PSV sizing verification for Alvheim process equipment during gas blowby scenarios

Abstract

The EPCI (Engineering, Procurement, Construction and installation) contractor which delivered the PSVs to Alvheim states that the PSVs are sized to handle a gas blowby scenario. Marathon Norge AS does not hold any documentation of this. The object for this thesis is to verify and document that the PSVs can handle a gas blowby scenario. The equipments which have been investigated are: The Alvheim/3rd party Inlet separator The 2nd stage separator The produced water degassing drum Glycol Flash Drum Cargo tanks It is concluded that it is not sufficient to only consider the gas blowby case without including the effect of closed outlets due to high pressure. It seems that the EPCI contractor has not included closed outlet when sizing the PSVs for a gas blowby scenario. The PSVs for Alvheim/3rd party Inlet separator and Glycol Flash drum are verified in this report by conservative calculations and simulations assuming a gas blowby scenario with closed outlets. The conservative computation does not verify that the PSVs for the 2nd stage separator, the produced water degassing drum and the cargo tanks are sized for gas blowby. However, the dynamic simulation shows that the conservative scenarios are too conservative. The trivial dynamic simulation shows that the PSVs for the 2nd stage separator are large enough to handle a gas blowby scenario with closed outlets. In spite of this result it is recommended that a more detailed dynamic simulation is to be designed to verify sufficient PSV capacity for these scenarios. First of all it is recommended to implement more details into the steady state simulation for the 2nd stage separator and the degassing drum and investigate if it is possible to assume open liquid outlets even though the downstream pumps trip.