Evaluation of combustion behaviour of coal blends for use in pulverized coal injection (PCI)

Generally, coal blends show unexpected combustion performance which cannot be explained on the basis of individual coal properties particularly coal rank and volatile matter. The current study investigates the combustion behaviour of four coals and their blends at different proportion under high oxygen concentrations more than 21% for use as feed coal in pulverized coal injection (PCI) in the blast furnace. Three different high rank coals blended with one relatively low rank coal in different proportions and combustion behaviour of the individual coals and their blends were studied in thermogravimetric analyser (TGA) and drop tube furnace (DTF) with enriched oxygen concentration. The results suggest that coal D is most suitable for PCI injection. The other three higher rank coals are not suitable for PCI and if charged singly, they can lead to significant proportions of unburnt char in the stack of the blast furnace. To accommodate wide variety of coals of different rank and types, blending of coal is considered as a suitable option for the PCI injection. Results of thermogravimetric analysis showed that low rank coal influenced the ignition temperatures of blends whereas high rank coals influenced their burnout behaviour. Both TGA and DTF study shows that blends containing up to 10% of high rank coal gives better combustion performance even that of low rank coal.