Beneficiation of coal fly ashes by oxygen chemisorption

This paper addresses the issue of unburnt carbon in fly ashes from coal-fired power stations. It has been shown that carbon-in-ash has much lower combustion reactivity than the original coal, because of the extensive thermal annealing experienced in the boiler. Thermal annealing reduces the rate of the first reaction step of which carbon combustion is composed, namely oxygen chemisorption. In the present work experiments have been carried out in order to verify if a preconditioning stage consisting of mild pre-oxidation with air is able to promote oxygen chemisorption thus increasing the combustion reactivity of ashes. Fly ashes with high LOI have been exposed to air at temperature