The use of Computational Fluid Dynamics (CFD) for slugging prediction in a two-phase geothermal production system

Abstract

Slugging is a flow phenomenon that occurs when gas and liquid phases coexist in a pipeline under certain conditions, causing pressure fluctuations and operational challenges. In geothermal production systems, slugging can compromise stable operation and safety of the power plant and separation equipment. It is important to predict and avoid slugging conditions in two-phase geothermal pipelines.
In this paper, we present a Computational Fluid Dynamics (CFD) approach for slugging prediction in a planned two-phase delivery pipeline for the Ngati Tuwharetoa Geothermal Asset (NTGA) Geothermal Field in Kawerau, New Zealand. We use CFD to model the pipeline geometry and the multiphase flow conditions and examine the results. A weakness in the results presented is that the pipeline being modelled has not yet been built, so the accuracy of model predictions has not yet been validated with field data.
We also present a study of two-phase flow into a separator and how this can lead to structural vibration. The focus was on adjusting the incoming pipework to reduce unsteady loads from the high liquid fraction. Achieving smooth, steady liquid entry helps prevent wall splashing and cyclic loading. The results were calibrated to movements measured in the operating separator.
One of the historic challenges of setting up a CFD model for slugging prediction is managing the size of the model and the calculation time for such large and complex systems. Our results show that, with the assistance of cloud-computing, a CFD approach to slugging prediction is now feasible and cost-effective. Our premise is that the CFD approach can provide useful insights for the design and operation of two-phase geothermal pipelines.