11-5785 JS StorageTank FINAL

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2014 Aspen Technology, Inc. AspenTech, aspenONE, the Aspen leaf logo, the aspenONE logo, and OPTIMIZE are trademarks of Aspen Technology, Inc. All rights reserved.11-5785-0614

Jump Start: Storage Tank Protection in Aspen HYSYS

and Aspen Plus

A Brief Tutorial (and supplement to training and online documentation)

Anum Qassam, Product Management, Aspen Technology, Inc.

Jennifer Dyment, Product Marketing, Aspen Technology, Inc.


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Jump Start: Storage Tank Protection in Aspen HYSYS and Aspen Plus

Table of Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Initial Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Adding a Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Tank Design Tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Initial Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Tank Design Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Normal Venting Tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Initial Set Up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Normal Venting Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Normal Venting Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Emergency Venting Tab. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Initial Set Up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Emergency Venting Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Emergency Venting Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12


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IntroductionWithout appropriate safety precautions, low pressure storage tanks can fail due to excessive pressure or vacuum. The

Safety Environment in Aspen HYSYS and Aspen Plus provides calculation methodologies to quantify the required normal

and emergency venting capacity of a low-pressure storage tank in accordance with the API 2000.

This is not meant to be used as a stand-alone reference document. AspenTech recommends that a range of other

resources be referenced to give the new user a comprehensive view of how to use Aspen HYSYS and Aspen Plus. These

may include:

Jump Start Guide: Relief Sizing in Aspen HYSYS and Aspen Plus V8.6

AspenTech support website (support.aspentech.com)

AspenTech courseware available in on-line and in-person versions

AspenTech business consultants

Additional jump start guidesavailable on a variety of related topics

This document provides a detailed overview of the steps required to determine the normal and emergency venting

requirements for low pressure storage tanks within the Safety Environment of Aspen HYSYS and Aspen Plus.

Aspen Plus or Aspen HYSYS can be used to follow this jump start guide. Use the example file PRESSURE RELIEF

STARTER.hsc in Aspen HYSYS or the example file Safety Analysis without PRD.bkp in Aspen Plus. Both files are

available on aspenONE Exchange.

Initial SetupAll examples and screenshots in this guide are based on the example file PRESSURE RELIEF STARTER.hsc in Aspen

HYSYS. If more familiar with Aspen Plus, use the Safety Analysis without PRD.bkp file instead. Make sure that the

correct units are selected when specifying parameters when prompted.

To begin, you should:

1. Open the file PRESSURE RELIEF STARTER.hsc or Safety Analysis Without PRD.bkp

2. Run the case (Aspen Plus only)

3. Enter the Safety Analysis Environment

Adding a Storage TankThis section describes how to add storage tanks to the Safety Environment. Open the Tank Manager by clicking on the

Storage Tank Protection button on the Home tab of the ribbon, shown in Figure 1. You can get to the Tank Manager by

selecting the Storage Tank Protection heading on the Navigation Pane, shown in Figure 2.
http://www.aspentech.com/Pressure-Safety-Valve-Sizing-HYSYShttp://support.aspentech.com/http://www.aspentech.com/Pressure-Safety-Valve-Sizing-HYSYShttp://support.aspentech.com/


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Figure 1: Open Tank Manager from Ribbon

Figure 2: Open Tank Manager from Navigation Pane

The Tank Manager should be visible. Click the Add button to add a new storage tank, as shown in Figure 3.

Figure 3: Add a Storage Tank on the Tank Manager Tab

Clicking the Add button will result in a new row added to the Tank Manager. Open up the Storage Tank tab by either (1)

selecting the newly-created entry and clicking the Edit button (see Figure 4) or (2) double-clicking on the Tank Manager

row to open up the Storage Tank tab.

Figure 4: Open a Storage Tank Form


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Figure 5: Adding a Storage Tank from Navigation Pane

You should now see the Storage Tank form, which is shown in Figure 6.

Figure 6: Tank Design tab

Tip: You can quickly add a storage tank by opening up the Storage Tank tab by right-clicking the Storage Tank

Protection heading on the Navigation Pane and selecting Add Storage Tank from the menu that appears, as shown

in Figure 5.


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Tank Design TabThis section details the various inputs in the Tank Design tab, and the effect of the input on the normal and emergency

venting calculations.

Initial Set Up

In the Tank Design tab, the Tank Name, Service, and Tank Design Code do not affect the storage tank calculation. These

inputs are only for reporting purposestheir parameters are highlighted in Figure 7.

Figure 7: Tank Parameters for Reporting Purposes Only

The Tank Type determines which equations are used to calculate the tank volume and tank exposed area to determine the

heat input for the emergency venting calculation. Available values for the Tank Type are shown in Figure 8. Technical

details on the calculation are available in the F1 help.

Figure 8. Tank Type Available Values

Select a Stream from the simulation environment to represent the fluid inventory in the tank. The Safety Environment will

use the selected Stream's properties for the following variables: Tank Vapor Molecular Weight, Relieving Gas

Temperature, and Relieving Gas Molecular Weight.

To select a stream from the simulation environment, check the Use Stream box, shown in Figure 9.

Figure 9: Use Simulation Stream to Represent Tank Fluid

In the dialog box that appears, select the stream from the Simulation Environment that best represents the fluid in the

tank. If following along with the example file, select the stream FeedStream, then click the OK button. These steps are

highlighted in Figure 10. Figure 11 displays the completed setup.


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Figure 10: Select Reference Stream Dialog Box

Figure 11: Example of Completed Storage Tank Set Up

Tank Design InputsThis section details the tank-specific parameters necessary for the normal and emergency calculations. Figure 12 shows

sample values for each parameter. Each parameter is then described in detail beneath the figure.

Figure 12: Tank Design Sample Inputs


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1. Barometric Pressure: This value is used to adjust gauge pressures in this tank system only.

2. Design Pressure: Maximum pressure that the tank wall and structure can handle.

3. Operating Pressure: Pressure during the normal operation of the tank. This value must be less than the Design

Pressure of the tank and the Set Pressure of protecting devices.

4. Diameter: Diameter of the tank.

5. Height: Height of the tank.

6. Maximum Operating Temperature: Maximum possible temperature during the normal operation of the tank. This

value is used to determine the Inbreathing/Outbreathing flow relationship used and Thermal C-factor for Normal

Venting calculations. This value must be less than the design temperature of the tank.

7. Latitude: Select the latitude of the system, which is used to determine the Y-factor in the thermal

Inbreathing/Outbreathing in the Normal Venting calculations.

8. Vapor Pressure: Select the type of Vapor Pressure, which is used to calculate the C-factor for the thermal

Inbreathing/Outbreathing in the Normal Venting calculations.

9. Evaporation Rate: Evaporation rate of the products in the tank. For products stored above 40C with Vapor

Pressure of less than 5 kPa, the Evaporation Rate is added to the Outbreathing term. Use zero when the Maximum

Operating Temperature is less than 40C (104F).

Insulation Details

This section describes how to account for insulation on the tank (if needed). If no insulation is present, then Insulation

Area Fraction is 0 and all other parameters are deactivated. Figure 13 shows sample values for each parameter, along with

descriptions for each below.

Figure 13: Insulation Sample Inputs

1. Insulation Area Fraction: In this field, type a real value between 0 and 1. The default value is 0 and is calculated as

the ratio of the insulated surface area of the tank to the total tank surface area (including the shell and the roof of

the tank). Use 1 for fully insulated tanks, 0 for non-insulated tanks, and 0 < Ainsulated / Atotal < 1 for partially

insulated tanks.

2. Insulation Thickness: In this field, type the wall thickness of the insulation layer.

3. Thermal Conductivity (Normal): In this field, type the value of the Thermal Conductivity, , of the insulation

material at operating temperature conditions. This value is used in the Normal Venting calculations to get the

thermal breathing insulation reduction factor.

4. Thermal Conductivity (Fire): In this field, type the value of the Thermal Conductivity, , of the insulation material

at fire temperature conditions (538 C or 1000 F). This value is used in the Emergency Venting calculations to

obtain the environmental (F) factor.


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Normal Venting TabThis section describes how to calculate the normal venting requirements (Inbreathing and Outbreathing).

Initial Set Up

Click on the Normal Venting tab shown in Figure 14 in the example file.

Figure 14: Normal Venting Tab

There are instances where Normal Venting calculations are not applicable, such as with floating roof tanks. You can

disable the Normal Venting calculations for a tank by unchecking the Calculate Normal Venting Size check box. For the

purposes of this example, the box will remain checked (see Figure 15).

Figure 15: Disable Normal Venting Calculations

The Normal Breathing Device Name and Breathing Device Type highlighted in Figure 16 are for documentation purposes

only.

Figure 16: Normal Venting Parameters for Reporting Purposes Only


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Normal Venting Inputs

In order to continue the Inbreathing and Outbreathing calculations, specify the PRD-specific calculaton parameters. Figure

17 shows sample values for each parameter, along with descriptions for each below.

Figure 17: Normal Venting Sample Inputs

1. Set Pressure: Type a real value between 0 and 15 psig. This is the pressure at the inlet of the device, at which the

relief device starts opening under service conditions.

2. Vacuum Set Pressure: Type a real value between 0 and 15 psig that is less than the tank's Operating Pressure. This

value is the pressure at the inlet of the relieving device that protects vacuum conditions.

3. Maximum Liquid Inflow: Maximum volumetric tank-filling rate; used to determine the Outbreathing flow.

4. Maximum Liquid Outflow: Maximum volumetric tank discharging rate; used to determine the Inbreathing flow.

5. Tank Vapor Molecular Weight: Molecular weight of vapor above the liquid content of the tank. The default value

is 28.8.

Normal Venting Results

After you type values for the basic information and the Normal Venting Inputs, calculated values for Inbreathing and

Outbreathing appear for the parameter shown in Figure 18. Each parameter is then described in detail beneath the figure.

Figure 18: Normal Venting Sample Results

1. Liquid Movement: The total Inbreathing/Outbreathing volumetric flow, expressed as flow of air (Nm3/h normal

conditions at 0C/32F or SCFH standard conditions at 15.6C/60F).

2. Thermal: Normal Inbreathing originating from a maximum decrease in the vapor-space temperature leading to

contraction or condensation of vapors. Normal Outbreathing originating from a maximum increase in the vapor-

space temperature leading to contraction or condensation of vapors.

3. Total: Sum of thermal and liquid transfer effects.


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4. Preliminary Device Area: The preliminary area required for the calculated volumetric Inbreathing and

Outbreathing relief load.

5. Preliminary Calculated Size: The preliminary orifice diameter required for the calculated volumetric Inbreathing

and Outbreathing relief load.

Emergency Venting TabThis section describes how to calculate the emergency fire venting requirement.

Initial Set Up

Click on the Normal Venting tab shown in Figure 19 in the example file. Emergency Device Name and Emergency Device

Type, highlighted in Figure 19, are for documentation purposes only.

Figure 19: Emergency Venting Tab

There are instances where Emergency Venting calculations are not applicable (no flammable inventory within tank farm,

for example). The user can disable the Emergency Venting calculations for a tank by unchecking the Calculate Emergency

Venting Size check box. For the purposes of this example, the box will remain checked (see Figure 20).

Figure 20: Disabling Emergency Venting Calculations


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Emergency Venting Inputs

In order to continue the Emergency Venting calculations, the user must specify the PRD-specific calculation parameters.

Figure 21 shows sample values for each parameter, along with descriptions for each below.

Figure 21: Emergency Venting Inputs

1. Set Pressure: Pressure at which the relieving device starts to open upon service conditions. Type a real value

between 0 and 15 psig.

2. Bottom Tan Above Grade: The vertical distance to the vessel from the nearest surface which could contain a pool

of flammable liquid.

3. Flame Height From Grade: Maximum height the flame would reach around the exterior of the tank. The default

value is 30 ft.

4. Calculate Environmental (F) Factor: Select Yes or No from the drop-down list. The default value is No. If you

select Yes, the Environmental (F) Factor is calculated using the fire insulation properties from the Tank Design

tab and API 2000. If you select No, you must manually type the Environmental (F) Factor.

5. Environmental (F) Factor: The factor used to account for tank protection reducing the fire relief rate, such as by

insulation or fireproofing equipment. Type a real value between 0 and 1. The default value is 1. Use 0 for total

protection and 1 for no protection.

6. Relieving Gas Temperature: Temperature of the vapor leaving the tank at the inlet of the relieving device. This

temperature is usually assumed to be the boiling temperature of the liquid stored in the tank.

7. Relieving Gas Molecular Weight: Molecular weight of relieving vapor that vaporizes from the stored liquid.

8. Fluid Latent Heat: The latent heat of vaporization of the stored liquid at relieving conditions. The default value is

27.7 kcal/kg (or 50 Btu/lb).

Notes:

Wetted area calculations are in accordance with API 2000 rules and may differ from API 521.

Standard flame height is different for the two API standards.

The Design Pressure (higher or lower than 1 psig) heavily affects the wetted area calculation for larger tanks.


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Emergency Venting Results

After you type values for the basic information and the Emergency Venting Inputs, calculated results appear, as shown in

Figure 22.

Figure 22: Emergency Venting Results

1. Calculated Exposed Area: Wetted Exposed Area of the tank. This is the area of the portion tank which is in

contact with both the flame and the liquid. Calculated as a percentage of the total surface area and/or area below

the maximum flame height.

2. Calculated Heat Input: Heat Input from exposure to fire. Calculated from a range of formulae that depend on the

Design Pressure and Exposed Area.

3. Calculated Relieving Flow: Venting requirement. This is the total flow that the relieving device is required to vent

off the tank to ensure complete protection.

4. Preliminary Device Area: The preliminary area required for the calculated volumetric relief load.

5. Preliminary Calculated Size: The preliminary orifice diameter required for the calculated volumetric Outbreathing

relief load.

ConclusionsAPI 521 recommends that all vessels under 25 ft. in elevation be protected for the fire overpressure scenario. Depending

on the protected system, varying levels of rigor may be required in determining the required relieving load.

The Safety Environment in Aspen HYSYS and Aspen Plus provides rigorous determination of the required fire relief load.

Users can now size relief devices for the fire overpressure scenarioquickly and easily.

References1. American Petroleum Inst., Venting Atmospheric and Low-pressure Storage Tanks, ANSI/API Std 2000, 6th Ed.,

November 2009.


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of Aspen Technology, Inc. All rights reserved. 11-5785-0614

About AspenTech

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engineering and construction, and other industries that manufacture and produce products from a

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Additional Resources

Public Website:

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http://www.aspentech.com/products/aspen-plus/

http://www.aspentech.com/products/relief-sizing/

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