Preparation method of double-layer iron ore carbon-containing pellets and its roasting method

Abstract

This invention relates to a method for preparing double-layer iron ore carbon-containing pellets and its roasting method, belonging to the field of ironmaking technology. The method involves preparing a core and an outer layer of powder. The core powder is obtained by uniformly mixing iron ore powder and carbon powder. The outer layer powder is obtained by uniformly mixing iron ore powder and a binder. Core pellet preparation involves spraying water onto the core powder to form pellets. The outer layer is then coated with water to coat the outer powder, resulting in double-layer iron ore carbon-containing pellets. The double-layer iron ore pellets prepared by this invention adopt a structure of carbon-containing core and ore-coated outer layer, which ensures a certain pellet strength and facilitates the supply of carbon to the core and the regulation of the internal reducing atmosphere. The inner layer of the double-layer iron ore pellets of this invention is a mixed layer of iron ore powder and carbon, while the outer layer consists only of iron ore powder and a binder. The double-layer iron ore pellets of this structure have a maximum compressive strength of 12.0 N / pellet, a maximum drop strength of 4.7 drops / 0.5m, and a bursting strength of 560℃, exhibiting good pellet strength and excellent reduction performance.

Description

Technical Field

[0001] This invention relates to a method for preparing carbon-containing double-layer iron ore pellets and its roasting method, belonging to the field of ironmaking technology. Background Technology

[0002] Non-blast furnace ironmaking is a type of ironmaking method relative to traditional blast furnace ironmaking, and direct reduction is one of the most important technical routes within it. Direct reduction refers to the process of directly reducing iron ore and other iron-containing oxides to metallic iron using gaseous or solid reducing agents, or both, under conditions below the softening or melting temperature of iron oxides. The product is commonly called direct reduced iron (DRI). Non-blast furnace ironmaking often uses carbon-containing pellets for reduction.

[0003] Carbon-containing pellets typically refer to iron- and carbon-containing furnace feedstock produced by mixing iron ore powder or iron-containing secondary resources with solid reducing agents such as coal powder, coke powder, and carbon powder, as well as an appropriate amount of binder, followed by pelletizing or briquetting. These pellets simultaneously carry the iron-containing raw materials and undergo reduction. Furthermore, carbon-containing pellets are highly adaptable to various raw materials and can be used for the utilization of various iron-containing dusts and metallurgical secondary resources, thus attracting widespread attention in the fields of low-carbon ironmaking and comprehensive resource utilization.

[0004] Application No. 2022109044090 discloses a method for preparing double-layer pellets containing carbon dust. The invention includes the following steps: S1: Raw material preparation: taking an appropriate amount of carbon dust, coke, and a pore-forming agent to obtain an inner layer pelletizing material; taking an appropriate amount of iron concentrate and a pore-forming agent to obtain an outer layer pelletizing material; S2: Preparing the inner layer pellets: feeding the inner layer pelletizing material into a disc pelletizer and adding water for mixing and pelletizing to obtain the inner layer pellets; S3: Preparing the double-layer pellets: continuing to feed the outer layer pelletizing material into the disc pelletizer from step S2, and adding water to continue pelletizing outside the inner layer pellets to allow the pellets to grow, ultimately obtaining double-layer pellets.

[0005] Application No. 2019103372441, a method for preparing double-layer carbon-containing pellets and its application. The invention: (1) Iron ore powder, coal powder and binder are prepared into a first mixture and a second mixture in different proportions; the molar ratio of carbon to oxygen in iron oxide in the first mixture is fixed at C / O = 0.95-1.15, and the mass percentage of binder in the first mixture is 1.0%-1.5%; the molar ratio of carbon to oxygen in iron oxide in the second mixture is fixed at C / O = 1.2-1.5, and the mass percentage of binder in the second mixture is 2.0%-3.0%; (2) The first mixture is made into an inner core with a diameter of 5-15 mm, and the second mixture is used to coat the outer part of the inner core to form a double-layer carbon-containing pellet with a diameter of 10-25 mm.

[0006] The inner and outer layers of the aforementioned double-layer carbon-containing pellets basically contain carbon or other substances (such as asphalt). However, the preparation and reduction processes of double-layer carbon-containing pellets still have problems such as uneven carbon source distribution, difficulty in balancing pellet strength and reduction performance, and the need to further improve carbon utilization efficiency. Summary of the Invention

[0007] To address the problems and shortcomings of the existing technology, this invention provides a method for preparing double-layer iron ore carbon-containing pellets and its roasting method. The double-layer iron ore pellets prepared by this invention adopt a structure with a carbon-containing core and an outer ore-coated core, which ensures a certain pellet strength while facilitating carbon supply to the core and adjustment of the internal reducing atmosphere. The inner layer of the double-layer iron ore pellets of this invention is a mixture of iron ore powder and carbon, while the outer layer consists only of iron ore powder and a binder. The double-layer iron ore pellets of this structure have a maximum compressive strength of 12.0 N / pellet, a maximum drop strength of 4.7 drops / 0.5 m, and a bursting strength of 560℃, exhibiting good pellet strength and excellent reduction performance. This invention is achieved through the following technical solutions.

[0008] A method for preparing carbon-containing pellets from double-layer iron ore, comprising the following steps: Step 1: Prepare the core and outer layer powders. Core powder: Mix iron ore powder and carbon powder evenly to obtain core powder; Outer layer powder: Mix iron ore powder and binder evenly to obtain mixed powder. Step 2, Core Sphere Preparation: Core spheres are obtained by spraying water onto the core powder to form spheres; Step 3, outer coating: Spray water onto the outer layer of the core sphere to coat the outer layer of powder to obtain a double-layer iron ore carbon-containing pellet.

[0009] In step 1, the ratio of iron ore powder to carbon powder in the core powder is 0.25-1.25.

[0010] The carbon-oxygen ratio is obtained using the formula: In the formula, The total mass of oxygen in the iron ore, in grams; The mass of the carbon sample is in grams. denoted as the mass fraction of carbon in char.

[0011] In step 1, the binder is sodium carboxymethyl cellulose, citric acid, lactic acid, sodium citrate, sodium tripolyphosphate, guar gum, xanthan gum, bentonite, emulsified silicone oil, nisin, and zinc citrate. The amount of binder added is 0.6%-1.4% of the mass of iron ore powder in the outer layer powder.

[0012] In step 2, the amount of water sprayed is 7%-8% of the mass of the core powder; in step 3, the amount of water sprayed is 7%-8% of the mass of the outer powder.

[0013] The core sphere preparation method in step 2 and the outer layer coating method in step 3 are disc sphere making or extrusion sphere making.

[0014] In step 2, the core sphere size is 8-10mm, and in step 3, the double-layer iron ore carbon-containing pellet size is 12-16mm.

[0015] A roasting method for double-layer iron ore carbon-containing pellets, comprising the following steps: The carbon-containing double-layer iron ore pellets prepared by the above method are sintered in an atmosphere of N2, H2, CO or CO-H2 at a temperature of 800℃-1100℃ for 1-90 min to obtain reduced iron.

[0016] The volume ratio of CO to H2 in the CO-H2 atmosphere is 4:1 to 1:4.

[0017] The beneficial effects of this invention are: (1) The double-layer iron ore pellets of this structure have a compressive strength of up to 12.0 N / piece, a drop strength of up to 4.7 times / 0.5m, and a bursting strength of 560℃. They have good pellet strength and good reduction performance.

[0018] (2) The inner layer of the double-layer iron ore pellet of the present invention is a mixture of iron ore powder and carbon, and the outer layer is only iron ore powder and binder. When sintered in N2, H2, CO or CO-H2 atmosphere, the reducibility is good during the reduction sintering process.

[0019] (3) When the carbon-oxygen ratio of the pellet core in the double-layer iron ore pellet is 0.75, the apparent reduction degree at the endpoint reaches a maximum of 0.9864 under H2 atmosphere; at 1000℃, the apparent reduction degree at the endpoint reaches a maximum of 0.9615 under CO atmosphere; and under CO-H2 mixed atmosphere, the apparent reduction degree at the endpoint reaches a maximum of 0.9635; further demonstrating that the double-layer magnetite pellet of the present invention has good reduction performance. Attached Figure Description

[0020] Figure 1 This is a graph showing the change in apparent reduction degree of uniform carbon-containing pellets under different conditions in N2 atmosphere according to Example 2 of the present invention. (a) is the core C / O=0.75 at 800℃ to 1100℃; (b) is the temperature at 1000℃ with different C / O ratios in the core. Figure 2 This is the XRD pattern of Embodiment 2 of the present invention after reduction calcination under N2 atmosphere (core C / O=0.75, 90min); Figure 3 This is a graph showing the change in apparent reduction degree of uniform carbon-containing pellets under different conditions in CO atmosphere in Example 3 of the present invention. (a) shows the core C / O = 0.75 at 800℃ to 1100℃; (b) shows the core C / O ratio at 1000℃ with different C / O ratios. Figure 4This is the XRD pattern of Example 3 of the present invention after reduction calcination in a CO atmosphere (core C / O=0.75, 1100℃, 90min); Figure 5 This is a graph showing the apparent reduction degree of uniform carbon-containing pellets under different conditions in H2 atmosphere in Example 4 of the present invention. (a) shows the core C / O = 0.75 at 800℃ to 1100℃; (b) shows the core C / O ratio at 1000℃ with different C / O ratios. Figure 6 This is the XRD pattern of Example 4 of the present invention after reduction calcination in H2 atmosphere (core C / O=0.75, 1100℃, 90min); Figure 7 This is a graph showing the apparent reduction degree of uniform carbon-containing pellets under different conditions in a CO-H2 atmosphere in Example 5 of the present invention. (a) shows different CO-H2 volume ratios at a core C / O ratio of 0.75 and a temperature of 800℃; (b) shows different CO-H2 volume ratios at a core C / O ratio of 0.75 and a temperature of 900℃; (c) shows different CO-H2 volume ratios at a core C / O ratio of 0.75 and a temperature of 1000℃; and (d) shows different CO-H2 volume ratios at a core C / O ratio of 0.75 and a temperature of 1100℃. Figure 8 This is the XRD pattern of Example 5 of the present invention after reduction calcination in a CO-H2 atmosphere (core C / O=0.75, 1000℃, 90min); Figure 9 This is a graph showing the apparent reduction degree of uniform carbon-containing pellets under different conditions in a CO-H2 atmosphere according to Example 6 of the present invention. (a) shows the core C / O ratio of 0.75, the CO-H2 volume ratio of 4:1, and the temperature range of 800℃-1100℃; (b) shows the core C / O ratio of 0.75, the CO-H2 volume ratio of 3:2, and the temperature range of 800℃-1100℃; (c) shows the core C / O ratio of 0.75, the CO-H2 volume ratio of 2:3, and the temperature range of 800℃-1100℃; and (d) shows the core C / O ratio of 0.75, the CO-H2 volume ratio of 1:4, and the temperature range of 800℃-1100℃. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] A method for preparing carbon-containing pellets from double-layer iron ore, comprising the following steps: Step 1: Prepare the core and outer layer powders. Core powder: Mix iron ore powder and carbon powder evenly to obtain core powder; Outer layer powder: Mix iron ore powder and binder evenly to obtain mixed powder. Step 2, Core Sphere Preparation: Core spheres are obtained by spraying water onto the core powder to form spheres; Step 3, outer coating: Spray water onto the outer layer of the core sphere to coat the outer layer of powder to obtain a double-layer iron ore carbon-containing pellet.

[0023] In some specific embodiments, the carbon-to-oxygen ratio of iron ore powder to carbon powder in the core powder in step 1 is 0.25-1.25. In a particular embodiment, the carbon-to-oxygen ratio of iron ore powder to carbon powder in the core powder is 0.25, 0.3, 0.4, 0.75, 1.0, or 1.25.

[0024] In certain embodiments, the binder in step 1 is sodium carboxymethyl cellulose, citric acid, lactic acid, sodium citrate, sodium tripolyphosphate, guar gum, xanthan gum, bentonite, emulsified silicone oil, nisin, or zinc citrate. The amount of binder added is 0.6%-1.4% of the iron ore powder mass in the outer layer powder. In a specific embodiment, the amount of binder added is 0.6%, 0.7%, 0.8%, 1.0%, 1.2%, or 1.4% of the iron ore powder mass in the outer layer powder.

[0025] In some specific embodiments, the amount of water sprayed in step 2 is 7%-8% of the mass of the core powder; the amount of water sprayed in step 3 is 7%-8% of the mass of the outer powder. In a specific embodiment, the amount of water sprayed in step 2 is 7%, 7.5%, or 8% of the mass of the core powder; the amount of water sprayed in step 3 is 7%, 7.5%, or 8% of the mass of the outer powder.

[0026] In certain specific embodiments, the core sphere preparation method in step 2 and the outer layer coating method in step 3 are disc sphere making or extrusion sphere making.

[0027] In some specific embodiments, the core sphere size in step 2 is 8-10 mm, and the size of the carbon-containing double-layer iron ore pellets in step 3 is 12-16 mm. In another specific embodiment, the core sphere size in step 2 is 8 mm, 9 mm, or 10 mm, and the size of the carbon-containing double-layer iron ore pellets in step 3 is 12 mm, 13 mm, 14 mm, or 16 mm.

[0028] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: The prepared double-layer iron ore carbon-containing pellets are sintered in an atmosphere of N2, H2, CO, or CO-H2 at a temperature of 800℃-1100℃ for 1-90 min to obtain reduced iron. In a specific embodiment, reduced iron is obtained by sintering at temperatures of 800℃, 900℃, 1000℃, or 1100℃ for 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 80 min, or 90 min.

[0029] In some specific embodiments, the volume ratio of CO to H2 in the CO-H2 atmosphere is 4:1 to 1:4; in a certain specific embodiment, the volume ratio of CO to H2 in the CO-H2 atmosphere is 4:1, 2:3, 3:2 or 1:4.

[0030] In the following examples, the apparent reduction degree of the bilayer carbon-containing pellets at time t is calculated: In the formula, for Time-lapsed particle appearance accuracy, % for The cumulative weight loss of the pellet at any given time, in grams; The mass of volatiles in the pellet, in grams; The total amount of oxygen that can be removed by reduction in the pellet, in grams; The mass of fixed carbon in the pellet, in grams. Example 1

[0031] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare the core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1; the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80 μm) is mixed evenly with carbon powder to obtain the core powder. The iron ore powder and carbon powder in the core powder are mixed at a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1; the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80 μm) is mixed evenly with a binder to obtain a mixed powder. The binder is bentonite, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder.

[0032] Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0033] The double-layer iron ore pellets prepared in this embodiment have a compressive strength of 12.0 N / pellet, a maximum drop strength of 4.7 drops / 0.5 m, and a bursting strength of 560℃, exhibiting good pellet strength. Example 2

[0034] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare 9 sets of core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm) is mixed evenly with carbon powder to obtain core powder. Among them, five sets of iron ore powder (the chemical mass percentage composition of iron ore powder is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm)) are mixed with carbon powder at carbon-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25, respectively, and the other four sets are iron ore powder and carbon powder at a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder is mixed evenly with a binder to obtain mixed powder. The binder is sodium carboxymethyl cellulose, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder. Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0035] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: The nine groups of carbon-containing double-layer iron ore pellets prepared by the above preparation method were subjected to a flow rate of 2 L / min under a N2 atmosphere. Reduced iron was obtained by sintering carbon-containing pellets of double-layer iron ore with carbon-to-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25 at 1000℃ for 1-90 min. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 1 As shown in (b); The other four groups were all reduced iron obtained by sintering iron ore powder and carbon powder at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a carbon-to-oxygen ratio of 0.75. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 1 As shown in (a).

[0036] from Figure 1(a) As can be seen, when the carbon-to-oxygen ratio in the core is 0.75, the apparent reduction degree of the bilayer carbon-containing pellets increases significantly with the reduction temperature from 800℃ to 1100℃. At 800℃, the apparent reduction degree is 0.1151; at 900℃, it increases to 0.1721; at 1000℃, it is 0.2936; and at 1100℃, it is 0.3194. This indicates that increasing the temperature facilitates the carbothermic reduction reaction of the bilayer carbon-containing pellets, especially in the medium-to-high temperature stages. This is because, with increased temperature, the gasification reaction of carbon in the core is more readily carried out, increasing the CO content. The generated gas diffuses from the inside of the pellets along the pores to the outside, further enhancing the indirect reduction of iron oxides in the shell. Therefore, in the bilayer structure, increasing the temperature not only improves the activity of the carbon-donating reaction in the core but also enhances the continuous reduction process in the shell region, significantly improving the overall apparent reduction degree of the pellets. Figure 1 (b) It can be seen that at 1000℃ and under a N2 atmosphere, as the carbon-oxygen ratio of the core increases from 0.25 to 1.25, the apparent reduction degree of the bilayer carbon-containing pellets generally shows an upward trend, but the rate of increase gradually decreases. After 90 min of reduction, the apparent reduction degrees at the endpoints of 0.1120, 0.1798, 0.2936, 0.3465, and 0.3716 are respectively when the core carbon-oxygen ratio is 0.25, 0.50, 0.75, 1.0, and 1.25. It can be seen that appropriately increasing the core carbon content can enhance the carbon supply capacity inside the pellets and improve the local reducing atmosphere, thereby promoting the reduction of iron oxides in the shell; however, when the carbon-oxygen ratio continues to increase, the improvement in carbon utilization efficiency is limited, and its promoting effect gradually decreases.

[0037] To further determine the changes in the reduction products, XRD analysis was performed on the bilayer carbon-containing pellets reduced under different temperature conditions. Figure 2 It can be seen that under N2 atmosphere, there are still obvious Fe3O4 and FeO peaks in the 900℃ sample. When the temperature is increased to 1000℃, the metallic Fe peak is significantly enhanced, while the high-valence iron oxide peak is weakened. This indicates that the pellet reduction is more complete after heating, and the product phase gradually changes from iron oxide to metallic iron. Example 3

[0038] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare 9 sets of core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm) is mixed evenly with carbon powder to obtain core powder. Among them, five sets of iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm)) are mixed with carbon powder at carbon-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25, respectively, and the other four sets are iron ore powder and carbon powder at a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder is mixed evenly with a binder to obtain mixed powder. The binder is bentonite, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder. Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0039] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: The nine groups of carbon-containing double-layer iron ore pellets prepared by the above preparation method were subjected to a flow rate of 2 L / min under a CO atmosphere. Reduced iron was obtained by sintering carbon-containing pellets of double-layer iron ore with carbon-to-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25 at 1000℃ for 1-90 min. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 3 As shown in (b); The other four groups were all reduced iron obtained by sintering iron ore powder and carbon powder at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a carbon-to-oxygen ratio of 0.75. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 3 As shown in (a).

[0040] Depend on Figure 3(a) As can be seen, when the carbon-to-oxygen ratio in the core is 0.75, the apparent reduction degree of the bilayer carbon-containing pellets increases significantly with the reduction temperature increasing from 800℃ to 1100℃, and the curve rises faster at higher temperatures. At 800℃, the pellet reduction process is relatively slow, with an initial apparent reduction degree of 0.6405; when the temperature rises to 900℃, the initial apparent reduction degree increases to 0.8630; at 1000℃, it further increases to 0.9309; and at 1100℃, the reduction is fastest, with an initial apparent reduction degree of 0.9640. This indicates that increasing the temperature can significantly promote the reduction of bilayer carbon-containing pellets in a CO atmosphere. The main reason is that after the temperature rises, the reducing power of external CO on iron oxides is enhanced, and at the same time, the core carbon is more likely to undergo the Boudouard reaction with CO2 at higher temperatures and continuously generate CO, thereby strengthening the indirect reduction process inside the pellets. In addition, the carbon in the bilayer structure is concentrated in the core, and the generated CO can diffuse into the shell and reduce the iron oxides in the outer layer. Therefore, the core-shell synergy is more obvious at high temperatures.

[0041] Depend on Figure 3 (b) It can be seen that under 1000℃ and CO atmosphere conditions, different core carbon-oxygen ratios have a significant impact on the reduction behavior of bilayer carbon-containing pellets. Overall, as the carbon-oxygen ratio increases from 0.25 to 1.25, the apparent reduction degree of the pellets generally shows an increasing trend, especially in the initial stage of reduction. When C / O=0.25, the apparent reduction degree of the pellets increases the slowest, with a final apparent reduction degree of 0.8818; when the carbon-oxygen ratio increases to 0.50 and 0.75, the reduction degree of the pellets further increases; when C / O=1.00 and 1.25, the reduction degree curve shifts upward overall, with the highest apparent reduction degree at C / O=1.25, reaching 0.9615. This indicates that appropriately increasing the core carbon-oxygen ratio is beneficial to enhancing the carbon supply capacity of bilayer carbon-containing pellets, increasing the generation of CO inside the pellets, and improving the local reducing atmosphere, thereby accelerating the reduction of iron oxides in the shell. However, the changes in apparent reduction also show that when the carbon-oxygen ratio increases to a higher level, the differences between the apparent reduction curves gradually narrow, indicating that further increasing the amount of carbon has limited effect on improving the reduction effect, and its promoting effect gradually weakens.

[0042] To further determine the changes in phase composition of the reduced products, XRD analysis was performed on the bilayer carbon-containing pellets after reduction at 1100℃ under a CO atmosphere. The results are as follows: Figure 4 As shown in the figure, a distinct Fe peak has formed in the sample, while a small amount of Fe3O4 peak can still be detected. This indicates that the bilayer carbon-containing pellets have reached a high degree of reduction under CO atmosphere, but some iron oxides are still not completely reduced. Example 4

[0043] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare 9 sets of core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm) is mixed evenly with carbon powder to obtain core powder. Among them, five sets of iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1, and the particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80μm)) are mixed with carbon powder at carbon-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25, respectively, and the other four sets are iron ore powder and carbon powder at a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder is mixed evenly with a binder to obtain mixed powder. The binder is emulsified silicone oil, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder. Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0044] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: Nine groups of carbon-containing double-layer iron ore pellets prepared by the above preparation method were subjected to a flow rate of 2 L / min under H2 atmosphere. Reduced iron was obtained by sintering carbon-containing pellets of double-layer iron ore with carbon-to-oxygen ratios of 0.25, 0.5, 0.75, 1, and 1.25 at 1000℃ for 1-90 min. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 5 As shown in (b); The other four groups were all reduced iron obtained by sintering iron ore powder and carbon powder at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a carbon-to-oxygen ratio of 0.75. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 5 As shown in (a).

[0045] Depend on Figure 5(a) It can be seen that when the carbon-to-oxygen ratio in the core is 0.75, the apparent activation energy of the pellets generally increases with the reduction temperature from 800℃ to 1100℃, and the apparent activation energy increases faster in the early stage of reduction under high temperature conditions. The apparent degree of reduction at 90 min for 800℃, 900℃, 1000℃, and 1100℃ are 0.7794, 0.8856, 0.9557, and 0.9864, respectively. This indicates that increasing the temperature under H2 atmosphere can significantly promote the reduction reaction of the bilayer carbon-containing pellets. The reason is that H2 itself has a high diffusion rate and strong reducing power. After the temperature increases, it not only enhances the direct reduction effect of H2 on the iron oxide in the shell, but also facilitates the continued reaction of the core carbon with the generated H2O or CO2, improves the local reduction atmosphere inside the pellets, and thus accelerates the overall reduction process. Compared with a CO atmosphere, the bilayer carbon-containing pellets under a H2 atmosphere exhibited a higher reaction rate in the initial stage of reduction, indicating that H2 has a more significant reducing effect on the shell iron oxides.

[0046] Depend on Figure 5 (b) It can be seen that different core carbon-to-oxygen ratios under H2 atmosphere at 1000℃ also have a certain influence on the reduction behavior of bilayer carbon-containing pellets. Overall, as the core carbon-to-oxygen ratio increases from 0.25 to 1.25, the apparent reduction degree of the pellets generally shows an increasing trend. The reduction degree of the pellets is lowest when C / O=0.25, with an apparent reduction degree of about 0.8575 at 90 min. When the carbon-to-oxygen ratio is increased to 0.50, 0.75 and 1.00, the reduction degree of the pellets further increases. When C / O=1.25, the apparent reduction degree curve is higher overall, with an endpoint apparent reduction degree of 0.9862, indicating that appropriately increasing the core carbon content is beneficial to improving the reduction degree of bilayer carbon-containing pellets under H2 atmosphere.

[0047] To further determine the changes in phase composition of the reduced products, XRD analysis was performed on the products of pellets with different core carbon-to-oxygen ratios after reduction at 1100℃ in H2 atmosphere. The results are as follows: Figure 6 As shown in the figure, the reduction products under different conditions are predominantly Fe phase, indicating that the pellets have achieved a high degree of reduction under these conditions. Example 5

[0048] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare sixteen sets of core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1. The overall particle size of this iron ore powder is relatively fine, mainly distributed in the range of 10-80 μm) is mixed evenly with carbon powder to obtain the core powder. Among them, the sixteen sets are iron ore powder and carbon powder with a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder is mixed evenly with a binder to obtain a mixed powder. The binder is bentonite, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder. Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0049] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: The 16 groups of carbon-containing double-layer iron ore pellets prepared by the above preparation method were subjected to a flow rate of 2 L / min under a CO-H2 atmosphere. Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 800℃ for 1-90 min with CO-H2 volume ratios of 4:1, 2:3, 3:2, and 1:4, respectively. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 7 As shown in (a); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 900℃ for 1-90 min with CO-H2 volume ratios of 4:1, 2:3, 3:2, and 1:4, respectively. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 7 As shown in (b); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 1000℃ for 1-90 min with CO-H2 volume ratios of 4:1, 2:3, 3:2, and 1:4, respectively. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 7 As shown in (c); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 1100℃ for 1-90 min with CO-H2 volume ratios of 4:1, 2:3, 3:2, and 1:4, respectively. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 7 As shown in (d).

[0050] from Figure 7(a) It can be seen that at 800℃, different mixing ratios have the most significant effect on the reduction behavior of bilayer carbon-containing pellets. At mixing ratios of CO:H2 = 4:1, 3:2, 2:3, and 1:4, the endpoint apparent reduction degrees are 0.5974, 0.5275, 0.6277, and 0.6648, respectively. This indicates that under this temperature condition, increasing the H2 ratio is generally more beneficial to improving the apparent reduction degree of the pellets.

[0051] from Figure 7 (b) It can be seen that when the temperature rises to 900℃, the apparent reduction degree of the pellets at all mixing ratios further increases. The endpoint apparent reduction degrees at CO:H2 mixing ratios of 4:1, 3:2, 2:3, and 1:4 are 0.7231, 0.6705, 0.7833, and 0.8078, respectively. Compared to 800℃, the differences between mixing ratios are smaller; however, the H2... Even under conditions of high content, it still exhibits a high degree of reduction.

[0052] Depend on Figure 7 (c) and (d) show that at 1000℃, the apparent reduction degrees at the endpoint are 0.8932, 0.9090, 0.9072, and 0.9278 for CO:H2 mixing ratios of 4:1, 3:2, 2:3, and 1:4, respectively. At 1100℃, these values ​​are 0.9409, 0.9469, 0.9520, and 0.9635. Compared to the low-temperature conditions, the differences between the various mixing ratios are much smaller, indicating that the influence of the gas mixture ratio on the endpoint reduction degree gradually weakens at higher temperatures. However, overall, the apparent reduction degree at the endpoint is still highest under the CO:H2=1:4 condition, indicating that increasing the H2 ratio still has a certain promoting effect on reduction, but this difference is no longer significant at high temperatures.

[0053] Figure 8 The XRD patterns of two mixed ratios after reduction of bilayer carbon-containing pellets at 1000℃ are presented. As can be seen from the figure, both groups of samples are dominated by the Fe phase, while there are still a small amount of FeO and Fe3O4 residues. Example 6

[0054] The method for preparing carbon-containing pellets from double-layer iron ore includes the following steps: Step 1: Prepare sixteen sets of core and outer layer powders. Core powder: Iron ore powder (the chemical mass percentage composition of iron ore is shown in Table 1. The particle size of this iron ore powder is generally fine, mainly distributed in the range of 10-80 μm) and carbon powder are mixed evenly to obtain the core powder. The sixteen sets are all iron ore powder and carbon powder with a carbon-oxygen ratio of 0.75. Outer layer powder: Iron ore powder and binder are mixed evenly to obtain the mixed powder. The binder is sodium carboxymethyl cellulose, and the amount of binder added is 1.4% of the mass of iron ore powder in the outer layer powder. Step 2, Core Sphere Preparation: Core spheres of 8mm are obtained by spraying water onto a disc to form core powder, wherein the amount of water sprayed is 8% of the mass of the core powder; Step 3, outer coating: Spray water (8% of the outer powder mass) on the outer layer of the core sphere to form a disc-shaped sphere and coat the outer powder with a size of 14mm to obtain a double-layer iron ore carbon-containing pellet.

[0055] The roasting method for the carbon-containing pellets of the double-layer iron ore includes the following steps: The 16 groups of carbon-containing double-layer iron ore pellets prepared by the above preparation method were subjected to a flow rate of 2 L / min under a CO-H2 atmosphere. Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a CO-H2 volume ratio of 4:1. The apparent reduction degree of the carbon-containing pellets is shown in the graph below. Figure 9 As shown in (a); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a CO-H2 volume ratio of 3:2. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 9 As shown in (b); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a CO-H2 volume ratio of 2:3. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 9 As shown in (c); Reduced iron was obtained by sintering four groups of carbon-containing double-layer iron ore pellets with a carbon-oxygen ratio of 0.75 at 800℃, 900℃, 1000℃, and 1100℃ for 1-90 min with a CO-H2 volume ratio of 1:4. The apparent reduction degree of the carbon-containing pellets is shown in the figure below. Figure 9 As shown in (d).

[0056] Depend on Figure 9 It can be seen that, under all mixing ratios, the apparent reduction degree of the bilayer carbon-containing pellets increases with the extension of reduction time, and the reduction degree increases significantly with increasing temperature. Overall, the pellet reduction is slow at 800℃, the reduction degree increases significantly at 900℃, and when the temperature rises to 1000℃ and above, the pellets under all ratios can reach a high apparent reduction degree in a relatively short time. Under the conditions of CO:H2=4:1 and 3:2, the apparent reduction degree of the pellets also increases with increasing temperature, but the overall reduction degree is still relatively low at low temperatures. In contrast, under the conditions of CO:H2=2:3 and 1:4, the pellets show a high reduction level at 1000℃ and 1100℃, and the initial increase is relatively rapid.

[0057] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method of producing double-iron-ore carbon-containing pellets, characterized by the steps of include: Step 1: Prepare the core and outer layer powders. Core powder: Mix iron ore powder and carbon powder evenly to obtain core powder; Outer layer powder: Mix iron ore powder and binder evenly to obtain mixed powder. Step 2, Core Sphere Preparation: Core spheres are obtained by spraying water onto the core powder to form spheres; Step 3, outer coating: Spray water onto the outer layer of the core sphere to coat the outer layer of powder to obtain a double-layer iron ore carbon-containing pellet.

2. The method for preparing carbon-containing pellets of double-layer iron ore according to claim 1, characterized in that: In step 1, the ratio of iron ore powder to carbon powder in the core powder is 0.25-1.

25.

3. The method for preparing carbon-containing pellets of double-layer iron ore according to claim 1, characterized in that: In step 1, the binder is sodium carboxymethyl cellulose, citric acid, lactic acid, sodium citrate, sodium tripolyphosphate, guar gum, xanthan gum, bentonite, emulsified silicone oil, nisin, nicotinamide, or zinc citrate. The amount of binder added is 0.6%-1.4% of the mass of iron ore powder in the outer layer powder.

4. The method for preparing carbon-containing pellets of double-layer iron ore according to claim 1, characterized in that: In step 2, the amount of water sprayed is 7%-8% of the mass of the core powder; in step 3, the amount of water sprayed is 7%-8% of the mass of the outer powder.

5. The method for preparing carbon-containing pellets of double-layer iron ore according to claim 1, characterized in that: The core sphere preparation method in step 2 and the outer layer coating method in step 3 are disc sphere making or extrusion sphere making.

6. The method for preparing carbon-containing pellets of double-layer iron ore according to claim 1, characterized in that: In step 2, the core sphere size is 8-10mm, and in step 3, the double-layer iron ore carbon-containing pellet size is 12-16mm.

7. A method for roasting double-layer carbon-containing iron ore pellets, characterized in that... The steps include: The carbon-containing double-layer iron ore pellets prepared by any one of the preparation methods described in claims 1 to 6 are sintered at a temperature of 800℃-1100℃ for 1-90 minutes in an atmosphere of N2, H2, CO or CO-H2 to obtain reduced iron.

8. The roasting method for double-layer iron ore carbon-containing pellets according to claim 7, characterized in that: The volume ratio of CO to H2 in the CO-H2 atmosphere is 4:1 to 1:4.

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