o10 pp 04.01_the distillation process

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Operations JG10

Module 4 Basic Distillation

Lesson 1 The Distillation Process

REV: F.02DATE: 23OCT20101-1

REF CODE: O10-232-04.01DOC: O10-PP-04.01

SASREF PCP-2


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Table of Contents

Lesson Objective

Introduction to Distillation

o Batch Distillation

o Repeated Evaporationand Condensation

o Economical Use of Heat

o Use of Reflux

o Continuous Distillation

The Distillation Column

oAtmospheric Distillation

o Pressure Distillation

The Distillation Process

Trays

o Sieve Tray

oValve Tray

Summary

Knowledge Reinforcement& Self Check

1-2REF CODE: O10-232-04.01


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Lesson Objective

After completing this lesson, you will be able to:

Describe the basics of the distillation process.

1-3REF CODE: O10-232-04.01


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Introduction to Distillation

Volatility

Distillation uses the difference in volatility of the compoundsto separate liquid/liquid mixtures

More volatile more easily evaporated

Closely connected to the boiling-point of a liquid

1-4REF CODE: O10-232-04.01


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100 kg mixture, (50%

pentane and 50%heptane)

50 kg pentane (C5H12,

boiling point 36C) 50 kg heptane (C7H16,

boiling point 98C)

Batch Distillation

1-5REF CODE: O10-232-04.01

Batch Distillation


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Batch Distillation

Temperature of 51C

Heptane and pentane contribute to total pressure in thevessel

At boiling point - total pressure is 1.013 bar

After analysis

o 90% pentane

o 10% heptane

Comparing original liquid composition with the formedvapour composition

o Liquid = 50% pentane and 50% heptane

oVapour = 90% pentane and 10% heptane

1-6REF CODE: O10-232-04.01


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Batch Distillation

1-7REF CODE: O10-232-04.01

Batch Distillation


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Batch Distillation

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Preferable method of separatinghomogeneous liquid mixtures

Using extraction, absorption, anddesorption methods

Distillation

Use differences in volatility of componentsto separate the liquids

Only used if the boiling points of theliquids are different

Liquid mixture is brought to boil, a vapourproduced

DistillationProcess

REF CODE: O10-232-04.01


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Repeated Evaporation and Condensation

Mixture

30% pentane (C5H12), boiling point 36o

C 70% heptane (C7H16), boiling point is 98

oC

1-9REF CODE: O10-232-04.01

Repeated Evaporation and Condensation

i l f


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Economical Use of Heat

Heat of Condensation

Used for the evaporation of the liquid Remove condensers between the vessels and burners

Vapour lines made longer

Add insulation

1-10REF CODE: O10-232-04.01

Economising the Process

E i l U f H


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Composition Change

Amount of heptane in thevapour is reduced

Small portion of heptane

remains in the product Pentane is not pure

Must find solution to createa final pure product

Economical Use of Heat

1-11REF CODE: O10-232-04.01

Composition Change in

Vessel A

U f R fl


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Use of Reflux

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Composition of

Liquid Mixture

Composition of

Vapour Formed

Boiling Point

Temperature

30% pentane

70% heptane

77% pentane

23% heptane60C

77% pentane

23% heptane

97% pentane

3% heptane42C

97% pentane

3% heptane

99% pentane

1% heptane37C

99% pentane

1% heptane100% pentane 36C

REF CODE: O10-232-04.01

U f R fl


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Reflux

Add branch to the rundownline

Return portion of

condensed and cooledproduct back to vessel D

Temperature at 36C

o Prevent increase of

heptaneo Composition of the

liquid in vessel D fixedat 99% pentane and

1% heptane

Use of Reflux

1-13REF CODE: O10-232-04.01

Reflux Line to Vessel D

C ti Di till ti


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Continuous Distillation

Continuous Process

Number of vessels increased

Mixture fed continuously

Function of loop seals

Feed mixture (30% pentane and 70% heptane) preheatedto 79C

o Fed into vessel D

o Feed partially evaporated

Composition of the vapour

o 46% pentane

o 54% heptane

1-14REF CODE: O10-232-04.01

C ti Di till ti


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1-15REF CODE: O10-232-04.01

Continuous Distillation Process

C ti Di till ti


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1-16

Feed streamVessel A

From other process liquids or from steamgenerated by waste heat

HeatSupply

Furnaces Heat exchangers

Heatingthe FeedStream

REF CODE: O10-232-04.01

Contin o s Distillation


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Reboiler

Heats returning liquid

Evaporation of liquid fromvessel A

Flow created Bottom product boiled twice

Advantage

o Bottom product (nearlypure heptane - 99.5%) -heated up again

o Evaporates nearly all ofthe remaining pentane


1-17REF CODE: O10-232-04.01

Reboiler



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1-18REF CODE: O10-232-04.01

Continuous Distillation Process with Reboiler



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Description

Set of vessels placed ontop of each other

Separated by perforated

plates trays Vapour and liquid flows are

inside the column


1-19REF CODE: O10-232-04.01

Distillation Column



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Process

Feed stream enters thedistillation column at tray D

Feed stream preheated to

79C Enters the tower as part

vapour and part liquid

Vapour rises

Liquid collects on the traysand drains to the bottom ofthe column


1-20REF CODE: O10-232-04.01

Distillation Column



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Rectification

Rising vapour - mixture ofpentane and heptane

Heptane is less volatile

o Condenses easier

o Collects on trays where itdrains to the bottom

Vapour rises

o Becomes more pure

pentane

Removal of the less volatilecomponents out of thevapour, by condensation with

the liquid on the tray


1-21REF CODE: O10-232-04.01

Distillation Column



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Stripping

Pentane removed out of thedownward flowing liquid

Pentane evaporates moreeasily

o Producing a more pureheptane product

Removal of the more volatilecomponents out of the liquid

on the tray throughevaporation

Light product

Heavy product


1-22REF CODE: O10-232-04.01

Distillation Column

Atmospheric Distillation


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General Information

Distillation in which thepressure in the distillationcolumn equals the pressure

of the surrounding air Pressure is 1.013 bar

Vent on top of theoverhead accumulator that

is open to the atmosphere

Atmospheric Distillation

1-23REF CODE: O10-232-04.01

Overhead Accumulator Vent

Pressure Distillation


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Pressure Distillation

General Information

Distillation under a pressure higher than atmosphericpressure

Example: propane

o Boiling point -42C under atmospheric pressureo Reflux as a liquid

o Cooling medium

Air or cooling water

Increase boiling point of propane

Increase pressure

Used if the top product cannot be condensed by coolingwater or air

1-24REF CODE: O10-232-04.01

Trays


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Trays

General Information

Separate column into sections where

o Light components are stripped out of the downwardflowing liquid

o Heavy components are removed out of the rising vapour Two types of trays:

o Sieve trays

oValve trays

1-25REF CODE: O10-232-04.01

Sieve Tray


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General Information

Plate with a number ofholes drilled through itcreating a sieve

Vapour can travel upwardthrough the holes, butcannot travel downward

Liquid collects on top of the

trayo Flows over the

downcomer to fall to thetray below

Sieve Tray

1-26REF CODE: O10-232-04.01

Sieve Tray

Sieve Tray


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General Information

Liquid falls from tray totray

o Interacts with the rising

vapouro Collects heat until the

more volatilecomponents in liquid

gain enough heat tovaporise and start theprocess over

Less volatile componentsfall to the bottom

Sieve Tray

1-27REF CODE: O10-232-04.01

Sieve Tray and Downcomers

Sieve Tray


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Sieve Tray

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Vapour spread by the holes in theplate

Good contact between vapour andliquid

Relatively inexpensive

Advantages

Only good for high vapour load

Vapour load is low, liquid flowsdownward through the holes,causing poor fractionation

Disadvantages

REF CODE: O10-232-04.01

Valve Tray


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Valve Tray

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Plate with holes and a downcomer

On valve tray, the downcomer is fittedwith a weir

Liquid level always maintained

Valves fitted into the holes on the tray

Description

No vapour

Valve is nearly closed

Vapour flow increases Pressure below the tray will increase

and lift the valve

ValveFunction

REF CODE: O10-232-04.01

Valve Tray


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Valve Tray

Vapour

Passes through the tray with the upward movement of thevalve.

Load increases valve lifts upward

Maximum open positiono Hooks pressed against the bottom side of the tray

Load decreases

o Mass of valve pulls it down, closing off the opening

1-30REF CODE: O10-232-04.01

Valve Tray


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Valve Tray

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Ability to handle load changes

Larger capacity than other tray types

Promotes good fractionation

Advantages

High cost

Sensitivity to dirt or debris

Dirt or debris may interfere with thevapour and liquid flows - affectingfractionation

Disadvantages

REF CODE: O10-232-04.01

Valve Tray


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Valve Tray

1-32REF CODE: O10-232-04.01

Valve Tray

Valve Tray


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Valve Tray

1-33REF CODE: O10-232-04.01

Top of Valve Tray

Valve Tray


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Effects of Pressure

Pressure under the traylifts the valve open to allowvaporto pass through

Valve travel limitedo Short legs at right

angles

Valve Tray

1-34REF CODE: O10-232-04.01

Tray Valve

Valve Tray


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Valve Tray

1-35REF CODE: O10-232-04.01

Double Valve

Summary


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Summary

In this lesson, you learned:

Separation by distillation is reached by repeated evaporation andcondensation

At a certain composition, a mixture starts boiling

In distillation, the heat of condensation of the vapour is used to

evaporate the liquid on the tray above To prevent heavy components (bottom product) from entering the

top product, a part of the top product is brought back as reflux intothe column

The purpose of the reflux

About rectification and stripping

About atmospheric distillation and pressure distillation

The advantages and disadvantages of a sieve tray

About the valve tray

1-36REF CODE: O10-232-04.01

Knowledge Reinforcement & Self Check


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The removal of heavy components out of the rising vapour is

called.

A. Evaporation

B. Condensation

C. Stripping

D. Rectification

1-37REF CODE: O10-232-04.01



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The removal of heavy components out of the rising vapour is

called.

A. Evaporation

B. Condensation

C. Stripping

D. Rectification

1-38REF CODE: O10-232-04.01



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The removal of the light components out of the downward

flowing liquid is called.

A. Stripping

B. Evaporation

C. Rectification

D. Condensation

1-39REF CODE: O10-232-04.01



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The removal of the light components out of the downward

flowing liquid is called.

A. Stripping

B. Evaporation

C. Rectification

D. Condensation

1-40REF CODE: O10-232-04.01



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List the advantages and disadvantages of a sieve tray.

1-41REF CODE: O10-232-04.01



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List the advantages and disadvantages of a sieve tray.

The advantage of a sieve tray is that the vapour isspread by the holes in the plate, so there is goodcontact between the vapour and the liquid. Another

advantage is that sieve trays are relativelyinexpensive, compared to other tray types.

The disadvantage of the sieve tray is that it is onlygood for high vapour load. When the vapour load isrelatively low, the liquid will flow downward throughthe holes, causing less contact between the vapourand the liquid and thus causing poor fractionation.

1-42REF CODE: O10-232-04.01



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List the advantages and disadvantages of a valve tray.

1-43REF CODE: O10-232-04.01



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List the advantages and disadvantages of a valve tray.

The advantage of valve tray is its ability to handleload changes. The valve tray has a larger capacitythan other tray types. The valve tray facilitates good

contact between the vapour and the liquid, andtherefore, promotes good fractionation.

The biggest disadvantages of the valve tray are itshigh cost and its sensitivity to dirt or debris in thetower.

1-44REF CODE: O10-232-04.01



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o g o

What is the purpose of reflux?

1-45REF CODE: O10-232-04.01



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g

What is the purpose of reflux?

The purpose of the reflux is to condense the heavycomponents out of the rising vapour, so the heavycomponents will flow downwards with the liquid as

bottom product.

1-46REF CODE: O10-232-04.01



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g

Explain how the volatility of a liquid affects its behaviour in adistillation column.

1-47REF CODE: O10-232-04.01



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g

Explain how the volatility of a liquid affects its behaviour in adistillation column.

The higher volatility components will go to the top, thelower volatility components will go to the bottom.

1-48REF CODE: O10-232-04.01

Document Revision History


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y

Rev No DRPF No Change Description Date Initial

A.01 New 22OCT2010 TDN

F.02 Ready for SASREF Initial Review 23OCT2010 DFH

o10 pp 04.01_the distillation process

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