Method for controlling carbon content of molten steel in microwave field by utilizing renewable energy sources

Abstract

The invention relates to the technical field of iron and steel smelting, and discloses a method for controlling the carbon content of molten steel in a microwave field by utilizing renewable energy sources, and the method comprises the following steps: mixing powdery biomass charcoal and powdery activated carbon, pressing the mixture into a carburant material block, and wrapping the carburant material block with a steel shell; and the steel sample to be recarburized is subjected to microwave heating to obtain molten steel at the preset temperature, then the recarburizer material block wrapped with the steel shell is added into the molten steel, microwave heating continues, and the finished steel sample is obtained after the reaction is completed. According to the method, the purity of the recarburized molten steel can be improved, the recarburization effect is improved, and the environmental protection property of the recarburization process is improved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and more specifically to a method for controlling the carbon content of molten steel using renewable energy under a microwave field. Background Technology

[0002] In the steelmaking process, to meet the carbon content requirements of different steel grades, it is often necessary to add carburizing agents to the molten steel to increase the carbon content. Traditional carburizing agents mainly use fossil fuels such as graphite, anthracite, and coke, which provide a heat source through electric heating or fossil fuel combustion to achieve the carburization treatment of molten steel.

[0003] However, traditional carbonization processes have the following problems: First, fossil fuel-based carbonization agents introduce impurities such as sulfur and nitrogen during use, leading to a decrease in the purity of the molten steel and a significant increase in nitrogen content after carbonization, affecting steel quality. Second, conventional heating methods have low heat utilization rates, and the chemical reactions during carbonization are not sufficient, resulting in a need to improve the carbonization effect. Furthermore, with increasingly stringent environmental protection requirements, the steel industry faces pressure to reduce its reliance on fossil fuels.

[0004] Therefore, existing technologies still need improvement. Summary of the Invention

[0005] The main objective of this invention is to provide a method for controlling the carbon content of molten steel using renewable energy under a microwave field, in order to solve the technical problems of how to reduce the impurities introduced during the carbonization process and how to improve the effectiveness and environmental friendliness of the carbonization process.

[0006] According to one aspect of the present invention, a method for controlling the carbon content of molten steel using renewable energy under a microwave field is proposed, comprising the following steps: S1, mixing powdered biochar and powdered activated carbon and pressing them into carbon-reinforcing agent blocks, and wrapping the carbon-reinforcing agent blocks with a steel shell; S2, microwave heating the steel sample to be carbonized to obtain molten steel at a predetermined temperature, then adding the carbon-reinforcing agent blocks wrapped in the steel shell into the molten steel and continuing microwave heating, and obtaining the finished steel sample after the reaction is complete.

[0007] According to one embodiment of the present invention, in step S1, the particle size of both the powdered biochar and the powdered activated carbon is less than 0.0075 mm.

[0008] According to one embodiment of the present invention, in step S1, the biochar is a carbonized biological raw material, which includes at least one of the following: wood, bamboo, and straw; the fixed carbon content of the biochar is 75% to 80%.

[0009] According to one embodiment of the present invention, in step S1, the mixing ratio of activated carbon and biochar is controlled according to a ratio of 2.0 to 3.0 of the fixed carbon mass provided by activated carbon to the fixed carbon mass provided by biochar.

[0010] According to one embodiment of the present invention, in step S1, the diameter of the carbon raiser block is 25~35mm and the height is 15~25mm; the pressing force for pressing the carbon raiser block is 20~25MPa; and the thickness of the steel shell is 3~7mm.

[0011] According to one embodiment of the present invention, in step S2, the steel sample to be carbonized is first cut into samples with dimensions of (15~25)×(15~25)×(15~25)mm, and then the samples are microwave heated.

[0012] According to one embodiment of the present invention, in step S2, the ratio of the fixed carbon mass provided by all the added carbon raiser blocks to the carbon mass that the molten steel needs to increase is 1.3 to 1.5.

[0013] According to one embodiment of the present invention, in step S2, the steel sample to be carbonized is microwave heated to obtain molten steel at 1850~1900K and kept at a constant temperature for 2~5 minutes. Then, a carbonizing agent block wrapped in a steel shell is added and microwave heating is continued to keep at a constant temperature for 1~3 minutes.

[0014] According to one embodiment of the present invention, in step S2, the microwave generating power is adjusted within the range of 1500~3000W.

[0015] According to one embodiment of the present invention, in step S2, microwave heating is performed under an inert atmosphere, and after the reaction is complete, the sample is cooled to room temperature under an inert atmosphere to obtain a finished steel sample.

[0016] In the technical solution of this invention, biochar and activated carbon are used as carbon-enhancing agents. Biochar and activated carbon have relatively few impurities, thus ensuring the purity of the product after the reaction. Furthermore, microwave heating can cause the molecules to vibrate at high frequency, increasing intermolecular interactions, promoting the chemical reaction, and improving the solubility of carbon in the reaction system, thereby effectively improving the efficiency of the carbon-enhancing process. In addition, the use of biochar and activated carbon can reduce the consumption of conventional fossil energy such as coal, improving the environmental friendliness of the carbon-enhancing process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a method for controlling the carbon content of molten steel using renewable energy under a microwave field, according to an embodiment of the present invention, is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0021] As mentioned in the background section above, the inventors of this application recognize that current traditional metallurgical processes primarily rely on fossil fuels for carbonization of molten steel. However, the metallurgical industry faces increasingly stringent environmental requirements, forcing metallurgists to seek new types of carbonizing agents. Renewable biomass, due to its wide distribution, low cost, and low pollution, has significant application potential. To reduce the traditional steel industry's dependence on fossil fuels, lower CO2 emissions, and achieve green, clean, and sustainable development, it is necessary to study the application of biomass-based carbonizing agents in metallurgical processes.

[0022] The inventors also recognized that current smelting processes suffer from insufficient heat sources and incomplete reactions, hindering carbon content control. Furthermore, the carbonization process introduces impurities such as nitrogen and sulfur, affecting the purity of the molten steel. Microwave heating offers advantages such as high energy efficiency, ease of control, and low pollution emissions. The inside-out heating characteristic under microwave conditions can break the traditional metallurgical energy structure reliant on fossil fuels. Microwave heating causes high-frequency vibrations of molecules, increasing intermolecular interactions, promoting chemical reactions, and improving the solubility of the reaction system. Combining microwave heating with biomass can create localized hot spots on the surface of the carbon medium, promoting the Bourdon reaction and increasing CO concentration. Additionally, during biomass combustion under microwave conditions, nitrogen is primarily released as gaseous nitrogen-containing precursors, while sulfur is mainly converted into sulfur oxides such as SO2 and escapes from the molten steel, effectively reducing the harmful effects of nitrogen and sulfur on the steel matrix.

[0023] Based on the above understanding, this application proposes the following technical solution, which adopts a process that combines biomass as a carbon source and microwave as a heat source, in order to provide the metallurgical industry with a transformation path of "renewable raw materials, low-carbon energy, and efficient processes".

[0024] refer to Figure 1 This invention proposes a method for controlling the carbon content of molten steel using renewable energy under a microwave field, comprising the following steps: S1, mixing powdered biochar and powdered activated carbon and pressing them into carbon refining agent blocks, and wrapping the carbon refining agent blocks with a steel shell; S2, microwave heating the steel sample to be carbonized to obtain molten steel at a predetermined temperature, then adding the carbonizing agent block wrapped in a steel shell into the molten steel and continuing microwave heating, and obtaining the finished steel sample after the reaction is complete.

[0025] In embodiments of the present invention, the microwave heating process causes the molecules of the substance to vibrate at high frequencies, increasing intermolecular interactions, promoting chemical reactions, and improving the solubility of carbon in the reaction system. Biochar, as a carbonizing agent, can reduce the impurity content introduced by conventional anthracite and other substances, improve the purity of the carbonized molten steel, and simultaneously reduce the consumption of conventional coal and other fossil energy sources, meeting the needs of sustainable resource development.

[0026] This invention utilizes renewable energy biochar and activated carbon as carbonizing agents and employs a microwave field to efficiently carbonize steel samples. The resulting molten steel exhibits C content ≥0.74%, N content ≤0.00029%, S content ≤0.010%, O content ≤0.0033%, and Al content ≤0.011% (all contents are by mass percentage). The carbon recovery rate is 93.74%~95.32%, N content is reduced by 14.71%~25%, and S content is reduced by 28.57%~33.33%. Microwave heating effectively achieves carbonization of molten steel while simultaneously reducing the N and S content.

[0027] In embodiments of the present invention, biochar is a carbonized biological raw material, which may include, but is not limited to, at least one of wood, bamboo, and straw. Biochar contains volatile matter and fixed carbon, and the fixed carbon content of biochar can be 75% to 80%.

[0028] This invention combines biochar and activated carbon as carbon raisers to achieve the following effects: optimizing reaction kinetics by utilizing the high reactivity and interfacial properties of biochar; ensuring thermodynamic conditions by utilizing the high carbon content and conductivity of activated carbon; and guaranteeing product cleanliness by utilizing the low ash content and porous structure of both. Specifically, biochar contains a certain amount of volatiles, which are released and decomposed to generate CO during microwave heating. This CO surrounds the reaction material, forming an interfacial layer that improves the interfacial reaction conditions between molten steel and carbon. Activated carbon, after activation treatment, has an extremely high fixed carbon content and a well-developed porous structure, ensuring sufficient carbon enters the molten steel. Simultaneously, activated carbon typically possesses a certain degree of conductivity, allowing it to more effectively absorb microwave energy in a microwave field, forming localized hot spots and providing energy for the endothermic carbon dissolution reaction. Furthermore, the gases generated by the reaction of impurity elements can be contained and escaped by the pores of biochar and the micropores of activated carbon, accelerating the impurity removal reaction.

[0029] This invention achieves the following effects by mixing and pressing powdered biochar and powdered activated carbon into carbon raiser blocks, and then encasing the carbon raiser blocks in a steel shell: increasing the overall density, overcoming buoyancy, allowing the carbon raiser blocks to smoothly enter the molten steel, and preventing them from being oxidized by slag on the surface of the molten steel or escaping with the airflow; at the same time, the steel shell melts rapidly at high temperature, allowing the carbon raiser to be released in situ inside the molten pool, fully contacting and reacting with the molten steel, thereby significantly improving the carbon recovery rate and absorption rate, and ensuring a uniform and stable carbon raising effect.

[0030] In some embodiments, in step S1, the particle size of both the powdered biochar and the powdered activated carbon is below 0.0075 mm, in order to increase the specific surface area of ​​the biochar and activated carbon and make the packing more compact after pressing. The block-shaped biochar and activated carbon with dimensions of (25~35)×(10~20)×(5~15) mm can be crushed and ground separately to a particle size below 0.0075 mm.

[0031] In some embodiments, in step S1, the mixing ratio of activated carbon and biochar is controlled according to a ratio of 2.0 to 3.0 of the fixed carbon mass provided by activated carbon to the fixed carbon mass provided by biochar. That is, the amount of carbon contributed by activated carbon in the carbon raiser is 2.0 to 3.0 times that contributed by biochar. This achieves an optimal balance in the proportion of the two, utilizing the high reactivity of biochar to promote carbon dissolution while leveraging the high carbon content of activated carbon to ensure carbon raising efficiency, and simultaneously controlling the total ash content to within limits. Assuming the fixed carbon mass provided by activated carbon is A, and the fixed carbon content of activated carbon is x, and the fixed carbon mass provided by biochar is B, and the fixed carbon content of biochar is y, then the ratio of the fixed carbon mass A provided by activated carbon to the fixed carbon mass B provided by biochar is C = A / B = 2.0 to 3.0, and the mass ratio of activated carbon to biochar is (A / x) / (B / y) = (A / B) × (y / x) = C × (y / x). Given x and y, the mass ratio of activated carbon to biochar can be determined based on C.

[0032] In some embodiments, in step S1, the diameter of the recarburizer block is 25-35 mm and the height is 15-25 mm. The pressing force for forming the recarburizer block is 20-25 MPa. The thickness of the steel shell is 3-7 mm. By setting these parameters, efficient, stable, and controllable addition of the recarburizer can be achieved, providing process assurance for improving carbon yield and removing impurity elements.

[0033] In some embodiments, in step S2, the steel sample to be carbonized is first cut into samples with dimensions of (15~25)×(15~25)×(15~25) mm, and then the samples are microwave-heated. For example, the steel sample to be carbonized can be made into a sample with dimensions of 20×20×20 mm by wire cutting. Cutting it into appropriately sized block samples helps to uniformly absorb energy in the microwave field and ensures that the steel sample melts rapidly in the microwave field.

[0034] In some embodiments, in step S2, the ratio D / E of the fixed carbon mass D provided by all the added recarburizing agent blocks to the carbon mass E that the molten steel needs to increase is 1.3 to 1.5. That is, the ratio between the total carbon provided by the recarburizing agent and the target carbon increase of the molten steel is 1.3 to 1.5. Excess recarburizing agent can compensate for carbon loss during the recarburizing process, ensuring that the final carbon content of the molten steel reaches the expected target.

[0035] In some embodiments, in step S2, a microwave reactor can be used to microwave-heat the steel sample to be carbonized to obtain molten steel at 1850~1900K and hold the temperature for 2~5 minutes. Then, a carbonizing agent block encased in a steel shell is added, and microwave heating continues for another 1~3 minutes. By precisely controlling the heating temperature and holding time, stable thermodynamic and kinetic conditions are provided for the carbonization reaction. In some embodiments, the microwave power can be flexibly adjusted within the range of 1500~3000W, and the microwave power can be continuously adjustable. In some embodiments, in step S2, microwave heating can be performed under an inert atmosphere, for example, by continuously introducing an inert gas (e.g., argon) into the microwave reactor for protection. After the reaction is complete, the sample can be cooled to room temperature under an inert atmosphere to obtain the finished steel sample.

[0036] The following description is based on specific embodiments.

[0037] Example 1 A method for controlling the carbon content of molten steel using renewable energy under a microwave field specifically includes the following steps: Step 1: The carbonizing agent is biochar (wood charcoal) and activated carbon, which are in block form and have a size of 30×15×10mm. The biochar and activated carbon are crushed and ground to below 0.0075mm. The steel sample to be carbonized is made into a sample with a size of 20×20×20mm by wire cutting.

[0038] The main chemical compositions of the carbon-enhanced steel sample and charcoal are shown in Tables 1 and 2.

[0039] Table 1: Main chemical composition of the steel sample to be carbonized (wt.%)

[0040] Table 2: Main chemical components of charcoal / wt.%

[0041] Step 2: The carbon raiser is prepared by mixing charcoal and activated carbon at a fixed carbon mass ratio of 1:2.5. The carbon mixture is prepared by mixing the fixed carbon mass provided by the carbon raiser with the carbon mass required to be added to the molten steel at a ratio of 1.4:1.0. The mixture is then pressed into blocks with a diameter of 30 mm and a height of 20 mm, with a pressing force of 25 MPa. The pressed carbon raiser is then wrapped in a steel shell with a thickness of 5 mm.

[0042] Step 3: Place the steel sample to be carbonized into a microwave reactor for microwave heating, and continuously introduce inert argon gas into the microwave reactor for protection. The microwave power is 2000W. Heat the steel sample to be carbonized to 1873K and hold it at that temperature for 3 minutes. Add the carbonizing agent wrapped in the steel shell into the molten steel and continue to hold it at that temperature for 2 minutes. After the reaction is complete, cool it to room temperature under inert gas conditions to obtain the finished steel sample.

[0043] The finished steel sample obtained in Example 1 was tested. By mass percentage, the C content was 0.74%, the N content was 0.00024%, the S content was 0.008%, the O content was 0.0029%, and the Al content was 0.011%. The carbon recovery rate was 93.74%, the N content decreased by 25%, and the S content decreased by 33.33%. Microwave heating effectively increased the carbon content of the molten steel while simultaneously reducing the N and S content.

[0044] Example 2 A method for controlling the carbon content of molten steel using renewable energy under a microwave field specifically includes the following steps: Step 1: The carbonizing agent is biochar (bamboo charcoal) and activated carbon, which are in block form and have a size of 30×15×10mm. The biochar and activated carbon are crushed and ground to below 0.0075mm. The steel sample to be carbonized is then made into a sample with a size of 20×20×20mm using wire cutting.

[0045] The main chemical compositions of the carbon steel sample and bamboo charcoal are shown in Tables 3 and 4.

[0046] Table 3: Main chemical composition of the steel sample to be carbonized / wt.%

[0047] Table 4: Main chemical components of bamboo charcoal / wt.%

[0048] Step 2: The carbon raiser is prepared by mixing bamboo charcoal and activated carbon at a fixed carbon mass ratio of 1.2:2.7. The carbon mixture is prepared by mixing the fixed carbon mass provided by the carbon raiser with the carbon mass required to be added to the molten steel at a ratio of 1.3:1.0. The mixture is then pressed into blocks with a diameter of 30mm and a height of 20mm, with a pressing force of 25MPa. The pressed carbon raiser is then wrapped in a steel shell with a thickness of 5mm.

[0049] Step 3: Place the steel sample to be carbonized into a microwave reactor for microwave heating, and continuously introduce inert argon gas into the microwave reactor for protection. The microwave power is 2000W. Heat the steel sample to be carbonized to 1873K and hold it at that temperature for 3 minutes. Add the carbonizing agent wrapped in the steel shell into the molten steel and continue to hold it at that temperature for 2 minutes. After the reaction is complete, cool it to room temperature under inert gas conditions to obtain the finished steel sample.

[0050] The finished steel sample obtained in Example 2 was tested. By mass percentage, the C content was 0.77%, the N content was 0.00029%, the S content was 0.010%, the O content was 0.0033%, and the Al content was 0.010%. The carbon recovery rate was 95.32%, the N content decreased by 14.71%, and the S content decreased by 28.57%. Microwave heating effectively increased the carbon content of the molten steel while simultaneously reducing the N and S content.

[0051] In summary, this invention utilizes a microwave external field to rapidly melt and control the carbon content of the steel sample to be carbonized, thereby increasing the carbon content in the molten steel. The microwave heating process causes high-frequency vibrations of molecules, increasing intermolecular interactions, promoting chemical reactions, and improving the solubility of carbon in the reaction system. The carbon-enhancing agent uses renewable energy sources such as biomass and activated carbon. On the one hand, this reduces impurities introduced by traditional anthracite and other fossil fuels, resulting in cleaner reaction products; on the other hand, it reduces the consumption of traditional anthracite and other fossil fuels, which is beneficial to the implementation of sustainable development strategies.

[0052] The present invention can achieve the following beneficial effects: (1) Compared with similar production processes, the operation method and process flow of the present invention have a shorter production process, are easier to operate, and are more practical.

[0053] (2) The raw materials used in this invention are steel samples to be carbonized, biomass, and activated carbon, etc., whose main components are basically iron-carbon alloys and carbon-containing substances. The carbon-containing biomass and activated carbon contain relatively few impurities, thereby ensuring the purity of the product after the reaction.

[0054] (3) Microwave heating causes molecules to vibrate at high frequencies, increasing intermolecular interactions, promoting chemical reactions, and improving the solubility of carbon in the reaction system. Using the microwave field as a heat source not only eliminates the need for drying raw materials, saving costs and process steps, but also allows for more complete and uniform reactions between materials due to the microwave's inside-out heating characteristic. Furthermore, microwaves can promote the breaking of bonds between molecules or clusters in the reactants' structures, resulting in a faster and smoother melting reaction between molten steel and the carburizing agent. Compared to conventional electric heating or fossil fuel heating methods, microwave heating offers higher reaction rates and higher heat utilization.

[0055] (4) During the carbonization process of molten steel under a microwave field, highly reactive biochar and activated carbon, compared with traditional fossil energy, are both renewable energy sources, which is conducive to the implementation of the sustainable development strategy. In addition, biochar contains a large amount of volatile matter, which is released and decomposed to generate CO during microwave heating, forming an interface layer around the reaction material. Under microwave heating conditions, the material has the characteristic of rapid temperature rise; the reaction material can be heated from room temperature to 1873K in only 12 minutes.

[0056] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for controlling the carbon content of molten steel using renewable energy under a microwave field, characterized in that, Includes the following steps: S1, mixing powdered biochar and powdered activated carbon and pressing them into carbon refining agent blocks, and wrapping the carbon refining agent blocks with a steel shell; S2, the steel sample to be carbonized is microwave-heated to obtain molten steel at a predetermined temperature, and then the carbonizing agent block wrapped in the steel shell is added to the molten steel and microwave-heated again until the reaction is complete to obtain the finished steel sample.

2. The method according to claim 1, characterized in that, In step S1, the particle size of both the powdered biochar and the powdered activated carbon is below 0.0075 mm.

3. The method according to claim 1, characterized in that, In step S1, the biochar is a carbonized biological raw material, which includes at least one of the following: wood, bamboo, and straw; the fixed carbon content of the biochar is 75% to 80%.

4. The method according to claim 1, characterized in that, In step S1, the mixing ratio of the activated carbon and the biochar is controlled according to a ratio of 2.0 to 3.0 of the fixed carbon mass provided by the activated carbon to the fixed carbon mass provided by the biochar.

5. The method according to claim 1, characterized in that, In step S1, the diameter of the carbon raiser block is 25~35mm and the height is 15~25mm; the pressing force for pressing the carbon raiser block is 20~25MPa; and the thickness of the steel shell is 3~7mm.

6. The method according to claim 1, characterized in that, In step S2, the steel sample to be carbonized is first cut into samples with dimensions of (15~25)×(15~25)×(15~25)mm, and then the samples are microwave heated.

7. The method according to claim 1, characterized in that, In step S2, the ratio of the fixed carbon mass provided by all the added carbon raiser blocks to the carbon mass that the molten steel needs to increase is 1.3 to 1.

5.

8. The method according to claim 1, characterized in that, In step S2, the steel sample to be carbonized is microwave-heated to obtain molten steel at 1850~1900K and kept at a constant temperature for 2~5 minutes. Then, the carbonizing agent block wrapped in the steel shell is added and microwave-heated again for 1~3 minutes.

9. The method according to claim 1, characterized in that, In step S2, the microwave generating power is adjusted within the range of 1500~3000W.

10. The method according to claim 1, characterized in that, In step S2, microwave heating is performed under an inert atmosphere, and after the reaction is complete, the sample is cooled to room temperature under an inert atmosphere to obtain the finished steel sample.

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