Claims:We Claim:
1. Hearth layer for improved productivity of sintering plant comprising:

of a hearth layer composition of lump iron ore and recycled sinter both having size (-16+10 mm).
2. Hearth layer as claimed in claim 1 comprising said mix of lump iron ore and recycled sinter both having size (-16+10 mm) having proportions in the range of 25:75 to 75:25.

3. Hearth layer as claimed in anyone of claims 1 or 2 wherein the hearth layer comprises of height of 40 to 65 mm preferably 60mm.

4. Hearth layer as claimed in anyone of claims 1 to 3 wherein chemical constitution of said lump iron ore and recycled sinter wt % comprises:

Chemical constituents Lump iron ore Recycled sinter
Fe (total) 50 to 65 preferably 63.15 52 to 55 preferably 53.58
SiO2 2 to 5 preferably 3.38 4 to 7 preferably 5.54
Al2O3 1 to 4 preferably 2.84 2 to 5 preferably 3.24
CaO 0.02 to 0.1 preferably 0.08 9 to 12 preferably 11.72
MgO 0.01 to 0.1 preferably 0.03 2 to 3 preferably 2.16
MnO 0.10 to 0.50. preferably 0.11 0.2 to 0.8 preferably 0.32
LOI 1 to 10 preferably 2.80 ---
Moisture 3 to 5 preferably 3.18 ---

5. Hearth layer as claimed in anyone of claims 1 to 4 enabling generation of sinter characteristics including:

Parameters
Lump Iron Ore : Recycled Sinter
Proportion of Lump iron ore: Sinter in hearth layer 25 : 75 to 75:25
Hearth Layer Height,( mm) 40 to 65 preferably 60.00
Tumbler index +6.3 mm, (%) 60 to 70 preferably 66.71
Sintering time (min) 20 to 30 preferably 24.30
Productivity + 5 mm, (t/h/m2) 1.5 to 2.5 preferably 1.95
Product Yield (+ 5 mm), % 80 to 90 preferably 84.06
Fines generation -5 mm, (%) 13 to 25 preferably 15.94

6. A process for the sintering involving the hearth layer as claimed in anyone of claims 1 to 5 comprising:

i) Preparation of raw sinter mix;
ii) Preparation of the hearth layer comprising a mix of lump iron ore and recycled sinter both having size (-16+10 mm) ;

iii) charging of the said hearth layer comprising a mix of lump iron ore and recycled sinter having size -16+10 mm 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.
7. A process as claimed in claim 6 wherein mix of lump iron ore and recycled sinter both having size (-16+10 mm) involved is in the range of 25:75 to 75:25 and said sinter raw mix for sintering comprises:

Overall sinter bed height (mm) 650 to 750 preferably 700
Iron ore fines, (%) 45 to 55 preferably 51.13
Sinter return fines, (%) 25 to 35 preferably 29.97
Lime stone, (%) 3 to 8 preferably 6.10
Dolomite, (%) 3 to 8 preferably 6.60
Calcined lime 1 to 3 preferably 2.00
Coke breeze 4 to 6 preferably 4.20
Total 100.00

8. A process as claimed in anyone of claims 6 or 7 which is carried out involving said hearth layer of mix of lump iron ore and recycled sinter having size fraction (-16+10 mm)
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm of water column
Thickness of the hearth layer : 40 to 65 preferably 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 55 to 60 preferably 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 25 to 30 preferably 27 kg/ton of sinter

9. A process as claimed in anyone of claims 6 to 8 comprising involving as said hearth layer the combination of lump iron and recycles sinter having chemical constituents wt %:
Chemical constituents Lump iron ore Recycled sinter
Fe (total) 50 to 65 preferably 63.15 52 to 55 preferably 53.58
SiO2 2 to 5 preferably 3.38 4 to 7 preferably 5.54
Al2O3 1 to 4 preferably 2.84 2 to 5 preferably 3.24
CaO 0.02 to 0.1 preferably 0.08 9 to 12 preferably 11.72
MgO 0.01 to 0.1 preferably 0.03 2 to 3 preferably 2.16
MnO 0.10 to 0.50. preferably 0.11 0.2 to 0.8 preferably 0.32
LOI 1 to 10 preferably 2.80 ---
Moisture 3 to 5 preferably 3.18 ---

10. A process as claimed in anyone of claims 6 to 9 carried out involving :
Parameters
Lump Iron Ore : Recycled Sinter
Proportion of Lump iron ore: Sinter in hearth layer
25: 75 to 75:25

Hearth Layer Height,( mm) 40 to 65 preferably 60.00
Tumbler index +6.3 mm, (%) 60 to 70 preferably 66.71
Sintering time (min) 20 to 30 preferably 24.30
Productivity + 5 mm, (t/h/m2) 1.5 to 2.5 preferably 1.95
Product Yield (+ 5 mm), % 80 to 90 preferably 84.06
Fines generation -5 mm, (%) 13 to 25 preferably 15.94

Dated this the 24th day of October, 2019
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION

The present invention relates to a process of iron ore sintering using blend of lump iron ore and sinter in hearth layer for improving sinter productivity and reducing internal return fines. More particularly, the present invention is directed to use of lump iron ore along with recycled sinter of same size fraction in hearth layer, which improves productivity and reduces internal return fines generation. The usual practice of using recycled sinter (-20+10 mm) in the hearth layer is selectively replaced with a blend made of significant fraction of lump iron ore mixed with recycled sinter in desired proportion. The proportion and size fraction of the blend for hearth layer were optimized through trials. Importantly, in the sintering process of present invention, a significant fraction of the recycled sinter is replaced with lump iron ore which ensures that it serves the purpose of hearth layer. In addition, the product output from the sinter machine including the preheated iron ore can be directly charged to the blast furnace, which results in improved productivity.
BACKGROUND OF THE INVENTION
The sintering process is based on treating a mix (mineral fines, return fines, fluxes, etc.) layer in presence of coke fines to the action of a burner placed in the surface of the layer. In this way, heating takes place from the upper to the lower sections. The mix layer rests over a strand system and an exhausting system allows to the whole thickness to reach the suitable temperature for the partial melting of the mix, and the subsequent agglomeration.

Conventional sintering involves making a blend mixture or iron ore fines, return fines, fluxes etc. which is added along with coke fines in a Dwight Lloyd sintering machine pallet car which moves in a grate consisting of a continuous chain of pallet cars. The process is begun by initiating the coke combustion, which progresses layer wise throughout the bed by the downward air draught of the machine. The combustion waves progresses through the bed, the resulting high temperature results in the agglomeration of the feed ore by sintering.

In the conventional sintering process, a hearth layer of recycled sinter (-20+10 mm) over which the green sinter mix is spread. This ensures that the hearth layer is not over heated and the grates and sinter machine structures are protected from high temperatures. The hearth layer is often made with recycled sinter of a desired fraction, which is constantly re-circulated in the sintering machine.

In the conventional sintering processes, the layer at the bottom of the sinter machine consists of a coarse granular material [10 to 20 mm size] built to a height of 40 to 65 mm. This layer protects the sinter grates from overheating during the process. The second layer consists of finer feed materials [0 to 8mm size] that include fine mineral, return fines, fluxes and coke. The sintering process needs to be carefully adjusted, so that the flame front reaches the bottom of the bed, known as the burn-through point (BTP), just before the discharge end. The BTP should be in the desired range of temperature measured in the wind box close to the discharge end, so that adequate fusion of mass takes place.

Table 1: Total hearth layer consumption in sinter plants at JSW Steel.

Parameters UOM SP-1 SP-2 SP-3 SP-4
Pallet area m2 204 204 496 224
Sinter bed height mm 700 700 715 705
Hearth layer height mm 60 60 75 65
Green mix bed height mm 640 640 640 640
Length of Machine m 68 68 124 68
Total hearth layer consumption TPD 1151 1151 3197 1369

Table 1 shows the daily consumption of hearth layer mass (TPD) in sinter plants at JSW steel limited.

STATE OF PRIOR ART

Chinese Patent - CN108149008 dated 21.06.2018 entitled “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, is spread on the sintering machine as a bed bottom. Particle size of less than 10 mm used in dispensing; the laterite nickel ore, returned ore fines and calcined lime are mixed with fuel.
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, the hearth layer comprises of a mixture of lump iron ore and recycled having size for both the material (-16+10 mm) is used as hearth layer in sintering process. It has been observed that the internal return fines is significantly reduced and increase in productivity in sintering process by using lump iron ore and recycled sinter in the size fraction of (-16+10 mm) in sinter hearth layer.

Applicant’s co-pending Patent application No. 201921025459, dated 26.06.2019 entitled “Method of improving blast furnace productivity by controlling fines generation in the upper stack region” disclosed iron ore lumps of -50+10 mm size range obtained from the process being charged directly into the Blast furnace (BF) with the use of this size fraction iron ore (-50+16 mm) in sinter bed hearth layer the overall fines generation at sinter plant got increased due to degradation of lump iron ore and removal of 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.

In this present study by using mixture of lump iron ore and recycled sinter having size (-16+10 mm) in sinter bed hearth layer there is an significant reduction in internal return fines generation and increase in productivity. It has been seen that the size fraction of lump iron ore having size fraction (-16+10 mm) does not take participate in the internal return fines generation at sinter plant.

In present innovation, purely hematite lump iron ore and recycled sinter having 10 to 16 mm size is used as hearth layer in sintering process. Thus, there is twin benefit of improved use of return fines and fresh iron ore. It has been observed that the internal return fines is significantly reduced and increase in productivity in sintering process by using mixture lump iron ore and recycled sinter in the size fraction of (-16+10 mm) in sinter hearth layer.

In the present study, applicant has used purely hematite iron ore (0-8 mm) in green mix for making sinter and mixture of lump iron ore and recycled sinter in which lump iron ore is varying in proportion from 0 to 100%. More specifically, applicants replaced recycled sinter used as a hearth layer in sinter plant by lump iron ore of the same size fraction. With the help of this study, we can replace 5151 tons of recycled sinter (75% of the total recycled sinter used as hearth layer) through lump iron ore.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to a process for iron ore sintering using purely hematite lump iron ore and recycled sinter having 10 to 16 mm size as hearth layer in sinter plant, to improve sinter productivity and reduce sinter fine generation.
A further object of the present invention is directed to a sintering process using purely hematite lump iron ore and recycled sinter of same size range as hearth layer, varying in proportion from 0 to 100% in sinter plant wherein purely hematite iron ore (0-8 mm) is used in green mix for making sinter.
A still further object of the present invention is directed to improvement in sintering process by reduction in internal return fines generation from 18.86% to 15.94%, i.e., overall reduction in return fines generation by 2.9%, and subsequently increase in productivity (+ 5 mm) from 1.74 t/h/m2 to 1.94 t/h/m2, i.e., overall increase in productivity by 0.2% at sinter plant by using mixture of lump iron ore and recycled sinter having size (-16+10 mm) used as a hearth layer.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to Hearth layer for improved productivity of sintering plant comprising:

of a hearth layer composition of lump iron ore and recycled sinter both having size (-16+10 mm).

A further aspect of the present invention is directed to said Hearth layer comprising said mix of lump iron ore and recycled sinter both having size (-16+10 mm) having proportions in the range of 25:75 to 75:25, preferably 75:25.

A still further aspect of the present invention is directed to said Hearth layer wherein the hearth layer comprises of height of 40 to 65 mm preferably 60mm.

A still further aspect of the present invention is directed to said Hearth layer wherein chemical constitution of said lump iron ore and recycled sinter wt % comprises:

Chemical constituents Lump iron ore Recycled sinter
Fe (total) 50 to 65 preferably 63.15 52 to 55 preferably 53.58
SiO2 2 to 5 preferably 3.38 4 to 7 preferably 5.54
Al2O3 1 to 4 preferably 2.84 2 to 5 preferably 3.24
CaO 0.02 to 0.1 preferably 0.08 9 to 12 preferably 11.72
MgO 0.01 to 0.1 preferably 0.03 2 to 3 preferably 2.16
MnO 0.10 to 0.50. preferably 0.11 0.2 to 0.8 preferably 0.32
LOI 1 to 10 preferably 2.80 ---
Moisture 3 to 5 preferably 3.18 ---

A still further aspect of the present invention is directed to said Hearth layer enabling generation of sinter characteristics including:

Parameters
Lump Iron Ore : Recycled Sinter
Proportion of Lump iron ore: Sinter in hearth layer 25 : 75 to 75:25
Hearth Layer Height,( mm) 40 to 65 preferably 60.00
Tumbler index +6.3 mm, (%) 60 to 70 preferably 66.71
Sintering time (min) 20 to 30 preferably 24.30
Productivity + 5 mm, (t/h/m2) 1.5 to 2.5 preferably 1.95
Product Yield (+ 5 mm), % 80 to 90 preferably 84.06
Fines generation -5 mm, (%) 13 to 25 preferably 15.94

Another aspect of the present invention is directed to a process for the sintering involving the hearth layer as described above comprising:

i) Preparation of raw sinter mix;
ii) Preparation of the hearth layer comprising a mix of lump iron ore and recycled sinter both having size (-16+10 mm) ;

iii) charging of the said hearth layer comprising a mix of lump iron ore and recycled sinter having size -16+10 mm 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.
Yet another aspect of the present invention is directed to said process wherein mix of lump iron ore and recycled sinter both having size (-16+10 mm) involved is in the range of 25:75 to 75:25 and said sinter raw mix for sintering comprises:

Overall sinter bed height (mm) 650 to 750 preferably 700
Iron ore fines, (%) 45 to 55 preferably 51.13
Sinter return fines, (%) 25 to 35 preferably 29.97
Lime stone, (%) 3 to 8 preferably 6.10
Dolomite, (%) 3 to 8 preferably 6.60
Calcined lime(%) 1 to 3 preferably 2.00
Coke breeze(%) 4 to 6 preferably 4.20
Total 100.00

A still further aspect of the present invention is directed to said process which is carried out involving said hearth layer of mix of lump iron ore and recycled sinter having size fraction (-16+10 mm)

The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm of water column
Thickness of the hearth layer : 40 to 65 preferably 60 mm
BTP (Burn through temp) : 300 - 350 ºC
Fuel rate : 50 to 60 preferably 58 kg/ton of sinter
Raw mix moisture : 7 - 8%
Quick lime : 25 to 30 preferably 27 kg/ton of sinter

A still further aspect of the present invention is directed to said process comprising involving as said hearth layer the combination of lump iron and recycles sinter having chemical constituents wt % :

Chemical constituents Lump iron ore Recycled sinter
Fe (total) 50 to 65 preferably 63.15 52 to 55 preferably 53.58
SiO2 2 to 5 preferably 3.38 4 to 7 preferably 5.54
Al2O3 1 to 4 preferably 2.84 2 to 5 preferably 3.24
CaO 0.02 to 0.1 preferably 0.08 9 to 12 preferably 11.72
MgO 0.01 to 0.1 preferably 0.03 2 to 3 preferably 2.16
MnO 0.10 to 0.50. preferably 0.11 0.2 to 0.8 preferably 0.32
LOI 1 to 10 preferably 2.80 ---
Moisture 3 to 5 preferably 3.18

A still further aspect of the present invention is directed to said process carried out involving :

Parameters
Lump Iron Ore : Recycled Sinter
Proportion of Lump iron ore: Sinter in hearth layer 25: 75 to 75:25

Hearth Layer Height,( mm) 40 to 65 preferably 60.00
Tumbler index +6.3 mm, (%) 60 to 70 preferably 66.71
Sintering time (min) 20 to 30 preferably 24.30
Productivity + 5 mm, (t/h/m2) 1.5 to 2.5 preferably 1.95
Product Yield (+ 5 mm), % 80 to 90 preferably 84.06
Fines generation -5 mm, (%) 13 to 25 preferably 15.94

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1: Variation of tumbler index (+6.3 mm) % with different proportion of lump iron ore and recycled sinter used in hearth layer.
Fig 2: Variation in sintering time (minutes) with different proportion of lump iron ore and recycled sinter used in hearth layer.
Fig 3: Variation in productivity +5 mm (t/h/m2) with different proportion of lump iron ore and recycled sinter used in hearth layer.
Fig 4: Variation in product yield (+5 mm), % with different proportion of lump iron ore and recycled sinter used in hearth layer.
Fig 5: Variation in fines generation (-5 mm), % with different proportion of lump iron ore and recycled sinter used in hearth layer.
Fig 6: Schematic diagram of pot sinter filled with green mix size -8 mm and hearth layer made of lump iron ore and recycled sinter (-16+10 mm).

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The basic aspect of the present invention is directed to a process for iron ore sintering for improving sinter plant performance by reducing the internal return fines generation (-5 mm) and increase in productivity (+5 mm) by using mixture of lump iron ore and recycled sinter both having size (-16+10 mm) in sinter bed hearth layer. Hearth layer comprises of mixture of lump iron ore and recycled sinter both having size (-16+10 mm). The proportion of lump iron ore in hearth layer composition is varied from 0 to 100% in the interval of 25% in order to observe its effect on sintering process. Hearth layer height kept constant i.e. 60 mm for all the experiments.
Below mentioned steps were followed during sintering experiments:
i) Preparation of raw sinter mix.
ii) Preparation of the hearth layer comprising a mix of lump iron ore and recycled sinter both having size (-16+10 mm) in the proportion mentioned below in table 2.

Table 2: Proportions of lump iron ore and recycled sinter used for sinter hearth layer.
Size fraction of raw materials for hearth layer (-16+10 mm)
Raw material used for hearth layer Proportions
Sinter: Lump iron ore 0:100
Sinter: Lump iron ore 50:50
Sinter: Lump iron ore 25:75
Sinter: Lump iron ore 75:25
Sinter: Lump iron ore (conventional) 100:0

iii) charging of the said hearth layer comprising a mix of lump iron ore and recycled sinter having size -16+10 mm in different proportion as mentioned in the above table 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.
The sinter raw mix percentage used in sintering process is mentioned in Table 3.
Table 3: Sinter raw mix percentage used for sintering process
Raw materials Weight %
Iron ore 45 to 55 preferably 51.13
Sinter return fines 25 to 35 preferably 29.97
Limestone 3 to 8 preferably 6.10
Dolomite 3 to 8 preferably 6.60
Calcined lime 1 to 3 preferably 2.00
Coke breeze 4 to 6 preferably 4.20

Table 4: Blend composition for sinter pot trials
Proportion of (Sinter: Lump iron ore) in hearth layer 100:0 75:25 50:50 25:75 0:100
Overall sinter bed height (mm) 700 700 700 700 700
Washed iron ore fines, (%) 51.13 51.13 51.13 51.13 51.13
Internal return fines, (%) 29.97 29.97 29.97 29.97 29.97
Lime stone, (%) 6.10 6.10 6.10 6.10 6.10
Dolomite, (%) 6.60 6.60 6.60 6.60 6.60
Calcined lime 2.00 2.00 2.00 2.00 2.00
Coke breeze 4.20 4.20 4.20 4.20 4.20
Total 100.00 100.00 100.00 100.00 100.00

The process parameters maintained during sintering process by using hearth layer made of mixture if lump iron ore and recycled sinter having size fraction (-16+10 mm)
The ignition temp : 1050 ± 50ºC
The sintering temperature : 1300 ± 100ºC
Draft rate (Suction pressure) : 1200 mm of water column
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

Table 5: Chemical analysis of lump iron ore and recycled sinter, wt. %
Chemical constituents Lump iron ore Recycled sinter
Fe (total) 63.15 53.58
SiO2 3.38 5.54
Al2O3 2.84 3.24
CaO 0.08 11.72
MgO 0.03 2.16
MnO 0.11 0.32
LOI 2.80 ---
Moisture 3.18 ---

Table 6: Sinter pot test results

Parameters Experiment No.
1 2 3 4 5
Proportion of Sinter: Lump iron ore
in hearth layer 100:0
(conventional) 75:25 50:50 25:75 0:100
Hearth Layer Height,( mm) 60.00 60.00 60.00 60.00 60.00
Tumbler index +6.3 mm, (%) 65.30 61.40 63.20 66.71 65.67
Sintering time (min) 25.30 26.00 25.00 24.30 26.30
Productivity + 5 mm, (t/h/m2) 1.79 1.78 1.80 1.95 1.74
Product Yield (+ 5 mm), % 81.14 81.25 79.02 84.06 79.35
Fines generation -5 mm, (%) 18.86 18.75 20.98 15.94 20.65

With the use of lump iron ore and recycled sinter in sinter hearth layer by varying the proportion of lump iron ore from 0 % to 100, significant improvement in sintering process were observed during sinter pot trials.
Details of the experimental trials carried out under the invention:
Expt (1) - Pot trials carried out with the use of 100% recycled sinter in sinter hearth layer
Expt (2) - Pot trials carried out with the use of 75 % recycled sinter and 25% lump iron ore in sinter hearth layer.
Expt (3) - Pot trials carried out with the use of 50 % recycled sinter and 50% lump iron ore in sinter hearth layer
Expt (4) - Pot trials carried out with the use of 25 % recycled sinter and 75% lump iron ore in sinter hearth layer
Expt (5) - Pot trials carried out with the use of 100 % lump iron ore in sinter hearth layer

Graphical representation of results of experiments:
As shown in Fig 1, variation of tumbler index +6.3 mm (%) is plotted against different proportion of lump iron ore and recycled sinter used in the sinter bed hearth layer. The tumbler index +6.3 mm (%) found 66.71 % in experiment no 4 where the composition of hearth layer maintained with of 25% recycled sinter and 75% lump iron ore in the size fraction of (-16+10 mm).
In accompanying Fig 2, Sintering time is found 24.30 minutes in experiment No. 4 with 25% recycled sinter and 75% lump iron ore in the size fraction of (-16+10 mm) used in hearth layer.
In accompanying Fig 3, productivity +5 mm (t/h/m2) is found 1.95 t/h/m2 in experiment No. 4 with 25% recycled sinter and 75% lump iron ore in the size fraction of (-16+10 mm) used in hearth layer.
In Fig 4, product yield (+5 mm), % is found 84.06 % in experiment No. 4 with 25% recycled sinter and 75% lump iron ore in the size fraction of (-16+10 mm) used in hearth layer.
In Fig 5, Fines generation (-5 mm) is found 15.94% in experiment No. 4 with 25% recycled sinter and 75% lump iron ore in the size fraction of (-16+10 mm) used in hearth layer.
Accompanying Fig 6, shows the schematic diagram of pot sinter filled with green mix (-8 mm) along with the hearth layer used made of mixtures of lump iron and recycled sinter.
It is thus possible by way of the present invention to provide a process for iron ore sintering with the use of mixtures of lump iron ore (75%) and recycled sinter (25%), both in the size range of (-16+10 mm), in hearth layer, to achieve significant improvement in reduction of internal return fines generation (-5 mm) from 18.86% to 15.94%. Further with the use of mixtures of lump iron ore (75%) and recycled sinter (25%), both in the size range of (-16+10 mm), in hearth layer, significant improvement in productivity (from 1.74 to 1.95 t/h/m2) was observed in same sinter plant.