CFD Analyses of the Influence Of Flow Conditioners on Liquid Ultrasonic Flow Metering. Oseberg Sor - A Case Study

摘要

Norsk Hydro experienced problems with an oil metering station consisting of two ultrasonic meters (USM 1 & 2) in series on the Oseberg Sor platform. Depending on the flow rates, the K-factor of USM 1 was outside the NPD requirements. USM 2, however, was inside the specifications. The problems could be caused by flow instability in USM 1. To investigate this a CFD study was carried out. Upstream of the meters was a flow conditioner (FC) in form of a seven-pipe tube bundle, and an asymmetric pipe contraction. The study revealed that the problems could be related to the tube bundle. The FC generated local jets after the pipes, and the distance from the FC to USM 1 was insufficient for proper mixing to take place. Different axial flow patterns were produced when the flow rate varied, giving unstable velocity profiles in USM 1. The CFD study was extended to look at the consequences of modifications to the flow line. Better results were obtained when the tube bundle was replaced with an Etoile (star) straightener, giving a more stable flow. Norsk Hydro has since then replaced the tube bundle with an Etoile FC, and recent results shows that both USM 1 and USM 2 will now satisfy the NPD requirements.