Multiphase CFD Simulation of Flow Inside Liquid Seal Drums of the Refinery Flare System

Abstract

The present work deals with improving the reliability of the liquid seal drum in the refinery flare system. CFD (based on volume of fluid concept) as well as theoretical modeling have been used for deciphering the hydrodynamics in two different designs (designated as design-1 and design-2) of the liquid seal drums. Results of the CFD simulations showed that the internals present in design-1 facilitate in bubble coalescing, thus resulting in large sized Taylor bubbles, which cause large fluctuations in the liquid level. Large level fluctuations create problems such as flare puffing, knocking, and dislodging of seal drum internals. On the basis of the CFD model findings, a one-dimensional model based on Taylor bubble phenomenon(1) has been adopted. Subsequently, the 1D model was used for calculating the Taylor bubble size and liquid level fluctuations. The 1D model was also used to predict the bubble size and liquid level fluctuation in another design (design-2) of the seal drum. Design-2 was also tested using CFD, which shows smooth passage of flare gas in the form of small bubbles with little fluctuation in liquid level. On the basis of the study, it was suggested to change the design-1 by design-2. Suggestions were implemented in the plant, which relieved it of problems faced with design-1. This led to reliability improvement and substantial monetary benefits.