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 PROCESS FOR SINTERING OF IRON ORE BLEND TO IMPROVE SINTER QUALITY, PRODUCT YIELD AND TO REDUCE RETURN FINES GENERATION.



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 invention relates to a method of sintering of iron ore blend to improve the cold strength property such as tumbler and shatter index by changing the continuous downdraft suction with a pulsating suction by switching on and off of the suction. In this process pulsating suction is optimized in such a way that the flame movement should stay long at particular zone and heat may be utilized in the incipient fusion. More particularly, the present invention is directed to provide a novel process to deal with iron ore sintering and to achieve better sinter quality with increased sinter strength that in turn reduces the in-plant return fines generation and hence improved plant productivity by maintaining the ratio of switch on and off time of suction. In the present invention improvement of almost 1.9 point in tumbler index in comparison to the conventional sintering process is achieved. The Product Yield, +5mm (%) of Sinter has also improved significantly under pulsating suction condition. The 2 minute suction off has shown significant improvement in Product Yield, +5mm (%) of Sinter and consequently the return fines generation has also reduced to a large extent.

BACKGROUND OF THE INVENTION:

During Dwight-Lloyd iron ore sintering process, the agglomeration of iron ore takes place via incipient fusion of iron ore particles in presence of other raw material constituents like limestone, dolomite, calcined lime, sinter return fines and steel plant wastes in presence of thermal energy supplied through combustion of solid fuel includes coke breeze and coal also added as a raw mix constituent. During this process, the temperature at the sintering bed raise up to 1300°C resulting in the formation of slag in presence of flux which bonds the ore particles through diffusion and slag bond to lump particle called iron ore sinter. This sinter cake break and screened to the required size possessing optimum cold strength and reducibility property as desired by blast furnace. Worldwide, sinter is being used as major (60-70%) burden material for blast furnace iron making which puts working pressure on the sinter plant to produce sinter of consistent quality with high productivity.

Though several factors influence the sinter quality and sinter plant productivity, the available heat for the incipient fusion of particles has major impact on it. It is reported in literature that the solid fuel and the flame front movement plays a major role in directing the sinter cold strength properties. To enhance the heat utilization coke coating on the green balls have reported in several reports. The optimization of suction and thus the flame front movement have also been reported by several researcher.

Nath and Mitra (N. K. Nath and K. Mitra, Optimisation of suction pressure for iron ore sintering by genetic algorithm, DOI: 10.1179/030192304225018118, Iron making and Steelmaking, 2004, VOL 31(3), PP 199-206) has modelled optimization of suction pressure during sintering. They claimed that the suction pressure plays important role in sinter productivity, sinter quality and fuel consumption and so it must be optimized. They claimed that at higher suction in the upper zone, melting may decrease drastically. However, at lower regions, hot gas from top layers preheat the sinter mixand the ignition zone becomes wider, malting may increase. There may be chance of losing the sensible heat through downdraft suction during sintering process. They modelled the sinter bed in three different zones and proposed an optimum suction pressure at each zone.

Hao ZHOU, Mingxi ZHOU, Zihao LIU, Ming CHENG, Kunzan QIU and Kefa CEN (Factors Controlling High-temperature Zone Resistance to Airflow during Iron Ore Sintering, ISIJ International, Vol. 55 (12),2015, pp. 2556–2565) have carried out on the high-temperature zone flow resistance during iron ore sintering and claimed that High-temperature zone flow resistance depends on sinter bed temperature and high-temperature zone structure which was related to melt volume, melt properties, bed voidage, drive force and high temperature zone thickness. They have also reported that sintering under lower suction will have greater high-temperature zone resistance and too much melt will deteriorate high-temperature zone permeability. Moreover, melt properties also have a great impact on high-temperature zone resistance; high viscosity is bad for gas channels formation in the high-temperature zone.

Brief description of the conventional sintering process:
In conventional sintering process, the raw material mixture (iron ore fines, solid fuel (coke breeze/coal), limestone, dolomite, calcined/burnt lime, sinter return fines etc.) is mixed thoroughly in a drum in absence of water for stipulated period, called dry mixing. This dry mix is further mixed in presence of water in a rotary drum for specified period for the formation of green ball under granulation. During granulation, intermediate and fine particles get coated over the coarser particles through inter-particle adhesion via water bridges, whereby larger granules or quasi-particles form that are larger in size and closer in size range than the original feed. Water plays an important role during granulation in mixing and nodulizing drum forms an interface between the finer and coarser iron ore particles during granulation to form relatively bigger granules. It promotes the adhering characteristics of iron ore fines and fluxes so that the bigger granules improve the bed permeability at sinter strand which in turn enhance the productivity of process and properties of sinter. In addition to the above, the bigger granules subsequently results in homogeneous burning as well as uniform suction during sintering. It also reduces the loss of valuable fines during suction of sintering. The sinter mixes on the strand are burnt from the top. The suction of air through the bed helps sustaining the combustion of the fuel and provides the downward movement of the combustion zone through the bed up to the bottom layer to raise the temperature to 1250-1300 ºC. During the process of sintering the granulated materials undergo incipient fusion.

In the present invention, the applicants have considered the melt formation which is controlled by switching on and off or providing the pulsating suction during sintering of iron ore which delays the heat flow to the downdraft suction and the heat utilization improves which in turn provide better bonding and thus improve the cold strength properties such as tumbler and shatter index of product sinter.

OBJECTS OF THE INVENTION:
The basic object of the present invention is directed to a process for sintering of iron ore blend for effective utilization of heat front or combustion zone in sinter making for improved sinter quality.

A further object of the present invention is directed to a process of sintering iron ore blend providing the pulsating suction through switching on and off of downdraft suction fan during sintering process.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a process for sintering of iron ore blend including Iron Ore, In-plant Return Fines, Calcined Lime/Quick Lime, Limestone, Dolomite and Coke breeze, comprising:

subjecting the sintering material having a top layer and a bottom layer supported on a sinter bed;

carrying out firing and flame generation at the top layer involving a cooperatively disposed ignition mechanism;

ensuring downdraft suction based air flow from the top to the bottom layer of the sintering material involving a suction mechanism;

selectively switching on and off the said suction mechanism for selective time durations such as to selectively control and block the duration of passage of hot air from top to bottom layers thereby selectively controlling the flame front based heat movement under suction and maintain heat during sintering by selectively blocking the passage of hot air for facilitating bonding and agglomeration of particles with generation of advanced cold strength properties including tumbler index and shatter index and also productivity.

A further aspect of the present invention is directed to said process wherein said selective time duration for switching on and off the said suction mechanism comprise sinter suction ON time constant for 5 minutes and the OFF time varied from 1 to 3 minutes for pulsating sintering with improved time of suction based sinter cold strength including Tumbler Index improvement.

A still further aspect of the present invention is directed to said process wherein the suction on:off time ratio of 5:2 is maintained for sinter strength improvement to almost 1.9 point in comparison to the conventional sintering process.

A still further aspect of the present invention is directed to said process comprising maintaining 2 minutes suction off for product yield improvement in the range of 72.02 to 74.48%, +5mm (%) of Sinter and consequently the return fines generation reduced to a extent of 27.98 to 25.72 %.

A still further aspect of the present invention is directed to said process comprises maintaining 5:2 minutes suction on and off ratio for improved cold strength property including Tumbler Index in the range of 64.0 to 65.9 and better mineralogy including slag melt with adjacent particle for better bonding.

The time duration of suction ON and OFF were never applied in iron ore sintering process before this present invention. However, the effect of suction and flame front movement plays an important role on sinter qualities and sinter plant productivity, which is well known by the sinter maker, worldwide. In the present work, the suction on and off has been worked out which has given significant improvement on product yield and sinter quality. Suction switching On and Off time ratio in minutes 5:1 , 5:2 & 5:3 maintained with corresponding sintering time 31, 32 & 37min respectively.

The suction on and off provides the longer heat stay in the bed without their loss through downward air suction. It has already known to the sinter makers that the change is air flow velocity or downdraft suction pressure plays an important role in sinter product quality, sinter yield and sinter plant productivity. However, no one has tried on putting it off because of the delayed sinter production and thus reduced sinter plant productivity. The sinter plant has to run at slow speed to bring down the flame front temperature to the lower part. As the suction closes for some time the flame front movement delays which result in later completion of sintering.

The above and other aspects and advantages of the present invention are described hereunder with reference to following accompanying non limiting illustrative drawings and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 (a): shows graphically Sinter productivity, +5mm (t/m2/h) @primary Y-axis and Sintering Time (minutes) @secondary Y-axis.
Figure 1 (b): shows Cold strength properties(Tumbler Index, +6.3mm, %) of Sinter obtained according to process of present invention compared to conventional.
Figure 1 (c): Abrasion Index, -0.5 mm, % of Sinter obtained according to process of present invention compared to conventional.
Figure 1 (d): Product Yield, +5mm (%) of Sinter obtained according to process of present invention compared to conventional.
Figure 1 (e-h): Mineralogy of sinter obtained (e) conventional versus those under different pulsating suction conditions of On and Off duration in minutes 5:1, 5:2 & 5:3.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLE

In present invention, the pot sintering experiments was conducted using pulsating suction i.e varying on and off time of suction fan during sintering to understand its impact on sintering behaviour and sinter quality performance. The raw materials proportions for experimental trials were decided by the JSW mass balance calculations to keep basicity, B2 (=CaO/SiO2) of the sinter product as 1.9 (approx).

Experimental Methodology adopted:

? Approximately 90 kg of sinter mix blended using balling drum. Blending condition: mixing @ 20 rpm for 300 seconds.
? One kg of each blended sinter mix sample was dried and analyzed for particle size distribution.
? Agglomerated the sinter mix in presence of moisture using a drum mixer; Agglomerating condition: mixing @ 20 rpm for 480 seconds.
? Sintered the material in pot grate with ignition conditions as under:
Ignition conditions:
Suction air flow volume before ignition 2.0 m3/min
Ignition holding time 120 sec
Suction pressure during suction -500 mm H2O
Suction pressure after ignition -1200 mm H2O (Switching On and Off, as mentioned in the Table)

• Raw materials were screened to obtain the desired size as given below.
Material Size
Base Mix As received
Calcined lime - 0.212 mm
Coke breeze - 3.15 mm

Pot-Sintering Experiment
Pot sintering experiments were conducted at lab scale using a round shaped sinter pot having a diameter of 300 mm with a provision to vary height of the pot from 600 to 850 mm. Removable grate bar were placed at the bottom of the pot for air suction during the sintering experiments. Raw material mixing was done in two stages: dry mixing in concrete mixer and wet mixing in drum. The chemical analysis of the raw materials used for sintering is given in Table 1. Raw materials proportions and its chemical analysis is given in Table 2 and 3, respectively.

Table1 : Chemical analysis of raw materials

Constituents T.Fe SiO2 Al2O3 CaO MgO LOI
%
Iron Ore-1 59.88 8.68 2.51 0.06 0.03 2.72
Iron Ore-2 62.01 3.01 2.71 0.04 0.04 3.08
Iron Ore-3 61.01 4.21 3.5 0.087 0.0395 9.5
Iron Ore-4 58.14 8.6 3.87 0.1 0.046 3.45
Iron Ore-5 59.68 3.21 4.5 0.03 0.04 2.8
In-plant Return Fines 53.59 6.15 6.15 3.25 11.95 0.50
Calcined Lime/ Quick Lime 0.31 0.81 0.28 93.94 1.49 3.05
Limestone 0.89 2.05 0.47 50.49 2.73 42.59
Dolomite 0.79 5.22 0.67 29.05 19.49 43.97
Coke breeze 0.63 7.72 4.43 0.67 0.16 86.62

Table 2: Raw materials proportions used for experimental trials
Constituents %
Iron Ore-1 8.18
Iron Ore-2 14.43
Iron Ore-3 9.62
Iron Ore-4 12.02
Iron Ore-5 3.84
In-plant Return Fines 34.00
Calcined Lime/ Quick Lime 7.00
Limestone 4.50
Dolomite 2.20
Coke breeze 4.20

Table 3: Sinter Chemical Analysis
Fe(t),% 54.03
SiO2,% 5.74
Al2O3,% 3.10
CaO,% 11.79
MgO,% 2.04
MnO,% 0.34
CaO/SiO2 2.06
Al2O3/SiO2 0.54

Drum mixer has provision of maintaining speed of the drum and having lifting facilities too. A known quantity of water was added during drum mixing for effective granulation. Times for dry and wet mixing were kept at 3 and 5 minutes, respectively. After mixing and granulation the materials were filled in the pot. Experiments were conducted in two phases. Before filling the mix in to the pot, hearth layer of 55-60 mm height were filled by sintered material with size (10-20) mm at the bottom of the pot. The purpose of filling hearth layer is to protect the grate bar and maintaining air suction without choking of the material to wind box pipe. Heat energy was supplied to the pot from its top using automated ignition burner with a flow of liquid petroleum gas (LPG) for one minute. Sintered product after cooling was sent to the impact crusher having an outer diameter of 700 mm and RPM of 1000 max with a crushing capacity of 10t/h. The crushed materials were screened for size range measurements using 50 mm, 40 mm, 30 mm, 20 mm, 16 mm, 10 mm and 5 mm screens. Cumulative +10mm fraction, mean particle size and -5 mm size fraction percentage were calculated. The chemical analysis of the sinter was conducted using X-ray fluorescence (XRF) after grinding the sintered material below 100 mesh using ball mill. The chemical analysis of the sintered material is given in Table 3.

RESULTS

The sintering process parameters and sinter qualities of the experimental trials are given in Table 4 and their graphical representations are given subsequently in figures 1(a-h).
Table 4: Sintering process parameters and sinter qualities
Pulsating Time (On:Off) in minutes Conventional 5:1 5:2 5:3
Sintering Time (mins) 30 31 32 37
Productivity (+ 5 mm), t/m2/h 1.32 1.29 1.28 1.09
Product Yield (+ 5 mm), % 72.02 73.19 74.28 73.02
Fines generation (-5 mm), % 27.98 26.81 25.72 26.98
TI % 64.00 65.47 65.93 65.13
AI % 6.20 5.33 5.07 5.33

Accompanying Figure 1(a) shows graphically Sinter productivity, +5mm (t/m2/h) @primary Y-axis and Sintering Time (minutes) @secondary Y-axis.
Figure 1(b) shows Cold strength properties(Tumbler Index, +6.3mm, %) of Sinter obtained according to process of present invention compared to conventional.
Figure 1(c) shows Abrasion Index, -0.5 mm, % of Sinter obtained according to process of present invention compared to conventional.
Figure 1 (d) shows Product Yield, +5mm (%) of Sinter obtained according to process of present invention compared to conventional.
Figure 1 (e-h) show images of Mineralogy of sinter obtained (e) conventional versus those under different pulsating suction conditions ratio of On and Off duration in minutes 5:1, 5:2 & 5:3.
The time duration of suction ON and OFF were never applied in iron ore sintering process before this present invention. However, the effect of suction and flame front movement plays an important role on sinter qualities and sinter plant productivity, which is well known by the sinter maker, worldwide. In the present work, the suction on and off has been worked out which has given significant improvement on product yield and sinter quality.

The suction on and off provides the longer heat stay in the bed without their loss through downward air suction. It has already known to the sinter makers that the change is air flow velocity or downdraft suction pressure plays an important role in sinter product quality, sinter yield and sinter plant productivity. However, no one has tried on putting it off because of the delayed sinter production and thus reduced sinter plant productivity. The sinter plant has to run at slow speed to bring down the flame front temperature to the lower part. As the suction closes for some time the flame front movement delays which result in later completion of sintering.

Inferences
? The pulsating suction during sintering has been studied for the first time. The sinter suction on time is kept constant for 5 minutes whereas the off time varies from 1 to 3 minutes with a variation of 1 minutes.
? The sinter cold strength property (Tumbler Index) has improved significantly under the pulsating suction sintering process.
? The suction on:off ratio of 5:2 is an optimum one where the sinter strength has improved to almost 1.9 point in comparison to the conventional sintering process.
? The Product Yield, +5mm (%) of Sinter has also improved significantly under pulsating suction condition. The 2 minute suction off has shown significant improvement in Product Yield, +5mm (%) of Sinter and consequently the return fines generation has also reduced to a large extent.
? The mineralogy of sinter shows better slag melt formation in suction on: off ration of 5:2, as shown in figure.

It is thus possible by way of the present invention to provide a process for sintering of iron ore blend comprising subjecting iron ore blend to a sintering process where the downdraft suction is pulsated to on and off mode by manually switching on and off the motor that delays the heat movement and resulted in improved bonding between the agglomerating particles which in turn provided improved cold strength properties such as tumbler index and shatter index, thereby increasing the product yield and reduced return fines generation with a loss of sinter plant productivity due to delayed movement of flame front.
, Claims:We Claim:

1. A process for sintering of iron ore blend including Iron Ore, In-plant Return Fines, Calcined Lime/Quick Lime, Limestone, Dolomite and Coke breeze, comprising :

subjecting the sintering material having a top layer and a bottom layer supported on a sinter bed;
carrying out firing and flame generation at the top layer involving a cooperatively disposed ignition mechanism;

ensuring downdraft suction based air flow from the top to the bottom layer of the sintering material involving a suction mechanism;

selectively switching on and off the said suction mechanism for selective time durations such as to selectively control and block the duration of passage of hot air from top to bottom layers thereby selectively controlling the flame front based heat movement under suction and maintain heat during sintering by selectively blocking the passage of hot air for facilitating bonding and agglomeration of particles with generation of advanced cold strength properties including tumbler index and shatter index and also productivity.

2. The process as claimed in claim 1 wherein said selective time duration for switching on and off the said suction mechanism comprise sinter suction ON time constant for 5 minutes and the OFF time varied from 1 to 3 minutes for pulsating sintering with improved time of suction based sinter cold strength including Tumbler Index improvement.

3. The process as claimed in anyone of claims 1 or 2 wherein the suction on:off time ratio of 5:2 is maintained for sinter strength improvement to almost 1.9 point in comparison to the conventional sintering process.

4. The process as claimed in anyone of claims 1 to 3 comprising maintaining 2 minutes suction off for product yield improvement in the range of 72.02 to 74.48%, +5mm (%) of Sinter and consequently the return fines generation reduced to a extent of 27.98 to 25.72 %.

5. The process as claimed in anyone of claims 1 to 4 comprises maintaining 5: 2 minutes suction on and off ratio for improved cold strength property including Tumbler Index in the range of 64.0 to 65.9 and better mineralogy including slag melt with adjacent particle for better bonding.

6. The process as claimed in anyone of claims 1 to 5 wherein the ignition condition comprising:
Suction air flow volume before ignition 2.0 m3/min
Ignition holding time 120 sec
Suction pressure during suction -500 mm H2O
Suction pressure after ignition -1200 mm H2O (Switching On and Off time ratio in minutes 5:1 to 5:3, with sintering time 31 to 37min)

Dated this the 27th February, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199