Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A METHOD FOR STEEL PRODUCTION IN EOF WITH IMPROVED DEPHOSPHORIZATION USING LIMESTONE PARTIALLY REPLACING LIME.



2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company.

Address : Salem Works, Pottaneri P.O., Mecheri, Mettur Taluk, Salem District- 636453, Tamil Nadu, India;

Having the Regd. Office at:
JSW CENTRE, BANDRA KURLA COMPLEX, BANDRA(EAST), MUMBAI-400051, MAHARASHTRA, INDIA.




3 PREAMBLE TO THE DESCRIPTION

COMPLETE








The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to a method of producing crude steel in the energy optimizing furnace (EOF) with substantially low phosphorous in tap steel achieved by partial replacement of lime with limestone that produces freshly prepared lime to the metal to get high degree of dephosphorization in this steel making process with reduced cost of steel production.
BACKGROUND OF THE INVENTION
The Energy Optimizing Furnace (EOF) is used to convert liquid hot metal from the blast furnace into liquid steel through the introduction of oxygen. Developed by the KORF group in the late 1970s, the EOF was designed based on modifications made to the open hearth furnace to compete with the basic oxygen furnace (BOF) and electric arc furnace (EAF). It combines features of both the BOF and EAF, including simultaneous oxygen blowing and continuous slag removal throughout the process. The furnace maintains a slag basicity close to 3, with FeO levels around 30% during operation and the tap phosphorus level typically ranges from 0.005% to 0.015% in this process.

PRIOR ART
Vidhyasagar et al. (2022) reported a static model for the energy optimizing furnace-steel making process along with the experimental data. It contains the data of the process parameters such as fluxes, coolants, chemical composition of input hot metal, output steel and slag, charge mix details and temperature details. Fluxes used were lime and calcined dolomite and the coolant used was iron ore. As per the data, the hot metal used had the chemical composition of 4.18 to 4.55% carbon, 0.37 to 1.09% silicon, 0.39 to 1.06% manganese, 0.144 to 0.17 phosphorous and 0.01 to 0.029% sulphur. tap phosphorous level achieved in this process ranges from 0.005% to 0.013% for the tap carbon level ranges from 0.034 to 0.098% with the tap temperature of 1615 to1656°C. The slag basicity used in this process ranges from 3.44 to 4.02 with the slag FeO level ranges from 27.42 to 36.77%.

Vidhyasagar et al. (2021) reported the typical performance of EOF with the help of the heat and mass balance study. The average heat data were represented based on the fifteen heats which were taken at EOF-2 at JSW Steel Ltd., Salem works. In the charge mix, 18.7% of scrap was used with the hot metal with the composition of 4.2-4.7% carbon, 0.3-1.0% silicon, 0.3-1.0% manganese, 0.1-0.15% phosphorous and 0.02-0.07% sulphur with the temperature of 1350⁰C. To produce a ton of liquid steel of 0.05% carbon, 0.0001% silicon, 0.1% manganese, 0.01% phosphorous and 0.03% sulphur by this process, the fluxes such as lime of 53.3kg and dololime of 5.7kg were used and the coolants such as iron ore of 23.8kg and EOF crushed slag of 22.4kg were used and the oxygen of 53.9 Nm3 were used. The typical yield (i.e., Liquid yield) of EOF based on the experiments to perform the mass balance was about 90.7% and it is including the tap additions weight also since the weight measurement can be done only after the tapping. The average FeO level in the process was about 29.8%. The blow time and tap to tap time of the process were 35 and 65 minutes respectively.

Co-pending Patent IN202241017038A (i.e., applied) reported, the adapted supersonic system with the improved availability and productivity in the energy optimizing furnace. A new supersonic system was made from movable to fixed along with the adaptions in the nozzle design reduced the maintenance time of the supersonic system during the relining of the furnace refractory. It has also reduced the cost of the production by the elimination the man power requirement for the maintenance during the bottom change. As per the process data reported in this new design, the refractory life was reported as 883 to 1212 heats. The lime consumption ranges from 52.79 to 57.12 kg/MT steel and the oxygen consumption ranges from 51.86 to 54.31 Nm3/MT steel. Manganese level in the hot metal ranges from 0.7 to 1.0%.

Vijay Sharma and Mariappan (2008) reported the optimization techniques of steel making practice in EOF process under Indian conditions. It includes productivity improvements and cost reduction of the process. Improvements were done to improve the charge to liquid metal yield of 45 metric tons (EOF-1) and 65 metric tons EOF (EOF-2). In EOF-1, improvements were seen with the liquid yield rising from 90.2% to 92.2% and blow time being cut from 36 minutes to 31 minutes. These gains were attributed to the adoption of catch carbon techniques, careful selection of hot metal based on its chemistry and temperature, and better management of liquid metal through the slag door, especially when excessive boiling occurred. The catch carbon approach resulted in a tap carbon level greater than 0.1% with 85% consistency and lowered the slag FeO content by 22%. When the carbon content fell below 0.1%, the FeO level rose to around 28%.
In EOF-2, which handles 65 metric tons, the liquid metal yield was about 90.1% with a charge mix of 80.11% hot metal and 19.89% solid scrap. This process had a blow time of 38 minutes, oxygen consumption of 66 m³/MT, and lime consumption of 58 m³/MT. Unlike previous methods, the current process does not utilize catch carbon practices. It achieves a tap carbon level between 0.02% and 0.07%, which is more susceptible to FeO oxidation compared to the >0.1% carbon level that Vijay Sharma recommended for better yield and reduced FeO oxidation.
EOF-1’s capacity has been upgraded to 65 metric tons with a new supersonic design, making direct comparisons with previous setups difficult. While the current process manages metal loss through the slag door and controls metal and slag output throughout the blowing phase, blow times remain at approximately 35 minutes in both traditional and new methods due to the tap carbon level generally being <0.1%. Despite this, the new method still achieves a higher liquid yield compared to the older 65 metric ton furnace process. Additionally, both lime and oxygen consumption are lower in the recent conventional and new methods compared to the previous process.

Patent IN 511324 reported an advanced method for producing low-carbon crude steel in an Energy Optimizing Furnace (EOF), demonstrating significant improvements over conventional processes. For each ton of tap steel, the method utilizes 15-20% scrap and 80-85% hot metal, with the hot metal comprising 4-5% carbon, 0.25-1.5% silicon, 0.25-1.5% manganese, 0.02-0.07% sulfur, and 0.1-0.2% phosphorus. The steel produced has a tap carbon content of 0.03-0.1%. The process involves adding 3100-3500 kg of lime, 300-800 kg of dolomite, and 500-1300 kg of coolant per heat of tap steel, and consumes 3300-3900 Nm³ of oxygen. With respect to per ton of crude steel, on an average 50.87 kg of lime, 8.16 kg dololime, 13.81 kg of iron ore and 55.94 kg of oxygen were used. Controlled oxygen blowing using supersonic lances, atmospheric injectors, and submerged tuyers, combined with non-continuous slag removal by tilting the furnace, reduces slag FeO levels to about 26.83% and improves crude steel yield to 90.22% and liquid steel yield to 91.69%. This method achieves notable enhancements in steel production efficiency. Compared to traditional continuous slag removal, it results in a reduction of slag FeO by at least 1%, increases crude steel yield by up to 1% (from 89.20% to 90.22%), and boosts liquid steel yield by up to 1.8% (from 90.14% to 91.69%). The process also eliminates hand lancing operations, which significantly lowers associated costs. Overall, this optimized method provides improved yield, reduced slag FeO, and cost savings, demonstrating its efficacy and advantages over conventional steelmaking practices.

Patent CN103993134A described a steelmaking slag melting agent designed to enhance the efficiency of steel production. This agent is composed of 30%-60% limestone powder, 30%-60% iron-containing raw materials, 0%-10% carbon powder, and 2% organic binder. These materials are uniformly mixed and pressed into a solid form using a high-pressure ball press machine. This product has the melting point between 1220-1250°C. The primary purpose of this slag melting agent is to facilitate the removal of phosphorus from molten iron, which is crucial for producing high-quality steel. By adding the agent and lime simultaneously after 1.5 minutes of converter blowing, the phosphorus content in the steel is significantly reduced. The ratio of the slag melting agent to lime is between 1.5:1 and 4:1. Additionally, the agent helps inhibit furnace slag drying by adding 5-13 kg/t steel during the medium decarburization period, which occurs 5-6 minutes into the blowing process. This reduces the iron oxide content in the slag and prevents drying. Furthermore, the agent prevents splashing in the converter by reducing the occurrence of CO bubbles during the decarburization period. By adding 2-5 kg/t steel of the agent, the incidence of splashing is minimized, ensuring a smoother steelmaking process. Overall, this invention aims to optimize the steelmaking process by improving slag formation and reducing production issues. It offers a practical solution to common problems faced in steel production, such as slag drying and converter splashing, leading to cost savings and improved productivity for steel manufacturers. By optimizing the slag formation process, the invention contributes to more sustainable and efficient steel production. This innovation is particularly relevant in the context of increasing environmental regulations and the need for cleaner production methods. Overall, the invention represents a significant advancement in the field of steelmaking, providing a comprehensive solution to improve the quality and efficiency of steel production.

Co-pending Patent IN 202321078466 reported a method of producing low phosphorous crude steel in an energy optimizing furnace (EOF) by adding calcium ferrite in three stages. The hot metal used in this process has a composition of 4.3-4.5% C, 0.41-1.22% Si, 0.05-0.62% Mn, 0.14-0.18% P, and 0.01-0.05% S. The output steel produced has a composition of 0.03-0.15% C, <0.005% Si, 0.005-0.015% P, and 0.01-0.08% S. The method achieves a high degree of dephosphorization, with levels ranging from 94.07% to 97.07%. Lime and dololime are added as fluxes during the blowing process to aid in the removal of impurities. The lime consumption is approximately 53.83 kg per metric tonne of steel, while dololime consumption is around 2.78 kg per metric tonne of steel. Oxygen is blown through supersonic lances, atmospheric injectors, and submerged tuyers, with an average consumption of 49.47 Nm³ per metric tonne of steel. Iron ore is also used in the process, with an average consumption of 25.11 kg per metric tonne of steel. The addition of calcium ferrite, which has a composition of 30-42% CaO, 50-65% Fe₂O₃, <5% SiO₂, <4% Al₂O₃, <0.1% P, and <0.1% S, significantly improves the dephosphorization efficiency. The method achieves >95% dephosphorization in 67% of the heats, compared to only 15% in the conventional process. The lowest tap phosphorous level achieved is 0.0044%, which is a significant improvement over the conventional method’s 0.0062%. The process also maintains adequate tap temperatures, ranging from 1603°C to 1697°C. The average slag composition achieved includes 32.95% CaO, 3.83% MgO, 11.53% SiO₂, 42.79% FeO, 2.07% MnO, 3.51% Al₂O₃, and 1.48% P₂O₅. The basicity of the slag is maintained at an average of 3.1. This innovative method results in better slag-metal reactions and continuous slag removal, leading to higher dephosphorization efficiency and lower phosphorous levels in the final steel product. However, it is important to note that the cost of calcium ferrite is approximately 5 to 8 times higher than lime, which could impact the overall cost-effectiveness of the process.

Prakash Gupta et al. (2024) explores the partial replacement of lime with limestone in Basic Oxygen Furnace (BOF) steelmaking to enhance sustainability and reduce CO2 emissions. Lime, produced by calcining limestone, is a flux in BOF steelmaking, but its transportation and reheating cause energy losses. The study investigates using limestone directly in the BOF, leveraging the heat available to decompose it, thus avoiding the need for calcination in lime kilns. Laboratory experiments assessed the behavior of limestone at high temperatures, focusing on size, exposure time, and temperature. Trials in a 160-ton BOF replaced 10% of lime with limestone, monitoring blow profiles, slag condition, and refractory wear. Results showed that limestone addition improved dephosphorization, reduced lime and iron ore consumption, and enhanced slag fluidity. The study found that limestone’s cooling efficiency is 20% lower than iron ore, necessitating adjustments in iron ore addition. The trial reported a 10 ppm reduction in turndown phosphorus and a 1% improvement in dephosphorization. SEM-EDS analysis revealed better utilization of lime and improved slag morphology. The study also noted a reduction in refractory wear and a potential decrease in indirect CO2 emissions by 2 kg per ton of crude steel. Overall, the research highlights the benefits of limestone addition in BOF steelmaking, including cost savings, energy conservation, and environmental impact reduction. The study also discusses the challenges of limestone use, such as slopping and fines generation, and the need for optimal size and timing of limestone addition. The findings suggest that limestone can be a viable alternative to lime, contributing to more sustainable steel production.
The study focused on the use of hot metal (HM) with a composition of C = 4.5%, Si = 0.6%, P = 0.18%, and Mn = 0.1%. The initial temperature of the HM was 1350°C, which increased to 1650°C during the process. The steel produced in a 160-ton basic oxygen furnace (BOF) had a turndown temperature of around 1636°C for trial heats and 1642°C for regular heats. The phosphorous content in the steel was 0.017% for trial heats and 0.018% for regular heats. The dephosphorization efficiency was 91% in trial heats, slightly higher than the 90% in regular heats. The phosphorous partition ratio (Lp) improved to 102 in trial heats compared to 98 in regular heats.
Limestone addition averaged 1074 kg per heat, replacing lime and iron ore. This showed a cooling efficiency of 24°C per ton, which is lower than the 30°C per ton for iron ore. The basicity of slag remained around 3.4 to 3.5 in both trial and regular heats. The off-gas composition indicated active decomposition processes, with increased CO and CO2 content. The addition of limestone resulted in lower refractory erosion and better utilization of lime. The trial also demonstrated cost reduction and a potential decrease in indirect CO2 emissions by 2 kg per ton of crude steel due to the lower energy requirement for limestone decomposition.

Hong Li et al. (2011) reported the industrial experiments using limestone instead of lime for slagging during the LD-steelmaking process at Shijiazhuang Iron & Steel Co., Ltd. (Shi Steel) and Xinshan Iron & Steel Co., Ltd. (Xinshan Steel). In Shi Steel, the reference furnace (No.1) used only lime, consuming 31 kg per ton of steel, with a heat size of 51.3 tons and no scrap added. The hot metal composition was 0.64% Si, 0.28% Mn, 0.092% P, and 0.038% S, resulting in final steel compositions of 0.23% C, 0.015% P, and 0.021% S. The slag composition included 16.07% TFe, 15.11% SiO2, 48.18% CaO, 8.35% MgO, 1.08% Al2O3, 2.29% MnO, 1.941% P2O5, and 0.018% S, with a yield of 564 kg/ton of steel. In the experimental furnaces, limestone substituted lime at rates of 40%, 60%, and 80%. For No.2, 14 kg of lime and 7.7 kg of limestone per ton of steel were used, with a heat size of 55 tons and 2.1 tons of scrap. The hot metal composition was 0.64% Si, 0.27% Mn, 0.093% P, and 0.052% S, resulting in final steel compositions of 0.10% C, 0.009% P, and 0.026% S. The slag composition included 16.31% TFe, 13.81% SiO2, 49.73% CaO, 8.19% MgO, 1.43% Al2O3, 2.17% MnO, 1.862% P2O5, and 0.034% S, with a yield of 903 kg/ton of steel. For No.3, 12 kg of lime and 7.1 kg of limestone per ton of steel were used, with a heat size of 55.4 tons and 3.2 tons of scrap. The hot metal composition was 0.57% Si, 0.27% Mn, 0.090% P, and 0.035% S, resulting in final steel compositions of 0.13% C, 0.012% P, and 0.026% S. The slag composition included 18.61% TFe, 12.77% SiO2, 48.84% CaO, 7.92% MgO, 1.55% Al2O3, 2.11% MnO, 1.767% P2O5, and 0.033% S, with a yield of 643 kg/ton of steel. For No.4, 6 kg of lime and 5.9 kg of limestone per ton of steel were used, with a heat size of 54.8 tons and 4.0 tons of scrap. The hot metal composition was 0.51% Si, 0.28% Mn, 0.092% P, and 0.052% S, resulting in final steel compositions of 0.15% C, 0.009% P, and 0.026% S. The slag composition included 17.36% TFe, 13.25% SiO2, 49.86% CaO, 7.28% MgO, 2.1% Al2O3, 2.16% MnO, 1.9% P2O5, and 0.029% S, with a yield of 956 kg/ton of steel. In Xinshan Steel, full limestone substitution was tested. For No.1, 2.5 kg of limestone per ton of steel was used, with a heat size of 38.5 tons and no scrap added. The hot metal composition was 4.33% C, 0.5% Si, 0.49% Mn, and 0.018% S, resulting in final steel compositions of 0.23% C, 0.14% Si, 0.36% Mn, 0.015% P, and 0.021% S. The slag composition included 16.09% TFe, 15.24% SiO2, 50.44% CaO, 7.91% MgO, and 3.31% Al2O3, with a yield of 3.31 kg/ton of steel. For No.2, 3 kg of limestone per ton of steel was used, with a heat size of 40 tons and no scrap added. The hot metal composition was 4.2% C, 0.42% Si, 0.48% Mn, and 0.020% S, resulting in final steel compositions of 0.10% C, 0.17% Si, 0.39% Mn, 0.009% P, and 0.026% S. The slag composition included 16.69% TFe, 14.91% SiO2, 50.17% CaO, and 6.47% MgO. For No.3, 2.4 kg of limestone per ton of steel was used, with 5% steel scrap added, and a heat size of 38 tons. The hot metal composition was 4.2% C, 0.42% Si, 0.48% Mn, and 0.020% S, resulting in final steel compositions of 0.13% C, 0.17% Si, 0.41% Mn, 0.012% P, and 0.026% S. The slag composition included 17.09% TFe, 15.89% SiO2, 49.64% CaO, and 6.04% MgO, with a yield of 3.12 kg/ton of steel. The sequence of limestone addition involved charging limestone into the converter along with hot metal and scrap, ensuring that the limestone was in contact with the hot metal and liquid slag to facilitate its decomposition and participation in the slagging process. These experiments demonstrated that using limestone instead of lime can effectively reduce lime consumption while maintaining the required steel quality and composition, with significant environmental and economic benefits.
REFERENCES
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.
M. Vidhyasagar, G. Murali and G, Balachandran G, Thermo-kinetics, mass and heat balance in an energy optimizing furnace for primary steel making. IronmakSteelmak. 2021;48(1):97–108.
Malaiyappan Vidhyasagar, MuthuKumararaja, PalvannanathanRamasubramanian, Durairaj Rajesh, S M, Kumar and SambandamManjini, Patent IN202241017038A, 2022.
V. Sharma, Optimization of Steel Making Process Through Energy Optimizing Furnace Under Indian Conditions Faculty of Mechanical Engineering Making Process Through Energy. 2008.
Malaiyappan Vidhyasagar, KadarkaraisamyKrishnakumar, DharmarSakkiah, PalvannanathanRamasubramanian, Durairaj Rajesh, JayapalDevakumar, S M, Kumar and SambandamManjini, Patent IN511324, 2024.
Wu Wei, Patent CN103993134A, 2014.
Malaiyappan Vidhyasagar, PalvannanathanRamasubramanian, Pandian Mageswar, Durairaj Rajesh, JayapalDevakumar, S. M. Kumar, SambandamManjini, Patent 202321078466, 2023.
P. Gupta, S. Sarkar and T. K. Roy, A Strategy for Partial Replacement of Lime by Limestone and Its Impact on Basic Oxygen Furnace Steelmaking, Steel res int., (2024) 2400030.
H. Li, L. F. Guo, Y.Q.Li, W. C. Song, J. Feng, M. Liang, D. X. Dong,G. L. Wang, H. W. Zhang, S. L. Li and T. F. Zhang, Industrial experiments of using limestone instead of lime for slagging during LD-steelmaking process. Advanced Materials Research, 233 (2011) 2644-2647.

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 cost crude steel with low phosphorous in the Energy Optimizing Furnace.
Hence, in the present work, a method was developed to produce low cost crude steel in the energy optimizing furnace (EOF) by adding limestone in place of lime with lower phosphorous level in the tap steel. 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 provide a method of producing steel in EOF with low phosphorous in tap steel by adding limestone partially replacing lime to dephosphorize a hot metal during EOF-steel making process.

A further object of the present invention is to provide a method of producing steel in EOF with low phosphorous in tap steel wherein amount and cost of flux addition is reduced.

A still further object of the present invention is to provide a method of producing steel in EOF with low phosphorous in tap steel wherein directly charging limestone into slag allows for simultaneous decomposition and dissolution, producing highly active lime that dissolves quickly.

A still further object of the present invention is to provide a method of producing steel in EOF with low phosphorous in tap steel wherein CO2generated by decomposition of limestone plays a crucial role in this process by creating local convection in the slag, enhancing heat transfer and accelerating limestone dissolution.

A still further object of the present invention is to provide a method of producing steel in EOF with low phosphorous in tap steel wherein unlike traditional lime dissolution, the high-melting point 2CaO•SiO2 layer does not form or restrict limestone dissolution due to the continuous destruction and removal of this layer by CO2.

A still further object of the present invention is to provide a method of producing steel in EOF with low phosphorous in tap steel wherein the process achieves an averaged phosphorization degree of 91.7% and a lowest tap phosphorus of 0.006%, with an average liquid yield of 88.84%, demonstrating its efficiency and cost-effectiveness.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method of steel production in an energy optimizing furnace (EOF) with advanced degree of dephosphorization with partial replacement of lime with lime stone comprising :

scarp charging ;

hot metal pouring ;

carrying out oxygen blowing in the presence of fluxes including lime and dololime and iron ore as source of iron oxide to thus generate slag and off gases which exit the furnace,

wherein the method includes the step of generating highly reactive lime for advanced degree of dephosphorization following the partial replacement of required lime by limestone in said EOF process of steel manufacture in stages including (i) an initial batch of limestone addition to scarp before hot metal pouring followed by (ii) a second stage of addition of limestone after said hot metal pouring and initiation of blowing and until completion of blowing whereby the limestone generates fresh lime highly reactive to hot metal by dissolving the freshly generated lime from limestone quickly into the slag under endothermic conditions for attaining reduced tap phosphorous..

A further aspect of the present invention is directed to said method which is carried out with 7.5 to 19 % of total lime content replaced by limestone comprising

charging of scrap inside the energy optimizing furnace (EOF) depending on a heat/batch size,

addition onto the scrap charge of 40 to 60% by wt of the total replaced limestone as lime replacement immediately after the scrap is charged inside the furnace and before pouring of the hot metal whereby the initial batch of limestone can take heat /enthalpy available inside furnace before charging of the hot metal;

pouring hot metal of selective composition in said furnace;

starting oxygen blowing inside furnace followed by adding the remaining 40 to 60% of the replaced limestone once the blow starts and completing lime stone addition by next 1-3 minutes preferably 2 minutes under

charge of flux including reduced lime and dololime and iron ore addition for required quantity and duration;
tapping steel produced with desired advanced dephosphorization level of tap phosphorous in the range of 0.006% to 0.14%

A still further aspect of the present invention is directed to said method wherein the freshly forming slag with iron oxide and silica is subjected to reaction with limestone and lime combination for reduced iron ore consumption wherein the heat required for calcination of limestone and forming fresh lime which is highly reactive to hot metal with evolving carbon dioxide from the calcination enabling breaking dicalcium silicate layer formed on top of limestone for advanced degree of dephosphorization by dissolving said freshly prepared lime quickly into the slag under endothermic conditions taking heat generated during blowing thus favouring reduced iron ore requirement and also flux requirements for a cost effective manufacture in EOF.

A still further aspect of the present invention is directed to said method wherein scrap weight charged is in the range of 12.87-14.09MT, Hot metal weight charged is in the range of 58.74-62.24MT, for Tap steel weight in the range of 61.00-67.50MT with Liquid steel Yield of 83.7-91.7%.

A still further aspect of the present invention is directed to said method wherein the hot metal composition comprising by wt % 4.3 to 4.5%C, 0.35 to 0.96%Si, 1.16 to 1.98%Mn, 0.12 to 0.13%P, 0.01 to 0.03% S and rest is iron.

A still further aspect of the present invention is directed to said method wherein limestone consumption in this process is 12.96 kg/metric ton of steel that can replace the lime consumption, the average lime consumption is reduced from 46.86 kg/metric ton of steel to 38.48 kg/metric ton of steel and the average iron ore consumption is reduced from 20.5 kg/metric ton of steel to 10.97 kg/metric ton of steel when the limestone method is used.

A still further aspect of the present invention is directed to said method wherein produced steel is tapped with the average temperature of 1664C and average tap phosphorous associated with this process is 0.010% with the average degree of dephosphorization of 91.9% for the replacement of 13% lime on an average with the limestone.

Another aspect of the present invention is directed to said method wherein the maximum replacement of the lime by limestone is 19%.

Yet another aspect of the present invention is directed to said method wherein average blow time and process time are 36 and 54 minutes respectively along with the average liquid yield of 88.84% even with the high manganese hot metal in puts.

A further aspect of the present invention is directed to said method wherein Tap to tap time is in the range of 44-66 minutes.

A still further aspect of the present invention is directed to said method wherein the slag composition comprising by wt % 37.8 to 45.7 CaO-7.7 to 14.3MgO-8.1 to 11.9SiO2-15.1 to 28.5FeO-4.0 to 6.1MnO-5.7 to 8.9Al2O3-1.1 to 1.9 P2O5, with basicity of 3.4-5.6.

A still further aspect of the present invention is directed to said method wherein addition of limestone decreases the lime consumption and also the iron ore consumption without decreasing the scrap added into the process, and said limestone addition method decreases the flux cost by 15% when compared with the lime only method.

Above and other aspects and advantages of the present invention are described hereunder with reference to following accompanying non limiting illustrative drawings and examples.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows various Inputs and outputs of EOF steel making process.
Figure 2: schematic Process flow for steel making in EOF with conventional lime addition only.
Figure 3: schematic Process flow for steel making in EOF according to present invention with addition of limestone partially replacing lime in slagging method.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLES
Present invention relates to a method of selectively adding limestone to partially replace the lime for producing crude steel with lower tap phosphorous level in the energy optimizing furnace. It results in lower flux cost to produce the crude steel in an energy optimizing furnace.

The input charge material has scrap and hot metal from 0 to 20% and 80-100% respectively. Inputs and outputs of the process are shown in are shown in Figure 1. The input hot metal has the typical composition of 4-4.5%C, 0.3-1.8%Si, 0.3-2.0%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, 0.005-0.02%P and 0.01-0.08%S. Oxygen is blown to react with the solute elements present in the hot metal such carbon, silicon, manganese and phosphorous. The products of this oxidation reaction reacts with the fluxes supplied to the process such as lime and dololime to form slag. Carbon escapes as carbon monoxide and carbon di oxide which makes the slag foamy. The main functions of this process are dephosphorization and decarbonization. Iron ore is supplied to decrease the temperature of the bath and to increase the iron oxide present in the slag. Silicon and manganese removal produces significant amount of the heat to the bath. Dephosphorization reaction is given in Equation (2) and (3) as shown below. The efficiency of dephosphorization is described by using degree of dephosphorization as given in Equation (3).
2[P]+5[O]→(P_2 O_5 ) (1)

2[P]+5(Fe_t O)+n(CaO)↔(nCaO.P_2 O_5 )+5[Fe_t] (2)

Degree of Dephosphorization (%)= (Hot metal %P-Steel %P)/(Hot metal %P)*100 (3)

CaCO_3 □(→┴∆ ) CaO+CO_2 (4)

The dissolution of lime during the blow supplies CaO to the reaction and removes phosphorous from the hotmetal. The traditional method of using lime for slagging in steelmaking involves calcining limestone in kilns as shown in Equation (4), which can lead to over burning and reduced lime activity. This results in a slow dissolution rate of lime in slag, creating a cycle of over burning and low activity. In contrast, directly charging limestone into slag allows for simultaneous decomposition and dissolution, producing highly active lime that dissolves quickly. CO2 plays a crucial role in this process by creating local convection in the slag, enhancing heat transfer and accelerating limestone dissolution. Unlike traditional lime dissolution, the high-melting point 2CaO•SiO2 layer does not form or restrict limestone dissolution due to the continuous destruction and removal of this layer by CO2. Consequently, limestone dissolves faster than lime under the same conditions.

CO2 exhibits weak oxidability at steelmaking temperatures and reacts differently with various elements in molten steel. It undergoes endothermic reactions with carbon ([C]) and iron ([Fe]), absorbing heat, while its reactions with silicon ([Si]) and manganese ([Mn]) are exothermic, releasing heat. Considering CO2injections at basic oxygen furnaces can lower the hot spot temperature in the Basic Oxygen Furnace (BOF), reducing the risk of iron evaporation and oxidation. Industrial applications of a CO2-O2 mix have shown benefits like reduced iron loss and dust production in Electric Arc Furnace (EAF) steelmaking.

Lime only method:
The process begins with charging scrap into the furnace from the top, followed by pouring hot metal through the launder, as depicted in Figure 1. The amount of scrap added depends on the chemistry and temperature of the hot metal, detailed in Table 1. This combination of hot metal and scrap forms the input charge. As shown in Figure 2, once the hot metal pouring starts, the operator initiates oxygen blowing through submerged tuyers, atmospheric injectors, and supersonic lances. Fluxes like lime and dololime are added in batches over 5 to 10 minutes. The oxidation of solute elements in the charge produces oxides that react with the flux to form slag and off-gas, which exits the furnace after post-combustion. The slag is expelled due to carbon monoxide bubbles and the action of submerged oxygen blowing. The furnace can tilt between +8° to -8°, aiding in slag removal and tapping the liquid steel. The blowing operation lasts 30-35 minutes, with an average blow time of 33 minutes and a tap-to-tap time of 54 minutes. Coolant addition starts midway through the blow and continues to adjust the tap temperature. Slag removal begins automatically at 7 minutes and continues until the end of the blow. After silicon removal, rapid decarburization and dephosphorization occur. Lime melts with the help of iron oxide generated during blowing, reacting with phosphorus oxide to form slag containing Mn, Si, and Fe oxides. The final slag composition averages 38.4%CaO-8.8%MgO-9.6%SiO2-30.5%FeO-4.4%MnO-5.5%Al2O3-1.4%P2O5. The final tap steel has 0.09% carbon, 0.011% phosphorus, a temperature of 1666°C, and an average yield of 87.3%, as shown in Table 1. The process achieves an averaged phosphorization degree of 91.7% and a lowest tap phosphorus of 0.006%. The average basicity level is 4.1.

Table 1 Lime method- EOF steel making performance
S. No. Parameters Unit Average Range
1 No. of heats Nos. 40
2 Hot metal weight Metric tonnes 60.98
58.07-66.43
3 Scrap weight Metric tonnes 13.03 8.17-14.01
4 Tap steel weight Metric tonnes 64.58 61.77-67.92
5 Liquid Yield % 87.27 82.66-91.32
6 Hot metal temperature °C 1315 1172-1389
7 Tap steel temperature °C 1666 1616-1672
8 Hot metal composition % 4.41C-0.66Si-1.57Mn-0.13P-0.02S 4.2 to 4.5C-0.35 to 1.26Si-0.86 to 2.33Mn- 0.12 to 0.15P- 0.01 to 0.04S
9 Tap carbon % 0.09 0.02-0.2
10 Blow time min 35 32-43
11 Tap to tap time min 58 43-82
12 Slag composition
(no of heats=6) % 38.4CaO-8.8MgO-9.6SiO2-30.5FeO-4.4MnO-5.5Al2O3-1.4P2O5 31.3 to 42.5 CaO-6.9 to 10.4MgO-7.6 to 12.7SiO2-25.3 to 41.8FeO-3.5 to 6.2MnO-3.9 to 7.8Al2O3-0.9 to 1.6 P2O5
13 Basicity
(No of heats=6) No unit 4.1 2.8 to 5.5
14 Lime consumption kg/metric tonne of steel 46.86 40.5-60.7
15 Oxygen consumption Nm3/metric tonne of steel 47.08 42.7-53.3
16 Dololime consumption kg/metric tonne of steel 12.3 10.2-13.9
17 Iron ore consumption kg/metric tonne of steel 20.5 6.4-48.4
18 Limestone consumption kg/metric tonne of steel 0 0
19 Degree of dephosphorization % 91.7 87.7 to 95.4
20 Tap steel phosphorus % 0.011 0.006-0.018

Limestone method
Limestone addition sequence, the quantity of lime addition and the quantity of iron ore addition are the main differences between the lime method and limestone method. As shown in Figure 3, the half of the limestone addition happens immediately after the scrap is charged inside the furnace and the remaining half of the limestone is added once the blow starts. The second batch of limestone addition completes before the blow time of 1-3 minutes preferably 2min. The initial batch of limestone that is added on to the scrap can take some of the heat/enthalpy which is available inside the furnace during themaintenance before charging the hot metal. When the hotmetal pouring starts, the second batch of addition will start along with the formation of slag that is created by using the oxidation of the elements present in the hotmetal and by the lime addition. The freshly forming slag with the high iron oxide and silica will react with the limestone and lime. It takes the heat required for the calcination of the limestone and forms fresh lime that is highly reactive to the hotmetal and the carbon di oxide that is evolving from the calcination can break the dicalcium silicate layer that is formed on top of the limestone. By this way the limestone addition will help in dephosphorization by dissolving the freshly prepared lime quickly into the slag. Since this reaction is endothermic, it takes the heat that is generated during the blowing operation that eventually reduces the iron ore requirement during the process. The iron ore requirement will come down while using the limestone along with the lime in EOF. As shown in Table 2, limestone consumption in this process is 12.96 kg/metric ton of steel that can replace the lime consumption and also the iron ore consumption.As shown in Table 1 and Table 2, the average lime consumption is reduced from 46.86 kg/metric ton of steel to 38.48 kg/metric ton of steel when the limestone method is used.The average Dololime consumption is as same as in both the methods and the average iron ore consumption is reduced from 20.5 kg/metric ton of steel to 10.97 kg/metric ton of steel. Usually lime and dololime are added as the fluxing components in the primary steel making process and Iron ore is added as the coolant and it can supply iron oxide to the slag. Here the flux cost consists lime, limestone, dololime and iron ore. The addition of limestone decreases the lime consumption and also the iron ore consumption without decreasing the scrap added into the process. When comparing with the lime only method, limestone method decreases the flux cost by 15%.
The tap temperature of the process is not significantly affected because of this process and tapped with the average temperature of 1664C. The average tap phosphorous associated with this process is 0.010% with the average degree of dephosphorization of 91.9% for the replacement of 13% lime on an average with the limestone. It shows that by replacing the lime with the limestone the process can able to give the low phosphorous levels. The tap phosphorous range is between 0.006% to 0.014% in this process and the maximum replacement of the lime by limestone that was experimented here is 19% and the minimum tap phosphorous level achieved is 0.006% as shown in Tabel 2. The average blow time and process time are 36 and 54 minutes respectively that shows that this process does not increase the process time along with the average liquid yield of 88.84% even though with the high manganese hot metal inputs and it is closer to the lime method also.

Table 2 Limestone method-EOF steel making performance
S. No. Parameters Unit Average Range
1 No. of heats Nos. 13
2 Hot metal weight Metric tonnes 60.98
58.74-62.24
3 Scrap weight Metric tonnes 13.45 12.87-14.09
4 Tap steel weight Metric tonnes 65.39 61.00-67.50
5 Liquid Yield % 88.84 83.7-91.7
6 Hot metal temperature °C 1333 1298-1376
7 Tap steel temperature °C 1664 1634-1725
8 Hot metal composition % 4.4C-0.58Si-1.54Mn-0.13P-0.02S 4.3 to 4.5C-0.35 to 0.96Si-1.16 to 1.98Mn- 0.12 to 0.13P- 0.01 to 0.03S
9 Tap carbon % 0.07 0.04-0.13
10 Blow time min 36 32-43
11 Tap to tap time min 54 44-66
12 Slag composition
(no of heats=6) % 41.05CaO-11.04MgO-9.8SiO2-23.56FeO-4.7MnO-6.76Al2O3-1.362O5 37.8 to 45.7 CaO-7.7 to 14.3MgO-8.1 to 11.9SiO2-15.1 to 28.5FeO-4.0 to 6.1MnO-5.7 to 8.9Al2O3-1.1 to 1.9 P2O5
13 Basicity
No unit 4.2 3.4-5.6
14 Lime consumption kg/metric tonne of steel 38.48 34.16-50.80
15 Oxygen consumption Nm3/metric tonne of steel 47.5 42.76-52.75
16 Dololime consumption kg/metric tonne of steel 12.11 11.56-13.26
17 Iron ore consumption kg/metric tonne of steel 10.97 0-16.95
18 Limestone consumption kg/metric tonne of steel 12.96 7.49-18.5
19 Degree of dephosphorization % 91.9 88.88-95.08
20 Tap steel phosphorus % 0.010 0.006-0.014
21 Lime replacement % 13 7.5-19
22 Cost of flux % 100 85

It is thus possible by way of the present invention to provide a method of producing steel in EOF with addition of limestone partially replacing lime upto 19%, to achieve low tap phosphorus levels with an average dephosphorization degree of 91.9% and a tap phosphorus range of 0.006% to 0.014%, reducing lime and iron ore consumption and lowering overall flux costs by 15%. The process achieves an average liquid yield of 88.84%, demonstrating its efficiency and cost-effectiveness.

, Claims:We Claim:

1. A method of steel production in an energy optimizing furnace (EOF) with advanced degree of dephosphorization with partial replacement of lime with lime stone comprising :

scarp charging ;

hot metal pouring ;

carrying out oxygen blowing in the presence of fluxes including lime and dololime and iron ore as source of iron oxide to thus generate slag and off gases which exit the furnace,

wherein the method includes the step of generating highly reactive lime for advanced degree of dephosphorization following the partial replacement of required lime by limestone in said EOF process of steel manufacture in stages including (i) an initial batch of limestone addition to scarp before hot metal pouring followed by (ii) a second stage of addition of limestone after said hot metal pouring and initiation of blowing and until completion of blowing whereby the limestone generates fresh lime highly reactive to hot metal by dissolving the freshly generated lime from limestone quickly into the slag under endothermic conditions for attaining reduced tap phosphorous..

2. The method as claimed in claim 1 which is carried out with 7.5 to 19 % of total lime content replaced by limestone comprising

charging of scrap inside the energy optimizing furnace (EOF) depending on a heat/batch size,

addition onto the scrap charge of 40 to 60% by wt of the total replaced limestone as lime replacement immediately after the scrap is charged inside the furnace and before pouring of the hot metal whereby the initial batch of limestone can take heat /enthalpy available inside furnace before charging of the hot metal;

pouring hot metal of selective composition in said furnace;

starting oxygen blowing inside furnace followed by adding the remaining 40 to 60 % of the replaced limestone once the blow starts and completing lime stone addition by next 1-3 minutes preferably 2 minutes under

charge of flux including reduced lime and dololime and iron ore addition for required quantity and duration;
tapping steel produced with desired advanced dephosphorization level of tap phosphorous in the range of 0.006% to 0.14%

3. The method as claimed in anyone of claims 1 or 2 wherein the freshly forming slag with iron oxide and silica is subjected to reaction with limestone and lime combination for reduced iron ore consumption wherein the heat required for calcination of limestone and forming fresh lime which is highly reactive to hot metal with evolving carbon dioxide from the calcination enabling breaking dicalcium silicate layer formed on top of limestone for advanced degree of dephosphorization by dissolving said freshly prepared lime quickly into the slag under endothermic conditions taking heat generated during blowing thus favouring reduced iron ore requirement and also flux requirements for a cost effective manufacture in EOF.

4. The method as claimed in anyone of claims 1 to 3 wherein scrap weight charged is in the range of 12.87-14.09MT, Hot metal weight charged is in the range of 58.74-62.24MT, for Tap steel weight in the range of 61.00-67.50MT with Liquid steel Yield of 83.7-91.7%.

5. The method as claimed in anyone of claims 1 to 4 wherein the hot metal composition comprising by wt % 4.3 to 4.5%C, 0.35 to 0.96%Si, 1.16 to 1.98%Mn, 0.12 to 0.13%P, 0.01 to 0.03% S and rest is iron.

6. The method as claimed in anyone of claims 1 to 5 wherein limestone consumption in this process is 12.96 kg/metric ton of steel that can replace the lime consumption, the average lime consumption is reduced from 46.86 kg/metric ton of steel to 38.48 kg/metric ton of steel and the average iron ore consumption is reduced from 20.5 kg/metric ton of steel to 10.97 kg/metric ton of steel when the limestone method is used.

7. The method as claimed in anyone of claims 1 to 6 wherein produced steel is tapped with the average temperature of 1664C and average tap phosphorous associated with this process is 0.010% with the average degree of dephosphorization of 91.9% for the replacement of 13% lime on an average with the limestone.

8. The method as claimed in anyone of claims 1 to 7 wherein the maximum replacement of the lime by limestone is 19%.

9. The method as claimed in anyone of claims 1 to 8 wherein average blow time and process time are 36 and 54 minutes respectively along with the average liquid yield of 88.84% even with the high manganese hot metal inputs.
10. The method as claimed in anyone of claims 1 to 9 wherein Tap to tap time is in the range of 44-66 minutes.

11. The method as claimed in anyone of claims 1 to 10 wherein the slag composition comprising by wt % 37.8 to 45.7 CaO-7.7 to 14.3MgO-8.1 to 11.9SiO2-15.1 to 28.5FeO-4.0 to 6.1MnO-5.7 to 8.9Al2O3-1.1 to 1.9 P2O5, with basicity of 3.4-5.6.

12. The method as claimed in anyone of claims 1 to 11 wherein addition of limestone decreases the lime consumption and also the iron ore consumption without decreasing the scrap added into the process, and said limestone addition method decreases the flux cost by 15% when compared with the lime only method.

Dated this the 20th day of September, 2024
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199