COMBUSTION OF COAL CHARS IN OXYGEN-ENRICHED ATMOSPHERES

Abstract

This work pertains to the high-temperature combustion of pulverized coal chars under oxygen-enriched atmospheres. Single char particles were burned in a drop-tube furnace, electrically-heated to 1300–1500 K, in 21%, 50% and 100% O₂, in a balance of N₂. Their luminous combustion histories were observed with two-color ratio pyrometry. A solution of the Planckian ratio-pyrometry equation for temperature was implemented, extending on Wien's approximation. The temperature and time histories for 45–53 µm bituminous chars experienced wide particle-to-particle disparity, and varied depending on oxygen mole fraction and furnace temperature. Average char surface temperatures increased from 1600–1800 K in air, to 2100–2300 K in 50% O₂, to 2300–2400 K in 100% O_2, at gas temperatures of 1300–1500 K, respectively. Combustion durations decreased from 25–45 ms in air, to 8–17 ms in 50% O₂, to 6–13 in 100% O₂. Thus, average particle temperatures increased by up to 45%, whereas burnout times decreased by up to 87% as combustion was progressively enriched in O₂ until 100% was attained. The apparent and intrinsic reactivity of the chars burning at 1500 K gas temperature were found to increase by factors of to 8 and 35, respectively, as the oxygen mole fraction increased by a factor of five, from 21% to 100%.

Keywords:

• Coal chars
• Combustion rate
• Oxygen mole fraction
• Pyrometry
• Temperature-time

Technical discussions with Dr. Nasser Fard on Statistical Analysis and with Dr. George Gavalas on Reaction Rates are gratefully acknowledged.