| Description |
Modeling and experimental studies of the oxy-combustion behavior of pulverized coal chars are detailed in this work. During oxy-combustion, nitrogen is separated from oxygen before the introduction of oxygen, recycled flue-gas, and fuel into a coal boiler. The nearly pure CO2 effluent (after condensation of H2O) can be captured through condensation, and then utilized or stored, preventing the climate changing impacts of this greenhouse gas. Although oxy-combustion has been considered and studied for over a decade, there are still misunderstood aspects of the science th a t this research aims to clarify through modeling and experimental studies. First, a detailed model of a single char particle is presented. The detailed model is employed to assess the impact of CO2 and steam gasification reactions on the oxy-combustion of coal chars. The detailed model indicates th a t gasification reactions reduce the predicted char particle temperature significantly. Lower temperatures reduce the radiant emission and rate of char oxidation, but the char carbon consumption rate actually increases by approximately 1 0%, since the gasification reactions are consuming carbon (in addition to the oxygen). Gasification reactions account for about 20% of the carbon consumption in low oxygen conditions, and about 30% of the carbon consumption under oxygen enriched conditions. Secondly, typical pulverized coal char combustion modeling assumptions are described and two simplified models are compared to the detailed model. The single-film model, wherein gas-phase reactions are ignored yields accurate results, with particle temperature predictions accurate to within 270 K, and carbon consumption rate predictions accurate to within 16%. Finally, an entrained flow reactor (EFR) was used to make measurements of singleparticle temperatures under a wide range of conditions for three coal chars. The environments ranged from 24-60% O2, 10-14% H2O, with N2 or CO2 serving as the diluent. Collected chars were also analyzed for burnout and surface area. Kinetic parameters were found for the simplified model to fit the experimental data, for each of the coal chars, over the wide range of environments studied. The model described herein and these kinetic parameters can be used in more complex CFD codes to accurately predict the oxy-combustion behavior of coal chars. |
