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 OF SLAG REMOVAL FOR STEEL MANUFACTURING IN ENERGY OPTIMIZING FURNACE.



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 slag removal for the steel-making in energy optimizing furnace (EOF) wherein the slag removal is controlled till the end of the blowing to ensure decreased slag FeO level and increased steel yield.

BACKGROUND OF THE INVENTION
Energy Optimizing Furnace (EOF) is a technology that uses oxygen to convert the hot metal into crude steel. This technology evolved from the modifications in the open hearth furnace to improve productivity and to compete with the other steel making technologies such as basic oxygen furnaces (BOF) and electric arc furnaces (EAF). It is also an autogenous process similar to BOF and has the continuous slag removing arrangements similar to EAF. EOF is a combined blowing, basic oxygen furnace where a combination of hot metal and scrap is converted to liquid steel suitable for secondary refining and continuous casting.

The charge material contains scrap and hot metal of about 15-20% and 80-85% respectively. The inputs, outputs and constructional features of the EOF are schematically shown in Figure 1. In this process, oxygen is supplied by means of supersonic lances (2 nos.), atmospheric injectors (4 nos.), submerged tuyers (2 or 3 nos.) and hand lances. As per the former design, scrap preheating setup was used to preheat the solid scrap for the next heat of the process with the help of the off gas heat generated during the process. Due to the maintenance issues the scrap preheating setup was removed in most of the Indian Furnaces.

The FeO level in the EOF slag is quite high compared to other similar oxygen steelmaking processes such as basic oxygen furnaces (BOF). This high level of FeO in the slag of EOF process is due to the design of the furnace. In EOF process, the slag is removed continuously during the blowing. The continuous slag removal process also decreases the yield of the process since the metal also goes along with the slag during the blowing. This reduces the productivity and increases the cost of steelmaking through the EOF process. Several measures were taken to improve the productivity and reduce the steel cost through EOF.

PRIOR ART
Very few published literatures and patents which describes the slag removal and yield improvement methodologies in the energy optimizing furnace.
In an experimental study on EOF reported by Vijay Sharma, steel making practice of EOF is optimized under Indian conditions. The author had also reported the improvements done in EOF process to increase its productivity and cost of the process. The improvement ideas that were used to improve the charge to liquid metal yield of 45 metric tons and 65 metric tons EOFs. Especially in EOF-1 (i.e., 45 metric tons), the liquid yield was improved from 90.2 to 92.2% and the blow time was reduced from 36 minutes to 31 minutes because of the catch carbon practice, selecting the proper hot metal in terms of its chemistry and temperature, reducing the liquid metal through the slag door especially when there was excessive boil inside the EOF. The catch carbon practice had given the tap carbon of >0.1% with 85% consistency and reduced the slag FeO level of 22%. The heats with the carbon contents ranges below 0.1%, FeO level was about 28%. In EOF-2 (i.e., 65 metric tons), the liquid metal yield was reported about 90.1 % for the input charge of 80.11 % hot metal and 19.89% solid scrap with the blow time of 38 minutes, oxygen consumption of 66 m3/MT and lime consumption of 58 m3/MT. The present invention always controls the liquid metal through the slag door and catch carbon practice is not used. The tap carbon of the new process goes to the level of 0.02 to 0.07% which is more prone level to FeO oxidation whereas the carbon range given by Vijay Sharma for the improved yield was >0.1% which is comparatively gives less FeO oxidation. At present the capacity of EOF-1 is increased to 65 metric tons and the supersonic design is also different and fixed which makes the setup completely different from them for the exact comparison. The metal outgoes from the slag door was controlled when there was excessive boiling but the present invention always controls to reduce the metal outgoes along with the slag till the end of the blowing. The present blow time is about 35 minutes in the conventional method as well as the new method since the tap carbon is mostly <0.1%. The new method’s liquid yield is still very high when compared with the 65 metric ton furnace with their method. The charge mix, lime and oxygen consumption of the recent conventional as well as the new method are low when compared with this method.
In an experimental study by M. Vidhyasagar, G. Murali and G. Balachandran, the typical performance of EOF was also represented along with the heat and mass balance studies. Only the average heat data were represented based on the fifteen heats which were taken at EOF-2. The continuous slag removal process was followed in those experiments. The typical yield (i.e., Liquid yield) of EOF based on the experiments to perform the mass balance was about 90.71% and it is including the tap additions weight also since the weight measurement can be done only after the tapping. The typical FeO level in the process was about 29.81%. The blow time and tap to tap time of the process were 35 and 65 minutes respectively. Lime and oxygen consumptions were 53.29 and 53.14 kg per metric tonne of tap steel and if it is taken per ton of crude steel it will increase. The conventional practice at the present has higher oxygen consumption compared with this and the tap carbon levels are lower. The present invention is different from this experimental study that describes the slag removal practices to achieve higher yield of the process. The FeO level in new process is lower and the fixed supersonic lance design is used in the new process where as this process used movable lance. The scrap ratio in this process is bit lower and crushed EOF slag is also again used in this process as the coolant in addition to the iron ore whereas the new method uses only iron ore as a coolant.
Co-pending Patent IN202241017038A (i.e., applied) reported, the adapted supersonic system for improving the availability and productivity of the energy optimizing furnace. The supersonic system was changed from movable to fixed along with the adaptions in the supersonic lance system resulted in reduced maintenance time of the supersonic system during the bottom change of the furnace. This new design also reduced the cost of the production by eliminating the man power requirement for the maintenance during the bottom change. The same supersonic system is used in the present invention but the present invention is different from this and it gives the detailed procedure to remove the slag from the furnace to get the higher yield levels of the process.
In another experimental study by M. Vidhyasagar, D. Kumar, N. N. Viswanathan, S. M. Kumar and S. Manjini, the mass flow of the process is modelled with the help of heat and mass balance coupled with thermodynamics and actual operational data. It quantifies the inputs and outputs of the process with the assumptions such as single slag removal practice, fixed CO/CO2 ratio, no atmospheric air effect and no excess oxygen in the off gas. Continuous slag practice was followed in the experimental studies reported by them and the operational data are also according to the same practice. Controlled slag removal practice reported in the present invention is different from this and has the predefined blow profile along with the furnace positioning to make use of the slag metal reactions for improving the efficiency of the process in terms of yield.
Other patents of EOF
Patent BRMU9002554U2 reported that addition of new provisions such as short discharge spout, electronic coupled hydraulic systems for the quick tilting of the furnace, adoption of a unique system for storing, dosing and transporting the additions, rotary discharge system, hydraulically actuated check valves and pressure loss monitoring and correcting systems resulted in increased operational efficiency and reduced maintenance of the EOF. The present invention is different from this and the changes are in the slag removal method of the EOF technology.
Patent BRPI1101553A2 reported the changes in the design of the submerged tuyers that supplies oxygen in the furnace through the side- bottom to promote the decarburization of the liquid metal bath to produce the steel from the hot metal. In this design, the submerged tuyers contains concentric tubes inserted into the refractory material gloves. The concentric tubes have strained copper as the inner tube to blow the oxygen and with an outer tube made of stainless steel where the atomized water and the argon gas are supplied for the cooling of the setup. The entire tuyer assembly is movable by the housing block along with the hydraulic mechanism attached with it and it can be adjusted based on the wear of the tuyer part. The present invention is different from it which describes the slag removal procedure and it used the submerged tuyer assembly that was adjusted manually and no other hydraulic mechanisms were used.

REFERENCES

Sharma, V., Optimization of Steel Making Process Through Energy Optimizing Furnace Under Indian Conditions Faculty of Mechanical Engineering Making Process Through Energy. (2008).
Vidhyasagar, M., G. Murali, and G. Balachandran. Thermo-kinetics, mass and heat balance in an energy optimizing furnace for primary steel making. Ironmaking & Steelmaking 48 (1) (2021): 97-108.
MALAIYAPPAN VIDHYASAGAR,MUTHU KUMARARAJA, PALVANNANATHAN RAMASUBRAMANIAN, DURAIRAJ RAJESH, S M, KUMAR AND SAMBANDAM MANJINI, Patent IN202241017038A, 2022.
Vidhyasagar, M., Kumar, D., Viswanathan, N.N., Kumar, S.M. and Manjini, S., A Static Model for Energy Optimizing Furnace, Steel Res Int., 93 (9) (2022):2200185.
HENRIQUE CARLOS PFEIFER and PEREIRA REVERTON ALVES, Patent BRMU9002554U2, 2013.
HENRIQUE CARLOS PFEIFER, Patent BRPI1101553A2, 2014.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide a method of slag removal for producing the steel in the energy optimizing furnace to reduce the level of FeO in slag and improve the yield of the process.

A further object of the present invention is directed to a method of steel making wherein the Energy Optimizing Furnace is selectively positioned to remove a significant quantity of slag at the end of blowing that reduces the chances of the metal outgoes along with the slag by controlling the furnace positioning and flow rate of the blowing oxygen.

A still further object of the present invention is directed to a method wherein sufficient time is allowed for the slag FeO to react with the carbon present in the hot metalso that it also gives the low phosphorous levels in the tap steel.

A still further object of the present invention is directed to a method wherein by using the controlled slag removal practice, there is an increase in the yield of the process along with the lower level of FeO in slag.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method of manufacture of low carbon crude steel in an Energy Optimizing Furnace (EOF) comprising:
involving the input charge of scarp 15-20 % and hot metal 80-85 % by wt. in the EOF;
carrying out oxygen blowing into the hot metal involving selectively supersonic lances, atmospheric injectors and submerged tuyers;
effecting slag removal by titling the furnace wherein
step of slag removal is carried out in a non-continuous manner by selectively controlling the furnace position/inclination comprising maintaining the furnace at 7.5to 8.5preferably at +80 inclination from the start to till the end of the blowing including initial period of blowing, boiling period of blowing and also peak blowing period of blowing during which carbon sampling of slag is carried out and 0 to -8%preferably at -80 during the slag removal enabling effective interaction of FeO in the slag with carbon in the molten metal in said furnace and thereby decreasing the slag FeO level by at least 1% with respect to continuous slag removal.
A further aspect of the present invention is directed to said method wherein said input hot metal comprises by wt.%:
C:4 to 5%;
Si: 0.25 to 1.5 %;
Mn: 0.25 to 1.5%;
S: 0.02 to 0.07%;
P: 0.1 to 0.2%; and the rest is iron and said scrap including iron scrap, steel scrap and directly reduced iron(DRI)/sponge iron and wherein step of oxygen blowing include controlled blowing stages including controlled flow rates for initial period, boiling period and peak blow period involving controlled lance flow rate, injector flow rate and said tuyers flow rate with controlled low phosphorous level in tap steel in the range of 0.006% to 0.02% preferably about 0.0095%.

A still further aspect of the present invention is directed to said method wherein the flow rates of supersonic lance oxygen is controlled in said initial period in the range of 1168 to 1216 Nm3/hr, in said boiling period in the range of 200 to 320 Nm3/min and in said peak blow period in the range of 1488 to 1552 Nm3/min thereby allowing the desired time of the metal to react with the slag and such as to prevent the slag to go out of the furnace before the carbon sampling wherein 75 to 85% of coolant is added before the blowing time of 90% and the small remainder of the coolant was added thereafter.
A still further aspect of the present invention is directed to said method wherein the bath temperature is maintained in the range of 1637 to 1677°C which along with CaO and CaO/SiO2 (basicity) present in slag along with the low level of slag FeO involved provide desired dephosphorization and increase in crude steel yield and liquid steel yield in the range of 0.72 to 1.3 preferably about 1 % and1.3 to 1.8 preferably about 1.5 % respectively.
A still further aspect of the present invention is directed to said method wherein the flow rates of the oxygen from supersonic lances are controlled in said initial period in the range of 1168 to 1216 Nm3/hr said boiling period in the range of 200 to 320 Nm3/min and said peak blow period in the range of 1488 to 1552 Nm3/min thereby allowing the desired time of the metal to react with the slag and during which about 15 to 25% preferably about 25 % of the slag can go out of the furnace before the peak blow period and thereby allowing selectively small quantity 15 to 25% of slag which is highly siliceous before peak blow period and performing coolant addition bit earlier preferably before the mid of the blow favoured reducing tap phosphorous levels in the process.
A still further aspect of the present invention is directed to said method comprising increasing the tap carbon levels during steel making which favoured the reduction in slag FeO level as well.
Another aspect of the present invention is directed to said method comprising supersonic lances’ flow rates are selectively varied during all the three periods of blowing, in the initial period, the flow rates are closer and even go bit lower and higher to reduce the slag flow out of the furnace along with increasing the oxygen input to the process to reduce the blow time, during the boiling period, flow rates are kept to reduce the metal goes out of the furnace to avoid the boiling effect that affects the yield and wherein in the boiling period also the flow rates are raised little bit to reduce the blow time and wherein in the peak blow period, the flow rates maintained in the process are in the range of 1488 to 1552 Nm3/hr which is higher than conventional to thereby increase the oxygen supply to the metal and attain lower blow time.
Yet another aspect of the present invention is directed to said method comprising maintaining the atmospheric injectors’ flow rates bit higher in the range of 61 to 63 Nm3/min more than the conventional process during the initial period and the peak blow period, during the boiling period, the flow rates are varied and bit lowered such as to reduce the slag flows out of the furnace and thereby also reduces the blow time significantly and also wherein the submerged tuyers flow rates are bit lower and it is in the range of 28 to 31 Nm3/min in the initial period then 12 to 17 Nm3/min in the boiling period but in the peak blow period it can be go higher in the range of 32 to 37 Nm3/min during the peak blow period which favours decrease in lime and coolant involvement and desired increase in crude steel yield of 0.72 to 1.3%preferably about 1 % and liquid steel yield in the range of 1.3 to 1.8% preferably about 1.5 %, slag FeO levels in the process are lower in the range of 0 to 2% preferably 1% alongwith increase in tap temperature of 0 to 200C preferably about 100C for the average tap carbon of 0.03 to 0.1 preferably about 0.05% and average basicity maintained in the range of 3.4 to 3.8 preferably at 3.68.
A further aspect of the present invention is directed to said method which is carried out free of any required hand lancing operations.
A still further aspect of the present invention is directed to said method which is carried out involving said scarp include iron scrap, steel scrap and directly reduced iron (DRI)/sponge iron; input hot metal temperature in the range of1280 to 1340˚C;Tap phosphorous(%) 0.006 to 0.02;Degree of Dephosphorization (%) 92.5 to 95; Lime3100 to 3500 kg; Dolomite 300 to 800 kg; coolant 500 to 1300 kg; oxygen 3300 to 3900 Nm3 ; blow time 30 to 38 min; Tap carbon (%)0.03 to 0.1, Tap temperature (°C) 1630 to 1680;slag FeO (%) 20 to 31and Basicity1.7 to 5 and wherein said controlled slag removal favours selectively (i) increase in the crude steel yield of the process to 1%(i.e., 90.22%) compared with the conventional continuous slag removal method (ii) savings in hand lancing cost (iii) increased liquid yield of 1.5% (i.e., 91.6%) and (iv) decreased slag FeO level of the process by 1%(i.e., 26.83%).

The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non-limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows the schematic of energy optimizing furnace along with the inputs and outputs.
Figure 2: shows conventional continuous slag removal practice followed in EOF.
Figure 3: shows graphically typical supersonic lances’ flow rate with respect to time for different slag removal practice.
Figure 4: shows graphically typical atmospheric injectors’ flow rate with respect to time for different slag removal practice.
Figure 5: shows graphically typical submerged tuyers’ flow rate with respect to time for different slag removal practice.
Figure 6: shows schematically the method of controlled slag removal practice followed in EOF according to present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLES
Present invention relates to a method of slag (105) removal for producing low carbon crude steel with higher yield in the energy optimizing furnace by controlling the position of the furnace and by the flow rates of the oxygen blowing sources. It decreases the cost of the production during the crude steel making process. More particularly, the present invention is directed to a process, wherein, the slag (105)FeO level, lime requirement and coolant requirement of the process are lower when compared to the conventional slag (105) removal practice. This new slag (105) removal process also enables higher tapping temperature along with the competent level of dephosphorization which is beneficial for the secondary steel-making process.

Conventional Method-Continuous slag removal process:
Accompanying Figure 1 shows the schematic of energy optimizing furnace along with the inputs and outputs as per the following part list shown in Table 1.
Table 1 Part Details of EOF
Part number and Name of the component
101-Water cooled panel 109-Off gas
102-Atmospheric Injector 110-Dust goes as sludge
103-Supersonic lance 111-Slag & Metal droplet
104-Slag door 112-Hot metal Launder
105-Slag 113-Steel Launder
106-Submerged tuyer 114-Tap hole
107-Refractory lining 115-Metal
108-Furnace Frame 116-Scrap

Referring to accompanying Figure 1 showing schematic of the EOF and Figure 2 illustrating the conventional continuous slag removal practice followed in EOF wherein the scrap (116) is charged inside the furnace from the furnace top and then the hot metal is poured through the hot metal launder (112). The oxygen blown in to the hot metal by using two supersonic lances (103), four atmospheric injectors (102) and two submerged tuyers (106). During the initial period of blowing, most of the flux additions such as lime and dololime are done. Furnace position is maintained at angle of >0 to +8° during the initial period of blowing as shown in Figure 2 a). A typical blow profile of this process is given by plotting the percentage of blow time with respect to the percentage of flow rate and mentioning the maximum limit of those parameters. The blow profile has three different periods with respect to the flow rates named as initial period, boiling period and peak blow period that will be discussed further. The furnace positioning during this period is represented in Figure 2 (a-c). The typical blow profile maintained in the oxygen carriers such as supersonic lances(103), atmospheric injectors (102) and submerged tuyers (106) are shown in Figure 3, Figure 4, and Figure 5 respectively. After reaching 25% of the total blow time, the slag (105) will come out of the furnace due to the large formation of carbon monoxide from the supplied oxygen and it is called as carbon boiling. This boiling can go up to 70% of the total blow time. During this period, whether the furnace is positioned at 0° or +8°, slag (105) will come out of the furnace since the design of the furnace itself for allowing continuous slag (105) removal. The operator can reduce the blow to some extent to control this heavy boiling but it is up to the limit where the reduction in flow rate will not affect the blow time that can also affect the cost of production. A significant amount of slag (105) will come out of the furnace during this period. Once the boiling is over, then hand lancing operation starts and it is used to dissolve the solid lime particles sticking in the refractory walls and slag door (104)-opening side of the furnace. During the hand lancing, the furnace is positioned mostly at 0° as shown in Figure 2 b) and 0 to -8° as shown in Figure 2 c) during this operation. The coolant addition is done at the mid of the blowing when there will be lower levels of FeO in the slag (105) and to maintain sufficient temperature of the metal (115). The coolant addition can go till the end of the blowing. After reaching 85-95% of blow time, metal (115) samples have been taken to identify the carbon level. After that, if the carbon level is > 0.1% then the blowing will be continued, otherwise the blow will end approximately within a minute. The tap carbon can vary with respect to the particular grade’s chemistry requirements. While taking the carbon sample, slag (105) will come out of the furnace and the blowing also continues till the tapping. Once the carbon level reaches very low level of <0.1%, the slag (105) will not overflow and the slag (105) is removed by tilting the furnace to -8° as shown in Figure 2 c). Nut coke addition will be carried out on to the slag (105) just before tapping to reduce the atmospheric air ingress and FeO in the slag (105). This practice is called as conventional-continuous slag (105) removal practice. Then the crude steel is tapped into the steel ladle through the tap hole (114) and the steel launder (113). During tapping alloys and fluxes are added based on the grade requirements and then the ladle moves to Ladle Refining Furnace.

The average data representing the parameters in the furnace are given in Table 2 and Table 3. In this practice, whenever the slag (105) goes out of the furnace obviously the metal (115) will also go out of the furnace which results in decreased yield level. Due to the continuous slag(105) removal, there is also an increase in FeO level of the slag (105) since the carbon or other solutes present in the hot metal do not get sufficient time to reduce with the slag(105)FeO. But the continuous slag (105) removal improves the dephosphorization of the process due to the early removal of high phosphorous containing slag (105) and reduction in the reversion of phosphorous from slag (105) to the metal (115) during the blowing. In the case of achieving lower phosphorous content in the tap steel, the yield of the process is compensated since good level of FeO is required in the slag (105) for the improved level of dephosphorization.
Table 2 Average performance of continuous and controlled slag removal methods at EOF-1
Parameters Continuous
slag removal Controlled slag removal
Method-1 Method-2
No of heats 667 10 26
Input hot metal chemistry(%) 4.42C-0.58Si-0.51Mn-0.16P-0.029S 4.43C-0.50Si-0.34Mn-0.16P-0.029S 4.44C-0.62Si-0.45Mn-0.16P-0.027S
Input hot metal Temperature (°C) 1325 1310 1315
Scrap in the input charge(%) 17.71 17.84 17.88
Tap phosphorous (%) 0.0094 0.012 0.0095
Degree of
dephosphorization (%) 94.21 92.19 93.93
Lime (kg/metric ton of crude steel) 53.33 47.82 50.87
Dololime (kg/metric ton of crude steel) 8.77 7.28 8.16
Coolant (kg/metric ton of crude steel) 15.81 16.74 13.81
Oxygen
(kg/metric ton of crude steel) 55.66 56.44 55.94
Hand lancing cost (%) 100 0 0
Crude steel yield (%) 89.20 90.18 90.22
Liquid Yield (%) 90.14 91.56 91.69
Blow time (min) 34.5 39.8 34.7
Tap carbon (%) 0.075* 0.046 0.050
Tap temperature (°C) 1648 1660 1658
*Excluding carbon additions during tapping for 263 heats

Table 3 Average performance of continuous and controlled slag removal methods at EOF-1 with respect to slag
Parameters Continuous
slag removal Controlled slag removal
Method-1 Method-2
No. of heats 69 5 11
Slag FeO(%) 27.95 29.71 26.83
Basicity 3.88 3.04 3.68

New Method-Controlled slag removal process
The present invention reduces the chances of the metal (115) outgoes along with the slag (105) by controlling the furnace positioning and flow rate of the blowing oxygen. It gives sufficient time for the slag (105)FeO to react with the carbon present in the hot metal and it also gives the low phosphorous levels in the tap steel. By using the controlled slag (105) removal practice, there is an increase in the yield of the process along with the lower level of FeO in slag (105) and same level of tap steel-phosphorous compared to the conventional process. The present invention is derived from the experimental results which will be discussed further.

Experimental Trials Carried Out by way of present invention:
Method-1:
A series of experiments have been carried out to regulate the slag (105) flow out of the furnace to reduce the metal (115) goes along with it. Most of the input raw materials used in this experiments are similar to the conventional method to make the input conditions similar and it is given in Table 2 as the average data. In this method the furnace is kept at +8° from the start to till the end of the blowing process as shown in Figure 6 a). During the slag (105) removal at the end of the blowing, the furnace is kept at -8° as shown in Figure 6 b). In this method, the flow rate of oxygen was controlled in supersonic lances (103), atmospheric injectors (102) and submerged tuyers (106) as shown in Figure 3, Figure 4 and Figure 5 respectively. The flow rates during the initial period, boiling period and the peak blow period were comparatively lower than the conventional process which kept the slag (105) inside the furnace and allowing the metal (115)to react with the slag (105). Most of the coolant additions are done before the blowing time of 95% and small quantity was only added after that. In the conventional method, there is no restrictions in the coolant addition quantity till the end of blowing.
As mentioned above, carbon present in the metal (115) can reduce the FeO present in the slag (105) and forms carbon monoxide gas as given in Equation 1. It also affects the phosphorous partition ratio (i.e., Equation 3) which is a function of FeO present in the slag (105) as shown in Equation 2 and Equation 4. Because of higher presence of FeO in EOF slag (105), this decrease in FeO levels will not affect the dephosphorization very significantly. Dephosphorization is also a function of bath temperature, CaO and basicity (i.e., CaO/SiO2) present in the slag (105) apart from the slag (105)FeO levels. It is adequate in the slag (105) maintained in the present method. Most of the lime charged during the blowing might dissolve in the slag (105) due to the rise in slag (105) temperature by the heat transfer from the metal (115) along with the higher FeO level. It eliminates the requirement of hand lancing operation to dissolve the undissolved lime.
[C] +(FeO)=CO_g+Fe 1

n(CaO)+2[P] +5(FeO)=nCaO.P_2 O_5+5Fe 2

logL_P=log⁡((%P_2 O_5)×(2 31/142))/([%P]) 3
□log (L_P/(Fe_t^2.5 ))=
0.073×[(%CaO)+0.148×(%MgO)+0.96×(%P_2 O_5 )+0.144×(%SiO_2 )+0.22×(%Al_2 O_3 ) ]+11570/T-10.46±0.1

4
Degree of Dephosphorization (%)= (Hot metal %P-Steel %P)/(Hot metal %P)*100 5

The results by means of average are compared with the conventional slag (105) removal method as shown in Table 2 and Table 3. Crude steel yield is calculated by taking the hot metaland scrap (116) as the input and tap steel excluding the tapping additions as output. If the tapping additions are included in the output, it is accounted as liquid yield. Till the sample has been taken for carbon, the slag (105) is kept inside the furnace as discussed above. By decreasing the flow rate of oxygen in all the sources, the average blow time is also increased.

As shown in Table 2, average tap phosphorous is higher in this method than the conventional one and it is also reflected in degree of dephosphorization also. Degree of dephosphorization is calculated as per Equation 5. Lime used in this method is significantly lower than the conventional method which is also another reason behind this higher tap phosphorous. Similar to lime, dololime is also lower in this process because of lesser slag (105) removal before the end of peak blow. Iron ore addition prediction is bit difficult in this method because of the metal (115) temperature rise could not be understood by the slag (105). It is also because the slag (105) visibility during the blowing is not good. It resulted in increased iron ore usage but the tap temperature is on the higher side. Increase in tap temperature along with lower carbon levels resulted in increased slag (105)FeO levels at the end of the process along with bit higher oxygen requirement. The basicity (i.e., CaO/SiO2) is lower in this process because of the large presence of silica in the slag (105) till the end of the process. By this method, the average crude steel yield and average liquid yield is increased by ~1% and ~1.4% respectively. There is no hand lancing operation involved in this method as used in the conventional method.

Method-2:
A series of experiments have been carried out in this method to mitigate the drawbacks of method-1. The furnace positioning in this method-2 is similar to method-1 but the flow rates of the oxygen supplying sources are different as shown in Figure 3, Figure 4 and Figure 5. The flow rates are bit higher than the method-1 and some times higher or lower than the conventional also in all the three oxygen sources. The slag (105) can go out of the furnace before the carbon sampling at the peak blow period in the method-2 whereas method-1 does not allow it to happen. About 25% of the slag (105) can go before the peak blow period in this process. By allowing the slag quantity of 15-25% (105)which is highly siliceous before the peak blow period and performing the coolant addition bit earlier before the mid of the blow reduced the tap phosphorous levels in this process. Also, the temperature control difficulties present in the method-1 are significantly reduced because of this. In addition to that by increasing the tap carbon levels little bit higher reduced the slag (105) FeO level.
As shown in Figure 3, the supersonic lances’ (103) flow rates are varied during all the three periods of blowing. In the initial period, the flow rates are closer and even go bit lower and higher to reduce the slag (105) flow out of the furnace along with increase in the oxygen input to the process to reduce the blow time. During the boiling period, flow rates are kept lower to reduce the metal (115) go out of the furnace since the boiling effect can affect the yield. But in the boiling period also the flow rates are raised little bit to reduce the blow time. In the peak blow period, the flow rates maintained in the process are higher than conventional as well as the method-1. It helps in increased oxygen supply to the metal(115) that warrants lower blow time.
As shown in Figure 4, the atmospheric injectors’ (102) flow rates are kept bit higher than the conventional process during the initial period and the peak blow period. During the boiling period, the flow rates are varied and bit lowered to reduce the slag (105) flow out of the furnace. In all the three periods, the flow rates of the method-2 are higher than the method-1 (i.e., mostly) which reduces the blow time significantly. As shown in Figure 5, the submerged tuyers (106) flow rates are bit lower than the conventional method till the peak blow period. It can go higher than the conventional method during the peak blow period.
The results obtained by using the method-2 are expressed in Table 2 and Table 3. The average values of the parameters such as tap steel phosphorous, degree of dephosphorization, oxygen consumption and dololime consumption of the method-2 are closer to that of the conventional method. There is a decrease in the lime and coolant requirements by using this method-2 compared to the conventional method. There is a significant improvement in the average crude steel yield of ~1% and the average liquid yield of ~1.5% in this process as shown in Table 2. In addition to that, the average slag (105)FeO levels in this process are lower by ~1% as shown in Table 3 along with the increase in average tap temperature of 10°C for the average tap carbon of 0.05%. The average basicity maintained in this process is bit lower in this process because of the lower lime addition and it also obtain without using the hand lancing operation. Because of the higher oxygen inputs by increasing the flow rate, blow time of this method is closer to that of the conventional method.
, Claims:We Claim:
1. A method of manufacturing of low carbon crude steel in an Energy Optimizing Furnace (EOF) comprising:
involving a charge of scarp (116) 15-20 % and hot metal 80-85 % by the total input charge weight in the EOF; carrying out oxygen blowing into the hot metal involving selectively supersonic lances (103), atmospheric injectors (102) and submerged tuyers (106);
effecting slag (105) removal by titling the furnace wherein
step of slag (105) removal is carried out in a non-continuous manner by selectively controlling the furnace position/inclination comprising maintaining the furnace at+7.5 to +8.5°preferably at +80 inclination from the start to till the end of the blowing including initial period of blowing, boiling period of blowing and also peak blowing period during which carbon sampling of slag (105) is carried out and 0 to -8° preferably at -80 during the slag (105) removal enabling effective interaction of FeO in slag (105) with carbon in molten metal(115)in said furnace and thereby decreasing the slag(105) FeO level by at least 1% with respect to continuous slag (105) removal.
2. The method as claimed in claim 1 wherein said input hot metal comprising by wt. %:
C: 4 to 5%;
Si: 0.25 to 1.5 %;
Mn: 0.25 to 1.5%;
S: 0.02 to 0.07 %;
P: 0.1 to 0.2 %; and rest is iron and said scrap (116) including iron scrap, steel scrap and directly reduced iron (DRI)/sponge iron and wherein step of oxygen blowing include controlled blowing stages including controlled flow rates for initial period, boiling period and peak blow period involving controlled lance (103) flow rate, injector (102) flow rate and said tuyers (106) flow rate with controlled low phosphorous level in tap steel in the range of0.006 to 0.02% preferably about 0.0095%.

3. The method as claimed in anyone of claims 1 or 2 wherein the flow rates of oxygen in supersonic lance (103) is controlled in said initial period in the range of 1168 to 1216 Nm3/hr, said boiling period in the range of 200 to 320 Nm3/min and said peak blow period in the range of 1488 to 1552 Nm3/min thereby allowing the desired time of the metal (115) to react with the slag (105) and such as to prevent the slag (105)to go out of the furnace before carbon sampling wherein 75 to 85% of coolant is added before the blowing time of 90% and the small remainder of the coolant was added thereafter.

4. The method as claimed in anyone of claims 1 to 3 wherein bath temperature is maintained in the range of 1630 to 1680°Cwhich along with sufficient CaO and CaO/SiO2 (basicity) present in slag (105) along with the adequate slag (105) FeO provide desired dephosphorization and increase in crude steel yield and liquid steel yield in the range of 0.72 to 1.3% preferably about 1 % and 1.3 to 1.8%to preferably about 1.5 % respectively.
5. The method as claimed in anyone of claims 1 or 2 wherein the flow rates of the oxygen supplying source-supersonic lances (103)are controlled in the said initial period in the range of 1168 to 1216 Nm3/hr, in said boiling period in the range of 200 to 320 Nm3/min and in said peak blow period in the range of 1488 to 1552 Nm3/min thereby allowing the desired time of the metal(115) to react with the slag (105) and during which about 15 to 25% preferably about 25 % of the slag (105) can go out of the furnace before the carbon sampling at the peak blow period and thereby allowing selectively small quantity 15 to 25% of highly siliceous slag (105) before peak blow period and performing coolant addition bit earlier preferably before the mid of the blow favoured reducing tap phosphorous levels in the process.
6. The method as claimed in claim 5 comprising increasing the tap carbon levels during steel making favoured reducing the slag (105)FeO level as well.
7. The method as claimed in anyone of claims 1 to 6 comprising supersonic lance (103) flow rates are selectively varied during all the three periods of blowing, in the initial period, the flow rates are closer and even go bit lower and higher to reduce the slag (105) flow out of the furnace along with increasing the oxygen input to the process to reduce the blow time, during the boiling period, flow rates are kept to reduce the metal (115) goes out of the furnace such as to avoid the boiling effect to affect the yield and wherein in the boiling period also the flow rates are raised little bit to reduce the blow time and wherein in the peak blow period, the flow rates maintained in the process are in the range of 1488 to 1552 Nm3/min which is higher than conventional to thereby increase in oxygen supply to the metal(115)and attains lower blow time.
8. The method as claimed in anyone of claims 1 to 7 comprising maintaining the atmospheric injectors (102) flow rates bit higher in the range of 61 to 63Nm3/min more than the conventional process during the initial period and the peak blow period, during the boiling period, the flow rates are varied and bit lowered such as to reduce the slag (105) flow out of the furnace and thereby also reduces the blow time significantly and also wherein the submerged tuyers (106) flow rates are bit lower and it is in the range of28 to 31 Nm3/min in the initial period then12 to 17Nm3/min in the boiling period but in the peak blow period it can be go higher in the range of32 to 37Nm3/min during the peak blow period which favour decrease in lime and coolant involvement and desired increase in average crude steel yield of 0.72 to 1.3%preferably about 1% and liquid steel yield in the range of 1.3 to 1.8% preferably about 1.5%, slag (105) FeO levels in the process are lower in the range of 0 to 2% preferably 1% alongwith the increase in tap temperature of 0 to 200C preferably about 100C for the average tap carbon of 0.03to 0.1 preferably about 0.05% and average basicity maintained in the range of 3.4 to 3.8 preferably at 3.68.

9. The method as claimed in anyone of claims 1 to 8 which is carried out free of any required hand lancing operations.
10. The method as claimed in anyone of claims 1 to 9 which is carried out involving said scarp (116) include iron scrap, steel scrap and directly reduced iron (DRI)/sponge iron; input hot metal temperature in the range of1280 to 1340˚C; Tap phosphorous(%) 0.006to0.02;Degree of Dephosphorization (%) 92.5 to95 ;Lime 3100 to 3500 kg; Dolomite 300 to 800 kg; coolant 500 to 1300 kg; oxygen 3300 to 3900 Nm3; blow time 30 to 38 min and; Tap carbon (%) 0.03 to 0.1, Tap temperature (°C) 1630 to 1680; slag(105)FeO (%)20 to 31 and Basicity 1.7 to 5and wherein said controlled slag (105) removal favours selectively (i) increase in the crude steel yield of the process to 1%(i.e., 90.22%) compared with the conventional continuous slag (105) removal method (ii) savings in hand lancing cost (iii) increased liquid yield of 1.5% (i.e., 91.6%) and (iv) decreased slag (105) FeO level of the process by 1%(i.e., 26.83%).

Dated this the 12th day of September, 2022
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199