Numerical Investigation of Oxygen-Enriched Pulverized Coal Combustion

This paper presents calculations of oxygen-enriched coal combustion. Enriching combustion air with oxygen is considered one of the most effective methods to improve thermal efficiency, reduce pollutant emissions such as NO_x, and facilitate capture of CO₂ pollutant from flue gas. In addition to solving transport equations for the continuous phase (gas), a discrete second phase (spherical particles) is simulated in the Lagrangian frame of reference. Reaction is modeled by a two-mixture fractions/PDF approach. Discrete phase modeling is used for the prediction of discrete phase trajectory and heat and mass transfer to and from particles. The coal used is a Canadian high sulfur bituminous coal. The mass fraction of oxygen in the combustion air was varied from 21% (air) to 100% (pure oxygen). The results show that the temperatures of the gas phase and coal particles increase, respectively, by 13% and 9% when the mass fraction of oxygen is increased from 21% to 100%. One important result is that the CO₂ in the oxygen/coal exhaust stream is at a much higher concentration (50% higher) compared with the air and coal exhaust stream highly diluted by N₂. This will help the capture of CO₂ emissions from flue gas and consequently reduce the CO₂ capture costs.