Clean and rapid smelting method in an electric arc furnace with full scrap steel

Abstract

A clean and rapid smelting method in an electric arc furnace with full scrap steel, is suitable for smelting process of 30-300 t electric arc furnace with full scrap steel. In the smelting process of the electric arc furnace with full scrap steel, different kinds of mediums are injected by an injection lance which is installed inside refractory material of sidewall at the bottom of the electric arc furnace in different stages of smelting. Carburization is utilized in molten pool to accelerate melting down and improve carbon content of the molten pool at the stage of recarburizing and fluxing. A reaction in the molten pool is intensified at the stage of high efficiency dephosphorization and deep denitrogenation, to enhance efficient dephosphorization and deep denitrification of the reaction in the molten pool, thereby accelerating the smelting speed of the electric arc furnace with full scrap steel, improving effect of dephosphorization and denitrification.

Claims

1. A clean and rapid smelting method in an electric arc furnace with full scrap steel, wherein online dynamic switching for different mediums including a pure gas, a carrier gas A with a recarburization powder, a carrier gas B with a dephosphorization powder in an injection mode is utilized, to finish a process of blowing in turn below a molten steel level of a molten pool in different stages of smelting for the different mediums; the process of blowing in turn comprises: in a stage of recarburizing and fluxing, injecting the carrier gas A with the recarburization powder into the molten pool to improve a carbon content of molten steel in the molten pool, and to improve a flow velocity of the molten steel, wherein the molten steel has formed the molten pool, and accelerating a melting process of the full scrap steel by carburization, wherein the carbon content of the molten steel in the molten pool reaches 0.40%-2.0% after the melting process of the full scrap steel is completed; in a stage of high efficiency dephosphorization, injecting the carrier gas B with the dephosphorization powder into the molten pool to improve kinetic conditions for the high efficiency dephosphorization, wherein the high efficiency dephosphorization in the electric arc furnace is achieved by systematic dephosphorization of slag particles in a molten state, to make a phosphorus content of the molten steel equal to or less than 0.010%; in a stage of deep denitrogenation, injecting O.sub.2 or a gas mixture of O.sub.2 and CO.sub.2 into the molten pool to intensify decarburization in the molten pool, and effectively removing nitrogen in the molten steel by a large number of CO bubbles produced by a metallurgical reaction in the molten pool; and in a stage of a smelting endpoint, injecting the carrier gas B with the dephosphorization powder to prevent the molten steel from rephosphorization, then Ar into the molten pool, to homogenize compositions and a temperature of the molten pool, wherein the carbon content of the molten steel is equal to or more than 0.10%, the phosphorus content of the molten steel is equal to or less than 0.004%, and a nitrogen content of the molten steel is equal to or less than 0.005%; wherein the online dynamic switching refers to that the switching between the mediums is controlled by a control system and is performed according to the different stages, wherein the word online in the online dynamic switching refers to that the switching between the mediums is controlled by a control system, and the word dynamic in the online dynamic switching refers to that the switching between the mediums is performed according to the different stages.

2. The clean and rapid smelting method in an electric arc furnace with full scrap steel according to claim 1, comprising the following steps: step 1: in a time period after steel is output from the electric arc furnace and before a furnace material is added, closing a recarburization path automatic shut-off valve by the control system, opening a dephosphorization path automatic shut-off valve by the control system, through a first transmission pipeline for the high efficiency dephosphorization, injecting N.sub.2 through a central tube and a circular seam tube of an injection lance, wherein a flow rate of the central tube is 50-500 Nm.sup.3/h, and a flow rate of the circular seam tube is 50-200 Nm.sup.3/h, to prevent the injection lance from blocking and burning; step 2: in a feeding stage of the electric arc furnace: through the first transmission pipeline for the high efficiency dephosphorization, injecting O.sub.2 by the central tube of the injection lance, wherein a flow rate of the central tube is 50-300 Nm.sup.3/h; injecting propane or natural gas by the circular seam tube, wherein a flow rate of the circular seam tube is 50-200 Nm.sup.3/h, to ensure a normal operation of the injection lance in the feeding stage of the electric arc furnace; step 3: in the stage of recarburizing and fluxing: injecting carbon powder into the molten pool formed by the melting process of the full scrap steel, to improve the carbon content of the molten steel in the molten pool, and accelerate the melting process of the full scrap steel by using the carburization, wherein this step comprises the following steps: 1) in an early stage of the melting process: opening the recarburization path automatic shut-off valve by the control system, and closing the dephosphorization path automatic shut-off valve by the control system; through a second transmission pipeline for recarburization, performing a carrier gas A with recarburization powder flow mode on the central tube of the injection lance, to accelerate the carburizing and the melting process of the full scrap steel, wherein the molten pool is formed in the stage, a velocity of a powder injection is controlled to improve a carburizing efficiency, a velocity of the powder injection is 1-5 kg/min, and a flow rate of the carrier gas A is 100-300 Nm.sup.3/h; and injecting propane or natural gas by the circular seam tube of the injection lance, wherein a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h; 2) in a middle stage of the melting process: through the second transmission pipeline for the recarburization, performing the carrier gas A-recarburization powder flow mode on the central tube of the injection lance, wherein the molten pool has a depth in the middle stage of the melting process, and a velocity of the powder injection is controlled to improve the carburizing efficiency, wherein a velocity of the powder injection is 5-10 kg/min, and a flow rate of the carrier gas A is 200-500 Nm.sup.3/h; and injecting propane or natural gas by the circular seam tube of the injection lance, and a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h; and 3) in a later stage of the melting process: through the second transmission pipeline for the recarburization, performing the carrier gas A-recarburization powder flow mode on the central tube of the injection lance, wherein the molten pool is deep in the later stage of the melting process, and intensifying the carburizing and stirring in the molten pool, wherein a velocity of the powder injection is 10-20 kg/min, and a flow rate of the carrier gas A is 200-600 Nm.sup.3/h; and injecting propane or natural gas by the circular seam tube of the injection lance, wherein a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h; step 4: in a stage of pipeline cleaning: performing pipeline cleaning by using a large flow of N.sub.2 or CO.sub.2, wherein the pipe cleaning comprise the steps of: opening the recarburization path automatic shut-off valve by the control system, and closing the dephosphorization path automatic shut-off valve by the control system; through the transmission pipeline for the high efficiency dephosphorization, injecting N.sub.2 or CO.sub.2 by controlling the central tube of the injection lance to perform the pipeline cleaning, wherein a flow rate of the N.sub.2 or the CO.sub.2 is 400-600 Nm.sup.3/h, and a time of injecting the N.sub.2 or the CO.sub.2 is 20-30 s; step 5: in the stage of the high efficiency dephosphorization: injecting high speed dephosphorization powder gas flow directly to the molten pool below the molten steel level, to effectively remove phosphorus in the molten steel, wherein this step comprises the following steps: through the first transmission pipeline for the high efficiency dephosphorization, performing a carrier gas B-dephosphorization powder flow mode on the central tube of the injection lance, and inputting the carrier gas B with the dephosphorization powder directly into the molten steel and intensifying a stirring ability of the molten pool, to dephosphorize efficiently, wherein a velocity of the powder injection is 10-50 kg/mm, and a flow rate of the carrier gas B is 100-1000 Nm.sup.3/h; and injecting propane or natural gas by the circular seam tube of the injection lance, wherein a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h; step 6: in a stage of deep denitrogenation: performing the deep denitrogenation by an intense carbon oxygen reaction inside the molten pool, wherein this step comprises the following steps: through the first transmission pipeline for the high efficiency dephosphorization, injecting a gas mixture of O.sub.2 and CO.sub.2 to intensify the decarburization in the molten pool, and using a large number of CO bubbles produced by the intense carbon oxygen reaction to effectively remove nitrogen in the molten steel, wherein a flow rate of the central tube is 100-1000 Nm.sup.3/h, and a volume flow rate of CO.sub.2 in the mixture gas is adjusted within a range of 0-100%; and injecting propane or natural gas by the circular seam tube of the injection lance, wherein a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h; step 7: in the stage of the smelting endpoint preventing the molten steel from rephosphorization, and further performing the denitrogenation to purify the molten steel, wherein this step comprises the following steps: 1) through the first transmission pipeline for the high efficiency dephosphorization, performing the carrier gas B-dephosphorization powder flow mode on the central tube of the injection lance, to prevent the molten steel from rephosphorization, wherein a velocity of the powder injection is 5-20 kg/min, and a flow rate of the carrier gas B is 100-500 Nm.sup.3/h; and injecting propane or natural gas by the circular seam tube of the injection lance, wherein a flow rate of the propane or the natural gas is 50-200 Nm.sup.3/h, and a time of injecting the propane or the natural gas is 1-5 min; and 2) when the smelting endpoint and a tapping process of the electric arc furnace are approaching, through the first transmission pipeline for the high efficiency dephosphorization, injecting Ar through the central tube of the injection lance, to further reduce the nitrogen content of the molten steel, to improve purity of the molten steel, wherein a first flow rate of Ar is 50-600 Nm.sup.3/h; and injecting Ar through the circular seam tube of the injection lance, wherein a second flow rate of Ar is 50-200 Nm.sup.3/h; and step 8: returning to the step 1 and waiting for next feeding in the electric arc furnace.

3. The clean and rapid smelting method in an electric arc furnace with full scrap steel according to claim 2, wherein the mediums injected by the central tube of the injection lance have three modes, wherein the three modes include a pure gas mode, a carrier gas A-recarburization powder flow mode and a carrier gas B-dephosphorization powder flow mode; in the pure gas mode, the pure gas is N.sub.2, Ar, O.sub.2, CO.sub.2 or a gas mixture of O.sub.2 and CO.sub.2, and a volume flow rate of the CO.sub.2 is 0-100%; in the carrier gas A-recarburization powder flow mode, the carrier gas A is air, N.sub.2 or CO.sub.2, the recarburization powder is carbon powder or graphite carburant, and a particle diameter of the recarburization powder is less than 2.0 mm; and in the carrier gas B-dephosphorization powder flow mode, the carrier gas B is O.sub.2 or a gas mixture of O.sub.2 and CO.sub.2, a volume flow rate of CO.sub.2 is 0-100%, the dephosphorization powder is lime powder or limestone powder, and a particle diameter of the dephosphorization powder is less than 2.0 mm.

4. The clean and rapid smelting method in an electric arc furnace with full scrap steel according to claim 2, wherein the full scrap steel is a full scrap steel of 30-300 t.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a connection diagram of the injection system used in the steelmaking process of an electric arc furnace for full scrap steel in the disclosure.

(2) FIG. 2 is a profile diagram for installation of injection lance of an electric arc furnace for full scrap steel in the disclosure (profile A-A, in FIG. 1).

(3) FIG. 3 is a mode chart of injection process of injection lance for clean and rapid smelting in an electric arc furnace for full scrap steel in the disclosure.

(4) In FIG. 1 and FIG. 2: 1. control system, 2. gas supply control valve group, 3. carrier gas A-recarburization powder injection system, 4. carrier gas B-dephosphorization powder injection system, 5. gas flow control system 1, 6. carbonization powder storage tank, 7. powder flow control system, 8. gas flow control system 2, 9. dephosphorization powder storage tank, 10. powder flow control system, 11, transmission pipeline for recarburization, 12. transmission pipeline for dephosphorization, 13. automatic shut-off valve for recarburization path, 14. automatic shut-off valve for dephosphorization, 15. Injection lance, 16. electric arc furnace, 17. furnace door, 18. steel-tapping hole, 19. refractory material in furnace wall, 20. slag layer, 21. molten steel level, 22. molten steel.

DETAILED DESCRIPTION

(5) In order to make the purpose, the technical scheme and the advantages of the disclosure more clear, the following detailed description of the disclosure is carried out in combination with the accompanying drawings and the embodiments. It should be understood that the specific embodiments described here are only used to explain the disclosure and are not used to limit the disclosure.

(6) In contrast, the disclosure covers any alternative, modification, equivalent method, and scheme in the essence and scope of the disclosure defined by the claim. Further, in order to make the public better understand the disclosure, the details of the disclosure are described in detail below and some specific details are described in detail. The present disclosure can be fully understood by those skilled in the art without the description of these details.

(7) Embodiment 1: the scheme is applied to 90 t electric arc furnace steelmaking, with two injection lance distributed at both sides of the electric arc furnace door; wherein the inner diameter of the injection lance is 12 mm, the gap of the circular seam is 1 mm, and stainless steel material is adopted. The outlet of the injection lance is located 800 mm below the molten steel level, and the angle between the outlet of the injection lance and the horizontal plane is 15. Decarburization powder is graphite carburant, dephosphorization powder is lime powder, particle diameter is 50 m, the velocity of powder injection of single lance is 0100 kg/min. The carrier gas A is air, the carrier gas B is oxygen, and the oxygen flow rate of single lance is 50800 Nm.sup.3/h. The gas in circular seam is N.sub.2, Ar or natural gas, and the flow rate of single lance is 10200 Nm.sup.3/h. The injection process of the lance is shown in FIG. 3.

(8) 12) In a time period after outputting steel from the electric arc furnace but prior to adding furnace material, injection is performed through a transmission pipeline for dephosphorization; N.sub.2 is injected through a central tube and a circular seam tube of an injection lance, and a flow rate of the central tube is 150 Nm.sup.3/h, a flow rate of the circular seam tube is 100 Nm.sup.3/h, so as to prevent the injection lance from blocking and burning.

(9) 13) In the feeding process of electric arc furnace, injection is performed continuously through the transmission pipeline for dephosphorization; O.sub.2 is injected by the central tube of the injection lance, and the flow rate is 100 Nm.sup.3/h; natural gas is injected by the circular seam tube, and the flow rate is 60 Nm.sup.3/h, which ensures a normal operation of the injection lance in the feeding process.

(10) 14) In 07 min after power supply, injection is performed through the transmission pipeline for recarburization; air-graphite carburant is injected by the central tube of the injection lance, the velocity of powder injection is 5 kg/min, and the flow rate of air is 150 Nm.sup.3/h; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 60 Nm.sup.3/h.

(11) 15) In 815 min, injection is performed continuously through the transmission pipeline for recarburization; air-graphite carburant is injected by the central tube of the injection lance, the velocity of powder injection is 8 kg/min, and the flow rate of air is 200 Nm.sup.3/h; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 60 Nm.sup.3/h.

(12) 16) In 1625 min, injection is performed continuously through the transmission pipeline for recarburization; air-graphite carburant is injected by the central tube of the injection lance, the velocity of powder injection is 12 kg/min, and the flow rate of air is 250 Nm.sup.3/h; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 60 Nm.sup.3/h.

(13) 17) Injection is performed through the transmission pipeline for dephosphorization; N.sub.2 is injected by the central tube of the injection lance to clean the pipeline, wherein the flow rate is 400 Nm.sup.3/h, the time is 20 s.

(14) 18) In 2633 min, injection is performed through the transmission pipeline for dephosphorization; O.sub.2-lime powder is injected by the central tube of the injection lance to dephosphorize efficiently, wherein the velocity of powder injection is 20 kg/min, and the flow rate of the carrier gas is 300 Nm.sup.3/h; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 100 Nm.sup.3/h;

(15) 19) In 3445 min, injection is performed continuously through the transmission pipeline for dephosphorization; gas mixture of O.sub.2CO.sub.2 is injected to intensify decarburization in the molten pool, and a large number of CO bubbles produced by the reaction is utilized to effectively removes [N] in the molten steel, wherein the flow rate of the central tube is 300 Nm.sup.3/h, the ratio of CO.sub.2 in mixture gas is 30%; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 100 Nm.sup.3/h;

(16) 20) In 4648 min, injection is performed continuously through the transmission pipeline for dephosphorization; oxygen-lime powder is injected by the central tube of the injection lance to dephosphorize efficiently, wherein the velocity of powder injection is 5 kg/min, and the flow rate of the carrier gas is 200 Nm.sup.3/h; natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 100 Nm.sup.3/h, and the time is 3 min;

(17) 21) In 4955 min, injection is performed continuously through the transmission pipeline for dephosphorization; Ar is injected through the central tube of the injection lance, to further reduce the nitrogen content of the molten steel, and improve the purity of molten steel, wherein the flow rate is 300 Nm.sup.3/h; Ar is injected through the circular seam tube of the injection lance, and the flow rate is 100 Nm.sup.3/h.

(18) 22) At the end of electric arc furnace tapping, return to step 1 and wait for a next feeding in the furnace.

(19) With the method described in the present disclosure, the content of phosphorus in the molten steel smelted in the electric arc furnace is less than 0.003% (mass percent), the nitrogen content is controlled below 0.005% (mass percent), the smelting cycle is shortened by 5 min and the electric energy consumption is reduced by 5 kWh/t. The cleanliness of molten steel is improved, the quality of the product is improved and the smelting speed is accelerated.

(20) Embodiment 2: the scheme is applied to 150 t electric arc furnace steelmaking, with four injection lance distributed evenly at both sides of the electric arc furnace door; wherein the inner diameter of the injection lance is 10 mm, the gap of the circular seam is 1 mm, and stainless steel is adopted as material. The outlet of the injection lance is located 900 mm below the molten steel level, and the angle between the outlet of the injection lance and the horizontal plane is 10. Decarburization powder is carbon powder, dephosphorization powder is lime powder, particle diameter is 300 m, the velocity of powder injection of single lance is 050 kg/min. The carrier gas A is N.sub.2, the carrier gas B is gas mixture of O.sub.2CO.sub.2, and the oxygen flow rate of single lance is 50600 Nm.sup.3/h. The gas in circular seam is N.sub.2, Ar or propane, and the flow rate of single lance is 10200 Nm.sup.3/h.

(21) 12) In a time period after outputting steel from the electric arc furnace but prior to adding furnace material, injection is performed through a transmission pipeline for dephosphorization; N.sub.2 is injected through a central tube and a circular seam tube of an injection lance, and a flow rate of the central tube is 100 Nm.sup.3/h, a flow rate of the circular seam tube is 50 Nm.sup.3/h, so as to prevent the injection lance from blocking and burning.

(22) 13) In a feeding process of electric arc furnace, injection is performed continuously through the transmission pipeline for dephosphorization; O.sub.2 is injected by the central tube of the injection lance, and the flow rate is 100 Nm.sup.3/h; propane is injected by the circular seam tube, and the flow rate is 50 Nm.sup.3/h, which ensures a normal operation of the injection lance in the feeding process.

(23) 14) In 010 min after power supply, injection is performed through the transmission pipeline for recarburization; N.sub.2-carbon powder is injected by the central tube of the injection lance, the velocity of powder injection is 5 kg/min, and the flow rate of N.sub.2 is 100 Nm.sup.3/h; propane is injected by the circular seam tube of the injection lance, and the flow rate is 50 Nm.sup.3/h.

(24) 15) In 1115 min, injection is performed continuously through the transmission pipeline for recarburization; N.sub.2-carbon powder is injected by the central tube of the injection lance, the velocity of powder injection is 8 kg/min, and the flow rate of N.sub.2 is 150 Nm.sup.3/h; propane is injected by the circular seam tube of the injection lance, and the flow rate is 50 Nm.sup.3/h.

(25) 16) In 1625 min, injection is performed continuously through the transmission pipeline for recarburization; N.sub.2-carbon powder is injected by the central tube of the injection lance, the velocity of powder injection is 12 kg/min, and the flow rate of air is 200 Nm.sup.3/h; propane is injected by the circular seam tube of the injection lance, and the flow rate is 50 Nm.sup.3/h.

(26) 17) Injection is performed through the transmission pipeline for dephosphorization; N.sub.2 is injected by the central tube of the injection lance to clean the pipeline, wherein the flow rate is 400 Nm.sup.3/h, the time is 30 s.

(27) 18) In 2635 min, injection is performed through the transmission pipeline for dephosphorization; O.sub.2CO.sub.2-lime powder is injected by the central tube of the injection lance to dephosphorize efficiently, wherein the velocity of powder injection is 15 kg/min, the flow rate of the carrier gas is 300 Nm.sup.3/h, and the ratio of CO.sub.2 is 20%; propane is injected by the circular seam tube of the injection lance, and the flow rate is 80 Nm.sup.3/h.

(28) 19) In 3645 min, injection is performed continuously through the transmission pipeline for dephosphorization; the gas mixture of O.sub.2CO.sub.2 is injected to intensify decarburization in the molten pool, and a large number of CO bubbles produced by the reaction is utilized to effectively removes [N] in the molten steel, wherein the flow rate of the central tube is 300 Nm.sup.3/h, and the ratio of CO.sub.2 in mixture gas is 40%; propane is injected by the circular seam tube of the injection lance, and the flow rate is 80 Nm.sup.3/h.

(29) 20) In 4647 min, injection is performed continuously through the transmission pipeline for dephosphorization; O.sub.2CO.sub.2-lime powder is injected by the central tube of the injection lance to dephosphorize efficiently, wherein the velocity of powder injection is 5 kg/min, the flow rate of the carrier gas is 200 Nm.sup.3/h, and the ratio of CO.sub.2 in mixture gas is 20%; propane is injected by the circular seam tube of the injection lance, and the flow rate is 80 Nm.sup.3/h, and the time is 2 min.

(30) 21) In 4856 min, injection is performed continuously through the transmission pipeline for dephosphorization; Ar is injected through the central tube of the injection lance, to further reduce the nitrogen content of the molten steel, and improve the purity of molten steel, wherein the flow rate is 200 Nm.sup.3/h; Ar is injected through the circular seam tube of the injection lance, and the flow rate is 80 Nm.sup.3/h.

(31) 22) At the end of electric arc furnace tapping, return to step 1 and wait for a next feeding in the furnace.

(32) After using the method described in the present disclosure, the content of phosphorus in the molten steel smelted in the electric arc furnace is less than 0.004% (mass percent), the nitrogen content is controlled below 0.005% (mass percent), the smelting cycle is shortened by 4 min and the electric energy consumption is reduced by 10 kWh/t. The cleanliness of molten steel is improved, the quality of the product is improved and the smelting speed is accelerated.