Thread: Modeling explosion in PHAST 6.54

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Modeling explosion in PHAST 6.54

Hi
I would modeling explosion in PHAST
How i can calculate "confined volume"?
thanks

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Originally Posted by nmerzak
Hi
I would modeling explosion in PHAST
How i can calculate "confined volume"?
thanks
first you should identify the areas in your plant where confinement may occur e.g. by the presence of parallel planes, barriers, physical obstructions to ventilation. These may be the air coolers, heavy loaded piperacks, elevated platforms, etc...

Then, a guidance of the fraction of flammable cloud to be considered as "confined" to give explosion can be found in the CPR 14E "methods for calculation of physical effects" (yellow book)

There are link somewhere in this forum where you can take this book.

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deep thanks safetyuser
the broblem is:
there is a leak in compressor station
if i take total volume "the building volume of the compresssor station"
how i can calculate
1/ confined volume
2/flammable mass in the cloud

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Originally Posted by nmerzak
"the building volume of the compresssor station"
how i can calculate
1/ confined volume
2/flammable mass in the cloud
Well, I don't know exactly your problem anyway from your few words I can suppose:
1- confinement is 100% if your compressor is totally enclosed in a building/box-shaped shelter and similar
2- the flammable volume in the cloud may be estimated in the worst case as the Upper Flammable Limit (UFL) of the congested gas, times the total confined volume. Use the gas density to turn into mass.

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Originally Posted by safetyuser
2- the flammable volume in the cloud may be estimated in the worst case as the Upper Flammable Limit (UFL) of the congested gas, times the total confined volume. Use the gas density to turn into mass.
It would be more correctly to use the difference between UFL and LFL.

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thanks for all
for worst case we can use :
confined volume =9,5 % total volume confinned
total volume confinned=total volume of building-volume obsructin if exist.
"9,5% total volume confinned" for a stoichiometric combustion.

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Check Chapter 17 of LOSS PREVENTION IN PROCESS INDUSTRIES - LEE VOLUME 2, It may help you. Book is availabe in the forum.

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Explosion Modelling

I understand from the discussion that you are trying to use the MultiEnergy model in Phast.

PHAST needs 3 inputs for VCE, flammable mass, confined volume and blast strength.

However in PHAST once you determine the confined volume, it considers that the entire confined volume is filled with stochiometric concentration and is available for explosion. Thus put flammable mass as say 1000kg. ( Otherwise based on the volume calculate the stochiometric flammable mass, but you will get the same results at the end , so as long as you are putting any value greater than stochiometric mass results are same).

Identify the confined area within the plant, the congested volume is typically the volume of the congestion minus the volume of the equipment located within the congestion. e.g. if there is a structure supporting 2-3 process equipment, then confined volume is structure volume ( L*B*H) - VOlume of the process equiment. ( Explosion happens due to flame acceleration i.e. due to congestion, flammable gas cloud from any source can lead to flammable gas to reside within the congested area. Assuming entire congested volume as described is worse case but widely used in Industry )

For the blast strength, use Kinsella method available in Yellow Book. DOnt use too much coservative values without any basis as the resultant peak overpressure will be much higer.

If you need any further help, you can contact me on

rajkumarlodha@hotmail.com

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Averaging-Time

i don't understand the concept related the Averaging-Time . Could someone provide me basic documentary tools.
I tried some books (too specialisied) but i find it difficult to understand.
tHANKS

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Hello,
Can we model dust explosion scenarion in phast.
What i have done,
Converted mass of sulphur to TNT equivalence mass and used TNTmodel. Have anybody tried this earlier?????

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Using TNT equivalence for dust explosion is not a good idea for 2 reasons (you are trying to use some correlations with VCE, for which TNT equivalence method widely applicable):
1) mechanism of burning of dust and vapor is very different - for dust explosion you may see up to 8 explosions for same mixture (coal, for example) - relay mechanism. As a result of this, dynamic of pressure generation and its max value for dust exp. and VCE are different.
2) you have no correlations for calculation of flammable mass of dust, because in different conditions the difference between flammable mass of dust in the same dust cloud may be up to 10 times.

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