MODELING OF JET DIFFUSION FLAME IN GAS FLARE SYSTEMS

Abstract

Safe disposal of waste gases are necessary in petroleum refineries and petrochemical plants during their steady state operation as well as during and plant failure or shut down. Waste gases are generally burnt in a flare system. Flare is an utility and therefore, it is necessary to design the flare system for optimum conditions. Burning of waste gases, results in the emission of heat. This heat is transported as the radiant heat flux, to the surrounding. Hence the flare needs to be designed in such a way that the surrounding vegetations, human lives and existing flammable materials do not suffer much damage. For this reason, the calculation of the flame height becomes essential. The flame height above the flare tip depends mainly on the source fuel temperature and the burner design (mainly burner diameter) and the stack exit velocity. The present dissertation entitled "Modeling of Jet Diffusion Flame in Gas Flare Systems" deals with the one dimensional modeling of the flare flame and describes the characteristics of the flame. The mathematical model is based on the laws of conservation of mass, momentum and energy. The unsteady state equations obtained from these conservation laws are converted into steady state ordinary differential equations and are then solved numerically by fourth order Runge — Kutta method. A reaction efficiency parameter (q) is introduced in the model to decipher the characteristics of combustion between the fuel and the entrained air. The model solution provides the variation of the flame geometry, the flame temperature and the flame velocity along the height and shows their dependency on the stack exit velocity. The study compares the flame height obtained by the present model with the experimental values of Zukoski et al. (1981) and those predicted by using different equations proposed by different researchers. It is found that, the model predictions are in agreement with the experimentally observed flame heights. The expected safe distance of separation from the flare system for surrounding vegetations, working personnel and neighbouring flammable materials is also estimated.