Kinetics of combustion of a pulverized brown coal char between 630 and 2200°K

• Published in: Combustion and flame 1973-10, Vol.21 (2), p.153-162
• Main Authors: Hamor, R.J., Smith, I.W., Tyler, R.J.
• Format: Article
• Language: English
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/S0010-2180(73)80020-3

Measurements have been made of the combustion kinetics of size-graded fractions (89, 49, and 22 μm) of a char prepared from Yallourn brown coal. Reactions were carried out in an entrainment reactor (between 900 and 2200°K) at oxygen partial pressures of about 0.2 and 0.1 atm, and in a fixed-bed reactor (between 630 and 760°K) at about 0.1 atm oxygen. Above 900°K, the 89 and 49 μm fractions were subject to rate control by the coupled processes of pore diffusion and chemical reaction on the pore walls; the rate coefficient, R a,c (the rate of carbon combustion per unit external area of the particle per (atmosphere of oxygen) 0.5), being given by R a , c = 9.3 exp [ − 16 , 200 / ( ℝ T p ) ] , g / [ cm 2 sec ( atm ) 0.5 ] , where T p is the temperature of the particle in °K and R is in cal/(mol °K). Below 760°K, the 89 and 49 μm fractions were found to react with rate control by chemical reaction alone. Above 900°K rate control for the 22 μm fraction lay intermediate between these two limits. At 1800°K the reactivity of the brown coal char is a factor of 4 higher than that of anthracite, and is 50% higher than that of a char from a low-rank bituminous coal; however, at 770°K the reactivity of the char is one to six orders of magnitude higher than the reactivities of other carbons.