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 OF UTILIZING MAGNESITE WASTES IN IRON ORE SINTERING.



2 APPLICANT (S)

Name : STEEL AUTHORITY OF INDIA LIMITED.

Nationality : Indian.

Address : Research & Development Centre for Iron & Steel,
Doranda, Ranchi, Jharkhand, India. PIN-834002.






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 process for iron ore sintering with partial substitution of dolomite in the iron ore sintering process. More particularly, the present invention is directed to addition of magnesite rejects/wastes of Almora Magnesite Plant, India as partial replacement of dolomite to evaluate their effects in sintering process. Actually this process is employed to simulate iron ore sintering process in laboratory scale under applicant’s Bokaro Steel Plant condition. Advantageously, this innovation creates an avenue to utilize the industrial wastes/rejects. This innovation has great favourable impact on environmental pollution.

BACKGROUND OF THE INVENTION:

The iron ore sintering was characterized as a relatively uniform process of solid material, coke combustion, various modes of heat transfer and the complicated physical changes of solid particles. Iron ore fines and coke are mixed, moistened with water and micro-pelletized to form the charge. The charge is loaded onto a pallet/grate and levelled to form a bed which is ignited by a gas-fuelled ignition hood. A heat wave and coke combustion zone travels down through the bed under the influence of a suction pressure. In conventional iron ore sintering process limestone and dolomite are added as flux to produce pre-fluxed sinter as per the sinter quality required for use in blast furnace. Unavailability of good quality dolomite has been a matter of concern to the iron and steel manufacturers in India and abroad. Moreover, being carbonate minerals, use of dolomite adds to the carbon emission during sintering process. On the contrary, olivine is a naturally occurring silicate mineral available in the Earth’s subsurface and it is composed of a mixed crystal lattice of the minerals Forsterite(Mg2SiO4) and Fayalite(Fe2SiO4). Several investigations have been reported on the partial substitution of dolomite by olivine in the iron ore sintering process. But, due to non-availability of olivine in India, magnesite wastes/rejects were used as partial replacement of dolomite to investigate their effects in sintering process.
The present invention relates to partial substitution of dolomite in the iron ore sintering process by addition of magnesite rejects/wastes of Almora Magnesite Plant, India as partial replacement of dolomite to examine their effects in sintering process and to simulate iron ore sintering process in laboratory scale under Bokaro Steel Plant condition. Advantageously, this innovation creates an avenue to utilize the industrial wastes/reject and having great impact on avoiding environmental pollution.

OBJECTIVE OF THE INVENTION:

The basic object of the present invention is directed to introduce magnesite rejects/wastes as partial replacement of dolomite in sinter composition to examine their effects in sintering process and sinter product properties

A further object of the present invention is directed to simulate iron ore sintering process in laboratory under Bokaro Steel Plant condition.

A still further object of the present invention is directed tocreate an avenue for utilization of industrial wastes/rejects.

A still further object of the present invention is directed to reduce carbon emission during sintering process by partial substitution of carbonate based dolomite with magnesite waste and thus saving environmental pollution.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to an iron ore sinter composition comprising:
co-acting partially replaced dolomite content containing flux with dolomite 70% by wt and partial dolomite replacement with magnesite waste 30% by wt. favouring vertical sintering speed.

A further aspect of the present invention is directed to said iron ore sinter composition comprising sinter mix composition of
Flux combination of dolomite 70% by wt and magnesite waste 30% by wt wherein said Magnesite waste has a composition of 3.9% FeT, 3.8% SiO2, 0.8% Al2O3, 1.7% CaO,, 46.7% MgO and 40.9%.

A still further aspect of the present invention is directed to saidiron ore sinter composition wherein said Magnesite wastes/rejects contain higher MgO (46%) than dolomite (18.5) and contains lower Al2O3 (0.8%) than dolomite (3%).

A still further aspect of the present invention is directed to said iron ore sinter mix composition comprising:
iron ore:72.36 % by wt
coke breeze in amounts of 5.70 % by wt;
mill scale in amounts of 0.99 % by wt;
flue dust in amounts of 0.57 % by wt; and
water 10.32 % by wt.

A still further aspect of the present invention is directed to said iron ore sinter composition favouring maintaining sinter productivity with properties of Reduction Degradation Index (RDI) 27.52%, Reducibility Index (RI) 60.21%, Tumbler Index (TI) 67.69%, granulometry: 11.60% (+40 mm), 67.45%(5-40 mm) & 25.06% (-5 mm).

Another aspect of the present invention is directed to said iron ore sinter composition wherein said sinter mix selectively provides sinter chemistry of :

Sinter Chemistry
FeT, % 57.22
SiO2,% 5.02
Al2O3,% 1.99
CaO,% 9.75
MgO,% 3.51
Basicity(%CaO / %SiO2) 1.94
Available Lime (%CaO - %SiO2) 4.73

A further aspect of the present invention is directed to a process for sintering iron ore comprising the step of sintering involving a sinter mix including a co-acting partially replaced dolomite containing flux combination of dolomite 70% by wt and magnesite waste 30% by wt. favouring achieving enhanced vertical sintering speed.

Another aspect of the present invention is directed to said process wherein said said Magnesite wastes/rejects used selectively contain higher MgO (46%) than dolomite (18.5%) favouring lower volume handling and contains lower Al2O3 (0.8%) than dolomite (3%) favouring waste utilization in sintering process.

The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to accompanying non limiting illustrative drawing and example.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING:

Figure 1: shows the schematic representation of the pot sintering unit for conducting iron ore sintering experiments according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWING AND EXAMPLE:

The present invention is directed to introduce magnesite rejects/wastes as partial replacement of dolomite in sinter composition to examine their effects in sintering process and sinter product properties. The invention is directed to simulate iron ore sintering process in laboratory pot sintering set-up under Bokaro Steel Plant condition.

Pot sintering is a pilot scale simulation of plant condition. The raw materials like iron ore, flux, coke breeze, mill scale, flue dust, water is manually weighed and fed into mixing and granulation drum. Granulated sinter mix then charged into cylindrical shaped sinter pot according to the bed height of the imitating plant. The schematic representation of the Pot Sintering System is shown in Figure 1.

Experimental Procedure:
Pot Sintering Studies carried out involving Magnesite Rejects of Almora as follows:
Several pot sintering experiments were carried out at laboratory with varying percentage of magnesite wastes/rejects of Almora in sinter mix as partial replacement of dolomite. In this case the bed height is fixed at 500 mm. Ignition is commenced with 300 mmWC suction for 2.5 min. The flame intensity is increased by opening the air supply valve completely. Post ignition suction is fixed at 550 mmWC. The end of sintering is defined as the time at which the peak exhaust gas temperature is measured, indicating that the flame front has travelled all the way through the sinter cake. After sintering is complete, the sinter cake is removed from the pot and then proceeds to physical testing. This starts with a set of drop tests followed by a drum breakdown procedure; after which the sample is screened to determine the size distribution of the final sinter. One base experiment without magnesite reject addition has been conducted. Five nos. of other pot sintering tests have been conducted with increasing magnesite rejects addition in sinter mix @ 10, 20, 30, 40 and 50 wt%.

Chemical analyses of Magnesite Rejects/Wastes and Dolomite used in the experiments are shown in following Table 1.

Table-1: Chemical analyses of Magnesite Rejects/Wastes and Dolomite

Component Magnesite Rejects Dolomite
FeT, % 3.9 0.53
SiO2,% 3.8 1.5
Al2O3,% 0.8 2.1
CaO,% 1.7 31.2
MgO,% 46.7 18.5
LoI,% 40.9 45.8

Results and Discussion:

The results of the pot sintering experiments with varying percent of magnesite rejects in partial replacement of dolomite in sinter mix including effect of vertical sintering speed and sinter product properties are presented in following Table 2.

Table – 2: Results of Pot Sintering Studies with Magnesite Rejects

Parameters Without Magnesite Reject With Magnesite Reject
10% 20% 30% 40% 50%
Vertical Sintering Speed, mm/min 16.65 16.26 16.65 17.14 16.32 16.17
Sinter Properties
DTI (Differential Tumbler Index), % +6.3 mm 68.37 66.84 64.95 67.69 66.70 65.24
RDI (Reduction Degradation Index), % 25.43 25.83 27.82 27.52 28.72 29.16
RI (Reducibility Index), % 58.74 58.61 59.35 60.21 57.64 55.92
Grannulometry
+ 40 mm 15.80 8.07 13.09 11.60 10.76 8.07
5 - 40 mm 59.27 67.28 65.09 67.45 62.53 62.28
- 5 mm 24.93 24.64 25.74 25.06 27.37 29.43

Sinter Chemistry
FeT, % 57.29 57.24 57.18 57.22 57.31 57.16
SiO2,% 4.85 4.97 4.99 5.02 4.94 4.89
Al2O3,% 2.16 2.02 2.00 1.99 1.97 1.96
CaO,% 9.60 9.72 9.74 9.75 9.77 9.68
MgO,% 3.10 3.38 3.42 3.51 3.64 3.68
Basicity(%CaO / %SiO2) 1.98 1.96 1.95 1.94 1.98 1.98
Available Lime (%CaO - %SiO2) 4.75 4.75 4.75 4.73 4.83 4.79

The observations of the experiments are summarized as follows:

(a) Pot sintering simulation with 30% Magnesite Rejects of Almora addition in sinter mix as partial replacement of dolomite doesn’t hamper the vertical sintering speed (16.65 for without magnesite reject and 17.14 mm/min with addition of 30% magnesite reject). The value also exhibits slightly better result. It is obvious that the factors affecting the sintering time would directly affect the sinter production rate. The sintering time is dependent to a large extent on the progress of the combustion zone and the subsequent cooling zone. The sintering and cooling period of the sinter increases with increasing addition of MgO% in the sinter mix.

(b) Pot sintering simulation with 30% Magnesite Rejects of Almora addition in sinter mix as partial replacement of dolomite doesn’t affect the product sinter properties. The DTI (Differential Tumbling Index) value gets slightly decreased (68.37 for without magnesite reject and 67.69 mm/min with addition of 30% magnesite reject). Calcium ferrite is the major mineral constituent of the sinter structure and it imparts strength to the sintered mass. The calcium ferrite phase decreases while magnetite and silicate melt phases increase with increasing MgO level in dolomite and pyroxene/magnesite sinter. The formation of a vitreous glassy matrix and of dicalcium silicate is harmful to the sinter strength as these structures exhibit a high degree of stress and therefore, results in a remarkable drop in the sinter tumbler index. It is a well-established fact that the strength of sinter is dependent to a large extent on the properties and quantities of the resultant matrix. Generally, dolomite sinter shows higher DTI values compared to pyroxene/magnesite sinter due to its higher content of calcium ferrites which are known to be a stronger phase in the sinter.

(c) The reduction degradation index (RDI) is a measure of disintegration susceptibility of the sinter under exposure to CO in the temperature range of 500 to 600°C. The low temperature reduction strength (RDI) of the sinters was determined by the ISO test procedure of static reduction followed by tumbling. This test simulates the blast furnace conditions in the upper stack regions with mild reducing conditions and relatively low temperatures. After reduction following the tumbling, the -3.15mm fraction generated is considered as RDI (-3.15mm) of the sinter and -3.15mm below 27% is considered as good RDI. The RDI (-3.15mm) magnesite and dolomite sinter decreased with increasing MgO percentage in sinter. The weakening and degradation of sinter is associated with volume increase due to the phase transformation of hematite to magnetite occurring in the sinter. With addition of MgO, the hematite content decreases and the magnetite content increases. Because of less availability of hematite less reduction takes place at lower temperature and less strain is generated in the sinter matrix structure in the upper shaft of the blast furnace and hence RDI decreases. The presence of MgO in the sinter mix may be attributed to the production of slag phase with some precipitation of magnesite (MgO•FeO•SiO2). These magnesites reduce the cracks during reduction. The RDI value of magnesite sinter was slightly higher compared to dolomite sinter (25.43% to 27.52%) because of the higher slag phase fraction.

(d) The reducibility was determined using the ISO 4695 test procedure. This test is carried out at an elevated temperature under a reducing gas atmosphere simulating blast furnace reduction conditions. The laboratory testing procedure used for testing the reducibility of iron ore sinter was as follows: Samples of +10-12.5mm diameter were selected by the sieving method. 500 g sinter sample was dried at 105°C for 30 min in an air oven and cooled to room temperature. The reacting vessel containing the sample was placed inside the heating chamber and N2 gas was started to pass through the reacting vessel at 5 lpm till the temperature in the retort reached 950°C. At that point the nitrogen flow was increased to 15 lpm till the sample weight became constant. Once the mass of the sample became constant, reducing gas (30% CO and 70% N2) was passed at 15 lpm for 3 hr. After 3 hr the reducing gas was stopped and N2 passed with 5 lpm till the sample reached the temperature of 100°C. Then the sample was taken out from the retort and cooled to room temperature. The sample weight was recorded using a digital electronic balance. The reducibility R (in %) was calculated as % oxygen removed from sinter. The reducibility depends on the physical and chemical characteristics of the sinter, which are particle size, porosity, mineralogical composition and internal physical structure. The sinter magnetite (Fe2O3•FeO) content increased and the reducibility decreased with increasing sinter MgO level. The negative influence of MgO addition on the reducibility of iron ore sinter was believed to be a result of decreasing hematite and calcium ferrite phases and increasing magnetite phase having lower reducibility. During the reduction process the conversion of hematite into magnetite takes place depending on the reducing atmosphere. The higher the amount of magnetite or wüstite in the sinter is, the lower the degree of reduction will be. This means the amount of oxygen removal per unit weight of iron is about 12% lower in magnetite than in hematite. The addition of MgO causes the disappearance of calcium ferrite and growth of MgO bearing phases like olivine. The resulting increase of the MgO/CaO ratio decreases the amount of ferrite and hematite with a related increase of magnetite content. Magnesite sinter showed a slightly higher reducibility due to the presence of a higher amount of hematite phase compared to dolomite sinter. Dolomite mixed with magnetite concentrate kept good sintering indexes. Improving contact condition of MgO and FeO could increase the solid solubility of MgO in the magnetite, thus decreased the content of MgO in calcium ferrite, and then increased the fluidity of bonding phase and strength of sinter. In this investigation the RI value of magnesite sinter was slightly higher compared to dolomite sinter (25.43% to 27.52%).

Usefulness of the Invention:
• Magnesite wastes/rejects is first time used as flux in iron ore sintering, replacing dolomite partly.
• Process route for using magnesite wastes/rejects with conventional dolomite has been developed.
• Magnesite wastes/rejects contain higher MgO (46%) than dolomite (18.5%), which gives lower volume of material handling in sintering process, upto a limited replacement ratio.
• It contains lower Al2O3 (0.8%) than dolomite (3%), which gives certain benefits in sintering process.
• The optimum replacement ratio i.e. 30% Magnesite Rejects and 70% Dolomite has been experimentally established and demonstrated.

Industrial Applicability:
The present invention relates to partial substitution of dolomite in the iron ore sintering process. More particularly, the present invention is directed to addition of magnesite rejects/wastes of Almora Magnesite Plant, India as partial replacement of dolomite to examine their effects in sintering process. Actually this process is employed to simulate iron ore sintering process in laboratory under Bokaro Steel Plant condition. Advantageously, this innovation creates an avenue to utilize the industrial wastes/rejects. This is applicable in any industrial sinter plant. Hence, this innovation is suitable for wide industrial application with significant utilization of magnesite rejects/wastes.

, Claims:We Claim :
1. Iron ore sinter composition comprising :

co-acting partially replaced dolomite content containing flux with dolomite 70% by wt and partial dolomite replacement with magnesite waste 30% by wt. favouring vertical sintering speed.

2. The iron ore sinter composition as claimed in claim 1 comprising sinter mix composition of

Flux combination of dolomite 70% by wt and magnesite waste 30% by wt wherein said Magnesite waste has a composition of 3.9% FeT, 3.8% SiO2, 0.8% Al2O3, 1.7% CaO,, 46.7% MgO and 40.9%.

3. The iron ore sinter composition as claimed in anyone of claims 1 or 2 wherein said Magnesite wastes/rejects contain higher MgO (46%) than dolomite (18.5) and contains lower Al2O3 (0.8%) than dolomite (3%).

4. The iron ore sinter composition as claimed in anyone of claims 1 to 3 comprising :
iron ore: 72.36 % by wt
coke breeze in amounts of 5.70 % by wt;
mill scale in amounts of 0.99 % by wt;
flue dust in amounts of 0.57 % by wt; and
water 10.32 % by wt.

5. The iron ore sinter composition as claimed in anyone of claims 1 to 4 favouring maintaining sinter productivity with properties of Reduction Degradation Index (RDI) 27.52% , Reducibility Index (RI) 60.21% , Tumbler Index (TI) 67.69%,granulometry; 11.60% (+40 mm), 67.45%(5-40 mm) &25.06% (-5 mm).
6. The iron ore sinter composition as claimed in anyone of claims 1 to 5 wherein said sinter mix selectively provides sinter chemistry of :

Sinter Chemistry
FeT, % 57.22
SiO2,% 5.02
Al2O3,% 1.99
CaO,% 9.75
MgO,% 3.51
Basicity(%CaO / %SiO2) 1.94
Available Lime (%CaO - %SiO2) 4.73

7. A process for sintering iron ore comprising the step of sintering involving a sinter mix including a co-acting partially replaced dolomite containing flux combination of dolomite 70% by wt and magnesite waste 30% by wt. favouring achieving enhanced vertical sintering speed.

8. The process as claimed in claim 7 wherein said said Magnesite wastes/rejects used selectively contain higher MgO (46%) than dolomite (18.5%) favouring lower volume handling and contains lower Al2O3 (0.8%) than dolomite (3%) favouring waste utilization in sintering process.

Dated this the 22nd day of March, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicants’ Agent)
IN/PA-199