PressureReliefCalculationsTocompletetheform,enterthedifferential setpointfortherupturedisk.Thisrepresents thepressuredifference across the rupturediskwhich is needed forthe disk to break.In an actual capacity run, the rupture disk is modeled as a pipe with anequivalent length to diameter (L/D) ratio. If no test data is available, use L/D=8fordisk diameterslarger than2 inches (5.08 cm),and15fordiameters 2inchesand smaller. In a code capacity run, the rupture disk is modeled as an idealnozzle with the appropriate discharge coefficient.For uncertified rupture disks.useadischargecoefficientof0.62.ReliefVentIfyou selectEmergencyRelief Ventasthetypeofreliefdevice,youmustcomplete the Relief Vent sheetto specify the emergency relief vent (ERV) to beused inthesimulation.Definetherelief ventintheManufacturer'sTablesframeOncetheManufacturer,Style,andNominalDiameterhavebeenselected,aunique ERV is described and Aspen Plus fills in the following data in:RecommendedSetpointDiameterTo complete the form, enter the differential setpoint for the relief vent.Thisrepresentsthepressuredifferenceacrosstheventwhichisneededfortheventtobegin opening.If you want to use an ERV not listed in the Manufacturer's Tables,you must typein values for the diameterand differential setpoint in the Vent Parametersframe. Note that if you select an ERV from the tables and then overwrite any oftheventparameters,allManufacturer'sTablesfieldswillbeblanked outERVs are modeled so that they open gradually to a fully open position calculatedusing the vent over-pressurefactor.SpecifyingtheVesselNeckThevesselneck is apieceofpipewhich connectsthevessel tothefirst lengthofinlet pipe or to the relief device if there are no inlet pipes. If you choose to specifyavesselneck,entertheassociated informationontheVesselNecksheet oftheReliefDevice form.The following data are required to describe the vessel neck:· LengthDiameter33-16AspenPlusUserGuideVersion 10.1-0
Aspen Plus User Guide Version 10.1-0 33-16 Pressure Relief Calculations To complete the form, enter the differential setpoint for the rupture disk. This represents the pressure difference across the rupture disk which is needed for the disk to break. In an actual capacity run, the rupture disk is modeled as a pipe with an equivalent length to diameter (L/D) ratio. If no test data is available, use L/D=8 for disk diameters larger than 2 inches (5.08 cm), and 15 for diameters 2 inches and smaller. In a code capacity run, the rupture disk is modeled as an ideal nozzle with the appropriate discharge coefficient. For uncertified rupture disks, use a discharge coefficient of 0.62. Relief Vent If you select Emergency Relief Vent as the type of relief device, you must complete the Relief Vent sheet to specify the emergency relief vent (ERV) to be used in the simulation. Define the relief vent in the Manufacturer's Tables frame. Once the Manufacturer, Style, and Nominal Diameter have been selected, a unique ERV is described and Aspen Plus fills in the following data in: • Recommended Setpoint • Diameter To complete the form, enter the differential setpoint for the relief vent. This represents the pressure difference across the vent which is needed for the vent to begin opening. If you want to use an ERV not listed in the Manufacturer's Tables, you must type in values for the diameter and differential setpoint in the Vent Parameters frame. Note that if you select an ERV from the tables and then overwrite any of the vent parameters, all Manufacturer's Tables fields will be blanked out. ERVs are modeled so that they open gradually to a fully open position calculated using the vent over-pressure factor. Specifying the Vessel Neck The vessel neck is a piece of pipe which connects the vessel to the first length of inlet pipe or to the relief device if there are no inlet pipes. If you choose to specify a vessel neck, enter the associated information on the Vessel Neck sheet of the ReliefDevice form. The following data are required to describe the vessel neck: • Length • Diameter
Chapter33Optional specifications on theVessel Neck sheet are shown belowwith theircorresponding defaults:DefaultSpecificationVerticalOrientationRoundedConnection TypeReducer resistance coefficient (Reducer K)0.040.04Expander resistance coefficient (ExpanderK)0.00015 ftRoughnessSpecifying the Inlet PipeFor inlet pipe sections, use the Pressure Relief InletPipes form to describe theinlet pipes which connect the vessel neck to the relief device. Up to two sectionsof pipe with the same or different diameters may be used.The InletPipes form contains four sheets:ToUse this sheetPipeSpecity the pipedimensions andoptional pipe parametersFitingsDescribethefttings inthepipesectionsuchaspipeconnections,butterflyorgatevalveselbows, and teesValvesDescribe a general purpose valve or control valve in the pipe sectiorThermalSpecify heat transfer parameters for energy transfer with surroundingsThe Pipe sheet is required for all sections of inlet pipe.The remaining sheets are used for specification of optional input. Each sheet isdescribed below.PipeUse the Pipe sheet toenterthepipe diameter and lengthforeachpipe section.Pipediameter and length are required specifications for allpipe sections.Aspen Plus User Guide33-17Version10.1-0
Aspen Plus User Guide Version 10.1-0 33-17 Chapter 33 Optional specifications on the Vessel Neck sheet are shown below with their corresponding defaults: Specification Default Orientation Vertical Connection Type Rounded Reducer resistance coefficient (Reducer K) 0.04 Expander resistance coefficient (Expander K) 0.04 Roughness 0.00015 ft Specifying the Inlet Pipe For inlet pipe sections, use the Pressure Relief InletPipes form to describe the inlet pipes which connect the vessel neck to the relief device. Up to two sections of pipe with the same or different diameters may be used. The InletPipes form contains four sheets: Use this sheet To Pipe Specify the pipe dimensions and optional pipe parameters Fittings Describe the fittings in the pipe section such as pipe connections, butterfly or gate valves, elbows, and tees Valves Describe a general purpose valve or control valve in the pipe section Thermal Specify heat transfer parameters for energy transfer with surroundings The Pipe sheet is required for all sections of inlet pipe. The remaining sheets are used for specification of optional input. Each sheet is described below. Pipe Use the Pipe sheet to enter the pipe diameter and length for each pipe section. Pipe diameter and length are required specifications for all pipe sections
PressureReliefCalculationsPipeFittingsValvesThermal1口Inlet pipe section.Pipe scheduleMateriatSchedule:Nominal diameter:国TPipeparameters口ftInner diameter.口Length.ftOptionalfReducerK:0.04Roughness:0.00015VPipe rise:ftExpanderK:0.04-Included with Aspen Plus are built-in Pipe Schedule Tables that aid in thespecification of commonpipe sizes.You can customize Aspen Plus by adding or modifying pipe schedule tables. Formore information on this, see the Aspen Plus System Management manual.To choose a pipe diameter from the built-in Pipe Schedule Tables:1.At the top of the Pipe sheet, select a pipe section from the Pipe Section field.2.In the Pipe Schedule frame, choose a material of construction for the pipesection,fromtheMateriallist.Availablematerialsincludecarbonsteel andstainless steel.3.Choose a pipe schedule in the Schedule field.4.Chooseanominal pipe diameterfromthe Nominal Diameter field.A unique pipe is described and the Inner Diameter is displayed in the PipeParametersframe.If you want to use apipenot listed in Pipe ScheduleTables,you must manuallyenterthepipeinnerdiameterintheInnerDiameterfield of thePipeParametersframe.Notethat if you select apipefrom thetables and then overwritethe innerdiameter,allPipeScheduleTablesfieldswill beblanked out.OptionalinputsonthePipesheetinclude:AbsolutepiperoughnessPipe Rise (elevation change)Resistance coefficient("K"factor)ofreducerfollowing thepipe sectionResistance coefficient ("K"factor) of expander following the pipe section33-18AspenPlusUserGuideVersion 10.1-0
Aspen Plus User Guide Version 10.1-0 33-18 Pressure Relief Calculations Included with Aspen Plus are built-in Pipe Schedule Tables that aid in the specification of common pipe sizes. You can customize Aspen Plus by adding or modifying pipe schedule tables. For more information on this, see the Aspen Plus System Management manual. To choose a pipe diameter from the built-in Pipe Schedule Tables: 1. At the top of the Pipe sheet, select a pipe section from the Pipe Section field. 2. In the Pipe Schedule frame, choose a material of construction for the pipe section, from the Material list. Available materials include carbon steel and stainless steel. 3. Choose a pipe schedule in the Schedule field. 4. Choose a nominal pipe diameter from the Nominal Diameter field. A unique pipe is described and the Inner Diameter is displayed in the Pipe Parameters frame. If you want to use a pipe not listed in Pipe Schedule Tables, you must manually enter the pipe inner diameter in the Inner Diameter field of the Pipe Parameters frame. Note that if you select a pipe from the tables and then overwrite the inner diameter, all Pipe Schedule Tables fields will be blanked out. Optional inputs on the Pipe sheet include: • Absolute pipe roughness • Pipe Rise (elevation change) • Resistance coefficient ("K" factor) of reducer following the pipe section • Resistance coefficient ("K" factor) of expander following the pipe section
Chapter33If you do not entervalues for these optional inputs,thefollowing default valuesare used.SpecificationDefaultRoughness0.00015 f0Pipe Rise0.04Reducer K0.04Expander KFittingsUse the Fittings sheet to describe any fittings contained in the an inlet pipesection.Anynumber of thefollowingfittingtypes maybespecified:Gate ValvesButterfly Valves90 degree ElbowsStraight TeesBranched TeesIn addition a miscellaneous flow resistance may be specified by entering in thenumber of pipe diameters equivalent to the resistance.ValvesUse the Valves sheet to specify a general purpose valve to be used in a pipesection. In the top section of the sheet, select a valve from the Manufacturer'sTables frame.Oncethe Manufacturer,Style,and Nominal Diameterhave beenselected, a unique valve is described and Aspen Plus fills in the following data intheValveParametersframe:FlowArea.FlowCoefficientIf you want tousea valve not listed in the Manufacturer's Tables,you must typein values for the parameters listed above. Note that if you select a valve from thetables and then overwrite any of the valveparameters, all Manufacturer's Tablesfields will be blanked out.You mayalso specify thevalveconstant for a control valvecontained in thepipesection. To do this, enter a value in the Valve Constant field of the Control Valveframe.AspenPlusUserGuide33-19Version 10.1-0
Aspen Plus User Guide Version 10.1-0 33-19 Chapter 33 If you do not enter values for these optional inputs, the following default values are used. Specification Default Roughness 0.00015 ft Pipe Rise 0 Reducer K 0.04 Expander K 0.04 Fittings Use the Fittings sheet to describe any fittings contained in the an inlet pipe section. Any number of the following fitting types may be specified: • Gate Valves • Butterfly Valves • 90 degree Elbows • Straight Tees • Branched Tees In addition a miscellaneous flow resistance may be specified by entering in the number of pipe diameters equivalent to the resistance. Valves Use the Valves sheet to specify a general purpose valve to be used in a pipe section. In the top section of the sheet, select a valve from the Manufacturer's Tables frame. Once the Manufacturer, Style, and Nominal Diameter have been selected, a unique valve is described and Aspen Plus fills in the following data in the Valve Parameters frame: • Flow Area • Flow Coefficient If you want to use a valve not listed in the Manufacturer's Tables, you must type in values for the parameters listed above. Note that if you select a valve from the tables and then overwrite any of the valve parameters, all Manufacturer's Tables fields will be blanked out. You may also specify the valve constant for a control valve contained in the pipe section. To do this, enter a value in the Valve Constant field of the Control Valve frame
PressureReliefCalculationsThermalUsetheThermal sheettospecifyenergybalanceparameters ifyou wanttomodelheat transferbetween the pipe section and the surroundings.Thefollowingmustbe specified:InletAmbientTemperatureOutletAmbientTemperatureU-value (overallheattransfercoefficient)Specifying the Tail PipeFor tail pipe sections, use the Pressure Relief TailPipes form to describe the tailpipes which connect the relief device to the discharge point. Up to two sections ofpipewith the same or different diameters maybeused.TheTailPipes formhasthesamefunctionalityas the InletPipesform, except that it applies totailpipesections.Formore details on specifying tail pipes, refer to Specifying the InletPipe, earlier in this chapter.Specifying Dynamic InputUse the DynamicInput form to describe the emergency event associated with adynamic scenario. Required data include a description of the vessel as well as theevent (fire or heat input) which is causing the release from the vessel.The sheets contained on the DynamicInput form are listed below:Use this sheetTo specifyVesselVessel and vessel head geometryDesign ParametersVessel design pressure and disengagement modelFireType of fire exposure engulfing the vesselFire CreditsCredits you can claim if systems to fight fire or minimize vessel releases are presentHeat InputThe rate of heat input into a vesselThe Vessel and Design Parameters sheets must be completed for all dynamicscenarios.Forheat input scenarios,theHeatInput sheetisalsorequired.Forfire scenarios, the Fire sheet is required, and the Fire Credits sheet is optional.Theuseof eachsheetisdescribed below.33-20Aspen Plus User GuideVersion 10.1-0
Aspen Plus User Guide Version 10.1-0 33-20 Pressure Relief Calculations Thermal Use the Thermal sheet to specify energy balance parameters if you want to model heat transfer between the pipe section and the surroundings. The following must be specified: • Inlet Ambient Temperature • Outlet Ambient Temperature • U-value (overall heat transfer coefficient) Specifying the Tail Pipe For tail pipe sections, use the Pressure Relief TailPipes form to describe the tail pipes which connect the relief device to the discharge point. Up to two sections of pipe with the same or different diameters may be used. The TailPipes form has the same functionality as the InletPipes form, except that it applies to tail pipe sections. For more details on specifying tail pipes, refer to Specifying the Inlet Pipe, earlier in this chapter. Specifying Dynamic Input Use the DynamicInput form to describe the emergency event associated with a dynamic scenario. Required data include a description of the vessel as well as the event (fire or heat input) which is causing the release from the vessel. The sheets contained on the DynamicInput form are listed below: Use this sheet To specify Vessel Vessel and vessel head geometry Design Parameters Vessel design pressure and disengagement model Fire Type of fire exposure engulfing the vessel Fire Credits Credits you can claim if systems to fight fire or minimize vessel releases are present Heat Input The rate of heat input into a vessel The Vessel and Design Parameters sheets must be completed for all dynamic scenarios. For heat input scenarios, the Heat Input sheet is also required. For fire scenarios, the Fire sheet is required, and the Fire Credits sheet is optional. The use of each sheet is described below