DESC:
Field of the Invention

The present invention relates to a development of novel compound “CAD9FC” used in external desulphurization of hot metal for producing low sulphur steel. More particularly, the present invention relates to the method of desulphurization of hot metal for reducing sulphur of hot metal in Ladle before steel making process in an integrated steel plant.

Background of the invention and related prior Art

In a typical system for such an operation molten cast iron is tapped into a transfer vessel such as a torpedo (or bottle) car. The metal flows through open runners from the blast furnace into the car, and some furnace slag is usually carried into the car. After the car is filled, it may be moved to a desulfurization station where desulfurizing agents are injected into the molten metal. The car is then transported to another station where it is emptied into a ladle. Slag is skimmed from the ladle, and the melt is then charged into a BOF.
Alternatively, the torpedo car may be moved after filling directly to a ladle station, and desulfurization may be conducted in a ladle after the car is emptied into it.

The document US3985550 relates to a method of producing steel by the bottom blown basic oxygen process in which the residual sulfur content is reduced to an exceptionally low level. The process comprehends a standard bottom blown basic oxygen steelmaking process incorporating the injection of a gas carrying particulate desulfurizing agent to desulfurize the steel while maintaining reducing conditions in the bath.
According to the document US20050056120 the invention discloses a method for the preparation of a sodium-based reactive desulphurizing agent for use in molten ferrous materials. The sodium in the reactive desulphurizing agent is a sodium silicate, a composition comprising of Na2O and SiO2. In a second embodiment of the invention, the sodium silicate reactive desulphurizing agent also comprises of an alkali or an alkaline material or other materials, such as oxides of calcium, aluminum and magnesium. Preferred raw materials for the oxides of calcium, aluminum and magnesium are, respectively, lime, alumina and dolomite. The premixed solid reactive desulphurizing agent is brought in contact with the molten ferrous material, allowing the desulphurization or the double replacement of the iron sulphur to take place and produce a ferrous oxide. The sodium in the reactive desulphurizing agent is rendered resistant to combustion or evaporation on contact with the molten ferrous materials by the flux activity of the silica. A metallic solid, such as aluminum, is introduced into the molten ferrous material to complete the reduction of the ferrous oxide.
The invention of the document US4600434 states a process for magnesium desulfurization of ferrous metal melts in a vessel comprising the provision of a fluid, high sulfur capacity slag wherein the weight ratio of slag constituents associated with sulfur to slag constituents associated with oxygen is greater than 0.8, followed by addition of magnesium to the melt in an amount sufficient to combine with the sulfur in the melt, transfer to the sulfur removed by the magnesium addition to the slag, and retention of the removed sulfur in the slag, thereby improving magnesium desulfurization efficiency and substantially eliminating sulfur reversion from the slag back to the melt.
To maximize the Desulphurization efficiency most of steel industries use injection techniques for injecting reagents in the hot metal to obtain the required sulphur content. The injection techniques can be mono-injection, co-injection and multi-injection depending on the hot metal chemistry, final sulphur to be obtained and the type of facility available at the shop floor. The reagents are injected directly into the bath with the help of dip lance. Inert gases such as nitrogen and argon are used as carrier gases for the material to flow.

The reagents used for desulphurization of hot metal such as lime, magnesium, calcium carbide and soda ash in various combinations have drawbacks. Large amount of Lime is used for desulphurization for attaining the desired amount of end sulphur which creates large volumes of slag generation, metal losses and temperature drop in the hot metal. Calcium carbide has problems in handling and agglomerization of the particle prevents reaction on surface, magnesium is highly volatile at that temperature. These reagents when used in the process have high consumption rate and also are not found to be cost effective.

Many other processes have been developed over the years that are also effective in external desulphurization of hot metal for producing low sulphur steel. Now there is a solution to it. Researchers have found out a way to convert these waste materials into high value products using a very simple technique of distillation followed by external desulphurization of hot metal for producing low sulphur steel.

Summary of the invention

The present invention relates to a development of novel compound “CAD9FC” used in external desulphurization of hot metal for producing low sulphur steel. More particularly, the present invention relates to the method of desulphurization of hot metal for reducing sulphur of hot metal in Ladle before steel making process in an integrated steel plant.

Detailed description of the invention

The present invention is based on the discovery that the a development of novel compound “CAD9FC” used in external desulphurization of hot metal for producing low sulphur steel.
The present invention will be understood and its advantages more apparent in view of the following detailed description and accompanying drawings with eight sheets according to the present invention.

Another object of the present invention is to a the method of desulphurization of hot metal for reducing sulphur of hot metal in Ladle before steel making process in an integrated steel plant.
Another object of the present invention is to a method of desulphurization wherein Sulphur less than 0.005% after treatment.
Another object of the present invention is to a method of desulphurization wherein Co injection is done with Magnesium.
Another object of the present invention is to a method of desulphurization wherein by using carbide based compound and magnesium in definite ratio to avoid the demerits of using magnesium alone as a desulphuriser.
Another object of this invention also relates to the improved method of desulphurization of hot metal wherein by using carbide based compound and magnesium in definite ratio to increase the efficiency of present CAD compound.

In the present scenario there is a demand of low sulphur steel. Sulphur is detrimental element present in steel which causes hot shortness in steel & our invention desulphurizing compound (CAD9FC) is useful for reducing sulphur of hot metal in Ladle before steel making process in an integrated steel plant. Hot metal thus obtained after treatment with the compound (CAD9FC) will fulfill the requirement of low sulphur.
The main objectives of this invention are-
• To Develop a Novel Compound that would reduce sulfur content of hot metal effectively.
• The compound thus produced to be found cost effective during desulphurization operations
• The compound shall remove problems in the bath related to high slag generation, temperature drop, low efficiency, high specific consumption, metal losses

1. Main Advantages :
The following advantages are obtained by using this reagent:
• Effective for reducing sulphur from 0.075% to 0.005%
• Cost effective
• High efficiency and Low consumption rate
• less slag generation, low metal losses
• less amount of temperature losses
• less fumes

2. Main finding/New principle: The newly developed desulphurization compound is CAD9FC. The composition of this compounds is as follows :
Typical composition of CAD9FC
%CaC2 50-55%
CaO 23-37%
Crayolite 2-3%
Lime Stone 2-4%
Fly/Coal Ash 2-4%.
Coal 1-3%
Alumina Powder 2-3%

The Size of this compound is as follows:
Size fraction (-) 0.063mm (-) 0.1mm
% 85 90

3. Process Summary: The hot metal which is produced in blast furnace is transported through torpedo car to steel making shop. The hot metal with high sulphur is tapped into ladle. The size of the ladle varies from 140-180T. The desulphurizing compound is injected into the hot metal through the dip lance where carrier gas causes the flow of the material. There are three kinds of popular injection techniques used are-Mono- injection, Co-injection, Multi injection. Our compound uses so injection technique in which CAD9FC and magnesium are injected in the hot metal. During external desulphurization process Initial bath temp is ranging from 1350- 1680oC. The main constituents of the compound that reacts with the sulphur in hot metal are calcium carbide & lime. The following is the kinetic reaction-
CaC2 + FeS + 2FeO CaS +3Fe + 2CO
CaO + FeS CaS + FeO
Crayolite acts as a slag fluidizer which breaks the silica bonds to make the slag thin thereby decreasing the metal losses due to stickiness of the slag. The carbonaceous material having Volatile matter helps in agitation of bath thereby increasing the surface area of reagent which helps in increased surface reaction. Thus the compound becomes highly efficient with less amounts of unreacted carbide and lime in the slag. Total injection time is around 15-25 min. After the injection the lance is pulled up and the slag is easily raked from the top of the bath.

4. New Results :
Results obtained after injecting CAD & Mag in optimum ratio are shown below. Specific consumption of CAD9FC varies from 0.047-0.055 kg/point sulphur drop/THM and for Magnesium 0.0061-0.0067 kg/point sulphur drop/THM respectively for lowering down 50 points of sulphur in 160T Ladle capacity.

Results obtained after injecting CAD & Mag in optimum ratio are shown below. Specific consumption of CAD & Mag varies from 0.048-0.055 kg/point sulphur drop/THM &0.0061-0.0067 kg/point sulphur drop/THM respectively for lowering down 30 points of sulphur in 160T Ladle capacity

BDS ADS Specific Consumption CAD(kg of compound used/points suplhur drop/ton of hot metal Specific Consumption Mag(kg of compound used/points suplhur drop/ton of hot metal Initial Temp(oC) Final Temp(oC) Temperature drop
0.0536 0.0057 0.0519 0.0062 1361.5746 1322.0514 38.4877
0.0554 0.0067 0.0491 0.0068 1383.3650 1353.1213 30.2438
The present invention consists of a compound “CAD9FC” used in external desulphurization of hot metal for producing low sulphur steel which comprises of CaC2, CaO, Crayolite, volatile matter, suplur, ash, LOI, Al2O3, by which low sulphur of <0.005% can be achieved ”.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact formulation as described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

,CLAIMS:1) A method of desulphurization of hot metal which comprises:
a) hot metal with high sulphur is tapped into ladle;
b) The desulphurizing compound is injected into the hot metal through the dip lance where carrier gas causes the flow of the material;
c) CAD9FC and magnesium are injected in the hot metal;
The carbonaceous material having Volatile matter helps in agitation of bath thereby increasing the surface area of reagent which helps in increased surface reaction.
d) After the injection the lance is pulled up and the slag is easily raked from the top of the bath.

2) The method of desulphurization of hot metal as claimed in claim 1 wherein Sulphur is less than 0.005% after treatment.
3) The method of desulphurization of hot metal as claimed in claim 1 wherein Co injection is done with Magnesium.
4) The method of desulphurization of hot metal as claimed in claim 1 in which by using carbide based compound and magnesium in definite ratio to avoid the demerits of using magnesium alone as a desulphuriser.
5) The method of desulphurization of hot metal as claimed in claim 1 in which by using carbide based compound and magnesium in definite ratio to increase the efficiency of present CAD compound.
6) The method of desulphurization of hot metal as claimed in claim 1 in which total injection time is around 15-25 min.
7) The method of desulphurization of hot metal as claimed in claim 1 wherein Crayolite acts as a slag fluidizer which breaks the silica bonds to make the slag thin thereby decreasing the metal losses due to stickiness of the slag.
8) The method of desulphurization of hot metal wherein during external desulphurization process Initial bath temp is ranging from 1350- 1680oC.