1.2 Steady State Simulation
1.2.6 Installing Unit Operations
In the last section you defined the feed streams. Now you will install the necessary unit operations for processing the gas.
Installing the Mixer
The first operation that you will install is a Mixer, used to combine the two feed streams. As with most commands in UniSim Design, installing an operation can be accomplished in a number of ways. One method is through the Unit Ops tab of the Workbook.
1. Click the Workbook icon to access the Workbook view. 2. Click the Unit Ops tab of the Workbook.
3. Click the Add UnitOp button.
Figure 1.36
The UnitOps view appears, listing all available unit operations.
4. Select Mixer by doing one of the following:
• Click on an operation in the Available Unit Operations list and type mixer.
• Click on an operation in the Available Unit Operations list an press the DOWN arrow key to scroll down the list of available operations to Mixer.
• Scroll down the list using the vertical scroll bar and click on
Mixer.
5. With Mixer selected, click the Add button or press the ENTER key. You can also use the filters to find and add an operation. For example, select the Piping Equipment radio button under
Categories. A filtered list containing just piping operations appears in the Available Unit Operations group.
The Mixer property view appears.
As with a stream, a unit operation’s property view contains all the information defining the operation, organized in tabs and pages. The four tabs shown for the Mixer, namely Design, Rating, Worksheet, and Dynamics, appear in the property view for most
Figure 1.37
Figure 1.38
You can also double- click an operation to install it.
operations. More complex operations have more tabs. UniSim Design provides the default name MIX-100 for the Mixer.
As with streams, the default naming scheme for unit operations can be changed on the Session Preferences view.
Many operations, such as the Mixer, accept multiple feed streams. Whenever you see a table like the one in the Inlets group, the operation will accept multiple stream connections at that location. When the Inlets table has focus, you can access a drop-down list of available streams.
6. Click the <<Stream>> cell.
The status bar at the bottom of the view shows that the operation requires a feed stream.
7. Open the <<Stream>> drop-down list of feeds by clicking on or by pressing the F2 key and then the DOWN arrow key.
8. Select Feed 1 from the list. The stream is added to the list of Inlets, and <<Stream>> automatically moves down to a new empty cell. 9. Repeat steps 6-8 to connect the other stream, Feed 2.
The status indicator now displays ‘Requires a product stream’. 10. Click in the Outlet field.
11. Type MixerOut in the cell and press ENTER.
UniSim Design recognizes that there is no existing stream named MixerOut, so it will create the new stream with this name.
The status indicator now displays a green OK, indicating that the
Figure 1.39
See Section 12.2.4 - Naming Page in the
UniSim Design User Guide for detailed
information on setting your Session
Preferences.
Alternatively, you can make the connections by typing the exact stream name in the cell, then pressing ENTER.
operation and attached streams are completely calculated.
12. Click the Parameters page.
13. In the Automatic Pressure Assignment group, leave the default setting at Set Outlet to Lowest Inlet.
UniSim Design has calculated the outlet stream by combining the two inlets and flashing the mixture at the lowest pressure of the inlet streams. In this case, both inlets have the same pressure (600 psia), so the outlet stream is set to 600 psia.
Figure 1.40
14. To view the calculated outlet stream, click the Worksheet tab and select the Conditions page.
15. Now that the Mixer is completely known, close the view to return to the Workbook. The new operation appears in the table on the Unit
Ops tab of the Workbook.
The table shows the operation Name, its Object Type, the attached streams (Feeds and Products), whether it is Ignored, and its Calculation Level.
When you select an operation in the table and click the View
UnitOp button, the property view for the selected operation
appears. Alternatively, double-clicking on any cell (except Inlet, Outlet, and Ignored) associated with the operation also opens the operation property view.
Figure 1.42
Figure 1.43
The Conditions page is a condensed Workbook page, displaying only those streams attached to the selected
You can also open the property view for a stream directly from the
Unit Ops tab. To open the property view for one of the streams
attached to an operation, do one of the following:
• Select the operation in the Unit Ops tab and double-click on the stream you want to access in the list at the bottom of the
Workbook view.
• Double-click on the Inlet or Outlet cell of the operation. The property view for the first listed feed or product stream appears.
Installing the Inlet Separator
Next you will install and define the inlet separator, which splits the two- phase MixerOut stream into its vapour and liquid phases.
1. In the Workbook property view, click the Unit Ops tab.
2. Click the Add UnitOp button. The UnitOps view appears. You can also access the Unit Ops view by pressing F12.
3. In the Categories group, select the Vessels radio button. 4. In the list of Available Unit Operations, select Separator. 5. Click the Add button. The Separator property view appears,
displaying the Connections page on the Design tab.
6. In the Name cell, change the name to InletSep and press ENTER. 7. Move to the Inlets list by clicking on the << Stream>> cell, or by
pressing ALT L.
8. Open the drop-down list of available feed streams.
9. Select the stream MixerOut by doing one of the following: • Click on the stream name in the drop-down list.
• Press the DOWN arrow key to highlight the stream name and press ENTER.
10. Move to the Vapour Outlet cell by pressing ALT V.
11. Create the vapour outlet stream by typing SepVap and pressing
12. Click on the Liquid Outlet cell, type the name SepLiq, and press
ENTER. The completed Connections page appears as shown in the
following figure.
13. Select the Parameters page. The current default values for Delta P, Volume, Liquid Volume, and Liquid Level are acceptable.
Figure 1.44
Figure 1.45
An Energy stream could be attached to heat or cool the vessel contents. For this tutorial, however, the energy stream is not required.
The Volume, Liquid Volume, and Liquid Level default values generally apply only to vessels operating in dynamic mode or with reactions attached.
14. To view the calculated outlet stream data, click the Worksheet tab, then select the Conditions page. The table appearing on this page is shown below.
15. When finished, click the Close icon to close the separator property view.
Installing the Heat Exchanger
Next, you will install the gas/gas exchanger.1. Access the Object Palette by pressing F4.
2. On the Object Palette, double-click the Heat Exchanger icon. The Heat Exchanger property view appears.
The Connections page on the Design tab is active.
3. In the Name field, change the operation name from its default E- 100 to Gas/Gas.
Figure 1.46
Figure 1.47
4. Attach the Inlet and Outlet streams as shown below, using the methods learned in the previous sections.
5. Click the Parameters page.
The Exchanger Design (End Point) is the acceptable default setting for the Heat Exchanger Model for this tutorial.
6. Enter a pressure drop of 10 psi for both the Tube Side Delta P and
Shell Side Delta P.
Figure 1.48
Figure 1.49
You will have to create all streams except SepVap, which is an existing stream that can be selected from the Tube
Side Inlet drop-down
list.
Create the new streams by selecting the appropriate input field, typing the name, then pressing ENTER.
8. In the Configuration group, click in the Tube Passes per Shell cell and change the value to 1, to model Counter Current Flow.
9. A warning appears to remind you that the number of tube passes must be an even multiple of the shell passes. Click the OK button. 10. Close the Heat Exchanger property view to return to the
Workbook view.
11. Click the Material Streams tab of the Workbook.
Stream CoolGas has not yet been flashed, as its temperature is unknown. The CoolGas stream is flashed later when a temperature approach is specified for the Gas/Gas heat exchanger.
Figure 1.50
Figure 1.51
Notice how partial information is passed (for stream CoolGas) throughout the flowsheet. UniSim Design always calculates as many properties as possible for the streams based on the available information.