What is Evaporator and Different Types of Evaporator used in Industry?

In Falling Film Evaporators the liquid flows downwards in the form of a film along with the vapors at the core in a parallel flow. The film mechanism and low residence time makes this evaporator ideally suited to heat sensitive non-salting and non-crystallizing solutions.

The liquid to be evaporated is initially pre heated to the boiling temperature and enters the heating tubes via distribution plates in the top bonnet of the evaporator.

In these evaporators sufficient wetting of the heating surface is very important for the heat economy and trouble free operation. The wetting rates can be increased by extending or splitting the individual evaporator effects.

Falling Film Evaporators can be particularly useful when the temperature difference between the liquid to be evaporated and the heating media is low.

Forced Circulation Evaporators are short tube evaporators and are ideally used when the boiling of feed liquid on the heating surfaces is to be avoided due to the salting and fouling characteristics of the liquid. Hence in these evaporators the flow velocity in the tubes is kept very high.

In these evaporators the liquid is circulated at high velocities in the tubes of the heat exchanger while steam is provided in the chest. This liquid is partially evaporated when the pressure is reduced in the vapor-liquid separator to the corresponding boiling temperature. High volume, low head axial flow circulation pumps are used for recirculating the crystal laden slurry in the evaporator and hence the operation of this evaporator is independent of the temperature difference. In the crystallizing operation crystals can be separated from the crystallizing slurry by adjusting the velocity of the circulating stream. These evaporators are ideal for handling liquors with high viscosity or which have a tendency to salt and scale during evaporation.

Batch evaporators are filled with the dilute material, heat is applied, and the material is gradually concentrated to the desired point by the application of heat and removal of vapors.

Additional dilute material might be added as the concentration occurs to replenish the evaporated liquid to a given level. Since each gallon of dilute material brings some solids with it into the evaporator, the evaporator eventually achieves the final solids concentration.

Scraped Surface Evaporator

This Evaporator Usually selected for products which are highly viscous or in paste / syrup forms products having a tendency to scale or salt out during evaporation can also be handled in this evaporator.

The rotating blades of these evaporators ensure that no material stays on the heat transfer surface for long duration thus preventing thermal degradation.

The liquid flow can be bottom to top or top to bottom. This flow pattern depends on the fluid properties, chances of scale or crystal formation. This system can be used along with the falling film or forced circulation evaporators as last finisher stage.