Falling film evaporator vs rising film evaporator

What is a falling film evaporator used for

  Falling film evaporator is widely used in many fields, including industrial factory, chemical engineering, petroleum and other fields. Falling film evaporator has a high efficiency on the separation of substances, so it is used on milk, glucose, starch, pharmaceutical, chemical, biological engineering, environmental engineering, waste liquid recovery and so on.

Falling film evaporator
Falling film evaporator

How does a falling film evaporator work?

 In falling film evaporator equipment, sample materials will be added from the top of falling film evaporator. Then the materials will be divided into thin films, in order to get heated and evaporated more easily. The heating temperature will be set on the boiling point of substance’s boiling point, which is about to get evaporated. After evaporating the substance, the mixture and substance will be separated.

 Rising film evaporator is upright mounted fixed tube plate heat exchanger. It is suitable for processing heat-sensitive substances with large evaporation volume and susceptible to thermal decomposition and foam-dependent substances. Falling film evaporator is a separation device that is specially suitable for the heat sensitive substances. Falling film evaporator and rising film evaporator both increase heat transfer coefficient through flow in film, but their reasons for forming films are different.

The difference between falling film evaporator and rising film evaporator

  Falling film evaporator and rising film evaporator are both to separate, concentrate or extract substances from mixtures, but there are still some differences between them:

  1. Reasons for forming films. The reason for forming films of falling film evaporator is through gravity. There are falling film distributor installed in the evaporator, in order to make the materials be distributed evenly in the tubes. And rising film evaporator has a high vapor velocity, which makes the liquid rise as a film along the tube wall.

  2. Falling film evaporator is suitable for the situations with low evaporation, while rising film evaporator is suitable for the situations with high evaporation. For example, in some equipment with two-stage evaporation, rising film evaporator is always used for the first stage evaporation and falling film evaporator is always used for the second stage evaporation.

Falling film evaporator
Falling film evaporator

Key benefits of falling film evaporator

Falling film evaporators are quite popular because they so have benefits. The benefits of falling film evaporator are as follows:

  1. A falling film evaporator can be used for the extraction and separation of heat-sensitive substances.
  2. A falling film evaporator can provide high efficiency for multiple effect designs, which saves more time and energy of the whole system for users.
  3. There will be less fouling in a falling film evaporator, because a falling film evaporator has low tube wall temperature and heat flux.
  4. During the working process of a falling film evaporator, there will be short product contact time, which can minimize thermal degradation effects.

Falling film evaporator problems and solutions

When users are using falling film evaporator, there can be some problems happening sometimes. These problems are some warnings for us to adjust the falling film evaporator or change some old accessories. These are some detailed problems and their solutions:

Problems:

  1. The vacuum decreases during the evaporating process, which leads to the decrease of evaporation.

  2. The vacuum of the falling film evaporator equipment is too low during the closed evaporation.

  3. Various effect material separators are often put on the sight glass, and the condensed water is heavily charged.

  4. When the steam consumption increases significantly, the nozzle of the heat pump should be checked for blockage or damage as the solution.

Falling film evaporator
Falling film evaporator

Solutions:

1. The solution aimed at this problem is to check the evaporator distribution plate. First of all, check if the distribution material hole got stuck, which leads the uneven distribution of material. Secondly, check if the heater tubes got stuck. Thirdly, check if the temperature difference between condenser inlet and outlet is too small.

2. The solution aimed at this problem is to check if vacuum got destroyed and if all the joints leak the vacuum.

3. The solution aimed at this problem is to check whether the circulation pumps are intact, and check whether there is air leakage in the pipeline in front of the pump, which causes cavitation of the pump.

4.  Under normal system evaporation, the amount of evaporation got reduced. The solution is to wash the car with 2% NaOH solution.

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