DESC:FIELD OF INVENTION

? The present invention relates to Desulphurization of hot metal (HMDS). In particular, it relates to the development of an alternate material, other than Magnesium (Mg), to carry out deoxidation function in hot metal during HMDS process.
? The alternate material developed in this invention is Calcium Silicide (CaSi).
? This alternate material replaces, partially or fully, Magnesium, which is currently being used for the intended application.

BACKGROUND INFORMATION

Desulphurisation of hot metal relates to removal of Sulphur from hot metal as high Sulphur initiates cracks during rolling process as -
• Sulphur affects both internal and surface quality of steel
• Formation of iron sulphide (lowers the melting point) which promotes granular weakness and cracks in steel during solidification
• Rolling and forging becomes very difficult due to hot shortness in the presence of Sulphur
For removing sulphur from hot metal calcium carbide, lime and magnesium are used either individually or in combination. Amongst these three, magnesium is the most hazardous material, in addition to its high price. Thus, replacing magnesium with some less hazardous material like CaSi powder is safe and economical.

OBJECTS OF THE INVENTION
1. The main object of this invention is to reduce usage of Magnesium in HMDS
2. Another object of this invention is to replace the deoxidation function of Mg by addition of an alternate material like Calcium Silicide
3. The third object of this invention is also to reduce cost of HMDS
4. The fourth object of this invention is to reduce/ eliminate the risk of hazards associated with Magnesium.

BRIEF DESCRIPTION OF THE INVENTION:

According to the invention, primary object is achieved when such a compound is prepared which can reduce magnesium usage as a desulphurising reagent. Reagent having below mention composition:
CaSi: 2-40%; Slag Conditioner:0-20%; melt agitator or gasifying agents e.g. coal, limestone, gilsonite, calcium carbide, aluminium etc.:0-30% and CaO : Remaining
This new reagent reduces the amount of magnesium used partially or fully as desulphurisation reagent. As magnesium is hazardous in nature and its availability is limited to certain geographical locations, this innovation establishes an alternative reagent which is less hazardous and more abundantly available.
Furthermore, the new reagent is cost effective when compared with the cost for co-injection of Lime based desulphurisation reagent with Magnesium or calcium carbide based with Magnesium.

DETAILED DESCRIPTION OF THE INVENTION:
Sulphur is considered as an impurity as it reduces mechanical properties of steel like impact toughness, ductility and initiates cracks in steels. Except in certain grades of steel like free cutting steels, sulphur is required for increasing machinability of steel. This innovative Desulphurising reagent is found very effective in removing Sulphur from hot metal with 70-80% reduction of magnesium and also at elimination of magnesium. The compositions of these reagents are as follows:
Composition of desulphurization reagents:
CaSi: 2-40%;
Slag Conditioner:0-20%;
melt agitator or gasifying agents e.g. coal, limestone, gilsonite, calcium carbide, aluminium etc.:0-30%;
CaO : Remaining
The development of innovative reagent involved 3 stages:
1. Lab Trials:
In lab trials, parameters like flowability and Granulometry of the trial lots were observed. The results obtained for flowability and Granulometry are shown in Fig1 and Fig2 respectively. On comparing with the results obtained by using fluidised lime based reagent, it was observed that there is no significant difference between flowability and Granulometry obtained by using new reagent.
Figure 1: Flowability Figure 2: Granulometry

2. Pilot Industrial Trials:
Prepared small batches of new reagent and organized trials and also modified process parameters for desulphurization and pilot scale were successfully conducted. Pilot scale trials successfully conducted trials in one Indian steel plant.
Average Hot metal chemistry details taken for pilot scale trials:
C(%) Mn(%) S(%) P(%) Si(%)
4.52 0.045 0.043 0.173 0.76

The results obtained by using the above reagent is shown in table
Parameters UOM Innovative reagent without magnesium Innovative reagent with magnesium
Avg. Before Desulphurisation Sulphur % 0.043 0.040
Avg. After Desulphurisation Sulphur % 0.010 0.004
Avg. consumption of Innovative reagent kg/thm 4.58 3.43
Avg. consumption of Magnesium kg/thm 0 0.13
Avg. Hot Metal Temperature 0C 1375 1403

The trial results are encouraging and show definite promise to eliminate magnesium partially or fully.

,CLAIMS:WE CLAIM:
1. This innovative desulphurisation reagent is injected into the ladle consisting of hot metal and after the injection process gets completed, the ladle is taken to the converter for further processes. This desulphurization reagent can be added:
a) Along with reduced 70% amount of magnesium from original consumption
b) Without Magnesium

2. The Reagent therein claimed in 1 comprises of atleast one of calcium bearing compounds like lime, calcium carbide, limestone and calcium chloride and also Calcium silicide

3. The Reagent therein claimed in 1 consists of slag conditioner comprising of mainly Sodium, aluminium and fluorine based compound

4. The Reagent therein claimed in 1 comprises of melt agitator or gasifying agents like coal, limestone, gilsonite, calcium carbide, aluminium etc.

5. The reagent as claimed in claim 1, wherein the said desulphurising reagent is composed of the following specification:
CaSi: 2-40%;
Slag Conditioner:0-20%;
Melt agitator or gasifying agents e.g. coal, limestone, gilsonite, calcium carbide, aluminium etc.:0-30%;
CaO : Remaining

6. The reagent as claimed in claim 1 reduces the cost of desulphurization reagent by over 5%.