Simulation of a spray combustion behavior for two kinds of slurry fuels. (Effect of two stage air introduction and spray characteristics on combustion)

The effect of two-stage combustion (TSC) air introduction and spray characteristics on combustion behavior was studied for two kinds of slurry fuels (pitch-water mixtures, PWM, and coal-water mixtures, CWM) spray combustion system. Experiments were carried out on the isothermal flow in an acrylic duct and on the combustion flow in two different furnaces. The velocity components and fluctuations of the isothermal flow field were measured by laser Doppler anemometry. The gas temperature, oxygen and NO concentrations in the furnace and NO and soot concentrations in the exhaust gas were measured in combustion experiments. Numerical analyses of the isothermal and combustion flow fields were performed. In these analyses it was difficult to simulate the TSC isothermal air flow pattern by two-dimensional axisymmetric analysis. For the combustion field, the NO concentration increased with the residence time of the combustion gas in the high-temperature region and the soot concentration decreased with an increase in the droplet residence time in the furnace and in the oxygen concentration. For spray characteristics, the combustion efficiency was enhanced by decreasing the initial droplet velocity even if the droplet mean diameter was larger.