Forced circulation type evaporators are ideally suited for highly viscous liquids or liquids containing suspended solids. The liquid to be evaporated is heated in tubular heater at large circulation volumes to obtain high liquid velocities. Evaporation takes place in a separator as the product is flashed down to its operating pressure.
The forced circulation evaporator sometimes used as a finishing stage of multiple effect evaporators, or for products with high boiling point elevations. Because of the high velocities in the finisher, scaling is kept to a minimum, therefore it can be used as a crystallizing evaporator.
Salient Features of Forced Recirculation evaporator
- Liquid circulated at high rate through the calandria.
- Higher coefficients are obtained.
- Boiling being prevented within the unit by virtue of a hydrostatic head maintained above the top tube plate. As the liquid enters the separator where the absolute pressure is slightly less than in the tube bundle, the liquid flashes to form a vapor.
- Since the velocity of flashing is very high, impingement deflector/ baffles are important to minimize entrainment.
- Liquid returns to the pump inlet from Vapor separator and meets incoming feed, vapor leave the top of evaporator body to a condenser, part of the liquid leaving the separator is continuously withdrawn as concentrate.
- Require large circulating pumps.
- The concentration level can be achieved upto 65 % TS.
- Useful for concentration of inversely soluble material or for material which is susceptible to scaling or crystallizing like distillery effluent, mango/tomato juice, Malt concentrate (70% TS).
- Malt mix slurry
- Tomato paste
- Mango pulp paste
- Sugar Syrup
- Black liquor
- Distillery effluent
- The concentrate upto 70% TS.