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.
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
Types Of Evaporators
The more common types of evaporators
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 Evaporators
The 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outdated technology, but it still used in a few limited applications,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.
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.
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
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.
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
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