1 reply to this topic

[sheiko]

Hello,

Suppose you are filling a batch vessel (no outlet) with gas. Normally the feed flowrate become differentially less and less as the filling of the vessel approaches an end. This is due to the decrease of the driving force (pressure differential) between the supply gas pressure upstream the vessel (assumed constant) and the accumulated pressure in the vessel (increasing).

I was wondering if the assumption of considering the initial supply pressure constant (and thus the driving force decreasing) is always true.

1/ What if the supply gas is from a well?
2/ What if a centrifugal compressor is delivering the gas to the vessel?
3/ What if a reciprocating compressor?

4/ Now suppose instead of filling a closed vessel, you are transporting gas in a long pipeline and you inadvertently close valve downstream. I assume the scenario will be the same than previously, ie. gas will accumulate in the pipeline. Right?

Edited by sheiko, 14 February 2010 - 10:21 AM.

[kkala]

Suppose you are filling a batch vessel (no outlet) with gas. Normally the feed flowrate become less and less, as the filling of the vessel approaches an end. This is due to the decrease of the driving force (pressure differential) between the supply gas pressure upstream the vessel (assumed constant) and the accumulated pressure in the vessel (increasing).
I was wondering if the assumption of considering the initial supply pressure constant (and thus the driving force decreasing) is always true.
1/ What if the supply gas is from a well?
Supply pressure from well remains constant for months, decreasing on the very long terms (on the condition that demand does not exceed specified limits, so that new gas replaces the quantity taken). Decreasing flow rate to the vessel .
2/ What if a centrifugal compressor is delivering the gas to the vessel?
After a while discharge pressure will increase, so compressor flow will decrease. Decreasing flow rate to vessel.
3/ What if a reciprocating compressor?
Practically constant flow to vessel irrespective of discharge pressure (3) (increased loses with pressure negligible). PRV necessary on the vessel .
Constant suction pressure assumed for 2/, 3/ .
4/ Now suppose instead of filling a closed vessel, you are transporting gas in a long pipeline and you inadvertently close valve downstream. I assume the scenario will be the same than previously, ie. gas will accumulate in the pipeline. Right?
Yes, gas pressure will increase from normal to some maximum value .
Note (3): Controls can dictate constant discharge pressure, even at constant compressor speed.