PhD project: Modelling and experiments for by-pass pigging with speed control
PhD student: Ir. Maurice Hendrix
Project start: October 2013
Offshore gas condensate trunklines are needed to transport the gas and oil (and water) to the downstream gas plant. These pipelines can span distances of hundreds of kilometers and need to be regularly cleaned and inspected. This is usually done with a pig, which is also known as Pipeline Inspection Gauge. This is a cylindrical device fitting the pipeline which is inserted in the pipe via a launching station without interrupting the flow of product in the pipeline. The pig then travels along with the product flow cleaning the pipe, driven by the downstream pressure gradient. During the pigging operation, liquid slugs will be collected in front of the pig, which need to be temporarily parked in a slugcatcher onshore. The volume of the liquid slug that is addressed to the pigging operation is called the Pig Generated Volume (PGV), which is zero if the pig would travel with the velocity of the liquid. The use of a pig with an opening in the center will allow some of the fast moving gas to stream through the pig during the pigging operation. The use of such a so-called by-pass pig will affect the velocity of the pig, since the by-pass area influences the pressure drop across the pig: a larger by-pass area reduces the pressure drop and slows the pig down closer to the liquid velocity. This will in return reduce the PGV, which is desirable since it allows the liquid slugcatcher onshore to be smaller. On the other hand, the by-pass area cannot be too large, because the pig might get stuck in the pipeline. This project is concerned with the multiphase flow in and around a by-pass pig using CFD. The pressure drop across the pig is of importance during the pigging operation, and a crucial control parameter is the by-pass area of the pig. Comparison with experimental data will be made to verify the modeling.