Method for recycling coke foam in production of reduced iron powder

Abstract

The invention relates to the technical field of metallurgical solid waste resource utilization and powder metallurgy, and discloses a method for realizing coke foam recycling in reduced iron powder production, and the method comprises the following steps: mixing, kneading and drying first-cycle coarse coke foam, dolomite powder and primary cross-linking bonding slurry to prepare a modified main reducing agent; mixing secondary circulation fine coke foam, rolled steel scale coarse powder, limestone powder and the slurry, pressing and air-drying to prepare a composite sacrificial block; the silicon carbide saggar is alternately filled with high-purity fine iron powder and a modified main reducing agent to form a bottom-layer material bed, and composite sacrificial blocks are laid on the top layer in a staggered mode; and after cooling and discharging from the kiln, stripping porous slag blocks formed by sintering at the top, and carrying out coarse crushing and magnetic separation on the material at the middle lower part to obtain a sponge iron product. Directional cyclic utilization of coke foam is achieved, mineral is utilized to absorb heat step by step to stabilize local heat load, an exhaust pressure relief path is constructed through material phase change shrinkage, sagger damage is avoided, and the impurity removal process is simplified.

Description

Technical Field

[0001] This invention relates to the fields of metallurgical solid waste resource utilization and powder metallurgy technology, specifically a method for recycling coke dust in the production of reduced iron powder. Background Technology

[0002] In the process of producing high-purity reduced iron powder using the tunnel kiln solid-phase reduction method, coke is typically used as the main reducing agent, mixed with iron concentrate and loaded into a silicon carbide crucible for high-temperature continuous reaction. After the reduction cycle, the system screens and recovers the unreacted carbon-based material. After undergoing high-temperature thermal degradation and mechanical handling and crushing, this recovered material produces a large amount of coke dust with uneven particle size. Attempts to directly recycle this coke dust in existing production sites often trigger a series of chain reaction process problems.

[0003] The recovered fine-grained coke dust with high ash content is directly added to the reaction bed. The fine particles quickly fill the gaps between the high-purity iron concentrate particles, significantly reducing the overall porosity of the bed. This deterioration in permeability directly hinders the outward diffusion of gases during the intense gas generation stage of thermal reduction. When large amounts of carbon monoxide and carbon dioxide gases are rapidly generated inside the system, the obstructed exhaust channels cause the gases to accumulate rapidly inside the silicon carbide crucible, leading to a surge in internal pressure. This can easily rupture the crucible lid seal and, in severe cases, cause structural cracks in the silicon carbide crucible itself, shortening its service life.

[0004] On the other hand, the continuous thermal reduction process in tunnel kilns is characterized by long cycles and large spans, making it difficult to maintain a balanced local heat distribution within the reaction bed. In the temperature zones where the reduction reaction occurs most intensely, the localized heat released or accumulated by the carbon-oxygen reaction can easily lead to heterogeneous over-sintering of the bottom layer of iron powder, causing it to agglomerate and lose its sponge-like porous physical activity. Simultaneously, coke dust directly mixed into the bed is highly susceptible to secondary pulverization after prolonged high-temperature roasting, and the accompanying silica and other impurities can mix with the reduced iron phase, even undergoing localized fusion. During the subsequent kiln-out crushing and separation stage, conventional physical sieving and magnetic separation equipment struggles to completely remove these deeply mixed fine ash particles, ultimately resulting in sponge iron products with excessive impurities, failing to meet the downstream application standards for high-purity iron powder.

[0005] Therefore, this invention proposes a method for recycling coke in the production of reduced iron powder to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for recycling coke dust in the production of reduced iron powder. This method solves the problems of difficulty in directly recycling coke dust at various stages in the production of reduced iron powder, the tendency for direct recycling to lead to poor permeability of the feed bed causing blockage and damage to the sagger, and the difficulties in local heat imbalance and final impurity separation during long-term thermal reduction.

[0007] To address the above problems, the present invention provides the following technical solution: This invention provides a method for recycling coke residue in the production of reduced iron powder, employing the following technical solution: A method for recycling coke residue in the production of reduced iron powder includes the following steps: S1. Mix and knead a coarse coke powder, dolomite powder and primary crosslinking adhesive slurry to allow the primary crosslinking adhesive slurry to penetrate and anchor into the pores on the surface of the coarse coke powder. Then, dry at a constant temperature to allow the surface of the coarse coke powder to undergo three-dimensional network curing and crosslinking, thus obtaining a modified main reducing agent with a moisture-proof crosslinked hard shell on the surface. S2. Mix the second-cycle fine coke powder, rolled steel scale powder, coarse limestone powder and primary cross-linking binder slurry, force-press it into flat spherical blocks and then air-dry it to obtain composite sacrificial blocks. S3. High-purity iron concentrate and the modified main reducing agent prepared in step S1 are alternately filled into the silicon carbide crucible from bottom to top to form a bottom layer material bed; composite sacrificial blocks are laid out in a staggered and tight manner on the top layer of the bottom layer material bed. S4. The silicon carbide sagger loaded with high-purity iron concentrate, modified main reducing agent and composite sacrificial block is pushed into the tunnel kiln and continuously thermally reduced according to the set temperature zone program. After the thermal reduction in the tunnel kiln is completed, the sagger is cooled and discharged from the kiln. The porous sponge-like solidified slag block formed on the top of the silicon carbide sagger due to iron lattice shrinkage and solid phase sintering is physically peeled off. The material in the lower part of the silicon carbide sagger is separated into high-purity sponge iron product after mechanical coarse crushing and magnetic separation.

[0008] By adopting the above technical solution, the present invention achieves the following reaction mechanism and technical effect: In the processing of coarse coke dust, after the primary cross-linking binder slurry enters the shallow pores of the coarse coke dust, the polymer chains undergo dehydration condensation under constant temperature drying, thereby initiating a three-dimensional network curing and cross-linking reaction. The cross-linking network physically encapsulates and anchors the pulverized free carbon particles and mineral powders on the surface of the coke dust, forming a moisture-proof cross-linked hard shell with a certain mechanical strength. This hard shell structure can block external moisture from penetrating the capillary channels inside the coarse coke dust, maintain the initial carbon potential inside the coarse coke dust, and prevent the material from pulverizing during the heating and dehydration period.

[0009] To address the problem of localized heat accumulation in tunnel kilns, this invention utilizes the endothermic decomposition mechanism of specific minerals at different temperature zones. The relevant reaction formula is: CaCO3→CaO+CO2, ΔH=+178 kJ / mol; CaMg(CO3)2→CaO+MgO+2CO2, ΔH=+302 kJ / mol; The coarse limestone powder contained in the composite sacrificial block undergoes a decomposition reaction in the preheating to the medium temperature range, absorbing surrounding heat and slowing down the heating rate of the top layer material. Subsequently, the dolomite powder adhering to the surface of the modified main reducing agent undergoes a pyrolysis endothermic reaction in the high temperature range. The above-mentioned stepwise endothermic process consumes the local excess heat, thereby forming an in-situ heat buffer mechanism and reducing the heterogeneous sintering and agglomeration rate of high-purity iron concentrate caused by local overheating.

[0010] To alleviate the accumulated gas pressure within the kiln, the composite sacrificial block undergoes a carbothermic reduction reaction with the coarse steel scale powder and the secondary circulating fine coke dust during continuous heating in the high-temperature zone. The relevant reaction formula is: Fe3O4 + C → 3FeO + CO; FeO + C → Fe + CO; In the coarse powder of rolled steel, iron(III) oxide is reduced to metallic iron. Accompanying the removal of oxygen atoms and lattice rearrangement, the volume of the material particles shrinks significantly. This microscopic volume shrinkage creates three-dimensional, interconnected physical gaps within the macroscopic structure of the composite sacrificial block. The large amounts of carbon monoxide and carbon dioxide generated during the intense gasification stage of the tunnel kiln's thermal reduction penetrate the sealing layer along these physical gaps and are released to the outside of the silicon carbide sagger, thus serving a venting and pressure-relieving function and preventing internal pressure accumulation that could damage the sagger structure.

[0011] Towards the end of the thermal reduction process, the newly formed elemental iron inside the composite sacrificial block undergoes solid-phase sintering under high temperature, resulting in iron lattice shrinkage. Simultaneously, silica in the residual ash of the coke reacts with calcium oxide and magnesium oxide generated from mineral decomposition, forming silicate liquid-phase slag. The combined effect of iron phase consolidation and slag bridging causes the top region of the sagger to shrink and aggregate into a monolithic, porous, sponge-like solidified slag block. This slag block physically encapsulates most of the impurities and ash, which can be easily removed mechanically after exiting the kiln, preventing impurities from contaminating the high-purity sponge iron product in the lower and middle sections.

[0012] Preferably, in steps S1 and S2, the method for preparing the primary crosslinking adhesive slurry includes: Lignosulfonate calcium powder was added to deionized water at a uniform speed to prepare a lignosulfonate calcium aqueous solution. Under continuous shearing and stirring conditions, quicklime powder was added to the lignosulfonate calcium aqueous solution, and the temperature and speed were maintained to continue the reaction. This allowed the free divalent calcium ions in the mixed system to undergo ionic complexation and bridging with the sulfonic acid groups and carboxyl groups on the lignin macromolecular chain, thus obtaining a primary crosslinking adhesive slurry with shear thinning properties.

[0013] By employing the above technical solution, the divalent calcium ions released by the ionization of quicklime powder act as physical cross-linking agents, coordinating and complexing with the anionic polar groups on the lignin molecular chains to form a reversible spatial network structure. When mechanical shearing is applied, the network segments disentangle, the apparent viscosity of the fluid decreases, making it easier for the slurry to penetrate into the micropores of coke; and once the shearing force is removed, the network rapidly reconstructs, fixing the slurry in situ within the pores and preventing the effective substances from migrating and diffusing with moisture.

[0014] Preferably, the process parameters for preparing the primary crosslinking adhesive slurry are as follows: The mass concentration of the calcium lignosulfonate aqueous solution is 15.0% to 20.0%; the amount of quicklime powder added relative to 100 parts by mass of the calcium lignosulfonate aqueous solution is 0.15 to 0.6 parts by mass. The reaction temperature is controlled at 15–30°C, and the reaction is stirred continuously for 15–30 minutes.

[0015] By adopting the above technical solution, the reaction environment can be controlled within the set temperature to maintain the thermodynamic equilibrium of the complexation reaction and avoid the oxidative breakage of the polymer chain. The limited concentration and time parameters are to ensure the binding rate of calcium ion crosslinking sites, thereby maintaining the stability of the slurry rheological properties.

[0016] Preferably, in step S1, the process parameters and proportions of the modified primary reducing agent are as follows: By weight, 95.5–97.0 parts of primary coarse coke powder and 1.5–2.0 parts of dolomite powder are dry-mixed, and then 8.5–12.5 parts of primary cross-linking adhesive slurry are evenly sprayed on and kneaded continuously for 10–15 minutes. The constant temperature drying temperature is 140-160℃, and the constant temperature drying time is 35-45 minutes.

[0017] By adopting the above technical solution, the drying conditions of 140-160℃ accelerate the vaporization process of surface moisture, promote the deposition and shrinkage of polymeric substances at the solid-liquid interface, and thus promote the closure and formation of the three-dimensional network hard shell.

[0018] Preferably, in step S2, the process parameters and proportions of the composite sacrificial block are as follows: By weight, 50.0–65.0 parts of secondary fine coke dust, 30.0–40.0 parts of rolled steel scale powder and 5.0–10.0 parts of coarse limestone powder are mixed, and 7.0–9.5 parts of primary cross-linking binder slurry are added and stirred continuously for 15 minutes. The mixed materials are forcibly pressed into flat spherical blocks with a diameter of 35-45 mm under a linear pressure of 15-25 MPa. The air-drying temperature is 70-90℃, and the air-drying time is 100-150 minutes.

[0019] By adopting the above technical solution, the molding pressure of 15-25MPa can provide the initial stacking structural force for the composite sacrificial block; the use of an air-drying temperature of 70-90℃, which is below the boiling point of water, to remove excess moisture is mainly to prevent the rapid vaporization of moisture from generating pore stress and thus damaging the integrity of the block.

[0020] Preferably, the specific process parameters for step S3 are as follows: In the bottom bed, the mass ratio of high-purity iron concentrate to modified main reducing agent is 100:35-45; The bottom layer of material bed is filled to 70.0% to 80.0% of the total internal volume of the silicon carbide sagger; after the composite sacrificial blocks are laid out in a staggered and compact manner, the polymer components in the composite sacrificial blocks are used to form a physical covering and sealing layer by thermoplastic softening and deformation in the preheating section of the tunnel kiln. After the physical sealing layer is formed, the top surface of the physical sealing layer is 2.0 to 4.0 cm away from the upper opening edge of the silicon carbide crucible.

[0021] By employing the above technical solution, the slurry carries the polymer components into the composite sacrificial blocks. When the ambient temperature in the preheating section of the tunnel kiln exceeds its glass transition point, this polymer undergoes thermoplastic softening. The misaligned, stacked, flattened spherical blocks, under the combined effect of their own weight and softening deformation, undergo edge flow and fusion, thus filling the initial stacking gaps and transforming into a continuous physical sealing layer. This sealing layer isolates oxygen from the external kiln gas, preventing direct contact with the bottom material bed and forming a relatively independent reducing microenvironment inside.

[0022] Preferably, in step S4, the operating time and ambient temperature control of each characteristic temperature zone of the tunnel kiln thermal reduction are as follows: The system operates for 3.5 to 4.5 hours within the temperature range from 25°C to 700°C. The system operates for 2.0 to 3.0 hours within a temperature range of 750℃ to 900℃. During this stage, the decomposition and heat absorption of coarse limestone powder in the composite sacrificial block are used to construct a heat distribution buffer across the temperature range. It then enters the high-temperature zone and is heated to 1040–1060℃ and maintained at that temperature for 28.0–32.0 hours. During the thermal reduction process in the tunnel kiln, the pyrolysis endothermic mechanism of dolomite powder in the high-temperature section provides an in-situ heat buffer for the thermal reduction system of the tunnel kiln; the deoxidation phase change of rolled steel scale powder in the high-temperature section generates volume shrinkage, providing a channel for exhaust and pressure relief during the intense gas generation stage of the thermal reduction in the tunnel kiln.

[0023] By adopting the above technical solution, the gradient temperature control program is consistent with the kinetic parameters of the mineral phase transformation and carbothermic reduction reaction in the material. The temperature control range set above not only stimulates the endothermic properties of limestone and dolomite, but also provides the necessary time for solid-phase diffusion of iron atoms and crystal growth, which is beneficial to improving the metallization rate of the product.

[0024] Preferably, the characteristic parameters of the first-cycle coarse coke powder and the second-cycle fine coke powder are as follows: The fixed carbon mass fraction of the coarse coke powder is not less than 80.0%, the ash mass fraction is not more than 15.0%, and the average particle size ranges from 1.0 to 3.0 mm. The fixed carbon mass fraction of the second-cycle fine coke is 60.0% to 70.0%, the ash mass fraction is not less than 20.0%, and the average particle size is less than 1.0 mm.

[0025] By adopting the above technical solution, the coke dust can be graded and utilized according to its physical properties. The coarse coke dust with intact structure is left at the bottom to provide carbon reduction potential, while the fine coke dust with high ash content is incorporated into the top solidified slag block system for subsequent removal, thus forming an effective material-oriented recycling path.

[0026] Preferably, the characteristic parameters of calcium lignosulfonate powder, dolomite powder, and rolled steel scale powder are as follows: The weight-average molecular weight of calcium lignosulfonate powder ranges from 8,000 to 15,000, and the molecular weight distribution index ranges from 3.0 to 5.0; the purity of dolomite powder is not less than 98.0%, and the particle size ranges from 200 to 325 mesh. The mass fraction of iron oxide in the coarse powder of rolled steel scale is not less than 90.0%, and the average particle size is less than 2.0 mm.

[0027] By adopting the above technical solution, the limited weight-average molecular weight range ensures that the polymer chain segments have sufficient complexing active sites; while the constraint on particle size is to control the suspension stability of mineral powder in fluid and the specific surface area of ​​thermal decomposition reaction.

[0028] Preferably, in step S4, the specific post-processing procedure is as follows: Silicon carbide saggers loaded with high-purity iron concentrate, modified main reducing agent and composite sacrificial blocks are sent into the cooling zone with the kiln car to be cooled to 90-98°C before being discharged from the kiln. After the material in the lower part of the silicon carbide crucible is mechanically crushed, the magnetic separation equipment used for separation has a rated magnetic field strength of 0.15T.

[0029] By adopting the above technical solutions, limiting the kiln outlet temperature threshold can prevent the nascent sponge iron from undergoing a secondary oxidation and exothermic reaction upon contact with air; in addition, using a low-intensity magnetic field of 0.15T to match the magnetic permeability characteristics of high-purity sponge iron can effectively separate non-magnetic silicate residues.

[0030] This invention provides a method for recycling coke residue in the production of reduced iron powder. It has the following beneficial effects: 1. This invention achieves graded recycling of coke dust at various stages while ensuring the permeability of the material bed. The primary cross-linking binder slurry is used to surface-knead and dry the coarse coke dust from the first cycle, promoting the three-dimensional network solidification and cross-linking of macromolecular chain segments to form a hard surface shell, preventing pulverization during the heating and dehydration period. Simultaneously, the high-ash fine coke dust from the second cycle, which is difficult to utilize directly, is forcibly pressed into composite sacrificial blocks with specific mineral powders and spread evenly on the top layer of the material bed. This distribution method consumes waste coke dust while avoiding pore blockage caused by fine powder directly mixing into the bottom layer of the material bed, maintaining the permeability required for the reduction process of the high-purity iron concentrate in the bottom layer.

[0031] 2. This invention effectively mitigates the problem of localized heat accumulation during long-term thermal reduction in tunnel kilns. The technical solution introduces a multi-stage mineral decomposition endothermic system, utilizing the decomposition endothermic reaction of coarse limestone powder incorporated into the composite sacrificial block in the mid-temperature zone, and the pyrolysis endothermic reaction of dolomite powder adhering to the surface of the modified main reducing agent in the high-temperature zone. These two mineral components undergo a step-by-step endothermic reaction in different temperature zones, consuming the localized excess heat load within the reaction system in situ, thus constructing a cross-temperature zone heat buffer mechanism. This reduces the heterogeneous sintering and agglomeration rate of the bottom-layer high-purity iron concentrate caused by localized overheating.

[0032] 3. This invention alleviates the internal gas pressure of the sagger and simplifies the impurity separation process at the end of reduction. During the high-temperature, intense gasification stage, the coarse iron scale powder inside the composite sacrificial block undergoes a deoxidation phase transformation, accompanied by significant volume shrinkage due to lattice restructuring. This reconstructs interconnected physical gaps within the top layer structure, providing a directional pressure relief path for carbon monoxide and carbon dioxide gases, preventing internal pressure surges that could damage the silicon carbide sagger. At the end of reduction, the newly generated solid iron phase sintering at the top, combined with the bridging effect of the silicate liquid slag, causes the top layer material to shrink and aggregate into a porous, solidified slag block, physically encapsulating most of the impurities and ash. After exiting the kiln, this slag block can be easily peeled off mechanically, blocking the pathway for top impurities to mix into the lower high-purity sponge iron product. Attached Figure Description

[0033] Figure 1 The graph shows the test results of the slurry rheology and aging performance of the modified reducing agent according to the present invention; wherein, Figure 1 (a) shows the apparent viscosity variation trends of the slurries prepared in Examples 1-3 and Comparative Example 2 at different shear rates; Figure 1 (b) The moisture absorption weight gain and compressive strength retention of the reducing agents in Examples 1-3 and Comparative Examples 1-2 under humid and hot conditions were compared. Figure 2The thermodynamic response test diagrams of the modified reducing agent and the sacrificial block material of the present invention are shown; wherein, Figure 2 (a) The differential scanning calorimetric response curves of the modified primary reducing agent of Example 1 and the primary reducing agent of Comparative Example 3 under programmed temperature rise conditions were compared. Figure 2 (b) The thermodynamic response curves of the composite sacrificial block of Example 1 and the composite sacrificial block of Comparative Example 4 were compared under the same heating conditions; Figure 3 This is a test diagram showing the volume shrinkage and air permeability pressure drop of the composite sacrificial block of the present invention; wherein, Figure 3 (a) shows a comparison of the macroscopic volume shrinkage rates of the blocks of Examples 1 to 3 and Comparative Example 5 before and after high-temperature reduction; Figure 3 (b) The fluid pressure drop curves of the above four groups of blocks measured at different apparent airflow rates were compared. Figure 4 This is a graph showing the mechanical stability test results of the reducing agent particles of the present invention; wherein, Figure 4 (a) is a comparison chart of the average powdering and peeling rates of Example 1 and Comparative Examples 1 and 2 after wet heat aging; Figure 4 (b) is a graph showing the trend of average compressive strength of Example 1 and Comparative Examples 1 and 2 under different aging times; Figure 5 This is a thermal and carbon consumption analysis chart for Test Example 5 of the present invention; wherein, Figure 5 (a) This shows a comparison of the abnormal fluctuations in core temperature deviating from the furnace ambient temperature when Example 1 and Comparative Examples 3 and 4 cross the 750°C temperature range during the heating phase. Figure 5 (b) Shows the statistical results of the comprehensive coke consumption ratio of the above three groups of samples when producing one unit of sponge iron; Figure 6 This is a correlation analysis graph of internal pressure and impurity content in Test Example 6 of the present invention. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] The first-stage coarse coke is a coarse-particle solid carbon-based material obtained by screening after metallurgical coke has undergone a previous reduction cycle. Its fixed carbon mass fraction is not less than 80.0%, ash mass fraction is not more than 15.0%, volatile matter mass fraction is not more than 2.0%, moisture content is not more than 3.0%, average particle size range is 1.0 to 3.0 mm, and porosity is 35.0% to 45.0%.

[0037] Second-cycle or third-cycle fine coke dust is fine-particle solid carbon-based waste obtained by screening after metallurgical coke has undergone two or three reduction cycles in the early stage. Its fixed carbon mass fraction is 60.0% to 70.0%, ash mass fraction is not less than 20.0%, and average particle size is less than 1.0 mm.

[0038] Calcium lignosulfonate, CAS number 8061-52-7, is an anionic polymer. Its molecular structure consists of substituted phenylpropane structural units interconnected by random condensation through carbon-carbon double bonds and ether bonds. The side chains contain sulfonic acid groups, methoxy groups, and phenolic hydroxyl groups. Its weight-average molecular weight ranges from 8,000 to 15,000, its molecular weight distribution index is 3.0 to 5.0, its reducing sugar content is not higher than 5.0%, its water-soluble content is not lower than 95.0%, and the pH of its aqueous solution is 4.0 to 6.0.

[0039] The chemical formula of dolomite powder is CaMg(CO3)2, the CAS number is 16389-88-1, the purity is not less than 98.0%, and the particle size range is 200-325 mesh.

[0040] The main chemical component of the steel rolling mill scale powder is iron(III) oxide, CAS number 1317-61-9, with a total iron content of not less than 70.0% and an iron(III) oxide content of not less than 90.0%, and an average particle size of less than 2.0 mm.

[0041] The main component of coarse-grained limestone powder is calcium carbonate, with CAS number 471-34-1. The mass fraction of calcium carbonate is not less than 95.0%, and the average particle size ranges from 0.5 to 1.5 mm.

[0042] The chemical name of quicklime powder is calcium hydroxide, with the chemical formula Ca(OH)2, CAS number 1305-62-0, purity not less than 95.0%, and moisture content not more than 1.0%.

[0043] The main chemical component of high-purity iron concentrate is iron(III) oxide (CAS number 1317-61-9), with a total iron content of not less than 71.5% and a silicon dioxide content of not more than 0.5%, and an average particle size of 75–150 μm.

[0044] Preparation Example 1: This preparation example provides a method for preparing a primary crosslinking adhesive slurry with film-forming activity, comprising the following steps: (1) At 15°C, 150.0g of dry calcium lignosulfonate powder was added to 850.0g of deionized water at a constant rate within 5 minutes, and stirred continuously at 100rpm for 10 minutes to prepare a calcium lignosulfonate aqueous solution with a mass concentration of 15.0%. (2) Increase the speed of the mixer to 200 rpm, and under continuous shearing and stirring conditions, sieve 1.5 g of quicklime powder into the above aqueous solution at a uniform speed within 3 minutes; (3) Maintain a temperature of 15°C and a rotation speed of 200 rpm, and continue stirring for 15 minutes to allow the free divalent calcium ions in the system to undergo ion complexation and bridging with the sulfonic acid groups and carboxyl groups on the lignin macromolecular chain, thereby obtaining a primary crosslinking adhesive slurry with shear thinning properties.

[0045] Preparation Example 2: This preparation example provides a method for preparing a primary crosslinking adhesive slurry with film-forming activity, comprising the following steps: (1) At 25°C, 180.0g of dry calcium lignosulfonate powder was added to 820.0g of deionized water at a constant rate within 5 minutes, and stirred continuously at 100rpm for 10 minutes to prepare a calcium lignosulfonate aqueous solution with a mass concentration of 18.0%. (2) Increase the speed of the mixer to 250 rpm, and under continuous shearing and stirring conditions, 3.6 g of quicklime powder is uniformly sieved into the above aqueous solution within 3 minutes; (3) Maintain a temperature of 25°C and a rotation speed of 250 rpm, and continue stirring for 25 minutes to allow the free divalent calcium ions in the system to undergo ion complexation and bridging with the sulfonic acid groups and carboxyl groups on the lignin macromolecular chain, thereby obtaining a primary cross-linking adhesive slurry with shear thinning properties.

[0046] Preparation Example 3: This preparation example provides a method for preparing a primary crosslinking adhesive slurry with film-forming activity, comprising the following steps: (1) Under the condition of 30℃, 200.0g of dry calcium lignosulfonate powder was added to 800.0g of deionized water at a uniform rate within 5 minutes, and stirred continuously at a speed of 100rpm for 10 minutes to prepare a calcium lignosulfonate aqueous solution with a mass concentration of 20.0%. (2) Increase the speed of the mixer to 300 rpm, and under continuous shearing and stirring conditions, sieve 6.0 g of quicklime powder into the above aqueous solution at a uniform speed within 3 minutes; (3) Maintain a temperature of 30°C and a rotation speed of 300 rpm, and continue stirring for 30 minutes to allow the free divalent calcium ions in the system to undergo ion complexation and bridging with the sulfonic acid groups and carboxyl groups on the lignin macromolecular chain, thereby obtaining a primary crosslinking adhesive slurry with shear thinning properties.

[0047] Example 1: This example provides a method for recycling coke residue in the production of reduced iron powder, including the following steps: (1) Preparation of modified primary reducing agent: 96.5 kg of coarse coke powder and 1.8 kg of dolomite powder were put into a roller mill kneader and dry-mixed for 3 minutes. 10.0 kg of the primary crosslinking adhesive slurry prepared in Preparation Example 1 was evenly sprayed into the kneader and continuously kneaded for 12 minutes under the mechanical extrusion of the roller mill rollers, so that the slurry penetrated and anchored into the pores on the surface of the coarse coke powder. The kneaded material was sent to a mesh belt dryer and dried at a constant temperature of 150°C for 40 minutes to completely remove the surface moisture and cause three-dimensional network curing and crosslinking, thus obtaining a modified primary reducing agent with a moisture-proof crosslinked hard shell on the surface.

[0048] (2) Preparation of dynamic breathing sacrificial blocks: 58.0 kg of secondary fine coke dust, 35.0 kg of rolled steel scale powder, and 7.0 kg of coarse limestone powder were added to a twin-shaft mixer, along with 8.0 kg of the primary crosslinking binder slurry prepared in Preparation Example 1. The mixture was stirred for 15 minutes until it was homogeneous. The mixture was fed into a roller briquetting machine and forcibly pressed into dense, flat spherical blocks with a diameter of 40 mm under a linear pressure of 20 MPa. The pressed blocks were then air-dried at 80°C for 120 minutes to obtain composite sacrificial blocks.

[0049] (3) Cascaded filling: In the standard silicon carbide sagger, high-purity iron concentrate and modified main reducing agent prepared in step (1) are alternately filled in a ratio of 100:40. The bottom layer of material bed fills 75.0% of the total internal volume of the sagger. On the flat surface of the top layer of material, a single layer of composite sacrificial block prepared in step (2) is laid in a staggered and tight manner. Thermoplastic softening deformation of the polymer components in the composite sacrificial block in the initial preheating section of the tunnel kiln is used to further bond and compact the gaps between the blocks under their own weight and the adjacent compression, forming a closed covering layer. The top surface of the covering layer is 3.0 cm away from the edge of the upper opening of the sagger. The sagger cover plate is put on and loaded onto the kiln car.

[0050] (4) Thermal Reduction and Post-processing in Tunnel Kiln: The kiln car is pushed into the industrial tunnel kiln for continuous thermal reduction. The running time and ambient temperature of the kiln car in each characteristic temperature zone are controlled: 4.0 hours in the range from 25℃ to 700℃; 2.5 hours in the range from 750℃ to 900℃; then it enters the high-temperature zone to heat up to 1050℃ and is kept at a constant temperature for 30.0 hours. After the reduction is completed, the kiln car enters the cooling zone to cool down to 95℃ and exits the kiln. The silicon carbide sagger is opened, and the integral porous sponge-like solidified slag block formed on the top due to iron lattice shrinkage and solid phase sintering is physically peeled off and removed. The reaction residues and reduction products in the middle and lower parts are mechanically crushed and then transported to a magnetic separator with a rated magnetic field strength of 0.15T to separate sulfur-containing residual coke and high-purity sponge iron products.

[0051] Example 2: This example provides a method for recycling coke residue in the production of reduced iron powder, including the following steps: (1) Preparation of modified primary reducing agent: 95.5 kg of coarse coke powder and 2.0 kg of dolomite powder were put into a roller mill kneader and dry-mixed for 3 minutes. 12.5 kg of the primary crosslinking adhesive slurry prepared in Preparation Example 2 was evenly sprayed into the kneader and continuously kneaded for 15 minutes under the mechanical extrusion of the roller mill. The kneaded material was sent to a mesh belt dryer and dried at a constant temperature of 160°C for 35 minutes to completely remove the surface moisture and cause three-dimensional network curing and crosslinking, thus obtaining a modified primary reducing agent with a moisture-proof crosslinked hard shell on the surface.

[0052] (2) Preparation of dynamic breathing sacrificial blocks: 50.0 kg of secondary fine coke dust, 40.0 kg of rolled steel scale powder, and 10.0 kg of coarse limestone powder were added to a twin-shaft mixer, along with 9.5 kg of the primary crosslinking binder slurry prepared in Preparation Example 2. The mixture was stirred for 15 minutes until it was homogeneous. The mixture was fed into a roller briquetting machine and forcibly pressed into dense, flat spherical blocks with a diameter of 45 mm under a linear pressure of 25 MPa. The pressed blocks were then air-dried at 90°C for 100 minutes to obtain composite sacrificial blocks.

[0053] (3) Cascaded filling: High-purity iron concentrate and modified main reducing agent are alternately filled inside the standard silicon carbide sagger at a mass ratio of 100:35. The bottom layer of material bed fills 70.0% of the total internal volume of the sagger. Composite sacrificial blocks are laid flat and staggered on the flat surface of the top layer of material. The high-molecular components in the composite sacrificial blocks undergo thermoplastic softening deformation in the initial preheating section of the tunnel kiln, which further binds and compacts the gaps between the blocks under their own weight and the squeezing action of adjacent blocks, forming a closed covering layer. The top surface of the covering layer is 4.0 cm away from the edge of the opening at the top of the sagger. The sagger cover plate is then placed on the sagger and loaded onto the kiln car.

[0054] (4) Thermal reduction and post-processing in tunnel kiln: The kiln car is pushed into the industrial tunnel kiln for continuous thermal reduction. The kiln car is controlled to operate in the temperature range of 25℃ to 700℃ for 3.5 hours; in the temperature range of 750℃ to 900℃ for 3.0 hours; then it enters the high temperature zone to be heated to 1040℃ and kept at a constant temperature for 32.0 hours. The kiln car enters the cooling zone to be cooled to 90℃ and exits the kiln. After de-calcination, the porous sponge-like solidified slag block at the top is peeled off and removed. The material in the middle and lower parts is mechanically coarsely crushed and then separated into sulfur-containing residual coke and high-purity sponge iron products by a magnetic separator with a magnetic field strength of 0.15T.

[0055] Example 3: This example provides a method for recycling coke residue in the production of reduced iron powder, including the following steps: (1) Preparation of modified primary reducing agent: 97.0 kg of coarse coke powder and 1.5 kg of dolomite powder were put into a roller mill kneader and dry-mixed for 3 minutes. 8.5 kg of the primary crosslinking adhesive slurry prepared in Preparation Example 3 was evenly sprayed into the kneader and continuously kneaded for 10 minutes under the mechanical extrusion of the roller mill. The kneaded material was sent to a mesh belt dryer and dried at a constant temperature of 140°C for 45 minutes to completely remove the surface moisture and cause three-dimensional network curing and crosslinking, thus obtaining a modified primary reducing agent with a moisture-proof crosslinked hard shell on the surface.

[0056] (2) Preparation of dynamic breathing sacrificial blocks: 65.0 kg of secondary fine coke dust, 30.0 kg of rolled steel scale powder, and 5.0 kg of coarse limestone powder were added to a twin-shaft mixer, along with 7.0 kg of the primary crosslinking binder slurry prepared in Preparation Example 3. The mixture was stirred for 15 minutes until it was uniformly mixed. The mixture was fed into a roller briquetting machine and forcibly pressed into dense, flat spherical blocks with a diameter of 35 mm under a linear pressure of 15 MPa. The pressed blocks were then air-dried at 70°C for 150 minutes to obtain composite sacrificial blocks.

[0057] (3) Cascaded filling: High-purity iron concentrate and modified main reducing agent are alternately filled inside the standard silicon carbide sagger at a mass ratio of 100:45. The bottom layer of material bed fills 80.0% of the total internal volume of the sagger. Composite sacrificial blocks are laid flat and staggered on the flat surface of the top layer of material. The high-molecular components in the composite sacrificial blocks undergo thermoplastic softening deformation in the initial preheating section of the tunnel kiln, which further binds and compacts the gaps between the blocks under their own weight and the pressure of adjacent blocks, forming a physical covering and sealing layer without a direct airflow channel. The top surface of the covering layer is 2.0 cm away from the edge of the upper opening of the sagger. The sagger cover plate is then placed on the sagger and loaded onto the kiln car.

[0058] (4) Thermal reduction and post-processing in tunnel kiln: The kiln car is pushed into the industrial tunnel kiln for continuous thermal reduction. The kiln car is controlled to operate in the temperature range of 25℃ to 700℃ for 4.5 hours; in the temperature range of 750℃ to 900℃ for 2.0 hours; then it enters the high temperature zone to be heated to 1060℃ and kept at a constant temperature for 28.0 hours. The kiln car enters the cooling zone to be cooled to 98℃ and exits the kiln. After de-calcination, the porous sponge-like solidified slag block at the top is peeled off and removed. The material in the middle and lower parts is mechanically coarsely crushed and then separated into sulfur-containing residual coke and high-purity sponge iron products by a magnetic separator with a magnetic field strength of 0.15T.

[0059] Comparative Example 1: Compared with Example 1, the difference is that in step (1), only an equal amount of pure water is used to replace the primary crosslinking adhesive slurry for kneading, and no dolomite powder is added; in steps (2) and (3), no composite sacrificial block is prepared and laid, but instead, a loose secondary fine coke foam of the same thickness is directly covered on the top layer, and the rest are the same.

[0060] Comparative Example 2: Compared with Example 1, the difference is that the bonding slurry used in steps (1) and (2) is a pure calcium lignosulfonate aqueous solution without added quicklime powder, and the rest are the same.

[0061] Comparative Example 3: Compared with Example 1, the difference is that in step (1), pure calcium carbonate powder of equal mass is used instead of dolomite powder, and the rest are the same.

[0062] Comparative Example 4: Compared with Example 1, the difference is that in the composite sacrificial block formula of step (2), coarse limestone powder is not added, but an equal amount of secondary fine coke powder is added instead, and the rest are the same.

[0063] Comparative Example 5: Compared with Example 1, the difference is that in the composite sacrificial block formulation of step (2), steel scale powder is not added, but instead an equal mass of inert high-alumina bauxite powder is added, while the rest are the same.

[0064] Test Example 1: Test objective: To verify the shear thinning characteristics of the primary cross-linked adhesive slurry and the physical barrier and anti-pulverization ability of the modified main reducing agent under humid and hot conditions.

[0065] The experimental steps are as follows: The primary crosslinking adhesive slurries prepared in Examples 1 to 3, and the pure calcium lignosulfonate aqueous solution without added quicklime powder in Comparative Example 2 were selected as rheological test objects. Each slurry sample was placed into a rotational viscometer test chamber equipped with a constant-temperature water bath jacket, and the circulating water bath was turned on to stabilize the test temperature at 25°C. The shear rate was sequentially set to 10 s. -1 50s -1 and 100s -1 After the instrument rotor runs stably and the reading fluctuation is less than 2%, record the apparent viscosity value corresponding to each shear rate. After cleaning the test cylinder for each group of samples, repeat the measurement three times and take the average value.

[0066] The modified main reducing agents prepared in Examples 1 to 3 were selected. Simultaneously, reducing agent particles prepared by directly mixing water without binder in Comparative Example 1 and reducing agent particles prepared by mixing with pure lignin aqueous solution in Comparative Example 2 were extracted as moisture resistance test subjects. 100.0 g of each group of fully dried particle samples was accurately weighed and evenly spread in pre-calibrated wide-mouth petri dishes. The petri dishes containing the samples were transferred to a constant temperature and humidity test chamber set at 30°C and a constant relative humidity of 95%. After 72 hours of continuous placement, the samples were quickly removed and weighed a second time. The moisture absorption weight gain rate was obtained by calculating the mass difference before and after aging.

[0067] Twenty particles of similar size and morphology were randomly selected from each group of samples that had undergone hygrothermal aging. The radial compressive strength of each particle was tested individually using a computer-controlled electronic universal testing machine. During the test, a slow loading rate of 1.0 mm / min was applied, and the system automatically recorded the maximum load value at the moment of macroscopic fracture. This average failure load was compared with the average compressive strength of the same batch of initially dried particles that had not undergone aging, and the single-particle compressive strength retention rate was calculated.

[0068] The experimental results are shown in Table 1: Table 1: Rheological parameters of different slurry systems and wet heat aging data of corresponding modified reducing agents

[0069] in conclusion: Based on the data in Table 1 and the reference appendix Figure 1 The primary crosslinking adhesive slurries of Examples 1 to 3 were prepared in 10s. -1 They all exhibited high initial viscosity at low shear rates, which decreased as the shear rate gradually increased to 100 s⁻¹. -1 Its apparent viscosity decreased significantly. This fluid characteristic provides hydrodynamic adaptability in actual operation, meaning that the slurry experiences less viscous resistance when pumped through pipelines and atomized through nozzles, reducing transport energy consumption. The atomized droplets can penetrate and adhere to the pores on the surface of the coarse coke foam, and after adhesion, it returns to a high viscosity state to reduce liquid dripping and loss. Data from Comparative Example 2 show that the pure lignin aqueous solution without the introduction of free calcium ions for room temperature complexation exhibits a relatively flat rheological curve. Its polymer chains failed to form a three-dimensional cross-linked network in space, lacking the physical conditions for in-situ thickening and film formation at the macroscopic level.

[0070] In the damp heat aging assessment, the differences in moisture resistance exhibited by the materials reflected the protective effect of the cross-linking mechanism on the reducing environment. Pure lignin aqueous solution retained a significant amount of hydrophilic free hydroxyl and sulfonic acid groups after drying. The particles in Comparative Example 2 absorbed ambient moisture at 95% relative humidity, with a moisture absorption weight gain of 8.45%. The lack of a cross-linking network caused them to swell and soften after absorbing water, with a single particle compressive strength retention rate of 22.4%. When removed from the test chamber in the laboratory, they pulverized upon application of slight pressure. In Examples 1 to 3, after introducing calcium hydroxide to induce room temperature cross-linking, the polar groups on the macromolecular chains were blocked by divalent calcium ions, making it difficult for moisture to penetrate the internal porous network. This suppressed the moisture absorption weight gain to below 1.24%, and after 72 hours of high humidity, the particles retained over 88.5% of their initial mechanical strength. This physical barrier capability provides a basis for anti-pulverization in the preheating section of the tunnel kiln, controlling carbon consumption of coke in the initial heating stage.

[0071] Test Example 2: Test objective: To verify the in-situ endothermic kinetic characteristics of the modified primary reducing agent and the composite sacrificial block in a specific temperature range, and to quantitatively determine their thermodynamic buffering capacity during programmed temperature rise.

[0072] The experimental steps are as follows: The modified primary reducing agent monomer and composite sacrificial block monomer prepared in Examples 1 to 3 were selected as the main test objects. The reducing agent monomer prepared by using pure calcium carbonate instead of dolomite in Comparative Example 3 and the sacrificial block monomer without the addition of coarse limestone in Comparative Example 4 were extracted as comparison samples. The solid samples of each group were ground into powder with a particle size of less than 74 micrometers in an inert gas protective glove box using a mortar and pestle.

[0073] Accurately weigh 15.0 mg of each ground sample powder and place it into a pre-cleaned and dried alumina miniature test crucible, then seal it tightly with the matching alumina lid. Prepare a crucible containing an equal amount of high-purity alumina powder that has undergone high-temperature calcination as a test reference.

[0074] The sample crucible and reference crucible were simultaneously placed on the microbalance tray of the heating furnace of the simultaneous thermal analyzer. The test environment was set to a high-purity argon atmosphere, with a gas flow rate controlled at 50 mL / min. The instrument temperature control program was set to linearly increase the temperature from room temperature to 1050℃ at a fixed rate of 10℃ / min. During the experiment, the system automatically and continuously acquired differential scanning calorimetry (DSC) data of the samples, recording the peak temperature corresponding to the endothermic peaks appearing in different temperature zones for each sample, as well as the enthalpy value converted from the integrated area of ​​the endothermic peak. Each sample was tested twice, and the arithmetic mean of the two valid data was recorded.

[0075] The experimental results are shown in Table 2: Table 2: Thermodynamic characteristics of samples with different reducing agents and sacrificial blocks during programmed temperature rise.

[0076] Note: The endothermic enthalpy values ​​in the table are all taken as the absolute value (positive value) of the integral area, representing the heat absorbed by each gram of sample within the decomposition temperature range.

[0077] in conclusion: Based on the data in Table 2 and the reference appendix Figure 2The modified primary reducing agents in Examples 1 to 3 exhibited a physically endothermic response in the 745 to 750°C range, with calculated endothermic enthalpies ranging from 15.7 to 20.3 J / g. This characteristic peak originates from the pyrolysis reaction of the magnesium carbonate component in the dolomite in the formulation. During the heating and operation phase within the reduction kiln, if the material experiences early reduction exothermic phenomena due to impurities, this pyrolysis process can provide in-situ endothermic compensation, delaying the local temperature rise. In the comparative group, Comparative Example 3 used pure calcium carbonate instead of dolomite, and the test results showed that the endothermic peak in the 750°C range disappeared, with the system only recording a single large-scale endothermic behavior near 888°C. The delayed thermophysical response timing means that the material lacks an endogenous heat buffering mechanism during the transition period near 750°C, making it easier for heated hot spots to accumulate inside the material bed, thus interfering with the overall stability of the reduction reaction process.

[0078] Regarding the calorific data of the top-layer composite sacrificial block, Examples 1 to 3 recorded a significant endothermic peak between 849 and 854 °C, with enthalpy values ​​ranging from 62.4 to 115.8 J / g. This endothermic peak corresponds to the decomposition reaction of coarse-grained limestone. In the thermal radiation heating condition of the tunnel kiln, the top-layer material, as the direct heating surface, generally exhibits a higher heating rate than the bottom bed. The curve in Comparative Example 4 shows a flat baseline in this temperature range, lacking a corresponding endothermic stage, with externally input heat mainly converted into the sensible heat rise of the material. By introducing this endothermic reaction, the examples constructed a heat distribution buffer zone at the 850 °C stage, regulating the temperature rise slope of the top-layer region. Relying on this cross-temperature-zone heat distribution method, the spatial temperature difference caused by the heat transfer lag in the deep bottom bed is compensated, providing physical conditions for the temporal synchronization of different levels of material in the reduction process.

[0079] Test Example 3: Test objective: To verify the macroscopic volume shrinkage characteristics of the composite sacrificial block during high-temperature reduction and to quantitatively determine the impact of this phase change shrinkage behavior on the hydrodynamic pressure drop generated when the bottom gas is discharged.

[0080] The experimental steps are as follows: Fifty composite sacrificial green blocks were randomly selected from each of Examples 1 to 3 as the main test objects. The sacrificial green block prepared in Comparative Example 5, using high-alumina bauxite powder of equal mass to replace steel mill scale powder, was extracted as a comparative test object. A three-dimensional laser scanner was used to perform morphological scanning and volume integration on each group of green blocks, and the initial average volume of each block was calculated.

[0081] The green samples, after volume measurement, were laid flat on a corundum support plate and placed in the isothermal zone of a tube furnace. A 1:1 volume ratio of carbon monoxide and nitrogen was introduced into the furnace tubes to simulate a reducing atmosphere. The furnace heating program was set, linearly increasing the temperature to 1050°C at a rate of 5°C per minute and holding it at that temperature for 120 minutes. After natural cooling to room temperature, the sintered blocks were removed. The final average volume of each block was measured again using a 3D laser scanner, and the macroscopic volume shrinkage rate was calculated by the difference between the initial and final volumes.

[0082] A steel cylinder with an inner diameter identical to that of a standard silicon carbide crucible was selected as the hydrodynamic test tube. Each group of sintered solid blocks was laid in a single layer on a permeable metal grid in the middle of the cylinder, following the staggered and tightly laid-out method described in the embodiment. A constant flow gas generator and a mass flow meter were connected to the flange at the lower end of the cylinder, and room temperature nitrogen gas was introduced upwards. The apparent airflow velocity of the empty tube was set to 0.5 m / s, 1.0 m / s, and 1.5 m / s, respectively. After the gas flow at each test velocity stabilized, the pressure drop generated by the gas passing through the physical cover layer was measured using differential pressure transmitters placed on both sides of the cover layer. Each gas velocity condition was tested three times, and the arithmetic mean was recorded.

[0083] The experimental results are shown in Table 3: Table 3: Volume Changes and Pressure Drops of Composite Sacrificial Blocks Before and After High-Temperature Reduction and at Different Gas Velocities

[0084] in conclusion: Based on the data in Table 3 and the reference appendix Figure 3 The green bodies from Examples 1 to 3 exhibited varying degrees of dimensional reduction after undergoing a reduction process at 1050°C, with macroscopic volume shrinkage rates ranging from 11.48% to 14.21%. This volume change stems from the lattice deoxidation and reconstruction of the rolled steel scale in the formulation at high temperatures. When iron(III) oxide is reduced to its initial state metallic iron by carbon monoxide, its true density changes due to the loss of lattice oxygen atoms, resulting in centripetal shrinkage stress within the monomer material. Fine crack patterns were observed on the surface of the sintered blocks when they were removed from the laboratory. Comparative Example 5 used high-alumina bauxite as a substitute material. The bauxite component did not undergo deoxidation reduction or phase transformation at 1050°C, and the recorded volume shrinkage rate was 1.19%, maintaining the geometric volume in the initial forming stage.

[0085] The data from the hydrodynamic pressure drop test reflect the venting effect of the aforementioned shrinkage behavior at the engineering level. When the bottom gas passed upward through the capping layer at an apparent rate of 1.0 m / s, the pressure drop measured at both ends of the capping layer in Examples 1 to 3 ranged from 0.76 to 0.94 kPa. Volumetric shrinkage and the associated network of cracks provided a porous network within the originally tightly packed physical seal, allowing the bottom gas flow to dissipate outward along these cracks, reducing resistance to gas flow through the bed. The calcined blocks in Comparative Example 5 did not exhibit significant shrinkage, maintaining a tightly compressed state at low temperatures. Under a gas flow rate of 1.0 m / s, its pressure dropped to 5.42 kPa, rising to 10.85 kPa when the gas flow rate increased to 1.5 m / s. The gas flow was obstructed as it passed through the densely packed bauxite blocks, and the dynamic pressure was converted into static pressure accumulating at the bottom of the capping layer. When there is no way to release the pressure in industrial operation, this internal pressure buildup can cause displacement or damage to the cover layer. The solution of introducing iron scale phase change contraction alleviates the pressure accumulation in the high-temperature gasification stage from a physical and geometric perspective.

[0086] Test Example 4: Test objective: To verify the protective effect of the cross-linked consolidation structure on the physical stability of reducing agent particles in the simulated tunnel kiln preheating section environment, and to evaluate its resistance to vibration and airflow erosion by quantifying the pulverization rate after wet heat aging.

[0087] The experimental steps are as follows: The modified reducing agent particles prepared in Example 1 were selected, and the reducing agent particles prepared by mixing binder-free water in Comparative Example 1 and the reducing agent particles prepared by mixing pure lignin aqueous solution in Comparative Example 2 were also extracted. The initial particle size of all samples was controlled within the range of 1.0 to 3.0 mm. Each group of samples was dried in a forced-air drying oven at 105°C to constant weight, and 500.0 g of each group of samples was weighed using an analytical balance as the initial mass.

[0088] The weighed samples were placed in a constant temperature and humidity chamber, with the ambient temperature set at 40℃ and the relative humidity at 90%, for a pre-aging treatment of 48 hours. After aging, the samples were removed. To eliminate the influence of surface-adsorbed moisture on weighing and subsequent friction coefficient, the samples were placed under a low-temperature infrared drying lamp. The irradiation distance was adjusted to maintain the sample surface temperature below 50℃ until the surface water was completely removed, while avoiding heat setting of uncrosslinked lignin caused by high temperature.

[0089] The processed particle sample was loaded into a small rotary abrasion cylinder with three lifting ribs on its inner wall. This device was used to simulate the vibration of the kiln car during travel and the scouring effect of the circulating airflow in the preheating section. The rotation speed of the abrasion cylinder was set to 30 revolutions per minute, and it was stopped after running continuously for 30 minutes. All the material in the cylinder was removed, ensuring that no residual powder remained.

[0090] The abraded material was sieved using a standard laboratory sieve with a 1.0 mm aperture. The mass of powder passing through the sieve openings was collected and weighed; this portion is the pulverization and sloughing component. The pulverization and sloughing rate was calculated based on the ratio of the mass of the material passing through the sieve to the initial mass. Each sample was tested three times, and the experimental data were recorded and the arithmetic mean was calculated.

[0091] The experimental results are shown in Table 4: Table 4: Data on powdering and spalling of different reducing agent particles after 48 hours of wet heat aging

[0092] in conclusion: Based on the data records in Table 4 and the reference appendix Figure 4 After 48 hours of damp heat aging and mechanical wear, the reducing agent particles in Example 1 maintained a pulverization and spalling rate between 1.31% and 1.67%, and no obvious erosion or cracks were observed on the particle surface under macroscopic observation. This phenomenon indicates that the calcium ion cross-linking reaction initiated by calcium hydroxide established chemical bonds between the lignin polymer chains, forming a protective layer with a certain degree of flexibility and insoluble in water on the particle surface. This structure not only prevents external moisture from penetrating into the particle interior but also maintains the physical bonding strength between particles, preventing structural collapse under continuous impact from the rotating drum.

[0093] In contrast, Comparative Example 1, lacking a binder, experienced a decrease in capillary force due to moisture drying within the particles after absorbing moisture, leading to a pulverization rate ranging from 16.32% to 20.85%, exhibiting rapid pulverization even in the early stages of wear. Comparative Example 2, while using lignin as a binder, lacked the curing effect of a cross-linking reaction, resulting in physical softening and partial resolubilization of its surface film under humid and hot conditions. Tests recorded a pulverization rate between 7.78% and 10.50%, exhibiting typical delamination and detachment characteristics. Data comparison indicates that without the cross-linking protective layer described in this solution, the material would undergo large-scale pulverization in the low-temperature section at the initial kiln entry. These fine powders undergo physical migration or loss under the influence of airflow within the kiln, causing the bottom layer material to be prematurely exposed to the oxidizing atmosphere. By constructing a more physically stable cross-linking network on the reducing agent surface, this solution ensures that the material retains its intact particle morphology before entering the high-temperature reduction section.

[0094] Test Example 5: Test objective: To verify the material system's ability to regulate local thermal fluctuations and reduction reaction process during the simulated tunnel kiln heating process, to examine the inhibitory effect of magnesium carbonate component on local temperature rise and the role of the top thermodynamic buffer layer in reducing ineffective loss of reducing agent, and to evaluate the economic efficiency of the process by monitoring abnormal temperature rise and calculating coke consumption ratio.

[0095] The experimental steps are as follows: The composite reducing agent and top cover block prepared in Example 1 were selected, and the reducing agent lacking magnesium carbonate component in Comparative Example 3 and the cover block lacking the top limestone thermodynamic buffer layer in Comparative Example 4 were extracted as parallel test objects.

[0096] A standard silicon carbide sagger is used for loading. High-purity iron powder to be reduced is placed in the bottom and middle of the sagger, and a reducing agent is added in proportion. A calibrated S-type platinum-rhodium thermocouple is pre-embedded at the geometric center of the sagger. The temperature sensing end of the thermocouple is led out through a micro-hole reserved in the sagger wall to monitor the temperature evolution of the material core in real time.

[0097] A top layer of covering blocks of a predetermined thickness is laid flat on top of the material. The filled sagger is then placed inside a high-temperature experimental furnace equipped with a programmed temperature control function. A heating program is set to simulate the operating conditions of a tunnel kiln, with a heating rate of 8°C per minute. This heating rate is designed to simulate the extreme thermal shock environment experienced by the material from the end of the preheating zone to the beginning of the high-temperature zone in the kiln. When the ambient temperature inside the furnace reaches 700°C, the data acquisition system records the values ​​of the core thermocouples once per second until the ambient temperature reaches 1050°C.

[0098] Record the maximum difference between the core temperature of the material and the ambient temperature inside the furnace during the heating process, and define it as the abnormal temperature rise peak. After the reaction is completed and the furnace cools naturally to room temperature, remove the reduction product from the crucible.

[0099] The produced sponge iron is weighed, and the total iron and metallic iron content is determined according to standard chemical analysis methods to calculate the metallization rate. Combined with the initial input mass of reducing agent, the total fixed carbon consumed per unit mass of sponge iron produced is calculated, i.e., the coke consumption ratio. The coke consumption ratio is calculated based on the mass of fixed carbon in coke consumed per unit mass of sponge iron produced to eliminate the interference of moisture and volatile matter on the data.

[0100] The experimental results are shown in Table 5: Table 5: Data on thermal disturbances and overall carbon consumption of different systems during the simulation and reduction process

[0101] in conclusion: Based on the data records in Table 5 and the reference appendix Figure 5In Example 1, when the temperature was raised to 750°C, the peak abnormal temperature rise in the core ranged from 13.5 to 16.2°C, while Comparative Example 3 recorded a temperature rise of 55.3 to 62.4°C. This thermal difference stemmed from the imbalance of thermal effects caused by the lack of magnesium carbonate in the reducing agent. After the reaction system crossed the threshold temperature of the Boudouard reaction (carbon gasification reaction), the reactivity of fixed carbon and carbon dioxide increased rapidly. If the chemical heat released by the reduction of iron oxides could not be absorbed in time, it would lead to excessively rapid local temperature rises. Example 1 utilized the stepwise endothermic decomposition characteristics of magnesium carbonate in a specific temperature range to offset the heat released in the early stage of the reduction reaction, thereby smoothing the temperature gradient inside the material. The comparative experiment observed that Comparative Example 3, lacking this regulatory mechanism, resulted in the carbon source being consumed before the iron oxides entered the efficient reduction stage, causing its fixed carbon coke consumption to increase by approximately 70 kg / t compared to Example 1.

[0102] Furthermore, the structural design of the top cover block also directly impacts carbon consumption reduction. Comparative Example 4, lacking limestone, saw its coke consumption ratio climb to 490.6-510.1 kg / t, and the metallization rate of the sponge iron was below 91%. This result indicates that the top reducing agent reaches its active reaction temperature earlier in the initial heating phase due to the lack of thermal shielding, and the released reducing gas escapes before the bottom main material is fully preheated, resulting in ineffective carbon loss. Example 1, by introducing limestone into the top block, utilizes the carbon dioxide and endothermic effect generated by its high-temperature decomposition to form a thermodynamic barrier that inhibits the gasification of the reducing agent in the cover layer. This design achieves matching between the downward conduction of the reduction front and the heating process of the bottom material, controlling the overall coke consumption ratio below 395 kg / t while maintaining the sponge iron metallization rate at around 94%. Data shows that through temperature control of magnesium carbonate and the thermal regulation effect of limestone, this scheme achieves controlled reduction process under extreme thermal shock environments.

[0103] Test Example 6: Test objective: To verify the pressure conduction capacity of the material system during the intense gasification stage of the reduction reaction and the structural stability of the top cover layer, to evaluate its suppression effect on cover plate jumping and local perforation under industrial conditions, and to quantify the barrier ability of the top component to ash migration by measuring the acid-insoluble content of the bottom sponge iron product.

[0104] The experimental steps are as follows: The composite reducing agent and top cover block prepared in Example 1 were selected, and the cover blocks of Comparative Example 1 and Comparative Example 5 that lacked the in-situ solid-phase sintering component were extracted as parallel test objects.

[0105] Static equivalent pressure simulation experiments were conducted. Miniature samples with the same loading structure were extracted from each group of samples and loaded into a laboratory high-temperature tube furnace. A corundum pressure-conducting pipe was pre-embedded in the center of the charge, with one end connected to a differential pressure transmitter and the other end placed at the reaction interface between the reducing agent and iron scale. The temperature was controlled according to the actual temperature rise curve of the tunnel kiln, and the maximum positive pressure peak inside the sagger was recorded when the material produced a large amount of gas at 950 to 1050℃.

[0106] The failure rate of industrial-grade sagger cover plates was statistically analyzed. On a tunnel kiln production line with an annual output of 10,000 tons, continuous production was carried out using the material systems of Example 1 and Comparative Examples 1 and 5, respectively. By tracking and recording the physical state of approximately 1500 to 2000 sagger units after exiting the kiln from 50 consecutive kiln cars, the proportion of sagger cover plate displacement or localized gushing perforations in the top covering layer was statistically analyzed for each group.

[0107] The finished sponge iron product indicators of the bottom layer were determined. After the material had completely reacted and cooled naturally with the kiln car, the top covering was peeled off, and sponge iron samples were extracted from the core area of ​​the bottom layer of the sagger. The metallization rate of the finished product was determined according to the chemical titration method specified in the national standard.

[0108] The mass fraction of acid-insoluble matter in the finished product was tested. Following the GB / T 3500 standard, the extracted sponge iron sample was ground to the specified particle size. The metallic iron matrix was dissolved using hot hydrochloric acid solution. After filtration, washing, and calcination of the residue, the mass of acid-insoluble matter was determined. This was used to assess whether the ash content of the top reducing agent, due to powdering and peeling, affected the quality of the bottom sponge iron.

[0109] The experimental results are shown in Table 6: Table 6: Comparison of Anti-Pressure Safety and Bottom Sponge Iron Finished Product Quality in Each Group

[0110] in conclusion: Based on the data records in Table 6 and the reference appendix Figure 6In Example 1, during the active gas-generating stage at 950-1050°C, the peak positive pressure inside the sagger remained stable at 1.28-1.46 kPa, lower than the 3.71-4.08 kPa generated in Comparative Example 1. In continuous industrial field observations of 1500-2000 sagger units, the abnormal displacement rate of the cover plate in Example 1 remained below 2.5%. This improved pressure relief capability, besides the effect of reasonable stacking voids between reducing agent particles, is more importantly due to the volume shrinkage and phase change process of the iron scale component during reduction, which forms microscale pathways within the material layer, allowing for a smooth release of internal pressure when the reducing gas volume surges. In contrast, Comparative Example 1, lacking structural optimization, could not effectively dissipate internal pressure, resulting in a cover plate displacement rate exceeding 10%. Heat loss and atmosphere runaway reduced the metallization rate of the finished product by approximately 2.5 percentage points compared to Example 1.

[0111] The quality analysis of the bottom layer of sponge iron further verified the stability of the top layer structure. The acid-insoluble matter content of the finished product in Example 1 remained stable between 0.13% and 0.16%, while in Comparative Example 5 it was as high as 0.51% to 0.59%. In the experimental observations of Comparative Example 5, because the top layer cover block used high-alumina bauxite instead of rolled steel scale powder, the bauxite component remained chemically inert at the reduction temperature and could not undergo phase transformation and in-situ solid-phase sintering through high-temperature deoxidation reduction like iron scale, making it difficult to form a continuous physically consolidated skeleton between the blocks. Under these circumstances, the coke dust and residual ash generated by the reducing agent in the cover block permeated downwards through the gaps in the material layer under the action of mechanical vibration and airflow. In contrast, the rolled steel scale in the top layer of Example 1, after being reduced, formed a sponge-like porous iron-phase solidified body. This iron-phase skeleton trapped the ash in the top layer residue, physically blocking the path of impurities migrating to the bottom layer of sponge iron. Comprehensive experimental data show that this scheme, while ensuring production safety, solves the problems of pressure buildup and ash leakage pollution during the tunnel kiln reduction process, thus providing conditions for the preparation of high-purity sponge iron.

[0112] 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 recycling coke residue in the production of reduced iron powder, characterized in that, Includes the following steps: S1. Mix and knead a coarse coke powder, dolomite powder and primary crosslinking adhesive slurry to allow the primary crosslinking adhesive slurry to penetrate and anchor into the pores on the surface of the coarse coke powder. Then, dry at a constant temperature to allow the surface of the coarse coke powder to undergo three-dimensional network curing and crosslinking, thus obtaining a modified main reducing agent with a moisture-proof crosslinked hard shell on the surface. S2. The second-cycle fine coke dust, rolled steel scale powder, coarse limestone powder and the primary cross-linking bonding slurry are mixed and stirred, and then forced into flat spherical blocks and air-dried to obtain composite sacrificial blocks. S3. High-purity iron concentrate and the modified main reducing agent prepared in step S1 are alternately filled into the silicon carbide crucible from bottom to top to form a bottom layer material bed; composite sacrificial blocks are laid out in a staggered and tight manner on the top layer of the bottom layer material bed. S4. The silicon carbide sagger containing the high-purity iron concentrate, modified main reducing agent and composite sacrificial block is pushed into the tunnel kiln and continuously thermally reduced according to the set temperature zone program. After the thermal reduction in the tunnel kiln is completed, the sagger is cooled and discharged from the kiln. The porous sponge-like solidified slag block formed on the top of the silicon carbide sagger due to iron lattice shrinkage and solid phase sintering is physically peeled off. The material in the lower part of the silicon carbide sagger is mechanically crushed and magnetically separated to separate the high-purity sponge iron product.

2. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, In steps S1 and S2, the preparation method of the primary crosslinking adhesive slurry includes: Lignosulfonate calcium powder was uniformly added to deionized water to prepare a lignin sulfonate calcium aqueous solution; quicklime powder was added to the lignin sulfonate calcium aqueous solution under continuous shear stirring, and the temperature and speed were maintained for continuous reaction, so that the free divalent calcium ions in the mixed system could undergo ionic complexation bridging with the sulfonic acid groups and carboxyl groups on the lignin macromolecular chain, thus obtaining the primary crosslinking adhesive slurry with shear thinning characteristics.

3. The method for recycling coke residue in the production of reduced iron powder according to claim 2, characterized in that, The process parameters for preparing the primary crosslinking adhesive slurry are as follows: The mass concentration of the calcium lignosulfonate aqueous solution is 15.0% to 20.0%; The amount of quicklime powder added is 0.15 to 0.6 parts by weight relative to 100 parts by weight of the calcium lignosulfonate aqueous solution; The reaction temperature is controlled at 15–30°C, and the reaction is stirred continuously for 15–30 minutes.

4. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, In step S1, the specific implementation method and ratio of the modified main reducing agent are as follows: By weight, 95.5 to 97.0 parts of the first-stage coarse coke powder and 1.5 to 2.0 parts of dolomite powder are dry-mixed, and then 8.5 to 12.5 parts of the primary cross-linking adhesive slurry are evenly sprayed on and kneaded continuously for 10 to 15 minutes. The constant temperature drying temperature is 140-160℃, and the constant temperature drying time is 35-45 minutes.

5. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, In step S2, the process parameters and proportions of the composite sacrificial block are as follows: By weight, 50.0-65.0 parts of the second-cycle fine coke powder, 30.0-40.0 parts of the rolled steel scale powder and 5.0-10.0 parts of the coarse limestone powder are mixed, and 7.0-9.5 parts of the primary cross-linking adhesive slurry are added, and the mixture is stirred continuously for 15 minutes. The mixed materials are forcibly pressed into flat spherical blocks with a diameter of 35-45 mm under a linear pressure of 15-25 MPa. The air-drying temperature is 70-90℃, and the air-drying time is 100-150 minutes.

6. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, The specific process parameters for step S3 are as follows: In the bottom bed, the mass ratio of high-purity iron concentrate to modified main reducing agent is 100:35-45; The bottom layer of material bed is filled to a height of 70.0% to 80.0% of the total internal volume of the silicon carbide sagger; After the composite sacrificial blocks are laid out in a staggered and tight manner, the polymer components in the composite sacrificial blocks are used to form a physical covering and sealing layer by thermoplastic softening and deformation in the preheating section of the tunnel kiln. After the physical covering sealing layer is formed, the top surface of the physical covering sealing layer is 2.0 to 4.0 cm away from the upper opening edge of the silicon carbide crucible.

7. The method for recycling coke dust in the production of reduced iron powder according to claim 1, characterized in that, In step S4, the operating time and ambient temperature of each characteristic temperature zone of the tunnel kiln thermal reduction are controlled as follows: The system operates for 3.5 to 4.5 hours within the temperature range from 25°C to 700°C. The system operates for 2.0 to 3.0 hours within a temperature range of 750°C to 900°C. During this stage, the decomposition and heat absorption of coarse limestone powder in the composite sacrificial block are used to construct a heat distribution buffer across the temperature range. It then enters the high-temperature zone and is heated to 1040–1060℃ and maintained at that temperature for 28.0–32.0 hours. During the thermal reduction process in the tunnel kiln, the dolomite powder provides an in-situ heat buffer for the thermal reduction system through the pyrolysis endothermic mechanism in the high-temperature section; and the deoxidation phase change of the rolled steel scale powder in the high-temperature section generates volume shrinkage, providing a channel for exhaust and pressure relief during the intense gas generation stage of the thermal reduction in the tunnel kiln.

8. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, The characteristic parameters of the first-cycle coarse coke powder and the second-cycle fine coke powder are as follows: The coarse coke powder has a fixed carbon mass fraction of not less than 80.0%, an ash mass fraction of not more than 15.0%, and an average particle size range of 1.0 to 3.0 mm. The fixed carbon mass fraction of the second-cycle fine coke is 60.0% to 70.0%, the ash mass fraction is not less than 20.0%, and the average particle size is less than 1.0 mm.

9. The method for recycling coke residue in the production of reduced iron powder according to claim 2, characterized in that, The characteristic parameters of the calcium lignosulfonate powder, the dolomite powder, and the rolled steel scale powder are as follows: The weight-average molecular weight of the calcium lignosulfonate powder ranges from 8,000 to 15,000, and the molecular weight distribution index ranges from 3.0 to 5.

0. The purity of the dolomite powder is not less than 98.0%, and the particle size range is 200-325 mesh. The mass fraction of iron tetroxide in the coarse powder of the rolled steel scale is not less than 90.0%, and the average particle size is less than 2.0 mm.

10. The method for recycling coke residue in the production of reduced iron powder according to claim 1, characterized in that, In step S4, the specific post-processing technology is as follows: The silicon carbide saggers containing the high-purity iron concentrate, modified main reducing agent and composite sacrificial blocks are carried into the cooling zone by the kiln car and cooled to 90-98°C before exiting the kiln. The rated magnetic field strength of the magnetic separator used for separation after the material in the lower part of the silicon carbide crucible is 0.15T.

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