Pharmaceutical Eng. 3rd sem Evaporation.pptx

EVAPORATION
• Evaporation is a process of vaporizing large
quantities volatile liquid to get a concentrated
product.
• Equipment used for the evaporation are known
as evaporators.
• Heat is supplied to the evaporator, which
transmits it to the evaporating liquid so as to
provide latent heat of vaporization.
• Steam is normally used as a source of heat.
• Evaporation is a surface phenamenon, i.e, mass
transfer takes place from the surface.

• Thus no boiling occurs.
• In practice, surface evaporation is slow,
therefore, the practical definition of
evaporation is the removal of solvent from the
solution by boiling the liquor in a suitable
vessel and withdrawing the vapour, leaving a
concentrated liquid residue in the vessel.

• Evaporation differs from boiling that
evaporation takes place at all temperatures
where as boiling takes place only at one
temperature at a given pressure.

• Below boiling point, vapour is formed from
the surface only.
• At boiling point, vapour is formed throughout
the body of the liquid as well as from surface.
• Boiling occurs when the vapour pressure of
the liquid becomes equal to the atmospheric
pressure.

• Evaporation differs from distillation that in
evaporation the solvent which is generally
water is not condensed and collected, where
as in distillation the solvent vapours are
condensed and are collected in a receiver.

Purpose of evaporation:
• To concentrate solution by removing the
vapour from a boiling liquid solution .
• In the majority of cases, evaporation refers to
the removal of water from an aqueous
solution.
• Example: concentration of aqueous solutions
of sugar, sodium chloride, sodium hydroxide,
glycerol, glue, milk, and orange juice.

• In these cases the concentrated solution is the
desired product and the evaporated water is
normally discarded.

APPLICATION OF EVAPORATION
• Evaporation is one of the most important
processes in the manufacture of pharmaceuticals.
• It is used in the preparation of
• 1. Liquid extracts, soft extracts & dry extracts.
• 2. In the concentration of blood plasma &serum.
• 3. It is also used in the manufacture of drugs
containing, antibiotics, enzymes, hormones &
many other substances.

• 4) Used in purification of vitamins.
• 5) Concentration of proteins.
• 6) Concentration of biological products.
• 7) Stripping(removal of gas or vapour) of solvents
from vegetable & plant
• or herbal extracts.
• 8) Removal of water & solvents from
• fermentation broths(A clear liquid made from
meat, vegetables etc).
• 9) Concentration of penicillin & related products

• Manufacturing of bulk drugs.
• Manufacturing of biological products(made for
natural source e.g sugar, protein etc).
• Manufacturing of food products.
• Manufacturing of demineralised water.
• Minimize the chances of chemical reactions.
• Prepare the product for next operation like
drying.
• Improve product storage life.
• Decrease the impact of microbial growth.

Evaporation and Distillation
In evaporation, vaporization takes
place below the boiling point.
In the distillation method,
vaporization takes place at the
boiling point
Evaporation takes place only from
the surface of the liquid
Distillation takes place from the
whole liquid mass.
It takes place below boiling point so
there is no bubble formation in
evaporation.
At the boiling point of the distillation
process, the liquid forms bubbles.
Evaporation is not necessarily
separation or purifying technique.
Distillation is a separation or
purifying technique
Evaporation is a slow process. Distillation happens rapidly.
Evaporation is one type of unit operation
where the atoms or molecules of the
liquid solution acquire sufficient
energy(boiling)and gets vaporized that is,
enters the gaseous state.
Distillation is one of the unit operation
which is defined as method of separation
and purification of components of a liquid
through vaporization and condensation.

In evaporation concentrated liquid
residue is required as product.
In distillation, condensed vapour is
required as the product.
Evaporating liquid is only one component
in most of the cases.
Evaporating liquid is a mixture of two or
more components.
Even if mixtures of vapours are present, it
is not necessary to separate them.
It is necessary to separate each
component.
Example: Evaporation process is carried
out in the manufacture of bulk drugs,
manufacture of biological
products(insulin). Biochemical products
(Penicillin) and also employ in the
preparation of blood products such as
blood plasma and serum
Distillation process is carried out for the
separation of volatile oils, purification of
organic solvents, refining of petroleum
products etc.

Evaporation and Drying
• The term drying usually refers the removal of
relatively small amounts of water from solid or
nearly solid material,
• Whereas Evaporation is usually limited to the
removal of relatively large amounts of water from
solutions.
• In most cases drying involves the removal of
water at temperatures below its boiling point,
whereas , Evaporation means the removal of
water by boiling a solution.

Evaporation and Drying
1.Evaporation is the unit operations
where the atoms or molecules of the
liquid solution acquire sufficient
energy(by boiling) and gets
vaporized(that is enters the gaseous
state)
1. Drying is defined as the process of
removing relatively small quantity of
water or moisture from the material, so
as to obtain dry product
2.Evaporation operation is employed
when concentrated liquid resolve is
required as the product
During operation is employed when dried
solid residue is required as the product.

Factors affecting evaporation
The fallowing are the factors which affect the rate of evaporation
of a liquid
M = ks/P(b-b1)
k=Constant
M=Mass of vapour formed per unit time
S=Surface area of the liquid exposed
P=Atmospheric pressure
b=Maximum vapour pressure at the temperature of air
b1=pressure due to the vapour of the liquid actually present
in the air

1.TEMPERATURE
• The rate of evaporation is directly
proportional to the temperature of the liquid.
• Higher the temperature higher will be the
evaporation but evaporation is maximum at
the boiling point of the liquid.
• The evaporation can be accelerated by
increasing the temperature but it will cause
decomposition of heat sensitive principles of
many drugs.

• Many glycosides and alkaloids are
decomposed at a temperature below 1000C.
• Hormones, vitamins, enzymes and antibiotics
being more heat-sensitive materials needs
special treatment in order to avoid
decomposition e.g, malt extract is
concentrated by evaporation under reduced
pressure to avoid loss of enzyme and
antibiotics are concentrated by freeze drying.

2.Temperature and time of
evaporation
• It has been observed that exposure to a
relatively high temperature for short period of
time may be less harmful to the active
principles of a drug than a lower temperature
with exposure for a longer period.
• On the basis of this fact, liquid is exposed to
high temperature for a short period in film
evaporator.

3.Temperature and moisture content
• Some drug constituents decompose more readily
in the presence of moisture if heated at a high
temperature. This is due to the hydrolysis of the
active constituents.
• To avoid decomposition of the active principles of
such materials the evaporation is done at a low
temperature and then the final drying is done at
a high temperature when only little moisture
remains in it.
• e.g, Dry extract of belladona is prepared in this
manner.

4.TYPES OF PRODUCT REQUIRED
• The type of product required will often decide
which method and apparatus should be
employed for evaporation.
• Evaporating pans or stills will produce liquid or
dry products.
• Film evaporators will yield only liquid
products.
• Spray dryer produces dry product with good
solubility.

• Vacuum evaporator gives porous product
suitable for conversion to granules, for
example, preparation of granular extract of
cascara for tablet making.

5.EFFECT OF CONCENTRATION(film and deposit)
• During evaporation the upper layer of the
liquid under evaporation has a tendency to
form a film and formation of precipitate in the
product may deposit on the heating surface
which results in lowering down of the rate of
evaporation.

• Film reduces the evaporating surface and
precipitated matter hinders the transfer of
heat.
• Therefore efficient stirring is required in order
to prevent degradation of the product at the
bottom due to excessive heat and it will also
prevent decomposition of solids.

6.SURFACE AREA
• The rate of evaporation is directly
proportional to the surface area of the
evaporator, in which the liquid is evaporated.
• The larger the surface area of the
evaporator,the shorter is the time it takes to
evaporate the liquid.

7.VAPOUR PRESSURE OF THE LIQUID
TO BE EVAPORATED
• The rate of evaporation is directly proportional to
the vapour pressure of the evaporating liquid.
• The liquid has maximum vapour pressure at its
boiling point.
• As such the rate of evaporation can be increased
by raising the temperature of the evaporating
liquid.
• The rate of evaporation of liquid is the maximum
at its boiling point.

• If the atmospheric aqueous vapour pressure
or moisture contents in the air are high, the
rate of evaporation will be slow.
• If the outer atmosphere is dry, the rate of
evaporation will be greater.
• Lower the external pressure, the lower the
boiling point of the liquid and hence greater
will be the rate of evaporation. This condition
is achieved by applying vaccum.

8.Vapour pressure
• The nature of liquid is also important for rate
of evaporation, liquid with low boiling points
evaporate quickly because of high vapour
pressures at low temperatures.
• Lower the external pressure, the lower the
boiling point of the liquid and hence greater
will be the rate of evaporation.

9.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
over all costs.

• For evaporation, heat is necessary to provide
the latent heat of vapourisation, hence, rate
of evaporation is controlled by rate of heat
transfer.
• Therefore, evaporator is designed to give
maximum heat transfer to the liquid.

EVAPORATING PANS(STEAM JACKETED
KETTLE)
• PRINCIPLE;
• Steam is supplied to a jacket kettle(evaporating
pan) in which aqueous extract is placed.
• Steam gives out heat to the kettle.
• The heat is transferred to the aqueous extract by
conduction and convection.
• The temperature rises and the escaping tendency
of the solvent molecules into vapour increases.
• Stirring further enhances the vaporisation of
solvent molecules.

CONSTRUCTION
• It is a hemispherical structure consisting of an
inner pan called kettle.
• It is enveloped with an outer pan called
jacket.
• The two pans are joined to enclose a space
through which steam is passed.

• Copper is an excellent material for the
construction of kettle because of its good
conductivity.
• If acidic materials are evaporated some quantity
of copper would dissolve.
• For such preparations, tinned copper(Tinned
copper wire is a type of copper wire coated in a
thin layer of tin to protect the copper from
corrosion) is used.
• Iron is used for the construction of the jacket
because it has minimum conductivity.

• To prevent rusting of the jacket, the iron is
either tinned(Tinning is the process of thinly
coating sheets of wrought iron or steel with
tin) or enameled(coat or decorate (a metallic
or hard object) with enamel(an opaque or
semi-transparent glossy substance ) on inner
surface.

• An inlet for the steam and outlet (vent) for
non condensed gases are provided near the
top of the jacket.
• Condensate leaves the jacket through one
more outlet provided at the bottom.
• The kettle is provided with one outlet for
product discharge at is bottom.

WORKING
• Aqueous extract to be evaporated is placed in
the kettle.
• Steam is supplied through the inlet.
• Steam gives out its heat to the contents and
the condensate leaves through the outlet.
• The contents must be stirred manually for
smaller volumes and mechanically for larger
volumes.

• The rate of evaporation is fast in the initial
stages and decreases gradually as the liquid
becomes concentrated.
• Any room where evaporation is carried by this
apparatus must have good ventilation to
remove the vapour.

• Otherwise the room is quickly filled with a
dense fog of condensed vapour and water falls
from the roof and runs down the walls.
• Fans fitted over the pan not only remove the
vapour and prevent condensation in the room,
but also accelerate the rate of evaporation by
quickly removing saturated air from the
surface of the liquid.

• The kettle may be fixed or made to tilt.
• A kettle about 90 liters capacity may be made
to tilt.
• But above this capacity the weight of the pan
along with its contents becomes to great to
tilt.
• Hence the bottom outlet is used to collect the
concentrated product.

ADVANTAGES
• 1.Evaporating pan is constructed both for
small scale and large scale operations.
• 2.It is simple in construction and easy to
operate, clean and maintain.
• 3.Its cost of installation and maintenance is
low.

• 4.Wide variety of materials can be used for
construction such as copper, stainless steel
and aluminium.
• 5.Stirring of the contents and removal of the
product is easy.

DISADVANTAGES
• 1.In evaporating pans, heat economy is less,
hence cost per unit material production is more.
• 2.It is not suitable for heat sensitive materials due
to long time of exposure.
• 3.The evaporating pan is an open one and the
vapours can pass direct to the atmosphere which
may lead to saturation of the atmosphere with
vapours.
• This in turn may cause discomfort to the worker.
• It may also slow down the process of
evaporation.

• 4.Boiling point of water cannot be reduced
since reduced pressure cannot be created in
open type evaporator.
• 5.The heating surface is limited and decreases
proportionally to increase in size of the pan.

USES
• Evaporating pan is suitable for concentrating
aqueous and thermostable liquors for
example liquorice extract.

FORCED CIRCULATION EVAPORATOR
• PRINCIPLE:
• In forced circulation evaporator, liquid is
circulated through the tubes as high pressure
by means of a pump.
• Hence, boiling does not takes place, the
boiling point is raised.

• Forced circulation of the liquid also creates
some form of agitation[the material is
agitated by stirring rod or by mechanical
propeller].
• When the liquid leaves the tubes and the
vapour head. Pressure fall suddenly.
• This leads to the flashing of super heated
liquor and vapour get removed.

CONSTRUCTION
• The steam jacketed tubes are held between two
tube sheets.
• The tube measures 0.1m inside diameter and
2.5m long.
• The part of the tubes projects into the vapour
head(flash chamber).
• which consists of deflector.
• The vapour head is connected to a return pipe,
which runs downwards and enters in to the inlet
of a pump.

Working
• Steam is introduced into calandria.
• Pump sends the liquid to the tubes with a
positive velocity.
• As the liquid moves up through the tubes, it gets
heated and begins to boil.
• As result the vapour and liquid mixtures rushes
out of the tubes at a high velocity.
• This mixture strikes the deflector which throws
the liquid downward.

• Results in effective separation of liquid and
vapour.
• The vapour enters the cyclone separator and
leave equipment.
• The concentrated liquid returns to the pump
for further evaporation.
• Finally the concentrated product is collected.

ADVANTAGE
• The heat transfer coefficient is high due to rapid
liquid movement.
• Salting,scaling(the accumulation and formation of
unwanted materials ) are not possible due to forced
circulation.
• The rapid evaporation rate makes this evaporation
useful for concentration of thermolabile materials
eg.Insulin and liver extract.
• It Is useful for high viscous preparations because of
pumping mechanism is used.

DISADVANTAGES
• It is expensive, because of power(pump)is required
for circulation.

USE
• If evaporation is conducted at reduced
pressure, its suitable for thermolabile
products,
• Used for concentration of insulin, liver
extracts.

HORIZONTAL TUBE EVAPORATOR
• PRINCIPLE
• Steam is passed through the horizontal tubes.
• Heat transfer takes place through the tubes
gets heated, boiling of the feed occurs leading
to vaporization of the solvent, and escapes
from the top of the evaporator.
• The concentrated liquid is collected from the
bottom.

CONSTRUCTION
• Large cylindrical body with conical or dome
shaped top and bottom.
• It is made up of cast iron(superior resistance to
mode rate corrosion) or plate steel.
• Size of the body 1.8 to 2.4 m diameter, 2.4 to 3.6
height. Lower part of the body consists of a
steam compartment with steam inlet.
• Steam condensate outlet may be one or two
number at the bottom, outlet for non condensed
gases,6 to 8 stainless steel horizontal tubes are
placed.

WORKING
• Feed is introduced through the feed inlet.
• The level of feed is slightly taken above the
level of the horizontal tubes.
• Steam is passed through the steam inlet, the
horizontal tubes receive heat from the steam
and transferred it to the liquid.
• Hence solvent gets evaporated and escapes
through the outlet placed at the top.

• This process continued until thick
concentrated liquid is obtained, is collected
from the bottom.

ADVANTAGES
• Cheap, easy to install.
• Evaporation process is less time consuming
when compared to evaporation pan.
• Suitable for substance which tend to form
foam, it has greater capacity to separate
vapour from the feed.
• Cost per square meter of heating surface is
less.
• Ease of tube removals.

DISADVANTAGE
• Liquid circulation is poor, not suitable for
viscous substances.

USE
• Suitable for non viscous solutions, do not form
scales, cascara extract can be concentrated.

LONG TUBE EVAPORATORS(climbing
film evaporator)
• PRINCIPLES
• In climbing film evaporator, tubes are heated externally
by steam cold or preheated liquor is introduced in to
the tube(1)
• 1.Heat is transferred to the liquor from walls and
boiling begins(2)Increasing in vigour(3)and (4).
• Eventually sufficient vapour has been formed for the
smaller bubbles to unite to a large bubble(5). As more
vapour is formed, the slug of liquid blown up the tube
,the tube is filled with vapour, while the liquid spread
as a film over the walls(6).
•

• This film of liquid continues to vaporise
rapidly, the vapour escaping up the tube and
because of friction between the vapour and
liquid, the film also dragged up the tube.
• The liquid film travels up the tube at velocities
of the order of 6 or 7 meter/second.

Construction
• In this evaporator, the heating unit consists of
steam jacketed tubes, having a length to
diameter ratio about 140 to 1.
• So that a large evaporator may have tubes
50mm in diameter and about 7m in length.
• Here the tubes (long and narrow) are held
between two plates.

• A separator is placed at the top to the vapour
head.
• The evaporator carries steam inlet, vent outlet
and condensate outlet.
• The liquor to be evaporated is introduced into
the bottom of the tube.

• At the top the mixed vapour and concentrated
liquid are ejected at a considerable speed into
a separator.
• The separator allows the vapour to escape
from the top and the concentrated liquid is
collected at the bottom.

Working
• In these evaporators a large number of vertical
tubes about 7 meters in length and 50mm in
diameter are enclosed in an outer jacket to which
steam is supplied.
• Thus the tubes are heated externally.
• The preheated feed liquid is admitted at the base.
• Here it boils and the vapours formed take the
liquid up the tube at a velocity of about 6 to 7
meters/second.

• The liquid takes only a few seconds to travel
the length of the tube.
• So the evaporator is very suitable for heat
sensitive substances.

ADVANTAGES
• 1.The use of long narrow tubes provide a large
area for heat transfer.
• 2.Since liquid flows at high velocity, the resistance
for heat transfer at the boundary layer is reduced.
As a result the heat transfer is enhanced.
• 3.The time of the contact between the liquid and
the heating surface is very short, so it is most
suitable for the concentration of a liquid
containing the thermolabile materials.

• 4.The evaporation rate is very high in spite of a
short heating time.
• 5.There is no elevation of boiling point
although the tubes are very long.
• 6.The method is suitable for materials which
produse foam.

DISADVANTAGES
• 1.Climbing film evaporator is expensive,
construction is quite complicated.
• 2.It is difficult to clean and maintain.
• 3.It is difficult to maintain at proper feed rate.
If is too high, the proper concetration will not
be made, If the feed rate is too low, the film
cannot be maintained.
• 4.It is not advisable for very viscous liquids,
salting liquids and scaling liquids.

USES
• Using climbing film evaporator, thermolabile
substances such as insulin, liver extracts and
vitamins can be concentrated.
• Clear liquids, foaming liquids and corrosive
solutions in large quantities can be operated.

SHORT TUBE EVAPORATOR(vertical
tube evaporator)(Not in syllabus)
• Principle;
• In standard vertical tube evaporator, the liquid is
passed through the vertical tubes and the steam
is supplied from outside the tubes.
• Heat transfer takes place through the tubes and
the liquid inside the tubes gets heated.
• The solvent evaporates and the vapour escapes
from the top.
• The concentrated liquid is collected from the
bottom.

CONSTRUCTION
• It consists of a large cylindrical body made up of
cast iron with dome shaped top and bottom.
• In side the body, calandria is fitted at the bottom.
• Calandria consists of a number of vertical tubes.
• These tubes are from 1 to 2m in length and from
0.05 to 0.075m in diameter, with the tubes up to
100 to 1000 in number in a vessel up to 2.5m or
more in diameter.

• In lets are provided for steam and feed.
• Outlets are provided for vapour, concentrated
product, non condensed gases and
condensate.

WORKING
• Steam is introduced out side the tubes,
• The condensate is passed through the
corresponding outlet and non condensed
gases escape through the vent.
• The feed is introduced in such a way as to
maintain the liquid slightly above the top of
the tubes so that the space which is left in the
evaporator can be used for the purpose of
separation of vapour from the boiling liquid.

• The liquid in the tube is heated by steam and
it begin to boil.
• The mixture of the liquid and vapour will
come out of the tube which sets up a
circulation with boiling liquid rising up in the
smaller tubes of calandria and returning down
the large central down take.

• It sets up a circulation of hot liquid which
enhances the rate of heat transfer.
• The vapour escapes through the top outlet.
• Steam is supplied until required concentration
of the product is obtained.
• Finally the product can be withdrawn from the
bottom outlet.

ADVANTAGES
• The heating area is increased by using a tubular
calandria.
• The coefficient of the heat transfer is 3-5 times
more as compared to the evaporating pan.
• The condenser and receiver can be attached to
the evaporator in order to recover the costly
solvent.
• A number of units can be joined to obtain more
efficient effect[multiple effect of evaporators].

DISADVANTAGES
• The liquid is maintained above the level of the
calandria.
• Hence, the top layers of the liquid need a long time for
getting heated.
• This problem can be minimised by removing
concentrated liquid slowly at the bottom.
• It is quite complicated and hence it is expensive to
construct it.
• It is difficult to clean it.
• The maintenance of the evaporator is quite costly.

USES
• Vertical tube evaporator is used in the
manufacture of cascara extract, sugar, salt,
caustic soda.

MULTIPLE EFFECT EVAPORATION
• In single effect evaporators, steam is used to
heat the liquid which provides the latent heat
of vaporisation.
• The vapours are condensed in condenser,
where the latent heat is given up to the
cooling water and it goes to waste.

• To avoid this wastage, two evaporators are
connected together with a piping
arrangement so that the vapours from
calandria of first effect(which is heated by
steam) is used to heat the calandria of the
second effect.

• This means that the calandria of the second
effect is used as condenser for the first effect,
so that latent heat of vaporisation is used to
evaporate more quantity of the liquid instead
of its going as waste.
• The vapour from second effect them taken to
a condenser and converted into liquid.

• In general, not more than two or three effects
are combined together to have an economical
and efficient evaporation of liquid.

Principle
• It is an arrangement of short tube evaporator
to achieve economy.
• In this arrangement, vapours formed in the
evaporator are used as the heating medium
for the next evaporator.
• In this way, the energy associated with the
vapours produced during evaporation is used
many times to achieve economy.

Construction
• The construction of multiple effect of evaporator
is using 3 evaporators, i.e triple effect evaporator.
• Construction of vertical tube evaporator(short
tube)remain same.
• The vapour from first evaporator serves as a
heating medium for 2nd evaporator serves as
heating medium for the 3rd evaporator.
• Last evaporator is connected to a vaccum pump.

Working
• Parallel feed:
• In this method, a hot saturated solution of the
feed is directly fed to each of the three
effects(evaporation) in parallel without
transferring the material from one effect to
the other.

• The parallel feed arrangement is commonly
used in the concentration of salt solutions.
• Where the solute crystallizes on concentration
without increasing the viscosity.

Operations
• In the beginning, the equipment is at room
temperature and atmospheric pressure.
• The liquid feed is introduced to all the three
evaporators up to the level of the upper tube
sheets.
• The following operations are attempted to
achieve the effects as specified below.

• 1. the vent valves V1,V2 and V3 are kept open and all
other valves are closed(To remove non condensed gas)
• 2. Now high vacuum is created in the liquid chambers
of evaporators.
• 3. The steam valve S1 and condensate valve C1 are
opened.
• Steam is supplied. Steam first replaces cold air in the
steam space of 1st evaporator.
• When all the cold air is removed, the valve V1 is closed.

• The supply of steam is continued until the
desired pressure P0 is created in the space of
1st evaporator.
• At this pressure the temperature of the steam
is t0.
• Steam gives its temperature to the liquid feed
in the 1st evaporator and gets condensed.
Condensate is removed through the valve C1.

• Due to heat transfer, the liquid temperature
increases and reaches the boiling point.
• During this process, vapour will be generated
from the liquid feed.
• So formed vapour displaces air in the upper
part of 1st evaporator. Moreover, the vapour
also displaces the air in the steam space of 2nd
evaporator.

• After complete displacement of air vapour in
the steam compartment of 2nd evaporator, the
valve V2 is closed.
• The vapour of 1st evaporator transmits its heat
to the liquid of 2nd evaporator and gets
condensed.
• Condensate is removed through the valve C2.
• These steps continue in 3rd evaporator also.

• As the liquid in the 1st evaporator gains
temperature, the difference in temperatures
between the liquid and steam decreases.
• As a result, the pressure in the vapour space
of 1st evaporator gradually increases to P1 by
increasing the temperature to t1 which is the
boiling point of the liquid in 1st evaporator,
decreasing the temperature difference(t0-t1)

• A similar change takes place in the 2nd evaporator
and the liquid reaches the boiling point. Similarly
the process will be repeated in 3rd evaporator.
• Finally three evaporators come to a steady state
with the liquid boiling in all the three bodies.
• As boiling proceeds, the liquid level in 1st
evaporator comes down. Feed is introduced
through feed valve to maintain liquid level
constant.

• To maintain liquid level constant feed valve F2 and
F3 are used for 2nd and 3rd evaporators. This
process continued until the liquid in all the
desired viscosity.
• Now the product valves are opened to collect
thick liquid.
• In this evaporator, there is continuous supply of
feed, continuous supply of steam and continuous
withdrawal of liquid from all three evaporators. It
works continuously.

• The evaporator can also fed by forward feed
method, backward feed method and mixed
feed method. In forward feed method the
mother liquor is introduced to 1st then 2nd and
3rd.
• In backward 3rd to 2ndto 1st.
• In mixed feed 2nd to 3rd to 1st evaporator.

Advantages
• Suitable for large scale and continuous operation.
• Highly economical when compared with single
effect.
• About 5 evaporator can be attached.
• Wastage of heat is minimized, hence more
economical. This is in comparison with single effect
which depicts more steam consumption is there
and it is less economical.
• Used in large scale basis.
• Improved heat transfer.

• Used in large scale basis.
• Improved heat transfer.

Dis advantages
• Capacity of triple effect evaporator is reduced
when compared to three individual standard
vertical tube evaporator.

Application
• Used when feed is costlier and instalment cost
in low.
• The reverse is seen in case of single effect
evaporator.

Selection criteria for the evaporation
• Highest heat transfer coefficient should be
reached
• Heat transfer coefficient even counter balance
the power required in including circulation

• Entrainment losses should be prevented or
minimized, it can be prevented by using a
deflector.
• Maximum steam economy should be
achieved, this is seen in the case of multiple
effect evaporator, where vapour from one
effect serve as the heating media for second
effect.
• Care should be taken in the prevention of
evaporation so as for minimize the problem of
salting,scaling,foaming,corrosive of
evaporator etc

• Appropriate evaporator is to be chosen by
considering the aspects of feed supplied and
desired product required.

Pharmaceutical Eng. 3rd sem Evaporation.pptx

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Pharmaceutical Eng. 3rd sem Evaporation.pptx