Effect of coal and coke ash on blast furnace slag formation:comparison between PCI, charcoal, fossil-based coke and bio-coke

Abstract Blast furnace is the most used process for production of pig iron in the world. It is charged mainly with metallurgical coke and ferrous materials such as pellets and/or sinter. When descending inside the blast furnace, iron bearing materials start to reduce and with other burden material start to melt, which leads into formation of so-called primary slags from which the final slag is formed as materials descend inside the furnace. Every primary slag originates from one charge material and has unique effect on the total composition of the blast furnace slag. This work focuses on the primary slags of coke and pulverized coal injection (PCI). The global trend is to decrease the use of fossil-based carbon by replacing it with bio-based carbon. The primary slags of the coke and PCI originate from coke ash and pulverized coal ash. The purpose of this work is to evaluate how blast furnace slag composition is changed when fossil-based coke is replaced with bio-coke and PCI is replaced with charcoal. The effect differs case-by-case as presented in this work, but it was found out that replacing fossil-based coke with bio-coke and PCI with charcoal the solidus and liquidus temperatures as well as CaO/SiO₂ — and MgO/Al₂O₃ -ratios are increased. This comparison is based on mass balance calculations