Pre-reduced Iron Ore Research Articles

Impact of Iron Ore Pre-Reduction Degree on the Hydrogen Plasma Smelting Reduction Process

To counteract the rising greenhouse gas emissions, mainly CO2, the European steel industry needs to restructure the current process route for steel production. Globally, the blast furnace and the subsequent basic oxygen furnace are used in 73% of crude steel production, with a CO2 footprint of roughly 1.8 t CO2 per ton of produced steel. Hydrogen Plasma Smelting Reduction (HPSR) utilizes excited hydrogen states with the highest reduction potentials to combine the simultaneous reduction and smelting of iron ore fines. Due to the wide range of iron ore grades available worldwide, a series of hydrogen plasma experiments were conducted to determine how pre-reduced iron ore and iron-containing residues affect reduction behavior, hydrogen consumption, overall process time, and metal phase microstructure. It was discovered that, during the pre-melting phase under pure argon, wet ore increased electrode consumption and hematite achieved higher reduction levels, due to thermal decomposition. The reduction of magnetite ore yielded the highest reduction rate and subsequent hydrogen conversion rates. Both hematite and magnetite exhibited high utilization rates at first, but hematite underwent a kinetic change at a reduction degree of 80–85%, causing the reduction rate to decrease. In comparison to fluidized bed technology, it is possible to use magnetite directly, and the final phase of the reduction can move along more quickly due to higher temperatures, which reduces the overall process time and raises the average hydrogen utilization. A combination of both technologies can be considered advantageous for exhaust gas recycling.

Effect of Types of Carbonaceous Material and CaO Addition on Reduction Behavior of Pre-reduced Iron Ore–Carbon Composite

Effect of Types of Carbonaceous Material and CaO Addition on Reduction Behavior of Pre-reduced Iron Ore–Carbon Composite

Evolution of deposited carbon during multi-stage fluidized-bed reduction of iron ore fines

The influence of reduction conditions on carbon deposition during fluidized-bed pre-reduction of iron ore fines was investigated experimentally. The results showed that reduction temperature and the composition of reducing gases had a significant effect on the rate of carbon deposition and the type of carbon deposits (graphite and Fe3C). Low reduction temperature, high CO content, and addition of H2 favored the deposition of carbon, especially graphite. The reduction conditions also significantly affected the surface morphology of the as-reduced iron ore fines. As the amount of deposited graphite increased, the formation of fibrous iron disappeared and graphite filaments were observed. The pre-reduced iron ore fines were further fluidized in pure CO at 850°C for final reduction. The results showed that graphite could suppress the formation of fibrous iron and decrease the surface viscosity, thereby inhibiting agglomeration during the final high-temperature reduction stage. Reactions that consume the deposited carbon during the final high-temperature reduction were identified and graphite was shown to be more reactive than Fe3C. To enhance the application of fluidization technology in producing sponge iron, a novel solid-state high-temperature reduction method via deposited carbon was proposed and demonstrated to be feasible.

Optimization of carbon deposition process during the pre-reduction of fine iron ore in a fluidized bed

Coating carbon on the iron ore powder is a quite promising way to prevent defluidization during its high-temperature direct reduction in the fluidized bed reactor, but usually causes excessive carbon content of the DRI production, thus the present study focuses on decreasing the critical carbon content (Ccritical value) needed for defluidization prevention by the optimization of the pre-reduction process. It was for the first time found that increasing the metallization ratio of the pre-reduced iron ore significantly could reduce the Ccritical value, since it inhibited the carbon consumption and formation of metallic iron during the early stage of high temperature reduction. Based on this result, optimization principle to reduce the Ccritical value was further proposed, i.e. increasing the pre-reduction rate (Rpre-reduction) and reducing the carbon deposition rate (Rcarbon deposition) during the pre-reduction, such as by increasing the temperature and the H2 mole fraction in CO–H2 mixture gas. And such principle was verified by the experiment results, where for the iron ore pre-reduced in CO–H2 mixture gas with the xH2≥0.9 at 600°C, its corresponding Ccritical value was less than 3.5wt.%, much lower than that of other conditions or the reported value in the literature.

Ironmaking System Including Coproduction of Carbon-Loaded Iron Oxide and Reformed Coke Oven Gas by Chemical Vapor Infiltration Process

Ironmaking system including coproduction of carbon-loaded iron oxide and reformed coke oven gas (COG) using coal tar, limonite ore, and waste heat is proposed to solve resource and energy problems in steelworks. In the proposed system, limonite ore, which is a low-grade iron ore with combined water, is first dehydrated to obtain a mesoporous solid. Then, during the chemical vapor infiltration, iron ore reduction, and reforming processes, the tar contained in the COG is deposited, leaving carbon in the mesopores of the ore. The ore is reduced by the COG and the tar is reformed by the combined sensible heat of the slag and COG, which acted as a heat source with the ore as a catalyst. The purpose of this study is to estimate the feasibility of the proposed system by process simulation using the Gibbs free energy minimization technique from the viewpoints of (1) the amount of coke required in steelworks, (2) the total chemical exergy of reformed COG, (3) the mass fraction of carbon deposited on carbon-loaded prereduced iron ore, and (4) available supplies of heat from the coke oven system to other systems under the reasonable assumptions given. The results of the analysis showed that, compared to the conventional ironmaking process, the proposed system can help decrease coke requirements by 9.62 % and increase the total chemical exergy by 14.2 %.

事前還元鉱石の焼結原料としての使用によるCO2排出削減

In order to reduce CO2 emissions at an ironmaking process, it is an effective measure to decrease a bonding agent rate at an iron ore sinter plant. In this study, effect of using a pre-reduced iron ore as a part of a sinter raw material on a sintering process was investigated mainly from a viewpoint of decreasing a bonding agent rate.Two brands of pisolitic iron ores were reduced up to wustite at 1173 K with reducing gas of which an oxidation degree was 55%. The pre-reduced iron ore was stable against reoxidation in the atmosphere and through a cyclic wet and dry treatment.Two brands of pisolitic iron ores and a Marra Mamba iron ore were pre-reduced and then used in a sinter pot test. A use of the pre-reduced iron ore was effective in decreasing a bonding agent rate at a given productivity. The reoxidation heat of the pre-reduced iron ore was estimated to be less than the combustion heat of the bonding agent being saved by use of the pre-reduced iron ore. The reoxidation heat is more effective in the sintering process than the combustion heat. The decrease of the bonding agent resulted in reduction of NOx emissions.A mass and heat balance shows that a use of a pre-reduced iron ore as a sinter raw material enables reduction of CO2 emissions not only at an ironmaking process but also at a whole integrated steel works.

Direct reduction of carburized pre-reduced pellets by microwave heating

A new iron-making process using carburized pre-reduced iron ore pellets and microwave heating is investigated. The pre-reduced pellets, with a porous structure, and fine particles are carburized homogeneously at 400–650 °C in a CO atmosphere. The carburized carbon not only acts reaction as a reduction agent, but also absorbs microwave in the reduction process. Hence, the carburized pre-reduced pellets can be rapidly reduced by microwave heating. There are three procedures involved in the process, namely, gas-based pre-reduction, low-temperature carburization and deep reduction by microwave heating. Carburized pre-reduced iron ore pellets show a rapid temperature rise that is twice as fast as the results for pre-reduced pellets in the laboratory. This not only improves the efficiency of the microwave heating, but also accelerates the reduction of iron oxides. The temperature of the pre-reduced pellets rises to 1050 °C in 45 min when the carburization rate is 2.02%, and the metallization rate and compressive strength reach 94.24% and 1725 N/pellet, respectively.

Reduction of CO2 Emissions by Use of Pre-reduced Iron Ore as Sinter Raw Material

In order to reduce CO2 emissions at an ironmaking process, it is an effective measure to decrease a bonding agent rate at an iron ore sinter plant. In this study, effect of using a pre-reduced iron ore as a part of a sinter raw material on a sintering process was investigated mainly from a viewpoint of decreasing a bonding agent rate.Two brands of pisolitic iron ores were reduced up to wustite at 1173 K with reducing gas of which an oxidation degree was 55%. The pre-reduced iron ore was stable against reoxidation in the atmosphere and through a cyclic wet and dry treatment.Two brands of pisolitic iron ores and a Marra Mamba iron ore were pre-reduced and then used in a sinter pot test. A use of the pre-reduced iron ore was effective in decreasing a bonding agent rate at a given productivity. The reoxidation heat of the pre-reduced iron ore was estimated to be less than the combustion heat of the bonding agent being saved by use of the pre-reduced iron ore. The reoxidation heat is more effective in the sintering process than the combustion heat. The decrease of the bonding agent resulted in reduction of NOx emissions.A mass and heat balance shows that a use of a pre-reduced iron ore as a sinter raw material enables reduction of CO2 emissions not only at an ironmaking process but also at a whole integrated steel works.

Dephosphorization Treatment of High Phosphorus Iron Ore by Pre-reduction, Mechanical Crushing and Screening Methods

The behavior of phosphorus in the solid state pre-reduction and dephosphorization treatment processes of high phosphorus iron ore by mechanical crushing and screening methods were investigated in the present work. The reduction behavior of high phosphorus iron ore by carbonaceous materials was evaluated as a function of reduction temperature, reduction time and carbon mixing ratio. Most of the phosphorus compounds were not reduced in the low temperature reduction process of high phosphorus iron ore and remained as oxides in the gangue phases. The gangue phase size increased from 5 μm order before pre-reduction up to 20–30 μm after pre-reduction, and most of the phosphorus was still concentrated in the gangue phases even when the degree of sintering and agglomeration of the phases proceeded with increasing the reduction temperature. The dephosphorization treatment of the pre-reduced iron ore by mechanical crushing and screening methods was evaluated as a function of the initial reduction condition, screen size, and the mechanical property of the reduced iron ore phase.

流動層での予備還元鉄鉱石とCO-H<SUB>2</SUB>-H<SUB>2</SUB>S混合ガスの反応による炭化鉄の生成:還元率の影響

流動層での予備還元鉄鉱石とCO-H<SUB>2</SUB>-H<SUB>2</SUB>S混合ガスの反応による炭化鉄の生成:還元率の影響

Numerical Analysis of Multiple Injection of Pulverized Coal, Prereduced lron Ore and Flux with Oxygen Enrichment to the Blast Furnace.

This paper introduces a modeling of the co-injection of pulverized coal, pre-reduced iron ore and flux into the blast furnace through the tuyere. This model treats the blast furnace as a multi-phase reactor. The pulverized coal and pre-reduced fine ore/flux have different chemical and thermophysical properties, thus these materials are treated as separate phases. Therefore this model considers six phases: gas, lump solids (iron ore, sinter, pellets and coke), pig iron, molten slag, pulverized coal and pulverized iron ore/flux. Conservation equations for mass, momentum, energy and chemical species are solved simultaneously based on the finite volume approach. Two operational practices are investigated. One is the injection of pre-reduced fine iron ore and pulverized coal, and the other is the co-injection of pre-reduced fine ore, flux and pulverized coal. The simulation results have contributed to better understanding the blast furnace phenomena with multiple injectants, and supported new improvements in the blast furnace operation. With this model, the injection of pulverized iron ore and flux together with pulverized coal has been proved to be possible at high rates keeping stable blast furnace operation. Moreover, the silicon content can be lowered and the furnace productivity can be largely increased.

Fundamental research on phosphorus behaviour in the smelting reduction process

The behaviour of phosphorus in the smelting reduction process was investigated in this paper. Experiments were carried out under the conditions of smelting reduction: the phosphate reduction in molten slag by solid carbon, liquid iron saturated with carbon and CO gas, respectively. Furthermore, experiments on the phosphate reduction in pre-reduced iron ore by liquid iron saturated with carbon were carried out respectively when liquid iron was in permanent contact with molten pre-reduced iron ore, and when powders of the pre-reduced iron ore were injected into the iron bath from the bottom. The results showed that there was considerable unreduced P2O5 in the slag. Part of the reduction product of phosphorus escaped from the bath, while the other part was absorbed by liquid iron. The pig iron with low content of phosphorus can be obtained by smelting reduction in comparison with blast furnace. In the process of liquid iron bath with coal-oxygen-ore injection, the phosphorus content in liquid iron could be kept constant in 100 kg scale tests. In dieser Arbeit wurde das physikalisch-chemische Verhalten von Phosphor während der Schmelzreduktion untersucht. Die Versuche wurden unter den bei der Schmelzreduktion herrschenden Bedingungen durchgeführt, also Phosphatreduktion in der flüssigen Schlacke mit festem Kohlenstoff, kohlenstoffgesättigtem Eisen und CO-Gas. Weitere Versuche beschäftigten sich mit der Reduktion des Phosphates in vorreduziertem Eisenerz durch flüssiges, kohlenstoffgesättigtes Eisen, das ständig mit dem aufgeschmolzenen vorreduzierten Eisenerz in Kontakt war. Dabei wurde auch das Einblasen von vorreduziertem Feineisenerz durch den Boden mitberücksichtigt. Die Ergebnisse zeigen, daß unter den Bedingungen der Schmelzreduktion eine beträchtliche Menge an unreduziertem Phosphat in der Schlacke zurückbleibt. Zum Teil entweicht der reduzierte Phosphor aus dem Bad, der Rest wird vom flüssigen Eisen absorbiert. Verglichen mit dem Hochofen liefert die Schmelzreduktion ein Roheisen mit niedrigem Phosphorgehalt. Versuche im 100-kg-Maßstab mit Bodeneinblasen von Gemischen aus Kohle, Sauerstoff und Erz zeigen, daß der Phosphorgehalt der Schmelze konstant gehalten werden kann.

Reaction rates for sulfur fixation with iron at 1100 to 1275 K

The rates of sulfidizing iron in a simulated coal gasification atmosphere were studied. Mixtures of H2S and CO were passed through fixed beds of coal char and prereduced iron ore, and effluent gas compositions were measured as a function of time. These mixtures ranged from 2.5 pct to 10 pct H2S at various flow rates, with temperatures from 1100 K to 1275 K and iron ore sizes from 10 mesh down to 100 mesh. Experimental conditions were established to form a steady state reaction profile in the fixed bed. Analysis of the exit gas provided a measurement of the profile. The slope of the profile was used directly as a measure of the reactivity of the solids in the bed. The development of this experimental technique and its experimental design requirements are discussed. The observed sulfidization rate of thein situ reduced iron ore is characterized by a single rate constantm (minutes-1), which varies primarily with temperature and particle size and is substantially independent of gas flow rate, bed configuration, and H2S content of the incoming gas. Accordingly, the rate constant m can be applied in the design of a combined sulfur fixation, coal gasification reactor to estimate the solids retention time, and the minimum mass of iron required per cross sectional area of reactor.

Progress report on the use of automobile scrap and directly reduced iron ore in production of electric furnace steel

The production of carbon steel by the continuous addition of prereduced iron ore to molten auto scrap in an electric furnace appears to have certain operational advantages over conventional cold-melt, batch-charging techniques. Among these are: (1) Lower tramp metal content in the ingot, (2) shorter heat times and lower electrical energy consumption, (3) improved energy input rate during the continuous addition, and (4) flexibility of charge composition by varying ratios of scrap to prereduced iron.

Smelting Prereduced Iron Ore Pellets

Prereduced pellets, made from magnetic taconite concentrates in the pilot plant of the Bureau of Mines Minneapolis Metallurgy Research Center, were smelted in the Bureau’s experimental blast furnace at Bruceton, Pa. The pellets averaged 79.0 pet Fe and 11.9 pet SiO2. Two additional supplies of prereduced pellets were obtained from The Steel Co. of Canada Ltd., Hamilton, Ontario, which averaged, respectively, 83.8 pet and 91.3 pet Fe, and 3.1 and 3.0 pet SiO2. Results from smelting these pellets were compared with results from conventional unreduced pellets from the Hilton mine in Quebec, and from Erie Mining Co., Hoyt Lakes, Minn. The blastfurnace tests established that substantial decreases in coke rates and correspondingly higher production rates result from the use of prereduced pellets.