Evaporator : Evaporator Equipment used in evaporation, the process of boiling a liquid in order to reduce its volume
Reduces transportation cost
Prepare for the next Unit operation – drying, crystallisation etc.
Reduces deteriorative chemical reactions
Better microbiological stability
Recovery of solvent http://avibert.blogspot.com Evaporator : Evaporator Driving force:
Temperature difference in between steam chest temperature and product temperature.
Volatile solvent is removed from the feed.
Solution (volatile solvent + non volatile solute)
Concentrate (Higher solute Conc.) http://avibert.blogspot.com Examples : Examples 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 http://avibert.blogspot.com Basic Parts of an Evaporator : Basic Parts of an Evaporator Heat-exchanger
Condenser http://avibert.blogspot.com Evaporator : Evaporator 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 http://avibert.blogspot.com Evaporator Type : Evaporator Type Batch Pan
Multiple Effect Evaporators http://avibert.blogspot.com Processing Factors : Processing Factors 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 http://avibert.blogspot.com Processing Factors : Processing Factors Steam pressure and temperature
Material of construction
Low heat transfer rate
Entrainment loss http://avibert.blogspot.com Heat Transfer Coefficient, h : Heat Transfer Coefficient, h A coefficient which indicates the amount of heat flow that is exchanged across a unit area of a medium or system in a unit amount of time with a unit of temperature difference between the boundary of the system.
S.I. unit W m-2 K-1. http://avibert.blogspot.com Overall Heat Transfer Coefficient, U : Overall Heat Transfer Coefficient, U In cases of combined heat transfer for a heat exchanger, there are two values for h.
Convective heat transfer coefficient for the fluid film inside the tubes
Convective heat transfer coefficient for the fluid film outside the tubes.
The thermal conductivity (k) and thickness (Dx) of the tube wall must also be accounted for.
So an additional term (Uo), called the overall heat transfer coefficient, must be used instead. http://avibert.blogspot.com Slide 11: http://avibert.blogspot.com Slide 12: http://avibert.blogspot.com Slide 13: http://avibert.blogspot.com Slide 14: http://avibert.blogspot.com Slide 15: http://avibert.blogspot.com Steam Trap : Steam Trap Function
Discharge condensate, air and other incondensable gases from a steam system while not permitting the escape of live steam http://avibert.blogspot.com Ball Float Steam Trap : Ball Float Steam Trap http://avibert.blogspot.com Slide 18: Reduces the ferocity of discharge and sound. Sound levels can be reduced by up to 80%. http://avibert.blogspot.com Slide 19: http://avibert.blogspot.com Slide 20: http://avibert.blogspot.com Slide 21: Vapor Out mvhv Steam in mshs Condensate out
mchc Water in mwhw QE QL http://avibert.blogspot.com Lab Calculation : Lab Calculation Calculate U, overall heat transfer coefficient for the evaporator
Perform a mass balance and energy balance
Calculate discrepancy http://avibert.blogspot.com Mass Balance : Mass Balance Feed Side:
m (feed in) = m (Vapor)
m (steam)= m (condensate collected) + m (flash) http://avibert.blogspot.com Flash Steam Loss : Flash Steam Loss The amount of flash steam produced during the pressure reduction can be expressed as:
w = (Hil - Hfl) / Hfe
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) http://avibert.blogspot.com Energy Balance : Energy Balance 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 http://avibert.blogspot.com Measurements : Measurements QS and QE
Mass Flow rate- condensate, feed water
T,P will give H Specific Enthalpy
Q = mH
QL =hA ∆T
QE = UA ∆T http://avibert.blogspot.com Slide 27: Further Reference
Transport Processes and Separation process principle by:
Christie. J. Geankoplis
Animations on evaporator visit:
www.rpaulsingh.com and click animations then evaporator http://avibert.blogspot.com Multiple-effect Evaporator : Multiple-effect Evaporator 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 vapor 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 http://avibert.blogspot.com Slide 29: http://avibert.blogspot.com Thank You : Thank You http://avibert.blogspot.com