Field of the Invention
The present invention relates to a composition of a product used for external desulphurization of
hot metal for producing low sulphur steel. More particularly, the present invention relates to the
composition for hot metal desulphurization which comprises CaC2, CaF2, SiO2, Al2O3, CaO,
Fe2O3, fixed carbon, volatile matter, etc in particular ratio. Moreover this invention related to the
composition which will reduce the sulphur of hot metal in ladle before steel making process in an
integrated steel plant. Moreover this invention relates to the process for producing low sulphur steel
by using desulphurizing composition.
Background of the invention and related prior Art
The document GB1512471 states that the production of steel by bottom blowing an impure melt
with oxygen, a desulphurizing step is incorporated by blowing a powdered desulphurizing agent,
e.g. lime, calcium carbide, into the melt with inert gas whilst maintaining reducing conditions
therein. The desulphurizing strip may be affected in the early stages of production, in which case
the unremoved C and Si provide the reducing conditions, or at any stage by supplying powdered
deoxidizing agents, e.g. Ti Zr Al, with the desulphurizing agent.
Accordingly, the basic concept of this invention involves the addition of a desulfurizing blow to the
conventional Q-BOP blowing practice In essence, there are two basic 100 embodiments of the
invention, one involves desulfurizing the bath at any time during the process, but particularly at
carbon contents below 3 percent, wherein a particulate desulfurizing agent, such as lime and/or 105
calcium carbide, and a finely divided strong deoxidizing agent, such as aluminum, zirconium,
titanium, a rare earth element, or any mixture thereof, are simultaneuosly injected into the bath
entrained in an inert 110 gas blow The deoxidizing agent deoxidizes the bath to render reducing

conditions so that the desulfurizing agent will react with and remove sulfur from the bath The other
embodiment involves desulfurizing the bath 115 during the early stages of the process before the
carbon content of the bath has been reduced to 3 percent In this embodiment, the original reducing
conditions are prolonged by injecting a particulate desulfurizing 120 agent with an inert carrier gas
blow with or without oxygen Since the bath already contains sufficient carbon and silicon to render
the necessary reducing conditions, a deoxidizing agent is not necessary in this 125 embodiment
Furthermore, since oxygen is not being blown, or is blown at a lesser rate, the reducing condition
can be main1,512,471 tained until the bath has been desulfurized to the final desired level.
The first embodiment described above involves charging a Q-BOP vessel in accordance with
conventional practice with scrap and a hot metal containing carbon, silicon and sulfur which are to
be removed therefrom The bath is then blown with shielded oxygen according to conventional
practice to remove carbon, silicon and other impurities such as phosphorus At some point during
this process, after the carbon content of the bath has been reduced to a value below 3 percent, an
inert carrier gas such as argon or nitrogen is substituted for the oxygen and preferably, also for the
shielding gas Blown into the bath with the inert gas is a particulate desulfurizing agent and a finely
divided strong deoxidizing agent As noted above, the deoxidizing agent will deoxidize the bath to
create reducing conditions so that the desulfurizing agent will react with and remove sulfur from
the bath.
The inert gas injected during the desulfurizing step may be any inert gas such as argon or nitrogen
Since the inert gas serves only as a carrier for the desulfurizing and deoxidizing agents, the blowing
rate thereof should be minimized in the interest of economy Therefore, a "soft blow" is preferred, i

e a low pressure, low volume inert gas blow in which the total fluid pressure is just sufficient to
overcome the ferrostatic pressure to get the reactants into the bath and prevent entry of molten
metal into the tuyeres In addition, a soft blow will serve to minimize slag-metal mixing to prevent
any possible phosphorus reversion from the slag to the metal.
Although it can be said that a soft blow is preferred for any of the embodiments of this invention,
other processing parameters are not so readily definable, but may vary widely depending upon the
specific reagents used, the various side reactions, the final product sought and the amount of sulfur
to be removed For example, it has already been noted that the desulfurizing step may be performed
at any point during the total refining process, e g it may be performed initially before any carbon is
removed, in which case a deoxidizing agent is not necessary, mid-way through the decarburizing
blow, or as a final blow after carbon and other impurities have been removed to the desired final
level The determining factor here will depend primarily upon economics and the final product
sought For example, if the final product sought is an aluminumkilled steel, then obviously, there
would be an advantage in performing the desulfurizing step as a final step since the essential
deoxidation step would serve to kill the steel.
On the other hand, if a rimming steel is sought, then obviously there would be an advantage in
desulfurizing the bath at some time other than as a final step so that the steel will not be in a
deoxidized condition when finished For example, desulfurization could be effected mid-way
through the decarburizing blow so that the final decarburizing blow will return oxygen to the steel.
In this case the bath is preferably de-slagged before the final oxygen blow To illustrate another

example, the final steel sought may be a high carbon steel, in which case it would be advisable to
desulfurize first and then blow oxygen with a conventional "catch-carbon" practice.
In line with the above considerations, it may be noted that although nitrogen may be a most suitable
inert gas for early desulfurizing practices, it may not be desirable to use nitrogen when
desulfurizing is the final step That is to say, using nitrogen as the inert gas will of course cause
nitrogen to be dissolved into the bath Such nitrogen will however be readily flushed from the bath
by any subsequent oxygen or argon blowing When nitrogen is used as the carrier gas in a
desulfurizing treatment before a final oxygen blow, the desulfurizing treatment is preferably
terminated while the bath content not less than 0 1 % carbon.
As noted above, if the desulfurizing blow is effected initially before any substantial amounts of
carbon and silicon are removed from the bath, the bath is sufficiently reducing in nature that a
deoxidizing agent need not be included in the blow Indeed, the bath is so reducing in nature that
oxygen may even be included in the blow Hence, desulfurization and decarburization may be
effected simultaneously, at least down to about 3 percent carbon Although this dual reaction could
be effected without using any inert gas, i.e a conventional Q-BOP blow with lime, at carbon levels
above 3 percent, the inert gas is nevertheless necessary to retard the decarburization rate, so that the
sulfur can be removed before the bath becomes oxidizing in nature It should be noted that since
oxygen can be included in such an initial desulfurizing blow, and since the inert gas may be
nitrogen, then obviously, air can be used For such practice however, it is preferable to use air
diluted with nitrogen For intermediate and final desulfurizing practices, i.e desulfurizing after
carbon has been reduced below 3 percent, reducing conditions in the bath must be artificially

maintained by injecting a strong deoxidizing agent To minimize the amount of such deoxidizing
agent used therefore, oxygen should not be blown in this practice, at least in any appreciable
amounts.
The amount of reagents used will depend of course on which reagents are used and the side
reactions which may result For example, when desulfurizing with lime and 1,512,471 deoxidizing
with aluminum, it is known that the deoxidation product, alumina, will react with lime to form
calcium aluminate Such a reaction may be represented by the following equation:
The other document GB992532 describes that a method of making steel castings having a sulphur
content of less than 0.005%, comprising treating molten pig iron in a ladle with a lime bearing
desulphurizing agent and a stream of nitrogen, thereby lowering the sulphur content of the molten
pig iron to less than 0.005%; converting said pig iron into steel in a furnace using sulphur-free fuel;
teeming said steel into ingots and mechanically working the said ingots and thus obtaining scrap
steel of low sulphur content; forming in an electric furnace a charge of steel containing sufficient of
said scrap steel to maintain the sulphur content therein below 0.005%; and teeming said electric
furnace charge into steel castings. The conversion process from pig-iron into steel may be carried
out in a Bessemer or L/D converter. Part of the electric furnace charge may comprise an increment
of the desulphurized pig-iron, a tolerated amount of other low sulphur content pig iron, or hot
molten metal from the converting operation. Examples are given of the composition of the metal at
each stage of the process.

According to the document 3628/DELNP/2006 a steel desulphurating agent, characterised in that it
comprises compared with the total weight of the agent: atleast10% of SiO2, at least 10% of C2S, at
least 35% of at least one calcium aluminate and optionally a calcium silico-aluminate.
Among the methods currently used for desulphuration however, none is totally satisfying. Thus the
use of sodium carbonate results in a yield of the order of 60% maximum of desulphuration with
emission of noxious smoke and the production of particularly aggressive slag.
The use of calcium carbide results in recarburising the metal, and also, the product must be kept
dry to avoid the risk of producing acetylene thus causing an explosion. The use of calcium
cyanamide results in nitriding and carburising the metal, which is what is trying to be avoided.
Magnesium is difficult to use because it vaporises on contact with the steel and can result in
explosions, and so must be coated in tar and placed in a bell.
The use of silico-calcium, blown into the mass to be purified results in globularisation of the
inclusions, and requires the use of alkaline slag and causes the steel to regain nitrogen. The use of
lime is advantageous, but its high melting point, about 2200°C, stops the lime reacting with the
liquid metal.
However, these products are expensive or not readily available. Thus a need exists for
desulphurating agents which remedy the disadvantages described above, while remaining less
expensive, more readily available than the state of the art compositions, and in particular
which could be obtained from industrial waste, particularly from steelworks slag.
The composition of the desulphurating agent, comprising a high concentration of C2S makes it

possible, apart from the advantages described above, to obtain a swelling of the desulphurating
agent, and thus a powder.
The desulphurating agent is preferably in the form of a powder with a specific surface comprised
between 1000 and 5000 cm2 /g, preferably from
1000 to 2000 cm2 /g. Methods for measuring the specific surface of a powder are well known to
those skilled in the art. Examples that can be quoted include processes based on the physical
adsorption of a gas at low temperature, for example the well-known method known as BET.
In particular, a method for preparing the desulphurating agent can consist in making a mixture of
alumina or products that generate alumina and steelworks slag, then heating the mixture to a
temperature comprised between 1250°C and 1450°C, in a partial oxygen pressure, comprised
between 10"1 and 10"6 bar.
The alumina, or the product generating alumina, can be added to the molten steelworks slag.
In general, the quantity of alumina that needs to be added to obtain the desulphurating agent from
steelworks slag is between 10 and 30% compared to the total weight of the slag, depending on the
composition of the slag and/or the required composition of the desulphurating agent.
The addition of alumina or of a compound that generates alumina makes the slag easier to melt
and more readily desulphurised. Preferably, the source of aldmina is selected from among: bauxite,
aluminium residues and red mud. The invention also relates to a steel desulphuration method
comprising the addition to the steel of the desulphurating agent as described above and lime
(CaO). Preferably the desulphurating agent and the lime are mixed together
before being added to the steel. Preferably the weight ratio of the desulphurating agent to the lime

varies from 1/0,5 to 1/2, and preferably is 1/1. The steel desulphuration process preferably takes
place at a temperature comprised between 1500°C and 1600°C, and most preferably at 1550°C.
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.
The primary concept of this invention is to modify earlier process wherein 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.
Summary of the invention
The present invention relates to a composition for external desulphurization of hot metal for
producing low sulphur steel. More particularly, the present invention relates to the composition
which comprises CaC2, CaF2,SiO2, Al2O3, CaO, Fe2O3 , Fixed carbon, volatile matter etc in
particular ratio. Moreover this invention relates to the composition which reduces the sulphur of hot
metal in ladle before steel making process in an integrated steel plant. Moreover this invention
relates to the process for producing low sulphur steel by using this composition.

Detailed description of the invention
The present invention is based on the composition for producing low sulphur. The present
invention will be understood and its advantages more apparent in view of the following detailed
description according to the present invention.
Another object of the present invention is to prepare a composition for external desulphurization of
hot metal for producing low sulphur steel.
Still other object of the present invention is to provide the desulphurizing composition which
comprises CaC2, CaF2, SiO2, A12O3, CaO, Fe2O3, fixed carbon, and volatile matter, LOI, ash, and
moisture in particular ratio.
Another object of the present invention is to provide the process which has a reasonable simple
process, operation, and low cost.
Another object of the present invention is to provide the process for the production of low content
of sulphur steel in which sulphur is less than 0.005% after treatment.
Another object of the present invention is to provide the advantages of the desulphurizing
composition which will remove problems in the bath related to high slag generation, temperature
drop, low efficiency, high specific consumption and metal losses.

Another object of the present invention is the process for producing low sulphur content steel by
using desulphurizing composition which is simple and the effect is excellent to avoid excessive
fumes generation and the price is low.
Another object of the present invention is that the process for producing low sulphur content steel
by using desulphurizing composition which comprises;
a) Tapping of high sulphur contained hot metal from torpedo to transfer ladle;
b) The desulphurizing composition is injected into the hot metal through the dip lance;
c) The composition reacts with the sulphur in hot metal;
d) After the injection the lance is pulled up and the slag is easily raked from the top of the bath.
Other objects of the present invention, together with means and methods for attaining the various
objects, will become apparent from the following description of preferred embodiments.
Novelty of this instant invention lies on the composition/product for producing low sulphur content
steel by using composition. The invention itself, additional objects and advantages thereof, will best
be understood from the following description of certain specific embodiments.
In the present scenario there is an extensive demand of low sulphur high quality steel. Sulphur is
detrimental element present in steel which causes hot shortness in steel & our invention/
composition is useful for reducing sulphur in hot metal thorugh ladle operations before steel
making process in an integrated steel plant. Hot metal thus obtained after treatment with the
compound will fulfill the requirement of low sulphur steel.

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 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. The new composition/compound uses co-
injection technique in which it is injected along with magnesium in the hot metal. During the
desulphurization process initial bath temp ranges from 1350- 1680°C. 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
Calcium fluoride 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 fewer amounts of un-

reacted calcium carbide and lime in the slag. Total injection time is around 20-25 min. After the
injection the lance is pulled up and the slag is easily raked from the top of the bath. The size of the
composition is shown below-

The results thus obtained after injecting composition/compound along with magnesium in 180T
ladle shown in the table below-

Specific consumption of compound varies from 0.047-0.055 kg/point sulphur drop/ Tons Hot Metal
and for magnesium 0.0061-0.0068 kg/point sulphur drop/ Tons Hot Metal respectively in 180T
Ladle capacity.
The results for HOT ladle operation are also shown in the table below-

Specific consumption of compound varies from 0.048-0.055 kg/point sulphur drop/Tons Hot Metal
and for magnesium 0.0061-0.0067 kg/point sulphur drop/ Tons Hot Metal respectively in MOT
Ladle capacity.

Advantages:
The following advantages are obtained by using this composition/product:
1) Can reduce sulphur from 0.075% to less than 0.005%;
2) Cost effective;
3) High efficiency and low consumption rate ;
4) less slag generation, low metal losses;
5) less amount of temperature losses and
6) less fumes generation
The present invention as described above, it is to be understood that this invention is not limited to
particular materials described, as these may vary as per the person skilled in the art. It is also to be
understood that the terminology used in the description is for the purpose of describing the
particular embodiments only, and is not intended to limit the scope of the present invention.
We claim:
1) A composition/product for external desulphurization of hot metal used for producing low
sulphur steel which comprises of CaC2, CaO, CaF2, SiO2, fixed Carbon, volatile matter,
sulphur, ash, LOI, Al2O3, Fe2O3 in a particular ratio;
2) The composition/product for external desulphurization as claimed in claim 1 wherein CaC2
is 40-56%, CaO is 23-37%, CaF2 is 3.5-4%, Si02 is 2.6-2.7%, Fixed Carbon is 3.3-35.5%,
volatile matter is 0.9-1.3%, sulphur is 0.2-0.4%, ash is 0.8-1.0%, LOI is 0.8-1.8%, Al2O3 is
0.01-.02%, Fe203 is 0.01-0.02%.

3) The composition/product for external desulphurization as claimed in claim 1 wherein the
above ingredients are 100% less than 1mm in size and 85 % less than 0.063mm.
4) The composition for external desulphurization as claimed in claim 1 wherein sulphur reduces
from 0.075% to 0.005%.
5) The composition for external desulphurization as claimed in claim 1 wherein after addition
of composition causes less slag generation and low metal losses.
6) The composition for external desulphurization as claimed in claim 1 for which Specific
consumption of composition/product varies from 0.048-0.055 kg/point sulphur drop/ Tons
Hot Metal and for magnesium 0.0061-0.0067 kg/point sulphur drop/ Tons Hot Metal.
7) The process for producing low sulphur content steel by using desulphurizing composition as
claimed in claim 1 wherein the composition is injected into the metal bath with magnesium.
8) The process for producing low sulphur content steel by using composition wherein the
carbonaceous material having volatile matter helps in agitation of bath thereby increasing the
surface area of reagent which helps in increased surface reaction.
9) The process for producing low sulphur content steel by using composition/compound with
Magnesium wherein total injection time is around 20-25 min.

ABSTRACT

The present invention relates to a composition for external desulphurization of hot metal for
producing low sulphur steel. More particularly, the present invention relates to the desulphurizing
composition which comprises CaC2, CaF2,SiO2, Al2O3, CaO, Fe2O3, Fixed carbon, volatile matter
etc in particular ratio. Moreover this invention relates to the desulphurizing composition which
reduces the sulphur of hot metal in Ladle before steel making process in an integrated steel
plant. Moreover this invention relates to the process for producing low sulphur steel by using
desulphurizing composition.