A method for producing high-purity low-oxygen-content sponge iron by reduction

Abstract

This invention relates to the field of ferrous metallurgy technology and discloses a method for the reduction production of high-purity, low-oxygen-content sponge iron. The method includes: feeding pellets and reducing materials into a rotary kiln for preheating and forming a metallic iron shell on the surface; pulse-injecting a composite reducing liquid into a high-temperature solid-phase bed in a deep reduction zone; using a rotary encoder for feedback to perform dynamic phase-controlled injection, achieving gas-liquid linkage control and nitrogen cooling maintenance; and collecting the finished product through end-stage homogenization, cooling, and magnetic separation. Ammonia gas generated by the pyrolysis of the composite reducing liquid penetrates the metal layer for deep reduction, and a chemical shielding layer is constructed using boron-carbon bonds formed on the microporous surface of the iron matrix. This invention effectively improves the metallization rate of sponge iron, significantly inhibits secondary oxidation of the finished product during kiln exit and storage, and solves the technical problem of high and unstable residual oxygen content in sponge iron.

Description

Technical Field

[0001] This invention relates to the field of ferrous metallurgy technology, specifically to a method for the reduction production of high-purity, low-oxygen-content sponge iron. Background Technology

[0002] Sponge iron, as a high-quality diluent for electric arc furnace steelmaking and a major form of direct reduced iron, occupies an important position in modern metallurgical industry. Currently, the coal-based rotary kiln method is one of the mainstream processes for producing sponge iron. Its main process involves feeding iron concentrate pellets, reducing coal, and flux into a horizontally rotating rotary kiln in a specific ratio, utilizing the reducing atmosphere generated by coal combustion to reduce the solid-phase pellets at high temperatures. With the increasing demands for raw material purity in the steel industry, further improving the metallization rate of sponge iron and reducing residual oxygen content has become a core direction in optimizing the rotary kiln production process.

[0003] Traditional coal-based rotary kiln reduction processes face severe mass transfer resistance problems in actual operation. Since the reduction reaction mainly relies on the diffusion of reducing gases from the kiln interior into the solid bed, once the pellet surface is reduced to a dense metallic iron shell in the preheating and initial reduction zones, this metallic layer significantly hinders the penetration of the external reducing medium into the pellet core. Under these limited diffusion kinetics, residual iron oxide inside the pellets is difficult to completely reduce, resulting in a limited overall metallization rate in the final product. Simultaneously, the high carbon dioxide concentration inside the bed and the presence of a locally weak oxidizing atmosphere further inhibit the deep equilibrium of the reduction reaction.

[0004] The chemical instability of sponge iron after production is another bottleneck affecting product quality. Due to the highly developed microporous structure and enormous specific surface area of ​​the elemental iron formed during the reduction process, sponge iron exhibits extremely high chemical reactivity. When the reduction product exits the high-temperature rotary kiln homogenization section and comes into contact with trace amounts of oxygen or water vapor during subsequent indirect cooling, magnetic separation, and storage and transportation stages, it is highly susceptible to violent secondary oxidation reactions. This oxidation not only directly leads to excessive residual oxygen content in the finished product but also causes degradation of the metallization rate due to exothermic oxidation, and even poses a safety hazard of spontaneous combustion. Existing processes often struggle to address this activity inhibition problem at the microstructural level, limiting the large-scale application of high-purity, low-oxygen-content sponge iron. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a reduction production method for high-purity, low-oxygen-content sponge iron. This method solves the problems of long diffusion paths and low mass transfer efficiency of reducing gas during the reduction process in coal-based rotary kilns, which leads to incomplete reduction inside the pellets. It also addresses the issue that the produced sponge iron is prone to secondary oxidation during high-temperature kiln exit and cooling, resulting in high oxygen content and unstable metallization rate in the finished product.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for producing high-purity, low-oxygen-content sponge iron by reduction, comprising the following steps: S1. Material preparation and feeding: Iron concentrate oxide pellets, reducing coal and flux are mixed and fed into a coal-based rotary kiln. In the preheating zone and initial reduction zone, the surface of the pellets is reduced to generate a metallic iron shell. S2. Deep reduction mass transfer enhancement: When the material reaches the deep reduction zone, control the spray guns evenly distributed along the kiln wall to pulsely inject composite reducing liquid into the high-temperature solid bed inside the kiln; S3. Dynamic phase control injection control: Based on the angle feedback of the rotary encoder, the spray gun is controlled to perform gas-liquid linkage action. When the spray gun rotates with the kiln body to the angle range where it is submerged in the material bed, the liquid channel and nitrogen channel are opened. When the spray gun rotates to the angle range where it is detached from the material bed and exposed to free space, the liquid supply is cut off and the nitrogen channel is kept open to continuously spray room temperature nitrogen into the kiln. S4. Homogenization and Cooling Separation: After the material travels to the kiln head homogenization section of the rotary kiln for end-of-line heat preservation and reduction, the reaction products are discharged and indirectly cooled to below 100°C. The coal ash and desulfurization by-products are removed by magnetic separation, and the sponge iron product is collected.

[0007] By adopting the above technical solution, the deep directional injection of the reducing medium into the material bed is achieved by utilizing the relative phase change between the spray gun and the material bed during the rotation of the rotary kiln. This pulse injection method enables the composite reducing liquid to vaporize and expand instantaneously under high temperature conditions, changing the traditional reduction process that relies solely on the free diffusion of the kiln atmosphere, and forcibly establishing a micro-positive pressure reduction environment in the gaps between the pellets.

[0008] The specific reaction process is described step by step as follows: The urea component in the composite reducing solution undergoes a pyrolysis reaction at high temperatures (>500℃), producing a highly permeable reducing gas: (NH2)2CO→NH3+HNCOHNCO+H2O→NH3+CO2; The generated ammonia gas has extremely strong diffusion capabilities, allowing it to penetrate the metallic iron shell formed in S1 and enter the center of the pellet, where it undergoes a heterogeneous reduction reaction with the residual iron oxide: 3Fe x Oᵧ+2yNH3→3xFe+yN2+3yH2O; This process rapidly releases active hydrogen atoms within the deep reduction zone, forcibly driving the reduction reaction toward metallization, significantly improving production efficiency. The temperature of the deep reduction zone is 900℃-950℃.

[0009] Preferably, the composite reducing solution is made from raw materials comprising the following weight percentages: 20%–25% industrial urea, 1.0%–3.0% polyethylene glycol with a number average molecular weight of 800–1000, 0.05%–0.15% industrial boric acid, and the balance being deionized water.

[0010] By employing the above technical solution, polyethylene glycol, as a nonionic surfactant, effectively reduces the surface tension of the reducing liquid during spraying, ensuring its rapid wetting and adsorption onto the surface of the high-temperature bed particles. The interfacial reaction between industrial boric acid and the iron matrix under a reducing atmosphere is one of the core mechanisms of this invention.

[0011] The specific modification process is as follows: In the reduction zone, boron atoms enter the lattice defects of iron atoms and form chemically stable boron-carbon bonds on the surface of the micropores of sponge iron: B₂O₃ + 3C + 2Fe → 2FeB + 3CO; This chemical structure exhibits characteristic peaks in the 189eV-191eV range of the B1s orbital in X-ray photoelectron spectroscopy. These stable chemical bonds effectively occupy the active sites on the surface of the sponge iron, constructing a chemical barrier that prevents oxygen atoms from penetrating into the iron matrix during subsequent homogenization, removal, and cooling stages, thus solving the industry-wide problem of secondary oxidation of sponge iron.

[0012] Preferably, before S1, a preparation step of the composite reducing solution is also included: at an environment of 20℃~30℃, each raw material is added to a mixing tank equipped with a mechanical stirring device, the stirring speed is controlled at 100rpm~300rpm, and the mixture is continuously stirred for 30min~60min until the solution is homogeneous.

[0013] By adopting the above technical solution, the determined preparation parameters ensure complete miscibility of high-concentration urea with polyethylene glycol and boric acid in the aqueous phase. This stable homogeneous fluid system avoids solute precipitation and blockage during high-temperature intermittent operation of the pulse nozzle, ensuring the continuous operational stability of the system.

[0014] Preferably, in step S2, the consumption of the composite reducing liquid is 15kg to 20kg per ton of finished sponge iron; the spray gun is a coaxial dual-channel radial spray gun, and the liquid supply pressure of its central inner tube is 1.5MPa to 2.0MPa.

[0015] By adopting the above technical solution, maintaining the liquid supply pressure is to ensure that the reducing liquid can overcome the static resistance generated by the dynamic tumbling bed, so that the reducing medium can achieve deep penetration in the radial direction, thereby ensuring the uniformity of the reduction effect in the entire cross-sectional direction.

[0016] Preferably, in step S3, the angle range of the spray gun immersing in the material bed is from the 4 o'clock to the 8 o'clock position of the kiln body cross-section; the angle range of the spray gun detaching from the material bed and being exposed in free space is from the 8 o'clock position of the kiln body cross-section in the direction of rotation to the 4 o'clock position.

[0017] By employing the above technical solution and utilizing rotary encoder feedback for precise phase control, it is ensured that the injection action occurs only during the material coverage period. This method significantly reduces the ineffective escape of reducing gas, maximizing the utilization rate of the reducing medium.

[0018] Preferably, in step S3, when the spray gun is submerged in the material bed and the gas-liquid linkage is activated, the nitrogen pressure is 0.1 MPa to 0.2 MPa; when the spray gun is exposed to free space and sprays room temperature nitrogen, the nitrogen pressure is reduced to 0.05 MPa to 0.1 MPa; and the room temperature nitrogen is forced to flow through the heat exchange tube of the external control valve to cool the control valve before entering the spray gun, and the preheated nitrogen is then sprayed into the kiln through the outer annular channel of the spray gun.

[0019] By adopting the above technical solution, the dynamic switching of nitrogen pressure enables online maintenance of the nozzles. During the non-injection phase, low-pressure nitrogen can continuously purge, preventing corrosion from dust inside the kiln. Simultaneously, by utilizing ambient temperature nitrogen to absorb heat from external pneumatic control valves, the system's waste heat is recycled, ensuring the operational lifespan of the actuators in high-temperature environments.

[0020] Preferably, in step S1, the mixing mass ratio of the iron concentrate oxide pellets, reducing coal, and flux is 100:30 to 50:3 to 10; the iron concentrate oxide pellets have a particle size of 8 mm to 16 mm, the reducing coal has a particle size of 1 mm to 5 mm, and the flux is limestone or dolomite with a particle size of 1 mm to 3 mm.

[0021] By adopting the above technical solution, this material gradation can maintain the balance of air permeability resistance during the turning process of the material bed. The particle size difference between the pellets and the reducing coal ensures the effective transfer of heat to the center of the material bed and provides the necessary diffusion channels for the reducing gas generated by the reducing liquid.

[0022] Preferably, the center temperature of the solid bed in the deep reduction zone is set to 900℃~950℃; the temperature of the homogenization section at the kiln head of the rotary kiln is controlled at 1000℃~1050℃ for end-stage heat preservation and reduction.

[0023] By adopting the above technical solution, a segmented temperature control strategy combined with chemical reduction enhancement methods is used to avoid premature softening and pore sealing of the pellet surface due to early high temperatures. Increasing the temperature in the homogenization stage facilitates the use of the reducing components that have penetrated in the early stage to complete the final deoxidation, making the internal structure of the product more compact.

[0024] Preferably, the metallization rate of the sponge iron product collected in S4 is ≥92wt%, the residual oxygen content is ≤0.8wt%, and the total boron element mass fraction is 28.1mg / kg~45.7mg / kg.

[0025] By adopting the above technical solution, the sponge iron produced by this process exhibits significant antioxidant stability. The boron-carbon bond signal confirmed by X-ray photoelectron spectroscopy is the key physical basis for determining the reduction depth and the product's antioxidant performance.

[0026] This invention provides a method for the reduction production of high-purity, low-oxygen-content sponge iron. It has the following beneficial effects: 1. This invention utilizes a controlled spray gun to pulse-inject a composite reducing liquid containing urea into a high-temperature solid-phase bed within a deep reduction zone. The instantaneous heating and flash evaporation of the reducing liquid within the bed's voids creates a locally reducing micro-positive pressure environment between the pellet particles. The ammonia gas generated by pyrolysis has the ability to penetrate the metallized layer on the pellet surface and directly enter the center of the pellet to undergo a heterogeneous reduction reaction with residual iron oxide, changing the traditional rotary kiln reduction mode that relies solely on atmospheric diffusion within the kiln. This deep-directed injection method solves the mass transfer resistance problem during the reduction process, ensuring thorough deep reduction of the material while shortening the reaction time.

[0027] 2. This invention introduces a specific proportion of industrial boric acid into the composite reducing solution, enabling boron atoms to participate in the interfacial reaction of the iron lattice under reducing conditions, forming chemically stable boron-carbon bonds on the surface of the micropores inside the sponge iron. This microstructure occupies the active sites on the iron matrix surface, forming a chemical shielding layer that blocks oxygen atom penetration, effectively inhibiting secondary oxidation reactions of the sponge iron during homogenization, kiln cooling, and subsequent storage and transportation. This chemical modification method solves the problem of oxygen content fluctuations caused by excessively high activity in sponge iron, ensuring the physical property stability of the finished product with low oxygen content.

[0028] 3. This invention achieves dynamic phase control of the spray gun through angle feedback from a rotary encoder, and combines this with the gas-liquid linkage logic of the nitrogen channel to ensure the continuous operating life of the spraying system in high-temperature dust environments. When the spray gun rotates with the kiln body to the non-spraying zone, ambient temperature nitrogen is used to continuously purge the nozzle and simultaneously flow through the external control valve for heat exchange and cooling. This prevents the high-temperature powder from clogging and corroding the pipelines, and also reduces the heat loss of the pneumatic actuators. This phase control and fluid self-cooling scheme improves the reliability of the internal spraying device of the rotary kiln and reduces the frequency of equipment maintenance. Attached Figure Description

[0029] Figure 1 This is a biaxial curve showing the comparison between the hydrogen concentration in the kiln gas and the operating temperature of the valve body according to the present invention. Figure 2 This is a biaxial curve comparing the microscopic boron element retention and electron energy spectrum binding energy characteristics of the finished sponge iron product of the present invention. Figure 3 This is a biaxial curve graph showing the comparison data of the core physicochemical indicators and residual oxygen content of the sponge iron finished product of the present invention. Figure 4 This is a biaxial curve showing the comparison between the coking frequency of the spray gun and the fault-free life of the actuator in this invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0032] The main chemical phase of the iron concentrate oxide pellets is ferric oxide, with the molecular formula Fe2O3 and CAS number 1309-37-1. The physical particle size of the pellets ranges from 8 mm to 16 mm.

[0033] Anthracite or bituminous coal is mainly composed of carbon, with the molecular formula C and CAS number 7440-44-0. The fixed carbon mass fraction is greater than or equal to 70 wt%, the volatile matter mass fraction is 8 wt% to 15 wt%, and the particle size range after crushing and screening is 1 mm to 5 mm.

[0034] Limestone is mainly composed of calcium carbonate, with the molecular formula CaCO3 and CAS number 471-34-1, and a particle size range of 1 mm to 3 mm; dolomite is mainly composed of calcium magnesium carbonate, with the molecular formula CaMg(CO3)2 and CAS number 16389-88-1, and a particle size range of 1 mm to 3 mm.

[0035] Industrial urea has the chemical name of carbonamide, the molecular formula of CO(NH2)2, the CAS number of 57-13-6, and a purity of ≥98%.

[0036] Polyethylene glycol is a nonionic, water-soluble homopolymer with the molecular formula HO(CH2CH2O)nH and CAS number 25322-68-3, where n is the average degree of polymerization of ethylene oxide and the repeating units are arranged in a homopolymer state. The number-average molecular weight of the polyethylene glycol used in this invention is 800 to 1000.

[0037] Industrial boric acid has the chemical name of orthoboric acid, the molecular formula of which is H3BO3, the CAS number of which is 10043-35-3, and the purity of which is greater than or equal to 99.5%.

[0038] Preparation Example 1: This preparation example provides a method for preparing a composite reducing solution, including the following steps: In a mixing vessel equipped with a mechanical stirrer at an ambient temperature of 20℃, 20 wt% industrial urea, 1.0 wt% polyethylene glycol with a number average molecular weight of 800, 0.05 wt% industrial boric acid, and 78.95 wt% deionized water were added sequentially. The mechanical stirrer was turned on and the stirring speed was controlled at 100 rpm for 60 minutes until the solution became a clear, homogeneous phase without any solid suspension. The pH value of the system was measured and found to be slightly alkaline, thus obtaining the desired composite reducing solution.

[0039] Preparation Example 2: This preparation example provides a method for preparing a composite reducing solution, including the following steps: In a mixing vessel equipped with a mechanical stirrer at an ambient temperature of 25℃, 22.5 wt% industrial urea, 2.0 wt% polyethylene glycol with a number average molecular weight of 800, 0.1 wt% industrial boric acid, and 75.4 wt% deionized water were added sequentially. The mechanical stirrer was turned on and the stirring speed was controlled at 200 rpm for 45 min until the solution was a clear homogeneous phase without any solid suspension. The pH value of the system was measured to be slightly alkaline, thus obtaining the desired composite reducing solution.

[0040] Preparation Example 3: This preparation example provides a method for preparing a composite reducing solution, including the following steps: In a mixing vessel equipped with a mechanical stirrer at an ambient temperature of 30℃, 25 wt% industrial urea, 3.0 wt% polyethylene glycol with a number average molecular weight of 1000, 0.15 wt% industrial boric acid, and 71.85 wt% deionized water were added sequentially. The mechanical stirrer was turned on and the stirring speed was controlled at 300 rpm for 30 minutes until the solution was a clear homogeneous phase without any solid suspension. The pH value of the system was measured to be slightly alkaline, thus obtaining the desired composite reducing solution.

[0041] Preparation Example 4: This preparation example provides a method for preparing a composite reducing solution, including the following steps: In a mixing vessel equipped with a mechanical stirrer at an ambient temperature of 25℃, 22.5 wt% industrial urea, 2.0 wt% polyethylene glycol with a number average molecular weight of 1000, 0.1 wt% industrial boric acid, and 75.4 wt% deionized water were added sequentially. The mechanical stirrer was turned on and the stirring speed was controlled at 200 rpm for 45 minutes until the solution was a clear, homogeneous phase without any solid suspension. The pH value of the system was measured and found to be slightly alkaline, thus obtaining the desired composite reducing solution.

[0042] Example 1: This embodiment provides a method for producing high-purity, low-oxygen-content sponge iron by reduction, including the following steps: Iron concentrate oxide pellets with a particle size of 8mm to 16mm, anthracite with a particle size of 1mm to 5mm, and limestone with a particle size of 1mm to 3mm are mixed in a predetermined metallurgical ratio and then fed into a coal-based rotary kiln with a length-to-diameter ratio of 15:1 via a continuous feeder at the kiln tail. Under the action of the rotary kiln's rotation and inclination, the material moves towards the kiln head. In the preheating zone and initial reduction zone, the ambient temperature gradually rises from room temperature to 850℃, and an initial dense outer shell of metallic iron is formed on the surface of the pellets.

[0043] When the material reaches the deep reduction zone, which is 60% of the axial length from the kiln tail feed end, the center temperature of the solid bed in this area is set to 920℃. Based on feedback from the absolute value rotary encoder, the control system controls the coaxial dual-channel radial spray guns evenly distributed along the kiln wall to perform pneumatic-hydraulic linkage operation. When the spray guns, moving with the kiln body, are completely submerged in the high-temperature solid bed at the bottom between the 4 o'clock and 8 o'clock positions, the system triggers the external high-frequency pneumatic angle seat valve. The central inner tube pulses the composite reducing liquid obtained in Preparation Example 2 into the bed at a pressure of 1.8 MPa. The consumption of the composite reducing liquid is controlled at 18 kg per ton of product. Simultaneously, high-pressure room-temperature nitrogen gas at a pressure of 0.15 MPa is introduced into the outer annular channel to assist in atomizing and shearing the liquid.

[0044] When the spray gun is rotated to the 8 o'clock to 4 o'clock position and exposed to the high-temperature free space above, the system immediately cuts off the supply of composite reducing liquid to the central inner tube. The outer annular channel remains open and is supplied with room temperature cold nitrogen gas with a pressure reduced to 0.08MPa to maintain a slightly positive pressure purging state. This part of room temperature cold nitrogen gas is forced to flow through the heat exchange tube outside the pneumatic angle seat valve for fluid self-cooling before entering the spray gun.

[0045] The material travels to the kiln head homogenization section, where the temperature is controlled at 1025℃ for end-stage heat preservation. Subsequently, the reaction products fall into a closed rotary cooling cylinder, where the solid material is cooled to below 100℃ under indirect cooling. After multi-stage magnetic separation to remove coal ash and desulfurization byproducts, high-purity sponge iron is collected as the final product.

[0046] Example 2: This embodiment provides a method for producing high-purity, low-oxygen-content sponge iron by reduction, including the following steps: Iron concentrate oxide pellets with a particle size of 8mm to 16mm, bituminous coal with a particle size of 1mm to 5mm, and dolomite with a particle size of 1mm to 3mm are mixed in a predetermined metallurgical ratio and then fed into a coal-based rotary kiln with a length-to-diameter ratio of 18:1 via a continuous feeder at the kiln tail. Under the action of the rotary kiln's rotation and inclination, the material moves towards the kiln head. In the preheating zone and initial reduction zone, the ambient temperature gradually rises from room temperature to 850℃, and an initial dense outer shell of metallic iron is formed on the surface of the pellets.

[0047] When the material reaches the deep reduction zone, which is 50% of the axial length from the kiln tail feed end, the center temperature of the solid bed in this area is set to 900℃. Based on feedback from the absolute value rotary encoder, the control system controls the coaxial dual-channel radial spray guns evenly distributed along the kiln wall to perform pneumatic-hydraulic linkage operation. When the spray guns, moving with the kiln body, are completely submerged in the high-temperature solid bed at the bottom (between the 4 o'clock and 8 o'clock positions), the system triggers the external high-frequency pneumatic angle seat valve. The central inner tube pulses the composite reducing liquid obtained in Preparation Example 1 into the bed at a pressure of 1.5 MPa. The consumption of the composite reducing liquid is controlled at 15 kg per ton of product. Simultaneously, high-pressure room-temperature nitrogen gas at a pressure of 0.1 MPa is introduced into the outer annular channel to assist in atomizing and shearing the liquid.

[0048] When the spray gun is rotated to the 8 o'clock to 4 o'clock position and exposed to the high-temperature free space above, the system immediately cuts off the supply of composite reducing liquid to the central inner tube. The outer annular channel remains open and is supplied with room temperature cold nitrogen gas with a pressure reduced to 0.05MPa to maintain a slightly positive pressure purging state. This part of room temperature cold nitrogen gas is forced to flow through the heat exchange tube outside the pneumatic angle seat valve for fluid self-cooling before entering the spray gun.

[0049] The material travels to the kiln head homogenization section, where the temperature is controlled at 1000℃ for end-stage heat preservation. Subsequently, the reaction products fall into a closed rotary cooling cylinder, where the solid material is cooled to below 100℃ under indirect cooling. After multi-stage magnetic separation to remove coal ash and desulfurization byproducts, high-purity sponge iron is collected as the final product.

[0050] Example 3: This embodiment provides a method for producing high-purity, low-oxygen-content sponge iron by reduction, including the following steps: Iron concentrate oxide pellets with a particle size of 8mm to 16mm, anthracite with a particle size of 1mm to 5mm, and limestone with a particle size of 1mm to 3mm are mixed in a predetermined metallurgical ratio and then fed into a coal-based rotary kiln with a length-to-diameter ratio of 20:1 via a continuous feeder at the kiln tail. Under the action of the rotary kiln's rotation and inclination, the material moves towards the kiln head. In the preheating zone and initial reduction zone, the ambient temperature gradually rises from room temperature to 850℃, and an initial dense outer shell of metallic iron is formed on the surface of the pellets.

[0051] When the material reaches the deep reduction zone, which is 70% of the axial length from the kiln tail feed end, the center temperature of the solid bed in this area is set to 950℃. Based on feedback from the absolute value rotary encoder, the control system controls the coaxial dual-channel radial spray guns evenly distributed along the kiln wall to perform pneumatic-hydraulic linkage operation. When the spray guns, moving with the kiln body, are completely submerged in the high-temperature solid bed at the bottom between the 4 o'clock and 8 o'clock positions, the system triggers the external high-frequency pneumatic angle seat valve. The central inner tube pulses the composite reducing liquid obtained in Preparation Example 3 into the bed at a pressure of 2.0 MPa. The consumption of the composite reducing liquid is controlled at 20 kg per ton of product. Simultaneously, high-pressure room-temperature nitrogen gas at a pressure of 0.2 MPa is introduced into the outer annular channel to assist in atomization and shearing of the liquid.

[0052] When the spray gun is rotated to the 8 o'clock to 4 o'clock position and exposed to the high-temperature free space above, the system immediately cuts off the supply of composite reducing liquid to the central inner tube. The outer annular channel remains open and is supplied with room temperature cold nitrogen gas with a pressure reduced to 0.1MPa to maintain a slightly positive pressure purging state. This part of room temperature cold nitrogen gas is forced to flow through the heat exchange tube outside the pneumatic angle seat valve for fluid self-cooling before entering the spray gun.

[0053] The material travels to the kiln head homogenization section, where the temperature is controlled at 1050℃ for end-stage heat preservation. Subsequently, the reaction products fall into a closed rotary cooling cylinder, where the solid material is cooled to below 100℃ under indirect cooling. After multi-stage magnetic separation to remove coal ash and desulfurization byproducts, high-purity sponge iron is collected as the final product.

[0054] Example 4: This embodiment provides a method for producing high-purity, low-oxygen-content sponge iron by reduction, including the following steps: Iron concentrate oxide pellets with a particle size of 8mm to 16mm, bituminous coal with a particle size of 1mm to 5mm, and dolomite with a particle size of 1mm to 3mm are mixed in a predetermined metallurgical ratio and then fed into a coal-based rotary kiln with a length-to-diameter ratio of 15:1 via a continuous feeder at the kiln tail. Under the action of the rotary kiln's rotation and inclination, the material moves towards the kiln head. In the preheating zone and initial reduction zone, the ambient temperature gradually rises from room temperature to 850℃, and an initial dense outer shell of metallic iron is formed on the surface of the pellets.

[0055] When the material reaches the deep reduction zone, which is 60% of the axial length from the kiln tail feed end, the center temperature of the solid bed in this area is set to 920℃. Based on feedback from the absolute value rotary encoder, the control system controls the coaxial dual-channel radial spray guns evenly distributed along the kiln wall to perform pneumatic-hydraulic linkage operation. When the spray guns, moving with the kiln body, are completely submerged in the high-temperature solid bed at the bottom between the 5 o'clock and 7 o'clock positions, the system triggers the external high-frequency pneumatic angle seat valve. The central inner tube pulses the composite reducing liquid obtained in Preparation Example 4 into the bed at a pressure of 1.8 MPa. The consumption of the composite reducing liquid is controlled at 18 kg per ton of product. Simultaneously, high-pressure room-temperature nitrogen gas at a pressure of 0.15 MPa is introduced into the outer annular channel to assist in atomizing and shearing the liquid.

[0056] When the spray gun is rotated to the 7 o'clock to 5 o'clock position and exposed to the high-temperature free space above, the system immediately cuts off the supply of composite reducing liquid to the central inner tube. The outer annular channel remains open and is supplied with room temperature cold nitrogen gas with a pressure reduced to 0.08MPa to maintain a slightly positive pressure purging state. This part of room temperature cold nitrogen gas is forced to flow through the heat exchange tube outside the pneumatic angle seat valve for fluid self-cooling before entering the spray gun.

[0057] The material travels to the kiln head homogenization section, where the temperature is controlled at 1025℃ for end-stage heat preservation. Subsequently, the reaction products fall into a closed rotary cooling cylinder, where the solid material is cooled to below 100℃ under indirect cooling. After multi-stage magnetic separation to remove coal ash and desulfurization byproducts, high-purity sponge iron is collected as the final product.

[0058] Comparative Example 1: Compared with Example 1, the difference is that the rotary kiln deep reduction zone is not equipped with a coaxial dual-channel radial spray gun, and no composite reducing liquid and room temperature cold nitrogen are sprayed into the kiln. Solid reduction is carried out only by conventional coal-based materials. All other aspects are the same.

[0059] Comparative Example 2: Compared with Example 1, the difference is that polyethylene glycol was not added to the injected composite reducing solution. The original mass percentage of polyethylene glycol was made up by deionized water. That is, the composite reducing solution consists only of industrial urea, industrial boric acid and deionized water, and the rest are the same.

[0060] Comparative Example 3: Compared with Example 1, the difference is that no industrial urea was added to the injected composite reducing solution. The original mass percentage of industrial urea was made up by deionized water. That is, the composite reducing solution consists only of polyethylene glycol, industrial boric acid and deionized water, and the rest are the same.

[0061] Comparative Example 4: Compared with Example 1, the difference is that no industrial boric acid was added to the injected composite reducing solution. The original mass percentage of industrial boric acid was made up by deionized water. That is, the composite reducing solution consists only of industrial urea, polyethylene glycol and deionized water, and the rest are the same.

[0062] Comparative Example 5: Compared with Example 1, the difference is that the control system does not perform the asymmetric exposure phase gas seal operation. When the spray gun is turned to be exposed to the high temperature free space above, the outer annular channel is completely closed at the same time, and room temperature cold nitrogen is no longer introduced to maintain the micro-positive pressure purging state. All other aspects are the same.

[0063] Comparative Example 6: Compared with Example 1, the difference is that before the ambient temperature cold nitrogen enters the outer annular channel of the coaxial dual-channel radial spray gun, it is directly connected to the spray gun by the external gas supply pipeline, and is not forced to flow through the metal heat exchange tube outside the pneumatic angle seat valve for fluid self-cooling isolation. All other aspects are the same.

[0064] Test Example 1: Hydrogen Production Kinetics and Valve Self-Cooling Efficiency Test in a Gas-Solid Two-Phase Reduction Field Test objective: To verify that the chemical reaction of urea autocatalytic cracking to produce hydrogen actually occurs inside the high-temperature bed, and the cooling effect of nitrogen heat exchange under non-external water cooling conditions of the pneumatic angle seat valve.

[0065] Test method: Examples 1 to 4, as well as Comparative Examples 1, 2, 3, and 6, were selected as the observation objects under continuous operation conditions. Data collection began after the rotary kiln system entered the thermal stability period and was continuously fed for 48 hours.

[0066] A corrosion-resistant online mass spectrometer was connected to the exhaust duct at the end of the rotary kiln. The probe was inserted into the center of the duct cross-section. The sampling frequency was set to once every 10 minutes. The volume concentration of hydrogen in the kiln gas was continuously recorded for 24 hours. After removing the punctured data caused by system fluctuations, the arithmetic mean was calculated.

[0067] Contact surface thermocouples were used, with their probes tightly attached to the radiation-receiving side of the metal valve body of each group of suspended high-frequency pneumatic angle seat valves. Under the same ambient temperature and continuous spraying operation conditions, the highest equilibrium temperature of the valve body outer wall was recorded in real time over 24 hours to assess the equipment operating environment. Since Comparative Example 1 did not have a spraying system installed, temperature data was not collected.

[0068] Experimental data: Table 1: Test data on kiln gas hydrogen concentration and valve body operating temperature

[0069] in conclusion: according toFigure 1 Based on the data in Table 1, observation of the gaseous products of various process schemes reveals that in Comparative Example 1, which relies solely on conventional coal-based materials for solid-state reduction, almost no free hydrogen is detected in the exhaust gas. This aligns with the objective law that traditional carbothermic reduction reactions are dominated by carbon monoxide in the gaseous phase. When the composite reducing liquid was injected into the bed, the hydrogen concentration in Examples 1 to 4 showed a significant jump, remaining within the range of 3.68% to 4.83%. This fundamental change in gaseous composition directly confirms that the urea component in the formulation underwent in-situ pyrolysis within the high-temperature bed. Furthermore, under the catalytic effect of the nascent metallic iron surface, the pyrolysis intermediates were further rapidly decomposed into small-molecule hydrogen, successfully constructing a solid-gas two-phase reduction field with high lattice diffusion capability at the microscale.

[0070] A noteworthy phenomenon during this process is that, although Comparative Example 2, which lacked polyethylene glycol and also contained sufficient urea, had a final detected hydrogen concentration of only 1.37%, far lower than the levels of the other examples. The reason for this drastically different hydrogen production efficiency is that when pure aqueous solution comes into contact with a high-temperature bed, a vapor barrier film easily forms due to the Leidenfrost effect. Droplets cannot effectively adhere to the surface of the semi-reduced pellets, causing urea molecules to escape with the flue gas or undergo ineffective homogeneous pyrolysis before entering the mesopores of the pellets. The addition of polyethylene glycol substantially alters the high-temperature rheological kinetics of the solution, forcibly disrupting the stability of the vapor film. The droplets instantly vaporize, absorbing a large amount of latent heat to achieve microscopic cooling, maintaining the unobstructed mesopore channels, thus allowing urea to be fully catalytically decomposed by metallic iron within the channels. Comparative Example 3, lacking industrial urea, saw its hydrogen concentration drop back to near the background value, which conversely confirms that the highly active hydrogen source in the system indeed originates from this specific component.

[0071] From the perspective of equipment thermal operation, the continuous thermal radiation from the rotary kiln lining in actual industrial settings typically causes a significant increase in the surface temperature of nearby equipment. Examples 1 to 4 employ a fluid self-cooling isolation mechanism. The introduced room-temperature nitrogen gas is forced to flow through the heat exchange tube outside the pneumatic angle seat valve before entering the spray gun. Utilizing throttling expansion and convective heat transfer, the accumulated radiant heat of the valve body is removed, steadily suppressing its maximum equilibrium temperature between 83.2°C and 91.7°C. This temperature range is entirely within the safe service limits of conventional fluororubber seals, allowing the equipment to operate stably for extended periods without the need for a complex external water-cooling circulation system. In contrast, Comparative Example 6, which omits the nitrogen pre-cooling pipeline, experiences a rapid surge in the valve body temperature to 242.4°C under continuous radiation. Under such extreme temperatures, the non-metallic sealing components inside the pneumatic angle seat valve undergo irreversible thermal aging and embrittlement, inevitably leading to seal failure and equipment shutdown. This fully demonstrates the engineering necessity and effectiveness of the hardware failure prevention mechanism design in this invention.

[0072] Test Example 2: Product Microscopic Chemical Fingerprint Retention and Spectral Traceability Characteristics Test Test objective: To verify whether trace boron components are successfully retained in macroscopic sponge iron products and form boron-carbon specific chemical bond features with specific traceability identification function in solid products, so as to achieve accurate anchoring and spectroscopic detection of the product's microscopic chemical structure.

[0073] Test method: Samples of sponge iron produced during continuous and stable operation of Examples 1 to 4 and Comparative Examples 1, 2, and 4 were taken from the cooling discharge port at the end of the rotary kiln. The samples were mechanically crushed and ground until they completely passed through a 200-mesh standard sieve to obtain representative metal powder samples for testing.

[0074] Equal masses of each group of metal powder samples were weighed and thoroughly digested in an aqua regia system using a microwave digester. The digested solution was then sent to an inductively coupled plasma atomic emission spectrometer for macroscopic elemental quantitative analysis. The absolute value of the mass fraction of total boron in the system was determined and recorded.

[0075] The remaining undigested powder sample was pressed into a thin sheet using a tablet press and placed in the ultra-high vacuum analysis chamber of an X-ray photoelectron spectrometer. The sample surface was scanned using an aluminum Kα ray source. Based on the acquisition of the full spectrum signal, high-resolution spectra of the C1s and B1s orbitals were acquired. After extrapolation to calibrate the binding energy with surface contamination carbon, peak fitting was performed to extract and confirm the presence of characteristic peak signals corresponding to boron-carbon bonds in the 189 eV to 191 eV range.

[0076] Experimental data: Table 2: Boron Retention and Photoelectron Spectroscopy Data of Finished Sponge Iron

[0077] in conclusion: according to Figure 2 As shown in Table 2, the total boron content in the base material produced by the conventional coal-based direct reduction process is extremely low. Combined with the test results of Comparative Examples 1 and 4, the boron content under this traditional process background hovers only at the edge of the instrument detection limit of 1 mg / kg to 2 mg / kg. X-ray photoelectron spectroscopy naturally cannot capture any meaningful boron orbital signals at this concentration. When industrial boric acid was introduced into the composite reducing solution formulation, the total boron mass fraction in the sponge iron products of Examples 1 to 4 steadily increased to between 28.1 mg / kg and 45.7 mg / kg. The significant change in macroscopic physicochemical data directly confirms that trace inorganic components, even after undergoing harsh kiln conditions of nearly 1000 degrees Celsius roasting accompanied by strong airflow, can still penetrate deep into the pores and effectively remain in the metallic solid phase product.

[0078] Exploring the microscopic chemical bond state information hidden behind the macroscopic element enrichment reveals that all samples exhibit significant and stable characteristic peaks in the binding energy range of 189.4 eV to 189.7 eV in the B1s orbital. This energy shift characteristic belongs to a typical boron-carbon covalent structure. The generation mechanism of this heteroatomic doping phenomenon originates from a complex microphase transition process occurring inside the high-temperature bed. After droplets containing orthoboric acid and polyethylene glycol penetrate into the nascent metal micropores, the orthoboric acid is dehydrated upon heating and transformed into molten boron oxide, which spreads along the inner wall of the pores. The polyethylene glycol macromolecules undergo in-situ deep carbonization within the oxygen-deficient, high-temperature, closed pores, generating highly thermodynamically active amorphous microcarbons. The molten boron oxide then undergoes a reduction doping reaction with these nascent active carbons at the solid-liquid interface, firmly anchoring the free boron element in the carbon framework to form a microscale doped carbon structure.

[0079] To verify the rigor of this symbiotic mechanism, the test results of Comparative Example 2 provide a crucial reference. Although this group was also sprayed with a reducing solution containing the same concentration of boric acid, the system completely lost the highly active in-situ carbon source provided by the polymer due to the removal of polyethylene glycol in the formulation. The final product actually detected not only showed a significant decrease in total boron retention to 15.6 mg / kg, but more importantly, its B1s orbital main peak was freed to an oxidation state position of 192.5 eV, exhibiting the characteristics of purely physical residual boron-oxygen bonds without forming boron-carbon bonds with specific properties. There is an extremely high reaction kinetic barrier between the physical residue of trace elements and the formation of specific chemical covalent bonds. This chemical microstructure, which depends entirely on the in-situ coupling of a specific polymer carbon source and trace boron source in a reducing metallurgical microenvironment, is difficult to replicate at low cost or remove industrially using conventional post-processing physical mixing methods. As a highly exclusive chemical fingerprint identifier, its ability to be accurately identified by modern spectroscopic equipment essentially endows the sponge iron produced by this process with a highly specific product label, constructing a stable and traceable microscopic feature system.

[0080] Test Example 3: Testing the effect of core physicochemical properties of metallurgy on deep mass transfer enhancement Test objective: To verify the synergistic irreplaceability of polyethylene glycol and urea in the composite reducing solution, and to evaluate the actual effectiveness of this scheme in breaking the thermodynamic dead zone of mesoporous closure and deep mass transfer bottleneck caused by high-temperature sintering.

[0081] Test method: Sponge iron products produced under continuous and stable operation of the rotary kiln system were collected. The samples included Examples 1 to 4, and Comparative Examples 1 to 4. Each batch sample was approximately 5 kg. The samples were subjected to multi-stage crushing using a jaw crusher and a vibratory mill, and the samples were reduced to quarters using the quartering method to ensure that all powders passed through a 100-mesh standard sieve to eliminate macroscopic segregation.

[0082] The potassium dichromate titration method was used to determine the total iron mass fraction and metallic iron mass fraction in the sample. A quantitative sample was weighed and placed in an Erlenmeyer flask. The metallic iron was selectively dissolved and separated by adding a mixed solution of ferric chloride and sodium acetate at a specific temperature. The metallic iron content was calculated by titration. Subsequently, another sample was subjected to total iron digestion titration. The metallization rate of the product was calculated based on the mass ratio of metallic iron to total iron.

[0083] The residual oxygen content of the sample was determined using an inert gas melting-infrared absorption spectrometer. A quantitative amount of powder sample was placed in a high-purity graphite crucible and pulsed-heated to melt it in a helium carrier gas environment. The combined oxygen in the sample reacted with graphite carbon to generate carbon monoxide and carbon dioxide. The mixed gas was then carried into the infrared detection cell along with the carrier gas to measure the absorbance, thereby determining the mass fraction of unreduced deep oxygen in the solid product.

[0084] Experimental data: Table 3: Comparative Test Data of Core Physicochemical Indicators of Sponge Iron Finished Products

[0085] in conclusion: according to Figure 3 As shown in Table 3, Comparative Example 1, which relies on coal-based materials for solid-state reduction, exhibits a significant mass transfer bottleneck in its metallurgical indicators. When the ambient temperature is above 900℃ in the deep reduction zone, the nascent metallic iron grains on the pellet surface readily undergo thermodynamically driven densification sintering. This closed physical structure directly blocks the inward diffusion path of carbon monoxide molecules and traps any remaining carbon dioxide, causing the reduction reaction to almost completely halt within this localized thermodynamic dead zone. This also explains why the metallization rate of Comparative Example 1 is only 84.31%, and the residual oxygen content is as high as 2.68%.

[0086] Examples 1 to 4, after introducing the composite reducing solution, exhibited distinctly different macroscopic metallurgical morphologies. The metallization rates of all four samples consistently exceeded the industrial high standard of 92%, while the residual oxygen content simultaneously decreased to below 0.8%. The core driving force behind this achievement stemmed from the synergistic phase transition of polyethylene glycol and urea under specific thermal conditions. This synergistic mechanism is not a simple superposition of the two components; this can be confirmed by the test results of Comparative Example 2. Although Comparative Example 2, lacking polyethylene glycol, injected an equivalent amount of urea into the bed, its metallization rate only slightly increased. In actual industrial observations, when pure aqueous solution contacts a high-temperature, red-hot bed, the Leidenfrost effect is instantly triggered, and the droplet surface is enveloped by a dense vapor barrier film, preventing wetting of the semi-reduced pellet surface. Urea molecules often undergo ineffective homogeneous pyrolysis with the high-temperature flue gas before entering the mesopores, failing to construct an effective hydrogen reduction field at the pellet core.

[0087] In contrast, the introduction of polyethylene glycol altered the surface tension and high-temperature rheological properties of the fluid, forcibly disrupting the stability of the vapor film. The latent heat absorbed during droplet adhesion and vaporization created a brief temperature gradient dislocation on the pellet surface, suppressing the local grain temperature below the sintering critical point and maintaining the unobstructed microporous channels. However, this unobstructed channel opening merely overcomes a physical bottleneck. In Comparative Example 3, where urea was removed and only polyethylene glycol was retained, the metallization rate ultimately stalled at 88.25%. This demonstrates that relying solely on the amorphous microcarbon generated from the pyrolysis of polyethylene glycol for short-range solid-phase contact reduction is still insufficient to overcome the kinetic barrier of deep deoxidation.

[0088] Only when unobstructed mesoporous channels cooperate with the highly reactive hydrogen produced by urea catalytic cracking can hydrogen, with its extremely high lattice diffusion coefficient, smoothly penetrate the dense phase to reach the core region and completely reduce the residual ferrous oxide. This two-phase reduction field, constructed by the gas-phase long-range diffusion and the in-situ carbon micro-region contact in the solid phase, constitutes the underlying logic for this scheme to overcome the bottlenecks of mass transfer and thermodynamic diffusion in traditional coal-based rotary kilns. Although Comparative Example 4, lacking industrial boric acid, showed good performance in terms of metallization rate and deoxidation index, this indicates that boric acid did not directly participate in the main deoxidation reaction. Its main role remains as a trace element in the chemical fingerprint anchoring mechanism, without interfering with the thermodynamic process of the main reduction reaction.

[0089] Test Example 4: Long-term operational stability and reliability testing of a dynamic phase-controlled fluid system Test objective: To verify the engineering reliability of the dynamic phase-controlled gas sealing mechanism and the fluid self-cooling protection mechanism under continuous harsh high-temperature conditions, and to evaluate the survival rate of the high-temperature fatigue resistance and failure prevention design during the actual industrial pilot test cycle.

[0090] Test method: A coal-based rotary kiln system in the continuous pilot production stage was selected as the hardware observation platform. The control programs and gas-liquid pipeline configurations of Examples 1 to 4 and Comparative Examples 5 to 6 were loaded into the independently operating production line. The single uninterrupted test cycle was set to 720 hours, and the feed rate and core thermal parameters were kept constant.

[0091] The operation status of the coaxial dual-channel radial spray gun is monitored by a precision flow meter and a high-frequency pressure sensor at the front end of the fluid pipeline. When the supply pressure of the central inner tube changes abnormally or the flow rate drops below the threshold, it is determined that coking and blockage have occurred inside the spray gun. On-site engineers intervene to perform manual cleaning and high-pressure backflushing. The cumulative number of blockages caused by high-temperature dust capillary backflow in each group during the entire 720-hour cycle is recorded in detail.

[0092] The mean time between failures (MTBF) of high-frequency pneumatic angle seat valves exposed to strong heat radiation outside the kiln is statistically analyzed. Daily timed and fixed-point action verification is performed. Once the valve body shows visible mechanical jamming, response time exceeding the standard setting value, or high-pressure fluid leakage caused by aging of fluororubber seals during the switching cycle, the time of this node is immediately recorded as the first failure time, and the valve body life timer for that group is terminated.

[0093] Experimental data: Table 4: Statistical data on the operational reliability of engineering equipment during the continuous pilot-scale testing period

[0094] in conclusion: according to Figure 4 According to the data in Table 4, in deep reduction conditions above 900 degrees Celsius, the high-temperature coal ash and nascent sponge iron powder inside the industrial rotary kiln exhibit extremely strong fluid-like intrusiveness under intense mechanical tumbling. Comparative Example 5, which eliminated the exposed phase gas seal operation, experienced as many as 17 instances of nozzle blockage throughout the entire test cycle. During actual on-site equipment inspections, it was observed that when the nozzle rotates with the kiln body into free space, minute negative pressure fluctuations inside the kiln instantly draw high-temperature dust into the stagnant fluid channels. This dust, along with the composite reducing liquid remaining on the pipe walls, rapidly carbonizes and hardens at high temperatures, ultimately forming a dense, cement-like coke that completely seals the spray channels. In stark contrast, the operating records of Examples 1 to 4 show that these four processes essentially achieved near-zero blockage continuous operation of the spray guns. This high hardware survival rate is directly attributed to the pure gas-phase positive pressure purging logic executed by the system in the exposed phase. The continuously supplied room-temperature cold nitrogen gas creates a rigid physical air curtain at the nozzle opening, which not only forcibly cuts off the capillary backflow path of external high-temperature dust, but also clears the residual liquid substances in the channel, eliminating the material basis for carbonization and coking from the root.

[0095] Further investigation into the thermal fatigue failure of external control actuators reveals the destructive force of high-temperature radiation on non-metallic seals in Comparative Example 6. An angle seat valve without front-end fluid self-cooling protection failed completely after only 89 hours of operation. On-site disassembly revealed severe discoloration, embrittlement, and even partial melting of its internal fluororubber main sealing ring, leading to severe internal leakage of high-pressure drive gas through the gaps. The rotary kiln surface maintains a thermal radiation environment of 200-300 degrees Celsius year-round. Traditional external water-cooling jacket solutions are not only cumbersome in terms of piping but also prone to boiling, scaling, and leakage. Examples 1 to 4 of this solution cleverly utilize the inherent cooling capacity of the process fluid, forcibly introducing ambient-temperature cold nitrogen gas into the metal heat exchange tubes outside the valve body before it enters the high-temperature kiln. Under the dual physical effects of throttling expansion and convective heat transfer, the gas continuously absorbs and carries away the accumulated radiant heat from the valve body. This self-cooling protection mechanism, built into the process flow, significantly extends the fault-free lifespan of the valve bodies in the example group to near or exceeding the pilot-scale limit of 720 hours. The preheated nitrogen gas, subsequently injected back into the kiln, also achieves lossless reuse of the system's internal enthalpy. Stable operation of the engineering equipment is a prerequisite for the industrial-scale scaling of any chemical phase change mechanism. The aforementioned hardware-related test data fully demonstrates the feasibility of implementing this combined process in harsh metallurgical environments.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing high-purity, low-oxygen-content sponge iron by reduction, characterized in that, Includes the following steps: S1. Material preparation and feeding: Iron concentrate oxide pellets, reducing coal and flux are mixed and fed into a coal-based rotary kiln. In the preheating zone and initial reduction zone, the surface of the pellets is reduced to generate a metallic iron shell. S2. Deep reduction mass transfer enhancement: When the material reaches the deep reduction zone, control the spray guns evenly distributed along the kiln wall to pulsely inject composite reducing liquid into the high-temperature solid bed inside the kiln; S3. Dynamic phase control injection control: Based on the angle feedback of the rotary encoder, the spray gun is controlled to perform gas-liquid linkage action. When the spray gun rotates with the kiln body to the angle range where it is submerged in the material bed, the liquid channel and nitrogen channel are opened. When the spray gun rotates to the angle range where it is detached from the material bed and exposed to free space, the liquid supply is cut off and the nitrogen channel is kept open to continuously spray room temperature nitrogen into the kiln. S4. Homogenization and Cooling Separation: After the material travels to the kiln head homogenization section of the rotary kiln for end-of-line heat preservation and reduction, the reaction products are discharged and indirectly cooled to below 100°C. The coal ash and desulfurization by-products are removed by magnetic separation, and the sponge iron product is collected.

2. The reduction production method of high-purity, low-oxygen-content sponge iron according to claim 1, characterized in that, The composite reducing solution is made from raw materials comprising the following weight percentages: 20%–25% industrial urea, 1.0%–3.0% polyethylene glycol with a number average molecular weight of 800–1000, 0.05%–0.15% industrial boric acid, and the balance being deionized water.

3. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 2, characterized in that, Before S1, there is also a preparation step of the composite reducing solution: at an environment of 20℃~30℃, each raw material is added to a mixing tank equipped with a mechanical stirring device, the stirring speed is controlled at 100rpm~300rpm, and the mixture is continuously stirred for 30min~60min until the solution is homogeneous.

4. The reduction production method of high-purity, low-oxygen-content sponge iron according to claim 1, characterized in that, In S2, the consumption of the composite reducing liquid is 15kg to 20kg per ton of finished sponge iron; the spray gun is a coaxial dual-channel radial spray gun, and the liquid supply pressure of its central inner tube is 1.5MPa to 2.0MPa.

5. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, In S3, the angle range of the spray gun immersing in the material bed is from 4 o'clock to 8 o'clock position of the kiln body cross-section; the angle range of the spray gun detaching from the material bed and being exposed to free space is from 8 o'clock to 4 o'clock position of the kiln body cross-section in the direction of rotation.

6. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, In S3, when the spray gun is submerged in the material bed and the gas-liquid linkage is activated, the nitrogen pressure is 0.1MPa to 0.2MPa; when the spray gun is exposed to free space and sprays room temperature nitrogen, the nitrogen pressure is reduced to 0.05MPa to 0.1MPa; and the room temperature nitrogen is forced to flow through the heat exchange tube of the external control valve to cool the control valve before entering the spray gun, and the preheated nitrogen is then sprayed into the kiln through the outer annular channel of the spray gun.

7. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, The length-to-diameter ratio of the coal-based rotary kiln is 15:1 to 20:

1.

8. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, In S1, the mixing mass ratio of the iron concentrate oxide pellets, reducing coal, and flux is 100:30 to 50:3 to 10; the particle size of the iron concentrate oxide pellets is 8 mm to 16 mm, the particle size of the reducing coal is 1 mm to 5 mm, and the flux is limestone or dolomite with a particle size of 1 mm to 3 mm.

9. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, The center temperature of the solid bed in the deep reduction zone is set to 900℃~950℃; the temperature of the homogenization section at the kiln head of the rotary kiln is controlled at 1000℃~1050℃ for end-stage heat preservation and reduction.

10. The method for producing high-purity, low-oxygen-content sponge iron by reduction according to claim 1, characterized in that, The metallization rate of the sponge iron product collected in S4 is ≥92wt%, the residual oxygen content is ≤0.8wt%, and the total boron element mass fraction is 28.1mg / kg~45.7mg / kg.

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