In a wiped film evaporator highly viscous and sticky products are processed. In a roto film evaporator viscous liquid can be concentrated by forming a thin film of the liquid, which the rotor scrapes away as evaporation occurs. A portion of vapor discharged from one effect is compressed by direct steam injection and the resulting mixture is used as the heating medium to bring down the specific steam consumption. The liquid is superheated as the static head is reduced during flow from the heater to the vapor separator and it flashes into a mixture of vapor and liquid. Liquid returns to the pump inlet where it is re-circulated.
Vapor leaves the top of the evaporator.
This type of evaporator is ideal for concentration of viscous liquids with high specific gravity or liquids that tend to form scaling. In a rising film evaporator liquid feed enters the bottom of the steam-heated tubes. The parallel movement of liquid and vapor along the tube surface causes effective water evaporation from the liquid feed. This type of evaporator is ideal for liquids, which attain high viscosity or have a fouling tendency. Combination Evaporator For products, which attain high viscosity during the concentration process, combination evaporators such as the falling film, followed by rising film, scraped surface, etc., are used.