remove part of the solvent and condense it is called evaporation. In most cases, the evaporator uses steam as the heating medium (usually called heating steam, primary steam or fresh steam), and indirectly transfers heat to the solution through the metal wall. After the solution is heated, the solvent boils and vaporizes, resulting in steam (mostly In this case, water vapor is also called secondary steam.
The vertical falling film evaporator and falling film reboiler are shown in Figure 1 below. The material liquid enters the material liquid distributor from the top. The material-liquid distributor distributes the material-liquid evenly 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, vaporization occurs on the inner surface of the strongly disturbed membrane, rather than at the interface between the heating tube and the liquid membrane (ie, the inner surface of the heating tube), so it is not easy to scale. The steam produced usually flows down side-by-side with the liquid film. Because the vaporization surface is large, the amount of liquid foam entrained in the steam is small, and the material liquid flows in a film on the inner wall of the pipe, and does not fill the entire section of the pipe, so the amount of material liquid passing through can be very small.
The material-liquid distributor is a key component of the falling-film evaporator. The heat exchange intensity and production capacity of the falling-film evaporator essentially depend on the uniformity of the distribution of the material-liquid along the heat exchange tube. The so-called uniform distribution not only means that the liquid must be evenly distributed into each tube, but also evenly distributed along the entire periphery of each tube, and to maintain its uniformity over the entire length of the tube. When the material liquid cannot evenly wet the inner surface of all the heating tubes, the lack of liquid or liquid surface may become fouled due to evaporation, and the fouled surface will in turn block the flow of the liquid film and cause heat transfer in the adjacent area. Conditions worsen