PRO/II Workbook
PRO/II Getting Started Workbook The software described in this document is furnished under a License agreement and may be used only in accordance with the terms of that agreement. Information in this document is subject to change without notice. SIMSCI-ESSCOR assumes no liability for any damage to any hardware or software component or any loss of data that may occur as a result of the use of the informa-tion contained in this document.
Copyright Notice Copyright © 2004 SIMSCI-ESSCOR All Rights Reserved. No part of this publication may be copied and/or distributed without the express written permission of SIMSCI-ESSCOR, Rancho Parkway South, Lake Forest, CA 92630.
Trademarks PRO/II SIMSCI, and SIMSCI-ESSCOR are registered marks of SIMSCI-ESSCOR.
Windows, Windows 95, Windows NT, Windows 2000, Windowns XP, and MS-DOS are registered marks and/or trademarks of Microsoft Corporation.
All other products are trademarks or registered trademarks of their respective companies.
Contents
Introduction. . . 1
Launching PRO/II . . . 6
Exploring the PRO/II Desktop . . . 7
Simulation Made Easy . . . 14
Building the Process Flow Diagram (PFD) . . . 16
Setting the Input Units of Measure . . . 18
Defining the Components . . . 21
Selecting the Thermodynamic Method. . . 34
Supplying Process Stream Data . . . 43
Supplying Process Unit Operations Data . . . 65
Using Specification and Define Features . . . 77
Distillation Basics . . . 81
Setting up a Case Study . . . 99
Working with Keyword Input Files. . . 102
Running the Simulation . . . 103
Generating Output. . . 107
Customizing the Flowsheet. . . 113
Introduction
PRO/II® is SIMSCI's steady-state flowsheet simulator, a product of four generations of development. Like its predecessors, PRO/II is a steady-state heat and material balance simulator - only better. PRO/II delivers rigorous and comprehensive engineering power in an intuitive user envi-ronment. The super-responsive graphical user interface gives PRO/II the flexibility of a true Windows™ environment. PRO/II helps you solve the widest range of industry applications with the greatest ease.
History of
PRO/II
SIMSCI designed its first flowsheet process simulator, SSI/100, after the distillation program SP05. Marketed in 1974, SSI/100 had break-through capabilities for its time.
A few years later, SIMSCI created the PROCESS simulation program. PROCESS expanded the component and thermodynamic databases. It added more unit operation calculations as well as flowsheet tools, like an optimizer and a calculator, which has in-line FORTRAN capabilities. This program made flowsheet simulators accessible, since it ran on nearly every mainframe and personal computer. Engineer-friendly terms became the standard for keywords and free formatting made data input easier.
Nevertheless, PROCESS eventually bowed to progress. Over time, the program's limitations became clear: it had a rigid architecture; it ran in batch mode; it was not interactive.
PRO/II - The Calculation Engine
That is when SIMSCI created PRO/II - the calculation engine of the future. It is easy to install on almost any computer. With a flexible archi-tecture, PRO/II will adapt to future needs, since there is no limit to the number of components, streams, units and recycle loops it can handle. With larger component databanks and enhanced thermodynamic data methods for chemical, refinery and gas processing systems, PRO/II gives you many powerful options for simulating your systems.
PRO/II technology includes:
■ A state-of-the-art chemical distillation algorithm with reactive and electrolyte distillation capabilities
■ Flexible and powerful refinery capabilities, including a flash-zone model, two types of thermosiphon reboilers and multiple assay blending options
■ Regression and data management tools
■ Solids handling
■ Modeling ability for electrolyte-hydrocarbon systems
■ Flexible modeling capabilities for reaction kinetics
■ Advanced flowsheet sequencing capabilities
■ And much more.
PRO/II - The Graphical User Interface
The graphical user interface opens PRO/II's architecture to a true Win-dows environment. This “PROVISION” interface displays your process flowsheet diagram with unprecedented clarity and flexibility.
PRO/II features include:
■ Short learning curve because of its easy-to-remember color scheme
■ A true 32-bit Windows-based application
■ Multiple view windows on your flowsheet
■ Graphical output: phase envelopes, assay curves, column profiles, etc.
■ Interactive execution
■ On-line help with hypertext jumps into the reference manual
■ Flash hotkey quickly determines feed stream phase compositions
■ Generate graphs, tables, and charts, and export your results to Excel™, AutoCAD™ and the Windows Clipboard
■ Flowsheet printing on multiple pages
■ OLE/DDE Functionality
■ And many more.
This comprehensive range of features enables your company to use one simulator for all phases of business.
Where to Find Additional Help
Documents
User manuals are shipped with your copy of PRO/II. A complete set ofdocuments is provided on the CD in the form of .PDF files that are most conveniently viewed using Adobe Acrobat Reader, supplied on the installation CD. If you required additional manuals, contact your sales representative.
Online Help
PRO/II comes with online Help, a comprehensive online reference toolthat accesses information quickly. In Help, commands, features, and data fields are explained in easy steps. Answers are available instantly, online, while you work. You can access the electronic contents for Help by selecting Help/Contents from the menu bar. Context-sensitive help is accessed using the <F1> key or the What's This? button by placing the cursor in the area in question.
Technical
Support
PRO/II is backed by the full resources of Simulation Sciences Inc. (SIM-SCI), a leader in the process simulation business since 1966. SIMSCI provides the most thorough service capabilities and advanced process modeling technologies available to the process industries. SIMSCI's comprehensive support around the world, allied with its training semi-nars for every user level, is aimed solely at making your use of PRO/II the most efficient and effective that it can be.
SIMSCI offers technical support for PRO/II for all questions sent by fax, E-mail or regular mail. In North America, call our hotline support at 1-800-SIMSCI1. When contacting Technical Support, please include the following in your correspondence:
■ Name and company, phone and fax numbers
■ Product version number
■ Problem description, including any error messages that you received and the steps necessary to duplicate the problem
■ If you are e-mailing your problem, please include an electronic copy of the .INP or .PRZ file.
■ When calling in a request, please have this workbook available and be near your computer to be able to walk through any difficulties.
About This Workbook
This workbook complements SIMSCI's Introduction to PRO/II training course. Since much of the course time is dedicated to hands-on exam-ples, you will not necessarily go through the document page by page. The workbook does, however, follow the course sequence and you may want to jot notes in the margin. We strongly recommend that you read this workbook from cover to cover once and then use it to refresh your memory later on.
Conventions
Before you begin this workbook, you should be aware of severalconven-tions. These include:
■ Text written in the SMALLCAPS style is used to denote unit operation
names. These items appear on the PFD palette. For example, FLASH, OPTIMIZER, COMPRESSOR and STREAMPROPERTYTABLE.
■ Italicized text denotes menu items, dialog box names and fields, and lists. For example, File, Save As..., the Source Data dialog box, and
Composition Defined.
■ Buttons within dialog boxes are represented as gray-filled boxes with white overlaid text, such as , , and .
■ Text in < > brackets indicates keyboard strokes.
■ The , icon indicates a cautionary note or a useful tip.
SIMSCI has made great efforts to ensure that PRO/II is compliant with Microsoft Windows. As a result, much of what follows will be familiar to experienced Windows users.
■ Click, Highlight or Select: Place the pointer on the item and press the
left mouse button.
■ Double-click: Same as click except you press the left mouse button
twice with only a very short pause between clicks.
■ Open: To open a dialog box or object, place the pointer on the object
and click or double-click the mouse.
■ Drag: Move the mouse while holding the left button down
Specific PRO/II features include:
■ "..." Ellipses indicate items that, when selected, bring up a window or dialog box, for example, and .
OK Status Add ->
■ Underlined words that appear within non-Help windows denote "linked text". Clicking on an underlined word will open a new win-dow or dialog box. A good example of linked text appears in the
Flash Drum dialog box when you select Product Specification: Parameter = value within the default tolerance
If you click on the word, value, for example, a dialog box will open that allows you to enter a number.
■ Underlined words that appear in one of PRO/II's Help screens are "jump text". If you click on the underlined text, you will jump to that section of the Help documentation.
■ Dotted, underlined words that appear in PRO/II's Help screens pop-up a short definition window when pressed. They differ from jump text in that they do not change the current Help window, they simply add an additional window to the screen.
,
Note: Save your work often! PRO/II does have an autosave featureLaunching PRO/II
To initiate a PRO/II session:
➤ Click Start on the taskbar, select Programs and then SIMSCI.
➤ Click on PRO/II.
A Welcome to PROVISION dialog box appears describing how colors indicate data entry status.
Figure 1: Welcome to PROVISION Dialog Box
➤ Click , then choose File from the menu bar. The File menu is described below.
Table 1: File Menu Options
Option Function
New Initialize a new simulation Open Open an existing simulation Close Close the active simulation
Save/Save As Save the active simulation to a file with the same name, or to a new file Delete Delete an existing simulation
Copy Create a new simulation as a copy of an existing one Import Load a keyword input file into PRO/II
Export Export the active simulation to a keyword input file, or the flowsheet drawing to the Clipboard, Autocad DXF, or Postscript file
Run Batch Run an existing keyword input file without loading it into PRO/II Print/Print Setup Print the flowsheet drawing or output report
Exit Close the active simulation and exit the program OK
Exploring the PRO/II Desktop
The visual engineering of PRO/II makes building a simulation easy. Functional colors, menu-graphics and picture icons guide you every step of the way. On-line references refresh your memory on equations and guidelines. And if you encounter trouble, Help is available when you need it.
Main
Window
The PRO/II main window, shown in Figure 2, is your primary work-space. This window forms the interface between you and the PRO/II pro-gram. This is where you will build and run all your simulations, as well as open files, save the current data, or exit the program.
You will use all the familiar Windows features such as multiple views, toolbar buttons, menus, dialog boxes, drop-down lists and hotkeys.
Figure 2: PRO/II Main Window
Menu Bar Directly below the title bar of the main PRO/II window you will find the main menu bar. It gives you easy access to the command menus.
Many of same commands are available through the buttons on the tool-bar.
Table 2: PRO/II Main Window Components
Component Description
Title Bar The window title contains the name of the current simulation and view. Menu Bar All functionality can be accessed through the menus.
Toolbar Shortcut buttons for many commonly used PRO/II operations are provided. These include data entry window buttons, pan and go-to buttons, run function buttons and PFD tool and drawing buttons.
Primary Workspace This is where you draw your flowsheet. You can have multiple views of the flowsheet open at the same time.
Scroll Bars The vertical and horizontal scroll bars enable you to move vertically and horizontally through a window.
Status Bar The bar at the bottom of the window gives quick help on the highlighted button or window.
PFD Palette Also known as the Unit Operations Palette, you use this to add unit operations and streams to your flowsheet. You can show or hide this palette and change its position on the screen.
Run Palette Use this palette to run your simulation interactively. You can show or hide this palette and change its position on the screen. Usually, the shortcut buttons on the toolbar are used instead.
Control-menu Box The standard Windows control-menu in the top left corner can be used to move, resize or close the application window.
Table 3: PRO/II Menu Bar
Menu Main Functions
File File operations: open, close save, import, etc. Edit Manipulate objects on the main window
Input Add input data - all data can be entered from this menu Output Define, create and view simulation output
Tools Flash streams, binary VLE curves, output to spreadsheet Draw Add text, lines or objects to the drawing
View Specify what appears on the main window Options Customize the working environment
Window Create and manage views on the flowsheet diagram Help Access the on-line help functions
Toolbar The toolbar appears just below the menu bar on the main PRO/II win-dow. Using the mouse, you can initiate many actions by clicking the but-tons on the toolbar.
If you have a low resolution screen, such as 640x480 VGA, you can change this standard toolbar to the compact toolbar (which contains fewer buttons) by selecting the Toolbar option on the View menu.
Table 4: PRO/II Toolbar Buttons
Button Description Button Description
Open a new flowsheet view Search for a unit in the current flowsheet
Hide or display the PFD palette Search for a stream in the current flowsheet
Provide a description for the
simulation Flash the selected feed stream
Select units of measurement Create a binary VLE plot
Select components Run the simulation
Specify component data Stop the simulation
Select thermodynamic methods View the results for a selected unit or stream
Specify assay cut point data and
characterization methods Generate an output report
Define reaction data Delete the currently selected flowsheet object
Enter kinetic reaction procedures Zoom in or out
Define a case study Display the entire flowsheet in the main window
Select calculation sequence Zoom in on a region of the flowsheet
Specify recycle convergence options
Clear extraneous lines and dots from your PFD
Display the pan view window Display help for the selected object (main window only)
Data Entry Windows
PRO/II provides dialog boxes that allow you to enter data in a logical manner. Throughout this workbook, you will see examples of data entry windows. Within these dialog boxes, there are many different types of data entry devices including check boxes, radio buttons and drop-down lists.
Grayed buttons indicate that the feature is not currently available.
Color Cues PRO/II uses color cues to inform you of the status of your simulation. Colors are used to indicate:
■ Completeness of data supplied for units, streams and overall simula-tion parameters
■ Real-time execution status of each of the unit operations.
The significance of the colors you will encounter while working with PRO/II are summarized below.
Table 5: Data Entry Window Buttons
Button Description
All data are saved and the dialog box is closed.
All data entered or modified are lost when the dialog box closes.
Displays context sensitive help for the active data entry field, or for the dialog box itself (if there is no active field).
Displays the main help dialog box for the data entry window.
Displays the results of the data consistency checks performed for the main dialog box.
Selects a units of measure set for the selected data entry field.
References one stream or unit parameter value to another stream or unit parameter.
Displays the valid range of values for the active data entry field. OK Cancel Help Overview Status UOM Define Range
Table 6: Color Significance During Data Entry
Color Significance
Red Required data Green Default data
Blue Data you have supplied or modified
Yellow Questionable data: supplied data value is outside the normal range Gray Data field is not available to you
Palettes PRO/II provides two palettes: a PFD palette and a Run palette. Both are displayed in Figure 2.
PFD Palette
You add unit operations and streams to the flowsheet with the icons on the PFD palette. You can show or hide the PFD palette using the PFD Palette button on the standard toolbar.
Run Palette
For most simulation calculations, the Run and Stop buttons on the tool-bar, which start and stop the calculations, are all you will need. The Run palette allows you to take more control of the calculations by calculating units one at a time or introducing breakpoints.
Viewing the
Flowsheet
PRO/II allows you to pan over the flowsheet, search for a specific unit or stream, and view multiple views of the same flowsheet.
Panning
You can pan the contents of the flowsheet using the Pan View window, which is opened by clicking the Pan View button or by selecting View/
Pan View from the menu bar. This window gives a panoramic view of the
entire flowsheet. A bounding box identifies the area of the flowsheet vis-ible in the active view. You can move the bounding box to view a differ-ent region of the flowsheet, or you can change its size to adjust how much of the flowsheet is visible in the active view.
Table 7: Color Significance During Execution
Color Significance
Pale Green Unit operation has not been calculate
Green Unit operation is in the process of being calculated Blue Unit operation has been solved
Red Unit operation has failed to solve Magenta Unit operation is at a breakpoint
Figure 3: PFD with Pan View Window
Searching for a Unit or Stream
PRO/II builds two lists to identify and locate flowsheet units and streams. The Unit List stores unit operation names, while the Stream List stores stream names. To search for a unit or stream, click on the appro-priate Search for button on the toolbar, or select View/Unit List from the menu bar. Highlight the unit or stream of interest. This centers the object in the active view.
Multiple View Capabilities
If you have a large flowsheet, you may want to take advantage of PRO/II's multiple view capabilities. With these capabilities, you can view different portions of your flowsheet at the same time. To get an additional view of your flowsheet, click the Multiple Viewport button on the toolbar, or choose Window/New View from the menu bar. You can change the region of the flowsheet, as well as the magnification level without affecting the original flowsheet view.
The Window menu also contains options for cascading and tiling your flowsheet views. Simply choose Cascade, Tile Horizontally, or Tile
Ver-tically from the Window menu. To change the active view, click on the
title bar of the desired view, or highlight the name of the view from the
Editing the
Flowsheet
You can use the options on the Edit menu to modify your flowsheet dia-gram. Most of these commands are accessible upon selecting (highlight-ing) one or more appropriate flowsheet objects. Table 8 describes these
Edit options in more detail.
Table 8: Edit Menu Options
Option Function
Undo Allows you to undo or redo the last action, if possible.
Cut Removes a single selected feed stream from the flowsheet. The cut stream and its data are stored in the Clipboard.
Copy Copies selected stream data or stream property table data to the Clipboard.
Paste Pastes feed stream data from the Clipboard into a flowsheet stream. Paste Special Pastes feed or product stream data into a flowsheet stream. Select All Selects (highlights) the entire flowsheet.
Select None Deselects all flowsheet objects.
Insert Object Inserts pictures or other objects onto the flowsheet. Delete Deletes any highlighted object(s).
Rotate Rotates the selected object(s).
Flip Flips the selected object(s) either horizontally or vertically. Restore Icon Size Restores the size of the selected icon(s) to their default size for the
current magnification level.
Align Text Left, right, or center justifies the selected text items. Display Style Changes the style of a highlighted unit operation icon.
Reroute Redraws an unobstructed path for the selected flowsheet stream(s). Collapse Collapses the selected units into one unit, as a block diagram
(sub-flowsheet).
Expand Expands a block diagram (sub-flowsheet), converting a single unit into its components.
Rename Renames a block diagram (sub-flowsheet).
Move Up With an external feed or product stream selected in a sub-flowsheet, the free end of this stream is moved up to the next flowsheet above the current sub-flowsheet.
Move Down With an external feed into a sub-flowsheet or an external product stream from a sub-flowsheet, the free end of the stream is moved down to the sub-flowsheet. The stream no longer appears on the main flowsheet, only in the sub-flowsheet.
Simulation Made Easy
Now you will learn how to set up simulations, run them, and analyze the results with PRO/II. When setting up a simulation, you can supply data in a number of ways. The color codes in PRO/II alert you when data are required, marking the pathway towards a completed simulation.
A Systematic Approach
Because some options depend on others, you should establish a routine, logical approach for entering the data. For instance, you cannot enter the stream composition or composition-based process specifications before declaring the components in the process. You may want to change the input set of units of measure before entering user-defined components and streams. All calculations hinge on your choice of thermodynamic methods.
When using PRO/II to develop a simulation, we recommend that you follow these steps:
Build the Flowsheet
Draw your process flow diagram (PFD) by selecting and positioning the unit operations. Next, draw the feed and product streams for each unit. Often a product stream from one unit is the feed stream to another unit. Entering such streams connects the flowsheet together and establishes the transfer of information within the simulation.
Check the Input Units of Measure
Almost every quantity has a unit of measure. Initially the global default for units of measure set is English. You can change this set for this simu-lation only, or change the global default for all simusimu-lations. You can also locally override individual dimensional units in data entry windows.
Build the PFD 1 Check the Units of Measure 2 Define the Components 3 Select the Thermo 4 Supply Stream Data 5 Provide Process Conditions 6 Run Simulation & View Results 7 1 2
Define the Components
You can directly define your components by typing their library compo-nent names, by selecting from lists of compocompo-nents, or by entering user-defined components, pseudocomponents, solids with associated particle size distributions, and polymer components.
Select the Thermodynamic Method
Selecting the proper thermodynamic methods is a critically important step in the solution of a simulation. For most simulations, a predefined set of thermodynamic methods for calculating K-values, enthalpies, entropies, and densities can be used. PRO/II offers numerous categories of method sets. Normally you will want to use one of the thermodynamic systems in the list of Most Commonly Used methods.
Supply Process Stream Data
For feed streams, you must supply thermal conditions, flowrates, and compositions for all external feed streams to the flowsheet. For assay streams, you must input the thermal conditions, flowrates, distillation curve data and average API or specific gravity. It is usually desirable, although not necessary, to provide estimated data for recycle streams to speed convergence of recycle calculations.
Supply Process Unit Data
Supply process data for each unit in your flowsheet. Unit operation iden-tifiers for which data entries are needed are marked with red borders. To enter information for a unit operation, double-click its icon to open the Unit data entry window.
Run the Simulation and View the Results
Before you try to execute the simulation, check that there are no red-bor-dered fields or red linked text. If all the borders are blue, green, or black on the toolbar buttons, unit operation labels, and stream labels then you have supplied enough information to run the flowsheet.
Output is written to the output (*.OUT) file. You can view your results in a variety of ways ranging from plots and tables to pop-up windows with values for each stream and unit.
The remaining chapters will explain each of these steps in extensive detail. 3 4 5 6 7
Building the Process Flow Diagram (PFD)
The first step in any simulation, no matter how small or large, is to draw the process flow diagram. While there is a close correspondence between an actual flowsheet and its simulation flowsheet, there are some notable differences. These are:
■ Time dependencies
■ Combined units
Time Dependencies
Because PRO/II is a steady-state simulator, process equipment that con-trol time-dependent phenomena are not directly relevant to your simula-tion. The depressuring unit is the only excepsimula-tion. Omit units such as control valves and instrumentation. However, consider the instrument settings when you are deciding on the specifications to make in your flowsheet.
Thus
simplifies to
All the control valves, pressure and temperature indicators have been eliminated. You can also eliminate utility systems such as cooling water (as here), steam and refrigerants from the simulation if you are only interested in the duties they provide.
TI TI
PI PI
Combined Units
Certain unit operations can be combined to simplify your PFD. For instance, the COMPRESSOR unit in PRO/II includes an aftercooler and
most unit operations include a downstream separator. Thus
becomes
The second compressor's aftercooler and separator have been eliminated because they are incorporated in the COMPRESSOR model. The first
com-pressor's aftercooler has been eliminated but we cannot eliminate the first separator because of the recycle from the second compressor.
Flowsheet Defaults
Figure 4 shows the default stream designations for the simple heat exchanger, the flash drum, and the column unit in PRO/II.
Figure 4: PRO/II Unit Defaults
Setting the Input Units of Measure
Almost every item of data you will enter in PRO/II will have Units of Measure. For simplicity, units of measure in PRO/II have been arranged into three standard pre-defined sets: English, Metric and SI. You select the set that nearest matches the needs of your simulation and then over-ride the pre-defined units for individual quantities. For example, you can select the Metric Set and override the Celsius temperature unit with
Kelvin.
You can set the units of measure on a global, simulation, and/or field level.
Simulation
Defaults
The easiest and most efficient way to enter data involves setting the input units of measure for the active single simulation, and then proceed to change the units of measure for a specific field of a unit dialog box, if necessary.
To change the default units of measure set for a simulation, click the Units of Measure button on the toolbar to open the Default Units of
Mea-sure dialog box.
Figure 5: Default UOM for Problem Data Input Dialog Box
➤ To change the default set, click , select a set, and click .
➤ Make any changes to individual units, as desired.
Initialize from UOM Library
You can also use this dialog box to override the true vapor pressure tem-perature basis, the Reid vapor pressure calculation method, and standard vapor conditions.
UOM Library
You can define and save your own customized sets by selecting Units of
Measure Lists from the Options menu.
Global
Defaults
By default, the standard English set is the global default used to start each simulation. You can change this global default with your own mod-ified set so that every subsequent simulation starts with that set.
➤ Select Simulation Defaults/Units of Measure from the Options menu and select your set from the list.
Figure 6: Default Sets of Units of Measure
Output Units of Measure
Normally, the output report is in the same units as the input set. How-ever, you can define a different set of units for the output.
➤ Select Simulation Defaults/Units of Measure from the Options menu and select from the lists.
If you do want output in a different set of units it is good practice to get it in the input unit set as well, so that you can check the correctness of your input data.
➤ Select Same as Input for the First Output and your required output set for the Second Output.
Changing
the UOM for
a Single
Field
When entering data in a data entry window, you can still enter individual data items in any appropriate unit.
➤ Place the cursor in the field for the item whose units you want to change.
➤ Click at the top of the dialog box to open the Convert Units of
Measure dialog box.
Here you can choose to change the units and retain the value you entered in the field, or to convert the value to the new units.
Figure 7: Convert Units of Measure Dialog Box
Notice, however, that the next time you open the data entry window the value will have been converted to the defined global unit of measure.
Standard
Sets
The units of measure in the standard sets are shown below. Table 9: Standard Units of Measure
English Metric SI
Temperature °F °C K
Pressure psia kg/cm2 kPa
Weight lb kg kg
Time hr hr hr
Length ft m m
Fine Length in mm mm
Velocity ft/sec m/sec m/sec
Energy Btu kcal kJ
Work hp kW kW
Duty 106 Btu/hr 106 kcal/hr 106 kJ/hr Heat Transfer Coefficient Btu/hr-ft2-°F kcal/hr-m2-°C kW/m2-K Thermal Conductivity Btu/hr-ft-°F kcal/hr-m-°C W/m-K
Viscosity cp cp Pa-sec
Kinematic Viscosity centistoke centistoke centistoke
Surface Tension dyne/cm dyne/cm N/m
Liquid Volume ft3 m3 m3
Vapor Volume ft3 m3 m3
Defining the Components
Types of
Components
In PRO/II, you can enter the chemical species, or components, that exist in the flowsheet in six ways:
■ As library components
■ As petroleum components (or an assay curve)
■ As user-defined components ■ As solid components ■ As polymer components ■ As ionic components Library Components
The PRO/II component libraries provide easy automatic access to prop-erty data for nearly 2000 pure components. When running a simulation, you can retrieve the thermophysical properties for a library component from the PRO/II database simply by using an access name or alias. Many components have more than one alias. For example, you can retrieve information on methane, using any of the following:
■ C1
■ CH4
■ METH
■ METHANE.
PRO/II contains extensive component databanks as well as comprehen-sive methods for component property prediction. In general when PRO/II retrieves component data from one of its libraries, it also retrieves the necessary component properties to successfully complete your simulation. If PRO/II has incomplete property information for a particular component, you can either "fill in the gaps" with established property prediction methods that are based on structural data or input your own component property data.
,
Note: As a general rule, if you have water in your system, it is wise➤ Click the Component Selection button on the toolbar or select Input/
Component Selection from the menu bar and select your components
using the Component Selection dialog box.
Figure 8: Component Selection Dialog Box
If you don't know the exact name or alias of a desired component, you can click and search through the available lists.
Figure 9: Component Selection - List/Search Dialog Box
Components are listed alphabetically, and then by case. For example, the component ammonia (NH3) would be listed as H3N. Calcium would be listed as Ca, not CA.
Databanks
The PRO/II component library is actually a composite of several estab-lished databanks.
By default, PRO/II searches the PROCESS databank first and the SIMSCI databank second. All the components in the PROCESS data-bank are in the SIMSCI datadata-bank. To change the order in which PRO/II searches for your components, click in the
Com-ponent Selection dialog box.
Petroleum Components
A component breakdown for petroleum-based streams, such as crude oil, is difficult to obtain, because they contain thousands of distinct com-pounds. Usually these hydrocarbon streams are characterized in terms of laboratory test data (known as assay data). This typically includes distil-lation data, gravity data, and an analysis of the low-boiling pure compo-nents (the lightends). PRO/II derives a set of petroleum compocompo-nents from this assay data by using industry standard characterization tech-niques. These derived components are used to model the streams given by assay data. This technique is discussed in the Process Stream chapter. PRO/II allows you to enter individual petroleum components, which are represented as cuts or sections of a hydrocarbon stream with defined average boiling points, specific gravities, and other thermophysical prop-erties. You can define individual components as petroleum components by specifying at least two of the following three properties for each com-ponent:
■ Normal boiling point
■ Gravity
■ Molecular weight.
➤ Click in the Component Selection dialog box and enter the data.
➤ You can provide names for the individual cuts, or have PRO/II define names based on the cuts' NBPs.
Table 10: Pure Component Databanks
Bank Description
PROCESS The PROCESS pure component databank. SIMSCI The SIMSCI pure component databank.
DIPPR The AIChE DIPPR databank, available as an optional PRO/II add-on. OLI The OLI databank, available as an optional PRO/II add-on.
bankid User databank, created and maintained using the Property Library Manager.
Databank Hierarchy...
Typically, normal boiling point and gravity data are available to define petroleum components and assays. If you do not supply the molecular weight for a petroleum component, PRO/II uses a method developed by SIMSCI to estimate molecular weight. This method is most effective for components within the 300°F to 800°F boiling temperature range and is based on the Watson K-factor. In order to ensure accurate characteriza-tion, you should supply the molecular weight, especially if the PRO/II correlation range is not valid for your data.
PRO/II generates all other properties using methods in the API technical databook. You can select these methods or have PRO/II use default methods for all component properties required for the simulation. If you want to change the methods used, click the Assay Characterization but-ton on the toolbar or select Input/Assay Characterization from the menu
bar, then click .
Petroleum components are useful in PRO/II simulations. Here are a few examples:
■ You should save petroleum components that have been characterized from assay data in a previous run, if you intend to run the simulation often, since this will reduce run time.
■ If you lack adequate assay data for environmental applications, you can choose to model heavy hydrocarbon contaminants as petroleum components.
■ Some companies process their own assay streams because they have proprietary procedures for calculating properties such as molecular weight. In this case, instead of entering assay data you can directly enter the petroleum components and any other proprietary thermo-physical properties (e.g., critical properties).
■ When simulating a process with primarily light hydrocarbons, you may want to use a petroleum component to represent all of the hydrocarbon components that are heavier than a certain defined component. This is often the case in gas processing applications where the majority of components are typically C5 or lighter.
Characterization Options...
,
Note: If you lump the heavy components of a mixture into a singlepetroleum component, you will most likely lose accuracy. Since the dew point is very sensitive to the heavy components in a mixture, the lumping together of heavy components should be minimized in simulations where the dew point is important.
User-defined Components
For the vast majority of PRO/II simulations, you will select components from the pure component library or define them as petroleum fractions. Occasionally you may want to use a component not in the PRO/II library. In this case you must supply all the properties that the simulation requires. These will depend on the needs of the thermodynamic system you select and the unit operations you use. For example, if you have a rigorous heat exchanger in the flowsheet you will need to supply trans-port property data.
➤ Click in the Component Selection dialog box and name your component.
➤ Click the Component Properties button on the toolbar and from the
Component Properties dialog box open the Fixed Properties and Temperature Dependent Properties dialog boxes to enter the
proper-ties (or to replace data for individual properproper-ties of a library compo-nent).
Figure 10: Component Properties Dialog Box
Property Prediction
Whether you are supplying a user-defined component or supplementing property data for an existing component, the quality of the results is sig-nificantly enhanced if you use reliable experimental data. If such data are insufficient or unavailable, you can access the property prediction capa-bilities of PRO/II. These estimation methods are valid for organic com-ponents that have molecular weights below 400 and fewer than 20 unique structural groups. Click in the Component
Properties dialog box to select the component(s) you want filled then
click to define the UNIFAC groups.
User-defined...
Fill from Structure... UNIFAC Structures...
Solid Components
If some of your components exist in the solid phase you must identify them as solid, liquid-solid or vapor-liquid-solid.
➤ Click in the Component Selection dialog box. By default, all non-library components are vapor-liquid. Solid library components default to the correct phase. All properties are entered in the same dialog boxes as for user-defined components.
If a component is molecular, you must enter its molecular weight. If it is a non-molecular component, it can exist in only the solid phase.
Particle size distribution is a property of a stream and is explained in the Process Stream chapter. However, you must first specify size intervals.
Click on the Component Properties dialog
box and enter distribution ranges.
Polymers Polymers are very high molecular weight, long-chain components made up of various combinations of monomer units with a recurring chemical structure. Using the optional Polymer add-on module, you can define the structure of polymer segments and specify how polymer components are constructed from these segments. The van Krevelen group contribution method is used to predict the thermophysical properties of polymers on the basis of the individual structural groups.
➤ In the Component Selection dialog box, click to define polymer components and polymer segments.
➤ Enter particle size distribution data for polymer components in the same way as for solid components. In the Component Properties
dia-log box, click .
Table 11: Component Property Data Required for Solid Components
Property Solid Liquid/Solid Vapor/Liquid/
Solid
Solid Specific Heat or Solid Enthalpy Required Required Required Solid Density Required Required Required Molecular Weight Conditional Required Required Normal Melting Point Conditional Conditional Heat of Formation (L or S) Conditional Conditional
Specific Gravity Required Required
Liquid Enthalpy Required Required
Liquid Density Required Required
Heat of Fusion Conditional Conditional
“Conditional” means that it may be required by some unit operations.
Component Phases...
Particle Size Distribution...
Polymer...
Ionic Components
Electrolyte models are available in an optional add-on module to simu-late aqueous systems in a wide range of industrial applications. The models apply to fixed component lists with a pre-defined set of thermo-dynamic methods for K-values, enthalpies and densities.
Component
Properties
Components in a PRO/II databank have a full range of properties. Com-ponent properties fall into six categories:
■ Fixed properties
■ Temperature-dependent properties
■ User Defined and Refinery Inspection properties
■ Solid properties
■ Polymer properties
■ Structure data
The pure component properties that you need to run a simulation may depend upon the selected thermodynamic method. The required proper-ties are listed for each method in the Thermodynamic Methods section of the PRO/II Reference Manual.
Following are a few of the most important data requirements:
■ With the exception of components declared to exist only as solids, all components must have a molecular weight and a specific gravity (which can be alternatively supplied as an API gravity or standard liquid density).
■ For calculations with an equation of state method (such as Soave-Redlich-Kwong or Peng-Robinson), PRO/II requires the critical temperatures and critical pressures of the components. Each compo-nent also requires either an acentric factor or a correlation for the equation's alpha parameter.
■ K-value calculations with liquid activity coefficient methods (such as NRTL and UNIQUAC) require pure component vapor pressures. Several of these methods also require other properties such as liquid molar volumes, solubility parameters, or van der Waals area and vol-ume parameters.
■ All enthalpy and entropy methods require ideal gas enthalpies for each component, with the exception of the Ideal and Johnson-Gray-son methods.
■ The Ideal method for liquid enthalpy requires the enthalpy of the sat-urated liquid. Use of this method for vapor enthalpies requires satu-rated liquid enthalpies, plus the latent heat of vaporization for each component. Ideal liquid densities require saturated liquid densities. Again, in most cases, you do not need to worry about such requirements because the components retrieved from PRO/II's databanks will have sufficient data for any thermodynamic method.
Fixed Properties
To display the fixed properties of the selected components in your simu-lation, click in the Component Properties dialog box. Here, you can enter user-defined component properties or replace data for library components. Table 12 displays the sub-dialog box in which each property is located.
Table 12: Location of Fixed Properties
Property Dialog Box / Sub-Dialog Box
Acentric Factor Fixed Properties / Miscellaneous Properties Carbon Number Fixed Properties / Miscellaneous Properties Critical Compressibility Factor Fixed Properties / Critical Properties Critical Pressure Fixed Properties / Critical Properties Critical Temperature Fixed Properties / Critical Properties Critical Volume Fixed Properties / Critical Properties Dipole Moment Fixed Properties / Molecular Constants Enthalpy of Combustion Fixed Properties / Miscellaneous Properties Enthalpy of Fusion Fixed Properties / Miscellaneous Properties Gibbs Energy of Formation Fixed Properties / Heats of Formation Freezing Point (Normal Melting Point) Fixed Properties / Miscellaneous Properties Gross Heating Value Fixed Properties / Miscellaneous Properties Heat of Formation Fixed Properties / Heats of Formation Heat of Vaporization Fixed Properties / Miscellaneous Properties Hydrogen Deficiency Number Fixed Properties / Miscellaneous Properties Liquid Molar Volume Fixed Properties / Miscellaneous Properties Lower Heating Value Fixed Properties / Miscellaneous Properties Molecular Weight Fixed Properties
Normal Boiling Point Fixed Properties
Rackett Parameter Fixed Properties / Miscellaneous Properties Radius of Gyration Fixed Properties / Molecular Constants Solubility Parameter Fixed Properties / Miscellaneous Properties Specific Gravity Fixed Properties
Triple Point Pressure Fixed Properties / Miscellaneous Properties Triple Point Temperature Fixed Properties / Miscellaneous Properties van der Waals Area and Volume Fixed Properties / Molecular Constants
Temperature-Dependent
Properties
You can enter the temperature-dependent properties given in Table 13 below in either tabular or equation form. Extrapolation of temperature-dependent properties outside the user-defined temperature limits is per-formed linearly, except for vapor pressure and viscosity, which are extrapolated as ln(property) versus the reciprocal of the absolute temper-ature. These methods are also used for interpolation and extrapolation of tabular property data and for extrapolation of the temperature-dependent property correlations retrieved from PRO/II's databanks.
➤ Click in the Component Properties dialog box.
➤ Click the appropriate button to enter user-defined component proper-ties or to replace data for library components.
You can also view correlation coefficients and generate graphical plots of temperature dependent property data. These plots are displayed in the Plot Viewer. Each plot generated is shown in a new window, allowing multiple plots to be displayed simultaneously. PRO/II plots can be exported to other external applications (for example, Microsoft Excel).
➤ Select the Phase by clicking the appropriate button.
➤ Select Correlation Coefficients (default) and click to display the coefficients.
Table 13: Location of Temperature Dependent Properties
Property Button
Enthalpy of Vaporization
Ideal Vapor Enthalpy
Liquid Density
Liquid Thermal Conductivity
Liquid Viscosity
Saturated Liquid Enthalpy
Solid Density
Solid Heat Capacity
Solid Vapor Pressure
Surface Tension
Vapor Pressure
Vapor Thermal Conductivity
Vapor Viscosity
Temperature Dependent...
Figure 11: Correlation Selection Dialog Box
➤ To view a plot, click and select the type of plot you want. For example, Figure 12 shows a plot of the vapor pressure of butane.
Figure 12: Vapor Pressure of Butane Plot
You can view the plot in any desired unit of measure.
Refinery Inspection Properties
You can enter global data for Refinery Inspection Properties by clicking in the Component Properties dialog box. These global data will be used for all thermodynamic systems but can be overridden in each thermodynamic system.
A refinery inspection property will not be calculated unless a method is selected for it during thermodynamic data entry.
User-Defined Properties
You can enter global data for user-defined properties by clicking in the Component Properties dialog box. These global data will be used for all thermodynamic systems but can be overridden in each thermodynamic system.
Solid Properties
All solid properties, fixed and temperature-dependent, are entered in the same dialog boxes as for user-defined components.
Polymer Properties
Click on the Component Selection dialog box to define polymer components and polymer segments. Enter particle size distribu-tion data for polymer components in the same way as for solid
compo-nents. Click in the Component Properties
dialog box to enter distribution function data for polymer components.
Structure Data Click in the Component Properties dialog box to
define UNIFAC structures for selected components.
Accessing
Property
Data with
DATAPREP
Within PRO/II you are limited to examining either the fixed component properties given in the printout, or those which can be viewed through the Component Properties dialog boxes. However, DATAPREP provides you quick and total access to the PRO/II component database without having to set up and run a simulation. Using the menu-driven interface of DATAPREP, you can view fixed and descriptive properties as well as temperature-dependent properties in tabular and graphical forms for all the components in the PRO/II databanks. DATAPREP also contains the following pure component fixed properties:
■ Lower flammability limit
■ Upper flammability limit
■ Auto-ignition temperature
■ Flash point.
Refinery Inspection Properties...
User-defined Special Properties...
Polymer...
Distribution Functions...
Furthermore, unlike PRO/II, DATAPREP gives information regarding the accuracy and source of the component data, as well as the tempera-ture limits for the temperatempera-ture-dependent correlations.
DATAPREP also gives you the option of viewing properties for families of components. You can view this data as either tables or graphs. Figure 13 shows a plot of vapor pressure versus temperature for a family of alcohols. The axes have been set to plot vapor pressure (on a logarithmic scale) versus inverse temperature. The top curve corresponds to metha-nol, followed by ethametha-nol, and then the remaining alcohols by increasing carbon number.
Figure 13: Vapor Pressure for Family of Alcohols
Figure 14 further illustrates the type of graphical information that DATAPREP provides for pure library components. This graph com-pletely describes the range in enthalpy of water from the solid to ideal gas phase, and includes several distinct stages, which are described below:
1. The diagram starts at the bottom, far left, with the solid enthalpy curve.
2. The first vertical line (at the melting temperature) equals the heat of fusion and marks the transition from the solid to the liquid phase. 3. The liquid line then continues to the right until it reaches the critical
temperature.
4. At the critical temperature the liquid enthalpy curve makes a contin-uous transition back to the left along the vapor line.
5. The vertical line connecting the liquid and vapor curves represents the heat of vaporization at the normal boiling point.
15 20 25 30 35 40 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 (10E- 4) (10E+ 3) 1/T (1/K) VA P O R P R E S S U R E (N /m ^ 2 )
0 :METHANOL 1 :ETHANOL 2 :n-PROPANOL 3 :n-BUTANOL 4 :1-PENTANOL 5 :1-HEXANOL 6 :1-HEPTANOL 7 :1-OCTANOL 8 :1-NONANOL 9 :1-DECANOL
5 4 3 2 1 0 6 7 8 9
Figure 14: Enthalpy Curve for Water
Component
Data
Printout
In the Component Data section of the output file (.OUT), each compo-nent defined in the simulation is listed, along with its compocompo-nent and phase type, and nine associated fixed properties. These include: molecu-lar weight, API, NBP, critical temperature, critical pressure, critical vol-ume, acentric factor, heat of formation, and Gibbs free energy of formation. -500 -250 0 250 500 750 -80 0 80 160 240 320 (10E+ 2) Temperature F E N TH A LP Y B TU /l bm ol Heat of Vaporization at NBP Saturated Vapor Curve Ideal Gas Curve Critical Point
Saturated Liquid Curve Solid Curve Heat of Fusion at NMP Enth al py (Bt u/ lb-mol) (ºF)
Selecting the Thermodynamic Method
Selecting the appropriate thermodynamic method for your flowsheet is a critically important decision. Obviously, if you choose a thermodynamic system that cannot accurately model the phase behavior of the process, the simulation results will be invalid.
Inappropriate choice of thermodynamic model is the largest single source of error in process simulation and it is always a good idea to ver-ify your selection of a thermodynamic system by comparing simulation results with actual plant operating data. Since it is not possible to develop a single thermodynamic method to model all chemicals under all conditions, PRO/II uses several different models. Each works well in some situations and poorly in others. It is up to you to select the most appropriate methods for your particular flowsheet. Polar components at high pressure should not be simulated with a thermodynamic method that was designed to model low pressure hydrocarbons. Just because a computer reports convergence to great precision does not mean you should believe that the answers accurately model your actual process. Use your experience and engineering judgment to check that results are reasonable.
Properties
and Systems
PRO/II offers numerous methods for calculating thermodynamic proper-ties. Generally you must select methods for calculating these thermody-namic properties:
■ Equilibrium K-values
■ Enthalpies
■ Entropies
■ Densities.
In PRO/II, thermodynamic methods are arranged into systems. When you choose a thermodynamic system, PRO/II will provide default meth-ods for each of these thermodynamic properties. You can override these defaults. For example, if the Soave-Redlich-Kwong thermodynamic sys-tem is selected, the default liquid density method is API. You can replace this with another method, for example, Kesler, should you feel Lee-Kesler will predict the liquid densities more accurately for your simula-tion.
➤ Click the Thermodynamic Data button on the toolbar or select Input/
➤ Click on a Category and choose a Primary Method from the selec-tion shown.
➤ Transfer your choice by clicking .
Figure 15: Thermodynamic Data Dialog Box
➤ To change a default, click in the Thermodynamic Data dialog box and make the desired changes.
Figure 16: Modification Dialog Box
The thermodynamic methods available in PRO/II can be classified into seven categories:
■ Ideal methods
■ Generalized correlations
■ Equations of state
■ Liquid activity methods
Add ->
■ Special packages
■ Electrolytes
■ Polymers. Ideal Methods
Ideal methods calculate the mixture properties as weighted sums of the pure component properties. Each component's contribution is propor-tional to its quantity in the mixture. While ideal methods often provide good approximations for enthalpies and densities, more sophisticated methods are almost always required for K-values.
Generalized Correlations
Generalized correlations are empirical or semi-empirical methods, mostly based on the principle of corresponding states. They generally do not contain any adjustable binary parameters and are primarily useful for nonpolar hydrocarbon mixtures. Examples of generalized correlations include the Braun K-10 (BK-10) and Grayson-Streed (GS) methods. Equations of State (EOS)
Equations of state are mathematical expressions relating the density, temperature, pressure, and composition of a fluid. From an equation of state, you can calculate component K-values as well as the departures of enthalpy and entropy from their ideal gas values. Well-known examples of equations of state are the ideal gas law and the Van der Waals equa-tion. More modern equations of state include the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) equations. These equations often involve the use of binary interaction parameters (usually denoted by kij) to account for interactions between different components. These param-eters can be:
■ Obtained from PRO/II's databanks or internal estimation techniques
■ Supplied by the user
■ Fit to experimental data.
The basic SRK and PR equations are useful for systems of nonpolar hydrocarbons; more sophisticated modifications are available to better represent systems containing polar components and to calculate rigorous vapor-liquid-liquid equilibrium.
Liquid Activity Coefficient Theory (LACT) Methods
LACT methods calculate K-values by starting with an ideal solution and correcting the result with activity coefficients. The activity coefficients are calculated from a model for the excess Gibbs energy of the liquid
mixture. The most commonly used methods are NRTL and UNIQUAC. Binary interaction parameters are usually necessary. They can be:
■ Obtained from PRO/II's databanks
■ Estimated using the UNIFAC method
■ Supplied by the user
■ Fit to experimental data.
Dissolved gases can be modeled with Henry's Law, and a heat of mixing option can be used to correct for nonideality in the liquid enthalpy. If the necessary parameters are available, LACT methods can successfully describe a wide variety of nonideal mixtures (particularly mixtures of components having similar volatility) including mixtures exhibiting two liquid phases.
Special Packages
PRO/II contains several special packages designed for thermodynamic calculations on specific systems. These include:
■ The Glycol package uses the SRKM method to calculate phase equi-libria for glycol dehydration applications.
■ The Sour package and the GPA Sour Water package were developed for sour water applications.
■ The Amine package can be used to model the removal of H2S and CO2 from natural gas streams using aqueous amine systems.
■ The Alcohol package uses the NRTL liquid activity method to calcu-late phase equilibria for systems containing polar compounds, such as alcohols and water.
Electrolytes
A special add-on of PRO/II is available for systems in which aqueous electrolyte chemistry is important. Consult your SIMSCI representative for further details.
Polymers
The polymers add-on provides special thermodynamic packages which are calculated by a variety of empirical methods including three activity coefficient K-value models using ideal enthalpy and density and two equations of state which predict all the required thermodynamic proper-ties.
Transport
Property
Methods
All simulations require selection of a thermodynamic method. Some also require transport properties, which are accessed through the
Modifica-tion dialog box by clicking .
The unit operations that need transport properties are:
■ Column (hydraulics)
■ Pipe
■ Rigorous heat exchanger
■ Dissolver
■ Depressuring unit
■ Output tables.
Transport properties include:
■ Viscosity
■ Thermal conductivity
■ Liquid diffusivity
■ Surface tension.
Four calculation methods are available for computing transport proper-ties:
■ Pure
■ Petroleum
■ Trapp
■ User-defined.
The Pure option applies simple mixing rules to the temperature-depen-dent pure component values available in the selected databanks to calcu-late mixture transport properties. Saturation values are not pressure corrected. The Petroleum method uses predictive correlations, including pressure corrections, that apply to bulk hydrocarbon mixtures. The Trapp option uses a one fluid conformal model to calculate vapor and liquid viscosities and thermal conductivities for hydrocarbons; it uses the Petroleum method to calculate surface tension. The User-defined option allows you to provide up to five subroutines to compute transport proper-ties.
PRO/II provides a default method for each transport property when you select a transport method (except User-defined). You can choose to over-ride these methods if necessary. For example, you can select the API
Technical Data Book liquid viscosity method to replace the default Pure
liquid viscosity method. Refer to the PRO/II Reference Manual and the
PRO/II Application Briefs Manual for selection of the proper transport
property method.
Water Handling in Hydrocarbon Systems
PRO/II can perform three-phase flash calculations for hydrocarbon-water mixtures. These calculations can be conducted either rigorously using VLLE thermodynamics or semi-rigorously using VLE thermody-namics with the water decant option.
Water Decant Option
The free water option is a convenient, efficient method to simulate the three phase behavior of hydrocarbon-water systems. This option should be used when the solubility of hydrocarbons in the liquid water phase is small and not important for the simulation. There are two product streams: the first is a liquid hydrocarbon phase with dissolved water, the second is a free water phase. The free water phase contains no dissolved hydrocarbons or light gases. If the amount of dissolved hydrocarbons in the water phase is important (for example, an environmental compliance application), use a rigorous three-phase calculation, such as SRKM or SRKKD.
Using the free water option will result in a semi-rigorous three phase cal-culation. The vapor phase is saturated with water at a fixed pressure, and water is dissolved in the hydrocarbon liquid up to its solubility limit. Any remaining water is decanted as a pure water phase. PRO/II com-putes the solubility of water in the hydrocarbon-rich liquid phase using one of its three water solubility correlations:
■ SIMSCI (based on SIMSCI proprietary methods)
■ KEROSENE (based on the data for the solubility of water in kero-sene from API Technical Data Book Figure 9A1.4)
■ EOS (based on computing the water K-value with the equation of state as the VLE K-value method).
A pure water liquid phase is formed when the partial pressure of water reaches its saturation pressure at the flash temperature. Details of the cal-culation are given in the PRO/II Reference Manual.
➤ Click in the Modification dialog box to switch on water decanting and to select the solubility calculation method.
Rigorous Vapor-Liquid-Liquid Equilibrium (VLLE) Calculations
Some thermodynamic systems have the ability to model VLLE as well as VLE systems. PRO/II can perform rigorous three-phase equilibrium calculations using the FLASH unit if you select the VLLE option for such
a thermodynamic system. Rigorous thermodynamic calculations can predict the existence and compositions of two immiscible liquid phases. In this case, the second product stream is designated as the second liquid phase.
For a hydrocarbon-water system, the water product stream is no longer pure, it does contain some dissolved hydrocarbon. This liquid water phase is considered as the denser of the two liquid phases.
A discussion on selection of the appropriate thermodynamic set for three-phase systems is given in the PRO/II Reference Manual.
Solid-Liquid
Equilibrium
Solid-liquid equilibria can be used with all thermodynamic systems. The van't Hoff solubility method calculates solid-liquid equilibrium K-values for nearly ideal non-electrolyte systems. The solute and solvent should be of a similar chemical nature. Select this method from the K-value (SLE) list on the Modification dialog box.
Alternatively, you can enter solubility data correlated as a function of temperature. Select User-supplied Data from the K-value (SLE) list on the Modification dialog box, and click .
Precipitation of solid salts and minerals from aqueous solutions can be calculated rigorously using the PRO/II Electrolytes add-on module.
Application
Examples
Table 14 shows some applications for the most common forms of ther-modynamic methods.
Enter Data...
Table 14: Thermodynamic Methods and Application Examples
Form Application Examples of
Thermodynamic Method
Generalized Correlation
Low pressure crude systems involving heavy hydrocarbons: vacuum and atmospheric crude
towers
BK-10, GS, IGS
Equation of State Light hydrocarbon systems, hydrogen-rich systems: reformers and hydrotreaters
SRK, PR
Liquid Activity Coefficient Method
Non-ideal chemical systems:
aromatic/non-aromatic extraction, chemical systems with small amounts of supercritical gases
NRTL, UNIQUAC, NRTL with Henry's law
Because the accuracy of the simulation hinges largely on the selection of the correct thermodynamic method, you should exercise great care in choosing a method. Though these guidelines give advice on which ther-modynamic sets best suit which process systems, it is always advisable to check that the results of your specific simulation are reasonable. Application guidelines are available in the PRO/II on-line Reference
Manual, supplied on the distribution CD, or are accessible through the
Help system. Alternately, in the Thermodynamics Data main dialog box, click on the toolbar to access the Help topic for that dialog box. Click on Application Guidelines on the first Help screen.
Multiple
Methods
For some complex processes, you may need to use different thermody-namic systems for different sections of the flowsheet. PRO/II allows you to define multiple thermodynamic systems for use in a single simulation.
➤ Click the Thermodynamic Data button, which is now blue to show that you have already made a selection.
➤ Click on a Category, choose a second Primary Method from the selection shown, and click . Any method from any category is satisfactory.
➤ Do this for as many different methods as you wish.
You can then select any of these Defined Systems for use within any unit operation. If you do not make an explicit selection in a unit operation, the unit will use whichever system you designate as the default. Desig-nate the default by selecting from the drop-down Default System list on the Thermodynamic Data dialog box.
Using Multiple Methods
Using multiple thermodynamic systems within a single simulation pre-sents no complications when the materials flowing through the process are not mixed. For example, you might use different methods for the hot and cold sides of a HEATEXCHANGER. On the other hand, if you are
feed-ing a product stream from a unit operation that uses one thermodynamic system into a unit that uses a different system, you must be careful not to introduce discontinuities in the flowsheet.
For example, a stream at a known pressure whose temperature has been calculated from its enthalpy by the Soave-Redlich-Kwong equation of state is fed to a constant pressure adiabatic flash unit which uses Peng-Robinson as its thermodynamic set. If nothing is done, the adiabatic flash will calculate a different temperature from the enthalpy of the stream.
Overview