Jagannath Pal

Effect of Blaine Fineness on the Quality of Hematite Iron Ore Pellets for Blast Furnace

Iron ore pellets are largely characterized by inherent physical and chemical properties of ore as well as pelletizing conditions including induration time, induration temperature, etc. These parameters essentially vary with types of ores. The production of high-quality pellets from hematite ore is challenging because of high level of fineness (Blaine number) and induration temperature requirement, ensuring severe degradation property during reduction, etc. In this work, the effect of Blaine number (Blaine fineness: expressed as the specific surface area of fines) on the pellets’ properties was studied. The paper presents the effect of Blaine number on green and dry strength, cold crushing strength, reducibility index, reduction degradation index, swelling index, apparent porosity, optical micro structure, etc. of the high alumina hematite ore pellets. The results showed improved properties of iron ore pellets at an optimum Blaine number (2150 cm2/g) but, reduction degradation index was found to be very poor for the given ore. Further investigation showed that when MgO containing flux viz. pyroxenite was added, the reduction degradation index and swelling index of the pellets were improved for identical Blaine number and other optimized process parameters.

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.

Development of carbon composite iron ore micropellets by using the microfines of iron ore and carbon-bearing materials in iron making

Iron ore microfines and concentrate have very limited uses in sintering processes. They are used in pelletization; however, this process is cost intensive. Furthermore, the microfines of non-coking coal and other carbon-bearing materials, e.g., blast-furnace flue dust (BFD) and coke fines, are not used extensively in the metallurgical industry because of operational difficulties and handling problems. In the present work, to utilize these microfines, coal composite iron oxide micropellets (2–6 mm in size) were produced through an innovative technique in which lime and molasses were used as binding materials in the micropellets. The micropellets were subsequently treated with CO2 or the industrial waste gas to induce the chemical bond formation. The results show that, at a very high carbon level of 22wt% (38wt% coal), the cold crushing strength and abrasion index of the micropellets are 2.5–3 kg/cm2 and 5wt%–9wt%, respectively; these values indicate that the pellets are suitable for cold handling. The developed micropellets have strong potential as a heat source in smelting reduction in iron making and sintering to reduce coke breeze. The micropellets produced with BFD and coke fines (8wt%–12wt%) were used in iron ore sintering and were observed to reduce the coke breeze consumption by 3%–4%. The quality of the produced sinter was at par with that of the conventional blast-furnace sinter.

Smelting characteristics of fluxed chromite sinter and its performance assessment in electric arc furnace to produce high carbon ferrochrome

More than 80% of the high grade chromite ores are fragile and tend to form fines during their handling. In order to utilise these chromite ore fine, in ferrochrome production, agglomeration is necessary. In the present study, the direct sintering of chromite ore fines in the presence of coke breeze has been carried out, which does neither require further grinding of ore fines ( − 10 mm) nor binder. It uses suitable fluxes and coke breeze as heat source to raise temperature up to 1600°C and produces a semifused mass (20% molten phases) with good strength. The developed sinter showed very good strength properties suitable for cold handling. Since it contains higher amount of fluxes than conventional pellet, the study on its smelting characteristics is necessary to assess its suitability in Fe–Cr production. In the present paper, smelting reduction characteristics and assessment of its performance with respect to the lump ore in a 50 kVA electric arc furnace have been studied in 10 kg scale. Different smelting parameters such as coke and flux requirement, energy consumption, etc. has been optimised through both thermodynamically and experimentally to get maximum extent of reduction, metallic yield and chromium recovery. Coke (21%), quartzite (7.52%) and bauxite (10%) addition with 45 kWh of heat input was found to be optimum to achieve 76% metallic yield and 91%, chromium recovery. In the comparative study in identical condition, the chromite sinter showed much better metallic yield (76%) and higher chromium content (54.6%) in the produced ferrochrome than the lump ore (70 and 51. 9% respectively) of the same grade.

Replacement of bentonite in hematite ore pelletisation using a combination of sodium lignosulphonate and copper smelting slag

Bentonite is the most common binder used in iron ore pelletisation owing to its good bonding properties in green and dry pellets at both ambient and elevated temperatures. However, due to its high alumina and silica content, it increases the slag volume and energy consumption in downstream processes. Organic binders may be used to replace bentonite; however, they fail to provide strength at a high temperature (700–900°C) due to poor thermal stability during pellet induration. In the present study, an organic binder Na lignosulphonate (NLS) has been used along with copper smelting slag (Cu-SS). FeO in Cu-SS provides diffusion bonding at high temperature and maintains the strength of pellets even after evaporation/burning of NLS. It also enhances recrystallisation bonding at relatively lower temperature to provide good strength. The study has been carried out with hematite ore and varying amounts of NLS and Cu-SS. Copper smelting slag (1.0%) addition with 0.5%NLS has been found to be optimum to provide very good green properties and ∼300 kg/pellet cold crushing strength (CCS) at 1250°C induration temperature. However, hematite pellets of similar basicity with 0.5% bentonite requires higher induration temperature (1300°C) to achieve a similar CCS. The developed pellet also shows better reducibility (80%), similar reduction degradation index (18%) and swelling index (10%) to the usual bentonite pellet. Thus, the induration temperature of hematite pellet has been lowered by 50°C using a combination of NLS and Cu-SS eliminating bentonite completely, which can provide a considerable energy and cost saving.

Carbon as in situ energy source in induration of hematite pellets and its effect on pellet properties

Abstract Fuel consumption during high temperature induration is one of the principal reasons for the cost intensiveness of the iron ore pelletisation process. While magnetite ore is oxidised to hematite during induration at high temperature and provides internal heat energy to the pellet, there is hardly any internal heat generation. Furthermore, magnetite is prone to form diffusion bonds at 950–1200°C, whereas with hematite ore, the diffusion bonding is much less at that low temperature and so requires very high temperature of induration (around 1300°C or above) and hence consumes more energy. In this study, the external heat energy in pellets has been supplied by adding coke fines as a source of carbon which is oxidised to CO or CO2 producing in situ heat to the pellets and also reduces a part of the hematite to magnetite during induration. These help in bond formation and lowering the external energy requirement. The study has been carried out with varying carbon percentage (0–5%) and the effect of carbon and its optimisation level has been determined. Up to 2% carbon has been found to be optimum to improve cold crushing strength, porosity, reducibility and decrease the reduction degradation index of pellets, as well as reduce the requirement of induration furnace temperature by 80°C and considerably decrease fuel consumption. However, excess addition of carbon increases the porosity markedly and reduces pellet strength.

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.

Performance Assessment of Partially Pre-fused Synthetic Flux in Basic Oxygen Steel Making

Lump lime as the most common flux and iron ore as a coolant are used in basic oxygen steel making. However, high melting point, poor dissolution property, fines generation tendency and hygroscopic nature of lump lime often create problems in operation. As the combination of both iron oxide (Fe2O3) and CaO shows eutectic at 1230 °C, a combined mass of iron oxide and lime melts at lower temperature and dissolves faster in a molten bath. A partially pre-fused synthetic flux (PSF) was prepared through an innovative way in combination of iron oxide fines viz. Linz Donawitz converter sludge and blast furnace flue dust and lime fines by micro-pelletization of the mix followed by coke breeze free sintering. The developed PSF shows good cold handling strength, low melting point (1 180 ºC), good thermal shock resistance, etc. As a low melting synthetic flux, its performance was assessed through dissolution/melting study in hot metal bath and refining of hot metal in a simulated bottom blown converter using (i) PSF, (ii) only lump lime and (iii) lump lime with iron ore when keeping other conditions identical. Very fast dissolution (27–80 s for 1–3 g lumps), enhanced removal of C and P (11–12 min), controlled slag foaming, and reduced oxygen consumption was obtained for using PSF.

A comparative study for smelting of chromite ore, pellets, briquettes and sinter

Abstract Ferrochrome (>62%Cr) and charge chrome (45–52%Cr) production using the submerged arc furnace (SAF) is an established practice in India. As the majority of Cr rich Indian chromite ore are friable in nature and available in fine form, utilisation of chromite fines for production of superior quality ferrochrome is essential. For this purpose, in the present study, the smelting of chromite pellets, briquettes, sinter and lump ore has been carried out in an electric arc furnace of 50 kVA. The energy consumption, yield, Cr recovery and quality of Fe–Cr produced have been compared for different Cr bearing materials. Sinters and pellets have found to be more suitable than briquettes and poor quality lump ore in terms of energy consumption and yield.