Title of Invention

A METHOD FOR DE- SILICONIZATION OF MOLTEN IRON OBTAINED THROUGH BLAST FURNACE ROUTE

Abstract

A method for reducing silicon content of hot metal, and in particular, a method for de-siliconization in the Blast Furnace runner, that conveys the finished hot metal tapped from the BF to the Ladles, using sinter fines. The present process also achieve advantageous drop in silicon content by about 0.1 to 0.2 % drop in normal range of silicon content of about 0.4 to 1.5%, without any loss of hot metal temperature. Importantly also the method of de-siliconization of the invention is adapted such that the transit heat loss also is reduced thereby making the process of steel making more effective and meet the growing demands of low levels of impurities and low cost steel. The method involves addition of sinter fines in the iron runner, selectively maintained in the range of 10-20 kg/thm and at a hot metal temperature in the range preferably above 1450°C. The high de-siliconisation efficiency of the method help reducing high cost of inputs and thus having prospects of wide industrial application with improved quality and reduced cost of final steel product.

Full Text

FORM 2THE PATENT ACT 1970(39 OF 1970)&The Patent Rules, 2003COMPLETE SPECIFICATION(See Section 10 and Rule 13)1 TITLE OF THE INVENTION :A METHOD FOR DE-SILICONIZATION OF MOLTEN IRON OBTAINED THROUGH BLAST FURNACE ROUTE.2 APPLICANT (S)Name : JSW Steel Limited.Nationality : An Indian Company.Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg India. ,Mumbai - 400 026, State of Maharastra,3 PREAMBLE TO THE DESCRIPTIONCOMPLETE The following specification particularly descibes the invention and the manner in which it is to be performed. FIELD OF INVENTION The present invention is directed to a method for reducing silicon content of hot metal and in particular to a method for de-siliconization in the BF runner, that conveys the finished hot metal tapped from the BF to the Ladles, using sinter fines. The present process also achieve advantageous drop in silicon content by about 0.1 to 0.2 % drop in normal range of silicon content of about 0.4 to 1.5%, without any loss of hot metal temperature. Importantly also the method of de-siliconization of the invention is adapted such that the transit heat loss also is reduced thereby making the process of steel making more effective and meet the growing demands of low levels of impurities and low cost steel. The present method eliminates the limitations of the conventional method of the silicon control in hot metal such as, low reducibility of iron ore or high moisture content of reducing agents leading to loss of hot metal and in the extreme case leading to explosions or high cost of inputs and thus having prospects of wide industrial application with improved quality and reduced cost of final steel product. BACKGROUND OF THE INVENTION It has been a known trend in the art of steel making, that the demand of steel is growing which require on one hand good quality with extremely low level of impurities and on the other hand the lowering the cost of such steel. This requirement has in turn imposed need for new target for meeting quality standards for the hot metal obtained from blast furnace (BF). It is well known in the art of iron and steel making that Blast furnace is the conventional route for conversion of iron ore into hot metal (molten iron) which takes place in a chamber, wherein large amount of heat is generated due to various chemical reactions. Preheated air, at a temperature as high as 1100°C is blown through the bottom part of the furnace through tuyeres; iron ore and coke in appropriate proportions are charged in the furnace from the top through a hopper. Preheated air when comes in contact with coke generates reducing gas at the bottom part of the furnace while the ascending reducing gases undergoes chemical reaction with the descending iron ore (oxides of iron) to reduce it to iron. During the reduction process the iron ore under goes various physical and chemical changes and finally the hot metal is accumulated in the hearth of the blast furnace. The slag produced floats on the top of liquid metal bath and the two are tapped out through different taping holes at regular intervals provided at respective heights. Normally, the silicon content in hot metal varies between 0.4-1.5%, however under abnormal conditions it exceeds even 2%. When the hot metal contains high silicon, excessive amount of lime is consumed in the steel making process, resulting in formation of higher amounts of slag during the refining process. This leads to phenomena such as slag foaming and thereby adversely affects overall yield in the steel making. Such phenomena also have adverse influence on the life of the refractory lining of the converter for steel making, steel quality and cost of production. The conventional methods of controlling the silicon content in the hot metal at the BF output is achieved by treating with a wide variety of de-siliconizing agents. These include iron ore fines, mill scale, non-metallic inorganic materials etc., which have been tried in the BF cast house for reducing hot metal silicon content. Iron ore fines and mill scales contain high level of moisture which leads to high heat loss and even explosion. On the other hand, non-metallic inorganic material is responsible for high input costs. The conventional process of control of silicon in hot metal therefore suffers from the limitations and disadvantages such as the iron ore fines have less reducibility as compared to sinter fines, iron ore fines and mill scales containing high moisture content which in turn leads to excessive loss of hot metal temperature with the possibility of occurrence of explosions, and the non-metallic inorganic material is highly expensive. There has been therefore been a continuing need in the BF reduction process of iron ores to obtain hot metal with lower silicon content by a de-siliconization process that would overcome the abovesaid limitations and disadvantages of the conventional methods of limiting the silicon content in molten iron at BF output, and in turn serve in achieving good steel quality at reduced cost. OBJECTS OF THE INVENTION The basic object of the present invention is therefore directed to a method for de-siliconization involving sinter fines in BF cast house such as to reduce the silicon content in the hot metal without significant loss of temperature or possibility of any explosion, at reasonable cost. A further object of the present invention is directed to a simple and cost-effective method of reducing silicon content in the hot metal through de-siliconization using sinter fines selectively such as in the BF runner i.e. the channel which conveys the hot metal tapped from the BF to the Ladles. A still further object of the present invention is directed to a process of de-siliconization using sinter fines providing high reducibility as compared to the iron ore fines and at less cost as compared to non-metallic inorganic materials conventionally used for the same purpose. A still further object of the present process of de-siliconization by sinter fines is to reduce heat loss from hot metal during transit and provide for a desired insulation and thereby ensuring the good hot metal temperature A still further object of the present invention directed to a process of high degree of de-siliconization obtained by sinter fines added with hot metal at the BF runner at desired proportion whereby the hot metal with silicon content as high as 1.2% could be treated to a drop silicon content by 0.1 to 0.2%, without loss of temperature. A still further object of the present process is directed to de-siliconization by sinter fines selectively added to hot metal in BF cast house , such that silicon undergoes an exothermic chemical reaction minimizing net heat loss and whereby silicon combines with oxygen that goes into the slag phase and iron into the metal phase, enabling obtaining the desired good quality of steel with reduced impurities at subsequent stage of steel making using this hot metal. Yet further object of the present invention is directed to making steel making more cost effective by providing avenues for controlling silicon and avoid problems of the hot metal containing high silicon when excessive amount of lime is consumed in the steel making process, resulting in formation of higher amounts of slag during the refining process leading to slag foaming, and thereby, affect overall yield in the steel making. Another object of the present invention is directed to favour steel making by way of effective control of silicon content in hot metal and in the process avoid silicon based concerns of the refractory lining life of the converter (steelmaking vessel), steel quality, cost, etc. A further object of the present invention is directed to address the problems of steel making such as related to poor reducibility of iron ore fines ,high moisture contents of iron ore fines and mill scale leading to excessive loss of hot metal temperature and even explosions and the highly expensive non-metallic inorganic materials which make the steel manufacture cost-extensive. SUMMARY OF THE INVENTION Thus according to the basic aspect of the present invention there is provided a method for de-siliconization of molten iron obtained through Blast Furnace (BF) route comprising: conveying tapped hot metal from the Blast Furnace to the Ladles through a runner and desiliconizing the hot metal using sinter fines in said runner. In accordance with a preferred aspect of the invention in the above method a sinter fine source is fitted above the runner for said supply of sinter fines for the desiliconization. Preferably, the sinter fine source used can comprise a box of desired capacity of fines above said runner mechanically fitted with chute and stopper for desired supply of the fines in said runner. Importantly, the discharge rate of the sinter fines is selectively provided and can be such as to have a discharge rate of sinter fines in the iron runner maintained in the range of 10-20 kg/thm. Also, the hot metal temperature, preferably above 1450°C is maintained during addition of the sinter fines. Advantageously, in the above method of the invention when the silicon fines come in contact with the hot metal in iron runner, silicon went into the slag phase and the iron separated into the metal phase under an exothermic reaction whereby the heat loss due to addition of fines is negligible. More advantageously, following the above method the transit heat loss is reduced due to formation of slag foam which acts as an insulation. The method is selectively adapted to achieve higher degree of desiliconization in the range of 20-30% is achieved in the runner with drop in silicon content of the hot metal in the range of 0.1 to 0.2%. In accordance with another aspect of the present invention there is provided a system for carrying out the method of de-siliconization using sinter fines in BF cast house as disclosed above comprising: a source of sinter fines provided above the iron runner which conveys the hot metal tapped from the BF to the Ladles preferably fitted with chute and stopper means for selective discharge of the sinter fines onto the hot metal in said runner. Thus the above disclosed method and system for desiliconization of the invention is thus adapted to achieve higher degree of de-siliconization ,favour drop in silicon content without any loss of hot metal temperature and reduction in transit heat loss. The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to non-limiting exemplary illustrations hereunder: BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE Figure 1: is the illustration of the trend of de-siliconization efficiency of the present process of de-siliconization with addition of sinter fines when plotted against silicon content of hot metal at BF output. DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES As discussed above, the present invention is directed to a process developed to reduce silicon content of hot metal through de-siliconization in the BF runner, that conveys the finished hot metal tapped from the BF to the Ladles, using sinter fines. The present invention is directed to a process of de-siliconization using sinter fines providing high reducibility as compared to the iron ore fines and at less cost as compared to non-metallic inorganic materials conventionally used for the same purpose. The present process is also directed to achieve the desired objective of good quality steel with low impurities finally produced using such hot metal having low silicon content, at reduced cost. Present process involves de-siliconization by addition of sinter fines to hot metal at the BF runner, such that silicon undergoes an exothermic chemical reaction minimizing net heat loss and whereby silicon combines with oxygen and goes into the slag phase whereas the iron into the metal phase. For the purposes of carrying out the above disclosed process of desiliconization of the invention in BF runner in accordance with an aspect of the invention arrangements are provided in the BF cast housing. More specifically the device involved for such desiliconization comprises providing metallic box sixe (1.0m X 1.0m X 1.0m =lm3 = 2 tons of sinter fines capacity) which is provided above the iron runner. The sinter fines source as above was mechanically fitted with chute and stopper. The method/process of de-siliconization according to an embodiment of the present invention for reducing silicon content by addition of sinter fines with hot metal at the BF runner was carried out involving the above arrangement as follows; a. The discharge rate of sinter fines in the iron runner was maintained in the range of 10-20 kg/ ton of hot metal; b. The hot metal temperature of at least 1480°C was ensured during addition of sinter fines; c. When the sinter fines came in contact with hot metal in runner, whereby the silicon went into slag phase and iron into the metal phase and the resulting chemical reaction was found to be exothermic as illustrated herein, and thereby heat loss due to addition is negligible; (Si)iron +(2/3 Fe203)sinter -> (Si02)siag+ (4/3Fe)ir0n + Heat The above process of silicon control by addition of sinter fines in BF runner achieved high degree of de-siliconization in the order of 20-30% which was observed when silicon content of hot metal was as high as 1.2%; The addition of sinter fines in the BF runner by the present process, achieved a drop in silicon content by 0.1 to 0.2% without any loss of hot metal temperature. Addition of One ton of sinter fines per ladle (100 tons of hot metal) decreases the silicon content in hot metal by nearly 15% and a maximum of 2 tons of sinter fines can be used for 100 tons of hot metal. The formation of slag foam found in the process advantageously acted as an insulation so that the transit heat loss from hot metal in runner is minimized. Reference is now invited to the accompanying Figure 1, that illustrates the plot of de-siliconization efficiency Vs the silicon content of hot metal wherein it is clearly demonstrated that the de-siliconization efficiency is increasing with the increase in hot metal silicon percentage and the efficiency is highest, being in the order of about 30% corresponding to the hot metal silicon content of about 1.2. It is thus possible by way of the present process of de-siliconization to provide means for reducing the silicon content in hot metal obtained from the BF reduction process, by advantageously adding sinter (Fe203) fines in the channel that carries hot metal from the BF outlet to the Ladles, without loss of temperature of the hot metal facilitating exothermic chemical reaction and thereby eliminating the limitations of the conventional silicon control methods such as using iron ore fines/mill scales or the non-metallic inorganic materials, that lead to either heat loss of metal and consequent drop in temperature/explosion due to presence of excess moisture content or are too expensive in terms of cost of inputs, thus resulting poor quality of finished steel at the subsequent stage and higher cost of production. The present process of de-siliconization of hot metal at BF output would favor obtaining superior quality steel using the said silicon controlled hot metal in steel making at reduced cost and would thus favor wide industrial application in iron and steel production in steel plants. WE CLAIM: 1. A method for de-siliconization of molten iron obtained through Blast Furnace (BF) route comprising: conveying tapped hot metal from the Blast Furnace to the Ladles through a runner and desiliconizing the hot metal using sinter fines in said runner. 2.A method as claimed in claim 1 wherein a sinter fine source is fitted above the runner for said supply of sinter fines for the desiliconization. 3. A method as claimed in anyone of claims 1 or 2 wherein said sinter fine source used comprises a box of desired capacity of fines above said runner mechanically fitted with chute and stopper & valve for desired supply of the fines in said runner. 4. A method as claimed in anyone of claims 1 to 3 wherein the discharge rate of sinter fines in the iron runner is selectively maintained such as in the range of 10-20 kg/thm. 5. A method as claimed in anyone of claims 1 to 4 wherein the hot metal temperature in the range preferably above 1450°C is maintained during addition of the sinter fines. 6. A method as claimed in anyone of claims 1 to 5 wherein when the silicon fines come in contact with the hot metal in iron runner, silicon went into the slag phase and the iron separated into the metal phase under an exothermic reaction whereby the heat loss due to addition of fines is negligible. 7. A method as claimed in anyone of claims 1 to 6 wherein higher degree of desiliconization in the range of 20-30% is achieved in the runner with drop in silicon content of the hot metal in the range of 0.1 to 0.2%. 8. A method as claimed in anyone of claims 1 to 7 wherein the transit heat loss is reduced due to formation of slag foam which acts as an insulation. 9. A system for carrying out the method of de-siliconization using sinter fines in BF cast house as claimed in anyone of claims 1 to 8 comprising: a source of sinter fines provided above the iron runner which conveys the hot metal tapped from the BF to the Ladles preferably fitted with chute and stopper means for selective discharge of the sinter fines onto the hot metal in said runner. 10. A method for de-siliconization of molten iron obtained through Blast Furnace (BF) route by addition of sinter fines in hot metal runner substantially as hereindescribed and illustrated with reference to the accompanying examples. ABSTRACT Title: A METHOD FOR DE-SILICONIZATION OF MOLTEN IRON OBTAINED THROUGH BLAST FURNACE ROUTE. A method for reducing silicon content of hot metal, and in particular, a method for de-siliconization in the Blast Furnace runner, that conveys the finished hot metal tapped from the BF to the Ladles, using sinter fines. The present process also achieve advantageous drop in silicon content by about 0.1 to 0.2 % drop in normal range of silicon content of about 0.4 to 1.5%, without any loss of hot metal temperature. Importantly also the method of de-siliconization of the invention is adapted such that the transit heat loss also is reduced thereby making the process of steel making more effective and meet the growing demands of low levels of impurities and low cost steel. The method involves addition of sinter fines in the iron runner, selectively maintained in the range of 10-20 kg/thm and at a hot metal temperature in the range preferably above 1450°C. The high de-siliconisation efficiency of the method help reducing high cost of inputs and thus having prospects of wide industrial application with improved quality and reduced cost of final steel product. Figure 1.

Documents:

1826-mum-2007-abstract.doc

1826-mum-2007-abstract.pdf

1826-MUM-2007-CLAIMS(AMENDED)-(18-4-2012).pdf

1826-MUM-2007-CLAIMS(AMENDED)-(28-5-2012).pdf

1826-MUM-2007-CLAIMS(MARKED COPY)-(28-5-2012).pdf

1826-mum-2007-claims.doc

1826-mum-2007-claims.pdf

1826-MUM-2007-CORRESPONDENCE(10-5-2012).pdf

1826-MUM-2007-CORRESPONDENCE(13-4-2009).pdf

1826-mum-2007-correspondence(25-10-2007).pdf

1826-mum-2007-correspondence-received.pdf

1826-mum-2007-description (complete).pdf

1826-mum-2007-drawings.pdf

1826-mum-2007-form 1(17-9-2007).pdf

1826-MUM-2007-FORM 18(13-4-2009).pdf

1826-mum-2007-form 2(title page)-(complete)-(17-9-2007).pdf

1826-mum-2007-form-1.pdf

1826-mum-2007-form-2.doc

1826-mum-2007-form-2.pdf

1826-mum-2007-form-26.pdf

1826-mum-2007-form-3.pdf

1826-MUM-2007-REPLY TO EXAMINATION REPORT(18-4-2012).pdf

1826-MUM-2007-REPLY TO HEARING(28-5-2012).pdf

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