TYPES OF EVAPORATOR

Types of Evaporator

Single effect evaporator

When a single evaporator is used, the vapor from the boiling liquid is condensed and discarded. This method is called single effect evaporation, and although it is simple, it utilizes steam ineffectively.

• The solution to be concentrated flows inside the tubes. 
• The heating medium is steam condensing on metal tubes. 
• Usually boiling liquid is enter under a moderate vacuum.
• This increases the temperature difference between the steam and boiling liquid.

Multiple effect evaporator

Increasing the evaporation per kilogram of steam by using a series of evaporators between the steam supply and the condenser is called multiple effect evaporator

• If vapor from one evaporator is fed into the steam chest of the second evaporator and the vapor from second is then sent to a condenser, the operation becomes the double effect. 
• The heat in the original steam is reused in the second effect, and the evaporation is achieved by a unit mass of steam in the same manner.

Once through evaporator

• In once-through evaporation, the feed liquor passes through the tube only once, releases the vapor, and leaves the unit as thick liquor. 
• All the evaporation is accomplished in a single pass. 
• The ratio of evaporation to feed is limited in single pass units: the evaporators are well adopted to multiple effect operation, where the total amount of operation can be spread over several effects. 
• Agitated film evaporators are always operated once- through  falling film and climbing film evaporators can also be operated in this way. 
• Once through evaporators are specially useful for heat-sensitive materials. 

Circulation evaporators

• In circulation evaporators a pool of liquid is held within the equipment. 
• Incoming feed mixes with the liquid from the pool, and the mixture passes through the tubes. 
• Unevaporated liquid discharged from the tubes returns to the pool so that only part of the total evaporation occurs in one pass. 
• All forced circulation evaporators are operated in this way; climbing- film evaporators are usually circulation units.
• These are adapted to single-effect evaporation. 
• These are not suited for heat-sensitive materials.