Claims:We Claim:

1. A supersonic lance system for facilitating combined and energy optimized blowing of oxygen jet from top of liquid metal bath under controlled pressure and flow rate in furnaces for conversion of pig iron into liquid steel involving oxygen supply comprising:
a supersonic lance including a water cooled supersonic nozzle assembly;
a lance holder for supporting said lance including said supersonic nozzle assembly;
a support frame and with cooperative support frame guide adapted for installation of said supersonic lance as a fixed unit with respect to the furnace top frame.

2. The supersonic lance system as claimed in claim 1 comprising a water cooled supersonic lance including supersonic water cooled nozzle assembly comprising a tubular water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end;
said water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end thereof comprising of an inner pipe obtained of corrosion resistant material preferably stainless steel, an outer pipe and an intermediate pipe there between said inner pipe and said outer pipe;
said inner pipe and said intermediate pipe connected to a water inlet and said intermediate pipe and said outer pipe connected to a water outlet such that the water can be continuously fed in through said inlet and released through said outlet thereby maintaining the lance and the nozzle cooled during the process of oxygen supply there through;

said nozzle end comprising of a nozzle throat including a convergent divergent nozzle adapted for supersonic velocity for oxygen supply there though.
3. The supersonic lance system as claimed in anyone of claims 1 or 2 wherein the lance length is in 2600 to 2800mm preferably about 2700mm.
4. Furnace for converting pig iron into crude liquid steel including involving oxygen blowing comprising:

hot metal bath having refractory lined bottom and side walls which is supported with respect to furnace frame structure;

atmospheric injectors and submerged tuyers

at least two fixed supersonic lance systems having angular disposition at height in the range of 1500 to 1700 preferably1603mmwith respect to the furnace base such as to deliver oxygen jet from top of the liquid metal bath;

said fixed supersonic lance system operatively connected to pressure and flow control means for required controlled supply of oxygen jet free of any required movement of said supersonic lances under operator control.

5. Furnace for converting pig iron into crude liquid steel as claimed in claim 4 wherein said supersonic lance system for facilitating combined and energy optimized blowing of oxygen jet from top of liquid metal bath under controlled pressure and flow rate in furnaces for conversion of pig iron into liquid steel involving oxygen supply comprises:

a supersonic lance including a water cooled supersonic nozzle assembly;

a lance holder for supporting said lance including said supersonic nozzle assembly;

a support frame and with cooperative support frame guide adapted for installation of said supersonic lance as a fixed unit with respect to the furnace top frame.

6. Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 or 5 wherein said supersonic lance system comprises a water cooled supersonic lance including supersonic water cooled nozzle assembly comprising a tubular water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end;

said water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end thereof comprising of an inner pipe obtained of corrosion resistant material preferably stainless steel, an outer pipe and an intermediate pipe there between said inner pipe and said outer pipe;

said inner pipe and said intermediate pipe connected to a water inlet and said intermediate pipe and said outer pipe connected to a water outlet such that the water can be continuously fed in through said inlet and released through said outlet thereby maintaining the lance and the nozzle cooled during the process of oxygen supply there through;

said nozzle end comprising of a nozzle throat including a convergent divergent nozzle adapted for supersonic velocity for oxygen supply there though.

7. Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 to 6 wherein the lance length is in 2600 to 2800mmpreferably about 2700mm.

8. Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 to 7 wherein said pressure and flow control means for required controlled supply of oxygen jet free of any required movement of said supersonic lances under operator control comprises Single Seated Flow Control valve and Pressure Reducing Station(PRS)- Control Valve, wherein only flow rate is controlled by the operator to control the slag and metal flushing out of the furnace and the pressure is self-adjusted according to flow rate.
9. Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 to 8 comprises

furnace frame having refractory lining inside;

a scrap preheater system, a water cooled panel, fixed with the help of frame;

two said supersonic lances mounted with fixed lance holder in selected inclined disposition, on supporting frame provided with support frame guide having better control of the lance operation;

a slag door opening for flushing out slag and tap hole for tapping steel provided in the shell frame with refractory wall;

a furnace roof placed on the roof columns to cover the furnace;

submerged tuyers fixed in the bottom of the furnace and its refractory lining which delivers the oxygen directly into the bath;

atmospheric injectors placed above the supersonic injectors which supplies the oxygen for the post combustion and the oxidation.

10. Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 to 9 comprising
Lance Details Construction
Lance Nozzle type 99.7to 100.0 preferably 99.9% Copper tip forged
Lance mounting angle with respect to horizontal (°) 22 to 24 preferably 23
Nozzle exit diameter (mm) 24 to 25 preferably 24.8
Nozzle throat diameter (mm) 19 to 23 preferably 22
No of nozzles 1 to 2 preferably 1
No of SS lance 1 to 2 preferably 2
Angle of the nozzle(°) 29 to31 preferably 30
Lance Length(mm) 2600 to 2800preferably 2700
Pressure Controller Means selected for Max Pressure of oxygen, (kg/cm2) 8 to 13 preferably 12
Flow Controller Mean selected for Max Flow rate of oxygen (Nm3/h) 1500 to 2000 preferably 1900

Dated the 25th day of March, 2022
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, 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 SUPERSONIC LANCE SYSTEM ADAPTED FOR IMPROVED AVAILABILITY AND PRODUCTIVITY OF THE 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 supersonic lance system for Energy Optimizing Furnace(EOF), and more particularly to a fixed supersonic lance including a water cooled supersonic nozzle assemblywhich is positioned at a particular distance between the furnace bottom level and the nozzle tip. The new design reduces the number of the auxiliary parts required for the supersonic lance movement and its associated maintenance. While performing the bottom refractory change after the campaign life of furnace, the time required for dismantling and assembling these auxiliary items are completely eliminated, which resulted in decreased down time, maintenance and man power deployment. The total down time of about 3-4hours for dismantling and remounting has been reduced, along with theman power requirement for maintenance. The earlier length of the supersonic lance which was 3500mm was reduced to 2700mm which saves the cost incurred in this item by 20%.

BACKGROUND OF THE INVENTION
At present, in an integrated steel plants the crude steel is produced either by Basic Oxygen Furnace (BOF) and Electric Arc Furnace (EAF). Apart from these two technologies, Energy Optimizing Furnace (EOF) is also available to produce the crude steel. The main function of this furnace is to convert the pig iron into the crude liquid steel with the help of oxygen. The process in EOF involves oxidation of impurity elements carbon, silicon manganese and phosphorous from the hot metal using oxygen input into the furnace by two supersonic (SS) lances, four atmospheric injectors and two submerged tuyers. The oxidation reactions are exothermic in nature which makes the process autogenous. Supersonic lance and atmospheric injectors are fixed with the de-Laval nozzles and deliver the oxygen jet from the top of the liquid metal bath and the submerged tuyersare fixed straight hole pipes which deliver oxygen from the bottomof the liquid metal. In the original design, the two supersonic lances are movable and the two atmospheric injectors are fixed at an angle to the liquid metal bath and the de Laval nozzlesare also fixed with an angle.The movable supersonic lance as per the original design gave several instabilities in the process that include slag and metal splashing out of the furnace and increased maintenance requirements. A new design involving a short-fixed supersonic nozzle was designed and replaced in place of the movable lance that drastically reduced the maintenance related issues and moderatelyimproved the productivity. During the refractory replacement after a campaign, the furnace bottom is easily opened for refractory replacement and the furnace is brought to operation within shorter duration increasing the furnace availability.

Energy optimizing furnace is one of the such technologies available to produce the steel and its size is small and limited to about 65MT as of now. KORF group developed this technology from their previous technological modifications in the open-hearth furnace. The introduction of supersonic lance design and combined blowing practice (SS lance, tuyers and injectors) along with the pure oxygen supply and the scrap preheating setup to utilize the off gas heat generated during the process were the unique features of this process. There are continuous modifications happened in this furnace to compete with the other steel making technologies and to improve its efficiency in terms of operation and maintenance such as water-cooling arrangements in place of refractory, oxygen supply components design, catch carbon practice, improved refractory life, double shell practice. Due to the maintenance issues the scrap preheating setup was removed in most of the Indian furnaces.

Very few published literatures and patents which describes the new designs for the improvements in the operations as well as the maintenance also.
1) Patent BRPI1101553A2 reports changes in the oxygen supplying equipment/component arrangements design mainly in the submerged tuyers fixed in the walls of the furnace to promote the submerged blowing of oxygen. It promotes the decarburization of the liquid metal bath for the production of steel. This design has the arrangements consists of concentric tubes with an inner tube of strained copper to blow the oxygen and with an outer tube of stainless steel in which the atomized water along with the argon gas is supplied for the cooling. It is inserted into the refractory material gloves. This submerged tuyer design slides over the housing block which makes the tuyer movement inside the furnace based on the refractory wear using a hydraulic mechanism. The present invention deals with the design improvements in another oxygen supplying components such as supersonic lances which different from the above study.
2) Patent BRMU9002554U2 reports a set of provisions introduced into the EOF such as short discharge spout, unique system for additions, pressure loss monitoring and correcting systems and electronic coupled hydraulic systems for the quick tilting of the furnace. These modifications resulted in greater efficiency in operation and maintenance of the EOF. The present invention is different from this and the design changes are mainly in the supersonic lance of the furnace.
3) A study on EOF by Vijay Sharma showed that the tip of the lance is 250mm height from the liquid metal bath and the supersonic lance length is about 1.2m. The lance was mounted in a car driven by an electric motor reducerwith a chain attached to its extreme and brake arrangement and it is mounted along with a support fixed in the furnace. It kept the lance in an angle of about 45° which made the oxygen injection vertical to the bath. They had also modified some of the furnace design which has no scrap preheating system, submerged tuyers and increased furnace volume from the existing design. It includes some of the maintenance improvements such as double shell practice, charge mix and catch carbon practices. The present invention is different from this in terms of supersonic lance angle, design and its assembly.
4) An experimental study by M. Vidhyasagar, G. Murali and G. Balachandran, thermo-kinetics, heat and mass balance in EOF shows that the movable SS lance was operated at the distance of 0.45m above the bath surface. The distance between the furnace bottom level and the SS lance exit were not stated clearly. The length of the supersonic lance was not stated. The present invention is different and it states that the optimized distance for SS lance from the bottom of the furnace and the length of the supersonic lance.

REFERENCES:
1. HENRIQUE CARLOS PFEIFER and PEREIRA REVERTON ALVES, Patent BRMU9002554U2, 2013.
2. HENRIQUE CARLOS PFEIFER, Patent BRMU9002554U2, 2014.
3. Sharma V, Optimization of Steel Making Process Through Energy Optimizing Furnace Under Indian Conditions Faculty of Mechanical Engineering Making Process Through Energy. 2008.
4. Vidhyasagar M, Murali G, Balachandran G. Thermo-kinetics, mass and heat balance in an energy optimizing furnace for primary steel making. Ironmak Steelmak. 2021;48(1):97–108.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide a supersonic lance system for energy optimizing furnace to improve furnace availability and productivity.

A further object of the present invention is directed to provide a supersonic lance system which isa fixed supersonic lance of shorter length and includes a water cooled supersonic nozzle assembly which is positioned at a particular distance between the furnace bottom level and the nozzle tip.

A still further object of the present invention is directed to provide a supersonic lance system which is fixed, not being movable as in existing longer supersonic lances, the number of the auxiliary parts required for the supersonic lance movement and its associated maintenance would be drastically reduced.

A still further object of the present invention is directed to provide a supersonic lance system for facilitating combined and energy optimized blowing of oxygen jet from top of liquid metal bath under controlled pressure and flow rate in furnaces for conversion of pig iron into liquid steel involving oxygen supply.

Another object of the present invention is directed to provide a supersonic lance systemwhich resulted in decreased down time, maintenance and man power deployment, reducing the total down time by about 3-4hours for dismantling and remounting, saves the cost incurred by 20% due to reduced length of lance.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a supersonic lance system for facilitating combined and energy optimized blowing of oxygen jet from top of liquid metal bath under controlled pressure and flow rate in furnaces for conversion of pig iron into liquid steel involving oxygen supply comprising:

a supersonic lance including a water cooled supersonic nozzle assembly;

a lance holder for supporting said lance including said supersonic nozzle assembly;

a support frame and with cooperative support frame guide adapted for installation of said supersonic lance as a fixed unit with respect to the furnace top frame.

A further aspect of the present invention is directed to said supersonic lance system comprising a water cooled supersonic lance including supersonic water cooled nozzle assembly comprising a tubular water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end;

said water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end thereof comprising of an inner pipe obtained of corrosion resistant material preferably stainless steel, an outer pipe and an intermediate pipe there betweensaid inner pipe and said outer pipe;

said inner pipe and said intermediate pipe connected to a water inlet and said intermediate pipe and said outer pipe connected to a water outlet such that the water can be continuously fed in through said inlet and released through said outlet thereby maintaining the lance and the nozzle cooled during the process of oxygen supply there through;
said nozzle end comprising of a nozzle throat including a convergent divergent nozzle adapted for supersonic velocity for oxygen supply there though.

A still further aspect of the present invention is directed to said supersonic lance wherein the lance length is in 2600 to 2800mmpreferably about 2700mm.

A still further aspect of the present invention is directed to furnace for converting pig iron into crude liquid steel including involving oxygen blowing comprising:

hot metal bath having refractory lined bottom and side walls which is supported with respect to furnace frame structure;

atmospheric injectors and submerged tuyers;

at least two fixed supersonic lance systems having angular disposition at height in the range of 1500 to1700mm preferably1603mmwith respect to the furnace base(bottom) such as to deliver oxygen jet from top of the liquid metal bath;

said fixed supersonic lance system operatively connected to pressure and flow control means for required controlled supply of oxygen jet free of any required movement of said supersonic lances under operator control.

A still further aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel wherein said supersonic lance system for facilitating combined and energy optimized blowing of oxygen jet from top of liquid metal bath under controlled pressure and flow rate in furnaces for conversion of pig iron into liquid steel involving oxygen supply comprises:

a supersonic lance including a water cooled supersonic nozzle assembly;

a lance holder for supporting said lance including said supersonic nozzle assembly;

a support frame and with cooperative support frame guide adapted for installation of said supersonic lance as a fixed unit with respect to the furnace top frame.

A still further aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel wherein said supersonic lance system comprises a water cooled supersonic lance including supersonic water cooled nozzle assembly comprising a tubular water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end;

said water coolant pathway surrounding lance pipeline carrying oxygen supply to a nozzle end thereof comprising of an inner pipe obtained of corrosion resistant material preferably stainless steel, an outer pipe and an intermediate pipe there betweensaid inner pipe and said outer pipe;

said inner pipe and said intermediate pipe connected to a water inlet and said intermediate pipe and said outer pipe connected to a water outlet such that the water can be continuously fed in through said inlet and released through said outlet thereby maintaining the lance and the nozzle cooled during the process of oxygen supply there through;

said nozzle end comprising of a nozzle throat including a convergent divergent nozzle adapted for supersonic velocity for oxygen supply there though.
Another aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel as claimed in anyone of claims 4 to 6 wherein the lance length is in 2600 to 2800mm preferably about 2700mm.

Yet another aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel wherein said pressure and flow control means for required controlled supply of oxygen jet free of any required movement of said supersonic lances under operator control comprises Single Seated Flow Control valve and Pressure Reducing Station(PRS)- Control Valve, wherein only flow rate is controlled by the operator to control the slag and metal flushing out of the furnace and the pressure is self-adjusted according to flow rate.

A still further aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel comprises

furnace frame having refractory lining inside;

a scrap preheater system, a water cooled panel, fixed with the help of frame;

two said supersonic lances mounted with fixed lance holder in selected inclined disposition, on supporting frame provided with support frame guide having better control of the lance operation;

a slag door opening for flushing out slag and tap hole for tapping steel provided in the shell frame with refractory wall;

a furnace roof placed on the roof columns to cover the furnace;

submerged tuyers fixed in the bottom of the furnace and its refractory lining which delivers the oxygen directly into the bath;

atmospheric injectors placed above the supersonic injectors which supplies the oxygen for the post combustion and the oxidation.

A still further aspect of the present invention is directed to said Furnace for converting pig iron into crude liquid steel having:

Lance Details Construction
Lance Nozzle type 99.7to 100.0 preferably 99.9%
Copper tip forged
Lance mounting angle with respect to horizontal (°) 22 to 24 preferably 23
Nozzle exit diameter (mm) 24 to 25 preferably 24.8
Nozzle throat diameter (mm) 19 to 23 preferably 22
No. of nozzles 1 to 2 preferably 1
No. of SS lance 1 to 2 preferably 2
Angle of the nozzle(°) 29 to31 preferably 30
Lance Length(mm) 2600 to 2800preferably 2700
Pressure Controller Means selected for Max Pressure of oxygen, (kg/cm2) 8 to 13 preferably 12
Flow Controller Mean selected for Max Flow rate of oxygen (Nm3/h) 1500 to 2000 preferably 1900

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure1(a): shows the earlier design assembly of the EOF-Front view.
Figure1(b): shows the earlier design assembly of the EOF-Plane view.
Figure 2: shows the new supersonic nozzle assembly of the EOF-Front view.
Figure 3: shows the supersonic nozzle design assembly of the EOF.
Figure 4(a): The new supersonic lance design installed on the EOF-Front view.
Figure 4(b): The new supersonic lance design installed on the EOF-Plan view.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention is directed to provide a supersonic lance system for energy optimizing furnace to improve furnace availability and productivity which isa fixed supersonic lance of shorter length and includes a water cooled supersonic nozzle assembly which is positioned at a particular distance between the furnace bottom level and the nozzle tip, reduces down time and improves furnace availability and productivity.

DETAILED EXPLANATION OF EOF OPERATION:
In EOF, the scrap is charged inside the furnace based on the input hot metal conditions after the completion of inspection and maintenance. After charging the scrap, the hot metal is poured into the furnace and then the oxygen is blown to reduce the dissolved elements in the hot metal and scrap through the oxidation reactions. Flux is charged inside the furnace which dissolves the impurity oxides and is discharged as slag. The oxygen for the reactions is blown by three different parts namely the atmospheric injectors, the supersonic lances and the submerged tuyers. The supersonic lances deliver the oxygen into the hot metal bath with supersonic velocity, which ensures shorter duration of the process. The atmospheric injectors and the submerged tuyers deliver oxygen from a fixed position in the original design. The supersonic lances are usually movable in the original design. When the lance height is varied by moveable supersonic lance, the C-O reaction intensity is high and there is higher amount of metal splashing. The carbon boil varies uncontrollably, when there is lack of control on the supersonic lance to bath distance. In addition, the process variations become dependent on the operator skill at maintaining the lance distance from the liquid bath.

When the lance distance is very short, the supersonic jet impingement creates high momentum that result in the metal and slag will splash out of the furnace, which sticks on the refractory walls and water cooled panels. Sometimes the metal droplets can hit the nozzle and puncture the nozzle tip which resulted in maintenance or replacement. Along with this, the metal and slag particles fall on top of the chain arrangement, which is fixed with the help of motor and pulley arrangements to move the lance up and down. This spillage causes arrests and strikes of the movement of the supersonic lance chain and its corresponding pulley and motor, which leads to the failure of chain, that requires chain replacement. Each replacement of the chain adds significant cost. EOF process involves a continuous foamy slag discharge practice during the oxygen blow. In the new design invented the supersonic lance was redesigned and positioned as a fixed lance instead of moveable lance. The control of the process was then modified for the maintenance of pressure and flow rate control, which is independent of operator control and is more amenable for control and automation.

The EOF bottom refractories are replaced at the end of a campaign. During this bottom refractory replacement of the EOF, the supersonic lance auxiliaries namely the lance frame, motor, gearbox and limit switch arrangements has to be dismantled from the furnace since the lance length is greater than the distance between the two columns of the shop roof. This operation involves additional work every time the bottom has to be changed. Additional operation delays and adequate man power has to be deployed to remove and re-fixing the lance every time bottom refractory change is implemented. This operation consumes a maintenance time of about 3-4 hours for dismantling and reassembling it. Hence, apart from maintenance delay associated with down time affects the furnace availability, productivity, increased manual work and associated costs. All these above difficulties, led to the development of new design of a short and fixed supersonic lance, which could be controlled by the pressure and flow rate of oxygen gas rather than by the adjustable lance distance.

THE NEW FIXED SUPERSONIC LANCE ACCORDING TO PRESENT INVENTION:
The presently invented supersonic lance, is a fixed lance which is positioned at a particular distance between the furnace bottom level and the nozzle tip. The new design reduces the number of the auxiliary parts required for the supersonic lance movement and its associated maintenance. While performing the bottom change, the time required for dismantling and assembling these auxiliary items are completely eliminated, which resulted in decreased down time, maintenance and man power deployment. The total down time of about3-4hours for dismantling and remounting has been reduced, along with the man power requirement for maintenance. The earlier length of the supersonic lance which was 3500mm was reduced to 2700mm which saves the cost incurred in this item by 20%.

Earlier the lance was under the control of the operator led to higher instability in the process that includes arbitrary slag and metal splashing during the process. The slag flushing and metal splashing during carbon boil was a function of the lance position. After the new design of the fixed lance, the process was more stable with controlled slag discharge and the reduced metal splashing in the process.

The original operating design of the EOF furnace is shown in schematic Figure1(a) for the frontal view and 1(b) for the top view. The furnace has a scrap preheater system 101, a water cooled panel 102, fixed with the help of frame 116 and there are movable supersonic lances 103 and 110. These lances are 3700mm length and it is fixed at about 1500mm above from the furnace bottom and it is driven by a motor and gear box 104 and it has a pulley and chain arrangement 111. The entire moveable lance is positioned in a lance frame 112. A sliding box105 is provided to enable movement of the supersonic lances. To ensure that the moving of the lance within the range of a distance there is a limit switch 107 in a limit switch assembly 108. The furnace frame 114 has refractory lining 113. In such an assembly, the innovation has come in the moving lance parts 103 and 110. The schematic shows the farthest (lance 103) and nearest moving positions of the lance (Lance 110) as per the original EOF design.

The plane view of the earlier design of EOF is schematically illustrated in Figure1(b). The slag is flushed in the part 117 slag door opening and the steel is tapped at part 121-tap hole provided in the shell frame 114 and the refractory wall 113. The furnace is under the roof which is placed on the roof column 118. The submerged tuyers 120 are fixed in the bottom of the furnace and its refractory lining 113 which delivers the oxygen directly into the bath. The atmospheric injectors 119 are placed above the supersonic injectors which supplies the oxygen for the post combustion and the oxidation.

The new innovation involves the design of a shorter supersonic lance installed as a fixed unit instead of moveable lance. Thus, the moving lances in part No.103 and 110 in Figure 1(a)-(b) has become shorter and fixed units. Due to this innovation, the following parts in the furnace were eliminated. The redundant parts were part motor and gear box 104, pulley and chain arrangement 111, Supersonic lance frame106 and limit switch and its arrangements 107 and 108.These parts are replaced with an arrangement shown in Figure 2 with a new supersonic lance 221, lance holder 222, supporting frame 223 and the support frame guide 224.

List of items shown in Figures 1 & 2 are as follows:

The design of the water cooled supersonic lance is shown in Figure3. It involves an outer steel pipe 301 and another intermittent steel pipe 302 that separates the water inlet and outlet. The inner pipe of the lance consists of a corrosion resistant stainless steel inner pipe 303. This is linked to a copper-based deLaval nozzle 304. The nozzle throat 305 is a convergent divergent nozzle as per part 306, designed to achieve supersonic velocity for oxygen. The water inlet 307 is separated from the water outlet 308.
List of items shown in Figure 3 are as follows:

Accompanying Figure 4(a) and Figure 4(b) shows the new supersonic lance system installed on EOF in front view and plan view wherein it has been shown that the components with part numbers 103,104,105, 106, 107, 108, 109 and 111in earlier design as in Figure 1(a) and Figure 1(b) have been removed and the new lance system with item numbers 221,222,223,224 have been incorporated showing the provision for fixed installation of shorter length supersonic lance.

Advantage in operation and maintenance of the new lance system:
The earlier design had the movable arrangements such as motor, gear box, pulley (sprocket) and chain, the corresponding limit switch arrangements and frames. The slag can splash out of the furnace during the blowing and it can stick to the water cooled panels and refractories as well as the chain and pulley (sprocket) arrangements. In the case, the slag sticks on the furnace then the chain and pulley (sprocket) movement will be arrested. So that the load to the motor becomes high and it will break the chain. So that, it has to be replaced or repaired. This work is eliminated completely with the new fixed lance.
During the bottom change, the supersonic lance and its auxiliary equipment setup has to be removed and after the inspection, it has to be fixed again as per the earlier design. The present design does not require any auxiliary equipment removal and fixing since it is a fixed lance.
During the blowing the operator has to control the slag and metal goes out of the furnace by controlling the lance distance and flow rate as per the earlier design. These two variables are subjected to change because of the input conditions and it can give the possibilities for more flushing of slag and metal out of the furnace. The new design eliminates the requirement to control the lance distance by the operators by using the fixed distance and restricted to use only the flow rate to control the slag and metal flushing out of the furnace.
The furnace performance did not significantly alter due to the new supersonic lance design. A comparison of the operating lance parameters and the benefits of the new design is shown in Table 1. The innovation resulted in reduced maintenance. The bottom change due to redesign and incorporation of fixed lance eliminated totally the bottom change time of3-4hours. Thus, the decreased maintenance time and improves the furnace availability. The new lance is fixed at 1603mm above the furnace-bottom refractory lining which enables lesser slag and metal splashing during the lance operation done at operator discretion.

Table 1 Difference between the old design and the new lance design.
Parameter Old lance design New lance
design
Cost of the lance If we take this as 100 % 80 % of the old design
Lance Nozzle type 99% Copper tip forged 99% Copper tip forged
Lance mounting angle with
respect to horizontal (°) 22 23
Nozzle exit diameter (mm) 25 24.8
Nozzle throat diameter (mm) 19.2 22
No of nozzles 1 1
No of SS lance 2 2
Angle of the nozzle(°) 30 30
Lance Length(mm) 3500 2700
Max Pressure of oxygen(kg/cm2) 13 13
Max Flow rate of oxygen(Nm3/h) 1500 1900
SS lance Maintenance time during
bottom change time (hours) 3-4 0
Man power cost for maintenance
during bottom change (%) 100 0

There are marginal improvements as in Table 2. The improvements are in the number of heats per month. The mean oxygen consumption has increased moderately which enables higher production of the steel. Lime consumption has marginally decreased as well. The increased Mn level was attributed to the higher Mn in the hot metal post installation of the new design of the lance. If the furnace were operated with similar Mn levels in the hot metal as before the new design the production levels would be still higher. The mean refractory life after the new lance installation shows a marginal improvement as in Table 3 and marginally decreased the gunning mass consumption.

Table 2 The blow time and Gross production before and after installation of the new lance
Parameter Old lance design New lance design
No of heats per month in 6 months before and after lance change Oct-20 693
Nov-20 694
Dec-20 588
Jan-21 727
Feb-21 690
Mar-21 755
Mean 691
May-21 729
Jun-21 685
Jul-21 702
Aug-21 706
Sep-21 647
Oct-21 734
Mean 700

Lime consumption
in 6 months before and after lance change

Oct-20 55.59
Nov-20 57.12
Dec-20 56.15
Jan-21 54.63
Feb-21 53.99
Mar-21 54.49
Mean 55.33
May-21 53.03
Jun-21 54.5
Jul-21 52.94
Aug-21 52.79
Sep-21 56.89
Oct-21 53.92
Mean 54.011

Oxygen consumption (NM3/MT) in 6 months before and after lance change

Oct-20 52.50
Nov-20 53.35
Dec-20 51.86
Jan-21 52.39
Feb-21 53.28
Mar-21 54.31
Mean 52.95
May-21 55.87
Jun-21 55.34
Jul-21 54.93
Aug-21 56.50
Sep-21 56.98
Oct-21 56.44
Mean 56.01

Mn levels in hot metal
(%)

Oct-20 0.64
Nov-20 0.60
Dec-20 0.70
Jan-21 0.36
Feb-21 0.32
Mar-21 0.24
Mean 0.478
May-21 0.70
Jun-21 0.74
Jul-21 0.73
Aug-21 0.88
Sep-21 1.00
Oct-21 0.72
Mean 0.80

As shown in Table 2, the earlier design there was a problem of lime dissolution also since the lance height can be varied but the present fixed lance provides better penetration and mixing makes the dissolution of the lime faster which makes a marginal decrease in lime consumption.
Increase in the average oxygen consumption in the new design compared to the earlier one as shown in Table 2. There is an increase in the hot metal manganese which obviously leads to increase in oxygen consumption. The oxidation of manganese will happen during the blowing and most of the manganese will be oxidized as manganese oxide before the removal of carbon. The process of blowing ends when the carbon level in the bath (steel) reaches below 0.1% and preferably at 0.05%.
The new design reduces the down time of the furnace by decreasing the bottom change time of the furnace (i.e., increased availability of the furnace) and it resulted in increased average number of heats compared to the earlier design as shown in Table 2.
Table 3: Refractory life and gunning mass consumption
Parameter Old Lance Design New Lance design
Refractory life in 4 campaigns before and after lance change

From Date To date Refractory Life
24.10.20 06.12.20 1022
13.12.20 25.01.21 1029
26.01.21 06.03.21 976
07.03.21 20.04.21 1078
Mean 1026.25
From Date To date Refractory Life
21.04.21 04.06.21 1029
05.06.21 12.07.21 883
13.07.21 01.09.21 1149
01.09.21 25.10.21 1212
Mean 1068.25

Gunning mass consumption (kg/MT of steel)

Oct-20 3.67
Nov-20 5.87
Dec-20 3.23
Jan-21 4.69
Feb-21 3.95
Mar-21 3.29
Mean 4.12
May-21 4.25
Jun-21 3.69
Jul-21 3.78
Aug-21 4.53
Sep-21 2.83
Oct-21 4.43
Mean 3.92

As shown in Table 3, the new design reduces the refractory erosion by means of less splashing tendency which results in less sticking of acidic oxides on to the refractory. This new design does not contribute much for the refractory erosion but still there is a minimal effect along with the improvement. There is also no difference in gunning mass consumption which usually rise in the case of increase in refractory erosion.
The blow profile/pattern may be the same as the earlier design but the lance distance is the variable. The pressure will be adjusted automatically according to the flow rate given by the operator.

It is thus possible by way of the present invention to provide a new shorter design of supersonic lance for EOF as fixed oxygen containing unit completely replacing the moveable supersonic nozzle. This innovation decreases the lance cost, eliminates a host of operational parts that include motor and gear box assembly, pulley and chain arrangement, Supersonic lance frame, limit switch and its arrangements. These parts are replaced with a much simpler maintenance free parts of new supersonic lance, a fixed lance holder, supporting frame and the support frame guide having better control of the lance operation with gas flow rate control which is amenable for control and automation. The operator discretion of lance operation is totally eliminated. The performance of the furnace was maintained with the change of moveable supersonic nozzle to fixed lance. There is a marginally higher number of heats per day, reduced lime consumption, refractory consumption. The furnace performance with the new lance design has a moderately higher mean oxygen consumption associated with higher Mn input in the hot metal and at similar levels of Mn content, the furnace has shown still minimal increase in oxygen consumption.