In-bed char combustion of Australian coals in PFBC. 2. Char combustion without secondary fragmentation

Abstract

Char combustion parameters that significantly affect the in-bed combustion of char in PFBC were determined experimentally using a batch-fed PFBC. The ratio of carbon to oxygen consumed on the surface of a burning char particle was determined and it was concluded that CO was the only product of char combustion in PFBC. Model simulations revealed that, for PFBC, mass transfer controlled the combustion of large char particles ≥2 mm, whereas the combustion of small char particles below 0.9–2 mm was controlled by both mass transfer and chemical kinetics. System pressure influenced the char combustion via the interaction between chemical kinetics and the mass transfer of oxygen to the char. Char particle temperature varied markedly with oxygen partial pressure in the particulate phase, indicating a distribution of char particle combustion rates in PFBC. In modelling char combustion in PFBC, the temperature of char particles in the bed should be calculated at different locations based on a heat balance around the burning char particle taking into account the local bed oxygen concentration.