Liquid slug generator for separated gas/liquid flow in pipes

The goal of the study is to develop a slug generator that can be used upstream of the Multiphase Capacitive Flow meter (MCF) developed by KSEPL. This meter operates only in the intermittent flow regime. The scope of application should be widened to the stratified and stratified annular flow regime by means of a slug generator. Objectives in the study are the design, modelling and validation of the device, the Slug Generator, meeting requirements for its operation. Slug generator operation requirements consist of an overall slug performance in the stratified and stratified annular flow regime, compact geometry, robustness, low pressure loss and assessment of measurability of the slugs produced. Literature study and slug generator design stages resulted in a device meeting these specifications. This device, the Slug Generator, consists of a kink and an inverted U-tube. Observations of the flow behaviour reveal that the kink continuously propagates shock waves encountering the incoming liquid flow in the pipe sections upstream of the Slug Generator. In this way instabilities are created from which liquid slugs are initiated. These slugs subsequently travel via the inverted U-tube to the downstream pipe, where they continue as liquid slugs over an appreciable pipe length. Such slugs can be used as input to the MCF. Slug Generator performance has been validated in a laboratory scale 2ft tubing air -' water test loop and a full scale 4" tubing air - gasoil test loop. The Slug Generator produces slugs over the entire range of validation covering the complete flow map. A deterministic and a probabilistic model of the Slug Generator have been developed. The slug generating mechanism of the Slug Generator bas been implemented in the models. This mechanism consists of a superposition of the hold-up building processes: stratified flow, liquid accumulating, shock wave propagation and slug initiation. The deterministic model computes the critical slug initiation level over the pipe sections upstream of the Slug Generator. The probabilistic model calculates an evolutionary probability density function in the slug generating zone; an upstream pipe section in which slug generation takes place. Both models provide information on slug generating zone length, slug frequency and Slug Generator operation limits. The models have been qualitatively validated in the 2" and 4" tubing test loops. The model can be quantitatively improved by adopting an interfacial shear wave model and improving the critical slug initiation level calculation. Pressure drop over the Slug Generator bas been modelled. It has been validated in a laboratory scale 2" tubing air - water test loop. It is sufficiently accurate in calculating the full scale 4" tubing air - gasoil test loop. The MCF is able to correlate on the slugs produced by the Slug Generator. It meters satisfactorily without any adjustments to hard- or software in the stratified flow area and a small part of the stratified annular flow area, whereas it operates normally in its operating envelope. Metering in the stratified flow area is successful if slugs are produced that have steady state characteristics. Therefore the MCF needs to be placed some 35 diameters from the Slug Generator; whereas in annular flow metering is successful if the MCF is placed some 15 diameters from the Slug Generator to prevent the slugs from being blown apart. A MCF position description is still acking. This can he achieved by implementing a model on slug stability, slug hold-up, slug length and slug velocity in the Slug Generator model. MCF performance can be improved by implementing a model on developing slug flow in the software.Hydraulic EngineeringCivil Engineering and Geoscience