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Evaporator system is used for batch or continuous concentration of solutions. The type of system selected depends on the product properties and capacities. Evaporator system is used singally or in combination with other systems like dryer, crystalisers, finishers.
The commonly used evaporation systems are named by the type of liquid flow pattern:-
Evaporators are offered as a complete packaged unit comprising of main evaporator calendries with vapour separators, transfer pumps, interconnecting pipe lines, upstream / downstream equipment, controls and instrumentation. Optionally accessories like cooling tower, boiler can also be supplied as an add on to the packaged unit. |
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| Forced Circulation |
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In this type of evaporator the feed to be concentrated is pumped through the heat exchanger tubes and heated to provide the energy required for evaporation. The preheated liquid is taken to the flash vapour separator where actually evaporation takes place. The concentrated liquid flows down to the re-circulating pump and gets further concentrated in a recirculation.
Evaporators are designed for a specified evaporation capacity depending upon the product characteristic and the capacity, multiple effect evaporator are energy efficient.
These are usually selected for the solutions which have a tendency to form crystals, scales or which may have high viscosity at high concentrations. This type of evaporator is also used when high temperature gradients are not permitted. The system can be designed to operate under pressure or vacuum. Forced Circulation evaporator is also used in a multisystem combining with falling film evaporators. |
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| Falling film |
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The feed to be concentrated is pumped to the top of the vertical calendria. The liquid is distributed across all the tubes and flows down as a thin film along the height of the tubes. The steam on the jacket side heats up the falling film evaporating the water.
These are usually selected for concentration of heat sensitive material and the material which do not have a tendency to form Crystals or highly viscous slurry or paste. The liquid temperature can also be maintained below at required temperature in this type of evaporator.
The plant can be designed to operate under vacuum to get the optimum utility economy. The evaporator system can be of multi stage calendria design. |
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| Scrapped Surface |
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Usually selected for products which are highly viscous or in paste / syrup forms products having a tendency to scale or salt out during evaporation can also be handled in this evaporator. The rotating blades of these evaporators ensure that no material stays on the heat transfer surface for long duration thus preventing thermal degradation.
The liquid flow can be bottom to top or top to bottom. This flow pattern depends on the fluid properties, chances of scale or crystal formation. This system can be used along with the falling film or forced circulation evaporators as last finisher stage. |
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