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Tutorial Depressuring First
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SDV
SDVSDV
SDV
SDV
BDVBDV
BDV
TO FLARE
TO FLARE
TO FLARE
1. Define the System
Process System2
SDV
SDV
SDV
SDV
SDV
SDV
2. Calculate each system volume inventory ; both piping and equipment.
Length Equivalent
Ratio
El. NPS Pipe Schedul
e
Internal Diamete
r
Equivalent Piping
VolumeVapour Liquid
From To Length fraction Volume (ft) (ft) (inch) (inch) (ft) (ft3) (ft3)
3P-SDV-0013 5000-V-60 161.7 1.2 0.0 4 S40 4.026 199.17 17.607 0.8077 3.38595000-V-60 5000-PSV-V-60 3.3 1.3 0.0 2 S80 1.939 4.26 0.087 1.0000 0.0000
3"-300# Valve 4"-B1-PHL-100 16.4 1.3 0.0 3 S80 2.901 21.32 0.979 1.0000 0.00005000-V-60 5000-PSE-V-60 32.1 1.3 0.0 2 S80 1.939 41.71 0.855 1.0000 0.00005000-V-60 Reducer 3" x 2" 5.2 1.3 0.0 3 S40 3.069 6.82 0.350 1.0000 0.0000
Reducer 3" x 2" 3P-BDV-0016 10.2 1.3 0.0 2 S40 2.067 13.22 0.308 1.0000 0.0000Reducer 3" x 2" 3P-PV-0023 3.7 1.3 0.0 3 S80 2.901 4.81 0.221 1.0000 0.0000
3"-GP-3P-022-BA1 VALVE 5.2 1.3 0.0 3 S40 3.069 6.82 0.350 1.0000 0.0000
2"-B1-BD-202 3P-PV-0022 16.1 1.3 0.0 2 S40 2.067 20.89 0.487 1.0000 0.0000
Example : Piping Inventory Calculation
Process System3
2"-B1-BD-202 3P-PV-0022 16.1 1.3 0.0 2 S40 2.067 20.89 0.487 1.0000 0.00002"-B1-BD-202 VALVE 5.6 1.3 0.0 2 S80 1.939 7.25 0.149 1.0000 0.0000
5000-V-60 3P-SDV-0015 20.5 1.3 0.0 2 S80 1.939 26.65 0.546 0.0000 0.54655000-V-60 3P-SDV-0014 4.3 1.3 0.0 2 S80 1.939 5.54 0.114 0.0000 0.1137
Total 22.0543 4.0461
ID Length Orientation HLL NLL LLL Volume HLL NLL LLL Total
Tag Number Equipment Name Total HLL NLL LLLWetted Area
Wetted Area
Wetted Area
Area
(ft) (ft) (ft) (ft) (ft) (ft3) (ft3) (ft3) (ft3) (ft2) (ft2) (ft2) (ft2)
5000-V-60HP TEST SEPARATOR
2.500 12.000 HORIZONTAL2.00
00.75
00.50
062.995
54.183
15.746
8.812 71.849 36.811 29.174 104.065
Total63.0
054.18
315.74
68.812 71.849 36.811 29.174 104.065
Example : Equipment Inventory Calculation
Process System4
1. Adjust massflow of related stream to achieve volume flow correspond toinventory 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
Tool Utilities
Process System5
# FIRE���� at design pressure or PAHH# ADIABATIC ���� at operating pressure
The higher the initial pressure, the grater the flowrate load to flare..
Because the time is set 15 minutes No matter the initial pressure
4. Tool/ Utilitiesor CTRL+U *)
*) want to know more HYSYS short cut ? check in my blog : www.process-eng.blogspot.comArticle : useful HYSYS shortcut
1. “Depressuring – Dynamic”
2. “Add Utility”
Process System6
2. “Add Utility”
3. “View Utility”
Process System7
Select vertical vessel
Select stream BASIS SIMULATION : “FIRE”re name to : FIRE CASE
Automatically calculated by HYSYSBut , You can manually fill to apply some margin of total inventory volume
HYSYS model the entirely system volume as a vertical cylinder with flat both bottom and top.
Fill volume of liquid
keep as it is
Process System8
Fill volume of liquidBased on NLL or HLL
HHL result worst case.Still remember the heat input ? Example : Q = 21000FA^0.82The wetted area based on HLL bigger than NLL.(The greater the wetted area the greater the heat input rate to vessel)
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.
Now, at this stage ���� we will skip this problem ���� this will need long explanation ���� I will include it in another tutorial
Select : Fire API 521
To be applied only if heat flux of 21.000 BTU/hr ft^1.64 orQ = : Q = 21000FA^0.82
For fire case : Heat Loss = None
no heat loss should be assumed in fire case
For fire case : Heat Loss = None
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
Process System9
assumed in fire case simulation for worst case
of 0.82C2 = 1
3. For vessel with insulation, or covered by earth, the environment factor less than 1.0ex = 0.3
Now, at this stage ���� we will skip those other problem ���� this will need long explanation ���� I will include it in another tutorial
*)check in my blog for detail explanation : www.process-eng.blogspot.comArticle : fire case – heat input rate
Select : Musoneilan
Fill Cf = 1
Fill Pb = 0
See table below !, it shows the result of sensitivity test for each vapor flow equation method.
For initial value, Pb =0If 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 !
Process System10
Fill Cf = 1
Parameter Unit Musoneilan Fisher Supersonic, (Cv in inch2) Subsonic, (Cv in inch2)
Pb psig 0 25 50 0 25 50 0 25 50 0 25 50
Cv USGPM ( 60f, 1psi) 4.044 4.052 4.126 8.400 8.406 8.406 0.102 0.1019 0.102 0.102 0.1038 0.109
Peak flow lb/hr 4210 4217 4292 4190 4193 4193 4191 4204 4204 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
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
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.
Process System11
In critical condition, the flowrate through control valve , nozzle, orifice, etc., ,will only depends on the inlet pressure.
*)check in my blog : www.process-eng.blogspot.comArticle : critical - subcritical
MUSONEILAN
Cf 0.9 0.95 1
Flow 4202.545 4205.035 4205.123
Cv 4.486085 4.252576 4.040034
SENSIVITY test resultFill Cf = 0.9 -1.0There is no worry about the result ^_^
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%
For gas-filled systems – 80% to 100%For liquid filled systems – 50% to 70%
Recommended value
“UN-CHECK”will result in greater peak flow rate
Process System12
A higher isentropic efficiency results in a lower final temperature. A lower isentropic efficiency results in a higher final peak flow rate
More liquid � more interaction between liquid and vapor.� decrease isentropic efficiencyFor small system inventory ( small vessel model) � more friction between fluid and the vessel wall �decrease isentropic efficiency
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.
Consideration of limiting flare capacity, the depressuring time longer than 15 minutes may be applied
Fill initial value“RUN” after “READY TO CALCULATE”
use “Calculate Cv” mode
Depressurized from design pressure*)
Process System13
The longer the depressuring time, the higher the depressuring loadSet final pressure = 100 psig Or 50 % design pressure *)
HYSYS will adjust the Cv value to achieve final pressure (e.g.100psig) at depressuring time (e.g. 15 min)
-100 psig for thickness less than 1 inch-and 50% DP for more
*)check in my blog : www.process-eng.blogspot.comArticle : basic depressuring - why 15 minutes?
“PERFORMANCE”
MAX. Cv
MIN. System Temperature (during depressuring)
MIN. outlet RO Temperature (during depressuring)
Process System14
MAX. FLOW for fire case
Result in peak flow to flare = 10740 lb/hrMax Cv = 16.63
Process System15
HYSYS ���� Tool / Utilitiesor CTRL+U *)
Rename : “Adiabatic Case”
1ST step
Select stream BASIS SIMULATION “ADIABATIC”
Process System16
2nd step
3rd step
Fill all of data similar with FIRE CASEexcept that volume of liquidbased 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 : AdiabaticNo 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 generallynot 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.
Process System17
“ SIMPLE” for ADIABATIC
I suggest you to use DETAILED modelfor accurate calculations IF ONLY you know what to do :- )(I myself don’t know how to use this option,,suusahhh cuuukkk).
Heat Loss Parameter:Use “NONE” for FIRE CASEUse “ SIMPLE” for ADIABATIC except for system which is the fluid temperature lower than environment , NONE model should be applied (for lower final temperature)
I suggest you to use SIMPLE heat loss model for accurate calculations.Use default values except the AMB temperature.
See page .10 about Pb
Fill CV as FIRE CASE resultCv = 16.63 see page 14
Cf = Cf in accordance with FIRE CASECf ���� 0.9 – 1.0
Process System18
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
Process System19
TRIAL depressuring timeto 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).
Depressurized from operating pressure*)
Process System20
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
Required adiabatic depressuring time
Min Temperatureoutlet RO
Process System21
Min TemperatureIn the system
Adiabatic peak flow
Process System22
Select File
Select :# Temperature# Pressure# Mass Flow
Process System23
VIEW strip chart���� Depressuring profile
VIEW result in Table���� Depressuring data
also click PERFORMANCE/ STRIP CHARTS
An example : show table
Process System24
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.
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.
Aspen HYSYS defaults the height and diameter vessel in accordance with the volume. This may be disproportionate to the actual total wetted area calculation.
Process System25
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.
BTU/hr ft^1.64. The method of spreadsheet can be used to model jet fire case.
PV work termgas-filled systems 80% to 100%liquid filled systems 40% to 70%A higher efficiency results in a lower final temperature
API recommends depressuring to the lower of 50% of the initial pressure or 100 psig / 6.9 barg.
Process System26
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