evaporators
DESCRIPTION
this ppt gives abrief and organised introduction to various types of evaporators employed in industries for the basic evaporation process, along with their specific adantages and disadvantages of one over the other. various evaporators like single effect, multiple effect, then horizontal tube, calandria type, vertical type, long tube, rissing film, falling film, forced circulation type evaporators have also been briefly discussed over in the presentationTRANSCRIPT
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Work of:-Abhinav,Aseem Mittal,Ashok Kumar and Naval Chaudhary
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Vaporization of an element or compound is a phase transition from the liquid phase to gas phase. There are two types of vaporization : evaporation and boiling.
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VAPORIZATION
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Evaporation:-Evaporation is a phase transition from the liquid phase to gas phase that occurs at temperatures below the boiling temperature at a given pressure. .
Boiling:-Boiling is a phase transition from the liquid phase to gas phase that occurs at or above the temperature the boiling temperature.
Note: 1-evaporation usually occurs on the surface.
2- Note boiling occurs below the surface.
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…
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EVAPORATION
V/S
DRYING
DISTILLATION
CRYSTALLIZATION
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…
(Fuel energy Latent heat (Latent heat or sensible heat
of vaporization)
Latent heat of vaporization)
CLASSIFICATION OF TUBULAR VAPORIZING
EQUIPMENT
BOILERSVAPORIZING
EXCHANGERS
EVAPORATOR
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Difference between….
1. Evaporator and Reboiler ,
2. Evaporator and Vaporizer,
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Types of evaporator…1. Power plant evaporator2. Chemical evaporator.
COMPERISION BETWEEN POWER PLANT & CHEMICAL EVAPORATOR
B.F.W. BLOWDOWN B.P.R.
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.
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CHEMICAL EVAPORATOR
SINGLE EFFECT MULTIPLE EFFECT
NATURAL CIRCULATION FORCED CIRCULATION
HORIZONTAL TUBE
CALANDRIA VERTICAL TUBE
BASKET VARTICAL TUBE
LONG TUBE VERTICAL
INSIDE VERTICAL HEATING ELEMENT
VERTICAL EXTERNAL ELEMENT
HORIZONTAL EXTERNAL ELEMENT
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CHEMICAL AND BIOCHEMICAL EVAPORATOR
Important terms………….. Concentration Foaming Temperature sensitivity Scaling and salting Materials of construction (M.O.C.)
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In this type, evaporator the vapor from the boiling liquid is condensed and discarded.
Single effects units can be operated in 1.Batch mode2.Semi batch mode 3.Continuous batch mode4.Continuous mode
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Are used when 1.Through put is low.2. Cheap supply of steam is available.3. Vapors are contaminated.
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It uses steam inefficiently. To evaporate 1 kg of water we need 1-
1.3 kg of steam.
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Series of evaporators between the steam supply and condenser is called multiple effect evaporator.
The vapors from one effect serve as the heating medium for the next.
Temp of vapors decreases and pressure also decreases.
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Four types of feeding systems- Forward feed Backward feed Mixed feed Parallel feed
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Liquid feed flows in same direction as vapors.
Pump is required for feeding and at the last effect.
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FORWARD FEED
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Liquid feed flows in reverse direction of vapors .
Pump is required at each effect.
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BACKWARD FEED
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The dilute liquid enters an intermediate effect.
Eliminates some of the pumps as needed in backward feed.
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MIXED FEED
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Fresh feed is provided to each effect and mother liqour is withdrawn from each effect
There is no transfer of liquid.
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PARALLEL FEED
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HORIZONTAL TUBE
EVAPORATOR
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STRUCTURE
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They consist of round or square shell and a horizontal tube bundle , which is square.
The consist steam in the tubes and feed outside.
0.75 in to 1.2 in outer dia.
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The require small head room.
Provide good space economy.
Small heat transfer coefficient.
Can not be used for high mineral and salt content.
Can not be used for forth liquid.
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Suited for the process where the final product is liquid, not solid; such as sugar syrup and edible drinks.
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Vertical type of evaporator. Tube sheets extending across the body
and central downtake. Tubes are rolled Between two tube
sheets, not more than 6’ high. Feed is introduced in the tubes. Flow area the downtake is one half area
of tubes and tubes having O.D. 3 in. Circulation is due to difference in
sp.gravity between bulk liquid and heated liquid.
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CALANDRIA TYPE EVAPORATOR
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CATCHALL
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Low head space required. High heat transfer coefficient. Lesser scaling problem . Relatively inexpensive. Not used for temp sensitive solution. Unsuitable for crystalline products. Used for concentration of sugarcane
juice.
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Removable tube bundle . Supported by internal brackets. Downtake occurs between the bundle
and the shell.
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BASKET TYPE EVAPORATOR
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No problem of differential expansion . Easy to clean.
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LONG
TUBE
EVAPORATOR
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FEED
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STRUCTURE & DETAILS….>>>
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Are also known by RISING FILM
EVAPORATORS.
Long Tubular Heating element.
Vapor Deflector present to Reduce
Entrainment.
Tube OD 5/4 to 2 in.
Tube length 12-32 ft.
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Advantages Disadvantages
Reduced floor space requirements
Relatively high heat transfer coff.
Ability to handle foamy liquids
High Head Room requirement
Hydrostatic head at bottom may increase product temperature & cause temp. sensitivity problems
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FALLING
FILM
EVAPORATOR
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STRUCTURE….>>>
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Feed fed from the top.
Feed distributors present.
Particularly used in application where
the temp. driving force b/w the heating
medium & liquid is small (less than 15 F)
Vapor/Liquid separator at the bottom.
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Advantages Disadvantages
Relatively low cost. Large heating
surface in one body. Low product hold-
up. Small floor
requirements. Good heat transfer
coff. at reasonable temp. differrences
High head room requirements.
Generally not suited for scaling and salting materials
Recirculation generally required.
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FORCED
CIRCULATION
EVAPORATO
RS
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STRUCTURE & DETAILS….>>>
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Difference b/w Natural & Forced
Circulation type evaporators.
Tube OD less than 2 in.
Used for conc. of sol. with poor flow,
scale & thermal characteristics.
Circulating Pump present at the bottom
to mix the feed & concentrate.
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Advantages Disadvantages
High heat transfer coff.
Reduced fouling & scaling.
Possibly high cost. A longer hold-up of
the product within the heating zone.
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Horizontal TypeForced CirculationEvaporators
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There is always liquid level above the topof a bundle of horizontal tubes. The
boiling pt. is being set up by the pressure at the liquid/vapor interface. This exerts the hydrostatic pressure upon the contact. The added pressure upon the liquid raises the boiling pt. at the heat transfer surface. This reduces the useful temp diff effective upon the heat transfer surface
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8.George G. B. , unit operations , pg no.474-482.
9.www.evaporator.com
10.www.wikipedia.org
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