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 SYSTEM FOR HOT METAL DESULPHURIZATION AND STIRRING BASED DESULPHURIZATION PROCESS INVOLVING THE SAME.


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 INVENTION
This invention relates to a system for hot metal desulphurisation and a stirring based desulphurization process of Hot Metal in steel making involving said system having areacion vesselcomprising a selectively configured rotating impeller with peddles and wedges disposed at eccentric position with respect to center line of vesselused for stirring the hot molten metal for increasing reactivity between the sulphur and the desulphurising agent and thereby improved desulphurization rate.

BACKGROUND OF THE INVENTION
The hot metal discharged from the blast furnace contains impurities such as C, Si, P, and S, and molten steel is manufactured by refining and removing these impurities. Generally, among impurities, C is removed by converter refining, Si and P are removed by converter refining or hot metal refining before converter refining, and S is mainly removed by hot metal refining. Here, the desulfurization reaction in the hot metal proceeds according to the following reaction formula (1) when a CaO-based desulfurization agent is used. [S] and [O] in the formula are S and O in the hot metal, respectively, and (CaO) and (CaS) are CaO and CaS in the slag, respectively.
Reaction formula (1): [S] + (CaO) = (CaS) + [O]
As one of the methods for desulfurizing hot metal, the hot metal is charged into a hot metal pan or the like, and the desulfurizing agent powder is added to the hot metal surface from above (addition on top) or while adding on top. There is a stirring based desulphurization method in which desulfurization is performed by rotating and stirring with an impeller. When performing the hot metal desulfurization method using impeller stirring, the desulfurizing agent powder on the surface layer enters the hot metal from the gap between the impeller blades, and is dispersed into the hot metal by the stirring flow pushed out between the blades. Since the desulfurizing agent powder dispersed in the hot metal has a specific gravity lighter than that of the hot metal, it floats on the surface of the molten metal. However, the utilization efficiency ? of the desulfurizing agent is lower and it can be improved by repeatedly entraining the desulfurizing agent powderin the hot metal with a proper designed rotating impeller and by disturbing the uniform vortex which is formed due to rotation of impeller.

Various stirring based desulphurization process were proposed in the prior art. For example, China Pat. No. CN100510111C illustrates stirring based desulphurization impeller which is used for desulphurization which includes air cooled pipe,junction parts of stir head, metal stir shaft, clasping part, fire-proof material lining and metal paddle, shape of the paddle fire-proof material lining is facing iron surface is convex anterior arc-like face, back iron surface is multisection arc like face, lateral face is a inclined plane from down to up.This patent relates to desulphurization of Hot Metal before the primary steelmaking.
Similarly, China Pat. No. CN201071378Y illustrates stirring based desulphurization impeller which is used for desulphurization which includes a joint lever and four vertical curved blades, wherein, the inner cores of the four vertical curved blades are all metallic material support bodies, and outer layers are all flame-proof material layers. The utility model is characterized in that the front faces and the back faces of the vertical curved blades are all inclines, and the inner lateral surfaces in helical shape are symmetrically fixed on the lower end of the joint lever. This patent relates toa kind of improvement of desulfurization agitator head for hot metal that has stirring and propulsion functions simultaneously advances stirring-head.
Likewise, JAPAN Pat. No. JP2005068506A illustrates impeller which is used for which includes a desulfurizing agent jet opening at the lower end of the rotating shaft was immersed and rotated, and the desulfurizing agent powder was blown into the hot metal while stirring the hot metal. This patent relates toa kind of improvement of desulfurization stirrer for desulphurization of Hot Metal.
Although the stirring based desulphurization impeller for desulphurization of Hot Metal are well known in the art, however, none of the above-mentioned patents illustrate design and position of a stirring based desulphurization impeller which can disturb the vortex formed during stirring based desulphurization process. Disturbance in vortex can enhance the entrainment of desulfurizing agent powder in the hot metal which can further improve the utilization efficiency ? of the desulfurizing agent.
Hence to overcome the above disadvantages and problems a novel stirring based desulphurization apparatus and process for desulphurization of Hot Metal has been developed.

OBJECT OF THE INVENTION
The basic object of the present invention is to solve above mentioned problems of the prior art and to provide a system for hot metal desulphurisation and a stirring based desulphurization process involving selective impeller configuration and impeller position for desulphurization of Hot Metal before the primary steel making.
A further object of the present invention is to provide an equipment that can improve the mixing of desulfurizing agent powder into the Hot Metal.
A still further object of the present invention is to provide said equipment with a selectively configured impeller/stirrer head which can improve the reaction between bath sulphur and desulphurizing agents.
Another object of the present invention is to provide said equipment which can decrease the consumption of desulfurizing agent powder in stirring based desulphurization process.
Yet another object of the present invention is to provide said equipment which can further lower the slag jamming on the shaft.
Yet another object of the present invention is to provide said equipment which can further lower the stirring based desulphurization process time.
Yet another object of the present invention is to improve the stirring based desulphurization process efficiency by incorporating a selective modification in the stirring based desulphurization impeller design and impeller position.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a system for carrying out hot metal desulfurization treatment in steel making comprising:
a reaction vessel for reaction between the hot metal and a desulfurizing agent;
a rotatable impeller comprising of a rotatable impeller shaft having plurality of peddles for stirring the molten metal with said desulphurizing agents
said rotatable impeller arranged for disturbing the uniformity of vortex formed by the rotatable impeller including wedges placed selectively on the paddles and the impeller shaft with said selectively provided wedges on paddles disposed within said reaction vessel in an eccentric position with respect to axial central line of the reaction vessel such that the combined effect of eccentricity in disposition of the rotatable impeller and the selectively disposed wedges on paddles promote the desired entrainment of the desulphurising agent into the hot molten metal and increases reactivity between the sulphur and the desulphurising agent;
wherein said rotatable impeller comprises an impeller shaft, four paddles and different types of wedges on the paddles selected from triangular, rectrangular,circular, elliptical of various sizes, with said wedges placed on the top of the paddles of the impellar with one perpendicular side of wedge adjacent to impeller shaft and the other with paddle.
A further aspect of the present invention is directed to said system, wherein the impeller has four peddles of the impeller dispoased at right angles to each other rotatably fixed to the vertical shaft and said wedges on the top of peddle of the impeller can be of any type of shapes like, triangular, rectangular, circular, elliptical etc. wherein the size of the wedges can be similar or varying.
A still further aspect of the present invention is directed to said system wherein size of wedges can vary from the same size of peddles to smaller or bigger wedges wherein preferably length of two bigger wedges are similar to the length of peddle of impeller and two smaller wedge is half the length of bigger wedges and wherein wedges are placed on thetop of the peddles of impeller with one perpendicular side of wedge adjacent to impeller shaft and other with peddle.
A still further aspect of the present invention is directed to said system, wherein said impeller is inserted from the upper part of the vessel disposed with 50-150 mm eccentric to the centre of the reaction vessel containing the hot metal, said vessel having a pan-shaped cross section.
A still further aspect of the present invention is directed to said system, wherein wedges on the top of impeller on rotation creates disturbance to the Hot Metal vortex during the desulphurisation process.
A still further aspect of the present invention is directed to said system wherein the inner core of shaft, four peddles and wedges are made of metallic substance as support with skin of refractory masses.
Another aspect of the present invention is directed to a method for stirring based desulfurization method using the system, comprising providing hot metal bath inside reaction vessel with said rotatable impeller including peddles and wedges disposed eccentrically immersed therein; adding desulphurisation agent in powder form therein said hot metal at desired rate; rotating said impeller at desired speed; wherein eccentric position of impeller produces non uniform and eccentric Hot Metal vortex on rotation whereby reaction between the hot metal and the desulfurizing agent is enhanced by the combined effect of stirring based desulphurization impeller with said eccentric position of the stirring based desulphurization impeller leading to increased desulphurization rate during the desulphurisation process.
A further aspect of the present invention is directed to said method wherein said desulphurization agent used comprising CaO—CaF2 based desulfurizing agent added at desired proportion.
A still further aspect of the present invention is directed to said method, wherein a particle size of the desulfurization agent powder is less than 3 mm.
Yet another aspect of the present invention is directed to said method, wherein the agitation is performed in a state in which wedges are partially submerged under a molten metal surface.
A still further aspect of the present invention is directed to said method having process parameters comprising
Unit Quantity
Diameter of Reaction Vessel m 3.74
Diameter of Impeller m 1.55
Speed of Impeller rpm 90
Hot Metal quantity Ton 180
Treatment time Minute 13
Quantity of CaO Kg/Ton of Hot Metal 9
Quantity of CaF2 Kg/Ton of Hot Metal 0.7

A still further aspect of the present invention is directed to a reaction vessel for stirring based desulphurisation treatment comprising a container for charging the hot metal, and a rotatable impeller installed freely rotatably inside the container from top for stirring the hot metal, the impeller having plurality of peddles attached radially to a vertical shaft with wedges on the top of peddles and with shaft extending upward out of the container having eccentric position of impeller in relation to center line of said reaction vessel.
The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1:illustrates an existing Impeller design.
Figure 2:illustratesa novel Impeller designaccording to a preferred embodiment of the present invention.
Figure 3:illustrates existing stirring based desulphurization process for desulphurization of Hot Metal.
Figure 4:illustrates novel stirring based desulphurizationprocess for desulphurisation of Hot Metal according to a preferred embodiment of the present invention.
Figure 5:illustrates the change in sulphur (BDS –ADS) during the existing and novel stirring based desulphurization processes.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

In recent years, there has been an increasing demand for ultra-low sulphur steel grades from the view point of improving material properties associated with increased added value of steel and expanded use of steel materials. In order to cope with this, in the steelmaking process for refining hot metal, it is necessary to smelt extremely low sulphur steel types without incurring an increase in production cost and slag generation amount, it is indispensable to increase the reaction between the desulfurizing agent and hot metal. In addition, in order to cope with the recent increase in steel demand, it is necessary to improve productivity, and it is also important to improve the reaction rate.
As a technology that meets these requirements, a hot metal desulfurization method using a mechanical stirring type desulfurization processing apparatus has been widely put into practical use and it is called stirring based desulphurization process. According to this technique, an impeller (also called “rotary blade” or “stirring blade”) is immersed in hot metal and rotated as shown in figure 4, and the hot metal and the desulfurizing agent are vigorously stirred, so that inexpensive CaO (lime) is mainly used. Even if a desulfurizing agent (hereinafter referred to as “CaO-based desulfurizing agent”) is used, the hot metal is desulfurized in a short time to a low sulfur concentration range of 0.002 to 0.004 mass%. is possible.

By the way, the hot metal desulfurization treatment in the mechanical stirring type desulfurization processing apparatus using the CaO-based desulfurization agent is performed by using a powdered or granular CaO-based desulfurization agent added to the hot metal surface, and a concentric hot metal vortex formed by rotating an impeller. The contact area between the CaO-based desulfurizing agent and the molten iron is increased to increase the utilization of the CaO-based desulfurizing agent. At this time, the hot metal is stirred by the rotation of the impeller, and the sulphur in the hot metal is sequentially supplied to the reaction interface (desulfurization agent surface), whereby the desulfurization reaction proceeds. Usually, the reaction vessel containing the hot metal is a pan-shaped cross section, and the impeller is inserted from the upper part of the vessel to the approximate centre of the reaction vessel.

However, it has become difficult to respond to the increasing demand for ultra-low sulphur steel in recent years using only the above-described conventional technology. Therefore, as a technique for further improving the reaction efficiency of the CaO-based desulfurization agent and further shortening the processing time in the hot metal desulfurization processing method in the mechanical stirring type desulfurization processing apparatus, the impeller is novel, the impeller is eccentrically inserted, and the reaction is performed.

The present invention relates to an improvedstirring based desulphurization impeller design such as installing different types ofwedges on thetop of impeller with eccentric position of impellerinhot metal ladle during desulphurisation of hot metal.Hence, a detailed investigation have beeen carried out before implementation of the novel design.

The basic aspect of the present invention is thus directed to provide a kind of above the deficiencies in the prior art that overcome, making Hot Metal and desulfurizing agent powder mixed properly during the stirring based desulphurization process, to prevent that desulfurizing agent powder from accumulating in centre of vortex and around the impeller shaftand getting jammed around the shaft of impeller, improvement in the desulphurization efficiency of stirring based desulphurization process.

For reaching above purpose, the technical scheme that adopted in this novel stirring based desulphurization process are impeller design and its. Impeller constitute of impeller shaft, four paddles and different types of wedges on the paddles like triangular, rectangular, circular, elliptical etc.wedges of different size.The inner core of shaft, four paddles and wedge is the metallic substance supporter,skin is refractory masses. Wedges are placed on the top of the paddles of impeller with one perpendicular side of wedge is adjacent to impeller shaft and other with paddle.The length of wedges can be the same as the length of the paddle or it can be varying.
The reaction between the hot metal and the desulfurizing agent is improved by the combined effect of novel stirring based desulphurization impeller and the eccentric position of the stirring based desulphurization impeller as compared to the stirring based desulphurization impeller of present use. Uniformity of vortex formed by the impeller by performing the desulfurization process is disturbed by the combined effect of eccentricity and novel stirring based desulphurization impeller which promotes the entrainment of the desulfurizing agent into the hot metal and increases the reaction between bath sulphur and desulphurizing agents.
Present invention is now described with reference to illustrative embodiments in accompanying drawings wherein:
FIG. 1 illustrates an existing stirring based desulphurization impeller, it has a shaft, four paddles and all four paddles are identical to each other. It has metallic inner core and skin of refractory mass.
FIG. 2 illustrates a novelstirring based desulphurization impeller, It has a shaft, four paddles and rectangular wedges on the peddles of impeller. It has metallic inner core and skin of refractory mass. Size of wedges can be vary from the same size of wedges to smaller and bigger wedges. In this invention, 2 smaller and 2 Biggerpaddles with wedges are used for experiments. Length of bigger wedge is similar to the length of peddle of impeller. Size of smaller wedge is half of the bigger wedge.
List Of Elements in novel stirring based Hot Metal desulphurization impeller design are:
100 Shaft
102 Peddles
104 Wedges
FIG. 3 illustrates a Hot metal desulfurization treatment by existing stirring based desulphurization process where impeller is immersed in hot metal contained in a reaction vessel, a desulfurizing agent is added while rotating the impeller, the hot metal and the desulfurizing agent are stirred, and the hot metal is desulfurized.Here, Impeller doesn’t have any wedges on the peddles and the impeller is inserted from the upper part of the vessel to the approximate centre of the reaction vessel.A concentric hot metal vortex formed due to concentric position of the impeller.The desulphurization rate is lower in existing stirring based desulphurization process due to uniform and concentric vortex formation.And it can be improved by repeatedly entraining the desulfurizing agent powder in the hot metal with a proper designed rotating impeller and by disturbing the uniform vortex which is formed due to rotation of impeller.
FIG. 4 illustrates a hot metal desulfurization treatment by a novel stirring based desulphurization process where impeller(1) is immersed in hot metal contained in a reaction vessel/ladle(3), a desulfurizing agent/flux(9) is added while rotating the impeller(1), the hot metal and the desulfurizing agent are stirred, and the hot metal is desulfurized. Here, Impeller(1) has wedges(2) on the top of peddles(4) attached to a vertical shaf(8) as shown in Figure 4 and the impeller is inserted from the upper part of the vessel with central axis of impeller(6) 50 to 150 mm eccentric(7) to the centre line(5) of the reaction vessel(3).An eccentric hot metal vortex is formed due to eccentric position(7) of the rotating impeller(1). It has been found that the reaction between the hot metal and the desulfurizing agent is improved by the combined effect of novel stirring based desulphurization impeller(1) and the eccentric position(7) of the stirring based desulphurization impeller as compared to the stirring based desulphurization impeller of present use which leads to increased desulphurization rate. Uniformity of vortex formed by the impeller(1) by performing the desulfurization process is disturbed by the combined effect of eccentricity(7) and novel stirring based desulphurization impeller which promotes the entrainment of the desulfurizing agent into the hot metal and increases the reaction between bath sulphur and desulphurizing agents.
Example:
In the specifications of desulfurization treatment equipment and desulfurization treatment conditions shown in table 1.The desulfurization treatment was performed on the hot metal using a desulfurizing agent, and the sulphur % were measured before and after of the treatmentin all cases as mentioned in table 2. The impeller was inserted in the vertical direction. As the desulfurizing agent, a CaO—CaF2 desulfurizing agent containing 7-8% by mass of fluorite (CaF2) was used, and the amount of desulfurizing agent used was constant 9 kg / Ton of Hot Metal in all experiments. .
Here, the desulfurization rate was defined by the following formula (1).
Desulfurization rate (%) = {(Sulfur concentration in hot metal before treatment (mass%))-(Sulfur concentration in hot metal after treatment(mass%))} x 100 / (Sulfur concentration in hot metal before treatment (mass%)) ... (1)
When the basic unit of desulfurizing agent used is the same, that is, under the same amount of desulfurizing agent used per ton of hot metal,the higher the desulfurization rate, the higher the reaction efficiency between the desulfurizing agent and hot metal. .
Table 1: stirring based desulphurization process parameters.
Unit Quantity
Diameter of Reaction Vessel m 3.74
Diameter of Impeller m 1.55
Speed of Impeller rpm 90
Hot Metal quantity Ton 180
Treatment time Minute 13
Quantity of CaO Kg/Ton of Hot Metal 9
Quantity of CaF2 Kg/Ton of Hot Metal 0.7

Table 2:stirring based desulphurization process condition during different cases.
Existing Present invention
Impeller design Existing Novel
Impeller Position Centric 50 mm eccentric
Change in sulphur (%) 0.0392 0.0440
Desulphurization rate (%) 88 99

According to the hot metal desulfurization treatment method and hot metal desulfurization treatment apparatus of the present invention, the reaction between the desulfurizing agent and the hot metal can be stably increased.Desulphurization rate for approximately constant BDS(Before desulphurization sulphur) value was increased for the novel stirring based desulphurization processes as shown in figure5. For novel stirring based desulphurization process, desulphurization rate was increased from existing 88 % to 99 %. Result of experiments show that the desulphurization rate of stirring based desulphurization process was improved significantly by present invention.It shows that the combined effect of new novel impeller andthe eccentric position of the impellerhas significant effect on the reaction between bath sulphur and desulphurizing agentswhich leads to increased desulphurization rate.
, Claims:We Claim
1. A system for carrying out hot metal desulfurization treatment in steel making comprising:
a reaction vessel for reaction between the hot metal and a desulfurizing agent;
a rotatable impeller comprising of a rotatable impeller shaft having plurality of peddles for stirring the molten metal with said desulphurizing agents
said rotatable impeller arranged for disturbing the uniformity of vortex formed by the rotatable impeller including wedges placed selectively on the paddles and the impeller shaft with said selectively provided wedges on paddles disposed within said reaction vessel in an eccentric position with respect to axial central line of the reaction vessel such that the combined effect of eccentricity in disposition of the rotatable impeller and the selectively disposed wedges on paddles promote the desired entrainment of the desulphurising agent into the hot molten metal and increases reactivity between the sulphur and the desulphurising agent.
wherein said rotatable impeller comprises an impeller shaft, four paddles and different types of wedges on the paddles selected from triangular, rectrangular,circular, elliptical of various sizes, with said wedges placed on the top of the paddles of the impellar with one perpendicular side of wedge adjacent to impeller shaft and the other with paddle.
2. The system as claimed in claim 1, wherein the impeller has four peddles of the impeller dispoased at right angles to each other rotatably fixed to the vertical shaft and said wedges on the top of peddle of the impeller can be of any type of shapes like, triangular, rectangular, circular, elliptical etc. wherein the size of the wedges can be similar or varying.
3. The system as claimed in anyone of claims 1 or 2 wherein size of wedges can vary from the same size of peddles to smaller or bigger wedges wherein preferably length of two bigger wedges are similar to the length of peddle of impeller and two smaller wedge is half the length of bigger wedges and wherein wedges are placed on thetop of the peddles of impeller with one perpendicular side of wedge adjacent to impeller shaft and other with peddle.
4. The system as claimed in anyone of claim 1 to 3, wherein said impeller is inserted from the upper part of the vessel disposed with 50-150 mm eccentric to the centre of the reaction vesselcontaining the hot metal, said vessel having a pan-shaped cross section.
5. The system as claimed in anyone of claims 1 to 4, wherein wedges on the top of impeller on rotation creates disturbance to the Hot Metal vortex during the desulphurisation process.
6. The system as claimed in anyone of claims 1 to 5 wherein the inner core of shaft, four peddles and wedges are made of metallic substance as support with skin of refractory masses.
7. A method for stirring based desulfurization method using the system as claimed in claims 1 to 6, comprising providing hot metal bath inside reaction vessel with said rotatable impeller including peddles and wedges disposed eccentrically immersed therein; adding desulphurisation agent in powder form therein said hot metal at desired rate; rotating said impeller at desired speed; wherein eccentric position of impeller produces non uniform and eccentric Hot Metal vortex on rotation whereby reaction between the hot metal and the desulfurizing agent is enhanced by the combined effect of stirring based desulphurization impeller with said eccentric position of the stirring based desulphurization impeller leading to increased desulphurization rate during the desulphurisation process.
8. The method as claimed in claim 7 wherein said desulphurization agent used comprising CaO—CaF2 based desulfurizing agent added at desired proportion.
9. The method as claimed in any one of claims 7 to 8, wherein a particle size of the desulfurization agent powder is less than 3 mm.
10. The method as claimed in anyone of claims 7 to 9, wherein the agitation is performed in a state in which wedges are partially submerged under a molten metal surface.
11. The method as claimed in anyone of claims 7 to 10 having process parameters comprising
Unit Quantity
Diameter of Reaction Vessel m 3.74
Diameter of Impeller m 1.55
Speed of Impeller rpm 90
Hot Metal quantity Ton 180
Treatment time Minute 13
Quantity of CaO Kg/Ton of Hot Metal 9
Quantity of CaF2 Kg/Ton of Hot Metal 0.7

12. A reaction vessel for stirring based desulphurisation treatment comprising a container for charging the hot metal, and a rotatable impeller installed freely rotatably inside the container from top for stirring the hot metal, the impeller having plurality of peddles attached radially to a vertical shaft with wedges on the top of peddles and with shaft extending upward out of the container having eccentric position of impeller in relation to center line of said reaction vessel.

Dated this the 19th day of January, 2024
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199