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 30300 t electric arc furnace with full scrap steel. In the smelting process of the electric arc furnace with full scrap steel, different kinds of medium is 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; 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, an online dynamic switching for different kinds of medium of pure gas, carrier gas A-recarburization powder and carrier gas B-dephosphorization powder in injection mode is utilized, to finish the process of blowing in turn below molten steel level of molten pool in different stages of smelting for the different kinds of media: in a stage of recarburizing and fluxing, the carrier gas A-recarburization powder is injected into the molten pool to improve the carbon content of the molten pool, and to improve flow velocity of the molten steel that has formed the molten pool; carburization is utilized to accelerate the melting of scrap steel, such that the carbon content of the molten steel in the molten pool reaches to 0.40%2.0% after completing melting process of scrap steel; in a stage of high efficiency dephosphorization, the carrier gas B-dephosphorization powder is injected into the molten pool to improve kinetic conditions for dephosphorization, and high efficiency dephosphorization in the furnace is achieved by systematic dephosphorization of slag particle in molten state, to make the content of phosphorus in molten steel equal to or less than 0.010%; in a stage of deep denitrogenation, O.sub.2 or gas mixture of O.sub.2CO.sub.2 is injected into the molten pool to intensify decarburization in the molten pool, meanwhile a large number of CO bubbles produced by the metallurgical reaction in molten pool effectively removes [N] in the molten steel; in a stage of smelting endpoint, the carrier gas B-dephosphorization powder is injected to prevent the molten steel from rephosphorization, then Ar is injected into the molten pool largely, to homogenize the composition and temperature of the molten pool, to finally achieve that 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 40*10.sup.6, and the nitrogen content of the molten steel is, equal to or less than 50*10.sup.6.

2. The clean and fast smelting method in the electric arc furnace with full scrap steel according to claim 1, comprising the following steps: step 1: in a time period after outputting steel from the electric arc furnace but prior to adding furnace material, a recarburization path automatic shut-off valve is closed by a control system, a dephosphorization path automatic shut-off valve is opened by the control system, and 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 50500 Nm.sup.3/h, a flow rate of the circular seam tube is 50200 Nm.sup.3/h, so as to prevent the injection lance from blocking and burning; step 2: a feeding stage of the 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 50300 Nm.sup.3/h; propane or natural gas is injected by the circular seam tube; and the flow rate is 50200 Nm.sup.3/h, which ensures a normal operation of the injection lance in the feeding process; step 3: a stage of recarburizing and fluxing: carbon powder is injected into the molten pool formed by melting of the scrap steel, to improve the carbon content of the molten pool, and carburization is utilized to accelerate the melting of scrap steel; following steps are performed: 1) an early stage of melting: the recarburization path automatic shut-off valve is opened by the control system, and the dephosphorization path automatic shut-off valve is closed by the control system; injection is performed through the transmission pipeline for recarburization; the mode of the carrier gas A-recarburization powder is performed in the central tube of the injection lance, to accelerate the carburizing and melting of the scrap steel; a shallow molten pool is formed in this stage, so the velocity of powder injection must be controlled to improve the carburizing efficiency, wherein the velocity of powder injection is 15 kg/min, the flow rate of the carrier gas A is 100300 Nm.sup.3/h; propane or natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; 2) a middle stage of melting: injection is performed continuously through the transmission pipeline for recarburization; the mode of A-recarburization powder is performed by the central tube of the injection lance; the molten pool has a certain depth in this stage, and the velocity of powder injection is controlled to improve carburizing efficiency, wherein the velocity of powder injection is 510 kg/min, the flow rate of the carrier gas A is 200500 Nm.sup.3/h; propane or natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; 3) a later stage of melting: injection is performed continuously through the transmission pipeline for recarburization; the mode of A-recarburization powder is performed in the central tube of the injection lance; the molten pool is deep in this stage, and carburizing and stirring are intensified in the molten pool, wherein the velocity of powder injection is 1020 kg/min, and the flow rate of the carrier gas A is 200600 Nm.sup.3/h; propane or natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; step 4: a stage of pipeline cleaning: pipeline is cleaned by using large flow N.sub.2 or CO.sub.2; the following steps are performed: the recarburization path automatic shut-off valve is opened by the control system, and the dephosphorization path automatic shut-off valve is closed by the control system; injection is performed through the transmission pipeline for dephosphorization; injection of N.sub.2 or CO.sub.2 by the central tube of the injection lance is controlled to clean the pipeline, wherein the flow rate is 400600 Nm.sup.3/h, the time is 2030 s; step 5: a stage of high efficiency dephosphorization: high speed dephosphorized particle-gas flow is injected directly to the molten pool below the molten steel level, to effectively remove phosphorus in the molten steel; following steps are performed: injection is performed continuously through the transmission pipeline for dephosphorization; the mode of the carrier gas B-dephosphorization is performed in the central tube of the injection lance, and the carrier gas B and dephosphorization powder are directly input into the molten steel and the stirring ability of the molten pool is intensified, to dephosphorize efficiently, wherein the velocity of powder injection is 1050 kg/min, and the flow rate of the carrier gas is 1001000 Nm.sup.3/h; propane or natural gas is injected in the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; step 6: a stage of deep denitrogenation: denitrogenation is performed by intense carbon oxygen reaction inside the molten pool; following steps are performed: 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 1001000 Nm.sup.3/h, the volume flow rate of CO.sub.2 in mixture gas can be adjusted in a range of 0100%; propane or natural gas is injected by the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; step 7: a stage of smelting endpoint: the molten steel is prevented from rephosphorization, and denitrogenation is further performed to purify the molten steel; following steps are performed: 1) injection is performed continuously through the transmission pipeline for dephosphorization, and the mode of the carrier gas B-dephosphorization is performed in the central tube of the injection lance, to prevent the molten steel from rephosphorization, wherein the velocity of powder injection is 520 kg/min, and the flow rate of the carrier gas is 100500 Nm.sup.3/h; propane or natural gas is injected by the circular seam tube of the injection lance, the flow rate is 50200 Nm.sup.3/h, and the time is 15 min; 2) approaching the smelting endpoint and the tapping process of the electric arc furnace, 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, to improve the purity of molten steel, wherein the flow rate is 50600 Nm.sup.3/h; Ar is injected through the circular seam tube of the injection lance, and the flow rate is 50200 Nm.sup.3/h; step 8: return to step 1 and wait for a next feeding in the furnace.

3. The clean and fast smelting method in the electric arc furnace with full scrap steel according to claim 2, wherein, the medium injected by the central tube of the injection lance has three modes of pure gas, carrier gas A-recarburization powder flow and carrier gas B-dephosphorization powder flow; for the pure gas mode, the pure gas is N.sub.2, Ar, O.sub.2, CO.sub.2 or O.sub.2CO.sub.2 gas mixture, and the volume flow rate of CO.sub.2 is 0100%; for the carrier gas A-recarburization powder mode, the carrier gas A is air, N.sub.2 or CO.sub.2, the recarburization powder is carbon powder, graphite carburant, coke powder or pulverized coal, and particle diameter of the recarburization powder is less than 2.0 mm; for the carrier gas B-dephosphorization powder mode, the carrier gas B is O.sub.2 or O.sub.2CO.sub.2 gas mixture and the volume flow rate of CO.sub.2 is 0100%, the dephosphorization powder is lime powder or limestone powder and the particle diameter of dephosphorization powder is less than 2.0 mm.

4. The clean and fast smelting method in the electric arc furnace with full scrap steel according to claim 2, wherein, the method is suitable for smelting full scrap steel of 30300 t using electric arc furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] 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).

[0024] 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.

[0025] 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, IS. 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

[0026] 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.

[0027] 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.

Embodiment 1

[0028] 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.

[0029] 1) 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.

[0030] 2) 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.

[0031] 3) 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.

[0032] 4) 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.

[0033] 5) 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.

[0034] 6) 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.

[0035] 7) 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;

[0036] 8) 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;

[0037] 9) 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;

[0038] 10) 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.

[0039] 11) At the end of electric arc furnace tapping, return to step 1 and wait for a next feeding in the furnace.

[0040] 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.

Embodiment 2

[0041] 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.

[0042] 1) 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.

[0043] 2) 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.

[0044] 3) 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.

[0045] 4) 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.

[0046] 5) 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.

[0047] 6) 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.

[0048] 7) 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.

[0049] 8) 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.

[0050] 9) 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.

[0051] 10) 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.

[0052] 11) At the end of electric arc furnace tapping, return to step 1 and wait for a next feeding in the furnace.

[0053] 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.