Coalescer Outlet Pressure Control 1

[RUBABU_imported]

thread124-376699

System: Crude Tank Vapor Recovery Unit Compressor/HC Condensate Pump Discharge
Coalescer in downstream of Condensate Pump discharge - for moisture/water removal before export to 35 km long pipeline with destination to a Gas Processing Plant
Pump: 1000 psi discharge Pressure


1. In the above referenced thread124-376699, coalescer P&ID has been attached. If a similar Coalescer is to be installed in the above system (i.e. downstream of Condensate Pump discharge), does it require a Pressure Control Valve in the Coalescer Outlet?

2. What other Over Pressure Protection is required other than PSVs in Coalescer like any Blowdown Valve BDV?

 

[georgeverghese]

Q1. A backpressure control valve, located preferably at the downstream end of this pipeline will be required if the minimum operating pressure at the downstream end could be less than the bubble point pressure of this condensate at the maximum arrival temperature. This then addresses the concern with any part of the 35km pipeline from operating in 2 phase liquid / vapor which could result in slugging and unstable flow into the downstream vessels at the GPP. It would then also prevent 2 phase operation in the coalescer at your plant.
If this pipeline is depressurised below condensate bubble point pressure for maintenance ops in the future, then a backpressure control valve may also be required downstream of this coalescer during pipeline restart. It may not be practical to repressure this entire pipeline with gas (prior to restart) for this case.
Q2. A blowdown valve is not a overpressure protection device - it serves to depressure the vessel during a fire / loss of containment event and thereby minimise the risk of vessel rupture during the fire event or reduce the quantity of flammable fluid that could be feeding a potential local fire if this is a loss of containment event.
For liquid full vessels like this, you've got a few options a)install a top exit BDV leading to the FKOD (b) install a bottom exit liquid pulldown BDV leading to a dedicated drain drum (c) provide passive fire protection (PFP) insulation on this vessel. Options (a) and (b) have their practical / safety limitations, so it usually would be better to go with (c). Talk to your plant safety engineer and set up this PFP based on process safety considerations.
In some cases with liquid full vessels, PFP may not be required, if there is sufficient liquid mass in the vessel to keep the vessel cool during a nominal 30minute pool fire event. The firecase PSV should relieve all vapor produced by the boiling liquid during this time.

 

[RUBABU_imported]

Thanks George Verghese for your valuable feedback. i need to check on the 2-phase formation in the loop.