Effect of Blending Carbon-Bearing Waste with Coal on Mineralogy and Reactivity of Cokes

Abstract

Because of rising costs, there is a constant demand to minimize coking coal use in favor of cheaper alternatives for ironmaking. A range of carbon-bearing additives were carbonized with a typical medium-rank Australian coking coal with the aims of minimizing the deterioration of coke quality while increasing the recycling of waste materials for ironmaking. Additives included two types of tire-recycling residues, coke breeze and a bituminous residue from the distillation column of benzol. Coke blends were prepared in a semi-pilot-scale coke oven, while a horizontal furnace was used to prepare char/coke samples of additives. The percentage of minerals in raw additive samples as well as coke blends was quantified by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to determine the mode of occurrence of the minerals, while a fixed-bed reactor was used to measure the apparent reaction rate with CO2. After pyrolysis, recycling tire chars indicated the highest reactivity, which was attributed to zinc dispersion in the carbon matrix. Coke breeze showed the least reactivity but still greater than the base coke reactivity. The bituminous pitch residue char reactivity was significantly higher than the base coke reactivity. Under the test conditions, magnetite formation was noted to be the most notable change in the mineralogy of the coke blends. The higher reaction rate of the coke blends is related to the increase in the magnetite content as well as an enlargement of the micropore size. The apparent reaction rate of the coke blends is shown to be related to the coke strength after reaction (CSR). The study has implications for the use of various carbon-bearing wastes in a cokemaking process.