LAUSR

Around 69% of the worldwide steel production is still based on pig iron production through the blast furnace (BF) route. Although the overall process and the chemical reactions inside a BF are well understood, it still remains a sort of black box when it comes to local flow conditions and the movement of solid particles, gas, and liquids inside. Thus, there are a lot of issues during BF operation which cannot be fully explained on the basis of the available measurement data. One of these issues is the irregular movements of the burden. Sometimes the descent of the burden comes to a stop or suddenly drops down even for a few meters. This behavior is usually termed “hanging” and “slipping.” Hanging and slipping of the burden can occur as local effects influencing only one or several neighboring tuyeres or can also appear on a large scale covering major parts or the entire BF. It can locally change the permeability of the burden and cause asymmetries in the BF, and they are also assumed as one of the reasons for the frequent occurrence of raceway blockages that can affect one or several tuyeres. Although, the reasons for hanging and slipping are yet not fully understood, there are some possible explanations for this behavior. From the theory of granular media, it is known that particles form force chains. This arching effects are of major interest for the discharging of granular material from hoppers as they can cause jamming and avalanching. For monodisperse spherical material, the probability of jamming during hopper discharge is influenced by the ratio of particle diameter and the outflow diameter. However, for technically relevant materials the formation of force chains is also influenced by the shape of the particles, and the differences in particle sizes for nonmonodisperse materials. In a lab-scale environment, these force chains can also be visualized experimentally. Comparably, counter-current reactors like BFs are also affected by arching and avalanching effects. All granular materials inside have an irregular shape and a wide distribution of particle sizes from the range of centimeters (coke and sinter) down to the micrometer range (dust and unburned coal particles from pulverized coal injection [PCI]). Especially, the cohesive zone is prone to form force chains and arching as the melting iron tends to glue particles together on one side and the consumption of coke and ore also produces additional voidage. A second reason for irregular burden movements is scaffolds at the furnace walls. These can be formed when alkalior zinc-rich components are vaporized in the lower hot areas and then condensate at the cooler walls. These scaffolds locally alter the gas and temperature distribution. Eventually, these structures will break off the walls when they become too large, especially when there are void regions formed below due to the consumption of coke. Although there are hundreds of measurement signals nowadays, there is still very few information available what is really going on inside the BF. Most data are temperature and pressure signals or signals related to the mass flow rates of burden and coke charged at the top, liquid iron and slag tapped from the bottom and the hot blast flow rates. There are basically only two regions where information can be obtained from inside the BF—the Dr. S. Puttinger Department of Particulate Flow Modelling Johannes Kepler University Altenbergerstrasse 69, 4040 Linz, Austria E-mail: [email protected] H. Stocker Research and Development voestalpine Stahl Donawitz GmbH Kerpelystrasse 199, 8700 Leoben, Austria