What Are Evaporators and What Are They For?

An evaporator is a heat exchanger designed whose purpose is to heat a given compound and separate water through evaporation.

Traditionally, evaporators are used in industrial processes. An example is the food sector, where water is eliminated from foods to increase the concentration of the solid part, obtain the desired taste and texture and increase shelf life. The pharmaceutical sector would be another example, especially where removing humidity makes the final product more chemically more stable.

Over the last years, evaporators started to be used also for energy production. In this case, after evaporation takes place, the steam is expanded in a turbine.

For the sectors where we mainly operate, such as food, chemical and petrochemical, we produce two main types of evaporators: vertical short tube and kettle.

How vertical short tube evaporators work

This type of evaporator, also called calandria or Robert, was the first one to be widely used in the industrial sector, and it’s still the most common today.

Inside a short tube evaporator, the bundle of tubes for the exchange of heat are enclosed in another steel cylinder (also called calandria), placed at the bottom part of the shell. Steam enters the cylinder and heats the tubes, which in turn will heat the compound where humidity has to be removed.

At the end of the evaporation cycle, the steam and the dehumidified compound will exit through the upper and bottom part respectively.

Calandra evaporators offer a few clear advantages:

  • They need less space
  • They can transfer large amounts of heat
  • They require a low initial investment

On the other hand, they are less efficient whenever there is a lot of difference of temperature between the tubes and the liquid to dehumidify or if this liquid has a high viscosity.

How kettle evaporators with immersed tubes work

The structure of Kettle evaporators resembles the one of the traditional shell-and-tube heat exchangers, with the addition of extra space where the evaporation process can take place.

These evaporators, also called "reboilers" are often employed at the base of distillation columns, to provide the initial heat that will initiate the whole process of separation.

An example of reboiler in our portfolio is the one we designed for a cumene and phenol plant built by Litwin in Leuna, Germany.