Distillation Column Design

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Other Important Topics in
Column Design

Outline
 Sub-Flowsheets
 Thermodynamic model (Fluid Package)

selection
 Solver selection

Sub-flowsheets
 HYSYS has a multi-flowsheet architecture.
 A big flowsheet can be split up into smaller

sub-flowsheets.
 Each sub-flowsheet has its own streams,
operations, PFD and an independent fluid
package.
 The column in HYSYS is a sub-flowsheet
where independent operations are possible

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Templates
 A template is a special type of HYSYS case

that can be inserted as a sub-flowsheet into
other HYSYS design cases
 To create a template
 Convert a whole flowsheet into a template
 Create a new template
 Convert part of a flowsheet into a template

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Convert a whole flowsheet
 Access the main properties (simulation-main

properties) and select ‘convert to template’
button.
 Set the ‘template tag’, ‘transfer basis’ and other information if necessary.
 Template tags are short names to identify the sub-flowsheets

associated with a stream
 Sub-flowsheets can use a different fluid package

 When you save simulation, it will e saved as a template

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Create a new flowsheet
 From ‘file’ menu, select ‘new’ then ‘template’  Build a regular flowsheet
 Access the main properties (simulation-main

properties) and set ‘convert to template’
button the ‘template tag’, ‘transfer basis’ and
other information if necessary.
 When you save simulation, it will be saved as
a template

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Covert part of a flowsheet
 On PFD, select all the unit ops and streams

you want to capture
 Right click and select ‘cut/paste objects’ andb
then ‘copy objects to file (export)’ and save the
objects.
 From ‘file’ menu, select ‘open’ and then
‘cut/copy/paste and navigate to the file we
just saved
 Convert the new case thus created to a
template as explained earlier

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Installing a template in a simulation
 Open the flowsheet
 Click on ‘flowsheet’ icon on the object palette

and pick ‘read an existing template’ and select
the template we just saved.
 Once the template is installed as a new subflowsheet, any subsequent changes will only affect the new flowsheet.

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Connections tab
 Here, enter the feed and product connections

between sub and main flowsheets
 Feed connections are the material or energy
streams inot the sub flowsheet and products
are out of the sub-flowsheet.
 Internal streams are streams in the subflowsheet and external streams are in the main flowsheets.

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Exercise: Work on an existing
flowsheet to apply what we
learned
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Non-ideal Liquid Mixtures
 EOS models corrects the non-idealities in the

gas phase
 To deal with non-idealities in the liquid phase,
we need to account for the activity coefficients
in liquid state
 For one liquid phase systems, most of the relevant

activity models should work (UNIQUAC, WILSON
etc). NRTL will not provide any additional
advantage
 For multiple liquid phase systems, use activity
models that can handle multiple phases (eg. NRTL).
NRTL is recommended for strongly nonideal
mixtures especially with immiscible systems.

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Basic steps
 Estimate unknown interaction parameters if there

are missing binary interaction parameters

Indication of
Nonrandomness
In the mixture

Binary
interaction
parameter

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Solver options

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Solver options
 Convergence tolerances are set to very low values
 Try to increase tolerances if there is difficulty in

convergence
 Always check the option to use the ‘save solutions
as initial estimates’

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Solving group method

 The default option may not work for highly non

ideal systems
 Modified HYSIM: Can handle mixer, tee and heat
exchangers inside column subflowsheet
 Sparse...
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