CHEMCAD Version 5.6
Flash tolerance: This parameter defines how close the results of iteration i+1 must be to the results of
iteration i for the stream to be considered converged by the flash calculation. Flash calculations are
It is recommended that the recycle tolerances be 1 to 2 orders of magnitude higher than the flash
For operations requiring high numerical accuracy, lower tolerances should be used.
Typically it is sufficient to lower the flash tolerance and recycle flow rate tolerance; the remaining
parameters are highly dependent on these two values.
• Calculation sequence: The default mode is sequential. In sequential mode, the RUN ALL command
will start with the first feed on the left and follow the ‘sequence’ of streams. Unit operations are run
In simultaneous modular mode CHEMCAD will attempt to use linear algebra to simultaneously solve
sections of the flowhseet. Distillation columns, recycle loops, and feedback controllers may converge
faster in simultaneous modular mode. Use of pressure node unitops requires calculation sequence to
be simultaneous modular.
In the Autocalc mode, rigorous logic is used to determine calculation sequence. Generally it is not
recommended to use autocalc for new models. The autocalc mode is an advanced feature with limited
• Steady state/dynamics: Indicate whether the flowsheet is a steady state or a dynamic process. The
default is steady state; placing a Dynamic vessel or batch reactor will automatically change this to
dynamic. Note that a dynamics license is required for dynamic calculation.
• Flow/Pressure Conversion: This feature is useful for dynamic simulations with pressure NODE
unitops. The default method (no conversion) has no effect on simulation. For dynamic flowsheets
with nodes, it is desirable to converge the steady state flowhseet using nodes as mixers/dividers and
then change to the dynamic mode. The option convert to flow driven will change all nodes and control
valves on the flowhseet to fixed flowrate modes. This is useful for obtaining the steady state
convergence of the flowhseet. The option convert to pressure driven simulation will change all nodes
and control valves to pressure based operation. This is generally the mode for nodes and flow
balancing unitops during a dynamic node simulation. Use of the conversion modes is optional; it is
possible to use no conversion mode and manually change all settings as necessary.
• Run one time step for dynamic simulation: A checkmark will cause a dynamic simulation to halt
after each time step. The user may review flowsheet parameters before proceeding with the next time
step. The run from initial state command button may be used to run the next time step.
• Allow dynamic editing anytime: A checkmark allows the user to make changes when the simulation
is not at time zero. If the simulation is paused, a change can be made and the dynamic command run
from current state can be issued. If an OTS time scale is entered, the user can enter dialogs and make
changes while calculation proceeds. The flowhseet will use the updated value at the next calculation.
• OTS real time scale: Enter a value and CHEMCAD will enter OTS mode. In OTS mode, CHEMCAD
will attempt to run dynamic simulations at [time scale] * [real time]. For example, if you enter a value of
5 CHEMCAD will attempt to run the model at 5 times real time (5 minutes of calculation for one minute
of real time. If a value is entered, dynamic editing anytime setting allows changes made during
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CHEMCAD Version 5.6
calculation. Using OTS mode is particularly powerful if the user has linked the simulation to external
data (control system, data historian, online training simulator).
• Display trace window: A checkmark will toggle on a display of the calculations CHEMCAD is
performing. Useful for troubleshooting convergence issues. If the simulation is set for simultaneous
calculation mode, the trace window will contain little information.
• Generate run history: A checkmark will cause the calculation history to be displayed after the run
finishes. Useful for troubleshooting convergence issues.
• Disable user interaction during simulation: A checkmark here will force CHEMCAD to ignore
mouse and keyboard action during calculation. During dynamic simulations warning messages,
convergence messages, and other dialogs from CHEMCAD will be suppressed. The only input
allowed will be canceling the run.
• Refresh data boxes after each run: A checkmark here will cause the data in stream databoxes,
unitop databoxes, and stream TP boxes to be refreshed after each run.
• Refresh data boxes after each iteration: A checkmark here will cause the data in stream databoxes,
unitop databoxes, and stream TP boxes to be refreshed after each iteration. Useful for troubleshooting
HOW TO REVIEW STREAM COMPOSITIONS
The overall procedure for viewing stream compositions (on the screen) is:
1. Select the Resu
lts command on the menu bar. The Results menu will appear.
2. Set the flow rate engineering units to be used to display the compositions. Clicking the Set Flow
Units option on the Results menu does this. The View Flow Rate Unit dialog box will appear.
This dialog box will display a list of options. Only one of these can be active at a time. The active
option will have a dot in the circle next to it. To change it, click on the circle for the desired option,
then close the dialog box.
3. Reopen the Results menu and highlight the S
tream Compositions option. The Stream
Compositions menu will open.
4. Select one of the five options on the Stream Compositions menu. Each option is a unique way to
select the streams to be displayed, and each is executed a little differently. Details are provided
below under “Selecting Streams”.
5. Once the streams have been selected, their compositions will be displayed in a Wordpad window.
In this window, the results may be scrolled, printed, edited, or filed using Wordpad commands.
When ready close the Wordpad window by clicking the Close button.
As mention previously, there are five options for selecting streams in the Results command:
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CHEMCAD Version 5.6
These options display the results in a Wordpad window, they operate as described below:
Choosing this command invokes the Select Stream(s) dialog box. This dialog box contains a blank
field where the stream ID numbers are to be entered either by typing or by clicking the streams on
the flowsheet. Once the desired streams have been selected, the dialog box is closed.
Selecting this option immediately displays the compositions of all the streams on the flowsheet.
This option automatically displays the compositions of all the feed streams of the flowsheet.
This option automatically displays the compositions of all the product streams on the flowsheet.
This option displays the compositions of all the inlet and outlet streams of a certain UnitOp. The
user must identify which UnitOp. When the Unit Streams option is selected, the Select UnitOp
dialog box appears. This dialog box contains a blank field where the UnitOp ID numbers are to be
entered either by typing or by clicking the UnitOps on the flowsheet. Once the desired UnitOps
have been selected, the dialog box is closed.
Clicking on the desired UnitOp with this cursor will cause the associated stream compositions to be
HOW TO SET FLOW UNITS FOR RESULTS AND REPORTS
It is possible to view stream compositions and include stream compositions in reports using flowrate
units, which are different from those set for the simulation. The procedure is as follows:
1. Select Results from the main menu bar.
2. The first item on the menu will be Set Flow Units. Select this command. The View Flow Rate Unit
dialog box will open.
3. Find the desired units on the list displayed.
4. Select the option by clicking on it or its radio button, then press [OK].
HOW TO VIEW STREAM PROPERTIES USING THE RESULTS COMMAND
The overall procedure for viewing stream properties (on the screen) is:
CHEMCAD Version 5.6
Select the Resu
lts command on the main menu bar. The Results menu will appear.
Highlight the S
tream Properties option of the Results menu. The Stream Properties menu
Select the Select Properties option from the Stream Properties menu. The View Property
Options dialog box will appear.
Select the desired properties and close the dialog box (see "Using the View Property Options
dialog box"). You will be returned to the main window.
Return to the Stream Properties menu and choose one of the five available options for
choosing streams. Each option is a unique way to select the streams to be displayed, and each
is executed a little differently. Details are provided above under "Selecting Streams".
Once the streams have been selected, their properties will be displayed as a report in a
Wordpad document. In this window, the results may be viewed, edited, printed, or filed.
Operation of this window is described below.
When ready, clicking the [Close] button closes the Wordpad document, and you are returned to
the CHEMCAD main window.
USING THE PROPERTIES OPTION DIALOG BOX
Selecting the Stream Properties options calls the View Property Options dialog box.
This dialog box offers two pages of property options. Default options are already checked. Turn on and
off the check mark in the box next to each option. This can be done by:
1. Moving the focus to the desired option then pressing the [SPACE BAR]. The focus is a dashed box
around the option label. It may be moved by the [TAB] key or the [ENTER] key.
2. Clicking the option with the cursor.
3. Once all selections have been made, click [OK].
The Composition Option prints stream composition with the stream properties. This is in addition
the stream property output selected above. You may choose the flow units to be used in the report by
opening the combo box and selecting an appropriate option.
HOW TO PLOT
CHEMCAD allows you to create a wide range of plots. These plots are initially displayed on the screen
where they can be reviewed and edited before a hardcopy is printed. There exist a total of twenty (20)
plot dialog boxes; of which fourteen (14) plots are common to both steady state and dynamic modes.
The steady state mode has sixteen (16) and the dynamic mode has eighteen (18) plots active at a time.
Each dialog box is specific to the type of plot being generated, and each offers options to define exactly
what and how information is to be displayed.
CHEMCAD Version 5.6
1. Select the P
lot command from the main menu bar. The P
lot menu will appear. The P
offers the plot categories mentioned above. These are described below under "Plot Menu
2. Select the appropriate option by clicking it, pressing the underscored letter key, or by moving the
highlight (with the [UP] or [DOWN] arrow keys) and pressing [ENTER].
3. Where applicable, you will be asked by a dialog box to identify the stream(s) or UnitOp(s) pertinent
to this plot by clicking it or typing its ID number. When this is finished, click [OK]. The selected
dialog box will appear.
4. Complete the dialog box as required. When finished, click [OK]. The plot will appear inside a new
window. In some cases, a Wordpad document with tabular data used for the plot will appear first.
You can browse this data if necessary, or you can simple close the window to see the plot window.
This window is similar to other graphics windows in CHEMCAD, and has the following commands
For printing, windows control and various bar selections
For copying exclusively.
For turning on and off toolbars and status bars
For editing graph style and information
For arranging windows, etc
For accessing CHEMCAD help
5. Modify the plot as desired, export the data to Excel, and generate any necessary hard copies. For
more specific instructions on how to use the graphics commands included in the plot edit window,
"How to Use the Chart Explorer".
A hardcopy of the plot can be obtained by pressing [CTRL + P], clicking the Print button, or by
going through the F
ile command on the menu bar. (See “How to Print”.)
6. When finished, close the Plot window by clicking the Close button. For certain plots, a new window
will appear containing a tabulation of the numerical values used to create the plot. These results
may be browsed and printed, but not modified. Close this window by clicking the Close button. You
will be returned to the Simulate Flowsheet Window.
PLOT MENU OPTIONS
From this menu, you can plot data ranging from stream properties to tower composition profiles and from
vapor liquid equilibrium diagrams to heat exchanger heat curves.
Plots compositions, temperature, and flow profiles for distillation
modules in either an XY or bar chart format.
Temperature, pressure, and composition equilibrium plot. It will
optionally plot experimental data points.
CHEMCAD Version 5.6
esidue Curve Map
Generates and plots a residue curve map. A residue curve map is
a graphical display of distillation zones, azeotropes, and residue
curves associated with a user specified ternary (3 component liquid
Generates a triangular plot useful for visualizing equilibrium of
Plots a phase envelope for a given stream. Highlights the critical
point of the mixture and can include plots at vapor fractions other
than zero (bubble point curve) and one (dew point curve).
Plots heating or cooling curves for heat exchangers.
Plots composite heat curves for the flowsheet.
Allows you to generate plots of properties for a given stream.
Displays a plot of one or more distillation curves for a stream.
Plug Flow Reactor Profile
Plots the temperature or composition profiles along the axial length
of a kinetic plug flow reactor.
Plots fluid properties for pipe unit operations with multiple
Plots the controller convergence error as a function of the iteration
Plots a batch reactor or a dynamic vessel history. This option is
available on a dynamic mode.
Batch Column History
Plots Batch Column value history.
Dynamic Column History
Plots Dynamic Column value history. This option is available on a
Dynamic Stream History
Plots dynamic stream value history. This option is available on a
Dynamic UnitOp History
Plots dynamic unit operation value history. This option is available
on a dynamic mode.
Stream Recorder History
Plots the data tracked by the stream recorder as a function of time
User Specified File
Plots data from a user designated file.
1. Tower Profiles
This command plots profiles for distillation columns. The column may be either a batch distillation
column or one of the rigorous steady state models. The main difference between the two is that
when you select a batch column the program will ask you to specify which operating step (the end
of) is to be plotted. The steady state models will not ask this question. In either case, the user is
presented with the Profile Options dialog box.
CHEMCAD Version 5.6
Clicking on this box will generate a plot of temperature versus stage number.
Total Vapor Flow? Total Liquid Flow?
Click next to either one (or both) of these boxes will cause the item to be included in the plot.
Decide which phase you wish to access when you ask for a composition versus stage number
plot. Click on the field to open the drop down list. The last two options only apply when there
are two liquid phases present. Options are:
Light Liquid Phase
Heavy Liquid Phase
Choose the flow units for the plot when displaying component flowrates. Options are:
Enter in this field the component position for the base component if you want to get a plot of
relative volatilities. CHEMCAD compares the volatility of the components listed below to that of
this base component.
Components to be Plotted
Select the component(s) you wish to plot using the combo box provided for each field. You
must specify these whenever you want to plot compositions or relative volatilities. Enter the
position in the component list.
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