Numerical Modeling of Flow in a Mist Eliminator for Geothermal Power Plants

Considering both durability and electricity production, the quality of steam extracted from a geothermal well and led into the turbine has an important impact on the overall performance of a geothermal power plant. To increase the steam quality, i.e. the share of pure steam in the two-phase mixture, mist eliminators are commonly used in industry. These devices consist of a drum in which the fluid is expanded and guided through a filter, where the droplets are separated from the steam. The design process of mist eliminators is often based on empirical data and the flow inside the drum is not well understood, yet. Hence, numerical simulations with the freeware OpenFOAM were performed during this project to develop a wider understanding of the single-phase flow behavior inside the eliminator. Eleven simulations were performed including three simulations as part of a mesh sensitivity analysis, one to investigate different numerical schemes and two simulations with different turbulence models. Further, three cases were run with varying inlet velocities and two with different inlet/outlet configurations. First, an appropriate simulation setup could be found based on comparison with a reference value and recommendations from the literature. This setup included a medium sized mesh (50 mm cell size), upwind scheme discretization and the k-ω-SST turbulence model. Second, the variation of the inlet velocities could be used to manipulate the pressure drop and the flow distribution within the wire mesh. Third, both of the geometry changes gave worse overall pressure drops, however, the flow distribution inside the wire mesh could be improved by the usage of vertically attached inlet pipes.