Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A SINTER MIX COMPOSITION INVOLVING BASIC OXYGEN FURNACE STEEL SLAG AS PARTIAL REPLACEMENT OF FLUX IN SINTER MAKING.



2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.



3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present disclosure relates to the field of agglomeration in general and in particular to a sinter mix compositioninvolving basic oxygen furnace (BOF) steel slag to optimize the production of quality sinter through an innovative combination of raw materials with reduced lime and dolomite consumption.
BACKGROUND OF THE INVENTION
Various types of slags, namely Blast Furnace (BF) slag, Basic Oxygen Furnace (BOF) slag, Electric Arc Furnace (EAF) slag, and Secondary Steelmaking Slag, generated at different stages of steel production were considered waste, is finding use as by-products for creation of value and reducing the environmental impact. In the Ironmaking and steelmaking processes, slagging agents, including limestone, dolomite, and silica sand, are introduced into the blast furnace or steelmaking furnaces. This addition aims to generate slag that can remove impurities from the product iron during smelting.The formation of slag results from intricate physical and chemical reactions involving non-metallic components such as lime, dolomite, and fluxes, along with ash content in coke and interaction with refractory bricks. The exceedingly high temperatures, reaching approximately 1500°C, during slag generation ensure the absence of organic substances in the resultant slags. These slags serve a crucial role in steel making by shielding the metal bath from oxygen and facilitating temperature regulation through the formation of a protective lid. Due to the fact that the slags are lighter than the liquid metal, and they float and may be easily removed. The generation of slag occurs concurrently with the primary processes of hot metal production in both ironmaking and steelmaking. Consequently, the slag generation process is integral to and considered an inherent component of the overall steel production process.
Slag generated during steelmaking in BOF is one of the important waste materials in an integrated steel plant. The typical generation rate of BOFslag is 150 to 180kg per ton of crude steel. The slag dumping in the slag yard is undesired steel plants, as it generates dust, causes loss of thermal energy present in liquid slag and requires considerable land space.Utilisation of the slag waste to whatever extent possible for productive end use is an area being actively pursued to reduce environment load and achieve cost reduction possible. Raw materials constitute a major portion of production cost. Therefore, if wastes can be used as substitute of raw materials, conservation of natural resources is possible with further lowering of environmental impact.
One such potential alternative to the slag waste is using it for sinter making. They usually contain considerable quantities of valuable flux and materials. These materials can be used in sinter making as a replacement of other prime raw materials.
Sintering is a generic term that is used to describe a high temperature process in which a raw materials mixture is converted into a particular form of agglomerate known as sinter. Iron ore sinters are suitable porous materials obtained by agglomeration processes of iron ore fine particles. These agglomerates are widely employed in blast furnaces to produce pig iron. Sufficient cold handling strength of sinter is required to minimise fines generation and different processes are used for this purpose. The type and amount of flux and fuel significantly affect the sinter quality.
The sintering process begins with the preparation of a sinter mixture consisting of iron ore fines, fluxes, solid fuel such as coke breeze, and return fines from the sinter plant and blast furnace as well as recycled ferruginous materials from downstream iron and steelmaking processes.
PRIOR-ART DISCLOSURE
BOF slag is a by-product of the BOF process, which converts molten pig iron and steel scraps into high quality steel. Most slags from steel plant derive from this process, with an average of 150-200 kg of slag generated per tonne of steel produced (T. Annunziata et al., Material Recycling - Trends and Perspectives, Vol. 1, 2012).Disposal of large quantities of slag becomes a big environmental concern. Slag handling, disposal and its reuse has become a critical environmental issue for steel producers (J. Pal et al., Journal of Metallurgy and Materials Science, Vol. 45, No. 2, 2003).Open dumping and landfills are some common management practices that are adopted for disposal of industrial wastes, thus resulting in environmental pollution in the form of dusts and leachate apart from huge economic accountability (S. Kalshetty et al., International Journal of Creative Research Thoughts, Vol. 6, No. 2, 2018).
BOF slag, a steel production by-product, is globally utilized as a cost-effective clinker substitute in cement production. Despite its higher CaO content, Indian cement manufacturers are cautious due to concerns about its impact on reinforced materials in concrete structures. Researchers suggest limiting BOF slag usage to 10% in cement making to ensure P2O5 stays below 0.3%, safe for Portland slag cement. Beyond this, challenges hinder widespread adoption (P. Lohiya et al., International Journal of Engineering Research in Current Trends, Vol. 2, No. 3, 2020).
Alternatively, BOF slag is used in civil engineering projects like road construction for its strength, but expansion from free lime, especially in moist conditions, may lead to cracks, limiting its road use. BOF slag presents opportunities and challenges in various applications (S. Banerjee et al., BioTechnology: An Indian Journal, Vol. 14, No. 4, 2018).
Huang Qingzhou et al. (Guangxi Beigang New Material Co., Ltd.), Patent No. CN108774684B, issued in 2018 discloses a method for utilizing stainless steel refining slag in laterite sintering. This innovative approach is particularly well-suited for chromium-nickel alloy preparation through the sintering process. The method involves substituting a portion of the quicklime flux with stainless steel refining slag, with the added slag comprising 3-7% of the total sintering ingredient mass. However, this application limits the use of sinter only for a specific grade production.
Hiroomi Miyata et al. (JFE Steel Corp.), Patent No. JP5950098B2, issued in 2016 reveals a technique for incorporating steelmaking slag into the sintering process. The approach involves converting the slag into pellets before incorporating it into the raw mix. A similar method has been suggested by SeiichiroSandoet al. (JFE Steel Corp.), Patent No. JP2015168828A, issued in 2018 for utilizing steelmaking slag and wet dust on the form of mini-pellet as a feed raw mix for iron ore sintering process. The mini-pellets consist of steel slag within a range of 0 to 25% of its total mass. This conversion process effectively contains the harmful effects of the steelmaking slag within the granulated particles, preventing adverse impacts on particles derived from raw materials other than steelmaking slag. Takahide Higuchi et al. (JFE Steel Corp.), Patent No. JP2015054991A, issued in 2016 utilized the steelmaking slag in sintering process with an approach involving to divide the raw material into two categories: materials other than steelmaking slag and steelmaking slag. Each category is granulated separately, producing sintered raw materials. The granulated particles of steelmaking slag are introduced into a granulation line designed for materials other than steelmaking slag. Subsequently, the particles of materials other than steelmaking slag are coated onto the surface of the granulated steelmaking slag particles. However, it's worth noting that all above the methods necessitates an additional step for separately granulating the steelmaking slag.
In India, the utilization of BOF slag is a meagre 25% compared to a high of 70–100% in other countries (P. Lohiya et al., International Journal of Engineering Research in Current Trends, Vol. 2, No. 3, 2020). Therefore, disposal of this huge mass of waste slag has become a problem due to environmental and space constraints in the steel plants. The utilization of integrated steel plant waste by an economical and environmental friendly technique will decrease a major portion of the production cost. Besides its use as road making and cement producing, it can very well replace lime addition to the steelmaking route due to its high lime content.
If these steel plant wastes are reused as a raw material substitute, then it is possible to conserve valuable natural resources like dolomite and limestone that are used as fluxing material to reduce the iron in steelmaking and thereby reduce the environmental hazards of mining the ore and reduce slag dumping space (P. Lohiya et al., International Journal of Engineering Research in Current Trends, Vol. 2, No. 3, 2020).
Most of the materials of Steel plant wastes are recycled through sinter making in most of the countries. Because of its physical, chemical and mineralogical properties, it can be used as raw material in process like sintering.BOF slag is one of the important waste materials generated in steel plants can act as a replacement of like dolomite and limestone in the sinter making.
With the current approach a combination of sinter mix is proposed without the requirement to alter the sintering process and to directly use the BOF slag as a part of sinter raw mix. With the use of BOF slag a part of fluxes including limestone and dolomite can be replaced still achieving the required sinter standards.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide a sinter mix composition involvingadvantageous use of BOF steel slag as an additive to iron ore sinter making process favouring desired sinter properties.
Another object of the invention is to make quality sinter, when the BOF slag is used in the selective sinter mix composition in the iron ore sinter making process.
Yet another object of the present invention is to reduce the flux requirement for sinter making.
A still further object of the present invention is to reduce the calcination load involved in the conversion of carbonates of lime and dolomite by usage of BOF steel slag.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a sinter mix composition involving basic oxygen furnace(BOF) steel slag partially replacing flux for sinter making comprising Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt % co-acting for generating sinter product with reduced limestone and dolomite content based Tumbler Index of 75 to 78 % and RDI of 19 to 23 %.
A further aspect of the present invention is directed to said sinter mix composition wherein said BOF steel slag comprises non-metallic BOF slag including FeO: 20.62 to 23.42 wt %, CaO: 41.38 to 43.50 wt %, SiO2: 13.52 to 15.05 wt %, MgO: 9.80 to 11.50 wt %, Al2O3: 3.14 to 3.50 wt %, MnO: 5.20 to 6.30 wt %, P2O5: 1.25 to 1.60 wt %.
A still further aspect of the present invention is directed to said sinter mix composition wherein size distribution for sinter raw mix constituents comprising
Size in mm Limestone Dolomite Coke and coal Non-metallic BOF slag Return Fines
+5 mm 0.68 0.96 1.05 57.2 1.70
-5 to +3.15 mm 12.17 15.99 11.47 13.77 48.12
-3.15 mm 87.14 83.05 87.48 29.05 50.18
and size distribution for iron ore comprising
Size in mm Weight %
+10 mm 6.14
-10+8mm 6.49
-8+6.3 mm 5.28
-6.3+5 mm 4.74
-5+3.15mm 7.49
-3.15+1 mm 14.30
-1+0.5 mm 5.53
-0.5+0.15 mm 10.70
-0.15 mm 39.35

A still further aspect of the present invention is directed to said sinter mix composition wherein the size range of the non-metallic BOF steel Slag in the sinter mix is 56 to 65% of size +5 mm, 11 to 18% of size -5 to +3.15 mm and rest part of size -3.15 mm.
Another aspect of the present invention is directed to a process for sintering using the sinter mix composition comprising
providing a selective sinter mix composition having reduced limestone and dolomite content comprising of Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt %;
mixing said sinter mix in a mixing drum at sinter plant and water is added to increase the moisture levels of the dry mix to7.5 to 8.5 % for granulation;
charging sinter mix into a sinter machine for assimilation of cake and filled upto a bed height of 700 mm;
igniting top of the sinter mix using a movable ignition/burner hood fuelled by coke oven gas while suction is applied across the bed, wherein ignition temperature is maintained at 1150 to 1250 °C preferably about 1200 °C while suction during ignition is maintained at 380 to 420 preferably 400 mm water column;
maintaining the speed of the belt such that ignition is continued for 1.75 to 2.25 preferably about 2 minutes and after the ignition process the suction is increased to 1150 to 1250 preferably about 1200 mm water column till sintering completion, to thereby obtain sinter product having Tumbler Index of 75-78% and RDI of 19-23%.
A further aspect of the present invention is directed to said process wherein after charging raw materials into the granulation drum, the same is inclined at 42 to 48 preferably 45° angle and set into rotation at a constant speed of 23 to 27 preferably about 25 rpm , said materials are allowed to mix in dry state for 3 to 5 preferably about 4 minutes, following which water is added to make the moisture levels of the dry mix reaches to a level of 7.5 to 8.5 preferably about 8% of the total mix weight wherein half the total amount of water is added and mixed intensely for 1.5 to 2.5 preferably about 2 minutes and rest of the water is then added and mixed for another 2.5 to 3.5 preferably about 3 minutes and the granules formed are allowed to grow without mixing during the last minute of granulation;
granulated sinter mix obtained from the granulation drum is then transferred to the sinter machine where Ignition temperature is maintained in the range of 1150 to 1250 °C, while suction during ignition is maintained at 380 to 420 preferably about 400 mm water column, said sinter machine speed is maintained such that the ignition is continued for 1.75 to 2.25 preferably 2 minutes, after which the suction is increased to 1150 to 1250 preferably 1200 mm water column and the sintering process is considered to be complete, when the wind box thermocouple recorded the maximum temperature (BTP-Burn through point).
A still further aspect of the present invention is directed to said process which produces a sinter chemistry of Fe (T): 50.66 to 52.15 wt%, FeO: 9.33 to 10.54 wt % CaO: 12.84 to 13.89 wt%, SiO2: 6.12 to 7.10 wt%, MgO: 2.06 to 2.28 wt%, Al2O3: 3.31 to 3.60 wt %, Basicity (CaO/SiO2): 1.95 to 2.17.
A still further aspect of the present invention is directed to said process wherein involving selectively said BOF steel slag in sinter mix composition, reduces lime consumption by 50% of conventional lime requirement and reduces dolomite consumption by 40 % of conventional dolomite requirement, said constituents being replaced with the use of BOF slag, thereby conserving the raw material usage, and reducing calcination load of the carbonate in terms of energy.
The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to illustrative embodiment.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a sinter mix compositionin wt % comprising of, Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt %.
The provision of composition as described above ensures effective utilization of the non-metallic part of BOF slag of 1 to 3 wt%. Further, there is reduction in usage of lime content which reduces from 7% conventionally to 3.2 - 5.2 wt%. There is a reduction in usage of dolomitefrom 6 - 7% to 4.4 - 5.4 wt %. The usage of the waste non-metallicBOF slag is quite economical as it saves the value of fresh limestone and dolomite. There is environmental benefit in usage waste and conservation of lime and dolomite. The sinter obtained with the usage of BOF slag as an ingredient show a Tumbler Index of 75 to 78 % and RDI value of19 to 23 %, which is industrially acceptable.
In a preferred embodiment, the non-metallicBOF slag comprises 41 to 45 wt % CaO; 20 to 28 wt % FeO; 10 to 16 wt % SiO2; 7 to 12 wt % MgO; 3.0 to 5 wt % Al2O3; 3 to 7 wt % MnO; and 1 to 2 wt % P2O5.
In another embodiment chemistry of the sinter is Fe (T): 50.66 to 52.15 wt%, FeO: 9.33 to 10.54 wt% CaO: 12.84 to 13.89 wt%, SiO2: 6.12 to 7.10 wt%, MgO: 2.06 to 2.28 wt%, Al2O3: 3.31 to 3.60 wt %, Basicity (Cao/SiO2): 1.95 to 2.17.
In yet another embodiment, Tumbler Index and RDI of the sinter obtained from the sinter mix is 75 to 78 % and 19 to 23 % respectively.
In yet another embodiment, the non-metallic BOF slag replaces Limestone and Dolomite.
In yet another embodiment, the size of the non-metallicBOF Slag in the sinter mix is 56 to 65% for size +5 mm, 11 to 18% for size -5 to +3.15 mm and rest for size -3.15 mm.
DESCRIPTION OF PREFERRED EMBODIMENT
In accordance with an embodiment of the invention, a sinter mix comprising of, Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt %.
The size distribution constituents used in the sintering process is shown below in the Table 1.
Table 1: Size distribution for sinter raw mix constituents
Size in mm Limestone Dolomite Coke and coal Non-metallic BOF slag Return Fines
+5 mm 0.68 0.96 1.05 57.2 1.70
-5 to +3.15 mm 12.17 15.99 11.47 13.77 48.12
-3.15 mm 87.14 83.05 87.48 29.05 50.18
The size distribution of the iron ore is shown below in the Table 2:
Table 2: Size distribution for Iron ore
Size in mm Weight %
+10 mm 6.14
-10+8mm 6.49
-8+6.3 mm 5.28
-6.3+5 mm 4.74
-5+3.15mm 7.49
-3.15+1 mm 14.30
-1+0.5 mm 5.53
-0.5+0.15 mm 10.70
-0.15 mm 39.35
In accordance with an embodiment of the invention, wherein the non-metallic BOF slag in wt % comprises of 41 to 45 wt % CaO; 20 to 28 wt % FeO; 10 to 16 wt % SiO2;7 to 12 wt % MgO; 3.0 to 5wt % Al2O3: 3 to 7 wt % MnO; and 1 to 2 wt % P2O5.
In accordance with an embodiment of the invention, the chemistry of the sinter is Fe (T): 50.66 to 52.15 wt%, FeO: 9.33 to 10.54 wt % CaO: 12.84 to 13.89 wt%, SiO2: 6.12 to 7.10 wt%, MgO: 2.06 to 2.28 wt%, Al2O3: 3.31 to 3.60 wt %, Basicity (Cao/SiO2): 1.95 to 2.17.
The composition of the sinter mix is so chosen can be well explained from the fact that theFeO in the sinter chemistry shall not go above 11 wt %. At the same time,the sinter basicity should be below 2.25. Also, the RDI is <25 value and the Tumbler Index is >74 which is as per industrial requirement.
ROLE OF COMPONENTS IN SINTERING
1. Iron ore: Iron ore primarily consists of haematitic ore and serves as the primary iron source, accompanied by silica and alumina as gangue materials.
2. Coke breeze: Coke breeze, containing approximately 80% carbon and residual volatile materials and impurities, is employed to generate the necessary temperature for reactions and to maintain a reducing environment.
3. Limestone: Limestone (CaCO3), is utilized to reduce the melting point of iron ore by creating a low-temperature melting phase. It also aids in forming a bonding matrix that enhances the cold strength of sinter, crucial for its transportation to the blast furnace.
4. Calcined Lime: Calcined lime in the iron ore sintering process serves as a fluxing agent, promoting the formation of a cohesive sinter bed essential for efficient iron production in the blast furnace. Its addition contributes to improved sinter strength, reducibility, and control of basicity, ensuring optimal conditions for the sintering reactions.
5. Non-metallic BOF Slag: Non-metallic BOF Slag, as per one embodiment, serves as a slag source rich in calcium silicates, functioning as a flux for sinter production.
6. Dolomite: Dolomite acts as a source of MgO and is employed to stabilize the necessary phases (like magnetite formation) essential for sinter high-temperature strength. It is commonly used as a substitute for pyroxenite, especially when SiO2 is supplied from alternative sources.
7. Return fines: Return fines refer to sinter particles below 5 mm, returned from the blast furnace due to their fine size. They possess a chemical composition similar to that of sinter and are recycled accordingly.
The Tumbler Index of the sinter obtained from the sinter mix is between 75 to 78 %. The RDI of the sinter obtained from the sinter mix is between 19 to 23 %.
The non-metallic BOF slag replaces limestone (CaCO3) and dolomite (MgO.SiO2). Conventionally, for sinter making the typical amount of limestone used is about 7 wt%of the ore and 6-7 wt%of dolomite, depending on the basicity requirement. As per the embodiments,the consumption of limestone has been drastically reduced to 3.2-5.2 wt %.Also, the consumption of dolomite has been reduced to 4.4-5.4wt%.
The sinter mix is further mixed in a mixing drum at sinter plant and moisture as per the requirement is added for granulation.The sinter mix is charged into a sinter machine for assimilation of cake and filled upto a height of 700 mm. The top of the sinter mix is ignited using a movable ignition/burner hood fuelled by coke oven gas while suction is applied across the bed. Ignition temperature is maintained at 1200 °C while suction during ignition is maintained at 400 mm water column. The speed of the belt is such that ignition is continued for 2 minutes and after the ignition process the suction is increased to 1200 mm water column.
The above-mentioned process for producing agglomerates of sinter and its benefit can be validated by the following examples. The following illustrations in form of examples are described to bring more clarity of the invention and should not be considered as limitation or drawback of the invention.
EXAMPLES
Raw materials were weighed in proportions in the experiments as per various Tables 3-8 to get the desired sinter mix chemistry and processed for sinter making.
Table 3
Material Weight % Tumbler Index RDI
Iron Ore 42.17 77.20 19.10
Coke breeze 2.80
Anthracite Coal 2.80
Calcined lime 3.00
Limestone 4.38
Dolomite 4.41
Return Fines 39.37
Non-metallic BOF Slag 1.07
Table 4
Material Weight % Tumbler Index RDI
Iron Ore 39.70 76.87 22.50
Coke breeze 3.71
Anthracite Coal 1.83
Calcined lime 3.18
Limestone 4.74
Dolomite 5.00
Return Fines 40.62
Non-metallic BOF Slag 1.22
Table 5
Material Weight % Tumbler Index RDI
Iron Ore 41.39 75.87 19.50
Coke breeze 3.39
Anthracite Coal 1.67
Calcined lime 3.08
Limestone 4.87
Dolomite 4.40
Return Fines 39.75
Non-metallic BOF Slag 1.44
Table 6
Material Weight % Tumbler Index RDI
Iron Ore 39.06 77.33 22.50
Coke breeze 3.66
Anthracite Coal 1.80
Calcined lime 3.11
Limestone 4.60
Dolomite 4.89
Return Fines 41.31
Non-metallic BOF Slag 1.57
Table 7
Material Weight % Tumbler Index RDI
Iron Ore 35.99 76.53 22.60
Coke breeze 3.79
Anthracite Coal 1.87
Calcined lime 3.20
Limestone 3.50
Dolomite 4.49
Return Fines 45.32
Non-metallic BOF Slag 1.85
Table 8
Material Weight % Tumbler Index RDI
Iron Ore 34.82 77.47 20.10
Coke breeze 2.63
Anthracite Coal 2.65
Calcined lime 3.20
Limestone 3.22
Dolomite 4.51
Return Fines 46.97
Non-metallic BOF Slag 2.00
The raw materials as per experiments in Tables 1 to 8, were charged into the granulation drum which was then inclined at 45° angle and set into rotation at a constant speed of 25 rpm. The materials were allowed to mix in dry state for 4 minutes, following which water is added to make sure that the moisture levels of the dry mix reaches to a level of 8% of the total mix weight. Half the total amount of water was added and mixed intensely for 2 minutes and rest of the water was then added and mixed for another 3 minutes.The granules were allowed to grow without mixing during the last minute of granulation.
Sinter mix from the granulation drum was then transferred to the sinter machine as mentioned above in the description. Ignition temperature was 1200 to 1250 °C while suction during ignition was maintained at 400 mm water column. The sinter machine speed was maintained such that the ignition was continued for 2 minutes, after which the suction was increased to 1200 mm water column. The increased suction was maintained throughout the experiment. The experiment was considered to be complete, when the wind box thermocouple recorded the maximum temperature (BTP-Burn through point, Completion of sintering process).
It is quite evident from the above-mentioned sinter mix composition from Tables 2-8, that though the composition of the limestone and dolomite has been reduced, their corresponding Tumbler index and RDI have been in permissible industrial range. The industrial permissible range for Tumbler Index is >74 and RDI is <25.
, Claims:We Claim:
1. A sinter mix composition involving basic oxygen furnace(BOF) steel slag partially replacing flux for sinter making comprising Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt % co-acting for generating sinter product with reduced limestone and dolomite content based Tumbler Index of 75 to 78 % and RDI of 19 to 23 %.
.
2. The sinter mix composition as claimed in claim 1 wherein said BOF steel slag comprises non-metallic BOF slag including FeO: 20.62 to 23.42 wt %, CaO: 41.38 to 43.50 wt %, SiO2: 13.52 to 15.05 wt %, MgO: 9.80 to 11.50 wt %, Al2O3: 3.14 to 3.50 wt %, MnO: 5.20 to 6.30 wt %, P2O5: 1.25 to 1.60 wt %.
3. The sinter mix composition as claimed in anyone of claims 1or 2 wherein size distribution for sinter raw mix constituents comprising
Size in mm Limestone Dolomite Coke and coal Non-metallic BOF slag Return Fines
+5 mm 0.68 0.96 1.05 57.2 1.70
-5 to +3.15 mm 12.17 15.99 11.47 13.77 48.12
-3.15 mm 87.14 83.05 87.48 29.05 50.18

and size distribution for iron ore comprising
Size in mm Weight %
+10 mm 6.14
-10+8mm 6.49
-8+6.3 mm 5.28
-6.3+5 mm 4.74
-5+3.15mm 7.49
-3.15+1 mm 14.30
-1+0.5 mm 5.53
-0.5+0.15 mm 10.70
-0.15 mm 39.35

4. The sinter mix composition as claimed in claim 1 to 3 wherein the size range of the non-metallic BOFsteel Slag in the sinter mix is 56 to 65% of size +5 mm, 11 to 18% of size -5 to +3.15 mm and rest part of size -3.15 mm.
5. A process for sintering using the sinter mix composition as claimed in claims 1 to 4 comprising
providing a selective sinter mix composition having reduced limestone and dolomite content comprisingof Iron ore 34 to 42 wt %, Coke breeze 2.6 to 4.6 wt %, Anthracite coal 1.6 to 2.8wt %, Calcined Lime 3.0 to 4.2 wt %, Limestone 3.2 to 5.2wt %, Dolomite 4.4 to 5.4wt % and Return fines 39 to 47wt %, non-metallic BOF slag 1 to 3wt %;
mixing said sinter mix in a mixing drum at sinter plant and water is added to increase the moisture levels of the dry mix to 7.5 to 8.5 % for granulation;
charging sinter mix into a sinter machine for assimilation of cake and filled upto a bed height of 700 mm;
igniting top of the sinter mix using a movable ignition/burner hood fuelled by coke oven gas while suction is applied across the bed, wherein ignition temperature is maintained at 1150 to 1250 preferably about 1200 °C while suction during ignition is maintained at 380 to 420 preferably 400 mm water column.
maintaining the speed of the belt such that ignition is continued for 1.75 to 2.25 preferably about 2 minutes and after the ignition process the suction is increased to 1150 to 1250 preferably about 1200 mm water column till sintering completion, to thereby obtain sinter product having Tumbler Index of 75-78% and RDI of 19-23%.
6. The process as claimed in claim 5 wherein after charging raw materials into the granulation drum, the same is inclined at 42 to 48 preferably 45° angle and set into rotation at a constant speed of 23 to 27 preferably about 25 rpm, said materials are allowed to mix in dry state for 3 to 4 preferably about 4 minutes, following which water is added to make the moisture levels of the dry mix reaches to a level of 7.5 to 8.5 preferably about 8% of the total mix weight wherein half the total amount of water is added and mixed intensely for 1.5 to 2.5 preferably about 2 minutes and rest of the water is then added and mixed for another 2.5 to 3.5 preferably about 3 minutes and the granules formed are allowed to grow without mixing during the last minute of granulation;
granulated sinter mix obtained from the granulation drum is then transferred to the sinter machine where Ignition temperature is maintained in the range of 1200 to 1250 °C, while suction during ignition is maintained at 380 to 420 preferably about 400 mm water column, said sinter machine speed is maintained such that the ignition is continued for 1.75 to 2.25 preferably 2 minutes, after which the suction is increased to 1150 to 1250 preferably 1200 mm water column andthe sintering process is considered to be complete, when the wind box thermocouple recorded the maximum temperature (BTP-Burn through point).
7. The process as claimed in claim 5 or 6which produces a sinter chemistry of Fe (T): 50.66 to 52.15 wt%, FeO: 9.33 to 10.54 wt % CaO: 12.84 to 13.89 wt%, SiO2: 6.12 to 7.10 wt%, MgO: 2.06 to 2.28 wt%, Al2O3: 3.31 to 3.60 wt %, Basicity (Cao/SiO2): 1.95 to 2.17.

8. The process as claimed in anyone of claims 5 to 7 wherein involving selectively said BOF steel slag in sinter mix composition, reduces lime consumption by 50% of conventional lime requirementand reduces dolomite consumption by 40 % of conventional dolomite requirement, said constituents being replaced with the use of BOF slag, thereby conserving the raw material usage, and reducing calcination load of the carbonate in terms of energy.
Dated this the 18th day of January, 2024
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199