Evaporators

Work of:-

Abhinav,Aseem Mittal,Ashok Kumar and Naval Chaudhary

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VAPORIZATION

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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 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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… DRYING

EVAPORATIO N

V/S DISTILLATION

CRYSTALLIZATION 4

… CLASSIFICATION OF TUBULAR VAPORIZING EQUIPMENT BOILERS

VAPORIZING EXCHANGERS EVAPORATOR

(Fuel energy

Latent heat

(Latent heat or sensible heat

of vaporization) Latent heat of vaporization)

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 Difference

between….

1. Evaporator and Reboiler ,

2. Evaporator and Vaporizer,

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 2. 3.



  

Types of evaporator… Power plant evaporator Chemical evaporator. COMPERISION BETWEEN POWER PLANT & CHEMICAL EVAPORATOR B.F.W. BLOWDOWN B.P.R.

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CHEMICAL EVAPORATOR

.

SINGLE EFFECT

NATURAL CIRCULATION

MULTIPLE EFFECT

FORCED CIRCULATION

HORIZONTAL TUBE

INSIDE VERTICAL HEATING ELEMENT

CALANDRIA VERTICAL TUBE

VERTICAL EXTERNAL ELEMENT

BASKET VARTICAL TUBE

HORIZONTAL EXTERNAL ELEMENT

LONG TUBE VERTICAL 9

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 3. Batch mode 4. Semi batch mode 5. Continuous batch mode 6. 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 24

The dilute liquid enters an intermediate effect.  Eliminates some of the pumps as needed in backward feed. 

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MIXED FEED 26

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 29

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. 33



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 38

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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 S

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FEED 47

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. 50







Reduced floor space requirements Relatively high heat transfer coff. Ability to handle foamy liquids

Advantages





High Head Room requirement Hydrostatic head at bottom may increase product temperature & cause temp. sensitivity problems

Disadvantages 51

FALLING FILM EVAPORATOR 52

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. 54

 

 



Relatively low cost. Large heating surface in one body. Low product hold-up. Small floor requirements. Good heat transfer coff. at reasonable temp. differrences

Advantages







High head room requirements. Generally not suited for scaling and salting materials Recirculation generally required.

Disadvantages 55

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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. 60





High heat transfer coff. Reduced fouling & scaling.

Advantages

 

Possibly high cost. A longer hold-up of the product within the heating zone.

Disadvantages

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Horizontal Type Forced Circulation Evaporators 62

There is always liquid level above the top of 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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