When ever 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 sea water collected in a blocks and allowed to observe heat from sun which make water to evaporate into the atmosphere and leaving out thick slurry of slat solution. Evaporation differs from distillation operation where evaporation is mainly considered for removing water from the solution, and vapor has no value when compared to the vapor generated during the distillation operation of a system.
Evaporation process merely depend on concentration of solution, it foaming, scale properties, the temperature sensitivity show direct effect on evaporation process.
The evaporators that handle evaporation are classified as
Based on effect
- single effect evaporator
- multiple effect evaporator
Based on circulation
- Natural circulation
- Long tube vertical falling film evaporator
- Long tube vertical climbing up evaporator
- Forced circulation
- Forced circulation evaporator with 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 take for completion of the operation. 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 few interesting methods to increase the capacity and economy or to obtain the optimized condition for particular system. A series of evaporators are connected in a stream which the outlet of first one become an inlet to the next so by doing this heat economy is increased. Their are four evaporator feeding methods.
- Forward feed
- Backward feed
- Mixed feed
- Parallel feed
Along with this a operation called vapor recompression is utilized for increase the economy of the evaporator and this have two types called
- Mechanical recompression
- Thermal recompression
PPT of Evaporation and Evaporators