Motion and Combustion Behavior of Single Char Particle in Oxy-Fuel Fluidized Bed: Experimental and Modeling Studies

Oxy-fuel fluidized bed combustion is a leading carbon capture, utilization, and storage technology that is gaining considerable attention from both academia and industry. The combustion of char particles in a fluidized bed is intricately linked to their motion and chemical reactions, with variations in heat transfer, mass transfer, and reaction rates across different locations. However, many theoretical studies on single-particle combustion assume a uniform emulsion phase, overlooking the influence of particle movement on combustion, which will greatly reduce the accuracy of the combustion model, especially in oxy-fuel combustion. In this study, we conducted combustion tests on char particles in a visualized fluidized bed reactor and systematically assessed the effects of various operating conditions on combustion. A combustion model for a single char particle in a fluidized bed was developed, considering forces, movement, gasification, and heat and mass transfer. The error of model was within 15% when compared to experimental results. We quantitatively analyzed the relationship between particle movement and periodic temperature changes and investigated the impact of various parameters through sensitivity analysis. The results show that changes in atmosphere and bed temperature minimally affect particle motion, whereas particle density, fluidization number, and size significantly influence it. Biomass char floats on the bed surface for about 30–40% of the combustion process, while bituminous coal char primarily remains in the emulsion phase. High oxygen concentrations or bed temperatures significantly enhance char gasification in O2/CO2 atmosphere. The gasification conversion ratio is more closely related to the average char temperature than to peak temperature. Temperature oscillations in char particles rise with oxygen concentration and fluidization number but decrease with bed temperature and particle size.