This paper addresses the problem 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 in particular 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 pre-conditioning with air is able to promote oxygen chemisorption thus increasong the combustion reactivity of ashes. Fly ashes with high LOI have been exposed to air at temperature <400°C for times up to 300minResults show that a satisfactory extent of oxygen chemisorption can be attained at 300-400°C with 1-2 hours holding time. After this conditioning, samples have been tested to check their combustion reactivity by means of non isothermal thermogravimetric analysis. Additionally combustion experiments have been carried in a purposely designed suspension reactor at temperature up to 1000°C. Results confirm that ash pre-conditioning reduces the burn-out time of carbon in ash. The idea resulted in the international patent application PCT/IB2010/052421.
Beneficiacion of coal fly ashes by oxygen chemisorption
OSenneca;
2011
Abstract
This paper addresses the problem 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 in particular 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 pre-conditioning with air is able to promote oxygen chemisorption thus increasong the combustion reactivity of ashes. Fly ashes with high LOI have been exposed to air at temperature <400°C for times up to 300minResults show that a satisfactory extent of oxygen chemisorption can be attained at 300-400°C with 1-2 hours holding time. After this conditioning, samples have been tested to check their combustion reactivity by means of non isothermal thermogravimetric analysis. Additionally combustion experiments have been carried in a purposely designed suspension reactor at temperature up to 1000°C. Results confirm that ash pre-conditioning reduces the burn-out time of carbon in ash. The idea resulted in the international patent application PCT/IB2010/052421.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
