Evaporation is a process used in the food industry to remove water from raw materials or foodstuffs to produce a more concentrated final product. It involves heating a liquid to vaporize its water content. Some key points: - Evaporation is used extensively in concentrating fruit and vegetable juices, milk, coffee extracts and in refining sugar and salt. - It reduces the weight, volume, storage and transportation costs of products while improving storage stability. - Multiple effect evaporators are more energy efficient as they use steam from one chamber to heat the next, allowing more water to be evaporated with the same amount of steam. - Food quality must be maintained during evaporation to minimize losses of nutrients

1. EVAPORATION
Mamta Sahurkar

2. • 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.
Introduction

3.  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.
Evaporation

5. DIFFERENCE BETWEEN EVAPORATION AND
VAPORIZATION

6. DIFFERENCE BETWEEN DRYING AND EVAPORIZATION

7. • Reduces transportation cost
• Storage costs
• Prepare for the next Unit operation –
drying, crystallisation etc.
• Reduces deteriorative chemical reactions
• Better microbiological stability
• Recovery of solvent
Why we need evaporation???

8. • 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.
Factors Affecting Evaporation

9. • 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

10. • 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.
Evaporator

11. Basic Parts of an Evaporator
• Heat-exchanger
• Vacuum
• Vapour separator
• Condenser

13. SELECTION OF EVAPORATOR
• 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.

14. • 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.

15. Energy Saving Evaporation Systems.
• Single effect evaporators
• Multiple effect evaporators
• Vapor Recompression Evaporators

16. • 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.
The single effect evaporator

17. • 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.

18. • 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.
MECHANISM

19. • 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.

20. • 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.
Multiple effect evaporator

22. FEEDING OPERATIONS
There are two feed operations - backward feed and forward feed operations.
Backward operation

23. • 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.

24. 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.

25. Chemical Industry
Dyes, Pickle Liquor, Plating
bath, Salt, Glycerin, Sodium
Nitrate, Sodium Sulphate,
Paints, Pigments.
Corn Industry
Whey, Gelatin, Malt Extract,
Glucose, Fructose, Dextrose,
Corn Steep Liquor, Sorbitol,
Maltodextrin.
Waste Water Treatment
Blow Down, RO reject, Floor
washings, Process effluents,
Black Liquor, Fish Sick Water.
Food Industry
Milk, Fruit Juice, Pulps, Tomato
Puree, Herbal Extracts, Coffee, Tea,
Protein, Gelatin, Coconut Water.
Pharmaceutical Industry
Bulk drugs, Glycerin, Sweet
water, Yeast
Extract, Protein
Hydrolysate
APPLICATIONS

26. • 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.
Food quality consideration

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