EVAPORATION

Delivered By: Hafiz Miqdad Masood

 Introduction

• Frequently in the food industry a raw material or a potential

foodstuff contains more water than is required in the final
product.

•When the food stuff is liquid, the easiest method of removing

the water, in general, is to apply heat to evaporate it.

•Evaporation is thus a process which is often used by food

technologist.
 Evaporation

 Evaporation is a physical separation process, which removes a

volatile component from a liquid solution or mixture by
vaporization, obtaining a concentrated product of the
nonvolatile components.

 For liquid foods, evaporation removes most of water resulting

in concentrated product which may be used as such or
processed further, e.g., by drying.

 Evaporation is used extensively in concentrating fruit and

vegetables juices, milk, coffee extracts and in refining sugar
and salt.

 Reduction of the water content reduces weight and volume of

the product, cutting storage and transportation costs, and
improving the storage stability of the product.
 DIFFERENCE BETWEEN EVAPORATION AND
VAPORIZATION
DIFFERENCE BETWEEN DRYING AND EVAPORIZATION
Why we need evaporation???

• Reduces transportation cost

• Storage costs
• Prepare for the next Unit operation –
drying, crystallisation etc.
• Reduces deteriorative chemical reactions
• Better microbiological stability
• Recovery of solvent
 Factors Affecting Evaporation
• Temperature:-
The rate of evaporation is directly proportional to the rate of
temperature. Higher the temperature higher will be rate of
evaporation but evaporation is maximum at boiling point of the
liquid.

• Surface Area:-
The rate of evaporation is directly proportional to the surface area of
the vessel exposed to evaporation. Greater the surface exposed to
evaporation higher will be rate of evaporation.

• Agitation:-
During evaporation the upper layer of liquid to be evaporated has a
tendency to form a scum or layer which lowers the rate of
evaporation. Therefore it becomes necessary to agitate or stirrer the
solution under evaporation. This will also prevent the decomposition
of product at the bottom due to excessive heat and will also prevent
the settling of solids at the bottom of container.
 Evaporator

• The equipment used to remove water from the food

product is called evaporator.

• Evaporators are used to separate materials based on

differences in their boiling temperatures.

• Its purpose is to concentrate nonvolatile solutes such

as organic compounds, inorganic salts, acids or bases.

• Typical solutes include phosphoric acid, caustic soda,

sodium chloride, sodium sulfate, gelatin, syrups and
urea.
 Evaporator

• An evaporator is used to evaporate a volatile solvent,

usually water, from a solution. Its purpose is to concentrate
non-volatile solutes such as organic compounds, inorganic
salts, acids or bases.

• Typical solutes include phosphoric acid, caustic soda,

sodium chloride, sodium sulphate, gelatin, syrups and urea.

• In many applications, evaporation results in the

precipitation of solutes in the form of crystals, which are
usually separated from the solution with cyclones, settlers,
wash columns, elutriating legs, filters or centrifuges.

• Examples of precipitates are sodium chloride, sodium

sulfate, sodium carbonate and calcium sulphate.

• The desired product can be the concentrated solution, the

precipitated solids, or both.
Basic Parts of an Evaporator

• Heat-exchanger
• Vacuum
• Vapour separator
• Condenser
 SELECTION OFEVAPORATOR

• Type of Product required

The selection of method and apparatus to be used for evaporation depends
upon the type of product required and product characteristics, including
heat sensitivity, viscosity and flow properties, foaming tendency, fouling
and precipitation, boiling behavior etc.

• Economic Factors
While selecting the method and apparatus employed for evaporation, due
consideration must be given to economy of labour, fuel, floor area and
materials. The recovery of solvents and the utilization of ‘waste’ heat are
also important factors which contribute significantly in the reduction of
overall costs.
• Capacity and operational data, including quantities,
concentrations, temperatures, annual operating hours,
change of product etc.

• Required operating media, such as steam, cooling water,

electric power, cleaning agents, spare parts, etc.

• Standards and conditions for manufacture delivery,

acceptance, etc.

• Site conditions, such as available space, climate (for

outdoor sites), connections for energy and product, service
platforms, etc.
Energy Saving Evaporation Systems.

•Single effect evaporators

•Multiple effect evaporators
•Vapor Recompression Evaporators
 The single effect evaporator

•The typical evaporator is made up of three

functional sections:

•The heat exchanger

•The evaporating section – where liquid boils

and evaporates

•Separator– in which vapor leaves the liquid

and passes off to the condenser or the other
equipment.

•In many evaporators all these three sections

are contained in a single vertical cylinder.
• In the centre of cylinder there is steam heating section, with pipes
passing through it in which the evaporating liquors rise.

• At the top of the cylinder the baffles which allow the vapors to
escape but check liquid droplets which may accompany the
vapors from the liquid surface this type of evaporator which may
be called conventional evaporator.

• In the centre of cylinder there is steam heating section, with pipes

passing through it in which the evaporating liquors rise.

•At the top of the cylinder the baffles which allow the
vapors to escape but check liquid droplets which may accompany
the vapors from the liquid surface this type of evaporator which may
be called conventional evaporator.
 MECHANISM

• In the heat exchanger section, called a calendria

in this type of evaporator, steam condenses in
the jacket and the liquid being evaporated boils
on the inside of the tubes and in the space above
the upper tube plate.

• The circulation of liquids greatly affects

evaporation rates but circulation rates and
pattern are very difficult to predict in any detail.

• As evaporations proceeds the remaining liquors

become more concentrated and because of this
the boiling temperature rise.
• The rise in temperature of boiling reduces the
available temperature drop, assuming no change in the
heat source. And so the total rate of heat transfer will
drop accordingly.

• Also the viscosity of liquid will increase, often quite

substantially, this affects circulations and heat transfer
coefficients leading again to lower rates of boiling.
 Multiple effect evaporator

•Multi-Effect Evaporation is an important procedure

adopted to economize the consumption of energy.

•Multi effect evaporation system is based on the

repeated use of the water vapors from one
evaporation unit (effect) to heat the next effect,
which operates at a lower pressure.

•Thus, 1kg of steam can evaporate more water,

depending on the number of effects and the
operating pressures.
 FEEDING OPERATIONS

There are two feed operations - backward feed and forward feed operations.

Backward operation
• In the backward operation, the raw feed enters the last (coldest)
effect and the discharge from this effect becomes a feed for the
next to last effect.

• This technique of evaporations is advantageous, in case the feed

is cold, as much less liquid must be heated to the higher
temperature existing in the early effects.

• The procedure is also used if the product is viscous and high

temperatures are required to keep the viscosity low enough to
produce good heat transfer coefficients.
 Forward operation

In the case of a forward feed operation, the raw feed is introduced

in the first effect and is passed from effect to effect parallel to
steam flow. The product is withdrawn from the last effect. This
procedure is highly advantageous if the feed is hot. The method is
also used if the concentrated product may be damaged or may
deposit scale at high temperature.
Chemical Industry Food Industry

Dyes, Pickle Liquor, Plating Milk, Fruit Juice, Pulps, Tomato

bath, Salt, Glycerin, Sodium Puree, Herbal Extracts, Coffee, Tea,
Nitrate, Sodium Sulphate, Protein, Gelatin, Coconut Water.
Paints, Pigments.

Corn Industry Pharmaceutical Industry

Bulk drugs, Glycerin, Sweet
Whey, Gelatin, Malt Extract, water, Yeast
Glucose, Fructose, Dextrose, Extract, Protein
Corn Steep Liquor, Sorbitol, Hydrolysate
Maltodextrin.

Waste Water Treatment APPLICATIONS

Blow Down, RO reject, Floor
washings, Process effluents,
Black Liquor, Fish Sick Water.
 Food quality consideration

• Evaporation should minimize the undesirable changes

in quality and nutritive value of heat sensitive food
materials.

• Such changes are losses of organoleptic quality( flavor,

aroma, and color), losses of vitamins, and production
of undesirable compounds( browning,
Caramelization).

• Losses of aroma components during evaporation of

fruit juices and aqueous extracts can be restored by
aroma recovery in the distillate or add-back of fresh
juice.