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 FLUX COMPOSITION AND A METHOD OF FOAMING THE LADLE TOP SLAG USING SAID FLUX IN REDUCING CONDITION AT LADLE REFINING FURNACE FOR SILICON KILLED STEEL MELT.



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 method of imparting foamability of the ladle top slag involving a flux composition for foaming ladle top slag in reducing condition at ladle refining process. During the process, the foaming slag protects the graphite electrodes from wear and covers the arcs. This allows for a higher productivity in the furnace, since it increases the heat transfer between electrode and the molten metal. It also reduces radiation losses, since the slag isolates the arc beams. This in turn protects the refractories from wear, which reduces the amount of down-time for maintenance work. The foaming slag also contributes to stabilization of the arc, ensuring a higher efficiency. In addition to this, the foam helps to reduce noise from the LF, which provides a better working environment. Another advantage with foaming slag is the reduction of power and voltage fluctuations.

BACKGROUND OF THE INVENTION:
Ladle top slag performs many vital functions in Secondary Steelmaking operation like protection of bath from atmospheric re-oxidation & nitrogen pickup, absorption/assimilating of deoxidation products and inclusions, desulphurisation, smooth arcing operation etc. Covering the electrode arc in ladle furnace and protecting the slag zone refractories from arc-flare is a very important function which is required from ladle top slag.
Poorly designed slag will be inert towards slag metal reactions and hence will do nothing to improve the quality of the steel. It will be incompatible with the refractory lining and will dissolve the refractories very fast. A "bad" ladle slag contain a large proportion of reducible oxides (FeO and MnO) that will react with the steel to cause Al, Si, and Mn fading.
The fluidity of the ladle top slag is also an important property. A good slag for the metallurgical practice should have a high fluidity (low viscosity), whereas, a good slag in terms of refractory wear should have a low fluidity (high viscosity) to insure minimum penetration and reaction, and good coating formation. To achieve both the requirements i.e., a slag that is still fluid enough to refine the metal but not to fluid to cause accelerated wear on the refractory, i.e., slags with a "creamy" in nature is considered good for secondary metallurgical operation.
However, in case of Si killed steel, too low basicity (CaO/SiO2 <1.2) results in excessive thinning of ladle top slag whereas too high basicity (CaO/SiO2 >1.8) results in crusty ladle top slag formation. Both the conditions are not desired for the smooth functioning of ladle furnace. In such cases, arcing at bare bath leads to higher power consumption (inconsistent heating rate), high noise level during arcing and damage to ladle slag zone lining.
In clean steelmaking process ladle furnace (LF) is the most important secondary refining device for controlling steel temperature and purity. The main purpose of LF refining is to form high basicity and reducing refining slag for desulfurization and non-metallic inclusions absorption. In practical industrial production process, low heating rate induce long refining cycle, high electrical energy consumption and low productivity.
In LF, heat is supplied by the radiation of the arcs. During heating process unavoidable energy losses (internal energy loss) induced by transformation of electric energy to heat energy and heat transfer from higher temperature zone (arc) to lower temperature zone (molten steel and slag), ladle wall heat transfer process, chemical reaction and alloys dissolution. The overall energy loss in the LF is around 13-15%. Slag foaming for submerged arc heating can significantly improve the efficiency of electric energy conversion, increase heating rate and is in favour of enhancing refining effect.
Slag engineering (i.e. conditioning and foaming practices) is becoming an essential issue due to the increasing demand by the end-users to cut costs and produce high quality steel. Slag foaming has been mainly used in electric arc furnaces (EAF) in order to protect the refractory materials from the high energy intensity (radiation) generated by electrodes, decrease the noise level, improve productivity and the energy efficiency of this equipment.
Slag foaming has an important impact on the thermal efficiency, refractory lining/electrodes consumption of EAF. Additionally, among the various techniques used to save energy in EAF (i.e., bath agitation, preheating of the scrap and/or solid pig iron used as cold charge, use of compressed air systems and others), the slag foaming process is seen to be the most efficient one.
Covering the electrode arc in ladle furnace and protecting the slag zone refractories from arc-flare is a very important function which is required from ladle top slag . However, in case of Si killed steel, too low basicity results in excessive thinning of ladle top slag whereas too high basicity results in crusty ladle top slag formation. Both the conditions are not desired for the smooth functioning of ladle furnace. In such cases, arcing at bare bath leads to higher power consumption (inconsistent heating rate), high noise level during arcing and damage to ladle slag zone lining.
At present, technology of foaming slag has been applied widely during oxidizing period of EAF, but its advantages are not fully utilized during reducing period of EAF and refining process in LF. In the current work foamy slag practice in ladle furnace (LF) for silicon killed steel was developed using an innovative flux mixture of limestone chips and coke breeze. The flux mixture was prepared in-house. The flux mixture produces a thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories.

OBJECTIVES OF THE INVENTION:
The basic object of the present invention is directed to a method for inducing certain foamability of the top slags involving a flux composition for foaming ladle top slag in ladle refining process of silicon killed steel under reducing condition in Ladle Furnace to achieve various operational advantages.
A further object of the invention is directed to said process wherein the foaming slag protects the graphite electrodes from wear and covers the arcs. This allows for a higher productivity in the furnace, since it increases the heat transfer between electrode and the molten metal. It also reduces radiation losses, since the slag isolates the arc beams. This in turn protects the refractories from wear, which reduces the amount of down-time for maintenance work.
Yet another object of the present invention is directed to said process wherein said foaming slag also contributes to stabilization of the arc, ensuring a higher efficiency. In addition to this, the foam helps to reduce noise from the LF, which provides a better working environment.
A still further object of the present invention is directed to said process wherein said foaming slag favour reduction of power and voltage fluctuations during refining process in LF.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a flux composition for foaming ladle top slag in a ladle furnace comprising :

calcium carbonate of in a range of 70-85% and coke breeze in the range of 30-15% as source of carbon favouring generation of CaO which is thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories.

A further aspect of the present invention is directed to said flux composition wherein said calcium carbonate is having particle size in the range of 5 mm to 15 mm and said coke breeze is having particle size in the range of 1 mm to 5 mm and having metallurgical properties including low moisture (< 5 %).

A still further aspect of the present invention is directed to said flux composition which is adapted to reduce noise levels upon addition during arcing in LFs.

A further aspect of the present invention is directed to a method of foaming the ladle top slag at ladle refining furnace for silicone killed steel melts comprising:
step of foaming the ladle top slag generated in a basic oxygen furnace -ladle furnace route of steelmaking for producing silicone killed steel comprising :
adding a flux composition comprising calcium carbonate in a range of 70-85% and coke breeze in the range of 30-15% as source of carbon such as to advance the fluidity of the top slag in a silicon killed steel melt at higher basicity (CaO/SiO2 > 1.5).

A further aspect of the present invention is directed to said method as claimed in claim 4 wherein said calcium carbonate is having particle size in the range of 5 mm to 15mm and said coke breeze is having particle size in the range of 1 mm to 5mm and having metallurgical properties including low moisture (< 5 %).

A still further aspect of the present invention is directed to said method wherein said foamy slag thus generated is provided to cover the generated arc between metal and electrode and absorb noise and thus attain significant reduction in noise levels during arcing in ladle furnaces.

A still further aspect of the present invention is directed to said method as claimed in anyone of claims 4 to 6 wherein said advancement in ladle top slag fluidity is achieved at higher basicity (CaO/SiO2 > 1.5) in silicon killed steel melts with said flux composition . and also due to in situ calcination of limestone chips and its dissolution in ladle top slag. In silicon killed steels dissolution of CaO into slag at higher basicity and whereby also the melting point of slag increases due to the presence of un-dissolved lime in the slag free of altering any slag chemistry.

Another aspect of the present invention is directed to said method which enabled reducing of the noise level during arcing by 10 to 20% preferably about 14% after the flux composition addition during arcing in ladle furnaces due to the induced foaminess in the slag and also reduction in power consumption in ladle furnace by 5% with involvement of said flux composition and wherein the improvement in steel De-Sulphurisation was attained by two fold without any bottom buildup in steel ladles and which generated a smooth thin coating of slag layer on refractory lining in ladles with said flux composition addition.

Yet another aspect of the present invention is directed to said method wherein in each stage around 50 to 150 kg by wt of flux composition is added depending upon the condition of incoming ladle top slag.
In case of carryover slag from BOF converter to ladle in the range of 5-10 kg/tcs, 100 to 150 kg of flux composition can be added in each stage of arcing. If during the entire treatment duration, arcing is done in 3 stages, then in each stage of arcing 100-150 kg of flux should be added. It should be noted that the flux addition should only be carried out only during arcing. In case of heavy carryover slag from BOF to ladle, 50 kg of flux composition to be added in each stage of arcing in ladle furnace.
Above and other aspects 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 ACCOMPANYING DRAWINGS
Fig.1 (a-b) : shows Ladle top foamy slag conditions at the end of refining.
Fig 2: shows the clean ladle bottom after slag dumping when refining process with foamy slag is carried out.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
At present, technology of foaming slag has been applied widely during oxidizing period of EAF, but its advantages are not fully utilised during reducing period of EAF and refining process in LF. Physical parameters of slag have an important influence on the slag foaming. In order to apply the technology of submerged arc slag during refining process, the refining slag should have appropriate physical parameters, such as viscosity, density and surface tension, etc.
There are basically two requirements for foaming namely (i) reactions or processes that generate small gas bubbles, and (ii) suitable slag properties to keep the bubbles as stable foam. Normally, gases resulting from chemical reactions tend to foam the slag with smaller bubbles, whereas the injection of gas phases (oxygen, argon, etc.) results in larger bubbles and less stable foams.
The present invention is developed and implemented in Applicant’s Steel Melting Shop at ladle furnaces (LFs) to use the various advantages of foamy slag in reducing environment for silicon killed steels having lower basicity (CaO/SiO2 - 1.4-1.8). In some steel plants, researchers have tried to build foaminess in the ladle top slag using combination of costly synthetic slags and calcium carbides. Most of the prior work on improving the ladle top slag foaminess under reducing condition has been done with high basicity slags (CaO/SiO2> 3).
An innovative flux mixture was conceptualized having calcium carbonate and coke breeze in a proportion of 4:1. Since the FeO+MnO level in ladle top slag at steel melting shop was in the range of 5-8%, the coke added in the mixture effectively trim down the level of these easily reducible oxides. The gases released as a result of reduction further facilitate the foaming of slag. Addition of small size of limestone chips helped in in-situ calcination of lime stone under very high temperature of arc. The gases released during the calcination process further lead to increase in the foaminess of slag.
In the current work foamy slag practice in ladle furnace for silicon killed steel was developed using in-house developed innovative flux mixture of limestone chips and coke breeze. The flux mixture produces a thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories. Effects of addition of mixture in LF was evaluated on the basis of power consumption, De-Sulphurisation, slag oxygen potential, top slag’s fluidity and noise level during arcing. The addition of flux was carried out in stages during arcing in ladle furnaces. In each stage around 100-150 kg of developed mixture was added depending upon the condition of incoming ladle top slag. In case of carryover slag from BOF converter to ladle is in range of 5-10 kg/tcs, 100 to 150 kg of flux composition can be added in each stage of arcing. If during the entire treatment duration, arcing is done in 3 stages, then in each stage of arcing 100-150 kg of flux should be added. It should be noted that the flux addition should only be carried out only during arcing. In case of heavy carryover slag from BOF to ladle , 50 kg of flux composition to be added in each stage of arcing in ladle furnace.
Noise levels were considerably reduced by 14% after the flux mixture addition during arcing in ladle furnaces due to the induced foaminess in the slag. Improvement was seen in power consumption by 5% (185 KWh/min of arcing from 194 KWh/min of arcing). An improvement in steel De-Sulphurisation was observed by ~8 points (0.008%) in most of the heats (avg. LF 1st -0.035%, Tundish – 0.027%).
The fluidity of ladle top slag was improved due to better dissolution of CaO in the ladle top slag as shown in accompanying Fig.1 –a & b. The ladle lining condition was also observed after continuous casting and slag dumping. No bottom and top jam was seen in ladles as shown in accompanying Fig 2. Also, a smooth thin coating of slag layer on refractory lining was observed in ladles with flux mixture addition.
The developed flux mixture was found to be very beneficial in improving the foaming property of ladle top slag under reducing conditions. The flux mixture was prepared using low cost in house resources and several benefits were obtained when it was partially or completely used in place of calcined lime in ladle furnace.
The main purpose of LF refining is to form high basicity and reducing refining slag for desulfurization and non-metallic inclusions absorption. Instability in the arcing process can lead to low heating rate inducing long refining cycle, high electrical energy consumption and low productivity.
Slag foaming for submerged arc heating can significantly improves the efficiency of electric energy conversion, increases heating rate and is in favour of enhancing refining effect.
In the current work foamy slag practice in ladle furnace for silicon killed steel was developed using in-house developed innovative flux mixture of limestone chips and coke breeze. The flux mixture produces a thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories.
Noise levels were considerably reduced after the flux mixture addition during arcing in ladle furnaces due to the induced foaminess in the slag. Improvement was seen in power consumption as well as in steel desulphurisation. The fluidity of ladle top slag was improved due to better dissolution of CaO in the ladle top slag. The ladle lining condition was also observed after continuous casting and slag dumping. No bottom and top jam was seen in ladles. Also, a smooth thin coating of slag layer on refractory lining was observed in ladles with flux mixture addition (main benefits are presented in table 1 & table 2).
Table 1: Benefits of innovative flux addition in Ladle Furnace
Power Cons. (KWh/t) Noise Level (@MCR)
dBA Avg.
Slag Basicity FeO+MnO
(%) Slag Viscosity
@1575°C
Pa.S
Conventional 42.03 94 1.98 5.8 1.60
All Trials
(mix addition) 39.93 81 2.06 4.3 1.43
Table 2:Effect of Flux addition on De-Sulphurisation at SMS, DSP
Hot Metal Sulphur Ladle (LDL) Sulphur Tundish (TND) Sulphur LDL - TND %De-S
(Ldl-Tund)
Conventional 0.049 0.036 0.031 0.005 13.8
Heats with Flux Addition 0.048 0.035 0.026 0.009 25.7
The developed flux mixture was found to be very beneficial in improving the foaming property of ladle top slag under reducing conditions. The flux mixture was prepared using low cost in house resources and several benefits were obtained (as mentioned above) when it was partially or completely used in place of calcined lime in ladle furnace.
Usefulness of the Invention
Slag foaming for submerged arc heating can significantly improve the efficiency of electric energy conversion, increase heating rate and is in favour of enhancing refining effect. Slag foaming has an important impact on the thermal efficiency, refractory lining/electrodes consumption of EAF.
At present, technology of foaming slag has been applied widely during oxidizing period of EAF, but its advantages are not fully utilised during reducing period of EAF and refining process in LF. In the current work foamy slag practice in ladle furnace for silicon killed steel was developed using in-house developed innovative flux mixture of limestone chips and coke breeze. The flux mixture produces a thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories. Noise levels were considerably reduced after the flux mixture addition during arcing in LFs.
Industrial Applicability
The developed flux mixture was found to be very beneficial in improving the foaming property of ladle top slag under reducing conditions. The flux mixture was prepared using low cost in house resources and several benefits were obtained (as mentioned above) when it was partially or completely used in place of calcined lime in ladle furnace. The developed flux mixture and its addition technique can be used readily in any Steel Melting Shop making Silicon killed heats.

, Claims:We Claim:
1. A flux composition for foaming ladle top slag in a ladle furnace comprising :

calcium carbonate of in a range of 70-85% and coke breeze in the range of 30-15% as source of carbon favouring generation of CaO which is thermally insulating, fluid, basic, efficient slag with excellent metallurgical properties to maximize heating efficiency and protect ladle refractories.

2. The flux composition as claimed in claim 1 wherein said calcium carbonate is having particle size in the range of 5mm to 15mm and said coke breeze is having particle size in the range of 1mm to 3mm and having metallurgical properties including low moisture (< 5 %).
3. The flux composition as claimed in anyone of claims 1 or 2 which is adapted to reduce noise levels upon addition during arcing in LFs.
4. A method of foaming the ladle top slag at ladle refining furnace for silicone killed steel melts comprising:
step of foaming the ladle top slag generated in a basic oxygen furnace -ladle furnace route of steelmaking for producing silicone killed steel comprising :
adding a flux composition comprising calcium carbonate in a range of 70-85% and coke breeze in the range of 30-15% as source of carbon such as to advance the fluidity of the top slag in a silicon killed steel melt at higher basicity (CaO/SiO2 > 1.5).

5. The method as claimed in claim 4 wherein said calcium carbonate is having particle size in the range of 5mm to 15mm and said coke breeze is having particle size in the range of 1mm to 3mm and having metallurgical properties including low moisture (< 5 %).

6. The method as claimed in anyone of claims 4 or 5 wherein said foamy slag thus generated is provided to cover the generated arc between metal and electrode and absorb noise and thus attain significant reduction in noise levels during arcing in ladle furnaces.

7. The method as claimed in anyone of claims 4 to 6 wherein said advancement in ladle top slag fluidity is achieved at higher basicity (CaO/SiO2 > 1.5) in silicon killed steel melts with said flux composition . and also due to in situ calcination of limestone chips and its dissolution in ladle top slag. In silicon killed steels dissolution of CaO into slag at higher basicity and whereby also the melting point of slag increases due to the presence of un-dissolved lime in the slag free of altering any slag chemistry.

8. The method as claimed in anyone of claims 4 to 7 which enabled reducing of the noise level during arcing by 10 to 20% preferably about 14% after the flux composition addition during arcing in ladle furnaces due to the induced foaminess in the slag and also reduction in power consumption in ladle furnace by 5% with involvement of said flux composition and wherein the improvement in steel De-Sulphurisation was attained by two fold without any bottom buildup in steel ladles and which generated a smooth thin coating of slag layer on refractory lining in ladles with said flux composition addition.

9. The method as claimed in anyone of claims 4 to 8 wherein in each stage around 50 kg to 150 kg by wt of flux composition is added depending upon the condition of incoming ladle top slag, wherein addition of flux is carried out in stages during arcing in ladle furnaces, so that in each stage around 100-150 kg of developed flux mixture is added depending upon the condition of incoming ladle top slag and in case of carryover slag from BOF converter to ladle in the range of 5-10 kg/tcs, 100 to 150 kg of flux composition is added in each stage of arcing, and for the entire treatment duration, if arcing is done in 3 stages, then 100-150 kg of flux is added in each stage only during arcing, whereas in case of heavy carryover slag from BOF to ladle, 50 kg of flux composition is added in each stage of arcing in ladle furnace.

Dated this the 28th day of February, 2023
Anjan Sen
Of Anjan Sen & Associates
( Applicant’s Agent)
IN/PA-199