High-conductivity phosphorus molten pig iron proportioning method

Abstract

The invention provides a proportioning method of high-conductivity phosphorus molten pig iron, and relates to the technical field of aluminum smelting. The invention relates to a proportioning method of high-conductivity molten phosphorus pig iron. The proportioning method comprises the following steps: S1, mixing a phosphorus pig iron raw material and an additive, and smelting in an intermediate frequency furnace; s2, blowing an auxiliary agent into the phosphorus molten pig iron in the intermediate frequency furnace for continuous smelting to obtain the high-conductivity phosphorus molten pig iron; wherein the additive comprises the following components in percentage by weight: 5-15% of copper, 40-50% of aluminum, 5-15% of zinc, 10-20% of silicon and 15-25% of columnar graphite; the auxiliary agent comprises a rare earth-transition metal composite core-spun yarn and an activating medium in a mass ratio of 1: (2-5). According to the method, the content of molten phosphorus pig iron elements is adjusted through the additive and the assistant, and the thermal expansion coefficient of phosphorus pig iron is reduced to be matched with the thermal expansion coefficient of a carbon anode, so that anode iron-carbon contact pressure drop is reduced, and the operation stability of an electrolytic bath is improved.

Description

Technical Field

[0001] This invention relates to the field of aluminum smelting technology, and more specifically, to a method for proportioning highly conductive phosphorus pig iron. Background Technology

[0002] As the "heart" of aluminum electrolysis production, the conductivity of prebaked anodes directly determines the energy conversion efficiency of the electrolytic cell. A 1% improvement in conductivity can reduce the daily power consumption of a single electrolytic cell by approximately 20 kWh. Under the current "dual carbon" goals, the aluminum industry, being a high-energy-consuming sector, has made electrolytic cell energy consumption a key indicator of core competitiveness. As a large-scale domestic aluminum electrolysis production facility with a 500KA electrolytic cell cluster (372 units) and an annual capacity of 500,000 tons, the anode group's conductivity performance is subject to extremely high requirements: a 1 mV reduction in anode group voltage drop can save approximately 1.8 million kWh of electricity annually for the entire workshop. Actual measurement data shows that the average voltage drop of the workshop's anode group is 355 mV, 14 mV higher than the industry benchmark (341 mV).

[0003] As a "conductive bridge" connecting the aluminum conductor rod and the carbon block, pig iron with phosphorus must simultaneously meet three core requirements: first, high conductivity, with a resistivity as low as possible to reduce energy loss; second, good fluidity, ensuring complete filling of the tiny gaps between the conductor rod and the carbon block during casting to avoid localized resistance due to poor contact; and third, thermal expansion matching, with its coefficient of thermal expansion close to that of the carbon block, otherwise cracking or gaps may occur after cooling, leading to a sharp increase in contact resistance. Currently, the commonly used pig iron with phosphorus formulations in the industry uses iron as the base material, optimizing performance by adjusting the proportions of various elements. However, limited by the inherent conductivity of iron-carbon alloys, the resistivity remains difficult to exceed 8.0 × 10⁻⁶. -4 Ω·cm threshold.

[0004] From a production practice perspective, the quality of pig iron directly affects the service life of the anode assembly during the anode assembly process. Poor conductivity can lead to localized overheating during electrolysis, causing premature breakage of the carbon blocks (shortening the average lifespan by 5-7 days). Insufficient bonding strength can cause the guide rod and carbon blocks to loosen, requiring machine shutdown for maintenance. The existing pig iron processing technology suffers from the following problems: 1. Insufficient precision in trace element control leads to drastic performance fluctuations. Traditional medium-frequency furnace smelting relies on manual experience to adjust the batching, lacking the detection and control of trace elements. Actual measurement data shows that the phosphorus content in different batches of pig iron fluctuates by ±0.2%, corresponding to a resistivity fluctuation of ±12%. This fluctuation results in a maximum voltage drop deviation of 25mV in the anode group, directly causing uneven current distribution in the electrolytic cell, excessive current density in some areas, and accelerated carbon block corrosion. Furthermore, the unstable performance also results in a casting iron ring qualification rate of only 92%, producing approximately 30 sets of rework pieces per month, increasing labor and material costs.

[0005] 2. Poor thermal expansion matching, resulting in persistently high interfacial contact resistance. The thermal expansion coefficient of traditional pig iron (11.2 × 10⁻⁶) is... -6 / ℃) and carbon blocks (4.5×10 -6 The difference in temperature (°C) is significant. When the pig iron shrinks to room temperature after casting, it is about 1.5 times greater than that of the carbon block, forming micro-gaps of 0.02-0.05 mm. These gaps increase the iron-carbon contact resistance by about 30% (from 1.2 × 10⁻⁶ mm). -4 Ω increased to 1.56 × 10 -4 Ω), becoming one of the main sources of pressure drop in the anode group. To reduce the gap, the existing process uses an increase in casting temperature (1300-1350℃) to prolong the fluidity of molten iron. However, high temperature will cause oxidation reaction on the surface of the carbon block (generating a Fe3C brittle layer with a thickness of about 5-8μm), resulting in a 20% reduction in the iron-carbon bonding strength. The iron ring breakage rate reaches 8% during the depressurization process, further increasing production costs.

[0006] 3. High energy consumption and low production efficiency. Due to performance defects, the existing process requires frequent parameter adjustments (testing the molten iron composition every 4 hours and adjusting the element ratio 3-4 times a day) to maintain basic performance, resulting in frequent start-ups and shutdowns of the induction furnace (each start-up and shutdown consumes an additional 50kWh of electricity), further increasing energy consumption. Summary of the Invention

[0007] The purpose of this invention is to provide a method for proportioning highly conductive phosphorus pig iron, which adjusts the element content of phosphorus pig iron by adding additives and auxiliaries, reduces the thermal expansion coefficient of phosphorus pig iron, and matches it with the thermal expansion coefficient of carbon anode, thereby reducing the contact pressure drop between anode iron and carbon and improving the operational stability of the electrolytic cell.

[0008] This invention is achieved through the following technical solution: A method for proportioning highly conductive phosphorus-containing molten iron includes the following steps: S1. The phosphorus pig iron raw material and additives are mixed and then smelted in an intermediate frequency furnace. The weight of the additives is 0.1-0.2% of the weight of the phosphorus pig iron raw material. S2. Additives are injected into the molten pig iron in the medium-frequency furnace for further smelting, using nitrogen as the carrier gas at a flow rate of 1.5-2 m³ / h. 3 / min, the weight of the additive is 0.5-1.2% of the weight of the phosphorus pig iron, thus obtaining highly conductive phosphorus pig iron; The additives, by weight percentage, consist of: 5-15% copper, 40-50% aluminum, 5-15% zinc, 10-20% silicon, and 15-25% columnar graphite, with a particle size of 5-20 μm. The components in the additives work synergistically: copper and aluminum reduce the resistivity of the iron matrix through solid solution strengthening; zinc improves the fluidity of molten iron, ensuring sufficient filling of gaps during casting; silicon regulates the coefficient of thermal expansion, reducing differences in cooling shrinkage; and columnar graphite forms a three-dimensional conductive network, increasing the density of conductive pathways by three times and significantly improving overall conductivity. The raw material for pig iron can be ferrophosphate blocks.

[0009] The additives include a rare earth-transition metal composite cored wire with a mass ratio of 1:2-5 and an activation medium. The rare earth-transition metal composite cored wire has an iron core, which comprises a rare earth silicon-magnesium alloy and nano-alumina powder with a mass ratio of 5-7:1. The core diameter accounts for 60-70% of the total diameter of the cored wire. The rare earth silicon-magnesium alloy contains ≥30% La+Ce rare earth elements and 8-12% magnesium. The nano-alumina powder has a particle size of 20-50 nm. The activation medium, by weight, includes 40-70 parts calcium oxide, 1-3 parts sodium carbonate, 5-8 parts sodium aluminate, 1-3 parts zinc oxide, 1-3 parts calcium fluoride, and 0.5-2 parts sodium fluoride. The rare earth elements (La / Ce) refine the grains, purify the molten iron, and reduce inclusions. The nano-alumina acts as a non-uniform nucleation core, promoting uniform graphite precipitation and reducing shrinkage cracks. The cored wire penetrates into the middle of the molten iron to release rare earth elements, preventing their loss. Nano-alumina is suspended at the slag-metal interface, enhancing desulfurization. Sodium aluminate and zinc oxide react to produce spinel, which adsorbs sulfur impurities. Sodium carbonate decomposes to generate CO2 bubbles, achieving gas-flocculated desulfurization. Calcium fluoride and sodium fluoride can reduce slag viscosity and improve desulfurization efficiency.

[0010] Furthermore, the smelting temperature is 1220-1280℃, with continuous stirring during the smelting process. The molten pig iron is subjected to 2-3 slag removal treatments, and the temperature is reduced to 1150-1200℃ before being poured into the furnace. After casting, it is cooled to 1000-1050℃ at a rate of 25-35℃ / min, and then cooled to room temperature at a rate of 3-8℃ / min to obtain the finished pig iron. Gradient temperature-controlled solidification can inhibit the precipitation of phosphorus eutectic, promote the formation of spheroidal graphite, and eliminate the tendency for white cast iron.

[0011] A three-dimensional mapping relationship was established between the amount of additives and auxiliaries, the melting temperature, and the element ratio. The traditional experience-based batching was upgraded to quantitative control of "parameters-performance". This reduced the fluctuation range of P element in different batches of pig iron from ±0.2% to ±0.03%, and the fluctuation range of resistivity of pig iron from ±15% to ±3%, solving the long-standing problem of process stability and facilitating large-scale application.

[0012] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention forms a two-phase structure system of "iron matrix + highly conductive phase": the additives are uniformly distributed in the molten iron, constructing a multi-dimensional optimization mechanism of "metallic phase conductive bridging - interfacial metallurgical bonding - thermal expansion gradient matching". Compared with traditional iron-carbon alloys, this structure breaks through the industry bottleneck of "difficulty in balancing high conductivity and high strength", promoting the performance improvement of pig iron. The synergistic effect of the additives' "rare earth purification + nano-nucleation + metallic phase conductivity + dual desulfurization" achieves simultaneous improvement in the conductivity and mechanical properties of pig iron. The average voltage drop of the conductor assembly decreased from 355mV in the traditional process to 334.8mV, a reduction of 5.7% (an absolute reduction of 20.2mV). The corresponding resistivity of pig iron decreased from 8.6×10⁻⁶. -4 Ω·cm decreased to 7.2×10 -4 Ω·cm (reduced by 16.3%), iron-carbon contact resistance from 1.56 × 10⁻⁶ Ω·cm. -4 Ω decreased to 1.02×10 -4 Ω (reduced by 34.6%), completely solving the problem of uneven current distribution.

[0013] This invention establishes a closed-loop optimization mechanism of "materials-process-efficiency": the introduction of additives and auxiliaries not only improves electrical conductivity but also simultaneously improves thermal expansion matching, reducing iron ring breakage and rework, thus reducing the thermal expansion coefficient of pig iron from 11.2 × 10⁻⁶. -6 / ℃ adjusted to 8.8×10 -6 / ℃, with carbon blocks (4.5×10 -6 The matching degree of ( / ℃) was improved by 21.4%, and the iron-carbon gap was reduced to 0.005-0.01mm after cooling (1 / 5 of the traditional process). At the same time, the interfacial activity of the additives inhibited the formation of the Fe3C brittle layer (the thickness was reduced to 1-2μm), the iron ring decompression fracture rate was reduced from 8% to 1.5%, and the anode assembly qualification rate was increased to 99%.

[0014] Due to improved conductivity, the intermediate frequency furnace no longer requires frequent parameter adjustments, reducing unit energy consumption from 65 kWh / ton to 58 kWh / ton (a 10.8% reduction), resulting in annual electricity cost savings of approximately 250,000 yuan. Simultaneously, the anode group replacement cycle is extended from 33 days to 38 days, improving the operational stability of the electrolytic cell and creating a positive cycle of "material innovation to reduce resistance → process optimization to reduce costs → stable operation to reduce energy consumption." Compared to existing industry solutions, this mechanism requires no new equipment, has low retrofit costs, and reduces overall energy consumption while improving conductivity, aligning with the trend of green manufacturing and providing a technological demonstration for the low-carbon transformation of the aluminum smelting industry. Detailed Implementation

[0015] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0016] Example 1 A method for proportioning highly conductive phosphorus-containing molten iron includes the following steps: S1. The ferrophosphorus blocks and additives are mixed and then smelted in an induction furnace. The particle size of the additives is 10μm, the smelting temperature is 1250℃, and the mixture is stirred continuously during the smelting process. The weight of the additives is 0.16% of the weight of the ferrophosphorus raw material. S2. Injecting an additive—a rare earth-transition metal composite cored wire with a mass ratio of 1:3 and an activation medium into the molten iron in the medium-frequency furnace, using nitrogen as the carrier gas at a flow rate of 1.5 m³ / h. 3 / min, the weight of the additive is 0.65% of the weight of the phosphorus pig iron, and the smelting continues to obtain highly conductive phosphorus pig iron; S3. The molten pig iron in the phosphorus state is subjected to two slag removal treatments, and the temperature is reduced to 1180℃ before being poured out of the furnace. After casting, it is cooled to 1020℃ at a rate of 30℃ / min, and then cooled to room temperature at a rate of 5℃ / min to obtain the finished pig iron.

[0017] The additives, by weight percentage, are: 10% copper, 45% aluminum, 10% zinc, 15% silicon, and 20% columnar graphite.

[0018] The rare-earth-transition-metal composite cored wire has an iron-clad core. The core consists of a rare-earth silicon-magnesium alloy and nano-alumina powder in a 6:1 mass ratio. The core diameter accounts for 65% of the total diameter of the cored wire. The rare-earth silicon-magnesium alloy contains ≥30% La+Ce rare-earth elements and 10% magnesium. The nano-alumina powder has a particle size of 40nm. The activation medium is a mixture of 60g calcium oxide, 2g sodium carbonate, 7g sodium aluminate, 2g zinc oxide, 2g calcium fluoride, and 1g sodium fluoride.

[0019] Example 2 A method for proportioning highly conductive phosphorus-containing molten iron includes the following steps: S1. The ferrophosphorus blocks and additives are mixed and then smelted in a medium-frequency furnace. The particle size of the additives is 5μm, the smelting temperature is 1220℃, and the mixture is stirred continuously during the smelting process. The weight of the additives is 0.1% of the weight of the ferrophosphorus raw material. S2. Injecting an additive—a rare earth-transition metal composite cored wire with a mass ratio of 1:2—and an activation medium into the molten iron in the medium-frequency furnace, using nitrogen as the carrier gas at a flow rate of 1.5 m³ / h. 3 / min, the weight of the additive is 0.5% of the weight of the phosphorus pig iron, and the smelting continues to obtain highly conductive phosphorus pig iron; S3. The molten pig iron in the phosphorus state is subjected to two slag removal treatments, and the temperature is reduced to 1150℃ before being poured out of the furnace. After casting, it is cooled to 1000℃ at a rate of 25℃ / min, and then cooled to room temperature at a rate of 3℃ / min to obtain the finished pig iron.

[0020] The additives, by weight percentage, are: 5% copper, 45% aluminum, 15% zinc, 20% silicon, and 15% columnar graphite.

[0021] The rare earth-transition metal composite cored wire has an iron-clad core. The core consists of a rare earth silicon-magnesium alloy and nano-alumina powder in a 5:1 mass ratio. The core diameter accounts for 60% of the total diameter of the cored wire. The rare earth silicon-magnesium alloy contains ≥30% La+Ce rare earth elements and 8% magnesium. The nano-alumina powder has a particle size of 20nm. The activation medium is a mixture of 40g calcium oxide, 1g sodium carbonate, 5g sodium aluminate, 1g zinc oxide, 1g calcium fluoride, and 0.5g sodium fluoride.

[0022] Example 3 A method for proportioning highly conductive phosphorus-containing molten iron includes the following steps: S1. The ferrophosphorus blocks and additives are mixed and then smelted in an induction furnace. The particle size of the additives is 20μm, the smelting temperature is 1280℃, and the mixture is stirred continuously during the smelting process. The weight of the additives is 0.2% of the weight of the ferrophosphorus raw material. S2. Injecting additives—rare earth-transition metal composite cored wire with a mass ratio of 1:5 and activation medium into the molten iron in the medium-frequency furnace, using nitrogen as the carrier gas with a flow rate of 2m³ / h. 3 / min, the weight of the additive is 1.2% of the weight of the phosphorus pig iron, and the smelting continues to obtain highly conductive phosphorus pig iron; S3. The molten pig iron in the phosphorus state is subjected to slag removal treatment three times, the temperature is reduced to 1200℃ and then poured out of the furnace. After casting, it is cooled to 1050℃ at a rate of 35℃ / min, and then cooled to room temperature at a rate of 8℃ / min to obtain the finished pig iron.

[0023] The additives, by weight percentage, are: 12% copper, 50% aluminum, 5% zinc, 10% silicon and 23% columnar graphite.

[0024] The rare-earth-transition-metal composite cored wire has an iron-clad core. The core consists of a rare-earth silicon-magnesium alloy and nano-alumina powder in a 7:1 mass ratio. The core diameter accounts for 70% of the total diameter of the cored wire. The rare-earth silicon-magnesium alloy contains ≥30% La+Ce rare-earth elements and 12% magnesium. The nano-alumina powder has a particle size of 50nm. The activation medium is a mixture of 70g calcium oxide, 3g sodium carbonate, 8g sodium aluminate, 3g zinc oxide, 3g calcium fluoride, and 2g sodium fluoride.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that no additives or auxiliaries are added, and the ratio of C, Si, Mn, P, and S is manually adjusted.

[0026] Comparative Example 2 The difference between this comparative example and Example 1 is that no additives are added.

[0027] Comparative Example 3 The difference between this comparative example and Example 1 is that no additives are added.

[0028] Comparative Example 4 The difference between this comparative example and Example 1 is that the additive is a rare earth-transition metal composite cored wire.

[0029] Comparative Example 5 The difference between this comparative example and Example 1 is that the additive is an activation medium.

[0030] Test case Following the methods of the examples and comparative examples, three independent batches of phosphorus pig iron were prepared using the same smelting process. Samples of the smelted pig iron were taken and analyzed to determine the phosphorus (P) content. The results are as follows: Table 1

[0031] As shown in Table 1, the P element content in the embodiment fluctuates by approximately ±0.03%, while the P element content in the comparative example fluctuates by approximately ±0.2%. This indicates that the method of the present invention can effectively reduce the fluctuation range of P element content in pig iron molten iron, thereby reducing the fluctuation range of resistivity in pig iron molten iron.

[0032] The performance of the finished phosphorus pig iron products from the examples and comparative examples was compared, and the results are as follows: Table 2

[0033] As shown in Table 2, after comparative testing, the guide rod assembly of the embodiment exhibits lower average pressure drop, lower coefficient of thermal expansion, and lower energy consumption, while maintaining a longer anode assembly replacement cycle. This indicates that the method of the present invention can better improve the conductivity and mechanical properties of pig iron phosphate, thereby enhancing the operational stability of the electrolytic cell.

[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of proportioning high-conductivity phosphorus pig iron melt, characterized in that, The method comprises the following steps: S1. mixing the phosphorus pig iron raw material and the additive and then placing them in a medium frequency furnace for smelting; S2. continuously smelting by spraying the additive into the phosphorus pig iron melt in the medium frequency furnace, thereby obtaining the high-conductivity phosphorus pig iron melt; The additive comprises, by weight percentage, 5-15% copper, 40-50% aluminum, 5-15% zinc, 10-20% silicon and 15-25% columnar graphite; and the additive comprises a rare earth-transition metal composite cored wire and an activating medium in a mass ratio of 1:2-5.

2. The high-conductivity phosphorous pig iron water proportioning method according to claim 1, characterized by, The weight of the additive is 0.1-0.2% of the weight of the phosphorus pig iron raw material, and the weight of the additive is 0.5-1.2% of the weight of the phosphorus pig iron melt.

3. The high-conductivity phosphorous pig iron water proportioning method according to claim 1, characterized by, The rare earth-transition metal composite cored wire is coated with iron sheet, and the core comprises a rare earth silicon magnesium alloy and nano alumina powder in a mass ratio of 5-7:

1.

4. The high-conductivity phosphorous pig iron water proportioning method according to claim 3, characterized by, The diameter of the core accounts for 60-70% of the total diameter of the cored wire, the content of rare earth elements La+Ce in the rare earth silicon magnesium alloy is greater than or equal to 30%, the content of magnesium is 8-12%, and the particle size of the nano alumina powder is 20-50 nm.

5. The high-conductivity phosphorous pig iron water proportioning method according to claim 1, characterized in that, The activating medium comprises, by weight fraction, 40-70 parts of calcium oxide, 1-3 parts of sodium carbonate, 5-8 parts of sodium metaaluminate, 1-3 parts of zinc oxide, 1-3 parts of calcium fluoride and 0.5-2 parts of sodium fluoride.

6. The high-conductivity pig iron water proportioning method according to claim 1, characterized by, The particle size of the additive is 5-20 μm.

7. The high-conductivity pig iron water proportioning method according to claim 1, characterized by, In S2, nitrogen gas is used as the carrier gas for spraying, and the carrier gas flow rate is 1.5-2 m 3 / min.

8. The high-conductivity pig iron water proportioning method according to claim 1, characterized by, The smelting temperature is 1220-1280 ℃, and the smelting process is continuously stirred; the phosphorus pig iron melt in a molten state is subjected to 2-3 times of slagging treatment, the temperature is reduced to 1150-1200 ℃, and then the furnace is tapped and poured.

9. The high-conductivity phosphorous pig iron water proportioning method according to claim 8, characterized in that, After pouring and forming, the temperature is cooled to 1000-1050 ℃ at a rate of 25-35 ℃ / min, and then cooled to room temperature at a rate of 3-8 ℃ / min.

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