Relief Valve Nameplate Capacity 1

[chemter]

I have a couple related questions concerning relief valve nameplate capacity. I sized a relief valve for nitrogen at relieving conditions of 305°F and 234.7 psia (200 psig + 10% overpressure + 1 atm). Using the API general vapor sizing equation for critical vapor flow, I came up with a rated capacity in lb/hr of nitrogen. The nameplate capacity of the relief valve is given in SCFM of Air at 60°F. If I convert my rated flow of lb/hr nitrogen to SCFM of Air at 60°F, shouldn't they be equal, or very close to equal? This also leads to my second related question. ASME code (Sec. VIII, Div. 1, M-7(a), states that the inlet pressure losses shall be based on the valve nameplate capacity, corrected for the characteristics of the flowing fluid. Is this "correction for the characteristics of the flowing fluid" the value you get when you use the API critical flow vapor sizing equation?
Thank you in advance for your time and help.

 

[MortenA]

Accordint to Campbell the conversion between mass flow and std. vol flow (in US units is):

lb/hr=110 (MMscfd)(MW gas).

The mol weight of N2 is 0.028 lb/lbmol so take your flow rate and divide it by 0.028 and 110 and you will have your flow rated in MMscfd.

With regards to the last part: The nameplate capacity may be given for a specific fluid (water/air whatever) - since the actual fluid may be different the losses shall be based on the physical properties of the actual fluid at he relieving conditions (sp+10 %, relieving temperature not std. conditions) etc.

Best regards

Morten

 

[mpritchett]

MortenA:

What is your source for N2 Molecular weight? Mine shows 28.0134 lb/lb-mole.

Cheers!

MPritchett

 

[MortenA]

ah

Im not used to lbmol - and i think you are right. its also 28 kg/kgmol and 28 g/mol - so yes! You must be right

Best regards

Morten