Claims:WE CLAIM:
1. A sinter making process, comprising:
layering with wustite (FeO) enrich material to the top surface of a sinter bed and sintering.
2. The sinter making process as claimed in claim 1, wherein the wustite (FeO) enrich material is mill scale/LD sludge/sinter return fines/magnetite iron ore fines or their combination(s).
3. The sinter making process as claimed in claim 2, wherein the wustite (FeO) enrich material comprising a size of -3.15mm with 90-95% passing.
4. The sinter making process as claimed in claim 3, wherein the wustite (FeO) enrich material size is preferably 92-93% passing.
5. The sinter making process as claimed in claim 1, wherein the thickness of layering to the sinter bed is 20-60mm.
6. The sinter making process as claimed in claim 5, wherein the thickness of layering to the sinter bed is preferably 30-40mm.
, Description:SINTER MAKING PROCESS

TECHNICAL FIELD
[0001] The present disclosure, in general, relates to the development of a lower thermal conductivity top layer in iron ore sintering process which basically consist of spraying the uniform thickness of FeO (Wustite) rich material on the top layer of sinter bed.
[0002] In particular, the present disclosure relates to a sinter making process.

BACKGROUND
[0003] 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.
[0004] In iron ore sintering, a mixture of various raw materials, such as iron ore fines, limestone fines, dolomite fines, pyroxenite fines, burnt lime and carbonaceous fuel like anthracite coal or coke breeze etc., are thermally agglomerated to convert them as a suitable feed for the blast furnace.
[0005] Sintering is a process in a sinter machine for agglomeration of iron ore and other raw material fines into a compact porous mass, i.e., sinter, use in Blast Furnaces as an iron-bearing input charge material for hot metal production. ‘Permeability’ of sinter-bed on sinter machine, i.e., the porosity in sinter-bed of charged materials, facilitates atmospheric air passes from the top to bottom across the depth of sinter-bed, when suction created from the bottom of the bed, for efficient heat carry over from top to bottom of the bed for complete burning of charged materials for effective sintering process controls the productivity of the sinter machine.
[0006] In the conventional sintering process, ‘heat deficiency’ at the top portion of sinter bed, the due insufficient presence of fuel materials at top causes generations of weak sinter fines leading to a reduction in ‘yield’ of sinter production. The heat pattern in the sintering bed of an actual sintering machine is non-uniform in the vertical direction of the bed (within the pallet), and there is a general tendency that the maximum temperature reached in the bed increases with increasing depth and that the temperature-fall speed slows down accordingly.
[0007] During the sintering process, the upper portion of the sintering material layer is lower in the bulk temperature and besides shorter in the length of time for exposure to elevated temperature than the intermediate and lower portions. This leaves the problem that a sintered ore formed in the upper portion is low in melt bonding and hence small in mechanical strength with reduced sintering yield when the flame front travel beneath the sinter bed the top layer of sinter experiences the maximum amount of thermal shock. The temperature of the top layer drops in higher magnitude compared to the middle and bottom layer. Hence, the top layer of sinter is fragile owing to results in sinter fine, this is more crucial as per the yield of sinter plant is considered.
[0008] The partial pressure of oxygen is also high at the top portion and hence the coke burns at a faster rate in the top layer as compared to the middle and bottom layer. The excess available oxygen in top layer results in the conversion of mot form wustite (FeO) into hematite, and so the top layer is so porous and fragile.
[0009] Further, around 20-30% of the total sinter bed is unusable owing to its fragile nature and hence it is always reported as return sinter fines (-5mm).
[0010] It is also found from experimental studies in pot sinter which is bottom suction iron ore fines also that the top layer if wustite (FeO) deficient as compare to middle and bottom. The FeO is an important factor in controlling the strength and high-temperature properties of sinter.
[0011] The level of ‘permeability’ in sinter-bed is depending upon the effectiveness of ‘charging chute’ in size-wise ‘segregation’ of charge materials across the depth in sinter-bed, achieved due to differences in the sliding velocities of particles during charging into the moving sinter-bed. The permeability achieved by the earlier conventional ‘charging chute’ was limited due to its design and positional constraints in sinter machine
[0012] It is well known that the productivity of a sinter machine is greatly depending upon “permeability” of the sinter bed, i.e., the porosity of sinter bed, which facilitates atmospheric air flow across the depth of bed and “yield. Permeability is greatly influenced by the size-wise ‘segregation’ of charged particles across the depth of sinter bed, achieved by a ‘charging chute’, provided below the raw mix hopper of the sinter machine.
[0013] To increase the sinter plant yield in terms of top layer strength, various approaches have adopted. For instance, a method for increasing yield of sintering ore by utilizing siderite was described by Zhang Yixian et al in patent number CN103834799A wherein sized siderite ore is used as hearth layer and roasted siderite was added to sinter production for calculating overall sinter yield.
[0014] Japanese Patent Publication Number 61-223136 discloses, for instance, that a sintering material layer to be formed on a pallet Should be reduced in its density by means of a Screen constituted with a plurality of wire materials extending along a flow of Sintering material being loaded on the pallet, and at the Same time, the Sintering material should be segregated with fine particles held in an upper layer and with coarse particles held in intermediate and lower layers so as to make the upper layer highly permeable to air with eventual improvement of yield and productivity of a sintered ore. This prior art method, however, has the problem that Since a sintering material of 7% or the like in water content is prone to get adhered to the wire materials, the resultant Sintering material layer is difficult to Stably retain in a Segregated State as originally desired.
[0015] A supporting plate clean chute segregation distributor and segregation distributing device for segregating wet granulated raw material and increasing productivity are reported by Kejian Liu et. al., Patent Number CN102032790 (A). However, such a method improves the permeability but it will not avoid the formation of the fragile layer at the top of the sinter bed and hence more return fines are generation is still a concern.
[0016] US 6349833 B1 describes a method of the magnetic loading of a sintering material, magnetically susceptible sinterable Substances of high magnetization and fine substances of slidable dropping at low speed are segregated in great amounts in an upper portion of a sintering material layer deposited on a pallet.
[0017] 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 Number KR20020088119 (A).
[0018] Above-cited approaches or disclosures mentioned new design incorporation in sinter plant for the production increase, by reducing the sinter fines and increasing the permeability of sinter bed.
[0019] The mentioned approaches involve the transfer of magnetic susceptible material present in sinter mix to travel in such a way that it gets an accumulated in the top bed of the sinter by virtue magnetically operated sophisticated chutes or hoppers.
[0020] Such approaches or methods demand the modification in sinter plants which is not economical. Similarly, owing to the continuous change in the raw mix in sinter making, it is difficult for the magnetic material to get accumulate on sinter top layer. Many times due to extra segregation of such material at the top results in more assimilation results in more melt generation and hence deteriorate permeability of the bed.
[0021] The segregation also tends to affect the overall segregation of coke and magnetic material across the sinter bed. As top gets richer in magnetic material the middle portion get deficient in wustite rich material and hence disturb the overall material balance of the sinter bed.

OBJECTS OF THE DISCLOSURE
[0022] 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.
[0023] It is a general object of the present disclosure to propose a method by which the lower thermal conductivity wustite (FeO) rich top layer is formed in the iron ore sintering process, where the top layer helps in lowering the thermal gradient of top layer leading to the strong and dense top layer.
[0024] It is an object of the present disclosure to propose a method of generating a lower thermal conductivity wustite rich top layer are developed by suitable charging the FeO rich material on the top of sinter bed with an optimum thickness in iron ore sinter making.
[0025] It is another object of the present disclosure to propose a method in which the gradient in FeO content with respect to sinter bed is reduced owing to balancing the FeO content by the presence of FeO rich layer on the top.
[0026] It is another object of the present disclosure to propose a method in which the FeO rich top layer is assimilated in similar fashion at given sintering temperature to that of the middle and bottom bed of the sinter.
[0027] It is another object of the present disclosure to propose a method of reducing the thermal shock resistance in top layer sinter results in lower sinter fines generation
[0028] It is another object of the present disclosure to reduce the rate of cooling of the sinter top layer.
[0029] It is another object of the present disclosure to produce more magnetite in the sinter top layer even in presence of higher partial pressure of oxygen at the top bed of sinter.
[0030] It is another object of the present disclosure to increase the shrinkage by more assimilation in sinter making through addition on FeO rich material on sinter top bed.
[0031] It is another object of the present disclosure to produce sinter using low-grade iron ore of high alumina and silica and high combined moisture at improved quality and increased productivity.
[0032] It is another object of the present disclosure to produce sinter at improved quality and increased productivity without increasing net carbon consumption
[0033] 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
[0034] This summary is provided to introduce concepts related to a sinter making process. 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.
[0035] In an embodiment, the present disclosure relates to a sinter making process. The process includes layering with wustite (FeO) enrich material to the top surface of a sinter bed and sintering.
[0036] In an aspect, the wustite (FeO) enrich material is mill scale/LD sludge/sinter return fines/magnetite iron ore fines or their combination(s).
[0037] In an aspect, the wustite (FeO) enrich material comprising a size of -3.15mm with 90-95% passing.
[0038] In an aspect, the wustite (FeO) enrich material size is preferably 92-93% passing.
[0039] In an aspect, the thickness of layering to the sinter bed is 20-60 mm.
[0040] In an aspect, the thickness of layering to the sinter bed is preferably 30-40 mm
[0041] 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
[0042] 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:
[0043] FIG. 1 illustrates a sinter base mix with 7.62% FeO;
[0044] FIG. 2 illustrates a sinter base mix with 10.32% FeO;
[0045] FIG. 3 illustrates a sinter base mix with 12.34 % FeO;
[0046] FIG. 4A illustrates a mechanism of FeO re-oxidation in the conventional sintering process;
[0047] FIG. 4B illustrates a mechanism of FeO generation and re-oxidation in presence of FeO rich lower thermal conductivity material at sinter top bed;
[0048] FIG. 5A illustrates a process Schematic of sinter plant;
[0049] FIG. 5B illustrates a process schematic of a proposed method of charging FeO rich material on sinter top bed at sinter plant, in accordance with an embodiment of the present disclosure;
[0050] FIG. 6 illustrates sinter produce with mill scale spread on sinter top bed (30 mm thickness);
[0051] FIG. 7 illustrates the variation in sinter FeO at a different location in pot test trials;
[0052] FIG. 8 illustrates a temperature variation of the sinter top bed prepared using a conventional method and proposed method;
[0053] FIG. 9 illustrates the tumbler index of sinter prepared using a conventional method and proposed method;
[0054] FIG. 10 illustrates net coke consumption of sinter prepared using a conventional method and proposed method;
[0055] FIG. 11 illustrates return fines generation in sinter prepared using a conventional method and proposed method;
[0056] FIG. 12 illustrates bed shrinkage in sinter prepared using a conventional method and proposed method;
[0057] FIG. 13 illustrates net coke consumption of sinter prepared using a conventional method and proposed method; and
[0058] FIG. 14 illustrates a microstructure of sinter top layer at different FeO levels in accordance with the present disclosure.

DETAILED DESCRIPTION
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] Embodiments explained herein pertain to a method by which sinter fines generation due to the top fragile top layer in sinter process is reduced, fuel requirement decreased and productivity of sinter plant is increased wherein the method proposed to charge the FeO rich lower thermal conductivity material on sinter top bed.
[0065] During the sintering process, the top layer of sinter experienced the highest temperature when it comes in contact with ignition furnace flame temperature. However, after the ignition of the top layer, the coke also burns simultaneously which makes the process autogenous. During subsequent suction in a downdraft suction sintering machine, the coke burning helps to increase the sintering reaction and slag formation to get agglomerate. Because of this, the top layer of the sinter experienced higher thermal shocks when it comes in contact with the ambient atmosphere. The top layer gets cooled in must faster rate than the middle and bottom bed of the sinter. Owing to higher partial pressure at the top of the sinter bed the FeO content reduces than the desired level and hence the poor assimilation at sinter top layer having lower strength.
[0066] The present disclosure counters such limitation where the addition of wustite (FeO) rich layer which not only increases the assimilation kinetics of sintering reaction but also acts as insulation layer owing to its nearly constant lower thermal conductivity with respect to temperature. The thermal conductivity of hematite and magnetite.
[0067] In the present subject matter, a method is developed wherein a tumbler index of sinter improved and return fines of the sintering process is reduced by the process of charging the lower thermal conductivity material preferably mill scale on sinter top layer. To produce FeO rich layer on the sinter top layer, the material can be spread on sinter top bed in such a way that the thickness of the top spread layer is maintained in the range of 20-30 mm.
[0068] In iron ore sintering, a minimum of shrinkage occurs due to incipient melt formation, solidification, and fusion. Therefore, to develop the purpose of maintaining higher wustite (FeO) in the sinter top layer helps in more shrinkage of sinter bed which is the indication of more melt formation on sinter top bed.
[0069] In an implementation, the bonding phase temperature is also studied with the addition of FeO bearing material mainly mill scale in the sinter base mix. To know how much FeO is required for better assimilation and melt formation at a lower temperature, iron ore fines, dolomite, pyroxenite, and limestone are doped with mill scale in different proportion and were heated in a dilatometer wherein the temperature required for hemisphere formation and flow of the melt noted. In dilatometer equipment, a small tablet of powdered samples is heated. With the increase in temperature, the sample undergoes a 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
[0070] In an aspect, when small tablet made of sinter base mix with 7.62% FeO was subjected to the heating in dilatometer equipment, the material starts to fuse at a temperature of 1274 ºC and the material starts to flow at a temperature of 1351 ºC (see FIG. 1)
[0071] However, when the proportion of mill scale addition is increased in such a way that the sintered base mix has 10.32% FeO, the tablet is then subjected to heating in dilatometer, material shows hemisphere deformation at temperature of 1247 ºC and complete flow temperature was found to be 1311 °C (see FIG. 2). when the proportion of mill scale addition is increased in such a way that the sintered base mix has 12.34 % FeO the tablet was then subjected to heating in dilatometer, the material shows hemisphere deformation at a temperature of 1218 ºC and complete flow temperature was found to be 1293 °C shown in FIG. 3. As observed from the data, with increasing FeO content in the tablets the fusion starts at a lower temperature. This FeO on further oxidation in sintering process get re-oxidized to secondary hematite and stable magnetite and this is the reason even after re-oxidation the FeO at top layer is maintained in the level of middle and bottom bed of the sinter.
[0072] In the conventional Sintering operation, the particle size distribution and compositional distribution of a sintering material deposited to correspond to the height of a sintering material layer bring about an important effect on successful sintering. Namely, at an initial Stage of ignition in an igniting furnace, air is allowed to pass through the sintering material layer from its ignited surface to its bottom upon Suction at a lower part of the pallet.
[0073] In this course of Sintering, air of normal temperature with higher partial pressure of oxygen is supplied without preheating to a sintered melt zone (for example, a region of higher than 1,200 ºC.) that has been defined in an upper portion of the sintering material layer at middle and last stages of sintering, however, air to be suctioned downwardly of the layer is passed through a completely sintered region in that upper portion and hence preheated, followed by feeding to sintered melt zones defined in the intermediate and lower portions of the layer.
[0074] Consequently, the upper portion of the sintering material layer is lower in the bulk temperature and besides shorter in the length of time for exposure to elevated temperature than the intermediate and lower portions. This leaves the problem that a sintered ore formed in the upper portion is low in melt bonding and hence Small in mechanical strength with reduced Sintering yield. The top layer experiences the maximum re-oxidation of formed FeO during sintering leading to more fragile and lower strength top layer, as explained before the assimilation temperature increases with reduction in FeO content the poor assimilation generates the more porous top layer with a population of cracks as shown in FIG. 4A.
[0075] Further, as shown in FIG. 4B, the addition of FeO material at the top layer of sinter bed more preferably the lower thermal conductivity material acts as an insulator during the subsequent sintering process. The sinter bed with FeO rich layer at the top get ignited fully when it comes in contact with the ignited flame of ignition furnace or induration furnace, during this period of time the material which in close contact with sinter base mix starts assimilation at a lower temperature as found in dilatometer results.
[0076] The higher kinetic of assimilation on top of sinter bed make denser layer when the sinter travels out from the ignition furnace, the top layer gets benefits of lower thermal conductivity properties of the material which acts as a barrier for heat dissipation from sinter bed to the atmosphere. This helps in more preheated air for the middle and bottom layer of sinter. As the top layer temperature is equipped with lower thermal conductivity material the thermal shock during subsequent sintering reduces drastically. The top layer is remaining at a higher temperature as compared to conventional sintering process results in higher FeO content like that of bottom sinter layer and hence achieve dense metallurgical structure full of magnetite ad having better physical strength.
[0077] As the top bed is now remaining at higher temperature throughout the process of sintering, owing to which more air gets preheated when it gets entrapped from the top layer to the middle and bottom bed of the sinter and hence sintering reaction kinetics at the middle and bottom bed of the sinter is improved.
[0078] The basic difference for operation purpose of the present invention and conventional sintering process is explained herewith.
[0079] The first schematic of conventional sinter plant operation is shown in FIG. 5A and is described below. In the conventional sintering method (FIG. 5A), wherein sinter return fines reduced in turn increases the sinter production with improved tumbler index of sinter, the basic raw materials are transported to a proportioning unit wherein raw material are weighed and proportioned as per the required material balance iron ore fines (A), limestone fines (B) and solid fuel (anthracite coal/coke fines (C), dolomite/ pyroxenite fines(D), and sinter return fines (E) is conveyed to mixing and granulation unit where water and lime fines (F) are added and mixing is done and wet granules are formed. The granulated mixture is then transported to feeding hopper of sinter plant straight grate furnace. Feeding hopper feeds the material on endless pallet car of sintering machine. Before feeding the mixture granules on the pallet cars, sinter of size (10-25 mm) are layered as hearth layer using hearth layer sinter bins. This bed of un-sintered mix having hearth layer at bottom and granules over it moves forward with the movement of the endless car in the forward direction. When the bed comes under ignition furnace, the top layer gets ignited and due to suction from the bottom, flame front proceeds downwards and sintering occurs.
[0080] At the end of the sintering process, sinter machine is tilted and sinter cake falls on spike crusher and crushed sinter is transported to sinter cooler. Cooled sinter, thereafter, screened into three fractions, minus 5 mm which goes to granulation unit for recycling, plus 5 mm which goes to blast furnace stock house.
[0081] In accordance with an embodiment as shown in FIG. 5B, in the proposed sintering method, wherein sinter return fines reduced in turn increases the sinter production with improved tumbler index of sinter, the basic raw materials are transported to proportioning unit wherein raw material are weighed and proportioned as per the required material balance iron ore fines (A), limestone fines (B) and solid fuel (anthracite coal/coke fines (C), dolomite/pyroxenite fines(D) and sinter return fines (E) is conveyed to mixing and granulation unit where water and lime fines (F) are added and mixing is done and wet granules are formed.
[0082] During the transfer of sinter base mix to the sinter machine the FeO rich material (F) it will either mill scale, sinter return fine, LD sludge from steel making shop or magnetite fines were used to spread on the sinter bed through perforated feeding hopper. The vibro motor is attached to the feeding hopper which is electrically driven which helps in continuously producing the vibration in the feeder so that the material can be uniformly spread on sinter top bed. the amplitude of perforated feeding hopper vibration is synchronized with the horizontal speed of the sinter machines. The synchronization helps in maintaining the desired thickness of the spread layer on top of the sinter bed.
[0083] The sinter bed with FeO rich layer at the top will then travel to ignition furnace will it get ignited and sintering reaction starts thereof.
[0084] The top layer provides the insulation to the sinter bed and hence reduces the thermal shock and improve the strength of the sinter by reducing thermal crack on sinter bed.
[0085] At the end of the sintering process, sinter machine is tilted and sinter cake falls on spike crusher and crushed sinter is transported to sinter cooler. Cooled sinter, thereafter, screened into three fractions, minus 5 mm which goes to granulation unit for recycling, plus 5 mm which goes to blast furnace stock house.
[0086] The present disclosure relates to developing a method where the FeO rich layer is produced on the top layer of sinter bed by the process of charging the FeO rich material on the sinter bed. The presence of such rich FeO layer on sinter top bed when exploring to higher temperature results in higher melt formation.
[0087] The higher FeO material presence at top layer results in better assimilation with other oxides present in the sinter base mix. The FeO content of the top layer during subsequent assimilation in higher as compared to the middle and bottom layer. The higher FeO helps in lowering the thermal gradient of the top layer as the flame front when travel from the top layer to the next sinter layer the top layer experienced the shock from the cold air sucking downwards in the sintering process.
[0088] The wustite (FeO) have inherent properties of having nearly constant thermal conductivity with respect to temperature. The wustite hence cooled at a lower rate at the top layer of the sinter as compare to the conventional sintering process.
[0089] The process of charging the FeO rich material basically consists of charging the specific size of the material on the top layer of sinter after whole bed of sinter base mix along with hearth layer is transfer in the pallet car of downward suction sintering machine. The thickness of the FeO rich lowe thermal conductivity insulating layer on sinter top bed is maintained in such a way that most heat gets a transfer to the next below a layer of the sinter bed. The heat losses to the atmosphere are restricted by maintaining the proper thickness of the spraying material.

Case Study:
[0090] In this work, two sets of sinter pot test were made to simulate the conventional sintering method as well as the method proposed in this work. Effect of proposed method of FeO rich top layer on sinter return fines, Tumbler index, and sinter bed shrinkage was also established.
[0091] Iron ore, Limestones fines, Pyroxenite, dolomite, and coke breeze of mentioned chemistry in Table 1 was used for preparing sinter base mix. The chemistry of the mill scale is also mentioned in Table 1:

Table 1: Chemistry of raw materials
MATERIAL T. Fe CaO SiO2 MgO Al2O3 FeO LOI
JODA Iron ore 62.93 0.00 0.08 0.01 2.58 2.77 3.36
Pyroxenite 5.26 0.00 0.41 50.12 39.43 0.65 1.57
Lime Fines 0.17 0.00 68.90 0.56 1.31 0.56 27.54
Limestone 0.00 0.00 36.56 7.49 33.48 20.25 0.00
Dolomite 0.83 55.45 32.82 2.61 6.00 0.67 0.00
Coke breeze -- 12.5 0.24 5.2 -- 79.22
Mill scale 66.861 1.44 1.07 -- -- 51.98 --

[0092] Iron ore used for sinter base mix preparation was first screened at -10 mm fraction. The mill scale having size range as shown in Table 2:

Table 2: Size Analysis of Mill scale used in the proposed work
Size in (mm) 10 8 6 5 3.15 1 0.5 0.25 0.15 -0.15
% 1.0 0.9 1.8 2.2 13.0 30.8 11.2 11.2 17.5 10.4

[0093] These materials were then mixed is preferred proportion in such the way that the basicity (CaO/SiO2) around 2. The material is the mix in the granulating drum along with moisture ~6-7%. The green mix was produced having a mean particle size of 2-3mm. Two sets of pot grate sintering test were taken wherein in base case the normal sinter was made without using FeO enrich at the top layer of sinter bed for purpose of comparison.
[0094] 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 %.
[0095] The sinter raw mix of 100 kg was mixed in mixer drum and moisture was also added to convert the fines into a micro ball having a mean particle size of 2. 5 mm. 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 the sintering process was kept constant (1300 mm of water column) and at 1100 °C respectively.
[0096] During the sintering process, the time to complete the sintering process was noted, i.e., after achieving the burn through the temperature of sinter bed (maximum temperature of waste gas). The fired sinter is then removed from the pot as shown in FIG. 6 and stabilized by dropping the whole mass of sinter for 4 times from 2-meter height. After dropping, minus 5 mm fraction of sinter fines were 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 microstructural analysis. During the sintering process, the top temperature of the sinter bed was measured to note the thermal behavior of the sinter top bed.
[0097] The samples for chemical analysis is collected from three sections of sinter pot, i.e., the top layer, middle layer and bottom layer of the sinter. The variation in FeO content of sinter bed compared with the conventional sintering process is shown in FIG. 7.
[0098] During sinter pot test trail of set1 and set2, the temperature of the top bed is noted by immersing the thermocouple in sinter top layer around 50 mm.
[0099] It is also observed that after 11 mins of sintering process the temperature of top layer in normal sintering (Set1) there is sudden drop in temperature i.e the temperature drop from 130 ºC to 78 ºC within 6 mins however as per the proposed method the temperature of top layer after 11 mins was 146 ºC and at the end of the sintering process it was 115 ºC.
[00100] It was also observed that the temperature of the sinter top layer with mill scale (set2) is reduced with the sintering time, i.e., 18 mins however as compare to conventional sintering process (set1) the temperature of top layer drastically reduce to 78ºC from 178 ºC. The present invention of adding mill scale on sinter top bed results in slower cooling of the sinter top bed owing to the lower thermal conductivity of wustite rich top layer, the temperature dropped to 115 ºC from 175ºC, the delta temperature is 60 ºC, while in conventional sintering process it is 100 ºC as shown in FIG. 8.
[00101] The results of the test are provided in FIGS. 9, 10, 11, 12, and 13 are described here. With the addition of mill scale at sinter top bed, tumbler improved by 3.14 points to 72.56 from 69.42, similarly the abrasion index improved by 1.93 points. Sinter return fines dropped by 2.17 point i.e sinter made with conventional sinter have 26.32% return sinter fines while that of sinter made in set2 with mill scale at top of sinter bed is 24.15%
[00102] FIG. 12 showing the bed shrinkage of sinter bed. It was found that owing to the higher rate of assimilation in the top layer due to the presence of FeO rich material will cause the bed to shrink more as compared to the conventional sintering process. The bed shrinkage of sinter in the proposed method is found to be 83.4 mm against 70mm in the normal sintering process.
[00103] As the tumbler index and abrasion index of sinter improved and with a reduction in sinter return fines in turns reduced the coke consumption by 1.6 points as shown in FIG. 13.
[00104] FIG. 14 illustrates a microstructure of sinter top layer at different FeO levels in accordance with the present disclosure. Iron ore sintering process is the combination of oxidation and reduction process, hence in conventional sintering process owing to higher oxidation potential available at top of the sinter bed the top layer oxidized rapidly and hence generation of the porous fragile layer at the top is the indication of more fines generation in the conventional sintering process.
[00105] As shown in image (A) of FIG. 14, the top layer of sinter contains more magnetite phase which is surrounded by silicate melt, as well as these, are solidified side by side, such microstructure is developed owing to the presence of higher FeO material on sinter top bed. The Mill scale as explained before acts as a barrier for the supply of oxygen to the sintered layer leading to lower oxidation of wustite (FEO) and hence the magnetite content is more. Similarly, the pores generated during sintering are smaller due to higher assimilation as compare to sinter produce by conventional sintering process as shown in image (B) of FIG. 14.
[00106] The sinter produces by the conventional method have more hematite phase and lower magnetite phase. The metallurgical phase transformation of magnetite to hematite at top layer leads to volume expansion and generates cracks, these effect is further enhancing by thermal gradient developed at the top layer of the sinter bed and the present invention helps in changing the overall metallurgical phases morphology and their fractions as compared to the conventional sintering process.
[00107] Accordingly, the present disclosure relates to the development of a method for producing the FeO enrich top layer on the sinter bed by spraying the lower thermal conductivity, heat insulating layer on the sinter bed for increasing iron ore sintering production and decreasing fuel consumption and return sinter fines generation.
[00108] Sinter return fines generally defined as the -5mm size sinter, which basically generated during the sintering process and during transportation.
[00109] In Iron ore sintering, the upper portion of the Sintering material layer is lower in the bulk temperature and besides shorter in the length of time for exposure to elevated temperature than the intermediate and lower portions. This leaves the problem that a sintered ore formed in the upper portion is low in melt bonding and hence Small in mechanical Strength with reduced Sintering yield.
[00110] The top layer of the sinter bed is responsible for lowering the overall yield of the sinter plant. The higher thermal gradient experienced by the top layer of the sinter as compare to bottom and a middle layer of the sinter makes the top layer so fragile that during subsequent cooing of the sinter the generation of -5mm size fraction of the sinter is increased in the range of 18-25%
[00111] To make the top layer strong and more melts must have formed at the top layer of the sinter bed, the material basically having higher FeO (wustite) content of required size ( -3.15 mm passing more than 90%) needs to be sprinkled at the top layer of the sinter bed.
[00112] The present disclosure relates to a method where the FeO rich layer is produced on the top layer of sinter bed by the process of charging the FeO rich material on the sinter bed. The presence of such rich FeO layer on sinter top bed when exploring to higher temperature results in higher melt formation.
[00113] The materials used for the present subject matter is FeO rich mill scale which is the oxidation product of slab or billet heated in the reheating furnace of hot rolling steel mills. The mill scale sprayed on the top of sinter bed with the thickness of 20-60 mm more preferably 30 mm on green sinter bed. On the subsequent firing of the sinter at a temperature of 1100-1200ºC the top layer experienced the temperature from the burner and presence of mill scale or FeO rich material at top layer starts melting by forming the lower eutectic with other oxides presence in sinter mix such as SiO2, Fe2O3, Fe3O4.
[00114] The present disclosure relates to developing a method where the FeO rich layer is produced on the top layer of sinter bed by the process of charging the FeO rich material on the sinter bed. The presence of such rich FeO layer on sinter top bed when exploring to higher temperature results in higher melt formation increases the kinetic of assimilation on top layer hence more melts gets generate at the top layer. The content of FeO get increased at the top layer as compared to middle and bottom layer however owing to the higher partial pressure of oxygen at the top of the sinter bed the FeO get oxidized to hematite and magnetite and hence the overall FeO content in final sinter product is controlled.
[00115] 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.
[00116] 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.
[00117] 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 information and knowledge available to the person having ordinary skill in the art.