Low-temperature air oxidation of caking coals. 1. Effect on subsequent reactivity of chars produced

Abstract

The effect of preoxidation of two highly caking coals in the temperature range 120–250 °C on weight loss during pyrolysis in a N 2 atmosphere up to 1000 °C and reactivity of the resultant chars in 0.1 MPa air at 470 °C has been investigated. Preoxidation markedly enhances char reactivity (by a factor of up to 40); the effect on char reactivity is more pronounced for lower levels of preoxidation. For a given level of preoxidation, the oxidation temperature and the presence of water vapour in the air used during preoxidation have essentially no effect on weight loss during pyrolysis and char reactivity. An increase in particle size of the caking coals reduces the rate of preoxidation as well as subsequent char reactivity. Preoxidation of caking coals sharply increases the surface area of the chars produced. Compared to heat treatment in a N 2 atmosphere, pyrolysis in H 2 of either the as-received or preoxidized coal results in a further increase in weight loss and a decrease in subsequent char reactivity.