Publications

In this study, char combustion of pulverized coal under oxy-fuel combustion conditions was investigated on the basis of experimentally observed temperature-size characteristics and corresponding predictions of numerical simulations. Using a combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometer, combustion characteristics (particle temperatures and apparent size) of pulverized coal char particles was determined for combustion in both reduced oxygen and oxygen-enriched atmospheres with either a N{sub 2} or CO{sub 2} bath gas. The two coals investigated were a low-sulfur, high-volatile bituminous coal (Utah Skyline) and a low-sulfur subbituminous coal (North Antelope), both size-classified to 75-106 {micro}m. A particular focus of this study lies in the analysis of the predictive modeling capabilities of simplified models that capture char combustion characteristics but exhibit the lowest possible complexity and thus facilitate incorporation in existing computational fluid dynamics (CFD) simulation codes. For this purpose, char consumption characteristics were calculated for char particles in the size range 10-200 {micro}m using (1) single-film, apparent kinetic models with a chemically 'frozen' boundary layer, and (2) a reacting porous particle model with detailed gas-phase kinetics and three separate heterogeneous reaction mechanisms of char-oxidation and gasification. A comparison of model results with experimental data suggests that single-film models with reaction orders between 0.5 and 1 with respect to the surface oxygen partial pressure may be capable of adequately predicting the temperature-size characteristics of char consumption, provided heterogeneous (steam and CO{sub 2}) gasification reactions are accounted for.

In this study, char combustion of pulverized coal under oxy-fuel combustion conditions was investigated on the basis of experimentally observed temperature-size characteristics and corresponding predictions of numerical simulations. Using a combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometer, combustion characteristics (particle temperatures and apparent size) of pulverized coal char particles was determined for combustion in both reduced oxygen and oxygen-enriched atmospheres with either a N{sub 2} or CO{sub 2} bath gas. The two coals investigated were a low-sulfur, high-volatile bituminous coal (Utah Skyline) and a low-sulfur subbituminous coal (North Antelope), both size-classified to 75-106 {micro}m. A particular focus of this study lies in the analysis of the predictive modeling capabilities of simplified models that capture char combustion characteristics but exhibit the lowest possible complexity and thus facilitate incorporation in existing computational fluid dynamics (CFD) simulation codes. For this purpose, char consumption characteristics were calculated for char particles in the size range 10-200 {micro}m using (1) single-film, apparent kinetic models with a chemically 'frozen' boundary layer, and (2) a reacting porous particle model with detailed gas-phase kinetics and three separate heterogeneous reaction mechanisms of char-oxidation and gasification. A comparison of model results with experimental data suggests that single-film models with reaction orders between 0.5 and 1 with respect to the surface oxygen partial pressure may be capable of adequately predicting the temperature-size characteristics of char consumption, provided heterogeneous (steam and CO{sub 2}) gasification reactions are accounted for.

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Previous research has highlighted the important role of reduced oxygen diffusivity through the particle boundary layer during oxy-fuel combustion with flue gas recirculation (i.e. high CO2 environments). Single-particle modeling of this process also revealed that partial conversion of the carbon oxidation product CO in the particle boundary layer was important during oxygen-enhanced combustion for particles approximately 130 μm in diameter. In this study, the influence of oxy-fuel combustion conditions on char combustion rates is being investigated both experimentally and through detailed modeling, for several different characteristic pulverized coal particle sizes. Both a high-volatile bituminous coal (Utah Skyline) and a typical PRB low-sulfur subbituminous coal (North Antelope) are being investigated. A combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometer is being used to determine the combustion kinetics of pulverized coal chars when burning in both reduced oxygen and oxygen-enriched atmospheres with either a N2 or CO2 bath gas. Preliminary calculations using the particle combustion code SKIPPY have shown that boundary layer conversion of CO becomes important for oxy-fuel combustion of char particles larger than 60 μm in diameter and, for a char particle reactivity characteristic of high-volatile bituminous coals, the boundary layer reactions result in over a 20% enhancement in the char burning rate for particle sizes between 70-80 μm in diameter. Copyright © (2009) by the International Pittsburgh Coal Conference.