Numerical study of effect of hydrogen content on the structure of syngas diffusion flame

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Syngas, produced during gasification reactions, primarily is composed of carbon-monoxide (CO) and hydrogen (H2), along with other gases like carbon-dioxide (CO2), nitrogen (N2) and methane (CH4). The composition of these gases produced during gasification varies with the type of fuel, oxidizer concentration, operational pressure and temperature. For instance, the amount of CO produced during the endothermic reactions depends strongly on the temperature. The flame structure for different syngas compositions would be an important input for designing a good syngas burner. This paper is an attempt to numerically study the effect of varying the hydrogen concentration in syngas, on the resulting flame structure. A straight cylindrical tube of 4 mm diameter has been considered as the burner tube. Length has been chosen such that flow completely develops within the tube. The jet emerging at the exit of the tube entrains air naturally and the flow is laminar. An axi-symmetric model with simplified Davis mechanism (detailed chemistry mechanism consisting of fourteen species) has been used. A detailed examination of the reaction zone indicates that along the radial direction, CO oxidation occurs followed by the formation of water vapor. The higher species diffusivity and kinetic rate coefficient values for the hydrogen- oxygen reaction over those of CO play a crucial role in determining the overall syngas flame characteristics.