CFD Modelling of the Demister in the Multi Stage Flash Desalination plant

Demisters are used to remove entrained brine droplets from flashed off vapor within the flashing stages of the multi stage flash desalination process (MSF). This is necessary to prevent accumulation of brine droplets on the outside surface of the condenser tubes and contamination of the desalinated water. The aim of this work is to design a new demister with lower pressure drop and unaffected separation efficiency which can be later installed in the flashing stages of the MSF plant and causes reduction in the required heat transfer area. In this work the demister performance is predicted as a function of design (wire diameter), and operating parameters (stage temperature). This objective was pursued through the use of commercial computational fluid dynamics (CFD) software. The wire mesh demister was modeled as a tube bank. The model was time dependent and was validated against experimental and field data obtained from large scale MSF units. This manuscript includes model development and computer solution using the FLUENT code. The model predictions for both experimental and large scale units show good agreement of measured pressure drop and separation efficiency against data from existing MSF plants.