The document discusses evaporation in the sugar industry. It explains that evaporation is used to concentrate sugarcane juice by boiling off water in a series of connected evaporator vessels under decreasing pressure. This produces a thick juice containing around 60% sugar that is then crystallized to produce sugar. The process of evaporation increases the boiling point of the sugarcane solution compared to water alone. Various factors that affect evaporation like concentration, foaming, temperature sensitivity, and scale formation are also discussed.

1. SUGAR TECHNOLOGY
CHEMISTRY OF EVAPORATION
BY
KAVYA PRIYA V,
18 06 023,
B.TECH CHEMICAL(III YR),
CIT.

2. IMAGINE…
Take some amount of salt
solution in a kettle and cover it
with a lid.
Gently heat the kettle for
sometime.
What happens now?

3. • Heating transforms the water into
vapour that escapes from the spout
of kettle.
• Now continue heating till all the
water gets converted into vapour.
• Only salt will be left behind in the
kettle.
• So the salt dissolved in water can
be separated from the water
through this process. This process
is known as EVAPORATION.

4. EVAPORATION
▪ EVAPORATION ordinarily
means vaporization of a liquid
or that of a solvent from a
solution.
▪ Examples: water evaporates
from river, cane-sugar juice is
evaporated to concentrate
sugar.

5. DEFINITION
 In chemical engineering terminology,
EVAPORATION means removal of a part of the
solvent from a solution of a non-volatile solute by
vaporization.
 (Here ‘non-volatile’ means the solute has negligible
volatility when compared to the solvent)
▪ Typical examples are : concentration of ammonium
sulphate in a fertilizer plant, concentration of cane-
sugar juice in a sugar plant.

6. • Evaporation happens when particles at the surface
of a liquid gain enough kinetic energy to break
their liquid bonds and escape as a gas.
• Evaporation causes cooling because the process
requires heat energy.
• In the case of change of phase from liquid to gas,
molecules of matter require energy to overcome
their potential energy by their kinetic energy. So,
the liquid takes this energy from its surroundings.
The energy is taken away by the molecules when
they convert from liquid into gas, and this causes
cooling on the original surface.

7. EVAPORATION ANIMATION

8. Why Evaporation?
▪ In Sugar Industry, the clarified juice
is evaporated to make it
supersaturated, because crystals grow
only in the supersaturated solution.
▪ Thus Evaporation of a solution is an
essential step in the operation of a
‘CRYSTALLIZATION’ unit.

9. • The sugar mill evaporator is a set of large standing
cylindrical vessels, where thin juice evaporates in
five successive stages.
• This extraordinary, smart and very ancient method
ensures that using one ton of steam, as much as
five tons of water evaporates from the juice.
• So-called thick juice leaves the evaporator, from
which sugar is made, while evaporated water
leaves the separate evaporator vessels in the form
of several kinds of steam of various pressures and
temperatures.
• These steams are then utilised for the heating of
juices in the cleaning process and also for boiling.
This multiple utilisation of steam is very efficient.

10. • The purified juice is a sugar solution
containing approximately 14% sugar and 1%
non-sugars.
• It is now necessary that this solution is
thickened up into a syrup by boiling off
excess water in a series of connected vessels.
• Under automatically controlled conditions in
the evaporator station, each subsequent vessel
operates under decreasing pressure with the
last one being under almost a total vacuum.
• This "thick juice" leaving the evaporator
section contains approximately 60% sugar.

11. Evaporationvideo

12. Two Content Layout with SmartArt

13. DIFFERENCE BETWEEN
DRYING AND EVAPORATION

14. DIFFERENCE BETWEEN
BOILING AND EVAPORATION

16. BOILING POINT ELEVATION
• The vapour pressure of aqueous solutions is less than that of
water at the same temperature.
• Consequently for a given pressure the boiling point of the
solutions is higher than that of pure water.
• Liquids that contain dissolved substances have increased
boiling points. This effect is called boiling point elevation,
and it's an example of a colligative property -- a property
that depends on the number of solute and solvent molecules
but not the identity of the solute.

17. • It is small for dilute solutions and for solutions of organic
colloids but may be as large as 80 degree Celsius for
concentrated solutions of ORGANIC SOLIDS.
• Boiling point elevation causes the boiling point of the solution
to increase and hence the temperature now required to
evaporate water also increases, thus the driving force
decreases.
• If the temperature cannot be increased to the maximum,
considering sensitivity of feed, the only option we have is to
reduce pressure as it would bring down the boiling point of the
feed.

18. LIQUID CHARACTERISTICS
The evaporation is greatly affected by character of liquor to
be concentrated. It is due to wide variation in liquor
characteristics that broadens this operation from a simple
heat transfer to a tedious process.
Some of the most important properties of evaporating
liquids are :
• Concentration
• Foaming
• Temperature sensitivity
• Scale

19. CONCENTRATION
• The boiling point of the solution may also rise considerably as the
solid content increases, so that the boiling temperature of a
concentrated solution may be much higher than that of water at the
same pressure.
• Continued boiling of a saturated solution causes crystals to form;
these must be removed or the tubes will clog.
• Some solutions deposit scale on the heating surface. The Overall
Coefficient of heat transfer then steadily diminishes, until the
operator shuts down and the tubes are cleaned.
• When the scale is hard and insoluble, the cleaning is difficult and
expensive.
SCALE

20. Some materials, especially organic substances, foam during vaporization. A
stable foam accompanies the vapour out of the evaporator, causing heavy
entertainment.
In extreme cases the entire mass of liquid may boil over into the vapour
outlet and be lost.
Many fine chemicals, Pharmaceutical products and foods are damaged
when heated to moderate temperatures for relatively short times. In
concentrating such materials special techniques are needed to reduce both
the temperature of the liquid and the time of heating.
TEMPERATURE SENSITIVITY
FOAMING

21. • The boiling point elevation of a thick liquor must be known before the
calculations for evaporator design are done, because the BPE reduces the
driving force compared to the case of boiling the pure solvent.
• The boiling point of a solution can be calculated only if the activity
coefficient of the solvent and the fugacity coefficient of the vapour are
known. It is difficult to theoretically calculate the BPE of concentrated
solutions. However in many practical situations only a limited volume of
boiling point data are available.
• The best use of this data can be made by taking help of an empirical rule
called the 'Duhring rule’. The rule states that the boiling point of a solution
of given concentration is a linear function of the boiling point of water.
DUHRING’S RULE

22. • So if we plot the boiling points of the solution at several pressure against
the corresponding boiling points of pure water, we will get a straight
line. A set of straight lines will be obtained if such plots are made for
solutions of different concentrations.
• However the lines are not parallel the slope being larger at a high
concentration. The rule works good over moderate ranges of pressures,
but does not give satisfactory correlation at a high pressure. Nevertheless
it is a practically useful rule.
• The main advantage is that when the boiling point of a solution at two
different pressures are known and the corresponding boiling points of
water are read from the steam tables, a 'Duhring line' through the points
can be drawn. This line can be used to predict the boiling point of a
solution at any other pressure.