Computational Fluid Dynamic Techniques for Validating Geothermal Separator Sizing

Abstract

Geothermal turbine unit sizes of 100 MW or more are increasingly common because they offer economies of scale that result in lower installed cost. Concurrently, SKM’s designs for fluid collection and separation systems for large power plant have progressively moved to more centralised separator stations located relatively close to the power plant. Consequently, clients have been expecting individual separators to handle increasing large fluid flows. While SKM achieves exceptionally good steam dryness and purity from its separators using empirical formulae to progressively improve base designs over several decades, such methods have limitations with the larger unit sizes now being routinely specified. To address this, SKM has employed Computational Fluid Dynamic (CFD) analysis techniques to model the separation process and validate the sizing for very large separators and a wide range of fluid conditions, including multiple stages of flash. Increasing separator size also increases the modes of vibration within the vessels. The CFD modelling outputs have therefore been applied to a Finite Element Analysis model to validate the mechanical design and check for potential vibration problems. The benefit for plant owners/operators is the realisation of economies of scale and avoidance of resonant vibrations while maintaining high steam purity that enables extended periods between routine maintenance of their large single unit turbines.