Experimentally Determined Overall Burning Rates of Coal Chars

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Abstract
-Simultaneous measurements of the size, temperature, and velocity of single pulverized-coal char particles are used to determine the overall burning rates of the chars flowing in hot. oxidizing gaseous environments. The single film model of a burning carbon particle is employed with CO as the sole heterogeneous reaction product. Arrhenius parameters which describe the chemical reaction rate coefficients are derived for the chars of a hvb-biturninous coal from Missouri, a North Dakota lignite and a high-swelling, bituminous coal from Kentucky. Gaseous environments in the temperature range 14S0 to 1550 K, having one, three and six mole-percent oxygen were employed. The measurements indicate that in the three and six mole-percent oxygen environments, the temperatures of particles in the size range 70 to 150 𝛍m exceed the local gas temperatures by as much as 150 K. The results suggest that at high particle temperatures, the chars of the coals burn in a regime in which the overall particle burning rate s are limited by the combined effects of pore diffusion and the intrinsic chemical reactivity uf the particle material. The data support burning at constant density with a decrease in particle size with mass loss. A value of 0.5 is recommended for the apparent reaction order with respect to the oxygen partial pressure for the carbon-oxygen heterogeneous reacti on.

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