A method and device for deoxidation in a steelmaking final melt furnace

Abstract

The present invention discloses a method and device for deoxidation in a melt furnace at the end of steelmaking, and belongs to the field of metallurgical technology. Before stopping oxygen blowing at the end of oxygen steelmaking blowing in a top-blown converter or electric arc furnace with oxygen blowing above the molten pool, the present invention adds a powder spraying function to the existing steelmaking furnace bottom blowing inert gas stirring system, and transforms it into a stirring / powder spraying system device as shown in Figure 1 or 2. The stirring gas channel is blown from the bottom of the steelmaking furnace, and the stirring gas is used as a carrier gas to spray carbon powder into the molten pool. 1) The oxygen content in the melt is reduced by the combined action of the carbon-oxygen reaction and its products and the bottom blowing stirring gas, especially the iron oxide content in the slag can be effectively reduced, and 2) the additional smelting cycle time increase and corresponding additional heat dissipation loss caused by static stirring with inert gas are reduced.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy, and more specifically to a method and device for deoxidizing slag and molten steel in a furnace by spraying carbon powder into a molten pool through a furnace bottom at the end stage of a steelmaking blowing process. Background Art

[0002] Modern oxygen steelmaking is a non-equilibrium oxidation process that uses pure oxygen to oxidize carbon and silicon, manganese, phosphorus and other elements in iron melt and oxidizes the iron melt from the initial composition to the final target composition. It is mainly achieved by continuously blowing a large amount of oxygen into the molten pool to first oxidize the iron element to form iron oxides, and then indirectly oxidize other elements in the molten pool that need to be oxidized by the iron oxides. According to thermodynamic equilibrium, most of the various elements required for oxidation and removal except carbon in the early stage of steelmaking blowing have entered the slag. In the middle and late stages of blowing, it is mainly a carbon oxidation process in which carbon monoxide bubbles are generated and discharged by carbon-oxygen reactions. Moreover, the required slag oxygen content (the proportion of iron oxides in the slag) continues to increase with the decrease of carbon content. When the carbon content in the molten steel in the molten pool is lower than 0.3%, the decarburization rate decreases significantly. Especially for top-blown converters or electric arc furnaces with oxygen blowing above the molten pool, due to the oxygen supply method that makes the slag rich in iron oxides float on the surface of the molten steel, the difficulty of mixing between steel slags and the static pressure suppression of the molten liquid column and other reaction conditions, the oxygen content in the melt to reach the target carbon content in a short time must be much higher than the equilibrium value. Therefore, when the final carbon element composition target is reached and oxygen supply to the melt is stopped, the oxygen content in the melt (especially the oxygen content in the molten steel for low-carbon steel grades, and especially the oxygen content of iron oxides in the slag) will greatly exceed the equilibrium value with the target carbon content, causing the quality of the steel to deteriorate, the consumption of deoxidation alloys to increase, and the iron loss in the smelting process to increase (for the smelting process of terminal slag dumping). Moreover, with the continuous pursuit of high efficiency and low cost in steelmaking, the oxygen supply intensity of blowing and the scrap steel ratio are increasing, resulting in lower and lower carbon content at the smelting end point and higher and higher oxygen content in the melt.

[0003] To improve this situation, the industry has begun to try to deoxidize the melt in various ways. For example, the bottom-blowing inert gas stirring system, which was originally designed to improve the metallurgical reaction kinetics of the molten pool during the blowing process, continues to maintain static stirring for a certain period of time (usually 30 seconds to 75 seconds) by blowing inert gas from the bottom of the furnace after the top-blowing oxygen stops. The oxygen content in the melt is reduced to a certain extent through reaction and diffusion before steel tapping begins. However, since the inert gas itself is not reducing, the gas flow rate that may be blown into the bottom-blown permeable bricks of a typical double-blowing steelmaking furnace is relatively small. The deoxidation rate is very low only through adsorption and desorption reaction and diffusion at the liquid-gas interface. Even after a certain period of static stirring, the actual effect is not ideal, and static stirring will also increase the additional smelting cycle time and corresponding additional heat dissipation losses. There are also methods such as adding reducing agent into the furnace through the end point or spraying carbon powder from the top of the melt (carbon oxygen gun on the top, side wall and door of the arc furnace), but they cannot be implemented before the top oxygen blowing in the smelting process is stopped. Also, due to the poor kinetic conditions during implementation, the effect is not good and the smelting cycle time will be increased. Summary of the invention

[0004] Problem to be solved

[0005] The purpose of the present invention is to provide a relatively quicker and more effective solution to the high oxygen content in the melt at the end of steelmaking in the prior art, or the additional increase in smelting cycle time and corresponding additional heat dissipation losses caused by blowing inert gas for static stirring to reduce the oxygen content of the melt.

[0006] Technical Solution

[0007] In order to solve the above-mentioned problems, the technical solution proposed in the present invention is: at the end stage of oxygen steelmaking blowing, carbon powder is sprayed into the molten pool through the bottom of the steelmaking furnace, and the excess oxygen content in the slag and molten steel in the furnace is reduced by the combined action of the carbon-oxygen reaction in the molten pool and its products and the carrier gas, etc., especially since all existing technologies cannot solve the problem of removing oxygen from the slag well.

[0008] The technical solution of the present invention is based on the specific technical principle of deoxidizing the melt by the injected carbon powder itself, which has the following six aspects:

[0009] 1) Carbon and oxygen directly react to reduce the oxygen content of the molten steel

[0010] After the carbon powder is sprayed into the molten pool from the bottom of the furnace, it floats up with the bubbles. Part of the carbon powder first contacts the molten steel and dissolves. It then directly reacts with the oxygen in the molten steel to deoxidize. [C] + [O] = CO (g) .

[0011] 2) Carbon and oxygen directly react to reduce the oxygen content of slag in the melt

[0012] The remaining carbon that is not dissolved and consumed in the molten steel floats up with the bubbles into the slag and directly reacts with the iron oxides in the slag to deoxidize. (s) +(FeO)=[Fe]+CO (g) , the reduced iron enters the molten steel with slag. Under the same carbon injection intensity, the particle size of the carbon powder has a great correlation with the effect of its direct deoxidation when entering the slag. If the particle size is too small, the volume of carbon will increase after the complete reaction in the bubble, the floating speed will be accelerated, the specific surface area will be small, which is not conducive to further interface reaction and interface diffusion. In addition, when the bubble floats and breaks between the molten steel and the furnace gas, the loss of the remaining carbon escaping from the melt with the gas will increase.

[0013] 3) The carbon monoxide generated by the direct carbon-oxygen reaction further reacts to generate carbon dioxide to deoxidize the melt. The carbon monoxide bubbles in the high-oxygen melt will further react with the oxygen adsorbed on the bubble surface to generate carbon dioxide. (g) +O=CO 2(g) , until it reaches the equilibrium value of carbon monoxide and carbon dioxide in the bubbles.

[0014] 4) Indirect reaction of carbon reduction of carbon dioxide to deoxidize the melt

[0015] The injection of carbon powder generates more bubbles, so that the carbon that is not dissolved in the molten steel and floats up with the carrier gas and the bubbles generated by the reaction will reduce the carbon dioxide generated by the above reaction inside the bubbles. (s) +CO 2(g) =2CO (g) ), the indirect reaction promotes more carbon monoxide to react with oxygen adsorbed on the bubble surface to generate carbon dioxide in balance with it, CO (g) +O=CO 2(g) , to achieve further deoxidation of the melt by injecting carbon.

[0016] 5) Oxygen balance between bubbles and melt in the molten pool

[0017] The injection of carbon powder generates bubbles of larger volume, and under the same stirring gas (carrier gas) supply intensity, a larger total specific surface area for reaction and diffusion between the bubbles and the melt can be obtained, which promotes the deoxidation of the melt by the bubbles.

[0018] 6) Oxygen balance between molten steel and slag in the molten pool

[0019] The injection of carbon powder generates more gas with stirring function. The increased stirring energy improves the kinetic conditions of reaction and diffusion. Under the joint stirring action of the carrier gas and the reaction generated gas, the mixing of molten steel and slag in the molten pool is more complete, which promotes the reaction and diffusion of bubbles with oxygen in the melt, further promotes the oxygen balance between molten steel and slag in the melt, and reduces the iron oxide content in the slag through a good balance.

[0020] The technical solution adopted by the present invention is realized by a device for deoxidation in a steelmaking end point melt furnace of the present invention. Carbon powder is metered and fluidized, and then pneumatically conveyed in a dilute phase and sprayed into the molten pool from the furnace bottom using a carrier gas. Structurally, the device of the present invention includes:

[0021] (1) A carbon powder storage bin and a conveying pipeline for storing and conveying carbon powder to the spray bin. Preferably, in order to ensure the conveyability of the carbon powder, a steam coil is used in the bin for external heat drying.

[0022] (2) A carbon powder spraying chamber, which is used for metering and pressure balancing of carbon powder. Preferably, the metering of carbon powder is carried out by a volumetric mechanical metering device under pressure balance with the carrier gas.

[0023] (3) Spraying and conveying pipeline, used to convey fluidized carbon powder and its spraying carrier gas, etc.;

[0024] (4) Mixer, used for fluidization of carbon powder, mixing with carrier gas and dilute phase pneumatic conveying to the steelmaking furnace;

[0025] (5) A gas-permeable nozzle buried in the furnace bottom is used to blow gas into the molten pool to stir the molten pool during the blowing process and to spray carbon powder into the molten pool at the end of the blowing process to deoxidize the melt in the furnace.

[0026] Beneficial Effects

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) By injecting carbon powder and its products, further reacting with the reduction of molten steel and slag, the oxygen content in the melt in the furnace, especially the iron oxide content in the slag, is reduced, and the smelting blow loss under the end-point one-time slag pouring process conditions is reduced;

[0029] 2) With the help of the high rate of direct and indirect reduction reaction of injected carbon powder and the increase of bubble specific surface area, the static stirring time at the end of blowing can be significantly reduced, and the smelting cycle time can be reduced accordingly;

[0030] 3) The gaseous products of the oxygen reduction reaction between carbon powder and melt can achieve greater stirring intensity, which is beneficial to the metallurgical reaction balance of the molten pool at the end of blowing and the homogenization of the temperature field and concentration field;

[0031] 4) Due to the generation of carbon-oxygen reaction product gas, the bottom blowing gas flow rate can be appropriately reduced while obtaining greater stirring intensity, which is beneficial to slow down the erosion of the end of the air brick and extend the life of the air brick, and helps to achieve stable bottom blowing in the entire smelting process of the entire furnace campaign;

[0032] 5) Due to the reduction of iron oxide content in the slag, the slag composition changes, the proportion of calcium ferrite and RO phase decreases, the relative calcium oxide content increases, and the distribution ratio of phosphorus between slag and steel increases. The dephosphorization rate of the smelting process can be improved under the conditions of reducing the slag basicity and reducing the slag amount;

[0033] 6) Due to the reduction of iron oxide content and the increase of relative calcium oxide content in slag, the distribution ratio of sulfur between slag and steel is also increased, and the desulfurization rate of the smelting process is improved (or the resulfurization rate is reduced);

[0034] 7) Since the static stirring after the end point of blowing is carried out at the highest temperature of the molten pool, reducing the static stirring time can reduce a large amount of heat loss accordingly;

[0035] 8) Due to the reduction of iron oxide content, the slag is thickened, and the slag above the tapping port in the late stage of converter tapping is not easily carried into the ladle by the vortex, the phosphorus regeneration of the molten steel in the ladle is reduced, and the consumption of subsequent molten steel deoxidation alloy and refined slag-making materials and the energy consumption of corresponding material heating are reduced;

[0036] 9) The reduction of iron oxide content in the slag increases the melting point of the slag, which is beneficial to the improvement of the subsequent anti-destruction and anti-corrosion capabilities of the converter slag splashing protection layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a device for deoxidation in a steelmaking terminal melt furnace of the present invention, wherein: 1-carbon powder storage bin, 2-carbon powder spraying bin, 3-carrier gas control valve and pneumatic conveying pipeline, 4-mixer, 5-furnace bottom powder spraying air-permeable bricks.

[0038] Figure 2 In order to implement the method for deoxidizing the melt in the steelmaking terminal furnace of the present invention under the conditions of the typical prior art, a schematic diagram of the device after the function expansion and transformation of the bottom blowing system of the steelmaking furnace is shown, in which: 01-a typical prior art steelmaking furnace bottom blowing system gas supply source and its control valve group, 02-a typical prior art bottom blowing system gas supply pipeline retained, 03-a conventional bottom blowing system gas supply pipeline removed after plugging and disconnection, 04-a bottom air permeable brick of the bottom blowing system;

[0039] 11-Added carbon powder storage bin, 12-Added carbon powder spraying bin, 13-Added conveying pipeline, 14-Added mixer. DETAILED DESCRIPTION

[0040] The invention discloses a method for deoxidation in a melt furnace at the end of steelmaking, which is characterized in that: at the end of oxygen steelmaking blowing, carbon powder is sprayed into the molten pool through the bottom of the steelmaking furnace, and the oxygen content in the slag and molten steel in the furnace is reduced by the combined action of the carbon-oxygen reaction in the molten pool and its products and the carrier gas.

[0041] Furthermore, the smelting end stage is the stage from when the carbon content of the molten steel in the molten pool is lower than 0.20% to when steel tapping begins; further, the particle size of the carbon powder is no greater than 0.3 mm;

[0042] Furthermore, the carbon powder is sprayed into the molten pool by means of a stirring gas channel of a bottom blowing system of a steelmaking furnace and the stirring gas is used as a carrier gas at the same time.

[0043] The method of the present invention is implemented by using a device for deoxidation in a steelmaking end point melt furnace (such as Figure 1 As shown in the figure, it includes: 1) a carbon powder storage bin and a conveying pipeline for storing and conveying carbon powder to a spray bin; 2) a carbon powder spray bin for metering and pressure balancing carbon powder; 3) a carrier gas control valve and a pneumatic conveying pipeline for controlling the carrier gas spray and fluidized carbon powder conveying; 4) a mixer for fluidizing carbon powder, mixing it with a carrier gas, and pneumatically conveying it to a steelmaking furnace in a dilute phase; 5) a furnace bottom powder spraying air brick for spraying fluidized carbon powder into the bottom of the steelmaking furnace molten pool.

[0044] Furthermore, the carbon powder storage bin is provided with a steam external heat drying system.

[0045] Furthermore, the carbon powder is measured using a mechanical volumetric device.

[0046] The following is a further description of the application of the present invention in conjunction with embodiments of the present invention.

[0047] Example 1

[0048] Basic conditions: 300-ton top and bottom double-blown converter, double-annular seam bottom blowing air-permeable bricks; production of ultra-low carbon steel, final target carbon content of 0.04%; nitrogen blowing in the early stage of bottom blowing and argon blowing in the middle and late stages, final stirring intensity of 0.12Nm3 / t*min; final static stirring for 60 seconds after stopping oxygen blowing; switch the argon flow rate to purge mode when starting to pour the furnace and tap steel; final carbon-oxygen product of 0.0017, final slag total iron of 18.3%.

[0049] Implementation plan:

[0050] 1) Modify the existing gas stirring bottom blowing system and add a carbon powder dilute phase fluidized blowing device (see Figure 2 );

[0051] 2) The existing bottom blowing gas supply process is fully maintained before the end of the blowing process;

[0052] 3) Start blowing carbon powder 20 seconds before stopping oxygen blowing until steel starts to be tapped. The gas supply intensity during powder spraying is adjusted to 0.10Nm3 / t*min, and the powder-gas ratio is 0.8-1.0kg / m 3 ;

[0053] 4) After stopping oxygen blowing, static stirring for 35 seconds starts to pour the furnace and tap steel (reducing the static stirring time by 25 seconds, that is, shortening the smelting cycle time by 25 seconds), and at the same time stops carbon powder injection (the actual carbon powder injection time is about 55 seconds), and after 10 seconds, the stirring argon flow rate is switched to the purge mode;

[0054] 5) The carbon-oxygen accumulation in the steel furnace is 0.0014, and the final slag has a total iron content of 16.1%.

[0055] Example 2

[0056] Basic conditions: 100-ton top and bottom combined blowing converter, using clustered tube breathable bricks; using the end-point carbon retention process, the end-point target carbon content is 0.15%; nitrogen is blown throughout the bottom blowing process, and the end-point stirring intensity is 0.06Nm3 / t*min; no end-point static stirring, the furnace is turned over and steel is tapped when the oxygen lance is raised from the furnace mouth, and the stirring nitrogen flow is switched to the purge mode at the same time; the carbon oxygen accumulation of the steel is 0.0024, and the final slag has a total iron content of 17.6%.

[0057] Implementation plan:

[0058] 1) Modify the existing gas stirring bottom blowing system and add a carbon powder dilute phase fluidized blowing device (see Figure 2 ), change the cluster tube type air brick to annular seam type air brick;

[0059] 2) The existing bottom blowing gas supply process is fully maintained before the end of the blowing process;

[0060] 3) Start blowing carbon powder 10 seconds before stopping oxygen blowing, with a powder-to-air ratio of 1.5-3.0kg / m 3 ;

[0061] 4) When the oxygen lance is lifted out of the furnace mouth, the furnace starts to discharge steel, and the carbon powder injection is stopped at the same time (the actual carbon powder injection time is about 25 seconds). After 10 seconds, the stirring nitrogen flow is switched to the purge mode.

[0062] 5) The carbon oxygen content of the steel is 0.0017, and the final slag has a total iron content of 15.2%.

[0063] Example 3

[0064] Basic conditions: 110-ton electric arc furnace, molten iron ratio 70% furnace charge structure; adopting the end-point carbon retention process, the end-point target carbon content is 0.10%; equipped with carbon powder oxygen guns for side wall and furnace door spraying; no bottom blowing and stirring system; smelting final slag full iron content 19.7%; EBT steel-making method, 40 tons of steel left in the furnace after steel-making.

[0065] Implementation plan:

[0066] 1) Add a carbon powder dilute phase fluidized injection device system equipped with three injection air bricks (see Figure 1 );

[0067] 2) In the early stage of the arc furnace smelting process, appropriate bottom blowing gas stirring is carried out to promote the melting of scrap steel;

[0068] 3) When the electrode is lifted at the end of smelting, the stirring gas volume at the bottom of the furnace is increased and carbon powder is sprayed immediately. The powder-gas ratio is 1.0-2.0kg / m 3 ;

[0069] 4) When 60% of the steel is discharged, the carbon powder spraying is stopped (the actual carbon powder spraying time is about 125 seconds), and the carrier gas flow is switched to the purge mode after 10 seconds.

[0070] 5) Final slag total iron content 16.1%.

[0071] Example 4

[0072] Basic conditions: 120-ton top and bottom combined blowing converter, annular seam breathable bricks; adopting the end-point carbon retention process, the end-point target carbon content is 0.12%; nitrogen is blown throughout the bottom blowing process, and the end-point stirring intensity is 0.10Nm3 / t*min; no end-point static stirring, the furnace is turned over and steel is tapped when the oxygen lance is raised from the furnace mouth, and the stirring nitrogen flow is switched to the purge mode at the same time; the carbon oxygen accumulation of the steel is 0.0023, and the final slag has a total iron content of 17.6%.

[0073] Implementation plan:

[0074] 1) Modify the existing gas stirring bottom blowing system and add a carbon powder dilute phase fluidized blowing device (see Figure 2 );

[0075] 2) The existing bottom blowing gas supply process is fully maintained before the end of the blowing process;

[0076] 3) Start blowing carbon powder 10 seconds before stopping oxygen blowing, with a powder-to-air ratio of 1.5-3.0kg / m 3 ;

[0077] 4) When the oxygen lance is lifted out of the furnace mouth, the steel begins to be discharged from the furnace, and the carbon powder injection is stopped at the same time (the actual carbon powder injection time is about 20 seconds). After 10 seconds, the stirring nitrogen flow is switched to the purge mode.

[0078] 5) The carbon-oxygen content of the steel is 0.0017, and the final slag has a total iron content of 15.8%.

[0079] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and so on quoted in this specification are only for the convenience of description, and are not used to limit the scope of implementation. The change or adjustment of their relative relationship should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

Claims

1. A method for deoxidation in a melt furnace at the end of steelmaking, characterized in that: In the final stage of oxygen steelmaking in a top-blown converter or electric arc furnace with oxygen blowing above the molten pool, before oxygen blowing is stopped, carbon powder is sprayed into the molten pool through the bottom of the steelmaking furnace to 1) reduce the excess oxygen content in the slag and molten steel in the furnace by means of the combined action of the carbon-oxygen reaction in the molten pool and its products and the carrier gas, and 2) reduce the additional smelting cycle time and corresponding additional heat dissipation loss caused by static stirring. The final stage of blowing is the stage from when the carbon content of the molten steel in the molten pool is lower than 0.20% to the beginning of steel tapping. The carbon powder is sprayed into the molten pool through the stirring gas channel of the bottom blowing system of the steelmaking furnace by means of a stirring / powder spraying system device with an expanded powder spraying function added to the bottom blowing stirring system of the steelmaking furnace and the stirring gas is used as a carrier gas. The particle size of the carbon powder is not greater than 0.3 mm. The reduction of the excess oxygen content in the slag in the furnace in the reduction of the excess oxygen content in the slag and molten steel in the furnace means that: (1) the remaining part of the injected carbon powder that is not dissolved in the molten steel and consumed by the reaction further floats up with the bubbles into the slag and directly reacts with the iron oxides in the slag to deoxidize C (s) +(FeO)=[Fe]+CO (g) (2) The injected carbon powder directly reacts with carbon and oxygen to generate carbon monoxide, which further reacts to generate carbon dioxide for deoxidation. (g) +O=CO 2(g) (3) The injected carbon powder floats along with the carrier gas and the bubbles generated by the reaction, and the carbon that is not dissolved in the molten steel reduces the carbon dioxide C generated by the above reaction. (s) +CO 2(g) =2CO (g) , more oxygen adsorbed on the bubble surface generates carbon dioxide CO (g) +O=CO 2(g) deoxidation, and (4) the injected carbon powder generates more gas with stirring function, the molten steel and slag in the molten pool are mixed more fully, and the iron oxide content in the slag is reduced through good balance; the stirring / powder spraying system device includes: (1) a carbon powder storage bin and a conveying pipeline for storing and conveying carbon powder to the spraying bin, (2) a carbon powder spraying bin for metering and pressure balancing of carbon powder, (3) a carrier gas control valve and a pneumatic conveying pipeline for controlling the spraying of carrier gas and fluidizing the carbon powder conveying, (4) a mixer for fluidizing the carbon powder, mixing it with the carrier gas and pneumatically conveying it to the dilute phase of the steelmaking furnace, and (5) a furnace bottom powder spraying air brick for spraying the fluidized carbon powder into the bottom of the molten pool of the steelmaking furnace.

2. The method for deoxidation in a steelmaking end point melt furnace according to claim 1, characterized in that: The carbon powder storage bin is provided with a steam external heat drying system; the carbon powder is measured by a mechanical volumetric device.

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