Claims:We Claim:

1. A method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace and related resistance to the gas flow inside the furnace comprising:
involving pre-processed lump iron ore size (-50+10 mm) which is pre-processed in sinter hearth layer for removal of LOI and moisture at sinter plant site and thereby controlling fines generation therefrom during its use in blast furnace.
2. A method as claimed in claim 1 wherein said pre-processed lump iron ore size (-50+10 mm) is obtained following subjecting the same to step of sintering in sinter plant as the sinter hearth layer such that the pre processing and removal of LOI and moisture takes place at sinter plant site and thus the fines are generated at sinter plant and subsequently favour reduction in fine input to the blast furnace by 5-6 %.
3. A method as claimed in anyone of claims 1 or 2 wherein said pre-processed lump iron ore size of (-50+10 mm) is fed into the blast furnace.
4. A method as claimed in anyone of claims 1 to 3 comprising sintering for providing the said pre-processed lump iron ore size (-50+10 mm) comprising the steps of :
i) preparation of raw sinter mix;
ii) preparation of the hearth layer comprising a mix of different size fraction of iron ore (-50+10 mm);
iii) charging of the said hearth layer comprising a mix of different size fraction of iron ore onto sinter pallets followed by charging of the said raw sinter mix; and
iv) subjecting the charge as above to heating thereby producing a semi-molten mass, which in turn solidifies into porous pieces of sinter having the required size and strength suitable for feeding into the blast furnace.
5. A method as claimed in anyone of claims 1 to 4
wherein the raw material composition for sintering process comprises:
Raw materials Weight %
Iron ore 45 to 55 %
Sinter return fines 25 to 35 %
Limestone 5 to 9 %
Dolomite 5 to 9 %
Calcined lime 1 to 3 %
Coke breeze 3 to 5 %

6. A method as claimed in anyone of claims 1 to 5 wherein said sintering is carried out following:
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm H2O
Thickness of the hearth layer : 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 27 kg/ton of sinter

7. A method as claimed in anyone of claims 1 to 6 comprising :

providing lump iron size (-50+10) mm as a sinter bed hearth layer ; and
the sinter cake is laid over the said hearth layer whereby lump iron ore stick at the interface layer of the green mix and hearth layer providing good permeability at the bottom layers of the sinter bed.
8. A method as claimed in claim 7 wherein lump iron ore in the size range of (-50+10 mm) which is stick to the green mix bottom most layer partially reduced to magnetite.
9. A method as claimed in anyone of claims 1 to 8 wherein the lump iron ore in the size range of (-50+10 mm) used is uncrushed and this size fraction is directly placed in the sinter bed hearth layer for sintering process which save the cost of crushing in bringing down the size range of lump iron ore particle form (-50+10 mm) to (-20+10 mm) usually required in conventional sintering.
10. A process for producing processed lump iron ore size (-50+10 mm) involving sintering comprising subjecting the said lump iron ore size (-50+10 mm) to sintering as sinter hearth layer and thereby effecting removal of LOI and moisture at sinter plant site.
11. A process as claimed in claim 10 wherein the hearth layer is of 50 to 70 mm and said lump iron ore in the size range of (-50+10 mm) used is uncrushed and this size fraction is directly placed in the sinter bed hearth layer for sintering.
12. A process as claimed in anyone of claims 10 or 11 wherein the provision of said lump iron ore in sinter bed hearth layer and sintering involving said hearth layer provides lump iron ore to stick at the interface layer of the green mix and hearth layer provided good permeability at the bottom layers of the sinter bed.
13. A process as claimed in anyone of claims 10 to 12 comprising:
i) Preparation of raw sinter mix;
ii) Preparation of the hearth layer comprising a mix of different size fraction of iron ore (-50+10 mm);
iii) Charging of the said hearth layer comprising a mix of different size fraction of iron ore onto sinter pallets followed by charging of the said raw sinter mix;
iv) Subjecting the charge as above to heating thereby producing a semi-molten mass, which in turn solidifies into porous pieces of sinter having the required size and strength suitable for feeding into the blast furnace.
14. A method as claimed in anyone of claims 10 to 13 wherein said sintering is carried out following:
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm H2O
Thickness of the hearth layer : 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 27 kg/ton of sinter
15. Processed lump iron ore size (-50+10 mm) suitable for use in blast furnace comprising
porous pieces of sinter which is having reduction in fine input 5-6 % with respect to the un sintered lump iron ore size (-50+10 mm).

Dated this the 26th day of June, 2019
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION
The present invention relates to a method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace involving a process of sintering using lump iron ore having size range of -50+10 mm in sinter machine hearth layer for feeding roasted lump ore in Blast furnace with reduced fines generation in the upper stack region of the blast furnace and improved furnace productivity. Iron ore lumps of -50+10 mm size range obtained from the process are charged directly into theBlast furnace (BF). The overall fines generation at sinter plant got increased due to degradation of lump iron ore and removal of Loss on Ignition(LOI) and moisture. Use of LOI and moisture free lump iron ore in blast furnace result in significant reduction in generation of fines in upper stack region of the blast furnace, thus favouring consistent bed permeability and improved furnace productivity.

BACKGROUND OF THE INVENTION
Raw materials constitute around 80% of the hot metal production cost and is a major factor contributing to the blast furnace productivity and hot metal quality. Quality of raw materials (iron ore, sinter, pellets, coke and flux) is the prime factor responsible for production of good quality hot metal. Low cost hot metal can be produced by maximizing the use of prepared burden into blast furnace, effective process control, recycling of solid wastes, adopting technological and operational excellence and implementing best practices. Good quality burden can be prepared by utilizing raw material of improvedstrength. The advantages of maximized usage of prepared burden (sinter and/or pellets) are low silicon hot metal, higher productivity and low fuel rate.
Conventionally, iron bearing materials (lump iron ore, sinter and pellets), coke and flux as feed are charged into the blast furnace from the top and hot blast is blown through tuyeres. The coke acts as reductant, fuel and supports the burden at the tuyere level. During reduction of iron oxides (i.e., conversion from hematite to magnetite, wustite and finally iron), considerable amount of fines is generated in the upper stack region of the blast furnace which increases the resistance to the gas flow inside the furnace and decreases the furnace productivity.

Blast furnaceat JSW Steel Ltd use approximately 61% sinter, 22% pellet and 17% lump iron ore respectively. In order to produce an average 5800 ton/day hot metal, around 1680ton/day lump iron ore is required. The size fractions of lump iron ore used by Blast furnace is mention below.

Table1: Size distribution of lump iron ore charged to the blast furnace

Yearly average data (wt %)
Size fraction of
Iron ore (mm) 2014-15 2015-16 2016-17 2017-18 2018-19
-50+40 11.95 5.92 3.97 6.67 11.10
-40+30 20.89 20.95 20.55 22.11 26.68
-30+20 38.46 44.00 45.95 43.99 38.82
-20+16 12.04 13.93 11.89 11.31 10.68
Sub-total 83.34 84.81 82.36 84.08 87.28
-16+10 16.66 15.19 17.64 15.92 12.72
Total 100 100 100 100 100

Above table shows the size fraction of lump iron along with their wt% consumption in the JSW blast furnace. The sum of the total wt% of the material going inside the blast furnace in the size range of (-50+16 mm) varies from 82.36 to 87.28% and (-16+10 mm) is varies from 12.72 to 17.64%.

The blast furnace smelting reactor is a counter current process wherein burden raw material descends from top to bottom and gases flow in opposite directions through passages and pores of burden materials and coke. The basic requisite for stable operation of the blast furnace is to maintain a moving layer of burden with an optimum permeability of the bed without much of a deviation. For a smooth functioning of the blast furnace, the stability of the gas flow is very important which depends permeability of the bed and measured by packing structure of burden (particle sizedistribution, fine particles ratio, etc.)

Due to direct intake of lump iron ore in this size fraction (-50+10 mm) into the blast furnaceat JSW steel limited, huge amount of fines is getting generated in the upper stack region of the blast furnace due to removal of LOI and moisture from this lump iron ore which reduce the permeability of the burden, reduce the gas velocity and productivity of the blast furnace.Degradation of lump iron ore inside blast furnace, strongly affects blast furnace performance as it determines the efficiency of gas utilization and hence coke rate and productivity.Loss on ignition (LOI) in iron ore minerals normally represents the chemically bonded moisture which can be removed at high temperature. Iron ore contains different phases like hematite, goethite, magnetite, limonite etc. LOI in iron ore is primarily contributed by the hydrated mineral phases like goethite, gibbsite, kaolinite, etc. Goethite [FeO (OH)] contains a significant amount of chemically bonded water. Iron ore of high LOI, when charged in furnace, disintegrates at upper stack of the furnace at the temperature above 300 ºC and thereafter decrease the permeability of decent burden. Cracks and disintegration of hematite grains appear together with reduction of hematite.

Reduction behaviour of Lump iron ore & its effect on structure of cohesive zone:
Lump iron ore in the size range (-50+10 mm) charged into the blast furnace contains iron oxides (ferrous & ferric oxide), gangue minerals and pores. All the iron ore used in JSW blast furnaceare hematite in nature. Depending upon the physical characteristics and mineralogical composition, reduction of hematite ores starts at temp above 300 ºC. The reduction process of hematite to magnetite results in distinct changes in morphology of magnetite. These changes depend on structural properties of parent hematite and reduction conditions.
Size wiseconsumption pattern of lump iron ore of two size ranges (-50+16) mm and (-16+10 mm) in blast furnace-I at JSW Steel Limited are shown graphically in accompanying Figure 1. Chemical composition of iron ore used for sinter making are as follows:
Raw materials Percentage (%)
Fe(total) 63.57
SiO2 3.24
Al2O3 2.67
CaO 0.10
MgO 0.03
K2O 0.02
MnO 0.11
Moisture 2.78
LOI 2.70

Iron ores include hematite, magnetite or mixture of them. Based on the particle size, iron ores could be in the form of lump, fines or concentrate. Iron ore lumps (-50+10 mm) are charged directly into theBF which generates large amount of fines during reduction. Availability of iron ore and stable supply is the key for efficient operation. Apart from that, iron ore with right physical, chemical and mineralogical properties are important for stable operation.

To avoid the problem of existing blast furnace operation as described above, a number of prior work has been carried out to limit the fines generation due to disintegration of lump ore adversely affecting furnace operation and efficiency as mentioned below:

PRIOR ART
Chinese Patent - CN108149008dated 21.06.2018entitled “Method using waste lump ore as hearth layer for sintering of laterite-nickel ore” reported that the low grade waste lump iron ore crushed and sieved, particle diameter of 10 mm to 16 mm particle is spread on the sintering machine as a bed bottom, particle size less than 10 mm size fraction as laterite nickel ore raw material involved in dispensing, the laterite nickel ore, returned ore fines, calcined lime is mixed with fuel and mix. In this study they crushed the low grade waste lump iron ore and brings down to particle having size range -16+10 mm which is an energy intensive operation and adds cost. In the present invention, lump iron of size -50+10 mm is directly used in sinter hearth layer. The fines generated during sintering of the lump iron ore is screened at sinter plant and the required size fraction of roasted lump ore only is charged into the blast furnace thereby reducing the fines generation in BF upper stack by 5-6 %.

Paper entitled “Experimental study on lump iron ores as sintering hearth layer”, published in Advance Material Research, Vol 266, (2011), pp 72-75 reported that with the use of lump iron ore in the size range of (-16+10 mm) used as sinter hearth layer almost has no influence on the permeability of the sinter bed. When the lump iron ore was used as sinter hearth layer instead of recycled sinter the sintering productivity is increased and fuel consumption is reduced, furthermore the tumbler strength and the reduction disintegration index of the sinter are also improved. In the present invention, lump iron of size -50+10 mm is directly used in sinter hearth layer. The fines generated during sintering of the lump iron ore is screened at sinter plant and the required size fraction of roasted lump ore only is charged into the blast furnace.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to advancement in method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace involving a sintering process using lump iron ore (-50+10 mm) in sinter hearth layer and subsequent use of roasted iron ore as blast furnace feed resulting in reduction in fines generation in the upper stack region of the blast furnace.
A further object of the present invention in directed to a process for sintering the wherein lump iron ore (-50+10 mm) is provided in sinter hearth layer favouring protection of grate bars in sinter machine.
A still further object of the invention is directed to a process of sintering in which lump iron ore of size range (-50+10 mm) is used as sinter hearth layer, which will reduce the cost of crushing of lump iron ore from -50+10 mm to -16+10 mm for use as sinter hearth layer as followed in present practice.
A still further object of the present invention is directed to a process of sintering involving use of lump iron size range (-50+10 mm) in sinter hearth layer which ensure improving permeability in the hearth layer by increasing voidage.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace and related resistance to the gas flow inside the furnace comprising:
involving pre-processed lump iron ore size (-50+10 mm) which is pre-processed in sinter hearth layer for removal of LOI and moisture at sinter plant site and thereby controlling fines generation therefrom during its use in blast furnace.
A further aspect of the present invention is directed to a method wherein said pre-processed lump iron ore size (-50+10 mm) is obtained following subjecting the same to step of sintering in sinter plant as the sinter hearth layer such that the pre processing and removal of LOI and moisture takes place at sinter plant site and thus the fines are generated at sinter plant and subsequently favour reduction in fine input to the blast furnace by 5-6 %.
A still further aspect of the present invention is directed to a method wherein said pre-processed lump iron ore size of (-50+16mm) is fed into the blast furnace in the range of 82.36 to 87.28%.
Another aspect of the present invention is directed to a method comprising sintering for providing the said pre-processed lump iron ore size (-50+10 mm) comprising the steps of :
i) preparation of raw sinter mix;
ii) preparation of the hearth layer comprising a mix of different size fraction of iron ore (-50+10 mm);
iii) charging of the said hearth layer comprising a mix of different size fraction of iron ore onto sinter pallets followed by charging of the said raw sinter mix; and
iv) subjecting the charge as above to heating thereby producing a semi-molten mass, which in turn solidifies into porous pieces of sinter having the required size and strength suitable for feeding into the blast furnace.
Yet another aspect of the present invention is directed to said method wherein the raw material composition for sintering process comprises:
Raw materials Weight %
Iron ore 45 to 55 %
Sinter return fines 25 to 35 %
Limestone 5 to 9 %
Dolomite 5 to 9 %
Calcined lime 1 to 3 %
Coke breeze 3 to 5 %

A further aspect of the present invention is directed tosaid method wherein said sintering is carried out following:
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm H2O
Thickness of the hearth layer : 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 27 kg/ton of sinter

A still further aspect of the present invention is directed to said method comprising :
providing lump iron size (-50+10) mm as a sinter bed hearth layer ; and
the sinter cake is laid over the said hearth layer whereby lump iron ore stick at the interface layer of the green mix and hearth layer providing good permeability at the bottom layers of the sinter bed.
A still further aspect of the present invention is directed to said method wherein lump iron ore in the size range of (-50+10 mm) which is stick to the green mix bottom most layer partially reduced to magnetite.
A still further aspect of the present invention is directed to said method wherein the lump iron ore in the size range of (-50+10 mm) used is uncrushed and this size fraction is directly placed in the sinter bed hearth layer for sintering process which save the cost of crushing in bringing down the size range of lump iron ore particle form (-50+10 mm) to (-20+10 mm) usually required in conventional sintering.
Another aspect of the present invention is directed to a process for producing processed lump iron ore size (-50+10 mm) involving sintering comprising subjecting the said lump iron ore size (-50+10 mm) to sintering as sinter hearth layer and thereby effecting removal of LOI and moisture at sinter plant site.
Yet another aspect of the present invention is directed to said process wherein the hearth layer thickness is of 50 to 70 mm preferably 60mm and said lump iron ore in the size range of (-50+10 mm) used is uncrushed and this size fraction is directly placed in the sinter bed hearth layer for sintering.
A further aspect of the present invention is directed to said process wherein the provision of said lump iron ore in sinter bed hearth layer and sintering involving said hearth layer provides lump iron ore to stick at the interface layer of the green mix and hearth layer provided good permeability at the bottom layers of the sinter bed.
A still further aspect of the present invention is directed to said process comprising:
i) Preparation of raw sinter mix;
ii) Preparation of the hearth layer comprising a mix of different size fraction of iron ore (-50+10 mm);
iii) Charging of the said hearth layer comprising a mix of different size fraction of iron ore onto sinter pallets followed by charging of the said raw sinter mix;
iv) Subjecting the charge as above to heating thereby producing a semi-molten mass, which in turn solidifies into porous pieces of sinter having the required size and strength suitable for feeding into the blast furnace;
A further aspect of the present invention is directed to a method wherein said sintering is carried out following:
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm H2O
Thickness of the hearth layer : 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 27 kg/ton of sinter

Another aspect of the present invention is directed toprovide processed lump iron ore size (-50+10 mm) suitable for use in blast furnace comprising
porous pieces of sinter which is having reduction in fine input 5-6 % with respect to the un sintered lump iron ore size (-50+10 mm).

The above and other objects and advantages of the present invention are described hereinafter in greater details with reference to accompanying drawings and example:
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows graphically the existing size wiseconsumption pattern of lump iron ore of two size ranges (-50+16) mm and (-16+10 mm) in blast furnace-I at JSW Steel Limited.
Figure 2: is the schematic illustration of the advanced system of the sinter making process only lump iron ore -50+10 mm size fraction as hearth layer.
Figure 3(a): is the image of hearth layer made of different size fraction of iron ore placed at the bottom of the green mix bed in the sintering process.
Figure 3(b): is the image of sinter cake after cooling laid on the hearth layer made of hearth layer comprises of lump iron ore in the size range of (-50+10 mm).
Figure 3(c): is the image of partially reduced iron ore particle which stick to the green mix layer during sintering process.
Figure 3(d): is the image of Hearth layer left over grate pallet after sintering process and the same is broken in pieces due to removal of LOI and moisture.
Figures 4: shows graphical representation of the experimental results in terms of tumbler index, sintering time, sinter fines generation, productivity and product yield.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The present invention is directed to a method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace involving a cost effective and improved process for sinter production using lump iron ore in different size fraction (-50+10 mm), in sinter machine hearth layer for providing permeability at the lower layers in the sinter bed hearth layer whereby sinter output in increased and reduction in fines generation at blast furnace site, due to removal of LOI and moisture from it at sinter plant. In existing operation, recycled sinter having size (-20+10 mm) are used earlier for hearth layer. These size fractions of sinter material are having high cold strength properties and less fines generation tendency. When -20+10 mm size fraction of sinter is sent to blast furnace along with sintered product, it will increase the net productivity of sinter plant, Tumbler index (+6.3 mm) %, and at the same time with the use of lump iron ore valuable iron content of lump iron ore is directly transferred to the blast furnace which increase the total Fe in the hot metal.

As already described herein before, a hearth layer is provided as the bottom most layer over sinter machine bed as insulating material to protect the grate bars of the sinter pallets during sintering process. The sinter mix charge is fed onto the hearth layer. Conventionally, the hearth layer is composed of good quality sinter product of 10-20 mm size fraction to ensure desired permeability and strength. Thus a significant part of the sinter product is recycled back as input hearth layer in sinter charge causing reduction in effective sinter output.
On the other hand, when lump iron ore in the size range of (-50+10) mm is directly fed into the blast furnace,high amount of fines is getting generated in the upper stack region of the blast furnace during removal of LOI and moisture from this iron ore.
Accompanying Figure 1 shows graphically the existing size wiseconsumption pattern of lump iron ore of two size ranges (-50+16 mm) and (-16+10 mm) in blast furnace-I at JSW Steel Limited.
The present invention thus attempts to pre-process this size fraction of lump iron ore (-50+10 mm)through sinter bed hearth layer favouring two fold benefits: On one hand whatever be the fines is getting generated at the blast furnace end due to this direct intake of lump iron ore will be generated at sinter plant site. The total reduction in fines input to the furnace is 5-6%.On the other hand, the cost involved in crushing of coarser size (+20 mm) iron ore into fine size -20+10mm is a direct saving.
Reference is now invited to the accompanying Figure 2 which schematically illustrate the advanced feeding system for producing sinter using lump iron ore of size fraction (-50+10) mm for hearth layer.
It is clearly apparent from Figure 2 that the sintering process begins with the preparation of raw mix from iron ores, fluxes (such as limestone, dolomite, calcined lime) and sinter return fines. These material is mixed and granulated. Water is added in order to assist the raw mix in obtaining optimum permeability. On the sinter machine, its surface is ignited, air being inducted through the ignited layer and sintering proceeds in the vertical direction in the sinter bed. Subsequently, the sinter is cooled, crushed and screened to require particle size. Undersize sinter that is not suitable for blast furnace (< 5 mm) is recycled to the return fines bin. A certain quantity 10-20 mm is screened out to re-circulated to the sinter machine, which serve as a hearth layer, protecting the grate bars of the pallets during the sintering process.
To avoid this deficiency of the existing sinter making process using recycled good quality sinter as hearth layer of sinter charge, a modified system and method is proposed by the way of the present invention wherein lump iron ore in the size fractionof (-50+10) mm in the desired proportion is used to build the hearth layer at the bottom of the sinter charge whereby sinter output is increased than by supplying earlier using recycled sinter size (-20+10) mm,and feeding directly to the blast furnace.
Accompanying Figure 3 shows the images of product sinter by using lump iron size (-50+10) mm as a hearth layer.
It is apparent from accompanying Figure 3a that by using lump iron ore in sinter bed hearth layer, lump iron ore stick at the interface layer of the green mix and hearth layer provided good permeability at the bottom layer of the sinter bed.
Accompanying Figure 3b shows that the sinter cake is laid over the hearth layer which is made of lump iron ore in the size fraction of (-50+10 mm).
Accompanying Figure 3c shows that lump iron ores in the size range of (-50+10 mm) which stick to the green mix bottom most layer, are partially reduced to magnetite.
Accompanying Figure 3d shows that remaining portion of the lump iron ore used for hearth layer left over on the grate bars after sintering process.
It is to be noted that in sinter plants, normally hearth layer is made of 10-20 mm fraction of sinter, as it provides better permeability when compared to sinter fines (< 10 mm).
In the present process, the lump iron ore in the size range of (-50+10 mm) will not be subjected to crushing, and this size fraction is directly placed in the sinter bed hearth layer for sintering process,thus saving the cost of crushing in bringing down the size range of lump iron ore particle form (-50+10 mm) to (-20+10 mm).

EXAMPLE- I:
1. Providing lump iron ore in the size range of (-50+10 mm) having sufficient strength to withstand the load of the sinter cake by placing this into the sinter hearth layer. Lump iron ore preferably with high iron ore content but not essentially is selected as input raw material for hearth layer.
2. The normal range of composition of lump iron ore used in the hearth layer comprises of
Table 4: Different size fraction of the lump iron ore along with their weight percentage used in sinter hearth layer
Size fraction of the Iron (mm) Wt% in different size fraction of I/O
-50+40 6.5
-40+30 19.75
-30+20 42.48
-20+16 13.12
-16+10 18.04
Total 100

Table 5: Chemical analysis of the Lump iron ore used in hearth layer
Chemical constituents UOM (%)
Fe (total) 63.15
SiO2 3.38
Al2O3 2.84
CaO 0.08
MgO 0.03
MnO 0.11
TiO2 0.18
LOI 2.80
Moisture 3.18

3. Preparing the sinter mix charge by blending the raw materials for sintering in the required proportion with the help of weighing balance; homogenizing and nodulising the materials in the mixing drums, where water is added at a controlled rate to maintain a moisture level of about 7-8%
4. Feeding the hearth layer comprises of lump iron ore having size (-50+10 mm) charged into the grate bars of the pot sinter machine up to a layer thickness of 60 mm before raw mix is charged.
5. Carrying out the sintering process using the following parameters
The ignition temp: 1050±50ºC
The sintering temperature: 1300±100ºC
Draft rate (Suction pressure): 1200 mm H2O
Thickness of the hearth layer: 60 mm
BTP (Burn through temp)- 300-350 ºC
Fuel rate – 58 kg/ton of sinter
Raw mix moisture – 7-8%
Quick lime addition – 27 kg/ton of sinter

6. The sinter produced is cooled, crushed and screened to required sizeand undersize sinter (< 5 mm) that is not suitable for the blast furnace is recycled as return fines. A certain quantity of -20+10 mm is screened out and re-circulated to the sinter machine where it serves as a hearth layer.
7. With the introduction of lump iron ore in the size range of (-50+10 mm) in hearth layer there is an increment in the fines generation at sinter plant site. No need to crush this size iron ore and bring down the size range of this iron ore to -16+10 mm for usage in hearth layer.
Furthermore, whatever be the fines generated inside the furnace comes down by using this size fraction of lump iron (-50+10 mm) in sinter bed hearth layer. The total fines load on the furnace will be reduced by 5-6%.

Table 6: Results
Raw material used for hearth layer Lump iron ore Lump Iron ore Recycled sinter
Size fraction of I/O for (hearth layer) -50+10 mm -16+10 mm -16+10 mm
Hearth Layer Height in mm 60.00 60.00 60.00
Hearth Layer Weight 6.80 8.10 7.21
Tumbler index +6.3 mm, (%) 65.27 64.20 62.80
Sintering time (min) 24.00 22.00 21.00
Productivity + 5 mm, (t/h/m2), 1.72 1.87 2.07
Product Yield (+ 5 mm), % 73.50 77.01 79.21
Fines generation -5 mm, (%) 26.50 22.99 20.79
Wind box temp (º C) 300.50 355.00 315.00
Blower RPM @ 400 mm H2O 564.50 814.00 852.00

Accompanying Figures 4 shows graphical representation of the above results in terms of tumbler index, sintering time, sinter fines generation, productivity and product yield.

8. It is observed from the above data there is a total fine generation at sinter plant is 26.50%. This total fines generation comprises of internal return fines and fines generated due to lump iron ore (-50+10 mm) in the sinter bed hearth layer.
18% fines generated as internal return fines due to sinter product and rest of 8.5% fines generated due to degradation of lump iron ore (-50+10 mm) in the hearth layer and removal of LOI and moisture from it.

It is thus possible by way of the present invention to a method of improving blast furnace productivity by controlling fine generation in the upper stack region of the blast furnace involving a method of sinter production using lump iron ore in the size range of (-50+10 mm) in sinter hearth layer and the roasted lump ore free of LOI and moisture is fed to Blast Furnace so as to reduce fine input to the blast furnace by 5-6 % favouring reduced fines generation at the upper stack region of the blast furnace and consequent decrease in resistance to the gas flow inside the furnace and increase in furnace productivity.