In the process of commissioning a nitrogen supply line (see attached isometric), i am facing the following problem:
When opening the pressure control valve (PV 112 25) to allow nitrogen to flow from the pressure regulators (PCV 112 17/19), the pressure indicated on the manometers PG 112 55/56 becomes erratic (pressure varies from min to max scale intempestively) and the pilot-operated pressure safety valves (PSV 112 11/12) start discharging (even chaterring). The whole system starts then to make a strange noise as if the PV and PCV were "pumping" (yeah i know its kind of vague description but my auditive memory is not that good...).
I believe the problem does not come from the PCV because when the PV is closed, the PG indicate the good value: 50 mbarg (the PCV setpoint. See process data below). In this case the PSV remain closed.
My opinion is that there is not enough distance (straight) and too much elbows between the PCV and rhe PSV, what would promote turbulence and, thus, cause the pressure to become erratic (i have not performed hydraulic calcs yet to make thiigs clear). Any other ideas? Have you ever experienced such a situation?
I was also wondering if you had seen such a configuration (pressure regulator + pressure control valve) before (i am asking because i was not part of the Engineering team of the project who decided such an arrangement...)?
Fluid is Nitrogen (MW = 28)
Normal Flowrate is 15 Nm3/h (0°C et 1 barg) and operating Temperature is 15°C
Design pressure upstream PCV is 15 barg
PCV reduce pressure from 10 barg to 50 mbarg (CV = 2.2 in US units)
PSV set pressure is 80 mbarg (sized for PCV failure scenario: 335 Nm3/h, inlet line pressure drop < 40 mbard and total backpressure is < 7 mbard)
PV inlet pressure = 50 mbarg
PV outlet pressure = 12 mbarg
Thank you in advance for your help.
Edited by sheiko, 01 October 2010 - 02:15 PM.