tutorial depressuring first [compatibility mode]

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