Mixing Characteristics of Additives in Viscous Liquid BOF Slag
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BASIC Oxygen Furnace (BOF) slag is conventionally disposed through landfill/dumping, leading to land occupation, environmental impact, and a waste of material resources.[1,2] In order to solve these problems, considerable efforts to reuse BOF slag have been made in the last decades.[2–4] However, the application of BOF slag is restricted by its volume expansion during natural aging due to the presence of free lime.[5,6] For the purpose of BOF slag valorisation, different hot stage engineering processes have been proposed.[7–11] Jingye Engineering in China developed the pyrolytic self-slaking process,[7] where molten BOF slag is poured into a tank with a cover, followed by spraying water into the tank. Water stream is generated and then reacts with the free lime in the BOF slag. After this treatment, the free lime is fully slaked[8] and more than 60 pct of the slag grains are smaller than 10 mm, which is easy to be separated or ground further, and the steel
YANNAN WANG, LINGLING CAO, ZHONGFU CHENG, BART BLANPAIN, and MUXING GUO are with the Department of Materials Engineering, KU Leuven, 3000 Leuven, Belgium. Contact e-mail: [email protected] Manuscript submitted February 11, 2020.
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entrapped in the slag can be recovered with a high yield. Apart from this process, the drum-granulation process[7,8] and the Baosteel’s Slag Short Flow (BSSF)[7,8] process can also effectively stabilize the free lime by water or water steam. After metal recovery, the stabilized BOF slag is applied in cement, concrete, and road construction material. Most of the industrial processes stabilize the slag only through cooling control (water and/or air granulation) and the processes only aim at free lime stabilization. No process was developed yet that is fully successful in valorizing BOF slag by altering slag chemistry at high temperature. To this end, the FEhS institute developed and implemented a process, where silica-rich additives are injected into the liquid BOF slag with nitrogen or oxygen as a carrier gas through a top submerged lance for the free lime stabilization and the microstructure/mineralogy control towards high added value products.[9–11] In this hot stage slag engineering process, fast mixing of the additives is desired for their rapid dissolution into slag, allowing sufficient time for the modifiers to react with the other components in the slag, for instance, with free CaO and MgO. Understanding the mixing behavior of the slag modifiers/additives is critically important to optimize the hot stage slag engineering process. Due to difficulties of high-temperature experiments (e.g., opacity of a slag pot, hazardous operating environment, lack of velocity measurement techniques at high temperature) and complex gas-liquid-solid multiphase flow, physical modelling[12–14] and numerical simulation[13–15] have been performed to understand the mixing behavior in high-temperature processes such
as ladle metallurgy. The mixing time is measured through the electrical conductivity of the aqueous solut
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