Evaporators

G.P MANDI ADAMPUR , HISAR

Copyright © 2014 Given to Diploma in food Technology

What is Evaporators ? EVAPORATION PROCESS:-Evaporation is a heating

process in which water is removed from the liquid substance.  The goal of evaporation is to vaporize most of the water from a solution which contains the desired product. Evaporators are widely used in the food processing industry to remove a portion of the water from food products. This reduces bulk and weight for subsequent processing, increases solids content (as for jams and molasses), helps in preservation of the product, provides convenience to the end consumer and concentrates color or flavor.

EXAMPLE OF EVAPORATION PROCESS

What is evaporators

Evaporators: - An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. The liquid is evaporated, or vaporized, into a gas. Many types of evaporators and many variations in processing techniques have been developed to various products.

Internal view of Evaporators PROCESS

Types Of Evaporators

The more common types of evaporators include:- 1. Batch pan Evaporators. 2. Forced circulation. 3. Natural circulation. 4. Rising film tubular. 5. Falling film tubular. 6. Rising/falling film tubular.

Batch pan EvaporatorsThe batch pan evaporator is one of the simplest and oldest types of evaporators used in food industry. Now-a-days it is outdated technology, but it still used in a few limited applications, such as the concentration of jams and jellies where whole fruit is present and in processing some pharmaceutical products. Up until the early 1960's, batch pan also enjoyed wide use in the concentration of corn syrups. In batch pan evaporator the product is heated in a steam jacketed spherical vessel. The heating vessel may be open to the atmosphere or connected to the condenser and vacuum. The heat transfer area per unit volume is in batch pan evaporator is small. Thus, the residence time normally is many hours. Therefore, it is essential to boil at low temperatures and high vacuum when a heat sensitive or thermo degradable product is involved.

Diagram of Batch pan Evaporators

Natural Circulation evaporators

In Natural Circulation evaporators, short vertical tubes, typically 1-2 m long and 50-100 mm in diameter, are arranged inside the tubes, and the product is concentrated. The concentrated liquid falls back to the base of the vessel through a central annular section. A shell-and-tube heat exchanger can be provided outside the main evaporation vessel to preheat the liquid feed. The most common application for this type of unit is as a reboiler at the base of a distillation column.

Example of Natural Circulation Evaporators

Forced Circulation Evaporator

The forced circulation evaporator was developed for processing liquors which are susceptible to scaling or crystallizing. Liquid is circulated at a high rate through the heat exchanger, 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

Example of Forced Circulation Evaporator

These are considered to be the first 'modern' evaporator used in the industry, the rising film unit dates back to the early 1900's. The rising film principle was developed commercially by using a vertical tube heated from the outside with steam. Liquid on the inside of the tube is brought to a boil, with the vapor generated forming a core in the center of the tube. As the fluid moves up the tube, more vapors are formed resulting in a higher central core velocity those forces the remaining liquid to the tube wall.

Rising-film Evaporators

Example of Rising-film Evaporators

The falling-film evaporators has a thin liquid film moving downward under gravity on the inside of the vertical tubes. The design of such evaporators is complicated by the fact that distribution of liquid in a uniform film flowing downward in a tube is more difficult to obtain than an upward-flow system such as in a rising- film evaporator. This is accomplished by the use of specially designed distribution or spray nozzles. The falling-film evaporators allow a greater number of effects then the rising-film evaporator. The falling-film evaporator can handle more viscous liquids than the rising film type. This type of evaporators is best suited for highly heat sensitive products such as orange juice

Falling-Film Evaporators

Falling-Film Evaporators

Rising/Falling Evaporator

In the rising/falling evaporator, the product is concentrated by circulation through a rising-film section followed by a falling-film section of the evaporator. The product is first concentrated as it ascends through a rising tube section, followed by preconcentrated product descending through a falling-film section, there it attains its final concentration.

Example of Rising/Falling Evaporator