COAL IGNITION TEMPERATURE IN AN OXYGEN-ENRICHED CFB BOILER

摘要

The oxygen-enriched Circulating fluidized bed (CFB) combustion technology is a new method to reduce CO_2 emissions. The coal ignition temperature, T_i~F, in an oxygen-enriched CFB boiler is an important parameter for designing the startup burner and for choosing the operating strategy during the startup process. The combustion of five types of coal under four different atmospheres (air, O_2 27 %, O_2 40%, O_2 53%, CO_2 as balance gas) was measured in a laboratory scale fluidized bed (FB) with an under-bed preheat system. Using thermocouples and a Gas Analyzer, the changes in bed temperature and the concentration of the different components, such as O_2, CO_2 and CO, in flue gas were directly measured to determine T_i~F. It was found that T_i~F decreased with increasing O_2 concentration. The differences between the ignition temperatures determined in air and with 27 % O_2 were not significant. At lower bed temperatures, for two coal types with higher volatiles, a two stage-ignition for volatiles and char was observed under a high O_2 concentration. The time delay between the two stages decreased and finally merged into one with increasing bed temperature. Similar results were obtained in air. The coal with the higher volatile content had a lower ignition temperature in an oxygen-enriched CFB. Comparison of the ignition temperatures obtained by different methods and the feed temperatures in industrial CFB boilers showd that the measured result in a fluidized bed can be used as a reference for oxygen-enriched CFB boilers.