Three-dimensional steady parabolic calculations of large scale methane turbulent diffusion flames to predict flare radiation under cross-wind conditions

Abstract

Results obtained during a program geared to the development of a computer code to predict flare radiation in off-shore platforms are presented. Emphasis is put on the novel features included in this diffusion flame model viz: o i) a pseudo stream function formulation of the three dimensional parabolic flow structure which describes strong cross-wind flare interactions. ii) an improved radiation model where the “equivalent emitting body” approach is developed to adequately describe radiation fluxes coming out of the flame and, iii) an improved soot production and oxidation model to take care of the soot contribution to the emitted radiative fluxes. Turbulent combustion is modelled via the k -ω technique coupled with Magnussen's turbulent rate of mixing approach. A short description of the developed numerical solution procedures is given with emphasis on the self consistency of the boundary condition formulations. Comparisons are shown between large scale experimental flare data (obtained for round methane gas flares) and calculated results. A±15% accuracy is obtained for methane flow rates ranging from 0.8 up to 15 kg/sec (gas exit velocities not superior to 300 m/sec) under both quiet and windy air conditions. Temperature and soot concentration profiles are presented under windy conditions to illustrate how weak aerodynamic interactions may generate very drastic changes on received radiative fluxes, especially for down-wind located targets.