Thermodynamic Analysis on the Dust Generation from EAF for the Recycling of Dust

Abstract

Recently, in addition to the large interest on the CO₂ emission problem, the energy saving and the environmental conservation become more and more important issue. Zero emission campaign is adopted by many companies. In such circumstances, most of steel companies were carrying out the recycling of dust by many ways. There are many aspects on the dust recycling. One of important purpose is the zinc recovery, and other is the utilization as a slag (e.g. roadbed material) by injection. Especially for the dust injection, many troubles such as an accumulation in the filtering system and an increase of the content of harmful elements in the dust will occur. Then, it become very important to understand the mechanism and the thermodynamics of the dust generation or/and precipitation form EAF to prevent those troubles.
In this study, the dust sampled from the impeller of blower in the dust filtering system of EAF was examined by XRD and XRF. Quite complicated compounds formed in Zn-Fe-Pb-Cr-Mn-O-Cl-F system were found in the dust according to the dust injection. Thermodynamic analysis was performed and the equilibrium composition obtained from the calculation was in excellent agreement with the actual composition in the dust. Main constituents in the dust are ZnFe₂O₄ and Fe₂O₃. Relatively dominant ones are as follows: Fluorides are FeF₃, ZnF₂ and PbF₂, chlorides are ZnCl₂ and PbCl₂, and oxides are ZnO and MnO₂. The fluorides deposit around 1000°C from gas phase. And the chlorides ZCl₂, PbCl₂ and oxides MnO₂ form less than 500°C. The partial pressure of chloride gas will become a maximum around 400°C, when there is no moisture.