4 replies to this topic

[rsk]

nitrogen is used as cover gas in a storage tank, cover gas pressure is being maintained by make up through riding cylinder PRV arrangement. assuming constant leakage, if on a single day 24 hrs pressure drops from 150 to 120 kg/cm2, using gas equation cylinder can be used for 5 days. But to my surprise it can be used for 3 to 4 days only. please i need ur valuable inputs on this.

Thanks

[fallah]

Please specify:Is 30 Kg/cm2 pressure drop related to which item?

and tell us why you assume constant leakage for the storage tank? Don't you have any inflow/outflow in the mentioned storage tank during 24 hr of a single day?

Regards

[djack77494]

rsk,
While you have not supplied enough information for us to be sure, it sounds as if you expect the pressure in a nitrogen cylinder to drop 150 to 120 to 90 to 60 to 30 to 0 kg/cm^2 (gauge?) over a five day period of time. That is not reasonable. If you used the gas equation as you claimed to do, then you would calculate a nitrogen consumption in kg or kg-moles based on the gas law (PV=nRT). The number "n" consumed in dropping from 150 to 120 is NOT the same as n would be in dropping from 60 to 30. (Remember that you must use absolute pressures and temperatures.) V is constant, and I would expect T could be assumed constant also. At this point I'll give you time to reconsider and recalculate and feel free to revisit this issue as needed.
Doug

[rsk]

thanks for reply
this is a cover gas system to maintain inert atmosphere at positive pressure, & cylinder through PRV is riding on to tank to make up for leakages only.
i am quiet confused, using gas eqn PV=nRT,
V=constant (cylinder volume)
T=can be taken as constant as cylinder is not insulated
Now Dp is directly proprtional to Dn,
so it tells at all pressures, equal drop in cylinder pressure will release same kgmoles of gas. please correct if i am wrong.

[djack77494]

Now Dp is directly proprtional to Dn,
so it tells at all pressures, equal drop in cylinder pressure will release same kgmoles of gas. please correct if i am wrong.

It appears as though I was confused about the approach. I agree with your assessment that equal pressure differentials should result in equal molar depletions. I'm sorry, but I cannot offer an explanation; hopefully someone will take the challenge and provide one.