Iron ore sintering method based on oak charcoal replacing coke breeze

Abstract

The present application belongs to the technical field of steel metallurgy, in order to solve the technical problems existing in the replacement of coke powder by biomass, a kind of iron ore sintering method based on oak charcoal replacing coke powder is disclosed, comprising the following steps: step 1, preparation of mixed material and mixed granulation: the mixed material, return to the mine, lime and coke-oak charcoal mixture are mixed, and water is added for granulation to obtain sintering mixed material; step 2, distribution: the sintering ore is placed in the sintering furnace as the bottom material, and the sintering mixed material is placed above the bottom material; step 3, ignition: open the exhaust system and the igniter to ignite; step 4: sintering: after ignition is completed. The present application compensates for the heat supply lag caused by the too fast burning speed through oxygen-enriched sintering, solves the excess and deficiency of heat in the vertical direction through layered distribution, and realizes a high proportion of 40%-55% replacement.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for sintering iron ore based on replacing coke powder with oak char. Background Technology

[0002] Sintering is currently the main preparation process for blast furnace feedstock in long-process steel production, accounting for more than 70% of the raw materials fed into the blast furnace. The traditional sintering process involves mixing iron ore powder, flux (limestone, quicklime, etc.), solid fuel (coke powder, anthracite), and return ore in a certain proportion, adding water to granulate, and then feeding the mixture onto the sintering machine trolley. After ignition and blast sintering, the mixture undergoes a physicochemical reaction at high temperature, producing a partial liquid phase that binds the mineral particles into lumps. Finally, the finished sintered ore is obtained through cooling, crushing, and screening.

[0003] However, the sintering process is also a major contributor to energy consumption and pollutant emissions in steel production. The sintering process suffers from the following problems: 1. Carbon emissions: Currently, sintering plants mainly use fossil fuels such as coke powder and anthracite, which generate a large amount of CO2 during combustion. According to statistics, the energy consumption of the sintering process accounts for about 10% to 15% of the total energy consumption of steel production, while its carbon emissions account for a relatively high proportion.

[0004] 2. Pollutant emissions: Coke powder contains high levels of sulfur (S) and nitrogen (N) elements (typically S content is high). 0.5%, N content (0.6%), resulting in high levels of SO2 and NO in the combustion exhaust gas. x Air pollution control in the steel industry is both a key focus and a challenge.

[0005] Under the national "dual-carbon" strategy, finding clean and renewable alternative energy sources has become an inevitable trend in the development of sintering technology. Biomass resources, as the fourth largest energy source after coal, oil, and natural gas, possess natural advantages such as carbon neutrality (CO2 absorbed during the growth process offsets combustion emissions), low sulfur content, and low ash content. Studies have shown that maximizing the use of biomass products can reduce CO2 emissions in the steel industry by 43%.

[0006] Although biomass has enormous potential to replace coke powder in terms of emission reduction, it faces many technical challenges in practical applications, as follows: 1. Not suitable for native biomass: Native biomass (such as straw, sawdust) has high moisture content and low carbon content (fixed carbon). It has the characteristics of low volatile matter content (20%) and low calorific value, and extremely high volatile matter content. Directly adding it to the sintering bed not only fails to provide sufficient melting heat, but also damages the bed structure and deteriorates permeability due to the large amount of volatile matter escaping, resulting in a significant decrease in the strength of the sinter.

[0007] 2. Defects of Ordinary Biochar: To improve performance, pyrolysis carbonization technology is usually used to convert biomass into biochar. However, commercially available biochar (such as straw charcoal, bamboo charcoal, and fruitwood charcoal) still has serious problems: Bamboo charcoal and straw charcoal: These materials are loosely textured, have low density, and poor mechanical strength. During the mixing and granulation process, they are easily broken into fine powder. Due to their strong hydrophobicity, they are difficult to participate in granulation and often exist as floating ash, leading to deterioration of the permeability of the sintering layer. Furthermore, due to their extremely high reactivity (excessively fast combustion rate), the combustion front velocity is much greater than the heat transfer front velocity, resulting in a very short high-temperature holding time, insufficient liquid phase formation, and a precipitous drop in sinter strength. Experimental data shows that when the bamboo charcoal substitution rate reaches 30%, the sinter drum strength and yield deteriorate sharply, and the return rate increases significantly.

[0008] Combustion characteristics mismatch: Ordinary biochar has extremely high porosity and large specific surface area, and contains alkali metals (K, Na) for catalytic combustion, which leads to excessively concentrated and rapid heat release during the sintering process. This results in large fluctuations in the sintering process, either "overcooling" or "overheating", making it impossible to maintain a stable ore-forming temperature range (1200℃~1400℃).

[0009] 3. Outdated ignition method: Traditional sintering uses gas (coke oven gas or blast furnace gas) for ignition. This method not only consumes secondary energy, but also causes moisture and CO2 produced during combustion to enter the surface of the material layer, affecting the permeability and flame propagation speed in the initial stage of ignition.

[0010] 4. Deterioration of Metallurgical Performance: As the proportion of biochar substitution increases, the FeO content in sinter often exhibits abnormal fluctuations. On the one hand, due to the high reactivity of biochar, the reducing atmosphere is difficult to control; on the other hand, in pursuit of high strength, excessive fuel consumption leads to excessively high FeO content, reducing reducibility; while insufficient fuel results in insufficient strength. How to reduce FeO content while maintaining strength is a key challenge in high-proportion biochar substitution sintering.

[0011] Therefore, there is an urgent need to develop a method that can adapt to high-proportion substitution ( This invention presents a new biomass sintering technology that achieves 30% reduction, maintains or even improves the quality of sintered ore, and enables deep emission reduction. Based on research into the physicochemical properties of oak char, a unique biomass fuel, and combining plasma ignition with process atmosphere control, this invention proposes a comprehensive systemic solution. Summary of the Invention

[0012] The purpose of this invention is to address the technical deficiencies in the prior art by providing a method for iron ore sintering based on replacing coke powder with oak charcoal.

[0013] The technical solution adopted to achieve the purpose of this invention is: A method for sintering iron ore based on replacing coke powder with oak charcoal includes the following steps: Step 1, Preparation of homogenized material and granulation: Mix the homogenized material, recycled ore, quicklime, and coke powder-rubber char mixture, add water and granulate to obtain sintered homogenized material; Step 2, Material Placement: Place the sintered ore in the sintering furnace as the bottom material, and place the sintered mixed material on top of the bottom material; Step 3, Ignition: Turn on the ventilation system and igniter to ignite; Step 4: Sintering: After ignition, sintering is carried out by exhaust ventilation.

[0014] In the above technical solution, in step 1, the mass ratio of oak charcoal in the coke powder-oak charcoal mixture is 5%~55%, more preferably 40%~55%, and even more preferably 40%.

[0015] In the above technical solution, in step 1, the mass ratio of the mixed material, the return ore, quicklime, and the coke powder-rubber charcoal mixture is (76~80):(9~12):(6~7.5):(4.0~5.0), preferably 78.5:10.3:6.7:4.5.

[0016] In the above technical solution, in step 2, the particle size of the sintered ore is 10mm to 16mm, and the thickness of the bottom material is 30cm to 40cm.

[0017] In the above technical solution, in step 2, the sintering mixture is arranged in layers, and from top to bottom, the mass ratio of rubber char in each layer of sintering mixture decreases layer by layer.

[0018] In the above technical solution, the layering is divided into 2 to 3 layers.

[0019] In the above technical solution, the mass ratio of rubber char in each layer of sintered homogenized material decreases linearly layer by layer, with each layer decreasing by 10-15% compared to the previous layer.

[0020] In the above technical solution, in step 3, the igniter is a plasma igniter.

[0021] In the above technical solution, in step 3, after the exhaust system is turned on, oxygen-enriched gas is introduced from the top of the sintering furnace. Preferably, the oxygen concentration in the oxygen-enriched gas is 23±0.25%~24±0.25%, and more preferably 23±0.25%.

[0022] In the above technical solution, the sintering time in step 4 is 35-40 minutes.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. The fixed carbon content of oak charcoal (84.31%) is significantly higher than that of coke powder (69.42%), meaning that oak charcoal provides more carbon source for combustion and reduction per unit mass. The ash content of oak charcoal (4.46%) is much lower than that of coke powder (29.36%), greatly reducing the introduction of ineffective minerals during sintering and thus improving the grade of sintered ore. Compared to fruitwood charcoal and bamboo charcoal, the volatile matter content of oak charcoal (5.90%) is controlled at a lower level, avoiding problems such as deflagration in the initial combustion stage and excessively large porosity.

[0024] 2. Oak charcoal has a higher net calorific value (28376.3 J / g) than coke powder (26631.8 J / g), exhibiting superior thermal performance. Furthermore, the sulfur content of oak charcoal (0.015%) is only 1.6% of that of coke powder (0.925%), and its nitrogen content is also significantly reduced (0.169% vs 0.676%), thus addressing the SO2 problem at its source. x and NO x The emissions problem.

[0025] 3. The combustion characteristic index P of oak charcoal is nearly 9 times that of coke powder, and its ignition point is nearly 200 degrees Celsius lower. Oak charcoal burns extremely fast, and if not controlled, it will cause the heat to be released too quickly and cannot be effectively absorbed by the material layer. This invention compensates for the lag in heat supply caused by the excessively fast combustion speed through oxygen-enriched sintering, and solves the problem of excess and insufficient heat in the vertical direction through layered material distribution, achieving a high proportion of replacement of 40%-55%. Attached Figure Description

[0026] Figure 1 The diagram shown is a structural schematic of a small sintering cup system.

[0027] In the diagram: 1-fan, 2-dust collector, 3-sampling hole, 4-igniter, 5-temperature measuring hole, 6-grate, 7-hydraulic jack, 8-sintering cup.

[0028] Figure 2 These are the process steps of the iron ore sintering method.

[0029] Figure 3 This is a graph showing the peak temperature of the combustion gas and the sintering endpoint time when oak char replaces coke powder.

[0030] Figure 4 This is a graph showing the temperature changes at various measuring points during the sintering process.

[0031] Figure 5 This is a peak temperature graph of the first temperature measuring point during the sintering process of replacing coke powder with oak charcoal.

[0032] Figure 6 This is a peak temperature graph of the second temperature measuring point during the sintering process of replacing coke powder with oak charcoal.

[0033] Figure 7This is a peak temperature graph of the third temperature measuring point during the sintering process of replacing coke powder with oak charcoal.

[0034] Figure 8 This relates to the impact of replacing coke powder with oak charcoal on the return rate.

[0035] Figure 9 This is a graph showing the change in TFe content in sintered ore when oak char replaces coke powder.

[0036] Figure 10 This is a graph showing the change in FeO content in sintered ore where oak char replaces coke powder.

[0037] Figure 11 The compressive strength distribution of oxygen-rich sintered ore after 40% replacement with oak charcoal.

[0038] Figure 12 This is a diagram showing the effect of layered carbon reduction sintering on the return ore rate.

[0039] Figure 13 This is a graph showing the effect of layered carbon reduction sintering on the FeO content in sintered ore.

[0040] Figure 14 This is a diagram showing the effect of layered carbon reduction sintering on the compressive strength of sintered ore.

[0041] Figure 15 This is a diagram showing the effect of layered carbon reduction sintering on the temperature of the sintering bed. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0043] The experimental system used in the following embodiments is a small sintering cup system, such as... Figure 1 As shown, the small sintering cup system includes a sintering cup 8, an igniter 4, and a dust collector 2.

[0044] The sintering cup 8 has a cup size of Φ300. The sintering cup is 1000mm in diameter, with both the inner and outer walls made of stainless steel. The inner wall is 4mm thick, and insulation material is filled between it and the outer wall. During operation, a gantry crane is used to hoist the mixed material into the sintering cup, and manual unloading is performed. A grate plate 6 is arranged at the bottom of the sintering cup to support the sintering material. A hydraulic jack 7 is installed at the bottom of the sintering cup 8. Temperature measuring holes 5 are arranged at 10cm intervals from top to bottom on the side wall of the sintering cup 8. Armored thermocouples (WRNK-191K) are installed in the temperature measuring holes 5 for insertion temperature measurement. An igniter 4 is installed at the top of the sintering cup 8. The igniter 4 is a plasma igniter (XL-PLA20S ignition device) in a four-unit combined mode.

[0045] The dust collector 2 is installed between the sintering cup 8 and the fan 1, and can intercept particulate matter in the exhaust gas. The dust collector 2 is connected to the bottom of the sintering cup 8 through the exhaust gas pipe, and a sampling hole 3 is provided on the exhaust gas pipe for sampling the exhaust gas.

[0046] The small sintering cup system also includes a computer control system: it transmits data such as gas flow rate, temperature at each measuring point, ignition temperature, and vacuum chamber negative pressure during the sintering process to the control system to generate sintering experiment data reports. Furthermore, it controls the igniter position, sintering cup rotation, and crusher startup.

[0047] Comparative Example 1 like Figure 2 As shown, a method for sintering iron ore based on replacing coke powder with oak charcoal includes the following steps: Step 1, Preparation and Granulation of the Hybrid Material: The mass proportioning method was used for batching. Since this sintering cup experiment did not involve changes in the iron ore powder raw material, the iron ore powder homogenized material prepared from a steel plant silo was used, with the specific proportions shown in Table 1. The homogenized material, recycled ore, quicklime, and coke powder were mixed in a mass ratio of 78.5:10.3:6.7:4.5. The order of addition to the mixer was approximately half of the homogenized material, quicklime, recycled ore, a certain amount of water, coke powder, and the remaining homogenized material, followed by a first mixing. Subsequently, a certain amount of water was added to control the moisture content of the entire sintering material at approximately 8±0.5%, followed by a second mixing and granulation to obtain the sintered homogenized material. A small cement mortar mixer was used for granulation. During both mixing processes, the opening of the mixer was sealed to effectively utilize the heat generated by the quicklime digestion and increase the temperature of the mixed material.

[0048] Table 1. Components of the Mixture The small cement mortar mixer measures Φ600mm×1000mm, operates at a speed of 20r / min, and has a primary mixing time of 5min and a secondary mixing and granulation time of 6min. After granulation, the product is called sintered homogenate. A portion of the sintered homogenate is selected for moisture content and particle size distribution determination.

[0049] Step 2, Material Preparation: Select sintered ore with a particle size of 10mm-16mm as the base material. Spread it evenly on the bottom grate to prevent material leakage while ensuring air permeability. The base material thickness is usually about 30cm-40cm. Use a gantry crane to load the sintered mixture obtained in Step 1 into the sintering cup to obtain the sintered material layer. At the same time, measure the mass and thickness of the base material and the mass and thickness of the sintered mixture. Then, insert thermocouples at five temperature measuring points, ensuring consistent insertion depth.

[0050] Step 3, Ignition: Before ignition, turn on the exhaust system and set the negative pressure to 6 kPa. During ignition, all four plasma generators are turned on simultaneously, the ignition temperature is 1050±25℃, and the ignition time is 4 minutes to ensure the sintering effect on the surface of the sintered material layer.

[0051] Step 4, Sintering: After ignition, sintering is performed under a negative pressure of 8 kPa, and the sintering cup experimental system is switched from ignition recording mode to sintering recording mode. When the exhaust gas temperature reaches its peak, it is determined as the sintering endpoint, the sintering time is recorded, and the vertical sintering speed is calculated.

[0052] Step 5, Sinter Cooling: After reaching the sintering endpoint, the temperature of the finished sinter is very high, making subsequent operations unsuitable. Negative pressure ventilation is continued to achieve air cooling. Once the temperature drops to room temperature, the control system is activated to unload the sinter and simultaneously perform crushing. All sinter is then collected for subsequent data measurement.

[0053] Step 6, Data Testing: The collected sinter is tested for return rate, yield, compressive strength, utilization coefficient, vertical sintering speed, solid fuel consumption, chemical composition and SEM electron microscopy scanning.

[0054] Example 1 In this embodiment, coke powder is replaced with a mixture of oak charcoal and coke powder, with oak charcoal accounting for 5% to 55% of the mass of the mixture, i.e., the replacement rate is 5% to 55%.

[0055] When oak char replaces coke powder in sintering, its excellent combustion characteristics, high fixed carbon content, and high calorific value significantly impact the sintering process. The peak temperature of the sintering tail gas and the sintering endpoint time were measured after the replacement, and the results are as follows: Figure 3 As shown, with the increase of the proportion of oak char replacing coke powder, the time to reach the sintering endpoint is faster. When the replacement rate is 55%, the time to reach the sintering endpoint is 45.45% earlier than when there is no replacement. This is due to the following two reasons: (1) Oak char itself burns quickly and the time required to reach complete combustion is short. Therefore, the increase of its content will inevitably lead to a shortening of the overall sintering time; (2) Oak char burns quickly and has a low ash content. After the oak char is completely burned, the remaining porosity can increase the permeability of the sintering material, allowing more oxygen to enter and promoting the combustion of coke powder, thereby increasing the vertical sintering speed.

[0056] The temperature of the sintering bed has a significant impact on the yield and quality of sintered ore. On the one hand, high temperatures ensure the molten state during the sintering process. As the temperature rises, diffusion and flow processes accelerate, promoting the development of the liquid phase in the sintered ore and increasing its strength. On the other hand, higher sintering temperatures can reduce the edge effect of the sintering machine or sintering cup to some extent, thereby increasing output. Studies have also shown that sintering temperature has a certain influence on the porosity characteristics of sintered ore.

[0057] Five temperature measuring points were designed sequentially on the sintering cup. Points 1, 2, and 3 extend directly into the sinter to reflect the sintering temperature in real time. Point 4, closest to the grate, reflects the temperature of the exhaust gas during sintering and helps determine the sintering endpoint. Based on the data from points 1, 2, and 3, a bubble diagram of the peak temperature at each measuring point was plotted during the sintering process of oak char replacing coke powder. The meaning of each indicator is detailed below. Figure 4 (No replacement of oak charcoal was performed), where peak temperature refers to the highest temperature measured at each temperature measuring point during the test; high temperature duration is the duration for which the temperature reaches 99% of the peak temperature, which can represent the thickness of the sintering combustion zone; and peak temperature time refers to the start time of sustained high temperature.

[0058] like Figure 5 , Figure 6 , Figure 7 As shown, with the increase in the replacement ratio of oak charcoal, the peak temperature at each temperature measuring point generally showed an upward trend. However, after the replacement rate reached 40%, the peak temperature at each point tended to stabilize without a significant trend. Specifically, the peak temperature at measuring point 1 increased from 1335℃ before replacement to 1365℃ with 50% replacement, an increase of 30℃; the peak temperature at measuring point 2 increased from 1336℃ before replacement to 1369℃ with 50% replacement, an increase of 33℃; and the peak temperature at measuring point 3 increased from 1339℃ before replacement to 1372℃ with 50% replacement, an increase of 33℃. Oak charcoal itself has a high calorific value and sufficient fixed carbon content. Under the same mass conditions, it can provide sufficient heat, which will inevitably lead to an increase in the temperature of the sintering layer and play a certain role in promoting the sintering process.

[0059] From the perspective of the high-temperature duration at each temperature measuring point, the high-temperature duration gradually shortens as the replacement ratio of oak char increases. This is unfavorable for the development of the liquid phase in the sintering bed, hindering liquid phase flow and diffusion, and resulting in a decrease in the overall cohesiveness of the sinter. The second temperature measuring point shows the largest decrease in high-temperature duration, with a reduction of 42.54% at a replacement rate of 55%. Under the same conditions, the reductions at the first and third temperature measuring points are 40.50% and 35.94%, respectively. However, considering that the temperature of the sintering bed does not significantly increase after the coke powder replacement rate reaches 40%, the reduction in high-temperature duration at each temperature measuring point when the replacement rate is 40% is calculated. The corresponding reductions for the first, second, and third temperature measuring points are 30.99%, 29.84%, and 27.24%, respectively. The high-temperature durations at the second and third temperature measuring points are longer than those at the first temperature measuring point without replacement, which meets the basic sintering requirements.

[0060] Effects on the combustion zone: The thickness of the combustion zone can be inferred to some extent by measuring the duration of peak temperatures at each temperature measurement point. The vertical sintering rate is calculated based on the sintering endpoint time; the product of the high-temperature duration and the vertical sintering rate is the thickness of the combustion zone. Table 2 shows the thickness of the combustion zone at various locations. In the combustion zone, the sintered material softens and melts, promoting the formation of the liquid phase. The thickness of the combustion zone significantly affects the yield and quality of the sinter. An increase in the thickness of the combustion zone leads to a thicker molten layer, which affects the permeability of the sintered material layer and thus the reaction efficiency.

[0061] Table 2. Thickness of the combustion zone at various locations As the replacement ratio of oak charcoal increased, the thickness of the combustion zone at temperature measuring points 1 and 2 did not change significantly. Compared to the unreplaced state, the thickness of the combustion zone fluctuated within 2 mm, with a range not exceeding 5.12%. The thickness of the combustion zone near temperature measuring point 3 generally showed an upward trend. Before the replacement rate reached 40%, the increase did not exceed 4.46%. After the replacement rate reached 45%, the thickness of the combustion zone increased significantly, which to some extent affected the permeability of the sintered material layer.

[0062] Impact on return rate The return ore rate has a significant impact on sintering production efficiency. Reducing the return ore rate can improve the utilization coefficient of sintering equipment and reduce fuel consumption and exhaust gas emissions. For example... Figure 8As shown, before the replacement rate reaches 15%, the return rate decreases continuously with the increase of the replacement rate, and the return balance also drops to a minimum of 0.60 when the replacement rate is 15%. When the replacement rate of oak charcoal is between 20% and 40%, the return rate is higher than when the replacement rate is below 20%, but it is still lower than when there is no replacement, remaining between 9.6% and 9.9%. When the replacement rate reaches more than 45%, the return rate increases significantly, exceeding the return rate when there is no replacement.

[0063] Effects on TFe: like Figure 9 As shown, the ash content of oak charcoal is only about 20% of that of coke powder. Therefore, it has fewer impurities remaining during the sintering process, which will indirectly increase the TFe content per unit mass of sintered ore. As the replacement ratio of oak charcoal increases, the proportion of TFe content will naturally increase gradually.

[0064] Effect on FeO content: The FeO content in sinter is a crucial indicator, having a dual impact on its performance. Both excessively high and low levels are detrimental to improving the yield, quality, and metallurgical properties of the sinter. The FeO content in sinter is closely related to the carbon content in the sintering mixture, as well as the temperature and atmosphere of the sintering bed. In our previous study, we found that as the proportion of coke powder replaced by oak char increased, the temperature of the sintering bed increased to some extent. Furthermore, since oak char has a higher fixed carbon content than coke powder, an equal mass replacement inevitably leads to an increase in the carbon content. Therefore, an increase in the oak char replacement rate will inevitably affect the FeO content in the sinter.

[0065] like Figure 10 As shown, before the oak char replacement rate reaches 40%, the FeO content in the sinter gradually increases with the increase of the oak char replacement rate. At a replacement rate of 40%, the FeO content increases by 23.68% compared to the unreplaced state. When the replacement rate exceeds 40%, the FeO content in the oak char begins to decrease significantly. At a replacement rate of 55%, its content is lower than that of the unreplaced state. Its trend is the same as the trend of compressive strength, indicating that under normal circumstances, there is a correlation between FeO content and sinter strength.

[0066] Normally, the FeO content in sinter should be between 8% and 10% in large-scale production; above 10%, the reducibility of the sinter decreases significantly. In this experiment, the FeO content exceeded 10% even without replacement because, in order to prolong the sintering time and control the details of the reaction process, the negative pressure value of the exhaust fan (8 kPa) was set slightly lower than the normal value (10 kPa). This resulted in a lower oxygen supply to the entire sintering system, causing some carbon to not burn completely, which reduced ferric iron.

[0067] While maintaining a consistent negative pressure during ventilation, increasing the replacement rate of oak charcoal promotes the increase of FeO content. Although this improves the strength of sintered ore to some extent, it reduces its reducibility, which is very detrimental to the subsequent blast furnace production efficiency and fuel consumption.

[0068] Example 2 To address the issues of excessively high FeO content and short high-temperature duration when the oak charcoal replacement rate is 40%, this embodiment improves upon Example 1 by increasing the oxygen content in the exhaust airflow to enhance the combustion rate and intensity of the fuel, compensate for the heat deficit caused by the rapid combustion of biochar, extend the high-temperature holding time, and simultaneously utilize a strong oxidizing atmosphere to suppress FeO formation.

[0069] With the proportion of oak char replacing coke powder controlled at 40% and other conditions remaining unchanged, an oxygen-enriching device is installed at the top of the sintering cup, as shown in the schematic diagram. Figure 11 As shown in the figure. Oxygen was introduced at the oxygenation point and mixed downwards by ventilation. The oxygen concentration was measured using a flue gas analyzer at the oxygen concentration test point. The oxygen concentration was increased from 21% to 25% in increments of 1% and maintained at this concentration. After ignition, oxygen-enriched sintering began and continued until the sintering endpoint was reached. The effect of this on the FeO content and strength of the sinter was investigated.

[0070] Effect of different oxygen enrichment concentrations on FeO content in sinter As shown in Table 3, under oxygen-enriched conditions, the oxygen concentration during sintering has a significant impact on the FeO content in the sinter. When the oxygen concentration reaches 23±0.25%, the FeO content is lower than when no oak char replacement is performed, positively promoting the reducibility of the sinter without affecting other components. However, we observe that the reduction in FeO content slows down after the oxygen concentration reaches 24±0.25%. This is because, with sufficient oxygen supply, the fuel in the upper sintering layer burns completely, further increasing the layer temperature and prolonging the high-temperature duration, resulting in sufficient liquid phase development and hindering the permeability of the sintering layer to some extent. Although the oxygen concentration increases during negative pressure ventilation, the amount of oxygen received by the lower sintering layer is limited due to permeability, causing incomplete combustion of fuel in the lower sintering layer and thus producing a certain amount of FeO. Overall, however, oxygen-enriched sintering is feasible for reducing the FeO content in sinter.

[0071] Table 3. Effects of different oxygen enrichment concentrations on sinter composition. Effect of different oxygen concentrations on the compressive strength of sinter Oxygen-enriched sintering places the entire sintering bed in a strong oxidizing atmosphere, allowing the fuel to burn completely and release a large amount of heat. This can raise the temperature of the entire sintering bed, resulting in better liquid phase development and higher strength.

[0072] like Figure 11 As shown, with 40% oak char replacement, the average compressive strength of the sinter gradually increased with the increase of oxygen concentration in the negative pressure exhaust system. At an oxygen concentration of 23 ± 0.25%, the average compressive strength reached 3558.1 N. Afterward, with further increases in oxygen concentration, the average compressive strength of the sinter did not show a significant increase. From the distribution of the sinter's compressive strength, under uncontrolled conditions, the compressive strength distribution range was wide, with high dispersion and a low lower limit. With increasing oxygen concentration, the compressive strength of the sinter gradually stabilized, while the upper and lower limits increased.

[0073] This is because, under the influence of oxygen enrichment, the temperature of the sintering bed increases. At an oxygen enrichment concentration of 23±0.25%, the temperature of the sintering bed can reach 1420℃. This high temperature allows for the development of a well-defined liquid phase in the surface sinter, and... Figure 11 Furthermore, we can see that the duration of the high temperature was also extended, further improving the compressive strength of the sinter. This raises the lower limit of the surface sinter, while the lower sinter layer itself has a high temperature and its strength can be guaranteed. As the layer continues to heat up, the upper limit of the sinter strength increases, but not significantly. Moreover, the upper sinter layer is in a good molten state at high temperatures, which affects the permeability of the entire sinter layer. Therefore, the increase in the compressive strength of the lower sinter layer is also limited.

[0074] Example 3 This embodiment is an improvement on Embodiment 1, and further improves upon it by performing layered carbon reduction sintering.

[0075] The sintering process has a heat storage effect, and the lower layer of material is preheated, often leading to overheating (overmelting) of the lower layer, resulting in a large amount of FeO and a large-pore, thin-walled structure. Since biochar itself burns quickly, it is more prone to overburning in the lower layer. By reducing the amount of char in the lower layer material, the heat distribution can be balanced.

[0076] With the proportion of oak char replacing coke powder controlled at 40%, and other conditions remaining unchanged, different sintering mixtures were prepared according to different carbon reduction ratios.

[0077] The heat storage effect of the sintered ore layer is a linearly increasing process from top to bottom. As the depth of the sintered ore layer increases, the temperature of the lower layers will become increasingly higher. Therefore, the ideal state of layered sintering is multi-layered smooth carbon reduction (gradually reducing the replacement rate of rubber char from top to bottom, starting from the side furthest from the bottom). This experiment aimed to explore the possibility of carbon reduction in the lower layers, and therefore used a relatively small number of layers. As shown in Table 4, the sintered ore was divided into 2-3 layers, with the top layer having a rubber char replacement rate of 40%, and the carbon reduction ratio being a decrease from that of the top layer.

[0078] Table 4. Stratified Experiment Content Impact on return rate The amount of carbon added during the sintering process directly affects the quality and performance of the sinter, and also has a significant impact on the yield of the sinter, which is directly reflected in the change in the return rate. Figure 12 This reflects the impact of layered carbon reduction sintering on the return ore rate. With a 40% oak char replacement rate, regardless of the layering mode, the return ore rate inevitably increases with the increase in carbon reduction rate. In 1:1, 1:2, and 1:1:1 layering scenarios, when the carbon reduction rate of the lower sintering layer is no higher than 10%, the improvement in the sintering return ore rate is almost negligible. The highest improvement is in the 1:2 layering scenario, where a 10% carbon reduction in the lower layer results in a 10.93% return ore rate, with an increase of 10.40% compared to the scenario without carbon reduction, still lower than the scenarios without replacement or carbon reduction. When the carbon reduction reaches 15%, the return ore rate deteriorates significantly, exceeding the baseline data, which is detrimental to the sintering process.

[0079] Effect of FeO content in sinter Many factors affect the FeO content in sinter, with the amount of carbon added being the most significant. With a high amount of carbon added, the fuel will not burn completely under the same negative pressure ventilation, producing a large amount of FeO. With a low amount of carbon added, the fuel will burn completely to provide heat, and there will not be too much carbon to reduce ferric iron.

[0080] like Figure 13 As shown, the FeO content in the sinter gradually decreases with the increase of the carbon reduction ratio. When the carbon reduction in the lower layer of sinter is around 5%, the FeO content in the sinter is almost the same as that in the benchmark sinter. When the carbon reduction in the sinter layer is more than 10%, the FeO content in the sinter is lower than that in the benchmark sinter. When the carbon reduction rate in the lower layer is 20%, its FeO content is less than 50% of the benchmark. In order to make the FeO content in the sinter better than the benchmark value, the carbon content in the lower layer of sinter should be reduced by more than 10%.

[0081] Effect on compressive strength of sinter Based on previous research, the compressive strength of sinter is significantly related to its FeO content. The purpose of this chapter is to reduce the FeO content in sinter while maintaining its quality. Reducing carbon content can lower the FeO content in sinter; therefore, we need to consider the changes in compressive strength after reducing the FeO content.

[0082] like Figure 14 As shown, with the increase in the carbon reduction ratio, the average compressive strength of the sinter gradually decreases and becomes more uniformly distributed, with a significant reduction in the upper limit of the sinter's compressive strength. When the carbon reduction rate in the lower layer is 10%, the average compressive strength of the sinter is basically the same as when no carbon reduction is achieved, remaining within an acceptable fluctuation range. Although the upper limit of the sinter's strength decreases, the proportion of high-strength sinter does not decrease. When the carbon reduction rate of the sintering layer reaches 15%, regardless of whether it is a 1:1 or 1:2 layering, the proportion of low-strength sinter gradually increases. Coupled with the decrease in the upper limit of strength, this results in a significant decrease in the average compressive strength of the sinter. When the carbon reduction continues to increase to 20%, the compressive strength of the sinter deteriorates significantly, the proportion of high-strength sinter decreases, and the sinter strength exceeds the lower limit.

[0083] Effect on the temperature of the lower sintering layer Lowering the FeO content is very beneficial to improving the reducibility of sinter. However, reducing the FeO content by reducing carbon will inevitably reduce the strength of sinter. The reason for this is that reducing carbon affects the peak temperature and high-temperature duration of the sintering bed, which hinders the development of the liquid phase in the sinter.

[0084] like Figure 15 As shown, a carbon reduction of less than 10% in the lower sintering layer, while affecting the peak temperature, has a small impact, remaining above the baseline value, and the duration of high temperature is not significantly affected. Therefore, the yield and compressive strength of the sinter do not deteriorate significantly, but the FeO content in the sinter is significantly reduced. When the carbon reduction rate exceeds 10%, the peak temperature of the sintering layer decreases significantly. At a carbon reduction rate of 15%, the peak temperature of the lower layer in a 1:1 stratified layer is close to the peak temperature at point 1 in the baseline experiment, while that in a 1:2 stratified layer is lower than the peak temperature at point 1 in the baseline experiment. When the carbon reduction rate reaches 20%, at its peak temperature, liquid phase development is significantly hindered, molten flow and fusion are insufficient, and the sintering reaction is uneven, thus reducing the compressive strength of the sinter.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for sintering iron ore based on replacing coke powder with oak charcoal, characterized in that, Includes the following steps: Step 1, Preparation of homogenized material and granulation: Mix the homogenized material, recycled ore, quicklime, and coke powder-rubber char mixture, add water and granulate to obtain sintered homogenized material; Step 2, Material Placement: Place the sintered ore in the sintering furnace as the bottom material, and place the sintered mixed material on top of the bottom material; Step 3, Ignition: Turn on the ventilation system and igniter to ignite; Step 4: Sintering: After ignition, sintering is carried out by exhaust ventilation.

2. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 1, the mass ratio of oak charcoal in the coke powder-oak charcoal mixture is 5% to 55%, more preferably 40% to 55%, and even more preferably 40%.

3. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 1, the mass ratio of the mixed material, the return ore, quicklime, and the coke powder-rubber charcoal mixture is (76~80):(9~12):(6~7.5):(4.0~5.0), preferably 78.5:10.3:6.7:4.

5.

4. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 2, the particle size of the sintered ore is 10mm to 16mm, and the thickness of the bottom material is 30cm to 40cm.

5. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 2, the sintering mixture is arranged in layers, and the mass ratio of rubber char in each layer of sintering mixture decreases from top to bottom.

6. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 5, characterized in that, The layering is divided into 2 to 3 layers.

7. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 5, characterized in that, The mass ratio of oak char in each layer of sintered homogenized material decreases linearly layer by layer, with each layer decreasing by 10-15% compared to the previous layer.

8. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 3, the igniter is a plasma igniter.

9. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 3, after the exhaust system is turned on, oxygen-enriched gas is introduced from the top of the sintering furnace. Preferably, the oxygen concentration in the oxygen-enriched gas is 23±0.25%~24±0.25%, and more preferably 23±0.25%.

10. The iron ore sintering method based on replacing coke powder with oak charcoal as described in claim 1, characterized in that, In step 4, the sintering time is 35-40 minutes.

Images