it is the slide gives information of the type of evaporators and their methods and of course their field of application ................

1. I N E V A P O R A T I O N P H Y S I C A L A N D C H E M I C A L
P R O P E R T I E S O F T H E S O L U T I O N B E I N G
C O N C E N T R A T E D
EVAPORATORS

2. Properties on which the evaporation
greatly depends
Concentration of the liquid : by time liquid becomes concentrated .heat
transfer coefficient becomes adequately low so the circulation or the turbulence
must be there to prevent the coefficient becomes sufficiently low
Solubility: by the variation in temperature effects the solubility of the
solution either .condensation of the liquid from cold liquid causes
crystallisation of the substance .effects the evaporation
Temperature sensitivity of the material : some material degrade due to prolong
heating
Foaming and frothing: foam and froth forms during boiling accompanies the
vapour coming out of the evaporator due to which entrainment loss occurs
Pressure and temperature :B.P. of the solution is related to pressure of the
system. The higher the operating pressure of the evaporator the higher the
temp at boiling . By increase in the concentration temperature of boiling may
rise
Scale deposition and material of construction : by these factors heat transfer
coefficient decreases causes the decrease in heat transfer.

3. Types of evaporators
1. Open kettle or pan
2. Horizontal type natural circular evaporation
3. Vertical type natural circulation evaporation
4. Long tube vertical type evaporator
5. Falling film type evaporator
6. Forced circulation type evaporator
7. Agitated film evaporator
8. Open pan solar evaporator

4. Open kettle or pan evaporator
Cheap and simple
Heat economy is poor
Paddles and scrappers
are used for agitation
Heat is supplied by
condensation of stream

5. Horizontal type natural circulation
evaporator
Similar heating tubes such in
heat exchangers are used
Vapour leaves the liquid
surface often goes through de
entrainment device such as
baffles are used to prevent
carryover of liq. Droplets
relatively cheap then the other
higher evaporator devices
Used for non viscous liquid
with heat transfer coefficient
(since circulation is poor )
Liquids that do not deposit on
the surfaces
Stream enters inside the tube
Not used for foamy liquids

6. Vertical type natural circulation
evaporator
Types are basket type(liquid
inside ) and standard
type(liquid outside )
Velocity :1-3 fps
Boiling increases de
Boiling increases density
liquid rises in the tube by
natural circulation and flows
downward through a large
central open space or
downcomer
Natural circulation increases
heat transfer coefficient
Not for viscous liquid
Also called as short tube
evaporator

7. long tube vertical type evaporator or
kestner evaporator
Heat transfer on stream side is
very high as compare to
evaporating liquid side so high
liquid velocities are desirable
Liquid run inside the tube
Length of 12-20 ft.
3-10 mm tubes
Formation of vapours inside the
tube causing pumping action
which gives quite high liquid
velocities
Not re circulated (contact time is
low )
Can be adapt for foamy liquids
Not for scaling and not for
liquids of high viscosity

8. Falling film type evaporator
Liquid is fed from top and
flow down as a thin film
Vapour liquid separation
usually takes place at the
bottom
Used widely for
concentrating heat
sensitive materials such as
orange juice and other fruit
juice
Holdup time is very small
(5-10)
High heat transfer
coefficient (due to high
velocities )

9. Forced circulation type evaporator
We use pump in film type
evaporator
Increase heat transfer coefficient
Useful for viscous fluid
External heating provide more
ease to cleaning to tubes more
complicated piping is used
For viscous we use positive
pumps and for colloidal we use
low power pumps
Heating element is placed at the
lower level to avoid boiling on
heating surface .this reduces the
rate of deposition of solids

10. Agitated film evaporator
Main resistance of the heat
transfer is on evaporator side
Heat transfer coefficient and
turbulence is increased by
mechanical agitation of this
liquid film
Modifying falling film evaporator
with a single large jacketed tube
containing internal agitator
Used for viscous fluids ,high
sensitive materials like rubber,
latex, gelatine, antibiotics and
fruit
Heat transfer coefficient
increases
High cost
Small capacity

11. Open pan solar evaporator
Low scale evaporation
Takes longer time
Cheap
Solar energy is used to
evaporate the water from
the solution

12. Method of operation of evaporation
Single effect evaporator
Forward feed multiple effect evaporator
Backward feed multiple effect evaporator
Parallel feed multiple effect evaporator
Mixed feed multiple effect evaporator

13. Single effect evaporator
Required capacity of operation is relatively small

14. Forward feed multiple effect evaporator
Feed should be near the B.P. of
the solution at the pressure in the
1st effect
Previous unit vapour serves as a
heating medium for the next
effect
Here latent of the vapour can be
reused and recovered again
Uses when feed is hot or when
the concentration product might
be damaged at high temperature
B.P decreases from effect to effect
Pressure is 1 atm at 1st effect and
under vaccum in other effects

15. Backward feed multiple effect evaporator
Uses when fresh feed is
cold
Flows from low to high
pressure for this to happen
we apply pumps at certain
places
Temperature increases
from effect to effect
Used when concentrated
product is highly viscous
High temperature and low
viscosity gives high heat
transfer coefficient

16. Parallel multiple effect evaporator
Adding and withdrawal
of concentrated product
from each effect
Feed almost saturated
and solid crystals are the
product
Eg- evaporation of brine
to make salt

17. Mixed multiple effect evaporator
When feed moves
forward with fresh feed is
entering at the 2nd or 3rd
effect k/a mixed type
Used in solutions having
considerable change in
viscosity with
temperature over
concentration range

18. Effects of processing variables on
evaporator
Effect of temperature : feed must be at temp greater or
equal to the b.p of the solution . Preheating the feed can
reduce the size of evaporator heat transfer area
Effect of pressure : a pressure of 101.32 kpa is used in the
vapour space which gives the b.p of the feed .if the rise in
temperature increases .means large difference in
temperature is desirable heating surface area and the
cost of the evaporator decreases .if pressure decreases
under vaccum condenser and pump are used
Effect of stream pressure :with increase in pressure of
the saturated stream difference in b.p of increases giving
small size and hence cost decreases

19. M A D E B Y : S H I K H A T H A P A
C O L L E G E N A M E : I N S T I T U T E O F T E C H N O L O G Y
G U R U G H A S I D A S C E N T R A L U N I V E R S I T Y
S T U D E N T O F C H E M I C A L E N G I N E E R I N G
S E M E S T E R : 5 T H
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