Metallurgical furnace with carbon injection lance

Abstract

To provide furnaces and more particularly submerged arc furnaces used in steel making.SOLUTION: A metallurgical furnace 10 comprises a closed furnace vessel 12 maintaining a reducing atmosphere. The vessel comprises at least one electrode 14.3 providing energy to a burden 16. The burden comprises a body of molten metal 20 having an upper surface 22. At least one carbon injecting lance 28.1 in an operational position thereof extends from an inlet end 30 thereof outside the vessel through a port 32 in the vessel to an outlet end 34 thereof inside the vessel where the lance terminates below the upper surface 22 of the metal body. The inlet end 30 is connected to a source of a carburizing agent. The lance is selectively movable between the operational position and a retracted position wherein the outlet end 34 is outside the vessel. The furnace further comprises a gastight enclosure 38.1 for the lance when in the retracted position, the enclosure locating over the port on the vessel in a gastight manner and maintaining the reducing atmosphere in the vessel.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a furnace, and more particularly to a submerged arc furnace for steelmaking.

Background Art

[0002] In the production of steel by a known submerged arc furnace (SAF), a molten iron bath containing 0 to 2.5% carbon is made from direct reduced iron (DRI). This carbon content is too low to be used as an alternative to blast furnace (BF) hot metal in steelmaking using the downstream SAF.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Therefore, an object of the present invention is to provide a furnace and a method of operating the furnace that can at least mitigate the above-mentioned drawbacks or can be a useful alternative to known furnaces and methods, as considered by the applicant.

Means for Solving the Problems

[0004] According to the present invention, a sealed furnace vessel that maintains a reducing atmosphere, comprising at least one electrode for supplying energy to the charge in the vessel, the charge including molten metal having an upper surface, a slag layer on the upper surface, and a feed material; at least one carbon injection lance that extends from an inlet end outside the vessel through a port provided in the vessel to an outlet end inside the vessel when in an operating position, and terminates below the upper surface of the molten metal, the inlet end of the at least one carbon injection lance being connected to a carburizing agent supply source, and the at least one carbon injection lance being selectively movable between the operating position and a retracted position where the outlet end is outside the vessel; A metallurgical furnace is provided, comprising: an airtight housing for the at least one carbon injection lance when it is in the retracted position, the airtight housing which is airtightly positioned over the vessel covering the port and maintaining a reducing atmosphere inside the vessel.

[0005] The furnace may operate as a submerged arc furnace (SAF) or as an open arc furnace.

[0006] The carburizing agent may be in the form of a dry, finely ground carburizing agent. In steelmaking applications utilizing SAF, the carbon injection lance may be used to increase the carbon content in the molten iron bath of directly reduced iron (DRI) to more than 4%, thereby allowing it to be used as a blast furnace (BF) alternative molten iron supply in downstream SAF steelmaking. The carburizing agent may also be in the form of coal, coke, graphite, or pure carbon.

[0007] The metallurgical furnace may include a plurality of carbon injection lances extending through each of the ports provided in the above-mentioned vessel, and each airtight housing for each carbon injection lance.

[0008] In some embodiments, the inlet end of each carbon injection lance may be connected to its respective carburizer supply source.

[0009] In other embodiments, the plurality of carbon injection lances may be divided into at least a first set of carbon injection lances and a second set of carbon injection lances, and the inlet ends of the first set of carbon injection lances and the inlet ends of the second set of carbon injection lances may be connected to their respective carburizing agent supply sources.

[0010] During operation, the carburizing agent may be continuously supplied to the inlet end of the carbon injection lance and discharged at the outlet end.

[0011] In other embodiments, the carburizing agent may be sequentially and alternately supplied to the inlet ends of the first set of carbon injection lances and the inlet ends of the second set of carbon injection lances.

[0012] The above container may be rectangular in shape and comprise a rectangular base having a main axis extending between its opposing ends, opposing rising side walls, opposing rising end walls, and a roof.

[0013] The metallurgical furnace may have multiple spaced electrodes located on the main axis.

[0014] In other embodiments, the container may be circular in shape and comprise a base having a central axis, circular side walls, and a circular roof.

[0015] In these embodiments, the multiple spaced electrodes may be located on a circle concentric with the main axis.

[0016] The above-mentioned port may be defined in any suitable part of the container, such as the side wall, but it is preferable that it be defined in the roof. The at least one carbon injection lance may be movable vertically between the operating position and the retracted position, or it may be movable diagonally.

[0017] The at least one carbon injection lance is mounted on a carriage that is movable on the rack between a first position corresponding to the operating position of the at least one carbon injection lance and a second position corresponding to the retracted position of the at least one carbon injection lance, and the carriage and the rack may be mounted inside the airtight enclosure.

[0018] The airtight enclosure may be elongated and may include a selectively operable inlet for pressurized inert gas into the enclosure, a selectively operable exhaust port from the enclosure, and a selectively openable door that allows at least a portion of the at least one carbon injection lance to be removed from the enclosure.

[0019] A cover for the port may be mounted inside the housing. The cover may be selectively movable between an open position and a closed position when the at least one carbon injection lance is in the retracted position.

[0020] A method for operating a metallurgical furnace, wherein the metallurgical furnace is a sealed furnace vessel that maintains a reducing atmosphere and is equipped with at least one electrode that supplies energy to a charge inside the vessel, the charge comprising a sealed furnace vessel having an upper surface, a slag layer on the upper surface and a supply material, and the method is When in the operating position, a carbon injection lance extending from the inlet end outside the container through a port provided in the container to the outlet end below the upper surface is used to inject the carburizing agent into the charge, The carbon injection lance is selectively retracted to a retracted position so that the outlet end is located outside the container. The present invention also includes a method for maintaining a reducing atmosphere inside the container by using an airtight enclosure for housing the carbon injection lance when it is in the retracted position, the airtight enclosure being airtightly positioned over the container and covering the port. [Brief explanation of the drawing]

[0021] Herein, the present invention will be further described for illustrative purposes only, with reference to the attached drawings. [Figure 1] Figure 1 is a schematic perspective view of an exemplary embodiment of a metallurgical furnace comprising a container with a roof and a carbon injection lance that penetrates the roof and extends into the container. [Figure 2]Figure 2 is a sectional view taken along line II of FIG. 1, showing the lance in the operating position with respect to the container. [Figure 3] Figure 3 is a similar view of the lance in the retracted position with respect to the container. [Figure 4] Figure 4 is an enlarged sectional view of the roof area defining the port through which the lance in the operating position extends into the container. [Figure 5] Figure 5 is a similar view to FIG. 4 of the lance in the retracted position. [Figure 6] Figure 6 is a similar view to FIG. 5 with the port closed by a lid.

Embodiments for Carrying Out the Invention

[0022] In FIGS. 1 to 3, an exemplary embodiment of a metallurgical furnace is generally indicated by reference numeral 10.

[0023] The metallurgical furnace 10 includes a sealed furnace container 12 in which a reducing atmosphere is enclosed and maintained. The container includes at least one electrode 14.1 to 14.6 for supplying energy to the charge 16 (shown in FIGS. 2 and 3) in the chamber 18 of the container. The charge 16 includes molten metal 20 having an upper surface 22, a slag layer 24 on the upper surface, and feed material 26. At least one carbon injection lance 28.1 to 28.4 extends from an inlet end 30 outside the container through a port 32 provided in the container to an outlet end 34 inside the container when it is in the operating position (shown in FIG. 2), where the lance terminates below the upper surface 22 of the molten metal 20. The inlet end 30 of the lance is connected to a carburizing agent supply source 36 (shown in FIG. 1). The at least one lance is selectively movable between the operating position and a retracted position (shown in FIG. 3) where the outlet end 34 is outside the container 12. The furnace further includes airtight housings 38.1 to 38.4 for the at least one lance when in the retracted position. The housings are positioned airtightly covering the port 32 on the container and maintain the reducing atmosphere inside the container.

[0024] In the exemplary embodiment shown in Figures 1 to 3, the furnace vessel 12 is rectangular in shape and includes a rectangular base 40 having a main axis 42 extending between opposing ends. The vessel further includes opposing rising side walls 44 and 46, opposing rising end walls 48 and 50, and a roof 52.

[0025] In the exemplary embodiment shown in Figures 1 to 3, the furnace 10 comprises six electrodes 14.1 to 14.6 spaced apart from each other on the longitudinal axis 42.

[0026] Typically, the furnace is housed in a building (not shown) that includes a steel structure or steel frame (not shown) for supporting the furnace components in a known manner. A control room (not shown) is also provided, which includes a central control unit (also not shown) for furnace and process control. All necessary measurements from the furnace system are displayed on a human-machine interface (HMI) in the control room.

[0027] The furnace may be equipped with several similar carbon injection lances. In some embodiments, there may be as many as 10 lances, but in the illustrated embodiment, there are four lances 28.1 to 28.4. Since these carbon injection lances have a similar configuration, only carbon injection lance 28.1 will be described in more detail. Lance 28.1 is tubular in shape, with its hollow portion extending between an inlet end 30 and an outlet end 34 for the carburizing agent. The carburizing agent is supplied by a supply source 36 and is in the form of a dry, finely ground carburizing agent entrained with an inert gas. As best shown in Figures 1, 2, and 4 to 6, lance 28.1 comprises a first permanent part 60 and a second replaceable consumable part 62, which are fluid-tightly joined by a flange 64 that cooperates with each other. This consumable part is made of a thick-walled steel pipe with an outer coating of high-alumina castable.

[0028] Therefore, the metallurgical furnace 10 is connected to a supply source 36 for receiving, storing, and handling the finely ground carburizing agent, in addition to a conventional supply system (not shown) for the solid feed material 16 (shown in Figures 2 and 3) required for steelmaking. The multiple carbon injection lances 28.1 to 28.4 serve to inject the carburizing agent into the charge at a position lower than the upper surface 22 of the molten metal.

[0029] The carbon injection lance 28.1 is supported on a movable carriage 66 on a vertical rack 67 on a mast, both of which are located within a housing 38.1. The first component 62 of the injection lance is preferably secured on the movable carriage 66 by a pneumatically operated auto-locking clamping device. The inlet end 30 of the lance is connected to the powder transport pipeline 68.1 by a pneumatically operated coupling device. The clamping device and coupling device are controlled from a local control panel.

[0030] The carriage 66 is mounted on the mast and can be selectively moved (raised or lowered) as needed by two rows of heavy-duty endless chains connected to both the upper and lower ends of the carriage 66. These chains are driven by an inverter-controlled geared motor unit (not shown), providing variable speed and good position control as the carriage moves up and down the mast during operation. An encoder monitors the position of the carriage 66, and a fixed limit switch outputs a final end position signal.

[0031] Therefore, as described above, the selectively movable carriage allows the carbon injection lance 28.1 to be selectively movable between an operating position (shown in Figure 2) in which its second end 34 is located below the upper surface 22 of the molten metal 20 and a retracted position (shown in Figure 3) in which the second part 60 of the lance can be serviced or replaced.

[0032] The metallurgical furnace further comprises separate airtight enclosures 38.1–38.4 for each carbon injection lance when it is in the retracted position. Since these enclosures have a similar configuration, only enclosure 38.1 will be described in more detail below. In this exemplary embodiment, the airtight enclosure 38.1 is airtightly mounted on the furnace roof 52, covering the port 32. The enclosure is elongated to accommodate the mast and rack and the injection lances 28.1 when they are in the retracted position. The enclosure comprises a selectively operable inlet 70 into the enclosure for pressurized inert gas, a selectively operable exhaust port 72 from the enclosure, and a selectively openable door 74 from which at least a portion of the at least one carbon injection lance can be removed from the enclosure. The enclosure further comprises a pressure relief valve 76. During operation, the enclosure 38.1, filled with inert gas at a pressure higher than the pressure in the chamber 18, “blocks” the port 32 when the lances 28.1 are in the first position. The sealed port 32 prevents gas from flowing out or leaking out of the chamber 18 while the lance is in the operating position. The housing and the sealed port also prevent oxygen from flowing into the chamber, thereby maintaining a reducing atmosphere inside the container.

[0033] The metallurgical furnace further includes a selectively operable lid 78 for port 32. The lid 78 is mounted inside the housing 38.1 and is rotatable about a hinge 80 by a pivot shaft 82 selectively driven by a pneumatic actuator 83. Thus, the lid is selectively movable between an open position (shown in Figures 2 to 5) and a closed position (shown in Figure 6) when the carbon injection lance 28.1 inside the housing 38.1 is in the retracted position. As shown in Figure 6, when the second end is in the second position, the pneumatic actuator 83 rotates the lid 78 to the closed position, and the lid seals port 32. During maintenance, the housing 38.1 is connected to the furnace's fume extraction system, allowing inert gas to be exhausted from the exhaust port 72 and fresh air to be introduced into the housing to further cool the lance and eliminate the risk of asphyxiation. The door 74 of the housing 38.1 can be opened, the lance can be removed, and the second part 62 can be replaced with a new second part to form a new lance.

[0034] In some embodiments (not shown), each injection lance may be connected to its respective carburizer supply source via its respective transport pipeline. In these embodiments, with the lances in the operating position, the carburizer can be continuously supplied to each lance and discharged below the surface 22.

[0035] In other embodiments, the plurality of lances may be divided into at least a first set of lances and a second set of lances, as shown in Figure 1, where the lances in housings 38.1 and 38.3 are included in the first set, and the lances in housings 38.2 and 38.4 are included in the second set. The first set of lances is connected to a first supply source 36.1 via a transport pipeline 68.1, and the second set of lances is connected to a second supply source 36.2 via a transport pipeline 68.2. In this embodiment, with the lances in the operating position, the carburizing agent can be continuously supplied to all lances and discharged below the surface 22. Alternatively, the carburizing agent may be supplied sequentially and alternately to the inlet ends of the first set of carbon injection lances and the inlet ends of the second set of carbon injection lances.

[0036] Referring again to Figure 1, the supply source 36 may also include first and second external receiving storage silos 80 and 82 for powdered carburizer. Directly below each storage silo are injection dispensers 84 and 86. The outlets of the injection dispensers are connected to powdered carburizer transport pipelines 68.1 and 68.2 that supply the two sets of injection lances.

[0037] The material levels inside the silo are continuously monitored by a full-length level radar probe (not shown). Self-cleaning displacement air filters 90 and 92 are installed at the top of the silo. Air removed due to filling, fluidization, and exhaust passes through these filters to prevent dust from being released into the atmosphere. The silo is also equipped with an overpressure detection transmitter and an overpressure rupture disc unit.

[0038] The injection dispenser is a pressure vessel. Both dispensers are supported by a self-supporting frame and mounted on a load cell (not shown) for measuring the contents. This measurement is used to control the injection flow rate, the position of the powder flow control valve, and the level inside the dispenser. The dispenser is equipped with flange connections to the exhaust line, pressurizing line, and fluidization line, as well as instruments for measuring pressure.

[0039] A series of valves for isolation and material flow control are located below the dispenser. The dispenser is connected to powder transport lines 68.1 and 68.2 for supplying a first set and a second set of injection lances. The powder transport lines are equipped with robust shot blast hoses with quick-release connectors for easy replacement as needed.

[0040] Nitrogen is used as the transport gas for conveying, fluidizing, and injecting the powdered carburizing agent. The pressure and flow rate of the nitrogen are controlled by a set of valves (not shown).

[0041] During carbon injection at the first position of lance 28.1, the actual injection rate is measured by the aforementioned load cell to which the powder injection dispenser is attached and calculated by the control system. The actually achieved injection rate is continuously compared with the required injection rate. The difference between the measured rate and the required rate is used to adjust the material flow control valve located below the injection dispenser. This valve opens and closes automatically, increasing or decreasing the actual injection rate to maintain a preset rate.

[0042] The supply source 36 continues to inject from one or both dispensers until injection becomes impossible or deemed impossible due to the supply source being nearly empty, the need for lance replacement, or a system malfunction. Injection is automatically stopped when the material level reaches the lower limit, when the operator initiates a stop sequence from the control system, and in the event of a malfunction.

[0043] Lance 28.1 begins to retract as carriage 66 moves lance 28.1 toward a second position, and the second end 34 moves away from the charge and slag surface. When the second end is no longer in contact with the slag surface, the injection dispenser shut-off valve closes, stopping the flow of powder from the dispenser. Any powder remaining in the powder transport pipeline 68.1 passes through the lance and is sprayed onto the slag surface. Once all powder has been discharged from the lance, the transport gas continues to flow at an increased rate for a short time to ensure that the powder transport pipeline 68.1 is completely empty, and then stops. The lance continues to move toward the position where it will be retracted and retained. The injection lance can be removed from door 74 if it has reached the end of its service life or if it has failed or become blocked prematurely. A new second part 62 can be fitted as described above. The new lance is then inserted into housing 38.1 and connected to carriage 66, with the inlet end 30 connected to transport pipeline 68.1.

[0044] If maintenance is required, a new lance is lowered towards the operating position. Before the outlet end 34 enters the hot slag surface, the powder transport gas is switched on, and the lance pauses until the gas flow rate stabilizes. Then, the powder discharge valve of the injection dispenser opens, allowing the powder to flow out into the powder transport pipeline 68.1 and through the lance. Once the minimum powder flow rate is established, the lance is pushed down into the charge so that the outlet end 34 is in a predetermined position below the surface 22 of the molten metal 20. To prevent the lance outlet from becoming blocked, the powder flow is established before the lance enters the slag and maintained until the lance leaves the slag.

Claims

1. A sealed furnace vessel that maintains a reducing atmosphere, comprising at least one electrode for supplying energy to a charge inside the vessel, wherein the charge includes molten metal having an upper surface, a slag layer on the upper surface, and a supply material, At least one carbon injection lance, when in the operating position, extending from an inlet end outside the container through a port provided in the container to an outlet end inside the container, terminating there below the upper surface of the molten metal, wherein the inlet end of the at least one carbon injection lance is connected to a carburizing agent supply source, and the at least one carbon injection lance is selectively movable between the operating position and a retracted position where the outlet end is outside the container, A metallurgical furnace comprising: an airtight housing for the at least one carbon injection lance when in the retracted position, the airtight housing positioned airtightly over the vessel, covering the port and maintaining a reducing atmosphere within the vessel.

2. The metallurgical furnace according to claim 1, comprising a plurality of carbon injection lances extending through each of the ports provided in the container, and each airtight housing for each carbon injection lance.

3. The metallurgical furnace according to claim 2, wherein the inlet end of each carbon injection lance is connected to its respective carburizing agent supply source.

4. The metallurgical furnace according to claim 2, wherein the plurality of carbon injection lances are divided into at least a first set of carbon injection lances and a second set of carbon injection lances, and the inlet end of the first set of carbon injection lances and the inlet end of the second set of carbon injection lances are connected to their respective carburizing agent supply sources.

5. The metallurgical furnace according to claim 3 or 4, wherein during operation, a carburizing agent is continuously supplied to the inlet end of the carbon injection lance and discharged at the outlet end.

6. The metallurgical furnace according to claim 4, wherein the carburizing agent is sequentially and alternately supplied to the inlet ends of the first set of carbon injection lances and the inlet ends of the second set of carbon injection lances.

7. The metallurgical furnace according to claim 1, wherein the container is rectangular in shape and comprises a rectangular base having a main axis extending between opposing ends, opposing rising side walls, opposing rising end walls, and a roof.

8. The metallurgical furnace according to claim 7, comprising a plurality of spaced electrodes located on the main axis.

9. The metallurgical furnace according to claim 1, wherein the container is circular in shape and comprises a base, circular side walls, and a circular roof.

10. The metallurgical furnace according to claim 9, comprising a plurality of spaced electrodes located on a circle concentric with the main axis.

11. The metallurgical furnace according to claim 7 or 9, wherein the port is defined in the roof, and the at least one carbon injection lance is movable vertically or diagonally between the operating position and the retracted position.

12. The metallurgical furnace according to claim 1, wherein the at least one carbon injection lance is mounted on a carriage that is movable on a rack between a first position corresponding to the operating position of the at least one carbon injection lance and a second position corresponding to the retracted position of the at least one carbon injection lance, and the carriage and the rack are mounted inside the airtight housing.

13. The metallurgical furnace according to claim 1, wherein the airtight enclosure is elongated and comprises a selectively operable inlet into the enclosure for pressurized inert gas, a selectively operable exhaust port from the enclosure, and a selectively openable and closable door from which at least a portion of the at least one carbon injection lance can be removed from the enclosure.

14. The metallurgical furnace according to claim 1, comprising a cover for the port, which is mounted inside the housing and is selectively movable between an open position and a closed position when the at least one carbon injection lance is in the retracted position.

15. A method for operating a metallurgical furnace, wherein the metallurgical furnace is a sealed furnace vessel that maintains a reducing atmosphere and comprises at least one electrode that supplies energy to a charge in the vessel, the charge comprising a sealed furnace vessel having an upper surface, a slag layer on the upper surface and a supply material, and the method is The process involves injecting a carburizing agent into the charge using a carbon injection lance that, when in the operating position, extends from the inlet end outside the container through a port provided in the container to the outlet end below the upper surface, The carbon injection lance is selectively retracted to a second retracted position such that the outlet end is located outside the container. A method comprising maintaining a reducing atmosphere inside the container by using an airtight housing for the carbon injection lance when it is in the retracted position, the airtight housing being airtightly positioned over the container and covering the port.

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