Fractional Distillation

Overview of Fractional Distillation – As we know that fractional distillation is very important for chemical engineers, process Engineers and project engineers . In this article we will study “what is fractional distillation ” what is distillation , lab level distillation set up , large industrial level fractional distillation , small scale fractional distillation ,and medium scale fractional distillation, distillation column, types of distillation column, packing, types of packing, structure packing, types of trays , bubble cap tray .

You can study types of distillation and what is distillation in previous article.

In this article cover some following points ,

A) Fractional Distillation Overview
B)Types
C)Equipment list
D)Process
E)Design

Fractional distillation

This is one of the separation process in which chemical compounds are separated by heating to them .

In this process mixture of chemical is heated indirectly , using steam or high therm oil as heating source. After Heating to mixture of chemicals , low volatile(or mixtures of two chemical) start to vaporize . Vapor then pass to column. Vapor of low volatile chemicals is then go to Condenser , condenser condense the material and we get the separation . However , this is not so simple as I told , separation is not possible in this way easily , to get separation we need maintained some reflux and do some other things too. We will discuss each thing in details.

Distillation is a process of getting purity of chemical or solvent. Chemicals are separated due to difference on there vapor pressure or boiling point . This is most widely used process in chemical,oil,pharma and distillery industry.This is simplest method to separate the mixture of chemicals or solvents. One of the example of this distillation is , crude oil distillation.

Types of Fractional Distillation

Depending on operation conditions, Fractional distillation is classified as

A)Reduced pressure fractional distillation(vacuum distillation)

B)High pressure fractional distillation

C)Atmospheric pressure fractional distillation

Reduced pressure Distillation (Vacuum distillation )

In this type separation process is carried out under reduced pressure or under vacuum .

This process is mostly used for chemicals having high boiling point . This is less expensive process than other distillation process. In vacuum distillation , vacuum pump or water ejector or steam ejector is use to reduce the pressure of distillation column or all distillation system.

As we know that relationship between boiling point and pressure , when we reduce the pressure then boiling point of chemical also get reduced.

Relationship of pressure and boiling point is

Increase the pressure ——– boiling point increase

Reduce the pressure —– boiling point decreases.

If you don’t know about relationships between pressure and boiling point then you have to study Antoine Equation .

Atmospheric Distillation

This distillation is carried out at atmospheric pressure .
This distillation is use for separation of low boiling compounds or chemicals.

High pressure distillation

This distillation is carried out at high pressure

We can do Classification of fractional distillation on the basis whether continue or batch also .

A) Continues distillation

B) Batch distillation
Continues Distillation

In this type , feed come continuously at bottom and product will get continues on top . It operation time is 24 hrs x 365 days ,until shutdown for until maintenance.

Batch Distillation

In batch distillation we will do operation batch wise .

P & ID of distillation | Fractional distillation

Fig PFD of fractional distillation

Equipment list

Pre-heater – to pre-heat the feed up to a certain temperature

Reboiler – used to evaporate the Crude mixture
Distillation column – for separation
Packaging or tray – to get quality in separation

Distributor – this column internal required to distribute the liquid on packing
Collector – to collect all liquid
Primary condenser or – to condense the vapor

Secondary Condenser – to un-condensed vapor
Reflux drum – to collect the condensed vapor
Product receiver – to collect the product

Product cooler – to cool the distillate
Reflux pump – to mention reflux if not possible by gravity
Bottom circulation pump – to circulate the column bottom from bottom to reboiler

white-space: pre-wrap;”>Residue Receiver – to collect residue of distillation F
Feed pump(Types of pumps) to feed the crude

Process

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Process of it include , preheating of feed (crude), heating of crude in reboiler to evaporate , separation of chemicals in column , condense the vapor in Condenser , reflux .

In this types of distillation we feed the crude in to ratiocination column at its feed point location .Feed may be Saturated liquid , cooled liquid ,sub-cooled liquid or mixture of vapor liquid ,it may depend on particular process. Feed enter to the distillation column and get boiling or evaporate at bottom using reboiler.

Some time pump(pump data sheet) is used to circulate the crude from bottom of distillation column to reboiler. Some time crude will get circulate due to density difference. Vapors are go to the distillation column . In distillation column there are two sections , first is stripping section and second is rectification section.

In stripping section , low volatile material is get striped from vapor of crude mixture . In rectification section high volatile material is get heated and go with vapor . Finally vapor get condensed in the condenser or partial condenser . After condenser, material is go to the reflux drum and get divide as refluxed or collection. Residue will get from bottom of distillation column.

Above is process of distillation in short .

Types of trays in distillation column

There are four types of distillation trays ,

1) Bubble cap trays

2) Sieve trays

3) Duel flow trays

4) valve trays

Types of packing in distillation column

There are two major types of distillation column packing.

1) Structure Packing

2) Random Packing

Tray verses Packing

Tray have high pressure drop as compared to packing .

Highest resistance will get in tray type distillation column

Design of Distillation Column

To design fractional distillation column ,first we need to decide the design parameters .

Design parameters

To design distillation column we need have some data like

a)Crude Feed composition

b)Crude state (vapor or liquid )

c)Required Distillate product purity

d)Bottom residue desired composition
e)Continues distillation or batch distillation

After getting above data , we can start to design process .

Design process of fractional distillation column

A) Make PFD with material balance

B) Do energy balance

C) prepare equipment list

D) Capacity design

E) Choose reboiler

F) Choose packing or tray

G) Calculate required number of tray
Conclusion

I hope ,you enjoy the above article . This article gives you knowledge about what is distillation , distillation column ,fractional distillation ,batch distillation , types of fractional distillation , continues distillation .If you still confused about process of fractional distillation please read above article once again . Also read the review of Fractional distillation.

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Fractional distillation is separation process in which chemicals are separated due to boiling point difference.vacuum Distillation, distillation column design ,batch Distillation, continues Distillation,simple Distillation.

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5.Fractional Distillation Advantage and dis-advantess