Evaporators-

Evaporators are used for reducing product volume, remove water prior to drying, and to improve product storage life. 

Evaporation is a highly energy-efficient way of removing water or other liquids and thus the primary process for the production of concentrates. Process time can be shortened by distributing the liquid to a greater surface area, or by using a higher temperature. Higher temperatures combined with longer residence times can, however, cause degrading of many foodstuffs.

Types of Evaporators-

Falling Film Tubular Evaporators

The Falling Film Tubular Evaporator consists of one or more vertical tubular heat exchangers with vapor separator, condenser and pumps.

Process
Evaporation takes place under vacuum, atmospheric pressure, positive, or a combination depending on product heat sensitivity and viscosity. Usually, vacuum is involved.
The process liquor to be evaporated is distributed uniformly as a film along the inside of the heat exchanger tubes. Steam (or vapor) is applied on the heating media side of the tubes in an amount suitable for the required evaporation.
Heat is transferred through the tube wall to the liquor, which starts boiling at a temperature corresponding to the pressure inside the tubes.
The concentrate and vapor flow from the bottom of the tubes to a separator, where they are separated. The concentrate is pumped out from the bottom of the separator, while vapor is condensed in a condenser or in the next stage.

 

Forced Circulation Evaporators

The Forced Circulation evaporator is designed for evaporation of liquids with a high solids content, high viscosity, tendency to foul, and also for crystallizers.

Process-
The system is often used as a finishing evaporator for concentration of liquids to a high solids content following a low solids multistage evaporator.
Boiling in the Forced Circulation evaporator is suppressed in the heat exchanger by back pressure and takes place when the liquid enters the lower pressing separator champer.

Applications
Typical applications include processes for salt, still-age, corn steep water, Calcium carbonate and crystallizing evaporators.

Gas Heated Evaporators

Gas heated evaporators achieve extremely high energy-efficiency by tapping the energy contained in off-gasses from existing plant operations instead of using steam. 

Process
In many cases off-gasses from existing plant operations such as dryers or scrubbers contain valuable energy which may be recovered as the energy source for gas heated evaporators.
Gas-heated evaporators consume considerably less energy than steam heated or mechanically driven alternatives. They also enable additional evaporative capacity without increasing energy costs.

Applications
Proven for more than 20 years in corn wet milling and alcohol processing, the gas-heated evaporator also has high potential for distilling, brewery operations and pharmaceutical production involving high volume fermentation processes.

Natural Circulation Evaporators

Natural circulation evaporators utilize vertical tubes which operate by the thermo siphon principle. 
ProcessThe density difference between the boiling liquor and the circulating liquor produces the driving force for liquid circulation.  In operation, feed enters the lower liquor chamber. As it travels up the tubes and reaches boiling point, vapor forms and carries liquor to the separator. 
Most installations require liquor recirculation. When feed quantities are sufficient, however, single pass operation is utilized.

ApplicationsTypical applications include anhydrous caustic, beet sugar, foamy liquors, low or moderately viscous liquors and precipitating liquids.

Recirculated Falling Film Evaporators

Recirculated falling film evaporators are used where insufficient feed liquor is available to utilize the heat transfer surface with single pass operation.

Process
A portion of the product liquor is combined with the feed stream and is pumped to the upper liquor chamber.  Product retention time is greater than for the single pass F.F. evaporator but is relatively short as the operating volume is small.

Applications
Typical applications include many moderately heat sensitive food, pharmaceutical and chemical applications.

 

Single Pass Falling Film Evaporators

Single pass falling film evaporators assure controlled retention time operation while avoiding internal recirculation. 

ProcessFeed liquor enters the upper liquor chamber where it is distributed to the tubes.  As the liquor travels down the tubes, a portion is vaporized.  The remaining liquor and vapor discharge from the bottom of the tubes. 
The liquor being processed is in contact with the heating surface for only a short time. Single pass operation also results in small operating volumes allowing start up and shutdown to be performed quickly.

Applications
Typical applications are concentration of dairy products, sugars and syrups, fruit juices, ammonium nitrate, pharmaceuticals and other heat sensitive materials.