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 CONTINUOUS DE-SILICONIZATION AND DE-SULPHURIZATION OF HOT METAL.
2 APPLICANT (S)
Name : JSW STEEL LIMITED.
Nationality : An Indian Company.
Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg, Mumbai - 400 026,
State of Maharastra, 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 process for desiliconisation and de-sulphurisation of hot metal in a single step in transfer ladles. More particularly, the present invention is directed to de-siliconization and de-sulphurisation of the hot metal in transfer ladle in a single step process at Hot metal pre-treatment station in terms of electrochemistry of molten slag and molten metal system and the concept of mixed potential at the slag metal interface. The developed process does not require intermediate de-slagging and results in a lower temperature drop and has significantly improved the logistics and helped in optimizing the input hot metal characteristics for primary steelmaking.
BACK GROUND OF THE INVENTION
Hot metal from iron making units such as blast furnace contains silicon and sulphur as primary impurities and varies significantly from unit to unit and ladle to ladle. These impurities need to be removed during the steel making process. In modern steel making process, hot metal from blast furnace is pre-treated for silicon at hot metal pre-treatment station (HMPT) in transfer ladles. This de-siliconised hot metal is de-sulphurised separately at hot metal de-sulphurisation station (HMDS) before charging into converter for final steel making process. De-siliconisation is an oxidation reaction and de-sulphurisatiion is a reduction reaction. Hence these are conventionally carried out in two stages at two different stations. De-Siliconisation is carried out using lime fines and sinter fines in a two lance process, whereas De-Sulphurisation is done using calcium carbide using a single lance. The ladles are de-slagged after each treatment step. These processes help in maintaining consistent hot metal chemistry for charging in the LD converter.
In the two step process, hot metal ladle is first de-siliconised at HMPT followed by slag raking - a process of draining off the impurities floated off in the form of slag, The ladle is further treated at HMDS for De-Sulphurisation again followed by slag raking. The two step pre-treatment improves steelmaking process but consumes significant time and results in significant temperature drop and metal loss. Total treatment time is 75 mins and temperature drop is >70°C which is not desirable for subsequent steelmaking processes.

There has been therefore a need in the art to developing a process to reduce the hot metal pretreatment time, avoid repeated slag raking steps and subsequent temperature and metal loss. A new and improved process is proposed by way of the present invention involving single step De-Siliconisation and De-Sulphurization process carried out at HMPT where by treatment time can be reduced with single slag raking step and less temperature drop favouring achieving consistent input hot metal quality for steel making in a faster and reliable manner.
OBJECTS OF THE INVENTION '
The basic object of the present invention is thus directed to providing a process for selective de-siliconization and de-sulphurisation of the hot metal in transfer ladle in a single step process at Hot metal pre-treatment station.
A further object of the present invention is directed to a single step process for de-siliconization and de-sulphurisation of the hot metal in transfer ladle which would favour reducing the total hot metal treatment time before steel making.
A still further object of the present invention is directed to a single step process for de-siliconization and de-sulphurisation of the hot metal in transfer ladle wherein 1st stage de-siliconisation carried out using lime fines, sinter fines and oxygen in a two lance process followed by de-sulphurization using lime fines through a single central lance in a continuous process in the same ladle and same HMPT station.
A still further object of the present invention is directed to a single step process for de-siliconization and de-sulphurisation of the hot metal in transfer ladle wherein two slag raking steps reduced to one.
A still further object of the present invention is directed to a single step process for de-siliconization and de-sulphurisation of the hot metal in transfer ladle wherein treatment time is reduced significantly.
A still further object of the present invention is directed to a single step process for de-siliconization and de-sulphurisation of the hot metal in transfer ladle wherein drop in hot metal temperature is substantially lower compared to conventional two step process.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a process for continuous de-siliconization and de-sulphurization of hot metal comprising:
subjecting the molten metal to simultaneous or single Step de-siliconization and de-sulphurisation in one step pre-treatment in same transfer ladle without requiring any intermediate de-slagging wherein initially the treatment of molten metal was carried out involving lime fines , sinter fines and oxygen followed by treatment with only lime fines.
A further aspect of the present invention is directed to said process for de-siliconization and de-sulphurization of hot metal wherein said one-step pre-treatment comprises an initial de-siliconization and partial de-sulphurization followed by remaining de-sulphurization.
A still further aspect of the present invention is directed to a process for de-siliconization and de-sulphurization of hot metal comprising a first stage of desiliconization carried out involving lime fines, sinter fines and oxygen involving two lance and second stage of de-sulphurization is carried out using only lime fines involving a single central lance.
A further aspect of the present invention is directed to said process for continuous de-siliconization and de-sulphurization of hot metal wherein said simultaneous or single step de-siliconization and de-sulphurisation is controlled such as to generate slag formed during the process having basicity (CaO/Si02) between 0.95 to 1.2 and preferably ~1.1 with the Si02 in the range of 30 to 40% and preferably 35%,CaO in the range of 35 to 45% and preferably 40%,Fe2O3 in the range of 2 to 5 % and preferably 3 % and Sulphur in the range of 0.2 to 0.3 % and preferably 0.25 %.
A still further aspect of the present invention is directed to said process for de-siliconization and de-sulphurization of hot metal comprising enhancing the transitory reaction of lime powder and controlling the slag composition to high sulphur capacity of 0.2 to 0.25 wt %.

A still further aspect of the present invention is directed to said process for de-siliconization and de-su!phurization of hot metal wherein said pre-treatment of molten metal for de-siliconization and de-sulphurization is completed in reduced time of 45 minutes from convectional process time of 75 minutes.
Yet another aspect of the present invention is directed to said process for de-siliconization and de-sulphurization of hot metal wherein the loss of temperature of said pre-treatment of molten metal for de-siliconization and de-sulphurization is reduced to a range of 30 to 40°C preferably about 30°C.
A still further aspect of the present invention is directed to said process for de-siliconization and de-sulphurization of hot metal comprising a process beginning with injection of lime fines through the immersed central lance at a rate of 35 kg/min to 45 Kg/min and preferably about 40 Kg/min followed by sinter fines addition in parallel operation through top chute starting 3 mins after the start of lime fines injection at a rate of about 145 kg/min to 170 kg/min preferably about 160 kg/min. for a period of next 12 mins, further followed by blowing of oxygen through top lance at a rate of 30 to 45 Nm3 preferably about 35 Nm3/min for a period of next 12 mins after the end of sinter fines addition.
Key aspect of the present invention is the continuation of lime fines injection through central immersed lance during sinter fines addition and oxygen blowing and for further next 15 mins after the termination of oxygen blowing for de-sulphurisation.
Advantageously, in said process for de-siliconization and de-sulphurization of hot metal , change in Silicon achieved is 0.5 wt% and change in Sulphur is 0.04 wt%.
Also said process for de-siliconization and de-sulphurization of hot metal comprises post pre-treatment carrying out single slag raking step,
The various other objects and advantages are described in greater details with reference to the following non limiting illustrative drawing.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 : is a chart showing schematically the blowing and addition pattern of the desiliconisation and desulphurization of hot metal in a single step process in transfer ladle.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWING
The present invention is directed to selectively de-siliconize and de-sulphurise the hot metal in transfer ladle in a single step process at Hot metal pre-treatment station.
Direction of promotion of anodic reaction of Silicon and cathodic reaction of Sulphur being known to be opposite, simultaneous de-siliconisation and de-sulphurisation seems contradictory. In the present invention a single step process for desiliconisation and de-sulphurisation has been implemented in terms of electrochemistry of molten slag and molten metal system and the concept of mixed potential at the slag metal interface. It is also a fact that electrochemical reaction taking place at slag-metal interface is coupled to each other through principle of electro-neutrality. Single step desiliconisation and desulphurisation thus is realized by using a slag with an extremely high sulphide capacity under oxidizing condition. Additionally, the effect of silicon content on overall degree of desulphurization is not significant. Hence in a process with three reaction zones, two simultaneous reactions can be attempted. During the pre-treatment process, reactions take place at three different sites.
1. Interface between injected flux powders and metal (transitory reaction).
2. An interface between slag on bath surface (top slag) and metal ( permanent reaction ), and
3. An interface between top blown oxygen gas, top slag at hot spot region and metal (hot spot reaction).

The first reaction (transitory reaction) takes place between the injected lime fines and Silicon in the hot metal. Lime also acts as silicon carrier to the surface. Silicon carried to the top reacts with the oxygen (permanent reaction) in the sinter fines and removed into the slag. As the concentration of Silicon decreases, the reaction slows down. To maintain the same reaction kinetics, oxygen is blown from the top, in the later part. The reaction between top blown oxygen gas, top slag and metal (hot spot reaction) in the hot spot region, increases the kinetics of the reaction. Hence in the present work, Simultaneous or single step de-siliconisation and de-sulphurisation has been attempted by enhancing the transitory reaction of lime powder and controlling the slag composition The ratio of lime consumption (CaO, Kgs) to oxygen consumption (O, Kgs) has been taken as a governing parameter for De-Si and De-S reactions. This index highlighted the influence of supply of method of oxygen in De-Si reaction. De-S reaction is suppressed by addition of solid oxygen sources (Sinter fines) and enhanced by gaseous oxygen and hence the gaseous oxygen was increased and sinter fines addition was reduced. This increased the de-siliconisation reaction in the vicinity of the oxygen lance and de-sulphurisation at the lime injection lance. Taking above points in consideration, an operational procedure has been developed to remove silicon and sulphur in a single step process. The process includes 1st stage de-siliconisation using lime fines, sinter fines and oxygen in a two lance process followed by de-sulphurization using lime fines through a single central fance in a continuous process in the same fadfe and same HMPT station. The developed process does not require intermediate de-slagging and results in a lower temperature drop. The flexible single step de-siliconisation and de-sulphurization process has significantly improved the logistics and helped in optimizing the input hot metal characteristics for primary steelmaking.
Reference is now invited to the accompanying Figure 1 wherein a chart shows schematically the blowing and addition pattern of the desiliconisation and desulphurization of hot metal in a single step process in transfer ladle according to the present invention.
A blowing and addition pattern according to an embodiment of the present invention to selectively de-siliconize and de-sulphurise the hot metal in a single step process using sinter fines, oxygen blowing and lime fines in transfer ladle at hot metal pre-treatment station as illustrated in Figure 1 comprise:

Step 1 First de-slag the ladles as received from Iron Making
Step 2 Position the ladles at the appropriate place
Step 3 Measure the bath Height
Step 4 Measure the Temperature and Chemistry
Step 5 Insert the injection lance upto 250 mm from ladle bottom (blowing the inert gas)
Step 6 Start the lime fines injection ~40 kgs /min and will continue till the end
Step 7 After 3 mins of lime fines injection start adding sinter fines @ 160 kgs /min and continue for 15 mins.
Step 8 After 15 mins of operation lower the oxygen lance upto 1000 mm from measured bath level.
Step 9 Start oxygen blowing @ 35 Nm3/mm and continue for 12 mins
Step 10 After the removal of oxygen lance, (which ends the desiliconisation process) continue lime fines injection ~35 kgs /min (reduced injection rate for increased residence time) and continue for 15 mins
Step 11 Measure the Temperature and Chemistry
It is thus possible by way of the present invention to achieve the following advantages from the process of simultaneous desiliconisation and desulphurization of hot metal in a single step process in transfer ladle:
-Two slag raking steps reduced to one at the end of process;
-Total treatment time lasts for 45 minutes wherein complete desiliconisation and
partial desulphurization takes place first within about 25 minutes and rest of
desulphurization takes place in remaining 20 minutes.
-The process achieved a Change in Silicon of 0.5 wt% and a change in Sulphur of
0.04 wt% and drop in hot metal temperature limited to about 30°C.

We Claim:
1. A process for continuous de-siliconization and de-sulphurization of hot metal
comprising:
subjecting the molten metal to simultaneous or single step de-siliconization and de-sulphurisation in one step pre-treatment in same transfer ladle without requiring any intermediate de-slagging wherein initially the treatment of molten metal was carried out involving lime fines , sinter fines and oxygen followed by treatment with only lime fines.
2. A process for continuous de-siliconization and de-sulphurization of hot metal as claimed in claim 1 wherein said one-step pre-treatment comprises an initial de-siliconization and partial de-sulphurization followed by remaining de-sulphurization.
3. A process for continuous de-siticonization and de-sulphurization of hot metal as claimed in anyone of claim 1 or 2 comprising a first stage of desiliconization carried out involving lime fines , sinter fines and oxygen involving two lance and second stage of de-sulphurization is carried out involving only lime fines involving a single central lance.
4. A process for continuous de-siliconization and de-sulphurization of hot metal as claimed in anyone of claims 1 to 3 wherein said simultaneous or single step de-siliconization and de-sulphurisation is controlled such as to generate slag formed during the process having basicity (CaO/Si02) between 0.95 to 1.2 and preferably ~1.1 with the Si02 in the range of 30 to 40% and preferably 35%,CaO in the range of 35 to 45% and preferably 40%,Fe2O3 in the range of 2 to 5 % and preferably 3 % and Sulphur in the range of 0.2 to 0.3 % and preferably 0.25 %.
5. A process for continuous de-siliconization and de-sulphurization of hot metal as
claimed in anyone of claims 1 to 4 comprising enhancing the transitory reaction of
lime powder and controlling the slag composition to high the slag composition to high
sulphur capacity of 0.2 to 0.25 wt %.

6. A process for continuous de-siliconization and de-sulphurization of hot metal as claimed in anyone of claims 1 to 5 wherein said pre-treatment of molten metal for de-siliconization and de-sulphurization is completed in reduced time of 30 to 35 mins
7. A process for continuous de-siliconization and de-su|phurization of hot metal as claimed in anyone of claims 1 to 6 wherein the loss of temperature of said pre-treatment of molten metal for de-siliconization and de-sulphurization is reduced to a range of 30 to 40°C preferably about 30°C.
8. A process for continuous de-siliconization and de-sulphurization of hot metal as claimed in anyone of claims 1 to 7 comprising a process beginning with injection of lime fines through the immersed central lance at a rate of 35 kg/min to 45 Kg/min and preferably about 40 Kg/min followed by sinter fines addition in parallel operation through top chute starting 3 mins after the start of lime fines injection at a rate of about 145 kg/min to 170 kg/min preferably about 160 kg/min. for a period of next 12 mins, further followed by blowing of oxygen through top lance at a rate of 30 to 45 Nm3 preferably about 35 Nm3/min for a period of next 12 mins after the end of sinter fines addition.
9. A process for continuous de-siliconization and de-sij|phurization of hot metal as claimed in anyone of claims 1 to 8 wherein change in Silicon achieved is 0.5 wt% and change in Sulphur is 0.04 wt%.
10. A process for continuous de-siliconization and de-Sulphurization of hot metal as
claimed in anyone of claims 1 to 9 comprising post pre-treatment carrying out single
slag raking step.