Method for improving foaming of LF refining slag based on biomass carbonization

Abstract

The invention relates to the technical field of steel smelting, in particular to a method for improving foaming of LF (ladle furnace) refining slag based on biomass carbonization, which comprises the following steps: (1) controlling ladle bottom blowing argon pressure and argon flow at the later stage of tapping, and controlling ladle bottom blowing argon pressure and argon flow after tapping; (2) adding limestone; (3) adding a biomass raw material; (4) covering the steel ladle, closing the bottom blowing argon of the steel ladle, and hoisting the steel ladle to an LF refining process; (5) opening the bottom blowing argon of the steel ladle, and controlling the argon pressure and the argon flow; and (6) the argon pressure and the argon flow are adjusted. According to the method, biomass charcoal is creatively used for improving foaming of the LF refining slag, biomass raw materials are carbonized through the temperature of the steel ladle slag, and the carbonization cost is saved; before the biomass raw material is added, the small-granularity limestone is added into the steel ladle, and the limestone is continuously decomposed, so that the hydrogen increase of the molten steel is reduced, and the foaming of the slag is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel smelting, and particularly relates to a method for improving the foaming of LF refining slag based on biomass carbonization. Background Art

[0002] The foamed slag in the LF refining process usually generates in the oxidizing slag with a relatively high iron oxide content, and uses a large amount of CO gas provided by the carbon-oxygen reaction in the slag layer as the gas source to make the slag foam. Theoretically analyzed, one of the basic conditions for the generation of foamed slag is that there must be a slag suitable for the generation and storage of bubbles, which is determined by the physical properties of the slag itself, such as the viscosity, surface tension, density, etc. of the slag. Generally, when the gas source conditions are certain, the foaming degree of the slag increases with the increase of the slag viscosity and the decrease of the surface tension. The physical properties of the slag itself are directly affected by factors such as the composition and temperature of the slag. Therefore, by adjusting the slag composition and temperature, the slag can have good bubble storage capacity. Another condition necessary for the generation of foamed slag is the gas source. If the amount of gas generated in or passing through the slag is large, the generation rate is high, and the residence time in the slag is long, then the slag foams violently and can maintain foaming well. The two conditions for the generation of foamed slag, the physical properties of the slag and the gas source, are interdependent. If the bubble storage capacity of the slag is weak, the bubbles in the slag are easily aggregated and escaped, and at this time, it is difficult to make the slag foam even if the gas source conditions are good; conversely, if the slag has good bubble storage capacity, but the amount of gas in the slag is small and the generation rate is slow, an ideal foamed slag cannot be formed either.

[0003] Biomass carbon is a carbon-rich carbon product prepared by subjecting biomass raw materials (such as wood, grass, rice straw, rapeseed straw, corn straw, waste wood, garden pruning materials, etc.) to controlled high-temperature decomposition in an oxygen-deficient environment. Research shows that: the increase of the pyrolysis temperature can increase the porosity and specific surface area of biochar, and both the carbon content and ash content of biochar increase. The rich multi-microporous structure of biochar makes it have a large specific surface area and surface activity. However, there is currently a lack of research on applying biomass carbon to improve the foaming of LF refining slag. Summary of the Invention

[0004] Aiming at the technical problem of unsatisfactory foaming of LF refining slag, the present invention provides a method for improving the foaming of LF refining slag based on biomass carbonization. The present invention creatively proposes to use biomass carbon to improve the foaming of LF refining slag, and ingeniously utilizes the temperature of ladle slag to carbonize biomass raw materials, saving the carbonization cost of biomass; considering the physical property matching, before adding biomass raw materials, small-grained limestone is first added to the ladle, and the small-grained limestone is dried, preheated and continuously decomposed by using the environmental heat in the ladle, reducing the hydrogen increase in molten steel and promoting the foaming of slag; at the same time, the flow rate of bottom-blowing argon in the ladle is controlled to ensure the best conditions for the viscosity of the slag itself and the surface tension of the molten slag, ensuring the best foaming and bubble storage capacity of the slag, improving the slag conditions, and enhancing the function and performance of the slag.

[0005] The technical solution of the present invention is as follows: A method for improving the foaming of LF refining slag based on biomass carbonization, comprising the following steps: (1) During normal tapping and slag blocking operations in the converter, control the bottom-blowing argon pressure in the ladle at 0.4 - 0.5 MPa and the argon flow rate at 30 - 50 L / min in the later stage of tapping. After tapping is completed, control the bottom-blowing argon pressure in the ladle at 0.2 - 0.4 MPa and the argon flow rate at 20 - 30 L / min. (2) Open the gate and vibrating screen of the bin, add limestone, and preheat and start continuous decomposition at the ladle environmental temperature. (3) After 1 minute, the limestone is mixed evenly under the stirring of bottom-blowing argon in the ladle, and biomass raw materials are put in and evenly covered above the slag layer. (4) Cover the ladle, close the bottom-blowing argon in the ladle, and lift the ladle to the LF refining process. During this process, the space above the slag layer in the ladle is in a slightly positive pressure and oxygen-deficient state, and the biomass raw materials continue to undergo oxygen-deficient pyrolysis at the ladle environmental temperature to generate biomass carbon. (5) Open the bottom-blowing argon in the ladle, and control the argon pressure at 0.2 - 0.4 MPa and the argon flow rate at 20 - 30 L / min. (6) After 5 minutes, adjust the argon pressure to 0.4 - 0.6 MPa and the argon flow rate to 50 - 70 L / min, and then perform subsequent processing operations according to the normal LF process.

[0006] Further, the later stage of tapping refers to the stage after half of the tapping time. For example, if the total tapping time of a certain heat is 3 minutes, the later stage of tapping for this heat means the stage after 1.5 minutes of tapping; if the total tapping time of another heat is 2.6 minutes, the corresponding later stage of tapping is the stage after 1.3 minutes of tapping.

[0007] Further, the particle size of the limestone added in step (2) is 3-8 mm. The added limestone is preferably a mixture of limestone with particle sizes of 3 mm, 5 mm, and 8 mm, and the corresponding feeding ratio is 3:2:1. The smaller the particle size of the limestone, the faster the decomposition rate. If the particle size is too large, it will affect the decomposition rate of the limestone. Limestones with different particle sizes control the decomposition rate. They decompose in sequence according to time, with the smaller-sized ones decomposing first and the larger-sized ones decomposing later, thus having continuous CO 2 bubbles discharged, which is beneficial to the formation of foamed slag.

[0008] Further, the limestone added in step (2) is dry limestone.

[0009] Further, the addition amount of limestone in step (2) is 1-2 kg / t of steel, and it is evenly spread on the slag layer on the upper part of the ladle by manual feeding.

[0010] Further, the addition amount of the biomass raw material in step (3) is 0.1-0.2 kg / t of steel, and it is evenly covered above the slag layer by manual feeding.

[0011] Further, the biomass raw material in step (3) includes at least one of wood, grass, rice straw, rape straw, corn straw, waste wood, and garden pruning waste.

[0012] Further, for the convenience of feeding operation into the ladle, the biomass raw material in step (3) is added to the ladle in the form of bales or bags.

[0013] The beneficial effects of the present invention are as follows: After the converter tapping is completed, the bottom blowing argon gas flow rate of the ladle is reduced. First, small-sized limestone is added, then biomass is added, and then the ladle is covered. The biomass is pyrolyzed and carbonized at high temperature during the ladle hoisting and transfer processes under an anoxic environment to obtain biomass carbon. After reaching the LF refining process, first, the bottom of the ladle is blown with a small flow rate to mix the slag, small-sized limestone, and biomass carbon. Then, the ladle cover is removed for refining treatment. The continuously decomposed CO 2 and the argon gas blown into the bottom of the ladle, as well as the biomass carbon with a rich multi-microporous structure, are retained in the molten slag, causing the molten slag volume to expand and form a densely arranged pore-like structure, promoting the foaming of the slag, improving the slag's bubble storage capacity, being beneficial to the formation and maintenance of foamed slag, being beneficial to good submerged arc in the refining process, significantly improving the performance of the refining slag, reducing the power consumption for refining heating and the consumption of slag-making materials, reducing the production cost of the refining process, and having significant economic benefits and a broad promotion prospect. Description of the Drawings

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the attached drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other attached drawings can also be obtained based on these drawings.

[0015] Figure 1 It is the control curve of the argon bottom blowing flow rate in the ladle in Embodiment 1. Specific embodiments

[0016] To enable those skilled in the art of this technology to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the attached drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0017] The normal LF processes used in each embodiment and comparative example in the specific embodiment part of the present invention are all the same.

[0018] Embodiment 1 A method for improving the foaming of the LF refining slag based on biomass carbonization, comprising the following steps: (1) During normal tapping and slag blocking operations in the converter, control the argon bottom blowing pressure in the ladle at 0.5 MPa and the argon flow rate at 50 L / min in the later stage of tapping (after half of the tapping time), and the argon bottom blowing pressure in the ladle is 0.4 MPa and the argon flow rate is 30 L / min after tapping is completed; (2) Open the bin gate and vibrating screen, and manually add dry limestone with a particle size distribution of 3 - 8 mm at a ratio of 1 kg / t of steel (limestone with particle sizes of 3 mm, 5 mm, and 8 mm is fed at a mass ratio of 3:2:1), so that the limestone is evenly spread on the slag layer on the upper part of the ladle, and preheat and start continuous decomposition at the ladle ambient temperature; (3) After 1 minute, the limestone is mixed evenly under the agitation of the argon bottom blowing in the ladle, and manually add the bundled or bagged biomass raw materials (wood, grass, rice straw, rape straw, corn straw, waste wood, garden pruning materials, etc.) at a ratio of 0.1 kg / t of steel, and evenly cover it above the slag layer; (4) Cover the ladle, close the argon bottom blowing in the ladle, and lift the ladle to the LF refining process. During this process, the space above the slag layer in the ladle is in a slightly positive pressure and oxygen-deficient state, and the biomass raw materials continue to undergo oxygen-deficient pyrolysis at the ladle ambient temperature, creating time conditions for the generation of biomass carbon; (5) Open the argon bottom blowing of the ladle, control the argon pressure at 0.4 MPa and the argon flow rate at 20 L / min; (6) After 5 min, adjust the argon pressure to 0.6 MPa and the argon flow rate to 50 L / min, and then carry out the treatment operation according to the normal LF process.

[0019] As Figure 1 shown, the 0-A time period in the figure represents the late tapping stage to the end of tapping and the argon closing stage, corresponding to the process of covering the ladle and closing the argon bottom blowing of the ladle in steps (1) to (4) of this embodiment; The A-B time period represents the ladle hoisting stage, corresponding to the process of hoisting the ladle to the LF refining process in step (4) of this embodiment; The B-H time period represents the stage after the ladle is hoisted to the LF refining process. Specifically, the B-C time period is the argon blowing stage before LF treatment after the ladle is hoisted to the LF refining process, and the B-20 min time period corresponds to steps (5) and (6) of this embodiment; the C-D time period represents the refining feeding and slag making stage; the D-E time period represents the electrode heating stage; the E-F time period represents the temperature adjustment and composition adjustment stage; the F-H time period represents the weak stirring stage at the end of treatment.

[0020] Example 2 A method for improving the foaming of LF refining slag based on biomass carbonization, comprising the following steps: (1) During normal tapping and slag blocking operations in the converter, control the argon bottom blowing pressure of the ladle at 0.4 MPa and the argon flow rate at 30 L / min in the late tapping stage (after half of the tapping time), and control the argon bottom blowing pressure of the ladle at 0.2 MPa and the argon flow rate at 20 L / min after tapping ends; (2) Open the gate of the bunker and the vibrating screen, and manually add dry limestone with a particle size distribution of 3-8 mm at a ratio of 2 kg / t of steel (limestone with particle sizes of 3 mm, 5 mm, and 8 mm is fed at a mass ratio of 3:2:1), so that the limestone is evenly spread on the slag layer on the upper part of the molten steel ladle, and preheat and start continuous decomposition at the ladle ambient temperature; (3) After 1 min, the limestone is mixed evenly under the stirring of the argon bottom blowing of the ladle, and manually add bailed or bagged biomass raw materials (wood, grass, rice straw, rapeseed straw, corn straw, waste wood, garden pruning, etc.) at a ratio of 0.2 kg / t of steel, and evenly cover it above the slag layer; (4) Cover the ladle, close the argon bottom blowing of the ladle, and hoist the ladle to the LF refining process. During this process, the space above the slag layer in the ladle is in a slightly positive pressure and oxygen-deficient state, and the biomass raw materials continue to undergo oxygen-deficient pyrolysis at the ladle ambient temperature, creating time conditions for the formation of biomass carbon; (5) Open the bottom argon blowing of the ladle, control the argon pressure at 0.2 MPa, and the argon flow rate at 30 L / min; (6) After 5 min, adjust the argon pressure to 0.4 MPa and the argon flow rate to 70 L / min, and then carry out the processing operation according to the normal LF process.

[0021] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the particle size of the limestone added in step (2) is different. The particle size of the limestone used in Comparative Example 1 is 1 - 3 mm, and the limestone with particle sizes of 1 mm and 3 mm is fed in a mass ratio of 1:1.

[0022] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the particle size of the limestone added in step (2) is different. The particle size of the limestone used in Comparative Example 2 is 8 - 10 mm, and the limestone with particle sizes of 8 mm and 10 mm is fed in a mass ratio of 1:1.

[0023] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the addition order of the limestone and the biomass raw material is reversed, that is, the order of steps (2) and (3) is reversed. The steps of Comparative Example 3 are as follows: (2) Open the bin gate and the vibrating screen, and manually add the baled or bagged biomass raw materials (such as wood, grass, rice straw, rapeseed straw, corn straw, waste wood, garden pruning waste, etc.) at a ratio of 0.1 kg / t steel by hand, and evenly spread them above the slag layer; (3) After 1 min, the biomass raw materials are mixed under the stirring of the bottom argon blowing of the ladle, and the dry limestone with a particle size distribution of 3 - 8 mm (the limestone with particle sizes of 3 mm, 5 mm, and 8 mm is fed in a mass ratio of 3:2:1) is manually added at a ratio of 1 kg / t steel, so that the limestone is evenly spread on the upper slag layer of the molten steel ladle, and is preheated and starts to decompose continuously at the ladle ambient temperature.

[0024] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the control method of the bottom argon blowing of the ladle is different. The specific steps of Comparative Example 4 are as follows: (1) During the normal tapping and slag blocking operation of the converter, control the bottom argon blowing pressure of the ladle at 0.5 MPa and the argon flow rate at 50 L / min in the later stage of tapping (after half of the tapping time), and the bottom argon blowing pressure of the ladle is 0.4 MPa and the argon flow rate is 30 L / min after the tapping is completed; (2)Open the bunker gate and vibrating screen, and manually add dry limestone with a particle size distribution of 3 - 8 mm at a ratio of 1 kg / t of steel (limestone with particle sizes of 3 mm, 5 mm, and 8 mm is fed at a mass ratio of 3:2:1), so that the limestone is evenly spread on the slag layer on the upper part of the ladle, and preheated and starts continuous decomposition at the ladle ambient temperature; if the argon pressure and flow rate are too large, part of the limestone is involved in the slag and the decomposition rate is accelerated, affecting the subsequent function of the limestone. (3)After 1 min, the limestone is mixed evenly under the stirring of bottom-blowing argon in the ladle, and manually add bailed or bagged biomass raw materials (wood, grass, rice straw, rapeseed straw, corn straw, waste wood, garden pruning, etc.) at a ratio of 0.1 kg / t of steel, and evenly cover it above the slag layer. (4)Cover the ladle, close the bottom-blowing argon of the ladle, and lift the ladle to the LF refining process. During this process, the space above the slag layer in the ladle is in a slightly positive pressure and oxygen-deficient state, and the biomass raw materials continuously undergo oxygen-deficient pyrolysis at the ladle ambient temperature, creating time conditions for the formation of biochar. (5)Open the bottom-blowing argon of the ladle, control the argon pressure to 0.2 MPa, and the argon flow rate to 20 L / min. (6)After 5 min, adjust the argon pressure to 0.5 MPa and the argon flow rate to 60 L / min, and then carry out the treatment operation according to the normal LF process. Take the slag from Examples 1 - 2 and Comparative Examples 1 - 2 for chemical analysis respectively, and the results are shown in Table 1 below. Since the biomass in Comparative Example 3 burns more and carbonizes less, the degree of slag foaming is significantly worse, and the argon pressure and flow rate in Comparative Example 4 are too small, resulting in a decrease in the degree of biomass foaming, so Comparative Examples 3 and 4 are not tested.

[0025] Table 1 Slag detection results of examples and comparative examples

[0026] The results show that the slag composition and properties of the two examples of the present invention are consistent with the slag composition and properties with good foaming performance of the refining slag provided in the relevant literature. The slag viscosity and melting temperature of Comparative Example 1 are on the low side, which cannot well ensure the foaming and bubble storage capacity of the slag. The slag viscosity and melting temperature of Comparative Example 2 are slightly on the high side, which is also not conducive to the improvement of the slag foaming and bubble storage capacity.

[0027] Although the present invention has been described in detail by reference to the accompanying drawings and in conjunction with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and all such modifications or substitutions should be within the scope of the present invention / Any person skilled in the art within the technical scope disclosed by the present invention can easily conceive of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A method for improving the foaming of LF refined slag based on biomass carbonization, characterized in that: The steps include: (1) The converter operates normally for tapping and slag blocking. The argon pressure at the bottom of the ladle is controlled to be 0.4~0.5MPa and the argon flow rate is 30~50L / min in the later stage of tapping. The argon pressure at the bottom of the ladle is controlled to be 0.2~0.4MPa and the argon flow rate is 20~30L / min after tapping. (2) Open the silo gate and vibrating screen, add limestone, preheat at the ladle ambient temperature and start continuous decomposition; (3) After 1 minute, the limestone is mixed under the stirring of argon blowing at the bottom of the ladle, and the biomass raw materials are added and evenly spread on the slag layer; (4) The ladle is covered, the argon blowing at the bottom of the ladle is turned off, and the ladle is hoisted to the LF refining process. The biomass raw materials are continuously cracked in the absence of oxygen at the ambient temperature of the ladle to generate biochar; (5) Open the bottom of the ladle to blow argon, control the argon pressure to 0.2~0.4MPa, and the argon flow rate to 20~30L / min; (6) After 5 minutes, adjust the argon pressure to 0.4-0.6 MPa and the argon flow rate to 50-70 L / min, and then perform the subsequent processing operations according to the normal LF process.

2. The method according to claim 1, characterized in that The late stage of steelmaking refers to the stage after half of the steelmaking time has passed.

3. The method according to claim 1, characterized in that The particle size of the limestone added in step (2) is 3-8 mm.

4. The method according to claim 3, characterized in that The limestone added in step (2) is a mixture of limestones with particle sizes of 3 mm, 5 mm and 8 mm, and the feed ratio of the three types of limestone is 3:2:

1.

5. The method according to claim 1, characterized in that The limestone added in step (2) is dry limestone.

6. The method according to claim 1, characterized in that In step (2), the amount of limestone added is 1-2 kg / t steel, and it is evenly spread on the slag layer on the upper part of the ladle by manual throwing.

7. The method according to claim 1, characterized in that In step (3), the amount of biomass raw material added is 0.1-0.2 kg / t steel, and it is evenly spread on the slag layer by manual throwing.

8. The method according to claim 1, characterized in that The biomass raw material in step (3) includes at least one of wood, grass, rice straw, rape straw, corn straw, waste wood, and garden trimmings.

9. The method according to claim 1, characterized in that In step (3), the biomass raw materials are added to the ladle in the form of bales or bags.

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