Chemical Structure of Chars Prepared under Conditions Prevailing in the Blast Furnace PCI Operation

Abstract

Using a drop tube furnace, char samples were prepared from coals of different ranks, under conditions similar to those prevailing during pulverized coal injection into the blast furnace. The chemical structure of resultant chars was determined by quantitative X-ray diffraction analysis (QXRDA) and high-resolution transmission electron microscopy (HRTEM), and investigated as a function of pyrolysis temperature, heating rate and coal type. Among the parameters examined, pyrolysis temperature was the key factor influencing char chemical structure. Char obtained at higher temperature is generally more ordered, with the distinctive peaks becoming sharper and the background intensity becoming lower. Heating rate is another important factor affecting char chemical structure. Char is more ordered at lower heating rate due to the longer residence time. Although considerable differences were still observed in the chemical structure of chars prepared from coals of different ranks, it is clear that such differences are reduced after coal pyrolysis. Char structural evolution during post-pyrolysis and combustion was also investigated. The importance and potential applications of this work to the blast furnace PCI operation have been outlined.