Characteristics of charcoal combustion and its effects on iron-ore sintering performance

Using biomass for partial or complete replacement of coke breeze in iron ore sintering process is an attractive technique for reducing emissions of greenhouse gas and gaseous pollutants. But one drawback of this technique is that low or medium grade charcoal may lead to the failure in achieving proper sintering performance. In this paper, the behaviors of coke combustion versus charcoal combustion in sintering bed were compared. The results of thermal profile and exhaust gas composition indicated that the sinters quality was deteriorated at high charcoal proportion. Lacking heat release in melting zone and the excessively high combustion rate were the reasons to weak sinters. In order to ensure the sintering performance when using medium grade charcoal in sintering bed, the effects of three improving measures (proposing the equivalent fixed carbon substitution approach, increasing charcoal particle size and adopting coated charcoal combustion) were experimentally tested. The results showed that equivalent fixed carbon substitution approach was more effective to produce sufficient heat in melting zone at medium grade charcoal combustion. Additionally, it was also found that increasing charcoal particles size and applying coated charcoal combustion method could reduce combustion rate to achieve a proper matching condition between flame front speed and heat transfer front speed. Consequently, with the help of equivalent fixed carbon substitution approach, coarse charcoal and coated charcoal particles, the peak temperature, holding time above 1100°C, melting quantity index and combustion efficiency were increased in the charcoal sintering process.