Shortcut Distillation

Agung Ari Wibowo, S.T., M.Sc

Politeknik Negeri Malang

Malang - Indonesia

The use of separation column in HYSYS

The column utilities in HYSYS can be used to model a widevariety of chemical separation techniques includingabsorption, liquid-liquid extraction and distillation

Shortcut distillation The primary purpose of the shortcut distillation is to allow for

users to perform a first pass estimate on the performance

requirements of a given system for a specified reflux ratio. The

values gathered from the shortcut distillation utility can be used

to assist the user when setting up the complete distillation utility

in HYSYS, or when attempting to find reasonable column

properties to allow the system to converge (e.g. number of

trays, feed location, etc.)

The shortcut distillation utility within HYSYS allows users to

quickly model a distillation separation of a stream with relatively

little known information. Once the user attaches a fully defined

inlet stream to the shortcut distillation column, the essential

information that must be specified are as follows:

The vapor/liquid quality of the top product

The light key component and composition in the bottoms product

The heavy key component and composition in the distillate (top)

product

The condenser pressure

The reboiler pressure

The external reflux ratio

Shortcut distillation

What is Light and Heavy Key?

Light Key : a lighter component means a component with alower boiling point. Defined as lightestcomponent in the bottom product in asignificant amount

Heavy key : a heavier component means a component with ahigher boiling point. Defined as heaviestcomponent in the overhead product in asignificant amount.

*Note : Both Light and Heavy key depend on the componentin the stream

Shortcut distillation

With this information, the utility will run and, if possible, converge on a solution that

will meet the key component specifications. The critical information that the utility

will calculate are as follows:

Fully specified distillate product stream (temperature, pressure, flow rate,

composition)

Fully specified bottom product stream (temperature, pressure, flow rate,

composition)

Condenser operating temperature and heat duty

Reboiler operating temperature and heat duty

Minimum number of trays (calculated by Fenske Methode)

Actual number of trays (minimum/theoritical tray devided by tray efficiency)

Optimum feed tray location

Reflux minimum (Calculated by Underwood Methode)

Shortcut distillation

A distillation column is used to separate mixed compound of Benzene,

Toluene and p-xylene. Feed entering to the column at 20°C and 1 atm

with mass flow 500 kg/hr. The attempt of this separation process is to

get benzene with purity of 99.9% (top product only Benzene and

Toluene) . And the benzene composition at the bottom will be 0.1%. If

the column operate isobarically and R= 1.18 Rm. What is the

composition of the product (top and bottom), and what is the

temperature of reboiler (Use Peng-Robinson as Fluid Package)?

Case

Feed Composition Mole Fraction

Benzene 0.35

Toluene 0.25

p-xylene 0.40

Case

Case

Case

Case

Case

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Case 2

Ethyl benzene is produced by the reaction of ethylene and benzene. The

reactor which being used has the maximum conversion of 80% and operated

adiabatically. The feed of the reactor consist of pure ethylene, benzene and

recycle stream from Flash Separator. The product from the reactor is cooled to

64 C, and then flash separated. The bottom product of the Flash Separator will

be separated using distillation column to get high purity E-benzene. If the

column bottom product only consist of Benzene and E-benzene in which the

mole fraction of benzene is 0.1% and in the Top product the mole fraction of

E-Benzene is 0.01%, determine in which stage feed should enter the column?

Column operated isobarically.

C2H4 + C6H6 →C8H10

Component Benzene Ethylene

Temperature (C) 25 25

Pressure (atm) 1 1

Molar Flow (kmol/hr) 500 450

Fluid Package (Peng-Robinson)

R = 1.26 Rm Distillate Phase : Vapor

Case 2

Case 2