ho to find relieving temprature 1

[standardeviation]

hi

i am new to psv sizing
i want to know how to find relieving temperature for psv sizing , fluid is LPG.

 

[Latexman]

It depends on the scenario. What is the scenario?

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[standardeviation]

i am entirely new to this psv sizing

i have to size psv for lpg bullet of 7.5m dia and 44m long

i am going to size psv for fire case.

so 1st i used equation q=21000 F A^0.82

in this i am stuck with A

since bullet is 75% filled how do i find wetted area (A).

i want to go step by step

thanx for response.

 

[standardeviation]

1st i calculated total surface area of bullet which comes to and multiplied by 0.75

but this seems to be wrong

so how should i proceed?

 

[Duwe6]

Doesn't matter how full the vessel is. The area exposed to fire is what gives the total heat input, and a PRV is there to release the energy from that heat input.

 

[Latexman]

What is the location? What standard is being followed? Looks like API 521.

Reason I ask, in U.S. for LPG, OSHA supercedes API for heat input equation. OSHA stipulates Q (Btu/hr) = 34,500(Total Surface Area)^0.82

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[standardeviation]

hi again

is it true what Duwe6 is saying?

because A is wetted area & according to what i know wetted area means surface area of vessel which is in contact with liquid

please correct me if i am wrong

latexman,

yes i am using API 520 & 521

the project in which my company working on is about LPG terminal situated in south africa

this bullets will store LPG coming via boat from sea side

is there anything more which i should mention?

please let me know

& guys please help me to size this psv so please stay till end with me.

 

[standardeviation]

i know all the equations involved in psv sizing

but i dont know how to obtain most of the various variables involved in these equations.

 

[Latexman]

What is vessel MAWP? What is the PSV set pressure?

If you have specific questions, please ask. We will not do your job for you.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[standardeviation]

vessel MAWP is 14.5kg/cm2g

I have taken MAWP as set pressure

 

[standardeviation]

Latexman

i am new to this psv sizing

i know no one will do my job for me

but this is 1st time for me

i have referred all online stuff for psv sizing also API's

but there is no one to tell me whether my thinking is right or wrong, hence this

there are few more questions from my side regarding psv sizing

 

[Latexman]

Set pressure = MAWP, therefore overpressure = accumulation.

Fire scenario, so accumulation = 21% above MAWP, and overpressure = 21% above set pressure.

Sizing pressure = 1.21 x MAWP.

Sizing temperature is the LPG vapor/liquid equilibrium temperature coincident to the sizing pressure.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[standardeviation]

Thank you.

 

[Duwe6]

The fire-sizing calc's use a misleading term: wetted area. In this instance, this means the area of the vessel that can be 'wetted' by fire, to include convection heat and radiation heat. And there are rules as to how much of the vessel you have to consider as 'wetted' by the fire. Some non-wetted areas are the tops of vessels, and the upper portions of columns. Son on a 100-ft column, the 'wetted' area stops at a distance above the 'ground' [area that can retain a pool of flaming liquid], and does not encompass the entire vertical area of that column.

 

[GHartmann]

First a cylindercal vessel that is 75% full does not have 75% of its surface wetted. There are tables and formulas to calculate this and you must take into account whether the ends are hemispherical, or 2/1 elliptical. You search these types of formulas on the web.

Second thing many of the codes (for example ANSI K61.1 and its new GSPA equivalent for ammonia) require use of the entire surface area in the determining the sizing case for fire.

For LPG or ammonia the gas reliving temperature is the equilibrium temperature at the relieving pressure. As Latexman stated.

The same would apply for a steam boiler.

Good luck.