Analysis of the errors associated with typical pulverized coal char combustion modeling assumptions for oxy-fuel combustion

• Published in: Combustion and flame Vol. 160; no. 8; pp. 1499 - 1509
• Main Authors: Hecht, Ethan S., Shaddix, Christopher R., Lighty, JoAnn S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.08.2013; Elsevier
• Subjects: Applied sciences; Carbon; Carbon dioxide; Coal; Coal combustion; Combustion; Combustion of solid fuels; Combustion. Flame; Computational efficiency; Computational fluid dynamics; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuel processing. Carbochemistry and petrochemistry; Fuels; Gasification; Mathematical models; Oxy-fuel; Penetration; Solid fuel processing (coal, coke, brown coal, peat, wood, etc.); Theoretical studies. Data and constants. Metering; Coal combustion; Gasification; Oxy-fuel; Error analysis; Computational fluid dynamics; Char; Fuel; Oxycombustion; Theoretical study; Pulverized coal; Combustion; Modeling
• DOI: 10.1016/j.combustflame.2013.02.015
• ISSN: 0010-2180

In CFD models of pulverized coal combustion, which often have complex, turbulent flows with millions of coal particles reacting, the char combustion sub-model needs to be computationally efficient. There are several common assumptions that are made in char combustion models that allow for a compact, computationally efficient model. In this work, oft used single- and double-film simplified models are described, and the temperature and carbon combustion rates predicted from these models are compared against a more accurate continuous-film model. Both the single- and double-film models include a description of the heterogeneous reactions of carbon with O2, CO2, and H2O, along with a Thiele based description of reactant penetration. As compared to the continuous-film model, the double-film model predicts higher temperatures and carbon consumption rates, while the single-film model gives more accurate results. A single-film model is therefore preferred to a double-film model for a simplified, yet fairly accurate description of char combustion. For particles from 65 to 135μm, in O2 concentrations ranging from 12 to 60vol.%, with either CO2 or N2 as a diluent, particle temperatures from the single-film model are expected to be accurate within 270K, and carbon consumption rate predictions should be within 16%, with greater accuracies for a CO2 diluent and at lower bulk oxygen concentrations. A single-film model that accounts for reactant penetration and both oxidation and gasification reactions is suggested as a computationally efficient sub-model for coal char combustion that is reasonably accurate over a wide range of gas environments.