The present invention provides a process of operating iron-making blast furnace with high alumina (20 – 25.4 weight %)slag.More specifically, the invention is related to utilizing iron ore with high alumina content.
Background of the Invention
In an iron-making blast furnace, all the gangue materials present in iron bearing material and flux reports to slag. The acidic impurities mainly silicon dioxide and aluminium oxide in slag, forms a network polymerized chain which affects the fluidity of slag in the melting state. To counter the adverse effects of acidic oxides, basic oxides such as calcium oxide and magnesium oxide are introduced through flux in slag which break the network of polymerized chain and therefore, improves the fluidity of slag. This increases fuel consumption in the blast furnace.
In India, high alumina content in iron ore makes the blast furnace operation very difficult. The slag produced with high alumina has high viscosity and liquidus temperature. Slag viscosity and liquidus temperature are important properties which affects the blast furnace performance in many ways. It affects the desulphurization capacity of slag, minor oxides reduction (SiO2, MnOetc), gas permeability, smoothness of operation, productivity etc.
Currently, raw flux mainly limestone (source of calcium oxide), dolomite (source of calcium oxide and magnesium oxide), dunite (source of magnesium oxide and silicon dioxide), pyroxenite (source of magnesium oxide and silicon dioxide) and quartzite (source of silicon dioxide) are added with the iron bearing material to dilute the slag alumina (~17 - 19 wt. %). Diluting slag alumina leads to lowering of viscosity and liquidus temperature of slag to tap the slag smoothly. This resultsin high slag volume, high demand of fuel and also reduction in productivity.
High alumina slag operation drives low cost of production but aggravates difficulty in smoothness of operation. So, there is a need for innovative methodology to operate the blast furnace operation with high slag alumina (20weight % and more) regime to improve the productivity and lessen fuel requirement. In past, many attempts have been made to solve the existing problem. Nippon Steel JP2005231918 patent application claimed the method of addition of modifying material to the molten blast furnace slag, eliminating the properties of slag such as sticking and growing of sintered lumpy material. However this invention did not mention the method of operating the blast furnace operation with high viscous slag as the material is added to slag after tapping.

Kawasaki Steel JPS6043411 A 19850308 [JP60043411] patent claimed the injection of lime (CaO) and silica (SiO2) through blast furnace tuyeres to keep the slag basicity in the range of 1.15 to 1.3 for controlling sulphur in hot metal and viscosity of slag. However this invention did not mention the effect of slag alumina on viscosity of slag.
Sumitomo Metal Ind ltd (SUMQ-C) JP2003013122-A claimed the method of operating blast furnace with slag alumina 16.5 weight % or more by adjusting magnesium oxide (MgO) content in slag and basicity (ratio of calcium oxide content to silica content) of slag. However this invention did not mention the method of maintaining fluidity of slag with alumina more than 20 weight %.
It is clear from the discussion that various attempts have been made for operating blast furnace with different slag regimes. However, no work has been reported on quantified effect of slag constituents for providing fluidity and liquidus temperature of slag at high alumina (> 20 weight %).
Objects of the Current Invention:
The main objective of the present invention is to develop a process that enable running blast furnace operation with high alumina slag.
Still another object of the invention is to develop a process that enables use of iron ore containing high amount of alumina.
One more object of the invention is to ensure that blast furnace operation runs without any impact on overall process parameters when operated with iron ore containing high alumina.
Summary of the Invention:
The process of the current invention involves adding a predetermined quantity of boron oxide in the blast furnace along with iron ore. The boron oxide is added to the burden mixture to ensure that slag fluidity is maintained even when blast furnace is operated with high alumina content. Boron tri-oxide (B2O3) is capable of improving fluidity of slag even at 25.4 weight % slag alumina without any process instability when added via either top charging through chute or injection through tuyeres.
Brief description of the Drawings & Figures:
Figure 1 shows the slag alumina weight %, slag boron tri-oxide weight % and slag rate, kg/ton of hot metal of five examples.
Figure 2 shows the slag alumina weight %, slag boron tri-oxide weight % and slag liquidus temperature, oC of five examples.
Figure 3 shows the slag alumina weight %, slag boron tri-oxide weight % and slag viscosity, centipoise of five examples.

Detailed descriptionof invention:
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.
In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

Definition and formulae:
Working volume of blast furnace: It is defined as the available volume between burden level and tuyeres.
Liquidus temperature: It is defined as the temperature above which slag is completely liquid.

To solve the problem prevailing in prior art, present invention focuses on providing new methodology to maintain fluidity of slag, thuseliminating limitation of operating blast furnace at high alumina slag.
The present inventionfinds outboron tri-oxide (B2O3) is capable of improving fluidity of slag even at 25.4 weight % slag aluminawithout any process instability when addedalong with burden mixture viaeither top charging through chute or injection through tuyeres.The quantity of boron oxide is determined in the burden mixture depending upon the target chemistry in the slag and other operational parameters such as alumina content in iron ore, level of fluidity desired etc. Boron trioxide (B2O3) is sourced from Colemanite (Ca2B6O11.5H2O) mineral containing boron trioxide (B2O3) or any other suitable mineral containing boron oxide.
In an embodiment of the invention, boron tri-oxide (B2O3) is introduced in the burden through sinter.
In another embodiment of the current invention boron tri-oxide (B2O3) is introduced in the burden through pellet.
In a separate embodiment of the current invention, boron tri-oxide (B2O3) is introduced in the burden as B2O3type flux.

In another embodiment of the invention boron tri-oxide is introduced through tuyeres in form of powdered boron tri-oxide (B2O3) type flux with blowing gas.
In another embodiment of the invention, predetermined quantity of boron tri-oxide can be introduced in blast furnace via a combination of methods as described above in various embodiments i.e. either charging via top chute or injection through tuyeres at bottom of the furnace
Thus, the present invention provides a method of maintaining the fluidity of slag at high alumina (20 – 25.4 weight %).The present invention is directed to a method of charging sinter containing boron tri-oxide (B2O3) along with pellet and sized lump ore, wherein alternate charging of iron bearing material and coke is done through the chute on top of the blast furnace. Iron agglomerates are in the proportion of 60 – 100 weight % along with 0 – 40weight % sized lump ore. 25 to 35 kg/ton of hot metal of nut coke (dry basis) of size 8 to 34 mm is charged along with iron bearing material.60 to 75 kg/ton of hot metal of centre coke (dry basis) of size 60 to 80 mm is charged in the centre region of the furnace, whereas 270 to 340 kg/ton of hot metal of surface coke (dry basis) of size 34 to 60 mm is charged in the intermediate and peripheral regions of the furnace.Burden basicity (ratio of weight % Calcium Oxide and Silicon di-oxide) is adjusted in such a way that no flux addition isrequired to achieve target of high alumina (20- 25.4 weight %) in slag.
The chemistry of iron bearing material which includes sinter, pellet and sized lump oreincludes at least 55 weight % total iron content;Ferrous oxide (FeO) less than 15 weight %;0.15 to 1 weight % boron trioxide (B2O3);Calcium oxide (CaO ) less than 14 weight %;2 to 8 weight % silicon dioxide (SiO2);1.5 to 3 weight % aluminium oxide (Al2O3); andMagnesium oxide (MgO) less than 3 weight %.
In an embodiment of the invention, the iron bearing material includes 0.15 to 0.3 weight % boron trioxide (B2O3);Calcium oxide (CaO) less than 6.0 weight %; 2 to 4 weight % silicon dioxide (SiO2); andMagnesium oxide (MgO) less than 2 weight %.
120 to 170 kg/ton of hot metal of pulverized coal is injected through tuyeresat the bottom of the furnace of which at least 87 % of the coal is below the size of 75 mm. Wet blast enriched with oxygen is blown in the range of 960 to 1300 Nm3/ton of hot metal at temperature of 1080 to 1170 oC through the tuyeres. Wet blast is having humidity at most75 g/Nm3of dry blast volume, and oxygen at most 29 % of dry blast.With these conditions, raceway adiabatic flame temperature is maintained in the range of 2000 to 2250oC.The pressure across the furnace is obtained in the range of 1.3 to 1.6barg.
With these burden composition and operating conditions, molten metal and slag are produced at hot metal temperature of 1480 to 1520oC. Slag is drained through tapping hole with 20– 25.4 weight % alumina in presence of boron tri-oxide 0.2 – 1.5 weight %.

The process of the current invention ensures significant fluidity and lower liquidus temperature of slag and enable the blast furnace operation with high slag alumina (20 – 25.4weight %). With concentrating slag alumina from 18.7to 25.4 wt. %, slag rate drops from 298 to 215 kg/ton of hot metal.The productivity is in the range of 2.2 to 2.6 ton of hot metal/day/m3 of working volume of blast furnace, while the utilization of exit gas is in the range of 45 to 53 %; exit gas comprisesof H2in the range of 2 to 5 volume % in dry basis and N246 to 53 volume % in dry basis at temperature in the range of 80 to 151oC.
The examples mentioned below demonstrate the present invention.
Examples 1 to 5 mentioned in table 1,2,3 and 4 describe the input, operating parameters and output of the blast furnace. Example 1 describes the blast furnace iron-making process as per the on-going practice and examples 2 to 5 describe the process as per the current invention.
Example 1: 39 weight % sinter which contains no boron tri-oxide with 40 weight % pellet and 21 % sized lump ore is charged onto top of the blast furnace. The overall chemistry of the iron bearing burden as well as the physico-chemical properties of sinter and pellet are also described in Table 1. 406 kg/ton of hot metal of coke and 144 kg/ton of hot metal of coal are used as a fuel in the blast furnace. The physico-chemical properties of coal and coke are described in Table 2. Coke is charged with alternate layers of iron bearing material onto top of the furnace whereas coal is injected through the tuyeres at the bottom of the furnace. 1105 Nm3/ton of hot metal of wet blast which includes 43 g/Nm3 of dry blast of humidity and 26.9 % O2(dry basis, includes O2 and N2) is blown through the tuyeres at the bottom of the blast furnace at temperature of 1149 oC. With this tuyere condition, RAFT is maintained at 2199 oC. The pressure difference across the furnace is obtained 1.4 barg. The productivity of the furnace is obtained 2.3 ton of hot metal/day/m3 of working volume. The utilization of exit gas is 49.7 %, and exit gas also comprises of 3.4 volume % H2and 50 volume % N2 andthe temperature of exit gas is 80oC.The slag rate is 298 kg/ton of hot metal at 1497 oC hot metal temperature. The slag contains 18.7 weight % alumina ( Al2O3), 8.4 weight % magnesium oxide ( MgO) with 1.1 basicity ( ratio of weight % of calcium oxide and silicon di-oxide ). At this condition, liquidus temperature of slag is 1399 oC and viscosity of slagis505centipoise at 1400 oC.
Example 2 to Example 5: 41 – 42 weight %sinter which contains 0.4 to 0.7 weight % boron tri-oxide (B2O3) with 41 to 45 weight % pellet and 13 to 17 weight % sized lump ore are charged onto top of the blast furnace. The overall chemistry of the iron bearing burden as well as the physico-chemical properties of sinter and pellet are also described in Table 1. 398 to 415 kg/ton of hot metal of coke and 157 to 164 kg/ton of hot metal of coal are used as a fuel in blast furnace. The physico-chemical properties of coal and coke are described in Table 2. Coke is charged with alternate layers of iron bearing material onto top of the furnace whereas coal is injected through the tuyeres at the bottom of the furnace. 1021 to 1112 Nm3/ton of hot metal of wet blast which includes 35 to 70 g/Nm3 of dry blast of humidity and 27.1 to 27.4 % O2 (dry basis, includes O2 and N2) is blown through the tuyeres at the bottom

of the blast furnace at temperature range of 1132 to 1150 oC.The pressure difference across the furnace is obtained in the range of 1.4 to 1.6 barg. The productivity of the furnace is obtained in the range of 2.3 to 2.4 ton of hot metal/day/m3 of working volume. The utilization of exit gas is in the range of 46.2 to 47.4 %, and exit gas also comprises of 3.3 to 4.4 volume % H2 and 47.2 to 48.0 volume % N2 and the temperature of exit gas is in the range 91 to 158oC.The stability of the process after addition of boron tri-oxide (B2O3) is confirmed as no significant changes are observed in fuel rate such as coke and coal rate and operating parameters such as wet blast rate, O2 % in dry blast, blast temperature and raceway adiabatic flame temperature (RAFT).The stability of the process is further confirmedas the productivity remains same and pressure difference across the furnace, utilization of CO, top gas temperature and hot metal temperature are within the band of control limit. The slag rate drops from 262 kg/ton of hot metal to 228 kg/ton of hot metal as alumina in slag increases from 20.2 % to 23.8 %. Slag contains 8.5 to 9.2 weight % magnesium oxide with 1.0 to 1.1 basicity (ratio of weight % of calcium oxide and silicon di-oxide). With this condition, liquidus temperature of slag decreases from 1379 oC to 1336 oC when boron tri-oxide increases from 0.23 to 0.83 wt. %. Viscosity of slag is in the range of 551to 659centipoise at 1400 oC in presence of 0.23 to 0.83 weight % boron tri-oxide in slag.
The examples 2 to example 5 clearly demonstrate that Slag rate drops from 298 kg/ton of hot metal to 228 kg/ton of hot metal as slag alumina concentrates from 18.7 wt. % to 23.8 wt. %. Slag was drained at high slag alumina in presence of 0.23 to 0.83 weight %boron tri-oxide as shown in figure 1.
Further, it is clear from table 4 and figure 2 that liquidus temperature drops from 1399 oC to 1336 oC, as boron tri-oxide in slag increase to 0.83 weight % even though slag alumina concentrates from 18.7 weight % to 21.9 weight %. However in case of example 5(23.8 wt. % Al2O3 and 0.74 wt. % B2O3) as mentioned in table 4, the liquidus temperature is 1369 oC which is 33 oC more than that of example 4 (21.9 wt. % Al2O3 and 0.83 wt. % B2O3). This is due to the drop of boron tri-oxide in slag from 0.83 % to 0.74 %.
Figure 3 shows that how viscosity of slag changes with increase in slag alumina and slag boron tri-oxide. The viscosity of slag is evaluated at 1400 oCas there is sudden drops in slag temperature around 100-150 oC when it comes to runner from blast furnace. The results are shown in table 4. When boron tri-oxide (B2O3) in slag is increased upto 0.83 weight %, the viscosity of slag is lower than the upper limit (700 centipoise at 1400 oC)of viscosity even in case of 23.8 % slag alumina permitting slag to be drained with significant fluidity.

WE CLAIM:
1. A process for operating an iron-making blast furnace with high alumina slag(>20weight
%), the process comprising:
charging iron bearing material with a predetermined quantity of boron tri-oxide (B2O3) in the blast furnace.
2. The process as claimed in claim 1, wherein the iron bearing material is selected from the forms consisting of sinter, pellet, sized lump ore and a combination thereof.
3. The process as claimed in claim 1, wherein the iron bearing material comprises:
at least 55 weight % total iron (Fe) content; Ferrous oxide ( FeO ) less than 15 weight %; 0.15 to 1 weight % boron trioxide (B2O3); Calcium oxide (CaO) less than 14 weight %; 2 to 8 weight % silicon dioxide (SiO2); 1.5 to 3 weight % aluminium oxide (Al2O3); and Magnesium oxide (MgO) less than 3 weight %.
4. The process as claimed in claim 3, wherein the iron bearing material preferably
comprises:
Calcium oxide (CaO) less than 6.0 weight %; 2 to 4 weight % silicon dioxide (SiO2); and Magnesium oxide (MgO) less than 2 weight %.
5. The process as claimed in claim 1, wherein iron bearing material comprises 60 to 100 weight % of iron ore agglomerates.
6. The process as claimed in claim 1, wherein the predetermined quantity of boron trioxide (B2O3) in iron bearing material is determined based upon percentage of alumina in the slag.
7. The process as claimed in claim 1, wherein the slag comprise alumina ( Al2O3) in the range of 20 to 25.4 weight %, boron tri-oxide (B2O3) in the range of 0.2 to 1.5 weight %, magnesium oxide ( MgO) in the range of 7 to 10 weight %.

8. The process as claimed in claim 1, wherein the process results in producing slag with basicity (ratio of weight % calcium oxide and silicon di-oxide) in the range of 1 to 1.1.
9. The process as claimed in claim 7, wherein the alumina content in the slag preferably varies in the range of 21 – 23.8 weight %.
10. The process as claimed in claim 1, wherein boron trioxide ( B2O3) in burden varies in the range of 0.15 to 1 weight %, preferably in the range of 0.2 to 0.5 weight %.
11. The process as claimed in claim 1, wherein, boron trioxide (B2O3) is added to the burden mixture through sinter.
12. The process as claimed in claim 1 further comprises addition of boron trioxide (B2O3) in the blast furnace either via top charging through chute or via injection through tuyeres at the bottom of the furnace.
13. The process as claimed in claim 1, wherein boron trioxide (B2O3) is added in the burden mixture through sinter, pellet and direct flux addition.
14. The process as claimed in claim 12, wherein flux powder containing boron trioxide (B2O3) is injected through tuyeres with blowing gas.
15. The process as claimed in claim 1, wherein boron trioxide (B2O3) is preferably sourced
from Colemanite (Ca2B6O11.5H2O) mineral containing boron trioxide (B2O3).
16. The method as claimed in one or more of the preceding claims, wherein slag rate drops from 298 kg/ton of hot metal to 215 kg/ton of hot metal when alumina in slag is increased from 18.7 to 25.4 weight %.
17. The method as claimed in one or more of the preceding claims, wherein liquidus temperature of slag drops at least by 30 deg C in presence of 0.2-1.5 weight % of boron tri-oxide in slag even though slag alumina increases from 18.7 to 25.4 weight %.
18. The method as claimed in 1 and one or more of the preceding claims, wherein viscosity of slag is maintained below 700 centipoise at 1400 deg C in presence of 0.2-1.5 weight % of boron tri-oxide in slag even though slag alumina increases from 18.7 to 25.4 weight %.

19. The method as claimed in one or more of the preceding claims further maintaining the
blast furnace operating parameters:
a. blast volume ( wet and O2 enriched ) blown through tuyeres at the bottom of
furnace in the range of 960 to 1300 Nm3/ton of hot metal;
b. oxygen of blast at most 29 % of dry blast volume;
c. humidity of blast at most 75 g/Nm3 of dry blast volume;
d. blast temperature in the range of 1080 to 1170 oC; and
e. raceway adiabatic flame temperature (RAFT) in the range of 2000 to 2250 oC
20. The method as claimed in 1 one or more of the preceding claims, wherein, fuel for use in the blast furnace comprises of coke and pulverized coal.
21. The fuel as claimed in claim 20, wherein coke comprises of surface coke, centre coke and nut coke.
22. The fuel as claimed in claim 21, wherein the size of surface coke, centre coke and nut coke are in the range of 34 mm to 60 mm, 60 mm to 80 mm and 8 mm to 34 mm.
23. The method as claimed in one or more of the preceding claims, wherein coke used as a fuel is in the range of 64 to 81 weight % of total fuel in dry basis which includes nut coke in the range of 4 to 8 weight % of total fuel in dry basis, centre coke in the range of 9 to 16 weight % of total fuel in dry basis and surface coke in the range of 43 to 72 weight % of total fuel in dry basis.
24. The method as claimed in one or more of the preceding claims, wherein coal used as a fuel is in the range of 19 to 36 weight % of total fuel in dry basis.
25. The method as claimed in one or more of the preceding claims, wherein pressure difference across the blast furnace is in the range 1.3 to 1.6barg.
26. The method as claimed in one or more of the preceding claims, wherein productivity of the blast furnace is in the range of 2.2 to 2.6 ton of hot metal/day/m3 of working volume.
27. The method as claimed in one or more of the preceding claims, wherein carbon monoxide (CO) utilization of top gas is in the range of 45 to 53 %.

28. The method as claimed in one or more of the preceding claims, wherein hydrogen (H2) and nitrogen (N2) of top gas are in the range of 2 to 5 volume % of dry gas and 46 to 53 volume % of dry gas respectively.
29. The method as claimed in one or more of the preceding claims, wherein temperature of top gas is in the range of 80 to 151 °C.
30. The method as claimed in one or more of the preceding claims, wherein hot metal temperature is in the range of 1480 to 1520 °C.