Laboratory Studies on Devolatilization and Char Oxidation under PFBC Conditions. 1. Volatile Release and Char Reactivity

摘要

Characteristics of solid fuels during devolatilization and char oxidation under pressurized FBC conditions have been recently studied in a laboratory-scale PFBC batch reactor. The reactor tube has an inside diameter of 60 mm and height of 1.2 m and can be controlled at well-defined operating conditions. Combustion behaviors, including devolatilization rate, volatile-C amount, devolatilization time, char burnout time, and char reactivity, were investigated under the base testing conditions (T_b = 850℃, p = 11 bar, O_2 = 3% v/v, V_f = 0.24 m/s) with 10 different fuels, from high-volatile peat to relatively low-volatile coke. A special focus of this study was the effect of pressure. It was examined in two parts: oxygen partial pressure (with changing either oxygen concentration in the fluidizing gas or system pressure) and total pressure (with changing system pressure and oxygen concentration simultaneously at fixed oxygen partial pressure). Results showed that both oxygen partial pressure and total pressure affected the processes of devolatilization and char oxidation. They affected devolatilization rate in the same direction but char reactivity in the opposite direction. The influences of other parameters, such as batch particle size, bed temperature, and fluidizing velocity, on the combustion characteristics were also studied in detail for three fuels: lignite, Illinois No. 6 coal, and Kiveton Park coal. Overall, devolatilization was controlled by chemical kinetics and char burning rate mainly by oxygen transfer and diffusion under the examined PFBC conditions.