Date of Award
Doctor of Philosophy
Robert C. Brown
This work introduces a method for determining coal devolatilization, char burning, limestone calcination, and sulfur sorption rates based on the analysis of CO[subscript]2 and SO[subscript]2 profiles from a fluidized bed combustor. The technique is non-intrusive and can be performed under realistic combustion conditions. The method involves batching coal or limestone samples in a fluidized bed heated with propane gas or other fuel. Carbon dioxide and sulfur dioxide profiles are analyzed with linear models to obtain characteristic time constants for coal devolatilization, char burning, and sulfur sorption. Time constants for coal devolatilization and char burning can be directly related to devolatilization times and char burnout times, respectively, for a coal sample. Characteristic times for calcination and sulfur sorption can be related to the rate of limestone calcination and sulfation in the fluidized bed, respectively;Experiments to validate the technique were carried out in a 0.2 m dia. pilot fluidized bed combustor. Single sized coal and limestone samples were used for the validation tests. Coal devolatilization and char burning times obtained by this technique are comparable to times measured by more conventional thermogravimetric and visual techniques. Activation energies obtained for limestone calcination are quite close to those obtained by thermogravimetric methods. However, lower than expected activation energies obtained for the sulfation of limestone were attributed to complex pore diffusion processes;Time constants for calcination were found to be proportional to particle size, suggesting that chemistry is rate limiting during this process. Sulfation time constants were weakly related to particle size, an idication that both chemistry and pore diffusion are rate limiting.
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Nearchos J. Christofides
Christofides, Nearchos J., "Determining char burning and sulfur sorption rates from dynamic analysis of CO2 and SO2 profiles " (1993). Retrospective Theses and Dissertations. 10220.