HYSYS Training 2013

1

CHEN64372: Distillation System Design

HYSYS Training

February 2013

1 – Getting Started with HYSYS

Open the HYSYS Getting Started Guide.pdf document and start HYSYS.

You can start HYSYS by doing one of the following:

1. From the Start > All Programs menu, select AspenTech > Process Modeling V7.3 > Aspen HYSYS >

Aspen HYSYS command.

2. Follow the path: C:\Program Files (x86)\AspenTech\Aspen Hysys V7.3\hysys.exe.

Work through the Getting Started Guide to start getting familiar with the concept of [steady state] process

simulation.

Your aim is to:

• familiarise yourself with HYSYS interfaces

• successfully open and save (in your own directory!) a HYSYS file

• learn how to interrogate a pre-prepared simulation case

• learn how to make changes to a pre-prepared simulation case

• start to become familiar with the Workbook feature of HYSYS

Note that AspenTech packages can only be run from University PCs (for licensing reasons). AspenTech

Process Modeling is available in B12, C32 of the Mill and the Barnes Wallis Cluster.

2 – Creating a process flowsheet in HYSYS

Intended learning outcomes:

• use HYSYS to set up a process flowsheet simulation

• view simulation inputs and check outputs using the Workbook function

Refrigerated Gas Plant – Workshop example kindly provided by AspenTech

Start HYSYS by doing one of the following:

1. From the Start > All Programs menu, select AspenTech > Process Modeling V7.3 > Aspen HYSYS >

Aspen HYSYS command.

2. Follow the path: C:\Program Files (x86)\AspenTech\Aspen Hysys V7.3\hysys.exe.

2

Background

Model description

In this HYSYS example we will build the above flowsheet by following the ste-by-step instructions below.

The feed (To Refrig) is a natural gas stream which may possibly contain a small amount of liquid (removed

in Inlet Separator if present). Before the gas can be sent to the export pipeline it must be chilled to knock

out any heavy hydrocarbons (which are removed in a second 2-phase separator). The gas is cooled by a

refrigerated chiller (called Chiller). In this model the refrigerant side of the exchanger is not simulated so a

Cooler unit operation is used. The feed gas is pre-chilled in a Heat Exchanger unit operation (Interchanger)

using the cold gas leaving the Low Temperature Separator.

The specification for the exported gas is that the dew point temperature at a pressure of 60 bar must not

be higher than -15 C. To simulate this a copy of the product stream is created called HC Dewpoint. A

Balance block (BAL-1) is used to copy the composition of the Sales Gas into this new stream. The other

conditions of the HC Dewpoint stream are set to 60 bar and vapour fraction of 1 (i.e. to be at its dew point

at 60 bar). Finally an Adjust block (ADJ-1) is used to automatically adjust the chiller exit until the 60 bar dew

point is at the specification of -15 C.

Creating a Fluid Package

The first step in HYSYS is to create a Fluid Package which is a set of components and your choice of a

physical property calculation method.

1 Start HYSYS and use menu option File > New > Case to create a new simulation (alternatively click on the

New Case icon or press Ctrl-N)

2 The simulation basis manager appears. This is where you choose components and physical property

methods. To add a component list, click on the Add button.

3

3 The add component form appears:

Add the following components: Methane, Ethane, Propane, i-Butane, n-Butane, i-Pentane, n-Pentane,

n-Hexane, Nitrogen, H2S, CO2.

You will see some of these components displayed at the top of the list of available components. Click on

the component to Select it and then click on the Add Pure button. For some of the other components

e.g. Nitrogen you will need to start typing the name in the Match field before you can select it.

When you have finished adding components, close the components window.

4 Switch to the Fluid Pkgs tab and click on the Add button:

4

5 Scroll down through the list of available property packages and select the Peng Robinson equation of

state. (This is a good general purpose package for hydrocarbons.) Rename the fluid package "GasPlant"

and close the Fluid Package window.

Creating a Process Flowsheet

6 Click on Enter Simulation Environment – see Step 4. The PFD

(Process Flow Diagram) window will open.

You can now start adding streams and unit operations using

the Palette (use F4 to make it appear and disappear or press

button )

a) Left-click once on an item, move into the window and

left-click again to 'drop' the item there, or

b) Drag and drop an item by using the right-click button

(click, hold, drag, let go)

7 Add a stream. Double-click on the stream to open its input form.

Name: ToRefrig

Temperature: 15°C

Pressure: 6200 kPa

Molar flow: 1440 kmol h–1

5

Click on Composition in the left pane and enter the stream composition. Close the input form for the

stream ToRefrig. As all properties of this stream are now determined, the colour of the bar at the

bottom of the input form will have changed from yellow to green. Additionally, the colour of the stream

icon will have changed from light to dark blue.

8 Next add a Separator unit operation on to the flowsheet to model the Inlet

Separator. It will be shown in Red as there are no streams connected yet.

Double click on the Separator to open its input form and select To Refrig as

the input stream. Enter the names of the product streams Inlet Sep Vap

and Inlet Sep Liq.

As soon as you have entered

the name of the second product

stream it will solve the

separator. (Note that no liquid

is produced.)

Click on the Worksheet tab to

see the results for the streams

connected to this unit

operation. (Note there is no

liquid product produced.)

Save your simulation (in your

p:\ drive).

Name To Refrig Inlet Sep Liq Inlet Sep Vap

Vapour 1 0 1

Temperature [C] 15 15 15

Pressure [kPa] 6200 6200 6200

Molar Flow [kgmole/h] 1440 0 1440

Mass Flow [kg/h] 29884.89251 0 29884.89251

Std Ideal Liq Vol Flow [m3/h] 88.29754564 0 88.29754564

Molar Enthalpy [kJ/kgmole] -81253.10473 -111185.1717 -81253.10473

Molar Entropy [kJ/kgmole-C] 149.3658883 118.6952453 149.3658883

Heat Flow [kJ/h] -117004470.8 0 -117004470.8

mole fractions

Methane 0.7576

Ethane 0.1709

Propane 0.0413

i-Butane 0.0068

n-Butane 0.0101

i-Pentane 0.0028

n-Pentane 0.0027

n-Hexane 0.0006

Nitrogen 0.0066

H2S 0.0003

CO2 0.0003

6

9 Add streams and unit operations to complete the flowsheet shown in the diagram on page 1.

i) Interchanger: Heat Exchanger Unit Operation – Note that there are several types

of heaters and coolers. Take care about which streams you allocate to the Tube

side and Shell side of the heat exchanger! The stream Inlet Sep Vap should enter

the Tube side and the stream LTS Vap should enter the Shell side.

Tube-side Delta-P 35 kPa; Shell-side Delta-P 5 kPa (Parameters form)

Exchanger UA 2.7e5 kJ/C.h (Parameter form or Specs form)

Model (Exchanger Design(Weighted) (Parameters form)

Do you understand why the message 'Not solved' appears?

ii) Chiller: Cooler Unit Operation

Delta-P 35 kPa

Enter a starting guess for the exit temperature of -16 C. Add this in the input form for the exit stream

“Gas to LTS”

Note that you must define an Energy stream for the Chiller (to represent the cooling duty) called

“Chiller Q”

7

ii) Low Temperature Separator – a Separator Unit Operation

The Low Temperature Separator is referred to as 'LTS' in stream names.

10 Viewing the process flow diagram

Can you tidy up the layout of the flowsheet for ease of use and clarity?

Hint: Right-click on a label for a stream or unit operation, select "Move/Size Label", click on the white

box around the label and drag the box to move the label.

11 Viewing stream data using the Workbook – icon is in the tool bar:

The Workbook presents tables of data for Material streams, Energy streams, Stream compositions and

summarises the Unit Operations present.

8

12 The model should completely solve with the above data. Click on the Workbook icon to see a summary

of the stream results, which should match these:

Adding Balance and Adjust blocks

13 Drop a Balance block on to the flowsheet (near to the Sales Gas stream). A Balance block is at the

bottom left of the Palette. Double click on it to open the input form:

Select Sales Gas as the Inlet Stream and enter “HC Dewpoint” as the name of the Outlet Stream. Switch

to the Parameters tab and select the Component Mole Flow option for the type of Balance. This simply

copies the molar flows of each component from the inlet stream to the outlet stream but leave the

other data undefined. Close the Balance input form.

Name To Refrig Inlet Sep Vap Inlet Sep Liq Gas to Chiller

Vapour Fraction 1 1 0 0.96721349

Temperature [C] 15 15 15 -4.618347677

Pressure [kPa] 6200 6200 6200 6165

Molar Flow [kgmole/h] 1440 1440 0 1440

Mass Flow [kg/h] 29884.89251 29884.89251 0 29884.89251

Liquid Volume Flow [m3/h] 88.29754564 88.29754564 0 88.29754564

Heat Flow [kJ/h] -117004470.8 -117004470.8 0 -119033606.8

Name LTS Vap Sales Gas Gas to LTS LTS Liq

Vapour Fraction 1 1 0.904129152 0

Temperature [C] -16 9.680660011 -16 -16

Pressure [kPa] 6130 6125 6130 6130

Molar Flow [kgmole/h] 1301.945978 1301.945978 1440 138.0540217

Mass Flow [kg/h] 25597.02898 25597.02898 29884.89251 4287.863526

Liquid Volume Flow [m3/h] 77.92694944 77.92694944 88.29754564 10.3705962

Heat Flow [kJ/h] -106166138.9 -104137002.9 -120569162.7 -14403023.74

9

14 Double click on the HC Dewpoint stream to open its input form. You can see the flow is shown in black

(i.e. a result not a model input) as 1302 kmol/h. Enter the pressure as 6000kPa (60 bar) and set the

Vapour Fraction to 1 (i.e. at its dew point). The stream should now calculate and the dew point

temperature should be displayed as -15.82°C.

15 You can change the temperature of the Gas to LTS stream manually and see how the dewpoint

temperature of the Sales Gas changes. It is convenient to use the Workbook:

16 We want the dew point to be exactly -15°C. Instead of manually changing the temperature of the

Chiller exit stream, we will use an Adjust block to automatically do this. Click on the Adjust block icon

, drop it onto the flowsheet and open its input form.

10

The Adjusted Variable will be the temperature of stream Gas to LTS. Click on the Select Var... button to

specify this.

In the same way specify the Temperature of stream HC Dewpoint as the Target variable. Specify -15°C

as the value of the Target Variable.

There is a warning about Unknown Maximum. Switch to the Parameters tab: Enter -30°C as the

minimum value for the adjusted variable and -5°C as the maximum. The Adjust block should solve as

soon as you have entered these limits.

11

Check the temperature of stream HC Dewpoint – it should be -15°C (plus or minus the tolerance of

0.1°C). Check the temperature of stream Gas to LTS – it should be close to -15.17°C.

17 Open the workbook and check your results.

18 Save your simulation (in your p:\ drive).

3 – Binary Distillation Modelling in HYSYS


• use HYSYS to predict binary vapour-liquid equilibrium

• use the shortcut distillation model in HYSYS for a binary separation

• use the rigorous distillation model in HYSYS for a binary distillation

• use the databook and case study tools in HYSYS

A binary mixture of benzene (1) and toluene (2) is to be separated by distillation at atmospheric pressure,

101.325 kPa. The feed and products are all saturated liquids at atmospheric pressure. You may assume that

the Peng-Robinson equation of state is suitable for representing this mixture.

Name To Refrig Inlet Sep Vap Inlet Sep Liq

Vapour Fraction 1 1 0

Temperature [C] 15 15 15

Pressure [kPa] 6200 6200 6200

Molar Flow [kgmole/h] 1440 1440 0

Mass Flow [kg/h] 29884.89251 29884.89251 0

Liquid Volume Flow [m3/h] 88.29754564 88.29754564 0

Heat Flow [kJ/h] -117004470.8 -117004470.8 0

Name Gas to Chiller LTS Vap Sales Gas

Vapour Fraction 0.968893565 1 1

Temperature [C] -4.231353288 -15.17291076 9.701386445

Pressure [kPa] 6165 6130 6125

Molar Flow [kgmole/h] 1440 1310.029538 1310.029538

Mass Flow [kg/h] 29884.89251 25818.23339 25818.23339

Liquid Volume Flow [m3/h] 88.29754564 78.50266912 78.50266912

Heat Flow [kJ/h] -118983714.8 -106845197.8 -104865953.8

Name Gas to LTS LTS Liq HC Dewpoint

Vapour Fraction 0.909742734 0 1

Temperature [C] -15.17291076 -15.17291076 -15.00034875

Pressure [kPa] 6130 6130 6000

Molar Flow [kgmole/h] 1440 129.9704623 1310.029538

Mass Flow [kg/h] 29884.89251 4066.659125 25818.23339


Heat Flow [kJ/h] -120449656.4 -13604458.55 -106744583

12

1 Start HYSYS and Open a New Case.

2 Create a Fluid Package

Add Components Benzene and Toluene by typing in to Match Full name/synonym. In the Fluid Pkgs

tab, Add the fluid package Peng-Robinson. Enter the Simulation Environment.

3 Add a stream to the flowsheet using the Palette. Use HYSYS to generate vapour-liquid equilibrium

data at atmospheric pressure. Plot the equilibrium data – i.e. mole fraction of benzene in the vapour

phase (y-axis) vs. mole fraction of benzene in the liquid phase (x-axis). Equilibrium information may

be obtained from Feed stream property table (K value).

4 Add a Feed stream with the following flow rate, composition and condition and product purities:

Composition (mole fraction of benzene)

Flow rate

(kg/h)

Feed thermal

condition, q

Feed,

z1

Distillate,

xD,1

Bottom

product, xB,1

30,000 1 0.44 0.975 0.035

Add a Short Cut Distillation unit to the process flow diagram.

Double-click on the unit to open the dialogue box. In the Design tab, on the Connections page,

provide names for the product streams and the reboiler and condenser duties.

`

In the Design tab, enter the design Parameters (including key components, their purities and the

actual reflux ratio once the minimum reflux ratio has been calculated). Note the minimum reflux

ratio.

You may assume that the column pressure is uniform and equal to atmospheric pressure. Select an

External Reflux Ratio that is 10% greater than the minimum reflux ratio to determine the number of

stages required for the separation.

13

The light key component is that which is mainly recovered in the Distillate and the heavy key

component is that recovered to the Bottom product.

View the results in the Performance tab – note the minimum reflux ratio, Rmin, actual reflux ratio, R,

and minimum number of stages, Nmin, for the required separation, as well as the duty of the

condenser and reboiler.

5 Apply the shortcut distillation model repeatedly for R/Rmin ratios of 1.02, 1.05, 1.1, 1.2, 1.5 and 2.

Record the results of:

External reflux ratio

Actual number of trays

Condenser duty

Reboiler duty

You may wish to plot the number of stages required (y-axis) vs. the reflux ratio (x-axis).

6 Use Databook to record multiple ‘states’. Select Databook from the Tools menu.

In the Databook form that appears, click Insert and then find the Object (the shortcut column) and

Variable (e.g. External reflux ratio) that you wish to select. Click Add. Repeat for the other variables

you wish to Add (Actual trays, condenser duty, reboiler duty). Close the Variable Navigator.

In the Data Recorder tab of the Databook, Add an Available Scenario and give it a name (e.g. Reflux

ratio). Check the Include boxes for all the variables.

14

Allow both the Column form (on the Design Parameters page) and the Databook form to be visible.

Enter the actual reflux ratio for the column (e.g. the value 1.02@Rmin) and click on Record in the

Databook form. Give the new solved state a name (e.g. “1.02Rmin”) then click OK. You can View your

results – select to view as a Table.

7 Using a Case study to generate multiple ‘states’. Choose the Case Study tab in the Databook form.

Add a case study and give it a name (e.g. Reflux ratio case study). As we have already defined

variables for the Databook, these are available for selection. For a case study, we need to select at

least one Independent variable, and select one or more Dependent variables. Here we select the

External reflux ratio as the independent variable and all the others as dependent variables.

Click on View to see the Case Studies Setup form; input the upper and lower bounds for the variable

(Low Bound, High Bound) and the step size. Choose a lower bound close to Rmin and an upper bound

of close to twice that value, with a relatively small step size (e.g 0.03 so that results close to Rmin can

be seen). Click Start and then click on Results (in a Table).

8 To carry out of rigorous simulation of a distillation column, create a new feed stream identical to the

first (apart from the name); add a rigorous distillation column.

Double-click on the column to open the Distillation Column Input Expert window and follow it to set

up the simulation. You will need to enter names for material and energy streams.

15

Use the result of the shortcut simulation to provide initial values for the number of stages and feed

stage location:

Column with 22 trays, and feed on the 13th

stage (from the top)

Condenser type: Total Condenser (i.e. liquid product and liquid reflux)

Reflux ratio of 1.73

Distillate flow of 150 kmol h–1

Condenser temperature 81°C

In the Input Expert on page 1 enter the number of stages, feed stage location, type of condenser and

names of material and energy streams. When these variables have all been specified, the Next>

button will become active. On page 2, leave the Reboiler Configuration with the default settings.

Click Next> to continue.

On page 3 of the Input Wizard, enter the condenser and reboiler pressure values as 101.325 kPa and

the pressure drop in the condenser as 0. Click Next>.

Click on Next> and continue to page 4 of the input expert. Temperature Estimates are not usually

needed; click on Next> to skip this step and to go to the final page of the Input Expert. Enter the

estimated values for distillate flow rate and reflux ratio (on a molar basis).

Click on Done once the Inputs are entered. The Column dialogue box will appear. As this is a new

column it will not automatically solve.

16

Switch to the Monitor page in the Design tab. This window is a good place from which to run the

column. Note there are four specifications: the two created by the Input Expert are Active (i.e. the

Active box is checked). To create an initial solution, click Run the column simulation. Use the

Worksheet tab on the column input form to check your results. The flow rates of distillate and

bottom product should be 150 and 199 kmol h–1

respectively.

9 At this stage, you have created two basic specifications (which can be changed later) for the

overhead product flow rate and the reflux ratio. To set the column specifications to describe the

required separation, it is convenient to use the Monitor page in the Design tab. To ensure that the

required separation is achieved, you can add alternative specifications. Whenever you set column

specifications, you need to ensure that the number of Degrees of Freedom is zero, or the column will

not run. If you set too few, or too many, specifications, this criterion will not be met. The number of

degrees of freedom is shown on the Monitor page of the Design tab. Click on Add Spec… in the

Design tab to add specifications. Select Column Component Fraction and complete the component

fraction form for both the distillate stream and bottom product. Rename the specification to

something specifically meaningful.

Be sure to check the “Active” flag for the new specifications (and uncheck it for the specifications you

will no longer be using) so that the number of degrees of freedom remains zero.

10 The results of the simulation can be seen in the Performance tab. Various Column profiles can be

generated, e.g. to show molar flows, and the Plots tab allows other results, such as K values, to be

tabulated or plotted.

17

Compare the reflux ratio required to meet the product specifications with that predicted by the

shortcut model. What are the main assumptions of the shortcut model? Consider the rigorous

simulation results to decide whether the assumptions are valid in this case.

11 Use the rigorous model to explore the relationship between number of stages and reflux ratio. Be

sure to set the specifications in terms of the separation performance. Repeat the rigorous simulation

of the column when it has fewer stages (starting from close to Nmin calculated by the shortcut model)

and more stages (up to around four or five times Nmin).

Plot your results and i) assess how the reflux ratio changes with the number of stages; ii) compare

the rigorous calculated value of Rmin to the minimum reflux ratio calculated using the shortcut model.

0

10

20

30

40

50

0 1 2 3 4 5

No

. st

ag

es

Reflux ratio

18

4 – Distillation Simulation in HYSYS


• use HYSYS to set simulate multicomponent distillation columns

• use the simulation to obtain simulation results

• change simulation inputs

Vinyl chloride separation – Workshop example kindly provided by AspenTech

Model Description

In this HYSYS example we will build the above flowsheet to separate a mixed stream of Vinyl Chloride, 1-2

Dichloroethane and HCl by following the step-by-step instructions below. The first distillation column (HCl

Column) removes HCl from the mixture as a vapour top product (HCl Out). The bottom product of this

column (HCl Col Residue) flows into the second column which separates the Vinyl Chloride top product

from the 1,2-Dichloroethane.

1 Open a new Case in HYSYS. C:\Program Files\AspenTech\Aspen HYSYS 2006.5\hysys.exe

2 Setting Preferences

Check your preferences – which Unit Sets are you using; in what format will results be reported, etc.

Open the Tools menu, select Preferences and click on the Variables tab.

3 Creating a Fluid Package

In the Simulation Basis Manager, add Components by typing in to Match Formula or Full

name/synonym. Then close the Components List View window.

Vinyl Chloride C2H3Cl or VinylChloride

1,2-Dichloroethane C2H4Cl2 or 12DiChloroEthane

HCl

In the Fluid Pkgs tab, Add the fluid package SRK (Soave-Redlich-Kwong). Change the Name of the

Fluid Package to SRK. Close the Fluid Package form and then Enter Simulation Environment.

19

4 Simulating a Column

Add unit operations or streams on to the flowsheet using the Palette. Add the feed stream and name

it HCl Column Feed. Enter the stream data:

Temperature 50°C

Pressure 2500 kPa

Define the stream Composition. Set the Composition Basis to Mass Flows (and then close Basis box).

Vinyl Chloride 60000 kg/h

1,2 Dichloroethane 80000 kg/h

Hydrogen Chloride 35000 kg/h

Close the Input Composition form. The green status bar

indicates that the stream is fully defined –in the Conditions you

should see the stream properties have been determined.

Add a distillation Column unit operation to the flowsheet using the Distillation Column

Icon in the Palette of unit operations. Place it to the right of the feed stream.

Double click on the Column to open its input form. In Input Expert on page 1 enter:

Condenser Type: Full Reflux (i.e. vapour product and liquid reflux)

Number of stages: 15; Feed stream is HCl Column Feed; Inlet stream is on 8_Main (Stage 8

from the top)

Condenser Energy Stream: Q Cond1

20

Reboiler Energy Stream: Q Reb1

Ovhd Vapour Outlet: HCl Out

Bottoms Liquid Outlet: HCl Col Residue

When all of the above specifications have been given, go to page 2 of the Input Expert, which lets you

choose the type of reboiler. Leave the default settings which are equivalent to a simple kettle

reboiler model.

Click on Next>. One the third page enter these pressure values:

Condenser pressure: 2400 kPa

Condenser pressure drop: 20 kPa

Reboiler pressure: 2430 kPa

Click Next> on page 3 of the input expert. Temperature Estimates are not usually needed. On the

final page of the Input Expert, enter estimated values for distillate flow rate and reflux ratio (on a

mass basis):

Vapour Rate: 35200 kg h–1

Note that HCl is to be recovered; its feed is 35000 kg h–1

.

Reflux ratio: 1.4

Click on Done once the Inputs are entered. As this is a new column it will not automatically solve.

21

Click on Monitor (Design page) and review the specifications: there are four specifications – the two

created by the Input Expert are Active (i.e. the Active box is checked). To create an initial solution,

Run the column simulation.

Check your results in the Worksheet tab on the column input form:

Name HCl Column Feed HCl Out HCl Col Residue

Vapour Fraction 0 1 0

Temperature [C] 50 -2.173 143.5

Pressure [kPa] 2500 2400 2430

Molar Flow [kgmole/h] 2728.5 963.0 1765.5

Mass Flow [kg/h] 1.75E+05 3.52E+04 1.40E+05


Heat Flow [kJ/h] -2.141E+08 -9.058E+07 -9.450E+07

Compositions (mole frac)

VinylCl 0.3519 0.0035 0.5419

12-ClC2 0.2963 0.0000 0.4579

HCl 0.3518 0.9965 0.0002

Save your Simulation (on the p: drive).

5 Specifying the Column Performance

The desired separation is to recover Vinyl Chloride in the bottom product – no more than 0.12@10–3

mole fraction of Vinyl Chloride is permitted in the overhead product – and to recover HCl in the top

product (with no more than 0.30@10–3

mole fraction HCl in the bottom product).

Use the Monitor page to check that the number of Degrees of Freedom is zero. If you set too few, or

too many, specifications, the column will not run.

To check the current performance of the column, Add new (inactive) specifications.

• Column Component Fraction (molar) of Vinyl Chloride in the HCl Out product = 0.12@10–3

• Column Component Fraction (molar) of HCl in the HCl Col Residue stream = 0.3@10–3

22

Note that you can rename the specifications to something more meaningful than the default. Close

the dialogue boxes after entering the new specifications.

The new specifications have been added to the list but are not Active. You can see the current value

of the newly specified variables. Check the Active box for the first new specification. The status

changes from green to red as the number of degrees of freedom is -1. Uncheck the Ovhd Vap Rate

specification.

The column will solve using the new combination of specifications. Now activate the second new

specification and uncheck the Reflux Ratio specification.

What is the calculated Reflux Ratio? It should be 1.22.

Save your Simulation, if you have not already done so!

6 Reviewing the Column Performance

The Column dialogue box allows access to a great deal of information about the column

performance. For example, in the Performance tab:

Summary of the overall mass balance on the column and the stream compositions;

Profiles of temperatures, pressures, flow rates, as well as the reflux ratio and reboil ratio

(molar ratio of vapour leaving reboiler to bottom product flow rate);

Plots (graphical or tabulated) of Tray by Tray properties in the column.

Explore some of these facilities in order to understand better the separation that is being carried out.

7 Adding the Second Distillation Column

The second distillation column shown in the flowsheet diagram above Step 1 separates the bottom

product of Column 1 to produce Vinyl Chloride (top product) and 1,2-Dichloroethane (bottom

product). Add a second distillation column and use the input wizard to enter the following data:

10 stages with the feed entering on stage number 7;

Total condenser;

Default reboiler (equivalent to simple kettle reboiler);

Condenser pressure 900 kPa; Condenser pressure drop 20 kPa; Reboiler pressure 930 kPa;

Mole fraction of 1,2-Dichloroethane in the overhead product is 0.005;

Mole fraction of Vinyl Chloride in the bottom product is 0.001.

Check your stream results for the column and plot the column temperature profile (Performance

Tab, Plots page). They should be similar to those shown below:

23

Name HCl Col Residue VC Product DCE Product

Vapour 0 0 0

Temperature [C] 143.3 56.5 176.6

Pressure [kPa] 2430 900 930

Molar Flow [kgmole/h] 1768.9 964.6 804.4

Mass Flow [kg/h] 140012 60439 79573


Heat Flow [kJ/h] -94.5e6 16.64e6 -116.4e6

Mole Fractions:

VinylCl 0.5427 0.9945 0.0010

12-ClC2 0.4570 0.0050 0.9990

HCl 0.0003 0.0005 0.0000

Condenser duty: 47.5e6 kJ/h Reboiler duty: 42.2e6 kJ/h

Temperature Plot: Flow Plot:

Use your simulation to check the feed stage location on both columns.

Add a heat exchanger to check the effect on reboiler duty of preheating the feed to column 1

Check the effect of letting down the pressure of the feed to column 2 and of cooling the feed to column 2.

In each case, assess the reboiler duty to evaluate the effect of the change on distillation performance.

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5 – Physical property modelling in HYSYS


• Understand the role of physical and thermodynamic property modelling in process design

• Appreciate the potential impact of inaccurate models on process design

Vapour-liquid equilibrium modelling

Example 11.2 in Sinnott and Towler (Chemical Engineering Design, 2009, p. 698) applies the McCabe-Thiele

method for distillation column design. The data of Kojima et al. (1968) are used. [Kojima et al., 1968,

Kagaku Kogaku 32, 149 – the data in Table 1 are provided in the file Acetone-water VLE data.xls.]

Table 1 Vapour-liquid equilibrium data for acetone and water at atmospheric pressure (101.3 kPa).

Temperature

(°C)

Mole fraction

acetone in

liquid

Mole fraction

acetone in

vapour

74.8 0.05 0.6381

68.53 0.1 0.7301

65.26 0.15 0.7761

63.59 0.2 0.7916

62.6 0.25 0.8034

61.87 0.3 0.8124

61.26 0.35 0.8201

60.75 0.4 0.8269

60.35 0.45 0.8376

59.95 0.5 0.8387

59.54 0.55 0.8455

59.12 0.6 0.8532

58.71 0.65 0.8615

58.29 0.7 0.8712

57.9 0.75 0.8817

57.49 0.8 0.895

57.08 0.85 0.9118

56.68 0.9 0.9335

56.3 0.95 0.9627

1 Use HYSYS to predict the vapour-liquid equilibrium behaviour of the same mixture (at 101.3 kPa) using

the following physical property models:

a. UNIQUAC using i) the fitted parameters available in HYSYS and ii) parameters estimated using

UNIFAC (VLE);

b. NRTL;

c. PRSV.

2 Once you have added the components Acetone and Water to your file, Add three property packages.

The first will be selected as your ‘default’ property package.

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3 Generating vapour-liquid equilibrium data in HYSYS is straightforward but it requires the stream

composition to be specified, so becomes repetitive. The Adjust function is useful for changing the

composition of a mixture.

Here I have treated the Pure Acetone stream flow rate as fixed, and select the Pure Water flow rate to

be the “Adjusted variable”, and require the flow rate of the Acetone-Water mixture (the “Target

variable”) to be constant at 100 kmol h–1

:

Together with the Databook feature, it is possible to change the “Independent variable” (in this case

the Pure Acetone flow rate) over a specified range (effectively 0 to 100 kmol h–1

) and collect the

vapour-liquid equilibrium results that are generated.

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Results may be viewed as a graph or table (or a ‘transposed table’ which can then be copied and pasted

conveniently into Excel).

4 Generate the x-y data for each physical property package (and for UNIQUAC with the default and

UNIFAC VLE parameters). You will need to change the Fluid Package for each feed stream and for the

mixer so that the same fluid package is used to model all streams in the process.

Alternatively, you can change the fluid package by going back to the Basis Environment (button ), on

the Fluid Pkgs tab > Flowsheet-Fluid Pkg Associations > Fluid Pkg To Use, and selecting the desired

Fluid Package from the drop-down menu.

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Change object by object:

Or change all objects simultaneously:

5 Compare your predicted vapour-liquid equilibrium behaviour with the experimental data. If the

experimental data are reasonably good, then they give an indication of reality – we wish to understand

which property package gives the most realistic predictions.

It is conventional to represent the experimental data as points (called ‘markers’ in Excel) without lines

between them, as no information exists between the points, and to represent the results of model

predictions as lines (without markers, as the exact values at which the model is applied is generally not

important):

6 Consider which of the three models (and which parameters) you would most trust for designing the

distillation column in this example. What might the consequences be of using a poor physical property

model?

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Mo

l% a

ceto

ne

in

va

po

ur

Mol% acetone in liquid

Kojima experimental data

UNIQUAC

HYSYS Training 2013

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