Evaluation of petrology and reactivity of coal blends for use in pulverized coal injection (PCI)

The current study investigates the combustion performance and properties of a Brazilian subbituminous coal (Faxinal Mine) for use as feed coal in pulverized coal injection (PCI) in the tuyeres of the blast furnace.Faxinal coal alone is not suited for PCI because of chemical properties such as the high ash, sulphur and alkali contents, but one mode of its utilization for PCI can be in coal blends with low-ash imported coals.For this purpose a coal from Faxinal Mine and two high-rank imported coals have been characterized chemically and petrologically and their combustion reactivity studied in a drop tube furnace (individual coals) and thermogravimetric analyzer (coals blends).The results of the combustion experiments in the drop tube furnace have been related to thermogravimetric tests run under air, with the aim of correlating the reactivity of the chars with their combustion behaviour under high temperatures and heating rates, such as those prevailing in pulverized fuel combustion and blast furnace injection. Samples of Faxinal coal blended with various proportions of imported coals were also submitted to thermogravimetric analysis in order to evaluate their reactivity to CO2.Optical analyses of the coal blends were able to identify the exact proportions of Faxinal and imported coal used in the various blends. Considering the chemical restrictions for PCI coals, the content of Faxinal coal in blend is viable up to a maximum of 50%.The burnouts achieved in the Drop Tube Furnace at the various atmospheres tested were significantly higher for the Brazilian coal than the imported coal, indicating that the former is easier to burn. Faxinal coal yielded preferentially isotropic highly reactive char whereas the imported coals yielded anisotropic harder to burn low-reactive char.The maximum reaction rate for Faxinal coal tested by thermogravimetry at 1050 °C and CO2 atmosphere is significantly higher than the maximum reaction rate for imported coals. The reactivity of the blended coals was found to depart from linearity with respect to the Faxinal content in the blend.