A method for preparing composite alkaline pellets with reduced adhesion rate

Abstract

This invention relates to the field of metal production or refining technology, specifically to a method for preparing composite alkaline pellets with reduced adhesion rate. The method includes the following steps: 1) preparation of homogeneous pellet batching and determination of homogeneous pellet adhesion rate; 2) preparation of composite pellet batching; 3) staged pelletizing; 4) oxidative calcination; and 5) performance testing and qualification judgment of the finished pellets. This method effectively reduces the adhesion rate of composite alkaline pellets, thereby improving the yield of composite alkaline pellets.

Description

Technical Field

[0001] This invention relates to the field of metal production or refining technology, specifically to a method for preparing composite alkaline pellets with reduced adhesion rate. Background Technology

[0002] The mainstream burden structure for blast furnace ironmaking typically consists of high-basicity sintered ore mixed with acidic pellets. In actual production, some iron ore raw materials have very fine particle sizes, with a high proportion of particles smaller than -0.045mm, which poses challenges to agglomeration. Taking certain magnetite ores as an example, multi-stage grinding and beneficiation are required, demanding that the proportion of particles smaller than -0.038mm be no less than 95% to obtain a qualified concentrate with a TFe content of ≥65%. Such fine-grained iron concentrates are prone to poor granulation, poor permeability of the material bed, and reduced ventilation efficiency during sintering, ultimately adversely affecting the quality of the sintered ore.

[0003] Blast furnace smelting requires slag basicity (CaO / SiO2) to be maintained within the range of 1.0 to 1.2 to ensure that the slag has suitable viscosity, melting point, and good desulfurization capacity, promoting effective slag-iron separation and stable blast furnace operation. To adapt to changes in the burden structure, flux needs to be added through pelletizing to supplement basicity; therefore, the research and application of basic pellets is of great significance.

[0004] Several practical applications of alkaline pellets have been implemented. For example, some companies have conducted industrial trials on MgO-based pellets, showing that as the MgO content increases, the iron grade and reducibility of the pellets rise, while the FeO content and reduction expansion rate decrease, resulting in improved metallurgical performance. Industrial production was achieved by adjusting the MgO addition amount. Other companies have successfully produced magnesian alkaline pellets with a binary basicity of 1.0, MgO content of 1.8%, and SiO2 content of 4.5%, providing raw material support for high-proportion pellet furnace charge structures.

[0005] However, the production of basic pellets still faces significant challenges: as basicity increases, Fe2O3 reacts with fluxes such as CaO during roasting to form low-melting-point phases like calcium ferrite and calcium silicate, leading to a significant increase in the amount of liquid phase. This excess liquid phase, at high temperatures, causes liquid-phase bridging at the contact surfaces of adjacent pellets, forming solid, agglomerated lumps. This phenomenon not only greatly increases the difficulty of pelletizing the product but also leads to a decrease in pellet yield, becoming a key technical bottleneck restricting the large-scale production and high-proportion application of high-basicity pellets. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a method for preparing composite alkaline pellets with reduced adhesion rate, which can effectively reduce the adhesion rate of composite alkaline pellets and thus improve the yield of composite alkaline pellets.

[0007] To achieve the above objectives, the present invention specifically includes the following steps: A method for preparing composite alkaline pellets with reduced adhesion rate employs a staged pelletizing process, with different formulation schemes for the inner and outer layers of the pellets. The method specifically includes the following steps: 1) Preparation of homogeneous pellets and determination of homogeneous pellet binding rate: According to the designed alkalinity, iron concentrate, binder and flux are mixed and formulated to obtain homogeneous alkaline iron-containing material A; Pellet A is pelletized in a pelletizing pan at a rotation speed of 40-45 r / min for 14-17 min to obtain green pellets I with a particle size of 12-13 mm and a moisture content of 8.0%-9.0%. Preheat the green pellets I to 890-950℃ at a rate of 8-12℃ / min and hold for 9-12 minutes. Then, increase the temperature to 1230-1260℃ at a rate of 4-6℃ / min and hold for 18-24 minutes for oxidation calcination; Then, the temperature was lowered to 300-400℃ at a rate of 10-15℃ / min, and the pellets were removed and air-cooled to obtain pellet I. Calculate the bonding rate of pellet I: The total mass of the calcined pellets is M1. Aggregates with more than 5 pellets bonded together are defined as bonded pellets, and the mass of the bonded pellets is M2. The bonding rate is (M2 / M1) × 100%. 2) Preparation of compound pellet ingredients: Based on the adhesion rate measured in step 1), the material is distributed to the inner and outer layers of the pellet according to the set alkalinity; The outer layer of the pellets is made from an acidic iron-containing material B, which is prepared by mixing iron concentrate and binder. The inner layer of the pellet is made from iron concentrate, binder and flux to form an alkaline iron-containing material C; 3) Phased ball-building: ①The target particle size of the inner layer pellets is 6~10mm. The alkaline iron-containing material C is pelletized in the first pelletizing tray, and after reaching the target particle size, it is sieved and removed. ②Then the inner layer pellets are placed in the second pelletizing tray and coated with acidic iron-containing material B until the pellet size reaches 12.5~14mm. The resulting composite green pellets are then obtained. 4) Oxidative roasting: Preheat the composite green pellets II to 880-960℃ at a rate of 8-12℃ / min and hold for 8-15min. Then, increase the temperature to 1200-1280℃ at a rate of 3-7℃ / min and hold for 15-25 minutes for oxidation roasting; Then, the temperature was lowered to 350°C at a rate of 6-10°C / min, and the pellets were removed and air-cooled to obtain pellet II. 5) Performance testing and qualification determination of finished pellets: Calculate the bonding rate of pellet II according to the formula in step 1) and compare it with the bonding rate of pellet I; when the basicity is 1.1 and the bonding rate decreases by 5%~10%, the basicity is 1.6 and the bonding rate decreases by 35%, or the basicity is 2.2 and the bonding rate decreases by 70%, the pellet II is a qualified finished pellet.

[0008] Further, in step 1), the alkaline iron-containing material A comprises, by weight percentage, 78% to 94% iron concentrate, 5% to 18% flux, and 1% to 5% binder.

[0009] Further, in step 2), the acidic iron-containing material B comprises 95% to 98% iron concentrate and 2% to 5% binder by weight, and the alkaline iron-containing material C comprises 73% to 94% iron concentrate, 5% to 22% flux and 1% to 5% binder by weight.

[0010] Furthermore, in step 2), the flux is one or more of quicklime, limestone, and dolomite.

[0011] Furthermore, in step 2), the adhesive is bentonite or an organic composite adhesive.

[0012] Furthermore, in step 3), the total water content of the pellets is 7.5%~9%.

[0013] Furthermore, in step 3), the total ball-making time is 10-20 minutes.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. Effectively solves the problem of high-basicity pellets sticking together during roasting, significantly improving yield: This invention, through a staged pelletizing process and a differentiated "inner alkali, outer acid" feed design, enables the pellet core and outer shell to exhibit different mineralization mechanisms and consolidation behaviors during oxidative roasting. The outer acidic material effectively inhibits the large-scale generation of low-melting-point liquid phase, fundamentally preventing strong sticking between adjacent pellets due to liquid phase bridging. This completely solves the serious sticking problem caused by excessive development of the outer liquid phase in basic pellets, thereby significantly improving the pellet yield.

[0015] 2. Breaking through the bottleneck of industrial production of alkaline pellets and expanding the upper limit of alkalinity operation: By precisely adjusting the alkalinity of the inner and outer layers and combining it with the optimization of pelletizing parameters, this invention effectively overcomes the technical bottleneck of large-scale pellet bonding under high alkalinity conditions while ensuring pellet strength. It achieves the feasibility of industrial production of alkaline pellets under higher alkalinity conditions and provides a new way to improve the performance of pellet ore and optimize the structure of furnace charge.

[0016] 3. Significantly improves the overall metallurgical performance of pellets: The alkaline core component ensures that the overall basicity of the pellets meets the requirements of blast furnace smelting and promotes the formation of beneficial binder phases such as calcium ferrite, thus ensuring the good reducibility and softening-melting performance of the pellets; the acidic material in the outer layer maintains the oxidation consolidation mode led by the recrystallization of hematite in acidic pellets, so that the pellets maintain excellent metallurgical performance while also having good cold strength, achieving a synergistic improvement in metallurgical performance.

[0017] 4. Adaptable to fine-grained iron concentrate raw materials, broadening the range of applicable raw materials: This method is particularly suitable for processing iron concentrate with fine particle sizes (e.g., a high proportion of -0.045mm). During the pelletizing process of alkaline pellets, the pelletizing speed is faster when the particle size is small (approximately 0-8mm); however, during the continued growth process (when the pellet diameter is 8-14mm), material adhesion is difficult, and pelletizing is slower. Therefore, staged pelletizing, while maintaining the total pelletizing time unchanged, correspondingly reduces the pellet growth time, thereby increasing the pellet rolling and compaction time. This helps improve the quality of green pellets and alleviates the drawbacks of single alkaline pellets where flux addition leads to difficulties in pelletizing and growth, providing an effective way to efficiently utilize fine-grained iron ore resources.

[0018] 5. Provide core raw material support for high-proportion pellet smelting in blast furnaces: The composite alkaline pellet product developed in this invention provides key raw material support for the large-scale use of high-proportion alkaline pellets in blast furnaces and the reduction of sinter ratio, significantly expanding the operational adjustment space of blast furnace ironmaking and conforming to the direction of low-carbon and green development of the steel industry. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0020] This invention discloses a method for preparing composite alkaline pellets with reduced adhesion rate. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0021] like Figure 1 As shown, a method for preparing composite alkaline pellets with reduced adhesion rate employs staged pelletizing, with different pelletizing processes and ingredient schemes for the inner and outer layers. Specifically, it includes the following steps: (1) Preparation of homogeneous alkaline pellets I: According to the set alkalinity scheme, iron concentrate, binder, and flux are mixed and formulated to obtain homogeneous alkaline iron-containing material A. Alkaline iron-containing material A comprises, by weight percentage, 78%–94% iron concentrate, 5%–18% flux, and 1%–5% binder. The flux is one or more of quicklime, limestone, and dolomite. The binder is bentonite or an organic composite binder.

[0022] Pelletizing was carried out using conventional methods. Pellet A was pelletized in a pelletizing pan at a rotation speed of 42 r / min for 16 min, resulting in green pellets with a particle size of 12.5 mm and a moisture content of 8.5%, which were designated as green pellets I.

[0023] The green pellets were preheated by heating them to 900°C at 10°C / min and holding them at that temperature for 10 min; then the temperature was increased to 1250°C at 5°C / min and held at that temperature for 20 min for oxidative roasting; then the temperature was reduced to 350°C at 10°C / min and the pellets were removed and air-cooled to obtain pellet I.

[0024] (2) Determine the bonding rate of homogeneous alkaline pellet I: The total mass of the pellets after calcination is M1. Aggregates with more than 5 balls bonded together are defined as bonded balls, and the mass of the bonded balls is M2. The bonding rate is (M2 / M1)×100%.

[0025] (3) Preparation of composite pellets: Based on the actual alkalinity, the homogeneous pellet bonding rate, and the difference in alkalinity between the inner and outer layers, a specific value between 6 and 10 mm for the inner layer pellet size under the designed alkalinity is determined by calculation, and the material is distributed between the inner and outer layers of the pellets according to the set alkalinity.

[0026] Among them, the outer layer of the pellet is made by mixing iron concentrate and binder to form acidic iron-containing material B, which contains 95% to 98% iron concentrate and 2% to 5% binder.

[0027] The inner layer of the pellet is made of iron concentrate, binder and flux mixed together to form an alkaline iron-containing material C. The alkaline iron-containing material C contains 73% to 90% iron concentrate powder, 5% to 22% flux and 1% to 5% binder.

[0028] The flux is one or more of quicklime, limestone, and dolomite. The binder is bentonite or an organic composite binder.

[0029] The types, grades, and varieties of iron concentrate used in acidic iron-containing material B, basic iron-containing material C, and basic iron-containing material A in step 1 are exactly the same.

[0030] The alkaline iron-containing material C is pelletized in the first pelletizing disc. After reaching the target pellet size, it is sieved and removed. At this time, the first pelletizing disc continues to pelletize to achieve continuous production.

[0031] After the pellets that have reached the target particle size in the first pelletizing pan are removed, they are placed in the second pelletizing pan. The inner layer of pellets is coated with acidic iron-containing material B and pelletizing continues. After the pellets reach a particle size of 12.5~14mm, they are removed and subjected to oxidative roasting to obtain pellet II.

[0032] The prepared pellet II was oxidized and calcined. The green pellets were preheated by heating to 880-960℃ at 8-12℃ / min and holding for 8-15 min. Then, they were oxidized and calcined by heating to 1200-1280℃ at 3-7℃ / min and holding for 15-25 min. After that, the temperature was reduced to 350℃ at a cooling rate of 6-10℃ / min. Finally, the pellets were removed and air-cooled to obtain the finished composite pellet II.

[0033] During the pelleting process, the total water content of the two types of pellets is the same, ranging from 7.5% to 9%; the total pelleting time is the same, ranging from 10 to 20 minutes.

[0034] (4) Performance testing and qualification determination of finished pellets: Calculate the bonding rate of pellet II according to the formula in step 1) and compare it with the bonding rate of pellet I; when the basicity is 1.1 and the bonding rate decreases by 5%~10%, the basicity is 1.6 and the bonding rate decreases by 35%, or the basicity is 2.2 and the bonding rate decreases by 70%, the pellet II is a qualified finished pellet.

[0035] Example 1: A method for preparing composite alkaline pellets with reduced adhesion rate specifically includes the following steps: (1) The conventional homogenized pellets were batched according to a basicity of 1.1. The batching scheme included iron concentrate powder, flux and binder. They were mixed to form conventional iron-containing material A, which contained 93.37% iron concentrate powder, 6.27% calcium carbonate and 1.3% bentonite. The percentages are by mass.

[0036] Pelletizing was carried out using conventional methods with the following parameters: pelletizing disc rotation speed 42 r / min, pelletizing time 16 min. This yielded green pellets with a particle size of 12.5 mm and a moisture content of 8.5%, which were designated as Green Pellet I.

[0037] The green pellets were preheated by heating them to 900°C at 10°C / min and holding them at that temperature for 10 min; then the temperature was increased to 1250°C at 5°C / min and held at that temperature for 20 min for oxidative roasting; then the temperature was reduced to 350°C at 10°C / min and the pellets were removed and air-cooled to obtain pellet I.

[0038] The bonding rate of pellet I was determined to be 15.13%.

[0039] (2) The materials for the inner and outer layers of the pellets were distributed according to an alkalinity of 1.1. The outer layer of the pellets consisted of an acidic iron-containing material B, which was prepared by mixing iron concentrate and binder, containing 98% iron concentrate and 2% bentonite. The inner layer of the pellets consisted of an alkaline iron-containing material C, which was prepared by mixing iron concentrate, binder, and flux, containing 90.64% iron concentrate powder, 8.46% calcium carbonate, and 1% bentonite. All percentages are by mass.

[0040] (3) The alkaline iron-containing material C is pelletized in the first pelletizing disc. The specific pelletizing parameters are as follows: a disc pelletizer is used in the pelletizing process. The disc radius is 1m and the rotation speed is 42r / min. The wet-mixed iron ore powder is added to the pelletizing disc in small amounts and multiple times for pelletizing. The pelletizing time is 10min. After the pellet size reaches 8mm, the pellet is screened and removed. At this time, the first pelletizing disc continues to pelletize to achieve continuous production.

[0041] After the pellets that have reached the target particle size in the first pelletizing pan are removed, they are placed in the second pelletizing pan, and the inner layer of pellets is coated with acidic iron-containing material B. The pelletizing parameters are: rotation speed 50 r / min, pelletizing time 6 min, and pelletizing is continued until the pellet size reaches 12.5 mm. Then, the pellets are removed to obtain composite green pellets II.

[0042] (4) Oxidize and roast the composite green pellets II. Preheat the composite green pellets II to 900℃ at 10℃ / min and hold for 10min. Then oxidize and roast them to 1240℃ at 5℃ / min and hold for 15min. After that, cool down to 350℃ at 10℃ / min and then air cool to obtain the finished pellets II.

[0043] (5) Take out the roasted pellets and weigh them. The total mass of the roasted pellets is M1. Aggregates with more than 5 balls bonded together are defined as bonded balls, and the mass of the bonded balls is M2. The bonding rate is (M2 / M1)×100%. Calculate the bonding rate of homogeneous pellet I and composite pellet II according to the above formula, and compare the bonding rates between homogeneous pellet I and composite pellet II.

[0044] In this embodiment, the bonding rate of pellet I is 15.13%, and the bonding rate of pellet II is 7.26%. Pellet II is a qualified finished pellet. The bonding rate of pellet II is significantly reduced, thereby improving the finished pellet yield.

[0045] The compressive strength of pellet I is 3027N, and the compressive strength of pellet II is 2805N. Although the compressive strength has changed, it still meets the blast furnace feeding standard.

[0046] Example 2: A method for preparing composite alkaline pellets with reduced adhesion rate specifically includes the following steps: (1) The conventional homogeneous pellets were batched according to a basicity of 1.6. The batching scheme included iron concentrate powder, flux and binder. They were mixed to form conventional iron-containing material A, which contained 87.94% iron concentrate powder, 10.56% calcium carbonate and 1.5% bentonite. The percentages are by mass.

[0047] Pelletizing was carried out using conventional methods with the following parameters: rotation speed 42 r / min and pelletizing time 14 min. This yielded green pellets with a particle size of 12.5 mm and a moisture content of 8.5%, which were designated as Green Pellet I.

[0048] The green pellets were preheated by heating them to 900°C at 10°C / min and holding them at that temperature for 10 min; then the temperature was increased to 1250°C at 5°C / min and held at that temperature for 20 min for oxidative roasting; then the temperature was reduced to 350°C at 10°C / min and the pellets were removed and air-cooled to obtain pellet I.

[0049] The bonding rate of pellet I was determined to be 45.86%.

[0050] (2) The materials for the inner and outer layers of the pellets were distributed according to an alkalinity of 1.6. The outer layer of the pellets consisted of an acidic iron-containing material B, which was prepared by mixing iron concentrate and a binder. This acidic iron-containing material B contained 98% iron concentrate and 2% bentonite. The inner layer of the pellets consisted of an alkaline iron-containing material C, which was prepared by mixing iron concentrate, a binder, and a flux. This alkaline iron-containing material C contained 86.91% iron concentrate powder, 12.09% calcium carbonate, and 1% bentonite. All percentages are by mass.

[0051] (3) The alkaline iron-containing material C is pelletized in the first pelletizing disc. The specific pelletizing parameters are as follows: a disc pelletizer is used in the pelletizing process. The disc radius is 1m and the rotation speed is 42r / min. The wet-mixed iron ore powder is added to the pelletizing disc in small amounts and multiple times for pelletizing. The pelletizing time is 10min. After the pellet size reaches 8mm, the pellet is screened and removed. At this time, the first pelletizing disc continues to pelletize to achieve continuous production.

[0052] After the pellets that have reached the target particle size in the first pelletizing pan are removed, they are placed in the second pelletizing pan, and the inner layer of pellets is coated with acidic iron-containing material B. The pelletizing parameters are: rotation speed 50 r / min, pelletizing time 4 min, and pelletizing is continued until the pellet size reaches 12.5 mm. Then, the pellets are removed to obtain composite green pellets II.

[0053] (4) Oxidize and roast the composite green pellets II. Preheat the composite green pellets II to 900℃ at 10℃ / min and hold for 10min. Then oxidize and roast them to 1250℃ at 5℃ / min and hold for 20min. After that, cool down to 350℃ at 10℃ / min and then air cool to obtain the finished pellets.

[0054] (5) Take out the roasted pellets and weigh them. The total mass of the roasted pellets is M1. Aggregates with more than 5 balls bonded together are defined as bonded balls, and the mass of the bonded balls is M2. The bonding rate is (M2 / M1)×100%. Calculate the bonding rate of homogeneous pellet I and composite pellet II according to the above formula, and compare the bonding rates between homogeneous pellet I and composite pellet II.

[0055] In this embodiment, the bonding rate of pellet I is 45.86%, and that of pellet II is 8.41%. Pellet II is a qualified finished pellet, and the significantly reduced bonding rate makes the basic pellets with a basicity of 1.6 suitable for production. The compressive strength of pellet I is 2859 N, and that of pellet II is 3158 N. Although the compressive strengths differ, they still meet the blast furnace feed standards.

[0056] Example 3: A method for preparing composite alkaline pellets with reduced adhesion rate specifically includes the following steps: (1) The conventional homogenized pellets were batched according to a basicity of 2.2. The batching scheme included iron concentrate powder, flux and binder. They were mixed to form conventional iron-containing material A, which contained 83.71% iron concentrate powder, 14.99% calcium carbonate and 1.3% bentonite. The percentages are by mass.

[0057] Pelletizing was carried out using conventional methods with the following parameters: rotation speed 42 r / min, pelletizing time 14 min. This yielded green pellets with a particle size of 13 mm and a moisture content of 8.5%, which were designated as Green Pellet I.

[0058] The green pellets were preheated by heating them to 900℃ at a rate of 10℃ / min and holding for 10 min; then oxidatively calcined by heating them to 1250℃ at a rate of 5℃ / min and holding for 20 min; finally, they were cooled to 350℃ at a rate of 10℃ / min and air-cooled to obtain pellet I. The binder rate of pellet I was determined to be 86.23%.

[0059] (2) The materials for the inner and outer layers of the pellets were distributed according to an alkalinity of 2.2. The outer layer of the pellets consisted of an acidic iron-containing material B, which was prepared by mixing iron concentrate and a binder. This acidic iron-containing material B contained 98% iron concentrate and 2% bentonite. The inner layer of the pellets consisted of an alkaline iron-containing material C, which was prepared by mixing iron concentrate, a binder, and a flux. This alkaline iron-containing material C contained 78.42% iron concentrate powder, 20.58% calcium carbonate, and 1% bentonite. All percentages are by mass.

[0060] (3) The alkaline iron-containing material C is pelletized in the first pelletizing pan. The specific pelletizing parameters are as follows: During the pelletizing process, a disc pelletizer is used. The disc has a radius of 1m and a rotation speed of 42r / min. The wet-mixed iron ore powder is added to the pelletizing disc in small amounts multiple times for pelletizing. The pelletizing time is 8min. After the pellets reach a particle size of 8.5mm, they are sieved and removed. At this time, the first pelletizing disc continues to pelletize to achieve continuous production.

[0061] After the pellets that have reached the target particle size in the first pelletizing pan are removed, they are placed in the second pelletizing pan. The inner layer of the pellets is coated with acidic iron-containing material B. The pelletizing parameters are: rotation speed 50 r / min, pelletizing time 6 min. Pelletizing is continued until the pellet size reaches 13 mm. The pellets are then removed to obtain composite green pellets II.

[0062] (4) Oxidize and roast the composite green pellets II. Preheat the composite green pellets II to 900℃ at 10℃ / min and hold for 10min. Then oxidize and roast them to 1270℃ at 5℃ / min and hold for 20min. After that, cool down to 350℃ at 10℃ / min and then air cool to obtain the finished pellets.

[0063] (5) Take out the calcined pellets and weigh them. Compare the bonding rates between homogeneous pellet I and composite pellet II.

[0064] In this embodiment, the bonding rate of pellet I is 86.23%, while that of pellet II is 9.6%. The significantly reduced bonding rate indicates that pellet II is a qualified finished pellet, thus enabling the production of alkaline pellets with a basicity of 2.2. The compressive strength of pellet I is 2901 N, and that of pellet II is 3576 N. Although the compressive strengths differ, they still meet the blast furnace feed standards.

[0065] Based on the above embodiments, the present invention provides a method for preparing composite alkaline pellets with reduced adhesion rate. Through an innovative process combining staged pelletizing with differentiated inner and outer layer formulations, this method exhibits significant technical advantages under different alkalinity conditions. Experimental data fully demonstrate that this method can effectively solve the severe adhesion problem during the roasting process of high-alkalinity pellets, significantly reduce the adhesion rate, and significantly improve the yield, while ensuring that the compressive strength of the pellets meets the requirements for blast furnace feeding. This provides a reliable technical path for the industrial production of high-alkalinity pellets and has important practical value for promoting high-proportion pellet smelting in blast furnaces.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing composite basic pellets with reduced caking rate, characterized by, Adopting the stage balling process, and the different material distribution scheme is used to the inner and outer layer of the pellet, specifically including the following steps: 1) Homogeneous pellet material preparation and homogeneous pellet adhesion rate determination: According to the design basicity, the iron concentrate, binder and flux are mixed to obtain homogeneous alkaline iron-containing material A; I is prepared by balling A in the balling disc at a speed of 40~45r / min for 14~17min, and the green ball I with a particle size of 12~13mm and a moisture content of 8.0%~9.0% is prepared; I is heated to 890~950℃ at a rate of 8~12℃ / min, and preheated for 9~12min; Then heated to 1230~1260℃ at a rate of 4~6℃ / min, and oxidized for 18~24min; Then cooled to 300~400℃ at a rate of 10~15℃ / min, and taken out for air cooling to obtain pellet I; The adhesion rate of pellet I is calculated: The total mass of the pellet after roasting is M1, the agglomerates with more than 5 balls are defined as the adhesion ball, the mass of the adhesion ball is M2, and the adhesion rate=(M2 / M1)×100%; 2) Compound pellet material preparation: According to the adhesion rate measured in step 1), the material distribution of the inner and outer layers of the pellet is carried out according to the set basicity; The outer layer of the pellet is prepared by mixing the iron concentrate and the binder to obtain the acidic iron-containing material B; The inner layer of the pellet is prepared by mixing the iron concentrate, the binder and the flux to obtain the alkaline iron-containing material C; 3) Stage balling: ① The target particle size of the inner layer pellet is 6~10mm, and the alkaline iron-containing material C is balling in the first balling disc, and the target particle size is taken out after sieving; ② Then the inner layer pellet is placed in the second balling disc, and the acidic iron-containing material B is used for coating balling, until the pellet particle size reaches 12.5~14mm, and the compound green ball II is taken out; 4) Oxidizing roasting: The compound green ball II is heated to 880~960℃ at a rate of 8~12℃ / min, and preheated for 8~15min; Then heated to 1200~1280℃ at a rate of 3~7℃ / min, and oxidized for 15~25min; Then cooled to 350℃ at a rate of 6~10℃ / min, and taken out for air cooling to obtain pellet II; 5) Performance detection and qualification of finished pellet: The adhesion rate of pellet II is calculated according to the formula in step 1), and compared with the adhesion rate of pellet I; when the basicity is 1.1 and the adhesion rate is reduced by 5%~10%, the basicity is 1.6 and the adhesion rate is reduced by 35%, or the basicity is 2.2 and the adhesion rate is reduced by 70%, the pellet II is the qualified finished pellet.

2. The compound alkaline pellet preparation method for reducing adhesion rate according to claim 1, wherein in step 1), the alkaline iron-containing material A includes 78%~94% iron concentrate, 5%~18% flux and 1%~5% binder by weight percentage.

3. The compound alkaline pellet preparation method for reducing adhesion rate according to claim 1, wherein ​ In step 2), the acidic iron-containing material B comprises 95% to 98% iron concentrate and 2% to 5% binder by weight, and the alkaline iron-containing material C comprises 73% to 94% iron concentrate, 5% to 22% flux and 1% to 5% binder by weight.

4. The method for preparing composite alkaline pellets with reduced adhesion rate according to claim 1, characterized in that, In step 2), the flux is one or more of quicklime, limestone, and dolomite.

5. The method for preparing composite alkaline pellets with reduced adhesion rate according to claim 1, characterized in that, In step 2), the adhesive is bentonite or an organic composite adhesive.

6. The method for preparing composite alkaline pellets with reduced adhesion rate according to claim 1, characterized in that, In step 3), the total water content of the pellets is 7.5%~9%.

7. The method for preparing composite alkaline pellets with reduced adhesion rate according to claim 1, characterized in that, In step 3), the total ball-making time is 10-20 minutes.

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