The falling film evaporator is a kind of film evaporator, which adds materials from the pipe box at the top of the falling film evaporator, passes through the film forming device of the liquid distributor, and evenly distributes them into the heat exchange tubes. Under the action of gravity and vacuum induced air flow, the materials flow from top to bottom in a uniform film form. During the flow process, they are heated and vaporized by the shell-side heating medium, and the generated steam and liquid phase enter the gas-liquid separator together, and the vapor-liquid are fully separated, The secondary steam enters the condenser for condensation (single effect evaporation) or enters the next effect evaporator (the next effect of multi-effect evaporator) as the heating medium to realize multi-effect operation, and the liquid phase returns to the bottom of the evaporator. After reaching the concentration ratio, it is delivered to the outside of the system through the discharge pump.

Process description:
The fresh raw materials are added into the pipe box at the bottom of the falling film evaporator, and then the mixed materials are sent to the pipe box at the top of the evaporator through the falling film circulating pump. The materials are evenly distributed into the heat exchange tubes through the liquid distributor. After the shell side water vapor is heated, the materials change phase and form a film distribution. Then the gas-liquid mixture is separated in the gas-liquid separator. The secondary steam is purified by the demister and discharged from the evaporator, and the concentrated materials flow into the bottom of the boiler by gravity, After reaching the concentration multiple, it will be discharged into the system through the discharge pump.

Advantages and disadvantages of falling film evaporator:
1. The material flows in the form of film in the heat exchange tube, with high heat transfer efficiency, short heating time, and greater protection of heat-sensitive substances.
2. High heat transfer coefficient, small heat exchange area, low investment and high cost performance.
3. Lower pressure drop, higher heat transfer temperature difference, and more energy saving when using mvr falling film evaporator.
4. Use materials with high viscosity, generally applicable to materials less than 0.1pa · s.
5. It is more suitable for evaporation of foaming materials.
6. It is not applicable to the evaporation of materials that are easy to scale or contain suspended solids.

Application range of falling film evaporator:
To sum up, compared with the rising film evaporator, the falling film evaporator can handle materials with higher viscosity, higher heat transfer coefficient, lower pressure drop, and is suitable for the evaporation process of foaming materials and heat-sensitive materials. Compared with the forced circulation evaporator, the investment cost and operating cost are lower. It is applicable to the evaporation and concentration of waste water and organic solvents in pharmaceutical, food, chemical and other industries, especially for the concentration process of heat-sensitive materials, such as tea polyphenols, milk and other materials.
The falling film evaporator and steam compressor are coupled to form a mvr falling film evaporator, and the falling film evaporator and multi-effect evaporator are coupled to form a multi-effect falling film evaporator.

Differences between mvr evaporator and falling film evaporator:
There is no inevitable gap between mvr evaporator and falling film evaporator, which are two concepts. mvr evaporator is a process of adding steam compressor to ordinary evaporator to use secondary steam, which is the classification of evaporator from the perspective of using secondary steam; Falling film evaporator is a pure evaporator classification, which is based on the evaporation form of materials. The two types of evaporators have different classification standards. The same evaporator can be called mvr evaporator or falling film evaporator. However, the evaporation process equipped with steam compressor is generally called mvr evaporator, and the evaporator with falling film can be called mvr falling film evaporator.