Coal-based reducing agents in ferroalloys and silicon production

Electrical Resistivity of Carbonaceous Bed Material at High Temperature

“…At elevated temperature, electrical resistivity of large particles further decreased from 70 mΩ•m at 1000 • C to approximately 12 mΩ•m at 1650 • C for semi-coke, from approximately 11.5 to 5.5 mΩ•m for metallurgical coke, and from 20 to 6 mΩ•m for coal. Similar values were reported for coal and coke in the literature[22,27,34,43]. Electrical resistivity of charcoal particles decreased from higher than 100 mΩ•m at 1000 • C to a range of 14 to 18 mΩ•m at 1600 • C.…”

“…The results at room temperature indicate that electrical resistivity increases with increasing particle size as reported in the literature [19,[32][33][34]. However, measurements at elevated temperature have shown that bulk density has just as great an influence on electrical resistivity as particle size for dry carbon beds.…”

“…The higher carbonization degree can enhance the mechanical stability by cross-linking and larger aromatic structures, whereas a lower bulk density is related to a higher porosity. Fines and small particles are harder and less porous than larger particles, providing a smaller contact area between particles [34]. Inner surface area decreased at temperature greater than 1000 • C by collapsing of small pores [20].…”

“…Otherwise, increasing compaction force improves the contact between neighboring particles by increasing the number of contact points [22,32] and decreasing the air gap between particles [28]. Contact resistance can be two to ten times larger than electrical resistance from solid material [22,32,34], in which a decreasing particle size results in an increasing electrical resistivity. However, this effect is balanced by an increased number of contacts and conductive paths through the bulk.…”

“…The main parameters that influence the electrical resistivity of carbon bed material are heat treatment temperature [3,5,27,28], compression pressure [3,[28][29][30][31], particle size [32][33][34], and volume fraction of the carbonaceous material [27,34]. Previous studies focused on the measurement of the electrical resistivity of powder materials [28], dry coke beds [19,22,32,35], or coke metal-oxide blends [27] of fossil fuels, whereas knowledge on the charcoal beds is limited.…”