Magnetite pellet low-temperature rapid oxidation consolidation method based on oxygen-enriched preheating roasting

Abstract

The invention discloses a magnetite pellet low-temperature rapid oxidation consolidation method based on oxygen-enriched preheating roasting. The method comprises the following steps: supplementing oxygen-enriched air 1 at a cooling blast position of a cooling section I of a circular cooler, introducing the oxygen-enriched air 1 into a rotary kiln through negative pressure formed by main pumping, and finally introducing the oxygen-enriched air 1 into a PH preheating section of a chain grate; oxygen-enriched air (2) is supplemented to a cooling blast position of a cooling section II of the circular cooler, and the oxygen-enriched air (2) is led to a TPH transition preheating section of the chain grate; oxygen-enriched air (3) is supplemented to a smoke hood of the PH preheating section of the chain grate machine; the oxygen-enriched air (1), the oxygen-enriched air (2) and the oxygen-enriched air (3) which are supplemented not only can ensure the oxygen concentration required by oxidation preheating of the pellets in the chain grate machine, but also can prevent nitric oxide from being generated by high oxygen concentration in the rotary kiln. The oxygen enrichment devices are additionally arranged at multiple positions, oxygen-enriched air is supplemented, reasonable oxygen concentration distribution in the chain grate and the rotary kiln is achieved, and low-temperature rapid oxidation and solidification of magnetite pellets are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a low-temperature rapid oxidation consolidation method for magnetite pellets based on oxygen-enriched preheating and roasting. Background Art

[0002] In the production of magnetite oxidation pellets, the core of the chain grate-rotary kiln-ring cooler process lies in converting Fe₃O₄ into Fe₂O₃ through an oxidation reaction and consolidating it to ensure the mechanical strength of the finished pellets. In traditional processes, oxygen is primarily supplied to the chain grate section via a hot air circulation system, using air blown from the ring cooler. However, actual operating data shows that due to oxygen consumption during the circulation process and system leakage, the oxygen concentration in the chain grate preheating section (PH section) generally drops to 17-19%.

[0003] Existing techniques typically increase the rotary kiln's roasting temperature to 1250-1350°C, increase system air volume, or prolong the pellets' residence time in the grate to compensate for insufficient oxygen concentration in the pH section of the grate. However, these measures directly lead to increased overall energy consumption and flue gas volume, accelerate the wear and tear of the rotary kiln's refractory materials (which typically have a lifespan of less than 12 months), and increase power consumption and equipment maintenance costs.

[0004] To address these shortcomings, the industry has attempted to improve them through oxygen enrichment technology within the rotary kiln. For example, Chinese patents (CN202310584739.0 and CN202411931587.8) propose introducing pure oxygen into the rotary kiln burner to improve fuel combustion efficiency, increase the oxygen concentration within the rotary kiln, and thus enhance pellet consolidation. However, this localized oxygen enrichment improvement technology presents the following technical issues: First, existing research shows that the grate is the main oxidation stage for pellets, and the oxidation rate of pellets in the grate section is 60% to 70%. Providing oxygen in the rotary kiln does not solve the fundamental problem of insufficient oxidation in the grate section. The kiln temperature still needs to be maintained above 1250°C, and the effect of reducing energy consumption is limited. Second, to improve fuel combustion, pure oxygen is usually injected into the kiln, which increases oxygen production costs and safety risks. Third, the increase in oxygen concentration at the burner will lead to the production of nitrogen oxides in the rotary kiln, increasing the burden on the denitrification system. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention proposes a low-temperature rapid oxidation consolidation method for magnetite pellets based on oxygen-enriched preheating and roasting, which can not only ensure the oxygen concentration required for oxidation preheating of the pellets in the chain grate and reduce the roasting temperature of the rotary kiln, but also avoid the generation of nitrogen oxides due to high oxygen concentration in the rotary kiln, achieve a reasonable oxygen concentration distribution in the chain grate and the rotary kiln, and realize low-temperature rapid oxidation consolidation of magnetite pellets.

[0006] To achieve the above-mentioned object, the present invention designs a low-temperature rapid oxidation consolidation method for magnetite pellets based on oxygen-enriched preheating and roasting, which is applicable to the production process of oxidation pellets using a chain grate, a rotary kiln, and an annular cooler. The method is particularly characterized in that it comprises the following steps: Oxygen-enriched air① is added to the cooling blast of the cooling section I of the ring cooler. The oxygen-enriched air① is led into the rotary kiln through the negative pressure formed by the main exhaust, and is used to oxidize and consolidate the green balls. The hot air at the tail of the rotary kiln is then led to the PH preheating section of the chain grate through the reheating fan, and is used to oxidize and preheat the green balls. Oxygen-enriched air ② is added to the cooling blast of the cooling section II of the ring cooler. The oxygen-enriched air ② is directed to the TPH transition preheating section of the grate machine for oxidation preheating of the green pellets. Add oxygen-enriched air ③ to the smoke hood of the PH preheating section of the grate machine. The oxygen-enriched air ③ increases the overall oxygen concentration in the grate machine and promotes the oxidation preheating of the pellets. The supplemented oxygen-enriched air ①, oxygen-enriched air ②, and oxygen-enriched air ③ can not only ensure the oxygen concentration required for oxidation preheating of the pellets in the chain grate and reduce the roasting temperature of the rotary kiln, but also avoid the generation of nitrogen oxides due to high oxygen concentration in the rotary kiln, achieve a reasonable oxygen concentration distribution in the chain grate and the rotary kiln, and realize low-temperature rapid oxidation consolidation of magnetite pellets.

[0007] Furthermore, the oxygen-enriched air ① added to the cooling blast of the cooling section I of the ring cooler is mixed with the air through an oxygen mixing device, and the mixing ratio of the oxygen-enriched air ① to the air is 0.6~0.8:1, thereby increasing the oxygen concentration of the cooling air in the cooling section I to 25%~30%.

[0008] Furthermore, the cooling air volume of cooling stage I is controlled to 90,000~100,000 Nm 3 / h.

[0009] Furthermore, the oxygen-enriched air ② added to the cooling blast of the cooling section II of the ring cooler is mixed with the air through an oxygen mixing device, and the mixing ratio of the oxygen-enriched air ② to the air is 0.8~1.0:1, thereby increasing the oxygen concentration of the cooling air in the cooling section II to 28%~35%.

[0010] Furthermore, the cooling air volume of cooling section II is controlled to 60,000~80,000 Nm 3 / h.

[0011] Furthermore, 3 to 6 oxygen-enriched air spray guns are installed at the smoke hood of the PH preheating section of the chain grate machine to increase the oxygen concentration in the PH preheating section to 28% to 38%.

[0012] Furthermore, the oxygen-enriched air injection rate at the hood of the PH preheating section of the chain grate is 5000~10000 Nm 3 / h.

[0013] Furthermore, the oxygen concentration of the oxygen-enriched air ①, oxygen-enriched air ②, and oxygen-enriched air ③ is 40% to 50%, and they are all prepared by membrane separation method.

[0014] The advantages of the present invention are: 1. The present invention, without changing the original production process and equipment of oxidation pellets, increases the oxygen concentration in the system, promotes the right shift of the equilibrium of the oxidation consolidation reaction of magnetite, and realizes oxygen-enriched preheating and roasting of magnetite pellets, thereby reducing the production temperature and shortening the preheating and roasting time, thereby increasing the table output and reducing fuel consumption; 2. In the production process of chain grate, rotary kiln and ring cooler, due to oxygen consumption and system leakage during the circulation process, the oxygen concentration in the preheating section (PH section) of the chain grate generally drops to 17-19%. The present invention adds oxygen enrichment devices at the cooling blast of cooling section I of the ring cooler, the cooling blast of cooling section II of the ring cooler, and the smoke hood of the PH preheating section of the chain grate. This allows the hot air from cooling section I to flow into the rotary kiln through the negative pressure formed by the main exhaust, and the hot air at the kiln tail of the rotary kiln is then passed through the heat recovery fan to the PH section of the chain grate; the hot air from cooling section II is passed to the TPH transition preheating section of the chain grate; and the hot air from the smoke hood of the PH preheating section of the chain grate enters the PH section, thereby timely replenishing some oxygen-enriched air, improving the overall oxygen concentration of the chain grate, and promoting the oxidation and consolidation of the pellets; The present invention is based on the low-temperature rapid oxidation consolidation method of magnetite pellets preheated and roasted with oxygen-enriched preheating. By adding oxygen enrichment devices in multiple locations, supplementing oxygen-enriched air, and coordinating the flow rate and oxygen concentration, a reasonable oxygen concentration distribution can be achieved in the chain grate and rotary kiln, and oxygen-enriched preheating and roasting of magnetite pellets can be achieved, thereby achieving the purpose of low-temperature rapid oxidation and consolidation of magnetite pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the present invention; Figure 2 This is a scanning electron microscope image of the pellet product in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the pellet product in Example 2 of the present invention; Figure 4 This is a scanning electron microscope image of the pellet product in the comparative example of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention.

[0018] like Figure 1 As shown, a method for low-temperature rapid oxidation and consolidation of magnetite pellets based on oxygen-enriched preheating and roasting is applicable to the production process of oxidation pellet chain grate-rotary kiln-ring cooler, comprising the following steps: First, oxygen-enriched air① is added to the cooling blast of the cooling section I of the ring cooler. The oxygen-enriched air① is led into the rotary kiln through the negative pressure formed by the main exhaust, and is used to oxidize and consolidate the green balls. The hot air at the tail of the rotary kiln is then led to the PH preheating section of the chain grate machine through the heat recovery fan, and is used to oxidize and preheat the green balls.

[0019] Preferably, the oxygen-enriched air ① added to the cooling blast of Cooling Section I of the ring cooler is mixed with air through an oxygen mixing device, with the mixing ratio of oxygen-enriched air ① to air being 0.6-0.8:1, thereby increasing the oxygen concentration of the cooling air in Cooling Section I to 25%-30%. Specifically, the oxygen mixing device is a Venturi oxygen mixing device.

[0020] Since the hot air from the cooling section I of the ring cooler is led to the rotary kiln, if the oxygen concentration is too high, the nitrogen oxide content in the kiln will increase, which will increase the denitrification cost. Therefore, after balancing the atmosphere in the kiln and the oxidation rate of the pellets, the oxygen concentration in the ring cooling section I is controlled at 25%~30%.

[0021] Preferably, the cooling air volume of cooling stage I is controlled to be 90,000~100,000 Nm 3 / h. Compared with the existing 120,000~130,000 Nm 3 / h of cooling air volume in cooling stage I. After increasing the oxygen concentration, the cooling air volume can be effectively reduced by 10~15%, while ensuring that the oxygen concentration of the kiln atmosphere is around 25%.

[0022] Second, oxygen-enriched air ② is added to the cooling blast of the cooling section II of the ring cooler, and the oxygen-enriched air ② is led to the TPH transition preheating section of the chain grate machine for oxidation preheating of the green balls.

[0023] Preferably, the oxygen-enriched air ② added to the cooling blast of Cooling Section II of the ring cooler is mixed with air through an oxygen mixing device, with the mixing ratio of oxygen-enriched air ② to air being 0.8-1.0:1, thereby increasing the oxygen concentration of the cooling air in Cooling Section II to 28%-35%. Specifically, the oxygen mixing device is a Venturi oxygen mixing device.

[0024] The hot air from the cooling section II is passed to the TPH section, where the temperature is 350°C to 500°C. During this stage, the pellets begin to undergo oxidation reactions, and the oxygen demand gradually increases. The pellets in the cooling section II are basically oxidized and almost no oxygen is consumed. Therefore, the hot air with an oxygen concentration of 28% to 35% passes through the TPH section, which can greatly increase the oxidation rate of the pellets in the TPH section, thereby shortening the oxidation time and increasing the hourly output. At the same time, since the temperature in this section is not high and the degree of pellet oxidation is limited, it is not necessary to provide an excessively high concentration of oxygen-enriched air, otherwise it will result in oxygen waste. At the same time, the pellets are not dense enough at this stage, and the oxidation rate is too fast, which will also cause pellet breakage and reduce the yield rate.

[0025] Preferably, the cooling air volume of cooling section II is controlled to be 60000~80000 Nm 3 / h. Compared with the existing 80000~90000Nm 3 / h of cooling air volume in cooling section II. After increasing oxygen concentration, the cooling air volume can be effectively reduced by 10%~15%, and the oxygen content in the TPH section can be increased to 28%~35%.

[0026] Third, oxygen-enriched air ③ is added to the smoke hood of the PH preheating section of the chain grate. The oxygen-enriched air ③ increases the overall oxygen concentration in the chain grate and promotes the oxidation preheating of the raw balls.

[0027] Preferably, three to six oxygen-enriched air lances are installed in the hood of the pH preheating section of the grate to raise the oxygen concentration in the pH preheating section to 28% to 38%. The pH section is the primary location of the pellet oxidation reaction on the grate. During this stage, the grate temperature is between 600°C and 950°C, and the pellets begin to undergo large-scale oxidation and densification. Therefore, considering the degree of pellet oxidation, three to six oxygen-enriched air lances are specifically installed in the pH fume hood during this stage to meet the needs of pellet oxidation.

[0028] Preferably, the oxygen-enriched air injection rate at the smoke hood of the PH preheating section of the chain grate is 5000~10000 Nm 3 / h. To increase the oxygen concentration in the pH range to 28%~38%, it is necessary to spray 5000~10000 Nm at the pH hood. 3 / h of oxygen-enriched air to meet the oxygen demand for rapid oxidation of the pellets at this stage. At the same time, during this stage, the pellets become more dense, and high-oxygen-concentration oxidation will not cause pellet breakage.

[0029] Preferably, the oxygen-enriched air (1), (2), and (3) have an oxygen concentration of 40% to 50% and are all produced using membrane separation. Compared to traditional sample preparation methods, membrane separation offers the advantages of ease of operation and high oxygen production capacity. Furthermore, its lower oxygen concentration facilitates a uniform gradient of oxygen concentration within the grate and rotary kiln, preventing localized excess oxygen concentration. Furthermore, once the oxygen concentration is controlled at 40% to 50%, the amount of oxygen-enriched air incorporated can be increased, facilitating industrial control.

[0030] The oxygen-enriched air ①, oxygen-enriched air ②, and oxygen-enriched air ③ added in the present invention can not only ensure the oxygen concentration required for oxidation preheating of the pellets in the chain grate and reduce the roasting temperature of the rotary kiln, but also avoid the generation of nitrogen oxides due to high oxygen concentration in the rotary kiln, achieve a reasonable oxygen concentration distribution in the chain grate and the rotary kiln, and realize low-temperature rapid oxidation consolidation of magnetite pellets.

[0031] Example 1 In this example, magnetite pellets were prepared using domestically produced iron ore concentrate, purchased iron ore concentrate, and a binder (bentonite). The main chemical compositions of the two raw materials (domestic and purchased iron ore concentrate) are shown in Table 1, and the particle size composition is shown in Table 2. The chemical composition and physical properties of the bentonite are shown in Tables 3 and 4, respectively.

[0032] Table 1 Chemical composition of self-produced iron ore concentrate and purchased iron ore concentrate (%) Table 2 Particle size sieving results of self-produced iron ore concentrate and purchased iron ore concentrate It can be seen from Table 2 that the particle size of self-produced ore is generally finer than that of purchased ore, with the content of -0.074mm particle size reaching 80.50%, while the content of this particle size in purchased ore is 74.33%.

[0033] Table 3 Chemical composition analysis of bentonite % Table 4 Physical properties of bentonite Industrial trials used the two iron ore concentrates mentioned above as raw materials. After high-pressure roller grinding, the specific surface area was increased, improving pelletizing performance. The ore blending process was then tailored to the raw material structure of industrial pelletizing, with a ratio of 75:25 between domestically produced magnetite concentrate and purchased hematite concentrate. Finally, a disc pelletizer was used to mix the blended iron ore and bentonite, gradually rolling them into pellets. Qualified green pellets with diameters between 8 mm and 16 mm were screened and transported to a chain grate by a belt conveyor.

[0034] The oxygen-enriched air used in the experiment was prepared by membrane separation and had an oxygen content of 40%. The ratio of oxygen-enriched air to air at the blast point of cooling section I of the fixed ring cooler was 0.6:1, the air oxygen concentration was 25%, and the oxygen-enriched cooling air volume was controlled at 90,000 Nm 3 / h; the ratio of oxygen-enriched air to air at the cooling section II of the ring cooler is 0.8:1, the oxygen concentration is 28%, and the cooling air volume is controlled at 60,000 Nm 3 / h. Three oxygen-enriched air spray guns were set at the hood of the PH preheating section of the chain grate used in the test. The oxygen concentration of the oxygen-enriched air sprayed was 40%, and the oxygen-enriched air spray volume was 5000 Nm 3 / h, the chain grate drying preheating speed is 3.0 m / min, the drying temperature is 150℃, the drying time is 5 minutes, and the preheating temperature is 800℃, the preheating time is 15 minutes. After preheating, the compressive strength of the pellets is above 600N / piece. The pellets then enter the rotary kiln and are roasted at 1200℃ for 15 minutes. Finally, they are cooled in an annular cooler to obtain the pellet products.

[0035] Under these conditions, the high oxygen concentration within the grate and rotary kiln enables rapid, low-temperature oxidation and consolidation of the magnetite pellets, thus enabling oxygen-enriched preheating and roasting of the magnetite pellets. The resulting pellets have a compressive strength exceeding 3300 N / piece. The roasting temperature and time are reduced by 50°C and 2.5 minutes compared to those in air (1250°C and 17.5 minutes, respectively). The chemical composition of the pellets is shown in Table 5.

[0036] Table 5 Chemical composition of pellet products (%) The SEM image of the pellet product in Example 1 is as follows: Figure 2 As shown in the figure, H represents hematite, M represents magnetite, and P represents pores.

[0037] Example 2 This example uses the same raw materials as in Example 1, including the domestically produced iron ore concentrate, purchased iron ore concentrate, and bentonite. A high-pressure roller mill increases the specific surface area of ​​the ore particles, improving ball-forming performance. Ore blending is then performed according to the industrial raw material composition, with a ratio of 75:25 between domestically produced magnetite concentrate and purchased hematite concentrate. Finally, a disc pelletizer is used to mix the blended iron ore and bentonite, gradually rolling them into pellets. Qualified green balls with diameters between 8 mm and 16 mm are screened and transported to a chain grate using a belt conveyor.

[0038] The oxygen-enriched air used in the experiment was prepared by membrane separation and contained 40% oxygen. The ratio of oxygen-enriched air to air at the blast point of cooling section I of the fixed ring cooler was 0.7:1, the air oxygen concentration was 28%, and the oxygen-enriched cooling air volume was controlled at 95,000 Nm 3 / h; the ratio of oxygen-enriched air to air at the cooling section II of the ring cooler is 0.9:1, the oxygen concentration is 30%, and the cooling air volume is controlled at 70,000 Nm 3 / h. Three oxygen-enriched air spray guns were set at the hood of the PH preheating section of the chain grate used in the test. The oxygen concentration of the oxygen-enriched air sprayed was 50%, and the oxygen-enriched air spray volume was 5000 Nm 3 The pellets were dried in a preheating oven at a rate of 3.0 m / min, with a drying temperature of 150°C and a drying time of 5 minutes. The preheating temperature was 800°C and the preheating time was 15 minutes. After preheating, the pellets achieved a compressive strength of over 620 N / piece. The pellets were then fed into a rotary kiln and calcined at 1200°C for 12.5 minutes. Subsequently, they were cooled in an annular cooler to obtain the pellets. Under these conditions, high-quality pellets were obtained in a short time at a relatively low calcination temperature, achieving a compressive strength of over 3350 N / piece. The calcination temperature and time were reduced by 50°C and 5.0 minutes compared to those in air (1250°C and 17.5 minutes in air). The chemical composition of the pellets is shown in Table 6.

[0039] Table 6 Chemical composition of pellet products (%) The SEM image of the pellet product in Example 2 is as follows: Figure 3 As shown in the figure, H represents hematite, M represents magnetite, and P represents pores.

[0040] Example 3 This example uses the same raw materials as in Example 1, including the domestically produced iron ore concentrate, purchased iron ore concentrate, and bentonite. A high-pressure roller mill increases the specific surface area of ​​the ore particles, improving ball-forming performance. Ore blending is then performed according to the industrial raw material composition, with a ratio of 75:25 between domestically produced magnetite concentrate and purchased hematite concentrate. Finally, a disc pelletizer is used to mix the blended iron ore and bentonite, gradually rolling them into pellets. Qualified green balls with diameters between 8 mm and 16 mm are screened and transported to a chain grate using a belt conveyor.

[0041] The oxygen-enriched air used in the experiment was prepared by membrane separation and contained 40% oxygen. The ratio of oxygen-enriched air to air at the blast point of cooling section I of the fixed ring cooler was 0.8:1, the air oxygen concentration was 30%, and the oxygen-enriched cooling air volume was controlled at 95,000 Nm 3 / h; the ratio of oxygen-enriched air to air at the cooling section II of the ring cooler is 1:1, the oxygen concentration is 35%, and the cooling air volume is controlled at 70,000 Nm 3 / h. Three oxygen-enriched air spray guns were set at the hood of the PH preheating section of the chain grate used in the test. The oxygen concentration of the oxygen-enriched air sprayed was 50%, and the oxygen-enriched air spray volume was 5000 Nm 3The pellets were dried in a preheating oven at a rate of 3.0 m / min, with a drying temperature of 150°C and a drying time of 5 minutes. The preheating temperature was 900°C and the preheating time was 10 minutes. The pellets then entered a rotary kiln and were calcined at 1200°C for 15 minutes. Subsequently, they were cooled in an annular cooler to produce the pellets. Under these conditions, high-quality pellets were obtained in a short time at a relatively low calcination temperature, with a compressive strength exceeding 3370 N / piece. The calcination temperature and time were reduced by 50°C and 2.5 minutes compared to air (1250°C and 17.5 minutes in air). The chemical composition of the pellets is shown in Table 7.

[0042] Table 7 Chemical composition of pellet products (%) Comparative Example In this comparative example, the self-produced iron concentrate, purchased iron concentrate, and bentonite in Example 1 were used as raw materials for roasting tests. The self-produced iron concentrate had an iron grade of 65.66% and a high ferrous oxide content of 26.84%, which is a typical high-grade magnetite. The purchased magnetite had an iron grade of 61.76% and a ferrous oxide content of 2.39%, which is a hematite.

[0043] The two iron ore concentrates were pre-treated using a high-pressure roller mill to increase the specific surface area of ​​the ore particles and improve ball-forming performance. The ore was then blended according to the raw material structure of industrial production, with the ratio of domestically produced magnetite concentrate to purchased hematite concentrate being 75:25. Finally, a disc pelletizer was used to mix the mixed iron ore concentrate and bentonite, gradually rolling them into pellets. Qualified green balls with a diameter of 8 mm to 16 mm were screened and transported to a chain grate by a belt conveyor. The scanning electron microscope image of the green balls is shown below. Figure 4 As shown in the figure, H represents hematite, M represents magnetite, and P represents pores.

[0044] Based on the test results of Example 1, this comparative example maintains stable green pellet properties. The chain grate-rotary kiln-annular cooler process used does not include an oxygen enrichment device. The chain grate drying and preheating speed is 3.0 m / min, the drying temperature is 150°C, the drying time is 5 minutes, the preheating temperature is 800°C, and the preheating time is 15 minutes. After preheating, the pellets have a compressive strength of 550N / piece. They then enter the rotary kiln, are calcined at a temperature of 1200°C, and are calcined for 15 minutes. Finally, the pellets are cooled in an annular cooler to obtain the pellet product. Under these conditions, all indicators of the pellet product are reduced, and its compressive strength is above 3000N / piece. The chemical composition of the pellet product is shown in Table 8.

[0045] Table 8 Chemical composition of pellet products (%) The SEM images of the pelletized products in the comparative example are as follows: Figure 4As shown in the figure, H represents hematite, M represents magnetite, and P represents pores.

[0046] In summary, the process conditions and finished product properties of Examples 1 to 3 and the comparative example are shown in Table 9.

[0047] Table 9 Process conditions and finished product properties of Examples 1 to 3 and Comparative Examples It can be seen from Table 9 that in the comparative example, since the grate machine-rotary kiln-annular cooler process is not equipped with an oxygen enrichment device, and the oxidation of the pellets mainly occurs in the preheating stage of the chain grate, the oxygen content in the preheating stage is lower than that in Example 1, the oxidation degree of the magnetite contained in the green balls is low, and the oxidation reaction releases less heat, which makes the solid-phase reaction inside the pellets relatively reduced, so the compressive strength of the pellets in the preheating stage is reduced; at the same time, the oxygen content inside the rotary kiln is also relatively reduced. During the roasting process, the pellets contain too much ferrous oxide. Since the affinity of ferrous oxide to calcium oxide is stronger than that of ferric oxide, the calcium oxide combined with ferric oxide is relatively reduced, the content of calcium ferrite in the pellets is reduced, and the liquid phase during the roasting process is reduced, thereby reducing the densification degree of the pellets and the compressive strength. In addition, the consolidation of the pellets is recrystallization consolidation, and the reduction in ferric oxide content directly leads to a reduction in recrystallized iron oxide, further reducing the compressive strength of the pellets.

[0048] The present invention is based on the low-temperature rapid oxidation consolidation method of magnetite pellets preheated and roasted with oxygen-enriched preheating. By adding oxygen enrichment devices in multiple locations, supplementing oxygen-enriched air, and coordinating the flow rate and oxygen concentration, a reasonable oxygen concentration distribution can be achieved in the chain grate and rotary kiln, and oxygen-enriched preheating and roasting of magnetite pellets can be achieved, thereby achieving the purpose of low-temperature rapid oxidation and consolidation of magnetite pellets.

[0049] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for rapid oxidation and consolidation of magnetite pellets at low temperature based on oxygen-enriched preheating and roasting, suitable for the production process of oxidation pellets using a chain grate machine, a rotary kiln, and an annular cooler, characterized in that: The steps include: Oxygen-enriched air① is added to the cooling blast of the cooling section I of the ring cooler. The oxygen-enriched air① is led into the rotary kiln through the negative pressure formed by the main exhaust, and is used to oxidize and consolidate the green balls. The hot air at the tail of the rotary kiln is then led to the PH preheating section of the chain grate through the reheating fan, and is used to oxidize and preheat the green balls. Oxygen-enriched air ② is added to the cooling blast of the cooling section II of the ring cooler. The oxygen-enriched air ② is directed to the TPH transition preheating section of the grate machine for oxidation preheating of the green pellets. Add oxygen-enriched air ③ to the smoke hood of the PH preheating section of the grate machine. The oxygen-enriched air ③ increases the overall oxygen concentration in the grate machine and promotes the oxidation preheating of the pellets. The supplemented oxygen-enriched air ①, oxygen-enriched air ②, and oxygen-enriched air ③ can not only ensure the oxygen concentration required for oxidation preheating of the pellets in the chain grate and reduce the roasting temperature of the rotary kiln, but also avoid the generation of nitrogen oxides due to high oxygen concentration in the rotary kiln, achieve a reasonable oxygen concentration distribution in the chain grate and the rotary kiln, and realize low-temperature rapid oxidation consolidation of magnetite pellets.

2. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 1, characterized in that: The oxygen-enriched air① added to the cooling blast of the cooling section I of the ring cooler is mixed with the air through the oxygen mixing device, and the mixing ratio of the oxygen-enriched air① to the air is 0.6~0.8:1, so that the oxygen concentration of the cooling air in the cooling section I is increased to 25%~30%.

3. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 2, characterized in that: The cooling air volume of cooling stage I is controlled at 90,000~100,000 Nm 3 / h.

4. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 1, characterized in that: The oxygen-enriched air ② added to the cooling blast of the cooling section II of the ring cooler is mixed with the air through the oxygen mixing device, and the mixing ratio of the oxygen-enriched air ② to the air is 0.8~1.0:1, thereby increasing the oxygen concentration of the cooling air in the cooling section II to 28%~35%.

5. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 4, characterized in that: The cooling air volume of cooling section II is controlled at 60,000~80,000 Nm 3 / h.

6. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 1, characterized in that: 3 to 6 oxygen-enriched air spray guns are installed at the smoke hood of the PH preheating section of the chain grate machine to increase the oxygen concentration in the PH preheating section to 28% to 38%.

7. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 6, characterized in that: The oxygen-enriched air injection rate at the hood of the PH preheating section of the chain grate is 5000~10000 Nm 3 / h.

8. The method for low-temperature rapid oxidation consolidation of magnetite pellets based on oxygen-enriched preheating and roasting according to claim 1, characterized in that: The oxygen concentration of the oxygen-enriched air ①, oxygen-enriched air ②, and oxygen-enriched air ③ is 40% to 50%, and they are all prepared by membrane separation method.

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