Three-Dimensional Flame Structure in Wall-Fired Swirl Flame Combustors

A CFD solver CFX is used to analyze the complex behavior of turbulent reacting flow inside the furnace. The flow characteristics for various combustor geometries, fuel/air ratios, and injection velocities, and swirl levels are investigated. Starting with a cylindrical furnace fired with gaseous fuel from a concentric tube burner (both with and without swirl), the mixture-fraction is predicted using the k-ε and RSM turbulence models. The discrepancies between the predictions and measurements are most significant in the flame core of upstream regions. It may stem from inappropriateness of the assumed inlet conditions and the combustion model. However, the calculated results are still qualitatively acceptable. After the validation work of the numerical model, a rectangular furnace with four wall-fired swirling combustors is employed to investigate the effect of neighbouring burners and geometry on combustion characteristics. The central recirculation zone which appeared in the isothermal flowfield vanished in the combustion case. It may be attributed to the fact that the hot gas suddenly expands outward and destroys the recirculation mechanism. Thus, the central flame could not hold. In addition, the four corner flames are stretching against the wall and their shapes are similar to a “cam” profile. The results are intended to assist in the development and validation of a numerical model for predicting furnace flows in wall-fired power plants.