Design and operation principle of falling film evaporator

Design and operation principle of falling film evaporator

Design shell and tube heat exchanger

1、Operating principle

The liquid to be concentrated enters the top of the heating pipe and flows downward along the inner wall of the heating pipe to form a film. In this process, due to the heating outside the tube, the liquid film in the tube begins to boil and partially evaporate. The downward movement of the liquid film is initially due to the action of gravity, and then the steam in the pipe is continuously generated. The downward steam drives the liquid film to accelerate its downward movement. In the centrifugal separator at the lower part of the tube and its downstream, the remaining liquid and steam can be separated. In order to ensure the function of falling film evaporator, it is very necessary that all heating surfaces, especially the lower area of heating tube, can be fully and evenly wetted by liquid. Otherwise, local dry wall will appear, resulting in serious crusting.

For complete wetting, it is very important to select a suitable liquid distributor and install it on the top of the evaporator. The wetting rate can be improved by using extended heating tubes, dividing the evaporator into several chambers, or circulating the product.

2. Characteristics

Best product quality – due to mild evaporation conditions, operating under vacuum in most cases, and very short residence time in the evaporator.

High energy efficiency – based on the theoretical Multi-effect can be designed based on minimum temperature difference, or thermal steam recompression MVR or mechanical steam recompression TVR can be designed.

Simple process control and Automation – due to the small liquid retention, the falling film evaporator can take rapid action according to the changes of energy supply, vacuum, feed volume, concentration, etc. This is a prerequisite for obtaining products of stable quality.

Flexible operation – the evaporator starts quickly, and it is easy to switch from production mode to cleaning mode. It is not complicated to change the type of products to be concentrated.

3. Scope of application

The required floor area is relatively small.

It is especially suitable for temperature sensitive materials.

It is applicable to solutions containing only a small amount of solids and solutions with only moderate crusting tendency.

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