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Getting Started 1 1 Getting Started © 2000 AEA Technology plc - All Rights Reserved. Chem 1_3.pdf

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  • Getting Started 1

    1

    Getting Started

    2000 AEA Technology plc - All Rights Reserved.Chem 1_3.pdf

  • 2 Getting Started

    2

    WorkshopThe Getting Started module introduces you to some of the basic concepts necessary for creating simulations in HYSYS. Some of the things you will learn from this module are:

    Methods for moving through different environments Selecting property packages and components Adding streams Attaching utilities

    You will use HYSYS to define three streams. You will learn how to determine the properties of these streams by using the Property Table utility.

    Learning ObjectivesOnce you have completed this section, you will be able to:

    Define a Fluid Package (Property Package and Components) Add Streams Understand Flash Calculations Attach Stream Utilities Customize the Workbook

  • Getting Started 3

    3

    Building the Simulation

    The Simulation Basis ManagerHYSYS uses the concept of the Fluid Package to contain all necessary information for performing flash and physical property calculations. This approach allows you to define all information (property package, components, interaction parameters, reactions, tabular data, hypothetical components, etc.) inside a single entity. There are three key advantages to this approach:

    All associated information is defined in a single location, allowing for easy creation and modification of the information

    Fluid Packages can be stored as a completely separate entity for use in any simulation

    Multiple Fluid Packages can be used in the same simulation; however, they are all defined inside the common Basis Manager.

    The Simulation Basis Manager is a property view that allows you to create and manipulate every Fluid Package in the simulation. Whenever you begin a New Case, HYSYS places you at this location. The opening tab of the Simulation Basis Manager, Fluid Pkgs, contains the list of current Fluid Package definitions. You can use multiple Fluid Packages within one simulation by assigning them to different flowsheets and linking the flowsheets together.

  • 4 Getting Started

    4

    Inside the Current Fluid Packages group, there are a number of buttons:

    View - this is only active when a Fluid Package exists in the case. It allows you to view the property view for the selected Fluid Package.

    Add allows you to create and install a Fluid Package into the simulation.

    Delete removes the selected Fluid Package from the simulation.

    Copy makes a copy of the selected Fluid Package. Everything is identical in the copied version, except the name. This is useful for modifying fluid packages.

    Import allows you to import a predefined Fluid Package from disk. Fluid Packages have the file extension.fpk.

    Export allows you to export the selected Fluid Package to a disk. The exported Fluid Package can be retrieved into another case, by using the Import function.

    You can use the hot key to re-enter the Simulation Basis Manager from any point in the simulation or choose the Enter Basis Environment button from the button bar.

    Basis Environment button

  • Getting Started 5

    5

    Defining the Simulation Basis1. Start a new case by selecting the New Case button.

    2. Create a Fluid Package by selecting the Add button from the Simulation Basis Manager.

    3. Click the Activity Model radio button and choose NRTL as the Property Package.

    4. Change the Name from the default Basis-1 to Stripper. Do this by clicking in the "Name" cell, and typing the new name. Hit the key when you are finished.

    5. Switch to the Components tab. From this tab, you add components to your case.

    New Case button

  • 6 Getting Started

    6

    You can select components for your simulation using several different methods:

    Note: You can add a range of components by highlighting the entire range and pressing the Add Pure button.

    To Use Do This

    Match Cell 1. Select one of the three name formats, SimName, Full Name/Synonym, or Formula by selecting the corresponding radio button.

    2. Click on the Match cell and enter the name of the component. As you start to type, the list will change to match what you have entered.

    3. Once the desired component is highlighted either:

    Press the key Press the Add Pure button Double click on the component to

    add it to your simulation.

    Component List 1. Using the scroll bar for the main component list, scroll through the list until you find the desired component.

    2. To add the component either:

    Press the key Press the Add Pure button Double click on the component to

    add it to your simulation

    Family Filter 1. Ensure the Match cell is empty, and press the Family Filterbutton.

    2. Select the desired family from the Family Filter to display only that type of component.

    3. Use either of the two previous methods to then select the desired component.

    4. To add the component either:

    Press the key Press the Add Pure button Double click on the component to

    add it to your simulation

  • Getting Started 7

    7

    5. Select the library components Chloroform, Toluene, Ethanol, H2O, Oxygen and Nitrogen.

    6. Go to the Binary Coeffs tab. Press the Unknowns Only button to estimate missing coefficients. View the Aij, Bij and ij matrices by selecting the corresponding radio button. The Aij matrix is shown below:

    To view the Bij or ij coefficients, click the appropriate radio button in the Coefficient Matrix to View group.

  • 8 Getting Started

    8

    Exporting Fluid PackagesHYSYS allows you to export Fluid Packages for use in other simulations. This functionality allows you to create a single common Fluid Package which you may use in multiple cases.

    1. On the Fluid Pkgs tab highlight the Stripper Fluid Package.

    2. Press the Export button.

    3. Enter a unique name (Stripper) for the Fluid Package and press the OK button.

    Now that the Fluid Package is now fully defined, you are ready to move on and start building the simulation. Press the Enter Simulation Environment button or the Interactive Simulation Environment button in the Button Bar.

    HYSYS will automatically add the file extension .fpk when it saves your Fluid Package. The file is automatically saved to the \HYSYS\paks subdirectory.

  • Getting Started 9

    9

    Selecting a Unit SetIn HYSYS, it is possible to change the unit set used to display the different variables.

    1. From the Tools menu, choose Preferences.

    2. Switch to the Variables tab, and go to the Units page.

    3. If it is not already selected, select the desired unit set. Both Field and SI units will be given in this course; you are free to use whichever is more comfortable for you.

    4. Close the window to return to the simulation.

  • 10 Getting Started

    10

    Changing Units for a SpecificationTo change the units for a specification, simply type the numerical value of the specification and press the space bar or click on the unit drop down box. Choose the units for the value you are providing. HYSYS will convert the units back to the default units.

    You can scroll through the unit list by starting to type the units, by using the arrow keys or by using the scroll bar.

  • Getting Started 11

    11

    Adding StreamsIn HYSYS, there are two types of streams, Material and Energy. Material streams have a composition and parameters such as temperature, pressure and flowrates. They are used to represent Process Streams. Energy streams have only one parameter, a Heat Flow. They are used to represent the Duty supplied to or by a Unit Operation.

    There are a variety of ways to add streams in HYSYS.

    In this exercise, you will add three streams to represent the feeds to an air stripper. Each stream will be added using a different method of installation.

    To Use This Do This

    Menu Bar Select Add Stream from the Flowsheet menu.

    Or

    Press the Hot Key.

    The Stream property view will open.

    Workbook Open the Workbook and go to the Material Streams tab. Type a stream name into the **New** cell.

    Object Palette Select Object Palette from the Flowsheet menu or press to open the Object Palette. Double click on the stream icon.

  • 12 Getting Started

    12

    Adding a Stream from the Menu BarThis procedure describes how to add a stream using the hot key.

    1. Press the hot key. The Stream Property view is displayed:

    You can change the stream name by simply typing in a new name in the Stream Name box.

    2. Change the stream name to Eth rich.

  • Getting Started 13

    13

    Entering Stream Compositions

    There are two different methods to enter stream compositions from the Worksheet tab.

    3. Double click on the Mass Flow cell. The Input Composition for Stream view displays.

    4. We want to define the composition of this stream by specifying the mass flows for each component. By default, HYSYS has chosen the basis for defining the composition as mass fraction. Press the Basis button and select the Mass Flows radio button in the Composition Basis group. You are now able to enter the data in the desired format.

    When Using the Do This

    Conditions page Double click on the Molar Flow cell to enter mole fractions.

    Or

    Double click on the Mass Flow cell to enter mass fractions.

    Or

    Double click on the LiqVolFlow cell to enter volume fractions.

    The Input Composition for Stream dialog is shown.

    Composition page Press the Edit button.

    The Input Composition for Stream dialog is shown.

  • 14 Getting Started

    14

    5. Enter the following compositions:

    6. Press the OK button when all the mass flows have been entered.

    7. Close the Stream Property view.

    For This Component Enter This Mass Flow, kg/h (lb/hr)

    Chloroform 2.5 (5.0)

    Toluene 0

    Ethanol 300 (600)

    H2O 100 000 (200, 000)

    Oxygen 0

    Nitrogen 0

    Note: If there are values, either enter 0 or press the Normalize button.

  • Getting Started 15

    15

    Adding a Stream from the WorkbookTo open or display the Workbook, press the Workbook button on the Button Bar.

    1. Enter the stream name, Tol rich in the **New** cell.

    2. Enter the following component mass flow rates. You will have to change the basis again.

    3. Close the Stream Property view.

    Workbook button

    For This Component Enter This Mass Flow, kg/h (lb/hr)

    Chloroform 1.5 (3.0)

    Toluene 140 (280)

    Ethanol 0

    H2O 100 000 (200, 000)

    Oxygen 0

    Nitrogen 0

  • 16 Getting Started

    16

    Adding a Stream from the Object Palette

    1. If the Object Palette is not open on the Desktop, press the hot key to open it.

    2. Double Click on the Material Stream button. The Stream Property view displays.

    3. Change the name of the stream to Strip Air.

    4. Double click on the Molar Flow cell and enter the following stream compositions:

    Saving your caseYou can use one of several different methods to save a case in HYSYS:

    From the File menu select Save to save your case with the same name.

    Form the File menu select Save As to save your case in a different location or with a different name.

    Press the Save button on the button bar to save your case with the same name.

    Material Stream button (Blue)

    For This Component Enter This Mole Fraction

    Chloroform 0

    Toluene 0

    Ethanol 0

    H2O 0

    Oxygen 0.21

    Nitrogen 0.79

    Save your case often to avoid losing information.

    Save button

    Save your case!

  • Getting Started 17

    17

    Flash CalculationsHYSYS can perform five types of flash calculations on streams: P-T, Vf-P, Vf-T, P-Molar Enthalpy and T-Molar Enthalpy. Once the composition of the stream and two of either temperature, pressure, vapour fraction or molar enthalpy are known, HYSYS performs a flash calculation on the stream, calculating the other two parameters.

    With the flash capabilities of HYSYS, it is possible to perform dew and bubble point calculations. By specifying a vapour fraction of 1 and either the pressure or temperature of the stream, HYSYS will calculate the dew temperature or pressure. To calculate the bubble temperature or pressure, a vapour fraction of 0 and either pressure or temperature must be entered.

    1. Perform a T-P flash calculation on the stream Tol Rich. Set the pressure to 101.3 kPa (14.7 psia) and the temperature to 90 C (200 F). What is the vapour fraction? __________

    2. Perform a dew point calculation on the stream Tol Rich. Set the pressure to 101.3 kPa (14.7 psia). What is the dew point temperature? __________

    3. Perform a bubble point calculation on the stream Tol Rich. Set the pressure to 101.3 kPa (14.7 psia). What is the bubble point temperature? __________

    Only 2 of these 4 stream parameters, Vapour Fraction, Temperature, Pressure or Molar Enthalpy can be supplied.

    If you try to supply temperature, pressure and vapour fraction, a consistency error can occur.

  • 18 Getting Started

    18

    Attaching UtilitiesThe utilities available in HYSYS are a set of useful tools that interact with your process, providing additional information or analysis of streams or operations. Once installed, the utility becomes part of the Flowsheet, automatically calculating when conditions change in the stream or operation to which it is attached.

    As with the majority of objects in HYSYS, there are a number of ways to attach utilities to streams.

    To Use the Do this

    Menu Bar Select Utilities from the Tools menu.

    or

    Press the hot key.

    The Available Utilities window displays.

    Stream Property View Open the stream property view.

    Switch to the Attachments tab and choose the Utilities page. Press the Create button.

    The Available Utilities window displays.

  • Getting Started 19

    19

    Adding a Utility from the Stream Property View

    The Property Table utility allows you to examine property trends over a range of conditions in both tabular and graphical formats. The utility calculates dependent variables for up to two user specified independent variable ranges or values.

    A Property Table utility will be added to the stream Tol rich from the stream property view.

    1. Use the hot key combination to open the Available Utilities window.

    2. Select Property Table from the menu on the right and press the Add Utility button. The Property Table view displays.

    3. Press the Select Stream button and select the stream Tol rich.

    4. Press the OK button to return to the Ind. Prop tab.

    5. By default, Temperature is selected as Variable 1, and Pressure is selected as Variable 2.

    6. Change the Lower Bound of the Temperature to 85 oC (185 oF) and change the Upper Bound to 100 oC (212 oF). Set the number on increments to 5.

    7. For the Pressure variable, use the drop down menu to change its mode to State, and enter the following values: 90 kPa (13 psia), 100 kPa (14.5 psia), 101.3 kPa (14.7 psia), 110 kPa (16.0 psia), and 120 kPa (17.4 psia).

    8. Switch to the Dep. Prop page.

  • 20 Getting Started

    20

    It is possible to choose multiple dependent properties for any of the single phases (liquid, aqueous or vapour) or for the bulk phase.

    9. Select the Bulk radio button and highlight a cell in the Property matrix.

    10. Choose Mass Density from the drop down list.

    11. Select the Liquid radio button, and select the Viscosity property.

    12. Select the Aqueous radio button, and select the Aq. Mass Fraction property.

    13. Select the Vapour radio button, and select the Vapour Mass Fraction property.

    14. Press the Calculate cell to generate the Property Table.

  • Getting Started 21

    21

    You can examine the Property Table results in either graphical or tabular formats on the Performance tab.

    Finishing the SimulationThe final step in this section is to add the stream information necessary for the case to be used in future modules.

    Add the following temperatures and pressures to the streams:

    Add a flowrate of 18 000 kg/h (39, 700 lb/hr) to the stream Strip Air.

    Examining the Results

    The Stream Property ViewWithin HYSYS, it is possible to view the properties of the individual phases for any stream.

    1. Open the property view for the stream Tol Rich.

    2. On the Worksheet tab, Conditions page, add a Temperature value of 90C (195F) and supply a pressure of 101.3 kPa (14.7 psia).

    3. Move the mouse cursor to the left or right side of the view until the cursor changes to resizing arrows.

    4. Press and hold the left mouse button and drag the edge of the view until all the phases can be seen.

    Pressure, kPa (psia) Temp., C (F)

    Eth rich 101 kPa (14.7 psia) 15C (60F)

    Tol rich 101 kPa (14.7 psia) 15C (60F)

    Strip Air 101 kPa (14.7 psia) 25C (77F)

  • 22 Getting Started

    22

    The pages Properties and Composition also show data for the individual phases.

  • Getting Started 23

    23

    Customizing the WorkbookHYSYS allows you to customize the Workbook at several different levels. You can add additional pages, change the variables which are displayed on the current pages, or change the format of the values which are displayed.

    In this exercise a new Workbook tab containing stream properties, Vap Frac on a Mass Basis, Molecular Weight, Mass Density and Mass Enthalpy, will be added.

    1. Open the Workbook by pressing the Workbook button on the button bar.

    2. From the Workbook menu, select Setup. The Setup window displays.

    3. Under the Workbook Tabs group, press the Add button, and in the view which appears, select +Stream and press OK.

    4. A new Workbook tab, Streams 2, will be listed in the Workbook Tabs group. Ensure that this new tab is highlighted.

    5. Highlight the Name cell in the Tab Contents group, and change the name to Other Prop.

    6. In the Variables group, press the Delete button until all the default variables are removed.

    7. Click the Add button to view the list of variables grouped under the Select Variable(s) For Main page.

    8. From the Variables list, select Vap Frac on a Mass Basis and click OK.

    Workbook button

  • 24 Getting Started

    24

    9. Repeat 7 and 8 for Molecular Weight, Mass Density and Mass Enthalpy.

    10. Close this view to return to the Workbook.

    The Workbook now contains the tab Other Prop which shows the vapour fraction on a mass basis, the molecular weight, the mass density and the mass enthalpy for all the components for the three streams.

  • Getting Started 25

    25

    Printing Stream and Workbook DatasheetsIn HYSYS you have the ability to print datasheets for Streams, Operations and Workbooks.

    Printing the Workbook Datasheet1. Open the Workbook.

    2. Right click (Object Inspect) the Workbook title bar. The Print Datasheet or Open Page pop-up menu appears.

    3. Select Print Datasheet and the Select Datablock(s) to Print for Workbook window is displayed.

    4. You can choose to print or preview any of the available datasheets (press the + collapse button to view all available datasheets). Clicking on the box will activate or deactivate the datasheet for printing or previewing.

    To print all streams:

    Customize the Workbook to contain all the stream info you want.

    Print the Workbook Datasheet.

  • 26 Getting Started

    26

    Printing an Individual Stream Datasheet

    To print the datasheet for an individual Stream, Object Inspect the stream property view title bar and follow the same procedure as with the Workbook.

    Save your case!

  • Getting Started 27

    27

    Exercise 1

    A. Use the Workbook to find the following values:

    1. The dew point temperature of stream Eth Rich at 101 kPa (14.7 psia). __________

    2. The bubble point pressure of stream Tol rich at 15C (60 F). __________

    3. The dew point pressure of stream Strip Air at 25C (77 F). __________

    4. The bubble point temperature of stream Strip Air at 101 kPa (14.7 psia). __________

    B. Perform the following flash calculations:

    1. The vapour fraction of stream Eth rich at 15C (60 F) and 101 kPa (14.7 psia). __________

    2. The temperature of stream Tol rich at 101 kPa (14.7 psia) and 0.5 vapour fraction. __________

    3. What is the molar fraction of toluene in vapour phase for stream Tol rich under the same condition? __________

    4. The mass density of stream Strip Air at 25 C (77 F) and 101 kPa (14.7 psia). __________

    5. The mass fraction of toluene in the aqueous phase of the stream "Tol rich" at 15 C (60 F) and 101.3 kPa (14.7 psia). __________

    Exercise 2

    The stream Eth Rich is stored in a 200 m3 (7000 ft3) vessel. Assuming the storage vessel has a 45 minute hold-up and the vessel is at atmospheric conditions (1 atm, 25C, 77 F):

    What is the composition of the vapor space? _________

    How full is the storage vessel? __________

  • 28 Getting Started

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  • Thermodynamics and HYSYS 1

    1

    Thermodynamics and HYSYS

    2000 AEA Technology plc - All Rights Reserved.Chem 2_5.pdf

  • 2 Thermodynamics and HYSYS

    2

    WorkshopOne of the main assets of HYSYS is its strong thermodynamic foundation. Not only can you use a wide variety of internal property packages, you can use tabular capabilities to override specific property calculations for more accuracy over a narrow range. Or, you can use the functionality provided through OLE to interact with externally constructed property packages.

    The built-in property packages in HYSYS provide accurate thermodynamic, physical and transport property predictions for hydrocarbon, non-hydrocarbon, petrochemical and chemical fluids. The database consists of an excess of 1500 components and over 16000 fitted binary coefficients. If a library component cannot be found within the database, a comprehensive selection of estimation methods is available for creating fully defined hypothetical components.

    HYSYS also contains a regression package within the tabular feature. Experimental pure component data, which HYSYS provides for over 1000 components, can be used as input to the regression package. Alternatively, you can supplement the existing data or supply a set of your own data. The regression package will fit the input data to one of the numerous mathematical expressions available in HYSYS. This will allow you to obtain simulation results for specific thermophysical properties that closely match your experimental data.

    However, there are cases when the parameters calculated by HYSYS are not accurate enough, or cases when the models used by HYSYS do not predict the correct behaviour of some liquid-liquid mixtures (azeotropic mixtures). For those cases it is recommended to use another of Hyprotechs products, DISTIL. This powerful simulation program provides an environment for exploration of thermodynamic model behaviour, proper determination and tuning of interaction parameters and physical properties, as well as alternative designs for distillation systems.

  • Thermodynamics and HYSYS 3

    3

    Proper use of thermodynamic property package parameters is key to successfully simulating any chemical process. Effects of pressure and temperature can drastically alter the accuracy of a simulation given missing parameters or parameters fitted for different conditions. HYSYS is user friendly by allowing quick viewing and changing of the particular parameters associated with any of the property packages. In addition, you are able to quickly check the results of one set of parameters and compare those results with another set.

    In this module, you will explore the thermodynamic packages of HYSYS and the proper use of their thermodynamic parameters.

    Learning ObjectivesOnce you have completed this module, you will be able to:

    Select an appropriate Property Package Understand the validity of each Activity Model Enter new interaction parameters for a property package Check multiphase behaviour of a stream Understand the importance of properly regressed binary

    coefficients

  • 4 Thermodynamics and HYSYS

    4

    Selecting Property PackagesThe property packages available in HYSYS allow you to predict properties of mixtures ranging from well defined light hydrocarbon systems to complex oil mixtures and highly non-ideal (non-electrolytic) chemical systems. HYSYS provides enhanced equations of state (PR and PRSV)for rigorous treatment of hydrocarbon systems; semi-empirical and vapour pressure models for the heavier hydrocarbon systems; steam correlations for accurate steam property predictions; and activity coefficient models for chemical systems. All of these equations have their own inherent limitations and you are encouraged to become more familiar with the application of each equation.

    The following table lists some typical systems and recommended correlations:

    Type of System Recommended Property Package

    TEG Dehydration PR

    Sour Water PR, Sour PR

    Cryogenic Gas Processing PR, PRSV

    Air Separation PR, PRSV

    Atm Crude Towers PR, PR Options, GS

    Vacuum Towers PR, PR Options, GS

  • Thermodynamics and HYSYS 5

    5

    Equations of StateFor oil, gas and petrochemical applications, the Peng-Robinson EOS (PR) is generally the recommended property package. HYSYS currently offers the enhanced Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state. In addition, HYSYS offers several methods which are modifications of these property packages, including PRSV, Zudkevitch Joffee (ZJ) and Kabadi Danner (KD). Lee Kesler Plocker (LKP) is an adaptation of the Lee Kesler equations for mixtures, which itself was modified from the BWR equation. Of these, the Peng-Robinson equation of state supports the widest range of operating conditions and the greatest variety of systems. The Peng-Robinson and Soave-Redlich-Kwong equations of state (EOS) generate all required equilibrium and thermodynamic properties directly. Although the forms of these EOS methods are common with other commercial simulators, they have been significantly enhanced by Hyprotech to extend their range of applicability.

    The Peng-Robinson property package options are PR, Sour PR, and PRSV.

    Soave-Redlich-Kwong equation of state options are the SRK, Sour SRK, KD and ZJ.

    For the Chemical industry due to the common occurrence of highly non-ideal systems, the PRSV EOS may be considered. It is a two-fold modification of the PR equation of state that extends the application of the original PR method for highly non-ideal systems.

    It has shown to match vapour pressure curves of pure components and mixtures, especially at low vapour pressures.

    It has been successfully extended to handle non-ideal systems giving results as good as those obtained by activity models.

    A limited amount of non-hydrocarbon interaction parameters are available.

    Activity ModelsAlthough equation of state models have proven to be very reliable in predicting properties of most hydrocarbon based fluids over a large range of operating conditions, their application has been limited to primarily non-polar or slightly polar components. Polar or non-ideal chemical systems have traditionally been handled using dual model approaches.

    Activity Models are much more empirical in nature when compared to

  • 6 Thermodynamics and HYSYS

    6

    the property predictions in the hydrocarbon industry. For example, they cannot be used as reliably as the equations of state for generalized application or extrapolating into untested operating conditions. Their tuning parameters should be fitted against a representative sample of experimental data and their application should be limited to moderate pressures.

    For every component i in the mixture, the condition of thermodynamics equilibrium is given by the equality between the fugacities of the liquid phase and vapour phase. This feature gives the flexibility to use separate thermodynamic models for the liquid and gas phases, so the fugacities for each phase have different forms. In this approach:

    an equation of state is used for predicting the vapour fugacity coefficients (normally ideal gas assumption or the Redlich Kwong, Peng-Robinson or SRK equations of state, although a Virial equation of state is available for specific applications)

    an activity coefficient model is used for the liquid phase.

    Although there is considerable research being conducted to extend equation of state applications into the chemical industry (e.g., PRSV equation), the state of the art of property predictions for chemical systems is still governed mainly by Activity Models.

    Activity coefficients are fudge factors applied to the ideal solution hypothesis (Raoults Law in its simplest form) to allow the development of models which actually represent real data. Although they are fudge factors, activity coefficients have an exact thermodynamic meaning as the ratio of the fugacity coefficient of a component in a mixture at P and T, and the fugacity coefficient of the pure component at the same P and T. Consequently, more caution should be exercised when selecting these models for your simulation.

    Activity Models produce the best results when they are applied in the operating region for which the interaction parameters were regressed.

  • Thermodynamics and HYSYS 7

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    The following table briefly summarizes recommended activity coefficient models for different applications (refer to the bulleted reference guide below):

    A = Applicable N/A = Not Applicable ? = Questionable G = Good LA = Limited Application

    Application Margules van Laar Wilson NRTL UNIQUAC

    Binary Systems A A A A A

    Multicomponent Systems

    LA LA A A A

    Azeotropic Systems A A A A A

    Liquid-Liquid Equilibria

    A A N/A A A

    Dilute Systems ? ? A A A

    Self-Associating Systems

    ? ? A A A

    Polymers N/A N/A N/A N/A A

    Extrapolation ? ? G G G

  • 8 Thermodynamics and HYSYS

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    Overview of Models

    Margules

    One of the earliest activity coefficient expressions was proposed by Margules at the end of the 19th century.

    The Margules equation was the first Gibbs excess energy representation developed.

    The equation does not have any theoretical basis, but is useful for quick estimates and data interpolation.

    In its simplest form, it has just one adjustable parameter and can represent mixtures which feature symmetric activity coefficient curves.

    HYSYS has an extended multicomponent Margules equation with up to four adjustable parameters per binary. The four adjustable parameters for the Margules equation in HYSYS are the aij and aji (temperature independent) and the bij and bji terms (temperature dependent).

    The equation will use parameter values stored in HYSYS or any user supplied value for further fitting the equation to a given set of data.

    In HYSYS, the equation is empirically extended and therefore caution should be exercised when handling multicomponent mixtures.

    van Laar

    The van Laar equation was the first Gibbs excess energy representation with physical significance. This equation fits many systems quite well, particularly for LLE component distributions. It can be used for systems that exhibit positive or negative deviations from Raoults Law. Some of the advantages and disadvantage for this model are:

    Generally requires less CPU time than other activity models. It can represent limited miscibility as well as three phase

    equilibrium. It cannot predict maxima or minima in the activity coefficient

    and therefore, generally performs poorly for systems with halogenated hydrocarbons and alcohols.

    It also has a tendency to predict two liquid phases when they do not exist.

    The Margules equation should not be used for extrapolation beyond the range over which the energy parameters have been fitted.

    The van Laar equation performs poorly for dilute systems and CANNOT represent many common systems, such as alcohol-hydrocarbon mixtures, with acceptable accuracy.

  • Thermodynamics and HYSYS 9

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    The van Laar equation implemented in HYSYS has two parameters with linear temperature dependency, thus making it a four parameter model. In HYSYS, the equation is empirically extended and therefore its use should be avoided when handling multicomponent mixtures.

    Wilson

    The Wilson equation, proposed by Grant M. Wilson in 1964, was the first activity coefficient equation that used the local composition model to derive the Gibbs Excess energy expression. It offers a thermodynamically consistent approach to predicting multi-component behaviour from regressed binary equilibrium data.

    Although the Wilson equation is more complex and requires more CPU time than either the van Laar or Margules equations, it can represent almost all non-ideal liquid solutions satisfactorily except electrolytes and solutions exhibiting limited miscibility (LLE or VLLE).

    It performs an excellent job of predicting ternary equilibrium using parameters regressed from binary data only.

    It will give similar results to the Margules and van Laar equations for weak non-ideal systems, but consistently outperforms them for increasingly non-ideal systems.

    It cannot predict liquid-liquid phase splitting and therefore should only be used on problems where demixing is not an issue.

    Our experience shows that the Wilson equation can be extrapolated with reasonable confidence to other operating regions with the same set of regressed energy parameters.

    NRTL

    The NRTL (Non-Random-Two-Liquid) equation, proposed by Renon and Prausnitz in 1968, is an extension of the original Wilson equation. It uses statistical mechanics and the liquid cell theory to represent the liquid structure. These concepts, combined with Wilsons local composition model, produce an equation capable of representing VLE, LLE, and VLLE phase behaviour. Like the Wilson equation, the NRTL model is thermodynamically consistent and can be applied to ternary and higher order systems using parameters regressed from binary equilibrium data. The NRTL model has an accuracy comparable to the Wilson equation for VLE systems.

    The NRTL combines the advantages of the Wilson and van Laar equations.

    The Wilson equation CANNOT be used for problems involving liquid-liquid equilibrium.

    The additional parameter in the NRTL equation, called the alpha term, or non-randomness parameter, represents the inverse of the coordination number of molecule i surrounded by molecules j. Since liquids usually have a coordination number between 3 and 6, you might expect the alpha parameter between 0.17 and 0.33.

  • 10 Thermodynamics and HYSYS

    10

    It is not extremely CPU intensive. It can represent LLE quite well. However, because of the mathematical structure of the NRTL

    equation, it can produce erroneous multiple miscibility gaps.

    The NRTL equation in HYSYS contains five adjustable parameters (temperature dependent and independent) for fitting per binary pair.

    UNIQUAC

    The UNIQUAC (UNIversal QUAsi Chemical) equation proposed by Abrams and Prausnitz in 1975 uses statistical mechanics and the quasi-chemical theory of Guggenheim to represent the liquid structure. The equation is capable of representing LLE, VLE and VLLE with accuracy comparable to the NRTL equation, but without the need for a non-randomness factor, it is a two parameter model.

    The UNIQUAC equation is significantly more detailed and sophisticated than any of the other activity models.

    Its main advantage is that a good representation of both VLE and LLE can be obtained for a large range of non-electrolyte mixtures using only two adjustable parameters per binary.

    The fitted parameters usually exhibit a smaller temperature dependence which makes them more valid for extrapolation purposes.

    The UNIQUAC equation utilizes the concept of local composition as proposed by Wilson. Since the primary concentration variable is a surface fraction as opposed to a mole fraction, it is applicable to systems containing molecules of very different sizes and shape, such as polymer solutions.

    The UNIQUAC equation can be applied to a wide range of mixtures containing H2O, alcohols, nitriles, amines, esters, ketones, aldehydes, halogenated hydrocarbons and hydrocarbons.

    In its simplest form it is a two parameter model, with the same remarks as Wilson and NRTL. UNIQUAC needs van der Waals area and volume parameters, and those can sometimes be difficult to find, especially for non-condensable gases (although DIPPR has a fair number available).

    Extended and General NRTL

    The Extended and General NRTL models are variations of the NRTL model, simple NRTL with a complex temperature dependency for the aij and aji terms. Apply either model to systems:

  • Thermodynamics and HYSYS 11

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    with a wide boiling point range between components where you require simultaneous solution of VLE and LLE, and

    there exists a wide boiling range or concentration range between components

    Extreme caution must be exercised when extrapolating beyond the temperature and pressure ranges used in regression of parameters. Due to the larger number of parameters used in fitting, inaccurate results can be obtained outside the original bounds.

    Chien-Null

    Chien-Null is an empirical model designed to allow you to mix and match models which were created using different methods and combined into a multicomponent expression. The Chien-Null model provides a consistent framework for applying existing activity models on a binary by binary basis. In this manner, Chien-Null allows you to select the best activity model for each pair in the case. For example, Chien-Null can allow the user to have a binary defined using NRTL, another using Margules and another using van Laar, and combine them to perform a three component calculation, mixing three different thermodynamic models.

    The Chien Null model allows 3 sets of coefficients for each component pair, accessible via the A, B and C coefficient matrices.

    Henrys Law

    Henrys Law cannot be selected explicitly as a property method in HYSYS. However, HYSYS will use Henrys Law when an activity model is selected and "non-condensable" components are included within the component list.

    HYSYS considers the following components non-condensable: Methane, Ethane, Ethylene, Acetylene, Hydrogen, Helium, Argon, Nitrogen, Oxygen, NO, H2S, CO2, and CO.

    The general NRTL model is particularly susceptible to inaccuracies if the model is used outside of the intended range.

    Care must be taken to ensure that you are operating within the bounds of the model.

    The Thermodynamics appendix in the HYSYS User Manual provides more information on Property Packages, Equations of State, and Activity Models, and the equations for each.

    No interaction between "non-condensable" component pairs is taken into account in the VLE calculations.

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    The extended Henrys Law equation in HYSYS is used to model dilute solute/solvent interactions. "Non-condensable" components are defined as those components that have critical temperatures below the system temperature.

    Activity Model Vapour Phase Options

    There are several methods available for calculating the Vapour Phase in conjunction with the selected liquid activity model. The choice will depend on specific considerations of your system.

    Ideal

    The ideal gas law can be used to model the vapour phase. This model is appropriate for low pressures and for a vapour phase with little intermolecular interaction. The model is the default vapour phase fugacity calculation method for activity coefficient models.

    Peng Robinson, SRK or RK

    To model non-idealities in the vapour phase, the PR, SRK, or RK options can be used in conjunction with an activity model.

    PR and SRK vapour phase models handle the same types of situations as the PR and SRK equations of state.

    When selecting one of these three models, ensure that the binary interaction parameters used for the activity model remain applicable with the chosen vapour model.

    For applications with compressors and turbines, PR or SRK will be superior to the RK or Ideal vapour model.

    Virial

    The Virial option enables you to better model vapour phase fugacities of systems displaying strong vapour phase interactions. Typically this occurs in systems containing carboxylic acids, or compounds that have the tendency to form stable H2 bonds in the vapour phase.

    HYSYS contains temperature dependent coefficients for carboxylic acids. You can overwrite these by changing the Association (ij) or Solvation (ii) coefficients from the default values.

    This option is restricted to systems where the density is moderate, typically less than one-half the critical density.

    Care should be exercised in choosing PR, SRK, RV or Virial to ensure binary coefficients have been regressed with the corresponding vapour phase model.

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    Binary CoefficientsFor the Property Packages which do include binary coefficients, the Binary Coefficients tab contains a matrix which lists the interaction parameters for each component pair. Depending on the property method chosen, different estimation methods may be available and a different view may be shown. You have the option of overwriting any library value.

    Equation of State Interaction Parameters

    The Equation of State Interaction Parameters group appears as follows on the Binary Coeffs tab when an EOS is the selected property package:

    For all EOS parameters (except PRSV),

    Kij = Kji

    so when you change the value of one of these, both cells of the pair automatically update with the same value. In many cases, the library interaction parameters for PRSV do have Kij = Kji, but HYSYS does not force this if you modify one parameter in a binary pair.

    The numbers appearing in the matrix are initially calculated by HYSYS, but you have the option of overwriting any library value.

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    If you are using PR or SRK (or one of the Sour options), two radio buttons are displayed at the bottom of the page in the Treatment of Interaction Coefficients Unavailable from the Library group:

    Estimate HC-HC/Set Non HC-HC to 0.0 this radio button is the default selection. HYSYS provides the estimates for the interaction parameters in the matrix, setting all non-hydrocarbon pairs to 0.

    Set All to 0.0 when this is selected, HYSYS sets all interaction parameter values in the matrix to 0.0.

    Activity Model Interaction Parameters

    Activity Models are much more empirical in nature when compared to the property predictions in the hydrocarbon industry. Their tuning parameters should be fitted against a representative sample of experimental data and their application should be limited to moderate pressures.

    The Activity Model Interaction Parameters group appears as follows on the Binary Coeffs tab when an Activity Model is the selected property package:

    The interaction parameters for each binary pair will be displayed. You can overwrite any value or use one of the estimation methods.

    Note that the Kij = Kji rule does not apply to Activity Model interaction parameters.

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    Estimation Methods

    When using Activity Models, HYSYS provides three interaction parameter estimation methods. Select the estimation method by choosing one of the radio buttons in the Coeff Estimation window. The options are:

    UNIFAC VLE UNIFAC LLE Immiscible

    You can then invoke the estimation by selecting one of the available cells.

    For UNIFAC methods the options are:

    Individual Pair calculates the parameters for the selected component pair, Aij and Aji. The existing values in the matrix are overwritten.

    Unknowns Only calculates the activity parameters for all the unknown pairs. If you delete the contents of cells or if HYSYS does not provide default values, you can use this option.

    All Binaries recalculates all the binaries of the matrix. If you had changed some of the original HYSYS values, you could use this to have HYSYS re-estimate the entire matrix.

    .

    For the Immiscible method the options are:

    Row in Clm pair estimates the parameters such that the row component (j) is immiscible in the column component (i).

    Clm in Row pair estimates parameters such that the column component (j) is immiscible in the row component (i).

    All in Row estimates parameters such that both components are mutually immiscible.

    In Module 1, you chose the NRTL Activity Model, then select the UNIFAC VLE estimation method (default) before pressing the Unknowns Only cell.

    When the All Binaries button is used, HYSYS does not return the original library values. Estimation values will be returned using the selected UNIFAC method. To return to the original library values, you must select a new property method and then re-select the original property method

    The UNIFAC (UNIquac group-Functional Activity Coefficient) method is a group contribution technique using the UNIQUAC model as the starting point to estimate binary coefficients. This, however, should be a last solution as it is preferable to try and find values estimated from experimental data.

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    Which Activity Coefficient Model Should I Use?This is a tough question to answer, but some guidelines are provided. If you require additional assistance, it is best to contact Hyprotechs Technical Support department.

    Basic Data

    Activity coefficient models are empirical by nature and the quality of their prediction depends on the quality and range of data used to determine the parameters. Some important things you should be aware of in HYSYS.

    The parameters built in HYSYS were fitted at 1 atm wherever possible, or were fitted using isothermal data which would produce pressures closest to 1 atm. They are good for a first design, but always look for experimental data closer to the region you are working in to confirm your results.

    The values in the HYSYS component database are defined for VLE only, hence the LLE prediction may not be very good and additional fitting is necessary.

    Data used in the determination of built in interaction parameters very rarely goes below 0.01 mole fraction, and extrapolating into the ppm or ppb region can be risky.

    Again, because the interaction parameters were calculated at modest pressures, usually 1 atm, they may be inadequate for processes at high pressures.

    Check the accuracy of the model for azeotropic systems. Additional fitting may be required to match the azeotrope with acceptable accuracy. Check not only for the temperature, but for the composition as well.

    If three phase behaviour is suspected, additional fitting of the parameters may be required to reliably reproduce the VLLE equilibrium conditions.

    UNIFAC or no UNIFAC?

    UNIFAC is a handy tool to give initial estimates for activity coefficient models. Nevertheless keep in mind the following:

    Group contribution methods are always approximate and they are not substitutions for experimental data.

    UNIFAC was designed using relatively low molecular weight condensable components (thus high boilers may not be well represented), using temperatures between 0-150 oC and data at modest pressures.

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    Generally, UNIFAC does not provide good predictions for the dilute region.

    Choosing an Activity Model

    Again, some general guidelines to consider.

    Margules or van Laar - generally chosen if computation speed is a consideration. With the computers we have today, this is usually not an issue. May also be chosen if some preliminary work has been done using one of these models.

    Wilson - generally chosen if the system does not exhibit phase splitting.

    NRTL or UNIQUAC - generally chosen if the system exhibits phase splitting.

    General NRTL - should only be used if an abundant amount of data over a wide temperature range was used to define its parameters. Otherwise it will provide the same modelling power as NRTL.

    Exploring with the SimulationProper use of thermodynamic property package parameters is key to successfully simulating any chemical process. Effects of pressure and temperature can drastically alter the accuracy of a simulation given missing parameters or parameters fitted for different conditions. HYSYS is user friendly in allowing quick viewing and changing of the particular parameters associated with any of the property packages. Additionally, the user is able to quickly check the results of one set of parameters and compare against another.

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    Exercise 1

    Di-iso-Propyl-Ether/H2O Binary

    This example effectively demonstrates the need for having interaction parameters. Do the following:

    1. Open case DIIPE.hsc.

    2. Enter the following conditions for stream DIIPE/H2O:

    3. Close the stream view and press the Enter Basis Environment button.

    4. Select the Binary Coeffs tab of the Fluid Package. Notice that the interaction parameters for the binary are both set to 0.0.

    5. Press the Reset Params button to recall the default NRTL activity coefficient model interaction parameters.

    6. Close the Fluid Package view.

    7. Return to the simulation environment by pressing the Return to Simulation Environment button.

    8. Open the stream view by double clicking on the stream DIIPE/H2O.

    Conditions

    Vapour Fraction 0.0

    Pressure 1 atm

    Molar Flow 1 kgmole/h (1 lbmole/hr)

    Composition

    di-i-P-Ether 50 mole %

    H2O 50 mole %

    What phases are present? __________

    What phases are now present? __________

    What is the composition of each? __________

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    Clearly, it can be seen how important it is to have interaction parameters for the thermodynamic model. The xy phase diagrams on the next page (figures 1 and 2) illustrate the homogeneous behaviour when no parameters are available and the heterogeneous azeotropic behaviour when properly fitted parameters are used. The majority of the default interaction parameters for activity coefficient models in HYSYS have been regressed based on VLE data from DECHEMA, Chemistry Data Services.

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    Fig. 1 - Interaction Parameters set to 0.

    Fig. 2 - Using the Default HYSYS Interaction Parameters.

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    Exercise 2

    Phenol/H2O Binary

    This binary shows the importance of ensuring that properly fitted interaction parameters for the conditions of your simulation are used. The default parameters for the Phenol/H2O system have been regressed from the DECHEMA Chemistry data series and provide very accurate vapour-liquid equilibrium since the original data source (1) was in this format. However, the Phenol/Water system is also shown to exhibit liquid-liquid behaviour (2). A set of interaction parameters can be obtained from sources such as DECHEMA and entered into HYSYS. The following example illustrates the poor LLE prediction than can be produced by comparing the results using default interaction parameters and specially regressed LLE parameters.

    1. Open the case Phenolh2o.hsc.

    2. Enter the following conditions for stream Phenol/H2O:

    Conditions

    Temperature 40C

    Pressure 1 atm

    Molar Flow 1 kgmole/h (1 lbmole/hr)

    Composition

    Phenol 25 mole %

    H2O 75 mole %

    What phase(s) are present? __________

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    To provide a better prediction for LLE at 40 oC (105 oF) the following Aij interaction parameters are to be entered. To enter the parameters do the following:

    1. Close the stream view and press the Enter Basis Environment button.

    2. Ensure the Fluid Package view is open and select the Binary Coeffs tab.

    3. Enter the Aij interaction parameters as shown here:

    4. Select the Alphaij/Cij radio button.

    5. Enter an Alphaij = 0.2.

    6. Close the Fluid Package view.

    7. Return to the simulation environment by pressing the Return to Simulation Environment button.

    8. Open the stream view for Phenol/H2O.

    The figures on the following page (figures 3 and 4) show the difference between the two sets of interaction parameters. Therefore, care must be exercised when simulating LLE as almost all the default interaction parameters for the activity coefficient models in HYSYS are for VLE.

    What phase(s) are present now? __________

    What are the compositions? __________

  • Thermodynamics and HYSYS 23

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    Fig. 3 - Using the Default (VLE) Interaction Parameters.

    Fig. 4 - Using the Fitted (LLE Optimizied) Interaction Parameters.

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    Exercise 3

    Benzene/Cyclohexane/H2O Ternary

    This example again illustrates the importance of having interaction parameters and also discusses how the user can obtain parameters from regression. To illustrate the principles do the following:

    1. Open the case Ternary.hsc.

    2. Enter the following stream conditions for Benzene/CC6/H2O:

    To provide a more precise simulation the missing CC6/H2O interaction parameter has to be obtained. Fortunately, some data is available at 25C giving the liquid-liquid equilibrium between CC6 and H2O. Using this data, and the regression capabilities within DISTIL, an AEA Technology Engineering Software conceptual design and thermodynamic regression product, you can obtain new interaction parameters. The temperature dependent Bij parameters are to be left at 0 and the alphaij term is to be set to 0.2 for the CC6/H2O. To implement these parameters, proceed with the steps on the following page.

    Conditions

    Temperature 25C

    Pressure 1 atm

    Composition

    Benzene 20 mole %

    H2O 20 mole %

    CC6 60 mole %

    How many phases are present? __________

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    1. Return to the Basis Environment by pressing the Enter Basis Environment button.

    2. Open the Fluid Package view and move to the Binary Coeffs tab.

    3. Enter the data in the Aij matrix as shown here:

    4. Select the Alphaij/Cij radio button.

    5. Enter a CC6/H2O alphaij value of 0.2.

    6. Close the Fluid Package view.

    7. Return to the Simulation Environment.

    8. Open the stream Benzene/CC6/H2O.

    The figures on the following page (figures 5 and 6) clearly show the behaviour of the ternary system. Without the regressed CC6/H2O binary, the thermodynamic property package incorrectly predicts the system to be miscible at higher CC6 concentrations. This prediction is correct given properly regressed CC6/H2O parameters.

    References1. Schreinemakers F.A.H., Z. Phys. Chem. 35, 459 (1900).2. Hill A.E. and Malisoff W.M., J. Am. Chem. Soc. 48 (1926) 918.

    How many phases are now present? __________

    What are the compositions? __________

  • 26 Thermodynamics and HYSYS

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    Fig. 5 - Without Regressed CC6/H2O Interaction Parameters.

    Fig. 6 - With Regressed CC6/H2O Interaction Parameters.

  • Flowsheeting 1

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    Flowsheeting

    2000 AEA Technology plc - All Rights Reserved.Chem 3_4.pdf

  • 2 Flowsheeting

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    WorkshopIn evaporation, a solution consisting of a non-volatile solute and a volatile solvent is concentrated by the addition of heat. In multiple effect evaporation, the volatile solvent recovered from the first evaporator is condensed and used as a heat source for the next evaporator. This means that the second evaporator must operate at a lower temperature and pressure than the first evaporator.

    In this module you will simulate a series of three evaporators to concentrate a solution of sucrose/water. Each evaporator is modelled using a flash tank. You will convert the completed simulation to a template, making it available to connect to other simulations.

    On the next page, a Process Overview is shown. This represents the actual process. On the third page a Simulation PFD is shown. This represents the simulation as you will build it in this module. Building the simulation in this way allows more flexibility in the design.

    Learning ObjectivesOnce you have completed this section, you will be able to:

    Add and connect operations to build a Flowsheet Add and use logical operations, Sets and Adjusts Use the graphical interface to manipulate flowsheets in HYSYS Understand information propagation in HYSYS Convert HYSYS flowsheet to templates

    PrerequisitesBefore beginning this section you need to know how to:

    Define a Fluid Package Define Streams Navigate the Workbook interface

  • Process Overview

  • Simulation PFD

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    Building the SimulationThe first step to building any simulation is defining a Fluid Package. A brief recap on how to define a Fluid Package and install streams is described below. For a complete description see: Defining the Simulation Basis, Module 1.

    Defining the Simulation Basis1. Start a New Case and add a Fluid Package.

    2. Use Wilson/Ideal as the Property Package with the components Sucrose and H2O.

    3. Move to the Binary Coefficients page. Notice that the interaction parameters for Aij and Bij are empty.

    The program warns you that the binary coefficients have not been determined and the model will assume values of zero. Answer OK to this message. Enter the Simulation Environment.

    The Wilson equation cannot be used for problems involving liquid-liquid equilibrium.

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    4. Add a stream with the following values.

    5. Add a second stream with the following properties:

    In this cell Enter

    Name Feed

    Vapour Fraction 0

    Pressure 101.3 kPa (14.7 psia)

    Flowrate 50 kg/h (110 lb/hr)

    Mass Fraction Surcose 0.3

    Mass Fraction H2O 0.7

    Note that the composition values for this stream are in Mass fractions. Double-click on the Mass Flow cell to enter these values.

    In this cell Enter

    Name Steam

    Vapour Fraction 1.0

    Pressure 275 kPa (40 psia)

    Mass fraction H2O 1.0

    What is the temperature of stream Feed? __________

    What is the temperature of stream Steam? __________

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    Adding Unit Operations to a FlowsheetAs with streams, there are a variety of ways to add Unit Operations in HYSYS:

    The Triple Effect Evaporator consists of six operations:

    A series of three evaporators modelled as flash tanks (2 Phase separators)

    Three coolers

    In this exercise, you will add each operation using a different method of installation.

    To use the Do this

    Menu Bar Select Add Operation from the Flowsheet menu.

    Or

    Press the hot key.

    The UnitOps window displays.

    Workbook Open the Workbook and go to the UnitOps page, then click the Add UnitOp button.

    The UnitOps window displays.

    Object Palette Select Object Palette from the Flowsheet menu or press to open the Object Palette and double click the icon of the Unit Operation you want to add.

    PFD/Object Palette Using the right mouse button, dragndrop the icon from the Object Palette to the PFD.

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    Adding a Separator

    The Evaporator is modelled using a Separator in HYSYS.

    The Separator will be added using the hot key.

    1. Press the hot key. The UnitOps window displays:

    2. Select Separator from the Available Unit Operations list.

    3. Press the Add button. The Separator property view displays.

    4. On the Connections page enter the data as shown here:

    Note: Drop down boxes, such as for Feed and Product streams, contain lists of available streams which can be connected to the operation.

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    Adding a CoolerAdd the first Cooler using the same method.

    1. Press the hot key

    2. The UnitOps window displays. Click the Category Heat Transfer Equipment and select Cooler.

    3. Press the Add button. The Cooler property view displays.

    4. On the Connections page enter the information as shown below:

    5. Go to the Parameters page.

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    6. Enter a value of 0 kPa (0 psi) for the Pressure Drop.

    7. Go to the Worksheet tab.

    8. Specify a Vapour Fraction of 0 for the stream Condensate.

    To completely define the separation we need to provide an energy flow.

    9. On the Worksheet tab, enter a value of 2.42e4 kJ/h (2.29e4 Btu/hr) for the Energy stream q1.

    What is the flowrate of Water in the stream L1? __________

    What is the temperature of the stream V1? __________

    What is the mass flow of steam through the Cooler? __________

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    Add the Second CoolerThis procedure describes how to add Unit Operations using the UnitOps page of the Workbook.

    1. Open the Workbook and click the UnitOps tab.

    2. Click the Add UnitOp button. The UnitOps window displays:

    3. Select Heat Transfer Equipment from the Categories group.

    4. Select Cooler from the Available Unit Operations list.

    5. Press the Add button. The Cooler property view displays.

    6. On the Connections page enter the information as shown below:

    7. On the Parameters page specify a Pressure Drop of 0 kPa (0 psi).

    8. Go to the Worksheet tab and specify the Vapour Fraction of the stream C2 as 0. Close this view.

    What is the Heat Flow for stream q2? __________

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    Add Another SeparatorThis procedure describes how to add a Separator using the Object Palette. The Object Palette contains icons for all the Streams and Unit Operations in HYSYS.

    1. Press the hot key. The Object Palette displays:

    2. Double click the Separator button on the Object Palette. The Separator property view displays.

    Separator button

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    3. On the Connections page enter the stream information as shown here:

    4. On the Parameters page, delete the pressure drop specification. The Separator should become unsolved; Unknown Delta P.

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    Add a Set OperationThe Set Operation is a steady-state logical operation used to set the value of a specific Process Variable (PV) in relation to another PV. The relationship is between the same PV in two like objects -- for instance, the temperature of two streams, or the UA of two exchangers.

    In order for the energy to flow from Cooler 2 to Effect 2, the Separator outlet temperature must be cooler then the condensate from the Cooler. A Set operation will be used to maintain this relationship.

    1. Add a Set operation by double-clicking on the Set icon in the object palette.

    2. Complete the Connections page as shown here:

    3. Go to the Parameters tab. Complete the view as shown below, if using field units the value for the offset will be -5 oF:

    What is the Delta P of Effect 2? __________

    Set operation button

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    Add the Third CoolerWorking with a graphical representation, you can build your flowsheet in the PFD using the mouse to install and connect objects. This procedure describes how to install and connect the Cooler using the Object Palette Dragndrop technique.

    To DragnDrop in the PFD:1. Press the Cooler button on the Object Palette.

    2. Move the cursor to the PFD. The cursor will change to a special cursor, with a box and a plus (+) symbol attached to it. The box indicates the size and location of the cooler icon.

    3. Click the left mouse button to drop the Cooler onto the PFD.

    There are two ways to connect the operation to a stream on the PFD:

    To connect using the Do this

    Attach Mode toggle button

    Insert Icon

    Press the Attach Mode toggle button.

    Place the cursor over the operation. The Feed stream connection point is highlighted in dark blue.

    Move the cursor over the stream you want to connect.

    Press and hold the left mouse button.

    Move the cursor to the operation icon and release the mouse button.

    key Press and hold the key and pass the cursor over the operation.

    Place the cursor over the stream you want to connect.

    Press and hold the left mouse button.

    Move the cursor to the operation icon and release the mouse button and the key.

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    4. Double click on the Cooler icon on the PFD. The Cooler property view displays. Enter the data shown below:

    5. On the Parameters page specify a Pressure Drop of 0 kPa (0 psi).

    6. Go to the Worksheet tab and specify the Vapour Fraction of the stream C3 as 0. Close this view.

    Add the Third Separator1. Drag n drop the Separator onto the PFD. Connect the stream L2

    as the Feed to the Separator.

    2. Double click on the Separator. Make the following connections:

    3. On the Parameters page delete the pressure drop specification.

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    Set Operation1. Add a Set operation and complete the Connections page as

    shown here:

    2. On the Parameters tab enter a value of 3 C (-5F) as the Offset, and 1.0 for the Multiplier.

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    Add an AdjustThe Adjust operation is a Logical Operation - a mathematical operation rather than a physical operation. It will vary the value of one stream variable (the independent variable) to meet a required value or specification (the dependant variable) in another stream or operation.

    It is desired to reach 15 weight% water in stream L3. The only parameter we have to manipulate this variable is the energy supplied to the first Effect. To meet a target concentration in L3 we can use an Adjust operation.

    1. Add the Adjust operation. The Adjust property view displays.

    2. Press the Select Var button in the Adjusted Variable group to open the Variable Navigator.

    3. From the Object list select q1. From the Variable list which is now visible, select Heat Flow.

    4. Press the OK cell to accept the variable and return to the Adjust property view.

    5. Press the Select Var button in the Target Variable group.

    What is the weight percent of Water in stream L3? __________

    Adjust button

    The adjusted variable must always be a user specified value.

    Always work left to right in the Variable Navigator. Dont forget you can use the Object Filter when the Object list is large.

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    6. Select L3 and Comp Mass Frac (H2O) as the target variable.

    7. On the Connections page, enter a value of 0.15 in the Specified Target Value box.

    The completed Connections page is shown below.

    8. Switch to the Parameters tab, and enter 2000 kJ/h (1900 Btu/hr) as the Step Size.

    9. Press the Start button to begin calculations. Note: once the case is solved (OK status), this button will disappear from the property view.

    10. To view the progress of the Adjust, go to the Monitor tab.

    When adjusting certain variables, it is often a good idea to provide a minimum or maximum which corresponds to a physical boundary, such as zero for pressure or flow.

    Note the Tolerance and Step Size values. When considering step sizes, use larger rather than smaller sizes. The Secant method works best once the solution has been bracketed and by using a larger step size, you are more likely to bracket the solution quickly.

  • 20 Flowsheeting

    20

    If you enter a step size too large for the energy HYSYS will not calculate because all the liquid has been flashed. You need to decrease the step size, enter a new value for q1 and restart the simulation.

    Note that HYSYS does not predict the formation of solids; this will have to be verified separately.

    Manipulating the PFDThe PFD is designed around using the mouse and/or keyboard. There are a number of instances in which either the mouse or the keyboard can be used to perform the same function. One very important PFD function for which the keyboard cannot be used is Object Inspection.

    You can perform many of the tasks and manipulations on the icons in the PFD by using Object Inspection. Place the mouse pointer over the icon you wish to inspect and press the secondary mouse button. An appropriate menu is produced depending upon the icon selected (Stream, Operation, Column, or Text Annotation).

    A list of the objects which you can Object Inspect are shown below with

    What is the energy required to achieve a concentration of 85 wt% of sucrose in the product stream? __________

  • Flowsheeting 21

    21

    the corresponding menus.

    Object... Object Inspection Menu...

    PFD

    Unit Operations

    Streams

  • 22 Flowsheeting

    22

    Customize the PFD by performing the following:

    1. Add a Title, Triple Effect Evaporator.

    2. Add a Workbook Table for the Material Streams in the simulation.

    3. Add a Table for stream L3.

    Adding Unit Operation Information to the Workbook

    Each WorkBook has a UnitOps page by default that displays all the Unit Operations and their connections in the simulation. You can add additional pages for specific Unit Operations to the WorkBook. For example, you can add a page to the WorkBook to contain only Coolers in the simulation.

    To add a Unit Operation tab to the WorkBook:1. Open the Workbook.

    2. In the Menu Bar, select Workbook, and then Setup.

    3. In the Setup view, press the Add button in the UnitOps group.

    4. From the New Object Type view, select Heat Transfer Equipment, then Cooler.

    5. Click OK. A new page, Cooler, containing only Cooler information is added to the WorkBook.

    Double clicking on a title with a "+" sign will open an expanded menu.

  • Flowsheeting 23

    23

    Adding Unit Operation Information to the PFD

    For each Unit Operation, you can display a Property Table on the PFD. The Property Table contains certain default information about the Unit Operation.

    Add Unit Operation information to the PFD:1. Open the PFD.

    2. Select the Separator Effect 1.

    3. Object Inspect the Unit Operation.

    4. Select Show Table from the menu.

    5. The Vessel Temperature, Pressure, Liquid Molar Flow, and Duty are shown as defaults in the table. Object Inspect the table and insert the Vapour Mass Flow.

    6. Create two tables for the streams Feed and L3 showing the Component Mass Fraction of Sucrose and the Mass Flow.

    Remember you can Object Inspect an object by selecting it and then clicking on it with the right mouse button.

    Save your case!

  • 24 Flowsheeting

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    Exploring with the SimulationExercise 1

    Try running the case for different final sucrose concentrations. Can you find any cases in which the program does not solve?

    Watch for cases when the Adjust block takes too large of a step in energy, causing all of the liquid to be flashed.

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    25

    Saving the Simulation as a TemplateA template is a complete Flowsheet that has been stored to disk with some additional information included that pertains to attaching the Flowsheet as a Sub-Flowsheet operation. Typically, a template is representative of a plant process module or portion of a process module. The stored template can subsequently be read from disk and efficiently installed as a complete Sub-Flowsheet operation any number of times into any number of different simulations.

    Some of the advantages of using templates are:

    Provide the mechanism by which two or more cases can be linked together

    Can employ a different property package than the main case to which it is attached

    Provide a convenient method for breaking large simulations into smaller, easily managed components

    Can be created once and then installed in multiple cases

    Before you convert a case to a template, it needs to be made generic so it can be used with gas plants of various flowrates.

    1. Delete the Flow and Composition of stream Feed.

    2. Choose Main Properties from the Simulation menu.

    3. Press the Convert to Template button.

    4. Press Yes to convert the simulation case to a template.

    5. Answer No to the question Do you want to save the simulation case.

    6. Save the template as 3-Effect-Evap.tpl.

    Note that once a case has been saved as a template, it can not be re-converted back into a normal simulation case.

  • 26 Flowsheeting

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  • Reactions 1

    1

    Reactions

    2000 AEA Technology plc - All Rights Reserved.Chem 4_4.pdf

  • 2 Reactions

    2

    WorkshopThis module demonstrates the HYSYS philosophy for building reactions within a simulation. HYSYS defines reactions within the context of the Fluid Package. This is important for a number of reasons:

    By associating reactions with the fluid system rather than a specific reactor unit operation, the user is free to model reactions anywhere they might take place: in flash tanks, tray sections, reboilers etc., as well as in reactors. Reactions are defined and simply attached to the equipment piece.

    By defining the reactions up front in the fluid system, the reactions need only be defined once, rather than each time a reactor unit is built. Additionally, any changes to the basic reaction data are updated throughout the model automatically.

    By separating the reaction definitions from the unit operations or model topology, component and reaction data may be saved out as an independent file for use in another case. The user can then create a reaction library or database for future use, thereby eliminating a repetitive task, reducing engineering time and working more efficiently.

    This module presents Steam-Methane Reforming.

    Learning ObjectivesOnce you have completed this section, you will be able to:

    Define reactions in HYSYS Model Conversion and Equilibrium reactors in HYSYS.

    PrerequisitesBefore beginning this section you need to know how to:

    Create a Fluid Package Add streams Add Unit Operations

  • Reactions 3

    3

    Reactions and ReactorsThere are five different types of reactors that can be simulated with HYSYS. By using combinations of these five reactors, virtually any reactor can be modelled within HYSYS. The five reactor types are:

    Conversion - given the stoichiometry of all the reactions occurring and the conversion of the base component, calculates the composition of the outlet stream.

    Equilibrium - determines the composition of the outlet stream given the stoichiometry of all reactions occurring and the value of equilibrium constant (or the temperature dependant parameters that govern the equilibrium constant) for each reaction.

    Gibbs - evaluates the equilibrium composition of the outlet stream by minimizing the total Gibbs free energy of the reaction system.

    CSTR - computes the conversion of each component entering the reactor. The conversion in the reactor depends on the rate expression of the reactions associated with the reaction type.

    PFR - assumes that the reaction streams pass through the reactor in plug flow in computing the outlet stream composition, given the stoichiometry of all the reactions occurring and a kinetic rate constant for each reaction.

    Note: The required input is different depending on the type of reactor that is chosen. CSTR and PFR reactors must have kinetic rate constants (or the formula to determine the kinetic rate constant) as inputs, as well as the stoichiometry of the reactions. All of the reactor types, except for the Gibbs type, must have the reaction stoichiometry as inputs.

    Reactions can also occur in the Tank, Separator, and Three Phase Separator Unit Operations if a reaction set is attached.

    Note that Kinetic, Kinetic RevEqb, and Langmuir-Hinshelwood reactions can only be modelled in the CSTR, PFR and Separator.

  • Process Overview

  • Reactions 5

    5

    Steam-Methane ReformerSteam reformation of methane is often undertaken in conjunction with processes which require large amounts of hydrogen for instance hydrotreating, ammonia production, or any process which may utilise such a synthesis gas. Successive reaction stages take advantage of thermodynamics and catalysts to enhance the production of hydrogen at the expense of the by-product gases carbon monoxide and dioxide. Finally, remaining carbon oxides are converted back into methane as completely as possible to minimise CO and CO2 carryover into the downstream process.

    In the course of this problem, we will use two of the reactor types in HYSYS to simulate the reactors in the steam reformation train: the Conversion and Equilibrium reactors.

  • 6 Reactions

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    Building the Simulation

    Defining the Simulation BasisFor this simulation we will use the Peng Robinson EOS with the following components: methane, carbon monoxide, carbon dioxide, hydrogen and water. The Fluid Package that you defined can be renamed to Steam-C1 reformer.

    Adding the Reactions

    The reactions which take place in this simulation are:

    Reactions in HYSYS are added in a manner very similar to the method used to add components to the simulation:

    1. Open the Fluid Package and select the Rxns tab. Press the Simulation Basis Mgr button to open the Simulation Basis Manager view.

    2. Press the Add Comps button to open the component selection view. Here, we will select the components that we will have use in our reactions.

    ReactionName

    Reaction

    Reform1 CH4 +H2O ---> CO + 3H2

    Reform2 CO + H2O ---> CO2 + H2

    Shift1 CO + H2O CO2 + H2

    Meth1 CO + 3H2 ---> H2O + CH4

  • Reactions 7

    7

    3. Ensure that the FPkg Pool radio button is selected. Press the Add This Group of Components button. This moves the entire component list over to the Selected Reaction Components group.

    4. Return to the Simulation Basis Manager view and press the Add Rxn button. Choose Equilibrium as the type from the displayed list.

    5. Press the Add Reaction button and enter the necessary information as shown:

    This has defined the stoichiometry of the first reaction:

    CH4 +H2O ---> CO + 3H2

    Note that reactants are defined with negative coefficients and products have positive coefficients; this is the HYSYS standard. All reactions must be defined this way.

    6. Move to the Basis tab and click the K vs T Table radio button.

  • 8 Reactions

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    7. On the Keq790 tab, enter the following values:

    8. Add the second Equilibrium reaction by selecting the reaction type as Equilibrium.

    CO + H2O ---> CO2 + H2

    9. For reaction 2, proceed as above and enter the following values for the Equilibrium Constant:

    The name of this reaction can be changed to Reform 2.

    In the absence of a catalyst and at 430 C (800F), the rate of reaction number 1 in the Shift Reactor is negligible, and reaction number 2 becomes the only reaction.

    HYSYS contains a library of some of the most commonly encountered chemical reactions with their Equilibrium Constants. For the Shift Reactor, you will use the library values for the Equilibrium Constant.

    Temperature, C (F) Keq

    595C (1100F) 0.5

    650C (1200F) 3

    705C (1300F) 14

    760C (1400F) 63

    815C (1500F) 243

    870C (1600F) 817

    Temperature, C (F) Keq

    675C (1250F) 1.7

    705C (1300F) 1.5

    730C (1350F) 1.3

    760C (1400F 1.2

    790C (1450F) 1.1

    815C (1500F) 1.0

  • Reactions 9

    9

    10. Add the third Equilibrium reaction by selecting the reaction type as Equilibrium. On the Library tab, highlight the reaction with the form CO + H2O = CO2 + H2. Press the Add Library Rxn button. This adds the reaction and all of the reactions data to the simulation.

    11. Rename the reaction Shift1.

    12. Add a Conversion reaction for the reverse of reaction number 1. The reaction is:

    CO + 3H2 ---> H2O + CH4

    13. Move to the Basis tab and enter CO as the Base Component and enter 100 for the Co term.

    14. Rename this reaction Meth1.

    Adding the Reaction Sets

    Once all four reactions are entered and defined, you can create reaction sets for each type of reactor.

    1. On the Reactions tab of the Simulation Basis Manager, press the Add Set button. Name the first Set Reformer Rxn Set, and add Reform1 and Reform2.

    Reactions are added by highlighting the field in the Active List group, and selecting the desired reaction from the drop down list. The

    Reaction Sets may contain more than one Reaction. There is limited flexibility for the mixing of reaction types within a Reaction Set.

    Equilibrium and Kinetic reactions can be within a single reaction set

    Conversion reactions cannot be in the same set as other reaction types

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    view should look like this after you have finished:

    2. Create two more reaction sets with the following information:

    Attaching Reaction Sets to the Fluid Package

    After the three reaction Sets have been created, they must be added to the current fluid package in order for HYSYS to use them.

    1. On the Reactions tab of the Simulation Basis Manager view, highlight the Reformer Rxn Set and press the Add to FP button.

    2. Select the only available Fluid Package and press the Add Set to Fluid Package button.

    3. Repeat Steps 1 and 2 to add all three reaction sets (Reformer, Shift and Methanator).

    Once all three reaction sets are added to the Fluid Package, you can enter the Simulation Environment and begin constructing the simulation.

    Name Active List

    Shift Rxn Set Shift1

    Methanator Rxn Set Meth1

  • Reactions 11

    11

    Adding the Unit Operations

    Add the Feed Streams

    Create two new material streams with the following information:

    Add a Mixer

    On the Parameters page, select the Set Outlet to Lowest Inlet radio button.

    In This Cell... Enter...

    Conditions

    Name Natural Gas

    Temperature 20C (70F)

    Pressure 520 kPa (75 psia)

    Mass flow 800 kg/h (1765 lb/hr)

    Composition

    Mass Fraction CH4 1.0

    Name Steam

    Temperature 180C (360F)

    Pressure 965 kPa (140 psia)

    Composition

    Mass Fraction H2O 1.0

    In This Cell... Enter...

    Connections

    Name Mix-100

    Inlets Natural Gas / Steam

    Outlet Mixed Feed

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    Add a Heater

    A Heater is needed to heat the feed to the reaction temperature.

    Add a Heater with the following information:

    In This Cell... Enter...

    Connections

    Name HX1

    Inlet Mixed Feed

    Energy HX1-Q

    Outlet Reform Feed

    Parameters

    Delta P 10 kPa (1.5 psi)

    Worksheet

    Reform Feed, Temperature 760C (1400F)

  • Reactions 13

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    Add a Set Operation

    A Set operation is needed to fix the steam rate relative to the methane feed rate.

    Add a Set operation with the following information:

    The Reform Feed stream should now be completely defined.

    Add the Steam Reformer

    An Equilibrium Reactor will be used to simulate the Steam Reformer.

    From the Object Palette, click General Reactors. Another palette appears with three reactor types: Gibbs, Equilibrium and Conversion. Select the Equilibrium Reactor, and enter it into the PFD. Make the following connections:

    In This Cell... Enter...

    Connections

    Name SET-1

    Target Object Steam, Molar Flow

    Source Natural Gas

    Parameters

    Multiplier 2.5

    Offset 0.0 kgmole/h (0.0 lbmole/hr)

    General Reactors button

    General Reactors palette

    In This Cell... Enter...

    Connections

    Name Reformer

    Inlet Reform Feed

    Vapour Outlet Reform Prod

    Liquid Outlet Reform Liq

    Energy Reform Q

    Parameters

    DeltaP 70 kPa (10 psi)

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    1. On the Parameters page, select the Heating radio button for the Duty.

    2. On the Worksheet tab, set the temperature of Reform Prod to 760C (1400F).

    3. On the Reactions tab, select the Reformer Rxn Set as the Reaction Set. This will automatically connect the proper reactions to this Reactor and the Reactor will solve.

    Add a Cooler

    Add a Cooler to cool the stream Reform Prod down to the Shift Reactors temperature. Enter the connections with the following information:

    What is the % conversion of Methane? __________

    How much CO and H2 were produced in the reaction; i.e. what is the molar flowrate of these two compounds in the reactors product stream? __________ & __________

    In This Cell... Enter...

    Connections

    Name HX2

    Inlet Reform Prod

    Energy HX2-Q

    Outlet Shift Feed

    Parameters

    Delta P 24 kPa (3.5 psi)

    Worksheet

    Shift Feed 427C (800F)

  • Reactions 15

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    Add the Shift Reactor

    Another Equilibrium Reactor will be used to model the Shift Reactor.

    Add an Equilibrium Reactor with the following data:

    1. On the Parameters page, choose the Cooling radio button for the Duty.

    2. On the Reactions tab, select Shift Rxn Set as the Reaction Set. This will automatically connect the proper reactions to this reactor.

    In This Cell... Enter...

    Connections

    Name Shift

    Inlet Shift Feed

    Vapour Outlet Shift Prod

    Liquid Outlet Shift Liq

    Energy Shift Q

    Parameters

    Delta P 70 kPa (10 psi)

    Worksheet

    Shift Prod, Temperature 430C (800F)

    What is the % conversion of CO in this reactor? __________

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    Add a Cooler

    Add a Cooler to cool the stream Shift Prod down to the Amine Plants temperature (the Amine Plant will be added next). Make the connections as follows:

    In This Cell... Enter...

    Connections

    Name HX3

    Inlet Shift Prod

    Energy HX3-Q

    Outlet Amine Feed

    Parameters

    Delta P 35 kPa (5 psi)

    Worksheet

    Amine Feed, Temperature 38C (100F)

  • Reactions 17

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    Add the Amine Plant

    Add a Component Splitter to model the Amine Plant. The purpose of this Splitter is only to remove the CO2 present in the flow. The connections are shown below:

    On the Splits page, specify the Fraction to Overhead as 1.0 for Methane, CO, Hydrogen and H2O. The "Fraction to Overhead" for the CO2 must be 0; this will force all CO2 to the bottom and all other components to the top.

    In This Cell... Enter...

    Connections

    Name Amine Plant

    Inlet Amine Feed

    Overhead Outlet Sweet Gas

    Energy Stream AmPl Q

    Bottoms Outlet CO2 Off

    Parameters

    Overhead Pressure 297 kPa (43 psia)

    Bottoms Pressure 297 kPa (43 psia)

    Worksheet

    Sweet Gas, Temperature 138C (280F)

  • 18 Reac