Abstract
The aim of the present investigation is to examine differences between O 2/N 2 and O 2/CO 2 atmospheres during devolatilization and char conversion of a bituminous coal at conditions covering temperatures between 1173 K and 1673 K and inlet oxygen concentrations between 5 and 28 vol.%. The experiments have been carried out in an electrically heated entrained flow reactor that is designed to simulate the conditions in a suspension fired boiler. Coal devolatilized in N 2 and CO 2 atmospheres provided similar results regarding char morphology, char N 2-BET surface area and volatile yield. This strongly indicates that a shift from air to oxy-fuel combustion does not influence the devolatilization process significantly. Char combustion experiments yielded similar char conversion profiles when N 2 was replaced with CO 2 under conditions where combustion was primarily controlled by chemical kinetics. When char was burned at 1573 K and 1673 K a faster conversion was found in N 2 suggesting that the lower molecular diffusion coefficient of O 2 in CO 2 lowers the char conversion rate when external mass transfer influence s combustion. The reaction of char with CO 2 was not observed to have an influence on char conversion rates at the applied experimental conditions.
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