Evaporation and Evaporators

Whenever a dilute solution is made to a concentrated solution by application of heat energy than this type of operation is considered to evaporation process. These operations are conducted in evaporators, you can understand this by observing the seawater collected in blocks and allowed to observe heat from the sun which makes water to evaporate into the atmosphere and leaving out a thick slurry of salt solution. Evaporation differs from distillation operation where evaporation is mainly considered for removing water from the solution, and vapour has no value when compared to the vapour generated during the distillation operation of a system.

Evaporation process merely depends on the concentration of the solution, it foaming, scale properties, the temperature sensitivity show the direct effect on evaporation process.

The evaporators that handle evaporation are classified as

Based on effect

  1. single effect evaporator
  2. multiple effect evaporator

Based on circulation

  • Natural circulation
    • Long tube vertical falling film evaporator
    • Long tube vertical climbing up the evaporator
  • Forced circulation
    • Forced circulation evaporator with the horizontal heating element
    • Forced circulation evaporator with vertical heating elements

Agitated film evaporator

Performance of evaporator is calculated based on Capacity and Economy functions. where capacity is the ratio of the amount of water vapor evaporated during the operation to the time taken for completion of the operation. The economy is given by the ratio of the amount of water vapor in weight evaporated from the evaporator to the total amount of steam in weight consumed for completion of the operation.

Their quite a few interesting methods to increase the capacity and economy or to obtain the optimized condition for the particular system. A series of evaporators are connected in a stream which the outlet of the first one become an inlet to the next so by doing this heat economy is increased. There are four evaporator feeding methods.

  1. Forward feed
  2. Backward feed
  3. Mixed feed
  4. Parallel feed

Along with this an operation called vapor recompression is utilized to increase the economy of the evaporator and thus have two types called

  1. Mechanical recompression
  2. Thermal recompression

PPT of Evaporation and Evaporators