Evaporator from net

8/7/2019 Evaporator from net

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Equipment used in evaporation, the process ofboiling a liquid in order to reduce its volume

NeedReduces transportation cost

Storage costs

Prepare for the next Unit operation drying,

crystallisation etc.Reduces deteriorative chemical reactions

Better microbiological stability

Recovery of solvent


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Driving force:Temperature difference in between steam chest

temperature and product temperature.

Result :

Volatile solvent is removed from the feed.

Solution (volatile solvent + non volatile solute)

Concentrate (Higher solute Conc.)


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Concentration of milk to produce condensedmilk

Concentration of juices

Concentration of NaOH, NaCl from aqueoussolutions to produce salt.

Ether recovery from fat extraction


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Heat-exchanger

Vacuum

Vapour separator Condenser


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Vapor out

Feed in

Steam in (Saturated

vapor)

Product out

Condensate out(Saturated Liquid)

Vapor

Separator

Heat Exchanger

Vaccum for non

condensable

Condensor unit

Coolant In

Coolant out


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Batch Pan

Rising Film

Falling Film

Multiple Effect Evaporators


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Conc of solute in feed

Conc of solute in product/concentrate

Pressure and Temp. of the system

Depends on temperature sensitivity of material.

Boiling point elevation


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Steam pressure and temperature

Material of construction

Foaming

Low heat transfer rate

Entrainment loss


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A coefficient which indicates the amount ofheat flow that is exchanged across a unit areaof a medium or system in a unit amount of

time with a unit of temperature differencebetween the boundary of the system.

S.I. unit W m-2 K-1.


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In cases of combined heat transfer for a heat

exchanger, there are two values for h.

Convective heat transfer coefficient for thefluid film inside the tubes

Convective heat transfer coefficient forthe fluid film outside the tubes.

The thermal conductivity (k) and thickness(Dx) of the tube wall must also be accountedfor.

So an additional term (Uo), called the overallheat transfer coefficient, must be used instead.


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Feed water Vaporised

tank feed water

Tank Volume out to

0.92 litre/cm atmosphere

Overflow

to drain Water

main

Steam in

Constantlevel Sight

device glass

Steam

trap

Condensate

out

Condensate

tank

Tank Volume

1.31 litre/cm


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Function

Discharge condensate, air and other incondensablegases from a steam system while not permitting the

escape of live steam


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Reduces the

ferocity of

discharge andsound. Sound

levels can be

reduced by up to

80%.


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Vapor Out

mvhv

Steam in

mshs

Condensate out

mchc

Water in mwhw

QQEE

QQLL


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Calculate U, overall heat transfer coefficient forthe evaporator

Perform a mass balance and energy balance

Calculate discrepancy


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Feed Side:m (kg/s)

m (feed in) = m(Vapor)

Steam Side

m (steam)= m

(condensatecollected) + m (flash)


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The amount of flash steam produced during thepressure reduction can be expressed as:

w = (Hil - Hfl) / Hfewhere

w = ratio of flash steam generated (kg flash steam/ kg condensate)

Hil = initial liquid enthalpy (kJ/kg)

Hfl = final liquid enthalpy (kJ/kg) Hfe = enthalpy of evaporation (kJ/kg)


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H (kJ/kg)

Energy from the steam to the water QE

The Heat Loss from the vessel to the room, QL

Amount of heat in condensing steam QS

QS = QE + QL


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QS and QE

Mass Flow rate- condensate, feed waterT,P will give H Specific Enthalpy

Q = mH QL

Surface area

Surface temperature

QL =hA T QE = UA T


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Further Reference

Transport Processes and Separation processprinciple by:

Christie. J. Geankoplis

Animations on evaporator visit:

www.rpaulsingh.com and click animations thenevaporator


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Water is boiled in a sequence of vessels, eachheld at a lower pressure than the last.

Because the boiling point of water decreases aspressure decreases, the vapor boiled off in onevessel can be used to heat the next

Generally the first vessel (at the highestpressure) requires an external source of heat


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Evaporator from net