50772070 process modeling using hysys with chemical industry focus

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Getting Started

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

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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

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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.

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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 <Ctrl><B> 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

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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 <Enter> key when you are finished.

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

New Case button

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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 <Enter> 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:


add it to your simulation

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

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:


add it to your simulation

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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 αij matrices by selecting the corresponding radio button. The Aij matrix is shown below:

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

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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.

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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.

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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.

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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 <F11> 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 <F4> to open the Object Palette. Double click on the stream icon.

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Adding a Stream from the Menu BarThis procedure describes how to add a stream using the <F11> hot key.

1. Press the <F11> 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.

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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.

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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 <empty> values, either enter 0 or press the Normalize button.

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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

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Adding a Stream from the Object Palette

1. If the Object Palette is not open on the Desktop, press the <F4> 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!

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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.

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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 <Ctrl><U> 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.

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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 <Ctrl><U> 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.

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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.

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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 90°C (195°F) 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) 15°C (60°F)

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

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

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

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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

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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.

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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.

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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!

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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 15°C (60 °F). __________

3. The dew point pressure of stream Strip Air at 25°C (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 15°C (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, 25°C, 77 °F):

What is the composition of the vapor space? _________

How full is the storage vessel? __________

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Thermodynamics and HYSYS 1

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Thermodynamics and HYSYS


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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 Hyprotech’s 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.


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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


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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 <10mm Hg, Braun K10, Esso K

Ethylene Towers Lee Kesler Plocker

High H2 Systems PR, ZJ or GS (see T/P limits)

Reservoir Systems PR, PR Options

Steam Systems Steam Package, CS or GS

Hydrate Inhibition PR

Chemical Systems Activity Models, PRSV

HF Alkylation PRSV, NRTL (Contact Hyprotech)

TEG Dehydration with Aromatics

PR (Contact Hyprotech)


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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


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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 (Raoult’s 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.


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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


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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 Raoult’s 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.


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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 Wilson’s 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.


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• 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:


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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.

Henry’s Law

Henry’s Law cannot be selected explicitly as a property method in HYSYS. However, HYSYS will use Henry’s 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 Henry’s 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.

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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 Hyprotech’s 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 40°C

Pressure 1 atm


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.


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? __________


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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 25°C 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 25°C

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.


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? __________


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

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

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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.


• 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 <F12> 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 <F4> 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, drag’n’drop 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 <F12> hot key.

1. Press the <F12> 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 <F12> 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 <F4> 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 Drag’n’drop technique.

To Drag’n’Drop 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.

<Ctrl> key Press and hold the <Ctrl> 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 <Ctrl> 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 (-5°F) 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. Don’t 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.

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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? __________

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the corresponding menus.

Object... Object Inspection Menu...

PFD

Unit Operations

Streams

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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.

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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!

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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.

Flowsheeting 25

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.

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Reactions 1

1

Reactions


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.


• 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

6


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

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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

8

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 (800°F), 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

595°C (1100°F) 0.5

650°C (1200°F) 3

705°C (1300°F) 14

760°C (1400°F) 63

815°C (1500°F) 243

870°C (1600°F) 817

Temperature, °C (°F) Keq

675°C (1250°F) 1.7

705°C (1300°F) 1.5

730°C (1350°F) 1.3

760°C (1400°F 1.2

790°C (1450°F) 1.1

815°C (1500°F) 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 reaction’s 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 <empty> 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

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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 20°C (70°F)


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

Composition

Mass Fraction CH4 1.0

Name Steam



Composition

Mass Fraction H2O 1.0


Connections

Name Mix-100

Inlets Natural Gas / Steam

Outlet Mixed Feed

12 Reactions

12

Add a Heater

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

Add a Heater with the following information:


Connections

Name HX1

Inlet Mixed Feed

Energy HX1-Q

Outlet Reform Feed

Parameters

Delta P 10 kPa (1.5 psi)

Worksheet

Reform Feed, Temperature 760°C (1400°F)

Reactions 13

13

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:


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


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 760°C (1400°F).

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 Reactor’s 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 reactor’s product stream? __________ & __________


Connections

Name HX2

Inlet Reform Prod

Energy HX2-Q

Outlet Shift Feed

Parameters

Delta P 24 kPa (3.5 psi)

Worksheet

Shift Feed 427°C (800°F)

Reactions 15

15

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.


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 430°C (800°F)

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

16 Reactions

16

Add a Cooler

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


Connections

Name HX3

Inlet Shift Prod

Energy HX3-Q

Outlet Amine Feed

Parameters


Worksheet

Amine Feed, Temperature 38°C (100°F)

Reactions 17

17

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.


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 138°C (280°F)

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18

Add a Heater

A Heater is needed to heat the feed to the Methanator Reactor temperature.

Add a Heater with the following information:


Connections

Name HX4

Inlet Sweet Gas

Energy HX4-Q

Outlet Methanator Feed

Parameters


Worksheet

Methanator Feed, Temperature 260°C (500°F)

Reactions 19

19

Add the Methanator Reactor

Add a Conversion Reactor with the following connections:

On the Reactions tab, choose the Methanator Rxn Set from the Reaction Set drop down menu.


Connections

Name Methanator

Inlet Methanator Feed

Vapour Outlet Product

Liquid Outlet Meth Liq

Energy Meth Q

Parameters


Worksheet

Product, Temperature 280°C (536°F)

What is the % conversion of CO? __________

How much Methane was produced in this reactor? __________

Save your case!

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20

Analysing the Results

Using the Case StudyThe Case Study tool allows you to monitor the steady state response of key process variables to changes in your process. You select independent variables to change and dependent variables to monitor. HYSYS varies the independent variables one at a time, and with each change, the dependent variables are calculated.

To illustrate the Case Study tool’s capabilities, imagine the following scenario: your boss approaches you one day and asks you to comment on the affects of varying the amount of Steam to the process on the flow of CO2 entering the Amine Plant and the flow of methane leaving the Methanator Reaction. He or she wants to compare steam flow rates of 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0 times that of the natural gas. The bad news is he or she wants the information first thing tomorrow morning (and you have a tee time in one hour). The good news is, you can use the Case Study tool in HYSYS to generate these numbers and still make your tee time!

1. From the Tools menu select Databook, or use the <Ctrl><D> Hot Key to open the Databook.

2. On the Variables tab, press the Insert button to open the Variable Navigator.

3. Select Shift Prod as the object, Comp Molar Flow as the variable, and CO2 as the variable’s specific.

Both the independent and the dependent variables are added to the Databook from the Variables tab.

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4. Add the two remaining variables as shown below: Product and SET-1.

5. Switch to the Case Studies tab.

6. Press the Add button to add a new Case Study.

7. Select the Multiplier of SET-1 as the Independent Variable, and select the remaining two variables as the Dependant Variables.

8. Press the View button to setup the Case Study.

Only user supplied variables can be selected as Independent Variables

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9. Enter values for Low Bound, High Bound, and Step Size of 1.5, 4.0 and 0.25 respectively.

10. Press the Start button to begin the case study analysis.

11. Press the Results button to view the calculations.

Reactions 23

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Exercise

Using the Adjust OperationIn this exercise, we will use the Adjust operation in HYSYS to determine what temperature in the Shift 1 reactor will produce a molar ratio of hydrogen to methane of 10:1 in the final product.

The Adjust operation in HYSYS is similar to a "steady state controller." It will manipulate one process variable (this variable must be specifiable) until another variable is equal to a set target value. In this case, we will manipulate the temperature of the outlet stream from the Shift 1 reactor until the desired molar ratio is achieved in the final product.

Normally, the target variable can be selected using the variable navigator; however, this is not the case here. The molar ratio of methane to hydrogen is not a normal process variable; therefore, we must use the Spreadsheet operation to calculate this value and transfer its value to another location that can be selected using the variable navigator.

The process for doing this will be given here:

1. Add a Spreadsheet operation to the flowsheet. We need to import two variable into this spreadsheet. There are several ways to do this; for this exercise, only one method will be illustrated, but keep in mind that this is only one possibility.

2. Right click on any spreadsheet cell (an example would be B1). From the menu that appears, select Import Variable, and use the variable navigator to choose the Mole Fraction of Hydrogen in the Product stream.

3. In another spreadsheet cell (say B2) import the Mole Fraction of Methane of the same stream.

4. In a third spreadsheet cell, enter the ratio formula. If you used cells B1 and B2 in the two steps above, the ratio formula will look like this: +B1/B2. The current value of this ratio should be around 7. (Note: return the multiplier value for SET-1 to the original value 2.5 before continuing here.)

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5. Now, we add the Adjust operation. Add the Adjust operation to the flowsheet. Make the following connections:

6. On the Parameters tab, enter the following information:

7. Press the Start button to begin the calculations. The progress of the calculations can be seen on the Monitor tab.


Adjust Variable Shift Prod - Temperature

Target Variable Sprdsht-1 -B3 (where "b3" is the cell that contains the formula result)

Specified Target Value 10


Method Secant (default)

Tolerance 0.01

Step Size 25

Maximum Iterations 30

What is the reactor temperature that produces the desired molar ratio? ________________

Save your case!

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ChallengeA new application of the Product stream has been found. However, it requires that the amount of methane in the stream be less than 1% of the amount of hydrogen. In other words, the molar ratio must be increased to 100.

What happens when the Specified Target Value is changed to 100? __________

What else can be changed to improve the composition of the Product stream? Hint: look at the beginning of this process; remember that the products of a process are influenced by the inputs. __________

Change the multiplier of the Set-1 operation to 5. Is the Adjust operation now able to converge with a target value of 100? __________

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Column Operations 1

1

Column Operations


2 Column Operations

2

WorkshopIn this module, you will simulate an Ethanol Plant. You will get more practice with the Column unit operation of HYSYS by:

• modeling columns with side draws • adding a column with real trays.

Typically an ethanol fermentation process produces mainly ethanol plus several by-products in small quantities: methanol, 1-propanol, 2-propanol, 1-butanol, 3-methyl-1-butanol, 2-pentanol, acetic acid, and CO2.

The CO2 produced in the fermentation vessel carries some ethanol. This CO2 stream is washed with water in a vessel (CO2 Wash) to recover the ethanol, which is recycled to the fermenter.

The ethanol rich product stream from the fermenter is sent to a concentration (Conc) tower. An absorber with a side vapour draw can be used to represent this tower. This vapour draw is taken from Stage 2 so as to have an azeotropic ethanol product with less methanol contamination. The top vapour is fed to a light purification tower (Lights) where most of the remaining CO2 and some methanol is vented.

The feed to the Rectifier (Rect) is the bottoms product of the Lights purification tower and the vapour draw from the concentration tower. The Rectifier is operated as a conventional distillation tower.

Methanol concentrates towards the top stages, so a small distillate draw is provided at the condenser. Also, a small vent for CO2 is provided at the condenser.

Another interesting point is the concentration of heavy alcohols in the interior of the Rectifier. These alcohols are normally referred to as Fusel oils. Fusel oils are a mixture of propanols, butanols and pentanols, with a potential value superior to that of ethanol. Accumulation of fusel oils in the Rectification Tower can cause the formation of a second liquid phase and subsequent deterioration of performance for these trays, so small side liquid draws of fusel oils are installed on the rectifier to avoid this problem.

Column Operations 3

3


• Model a distillation column with side draws• Add specifications to a column• Add efficiencies to a column

PrerequisitesBefore beginning this section, you need to be able to:

• Add streams, operations and columns.

Process Overview

Column Operations 5

5

Column OverviewsCO2 Wash

Concentrator

Lights

6 Column Operations

6

Rectifier

Column Operations 7

7


Defining the Simulation BasisAny activity model (except Wilson, which cannot predict two liquid phases) can be used to solve this problem.

1. Start a new case and select NRTL as the Property Package.

2. Use the following components: Ethanol, H2O, CO2, Methanol, Acetic Acid, 1-Propanol, 2-Propanol, 1-Butanol, 3-M-1-C4ol, 2-Pentanol and Glycerol.

3. On the Binary Coeffs tab of the Fluid Package use UNIFAC VLE and press the Unknowns Only button to estimate the missing interaction parameters.

Adding Streams and Unit Operations

Input the material streams required for the flowsheet:


Conditions

Stream Name Wash H2O



Mass Flow 2340 kg/h (5165 lb/hr)

Composition - Mass Fraction

H2O 100%

8 Column Operations

8

Conditions

Stream Name FromFerm



Mass Flow 46 720 kg/h (1.03e+05 lb/hr)


Ethanol 0.0637

H2O 0.8759

CO2 0.0601

Methanol 4.433e-5

Acetic Acid 1.026e-5

1-Propanol 2.802e-5

2-Propanol 2.808e-5

1-Butanol 2.505e-5

3-M-1-C4ol 9.727e-5

2-Pentanol 2.457e-5

Glycerol 3.141e-5

Conditions

Stream Name Steam A



Mass Flow 11 000 kg/h (24,250 lb/hr)


H2O 100%

Column Operations 9

9

CO2 Vent Separator

The CO2 Vent Separator separates products from the Fermentor. The liquid bottoms of the separator are sent to the distillation section of the plant (Concentrator Tower), while the overhead vapour goes to the CO2Wash Tower.

Install a Separator and make the connections shown here:


Conditions

Name CO2 Vent

Inlets FromFerm

Vapour Outlet To CO2 Wash

Liquid Outlet Beer

10 Column Operations

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The Column Operation

Column SubFlowsheet

A SubFlowsheet contains equipment and streams and exchanges information with the Parent Flowsheet through the connected streams. From the Main Environment, the Column appears as a single, multi-feed multi-product operation. In many cases, you can treat the column in exactly that manner.

You can enter the Column SubFlowsheet by pressing the Column Environment button on the Column Property View. Once inside the Column Environment you can return to the Parent Environment by pressing either the Parent Environment button on the Column Runner view or the Parent Simulation Environment button in the Button Bar.

The Column SubFlowsheet provides a number of advantages:

Independent Fluid Package

HYSYS allows you to specify a unique Fluid Package for the Column SubFlowsheet, as the Fluid Package in the Main Flowsheet may not necessarily be the best one in which to run the Column. That is the case if a Column does not use all the components of the Main Flowsheet, or if different Interaction Parameters are best suited to the Column conditions.

Isolation of Column Solver

When you are in the Column runner, the main simulation can be “checked” by unchecking the Update Outlets box. All aspects of the Main Environment downstream of the Column will be paused until you are satisfied with the behaviour of the Column. To update the rest of the Flowsheet, check the box again. This allows you to make changes and focus on the Column without re-calculating the entire Flowsheet. Once you have made the necessary changes, simply run the Column again to produce a new converged solution. In the Column runner, you are free to view profiles, stage summaries, and other data, as well as make changes to Column Specifications, parameters, equipment, efficiencies, reactions, and so on.

Parent Simulation Environment button

Column Operations 11

11

Use of Simultaneous Solution Algorithm

The Column SubFlowsheet does not use the standard non-sequential solver, but a simultaneous one whereby all operations within the SubFlowsheet are solved simultaneously. The simultaneous solver permits in particular the user to install multiple unit operations within the SubFlowsheet without the need for Recycle blocks.

Once a Column is converged, if changes are made to the parent Flowsheet, the Column will automatically be up-dated and re-run.

Column Types

HYSYS has several basic Column Templates (pre-constructed column configurations) which may be used for installing a new Column, allowing HYSYS to model several different separation processes.

This module will introduce the Absorber. Subsequent modules will present different columns so that, by the end of this course, most types of columns will have been used.

Initial Estimates

In order to calculate, the Column solver in HYSYS requires user-supplied estimates ranging from condition parameters to feed and draw locations. These data can be supplied in several ways. The first interface when you select a Column requires values for the Number of Trays, Reflux, Pressure, and so on. In the Column Solver, on the Work Sheet tab, Conditions page, data can also be supplied. On the Design tab, Specs page, HYSYS allows you to choose from a library of specifications gathered in the Column Specification Types window, activated when you press the Add button. Specification Types can be supplied as Estimates or as Active specifications. Only Active specifications fill the Degree of Freedom of the Column which must be zero for the solver to calculate. Inactive specifications (Estimates) are used only as initial estimates for the convergence algorithm and never use a degree of freedom. Alternatively, Estimates can be supplied on the Estimates page under the Parameters tab. However, they will not appear on the Monitor, and hence cannot be set as Active specifications.

If the user does not have initial estimates HYSYS generates them. However for chemical systems, it is recommended to use the HYSYS Estimate Generator tool. In the Column Environment, on the Parameters tab, Solver page, there is the Initial Estimate Generator


12

Parameters box. By checking the box, the IEG will perform iterative flash calculations to provide the initial estimates for the temperature and composition profiles. No user estimates are required when the Iterative IEG check box is activated.

CO2 Wash Tower

The CO2 Rejection Tower is a simple Absorber. Water is used to strip any ethanol entrained in the off gas mixture, this produces an overhead of virtually pure CO2. The bottoms product from the tower is recycled to the Fermentor (however the recycle is not a concern in this example).

The Input Expert will guide you through the installation of the column.

1. Add an Absorber with the information shown here on the first Connections page. Absorber button


13

2. On the Pressure Profile page, enter the following values. If using field units, the values for the Top and Bottom stage pressures will be 14 and 15 psia, respectively.

3. Press the Done button to complete the column installation.

4. Press the Run button on the column property view to converge the column.

Save your case!


14

Concentrator

This tower removes most of the Methanol from the Fermentor products.

The Concentrator is an Absorber with a side vapour draw.

By default, whenever a side draw stream is added to a column, HYSYS automatically creates a Draw Rate specification for that stream. This eliminates the additional DOF that adding the side draw stream would normally produce.

However, in this case, we do not need a Draw Rate specification for this stream; therefore, we need to replace the Draw Rate specification that HYSYS added automatically with one that we will define to meet our simulation needs.


Connections

Column Name Conc

No. of Stages 17

Feed Beer (Top Stage)

Steam A (Bottom Stage)

Ovhd Vapour To Light

Bottoms Liquid Stillage A

Vapour Side Draw Rect Feed, Stage 6

Pressure

Top Stage Pressure 100 kPa (14.5 psia)

Bottom Stage Pressure 102 kPa (15 psia)

Temperatures

Stage 1 Temp Estimate 90°C (195°F)

Stage 17 Temp Estimate 110°C (230°F)


15

1. Go to the Specs page on the Design tab of the column property view.

2. Press the Add button in the Column Specifications group to create a new specification.

3. Select the specification you want from the list that appears.In this case, we want to add a Column Component Recovery specification.

4. Press the Add Spec(s) button.


16

5. Complete the specification’s property view as shown below.

This specification will set the ratio of ethanol recovered in the specified stream compared to the amount of ethanol fed to the column. Here, we have set this ratio at 0.95, meaning that 95% of the ethanol supplied to the column is recovered in the Rect Feed stream.

We are not concerned about where the other 5% goes, although it must exit the column in one of the other product streams.

6. With the column’s DOF (degrees of freedom) at 0, and we need to set which specifications should be active and which HYSYS can use as estimates only. On the Monitor page of the Design tab, ensure that the Ethanol Recovery specification is active and that all others are inactive.

7. We can now start the column runner and allow HYSYS to find a solution for this column. Press the Run button now to begin the column solver.

8. Save your case.

Save your case!


17

Lights

The Lights Tower is a purification tower.

Add the Refluxed Absorber column and enter the following data.

Refluxed Absorber buttonIn this cell... Enter...

Connections (Input Expert Page 1)

Column Name Lights

No. of Stages 5

Bottom Stage Inlet To Light

Condenser Type Partial

Bottoms Liquid To Rect

Condenser Energy CondDuty

Overhead Outlets Light Vent, 2nd EtOH

Pressure (Input Expert Page 2)


Condenser Pressure 97 kPa (14 psia)

Bottom Stage Pressure 100 kPa (14.5 psia)

Temperatures (Input Expert Page 3)

Not Required

Specifications (Input Expert Page 4)

Vapour Flow 1.6 kgmole/h (3.5 lbmole/hr)

Reflux Ratio 5


18

The Lights column requires 1 more specification; currently the DOF = 0, but we do not want to use these specifications to converge the column. The Reflux Ratio of 5 is only an estimate, and we will need to add another specifications that HYSYS will use to solve the column.

Add a Column Component Fraction specification with the following information:

The Active specifications for this column should be changed to:

• Vap Prod Rate• Ethanol Purity

So, deactivate the Reflux Ratio specification and activate the Ethanol Purity specification.

Press the Run button to converge the column.

In this Cell... Enter...

Name Ethanol Purity

Stage Condenser

Flow Basis Mass Fraction

Phase Liquid (default)

Spec Value 0.88

Component Ethanol


19

Rectifier

The primary product from a plant such as this would be the azeotropic mixture of ethanol and water. The Rectifier serves to concentrate the water/ethanol mixture to near azeotropic composition. The Rectifier is operated as a conventional distillation tower. It contains a partial condenser as well as a reboiler.

Add a Distillation Column and enter the data shown here.Distillation column button


Connections

Column Name Rect

No. of Stages 59

Inlet Streams ToRect, Stage 38

RectFeed, Stage 44


Overhead Vapour RectVap

Overhead Liquid RectDist

Bottoms Liquid Stillage B

Condenser Energy RectCond Q

Reboiler Energy Rect Reb Q

Optional Side Draws

Stream 1st Prod, Type L, Stage 2

Fusel, Type L, Stage 37

Pressures

Condenser 100 kPa (14.5 psia)

Reboiler 105 kPa (15 psia)

Specifications

Reflux Ratio 7100

Ovhd Vap Rate 4.3 kg/h (9.5 lb/hr)

Distillate Rate 2.0 kg/h (4.4 lb/hr)


20

Adding Additional Specifications

This column will require 5 active specifications in order to solve. We need to add at least two more; however, we will add three, with the third one acting only as an estimate.

We will add two Column Draw Rate specifications and one Component Fraction specification.

1. Remember that when we added the two side draw streams to the column, HYSYS automatically created Draw Rate specifications for those streams. On the Monitor page, enter the following values for these two Draw Rate specifications.

2. Add one Column Component Fraction specification with the following information:

3. Make following specifications active and all others inactive:

• Reflux Ratio• Ovhd Vap Rate• Distillate Rate• Fusel Rate• Product Purity

Specification 1 Specification 2

Name 1st Prod Rate Fusel Rate

Spec Value 3000 kg/h

(6500 lb/hr)

2 kg/h (5 lb/hr)


Name Product Purity

Target Type Stream (radio button)

Draw 1st Prod

Basis Mass Fraction

Spec Value 0.95

Component Ethanol


21

4. On the Efficiencies page of the Parameters tab, add Stage Efficiencies of 0.55 for all the stages except feed and product stages (2, 37, 38, 44, and 59), where it must remain at 1. You can save time during this step by entering the value (0.55) in the Eff. Multi. Spec cell, selecting a number of cells on the right, and pressing the Specify button.

5. On the Solver page of the Parameters tab, set the Damping Factor to Adaptive and ensure that the Azeotropic check box is checked. Due to the azeotropic nature of ethanol and water, we need to have this box checked so that HYSYS is able to handle this situation. Setting the damping factor at adaptive allows HYSYS to adjust this parameter to help ensure that the solver can reach a solution.

6. Press the Run button to converge the column. If the column does not converge quickly, stop the solver and increase the Fusel draw rate spec value to 10 kg/h (20 lb/hr), and try again. Once the column has converge, the Fusel draw rate can be returned to its original level.

Draw Stream Location

Theoretical trays assume that the liquid and vapour products are in thermodynamic equilibrium. In reality, columns can never achieve this perfect mixing and separation. There are two ways of accounting for less than ideal stages in HYSYS. An overall efficiency can be applied when setting up the column or efficiencies can be specified for specific trays in the column.

Applying an overall efficiency is the most straightforward, and in most situations, the recommended approach for modelling any tower. Simply taking the actual number of trays and multiplying by the efficiency less than 1.0 generates the theoretical stages. Feed, draws and equipment must be located appropriately.

In HYSYS, efficiencies are defaulted to 1.0. They can be user-modified in the appropriate tab of the Column Property view. Efficiencies are applied to individual stages calculation using Murphree’s formula.1

The side liquid draw, Fusel, is added at stage 37 of Rect. To determine if this is an appropriate stage to recover the heavy alcohols, you can view

What is the mass fraction of Ethanol in the "1st Prod" stream when the column is converged? ____________

1. Murphree, E.V., Ind. Eng. Chem., 17, 747, 1925.

The stage efficiencies for all feed and product stages must remain at 1. The HYSYS column solver is not able to handle non-ideal feed and draw stages at this time.

Due to the fact that HYSYS calculation of non-ideal trays does not take into account side-streams, efficiencies on stages with feeds, draws (reboilers and condensers included) and equipment connected to columns, have to be left at their default value of 1.0.


22

the stage by stage composition profile:

1. Move to the Performance tab in the Column Runner.

2. Go to the Profiles page. Highlight Composition in the Tray by Tray Properties group

3. Press the View Graph button. In this view we can see the compositions on each tray.

We wish to view the 1-Propanol composition on Tray 37. The initial graph will not contain this component. To modify the components in this view, you must press the Properties button. This will open the Properties View:

1. Check the 1-Propanol box in the Components group.

2. Close this view to return to the graph.

Stage 37 has the highest concentration of 1-Propanol (which has the greatest concentration among the heavy alcohols). Therefore, we have selected the appropriate stage for the Fusel draw.

Save your case!


23

Optional ChallengeReplacing the Kettle Reboiler with a Thermosyphon Reboiler

In this portion of the module, we will replace the default kettle type reboiler on the Rectifier column with a "Thermosyphon" type reboiler.

Thermosyphon reboilers are commonly used in this type of application, and it is often desired to use HYSYS to simulate the operation of the column with this type of reboiler as it will provide a more accurate simulation of the actual physical set-up of the equipment.

In order to change the kettle reboiler to a thermosyphon, we will have to add one additional stage to the column. This additional stage functions as a liquid sump that allows liquid to be drawn from the column and liquid to be fed to the column from the reboiler. With thermosyphon reboilers, both liquid and vapour are returned to the column rather than just the vapour that is returned to the column with standard kettle reboilers.

Following the steps below will allow you to replace the standard kettle reboiler with a thermosyphon type reboiler.

1. Change the number of stages in the column to 60. This value can be accessed from the Connections page of the column’s property viewer.

2. Enter the Column Environment by pressing the Column Environment button on the property viewer.

3. Disconnect the "Stillage B" stream from the reboiler and reattach it as a material withdraw stream from stage 60.

4. Disconnect the "Boilup" stream from stage 60 and reattach it to stage 59. You will need to expand the trays shown by the column icon in order to attach the stream to this tray. Right-click on the tray section, and select Show Trays. Use the Radio button to select Full Expansion, or scroll down and check to Show box for stage 59.

5. Attach the reboiler’s liquid product outlet (formerly the location of "Stillage B" stream) to the inlet point on stage 60.


24

6. The reboiler should now be setup as follows:

7. Adding another Side Draw to the column (Stillage B) means that HYSYS has created another Draw Rate specification and the DOF remains at 0.

8. Add a Column Vapour Fraction specification to the column with the following information:

9. Activate this new specification, and deactivate the Draw Rate specification that HYSYS created. The column should resolve automatically; if it does not, press the Run button to allow the column to converge.

Note that adding the additional stage and modifying the reboiler has not changed the operating behaviour of the column. The bottom stage of the column (#60) does not function like a true equilibrium stage (there is no contacting vapour from the bottom). The boil-up provided by the thermosyphon reboiler will be the same as for the kettle reboiler. This is independent of the reboiler type.


Name Reboiler V.F.

Stage Reboiler

Spec Value 0.9

Save your case!

Ethylene Glycol Plant 1

1

Ethylene Glycol Plant


2 Ethylene Glycol Plant

2

WorkshopEthylene glycol has many industrial uses: a feed stock for polyester resins, a hydrate inhibitor in natural gas pipelines, an all-weather antifreeze and coolant, or an industrial solvent. Ethylene oxide and water are fed to a reactor to produce ethylene glycol. The product stream is fed to a distillation column where the excess water and ethylene oxide are stripped off the top and the ethylene glycol is the bottom product.

Learning ObjectivesAfter completing this module, you will be able to:

• Simulate CSTR reactors• Simulate an Ethylene glycol plant• Use the recycle operation in HYSYS• Choose suitable locations for recycles

PrerequisitesBefore beginning this module, you need to be able to:

• Add and define the simulation basis, including components, property packages, and reactions.

• Add streams and operations to a simulation.

Process Overview

Column Overview


5


Defining the Simulation BasisStart a New case and choose the NRTL Activity Model. The components are Ethylene Oxide (C2H4O), Water (H2O) and Ethylene Glycol (C2H6O2).

These components can be hard to find in the long list of available components in HYSYS. Use the Formula filter and type the chemical formulas given above into the Match Cell. This will help you find the desired components quickly and easily.

Go to the Binary Coeffs tab. Select UNIFAC VLE as the Coeff Estimation method to estimate the missing binary coefficients and press Unknowns Only. This will estimate the coefficients for the ethylene oxide / ethylene glycol pair.

Adding the Reactions

On the Rxns tab, add the following reaction to the Fluid Package:

C2H4O + H2O → C2H6O2

1. To define the reaction, press the Simulation Basis Mgr button and select the Reactions tab.

2. Add all of the Fluid Package components by selecting the Add Comps button and pressing the Add this Group of Components button in the window that appears.

3. Press the Add Rxn button, choose Kinetic, and press the Add Reaction button.

In the Stoichiometry and Rate Info group, define the reaction stoichiometry of the reaction previously stated (-1 for reactants, and 1 for product comps).

Fast track to page 11.


6

4. Complete the Basis and Parameters pages as below:

No reverse reaction is defined in this example.

5. Return to the Simulation Basis Manager by closing the Kinetic Reaction window. Return to the Rxns tab of the Fluid Package. Press the Add Set button to add the Global Rxn Set to the Current Reaction Sets group. Close the Fluid Package view.

6. Press the Enter Simulation Environment button.


Basis

Basis Molar Concn

Base Component C2Oxide

Rxn Phase Combined Liquid

Basis Units kgmole/m3

Rate Units kgmole/m3-s

Parameters

Forward Reaction

A 5.0e+06

E 5.0e+04


7

Adding the Feed streams

Add two feed streams with the following information. All compositionsare entered as mole fractions


Conditions

Name EOx Feed


Pressure 120 kPa (17.4 psia)


Composition

C2Oxide 1.0

H2O 0.0

EGlycol 0.0

Conditions

Name Water Feed


Pressure 120 kPa (17.4 psia)


Composition

C2Oxide 0.0

H2O 1.0

EGlycol 0.0

Save your case!


8

Adding the Unit Operations

CSTR Reactor

Add a CSTR operation and enter the following information. Be sure to assign the Global Rxn Set as the Reaction Set for the separator to model the reactor.

1. On the Reactions tab, select the Global Rxn Set and Rxn-1 as the Reaction.

2. Specify the temperature of stream Rx Liquid to be 65°C (150°F).

CSTR button


Connections

Name Reactor

Inlets EOx Feed

Water Feed

Vapour Outlet Rx Vapour

Liquid Outlet Rx Liquid

Energy Rx Coolant

Parameters

Pressure Drop 10 kPa (1.5 psi)

Volume 2 m3 (71 ft3)

From the Reaction results, what is the % Conversion of Ethylene Oxide? __________


9

Ethylene Glycol Tower

The Ethylene Glycol tower will be modelled as a Distillation Column. Add the column with the following information:

Note: HYSYS generates column temperature estimates if none are provided.


Connections

Name T-100

No. of Stages 10

Inlet Rx Liquid, Stage 5


Ovhd Vapour Vent

Ovhd Liquid Distillate

Bottoms Liquid Bottoms Product

Condenser Energy Cond Duty

Reboiler Energy Reboiler Duty

Pressures


Condenser Delta P 0 kPa (0 psi)


Specs

Vapour Rate 0.0 kgmole/h (0.0 lbmole/hr)

Reflux Ratio 3.0

Reboiler Temperature 150°C (300°F)

Save your case!


10

Installing the RecycleA Recycle operation is a mathematical unit operation and is installed as any other. It has an inlet (calculated) stream and an outlet (assumed) stream. The operation is called/calculated whenever changes to the inlet stream fall outside of the converged tolerance.

The Recycle installs a theoretical block in the process stream. The feed into the block is termed the calculated recycle stream, and the product is the assumed recycle stream. The following steps take place during the convergence process

• HYSYS uses the conditions of the assumed stream (outlet) and solves the flowsheet up to the calculated stream (inlet).

• HYSYS then compares the values of the calculated stream to those in the assumed stream.

• Based on the difference between the values, HYSYS modifies the values in the calculated stream and passes the modified values to the assumed stream.

The calculation process repeats until the values in the calculated stream match those in the assumed stream within specified tolerances.

In general, a Recycle operation is required for material transfer and not for thermal recycles.

Always supply a guess or starting point for the outlet stream of the Recycle, never the inlet. A guess close to the solution will result in a faster convergence time.


11

Recycle the Water Stream

The stream Distillate contains mostly unreacted water. This water can be recycled to the reactor in order to reduce the feed water requirements (as well as eliminate a waste stream).

Install a Recycle block operation. The inlet stream is the Distillate and the outlet stream should be mixed with the pure Water Feed stream, before entering the Reactor.

Delete the specified molar flow rate of the Water Feed stream. This value will be back-calculated from the outlet of the mixer.

Specify the molar flow of the mixer outlet stream, Water to Reactor, as 150 kgmole/h (330 lbmole/hr). Once the flow rate in this stream is set, HYSYS will automatically calculate the flowrate of the Water Feed stream. If we had not deleted the specified value, HYSYS would report a consistency error, because a the two values would be in conflict with each other.

What value does HYSYS calculate for the flowrate of the stream "Water Feed"? __________

Open the case OptRecy.hsc


12

Parameters tab

Tolerance page

HYSYS allows you to set the convergence criteria or tolerance for each of the Recycle variables. In this example, leave everything at the default.

Numerical Page

This page contains the options for the two types of Recycles, Nested and Simultaneous.

• Nested - this type of recycle gets called whenever it is encountered during calculations. Use this type if you have a single Recycle or if you have multiple recycles which are not connected.

• Simultaneous - all recycles set at Simultaneous will be called at the same time. Use this option if your Flowsheet has multiple inter-connected recycles.

Change the Maximum Iterations number to 20.

The smaller the tolerance value, the tighter the tolerance. Generally it is a good idea to start with the default tolerance until you have a converged solution and then tighten the tolerance.


13

Monitor tab

This page displays convergence information as the calculations are performed. Any variable that changes between iterations is displayed in this table.

Worksheet tab

The Recycle WorkSheet page displays the Inlet and Outlet stream information. In this instance, notice that the Inlet and Outlet streams have the same values. This is because before we installed the Recycle, the Inlet stream was already calculated by HYSYS. When the Recycle was connected, the known Inlet conditions were automatically passed to the Outlet stream to serve as the starting guess.


14

Exploring with the Simulation

Exercise 1Create a Case Study to plot the Ethylene Glycol molar flow in the liquid product against the Reactor Outlet Temperature. The temperature range can be between 45 and 110 °C (100 and 240 °F), with a step of 10 °C (20 °F). Be sure to "Ignore" the Recycle operation before starting the Case Study.

Remember to save the file under a different name if you wish to save it!

Exercise 2Set up an Adjust operation to make sure the molar flow of Ethylene Glycol in the Rx Liquid stream is equal to 110 kgmole/h (240 lbmole/hr), by adjusting the EOx Feed molar flow with a step size of 1 kgmole/h (2 lbmole/hr).

What temperature produces the maximum Ethylene Glycol flow? __________

What problems will be encountered if the temperature exceeds approximately 115 oC? __________

What EtOx feed rate is required to produce the specified molar flow of Ethylene Glycol? __________


15

Advanced ModellingBecause the Recycle operation is a mathematical representation of a physical process, its location in a simulation is a particularly important one. The location of the tear stream can often determine success or failure to converge a recycle

Choose a Tear Location to Minimize the Number of Recycles

Reducing the number of locations where the iterative process is required will save on the total convergence time. Choosing the location of the Recycle will depend on the Flowsheet topology. Attempt to choose a point such that specifying the assumed stream will define as many streams downstream as possible. It generally occurs downstream of gathering points (mixers) and upstream of distribution points (tees, separators, and columns).

Choose a Tear Location to Minimize the Number of Recycle Variables

Variables include vapour fraction, temperature, pressure, flow, enthalpy and composition. Choose the tear stream so that as many variables as possible are fixed, thus effectively eliminating them as variables and increasing convergence stability. Good choices for these locations are at separator inlets, compressor after cooler outlets and trim heater outlets.

Choose a Stable Tear Location

The tear locations can be chosen such that fluctuations in the recycle stream have a minimal effect. For example, by placing the tear in a main stream, instead of the physical recycle, the effect of fluctuations will be reduced. The importance of this factor depends on the convergence algorithm. It is more significant when successive substitution is used.

A very poor choice of a tear stream is a stream with an Adjust operation controlling one of its variables.


16

Recycle Exercises

Choosing the Right LocationWhen installing Recycle operations in a HYSYS simulation, it is vital that right location for the operation be chosen. Several guidelines were given on a previous page, and several different problems will be given here. Note that some of these flowsheet may require more than one Recycle operation.

Flowsheet 1

Where should the Recycle be placed in this flowsheet and why? Assume that you know the following information:

• Temperature and Vapour Fraction of "Cond Out".• Pressure drop and Duty of "Chiller" operation.• Pressure of "Chiller Out" stream.• Pressure drop of "Condenser" Operation.• The Mixer is set to "equalize all."


17

Flowsheet 2

Where should the Recycle be placed in this flowsheet and why?

Assume that the Feed is fully defined, Shell and Tube Side pressure drops are known, as well as the Column Feed temperature.

Flowsheet 3


Assume the Feed is completely defined, shell and tube side pressure drops for E-100 and E-101, and the temperatures of streams 3 and 4 are known.


18

Flowsheet 4


Assume the Feed is completely defined, and the shell and tube side pressure drop for E-100 is known.

Aromatic Stripper 1

1

Aromatic Stripper


2 Aromatic Stripper

2

WorkshopThis example demonstrates a typical application of the recycle operation. An aromatic stripper to remove Benzene and Toluene from water is simulated with the help of a reboiled absorber. The column has two feeds: the main column feed and a reflux, which is the recycled overhead vapour after being cooled and going through a three phase separator.

This example will also illustrate the flexibility of HYSYS that allows the user to use a different Fluid Package in the column subflowsheet from the one in the main flowsheet. This allows the user to use a property package tailored towards a certain behaviour in the Main Flowsheet and another package tailored towards a different behaviour in the Column environment.

Here, the feed stream is mostly water that is laced with a small amount of benzene and toluene. The objective of this process is to produce two product streams, one of virtually pure water, and the second, a concentrated stream of aromatics.


• Use different sets of Binary Coefficients.• Use different Fluid Packages within the same simulation.• Model Three-Phase separators.

Process Overview

Column Overview

Aromatic Stripper 5

5


Defining the Simulation BasisStart a new case using the NRTL Fluid Package. Add the following components: Water, Benzene and Toluene. Name the Fluid Package Arom Strip.

Two sets of Activity Coefficients will be used. The stripper is controlled by vapour-liquid equilibrium, but the condenser is controlled by liquid-liquid equilibrium. The main flowsheet will therefore be an LLE dominated case, and the column will be attributed a VLE set of parameters.

VLE Case

1. Go to the Binary Coefficients tab. For this case the default values for Aij and Alphaij are used (Bij is empty).

LLE Case

1. Return to the Fluid Pkgs tab of the Basis Manager.

2. Use the Copy button to make a copy of the Arom Strip Fluid Package. Name the new Fluid Package Condenser.

3. Go to the Binary Coefficients tab. Here, we will enter parameters that have been specifically regressed for these components.

4. Enter the values given on the next page.

6 Aromatic Stripper

6

The Activity Coefficients for Aij, Bij, and Alphaij are shown below:

Aij Interaction

Bij Interaction

Alphaij Interaction

H2O Benzene Toluene

H2O 11090.13 4788.593

Benzene -1973.516 -14.555

Toluene -1973.516 3.389

H2O Benzene Toluene

H2O -37.12 -7.364

Benzene 50.206 0.00

Toluene 21.172 0.00

H2O Benzene Toluene

H2O 0.038 0.200

Benzene 0.038 0.303

Toluene 0.200 0.303

Aromatic Stripper 7

7

5. Return to the Basis Manager, Fluid Packages tab. In the Flowsheet - Fluid Pkg Associations group, change the Case (Main) Flowsheet to Condenser.

6. Press the Enter Simulation Environment button.

8 Aromatic Stripper

8

Starting the Simulation

Add the following streams with the following information:


Conditions

Stream Name Feed



Mass Flow 10 000 kg/h (22,050 lb/hr)


H2O 0.9982

Benzene 0.0013

Toluene 0.0005

Stream Name Reflux




Composition - Mole Fraction

H2O 1.0

Benzene 0

Toluene 0

The information supplied here is only an initial estimate. Eventually, this stream will be part of the recycle loop.

Aromatic Stripper 9

9

Add A Mixer

Install a Mixer with the following values:

Add a Reboiled Absorber

Add a Reboiled Absorber with the following information:

1. Go to the Specs page and specify a Component Mass Fraction of 0.00001 for Benzene and Toluene for the second stage. On the Monitor page, make the new specification Active.

2. On the Parameters - Profiles page enter temperature estimates for stages 1 and the Reboiler of 100°C (212°F) and 125°C (260°F)respectively.

3. Close the view and enter the Basis Environment.

In this cell... Enter...

Connections

Name MIX-100

Inlets Feed, Reflux

Outlet Strip Feed

Reboiled Absorber buttonIn this cell... Enter...

Connections

Column Name Stripper

No. of Stages 2

Top Stage Inlet Strip Feed

Ovhd Vapour Outlet Vapour

Reboiler Energy Stream RebQ

Bottoms Liquid Outlet Bottoms

Top Stage Pressure 230 kPa (33 psia)

Reboiler Pressure 240 kPa (35 psia)

10 Aromatic Stripper

10

4. Assign Arom Strip as the Fluid Package to use for the column.

5. Return to the Simulation Environment.

Note: A message will appear warning you about the P-H Flash as a transfer basis. Because we are now using two fluid packages with different interaction coefficients, the program allows you to select the type of flash that will occur between the two fluid packages, i.e., between the column overhead vapour product (using VLE data) and the condenser unit (using LLE data).

Use the default flash, P-H, and press the Return to Simulation Environment button again.

6. Open the Stripper property view and press the Run button. Close the view once it has converged.

Aromatic Stripper 11

11

Simulating the CondenserThe Condenser is represented by a Cooler, the accumulator is modelled as a 3-phase Separator, and a pump is used to pump the liquid back to the required pressure. Finally, a Recycle operation completes the loop, providing the Reflux back to the Column.

Add a Cooler

Add a Three Phase Separator

Add a Three Phase Separator with the following information:


Connections

Name Condenser

Inlet Vapour

Energy Cond Q

Outlet Condensed

Parameters


Worksheet

Vapour Fraction, Condensed 0.0


Connections

Name Separator

Feeds Condensed

Vapour Cond Ovhd

Light Liquid Aromatic Product

Heavy Liquid Heavy Liquid


12

Add a Pump

Add a Recycle

Add a Recycle operation with the following information:


Connections

Name Pump

Inlet Heavy Liquid

Outlet To Recycle

Energy Pump Q

Parameters


Save your case!


Connections

Name RCY-1

Inlet To Recycle

Outlet Reflux

Save your case!

Aromatic Stripper 13

13

Does the simulation solve properly? ______________

Can you see the benefit of defining a different fluid package for the column and main environments? __________

Can you think of any other situations where this feature could be used? ______________


14

The Optimizer 1

1

The Optimizer


2 The Optimizer

2

WorkshopIn this example, a simple distillation column to separate Tetrahydrofuran (THF) from Toluene is simulated. The object of the exercise is to select the product specifications such that profit is maximized. A special tool in HYSYS, the Optimizer, will be used to find the optimum operating conditions.


• Use the Optimizer tool in HYSYS to optimize flowsheets• Use the Spreadsheet to perform calculations

PrerequisitesBefore beginning this section you need to be able to:

• Add Streams and Operations• Model columns in HYSYS

Fast track to page 9.

Process Overview

Column Overview

The Optimizer 5

5


Defining the Simulation BasisFor this case, you will be using the Wilson Activity Model. The components are: Tetrahydrofuran and Toluene.

1. On the Binary Coeffs tab, check that the UNIFAC VLE estimation method is chosen, and press the Unknowns Only button to estimate the missing Interaction Parameters.

2. Enter the Simulation Environment.

Adding the Feed Stream

Add a material stream with the following values:

Binary interaction parameters are used to correlate lab data with a thermodynamic model. When lab data is not available, you can estimate the parameters with HYSYS UNIFAC estimation method.


Conditions

Name Feed





THF 0.44

Toluene 0.56

6 The Optimizer

6

Add the Distillation Column

Add a Distillation Column with the following values:

Make the following specifications:


Connections

Column Name T-100

No. of Stages 10

Feed Feed, Stage 5

Condenser Type Total

Bottoms Liquid Toluene

Ovhd Liquid THF

Condenser Energy Stream Cond Q

Reboiler Energy Stream Reb Q

Pressure

Delta P, Condenser and Reboiler 0 kPa

Condenser 103 kPa (15 psia)

Reboiler 107 kPa (15.5 psia)


Specs

Reflux Ratio 2 (Estimate)

Distillate Rate 1500 kg/h (3305 lb/hr) (Estimate)

The Optimizer 7

7

Create two new Column Component Fraction specifications as shown below:

These two specifications should be Active. The DOF for the column should now be 0.

The column should now solve automatically. If it does not, press the Run button to start the solver.

Save your case!

8 The Optimizer

8

Changing the Column Tolerances

In order for the optimizer to work properly, we have to tighten the tolerances of the column solver. There are two tolerances that the column must meet before it can be considered as solved.

• The Equilibrium Error Tolerance• The Heat/Spec Error Tolerance

We want to set the value for both of these tolerances at 1e-6. Note that this will increase the solving time of the column, but this column solves very fast anyway, so the tighter tolerances are acceptable in this case.

To change the tolerances, follow these steps:

1. Access the Solver page of the Parameters tab.

2. Enter 1e-6 for both the tolerance values. These cells are located in the Solving Options group box.

This completes the changing of the tolerances. We are now ready to begin to optimize the column.

The Optimizer 9

9

Adding the OptimizerIn today’s highly competitive market place, with stringent plant emissions controls and increased competition, a plant’s survivability is often determined by its ability to remain competitive. Optimization methods are now available that give the process engineer the necessary tools to perform on-going process improvement studies. Optimization studies lead directly to improved plant performance, efficient plant operation and finally to increased profitability. Typically, optimization studies involve an ‘economic model’ composed of a Profit Function and operating constraints.

HYSYS contains a multi-variable Steady State Optimizer. Once your Flowsheet has been built and a converged solution has been obtained, you can use the Optimizer to find the operating conditions which minimize or maximize an Objective Function. The Optimizer owns its own Spreadsheet for defining the Objective Functions as well as any constraint expressions to be used. This allows you to construct Objective Functions which maximize profit, minimize utilities or minimize exchanger UA.

• Primary Variables - these are flowsheet variables whose values are manipulated in order to minimize (or maximize) the objective function. You set the upper and lower bounds for the primary variables, which are used to set the search range.

• Objective Function - this is the function which is to be minimized or maximized. The function has to be defined within the Spreadsheet. This allows the user a great deal of flexibility in defining the function.

• Constraint Functions - inequality and equality functions are defined in the Spreadsheet. In solving the Objective Function, the Optimizer must also meet any constraints that are defined by the user.

Open the case OptOptimizer.hsc

Only user-specified process variables can be used as Primary Variables

Restrictions on the Optimizer

• only available for Steady-State calculations

• it cannot be used in Templates.

10 The Optimizer

10

In our column example, the Profit Function/Cost Function (sometimes referred to as the Objective Function, Performance Criterion or Performance Index) requires calculating a net profit for the column. The Profit Function is a function of the revenue generated from desired products THF and Toluene, within the limit of product purity constraints. While increased profits is directly linked to increased production of the desired product, plant profitability is generally offset by operating costs. In our column, operating costs are associated with the column utility requirements for the reboiler and condenser. In general a profit function is given by:

where:

PF = Profit Function/time

= Product Flows * Product Values

= Feedstock Flows * Feedstock Costs

OC = Operating Costs

Profit = (THF Product + Toluene Product) – Heating Cost – Cooling Cost – Feed Cost

Typically, the economic model includes operating constraints (equality or inequality constraints or equations). The operating constraints comprise the model of the process or equipment. In this case, we have no process constraints.

To invoke the Optimizer, select Optimizer under Simulation in the Menu Bar, or press <F5>.

Which variable can we change to affect the Revenue?________

PF F

p∑ pMp FfMf

f∑– OC–=

FpMp∑FfMf∑

The Optimizer 11

11

Variables tab

When you invoke the Optimizer for the first time, you are placed on the Variables tab. On the Variables tab you define the Adjusted (Primary) Variables to be used in the optimization.

In this case, our Primary Variables are the purity of our products, THF and Toluene.

1. Press the Add button to add the first variable, T-100, Spec Value, THF Purity Spec.

2. Set the Upper Bound at 0.9, and the Lower Bound at 0.90.

3. Add the second variable, T-100, Spec Value, Toluene Purity Spec, with the same bounds as above.

12 The Optimizer

12

Defining the SpreadsheetThe Optimizer has its own Spreadsheet for defining the Objective and Constraint functions. Primary Variables may be imported and functions defined within the Optimizer Spreadsheet, which possesses the same capabilities as the Main Flowsheet Spreadsheet

1. Press the Spreadsheet button on the Optimizer view to open the Spreadsheet.

2. Move to the Spreadsheet tab.

Importing and Exporting Variables

You may import virtually any variable in the simulation into the Spreadsheet and you can export a cell’s value to any specific field in your simulation.

• Object Inspection - object inspect (secondary mouse button) the cell which you want to Import into, or Export from. From the Menu that appears, select Import Variable or Export Formula Result. Then, using the Variable Navigator, select the variable you wish to import or export.

• Connections page tab - select the Add Import or Add Export button. Then, using the Variable Navigator, select the variable you wish to import or export.

• Drag ‘n’ Drop - using the secondary mouse button, click the variable value (from the WorkBook or Property View) you wish to import, and drag it to the desired location in the Spreadsheet. If you are exporting the variable, drag it from the Spreadsheet to the exported location.

The Spreadsheet is an operation and thus the Spreadsheet cells get updated when Flowsheet variables change

The Optimizer 13

13

Adding Formulas

Complex mathematical formulas can be created, using syntax that is similar to conventional Spreadsheets. Arithmetic, logarithmic and trigonometric functions can be performed in the Spreadsheet.

All common functions must be preceded by a + symbol. Special Functions must be preceded by the @ symbol.

Some of the functions available are:

• Addition (+): +A1+A2• Subtraction (-): +A1-A2• Multiplication (*): +A1*A2• Division (/): +A1/A2• Power (^): +A1^3• Absolute Value (@ABS):@ABS(A1)• Square Root (@SQRT):@SQRT(A1)• Natural Log (@ln):@ln(A1)• Exponential (@exp):@exp(A1)

The following variables need to be imported into the Spreadsheet. Text entries are added to the spreadsheet by typing them in the appropriate cell.

The quickest way of importing variables is to right-click on the desired cell. Select Import Variable, and use the variable navigator to locate the desired variable.

Use this method to import the variables above now.

Press the Function Help button to view the Available Spreadsheet Functions and Expressions.

Cell... Object... Variable...

B1 Cond Q Heat Flow

B2 Reb Q Heat Flow

B3 THF Mass Flow

B4 THF Comp Mass Frac THF

B5 Toluene Mass Flow

B6 Toluene Comp Mass Frac Toluene

B7 Feed Mass Flow

14 The Optimizer

14

Enter the following constants on the spreadsheet. The comments can be added, if desired.

Enter the following product prices:

Note: the prices of the products decrease as the impurities increase.

The Objective Function is placed in Cell D8. The equation is:

+(b3*d4+b5*d6)-b7*d7-(b1*d1+b2*d2)/3600

Pay special attention to the units in this equation. If using field units, you may have to add an additional term to this equation to convert between hours and days.

Cell Value (SI Units) Value (Field) Comment

D1 0.471 ($/kWh) 138 ($/MMBtu) Cooling Cost

D2 0.737 ($/kWh) 216 ($/MMBtu) Heating Cost

D7 0.05 ($/kg) 0.024 ($/lb) Feed Cost

CellEquation(SI Units)

Equation (Field) Description

D4 +0.333*b4^3 ($/kg) +0.151*b4^3 ($/lb) THF Price (corrected for purity)

D6 +0.163*b6^3 ($/kg) +0.074*b6^3 ($/lb) Toluene Price (corrected for purity)

What is the value of cell D8, the Profit? __________

You can change the Variable Type to Unitless for dollar value variables.

The Optimizer 15

15

Functions tab

The Functions tab contains two groups, the Objective Function and the Constraint Functions. However, in this example we do not have constraint functions.

1. In the Cell area of the Objective Function group, specify the Spreadsheet cell that defines the Objective Function. Use the drop down menu in the Edit Bar to select the appropriate cell. The Current Value of the Objective Function will be provided.

2. Select the Maximize radio button.

16 The Optimizer

16

Parameters tab

The Parameters tab is used for selecting the Optimization Scheme.

• Box - Handles inequality constraints but not equality constraints. It generally requires a large number of iterations to converge on the solution.

• SQP - Sequential Quadratic Programming, handles inequality and equality constraints. Considered by many to be the most efficient method for minimization.

• Mixed - Handles inequality constraints only. It is a combination of the Box and SQP methods. It starts the minimization with the Box method using a very loose convergence tolerance. After convergence, the SQP method is used to locate the final solution.

• Fletcher Reeves - Does not handle constraints. Efficient method for general minimization.

• Quasi-Newton - Does not handle constraints. Similar method to Fletcher Reeves.

1. Select the Mixed method as the Scheme.

2. Use the defaults for Tolerance and Number of Iterations.

Monitor tab

The Monitor tab displays the values of the Objective Function and Primary Variables during the Optimizer calculations.

1. Move to the Monitor tab and press the Start button to begin the optimization.

For more information on the Optimization Schemes, refer to the manual section 17.2 or the on-line Help.

Save your case!

The Optimizer 17

17

Analysing the ResultsOnce the Optimization is complete, examine the results and fill in the following table:

Base Case Optimized Case

THF mass flow 1650.8 kg/h (3639.4 lb/hr)

THF purity 0.95

Toluene mass flow 2049.2 kg/h (4517.7 lb/hr)

Toluene purity 0.95

Cond duty 9.926e5 kJ/h (9.408e5 Btu/hr)

Reb duty 1.5980e6 kJ/h (1.5146e6 Btu/hr)

Profit 106.3 $/hr

18 The Optimizer

18

Exercise 1

We are going to introduce a constraint on the liquid volume flow of the stream THF and examine how it affects the results, profit and products purities.

First, the case must be set back to its state before the optimization.

1. Go to the column subflowsheet.

2. On the Design tab, Monitor page, enter the initial value of 0.95 for the THF and Toluene purity specifications.

3. Re-run the column.

The constraint on the liquid flow is that it must not exceed 1.85 m3/h (65.5 ft3/hr).

The THF Liquid Flow must first be imported into the spreadsheet (use an empty cell), and the constraint value must be written in the spreadsheet. Remember to write the comments next to the values so that they can be understood.

1. On the Functions tab of the Optimizer press the Add button.

2. Type in the reference of the cell where the variable constraint is located.

3. In the Cond column, use the scroll down arrow to find the less than sign. Type in the reference of the cell where the value of the constraint is written.

4. Go to the Monitor tab and start the Optimizer.

The constraint values are positive if inequality constraints are satisfied and negative if inequality constraints are not satisfied.

The Optimizer 19

19

What differences, if any, does the constraint make to the first optimized solution? Fill in the following table:

Base CaseOptimized Case

Optimized Case 2

THF Mass Flow 1650.8 kg/h

THF Purity 0.95

Toluene Mass Flow

2049.2 kg/h

Toluene Purity 0.95

Cond Duty 9.926e5 kJ/h

Reb Duty 1.5980e6 kJ/h

Profit 106.3 $

20 The Optimizer

20

Exercise 2

Here, we are going to model the reboiler with a steam-heated shell and tube heat exchanger. The heat exchanger will be modelled with 115 psia steam and the maximum flow of steam available to the reboiler is limited to 840 kg/h (1850 lb/hr). (Note that there are a few approaches that can be taken with the heat exchanger modelling so two of the possibilities are listed). The cost of the 115 psia steam is 0.682 $/kWh ($200/MMBtu).

1. Add Water as a component. This must be done in the Basis Environment.

2. Open the Column’s Property viewer; on the Monitor page, reset the THF and Toluene purity specifications to 0.95.

3. Add a new internal stream (on the Flowsheet tab), ToReb with the following attributes:

4. Run the column.

5. Return to the Main Environment (notice that the "To Reb" stream is now shown on the PFD. Add a heat exchanger. The stream ToReb is the shell side feed and steam is on the tube side.

6. Set the Shell and Tube side pressure drops to 0.

7. Specify the Steam inlet conditions at Vf = 1.0; P = 790 kPa (115 psia); Flow = 770 kg/h (1700 lb/hr). The outlet steam is at its bubble point (Vf = 0.0).

8. Add a Duty Spec to the Heat Exchanger but do not specify a value (pass is Overall).

Use the Mixed optimization scheme for this exercise.


Type Liquid

Net/Total Total

Stage 10

Export Yes

What is the Heat Exchanger Duty? __________

The Optimizer 21

21

9. Add an Adjust operation. The Adjusted Variable is the Steam flow rate and the Target Variable is the Spec Calc Value (Duty Spec).

10. Export the RebQ Heat Flow value (you will have to make this Exportable first) from the Optimizer spreadsheet into the Target value for the Adjust operation. A cell on the spreadsheet can not be simultaneously imported and exported. Copy the value of cell B2 to another empty cell by entering the formula "+B2". The value in this new cell can then be exported to the Target Value of the Adjust operation.

11. Change the Heating Cost value to 0.682 $/kWh ($200/MMBtu) (Cell D2 on the spreadsheet) and Start the Adjust.

12. Add the Steam Mass Flow (must be less than 840 kg/h (1850 lb/hr)) constraint to the Optimizer.

13. Start the Optimizer.

What is the Exchanger Duty and what is the Steam mass flow rate? __________ & __________

22 The Optimizer

22

Azeo Distillation with LL Extractor 1

1

Azeo Distillation with LL Extractor


2 Azeo Distillation with LL Extractor

2

WorkshopAn azeotropic mixture of Benzene and Cyclo-Hexane is to be separated in a distillation column using Acetone as the entrainer. Nearly pure Benzene is produced from the bottom of the column, while a near azeotropic mixture of Acetone and Cyclo-Hexane is produced overhead. The overhead mixture will be separated in a Liquid-Liquid extractor using water as the solvent, with Cyclo-Hexane being recovered as the overhead product. The Acetone/Water mixture will then be separated in a vacuum tower with the Acetone and Water products being recycled through the flowsheet.

The process will be separated into four sections, the Azeotrope tower, the Liquid-Liquid extractor, the Solvent Recovery tower and finally the recycling system.

The problem could be solved with a single set of interaction parameters. However, the problem may be solved more accurately by using one set of binary coefficients which will predict the liquid phase splitting in the Extractor, and another set which will predict VLE behaviour in the Distillation Columns.


• Import Fluid Packages• Model Azeotropic Distillation Columns• Model Liquid-Liquid Extraction Columns

Process Overview


4

Azeotropic Distillation Column

Solvent Recovery Tower


5


Defining the Simulation BasisTwo Fluid Packages will be used in this example. Both Fluid Packages will use the UNIQUAC Activity Model, and contain the components Benzene, Cyclohexane, Acetone and H2O. The first Fluid Package (VLE-BASIS), will use the default library VLE binary interaction parameters and UNIFAC estimated parameters. The second Fluid Package (LLE-BASIS), will replace those interaction coefficients with UNIFAC LLE estimated binary coefficients and those regressed from HYSYS Conceptual Design Application.

1. Add the first Fluid Package in the usual manner and change the default name to VLE Basis.

2. On the Binary Coeffs tab, view the binary coefficients for the UNIQUAC activity model.

The binary coefficients for the Cyclohexane/Water pair are not available from the database, so it is necessary to obtain them by estimation or from another source.

In this example, the binary coefficients for the Cyclohexane/Water pair in the VLE Basis will be estimated by the UNIFAC VLE estimation method. Press the Unknowns Only button to estimate this pair.

The second Fluid Package (for the Liquid-Liquid Extractor) will be imported.

1. On the Fluid Pkgs tab of the Simulation Basis Manager, press the Import button and import the Fluid Package LLEBasis.fpk. This file should be located on the course disk supplied with this material.

2. Press the View button to see the new Fluid Package. Go to the Binary Coeffs tab to view the binary coefficients.

If you examine the LLE Coefficients for VLE Basis and LLE Basis you will see they are different, because they have been taken from different sources.

VLE Basis will be used for most of the simulation, while LLE Basis will be used as the Fluid Package for the Liquid-Liquid Extractor.

Enter the Simulation Environment.

Ensure that VLE Basis is the Default Fluid Package when you leave the Basis Environment.


6

Adding the Feed Stream1. Enter the following stream Azeo Feed as follows:

2. Enter the stream Acetone as follows:

3. Enter a mass fraction of 1.0 for Acetone.


Conditions

Stream Name Azeo Feed




Composition - Mass Frac

Benzene 0.518

Cyclohexane 0.482


Conditions

Stream Name Acetone





7

Azeotrope TowerPublished documentation on this process indicates that the overhead composition from the Azeotrope Tower is a near azeotropic mixture of Acetone and Cyclohexane. Using less Acetone than is necessary to produce the azeotrope will prevent the original Benzene/Cyclohexane azeotrope from being separated.

The flow of Acetone required to separate this azeotrope and produce a mixture near azeotropic Cyclo-Hexane/Acetone, can be calculated from the azeotrope composition, (0.688 Acetone and 0.312 Cyclo-Hexane mass fractions). These values can be obtained through HYSYS Conceptual Design Application or the HYSYS Extension Binary Plots.

The T-x-y diagrams for the Benzene/Cyclo-hexane and Acetone/Cyclo-hexane binaries are shown here:

The Binary extension is available on our website. www.aeat.software.com


8

Calculation for Required Acetone Flow

Then, for an initial mass flowrate of the Azeo Feed stream of 85 kg/h with the given composition, the amount of Acetone required will be 90.34 kg/h (85*0.482*0.688/0.312). A slightly greater flow will be used (95 kg/h {210 lb/hr}) to ensure separation of the Benzene/Cyclohexane azeotrope.


9

Adding the Azeotropic Distillation Column1. Insert a Distillation Column with the following data:

2. On the Parameters tab, Solver page, check the Azeotropic box and supply a Fixed Damping Factor of 0.5.

3. Run the column.


Connections

Column Name T-100

No. of Stages 28

Condenser Energy Stream Q-Cond

Inlet Streams Azeo Feed, Stage 6

Acetone, Stage 21


Overhead Liquid Azeo Liq

Bottoms Liquid Outlet Benzene

Reboiler Energy Stream Q Reb

Pressures

Delta P 0


Reboiler 101.3 kPa (14.7 psia)

Temp. Estimates

Condenser 55°C (130°F)

Reboiler 80°C (175°F)

Specifications

Benzene Recovery in Reboiler 0.998

Acetone Recovery in Cond 0.998

Reflux Ratio (Estimate) 10.0

Azeo Liq Draw (Estimate) 130 kg/h (285 lb/hr)

Because we expect an azeotrope to be present in this column, we must check the Azeotropic box on the Solver page.


10

The Liquid-Liquid Extractor

Liquid-liquid extraction is used as an alternative to distillation in situations where distillation is either ineffective or very difficult. These situations can be found in all process industries. The extraction of penicillin from fermentation broth and the extraction of aromatics from lube oil fractions are two industrial examples. Extraction based on chemical differences is sometimes preferable to distillation, which is separation based on relative volatilities. Some examples of situations when extraction is preferred are listed below:

• Excessive amounts of heat are required for distillation - relative volatility of the components is near one

• Separation via distillation is limited due to the formation of azeotropes

• The high temperatures of distillation cannot be withstood by the components, even under vacuum conditions

• There are only small amounts of solute in the feed solution• The components to be separated are extremely different in

nature

Extraction involves the separation of a solute from a feed solution by mixing in a solvent in which the solute is preferentially soluble. In addition, the solvent must be insoluble, or have a limited solubility in the feed solution. The extraction operation, on a stage by stage basis, can therefore be discussed in terms of two processes:

• The mixing of a feed solution, a solvent, and any external feeds• The separation of the two immiscible liquid phases which result

from the mixing

HYSYS models the liquid-liquid extraction process using counter-current flow in a column similar to the absorber template.


11

Property Package

The Liquid-Liquid Extractor cannot be used with the following property packages:

• Wilson• Antoine• BraunK10• Esso Tabular• Steam• Amine• Chao-Seader• Grayson-Streed• Sour PR• Sour SRK

Activity Models are recommended for most applications.

Overhead Estimate

You will not be required to provide an estimate for the Overhead Product Flow. The Extractor will generate an estimate from a mole weighted TP-Flash of the combined tower feeds.

Column Sizing Utility

The column sizing utility in HYSYS is designed for columns with vapour and liquid traffic; therefore, it is not applicable to the Extractor unit operation.

Stage Efficiencies

The HYSYS Extraction algorithm models the Extractor as a staged tower, allowing you to specify either ideal stages or actual stages with efficiencies.

Side Draw

If you require a Side Draw on the Extractor, you can choose to draw either the Light or Heavy phase from a stage. HYSYS will perform a three phase flash on the entire contents of the stage to produce the conditions and composition of the specified draw.

Use only property packages that support 2 liquid phases.


12

The purpose of the Liquid-Liquid Extractor is to determine the required solvent flow (in this case water) which will cause a mixture to phase split, forming two liquid phases. A rough estimation of the solvent flow can be obtained by using a Mixer, and then examining the phase separation while varying the solvent flow. However, because the extractor is divided into stages, the flow determined can only be used as an estimate. Use a flow of 200 kg/h (440 lb/hr) of Water.

1. Enter the following data for the stream Water:


Conditions

Stream Name Water




Mass Fraction H20 1.0


13

2. Add the Liquid-Liquid Extractor with the following data:

3. On the Parameters tab, Profiles page, supply an estimate of 48 kg/h (105 lb/hr) for the overhead light liquid.


Connections

Column Name T-101

No. of Stages 20

Top Stage Inlet Water

Bottom Stage Inlet Azeo Liq

Ovhd Light Liquid CycloC6

Bottoms Heavy Liquid Rich Solv

Pressures

Top Stage 101.3 kPa (14.7 psia)

Bottom Stage 101.3 kPa (14.7 psia)

Temperature Estimates

Top Stage 25°C (77°F)

Stages 2-18 25°C (77°F)

Stage 19 28°C (82°F)

Stage 20 33°C (91°F)

The Temperature Estimates for Stages 2-19 can be supplied on the Parameters tab, Profiles page of the column property view.


14

4. Go to the Basis Environment and select LLE Basis as the Fluid Package for the Liquid-Liquid Extractor. Return to the Simulation Environment.

5. Run the column.


15

Adding the Solvent Recovery Tower

The Solvent Recovery tower, which separates the Acetone from the Water, presents a difficult separation at atmospheric pressure. To keep the number of stages reasonable, an overhead pressure of 53 kPa will be used. (Once again the data was obtained from HYSYS Conceptual Design Application).

1. Add the Solvent Recovery Tower as a Distillation Column with the following data:

2. Supply a Damping Factor of 0.8.

3. Run the column.


Connections

Column Name T-102

No. of Stages 20

Inlet Streams RichSolv, Stage 17


Overhead Liq AcetRich

Bottoms Liquid Outlet H2O Rich

Condenser Energy Stream RecCond Q

Reboiler Energy Stream RecReb Q

Pressures

Condenser Pressure 53 kPa (7.75 psia)

Reboiler Pressure 56 kPa (8 psia)

Temperature Estimates

Condenser 35°C (95°F)

Reboiler 80°C (175°F)

Specifications

Reflux Ratio 7

Acetone Recovery (Cond) 0.9998


16

Solvent Recycles

Finally, the two products from the Solvent Recovery tower have to be recycled to the previous two towers. Because of the temperature and pressure of the Solvent Recovery tower, each recycle stream will require a Pump and a Cooler/Heater operation to return the stream to the necessary tower conditions.

Add a Pump

Add a Pump to the stream H2O Rich with the following information:

The pressure of stream H2O Atm is 101.3 kPa (14.7 psia).


Connections

Name P-100

Inlet H2O Rich

Outlet H2O Atm

Energy Q 100

Parameters

Adiabatic Efficiency 75%


17

Add a Cooler

Add a Cooler downstream of P-100 with the following information:

The temperature of stream H2O Cool is 25°C (77°F).


Connections

Name E-100

Inlet H2O Atm

Energy Q102

Outlet H2O Cool

Parameters

Delta P 0 kPa


18

Add the Second Pump

Add another Pump from the T-102 product with the following information:

The pressure of Acet Atm is 101.3 kPa (14.7 psia).

Add a Heater

Add a Heater operation downstream of Acet Atm with the following information:

The temperature of Acet Warm is 55°C (130°F).


Connections

Name P-101

Inlet Acet Rich

Outlet Acet Atm

Energy Q 101

Parameters

Adiabatic Efficiency 75%


Connections

Name E-101

Inlet Acet Atm

Energy Q 103

Outlet Acet Warm

Parameters

Delta P 0 kPa


19

Adding the Recycles

Make-up streams are necessary to compensate for the losses of Acetone and Water in the process product streams. To calculate the exact amount that is lost in the products, Balance operations are used. These are not real operations but only mathematical ways of obtaining the make-up values.

A Mole Balance operation will be used to create two streams (Rec Acet and Rec Water) with the same flowrates and compositions as the tower product streams Benzene and CycloC6, respectively.

These streams are then sent to a Component Splitter and split into two streams: one containing the product and the other containing traces of the lost solvent.

The streams containing the lost solvents are the make-up streams which will be mixed with the recycled streams from the solvent Recovery Tower.


20

Add the Balance Operations

Add two Balance operations with the following data:

1. On the Parameters tab, specify the Balance Type as Mole.

2. Specify the Temperature and Pressure of Rec Acet to be 55°C (130°F) and 101.3 kPa (14.7 psia).

3. Add the second balance operation with the following information.

1. On the Parameters tab, specify the Balance Type as Mole.

2. Specify the Temperature and Pressure of Rec H2O to be 25°C (77°F)and 101.3 kPa (14.7 psia).


Connections

Name BAL-1

Inlet Streams Benzene

Outlet Streams Rec Acet


Connections

Name BAL-2

Inlet Streams CycloC6

Outlet Streams Rec H2O


21

Add the Component Splitters

Add two Component Splitters with the following information:

Specify the temperature of one of the product streams to be 25°C (77°F). The temperature in the other stream will be calculated from the energy balance around the operation.


Connections

Name X-100

Inlets Rec H2O

Overhead Outlet H2O Make-up

Bottoms Outlet Frac CycloC6

Parameters

Overhead Pressure 101.3 kPa (14.7 psia)

Bottoms Pressure 101.3 kPa (14.7 psia)

Splits

Benzene 0

CycloC6 0

Acetone 1.0

H2O 1.0


22

Specify the temperature of the product streams to be 55°C (130°F).


Connections

Name X-101

Inlets Rec Acet

Overhead Outlet Acet Make-up

Bottoms Outlet Frac Benzene

Parameters

Overhead Pressure 101.3 kPa (14.7 psia)

Bottoms Pressure 101.3 kPa (14.7 psia)

Splits

Benzene 0

CycloC6 0

Acetone 1.0

H2O 1.0


23

Add the Mixer Operations

Add two Mixer operations with the following information:


Connections

Name MIX-100

Inlets Acet Warm

Acet Make-up

Outlet Acet to Rec

Connections

Name MIX-101

Inlets H2O Cool

H2O Make-up

Outlet H2O to Rec


24

Add the Recycles

The input for the recycles is shown below. Note that because of the nature of the process, the Flow Tolerance is set to 1 and the Composition Tolerance is set to 1. The Recycles are installed as Simultaneous. Put the case in Hold mode before adding the recycles.


Connections

Name RCY-1

Inlet H2O to Rec

Outlet Water

Parameters

Vapour Fraction 10.0

Temperature 10.0

Pressure 10.0

Flow 1.0

Enthalpy 10.0

Composition 1.0

Connections

Name RCY-2

Inlet Acet to Rec

Outlet Acetone

Parameters

Vapour Fraction 10.0

Temperature 10.0

Pressure 10.0

Flow 1.0

Enthalpy 10.0

Composition 1.0


25

Press the Go button to begin calculations.

Having completed the recycles and converged the whole flowsheet, operations can be opened again in order to be examined.

Save your case!


26

Reactive Distillation 1

1

Reactive Distillation


2 Reactive Distillation

2

WorkshopWith the continuous removal of reaction products, reactive distillation has found acceptance as a means of improving the technical and economic operation of processes where it is applicable. Advantages of this process include higher yields, energy savings and reduced capital costs.

In this example, you will study the manufacture of Methyl Acetate, an important oil resin used in the manufacture of artificial leathers. You will simulate the synthesis of Methyl Acetate from Methanol and Acetic Acid in a catalytic distillation column.


• Model reactive distillation columns

Fast Track to page 7

Process Overview

Column Overview


5


Defining the Simulation Basis1. Start a new case using the Wilson Activity Model. The

components are: Methanol, Acetic Acid, M-Acetate and Water.


Add the Feed Stream

Add the feed stream with the following values:

In the HYSYS component database, M-Acetate is the SimName and Methyl-Acetate is the FullName.


Conditions

Stream Name Feed




Composition - Mole Fractions

Methanol 0.4

Acetic Acid 0.4

M-Acetate 0.1

Water 0.1


6

Add the Distillation ColumnAdd a Distillation Column with the following connections:

Go to the Monitor page of the Design tab and run the column. Complete the following table with information from the simulation:


Connections

Column Name Reactive Distil

No. of Stages 15

Feed Feed, Stage 10


Ovhd Liquid Distillate

Bottoms Liquid Bottoms

Condenser Energy Cond Q

Reboiler Energy Reb Q

Pressure

Delta P, Condenser 0 kPa (0 psi)

Condenser 90 kPa (13 psia)


Specs

Reflux Ratio 5

Distillate Rate 20 kgmole/h (44 lbmole/hr)

ComponentDistillate - Mole Fraction

Bottoms - Mole Fraction

Methanol

Acetic Acid

Methyl Acetate

Water


7

Adding the Reaction

Another way to add reactions in HYSYS is through the Simulation Environment.

The reaction occurring in this simulation is a Kinetic reaction,

CH3OH + CH3COOH = CH3CH3COO + H2O

1. From the Flowsheet menu, select Reaction Package.

2. From the Available Reactions group, press the Add Rxn button.

3. Select Kinetic from the list of reactions and press the Add Reaction button.

4. Enter the stoichiometric coefficients on the Stoichiometry tab. Remember that reactants are negative and products are positive.

5. Go to the Basis tab. The Base Component is methanol and the RxnPhase is Liquid. Leave the Basis and Rate Units at their default values.

6. On the Parameters tab, for the Forward Reaction enter the Arrenhius Parameter as A=1.0e5, and for the Energy Parameter E=2.3e4 kJ/kgmole (1.0e4 Btu/lbmole). The reaction status should now be Ready. Close the view.

7. Add the Global Rxn Set to the Current Reaction Sets group by pressing the Add Set button.

Open the case OptReact.hsc


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Adding the Reaction to the Column

In this case, the reaction occurs on stages 5 - 10 of the column. Reaction Sets in HYSYS can be attached to any of the stages in the column, including the Condenser, Reboiler and Side operations.

1. On the Reactions tab, press the New button. Enter the following data:

2. Check the Active box on the ColumnReaction view. The default column solver in HYSYS "HYSIM Inside-Out" is not capable of handling reactions in the column. Therefore, HYSYS will change the solver to Newton-Raphson Inside-Out.

3. However, for this column, we need to use the Sparse Continuation Solver. Select this solver on the Solver page of the Parameters page.

4. Run the column. (The column may run automatically after the solver is changed.)

5. Due to the substantial changes that were introduced as part of adding the reaction to the column. The column may not solve. On the Profiles page of the Parameters tab, enter a condenser temperature estimate of 50 oC (122 oF), an estimate of 55 oC (130 oF) for the 15th tray, and 100 oC (212 oF) for the Reboiler.

6. Rerun the column by pressing the Run button. The column should now solve.

7. You can view the results on the Performance tab, and the reaction results on the Reactions tab, Results page.

The Sparse Continuation Solver can be used for highly non-ideal, unusual profiles, or otherwise difficult to converge towers. It is good for Chemical Systems when Inside-Out is not successful and for 3-Phase distillation.


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8. Complete the following table with information from the simulation.

ComponentDistillate - Mole Fraction

Bottoms - Mole Fraction

Methanol

Acetic Acid

Methyl Acetate

Water

Does the reaction inside the column have any effect on the compositions of the product streams? __________

Save your case!


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Three Phase Distillation 1

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Three Phase Distillation


2 Three Phase Distillation

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IntroductionIn previous modules, we have installed distillation columns design for two phases. However, these columns will not work for three phase systems. When dealing with three phase systems, it is necessary to use a different type of column that uses a different Input Expert, and a different default solver.

Due to the addition of a second liquid phase in the column, it is very difficult to model this type of column. For this reason, we must use the Sparse Continuation Solver to solve these systems.

The three phase system in this example consists of a 2-butanol, water, n-butyl-acetate system. The feed to the column is saturated liquid at atmospheric pressure. The liquid product from the condenser is 98% pure water, and the liquid product from the reboiler is a mixture of the two other components (2-butanol and n-butyl-acetate).

Learning ObjectivesIn this module, you will learn:

• How to use the three phase distillation column in HYSYS.• When to use the Dynamic Initial Estimate Generator (IEG).• Why the Sparse Continuation Solver must be used to solve

three phase columns.

PrerequisitesBefore beginning this module, you should have some experience with installing distillation columns in HYSYS. Previous experience with normal two phase systems will help you understand the principals behind the operation of three phase systems.


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BackgroundThe three phase stream that will be distilled here will consists of three components: water, n-butyl-acetate, and 2-butanol. The ternary diagram for these three components at 25 oC (77 oF) and 101.3 kPa (14.9 psia) looks something like this:

This plot was generated using the DISTIL software package produced by AEA Technology Engineering Software.

The composition of the feed stream is given in the following table:

As you can see (using the ternary graph above), this stream will lie within the two liquid phase region.

Component Mole Fraction

Water 0.35

n-Butyl-Acetate 0.40

2-Butanol 0.25


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The Differences Between Two and Three Phase DistillationWith a normal two phase distillation setup, it would be impossible to distil the stream described on the previous page. Fortunately, HYSYS is able to model the distillation of streams like this by using a different column setup routine.

Different Solvers

With two phase distillation the most common solver that is used is the "HYSIM Inside-Out" solver. This solver is good for most hydrocarbon systems, but it can not handle highly non ideal chemical systems, including three phase systems.

The default solver for three phase columns is the "Sparse Continuation" solver. This more advanced solver is able to handle three phase, non ideal chemical systems, that other solvers can not calculate.

Different Input Experts

The second major difference between two and three phase distillation is the different input experts that each uses. You have already seen the input expert used by the "normal" two phase distillation column. The input expert used by the three phase column is similar though slightly more complex. You will use this interface when we install the three phase column later in this module.

Different Column Specifications

Finally, the third major difference between the two column types is the additional column specification that are available when using the three phase column operation. Due to the complications that a second liquid phase adds to the column operation, additional specifications are required to help the column converge.

Despite these apparent differences, setting up columns to handle three phase streams is not that much more complicated than setting them up to handle two phase streams.

You already have experience with two phase systems, and you will find that setting up the three phases system is not that much more complicated.

Process Overview


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Column PDF


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The Basis EnvironmentIn this case, we will use the NRTL Activity model with the UNIFAC VLE estimated interaction parameters for the unknown binaries.

Begin a new HYSYS case and select the NRTL Activity model as the Property Package. The three required components are:

• Water• 2-Butanol• n-B-Acetate

On the Binary Coefficients tab, press the Unknowns Only button.


The Simulation Environment

Adding the Feed Stream

Create a new stream and define it with the following information:


Name Feed

Vapour Fraction 0.0



Mole Fraction - Water 0.35

Mole Fraction - 2-Butanol 0.25

Mole Fraction - n-B-Acetate 0.40

The mass densities of the phases can be found on the Properties page. You will have to stretch the window in the horizontal direction in order to view all the information.

What is the Mass Density of the Liquid Phase? __________ and the Aqueous Phase? __________

Which phase is the "heavy" phase? ______________


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Adding the Distillation Column

Add a Three Phase Distillation Column operation to the simulation using one of the available methods.

Note: Make sure that you install the Three Phase column operation, not the two phase one.

As mentioned before, the Input Expert for the Three Phase column is slightly different than the one used for an ordinary Two Phase column. For this reason, each page will be shown here.

The input expert for the three-phase distillation column is different from the input expert that was seen previously. The first page of the expert allows you to select the type of column that you want to add to the model. Select the Distillation radio button and press the Next button.

The Three Phase Distillation Column icon.


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On the next page, set the number of stages at 6, and set the "Two Liquid Phase Check" on the top five stages.

On the third page, enter names for the streams around the condenser. For this column, the Reflux Stream will be the Lights only; therefore, select the appropriate radio button in this group box.


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On the fourth page, set the vapour rate to 0.0 and the Light Reflux Fraction to 1.0. The degrees of freedom should read 0, once both of these values are entered.

On the fifth page, attach the Feed stream to stage 1. Also, define the reboiler energy stream and attach a liquid product stream to the reboiler. From now on, the screens will look familiar to the input expert screens that you have seen previously.


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On the next page, set the condenser pressure at 101 kPa (14.9 psia), and the reboiler pressure at 105 kPa (15.5 psia).

On the next page, you are asked to supply optional temperature estimates. Enter values of 85, 90, and 95 oC (185, 195, and 205 oF) for the condenser, top stage and reboiler temperature estimates, respectively.


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We are now done. Press the Done button to close the input expert. Note that if the formation of azeotropes were a concern in this column, the Azeotropic Initialization button would have been pressed, and HYSYS would have checked for possible azeotropes among the selected components.

You are automatically placed on the Column’s property view; move to the Monitor page of the Design tab.

Enter a Bot Prod Rate of 33 kgmole/h (75 lbmole/hr). Press the Run button to converge the column; the column should start to solve, and will reach a converged solution quickly. If the column does not solve in the first attempt, increase the Bot Rate Spec value to 35 kgmole/h (80 lbmole/hr) and try again. Once the column converges, decrease the spec back to its original value.

How many Degrees of Freedom are shown here? __________

50772070 process modeling using hysys with chemical industry focus

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