A sintering method for reinforcing ultrafine particle grade ultra-high proportion fine powder

Abstract

The application relates to a sintering method for reinforcing super-fine particle grade super-high proportion fine powder, realizes improvement of a sintering utilization coefficient, stable improvement of a sinter ore ferrous oxide (FeO) content and improvement of drum strength, belongs to the technical field of steel metallurgical sintering, constructs four continuous steps of cylinder quicklime digestion, strong mixing, cylinder pre-nucleation and cylinder granulation and a water distribution mode, and strengthens sintering process control. The method fundamentally improves sintering material layer air permeability, improves the utilization coefficient, reduces solid fuel consumption, and significantly improves sinter ore composition stability and metallurgical properties.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgical production technology, specifically to a sintering method for strengthening ultrafine particle size and ultra-high proportion of refined powder, so as to improve the sintering utilization coefficient, stabilize and increase the ferrous oxide (FeO) content of sintered ore, and improve the drum strength. Background Technology

[0002] The utilization coefficient of sintering is one of the most critical indicators in sintering production. Sintering of ultrafine-grained, high-proportion fine powders suffers from poor granulation effects and high powder removal rates, leading to deteriorated permeability, decreased utilization coefficient, and increased power consumption. The main problems are as follows: 1. Difficult granulation and deteriorated permeability: Ultrafine mineral powders have a huge specific surface area and strong moisture adsorption capacity, making it difficult to form granulation nuclei. Tight packing easily forms between particles, significantly reducing the porosity of the sintered material layer and severely hindering airflow, becoming the core contradiction restricting the sintering process.

[0003] 2. Uneven combustion and thermal instability: Poor permeability of the material layer leads to uneven airflow distribution, with the upper fuel prone to premature combustion and insufficient airflow in the lower part. This vertical heat unevenness makes the sintering process less uniform, easily producing a large amount of undercooked material with low strength and poor reducibility, and increasing the proportion of returned ore.

[0004] 3. High fuel consumption and low efficiency: To compensate for insufficient heat caused by poor permeability, the proportion of solid fuel is forced to increase. This not only increases energy consumption and cost, but also easily causes local overheating, deteriorates the metallurgical performance of sintered ore, and forms a vicious cycle of "high consumption and low quality".

[0005] 4. Deterioration of sinter quality and structure: An excessively high proportion of ultrafine powder can lead to rapid and uneven liquid phase formation and distribution, increasing the brittleness of the sinter structure and raising the reduction and pulverization rate. Simultaneously, excessively fine raw materials are not conducive to forming a microporous structure with both excellent strength and reducibility, thus affecting the smooth operation of the blast furnace.

[0006] Therefore, it is urgent to systematically reconstruct the sintering process by taking measures such as improving granulation effect in order to adapt to the new challenges of sintering ultrafine particles with an ultra-high proportion of fine powder.

[0007] The purpose of this invention is to provide a sintering method for ultra-fine, high-proportion fine powder. Through the invented "four-step" mixing and granulation method, the inherent challenges of sintering ultra-fine powder with a high proportion of fine particles are systematically solved. First, ideal quasi-particles with micro-cores and well-developed pores are formed. Then, granulation and pelletizing are intensified to improve the overall permeability of the material layer and the uniformity of the vertical thermal field. This ensures particle uniformity and strength from the source of raw material pretreatment, laying the foundation for uniform and appropriate liquid phase generation during sintering. Ultimately, this promotes the formation of high-strength, highly reducible, high-quality sinter, ensuring the efficient and smooth operation of the blast furnace. Summary of the Invention

[0008] The purpose of this invention is to address the above-mentioned problems by providing a sintering method for strengthening ultrafine particle size and ultra-high proportion of refined powder.

[0009] The objective of this invention is achieved as follows: A sintering method for enhanced ultrafine particle size and ultra-high proportion of refined powder, comprising the following steps: Step 1: The sintering mixture enters a cylindrical mixer, where a high proportion of quicklime in the mixture undergoes a digestion reaction with water. The large amount of chemical heat released during this reaction preheats the mixture, raising the overall temperature of the material to 50-60°C. The amount of water added in the first step is controlled to be 80%-85% of the total water added, with a moisture content of 6-6.5% sufficient to fully digest the quicklime while also meeting the moisture requirements for granulation. Step 2: The preheated material then enters a high-pressure mixer. The equipment operates at a speed of 880-920 r / min and a high shear force of 1500-2400 Pa. The material is vigorously stirred to form a homogeneous mixture matrix, with a mixing time of 55-70 seconds. Step 3: The mixture is conveyed to a cylindrical pellet mill for pre-nucleation. The amount of water added in the second step is controlled to be 15-20% of the total water added. The moisture content of the mixture during pelleting is 7.5-7.9%. The mill rotates at a low speed of 5.5-6.5 rpm for 2-2.5 minutes. Step 4: The material enters the cylindrical pellet mill, and additional atomized water is sprayed onto the material to form quasi-granules.

[0010] The total amount of water added in steps one and three is 60-70 tons.

[0011] The beneficial effects of this invention are: fundamentally improving air permeability and structure, achieving efficient and low-consumption production. The "micro-nucleus-layered growth" quasi-particle structure generated by the process significantly increases the proportion of ideal particle size (+3mm) in the granulated pellets from 58.6% to 70.5%, while suppressing excessively coarse particles (the proportion of +8mm particles decreased from 14.2% to 10.1%) and reducing the granulation moisture content to 7.8%. This more uniform and porous particle composition fundamentally improves the air permeability of the material layer. It directly reduces the power consumption of the main exhaust fan by 1.23 kWh / t, and makes it possible to achieve stable sintering with "low negative pressure and high material layer" under ultra-high proportion of ultrafine powder, thereby effectively increasing the sintering utilization coefficient from 1.10 t·m² / h to 1.28 t·m² / h, achieving a synergistic effect of increased production and energy saving.

[0012] 2. Optimized combustion process, significantly reducing fuel consumption. The preheating and vigorous wetting of quicklime, combined with improved vertical thermal field uniformity resulting from increased permeability, fundamentally reduces the need for lower-level heat compensation. Solid fuel consumption is thus reduced, while the physical heat of material preheating and more complete combustion further enhance overall thermal efficiency.

[0013] 3. Comprehensive improvement in sinter quality and compositional stability. Uniform pretreatment and ideal particle structure ensure the homogeneity and stability of chemical reactions during sintering. This is directly reflected in a significant leap in the stability of key chemical components in the sinter: the basicity (R) ±1 stability rate increased from 94.20% to 97.70%, and the FeO ±1 stability rate increased dramatically from 76.10% to 90.30%. This provides a highly stable and high-performance raw material guarantee for the blast furnace to achieve high efficiency, low consumption, and long-term smooth operation. Attached Figure Description

[0014] The present invention will now be further described with reference to the accompanying drawings.

[0015] Figure 1 This is a flowchart of the "four-step" mixing and granulation process of this invention. Detailed Implementation

[0016] In the sintering and granulation process, ultra-fine particles with a high proportion of fine powder lack core particles, making it difficult for them to grow into large spheres. This results in a decrease in the content of coarse particles and an increase in the content of fine particles in the granulated mixture. The gaps between coarse particles are filled with a large number of fine particles, which increases the resistance when the airflow passes through the material layer. The permeability of the original material belt deteriorates, leading to a decrease in permeability and a high negative pressure during the sintering process. This reduces the sintering production efficiency and causes a decline in quality indicators.

[0017] A method for enhancing sintering and setting appropriate moisture content by combining "cylindrical quicklime digestion + vigorous mixing + cylindrical pre-nucleation + cylindrical granulation" was developed. 1. Significant improvements were made to the uniformity of sintering material mixing and granulation effect: the proportion of +3mm granules increased from 58.6% to 70.5%, while the proportion of +8mm granules decreased from 14.2% to 10.1%, and the granulation moisture content decreased from 8.3% to 7.8%. 2. Sintering yield indicators were improved: the utilization coefficient of ultrafine-grained, high-proportion refined powder under low negative pressure and high material layer sintering was increased from 1.10 t∙m. 2 / h increased to 1.28t∙m 2 / h; 3. Improved stability of chemical composition of sinter: The stability of R (basicity) and FeO±1 of sinter increased from 94.20% and 76.10% to 97.70% and 90.30%, respectively.

[0018] This invention provides an enhanced process technology solution for sintering ultra-high proportion ultrafine powder, optimizing the granulation process from the raw material and water source. Through the invented "four-step" mixing and granulation method, the inherent problems of ultra-high proportion ultrafine powder sintering are systematically solved. This is achieved by improving the granulation starting point and addressing the production bottleneck of poor air permeability in ultrafine particles with a high proportion, by optimizing the sequence of steps such as "cylindrical quicklime digestion," "intensive mixing," and "pelleting." The proportion, sequence, and control center line of water addition to the mixture are also addressed during the granulation process.

[0019] The preliminary preparation process is as follows: 5-8 kinds of iron-containing raw materials are piled up according to the requirements of composition and performance. The number of pile layers is more than 4,000, forming a relatively uniform ore pile of about 60,000 to 80,000, which is used as raw material for sintering. The standard deviation of Tfe in the uniform ore pile is ≤0.39, and the standard deviation of SiO2 is ≤0.19.

[0020] The homogenized ore, quicklime, limestone, dolomite, coke powder, coal powder, and return ore are fed onto the same conveyor belt by a disc feeder according to the calculated proportions and then enter the cylindrical mixer.

[0021] The core of this technical solution lies in deconstructing and upgrading the traditional simple mixing and granulation process into four consecutive, precisely coordinated steps: 1. The material enters the cylindrical mixer. Here, a high proportion of quicklime undergoes a vigorous digestion reaction with a large amount of added water, effectively preheating the mixture by utilizing the large amount of chemical heat released. This step increases the overall temperature of the material (50-60℃), and more importantly, the generated steam can quickly penetrate and evenly surround the surface of the ultrafine powder particles, laying the thermodynamic and humidity foundation for subsequent deep mixing.

[0022] In this process, the initial target water addition (atomized water, pressure ≥0.25Mpa) is controlled at about 80%, and the appropriate moisture content is reduced from the original 7% to about 6%. Because the subsequent strong mixing can make the water more evenly dispersed on the surface of the material, the ineffective water in the granulation process is reduced, thus achieving better mixing and granulation results under the condition of significantly reduced moisture.

[0023] 2. The preheated material then enters the high-intensity mixer. This equipment uses high speed and high shear force to vigorously stir the material. Its main purpose is to completely break down the agglomeration and adsorbed water film between ultrafine powder particles under high temperature and high humidity conditions, so as to achieve a highly uniform distribution at the microscale of iron, flux, fuel and return ore, ensuring that moisture is evenly wrapped around each particle in the form of a "molecular film", completely eliminating the "dead core" of dryness, and forming a homogeneous mixture matrix.

[0024] Under the combined effects of shearing, impact, and convection from the four high-speed rotating rotors and stators, the material is violently agitated and stirred. The mixing time is greater than or equal to 60 seconds.

[0025] 3. The mixture is conveyed to the crucial cylindrical pellet mill pre-nucleation unit. This equipment is a low-speed rotating cylinder with flexible liners and guide plates on its inner wall. The extremely fine particles (<0.25mm), which have been fully wetted and uniformly coated, collide and adhere to each other during the rolling process due to their high capillary water and molecularly bound water content, gradually forming dense and robust primary micronuclei with return ore or a small amount of coarse particles as the core. This step aims to "manufacture" a large number of stable pellet "nuclei" with sufficient strength.

[0026] During this process, the added water content of the mixture is controlled to be around 20% (atomized water, pressure ≥0.25Mpa), and the suitable granulation moisture content is reduced from the original 8.5% to around 7.6%.

[0027] 4. The material enters the final cylindrical granulator. At this stage, atomized water is precisely sprayed onto the rolling material, which already contains numerous robust micronuclei. During continuous rolling, the finer particles on the periphery, through capillary action, gradually coat the existing micronuclei, causing the particles to grow larger. Ultimately, this results in ideal sintering "quasi-granules" with micronuclei as the core, well-developed pores, a reasonable particle size distribution (e.g., a significantly increased proportion of 1-3mm particles), and high mechanical strength.

[0028] In the first, second, and fourth stages of atomized water addition and multi-angle spraying, the addition of micron-level atomized water during granulation ensures uniform water addition. The water atomization and segmented multi-angle spraying device consists of a water tank, pipelines, steam heating, pipeline pressurization pump, flow control valve, spiral nozzle, and compressed air pressurization, forming a complete controlled atomization system for filtration, heating, and pressurization. This improves water utilization efficiency, reduces ineffective dripping water, meets the optimal granulation moisture requirements, and achieves low-water granulation.

[0029] After the above-mentioned improvements to the strengthening process, the powder removal rate after three drops of granulated pellets and drying was improved. In particular, the powder removal rate after drying was reduced from 15.6% to 10.5%. This method significantly improved the strength of the granulated pellets, supported the improvement of sintering process parameters and the quality of sintered ore, reduced the amount of dust generated during sintering, and also helped to reduce the emission concentration of particulate matter in sintering flue gas, thus promoting the achievement of ultra-low emission targets.

[0030] The technical solution and subsequent sintering production operation parameters are controlled as follows: 1. Machine speed is stable at 1.8-2.05 m / min; 2. Material layer is above 810-830 mm; 3. Moisture content of the mixture is 7.8±0.2%; 4. Temperature of No. 17 air box is maintained at 100-140℃; 5. The final temperature is guaranteed to be 400-450℃. Example 1

[0031] A steel company uses a 450㎡ large sintering machine to produce sintered iron concentrate, primarily using its own ultrafine iron concentrate. The iron concentrate proportion in the sintering process is 85-90%, and some materials have a specific surface area of ​​800 μm. 2The iron concentrate content is above 60%, but the excessively high proportion of iron concentrate results in a binder content of over 60% in the sintering raw materials. This leads to a lack of core particles during granulation, making it difficult for the particles to grow into large spheres. Consequently, the content of coarse particles in the granulated mixture decreases while the content of fine particles increases. The gaps between coarse particles are filled with a large number of fine particles, increasing the resistance when the airflow passes through the material layer. This worsens the permeability of the original material strip, reduces the sintering utilization coefficient by 10.56%, decreases the drum strength by 1.53%, and deteriorates both the output and quality.

[0032] The method provided by this invention is implemented as follows: the homogenized ore ratio used in this sintering process is shown in the table below.

[0033]

[0034] The actual concentrate content accounts for 80-90% of the iron material. The standard deviation of Tfe in the homogenized ore pile is ≤0.39, the standard deviation of SiO2 is ≤0.19, Tfe is 63-64.5%, SiO2 is 5.10-5.15%, MgO is 0.69-0.75%, and CaO is 1.0-1.35%.

[0035] A high proportion of quicklime is added to the batching room to enhance sintering.

[0036]

[0037] Binary alkalinity R = 2.2.

[0038] The key points for production control are as follows: 1. The machine speed should be stable at around 1.9 m / min; 2. The material layer should be above 820 mm; 3. The moisture content of the mixture should be 7.8 ± 0.1%; 4. The temperature of the No. 17 air box should be maintained above 100℃; 5. The final temperature should be guaranteed to be 400-450℃; 6. The overall feeding rate should be 850 t / h.

[0039] The main methods and equipment (facilities) for enhanced granulation and sintering are as follows: 1. Cylindrical quicklime slaking and mixing machine: Equipment parameters: Specifications: φ4400×17000mm, Production capacity: 1200t / h, Material bulk density: 1.63~1.7t / m³ 3 Filling rate: 12-13%, cylinder inclination angle: 2.2°, rotation speed: 6 r / min, mixing time: 2.7-2.9 min.

[0040] Material Proportioning and Operation: A mixture of quicklime (CaO 88.2-93.2%) at a ratio of 9.5%-11.5% (by mass) is fed into a digester (cylindrical mixer). Simultaneously, digestion water equivalent to 60%-80% of the quicklime's mass is added via a water addition (spray) device. The quicklime reacts violently with water, resulting in a violent exothermic reaction. The released chemical heat rapidly raises the material temperature to the range of 50℃-75℃, while simultaneously generating a large amount of water vapor.

[0041] Function and Effects: The core of this step is to effectively preheat all materials using the heat of digestion, and to rapidly penetrate and pre-wet the surface of the ultrafine powder particles using steam. The high-temperature and high-humidity environment creates ideal conditions for subsequent vigorous mixing, initially alleviating the "dry core" problem of the ultrafine powder. The residence time of the material in the cylinder is controlled at 2-4 minutes to ensure that the quicklime is fully digested and the heat distribution is relatively uniform.

[0042] 2. High-power mixing: Equipment parameters: Model: SEW3C630NE-1395, Center distance: 1395mm, Speed ​​ratio: 33, Open gear: Module: 40, Speed ​​ratio: Z2 / Z1=134 / 27, Micro-motion device: Reducer model: XWD18.5-8195-1 / 29, Motor power: 18.5KW.

[0043] Operation: The preheated material is fed into the high-intensity mixer via a conveyor belt. Under the combined effects of shearing, impact, and convection from the high-speed rotating rotor and stator, the material is violently agitated and stirred. The mixing time is typically 60-120 seconds.

[0044] Function and Effects: This step aims to achieve microscopic homogenization of the materials. The powerful mechanical force thoroughly breaks up agglomerates of ultrafine powder, ensuring a highly uniform mixture at the molecular scale of the iron, flux (including hydrated lime), fuel (coke powder or anthracite), and return ore particles. Simultaneously, it ensures that moisture is uniformly coated on the surface of each solid particle in the form of an extremely thin "molecular film," completely eliminating areas of excessive moisture or dryness, and forming a homogeneous and fully wetted mixture matrix. This is the physicochemical basis for forming high-quality quasi-particles.

[0045] 3. Pre-nucleation of cylinders: Equipment parameters: φ4400×18000mm; Production capacity: Normal 640t / h, maximum 874t / h; Material bulk density: 1.63~1.7t / m³ 3 Filling rate: Fastest: 10.8%, Slowest: 11.95%; Cylinder inclination angle: 1.6°; Rotation speed: 5.5~7r / min; Granulation time: 3.584~4.562min.

[0046] Procedure: The homogenized material after vigorous mixing is fed into a cylinder for pre-nucleation. No additional moisture is added during this process.

[0047] Function and Effect: Under the gentle shearing environment of low-speed rolling, finely sized (e.g., <0.25mm) material particles, which have been fully and uniformly wetted, adhere to each other through continuous collisions and contact, with return ore particles or a small amount of slightly coarser material as the core. This process gradually forms a large number of robust "micronuclei" with a particle size of 0.5-1.5mm, a dense structure, and high mechanical strength. These micronuclei serve as "seeds" for subsequent particle growth, and their quantity and quality directly determine the uniformity and strength of the final quasi-particles. The material residence time in this step is approximately 3-5 minutes.

[0048] 4. Cylindrical Granulation: Equipment parameters: φ4400×15000mm; Production capacity: Normal 1000t / h, maximum 1200t / h; Material bulk density: 1.63~1.7t / m³ 3 Filling rate: 13-14%; cylinder inclination angle: 2.2°; rotation speed: 6.5 r / min; mixing time: 1.15-1.25 min.

[0049] Operation: The material containing a large number of solid micro-cores is transported to the cylindrical pellet mill. As the material rolls up and falls with the cylinder, moisture (granulation water) is precisely and evenly sprayed into the material flow through atomizing nozzles. The amount of water added is controlled according to the target final moisture content (target 7.8±0.1%).

[0050] Function and Effect: During the rolling process, the added water, under the action of capillary force, causes the finer particles (mainly in the 0.25-1mm range) that have not yet adhered to the substrate to be layered onto the pre-formed, robust micronuclei, and the particles gradually grow like a snowball. Ultimately, "quasi-particles" are formed with micronuclei as the core, a distinct hierarchical structure, a rough surface, and well-developed internal pores. The particle size distribution is more reasonable, with a significant increase in the proportion of ideal intermediate particle sizes (such as 1-3mm and 3-5mm) and a decrease in the proportion of excessively coarse particles (such as >8mm).

[0051] Implementation Results: 1. Improved Granulation Indicators: In the granulated granules, the proportion of ideal particle size of +3mm increased significantly from 58.6% in the traditional process to 70.5%, while the proportion of oversized particles of +8mm decreased from 14.2% to 10.1%. The average particle strength was improved, and the permeability index of the material layer improved by about 15%.

[0052] 2. Improved production indicators: While maintaining a high material layer (≥820mm), the sintering machine can achieve stable operation under low negative pressure (≤15kPa) due to the fundamental improvement in material layer permeability. The sintering speed is accelerated, and the utilization coefficient increases from 1.10t·m² / h to 1.28t·m² / h.

[0053] 3. Optimized Quality Indicators: The sintering process is more stable and uniform, and the fluctuation of chemical composition of the sinter is reduced. Specifically, the stability rate of basicity (R) ±1 increased from 94.20% to 97.70%, and the stability rate of FeO content ±1 significantly increased from 76.10% to 90.30%. The drum strength of the sinter increased by 0.32%, and the reduction pulverization rate (RDI+3.15) decreased by approximately 1.5%.

[0054] 4. Energy consumption index decreased: Due to improved material layer permeability and uniform vertical thermal field, solid fuel consumption decreased by about 0.55 kg / t, and the main exhaust fan power consumption decreased by about 8%.

[0055] In summary, the present invention, through the systematic implementation of the above-mentioned four-step strong mixing process, effectively solves the industry problem of sintering ultra-high proportion ultrafine powder, and achieves synergistic optimization of increased production, improved quality, and reduced consumption.

[0056] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A sintering method for strengthening ultrafine particle size with an ultra-high proportion of refined powder, characterized in that: Includes the following steps: Step 1: The sintering mixture enters the cylindrical mixer. Here, a high proportion of quicklime in the mixture undergoes a digestion reaction with water. The large amount of chemical heat released is used to preheat the mixture, raising the overall temperature of the material to 50-60℃. The amount of water added in the first step is controlled to be 80%-85% of the total water added. A moisture content of 6-6.5% is sufficient to fully digest the quicklime and meet the moisture requirements for granulation of the mixture. Step 2: The preheated material is then fed into a high-intensity mixer. The speed of this equipment is 880-920 r / min and the high shear force is 1500-2400 Pa. The material is vigorously stirred to form a homogeneous mixture matrix. The mixing time is 55-70 seconds. Step 3: The mixture is conveyed to the cylindrical pellet mill for pre-nucleation. The amount of water added in the second step is controlled to be 15-20% of the total water added. The moisture content of the mixture during pelleting is 7.5-7.9%. The mill rotates at a low speed of 5.5-6.5 rpm for 2-2.5 minutes. Step 4: The material enters the cylindrical pellet mill, and additional atomized water is sprayed onto the material to form granules.

2. The sintering method for strengthening ultrafine particle size and ultra-high proportion of refined powder according to claim 1, characterized in that: The total amount of water added in steps one and three is 60-70 tons.

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