8 replies to this topic

[Sevail]

it seems that there are two way for calculation of reliefing temperature in gas expansion
1- considering a compressor to increase pressure from operating to relief pressure with 100% effi.
(By Hysys)
2-using API-521 formula for gas expansion(T2=(P2/P1)*T1)

But the result of above items are different while real situation is compression of gas in constant volume.

[joerd]

So what is your question?

[djack77494]

Sevail,
Please supply a better indication of what you seek. I read your posting and don't know if you're interested in a compressor or a releif valve. The quality of the responses is directly proportional to the quality of the question.

[fallah]

it seems that there are two way for calculation of reliefing temperature in gas expansion
1- considering a compressor to increase pressure from operating to relief pressure with 100% effi.
(By Hysys)
2-using API-521 formula for gas expansion(T2=(P2/P1)*T1)

But the result of above items are different while real situation is compression of gas in constant volume.

Second way (API-521 FORMULA) is nearly the same as what you mentioned as real situation.

[joerd]

2-using API-521 formula for gas expansion(T2=(P2/P1)*T1)

You might as well credit Joseph Louis Gay-Lussac (1802) with that equation.

[Zhejang Chenggao Valve Co.]

You need to caculate with your experience also. Knowledge is just a basic and in the ideal situation.The results are alway something differ.

[sheiko]

Item 1/
I usually use that method to determine the relieving temperature in a blocked gas outlet case (so gas compression not expansion).

Item 2/
Applicable for a gas-filled vessel in external fire case (with the assumption that inlets and outlets are all closed => constant volume).

[demank]

I always use HYsys to get the relief temperature.
The formula of (T2=(P2/P1)*T1) is valid for gases.
THen for liquid case, hysys's help is needed to know the temperature when liquid became gas at the reliving pressure

[diego]

An ancient rule of thumb for natural gas says "-1°C every 2 bars" in depressurisation.....

not for official documents but not too bad for simply evaluation

in any case hysys depressuring utility...........

bye

diego