evaporators

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

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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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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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

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

Liquid feed flows in reverse direction of vapors .

Pump is required at each effect.

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BACKWARD FEED

The dilute liquid enters an intermediate effect.

Eliminates some of the pumps as needed in backward feed.

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MIXED FEED

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

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

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

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….>>>

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….>>>

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….>>>

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

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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