gas pipeline grid pressure reduction

[nesamani1983]

Hi,
Assume that the entity (A) is operating a gas pipelines grid of 900 km long at 50 kg/cm2. Gas is transferred to Another entity (B) at Dispatch terminal (DT), where B has compresser to take gas, at 50 kg/cm2, B transfers the gas to their pipeline network of 2000 km.. Flow is 120000 MMBTU (3120000 SCMD or 3.12 MMSCDM).
for the last 2 days, B reduced their compressor inlet pressure to 40 kg/cm2. To protect the grid pressure of A, A has throttled the 18'' Ball valve at DT.
Due to the pressure reduction by B, flow is 25000 SCM more than the normal flow.
1) What are the future problems in this change in hydrualics?
2) If the 18'' ball valve is continuously kept in throttled position, seat may damage.
3) What are the changes in velocity. share me the excel sheet to calculate the flow velocity. Z=0.91.

 

[goutam_freelance]

Additional points:

1. The downstream compressors needs to be checked for additional flow and flow instability (surges etc).
2. The throat velocity at the valve needs to be checked to determine the possibility of erosion. It is better to install a recovery turbine which may generate about 750 kW for 10 kg/cm^2 pressure drop.
3. As above

 

[LittleInch]

This begs lots of questions.

1) You don't operate a grid at a set pressure unless there is no flow. so what you mean about 50kg/cm2? Max pressure? Delivery pressure at the connection point?
2) Who is controlling and metering flow and how? Sounds like its the take off party which is quite strange.
3) Future problems? Who knows based on this snippet of information. In the short term you have more gas going out than before so the shortfall needs to be made up from somewhere, either more gas in or less gas for others.
4) Throttling using an isolation valve will destroy it fairly quickly. You need a proper control valve, controlled by you, not party B
5) Velocity change is change in flow multiplied by old pressure divided by new pressure. More or less.

 

[georgeverghese]

Flow has increased by a miniscule amount from 3.12mmscmd to 3.15mmscmd
Offtake at B is controlled by B compressor process flow-discharge- speed controls
For long term operation, better to automate and transfer this pressure control function to a PIC-PCV at inlet to B compressor station. PCV maybe a ball type control valve if desired.