TUTORIAL DEPRESSURING first [Compatibility Mode

1. Define the System TO FLARE SDV BDV BDV TO FLARE TO FLARE SDV SDV BDV SDV SDV SDV SDV SDV SDV 2 Process System SDV 2. Calculate each system volume inventory ; both piping and equipment. Example : Piping Inventory Calculation Length From To 3P-SDV-0013 5000-V-60 3"-300# Valve 5000-V-60 5000-V-60 Reducer 3" x 2" Reducer 3" x 2" 5000-V-60 5000-PSV-V-60 4"-B1-PHL-100 5000-PSE-V-60 Reducer 3" x 2" 3P-BDV-0016 3P-PV-0023 (ft) 161.7 3.3 16.4 32.1 5.2 10.2 3.7 3"-GP-3P-022-BA1 VALVE 5.2 2"-B1-BD-202 2"-B1-BD-202 5000-V-60 5000-V-60 3P-PV-0022 VALVE 3P-SDV-0015 3P-SDV-0014 Equival ent El. Ratio (ft) 1.2 0.0 1.3 0.0 1.3 0.0 1.3 0.0 1.3 0.0 1.3 0.0 1.3 0.0 NPS (inch) 4 2 3 2 3 2 3 Internal Equivale Pipe nt Diamete Schedul r Length e (inch) (ft) S40 4.026 199.17 S80 1.939 4.26 S80 2.901 21.32 S80 1.939 41.71 S40 3.069 6.82 S40 2.067 13.22 S80 2.901 4.81 Piping Volume Vapour Liquid fraction (ft3) 17.607 0.087 0.979 0.855 0.350 0.308 0.221 0.8077 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 Volume (ft3) 3.3859 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 1.3 0.0 3 S40 3.069 6.82 0.350 1.0000 0.0000 16.1 1.3 5.6 1.3 20.5 1.3 4.3 1.3 Total 0.0 0.0 0.0 0.0 2 2 2 2 S40 S80 S80 S80 2.067 1.939 1.939 1.939 20.89 7.25 26.65 5.54 0.487 0.149 0.546 0.114 22.0543 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.5465 0.1137 4.0461 Example : Equipment Inventory Calculation ID Tag Number Equipment Name 3 HP TEST SEPARATOR Process System Volume Total HLL NLL LLL (ft) (ft) (ft) (ft3) (ft3) (ft3) (ft3) 2.00 0.75 0.50 62.9 54.18 15.74 2.500 12.000 HORIZONTAL 8.812 0 0 0 95 3 6 63.0 54.18 15.74 Total 8.812 0 3 6 (ft) 5000-V-60 Length Orientation HLL NLL LLL (ft) HLL Wetted Area (ft2) NLL Wetted Area (ft2) LLL Wetted Area (ft2) Total 71.849 36.811 29.174 104.065 71.849 36.811 29.174 104.065 Area (ft2) 4 Process System Tool Utilities 1. Adjust massflow of related stream to achieve volume flow correspond to inventory calculation 2. Mix those stream, the result is as BASIS COMPOSITION 3. Balance it to initial pressure condition, the result is as BASIS SIMULATION Initial condition as follow : # FIRE at design pressure or PAHH # ADIABATIC at operating pressure 4. Tool/ Utilities or CTRL+U *) The higher the initial pressure, the grater the flowrate load to flare.. 5 Process System Because the time is set 15 minutes No matter the initial pressure *) want to know more HYSYS short cut ? check in my blog : www.process-eng.blogspot.com Article : useful HYSYS shortcut 1. “Depressuring – Dynamic” 2. “Add Utility” 3. “View Utility” 6 Process System 7 Process System re name to : FIRE CASE Select stream BASIS SIMULATION : “FIRE” Select vertical vessel HYSYS model the entirely system volume as a vertical cylinder with flat both bottom and top. Automatically calculated by HYSYS But , You can manually fill to apply some margin of total inventory volume keep as it is Fill volume of liquid Based on NLL or HLL HYSYS will adjust vessel size both Diameter and Height so that both the total and liquid volume are correct correspond to the input value. Is it difficult to achieve that volume ? As a matter of fact, it is not. Actually, the real problem is, the wetted area based on HYSYS’s vessel size is not equal with the actual wetted area. 8 Process System Now, at this stage we will skip this problem I will include it in another tutorial HHL result worst case. Still remember the heat input ? Example : Q = 21000FA^0.82 The wetted area based on HLL bigger than NLL. (The greater the wetted area the greater the heat input rate to vessel) this will need long explanation Select : Fire API 521 To be applied only if heat flux of 21.000 BTU/hr ft^1.64 or Q = : Q = 21000FA^0.82 For fire case : ForLoss fire case : Heat = None Heat Loss = None no heat loss should be assumed in fire case simulation for worst case Now, at this stage we will skip those other problem explanation I will include it in another tutorial 9 Process System other cases , such as *) 1. Jet fire , the heat flux is 94,500 BTU/ft2/hr. C1 = 94,500 2. For small system, the fraction area exposed by fire is 1.0 instead of 0.82 C2 = 1 3. For vessel with insulation, or covered by earth, the environment factor less than 1.0 ex = 0.3 this will need long *)check in my blog for detail explanation : www.process-eng.blogspot.com Article : fire case – heat input rate Fill Pb = 0 For initial value, Pb =0 If the vapor flow equation is “SUBSONIC” , the value should be updated based on flareNet study result. # Pb has no significant effect for other vapor flow equation. See table below ! Select : Musoneilan See table below !, it shows the result of sensitivity test for each vapor flow equation method. Fill Cf = 1 It is critical flow factor, generally the value close to 1.0 Ex : 0.90 , 0.94 … Cf = 1 for worst case of peak flow Parameter Pb Cv Peak flow Unit Musoneilan psig 0 25 50 USGPM ( 60f, 1psi) 4.044 4.052 4.126 lb/hr 4210 4217 4292 0 8.400 4190 Fisher 25 8.406 4193 50 8.406 4193 Supersonic, (Cv in inch2) 0 25 50 0.102 0.1019 0.102 4191 4204 4204 Subsonic, (Cv in inch2) 0 25 50 0.102 0.1038 0.109 4201 4264 4423 The method selection has no significant effect to the result (peak flow) Now, you can choose one of the method with no worry about the result, personally , I prefer using “MUSONEILAN” In my opinion, Musoneilan is the most simple and easy to be used. DON’T use SUBSONIC if the system is not in sub-critical condition 10 Process System The back pressure has significant effect only for SUBSONIC method This equation show ; the back pressure has effect to the depressuring result,, Do you know,, Why the back pressure has effect only for subsonic method ? *) In sub critical condition, the flowrate through control valve , nozzle, orifice, etc., ,will depends on the differential pressure between inlet and outlet. In critical condition, the flowrate through control valve , nozzle, orifice, etc., ,will only depends on the inlet pressure. Cf Flow Cv 11 MUSONEILAN 0.9 0.95 1 4202.545 4205.035 4205.123 4.486085 4.252576 4.040034 Process System SENSIVITY test result Fill Cf = 0.9 -1.0 There is no worry about the result ^_^ *)check in my blog : www.process-eng.blogspot.com Article : critical - subcritical Fill PV work : 50 % for FIRE CASE PV Work Term Contribution refers to the isentropic efficiency of the process. A reversible process should have a value of 100% and an isenthalpic process should have a value of 0% Recommended value “UN-CHECK” will result in greater peak flow rate For gas-filled systems – 80% to 100% For liquid filled systems – 50% to 70% More liquid more interaction between liquid and vapor. decrease isentropic efficiency For small system inventory ( small vessel model) more friction between fluid and the vessel wall decrease isentropic efficiency A higher isentropic efficiency results in a lower final temperature. A lower isentropic efficiency results in a higher final peak flow rate 12 Process System Depressurized from design pressure*) Set depressuring time = 15 minutes *) Considering of the maximum reduction of the vessel stress, vessel with thickness less than 1 inch, generally requires faster depressuring rate. use “Calculate Cv” mode Consideration of limiting flare capacity, the depressuring time longer than 15 minutes may be applied “RUN” after “READY TO CALCULATE” Fill initial value HYSYS will adjust the Cv value to achieve final pressure (e.g.100psig) at depressuring time (e.g. 15 min) The longer the depressuring time, the higher the depressuring load Set final pressure = 100 psig Or 50 % design pressure *) -100 psig for thickness less than 1 inch -and 50% DP for more 13 Process System *)check in my blog : www.process-eng.blogspot.com Article : basic depressuring - why 15 minutes? MAX. Cv MIN. System Temperature (during depressuring) “PERFORMANCE” MIN. outlet RO Temperature (during depressuring) MAX. FLOW for fire case Result in peak flow to flare = 10740 lb/hr Max Cv = 16.63 14 Process System 15 Process System HYSYS Tool / Utilities or CTRL+U *) Select stream BASIS SIMULATION “ADIABATIC” Rename : “Adiabatic Case” 1ST step 2nd step 3rd 16 Process System step Fill all of data similar with FIRE CASE except that volume of liquid based on LLL LLL mean lower liquid increase isentropic efficiency will result in lower final temperature (see page 12) Lower liquid lower flashed vapor formed from liquid phase will result in shorter depressuring time Select : Adiabatic No heat input Select : None HYSYS does not account for any heat loss During a fire case the vessel is covered with flame. In this case, heat loss to the surrounding atmosphere determined by taking a normal atmospheric temperature is generally not correct as the vessel's surrounding temperature is very high. You should use no heat loss, select “ NONE” for FIRE CASE “ NONE” for ADIABATIC Can be applied if the fluid temperature is lower than the environment temperature. “ SIMPLE” for ADIABATIC Heat Loss Parameter : Use “NONE” for FIRE CASE Use “ SIMPLE” for ADIABATIC except for system which is the fluid temperature lower than environment , NONE model should be applied (for lower final temperature) 17 Process System I suggest you to use SIMPLE heat loss model for accurate calculations. Use default values except the AMB temperature. I suggest you to use DETAILED model for accurate calculations IF ONLY you know what to do :- ) (I myself don’t know how to use this option,,suusahhh cuuukkk). See page .10 about Pb Fill CV as FIRE CASE result Cv = 16.63 see page 14 Cf = Cf in accordance with FIRE CASE Cf 0.9 – 1.0 18 Process System Fill 100% for worst case For gas-filled systems – 80% to 100% For liquid filled systems – 50% to 70% For small system, or liquid filled system, engineering adjustment should be used. The lower efficiency shall be used for accurate calculation 19 Process System Depressurized from operating pressure*) TRIAL depressuring time to meet final pressure 0 psig HYSYS will calculate final pressure based on depressuring time use “Calculate Pressure” mode In some cases, the final pressure can’t meet 0 psig, (slightly above 0 psig). The system can’t be decrased to lower pressure. it’s OK The fact, the fluid is released to flare. The pressure of the system is correspond to the back pressure . Therefore, the final pressure is slightly above atmospheric condition 20 Process System Required adiabatic depressuring time Min Temperature outlet RO Min Temperature In the system Adiabatic peak flow 21 Process System 22 Process System Select File Select : # Temperature # Pressure # Mass Flow VIEW strip chart Depressuring profile VIEW result in Table Depressuring data 23 Process System also click PERFORMANCE/ STRIP CHARTS An example : show table 24 Process System Aspen HYSYS does not take the volume of the vessel heads into account so the volume will be the liquid in the cylindrical portion only. Aspen HYSYS defaults the volume to be equal to the volumetric flow of the feed ‘BASIS SIMULATION”. This will be disproportionate to the total volume inventory calculation where the certain margin volume is applied. Aspen HYSYS defaults the height and diameter vessel in accordance with the volume. This may be disproportionate to the actual total wetted area calculation. At present, Aspen HYSYS does not have the option for jet fire case where the heat flux is more than 21.000 BTU/hr ft^1.64. The method of spreadsheet can be used to model jet fire case. API recommends depressuring to the lower of 50% of the initial pressure or 100 psig / 6.9 barg. PV work term gas-filled systems 80% to 100% liquid filled systems 40% to 70% A higher efficiency results in a lower final temperature If one is checking that the minimum temperature of the vessel will not fall below a certain value (for example, for validating the steel alloy grade), and then 100% will give the most conservative result. 25 Process System 26 Process System