Aspen Flare System Analyzer
Getting Started Guide
Version Number: V8.0 December 2012 Copyright (c) 1981-2012 by Aspen Technology, Inc. All rights reserved. Aspen Flare System Analyzer, Aspen Flarenet, and the aspen leaf logo are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies.
This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 200 Wheeler Road Burlington, MA 01803-5501 USA Phone: Phone: (781) 221-6400 221-6400 Toll free: (888) 996-7001 Website http://www.aspentec http://www.aspentech.com h.com
Version Number: V8.0 December 2012 Copyright (c) 1981-2012 by Aspen Technology, Inc. All rights reserved. Aspen Flare System Analyzer, Aspen Flarenet, and the aspen leaf logo are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies.
This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 200 Wheeler Road Burlington, MA 01803-5501 USA Phone: Phone: (781) 221-6400 221-6400 Toll free: (888) 996-7001 Website http://www.aspentec http://www.aspentech.com h.com
Contents 1 Introduction............ Introduction ......................... .......................... ......................... ......................... .......................... ......................... ......................... .................2 ....2 About this document.................. document............................... .......................... ......................... ......................... .......................... ....................2 .......2 Audience ............. .......................... ......................... ......................... .......................... .......................... .......................... .......................... ...............2 ..2 Related Documentation...................... Documentation................................... .......................... .......................... .......................... ........................2 ...........2 Technical Support ............ ......................... .......................... .......................... .......................... .......................... .......................... ...............2 ..2 2 Building B uilding and Running a Model .......................... ...................................... ......................... .......................... ......................... ..............4 ..4 Overview..................... Overview.................................. .......................... .......................... .......................... .......................... .......................... ...................4 ......4 Data Requirements.............. Requirements.......................... ......................... .......................... .......................... .......................... ..........................5 .............5 Pipe Segment Data..................... Data................................. ......................... .......................... .......................... ......................5 .........5 Relief Source Data............................ Data......................................... .......................... .......................... ......................... ...............6 ...6 System Design Constraints.................. Constraints............................... .......................... .......................... ......................... .............. 7 Starting Aspen Flare System Analyzer.................................................................7 Starting a New Model............................ Model......................................... ......................... ......................... .......................... ......................8 .........8 Saving the Model ........... ........................ .......................... .......................... .......................... .......................... ......................... ............... ... 12 Building the Pipe Network ............ ......................... .......................... .......................... ......................... ......................... ................ ... 12 Starting the Pipe Network ................................ ............................................. .......................... ........................ ...........12 12 Completing the Pipe Network ............. .......................... .......................... ......................... ......................... ............... 16 Defining the Scenarios ............. .......................... ......................... ......................... .......................... .......................... .................... ....... 26 Defining the Sources ............. ......................... ......................... .......................... .......................... .......................... ...................... ......... 33 Rating the Network ............ ......................... .......................... .......................... .......................... .......................... ........................ ...........44 44 Printing Data and Results ............. .......................... .......................... .......................... ......................... ......................... ................ ... 47 3 Developing the Model ........................ .................................... ......................... .......................... ......................... ......................... ...............49 ..49 Overview..................... Overview.................................. .......................... .......................... .......................... .......................... .......................... ................. .... 49 Data Requirements.............. Requirements.......................... ......................... .......................... .......................... .......................... ........................ ...........50 50 Pipe Segment Data..................... Data................................. ......................... .......................... .......................... .................... ....... 50 Relief Source Data............................ Data......................................... .......................... .......................... ......................... .............. 51 System Design Constraints.................. Constraints............................... .......................... .......................... ........................ ...........53 53 Opening the Old Model................... Model................................ .......................... .......................... .......................... ......................... .............. 53 Updating the Model ............ ......................... .......................... .......................... .......................... .......................... ........................ ...........54 54 Defining the Scenarios ............. .......................... ......................... ......................... .......................... .......................... .................... ....... 63 Defining the Sources ............. ......................... ......................... .......................... .......................... .......................... ...................... ......... 66 Sizing the Network ........... ........................ .......................... .......................... .......................... .......................... .......................... .............73 73 Design Calculations ............. ......................... ......................... .......................... .......................... .......................... ........................ ...........75 75
1 Introduction
This section provides information on the following topics:
About this Document Document Audience
Related Documentation
Technical Support
About this document The guide provides step by step instructions to the most commonly used features within Aspen Flare System Analyzer (previously named Aspen Flarenet).
Audience This guide is intended for process and process systems engineers.
Related Documentation Title
Conte nt
Aspen Flare System Analyzer Reference Manual
Reference Manual for Using Aspen Flare System Analyzer
Technical Support AspenTech customers with a valid license and software maintenance agreement can register to access the online AspenTech Support Center at: http://support.aspentech.com This Web support site allows you to:
Access current product documentation
Search for tech tips, solutions and frequently asked questions (FAQs)
Search for and download application examples
Search for and download service packs and product updates
Submit and track technical issues
Send suggestions
Report product defects
Review lists of known deficiencies and defects
Registered users can also subscribe to our Technical Support e-Bulletins. These e-Bulletins are used to alert users to important technical support information such as:
Technical advisories
Product updates and releases
Customer support is also available by phone, fax, and email. The most up-todate contact information is available at the AspenTech Support Center at http://support.aspentech.com.
2 Building and Running a Model
This section provides information on the following topics:
Overview
Data Requirements
Starting Aspen Flare System Analyzer
Starting a New Model
Saving the Model
Building the Pipe Network
Defining the Scenario
Defining the Sources
Overview This Getting Started tutorial shows the fundamental principles involved in using Aspen Flare System Analyzer to design and rate a new flare system. This guided tour will expose you to most of the major features of Aspen Flare System Analyzer. This tutorial assumes that you are familiar with the use of Microsoft Windows and have some prior experience in the design of flare systems. This example consists of the following main parts: 1
Building The Pipe Network - Pipes and nodes will be added using either the Process Flowsheet or Pipe Manager.
2
Defining the Scenarios - Different scenarios will be set up to simulate various process conditions.
3
Defining The Sources - Relieving sources will be added to each scenario.
4
Sizing the Network - Finally, the pipe network will be simulated and results will be viewed both in textual and graphical form.
Data Requirements Before you can start to build a computer model of the flare header system, you must first define all the data that will determine your system. When you are sizing a flare system, the initial pipe diameters may affect the solution when there is a liquid phase and the liquid knockout drum is modeled. You should initially size a network using vapor phase methods.
Pipe Segment Data Data
Description
Connectivity
You would normally have prepared a system sketch that defines the nodes to which the pipe segments are connected.
Length and fittings loss coefficients for each pipe segment
These will be based upon either a preliminary or detailed isometric drawing of the piping.
Diameter and pipe schedule for each pipe segment
If you are rating an existing network, these will normally be taken from the flare system P&ID. If you are sizing a new flare system, the pipe diameters that you define are relatively unimportant since they will be overwritten by the sizing algorithms. It is recommended that reasonable diameters be defined, so that the sizing algorithm initializes to a condition that will give faster convergence.
The following diagram shows the connectivity of the system that you will be designing in this example.
Fig 2.1
The piping in the network diagram is detailed in the following table:
Item
Length (m)
Internal Diameter (mm)
Wall Thickness (mm)
Flare Tip
Fittings Loss
Elevation Change (m)
3.0
0
Stack
100
876.3
19.05
0
100
Header 3
50
876.3
19.05
0
0
Tail Pipe 1
25
428.65
14.275
0
0
Tail Pipe 2
25
428.65
14.275
0
0
The flare tip is not a pipe segment, but rather a node that represents a zero length piece of pipe with defined fittings loss coefficients. Since the internal diameter is not specified, it will assume the same diameter as the upstream pipe segment. Fittings loss coefficients for the flare tip exclude pipe enlargement and junction losses for the connection to the upstream pipe which will automatically be calculated.
Relief Source Data The following data must be specified for the sources: Data
Description
Flow and Composition
These may vary for each scenario that you are evaluating. If a relief source is not used in a particular scenario, the flow may be set to zero. Flow refers to the quantity of fluid that the source valve must pass as a consequence of the plant upset condition. Rated Flow refers to the quantity of fluid that the source valve will pass due to its physical construction . Rated Flow must always be greater than or equal to Flow.
Maximum Allowable Back Pressure (MABP)
This is the maximum pressure that can exist at the outlet of the device (source) without affecting its capacity.
Downstream temperature
This temperature is used as the pressure independent temperature at which the source enters the network. This temperature is used when ideal gas enthalpies are used to calculate the heat balance, or as an initial guess when any other enthalpy method is used.
Upstream pressure and temperature
These are only used if Ideal Gas enthalpies are not used for the heat balance. These may vary for each scenario that you are evaluating. With relief valves, the flowing pressure should be used.
Discharge flange size
This will normally be determined from the relief valve sizing calculations. If this value is unknown then the field should be left empty to ignore the pressure change from the valve to the downstream pipe due to the swage.
In this example, you will consider three scenarios that represent one fire case and two single blocked discharge cases. The following tables define the source data for each scenario.
Default Source Data
Source Name
Flowrate (kg/hr)
Flange Size (mm)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
100000
300
20
15
15
10
5.0
Source 2
100000
300
25
15
15
10
5.0
Source 1 is a control valve while Source 2 is a relief valve.
Source 1 Only Data Source Name
Flowrate (kg/hr)
Flange Size (mm)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
100000
300
20
15
15
10
5.0
Source 2
0
300
25
15
15
10
5.0
Source 2 Only Data Source Name
Flowrate (kg/hr)
Flange Size (mm)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
0
300
20
15
15
10
5.0
Source 2
100000
300
25
15
15
10
5.0
System Design Constraints In this case, the following data is used for both scenarios:
Maximum allowable mach number - 0.50 for both main headers and tailpipes. Maximum allowable noise – 100 dB for both main headers and tailpipes.
Starting Aspen Flare System Analyzer The installation process creates a short-cut to Aspen Flare System Analyzer in the Start menu. To Start Aspen Flare System Analyzer: 1
Select the Start menu.
2
Navigate to and click the Aspen Flare System Analyzer icon under Programs | AspenTech | Process Modeling Now you are ready to begin working with Aspen Flare System Analyzer.
When you start Aspen Flare System Analyzer, the Aspen Flare System Analyzer application window appears. Before setting up the Getting Started case, you should choose the Aspen Flare System Analyzer units set for displaying information. You can check your current units set by accessing the Preferences Editor:
1
Click the aspenONE Button which is on the upper left corner of the application window; then select Preferences from the Application Menu. The Preferences Editor is displayed.
Fig 2.2
2
The current unit set is shown in the Units box. The default unit set is Metric, which will be used for this example.
3
Confirm that the Edit Objects on Add check box is selected. This option will open the object editor view each time a new object is added.
4 Click OK to close the Preferences Editor.
Starting a New Model To start a new case, do one of the following: 1 Click New on the Quick Access Toolbar beside the aspenONE Button; or, click the aspenONE Button, then click New from the Application Menu. The Documentation Editor is displayed. 2
Enter the appropriate data into the User Name, Job Code, Project, and Description fields, and then click OK. The Component Manager is displayed.
Fig 2.3
Note: The Selected component list is empty, indicating that no components have yet been installed in the case. There are a number of ways to select components for your simulation. One method is to filter the database for a certain component type. In this model, we will be using the following components: Methane, Ethane and Propane. To add Methane using the filter option: 1
Ensure that the HC check box in the Component types group is selected.
2 Typing methane in the Selection filter field. Notice that as you are typing, the Available components list will be filtered out to show only the matching components. 3 Double-click Methane in the Available components list. Methane will now be selected and shown in the Selected components list. Note: Initially, all the check boxes in the Component types group are selected. You can clear them by clicking Invert.
Fig 2.4
4
Repeat the previous step with Ethane and Propane. As an alternative method, you may scroll through the Available components list until you see the desired component. Highlight the component by clicking it, and then click Add to place it in the Selected components list.
Note: Notice that now all the required components are shown in the Selected components list, indicating that they have been installed in the case. The Component Manager will now appear as follows:
Fig 2.5
5 Click OK to close the Component Manager and accept the list of components. 6
In the Navigation Pane, double-click Inputs on the Views pane, and then select Components from the list. The Components data view will be displayed:
Fig 2.6
Note: You can use the horizontal scroll bar at the bottom of the sheet to view all of the component properties.
Saving the Model It is good practice to periodically save your case by doing one of the following:
Click the Save icon on the Quick Access Toolbar. Click the aspenONE Button on the upper left corner of the application window, and then select Save from the Application Menu. Press Ctrl+S.
As this is the first time you have saved your case, the All Files dialog box will be displayed. After selecting an appropriate disk drive and directory in the Save in list, enter the name of the file to which you want to save the case in the File name field. Note: You do not need to include the .fnwx extension; Aspen Flare System Analyzer will add it automatically. Click Save to close the dialog box and save the file.
Building the Pipe Network Since all scenarios have a common pipe network, you should first build the pipe network model via the Process Flowsheet.
Starting the Pipe Network 1 Click Process Flowsheet in Views group on the Home tab of the Ribbon. The Process Flowsheet will be displayed, and the Process Flowsheet tab will be shown on the Ribbon. Note: Before proceeding any further, make sure that the Edit Objects on Add check box on the General tab of the Preferences Editor is selected.
Fig 2.7
At this point the flowsheet should be blank, since we have not added a single object yet. The desired objects can be added by using either of the following methods:
Clicking the Palette on the Process Flowsheet tab will open the Palette, which displays all the objects available in Aspen Flare System Analyzer. You can add an object by dragging it onto the Process Flowsheet.
Fig 2.8
Objects can also be added via the Pipe Manager and the Node Manager. These are accessible through Pipes and Nodes in the Build group on the Home tab of the Ribbon, respectively.
For example, to add a pipe: 2
Click the pipe icon in the Palette, drag and drop it to a proper place on the Process Flowsheet. In the Pipe Editor that is displayed, type Stack in the Name field. Click OK to close the Pipe Editor.
3
Next, add a Flare Tip. Drag the Flare Tip icon on the Palette to the Process Flowsheet. Since the Edit Objects on Add check box is selected, The Flare Tip Editor will be displayed after the Flare Tip is installed to the flowsheet:
Fig 2.9
By default the Flare Tip has been named as FlareTip1, which can be changed to a more appropriate name as follows: 4
Click in the Name field on the Connections tab of the Flare Tip Editor.
5
Delete the default name and type Flare Tip as the new name. Since this example is of smaller size, the Location field will be left blank. This field is only useful for larger cases with multiple sections (areas) within a same plant. Now you need to specify the pipe, which will be simulated as a flare stack, and it is attached to the Flare Tip.
6 Select Stack from the list in the Upstream node field. 7
In the At field, select Downstream as the pipe end connected to the Flare Tip.
In order to complete the input on the Flare Tip Editor, you need to specify the Diameter and the Fitting Loss values on the Calculations tab. Note: The Fitting Loss Coefficient Basis should be set to Total Pressure to indicate that the loss coefficient we are defining will calculate the pressure loss in the Flare Tip including the velocity pressure loss. 8
On the Calculations tab, enter 876.3 as the diameter and 3 as the fitting loss in the appropriate fields.
Fig 2.10
Now you have provided all the necessary information about the Flare Tip. 9 Click OK to close the view. Notice that now two new objects have been added to the Process Flowsheet. These may be drawn one on top of the other so you should manually arrange them by clicking and dragging the object icons. 10 Open the Stack Object Editor by double-clicking the pipe icon on the flowsheet and move to the Dimensions tab. 11 Specify the Length as 100 m and the Elevation Change as 100 m. This will result in a vertical pipe measuring 100 m tall. 12 Select the Nominal Diameter as 36 inch and the Pipe Schedule as 40.
Fig 2.11
13 On the Methods tab, confirm that Vertical Pipe and VLE Method are set as Model Default. In this example, every pipe segment uses the default models which are specified on the Methods tab of the Calculation Options Editor. 14 Click OK to close the Stack Object Editor. Now you need to add another pipe segment which will be added using the Pipe Manager.
Completing the Pipe Network 1 Click Pipes in the Build group on the Home tab of the Ribbon. The Pipe Manager will be displayed.
Fig 2.12
2 Click Add. A new pipe will be added to the list. Click Edit. The Pipe Editor will be displayed.
Fig 2.13
3
Change the name to Header 3.
4
Move to the Dimensions tab and enter the following data in the appropriate fields: Field
Value
Length (m)
50
Nominal Diameter (inch)
36
Pipe Schedule
40
5 Click OK to close the Pipe Editor. 6
Close the Pipe Manager by clicking Close. You need to attach Header 3 with Stack using a node. Aspen Flare System Analyzer allows you to choose between a variety of nodes, since you need a simple connection between the two pipes, a Connector node will be used.
7
On the Palette, click the Connector icon and drag it to the Process Flowsheet. This will open the Connector Editor.
Fig 2.14
8
On the Connections tab, enter the new name as Con 1.
9
In the Downstream node field, select Stack and specify the connection at Upstream (of Stack) in the At field.
10 In the Upstream node field, select Header 3 and specify the connection at Downstream (of Header 3) in the At field. 11 Move to the Calculations tab.
Fig 2.15
Notice that by default the Angle has a value of 90 deg and the Fitting loss method is set as Calculated. These and the other entries may be left at their default values for this example. 12 Click OK to close the Connector Editor. Now, a tee will be added, using the Node Manager, to combine the flow from the two sources. 13 Click Nodes in the Build group on the Home tab of the Ribbon. The Node Manager will be displayed.
Fig 2.16
14 Click Add and Select Tee from the list. A new Tee will be added. Click Edit. The Tee Editor will be displayed.
Fig 2.17
15 Change the name to Tee 1 in the Name field. 16 Specify the Downstream node connection to be Header 3 and select Upstream from the At field. 17 Move to the Calculations tab and verify that the Fitting loss methods setting is Miller. The remaining fields may be left at their default values. 18 Close the Tee Editor by clicking OK. 19 Click Close to close the Node Manager. Now, you can add two pipe segments to the upstream and branch section of Tee 1 using the Pipe Manager. 20 Open the Pipe Manager by clicking Pipes in the Build group.
Fig 2.18
21 Click Add to add a new pipe segment. Click Edit to open the Pipe Editor. 22 Change the default pipe name to Tail Pipe 1. 23 Specify Tee 1 as the Downstream node connection and select Branch in the At field. Note: Setting the tailpipe option to Yes will cause the pressure drop to be calculated using the rated flows rather than the actual flow. For this pipe which is a tail pipe to a control valve source, the rated flow and actual flow will be the same so the setting of this option will have no effect.
Fig 2.19
24 Move to the Dimensions tab and specify the Length as 25 m. 25 Set Nominal Diameter as 18 inch from the list. 26 Click OK to close the Pipe Editor for Tail Pipe 1. Repeat Step 21 to add another pipe segment. 27 Change the new pipe segment name to Tail Pipe 2. 28 Specify Tee 1 as the Downstream node connection and select Upstream in the At field. Since this pipe is a tail pipe for a relief valve, set the Tailpipe option to Yes. 29 Move to the Dimensions tab and specify the Length as 25 m. 30 Set Nominal Diameter as 18 inch from the list.
Fig 2.20
31 Click OK to close the Pipe Editor. 32 Close the Pipe Manager by clicking Close. In the Navigation Pane area which is docked to the left side of the Process Flowsheet, select Inputs | Pipes on the Views pane. The Pipes data sheet displays the data for all of the pipe segments:
Fig 2.21
You could also check the Process Flowsheet to ensure that the proper connections have been made. A portion of the Process Flowsheet is displayed below:
Fig 2.22
Defining the Scenarios You now need to define the data for the entire scenario, the Default Scenario, Source 1 Only and Source 2 Only scenarios. Since each case must contain at least one scenario, a set of default scenario data is created when you start a new case. We need to modify this data. 1 Click Scenarios in the Build group on the Home tab of the Ribbon. The Scenario Manager will be displayed.
Fig 2.23
2 Double-click Default Scenario in the Scenarios list.
Fig 2.24
3
The Scenario Editor will be displayed. Alternatively, you could select Default Scenario in the Scenarios list, and then click Edit. Update the header Mach Number limit on the Constraints tab for the Default Scenario as shown below, then click OK to close the Scenario Editor and return to the Scenario Manager.
Fig 2.25
Now we should add the data for the Source 1 Only scenario. 4
Make sure that Default Scenario is highlighted in the Scenarios list on the Scenario Manager. Click Clone. A new scenario will be added to the list as shown below.
Fig 2.26
5 Click Edit to open the Scenario Editor for the new scenario. 6
Change the default name to Source 1 Only and verify the data for the Source 1 Only scenario is the same as shown below.
Fig 2.27
7 Click OK to close the Scenario Editor for Source 1 Only. Repeat Step 4 to add a new scenario. 8
Change the name for the new scenario to Source 2 Only.
Fig 2.28
9
Verify the data for the new scenario on the Constraints tab is the same as shown below.
Fig 2.29
10 Click OK to close the Scenario Editor and return to the Scenario Manager, then click Close to close the Scenario Manager.
Defining the Sources You will now enter the source data for the sources in all scenarios. Since for the first part of the example you will be defining the source compositions in terms of molecular weight, the program preferences must be set to accept the compositions on this basis. 1
Click the aspenONE Button at the upper left corner of the application window. Select Preferences from the Application Menu that is displayed. The Preferences Editor will be displayed.
Fig 2.30
Ensure that Molecular Weight is selected in the Composition Basis field on the Defaults tab.
Fig 2.31
2 Click OK to close the Preferences Editor. Before defining a set of source data, you must select the scenario which corresponds to this data. You will start by defining the data for the Default Scenario. 3
Make sure that the Default Scenario is selected in the Run group on the Home tab of the Ribbon. Any open data views would now display data for this scenario. This field is regarded as the Scenario Selector. You can now add the data corresponding to this scenario for each source.
4 Click Nodes in the Build group. The Node Manager will be displayed:
Fig 2.32
5 Click Add and select Control Valve from the list that is displayed.
Fig 2.33
Click Edit. The Control Valve Editor will be displayed. 6
Change the name to Source 1. Select Tail Pipe 1 in the Outlet field and set connection to be at Upstream (of Tail Pipe 1).
Fig 2.34
7
Move to the Conditions tab and set the Mass Flow as 100000 kg/hr. In this example, the inlet pressure and temperature are the same as the default values, but this will not normally be the case.
Fig 2.35
8
On the Composition tab, specify the Mol. Wt. to be 20. Once you have entered the Mol. Wt. and tabbed to the next field, you will notice the composition will be calculated to give the required Mol. Wt.
Fig 2.36
Note: The Mole Fractions are automatically estimated from the Molecular Weight. Because HC is selected from the list, only hydrocarbon components will be used to match the Molecular Weight. 9 Click OK to close the Control Valve Editor for Source 1. Click Add in the Node Manager to add a new source. The node selection list will again be displayed. 10 Select Relief Valve from the list, and then click Edit to open the Relief Valve Editor. 11 Name the new source as Source 2 on the Connections tab. 12 Select Tail Pipe 2 in the Outlet field and set connection to be at Upstream (of Tail Pipe 2).
Fig 2.37
13 On the Conditions tab, check that the relief valve set pressure or MAWP is set to the default value of 10 bar which is correct for this source. Select the Auto check box next to the Relieving Pressure field. This tells Aspen Flare System Analyzer to calculate the relieving pressure from the MAWP and the selected Contingency, which should be left as Operating in this case. Check that the relieving pressure is calculated as 10.89 bar. 14 Still on the Conditions tab, check that the Allowable Backpressure is set to 5.0 bar. Enter the required Mass Flow rate for this source of 100000 kg/ hr. Select the Auto check box next to the Rated flow field. This tells Aspen Flare System Analyzer to calculate the rated flow for the valve from the specified fluid conditions and properties, valve type and orifice area. 15 Still on the Conditions tab, click the box next to the Orifice Area Per Valve field to select orifice code api_T. Check that the orifice area is
updated to 16774 mm2 and notice the rated flow calculation is updated to reflect the increased orifice area. 16 On the Composition tab, specify the Mol. Wt. of the fluid to be 25. When you tab away from this field, Aspen Flare System Analyzer will calculate the composition of the fluid from the mole weight. Click back on the Conditions tab to confirm that the Rated flow calculation has been updated to give a rated flow of 108,214 kg/hr.
Fig 2.38
17 Click OK to close the Relief Valve Editor. The Node Manager will now appear as follows:
Fig 2.39
18 Close the Node Manager by clicking Close. 19 In the Navigation Pane area which is docked to the left of the Process Flowsheet, select Inputs | Sources on the Views pane. The Sources data sheet for the Default Scenario will be displayed:
Fig 2.40
You must now add the source data for the other two scenarios. 20 Select the Source 1 Only scenario from the Scenario Selector list in the Run group on the Home tab of the Ribbon. Any open data views will now display data for this scenario. 21 Make the following changes to the flowrates from the Sources data sheet in the Source 1 Only scenario (all other information remains the same):
Source 1 - Mass Flow 100000 kg/hr, Mol. Wt. 20
Source 2 - Mass Flow 0 kg/hr, Mol. Wt. 25
Finally reselect the Default Scenario from the Scenario Selector. 22 Next, select the Source 2 Only scenario from the Scenario Selector list in the Run group on the Home tab of the Ribbon. Make the following changes to the Source 2 Only:
Source 1 - Mass Flow 0 kg/hr, Mol. Wt. 20
Source 2 - Mass Flow 100000 kg/hr, Mol. Wt. 25 Finally reselect the Default Scenario from the Scenario Selector.
Rating the Network We have now entered all the model data and can now make the sizing calculations. We will need to set the calculation options before starting the calculations. 1 Click Options in the Run group on the Home tab of the Ribbon. The Calculation Options Editor will be displayed:
Fig 2.41
2
For this example, we are going to use the default methods and settings defined when Aspen Flare System Analyzer creates a new model. This includes the following key options: On the General tab, Calculation Mode should be set to Rating, Enable Heat Transfer check box should be cleared, Include Kinetic Energy check box should be cleared. On the Scenarios tab, Calculate should be selected for All Scenarios.
On the Methods tab, the VLE Method should be set to Compressible Gas, the Enthalpy Method to Ideal Gas and all pressure drop methods to Isothermal Gas. Click OK to close the Calculation Options Editor. You can now start the calculations.
3 Click Run in the Run group on the Home tab.
Fig 2.42
Once the calculations are complete you can review the results. 4 Select Results | Messages from the Views tab on the Navigation Pane. The Messages data view will be displayed.
Fig 2.43
The above view contains general information and warning messages regarding the calculations. 5 Select Source 1 Only from the Scenario selector in the Run group on the Home tab. 6 Select Results | Pressure/Flow Summary from the Navigation Pane. The Pressure/Flow Summary will be displayed:
Fig 2.44
With the Pressure/Flow Summary sheet open, select each scenario in turn using the Scenario Selector in the Run group. Note: In the scenario Source 1 Only, the mach number problem on Tail Pipe 1 is automatically highlighted. 7
At this point, save the model using either the Save icon on the Quick Access Toolbar, or click the aspenONE Button at the upper left corner of the application window then select Save from the Application Menu.
Printing Data and Results To print data and results: 1
Click the aspenONE Button, and then select Print from the Application Menu. The Print dialog box will be displayed.
2
Select the appropriate check boxes for the items that you want to print. Also select the All Scenarios check box to print the results for all of the scenarios instead of just the current scenario. If you want to print to a file, click Text, then specify the file location and File name in the Save dialog box.
3 Click Preview to preview the layout in the Print Preview window before anything is printed.
3 Developing the Model
This section provides information on the following topics:
Overview
Data Requirements
Opening the Old Model
Updating the Model
Defining the Scenarios
Defining the Sources
Sizing the Network
Design Calculations
Overview In this chapter of the Getting Started tutorial you will change the network designed in Chapter 2 to model the tie-in of two new control valves into our current system. The modified system will be simulated for two new scenarios, one each for the new sources. This tutorial assumes that you are familiar with the use of Microsoft Windows and have some prior experience in the design of flare systems. Note: This tutorial is a continuation of the one in the previous chapter and requires that you complete that chapter before continuing with this one. This example consists of the following main parts: 1
Building The Pipe Network - Pipes and nodes will be added using either the Process Flowsheet or the Manager views.
2
Defining the Scenarios - Different scenarios will be set up to simulate various process conditions.
3
Defining The Sources - Relieving sources will be added to each scenario.
4
Sizing the Network - Finally, the pipe network will be simulated and results will be viewed both in textual and graphical form.
Data Requirements Before you can start to upgrade a computer model of the existing flare header system, you must first define all the data that will determine your system.
Pipe Segment Data Data
Description
Connectivity
You would normally have prepared a system sketch that defines the nodes to which the new pipe segments are connected.
Length and fittings loss coefficients for new pipe segment
These will be based upon either a preliminary or detailed isometric drawing of the piping.
Diameter and pipe schedule for each pipe segment
If you are rating an existing network, these will normally be taken from the flare system P&ID. If you are sizing a new flare system, the pipe diameters that you define are relatively unimportant since they will be overwritten by the sizing algorithms. It is recommended that reasonable diameters be defined, so that the sizing algorithm initialises to a condition that will give faster convergence.
Note: When you are sizing a flare system, the initial pipe diameters may affect the solution when there is a liquid phase and the liquid knockout drum is modelled. You should initially size a network using vapour phase methods. The following diagram shows the connectivity of the system which includes the new sources you will be adding in this example.
Fig 3.1
The pipe segments in the network diagram are detailed in the following table. Segment Name
Length (m)
Nominal Diameter (inch)
Schedule
Fittings Loss
Elevation Change (m)
Stack
100
36
40
0
100
Header 1
50
28
30
0
0
Header 2
50
28
30
0
0
Segment Name
Length (m)
Nominal Diameter (inch)
Schedule
Fittings Loss
Elevation Change (m)
Header 3
50
36
40
0
0
Tail Pipe 1
25
18
40
0
0
Tail Pipe 2
25
18
40
0
0
Tail Pipe 3
25
12
40
0
0
Tail Pipe 4
25
18
40
0
0
The new pipe segments Header 1, Header 2, Tail Pipe 3 and Tail Pipe 4 will be added.
Relief Source Data The following data must be specified for the sources: Data
Description
Flow and Composition
These may vary for each scenario that you are evaluating. If a relief source is not used in a particular scenario, the flow may be set to zero. The Flow refers to the quantity of fluid that the source valve must pass as a consequence of the plant upset condition. The Rated Flow refers to the quantity of fluid that the source valve will pass due to its physical construction. Rated flow must always be greater than or equal to flow.
Maximum Allowable Back Pressure (MABP)
This is the maximum pressure that can exist at the outlet of the device (source) without affecting its capacity.
Downstream Temperature
This temperature is used as the pressure independent temperature at which the source enters the network. This temperature is used when ideal gas enthalpies are used to calculate the heat balance, or as an initial guess when any other enthalpy method is used.
Upstream Pressure and Temperature
These are only used if the Ideal Gas enthalpies are not used for the heat balance. These may vary for each scenario that you are evaluating. With relief valves, the flowing pressure should be used.
Discharge Flange Size
This will normally be determined from the relief valve sizing calculations.
In this example, you will consider five scenarios that represent one fire case and four single blocked discharge cases. The following tables define the source data for each scenario. The discharge flange size values are left undefined. In this case, they are assumed to have the same diameter as the attached pipes.
Default Source Data Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
100000
20
15
15
10
5.0
Source 2
100000
25
15
15
10
5.0
Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 3
100000
30
15
15
10
5.0
Source 4
100000
35
15
15
10
5.0
Source 1 Only Data Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
100000
20
15
15
10
5.0
Source 2
0
25
15
15
10
5.0
Source 3
0
30
15
15
10
5.0
Source 4
0
35
15
15
10
5.0
Source 2 Only Data Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
0
20
15
15
10
5.0
Source 2
100000
25
15
15
10
5.0
Source 3
0
30
15
15
10
5.0
Source 4
0
35
15
15
10
5.0
Source 3 Only Data Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
0
20
15
15
10
5.0
Source 2
0
25
15
15
10
5.0
Source 3
100000
30
15
15
10
5.0
Source 4
0
35
15
15
10
5.0
Source 4 Only Data Source Name
Flowrate (kg/hr)
Mol. Wt.
US Temp (C)
DS Temp (C)
US Pres. (bar abs)
MABP (bar abs)
Source 1
0
20
15
15
10
5.0
Source 2
0
25
15
15
10
5.0
Source 3
0
30
15
15
10
5.0
Source 4
100000
35
15
15
10
5.0
System Design Constraints In this case, the following data is used for all scenarios:
Maximum allowable mach number - 0.50 for both main headers and tailpipes. Maximum Noise – 100 dB for both main headers and tailpipes.
Opening the Old Model 1
Start Aspen Flare System Analyzer and open the previously stored case that you have just saved in Chapter 2.
2 Click Open from the Quick Access Toolbar that is docked beside the aspenONE Button on the upper left corner of the application window. -orClick the aspenONE Button, then click Open from the Application Menu that is displayed. -orPress Alt then 2. 3
The Open File dialog box will be displayed.
Fig 3.2
4
Click the Look in field to select the appropriate disk drive and directory.
5
Next, select the file that you created in Chapter 2 from the list, and then click Open.
Updating the Model You need to add new pipe segments to the existing model, but first you must delete the connection between Tee 1 and Header 3. Open the Process Flowsheet and delete the connection as follows: 1 Click Toggle Connect/Arrange Mode on the Process Flowsheet tab on the Ribbon to switch to Connect mode and select the connection between Tee 1 and Header 3.
Fig 3.3
2 Press DELETE. Click Toggle Connect/Arrange Mode again to switch back to Arrange mode. To add a Tee section after Header 3: 3
Open the Node Manager by clicking Nodes in the Build group on the Home tab on the Ribbon.
Fig 3.4
4 Click Add and select Tee from the list that is displayed. Click Edit. The Tee Editor will be displayed:
Fig 3.5
5
Specify the name to be Tee 3, the Downstream node connection to be Header 3 and select Upstream from the At field.
Note: Since this example is of smaller size, therefore the Location field will be left blank. This field is only useful for larger case with multiple sections (areas) within a same plant. 6
Move to the Calculations tab and verify that the Fitting Loss Method setting is Miller.
7
Close the Tee Editor by clicking OK.
8 Click Close to close the Node Manager. Now, you can add two pipe segments to the upstream and branch section of Tee 3 using the Pipe Manager. 9
Open the Pipe Manager by clicking Pipes in the Build group.
Fig 3.6
10 Click Add to add a new pipe segment. Click Edit to open the Pipe Editor. 11 Change the default pipe name to Tail Pipe 4. 12 Specify Tee 3 as the Downstream node connection and select Branch in the At field.
Fig 3.7
13 Move to the Dimensions tab and specify the Length as 25 m. 14 Select Nominal Diameter as 18 inch from the list provided. 15 Click OK to close the Pipe Editor. Repeat Step 10 to add another pipe segment. 16 Change the default name of the new pipe segment to Header 2. 17 Specify Tee 3 as the Downstream node connection and select Upstream in the At field. 18 Move to the Dimensions tab and specify the Length as 50 m. 19 Set Nominal Diameter as 28 inch and Schedule as 30 from the list provided.
Fig 3.8
20 Click OK to close the Pipe Editor. 21 Close the Pipe Manager by clicking Close. Notice that three new objects have been added to the Process Flowsheet. You can manually arrange them by clicking and dragging the object icons. Now you will add a tee section using the Palette. 22 Open the Palette (if it is not displayed) by clicking the Palette icon on the Process Flowsheet tab on the Ribbon. 23 Click the Tee icon in the Palette window, drag and drop it to the Process Flowsheet. Since the Edit Objects on Add check box is selected, The Tee Editor will be displayed.
Fig 3.9
24 Change the default name to Tee 2. 25 Specify Header 2 as the Downstream node connection and select Upstream in the At field. On the Calculations tab, verify the Fitting loss method is Miller. 26 Close the Tee Editor by clicking OK. Now, you can add two pipe segments to the upstream and branch section of Tee 2 using the Palette. 27 Click the Pipe icon, drag and drop it onto the Process Flowsheet to add a new pipe segment. 28 On the Pipe Editor, change the default pipe name to Tail Pipe 3. 29 Specify Tee 2 as the Downstream node connection and select Branch in the At field.
Fig 3.10
30 Move to the Dimensions tab and specify the Length as 25 m. 31 Verify that the Nominal Diameter is 12 inch. 32 Close the Pipe Editor by clicking OK. 33 Repeat Step 27 to add another pipe segment. 34 Change the default name of the new pipe segment to Header 1. 35 Specify Tee 2 as the Downstream node connection and select Upstream in the At field. 36 Specify Tee 1 as the Upstream connection and select Downstream in the At field. 37 Move to the Dimensions tab and specify the Length as 50 m. 38 Set Nominal Diameter as 28 inch and Schedule as 30.
Fig 3.11
39 Click OK to close the Pipe Editor. Select Inputs | Pipes from the Views menu on the Navigation Pane. The Pipes data sheet displays the data for all of the pipe segments:
Fig 3.12
At this point you might want to rearrange the new items on the Process Flowsheet. The Process Flowsheet should be similar as displayed below:
Fig 3.13
Defining the Scenarios You now need to define the data for the new scenarios, the Source 3 Only and Source 4 Only scenarios. The existing model already contains three scenarios which you will still be using in this example. To add the new scenarios: 1 Click Scenarios in the Build group on the Home tab o the Ribbon. The Scenario Manager will be displayed.
Fig 3.14
2 Click Default Scenario in the Scenarios list to highlight it. Click Clone. A new scenario is added to the list.
Fig 3.15
3 Click Edit to open the Scenario Editor. 4
Change the default name to Source 3 Only. On the Constraints tab, verify that the values of the Mach Number in both Headers and Tailpipes groups are 0.5 as shown below:
Fig 3.16
5
Repeat Step 2 to add a new scenario. Click Edit.
6
Change the default name for the new scenario to Source 4 Only.
Fig 3.17
7
Verify that the values of the Mach Number on the Constraints tab in both Headers and Tailpipes groups are 0.5.
8 Click OK to close the Scenario Editor and return to the Scenario Manager. Now select Default Scenario and click Current to make this the working scenario. Click Close to close the Scenario Manager.
Defining the Sources You will now enter the source data for the sources in all scenarios. Since for the first part of the example you will be defining the source compositions in terms of molecular weight, the program preferences must be set to accept the compositions on this basis as described in Chapter 2. 1 Click Nodes in the Build menu on the Home tab. The Node Manager will be displayed.
Fig 3.18
2 Click Add and select Control Valve from the list displayed.
Fig 3.19
Click Edit. The Control Valve Editor will be displayed:
Fig 3.20
3
Change the default name to Source 3. Select Tail Pipe 3 in the Outlet field and set connection to be at Upstream (of Tail Pipe 3).
4
Move to the Conditions tab and set the Mass Flow as 100000 kg/hr.
Fig 3.21
5
On the Composition tab, specify the Mol. Wt. to be 30.
Note: The composition will be calculated as soon as you tab away from the Mol. Wt. field.
Fig 3.22
Note: The Mole The Mole Fractions Fractions are automatically estimated from the Molecular Weight. Because HC HC is is selected, only hydrocarbon components will be used to match the Molecular Weight. 6 Click OK to OK to close the Control the Control Valve Editor for Source for Source 3. 3. 7
Repeat Repeat Step 2 to add a new source. source. Again select select Control Control Valve and the Control Valve Editor will be displayed.
8
Name the the new source source as as Source 4. 4.
9 Select Tail Select Tail Pipe 4 in 4 in the Outlet the Outlet field field and set connection to be at Upstream (of Tail Tail Pipe 4). 4).
Fig 3.23
10 Repeat 10 Repeat 4-6 to add all the information required by the scenario. Specify Mole Wt. to Wt. to be 35 on 35 on the Composition the Composition tab. tab. 11 Click 11 Click OK to OK to close the Control the Control Valve Editor. Editor . The Node The Node Manager will now appear as follows:
Fig 3.24
12 Close 12 Close the Node the Node Manager by clicking Close clicking Close.. 13 Select 13 Select Inputs Inputs | Sources from the Views the Views menu menu on the Navigation Pane. The Sources The Sources data data sheet for the Default the Default Scenario will be displayed:
Fig 3.25
14 You 14 You must now add the source data for the four scenarios. 15 Select 15 Select the scenarios from the Scenario Selector in Selector in the Run group Run group on the Home tab. Home tab. Any open data views will display data for the selected scenario. Make the following changes to the flowrates in all scenarios: Scena enarios
Source 1 (kg/hr)
Source 2 (kg/hr)
Source 3 (kg/hr)
Source 4 (kg/hr)
Source 1 Only
100000
0
0
0
Source 2 Only
0
100000
0
0
Scena enarios
Source rce 1 (kg/hr)
Source 2 (kg/hr)
Source 3 (kg/hr)
Source 4 (kg/hr)
Source 3 Only
0
0
100000
0
Source 4 Only
0
0
0
100000
For each scenario, ensure that the sources which have a flowrate of 0 are ignored (i.e. ignored (i.e. select the Ignore check Ignore check box for the source). Note: You Note: You can also add the single source scenarios by selecting the Add Single Source Scenarios tool from Source from Source Tools in Tools in Tools group group on the Home tab. Home tab.
Sizing the Network You have now entered all the model data and can now make the sizing calculations. You will need to set the calculation options before starting the calculations. 1 Select Options Select Options in in the Run group Run group on the Home the Home tab. tab. The Calculation The Calculation Options Editor will Editor will be displayed:
Fig 3.26
2
For the first calculation of this example ensure that the following options are set: On the General tab, Calculation Mode should be set to Rating, Enable Heat Transfer check box should be cleared, Include Kinetic Energy check box should be cleared, Ignore Source to Pipe Pressure Loss in Design Mode should be selected.
On the Scenarios tab, the Calculate box should be set to Current Scenario. On the Methods tab, the VLE Method should be set to Compressible Gas, the Enthalpy Method to Ideal Gas and all the Pressure Drop methods to Isothermal Gas.
3 Click OK to close the Calculation Options Editor. Ensure that the Default Scenario is selected using the Scenario Selector on the Home tab. You can now start the calculations. 4 Click Run in the Run group.
Fig 3.27
Once the calculations are complete you can review the results. 5 Select Results | Messages from the Views pane on the Navigation Pane. The Messages sheet will be displayed.
Fig 3.28
The above view contains general information and warning messages regarding the calculations. In this case the mach number exceeds the design value of 0.5 for Tail Pipe 3, which was defined for each scenario. It also shows both upstream and downstream pipe segment mach number for each violation. It is due to smaller pipe segments causing very high fluid velocities across the pipe segment. At this point, it is a good idea to save your case before doing detail design. 6
Click the aspenONE Button on the upper left corner of the application window, and then select Save As from the Application Menu that is displayed. Save the file as Getting Started 2 Rating.fnwx.
Design Calculations 1
We will now use Aspen Flare System Analyzer's design capabilities to redesign the network to resolve the mach number problem we have identified in the rating calculation we have just completed.
Use the Calculation Mode selector in the Run group on the Home tab of the Ribbon to change the calculation mode to Debottleneck. This calculation mode will redesign the flare system to meet our defined system limits without reducing the current sizes of any pipes. 2
Click the Run icon on the Ribbon. After the calculation has been completed, you can review the new results.
Fig 3.29
3 Select Results | Messages from the Views pane, and then select the Sizing tab to see a list of changes that Aspen Flare System Analyzer has made to the network. 4 Select Results | Pressure/Flow Summary. The Pressure/Flow Summary data sheet will be displayed.
Fig 3.30
Notice that the upstream and downstream mach numbers are now within the design specification for the given scenario. You can use the bottom scroll bar to move across the columns. We now have a flare system that is designed correctly for the Default Scenario where all sources are relieving but we have not yet checked that it is adequate for all of the scenarios. To do this we will do a Rating calculation for all of the scenarios.
5
Open the Calculation Options Editor by clicking Options in the Run group on the Home tab. Set the Calculation Mode to Rating on the General tab. On the Scenarios tab, set the Calculate option to All Scenarios. After closing the Calculation Options Editor, click the Run icon to run the rating check.
6
When the calculations have finished, select Results | Messages from the Views pane. Click the Problems tab where any violations of our system design limits will be displayed. You will see that Aspen Flare System Analyzer has detected a violation of the mach number limits for the tail pipes in the single source scenarios.
Fig 3.31
The reason for this is that the lower back pressure in the system when only a single source is relieving means that the gas density is reduced resulting in higher velocities. 7
To fix this problem with our design we will re-run the Debottleneck calculations for all the scenarios. Use the Calculation Mode selector on the Ribbon to change the calculation mode to Debottleneck and then click the Run icon.
8
When completed, review the Problems tab of the Messages view to confirm that the flare system now meets all our design limits in all scenarios. The Sizing tab will show which pipe sizes have been increased.
Fig 3.32
Note: We could have run the Debottleneck calculations for all scenarios immediately after our first rating calculation and obtained the same results. While this might have been faster, we have obtained a better understanding of which scenarios have caused changes to pipe sizes by doing our calculations in stages. 9 Select Results | Pressure/Flow Summary from the Views pane on the Navigation Pane. The Pressure/Flow Summary will be displayed.
Fig 3.33
Notice that the upstream and downstream mach numbers are now within the design specification for the given scenario. You can use the bottom scroll bar to move across the columns.
