Wetting and interfacial reaction investigations of coke/slag systems and associated liquid permeability of blast furnaces

Abstract

An interfacial study between metallurgical coke and synthetic slags representing typical slag chemistry of bosh regions of an operating blast furnace was conducted at 1500°C using a horizontal laboratory furnace. The wetting characteristics of coke with slag was studied by measuring dynamic contact angle of sessile droplet of slag on coke substrate, while reaction kinetics of interface was monitored by measuring the amount of CO and CO 2 gases with the help of infrared analyzer. The interface chemistry was also examined by SEM/EDS/EPMA. The study demonstrated that coke wettability was strongly dependent both on the slag composition as well as coke chemistry such that low basicity (CaO/SiO2) of slag, that is high amounts of oxides of silicon enhanced the wetting propensity of slag. The study further showed that the wettability of coke with slag was found to improve with increased extent of gasification, and was attributed to higher ash content of partially gasified cokes. The CO/CO2 measurements of off gases from the reacting chamber were used to demonstrate that slag wettability with coke was primarily controlled by the kinetics of reduction of metal oxides at the slag/coke interface particularly that of silica. The study demonstrates that in addition to slag composition, coke properties could also influence the liquid permeability of lower zone of the blast furnace, and hence needs attention while optimizing the bosh slag composition for high productivity blast furnace operation. © 2005 ISIJ.