EFFECTS OF CAO, HIGH-TEMPERATURE TREATMENT, CARBON STRUCTURE, AND COAL RANK ON INTRINSIC CHAR OXIDATION RATES

The low-temperature kinetics of oxidation of Dietz sub-bituminous coal char prepared in a methane flat-name burner (4% post-name oxygen) was studied by TGA both in the presence and in the absence of calcium min erals. The reactivities of untreated and calcium-reloaded chars at 600 K are 5 and 2 times higher than acid-washed char, indicating a signif icant catalytic effect for CaO. The intrinsic reactivities of these ch ars after oxidation in a drop-tube reactor at a particle temperature o f about 1900 K and 5% O-2 also show a similar trend, although the reac tivity of each char is lowered by about a factor of 10 due to this hig h-temperature oxidation. The physical properties of these chars are al so significantly altered due to high-temperature oxidation treatment. Comparison of intrinsic oxidation rates of unloaded Spherocarb and dem ineralized (acid-washed) chars of Zap and Dietz coals based on availab le carbon mass shows a trend of increasing intrinsic rate with decreas ing skeletal density suggesting that the intrinsic rate is a function of carbon structure. However, in the presence of CaO, the intrinsic ox idation rate based on CaO surface area is found to increase with decre asing coal rank. Dispersion of CaO is significantly higher for the ori ginal Dietz char prepared in a flat-flame burner (34%) than for the Ca -loaded char (12%), indicating that the Ca-reloading procedure could b e improved.