Analysis of Combustion Characteristics and Investigation of the Cause of Thermal Stress in the Gas Refinery Flare, using the CFD Technique

In this study, CFD simulation of low-pressure flare (LP) of the gas refinery has been investigated to evaluate the effects of geometric parameters of flare tip, especially the effect of steam injection on the combustion characteristics of flame, as well as no flame backflow. The computational model was developed by considering related transport phenomena (momentum, heat, mass, radiation, turbulence and chemical reactions). In order to create the suitable computational mesh, finer meshes were selected around the steam injection nozzles and internal parts of the flare. The results of the developed computational model include temperature and velocity profiles (shape and appearance of the flame), profiles of the gas species, tracking of the injected steam, as well as profiles of the combustion products. The results of the CFD simulation showed that due to the injection of steam from the nozzles in the center of the flare tip and its very high speed, a complex hydrodynamics is created in the opening of the flare tip, which leads to the formation of vortices. Due to the formation of a vortex at the flare tip, some of the surrounding air is drawn into the flare tip, which is in the form of a flame in the gas seal to the perforated plate of the flare tip. For this reason, the body temperature of the flare tip increases up to 2200K in some parts of the perforated plate and gas seal plates. The results of the simulation regarding the return of the flame into the flare tip are consistent with the observations in the industrial unit. The internal body of the LP flare tip in the industrial unit due to the flame being drawn into the flare tip faced with thermal stresses, and as a result causes its rapid destruction.