Reduction Degradation Index Research Articles

Oxidizing Roasting Performances of Coke Fines Bearing Brazilian Specularite Pellets

Abstract Oxidized pellets, consisting of Brazilian specularite fines and coke fines, were prepared by disc pelletizer using bentonite as binder. The roasting process of pellets includes preheating stage and firing stage. The compressive strength of preheated pellets and fired pellets reached the peak value at 1.5% coke fines dosage. During the initial stage of preheating, some original Fe2O3 was reduced to Fe3O4 because of partial reduction atmosphere in pellet. During the later stage of preheating and firing stage, coke fines were burnt out, and the secondary Fe2O3 (new generation Fe2O3) was generated due to the re-oxidization of Fe3O4, which improved the recrystallization of Fe2O3. Compared with the fired pellets without adding coke fines, fired pellets with 1.5% coke fines exhibited the comparable RSI (reduction swelling index) and RDI+3.15 mm (reduction degradation index), and slightly lower RI (reducibility index).

Optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite

The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated systematically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was increased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the compressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content (2.63wt%) matching the pellet with a low MgO content (less than 1.14wt%) was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.

Influence of Basicity on High-Chromium Vanadium-Titanium Magnetite Sinter Properties, Productivity, and Mineralogy

The effect of basicity on high-chromium vanadium-titanium magnetite (V-Ti-Cr) sintering was studied via sintering pot tests. The sinter rate, yield, and productivity were calculated before determining sinter strength (TI) and reduction degradation index (RDI). Furthermore, the effect of basicity on V-Ti-Cr sinter mineralogy was clarified using metallographic microscopy, x-ray diffraction, and scanning electron microscopy-energy-dispersive x-ray spectroscopy. The results indicate that increasing basicity quickly increases the sintering rate from 25.4 mm min−1 to 28.9 mm min−1, yield from 75.3% to 87.2%, TI from 55.4% to 64.8%, and productivity from 1.83 t (m2 h)−1 to 1.94 t (m2 h)−1 before experiencing a slight drop. The V-Ti-Cr sinter shows complex mineral composition, with main mineral phases such as magnetite, hematite, silicate (dicalcium silicate, Ca-Fe olivine, glass), calcium and aluminum silico-ferrite (SFCA/SFCAI) and perovskite. Perovskite is notable because it lowers the V-Ti sinter strength and RDI. The well intergrowths between magnetite and SFCA/SFCAI, and the decrease in perovskite and secondary skeletal hematite are the key for improving TI and RDI. Finally, a comprehensive index was calculated, and the optimal V-Ti-Cr sinter basicity also for industrial application was 2.55.

Reduction of solid fuel consumption in sintering of Indian iron ore

The present investigation deals with the sinterability of Goa (India) iron ore having high Fe (65.2%) content. The sinter basicity (CaO/SiO2) and its MgO were varied in the 2.0 to 2.5 and 1.5 to 3.0 range. The effect of process variables on the quality parameters of sinter namely, tumbler index (TI), reduction-degradation index (RDI) and reducibility index (RI) as well as the productivity of sinter was studied. The studies have shown that the consumption of coke (C: 74%) was inter-influenced by the sinter basicity and its MgO content. Increasing the solid fuel consumption was not a viable solution to improve TI and RI simultaneously. The content of coke in the mix could be reduced to as low as 4% through `low temperature sintering? at the balanced return fines recirculation (~ 33 wt. percent). The sintering indices in terms of productivity of sinter and its quality improve quite significantly at a higher sinter basicity (CaO/SiO2 ~ 2.5) and its lower MgO content (1.5%).

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.

Influence of MgO in form of magnesite on properties and mineralogy of high chromium, vanadium, titanium magnetite sinters

MgO in blast furnace slag provides an optimum condition in terms of both good flow ability and desulphurisation. The effect of MgO on blast furnace slag is fairly well established, but its effect on sintering and sinter quality is unclear especially on high chromium, vanadium, titanium magnetite (Cr–V–Ti magnetite) sinters. In the present study the effect of MgO, in the form of magnesite (MgCO3), on sintering rate was calculated. Cr–V–Ti magnetite sinters with varying MgO content (1·95–3·01%) were tested for yield, strength and reduction degradation index. Productivity and comprehensive index were evaluated. Mineralogical microstructure and SEM–EDS analysis was done to measure the chemical analysis of oxide and slag phases, and XRD and XRD mapping was carried out to understand the interaction mechanism of MgO.From the results, it was observed that with increasing MgO, yield and TI initially increased then decreased with MgO addition, which is unfavourable for the formation of calcium ferrites but increases the silicate phases, and stabilises the crystal of magnetite in Cr–V–Ti magnetite Sinter. RDI was found to improve, productivity fluctuated, comprehensive index improved substantially in the range of 1·95–2·63%MgO but then decreased quickly. The studies revealed that most of the Mg2+ was picked up by magnetite phase to form (Fe,Mg)O·Fe2O3 and (Mg·Fe)O·Fe2O3.

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

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.

Influence of sinter basicity (CaO/SiO2) on low and high alumina iron ore sinter quality

Iron ore sinter, constituting a major proportion of blast furnace burden, significantly impacts the blast furnace performance. The chemical composition of iron ore fines, particularly alumina, sinter basicity and sinter MgO together with the thermal conditions that sinter blends are subjected to play an important role in the formation of mineral phases in sinter. To increase the sinter proportion (70–80%) in blast furnace, lowering of CaO in sinter mix is a vital parameter to balance the flux supply without affecting the slag volume and productivity. At present, the alumina content in the sinter grade iron ore fines at JSW Steel varies from 4 to 6%. The quality of iron ore presently being used calls for extensive investigations to produce low basicity sinter with high alumina iron ore. Studies have been carried out on low and high alumina iron ore fines to know the influence of sinter basicity and fuel (coke breeze) addition on sinter mineralogy, properties and productivity. It is found that with increase in sinter basicity, sinter productivity and reduction degradation index (RDI) decreased and tumbler index (TI) increased for both low and high alumina sinter at coke breeze rate of 65 kg t−1 of sinter. The low alumina sinter showed higher productivity and strength, and lower RDI due to the presence of higher silico ferrites of calcium and aluminium (SFCA) and magnetite phase, and lower pore phase as compared to high alumina iron ore sinter. The sinter productivity decreased and physical and metallurgical properties improved with increase in coke breeze addition by increasing the sinter basicity for high alumina sinter.

Computational Insights into Interactions between Ca Species and α-Fe2O3 (0 0 1)

CaCl2 can be sprayed onto sinter surface, which can improve the low temperature reduction degradation index (RDI+3.15) of sinter. This has been recognized; however, there are various opinions on the inhibition mechanism of it. At the same time, the corrosion of Cl element on equipment is very serious. First-principle calculations based on density functional theory were performed to investigate the binding mechanisms of calcium species on a α-Fe2O3 (0 0 1) surface. This is crucial in demonstrating the role of the CaCl2 on improving the low temperature reduction degradation index. It has been determined that Cl could greatly increase the adsorption of the vacuum layer for the Ca/Fe2O3 system and the relaxation produced by adsorption made bond length decrease, bond energies increase and structure compact. Those are the main reasons that inhibiting the reduction disintegration of sinter.

Characteristics of Calcined Magnesite and Its Application in Oxidized Pellet Production

Calcined magnesite is a binding additive and an MgO-bearing flux for pellets production. The effects of calcination temperature and time on the characteristics of calcined magnesite were investigated. Experimental results indicated that the best calcination condition was 850 °C and 1 h. Under this condition, the hydration activity of the calcined magnesite was 80. 56%, and the average diameter of crystal grain D, specific surface area S and the medium particle size D50 were 25. 4 nm, 45. 40 m2/g and 3. 41 μm, respectively. This kind of calcined magnesite was a good binding additive for pellets production. At the same proportion of calcined magnesite, the effects of activities of calcined magnesite on metallurgical properties of green pellet and indurated pellet showed that calcined magnesite with high activity could improve the dropping strength and compressive strength of green pellet and enhance the burst temperature of green pellet; however, the effects of activity on compressive strength, low-temperature reduction degradation index, reduction swelling index and reduction index of indurated pellet were not obvious.

Development on Iron Ore Pelletization Using Calcined Lime and MgO Combined Flux Replacing Limestone and Bentonite

CaO and MgO bearing fluxes are widely used in sinters and pellet to improve their basicity and other properties viz. strength and physico-chemical properties especially, for lowering reduction degradation index of high alumina ore agglomerate. Limestone (CaCO3 mineral) is presently used as CaO input in agglomeration. Endothermic calcination of CaCO3 at elevated temperature is energy consuming and kinetic driven process. Grinding to powder also consumes energy. In contrary, calcined lime is relatively softer and disintegrates on hydration. Calcined and hydrated lime both has very good green bonding property also. Though, calcined/hydrated lime is used in sintering replacing limestone, it is hardly used in pelletization. This is because of facing problems viz. crack formation in pellet, loss in bonding efficiency of bentonite, handling of hydrated lime etc. However, suitable adjustment of flux composition and process parameters can make the calcined lime usable in pelletization as advantage. This study is concentrated on optimization of MgO (olivine) flux addition and basicity and finally used calcined lime in place of limestone in developing good quality iron ore pellets with combined flux. It is found that calcined lime fluxed pellet without bentonite and limestone shows very good dry compressive strength (3.5 kg/pellet) and improved green compressive strength (1.5 kg/pellet), drop numbers (12 Nos ), cold crushing strength (310 kg/pellet) and reduction properties. The complete replacement of limestone and bentonite is found with better pellet properties. The bentonite elimination will help minimizing alumina and silica input in pellet and reduce the cost in pelletization.

Development of Pellet-Sinter Composite Agglomerate for Blast Furnace

Microfines of iron ore are generally utilized in Blast furnace in form of indurated pellets because sinter bed has limitation of accepting fines. Charging of acid pellets with basic sinter is the normal practice in blast furnace. However induration of pellets is very cost intensive. Further more, due to low angle of repose pellets distribution during charging with other materials in blast furnace creates inhomogeneous distribution. In order to alleviate the above problem, a composite mass of acid pellet and basic sinter has been developed, wherein; green pellets made-up of microfines were mixed with basic sinter mix and sintered the combined mass in a sinter bed of 10–12 kg scale. A composite mass of indurated pellet and sinter named as ‘Pellet-Sinter Composite Agglomerate’ was obtained. Linz Donawitz converter sludge and mill scale were used in pellet mix to provide in-situ heat in pellets that enhances incipient fusion to form bond in pellets. The developed sinter shows good shatter index (92%), tumbler index (67.5%) abrasion index (7.5%) and reducibility index (70%) and low reduction degradation index (27%), which are comparable with the conventional iron ore sinter made in the same set-up keeping other condition identical. This innovative technique help improving 30% microfines utilization in sinter bed, reduce coke breeze/energy consumption, reduce overall basicity of sinter and decrease flux composition.

Influence of sinter grate suction pressure (flame front speed) on microstructure, productivity and quality of iron ore sinter

From a sinter production point of view, it is important to optimise the sintering process with regard to both sinter quality and production rate. In sintering, airflow rate within the sinter bed decides the production rate and its physical and metallurgical properties. To study the influence of airflow rate (flame front speed) on sinter production and sinter quality, pot grate sintering experiments were conducted at sinter grate suction pressures ranging from 900 to 1700 mm water column over the sinter bed. During sintering, time–temperature data were recorded, and mineralogical studies were carried out. This study reveals that increase in sinter grate suction pressure through the sinter bed from 900 to 1700 mm water column significantly improved the sinter productivity from 34·37 to 48·90 t/m2/day; however, the physical and metallurgical properties of the sinter at higher suction pressure were not optimum with respect to blast furnace requirements. The maximum sinter productivity with desired physical and metallurgical properties was obtained at suction pressure 1300 mm water column. At this pressure, improvement in sinter quality was due to optimum firing temperature and enough retention time available for formation of mineral phases. At an airflow rate 1300 mm water column, sinter productivity was 41·0 t/m2/day, sinter strength (TI) was 73·10%, reduction degradation index was 25·0 and reducibility was 71·50%.

Influence of MgO addition on microstructure and properties of low and high silica iron ore sinter

The quality of iron ore sinter mainly depends on sinter mineralogy, which in turn depends on the chemical composition of the sinter mix. Dolomite is the critical additive for fluxing the sinter and controlling the sinter MgO. Recently, the silica level in the sinter product of the sinter plant 1 has been varying in the range of 5·51 to 9·58% owing to variation in silica content of iron ore fines. At the same time, as per the blast furnace requirement, the rate of addition of dolomite has been changed from 2·40 to greater than 3·00% at the sinter plant 1. In iron ore sinter, MgO plays different roles on sinter properties at different silica ranges. Because of wide range of fluctuation in iron ore silica it is essential to optimise the MgO addition in sinter mix to get desired properties. Laboratory pot grate sintering experiments have been carried out to know the influence of MgO addition on microstructure and properties of low silica and high silica sinter. MgO addition has been varied from 1·40 to 3·20% for low silica (4·47%), and high silica (6·25%) iron ore fines. High silica with high MgO sinter showed lower strength, higher reduction degradation index, and lower reducibility compared to low silica with low and high MgO and high silica with low MgO sinter. To achieve better sinter properties MgO content in the sinter should not be more than 2·80% when silica is more than 6·0%.

Influence of basicity and MgO content on metallurgical performances of Brazilian specularite pellets

Influence of basicity (CaO/SiO2 ratio) by adding limestone and MgO content in the form of magnesite on metallurgical performances of Brazilian specularite pellets was investigated. Pellets with varying basicity (0.12 to 1.20) and MgO content (0.08% to 3.0%) were studied for RI (reducibility index), RSI (reduction swelling index) and RDI (reduction degradation index) tests. SEM (scanning electron microscope) with EDS (energy dispersive spectrometry) and optical microscope were employed to test the microstructure and chemical analysis of iron oxide and slag of fired pellets. Meanwhile, measurement of the microstructure of reduced pellets after RSI and RDI tests was also carried out by using an optical microscope. With increasing basicity or MgO content, RI and RDI were improved. In the basicity range of lower than 0.20 or higher than 0.80, pellets exhibited low RSI. In the basicity range of 0.20 to 0.80, abnormal swelling occurred and RSI was higher than 20%, which attributed that more amount of low melting point slags appeared at this basicity range. Due to the presence of MgO that decreased the amount of liquid phases, with increasing MgO content, RSI was restrained. The basicity between 0.20 and 0.80 should be avoided during producing pellets using Brazilian specularite due to the abnormal swelling.

Utilization of High Sulfur Raw Materials in Iron Ore Pellets

Pyrite cinder and high sulfur magnetite were used as raw materials to produce iron ore pellets. Good qualities of green balls and fired pellets were obtained from the feed comprising 50% pyrite cinder and 50% high sulfur magnetite concentrate at a small scale. Small-scale tests were proven by pilot-scale tests. The high grade fired pellets, assaying 63.22% Fe, were analyzed, and the compressive strength of fired pellets was over 2500 N/pellet. The fired pellets possessed excellent metallurgical performances, such as reducibility index higher than 67%, reduction swelling index lower than 15% and low temperature reduction degradation index (+ 3.15 mm) higher than 1%, which can be used as the burden for blast furnace.

Effects of MgO Containing Additive on Low-Temperature Metallurgical Properties of Oxidized Pellet

As a main charging form of BF (blast furnace), pellets play an important role in blast furnace process. However, comparing with sinters, pellets have many disadvantages, such as reduction swelling, low softening and melting temperature and so on. Therefore, the flux pellets have been applied in blast furnace widely, especially MgO containing pellets. The light burned magnesite is applied as MgO containing additive in pellet production. The characters of light burned magnesite are explored. Meanwhile, the effects of it on low-temperature metallurgical properties are investigated such as low-temperature reduction degradation index (RDI), compressive strength (CS) and the reduction swelling index (RSI). The light burned magnesite calcined at 850 °C manifests better grindability, larger specific surface area, and higher hydration activity. It is found that the addition of light burned magnesite can improve low-temperature metallurgical properties (RDI, RSI) of the pellets. With the increase of light burned magnesite in pellets, the RSI and RDI decrease gradually; when the proportion of light burned magnesite does not exceed 2.0% in pellets, the CS decreases slightly, but it still surpasses 2 689 N, which can still meet the demand of BF.

Sintered Ore Sprayed by Acid and Alkaline Waste Water Resulted From Cold Rolling

In order to prevent the powdering of a sintered ore from influencing the smooth operation of a blast furnace, the conventional way to deal with it is that the CaCl2 solution is prepared by tap water, and then the solution is sprayed onto the sintered ore for improving its RDI (low temperature reduction degradation index). The CaCl2 solution prepared by adding acid and alkaline waste water resulted from cold rolling is sprayed onto the sintered ore to improve its RDI. The values of RDI+6.3 and RDI+3.15 of the sintered ore which is sprayed by the CaCl2 solution with the CaCl2 concentration of 3. 5% (mass percent) are increased by 17. 5% and 11. 63%, but the index of RDI−0.5 is decreased by 3. 1 % when the spraying amount of the solution is making up 0. 5 % of the total sintered ore sprayed in comparison with those of the sintered ore which is not sprayed by using the CaCl2 solution. Experimental results show that after the CaCl2 solutions prepared by adding the acid and alkaline waste water are sprayed on the sintered ore, RDI of the ore can be remarkably improved and therefore another way for recycling acid and alkaline waste water can be available, by which both cost for treating waste water and cost for producing a sintered ore can be decreased and environment is free of pollution by harmful substances in the waste water.

Optimization and Selection of Solid Fuel Type in Sintering Process

In order to use resonably fuel resources and reduce cost of manufacture, the effects of coke and coal powder on chemical coposition and metallurgical properties of sinter were studied with the iron ore blender as the iron-contained materials. Results shown that the reducibility at 900°C was slightly improved and the low temperature reduction degradation index was worsened with the coke powder as the solid fuel relative to coal powder under the equal calorific value condition. However, with the increasing of solid fuel ratio, the mechanical strength and low temperature reduction degradation index was improved.

Effect of MgO in the form of magnesite on the quality and microstructure of hematite pellets

MgO addition to pellets improves their high temperature properties by improving the oxide and slag phases. In the present study, effect of MgO, in the form of magnesite flux, on pellet quality, melt formation and microstructure during the induration was examined. Fired pellets with varying MgO contents (0 to 3.0%) were tested for cold crushing strength, reduction degradation index, reducibility and swelling characteristics. Optical microstructural studies with image analysis were carried out to estimate the amount of different phases. SEM–EDS analysis was done to measure the chemical analysis of oxide and slag phases. X-ray mapping was also carried out to understand the distribution of CaO, MgO, SiO2 and Al2O3 in different phases. From the results, it was observed that with increasing MgO, RDI and swelling characteristics of pellets were found to be improved. Reducibility of the pellets improved substantially in the range of 0.5 to 1.5% MgO. Formation of magnesioferrite phase and high melting point slag formed during induration could be attributed to the improved quality of pellets. Pellets with 2 to 3% magnesite addition, to get 1.0 to 1.5% MgO, exhibited optimum metallurgical properties among all the pellets studied.