Manik Chandra Goswami

Development of fluxed micropellets for sintering utilising iron oxide waste fines

Abstract Ultrafine iron oxide wastes such as slime, blue dust and Linz–Donawitz (LD) converter sludge have very limited use in sintering of iron ore due to their excessive fineness (−50 μm). Pelletisation of these ultrafine materials for use in blast furnace involves high temperature curing, which is a highly energy intensive process. Briquetting of LD sludge requires costly binders and contains high moisture, which creates problem at high temperature of the downstream process. In order to alleviate these problems, the current study has developed a process for preparing micropellets of waste iron oxide fines (2–6 mm size) without using any binder. The strength of the micropellet has been increased by a novel CO2 treatment process at room temperature. Developed micropellets exhibit very suitable drop strength (125 Nos), tumbler properties and cold compressive strength (∼9 kg/pellet) to withstand cold handling. Low lime containing micropellets have the possibility of being used as a mixed material in usual sinter making, and high lime containing micropellets may be exploited for making super fluxed sinter that can be used as synthetic flux in the basic oxygen furnace process towards the formation of low melting oxidising slag at the early stage of blow.

Behavior of fluxed lime iron oxide pellets in hot metal bath during melting and refining

Lump lime as a flux material in a basic oxygen furnace (BOF) often creates problems in operation due to its high melting point, poor dissolution property, hygroscopic nature, and fines generation tendency. To alleviate these problems, fluxed lime iron oxide pellets (FLIP) containing 30% CaO were developed in this study using waste iron oxide fines and lime. The suitable handling strengths of the pellet (crushing strength: 300 N; drop strength: 130 times) of FLIP were developed by treating with CO2 or industrial waste gas at room temperature, while no separate binders were used. When the pellet was added into hot metal bath (carbon-containing molten iron), it was decomposed, melted, and transformed to produce low melting oxidizing slag, because it is a combination of main CaO and Fe2O3. This slag is suitable for facilitating P and C removal in refining. Furthermore, the pellet enhances waste utilization and use of CO2 in waste gas. In this article, emphasis is given on studying the behavior of these pellets in hot metal bath during melting and refining along with thermodynamics and kinetics analysis. The observed behaviors of the pellet in hot metal bath confirm that it is suitable and beneficial for use in BOF and replaces lump lime.

Dissolution Characteristics of CO2-Treated Fluxed Pellets in Hot Metal Bath

Lump lime and iron ore are generally used in the basic oxygen furnace as flux and cooling material, respectively. Owing to high melting point, poor dissolution property, fines generation tendency, and hygroscopic nature of lump lime, delay in process and operational complexities are generally encountered. On the other hand, iron ore charging creates slag foaming. In order to alleviate the above problems and to utilize waste materials, fluxed lime–iron oxide pellets (FLIP) containing waste iron oxides and lime fines (10%–40%) were prepared and subsequently strengthened with CO2 gas treatment. FLIP may have the potential to partially replace scrap and lump lime in the conventional basic oxygen furnace charge. In order to assess the applicability of FLIP in steelmaking, the dissolution characteristics of these pellets were studied in a high-temperature pot furnace equipped with a charge-coupled device (CCD) camera under varying experimental conditions. It was found that the dissolution time decreased with increasing hot metal temperature, increasing specific surface area of the pellet, and decreasing lime content of the pellet. The melting of the pellet in the absence of hot metal took much higher time than its presence.