A multiple-effect evaporator, as defined in chemical engineering, is an apparatus for efficiently using the heat from steam to evaporate water.[1] In a multiple-effect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last. Because the boiling temperature of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel (at the highest pressure) requires an external source of heat. While in theory, evaporators may be built with an arbitrarily large number of stages, evaporators with more than four stages are rarely practical except in systems where the liquor is the desired product such as in chemical recovery systems where up to seven effects are used. The multiple-effect evaporator was invented by an African-American inventor and engineer Norbert Rillieux. Although he may have designed the apparatus during the 1820s and constructed a prototype in 1834, he did not build the first industrially practical evaporator until 1845. Originally designed for concentrating sugar in sugar cane juice, it has since become widely used in all industrial applications where large volumes of water must be evaporated, such as salt production and water desalination. Multiple effect evaporation commonly uses sensible heat in the condensate to preheat liquor to be flashed. In practice the design liquid flow paths can be somewhat complicated in order to extract the most recoverable heat and to obtain the highest evaporation rates from the equipment. Multiple-effect evaporation plants in sugar beet factories have up to eight effects. Six effect evaporators are common in the recovery of black liquor in the kraft process for making wood pulp.

1. Presented By – Sumer Pankaj
Class – M.Sc. EST
Semester – 3rd
Roll no. - 41
Institute of Science and Technology for Advanced Studies and Research
Affiliated to Sardar Patel University Recognized under section 2(f) and 12 (B) of
UGC act 1956 Mota Bazaar, Vallabh Vidyanagar, Anand, Gujarat 38812058
PG Department of Environmental Science and Technology

2.  What are Evaporators
 Basic mechanism of evaporators
 Principle of Evaporators
 Application of Evaporators in Industrial sector
 Application of evaporators
 Factors to be taken care of
 Types of Evaporators
 Single Effective Evaporates (SEE)
 Multiple Effective Evaporator (MEE)
 Mechanism of MEE
 Construction of MEE
 Working of MEE
 Efficiency of MEE
 Types of MEE
 Advantages of MEE
 Cost reduction in MEE plants
 Criteria for selection of MEE plant
 Checklist for designing and operation of MEE plant
 Construction material of MEE plants in various industries
 Safety measures during designing of MEE plan

3.  Equipment used in evaporation, the process of boiling a liquid in
order to get a concentrated solution or in to recover maximum
percentage of water.
 Driving force:
Temperature difference in between steam chest temperature and product
temperature.
 Result :
Volatile solvent is removed from the feed.
Feed = Solution (volatile solvent + non volatile solute)
Concentrate (Higher solute Conc.)

4. Vapour out
Feed in
Steam in
(Saturated vapour)
Product out
Condensate out
(Saturated Liquid)
Vapor
Separator
Heat Exchanger
Condenser unit
Vacuum for non
condensable
Coolant In
Coolant out

5.  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, gelatine,
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.

6.  Concentration of milk to produce condensed milk
 Concentration of juices
 Concentration of NaOH, NaCl from aqueous solutions
to produce salt.
 Ether recovery from fat extraction

7. Heat-
exchanger
Vacuum
Vapour
separator
Condenser

8.  Concentration of solute in feed.
 Concentration of solute in product/concentrate.
 Pressure and Temp. of the system
▪ Depends on temperature sensitivity of material.
▪ Boiling point elevation
 Steam pressure and temperature
 Material of construction
 Foaming
 Low heat transfer rate
 Entrainment loss
In the U.S. MEE plant

9. Types of
Evaporators
Open kettle
or pan Single
Effective
evaporator
Multiple
Effective
evaporator
Horizontal
type natural
circular
evaporation
Vertical
type natural
circulation
evaporation
Long tube
vertical type
evaporator
Falling film
type
evaporator
Forced
circulation
type
evaporator
Agitated
film
evaporator
Open pan
solar
evaporator

10. Feed water Vaporised
tank feed water
Tank Volume out to
0.92 litre/cm atmosphere
Overflow
to drain Water
main
Steam in
Constant
level Sight
device glass
Steam
trap
Condensate
out
Condensate
tank
Tank Volume
1.31 litre/cm
Figure 1. The Evaporator

11.  A multiple-effect evaporator, as defined in chemical engineering,
is an apparatus for efficiently using the heat from steam to
evaporate water.
 Water is boiled in a sequence of vessels, each held at a lower
pressure than the last.
 Because the boiling point of water decreases as pressure decreases,
the vapour boiled off in one vessel can be used to heat the next
 Generally the first vessel (at the highest pressure) requires an
external source of heat
 Multiple Effect Evaporation remains one of the popular methods
used for the concentration of aqueous solutions. Water is removed
from a solution by boiling the liquor in an evaporator and
withdrawing the vapour.

12. Pre-heating of a solution prior to evaporation – The
feed solution is brought to its respective boiling point
before feeding it into the MEE plant.
Removal of water (solvent) as vapour by steam
heating - steam injected in the steam chest jacket
gives an efficient heating to the feed solution by
transferring its heat, hence the vapour of solvent rises
due to temperature difference.
Condensing the vapour removed – ones the vapour
is separated from the fees then a cold inlet in given to
condense the vapours and the clean solvent is
collected.

13.  A multiple effect evaporator system for concentrating a process liquid
comprises:
(a) a plurality of evaporator effects arranged in series, each effect including a
process liquid inlet and a process liquid outlet; a heating fluid inlet and heating
fluid outlet;
(b) heat exchange means in each effect for passing said process liquid in heat
exchange relationship with heating fluid for evaporating water out of said
process liquid; and wherein evaporated water from one effect serves as heating
fluid for an adjacent effect; and
(c) an evaporative condenser provided with liquid inlet means for receiving
process liquid from one of said evaporator effects, and liquid outlet means for
transmitting said process liquid to another of said evaporator effects; and means
for receiving heating fluid vapor and for passing said heating fluid vapor in heat
exchange relationship with cooled process liquid in a cooling circuit, for
condensing said heating fluid vapor.

14. Thermal recompression
unit
Steam for
heating
Feed in
Calandria
Feed out
Vapor Separator
Pre-heater
Condenser
Cooling water in
Cooling water return

15.  Multiple effect evaporator Due to heat transfer, the liquid
temperature increases & reaches the B.P. during this process,
vapor well be generated from the liquid feed.
 So, formed vapor displaces air in the upper part of 1st
evaporator.
 Moreover, the vapor also displaces the air in the steam space of
the 2nd evaporator.
 After complete displacement of air by vapor in the steam
compartment of 2nd evaporator, the second
 valve is closed.
 The vapor of 1st evaporator transmits its heat to the liquid of
2nd evaporator & gets condensed.
 Condensate is removed through the second condensate valve.
These steps continue in the 3rd evaporator also.

16.  As the liquid in 1st evaporator gains temperature the
difference in temperature between the liquid & steam
decreases, hence, the rate of condensation decreases.
 As a result, the pressure in the vapor space of 1st
evaporator gradually increases to P1 by increasing
temperature to T1 , which is the B.P. of the liquid in first
evaporator & decreasing the temperature difference (t0-
t1).
 A similar change takes place in the 2nd evaporator &
the liquid reaches the B.P.
 similarly, the process will be repeated in 3rd evaporator.
Finally 3 evaporators come to a steady state with the
liquid boiling in all the 3 bodies.

17.  As boiling proceed, liquid level in 1st evaporator comes down.
Feed is introduced through the feed valve to maintain the
liquid level constant.
 Similarly evaporation of liquid takes place in 2nd & 3rd
evaporators.
 To maintain the liquid levels constant, feed valves F2 & F3 are
used for 2nd & 3rd evaporator respectively.
 This process is continued until the liquid in all the evaporators
reaches the desired viscosity.
 Now the product valves are opened to collect the thick liquid.
 Thus in this evaporators, there is continuous supply of feed,
continuous supply of steam & continuous withdrawal of liquid
from all 3 evaporators. Hence, evaporators work continuously.

18.  It is the quantity of vapor produced per unit steam
admitted.
 Feed is admitted at its B.P. so it does not require any
more heat to raise its temp.
 Hence, the supplied steam is condensed to give heat
of condensation. This heat will then transferred to
the liquid.
 The heat transferred now serves as latent heat of
vaporization, i.e. liquid undergoes vaporization by
receiving heat. Loss of heat by means is negligible.

19.  There are four types of MEE based upon feeding methods:
Backward
feeding
Mixed
feeding
Parallel
feeding
Forward
feeding

20.  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
 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

21. Steam
Feed

22.  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
FeedSteam

24.  A hot saturated solution of the feed is
directly fed into each of the three
effects in parallel without
transferring the material from one to
another. This is commonly used in
the concentration of the salt solution,
where the solute crystallizes on
concentration without increasing the
viscosity.
 Operations :-The equipment is at
room temp. & at atm. Pressure at the
beginning. The liquid feed is
introduced into all the 3 evaporators
up to the level of upper tube sheets.
 Eg- evaporation of brine to make salt
Feed
Feed
Feed
Steam

26.  When feed moves
forward with fresh feed
is entering at the 2nd or
3rd effect called as
mixed type.
 Used in solutions
having considerable
change in viscosity
with temperature over
concentration range

27. FeedSteam

28.  Suitable for large scale & for
continuous operation.
 Highly economical when compared to
single effect.
 Multiple effects, or stages, are now used
to minimize the energy input required to
evaporate or boil off undesirable water
content.
 The total evaporation achieved in these
systems is approximately the number of
effects times the energy input to the first
effect.

29.  Effect of temperature : feed must be at
temp greater or equal to the boiling point 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 boiling point 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 vacuum condenser and pump are
used
 Effect of stream pressure :with increase in
pressure of the saturated stream difference
in boiling point of increases giving small
size and hence cost decreases.

30. 1. Product
characteristi
cs
Heat
sensitivit
y
Viscosity
Boiling
behaviou
r
Fouling
and
precipitat
ion
Foaming
tendency
Flow
propertie
s
• Quantities
• Concentrations
• Temperatures
• Annual Operating
Hours
• Change of product
• Controls automation
2. Capacity and
Operational data
Steam,
Cooling
water
3. Operating
Media
Electric
power,
Cleaning
agents

31.  Must prevent entrainment due to product loss
 Contamination of the vapor phase (pollution)
 Condensation of vapor onto surfaces (corrosion and fouling)
 Overhead mist or spray may cause troublesome deposits
 Vortices increase pump head requirements and therefore equipment
 Configuration
 Short circuiting a big problem as it presents the problem of cavitation
 (there must be a net positive suction head)
 Liquid concentration - relates to viscosity and heat transfer
 Temperature and Pressure
 Boiling temperature is inversely proportional to pressure.
 Boiling points may increase as solution get concentrated (boiling
point rise)
 Foaming - will determine the height of your freeboard in the
Design
 Solubility of materials - May be the limit to the concentration that you can achieve.
 Scale deposits - decrease your heat transfer coefficient.

32. INUSTRIES/PRODUCT MATERIAL OF CONSTRUCTION
Most dairy and food products 304/316 stainless steel
Most fruit juices 316 stainless steel
Sugar products Carbon steel /304/316
Foods containing high salt (NaCl) Titanium/Monel
High alloy stainless steels
Duplex stainless steels
Caustic soda < 40% Stress relieved carbon steel
Caustic soda high concentration Nickel
Hydrochloric acid Graphite/Rubber lined carbon steel

33. Possible Causes Possible Remedies
• The product may be backing up in the
evaporator body due to choking.
• Open discharge lines to check and
eliminate cause of choking.
• The evaporator body may be heavily
scaled.
• Dismantle the unit and check for scaling.
• The feed rate is excessive. • Control the feed rate.
• There might be a problem with the drive
motor.
• Check for malfunctioning of the drive
motor.
• System starts vibrating
• There may be heavy scaling. • Go through the cleaning procedure.
• The product is backing up in the body due
to choking.
• Check and eliminate the cause of product
backup.
• Uneven heating of evaporator shell
causing thermal stresses on its body.
• Check the steam pressure of
thermocompressor.

34. Thank you…