METHOD FOR PRODUCING IRON ORE SINTER FROM HIGH ALUMINA IRON ORE FINES

TECHNICAL FIELD
[0001] The present disclosure, in general, relates to the field of metallurgy and, more particularly, to a method of producing iron ore sinter from high alumina iron ore fines without deteriorating the quality of the former.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Sintering is a thermal agglomeration process based on treating a mix (mineral fines, return fines, fluxes, etc.) layer in presence of coke dust to the action of a burner placed in the surface of the layer. In this way, heating takes place from the upper to the lower sections. The mix layer rests over a strand system and an exhausting system allows to the whole thickness to reach the suitable temperature for the partial melting of the mix, and the subsequent agglomeration. The purpose of the sintering process is producing a lumpy material with the suitable characteristics (thermal, mechanical, physical, chemical and metallurgical) to be fed to the blast furnace.
[0004] The key factors affecting the structure and quality of iron ore sinter are the properties of the iron ore, their composition mainly alumina and silica content, granulation efficiency, nucleus stability and primary sinter melt volume and, flux and their granulometry. All the mentioned parameter controls the sinter minerology and phase distribution.
[0005] In the sintering process, main raw material used is iron ore fines, quality of the iron ore fines influences the process of sintering significantly. Ore with higher alumina content is usually detrimental in forming the sinter matrix due to the low reactivity of alumina bearing minerals and the high viscosity of primary melts. A small increase in the alumina content of sinter blend can have a significant adverse impact on the strength and reduction degradation characteristics of the final sinter leading to deterioration in gas permeability in the upper part of the blast furnace. The most harmful effect of alumina is to worsen the sinter RDI, which increases as the alumina content rises. Industrial experience with the blast furnace shows that within a 10-10.5% CaO (Calcium Oxide) content range an increase of 0.1% in the alumina content raises the RDI by 2 points.
[0006] The strength and quality of sinter deteriorate as the alumina content rises. Alumina promotes the formation of SFCA (Silico-ferrite of Calcium and Aluminum), which is beneficial for sinter strength, but the strength of the ore components is lower, since a high alumina content in their lattice has been reported to be the main cause of the observed lower strength. Alumina increases the viscosity of the primary melt that forms during the sintering process, leading to a weaker sinter structure with more interconnected irregular pores. It could also alter the composition and properties of the primary melt formed in the sinter located near the cohesive zone of the blast furnace, which would have a negative impact on the gas and liquid permeability and reducibility of sinter in the lower part of the blast furnace.
[0007] An increase in the mean particle size of the iron ore fines promotes the productivity of the sintering machine, saves the specific fuel consumption but reduces the sinter strength. Dense low alumina iron ores give a better sinter strength and lower specific fuel consumption. Very high level of micro-fines in the ore decreases the granulation efficiency and consequently, decreases the bed permeability and affects productivity of sintering adversely.
[0008] Iron ores with high loss on ignition in presence of aluminous goethite (source of alumina in sinter) in raw material affects the sintering process in a negative way by reducing the productivity, increasing the specific fuel consumption and reducing the sinter strength.
[0009] High quality agglomerate in the form of sinter improves productivity of blast furnace and reduces coke consumption. With low availability of high grade iron ore, now low-grade iron ores with high alumina, hydrates and other impurities are needed to be used. These impurities and gangue specially alumina, decreases the quality of iron ore sinter and productivity significantly and therefore it has become important to overcome these issues by means of innovative approach.
[0010] To improve quality of iron ore sinter and increase its productivity, various different approaches have been adopted. For instance, a method of Reduction Degradation Index (RDI) improvement composition of sinter ore, preparing method for the same, and method of surface treatment of sinter ore using the same are described by Songbang et al in Patent bearing number KR20050009771A, wherein a combination of boron compound, chlorides, and lithium compound were used for the same. The method of Songbang stated about the usage of calcium chloride and lithium compound to improve the RDI of sintered ore which is very low in alumina content ~1.8%. However, addition of such elements, like chlorides and lithium, will cause maintenance problem because of corrosion caused by these elements and their compounds.
[0011] In another approach, a method for increasing yield of sintering ore by utilizing siderite was described by Zhang Yixian et al in patent bearing number CN103834799A wherein sized siderite is used as hearth layer and roasted siderite thus produced was added to sinter production for calculating overall sinter yield. The patent discloses the yield improvement but the return fines generation is the concern and even it is higher in sintering of higher alumina iron ore fines
[0012] In another approach, a supporting plate clean chute segregation distributor and segregation distributing device for segregating wet granulated raw material and increasing productivity is reported by Kejian Liu et. al., Patent bearing number CN102032790 (A). The subject matter of the Kejian’s patent concentrate on improving the permeability of sinter bed by sinter mix distribution which require heavy engineering modification in current running sinter plant.
[0013] In another approach, an apparatus for improving air permeability of sintering layer to improve quality and productivity of sinter produced by mounting a puff pipe on the lower part of a backward inclined plate of a charging unit is reported by Byun Sang Geun et al., Patent bearing number KR20020088119 (A).
[0014] In another approach, a Method of increasing sinter rate was described by Bradwell Cyril in patent bearing number US2767074A in which Bradwell proposed a method of increasing sintering rate by preheating the mix with hot water and steam. Preheating the mix by hot water and steam does not work to the expectation as todays raw material with high combined moisture results in cold process air generation to decrease mix temp as well as provide extra moisture for moisture front formation.
[0015] In another approach, a Method for improving strength and size composition of sinter is described by Li Binglai in Patent bearing number CN103343218B in which special brucite fibers are used for improving sinter quality. Materials like brucite fibers are not so easily available for commercial usage and will be costly replacement of any flux.
[0016] All the approaches described hereinabove have a major drawback that they do not cover how the sinter quality and productivity will be improved or at least not decreased if the raw material quality deteriorates. Additional drawbacks are that they either mentioned new design incorporation in sinter plant for production increase or suggested use of some different material as hearth layer in sinter making whose chemical composition is not same to sinter.
[0017] Therefore, it is desired to have a process for producing needle coke for low CTE graphite electrodes, which does not require the use of a petroleum-derived feedstock. Indeed, it would be desirable to have a process for converting coal tar pitch and coal tar distillate mixture into needle coke which results in a high coke yield.

OBJECTS OF THE DISCLOSURE
[0018] In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0019] It is a general object of the present disclosure to improve kinetics of assimilation/bond formation, quantity or extent of assimilation/bond formation as well as quality of assimilation/bond formation for producing good quality sinter with higher alumina.
[0020] It is an object of the present disclosure to lower the melting temperature of high alumina sinter mix.
[0021] It is another object of the present disclosure to enhance the rate kinetics and assimilation of alumina in sinter phases by adding the lower melting point compound of iron ore and calcium oxide in sinter making for making higher alumina product sinter.
[0022] It is another object of the present disclosure to increase the content of Acicular SFCA (Silico ferrite of calcium and aluminium) in product sinter with higher alumina specifically SFCA-1 which is richer in iron.
[0023] It is another object of the present disclosure to improve the Reduction degradation index of iron ore sinter by forming preferred metallurgical phases as required.
[0024] It is another object of the present disclosure to decrease the abrasion index of iron ore sinter by improving the microstructure of the sinter formed using low melting synthetic calcium ferrite compound in mixture.
[0025] It is another object of the present disclosure to increase the strength of the sinter measured in terms of tumbler index, by increasing the time of bond formation and therefore bonding phases amount, through addition of low melting synthetic calcium ferrite compound in sinter raw material.
[0026] It is another object of the present disclosure to decrease the return fines generation (minus 5 mm undersize sinter) by improving the bonding phases as well as granulometry of sinter mixture by low melting synthetic calcium ferrite compound addition in required quantity and size.
[0027] It is another object of the present disclosure to decrease the sintering time or increase the flame front speed of sinter making by improving the kinetics of reaction in sinter making through addition of low melting synthetic calcium ferrite compound.
[0028] It is another object of the present disclosure to produce sinter using iron ore of high alumina and high combined moisture at improved quality and increased productivity.
[0029] It is another object of the present disclosure to produce sinter of high alumina and high crystallized water iron ore at improved quality and increased productivity without increasing net carbon consumption.
[0030] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0031] This summary is provided to introduce concepts related to a method of producing iron ore sinter from high alumina iron ore fines. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0032] In an embodiment, the present disclosure relates to a method of producing iron ore sinter from high alumina iron ore fines. The method includes mixing synthetic calcium ferrite (SCF) with 2-10 wt%, with high alumina ore fines, pyroxenite, limestone, dolomite, calcined lime fines, return sinter fines, and coke, the SCF comprising T(Fe): 48-52%, CaO: 28-32%, Al2O3: 2.5-3.2 % and SiO2- 4.8%; and granulating the said mix with moisture to convert the fines into micro pellets/mini agglomerates via sintering process.
[0033] In an aspect, the composition of high alumina ore fines is 56 wt%, pyroxenite is 1.8 wt%, limestone is 11 wt%, dolomite is 3 wt%, calcined lime fines is 1.5 wt%, and return sinter fines is 15 wt%, and coke is 6.5 wt%.
[0034] In an aspect, the moisture is 6.5 wt%.
[0035] In an aspect, the SCF comprises T. Fe: 46.45, FeO: 6.24, CaO: 28.48, MgO: 0.6, SiO2: 4.16, Al2O3: 3.11.
[0036] In an aspect, the SCF is -5 mm size 100% passing.
[0037] In an aspect, the SCF is -3.15 mm 100 % passing.
[0038] In an aspect, the SCF has melting temperature of 1100- 1220 ºC.
[0039] In an aspect, the Reduction Degradation Index (RDI) of the iron ore sinter is 18-20 %.
[0040] In an aspect, the tumbler index of the iron ore sinter is 70-74%.
[0041] In an aspect, the sintering time is 16-17 minutes.
[0042] In an aspect, the return sinter generation 15-17%.
[0043] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[0044] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0045] FIG. 1 illustrates a graphical representation of temperature at which tablet of different samples melted to form hemisphere in accordance with an embodiment of the present disclosure;
[0046] FIG. 2 illustrates a graphical representation of temperature at which samples completely melted and flow occurred in accordance with an embodiment of the present disclosure;
[0047] FIG. 3A illustrates a mechanism of sintering reaction in conventional sintering process;
[0048] FIG. 3B illustrates a mechanism of sintering reaction with low melting synthetic calcium ferrite compound in sinter mix in accordance with an embodiment of the present disclosure;
[0049] FIG. 4 illustrates a graphical representation of variation in tumbler index with sinter alumina and percentage of synthetic calcium ferrite in accordance with an embodiment of the present disclosure;
[0050] FIG. 5 illustrates a graphical representation of variation in abrasion index with sinter alumina and percentage of synthetic calcium ferrite in accordance with an embodiment of the present disclosure;
[0051] FIG. 6 illustrates a graphical representation of variation in reduction degradation index with sinter alumina and percentage of synthetic calcium ferrite in accordance with an embodiment of the present disclosure;
[0052] FIG. 7 illustrates a graphical representation of variation in return sinter generation with sinter alumina and percentage of synthetic calcium ferrite in accordance with an embodiment of the present disclosure;
[0053] FIG. 8 illustrates a graphical representation of variation in sintering time with sinter alumina and percentage of low melting synthetic calcium ferrite in accordance with an embodiment of the present disclosure; and
[0054] FIG. 9 illustrates a method for making a calcined needle coke in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0055] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0056] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0057] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0058] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0059] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0060] Embodiments explained herein pertain to a method of improving the sinter quality with higher alumina iron ore fines Alumina in sinter raw mixture is believed to promote and stabilize SFCA (Silico-ferrite of calcium and aluminum) phase. However, the yield and strength of the sinter decrease with the increasing of the high alumina.
[0061] The reason behind this is the presence of higher alumina in sinter promotes the formation of iron deficient Silico ferrite of calcium and aluminum which is not supportive to get the optimized sinter physical and metallurgical properties. With the increasing of alumina content, more alumina will dissolve into the hematite, SFCA and glass phase. The strength of these minerals will then decrease, it is expected to demand a high sintering temperature and a longer sintering time to promote melt formation and to produce a sinter with reasonable quality.
[0062] As a result, the fuel rate will increase and the sintering productivity decrease. The sinter SFCA morphology under such condition will be columnar colonies of SFCA, More relict hematite, Non uniform connected large pores and hence owing to higher porosity enhances the secondary hematite formation. Such morphology of sinter results in lower shatter, tumbler and RDI of iron ore sinter.
[0063] Now detrimental effects of high alumina in iron ore sintering process is nullified by adding low melting synthetic compound called as low melting synthetic calcium ferrite. The addition of this novel flux/compound suppresses the formation of complex phases during sintering, which decreases the viscosity of melts and improves the diffusion of gangue oxides in the melts. The low melting synthetic calcium ferrite compound owing to its better affinity towards alumina provides more time for reaction with silica and alumina because of better reaction kinetics as preformed low melting synthetic calcium ferrite compound starts absorption of calcium aluminate as soon as the required temperature is reached.
[0064] This present disclosure also relates to a method by which tumbler index of the sinter is increased, abrasion index is decreased, Reduction degradation of sinter is decreased, sintering time is decreased, return fines generation is decreased.
[0065] This present disclosure also relates to a method by which mixing of low melting synthetic calcium ferrite promotes the formation of better sinter phase morphology specifically SFCA phase which is mainly acicular in nature as compare to conventional high alumina sinter which is more columnar and blocky.
[0066] An important factor affecting the structure and quality of iron ore sinter is primary melt formation temperature and primary melt volume formed from slag and other components of iron ore sinter. During sintering, the temperature in the sintering zone reaches as high as 1350 degree centigrade which results in incipient melt formation and fusion of different constituents of sinter mix and subsequent production of large sintered porous mass. Due to reaction of fluxing components with the iron ore constituents at high temperature, a melt is formed. This melt promotes the diffusion of different components of the slag forming compounds across the grains through melt and subsequent solidification of this melts binds the grains to each other. Therefore, an early formation of this melt and amount of the melt formation plays a significant role in sintering.
[0067] Ore with higher alumina content and high amount of crystallized water is usually detrimental in forming the sinter matrix due to high heat demand for dihydroxylation reaction and the low reactivity of alumina bearing minerals and the high viscosity of primary melts. A small increase in the alumina content of sinter blend can have a significant adverse impact on the strength and reduction degradation characteristics of the final sinter because of poor characteristics of primary melt in term of melting point and viscosity.
[0068] To counter any adverse effect of poor quality iron ore, primarily due to presence of high alumina and hydrates, a special approach is required. In this work, a special low melting compound of iron ore and CaO is called as low melting synthetic compound is used for doping in sinter raw mixture. As per as pure CaO and Fe2O3 in a pre-defined ratio can react to form a compound having a melting point as low as 1205. Addition of such flux in sintering process of high alumina iron ore can support in assimilation of poor quality iron ore in sinter making.
[0069] During sintering because of heat supplied by the coke fines burning, low melting synthetic calcium ferrite compound added in the mixture melts at relatively low temperature and thereby initiates diffusion of different slag components of raw material constituents at lower temperature which otherwise would happen at higher temperature. As the temperature rises, more melt formation, diffusion across those melts and subsequent solidification, further strengthens the product sinter.
[0070] In this disclosure, a method is proposed which enables to improve the Reduction degradation index of iron ore sinter, increase the strength of the sinter measured in terms of tumbler index, decrease the abrasion index and return fines generation of iron ore sinter, decrease the sintering time by increasing sintering reaction kinetics. Additionally, the method enables to produce sinter from high alumina and high crystallized water iron ore at improved quality and increased productivity without increasing net carbon consumption.
[0071] In the method proposed in this disclosure, a lower liquidous compound of iron ore and calcium oxide, named as low melting synthetic calcium ferrite compound, is used as the doping agent to counter the negative effect of alumina on sinter properties and mineral morphology. The lower liquidus/melting point compound of iron ore and calcium oxide, i.e. low melting synthetic calcium ferrite compound, is added in raw material of iron ore sintering to get the benefits of its lower melting point in assimilation kinetics of iron ore sintering.
[0072] It is to be noted that not only the temperature of primary melt formation but also the viscosity of the primary melt formation is significantly important in iron ore sintering. In presence of low melting synthetic ferrite compound in sinter making along with higher alumina in sinter raw mixture, the temperature of primary melt formation is lower down, than bonding phases will form at lower temperature and will remain a that temperature or higher temperature for longer duration as temperature of that zone still increasing. This way the bonds, thus formed do not get thermal shock due to sudden cooling by process air and do not become brittle. Also, if the viscosity of the melt is lowered down than the melt will flow outwards into nearby pores and after undergoing solidification, results in bonding of more grains effectively.
[0073] On the other hand, in absence of said low melting compound the temperature of primary melt formation is high than that melt will form at very later stage in sintering and will get cooled immediately by process air, resulting in thermal shock and brittle phases formation. Additionally, the viscosity of the primary melt is high then then it will not flow to nearby pores and will not bind the grains effectively. Hence, this is the reason of lowering in iron ore sinter properties in presence of higher alumina in sinter mineral phases.
[0074] To understand a melting behavior of CaO and Iron Ore compound (synthetic calcium ferrite), temperature of primary melt formation as well as viscosity of the primary melt was studied using dilatometer. In a dilatometer equipment, a small tablet of powdered samples is heated. With increase in temperature, the sample undergoes different degree of shrinkage, deformation and becomes hemispherical due to primary melt formation. Finally, with further increase in the temperature, the hemispherical sample formed earlier, melts completely and flows away. The temperature at which samples flows can be correlated to viscosity of the melt. If the temperature is high, then it can be correlated to its high viscosity. If the temperature at which spherical shape is formed is high, it can be correlated to its high primary melt formation temperature. The powder tablet of same was tested in dilatometer. Table 1 provides the results of dilatometer test. It can be seen that the hemisphere formation occurred at 1199 °C and it quickly flowed with only 4 °C additional rise in temperature to 1203°C.
Table 1: Dilatometer data showing hemisphere and flow temperature of low melting synthetic calcium ferrite compound
Sample Tablet Hemisphere Formation on heating Flow on heating
Low melting Synthetic calcium ferrite

[0075] After confirmation from dilatometer tests, Iron ore fines, Lime fines, Limestone fines and Coke fines suitable to raise the temperature to 1250 °C, were mixed together in mixing drum and granulated by adding moisture. They were then fired the same way as for making iron ore sinter in bottom suction draught sintering pot machine used for making iron ore sinter. Though sinter pot was used for making low melting synthetic calcium ferrite compound but this mixture can be fired using other furnaces like muffle, microwave, tubular etc. During firing, the component reacted to each other and low melting compound was obtained.
[0076] In the second stage of this approach, low melting compound was taken out from the suction pot and crushed below 5 mm size. This finer material was then added to high alumina iron ore mixture and sintering of same was done in bottom suction draught sintering apparatus. It was observed that addition of low melting synthetic calcium ferrite compound ion sinter making raw material resulted in improved quality of sinter at increased productivity even with higher level of alumina and higher crystallized water content.
[0077] Before making sinter from the low melting synthetic calcium ferrite compound doped raw material, Dilatometer tests were again conducted for high alumina and low alumina iron ore sinter as it is and with addition of low melting synthetic calcium ferrite compound in different proportion to understand the effect of low melting synthetic calcium ferrite compound on primary melt formation temperature and viscosity of flow temperature. The results obtained are provided in table 2. From table 2, one can observe that temperature of hemisphere formation in 2.5% alumina sinter mix is 1339 °C which increased to 1360 °C for 3.1% alumina sinter mix. Additionally, though the temp at which melt flowed was not detected in both the cases of 2.5% alumina mix and 3.1% alumina mix till 1364°C but the contact angle for 2.5 % alumina mix at 1364°C was lower w.r.t. 3.1 % alumina mix, which shows that 2.5% alumina mix has better flowable characteristics. To improve the primary melt formation temperature and flow characteristics, low melting synthetic calcium ferrite compound prepared separately as discussed, was added to the mix of high alumina sinter. Upon heating the tablets prepared from different level of low melting synthetic calcium ferrite compound addition, hemisphere formation temperature decreased and temperature at which material flowed was detected. Variation in temperature of hemisphere formation and flow temperature is shown in FIGS. 2 and 3 respectively. Both the hemisphere formation temperature and flow temperature were decreased with the addition of low melting synthetic calcium ferrite compound therefore it is concluded that low melting synthetic calcium ferrite compound addition in sinter making raw material will decrease primary melt formation temperature and decrease the viscosity of the primary melt which will promote early start of sintering process i.e. at low temperature and therefore provide more time for sintering to occur.
Table 2. Dilatometer data showing hemisphere formation and flow of different samples
Sample Tablet Hemisphere Formation on heating Flow on heating
2.5 Alumina mix

(Flow Not
Detected till 1364°C) (Contact angle at 1364 =21°)
3.1% Alumina mix

(Flow Not
Detected till 1364°C) (Contact angle at 1364 =23°)
3.1% alumina mix with 2% synthetic calcium ferrite compound

3.1% alumina mix with 2% synthetic calcium ferrite compound

3.1% alumina mix with 6% low melting synthetic calcium ferrite compound

[0078] FIGS. 3A and 3B explain the difference in the mechanism of conventional sintering and sintering when low melting synthetic calcium ferrite compound is added to it.
[0079] During conventional sintering, the temperature in the sintering zone reaches as high as 1350 degree centigrade which results in incipient melt formation and fusion of different constituents of sinter mix.
[0080] The stages of sintering for high alumina iron ore is as follows: -
[0081] Sintered ore is produced by mixing fine iron ore with limestone (flux) and coke breeze (heating fuel) and iron ore fines in presence of moisture, granulating the mixture into pseudo-particles as shown in FIG 3A(1).
[0082] As shown in FIG. 3A(2), the temperature of sinter mass when reaches to 800 to 1100 ºC by combustion of the fine coke, the hematite particle gets reduced to magnetite owing to CO generation and reaction of it with iron ore (hematite) particles in presence of coke particle, at the same temperature the limestone starts calcination and it reacts with the iron ore particle in its vicinity. The Silica and alumina starts to react with the calcium ferrite to the form the complex slag components.
[0083] However, the rate of reaction is very slow as higher CaO in sinter supports the formation of Calcium aluminate and monocalcium ferrite during sintering but also required more heat for limestone calcination. More CaO and More alumina will result in formation of more Calcium aluminate which will demand more Calcium ferrite for dissolution.
[0084] When the temperature further increased during sintering process the rate of melt formation is gradually increased as shown in FIG. 3A(3). Owing to the presence of high amount of calcium aluminate generated as explain above, the viscosity of melts is higher and having low flowable property, this hinders the kinetics of reacting the flux and gangue components completely with the melts. The formation of calcium ferrite is diffusion rate controlling process and since the calcium and iron are not predominantly available for reaction, it results in iron deficient calcium ferrite formation in later stage of sintering process, also Owing to the presence of high alumina and silica in sinter raw mix, these gangues have lower mineralization ability and reaction activity much lower than free Silica and alumina. So, it is difficult to react with the iron minerals and flux to form complex calcium ferrite, but easy to exist as glassy phase. And, it finally results in iron deficient calcium ferrite content and high glassy phase content in sinter.
[0085] During solidification in sintering process the melts starts to precipitate as the new phase called as SFCA (silica ferrite of calcium and aluminum). Owing to the higher viscosity of the melts and lower assimilation of the calcium, alumina and silica in the melts results in lesser fraction of beneficial phase called as acicular SFCA however such phase is iron deficient since its precipitate from lower viscosity, lower flowable and less assimilated complex melts as shown in FIG. 3A(5).
[0086] The solidification of complex melts above 1300 ºC results in non-beneficial phase called as columnar SFCA. The growth of the grain in preferred orientation and direction is controlled by melts viscosity and diffusion of complex slag component in sintering phases. Owing to higher viscosity the grain growth restricted results in columnar grains of higher thickness and more macro porous sinter structure. The pores in sinter have high partial pressure of oxygen which convert the magnetite into secondary hematite as shown in FIG. 3A(6). The combination of such phase is bad of high and low mechanical as well as metallurgical properties of sinter.
[0087] As shown in FIG. 3B(1A) where the low melting compound i.e. low melting Synthetic calcium ferrite (SCF) is also the parts of Pseudo particle of iron ore, limestone, coke breeze. The lower size and higher surface area of low melting synthetic calcium ferrite compound (-5 mm) helps in better homogenization and distribution in sinter mix.
[0088] During subsequent burning of coke as the temperature reaches to 800 to 1200 ºC, the preformed low melting synthetic calcium ferrite compound starts reacting with the alumina, silica and lime available in its vicinity. The calcination of limestone also takes place simultaneously. The hematite particle gets reduced to magnetite as explain previously.
[0089] As shown in FIG. 3B(2A), the low melting synthetic calcium ferrite compound owing to its better affinity towards alumina provides more time for reaction with silica and alumina because of better reaction kinetics as preformed low melting synthetic calcium ferrite compound starts absorption of calcium aluminate as soon as the required temperature is reached.
[0090] The total amount of calcium ferrite which is iron rich is continuously increasing with increase in time and temperature during sintering. The fraction of calcium aluminate is restricted due to unavailability of sufficient amount of alumina required for formation as most of alumina is now absorbed by preformed low melting synthetic calcium ferrite compound melt as shown in FIG. 3B(3A).
[0091] As shown in FIG. 3B(4A), the amount of melt and rate of assimilation of alumina and silica is higher in proportion as compare to sinter made without low melting synthetic calcium ferrite compound. Though the smaller quantity of calcium aluminate is formed owing to heterogeneity nature of sintering process. But this is not significant enough to deteriorate the sinter metallurgical structure morphology.
[0092] If the temperature of primary melt formation is low than bonding phases will form at lower temperature and will remain a that temperature or higher temperature for longer duration as temperature of that zone still increasing. This way the bonds, thus formed do not get thermal shock due to sudden cooling by process air and do not become brittle. Also, if the viscosity of the melt is lower than it will flow outwards into nearby pores and after undergoing solidification, results in bonding of more grains effectively.
[0093] As shown in Fig 3B(5A), more CaO and Al2O3 are assimilated in the melt, this reacts with the iron oxide and generates acicular calcium ferrite and presence of the low melting synthetic calcium ferrite compound melt further promotes the formation of iron rich acicular SFCA. Lower Viscosity of melts at lower temperature helps in more grain growth during solidification, and since its happens at lower temperature the SFCA formed is more acicular as compare sinter without low melting synthetic calcium ferrite compound.
CASE STUDY
[0094] To establish and explain the benefit of low melting synthetic calcium ferrite compound doped sintering, 5 sets of trial were taken. In trial 1, sinter with 2.5% alumina and no low melting synthetic calcium ferrite compound addition was prepared in pot grate sintering set-up. In trial 2, sinter with 3.1% alumina and no low melting synthetic calcium ferrite compound addition was prepared in pot grate sintering set-up. The quality and productivity of the sinter produced in trial 1 and 2 were compared. In trial 3, 4, and 5, sinter with 3.1% alumina with low melting synthetic calcium ferrite compound addition in increasing order were prepared to establish the effect of low melting synthetic calcium ferrite compound addition in sinter making. In trial 3, 4 and 5 low melting synthetic calcium ferrite compound addition was 2%, 4% and 6 % respectively.
[0095] Table 3 provides chemical composition of sinter produced in 5 sets of trial as well as chemistry of low melting synthetic calcium ferrite compound used and other raw material used.
Table 3: Chemical composition of sinter and other raw material used in this study
Material T. Fe FeO CaO MgO SiO2 Al2O3 LOI
Sinter of Trial 1 55.16 9.88 11.32 1.86 4.82 2.51 0
Sinter of Trial 2 54.28 10.03 11.26 1.9 4.85 3.12 0
Sinter of Trial 3 54.62 10.45 11.41 1.88 4.89 3.17 0
Sinter of Trial 4 54.71 10.62 10.89 1.93 4.78 3.19 0
Sinter of Trial 5 54.67 10.88 11.26 1.94 4.91 3.22 0
low melting synthetic calcium ferrite compound 46.45 6.24 28.48 0.6 4.16 3.11 0
Low Alumina Iron Ore 61.23 0.21 0.05 0.04 3.48 2.41 2.6
High Alumina Iron Ore 60.01 0.13 0.06 0.03 4.1 2.96 3.99
Limestone Fines 0.6 0 50.2 1.6 4.1 0.7 42.32
Dolomite Fines 2 0.08 27.18 19.24 8.19 0.49 40.01
Pyroxenite Fines 2.78 1.29 22.32 23.5 23.11 1.03 2.78
Lime Fines 0.32 - 66.35 0.88 1.54 0.79 21.24
Coke Fines/breeze - - - 0.24 5.6 5.1 81.26

[0096] The sinter was made with target chemistry, i.e., the basicity (CaO/SiO2) of 2.3 and MgO at 1.9 %. The Coke rate in all set of trials was kept constant at 6.5 %.
[0097] The sinter raw mix of 100 kg was mixed in mixer drum and moisture was also added to convert the fines into micro ball having mean particle size of 2. 5mm. The Green sinter mix was then transferred to pot sinter. In all set of trials, the suction rate and the ignition flame temperature for firing the sinter in sintering process was kept constant (1300 mm of water column) and at 1000 °C respectively.
[0098] During sintering process, the time to complete the sintering process was noted, i.e., after achieving the burn through temperature of sinter bed (maximum temperature of waste gas). The fired sinter was then stabilized by dropping the whole mass of sinter for 4 times from 2-meter height. After dropping, minus 5 mm fraction of sinter fines was removed and weighed and the remaining sinter was further screened in size range -40 mm to +10 mm for tumbler test. The sinter is then tested for Reduction degradation index and microstructural analysis.
[0099] The results of the test are provided in FIGS. 4, 5, 6, 7, and 8 are described here. Tumbler index dropped by 2.11 point when alumina increased from 2.5 to 3.1% in sinter. With addition of low melting synthetic calcium ferrite compound to 6% of the mix, tumbler improved by 4.74 points to 72.86. FIG. 5 shows that abrasion index increased by 2 points to 7.75 from 5.75 when alumina in sinter increased to 3.1 from 2.5%. With low melting synthetic calcium ferrite compound doping it gradually decreased to 5 points with 6% low melting synthetic calcium ferrite compound addition at higher alumina level of 3.1%. Similarly, RDI increased by 4.11 points to 26.36 with increase in alumina and was brought down to 18.45 with addition of 6% low melting synthetic calcium ferrite compound. Sintering time and return fines were also increased by increase in sinter alumina which were decreased by low melting synthetic calcium ferrite compound addition as shown in FIGS. 7 and 8.
[00100] Microstructural examination was carried out using optical microscope to study the kind of phases formed. These are provided in table 4. It was observed from microstructural images that with increase in alumina poor microstructure formation occurred where more columnar and glassy phases along with secondary hematite were formed which are not desirable while with increase in low melting synthetic calcium ferrite compound addition in the sinter mix, well distributed and more acicular SFCA was formed.
Table 4: Microstructure of sinter and low melting synthetic calcium ferrite compound studied in this work
Good microstructure with more acicular SFCA Poor microstructure with less Acicular and SFCA Microstructure formed from melt

[00101] The low melting synthetic calcium ferrite compound lower the sintering temperature which promotes the formation of SFCA-1 phase (higher assimilation of alumina in sinter melts), by suppressing the formation and assimilation of complex calcium aluminate in the melt.
[00102] The low melting synthetic calcium ferrite compound is reduce the flow temperature of high alumina sinter to 1320-1310 ºC.
[00103] The SCF compound modify the contact angle of sinter melts from 25º to 17º in higher alumina sinter fines.
[00104] FIG. 9 illustrates an example method 900 for producing iron ore sinter from high alumina iron ore fines. The order in which the method 900 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 900, or an alternative method.
[00105] At block 902, the method 900 includes mixing synthetic calcium ferrite (SCF) with 2- 10 wt%, with high alumina ore fines, pyroxenite, limestone, dolomite, calcined lime fines, return sinter fines, and coke, wherein the SCF comprising T(Fe): 48-52%, CaO: 28-32%, Al2O3: 2.5-3.2 % and SiO2- 4.8%.
[00106] At block 904, the method 900 includes granulating the said mix with moisture to convert the fines into micro pellets/mini agglomerates via sintering process.
[00107] In an aspect, the composition of high alumina ore fines is 56 wt%, pyroxenite is 1.8 wt%, limestone is 11 wt%, dolomite is 3 wt%, calcined lime fines is 1.5 wt%, and return sinter fines is 15 wt%, and coke is 6.5 wt%.
[00108] In an aspect, the moisture is 6.5 wt%.
[00109] In an aspect, the SCF comprises T. Fe: 46.45, FeO: 6.24, CaO: 28.48, MgO: 0.6, SiO2: 4.16, Al2O3: 3.11.
[00110] In an aspect, the SCF is -5 mm size 100% passing.
[00111] In an aspect, the SCF is -3.15 mm 100 % passing.
[00112] In an aspect, the SCF has melting temperature of 1100- 1220 ºC.
[00113] In an aspect, the Reduction Degradation Index (RDI) of the iron ore sinter is 18-20 %.
[00114] In an aspect, the tumbler index of the iron ore sinter is 70-74%.
[00115] In an aspect, the sintering time is 16-17 minutes.
[00116] In an aspect, the return sinter generation 15-17%.
[00117] Furthermore, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[00118] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[00119] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with

Claims:

1.method for producing iron ore sinter from high alumina iron ore fines, comprising:
mixing synthetic calcium ferrite (SCF) with 2- 10 wt%, with high alumina ore fines, pyroxenite, limestone, dolomite, calcined lime fines, return sinter fines, and coke, wherein the SCF comprising T(Fe): 48-52%, CaO: 28-32%, Al2O3: 2.5-3.2 % and SiO2- 4.8%; and
granulating the said mix with moisture to convert the fines into micro pellets/mini agglomerates via sintering process.
2. The method as claimed in claim 1, wherein composition of high alumina ore fines is 56 wt%, pyroxenite is 1.8 wt%, limestone is 11 wt%, dolomite is 3 wt%, calcined lime fines is 1.5 wt%, and return sinter fines is 15 wt%, and coke is. 6.5 wt%.
3. The method as claimed in claim 1, wherein the moisture is 6.5 wt%.
4. The method as claimed in claim 1, wherein the SCF comprises T. Fe: 46.45, FeO: 6.24, CaO: 28.48, MgO: 0.6, SiO2: 4.16, Al2O3: 3.11.
5. The method as claimed in claim 1, wherein the SCF is -5mm size 100% passing.
6. The method as claimed in claim 5, wherein the SCF is -3.15 mm 100 % passing.
7. The method as claimed in claim 1, wherein the SCF has melting temperature of 1100- 1220 ºC.
8. The method as claimed in claim 1, wherein the Reduction degradation index of the iron ore sinter is 18-20 %.
9. The method as claimed in claim 1, wherein the Tumbler index of the iron ore sinter is 70-74%.
10. The method as claimed in claim 1, wherein the sintering time is 16-17 minutes.