Description:FIELD OF INVENTION
The present invention relates to a method of producing low phosphorous crude steel in the energy optimizing furnace (EOF) by adding calcium ferrite that promotes faster flux dissolution to get higher degree of dephosphorization in this steel making process.
BACKGROUND OF THE INVENTION
Energy Optimizing Furnace (EOF) is one of the primary steel making technologies that uses oxygen blowing to produce the liquid steel from the liquid pig iron. In the late 1970s, KORF group started modifying the open hearth furnace to compete it with the basic oxygen furnace (BOF) and electric arc furnace (EAF). These modifications resulted in the new technology named as Energy Optimizing Furnace and it had the advantages of both the BOF and EAF by means of combined-oxygen blowing, continuous slag removal and furnace tilting during the blowing. As per the original design, EOF had scrap preheating setup to utilize the off gas heat that is generated during the process. Because of the maintenance issues caused by scrap melting and the resulted blockage of exhaust gas, the whole setup was removed.
The slag FeO level maintained in this process is closer to 30% and the basicity is about 3. The most of the times the tap phosphorous level ranges from 0.006-0.009% and the lowest tap phosphorous level achieved in this process is about 0.005%.

PRIOR ART
Vidhyasagar et al. (2022) reported the experimental data while creating a static model for the energy optimizing furnace-steel making process. It involves the flux addition sequences, coolant addition, blowing practice and deslagging similar to the conventional process. Flux addition in this process contains only lime and dololime and the coolant addition was only iron ore. In this process, the lowest tap phosphorous level achieved in EOF process was about 0.005% and the tap carbon ranges from 0.034 to 0.098% with the tap temperature of 1615 to1656°C. The basicity used in this process ranges from 3.44 to 4.02 with the slag FeO level ranges from 27.42 to 36.77%.
Wu Wei and Liu Yue (2017) reported a detailed experimental method to use the pre-melted calcium ferrite slag in a 300t converter during blowing. In this method, two-thirds of lime, all the dolomite and a half of the all the sintered ore or calcium ferrite pellet are added in the beginning of the blowing. The remaining lime was added at one quarter of the blowing time and the remaining sintered ore or calcium ferrite pellet was added. The effect of sintered ore and calcium ferrite on the converter process was compared in this work. Instead of fluorite slag formation, pre-melted calcium ferrite slag was developed and applied to dephosphorize the hot metal and it resulted in decrease of raw materials consumption and improved the hot metal dephosphorization. The consumption of slag formation material was 71kg per ton of steel and by doing single slag removal, the dephosphorization rate of hot metal was averagely 85% with the hot metal phosphorus level of 0.105~0.13% while using the calcium ferrite pellet. When comparing the effect of calcium ferrite pellet with the sintered ore on the parameters involved in the dephosphorization of hot metal, the slag basicity was same, total Fe content was reduced by 3% and P2O5 content was increased by 0.2% in the calcium ferrite added heats.
Patent 201931043779A gives a method for dephosphorization of a hot metal during the steel making process in a Linz-Donawitz (LD) vessel or a basic oxygen furnace (BOF) converter by two stage addition of a slag forming reagent named calcium ferrite. The patent describes the procedure of two-stage calcium ferrite addition in LD vessel during the steel manufacturing process for producing low phosphorous (0.01%) steel. It includes the sequence such as the addition of iron-bearing scrap at first, adding first stage/batch of the calcium ferrite, adding lime in the vessel, pouring the hot metal in the vessel and blowing oxygen into the said vessel using an oxygen lance forming slag. After blowing for 8-9 minutes the remaining batch of calcium ferrite was added in 9-10 minutes. The blowing time of the process was about 15 to 17 minutes. Calcium ferrite was added in two batches and in the first batch, 0.75%-1.0625% of the weight of heat was added. In the second batch, calcium ferrite of 0.3%-0.4% of the weight of heat was added. The average output steel phosphorous content was decreased from 0.0162% to 0.011%. The average degree of dephosphorization was improved from 90.27% (i.e., with the average level of 0.67%Si& 0.166%Pinhotmetal) to 93.8%(i.e., with the average level of 0.549%Si& 0.178%Pin the hotmetal). The range in the degree of dephosphorization was increased from 72-97.7 % to 86.2%-98%.
Patent WO2020/161136A1 describes the process for refining the steel by using the different dephosphorizing agent and it also describes the method by which the rate of dephosphorization can be improved in the converter process. In their normal process the lowest tap phosphorous achieved in this process was 0.018% with the input phosphorous content of 0.091%. The input lime content of 54 kg/MT and oxygen of 63 Nm3/MT, slag basicity was 4.1, Fe in slag 15 and the tap steel temperature was 1673°C. In this conventional process, a compound with 40% CaO and 30% Fe2O3 called as slag conditioner was added in the process. In the slag conditioner, the mass ratio of mono calcium ferrite to di calcium ferrite was 0.5 or more. Preferably, a predetermined amount of slag conditioner was added to the converter before blowing the oxygen and alternatively, a predetermined amount of slag conditioner was added during the oxygen blowing. By the help of the slag conditioner, the lowest tap phosphorous achieved in this process was 0.008% with the input phosphorous content of 0.075%. The input quick lime content was 56 kg/MT, oxygen was 50 Nm3/MT, slag conditioner was 10kg/MT, slag basicity was 4.1, Fe in slag was 22.2% and the tap steel temperature was 1695°C. By using the iron oxide, the lowest tap phosphorous achieved in this process was 0.009% with the input phosphorous content of 0.084%. The input quick lime content was 34 kg/MT, oxygen was 55 Nm3/MT, iron oxide was 16 kg/MT, slag basicity was 3.5, Fe in slag 17.0 and the tap steel temperature was 1687°C. The lowest tap phosphorous of 0.008% was achieved by using the slag conditioner in this process.
Wu et al. (2020) reported the producing methodology of calcium ferrite by using the solid by products obtained in the steel plants that include lime powder and mill-scales. The ratio of iron oxides to calcium oxide was selected as 3:1 to get the best results in terms of melting characteristics. The inventors also reported the experimental results of using
calcium ferrite slag on the dephosphorization of hot metal during pre-treatment in 120 t BOF converter in the BOF converter. The hot metal with 3.46–6.81%C, 0.1–1.16%Si, 0.12–0.30%Mn, 0.10–0.18%P, 0.017–0.13%S and the temperature of 1234–1430°C.The slag forming materials used in this process were lime, light-burned dolomite, sintered ore and the calcium ferrite pellets. At the beginning of the oxygen blowing, lime and light burned dolomite needed for the first slag were added. Then the sintered ore and
calcium ferrite pellets were charged at the blow time of 3minutes during the
slag forming. After the blow time of 6minutes, converter was tilted to tap the
phosphorous enriched slag. The slag basicity is changed from 1.2-1.4 to 1.8-2.0 with the same lime consumption when calcium ferrite was not used in the
process. By this new process, the slag height was increased from 1.8m-2m to
2.5m-3m, the slag dumping slag rate was also increased from 30-40% and the dephosphorization rate was also improved from 82-85% to 90-94%.

REFERENCES
1. M. Vidhyasagar, D. Kumar, N. N. Viswanathan, S. M. Kumar and S. Manjini, A Static Model for Energy-Optimizing Furnace. steel research international, 93(9) (2022), 2200185.
2. W. Wu and Y. Liu,The development of calcium ferrite pellet used as dephosphorizing or slagging agents for Steelmaking and its application. In 2017 6th International Conference on Energy and Environmental Protection (ICEEP 2017), Atlantis Press (2017), pp. 385-389.
3. TAPAS KUMAR ROY, AKSHAY KHULLAR, HARPANAHALLI MAHESHBABU, SAROJ KUMAR SINGH, RAHUL BHATTACHARYA, RABINDRA KUMAR AND RISHABH SINGH, Patent 201931043779A, 2019.
4. MICHAEL NISPEL AND JOSE NOLDIN, Patent WO2020/161136A1
5. W. Wu, Q. Yang, G. A. O. Qi and Zeng, J. Effects of calcium ferrite slag on dephosphorization of hot metal during pretreatment in the BOF converter, Journal of Materials Research and Technology, 9(3) (2020), 2754-2761.

Traversing the prior arts, it was observed that very few work has been done in the field of development of a method of producing low phosphorous crude steel with high degree of dephosphorization in the Energy Optimizing Furnace.
Hence, in the present work, a method was developed producing low phosphorous crude steel in the energy optimizing furnace (EOF) by adding calcium ferrite that promotes faster flux dissolution to get higher degree of dephosphorization in this steel making process. The present method is different from the prior arts as mentioned above and it is clearly explained in the new method. The sequence of addition is different from the sequence that is mentioned in the prior art patents/papers.

OBJECTIVE OF THE INVENTION
The main objective of this invention is to develop a method for achieving higher dephosphorization of a hot metal during a EOF-steel making process by the addition of calcium ferrite producing low phosphorous crude steel.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method of efficient dephosphorization of metal in energy optimizing furnace (EOF) comprising:
subjecting the scrap and hot metal wherein the input hot metal including 0.1 to 0.2 % P to steps of dephosphorization and decarburization
said step of dephosphorization including involving flux and blowing of oxygen in the presence of calcium ferrite having composition of 30-42%CaO, 50-65%Fe2O3, <5%SiO2, <4% Al2O3, <0.1%P and <0.1%S,
such as to achieve efficient dephosphorization in the range of 94.07 to 97.07 %
A further aspect of the present invention is directed to the method wherein sequentially controlled addition of said calcium ferrite in relation to the said flux involved include lime and dolomite and blowing period provided for selectively controlled level of dephosphorization with increase in level of >95 % dephosphorization of heats in the range of 47% to 67% vis a vis 15% in case of conventional dephosphorization free of any calcium ferrite addition.
A still further aspect of the present invention is directed to the method which is carried out with two stage addition of calcium ferrite twice during the blowing operation following the sequence of :
i) lime addition carried out twice during the blowing operation wherein first batch is continued till about 30 to 35% blow time that is about ~90% of the lime requirement and the second stage addition takes place at ¾ of the blow time and about ~10% of the total lime requirement 74% of the blow time ii) Dololime as input charge is added initially on the top of the scrap and along with this a first batch of calcium ferrite is added followed by the hot metal pouring whereby the dissolution of dololime and the lime added during the blowing is faster;
iii) a second batch of calcium ferrite is next added during 1/4th of the blow time and it is continued till the mid of the blow to make faster progressive dissolution of flux , said addition of calcium ferrite in two stages till the mid of the blowing enabling lowering the melting point of the slag that forms during the blowing;
iv) after 50% of the blow time, iron ore addition along with the lime makes the slag that can form a low melting compound.
A still further aspect of the present invention is directed to the method which is carried out with three stage addition of calcium ferrite thrice during the blowing operation following the sequence of :
calcium ferrite is added in three stages for speedy dissolution comprising (a) the first batch is added on top of the scrap and it is about 40 to 45% of the total calcium ferrite added in the process (b) the second stage addition of calcium ferrite is carried out at the mid of the blow about 46 % of blow time and which is 30 to 35% of the total calcium ferrite addition; (c ) the third batch is added at ¾th of the blow time of about 71% of the blow time and which is about 20-30% of the total calcium ferrite addition wherein any increased amount of calcium ferrite addition, the iron ore consumption is decreased to the lowest possible such as to function as a coolant during the process apart from supply the oxygen to the system wherein the major quantity of calcium ferrite is added as said first batch at the beginning of the blow for favouring melt quickly during the blow, once the lime and dololime consumes the added calcium ferrite then the said second batch is added and there is a time gap for the melting and dissolution followed by further the said third batch addition and optionally repeating the similar phenomena till 3/4th of the blow time to make the phosphorous removal continuous and also the faster progressive flux dissolution.
Another aspect of the present invention is directed to the process carried out to control the average slag composition of 32.95%CaO, 3.83%MgO, 11.53%SiO2, 42.79%FeO, 2.07%MnO, 3.51%Al2O3,1.48%P2O5 with the average slag basicity of 3.1 and with increase in the flux consumption beneficial in the dephosphorization and wherein very high FeO level in the range of 39.25 to 45.86% is maintained which is also beneficial in terms of flux dissolution and also the dephosphorization and wherein the average degree of dephosphorization is about 95.82% (max of 97.07%) and the average tap phosphorous level maintained in this process is about 0.0063% and with the lowest tap phosphorous level achieved in this process is about 0.0044%.
Another aspect of the present invention is directed to the method wherein the input charge comprising the hot metal weight of 57.74 to 61.74 metric tonnes, scrap weight of 10.18 to 13 metric tonnes, average hot metal composition of 4.3 to 4.5 % C, 0.41 to 1.22% Si, 0.05% to 0.62%. Mn, 0.14% to 0.18% P, 0.01 to 0.05% S with an average yield of 86.63 to 92.28 % wherein;
the calcium ferrite addition of 13.44 to 14.17 kg/metric tonne of input charge is added in three stages till the mid of the blowing lowering the melting point of the slag that forms during the blowing with >95% degree of dephosphorization level achieved in 67% of the heats.
Yet another aspect of the present invention is directed to the method wherein hot metal temperature varies from 1301 to 1374°C, tap steel temperature varies from 1603 to 1697°C, blow time varies from 28 to 35 minutes, average tap to tap time varies from 48 to 69 minutes and average tap carbon in the range varies from 0.04 to 0.09 % and avg. tap phosphorous varies in the range of 0.0044 to 0.0089%
A still further aspect of the present invention is directed to the method wherein addition of calcium ferrite of 13.44 to 14.17 kg/metric tonne of input charge is done in three stages till the mid of the blowing that lowers the melting point of the slag to <1500oC that forms during the blowing.
Another aspect of the present invention is directed to the method wherein the output steel has the composition of 0.03-0.15%C, <0.005 Si, 0.005-0.015%P and 0.01-0.08%S and lowest tap steel phosphorous level of 0.0044% in the energy optimizing furnace steel making process.

The advancement is described here under in greater detail in relation to the following non-limiting exemplary illustrations as per the accompanying figures wherein:
Figure 1 : Schematic of energy-optimizing furnace (EOF) with inputs and outputs[1]
Figure 2: Process flow chart of the conventional method without the calcium ferrite addition.
Figure 3: Degree of dephosphorization of the heats processed in the conventional method.
Figure 4: Process flow chart of the new method with the 9kg calcium ferrite addition.
Figure 5: Degree of dephosphorization of the heats processed in the new 9kg calcium ferrite method.
Figure 6: Process flow chart of the new method with the 14kg calcium ferrite addition.
Figure 7: Degree of dephosphorization of the heats processed in the new 14kg calcium ferrite method.
DETAILED DESCRIPTION OF THE INVENTION
Present invention relates to a method of adding calcium ferrite for producing crude steel with lower tap phosphorous level in the energy optimizing furnace. This method produces higher degree of dephosphorization at the end of the steel making process by improving the flux dissolution. It results in better slag metal reaction and the continuous slag removal feature of the energy optimizing process aids in the removal of phosphorous from the hot metal through slag removal.
The present charge material has scrap and hot metal from 0 to 20% and 80-100% respectively. The typical mass flow in the process by means of inputs and outputs are shown in Figure 1. The input hot metal has the typical composition of 4-4.5%C, 0.3-1.3%Si, 0-1.0%Mn, 0.1-0.2% P and 0.01-0.08%S. The output steel has the composition of 0.03-0.15%C, <0.005 Si, 0.005-0.015%P and 0.01-0.08%S. The major operation in this process is dephosphorization and decarbonization. Dephosphorization is achieved by means of adding the flux and blowing the oxygen. The flux inputs such as lime and dololime are added to the hot metal while blowing to remove the impurities that comes out in the form of oxides. The reaction between the phosphorous in the hot metal and the flux along with the oxygen supply is given in Equation (2) Decarbonization is achieved primarily by means of oxygen blowing through the supersonic lances, atmospheric injectors and submerged tuyers. The generation of FeO during the oxygen blowing is also higher (i.e., 30%FeO) than the other BOFs and along with this the continuous slag removal gives excellent dephosphorization level in the EOF process but this high FeO level and continuous slag removal result in yield loss.
Dephosphorization efficiency of the process is measured by means of degree of dephosphorization and it is the percentage of decrease in the phosphorous level from the input hot metal to the output steel as given in Equation(3). In this process,>95%dephosphorization is achieved in 15% of the heats. To improve the dephosphorization of the EOF process, calcium ferrite is added during the blowing process along with the flux. Calcium ferrite has the composition of 30-42%CaO, 50-65%Fe2O3, <5%SiO2, <4% Al2O3, <0.1%P and <0.1%S.
(1)

(2)

(3)

Calcium ferrite is a kind of slag forming material that contains calcium oxide and iron oxide. It gives low melting point (~1250°C) when compared to the lime(2572°C) that is added as a flux. The mineral phase of calcium ferrite is mainly of CaO.Fe2O3 and 2CaO.Fe2O3 and its melting points are 1228°C and 1449°C respectively. Calcium Ferrite can accelerate lime dissolution and acts as a coolant of the steel making process. By adding small amount of fluxing agents into the slag, the overall mass transfer coefficient of phosphorous will increase.

Conventional Method (No calcium ferrite addition):
As shown in Figure 1, the scrap is charged inside the furnace from the furnace top then the hot metal is poured through the hot metal launder. The quantity of scrap that can be added inside the furnace is based on the input hot metal chemistry and temperature. The input hot metal weight, scrap weight, hot metal chemical composition and temperature is given in Table 1. The hot metal and scrap forms the input charge of the process. The typical conventional process flow is given in Figure 2. Once the hot metal pouring starts, the operator slowly starts the oxygen blowing through submerged tuyers, atmospheric injectors and supersonic lances as shown in Figure 1. Then the fluxes such as lime and dololime are added batch by batch continuously for the blow time of 5 to 10 minutes. Oxidation of the solute elements present in the input charge by means of blowing produces oxides that reacts with the supplied flux and forms the slag. It also gives the off gas that goes out of the furnace after the post combustion. The slag that was formed in the furnace comes out because of the carbon monoxide bubble formation and also because of the squirts produced by the action of submerged oxygen blowing at the bottom. The furnace also has the tilting arrangement of +8 to -8° that also helps in the removal of the slag whenever it is required and it is also used for tapping the liquid steel that was made in the process. The blowing operation is continued for the time of 30-35minutes. The average blow time and tap to tap time are 33 minutes and 54 minutes respectively. Usually at the mid of the blow time, coolant addition starts and it is continued till the end of the blow to adjust the tap temperature. The slag comes out of the furnace automatically from the blow time of 13 minutes and it continues till the end of the blowing.
Once the silicon removal is completed then the decarburization happens at very high rate and dephosphorization will also happen. Lime supplied melts by the help of the iron oxide that is generated during the blowing. It reacts with the phosphorous oxide and forms the slag that has the oxides of Mn, Si and Fe. The final slag before the end of the blowing has 43.35% CaO-7.03% MgO-12.66%SiO2-26.77%FeO-2.88%MnO-3.61%Al2O3 and 2.02%P2O5 (i.e., average composition). The final tap steel will have 0.06% carbon and 0.010% phosphorpous with the temperature of 1651°C and the yield of 89.39% (i.e., average) as shown in Table 1. The average degree of dephosphorization achieved in this process is 93.62% and the maximum degree of dephosphorization can go up to 95.6%. The resultant lowest tap phosphorous in this process is 0.0062%. The average basicity level maintained in this process is 3.45. Other consumption details such as lime, dololime, oxygen and iron ore per metric tonne of the tap steel is given in Error! Reference source not found..
Based on the experimental data of 39 heats, the degree of dephosphorization range is classified into <93%, >93-95 and >95% and the corresponding percentage of heats fall in this classification are shown in Figure 3. Only 15% of the heats have >95% degree of dephosphorization by this process and most of the heats (i.e., 56%) have >93 to 95% degree of dephosphorization.

Table 1 Conventional EOF steel making performance
S. No. Parameters Unit Average Range
1 No. of heats Nos. 39
2 Hot metal weight Metric tonnes 61.38
55.96-72.34
3 Scrap weight Metric tonnes 11.32 0-14.47
4 Tap steel weight Metric tonnes 64.97 59.56-69
5 Liquid Yield % 89.39 84.57-95.38
6 Hot metal temperature °C 1330 1253-1377
7 Tap steel temperature °C 1650 1651
8 Hot metal composition % 4.43C-0.55Si-0.41Mn-0.15P-0.022S 4.3 to 4.5C-0.26 to 0.94Si-0.24 to 0.47Mn-0.12 to 0.17P- 0.014 to 0.046S
9 Tap carbon % 0.06 0.04-0.1
10 Blow time min 33 25-41
11 Tap to tap time min 54 38-75
12 Slag composition % 43.35CaO-7.03MgO-12.66SiO2-26.77FeO-2.88MnO-3.61Al2O3-2.02P2O5 37 to 48 CaO-2 to 15MgO-10 to 16SiO2-18 to 35FeO-2 to 4MnO-3 to 6Al2O3-0.3 to 2P2O5
13 Basicity No unit 3.45 2.8 to 4.5
14 Lime consumption kg/metric tonne of steel 53.27 46.7-66.3
15 Oxygen consumption Nm3/metric tonne of steel 52.92 46.7-61.3
16 Dololime consumption kg/metric tonne of steel 2.98 0-10
17 Iron ore consumption kg/metric tonne of steel 21.98 0-84
18 Calcium ferrite consumption kg/metric tonne of input charge 0 0
19 Degree of dephosphorization % 93.62 88.2 to 95.6
20 Tap steel phosphorus % 0.010 0.0062-0.018

EXAMPLES
1. 9kg/metric tonne input-calcium ferrite addition in two stages
In the present method, two stage addition of calcium ferrite, dololime addition sequence and two stage addition of lime makes the significant difference when compared with the conventional method. In the conventional method, lime was added continuously from the start of the blowing to the blowtime of 12 minutes as shown in Figure 2 and during the lime addition, dololime was also added. In the new method as shown in Error! Reference source not found., the lime addition takes place twice during the blowing operation. First batch is continued till 30 to 35% blow time (i.e., here 32% blowtime) that is about ~90% of the lime requirement. The second stage addition takes place at ¾ of the blow time and about ~10% of the total lime requirement will be added (i.e., here 74% of the blow time -25 min). Dololime of about 5.4kg per ton of input charge is added at initially on the top of the scrap and along with this the first batch of calcium ferrite (i.e., 1.4kg per tonnes of input charge) is added then the hot metal pouring takes place. This makes the dissolution of dololime and the lime that will be added during the blowing faster. The second batch of calcium ferrite was added during 1/4th of the blow time (i.e., here 24% of blow time/8 min) and it is about 7.4kg per tonne of input charge and it is continued till the mid of the blow to make faster progressive dissolution of flux as shown in Figure 4. In the present method, the calcium ferrite addition of 8.8kg/metric tonne of steel is added in two stages till the mid of the blowing that can lower the melting point of the slag that forms during the blowing. This method is called as 9kg method. The melting point of the calcium ferrite is about 1250°C. After 50% of the blow time, iron ore addition along with the lime makes the slag that can form a low melting compound. The remaining operations are similar to the conventional method.
Table 2 9kg-two stage calcium ferrite addition method performance
S. No. Parameters Unit Average Standard Deviation
1 No. of heats Nos. 17
2 Hot metal weight Metric tonnes 60.74 59.4-62.4
3 Scrap weight Metric tonnes 12.72 10.23-13.71
4 Tap steel weight Metric tonnes 66.06 1272-1376
5 Yield % 89.92 84.86 to 94.08
6 Hot metal temperature °C 1332 1272 to 1376
7 Tap steel temperature °C 1662 1627 to 1693
8 Hot metal composition % 4.4C-0.66Si-0.44Mn-0.14P-0.021S 4.2 to 4.4C-0.4 to 1Si-0.09 to 0.7Mn-0.12 to 0.16P-0.014 to 0.04S
9 Tap carbon % 0.05 0.024-0.074
10 Blow time min 35 30-42
11 Tap to tap time min 55 43-78
12 Slag composition % 43.13CaO-2.89MgO-10.17SiO2-33.86FeO-3.36MnO-2.97Al2O3-1.33P2O5 27.87 to 48.6CaO-2.36 to 5.63MgO-8.48 to 15.31SiO2-26.95 to 42.11FeO-0.92 to 5.05MnO-2.08 to 4.03Al2O3-0.47 to 4.03P2O5
13 Basicity No unit 4.31 2.91 to 5.61
14 Lime consumption kg/metric tonne of steel 53.83 44.68 to 61.03
15 Oxygen consumption Nm3/metric tonne of steel 49.47 43.46 to 55.16
16 Dololime consumption kg/metric tonne of steel 2.78 0 to 10.19
17 Iron ore consumption kg/metric tonne of steel 25.11 0 to 45.76
18 Calcium ferrite consumption kg/metric tonne of input charge 8.72 8.05 to 9.08
19 Degree of dephosphorization range % 93.96 88.69 to 97.04
20 Tap steel phosphorus % 0.008 0.0043 to 0.014

The present method is experimented in 17 heats and its effect on different parameters is given in Table 2. The average input charge and tap steel weight are closer to the conventional method. The average yield in this process is about 89.92%. The input and output temperature in both the processes are closer as shown in Error! Reference source not found. and Table 2. The average final slag composition achieved in this process is 43.13%CaO, 2.89%MgO, 10.17%SiO2, 33.86%FeO, 3.36%MnO, 2.97%Al2O3, 1.33%P2O5 with the average basicity of 4.31. The calcium ferrite addition has increased the slag FeO level when compared to the conventional method and it has also diluted the other oxides which can be seen lower than the conventional method as shown in Error! Reference source not found. and Table 2. This effect can reflect in the consumption of oxygen as well as coolant since the iron oxide supply directly comes from the calcium ferrite and it can also take the heat similar to the coolant. The lime and dololime consumption stands at 53.83 and 2.78 kg/MT of tap steel that is similar to the conventional method. But the average oxygen consumption is about 49.47 Nm3/metric tonne of steel (i.e., shown in Table 2) and it is 3.45kg/metric tonne of steel lower when compared with the conventional method as shown in Error! Reference source not found.. The coolant consumption in this new method is also same as the conventional method. The blow time and tap to tap time are 35 minutes and 55 minutes respectively.
The average tap phosphorous level in this process is 0.008% that is 20% lower than the conventional method (i.e., 0.01%). It resulted in the average degree of dephosphorization of 93.96% and the degree of dephosphorization ranges from 88.69% to 97.04%. The lowest tap phosphorous is about 0.0043% that is 30% lower than the conventional process as shown in Error! Reference source not found.. The distribution in terms of degree of dephosphorization is changed because of the addition of calcium ferrite as per the present method and it is expressed in Figure 5.
Based on the experimental data of 17 heats, the degree of dephosphorization range is classified into <93%, >93-95 and >95% and the corresponding percentage of heats fall in this classification are shown in Figure 5. About 47% of the heats in this present method have >95% degree of dephosphorization by this process and most of the heats falls in this category. It is significantly higher when compared with the conventional method which only has 28% in this category. In >93 to 95% degree of dephosphorization category, 24% of the heats falls and in <93% degree of dephosphorization category only 29% of the heats falls.

Table 3 14kg-three stage calcium ferrite addition method performance
S. No. Parameters Unit Average Range
1 No. of heats Nos. 6
2 Hot metal weight Metric tonnes 59.82 57.74 to 61.74
3 Scrap weight Metric tonnes 12.46 10.18 to 13
4 Tap steel weight Metric tonnes 64.26 62.61 to 66.20
5 Yield % 88.93 86.63 to 92.28
6 Hot metal temperature °C 1333 1301 to 1374
7 Tap steel temperature °C 1643 1603 to 1697
8 Hot metal composition % 4.4C-0.72Si-0.16Mn-0.15P-0.021S 4.3 to 4.5C-0.41 to 1.22Si-0.05 to 0.62 Mn- 0.14 to 0.18P-0.01 to 0.05S
9 Tap carbon % 0.06 0.04 to 0.09
10 Blow time min 31 28 to 35
11 Tap to tap time min 56 48 to 69
12 Slag composition % 32.95CaO-3.83MgO-
11.53SiO2-42.79FeO-2.07MnO-3.51Al2O3-1.48P2O5 22.51 to 37.87CaO-2.26 to 6.54MgO-
8.9 to 18.3SiO2-39.25 to 45.86FeO-0.82 to 3.62MnO-2.64 to 4.49Al2O3-0.74 to 2.04P2O5
13 Basicity No unit 3.10 1.23 to 4.21
14 Lime consumption kg/metric tonne of steel 55.98 43.08 to 69.38
15 Oxygen consumption Nm3/metric tonne of steel 50.90 48.91 to 53.09
16 Dololime consumption kg/metric tonne of steel 5.58 0 to 7.37
17 Iron ore consumption kg/metric tonne of steel 10.92 0 to 29.53
18 Calcium ferrite consumption kg/metric tonne of input charge 13.84 13.44 to 14.17
19 Degree of dephosphorization % 95.82 94.07 to 97.07
20 Tap steel phosphorus % 0.0063 0.0044-0.0089

2. 14kg/metric tonne input-calcium ferrite addition in three stages
The dephosphorization efficiency is marginally improved in the 9kg method but to improve it further the quantity of addition is further increased to 14kg/metric tonne of the input charge. It is approximately 1.5 times of the 9kg method and it is called as 14kg method. The sequence of addition and the quantity of addition is also varied to get the highest possible dephosphorization in the process. The performance of adding calcium ferrite of 14kg/metric tonne of input in EOF process is given in Table 3 and it is the experimental results of 6 heats. When compared to the 9kg method, in the present 14kg method, calcium ferrite is added in three stages to make the fastest dissolution. The first batch is added on top of the scrap and it is about 40 to 45% of the total calcium ferrite that will be added in the process (i.e., here 44%) as shown in Figure 6. The addition quantity is about 5.9kg/metric tonne of the input charge. The second stage addition of calcium ferrite is carried out at the mid of the blow and here it is 46% of the blow time. The quantity added in the second stage is 4.4kg per metric tonne of the input charge and it is 30 to 35% of the total calcium ferrite addition. The next batch is added at ¾th of the blow time and here in the example heat, it is 71% of the blow time. The quantity added in the third stage is 3.2kg/metric tonne of the input charge and it is 20-30% of the total calcium ferrite addition. Due to the increase in the calcium ferrite addition quantity, the iron ore consumption is decreased to the lowest possible used in the process (i.e., average value of 10.92kg/metric tonne of steel) since it can act as a coolant during the process. Apart from that the calcium ferrite can also supply the oxygen to the system that is seen in the oxygen consumption level (i.e., 50.9Nm3/metric tonne of steel). Here the major quantity of calcium ferrite is added at the beginning of the blow makes this process much simpler and it can melt quickly during the blow. Once the lime and dololime consumes the added calcium ferrite then the second batch is added and there is a time gap for the melting and dissolution. Further the third batch is added and the similar phenomena is repeated till 3/4th of the blow time to make the phosphorous removal continuous and also the faster progressive flux dissolution. This process resulted in the average slag composition of 32.95%CaO, 3.83%MgO, 11.53%SiO2, 42.79%FeO, 2.07%MnO, 3.51%Al2O3,1.48%P2O5 with the average slag basicity of 3.1. There is an increase in the flux consumption but the it is beneficial in the dephosphorization. Very high FeO level maintained in this process is also beneficial in terms of flux dissolution and also the dephosphorization. There is no significant loss in the average yield of the process since it vigorously involved in the flux dissolution. The average degree of dephosphorization achieved in this new process is about 95.82 (max of 97.07%) and the average tap phosphorous level maintained in this process is about 0.0063%. The lowest tap phosphorous level achieved in this process is about 0.0044% and it is very low when compared with the conventional EOF steel making process as shown in Table 1.
The dephosphorization efficiency is depicted in terms of the degree of dephosphorization range as shown in Figure 7. In the 14kg method, all the heats have >93% degree of dephosphorization. About 67% of the heats have >95% degree of dephosphorization and 33% of the heats have >93 to 95% degree of dephosphorization.

ADVANTAGES OF THE INVENTION:
Primary advantages of the beneficiation process are as follows:
The method provides higher dephosphorization of a hot metal during a EOF-steel making process by the addition of calcium ferrite, thereby producing low low phosphorous crude steel
The method provides lowest tap steel phosphorous level of 0.0044% in the energy optimizing furnace steel making process
The method achieves highest degree of dephosphorization level of 97.07%
The method achieves >95% degree of dephosphorization level in 67% of the heats
The method achieves >93% degree of dephosphorization level in 100% of the heats
, Claims:We claim:

1. A method of efficient dephosphorization of metal in energy optimizing furnace (EOF) comprising:
subjecting the scrap and hot metal wherein the input hot metal including 0.1 to 0.2 % P to steps of dephosphorization and decarburization
said step of dephosphorization including involving flux and blowing of oxygen in the presence of calcium ferrite having composition of 30-42%CaO, 50-65%Fe2O3, <5%SiO2, <4% Al2O3, <0.1%P and <0.1%S,
such as to achieve efficient dephosphorization in the range of 94.07 to 97.07 %
2. The method as claimed in claim 1 wherein sequentially controlled addition of said calcium ferrite in relation to the said flux involved include lime and dolomite and blowing period provided for selectively controlled level of dephosphorization with increase in level of >95 % dephopshorisation of heats in the range of 47% to 67% vis a vis 15% in case of conventional dephosphorisation free of any calcium ferrite addition.
3. The method as claimed in anyone of claims 1 or 2 which is carried out with two stage addition of calcium ferrite twice during the blowing operation following the sequence of :
i) lime addition carried out twice during the blowing operation wherein first batch is continued till about 30 to 35% blow time that is about ~90% of the lime requirement and the second stage addition takes place at ¾ of the blow time and about ~10% of the total lime requirement 74% of the blow time ii) Dololime as input charge is added initially on the top of the scrap and along with this a first batch of calcium ferrite is added followed by the hot metal pouring whereby the dissolution of dololime and the lime added during the blowing is faster;
iii) a second batch of calcium ferrite is next added during 1/4th of the blow time and it is continued till the mid of the blow to make faster progressive dissolution of flux , said addition of calcium ferrite in two stages till the mid of the blowing enabling lowering the melting point of the slag that forms during the blowing;
iv) after 50% of the blow time, iron ore addition along with the lime makes the slag that can form a low melting compound.
4. The method as claimed in anyone of claims 1 or 2 which is carried out with three stage addition of calcium ferrite thrice during the blowing operation following the sequence of :
calcium ferrite is added in three stages for speedy dissolution comprising (a) the first batch is added on top of the scrap and it is about 40 to 45% of the total calcium ferrite added in the process (b) the second stage addition of calcium ferrite is carried out at the mid of the blow about 46 % of blow time and which is 30 to 35% of the total calcium ferrite addition; (c ) the third batch is added at ¾th of the blow time of about 71% of the blow time and which is about 20-30% of the total calcium ferrite addition wherein any increased amount of calcium ferrite addition, the iron ore consumption is decreased to the lowest possible such as to function as a coolant during the process apart from supply the oxygen to the system wherein the major quantity of calcium ferrite is added as said first batch at the beginning of the blow for favouring melt quickly during the blow, once the lime and dololime consumes the added calcium ferrite then the said second batch is added and there is a time gap for the melting and dissolution followed by further the said third batch addition and optionally repeating the similar phenomena till 3/4th of the blow time to make the phosphorous removal continuous and also the faster progressive flux dissolution.
5. The process as claimed in claim 4 carried out to control the average slag composition of 32.95%CaO, 3.83%MgO, 11.53%SiO2, 42.79%FeO, 2.07%MnO, 3.51%Al2O3,1.48%P2O5 with the average slag basicity of 3.1 and with increase in the flux consumption beneficial in the dephosphorization and wherein very high FeO level in the range of 39.25 to 45.86% is maintained which is also beneficial in terms of flux dissolution and also the dephosphorization and wherein the average degree of dephosphorization is about 95.82% (max of 97.07%) and the average tap phosphorous level maintained in this process is about 0.0063% and with the lowest tap phosphorous level achieved in this process is about 0.0044%.
6. The method as claimed in claim 1 wherein the input charge comprising the hot metal weight of 57.74 to 61.74 metric tonnes, scrap weight of 10.18 to 13 metric tonnes, average hot metal composition of 4.3 to 4.5 % C, 0.41 to 1.22% Si, 0.05% to 0.62%. Mn, 0.14% to 0.18% P, 0.01 to 0.05% S with an average yield of 86.63 to 92.28 % wherein;
the calcium ferrite addition of 13.44 to 14.17 kg/metric tonne of input charge is added in three stages till the mid of the blowing lowering the melting point of the slag that forms during the blowing with >95% degree of dephosphorization level achieved in 67% of the heats.
7. The method as claimed in claim 1 wherein hot metal temperature varies from 1301 to 1374°C, tap steel temperature varies from 1603 to 1697°C, blow time varies from 28 to 35 mins, average tap to tap time varies from 48 to 69 mins and average tap carbon in the range varies from 0.04 to 0.09 % and avg. tap phosphorous varies in the range of 0.0044 to 0.0089%
8. The method as claimed in claim 1 wherein addition of calcium ferrite of 13.44 to 14.17 kg/metric tonne of input charge is done in three stages till the mid of the blowing that lowers the melting point of the slag to <1500oC that forms during the blowing.
9. The method as claimed in claim 1 wherein the output steel has the composition of 0.03-0.15%C, <0.005 Si, 0.005-0.015%P and 0.01-0.08%S and lowest tap steel phosphorous level of 0.0044% in the energy optimizing furnace steel making process.

Dated this the 18th Day of November, 2023
AnjanSen
Of AnjanSen & Associates
(Applicants Agent & Advocate)
IN/PA-199