FORM 2
THE PATENT ACT 19 70 (39 of 1970)
The Patents Rules, 2003 COMPLETE SPECIFICATION 'See Section 10, and rule 13
1. TITLE OF INVENTION
A METHOD OF INCREASING THE EFFICIENCY OF FURNACE BY REDUCTION OF FEO PERCENTAGE IN ELECTRIC ARC FURNACE SLAG

2. APPLICANT(S)
a) Name
b) Nationality
c) Address

ISPAT INDUSTRIES LIMITED INDIAN Company CASABLANCA - PLOT NO. 45, SECTOR - 11, CBD BELAPUR, NAVI MUMBAI - 400614 MAHARASHTRA

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

A METHOD OF INCREASING THE EFFICIENCY OF FURNACE BY REDUCTION OF FeO PERCENTAGE IN ELECTRIC ARC FURNACE SLAG
FIELD OF INVENTION:
The present invention relates to a method of improving the yield of a conarc furnace by reducing percentage of FeO in an electric arc furnace (EAF) slag in steel manufacturing process. More particularly, the present invention relates to a modified attempt to decrease the percentage of FeO in an electric arc furnace (EAF) slag that consequently increases the percentage of iron metal yield in steel making process by conarc furnace particularly during arcing process.
BACK GROUND OF THE INVENTION :
The Conarc design combines the conventional basic oxygen furnace process with electric steelmaking in a single production unit which consists of two identical vessels. The sreeimaking process is split into two main phases, which are the converter process to decarbonise the liquid hot metal through the top lance injection of strong/ intense oxygen blowing for removal of carbon, while the electric arc furnace process is used to melt down all cold charge materials, using electrical energy, and to superheat the complete steel bath to tapping temperature. Once the impurities in the liquid metal are oxidized, they leave the furnace in the form of gas and slag. A combination of hot metal and scrap/ direct reduced iron (DRI) (needing arcing) as feed to furnace in any proportion can easily be handled in this process. The process essentially consists of blowing oxygen from the top by a top lance as discussed above and in the later process the arcing takes place.
The current practice while steel making using conarc technology is that during arcing, the Cojet lances (the gas injection system that delivers a laser-like supersonic jet of oxygen into the molten steel bath of a steel furnace. It
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uses a lance and lance tip design with an injector nozzle that delivers coherent streams of oxygen more than five times the normal distance from the nozzle tip while maintaining their original diameter and velocity. As a result the oxygen jets penetrate more deeply into the molten bath, providing more controlled and intense bath mixing) are continuously used throughout the entire process. Because of this type of furnace operation, excess oxygen is always supplied to the molten steel present within the furnace. This molten steel which is exposed to excess oxygen has a higher tendency of getting oxidized.
The oxidized molten steel now gets into the slag, which flows out of the furnace continuously thereby increasing metal loss. The iron loss through EAF slag is an important parameter in steel making to be controlled. This results in the loss of overall yield for the process which is any detrimental to any process plant. In the Conarc process the percentage of FeO is lesser in the blowing period (approx. 15-20%) compared to the arcing period (approx. 30-35%) and that's why it is important to emphasize the control of iron loss in the arcing period. Such a long standing problem is associated with steel industry and efforts are continuously made to minimize the amount of iron that goes along with the slag. If there is a decrease in the percentage of iron (especially iron oxide) in the discarded slag then certainly the yield oi steel increases as well as the furnace efficiency.
Initially, the cojet lances were continuously used during the arcing process which leads to the excess oxidation of Fe that converts to FeO, reaches the slag and flushes out from the furnace.
We have attempted to modify the method adopted within the existing technology to improve the yield oi steel in a conarc furnace by reducing percentage of FeO in an electric arc furnace (EAF) slag in steel manufacturing process. More particularly, our invention relates to a method of decreasing the percentage of FeO in the electric arc furnace (EAF) slag to increase the
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percentage of iron metal yield in steel making process by conarc furnace particularly during arcing process.
OBJECTIVE OF THE INVENTION :
The main objective of the invention is to devise a method that reduces the percentage of FeO in the electric arc furnace (EAF) slag.
One more objective of the invention is to increase the percentage of iron metal yield in steel making process consequently increasing the efficiency of conarc furnace.
One further objective of the invention is to devise a simple method with the existing technology by deduction in the percentage of iron oxide (FeO) in the electric arc furnace slag.
It is yet another object of the present invention to provide a method for recovering high yield of iron/steel in conarc furnace by reducing iron oxide content especially during arcing operation.
SUMMARY OF THE INVENTION:
The present invention relates to a method of improving the yield of a conarc furnace by reducing percentage of FeO in an electric arc furnace (EAF) slag in steel manufacturing process. More particularly, the present invention relates to a modified attempt to decrease the percentage of FeO in an electric arc furnace (EAf) slag. The invented method utilizes the existing technology in the said field with modification in the operating method only during arcing that consequently increases the percentage of iron metal yield in steel making process by conarc furnace particularly during arcing. This is a simplest modified approach during operation of conarc furnace and instead of injecting oxygen through the side lance in arcing period throughout it is injected after a predetermined time for which the applicant seeks protection.
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DETAILED DESCRIPTION OF THE INVENTION :
Since the challenging task in steel making industry is to rrunimize the loss of iron in the slag which is expensive enough to be recovered, a modified approach was inevitable by which the loss of iron can be controlled before its association with the slag. Accordingly in order to achieve the above mentioned object, the present modification exclusively related to the operation of side lance for oxygen injection during the arcing period in conarc furnace.
The method followed in steel industry using conarc furnace encounter a loss of around 32% of iron oxide (FeO) during arcing period only. In order to encounter such a loss during arcing/ the modified method of the present invention involves oxygen injection through side lance in arcing furnace in controlled manner only after the charge reaches 210T of the total charge.
During this time the FeO generated during the blowing period and the iron oxide from the direct reduced iron (DRI) are likely to be completely reduced to the elemental iron by the carbon injection operation from the nozzle by the following stoichiometric equation:
C + FeO -» CO + Fe
(from coke) (from slag) (gas bubbles in slag) (iron)
After 210T of total charge, the oxygen from side lance (one injector only) is
injected to decarburize the steel and to achieve the target steel chemistry. If
one injector is not sufficient to decarburize the steel then the top lance is used
at the end of processing to achieve the target steel carbon. By this modified
method there is a gain of around 10% of FeO from going into the slag. In a
large scale process this 10% retention of FeO which does not go into the slag
is having tremendous contribution to the efficiency of the furnace.
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The above and the other objects, features add advantages of the claimed invention will become apparent from following description read in conjunction with the accompanying drawings.
Figure 1: Shows the overall view of electric arc furnace (EAF) with the positions of Cojet lance and carbon injection liner.
Figure 2: Shows the enlarged view of the portion "A" shown in figure 1 showing cojets with nozzle arrangements.
Figure 3: Shows the difference in percentage of FeO in slag before and after modification in the process technology.
Now referring to figures 1 and 2, the steel manufacturing technology presently employs the cojets (1) continuously without any break throughout the arcing process. The nozzle has a central hole (5) for main oxygen as usual. Surrounding it, there in another annular hole (3) through which a jet of natural gas comes out to produce a high pressure flame acting as a sheath around central oxygen jet. Auxiliary oxygen (4) is also being sent through the cojet A water cooled jacket (2) of the cojet is provided for cooling during the operation of the process.
According to the invention for which protection is sought, the oxygen injection through cojets (1, 3, 4, 5) are turn off till the charge reaches 210T of the total charge of the furnace. During this time, the remaining direct reduced iron (DRI) is also continuously fed into the furnace from top and the carbon fines from carbon injectors (6) are injected over the bath to reduce FeO (iron oxide) chemically to Fe (iron) which is generated during the blowing period and that coming from DRI. By the reduction process of reduction of FeO to Fe by carbon, carbon monoxide (CO) bubbles are escaped as gas from the furnace. After the charge reaches 210T of the total charge, the cojets (1, 3, 4, and 5) are turned on to decarburize the bath and to achieve the target steel chemistry.
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If one injector is not sufficient to decarburize the steel to the desired level, then top lance is used at the end of processing to achieve the target steel carbon. A comparative study in connection with the percentage of decrease in the level of iron oxide (FeO) in the EAF slag with and without the modified method is carried out. This modified method wherein the cojets are turned on to inject oxygen in the arcing process only after the charges reaches 210T of the total charge resulted into gain of approx. 10% of FeO (From 32% in the earlier practice to 22% in the current practice) as shown in figure 3.
This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.
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WE CLAIM :
1. A modified method of increasing the efficiency of Conarc by
reducing the percentage of iron oxide (FeO) in the electric arc
furnace (EAF) slag comprising the steps of:
Feeding direct reduced iron (DRI) continuously from the top of the furnace; simultaneously injecting carbon through carbon injector operation to the furnace; chemically reducing the excess FeO which is generated during blowing period and inherently contained in direct reduced iron by the carbon injected in the above step during arcing; and injecting the oxygen from the side cojet lance to decarburize the steel to achieve the target steel chemistry characterized by the fact that the oxygen injection through the cojet lance is turned off during the said operation and is injected to decarburize steel only after the charge reaches 210T of the total charge.
2. The modified method as claimed in claim 1 is further characterized in that the top lance at the end of the processing is used to inject oxygen to decarburize the steel if one injector from the side lance is not sufficient to decarburize the steel to the desired level.
3. The modified method as claimed in claim 1 characterized in that the loss in iron oxide (FeO) content in the slag is achieved during arcing period only.
4. The modified method as claimed in claim 3 characterized in that about 10% of iron oxide (FeO) is reduced in the slag coming out of the furnace.
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5. The modified method as claimed in claim 1 characterized in that the original furnace set up is not disturbed during the operation of the process.
6. A modified method as claimed in claim 1 characterized in that the efficiency of conarc furnace is enhanced with decrease in FeO percentage in the slag.
7. The modified method of increasing the efficiency of Conarc by reducing the percentage of iron oxide (FeO) in the electric arc furnace (EAF) slag as substantially herein described with reference to the disclosure.
Dated this 24th day of NOVMBER. 2008.
HEMANT KUMAR PRESIDENT LEGAL ISPAT INDUSTRIES LIMITED
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