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Jump Start: Pressure Safety Valve Sizingin Aspen HYSYS
A Brief Tutorial (and supplement to training and online documentation)
Nicholas Brownrigg, Product Marketing, Aspen Technology, Inc.
Wilfried Mofor, Product Management, Aspen Technology, Inc.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Adding a Pressure Relieving Device to a HYSYS Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Designing and Sizing a Pressure Safety Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Valve Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Scenario Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Sizing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Multiple Valve Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Line Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Documentation Builder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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IntroductionWhen designing a chemical process and its equipment, safety is of substantial concern. All possible strategies should be
considered to eliminate the risk of accident and injury when implementing a process design.
One safety concern that occurs frequently in a plant is the over-pressurization of equipment or piping. In order to prevent
dangerous bursts, explosions, and fires, pressure relief valves are designed and installed to bleed out excess liquid or vapor
causing pressure build-up.
Process conditions vary vastly at each location of a pressure relief valve. Because of this, and the strict regulation of safety
equipment, completing a design of a pressure relief valve by hand can be a time consuming and laborious exercise. To
solve this problem, Aspen HYSYS V8.3 has a pressure safety valve sizing feature, which uses data from a process
simulation to help automate PSV calculations.
Aspen HYSYS uses common valve design standards, most notably API 520, 521, to determine pressure relief valve sizing
information and values. 25 common overpressure scenarios are included in the program and can be analyzed and sized for.
Aspen HYSYS also features a line sizing functionality, allowing the user to quickly choose the schedule and diameter
according to pressure drop and fluid velocity constraints for piping entering and leaving the pressure safety valve. Line
sizing is completed in Aspen HYSYS without having to perform any fluid flow computations.
The documentation builder pulls valve sizing and process variable information directly from simulation to automatically
complete required forms normally requiring manual incorporation.
This Jump Start guide will walk the reader through the process of using pressure relief valve features in Aspen HYSYS
towards designing a pressure relief valve. AspenTech recommends that a range of other resources be called upon in
conjunction with this document to give the user a comprehensive view of how to use Aspen HYSYS. These may include:
AspenTech support website (support.aspentech.com) contains information on the use of AspenTech products and
provides answers to frequently asked questions.
AspenTech courseware available in on-line and in-person versions
AspenTech business consultants
This document will show how to size pressure safety valves using Aspen HYSYS V8.3. It assumes that the user has Aspen
HYSYS V8.3 or higher installed on her or his computer and a functional process design completed.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Adding a Pressure Relieving Device to a HYSYS SimulationIn order to add a pressure safety valve to a HYSYS process flowsheet, the user must enter the Safety Analysis
environment. This environment provides a setting for relief scenario setup and PSV sizing and documentation.
After designing a process in Aspen HYSYS and converging the simulation, click on Pressure Relief in the Home ribbon of
the HYSYS Simulation environment to enter the Safety Analysis environment. Alternatively, the Safety Analysis button,
located on the bottom left of the Aspen HYSYS program, can be used. Both options are shown below in Figures 1 and 2.
Figure 1. Pressure Relief Button on Home Tab
Figure 2. Safety Analysis Option in Aspen HYSYS
After opening the Safety Analysis viewing window, select the Unit Operations option in the navigation pane on the left of
the screen. This will display all the unit operations and subflowsheets present in the simulation for which a pressure safety
valve can be designed. Also, in the navigation pane is the Unattached Streams option, in which floating/dangling
streams with no connections to process models are located (Figure 3).
Figure 3. Location of Unit Operations and Unattached Streams Menus in Safety Analysis Panel
To add a PSV to a simulation, click the Add PSV option on the ribbon in the Safety Analysis environment. This switches
the cursor into attach mode. Move the mouse to hover over the arrow of a stream on which a PSV is necessary. A blue
box appears as the target for unit operation exit streams. Click on the blue box to attach a relief valve to that location.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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Figure 4. Add PSV Option in Safety Analysis Environment
A PSV can also be added using the navigation pane. Open the Unit Operations or Unattached Streams node and right
click the desired block or stream. Scroll to highlight the Create PSV option. When prompted, select which stream the
valve should be located on. An example of this PSV addition method is shown in Figure 5.
Figure 5. Adding a Pressure Safety Valve and Selecting the Appropriate Stream
A PSV will be placed on the flowsheet in the Safety Analysis environment after following one of the methods described
above. Figure 6 shows an example flowsheet with a PSV attached to a stream connected to a process unit, while Figure 7
shows a PSV attached to a single stream unaffiliated with any unit operations.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Figure 6. Process Stream with PSV
Figure 7. Unattached Stream with PSV
Designing and Sizing a Pressure Safety ValveAdding a pressure safety valve to a unit operation in a simulation allows the user to open tabs in which the pressure safety
valve can be designed and sized to meet relief specifications and requirements.
Valve Design
Double-clicking on a pressure safety valve on the flowsheet opens the Valve Design tab, shown in Figure 8. In this tab,general valve design details are input.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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Figure 8. Valve Design Tab
First, choose the appropriate options from the dropdown menus to define the valve material of construction, valve type,
and valve discharge. Next, the valve design temperature and the set pressure at which the valve opens should be specified.
After doing so, set a value for the superimposed backpressure present in the valve, according to design calculations.
If the valve will have a rupture disk, ensure that the Rupture Disk Factor entry has a value of 0.9. If there will be no rupture
disk, this value should be 1.
Click the Create Scenario button above the scenario list table to evaluate multiple relief scenarios for which a relief valve
is necessary and obtain PSV sizing for each scenario. The Create Scenario button and a populated scenario list table are
shown in Figure 9.
Figure 9. Creating a Scenario in the Valve Design Tab
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
After clicking the Create Scenario option, a new pressure relief scenario is created in the scenario list table. To open the
Scenario Setup tab and obtain a relief load and PSV size, simply click the emergency scenario name on the scenario list
table.
Another method of opening the Scenario Setup tab is to return to the Unit Operations tree in the navigation pane (Figure
10). Click the PSV option under its corresponding unit block to open the scenario listing. Then, choose the applicablescenario to open the Scenario Setup tab.
Figure 10. Opening Scenario Setup Tab from Unit Operations Tree
Scenario Setup
After clicking on a scenario or choosing a scenario from the navigation pane, the Scenario Setup tab, shown in Figure 11,
appears.
Figure 11. Scenario Setup Tab
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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Included in Aspen HYSYS are four different design codes. The four codes are API 520 & 521, ASME VIII, PD 5500, and EN
13445. Select the pertinent design code from the dropdown menu before continuing.
Enter the relieving temperature necessary for the given relief scenario being analyzed before proceeding to calculation of
the relieving pressure. Click the Calc button next to the Relieving Pressure box to bring up the window shown in Figure
12.
Figure 12. Relieving Pressure Calculation Window
In the Relieving Pressure Calculation window, input the allowable overpressure percentage, which determines the amount
of pressure that can build up beyond the set pressure before the valve opens. After finishing, verify that the relieving
pressure is correct, and select OK to continue.
Similar to the Relieving Pressure Calculation window, clicking Calc next to the Total Backpressure box opens the
window displayed in Figure 13. Set the parameters describing the backpressure and click OK to continue.
Figure 13. Backpressure Calculation Window
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Enter the valve discharge coefficient if the value differs from the default value of 0.9750. Then, choose the failure scenario
type under the Relief Load grouping. To obtain a relieving flow load, a manually calculated value can be entered or the
reference flow value from the HYSYS process stream that the PSV is attached to can be used. Additionally, if a relief
scenario that is highlighted in blue on the scenario list (Fire, Control Valve Failure, Exchanger Tube Rupture, Fan Failure, or
Reflux Failure) is chosen, the relief load can be calculated in Aspen HYSYS by selecting the Calculated radio button and
by providing more parameters surrounding the scenario where prompted. Figure 14 shows the scenarios available in the
Scenario Type list, while Figure 15 shows a sample relieving load calculation for a Fire relief scenario..
Figure 14. Relief Load Scenarios Available
Figure 15. Sample Calculation of Relieving Flow for Fire Relief Scenario
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Figure 17. Selected Orifice Dropdown Box with Options
If the scenario being analyzed is the basis case for which the valve is sized, select the Sizing Case box, next to theScenario Name input box. Then, return to the Valve Design tab to proceed to line sizing for the relief valve.
Multiple Valve Sizing
If the computed relief load is too large to be relieved using just one pressure safety valve, it is necessary to pass the
relieving flow through multiple pressure valves. Successful sizing of multiple valves for a stream in Aspen HYSYS requires
returning to the Simulation environment and using a tee splitter block to divide the relief load stream into multiple streams
equal to the number of relief valves necessary. Figure 18 shows an example flowsheet with a tee splitter for the Vap
Outlet stream in the process split into two separate relief load streams.
Figure 18. Tee Block to Size Multiple Valves for Vap Outlet Stream
Double-click the stream entering the tee block, and define its conditions, properties, and composition by selecting the
Define from Other Stream button that appears in the material stream window (Figure 19), and then select the
appropriate stream to be relieved by multiple valves.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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Figure 19. Define from Other Stream Option in Relief Load Material Stream Window
Return to the flowsheet, double-click the tee block, go to the parameters section, and input the appropriate flow ratio for
each stream exiting the splitter to define how the flow of the relief load will be split amongst the valves (Figure 20).
Figure 20. Defining the Flow Ratio for the Relief Load Splitter
After setting up the tee block to split the relief load flow, return to the Safety Analysis environment. Add a PSV to each
stream exiting the tee block, such that the streams exiting the tee block look similar to the ones shown in the flowsheet in
Figure 21.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Figure 21. Safety Analysis Environment Flowsheet with PSVs Attached
Proceed to size the safety valves as previously described in this guide, except use a 16% allowable overpressure when
determining the relieving pressure for the valve with the highest flow rate and an 11% allowable overpressure for allsubsequent valves with lesser flowrates.
Line SizingReturn to the Valve Design tab after creating and sizing all scenarios requiring a pressure relief valve. The scenario list in
the Valve Design tab will now be populated with sizing information regarding each scenario. If not done before, use the
Sizing Case check box on the scenario list, Figure 22, to choose which failure scenario the valve will be sized for.
Figure 22. Scenario List Table Inside Valve Design Tab with Selected Sizing Case Scenario
Selecting a sizing case enables the Line Sizing tab for selection. Click the Line Sizing tab, as shown in Figure 23, to begin
line sizing for the pressure safety valve.
Figure 23. Location of Line Sizing Tab
Under the line sizing tab, the piping in and out of the pressure safety valve can be chosen. If the pipe size chosen by the
user is too small to accommodate relief flow or too large such that the pressure gradient will not allow for relief flow,
Aspen HYSYS will alert the user using the bar on the bottom of the tab so that an incorrect design is not selected. If the
bar is green, it means that an appropriate line size has been selected, while yellow means there is either a fluid pressure or
velocity constraint being violated by the chosen line sizing.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Figure 26. Example Built-in HYSYS PSV Calculation Report
Clicking the Documentation Builder option initiates Microsoft Access, which houses the customizable forms to be
completed after designing and sizing a pressure relief valve. From the documentation builders home screen, shown below
in Figure 27, a list of relief devices sized in Aspen HYSYS can be edited or viewed. Additionally, process data sheets,
mechanical data sheets, calculation summary sheets, or relief load summary sheets can be constructed. Information from
the sheets can be exported to Microsoft Excel by selecting any of the respective Export options.
Figure 27. Microsoft Access Documentation Builder Selection Screen
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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Choosing the edit option for any of the forms from the documentation builder brings up a screen allowing the user to
change the information that will appear in the final, viewable report. Many entries are already populated by values pulled
directly from Aspen HYSYS. These are denoted in grey. The spaces in white require user input to be completed. A sample
edit page for a mechanical data sheet is shown in Figure 28.
Figure 28. Edit Page for Mechanical Data Sheet
After entering the pertinent information for a datasheet on its edit page, return to the documentation builder home
screen, then select View to see a copy of the finalized version of the document chosen. After opening a document using
the View option, it can then be saved electronically or printed. Figure 29 shows a completed sample mechanical data
sheet, given the input information from the edit page shown in Figure 28.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
Figure 29. Completed Example Mechanical Data Sheet
Completing documentation using the documentation builder in Aspen HYSYS reduces the time needed to complete safety
valve paperwork to submit to regulatory agencies and valve vendors.
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Jump Start: Pressure Safety Valve Sizing in Aspen HYSYS
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ConclusionsPressure relief valve design and sizing can be a tedious, lengthy process. Relief valve sizing in Aspen HYSYS allows the
user to design pressure relief valves quickly using a small amount of process information at the location of the valve.
Aspen HYSYS now encompasses all facets of the valve design process into one convenient location. In addition, various
scenarios involving multiple valves can be explored to find the most optimal relief schedule for a unit.
Aspen HYSYS can also serve as an accuracy check to ensure that safety equipment has been properly rated and will
perform properly, if needed. It helps designers complete their work faster so that safety equipment can be installed and
implemented sooner. All processes need to have proper safety precautions to avoid disaster and Aspen HYSYS continues
to help make all processes as safe as possible with each use.
References1. American Petroleum Inst., Sizing Selection, and Installation of Pressure-Relieving Devices in Refineries, ANSI/API
RP 520, 8th Ed., Part 1: Sizing and Selection, Washington D.C., Dec. 2008.
Additional Resources
Public Website:
http://www.aspentech.com/products/aspen-hysys.aspx
Online Training:
http://www.aspentech.com/products/aspen-online-training
AspenTech YouTube Channel:
http://www.youtube.com/user/aspentechnologyinc
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