(552a) Large Eddy Simulation of Axial Pulverized Coal Flames in O2/CO2 Environments

Oxy-coal combustion, in which an O2/CO2 mixture replaces air, is one of the few possible capture technologies to enable CO2 sequestration for existing coal-fired boilers. Burning coal with relatively pure oxygen, together with recycled flue gases, can produce a highly concentrated (up to 95% CO2) flue gas stream, which makes carbon sequestration more economical. One issue of interest in rapidly implementing a strategy to retrofit existing air-fired burners is to understand how replacing air by a O2/CO2 mixture affects the kinetics, aerodynamics and flame ignition in the near burner region. This study presents Large Eddy Simulations (LES) potential to predict oxy-coal flame characteristics and to be an important tool in the retrofitting process. In a turbulent coal flame, accurate predictions of the particle size and velocity distributions are critical for predicting the flame characteristics. Stokes number analyses suggest that LES has the capabilities to resolve all the turbulent length scales affecting coal particles in a coal flame, and could therefore lead to more accurate simulations. The Direct Quadrature Method of Moments was used to track the particle phase in an Eulerian framework. Simulations results show predictions of both the gaseous and solid phase dynamics and kinetics. The effect of partial pressure of oxygen on flame stand-off distance was investigated.