evaporator v2
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EvaporatorEvaporator Equipment used in evaporation, the process of Equipment used in evaporation, the process of boiling a liquid in order to reduce its volume boiling a liquid in order to reduce its volume
NeedNeedReduces transportation costReduces transportation costStorage costs Storage costs Prepare for the next Unit operation – drying, Prepare for the next Unit operation – drying, crystallisation etc.crystallisation etc. Reduces deteriorative chemical reactions Reduces deteriorative chemical reactions Better microbiological stability Better microbiological stability Recovery of solventRecovery of solvent
EvaporatorEvaporator Driving force:Driving force:Temperature difference in between steam chest Temperature difference in between steam chest
temperature and product temperature.temperature and product temperature. Result :Result :Volatile solvent is removed from the feed.Volatile solvent is removed from the feed.
Solution (volatile solvent + non volatile solute)Solution (volatile solvent + non volatile solute)
Concentrate (Higher solute Conc.)Concentrate (Higher solute Conc.)
ExamplesExamples Concentration of milk to produce condensed Concentration of milk to produce condensed
milkmilk Concentration of juicesConcentration of juices Concentration of NaOH, NaCl from aqueous Concentration of NaOH, NaCl from aqueous
solutions to produce salt.solutions to produce salt. Ether recovery from fat extractionEther recovery from fat extraction
Basic Parts of an EvaporatorBasic Parts of an Evaporator Heat-exchanger Heat-exchanger Vacuum Vacuum Vapour separator Vapour separator Condenser Condenser
EvaporatorEvaporatorVapor out
Feed inSteam in (Saturated vapor)
Product out
Condensate out (Saturated Liquid)
Vapor Separator
Heat Exchanger
Vaccum for non condensable
Condensor unit
Coolant In
Coolant out
Evaporator Type Evaporator Type
Batch Pan Batch Pan
Rising Film Rising Film
Falling Film Falling Film
Multiple Effect EvaporatorsMultiple Effect Evaporators
Processing FactorsProcessing Factors
Conc of solute in feedConc of solute in feed
Conc of solute in product/concentrateConc of solute in product/concentrate
Pressure and Temp. of the systemPressure and Temp. of the system Depends on temperature sensitivity of material.Depends on temperature sensitivity of material. Boiling point elevationBoiling point elevation
Processing FactorsProcessing Factors Steam pressure and temperatureSteam pressure and temperature
Material of construction Material of construction
FoamingFoaming Low heat transfer rateLow heat transfer rate Entrainment lossEntrainment loss
Heat Transfer Coefficient, hHeat Transfer Coefficient, h A coefficient which indicates the amount of A coefficient which indicates the amount of
heat flow that is exchanged across a unit area heat flow that is exchanged across a unit area of a medium or system in a unit amount of of a medium or system in a unit amount of time with a unit of temperature difference time with a unit of temperature difference between the boundary of the system. between the boundary of the system.
S.I. unit W mS.I. unit W m-2-2 K K-1.-1.
Overall Heat Transfer Coefficient, UOverall Heat Transfer Coefficient, U In cases of combined heat transfer for a heat In cases of combined heat transfer for a heat
exchanger, there are two values for h. exchanger, there are two values for h.
Convective heat transfer coefficient for the fluid film Convective heat transfer coefficient for the fluid film inside the tubes inside the tubes
Convective heat transfer coefficient for the fluid Convective heat transfer coefficient for the fluid film outside the tubes. film outside the tubes.
The thermal conductivity (k) and thickness (Dx) of The thermal conductivity (k) and thickness (Dx) of the tube wall must also be accounted for. the tube wall must also be accounted for.
So an additional term (Uo), called the overall heat So an additional term (Uo), called the overall heat transfer coefficient, must be used instead. transfer coefficient, must be used instead.
Feed water Vaporisedtank feed water
Tank Volume out to0.92 litre/cm atmosphere
Overflowto drain Water
main
Steam in
Constantlevel Sight
device glass
Steamtrap
Condensateout
Condensatetank
Tank Volume1.31 litre/cm
Figure 1. The Evaporator
Steam TrapSteam Trap FunctionFunction
Discharge condensate, air and other incondensable Discharge condensate, air and other incondensable gases from a steam system while not permitting the gases from a steam system while not permitting the escape of live steam escape of live steam
Ball Float Steam TrapBall Float Steam Trap
Reduces the ferocity of
discharge and sound. Sound levels can be
reduced by up to 80%.
Vapor Out mvhv
Steam in mshs
Condensate out
mchc
Water in mwhw
QQEE
QQLL
Lab CalculationLab Calculation Calculate U, overall heat transfer coefficient Calculate U, overall heat transfer coefficient
for the evaporatorfor the evaporator
Perform a mass balance and energy balancePerform a mass balance and energy balance
Calculate discrepancy Calculate discrepancy
Mass BalanceMass Balance Feed Side:Feed Side:m (kg/s)m (kg/s)m (feed in) = m (Vapor)m (feed in) = m (Vapor)
Steam SideSteam Sidem (steam)= m (condensate m (steam)= m (condensate
collected) + m (flash)collected) + m (flash)
Flash Steam LossFlash Steam Loss The amount of flash steam produced during the The amount of flash steam produced during the
pressure reduction can be expressed as:pressure reduction can be expressed as:w = (Hw = (Hilil - H - Hflfl) / H) / Hfefe
wherewhere w = ratio of flash steam generated (kg flash steam w = ratio of flash steam generated (kg flash steam
/ kg condensate)/ kg condensate) HHilil = initial liquid enthalpy (kJ/kg) = initial liquid enthalpy (kJ/kg) HHflfl = final liquid enthalpy (kJ/kg) = final liquid enthalpy (kJ/kg) HHfefe = enthalpy of evaporation (kJ/kg) = enthalpy of evaporation (kJ/kg)
Energy BalanceEnergy Balance H (kJ/kg)H (kJ/kg)
Energy from the steam to the water QEnergy from the steam to the water QEE
The Heat Loss from the vessel to the room, QThe Heat Loss from the vessel to the room, QLL
Amount of heat in condensing steam QAmount of heat in condensing steam QSS
QQS = S = QQE + E + QQLL
MeasurementsMeasurements QQS and S and QQE E
Mass Flow rate- condensate, feed waterMass Flow rate- condensate, feed water
T,P will give H Specific EnthalpyT,P will give H Specific Enthalpy
Q = mHQ = mH
QQLL
Surface areaSurface area Surface temperatureSurface temperature QQLL =hA =hA ∆∆TT
QQEE = UA = UA ∆∆TT
Further ReferenceFurther ReferenceTransport Processes and Separation process Transport Processes and Separation process
principle by:principle by:Christie. J. GeankoplisChristie. J. Geankoplis
Animations on evaporator visit:Animations on evaporator visit:www.rpaulsingh.comwww.rpaulsingh.com and click animations then and click animations then
evaporatorevaporator
Thank YouThank You
Multiple-effect EvaporatorMultiple-effect Evaporator Water is boiled in a sequence of vessels, each Water is boiled in a sequence of vessels, each
held at a lower pressure than the last. held at a lower pressure than the last.
Because the boiling point of water decreases Because the boiling point of water decreases as pressure decreases, the vapor boiled off in as pressure decreases, the vapor boiled off in one vessel can be used to heat the nextone vessel can be used to heat the next
Generally the first vessel (at the highest Generally the first vessel (at the highest pressure) requires an external source of heat pressure) requires an external source of heat