Two-section type variable-binder and variable-rotating-speed pelletizing method

Abstract

The invention discloses a two-stage variable-binder variable-rotating-speed pelletizing method which comprises the following steps: dividing raw material iron ore powder into two parts, mixing the first part of iron ore powder with an organic binder to form a pelletizing raw material A, and mixing the second part of iron ore powder with an inorganic binder to form a pelletizing raw material B; the pelletizing raw material A is subjected to mother pellet pelletizing under the condition that the rotating speed is 25-40 r / min; and then the rotating speed is adjusted to be 10-25 r / min, the pelletizing raw material B is put in for final pelletizing, and green pellets are obtained. According to the method, different binders and different rotating speeds are matched and used in stages, so that the nucleating rate and the pelletizing rate can be increased, the mechanical strength of green pellets can be remarkably improved, the energy consumption of a pelletizer can be reduced while the pelletizing rate is increased, particularly, the abrasion rate of a disc lining plate can be remarkably reduced in the low-speed growth stage, and the service life of the disc lining plate is prolonged. And double optimization of production efficiency and energy consumption is achieved, good performance is provided for follow-up smelting, and good industrial application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and particularly relates to a pelletizing method with variable binder and variable rotation speed in two stages. Background Art

[0002] The iron and steel industry has large carbon consumption and carbon emissions, accounting for about 16% of the total carbon emissions in China. The carbon emissions in the ironmaking process account for 70% of the total carbon emissions in the iron and steel industry. Therefore, the development of low-carbon ironmaking technology is the key to achieving carbon reduction and emission reduction in the iron and steel industry. New technologies such as high-proportion pellet smelting in blast furnaces and new hydrogen-based shaft furnace reduction ironmaking processes have developed rapidly, greatly increasing the demand for high-quality pellet ores. The production of high-quality pellets depends on the type and addition amount of binders and the selection of pelletizing process parameters.

[0003] Binders play a key role in the process of iron ore concentrate pelletization, directly affecting the pelletization rate, strength and metallurgical properties of pellets. Common binders include inorganic binders, organic binders and composite binders, etc. Traditional pelletizing processes often use inorganic binders such as bentonite, which is inexpensive. However, to achieve a good binding effect, its addition amount is usually greater than 1.5 wt%, which not only introduces a large amount of silicon and aluminum impurities, but also generates an additional about 5 - 8% of CO 2 emissions. Organic binders have attracted attention due to their low addition amount of 0.1 - 0.5 wt% and low ash content characteristics. However, organic binders often have complex components and high costs, and are prone to losing their binding effect due to pyrolysis at high temperatures. Although composite binders can effectively improve the high-temperature performance of organic molecules, the mixing of organic-inorganic binders leads to competitive adsorption of functional groups between particles, such as the chelation of COO- and Ca2+, resulting in a decrease in the comprehensive binding efficiency of more than 37%. Patent CN119162456A uses a modified material to modify artificial sodium bentonite to prepare a bentonite-based composite material. Although it can improve the particle binding effect, the modification process is complex and unnecessary elements are introduced, which is not conducive to the subsequent smelting of pellet ores. Summary of the Invention

[0004] Aiming at the above deficiencies existing in the prior art, the purpose of the present invention is to provide a pelletizing method with variable binder and variable rotation speed in two stages, so as to solve the problems in the prior art that the addition amount of binder bentonite is large, introducing silicon and aluminum impurities leads to an increase in subsequent smelting energy consumption; organic binders have complex components, high costs and are prone to losing their binding effect due to high-temperature pyrolysis, and the binding efficiency of composite binders is not high.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A pelletizing method with variable binder and variable rotation speed in two stages includes the following steps:

[0007] The raw iron ore powder is divided into two parts. The first part of the iron ore powder is mixed with an organic binder to form pelletizing raw material A, and the second part of the iron ore powder is mixed with an inorganic binder to form pelletizing raw material B. Moreover, the weight of the first part of the iron ore concentrate is less than or equal to the weight of the second part of the iron ore concentrate.

[0008] Pelletizing of mother pellets is carried out on pelletizing raw material A under the condition that the rotation speed is 25 - 40 r / min; then the rotation speed is adjusted to 10 - 25 r / min, and pelletizing raw material B is put in for final pelletizing to obtain green pellets; among them, the rotation speed in the mother pelletizing stage > the rotation speed in the final pelletizing stage. In the present invention, pelletizing of mother pellets is carried out under the condition that the rotation speed is 25 - 40 r / min, and this rotation speed range refers to the rotation speed in the mother pelletizing stage. Then the rotation speed is adjusted to 10 - 25 r / min for final pelletizing, and this rotation speed range refers to the rotation speed in the final pelletizing stage.

[0009] Preferably, the organic binder is pectin or carboxymethyl cellulose; in pelletizing raw material A, the addition amount of the organic binder is 0.1 - 1.0 wt%.

[0010] Preferably, the inorganic binder is bentonite; in pelletizing raw material B, the addition amount of bentonite is 1.2 - 3.0 wt%.

[0011] Preferably, the weight of the first part of the iron ore powder accounts for 20 - 50 wt% of the total weight of the iron ore powder.

[0012] Preferably, the process time of mother pelletizing is 1 - 3 min, and the particle size of the formed mother pellets is 2 - 5 mm.

[0013] Preferably, the final pelletizing includes two stages: the mother pellet growth stage and the dense pellet stage; among them, under the condition that the rotation speed remains 10 - 25 r / min, the time of the mother pellet growth stage is 3 - 8 min, and the time of the dense pellet stage is 2 - 6 min; green pellets with a particle size of 10 - 13 mm are obtained.

[0014] Preferably, during the mother pelletizing process, water is added in a dropping manner; during the final pelletizing process, water is added in a spraying manner; finally, the water content in the obtained green pellets is controlled at 7 - 9 wt%.

[0015] Preferably, the iron ore powder is iron ore concentrate.

[0016] Preferably, the green pellets are used for low - carbon ironmaking.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. In view of the problems of traditional binders, the present invention improves them from multiple perspectives. According to the respective characteristics of the nucleation period, growth period, and compaction period experienced in the pelletizing process, the selection of the binder is adjusted. In the nucleation stage of the mother pellet, an organic binder is selected. Its chain-like structure is not only more conducive to adsorbing on the surface of iron ore concentrate particles. At the same time, the thermosensitive gel property of pectin is used to quickly wrap the iron ore concentrate particles to form a mother pellet with a stable structure; in the growth stage of the mother pellet, an inorganic binder bentonite is selected. The layered structure of bentonite is not only conducive to the layered attachment of outer iron ore concentrate particles on the surface of the green pellet, improving the pelletizing rate and accelerating the pelletizing speed, reducing the pelletizing energy consumption, but also can fill the pores through the shear thinning property of layered silicates, further enhancing the stability and mechanical strength of the pellet in the compaction period; finally, the method of the present invention can effectively promote the formation of mother pellets and improve the pelletizing speed, and the average pelletizing time is reduced by 0.27% / min.

[0019] 2. The present invention has an unexpected discovery about the rotation speed in the pelletizing process from a physical perspective. In the nucleation stage of the mother pellet, a higher rotation speed is conducive to promoting particle collision. Combining with the chain-like structure of the organic binder, a flexible three-dimensional network structure can be formed during high-speed pelletizing, promoting the adsorption of polar groups in the molecular chain-like structure of the organic binder on the surface of iron ore concentrate particles, enabling the iron ore concentrate particles to overcome the van der Waals force barrier and fully contact and bond to form nuclei; while in the growth stage of the mother pellet, a lower rotation speed is selected, which helps to promote the layered growth of particles on the surface of the mother pellet and makes the layered structure of the inorganic binder arrange particles more effectively, improving the pelletizing efficiency and the uniformity of pellet pores; at the same time, the organic binder used in the present invention has a low dosage and is green and pollution-free, which can effectively reduce the introduction of various harmful elements and improve the iron grade of the pellet.

[0020] 3. The method of the present invention uses different binders and rotation speeds in different stages in a combined manner, which can not only improve the nucleation rate and pelletizing rate, but also significantly enhance the mechanical strength of the green pellet, reduce the energy consumption of the pelletizer while increasing the pelletizing rate, especially in the low-speed growth stage, it can significantly reduce the wear rate of the disc liner, achieve the dual optimization of production efficiency and energy consumption, provide good properties for subsequent smelting, and have good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart of a pelletizing method with variable binders and variable rotation speeds in two stages according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the present invention belong to the scope of protection of the present invention.

[0023] Unless otherwise indicated in specific circumstances, the numerical ranges listed herein include the upper and lower limit values, as well as all integers and fractions within that range, without being limited to the specific values listed when defining the range.

[0024] I. A pelletizing method with variable binder and variable rotation speed in two stages

[0025] The raw material iron ore powder is divided into two parts. The first part of the iron ore powder is mixed with an organic binder to form pelletizing raw material A, and the second part of the iron ore powder is mixed with an inorganic binder to form pelletizing raw material B, and the weight of the first part of the iron concentrate powder is less than or equal to the weight of the second part of the iron concentrate powder;

[0026] The pelletizing raw material A is pelletized into mother pellets under the condition that the rotation speed is 25 - 40 r / min; then the rotation speed is adjusted to 10 - 25 r / min, and the pelletizing raw material B is put in for final pelletizing to obtain green pellets; wherein, the rotation speed in the mother pelletizing stage > the rotation speed in the final pelletizing stage.

[0027] When studying the existing pellet production technology, the present invention found that the traditional binder bentonite in the existing technology is widely used in pellet production due to its low price. However, in order to achieve a better bonding effect, the addition amount of bentonite is often large (generally greater than 1.5 wt%, and in most cases far higher than this amount), which causes a large amount of silicon-aluminum impurities in the raw materials, resulting in a decrease in the iron grade of the pellets. In the heat treatment stage, additional treatment is required, leading to additional energy consumption and CO 2 emissions. For this reason, the present invention considered adjusting the binder system and used an organic binder to replace bentonite, but the effect was not ideal. If the pellets were prepared completely with an organic binder, the strength of the obtained pellets after preheating and roasting would be insufficient, seriously affecting the effect of subsequent high-temperature reduction smelting. Moreover, the present invention also found that even using a composite binder could not solve the above technical problems, and a single binder system was difficult to adapt to the nucleation and growth requirements of iron concentrate powder in different pelletizing stages. At the same time, the present invention also found that the existing technology generally uses a constant rotation speed (20 - 30 r / min) for pelletizing production. Since the rotation speed is constant throughout the pelletizing process, this leads to a mismatch in the mechanical environment during the nucleation period and the growth period: insufficient rotation speed during the nucleation period results in low particle kinetic energy, making it difficult to promote the release of the activation energy on the particle surface, which not only causes a decrease in the nucleation rate of mother pellets but also affects subsequent growth, resulting in too high porosity inside the pellets, unstable structure, weak binding force between particles, and difficult to improve the compressive strength of the pellets. Not only that, this production process maintains high-speed pelletizing throughout, with redundant motor power consumption, and the effective energy consumption ratio during the nucleation period is only about 40%. The disk pelletizer not only has high energy consumption but also large wear.

[0028] Based on this, the present invention discovers that it is necessary to improve both the binder and the pellet production technology simultaneously. During the nucleation period, a relatively high and reasonable rotational speed needs to be maintained to form a sufficiently high shear force, accelerate the collision frequency between iron ore concentrate particles, and achieve the breakthrough of the surface activation energy of particles through such high-speed collisions, effectively overcoming the van der Waals force barrier, ensuring sufficient contact between particles and enabling them to strongly bond and nucleate. This can not only form balls quickly but also fundamentally enhance the stability of the green balls, laying a good foundation for the subsequent growth of green balls. However, the rotational speed in this stage should not be too high, as too high a speed will be disadvantageous to the formation of nuclei. At the same time, during this process, an organic binder is used as the binder, and the organic binder is pectin or CMC (carboxymethyl cellulose), preferably pectin. Its chain-like structure is not only more conducive to adsorption on the surface of iron ore concentrate particles. Furthermore, the thermosensitive gel property of pectin is used to quickly wrap the iron ore concentrate particles to form green balls with stable structures, fundamentally enhancing the stability of green balls and also providing a basis for improving the mechanical strength of subsequent green balls. However, even though they are both organic binders, there are still certain differences in the effects of pectin and CMC. This point needs to be considered if other organic binders are to be used.

[0029] In the stage of green ball growth, the rotational speed is adjusted to a relatively low level, which is conducive to promoting the orderly superposition of particles on the green balls, enabling the green balls to grow in an orderly laminar manner, and forming a uniform pore structure inside the pellets, making the overall structure of the pellets more uniform. This can not only accelerate the growth rate of the pellets but also enhance the bonding force between particles during the growth of the pellets, thereby improving and strengthening the pellet strength. At the same time, a relatively low rotational speed can avoid excessive centrifugal force, resulting in too high collision energy between spheres and causing the spheres to break, making it impossible to form a sufficient amount of qualified pellets. During this process, the binder selected is the inorganic binder bentonite. The layered structure of bentonite is not only conducive to the layered attachment of outer iron ore concentrate particles on the surface of the green balls, improving the ball formation rate, accelerating the balling speed, and reducing the balling energy consumption, but also can fill the pores through the shear thinning property of layered silicates, further enhancing the stability and mechanical strength of the pellets during the compaction period.

[0030] The present invention uses a two-stage variable speed mode and a combination of two different binders for different growth stages of pellets to form pellets, which can fundamentally solve the problems in the prior art, such as a large amount of bentonite binder added, introduction of silicon-aluminum impurities resulting in increased energy consumption in subsequent smelting; complex components, high cost and easy loss of binding effect due to high-temperature pyrolysis of organic binders, and low binding efficiency of composite binders. At the same time, it can also solve the problems of uneven particle size distribution, low pelletization rate, and low compressive strength in the prepared pellets, significantly increasing the number of qualified pellets and improving the properties of the pellets, so as not to have an adverse impact on the subsequent smelting process. In particular, the method of the present invention uses different binders in stages and different rotation speeds in different pelletizing stages, which can not only improve the nucleation rate and pelletization rate, but also significantly improve the mechanical strength of green pellets, reduce the energy consumption of the pelletizer while increasing the pelletization rate, especially significantly reducing the wear rate of the disc liner in the low-speed growth stage, achieving double optimization of production efficiency and energy consumption, providing good properties for subsequent smelting, and having good industrial application prospects.

[0031] In some embodiments of the present invention, the organic binder is pectin or CMC (carboxymethyl cellulose), and further preferably pectin; in the pelletizing raw material A, the addition amount of the organic binder is 0.1-1.0 wt%. The present invention finds that the main chain of pectin is a typical linear chain structure. Due to the existence of side chains, the overall molecule may exhibit certain branching. This chain structure is more conducive to pectin adsorbing on the iron ore concentrate particles, thus quickly forming mother balls with very stable structures. Pectin has thermosensitive gel properties, enabling it to quickly wrap the iron ore concentrate particles, not only enhancing the structural stability of the mother balls, but also quickly forming pellets and significantly increasing the pelletizing speed. This also makes pectin superior to other organic binders (such as carboxymethyl cellulose CMC) under the condition of the same addition amount. The addition amount of the organic binder should not be too low, which will not only be difficult to achieve a suitable binding effect, but also reduce the nucleation speed; but if it is too high, due to its unique chain structure, entanglement will occur between the organic binder molecules, reducing the connection between the organic binder molecules and the iron ore concentrate particles, thus reducing the binding effect. Therefore, the addition amount of pectin can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1.0 wt%, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation examples, any of the above ranges can be combined with any other range.

[0032] In some embodiments of the present invention, the inorganic binder is bentonite; in the pelletizing raw material B, calculated by mass percentage, the addition amount of bentonite is 1.2 - 3.0 wt%. In the mother ball growth stage, the layered structure of bentonite not only facilitates the layered attachment of outer iron ore concentrate particles on the surface of the green balls, improves the pelletizing rate, speeds up the pelletizing speed, reduces the pelletizing energy consumption, but also can fill pores through the shear thinning characteristics of layered silicates, and further improves the stability and mechanical strength of the pellets during the compaction period. The addition amount of bentonite also needs to be controlled. When it is too low, it is difficult to achieve a suitable bonding effect, and when it is too high, it will significantly reduce the iron grade of the pellets, which has an adverse impact on subsequent ironmaking. Therefore, the addition amount of bentonite can be 1.2 wt%, 1.5 wt%, 1.7 wt%, 1.8 wt%, 2.0 wt%, 2.5 wt% or 3.0 wt%, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0033] In some embodiments of the present invention, the mother ball pelletizing is carried out under the condition that the rotation speed is 25 - 40 r / min. This speed should not be too low or too high. If it is too low or too high, it will be difficult for the mother balls to form, and even if the formed mother balls will have problems with insufficient self-stability. Therefore, the rotation speed can be 25 r / min, 27 r / min, 28 r / min, 30 r / min, 34 r / min, 35 r / min, 38 r / min or 40 r / min, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0034] In some embodiments of the present invention, the final pelletizing is carried out under the condition that the rotation speed is 10 - 25 r / min. This speed should also not be too low or too high. If it is too low, it is not conducive to the growth of mother balls, and if it is too high, it will cause the mother balls to break, both of which will affect the formation of qualified pellets. Therefore, the rotation speed can be 10 r / min, 12 r / min, 15 r / min, 16 r / min, 18 r / min, 20 r / min, 21 r / min, 24 r / min or 25 r / min, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0035] In some embodiments of the present invention, the rotation speed in the mother ball pelletizing stage > the rotation speed in the final pelletizing stage, preferably: the rotation speed in the mother ball pelletizing stage - the rotation speed in the final pelletizing stage ≥ 8 r / min. If the rotation speeds in these two stages do not differ much, it will not have a beneficial effect. Instead, if the difference is smaller, it will have an adverse effect, and this adverse effect may even make the final effect inferior to the properties of the green balls prepared by the constant speed preparation method.

[0036] In some embodiments of the present invention, the weight of the first part of the iron ore powder accounts for 20 - 50 wt% of the total weight of the iron ore powder. The iron ore powder is added to the disk pelletizer in batches for production, and the weight of the first part of the iron ore powder accounts for 20 - 50 wt% of the total weight of the iron ore powder. The weight ratio of the first part of the iron ore powder can be 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0037] In some embodiments of the present invention, the process time of mother ball pelletizing is 1 - 3 min, and the particle size of the formed mother balls is 2 - 5 mm. The process time of mother ball pelletizing can be 1 min, 1.5 min, 2 min, 2.5 min or 3 min, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0038] In some embodiments of the present invention, the final pelletizing includes two stages: the mother ball growth stage and the dense pellet stage; wherein, under the condition that the rotation speed is maintained at 10 - 25 r / min, the time of the mother ball growth stage is 3 - 8 min, and the time of the dense pellet stage is 2 - 6 min; green balls with a particle size of 10 - 13 mm are obtained. Therefore, the time of the mother ball growth stage can be 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, or within the numerical range formed by any two of the above specific values as endpoints; the time of the dense pellet stage can be 2 min, 3 min, 4 min, 5 min or 6 min, or within the numerical range formed by any two of the above specific values as endpoints. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0039] In some embodiments of the present invention, during the process of forming green balls from the mother balls, water is added in a dropping manner, and mother balls are formed by dropping water droplets into the ball-making raw materials. During this process, the amount of water added needs to be controlled, and the amount of water added during this process is about 1-9 wt% of the iron ore concentrate used for forming the mother balls. In the final ball-making process, water is added in a spraying manner, and an appropriate amount of water is sprayed in a misty and batch-wise form. The amount of water added in this step is regulated according to the water content requirement in the final green balls, so that the water content in the obtained green balls is controlled within 7-9 wt%.

[0040] In some embodiments of the present invention, the iron ore powder is iron ore concentrate. The method of the present invention is theoretically not limited to the preparation of iron ore pellets for ironmaking, but can also be applied to the preparation of other metal pellets for smelting.

[0041] In some embodiments of the present invention, the green balls are used for low-carbon ironmaking.

[0042] II. Examples and Comparative Examples

[0043] Example 1

[0044] The specific step flow is as Figure 1 shown:

[0045] Step 1: Take out 200 g of iron ore concentrate and mix it thoroughly with 0.4 g (0.2 wt%) of pectin as the ball-making raw material A. Take another 800 g of iron ore concentrate and mix it thoroughly with 13.6 g (1.7 wt%) of bentonite as the ball-making raw material B. The chemical composition analysis and water content of the iron ore concentrate are shown in Table 1;

[0046] Step 2: Place the ball-making raw material A in a disk pelletizer with a rotation speed of 34 r / min, and drop 10 g of water into it within 2 min to form mother balls until the mother balls nucleate to a suitable particle size;

[0047] Step 3: Adjust the rotation speed of the disk pelletizer to 24 r / min, add the ball-making raw material B to the mother balls made in Step 2 in 4 batches within 5 min, add 200 g of the ball-making raw material B each time, and spray about 2.5 g of water mist until the mother balls grow to a suitable particle size;

[0048] Step 4: Keep the rotation speed of the disk pelletizer at 24 r / min, and continue to rotate the prepared pellets tightly at this speed for 4 min and then take them out, regarded as the green balls of Example 1.

[0049] Step 5: Dry the green balls of Example 1 at 105°C for 3 h, preheat them at 950°C for 15 min and then roast them at 1250°C for 15 min.

[0050] Example 2

[0051] Based on Example 1 with adjustments, the difference lies in that the dosage of pectin is 0.1 wt%. The other steps are exactly the same as those in Example 1. After preparing the green balls of Example 2, perform the treatment of Step 5 in Example 1 on them.

[0052] Example 3

[0053] Based on Example 1 with adjustments, the difference lies in that the dosage of bentonite is 1.2 wt%. The other steps are exactly the same as those in Example 1. After preparing the green balls of Example 3, perform the treatment of Step 5 in Example 1 on them.

[0054] Example 4

[0055] Based on Example 1 with adjustments, the difference lies in that the dosage of bentonite is 3.0 wt%. The other steps are exactly the same as those in Example 1. After preparing the green balls of Example 4, perform the treatment of Step 5 in Example 1 on them.

[0056] Example 5

[0057] Based on Example 1 with adjustments, the difference lies in that the dosage of pectin is 1.0 wt% and the dosage of bentonite is 3.0 wt%. The other steps are exactly the same as those in Example 1. After preparing the green balls of Example 5, perform the treatment of Step 5 in Example 1 on them.

[0058] Example 6

[0059] Based on Example 1 with adjustments, the difference lies in that the pectin in Example 1 is replaced with 0.4 wt% of CMC. The other steps are exactly the same as those in Example 1. After preparing the green balls of Example 6, perform the treatment of Step 5 in Example 1 on them.

[0060] Comparative Example 1

[0061] Step 1: Thoroughly mix 0.4 g of pectin and 13.6 g of bentonite to make composite binder A, and then mix composite binder A with 1000 g of iron ore concentrate as the pelletizing raw material.

[0062] Step 2: Take out 200 g of the pelletizing raw material and place it in a disk pelletizer with a rotation speed of 34 r / min. Drop 10 g of water into it within 2 min to form mother balls until the mother balls nucleate to a suitable particle size.

[0063] Step 3: Reduce the rotation speed of the disk pelletizer to 24 r / min, and add the remaining 800 g of the pelletizing raw material to the mother balls made in Step 2 in 4 times within 5 min, adding 200 g of pelletizing raw material B each time, and spraying about 2.5 g of water mist until the mother balls grow to a suitable particle size.

[0064] Step 4: Keep the disc pelletizing machine speed at 24r / min, continue to rotate the prepared pellets at this speed for 4 minutes, and then take them out, which are regarded as the raw balls of Comparative Example 1.

[0065] Step 5: Dry the green balls of Comparative Example 1 at 105°C for 3 hours, preheat at 950°C for 15 minutes, and then calcine at 1250°C for 15 minutes.

[0066] Comparative Example 2

[0067] Step 1: 0.8g CMC and 13.6g bentonite were fully mixed to prepare composite binder B, and then the composite binder B was mixed with 1000g iron ore concentrate to be used as a pelletizing raw material;

[0068] Step 2: Take out 200g of pelletizing raw materials and place them in a disc pelletizing machine with a rotation speed of 34r / min. Add 10g of water into the disc pelletizing machine within 2min to form mother balls until the mother balls are nucleated to a suitable particle size.

[0069] Step 3: Reduce the speed of the disc pelletizer to 24r / min, add the remaining 800g of pelletizing raw material into the mother ball made in step 2 in 4 times within 5min, add 200g of pelletizing raw material B each time, and spray about 2.5g of water mist until the mother ball grows to a suitable particle size;

[0070] Step 4: Keep the speed of the disc pelletizer at 2r / min, continue to rotate the prepared pellets at this speed for 4 minutes, and then take them out, which are regarded as the raw balls of Comparative Example 1.

[0071] Step 5: Dry the green balls of Comparative Example 1 at 105°C for 3 hours, preheat at 950°C for 15 minutes, and then calcine at 1250°C for 15 minutes.

[0072] Comparative Example 3

[0073] An improvement is made on the basis of Example 1, which differs therefrom in that: in step 2, step 3 and step 4, the rotation speed of the disc ball making machine is kept unchanged at 34r / min, and the other steps are exactly the same as in Example 1, and the raw balls of Comparative Example 3 are prepared.

[0074] Table 1 Chemical composition and water content of iron ore concentrate (mass percentage / %)

[0075] Iron concentrate powder TFe CaO <![CDATA[SiO 2 > MgO <![CDATA[Al 2 O 3 > <![CDATA[SO 3 > <![CDATA[TiO 2 > <![CDATA[V 2 O 5 > <![CDATA[H 2 O]]> Content 52.33 0.29 4.31 4.54 4.02 0.94 9.76 0.72 7.54

[0076] Table 2 Nucleation rate and ball formation rate of the embodiments and comparative examples

[0077]

[0078] Nucleation rate of mother balls: Balls with a particle size of 2 - 5 mm are regarded as mother balls, and the proportion of the mass of this part in the mass used for making mother balls is counted as the nucleation rate; Ball forming rate: Pellets with a particle size of 9 - 16 mm that have already formed balls, and the proportion of the mass of all pelletizing raw materials is counted as the ball forming rate.

[0079] It can be seen from Table 2 that:

[0080] (1) The type of binder has a very obvious impact on both the nucleation rate and the ball forming rate. In the examples, pectin and CMC, as binders used for mother ball formation, have a significantly better nucleation rate than other types of binders. However, under the condition of the same dosage, the effect of pectin is better than that of CMC, and CMC needs to increase the dosage to achieve the same effect as low - dosage pectin. However, the dosage of pectin should not be too high either. When the dosage reaches 1.0 wt% (Example 5), due to the change in hydrogen bond energy formed between the unique chain - like structure of pectin and iron ore concentrate particles, the nucleation rate shows a very significant decrease. Therefore, the dosage of pectin should not exceed 1.0 wt%. In the stage of mother ball growth, the change in the dosage of bentonite also has a relatively obvious impact on the final ball forming rate. If the dosage of bentonite is less than 1.2 wt%, the ball forming rate will be less than 80%. Therefore, maintaining the dosage of bentonite between 1.2 - 3.0 wt% can obtain a relatively high ball forming rate.

[0081] (2) In the stage of mother ball formation, the effect of the composite binder is not ideal. In the present invention, the dosage of the composite binder is screened. Comparative Example 1 and Comparative Example 2 are both the dosages with the best effects. However, under this condition, both the nucleation rate and the ball forming rate are not as good as those in the examples. This shows that the type of binder has a very obvious impact on both the mother ball formation stage and the mother ball growth stage. Moreover, the effect of using different types of binders in these two stages is significantly better than that of using a single type of binder.

[0082] (3) Different rotation speeds in the mother ball formation stage and the mother ball growth stage of the pelletizing process will affect the final ball forming rate. It can be seen from Example 1 and Comparative Example 3 that Example 1 adopts a process with different rotation speeds in the two stages, and Comparative Example 3 adopts a constant rotation speed process. Both have a good nucleation rate in the mother ball formation stage, but in terms of the final ball forming rate, Comparative Example 3 shows a very significant decrease. This shows that if the process of continuously maintaining a constant rotation speed is adopted, the rotation speed cannot provide a favorable impact on ball formation in the mother ball growth stage, but will instead reduce the formation of pellets.

[0083] The green balls prepared from the above - mentioned examples and comparative examples were subjected to performance tests (measured in accordance with the national standard YB / T4848 - 2020), and the green ball strength, water content, pre - heated pellet strength, and roasted pellet strength were respectively tested. The results are shown in Table 3.

[0084] Table 3 Pellets of Examples and Comparative Examples

[0085]

[0086] It can be seen from Table 3 that:

[0087] The pellets prepared in Examples 1 to 4 and Example 6 have excellent strength and are superior to the comparative examples. This indicates that using different types of binders in the mother ball formation stage and the mother ball growth stage respectively can make the obtained pellets have better stability and higher strength, and the pelletizing effect is significantly better than that of using the same binder in these two stages.

[0088] Combining Table 2 and Table 3, it can be known that:

[0089] (1) In the examples, when using iron ore concentrate with an organic binder added for mother ball nucleation in a high-speed disk pelletizer, the high surface activity unique to the organic binder can quickly wet the surface of the iron ore concentrate under the strong centrifugal force generated by high speed, and achieve rapid bonding between particles through hydrogen bonds and van der Waals forces. Moreover, its chain-like molecular structure helps to slow down the collision energy between particles, reduce the breakage rate in the nucleation stage, and thus increase the nucleation rate.

[0090] (2) In the examples, when using iron ore concentrate with an inorganic binder added for mother ball growth in a low-speed disk pelletizer, the layered structure of bentonite can evenly adsorb on the iron ore concentrate particles on the surface of the mother ball, enabling the mother ball to grow in layers more stably. And the water absorption and swelling characteristics of bentonite can effectively prevent the evaporation of water inside the mother ball during rotation, preventing the reduction of the bonding effect of the organic binder.

[0091] (3) In the comparative examples, in the premixed composite binder, the chain-like structure of the organic binder is mainly used to interact with bentonite, resulting in limited adsorption effect on the surface of iron ore concentrate particles. Due to the too high particle collision frequency of bentonite, its layered structure has not been able to fully absorb water and swell and is immediately destroyed by mechanical force. And because the functional groups of the organic binder react with the cations in bentonite to form chelation reactions, it is difficult for the montmorillonite lamellae to effectively unfold and act on the surface of the mother ball.

[0092] (4) In the comparative examples and examples, when adding an organic-inorganic composite binder during pelletizing, the advantages of the two types of binders are difficult to play, resulting in the pelletizing rate, pelletizing speed, and pellet properties of the pellets being lower than those of the pellets prepared by adding organic and inorganic binders in stages. Using different rotation speeds in the mother ball nucleation stage and the mother ball growth stage can cooperate with different types of binders to further improve the overall pelletizing effect, with a high pelletizing rate, fast pelletizing speed, reduced energy consumption of the disk pelletizer, and significant improvement in the compressive strength of green pellets and dry pellets. Also, due to the reduction of the bentonite usage amount, the slag amount of the pellets is reduced.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions shall be covered by the scope of the claims of the present invention.

Claims

1. A two-stage variable binder and variable speed pelletizing method, characterized in that: The steps include: The raw material iron ore powder is divided into two parts, the first part of the iron ore powder is mixed with an organic binder to form a pelletizing raw material A, and the second part of the iron ore powder is mixed with an inorganic binder to form a pelletizing raw material B, and the weight of the first part of the iron ore concentrate is less than or equal to the weight of the second part of the iron ore concentrate; The ball-forming raw material A is used to form a mother ball at a rotation speed of 25 to 40 r / min; then the rotation speed is adjusted to 10 to 25 r / min, and the ball-forming raw material B is added for final ball-forming to obtain raw balls; wherein, the rotation speed of the mother ball in the ball-forming stage is greater than the rotation speed of the final ball-forming stage.

2. The pelletizing method according to claim 1, characterized in that: The organic binder is pectin or carboxymethyl cellulose; in the pelletizing raw material A, the amount of the organic binder added is 0.1-1.0 wt%.

3. The pelletizing method according to claim 1, characterized in that: The inorganic binder is bentonite; in the pelletizing raw material B, the added amount of bentonite is 1.2-3.0wt%.

4. The pelletizing method according to claim 1, characterized in that: Calculated by weight percentage, the weight of the first part of the iron ore powder accounts for 20-50wt% of the total weight of the iron ore powder.

5. The pelletizing method according to claim 1, characterized in that: The process time of the mother ball forming is 1 to 3 minutes, and the particle size of the formed mother ball is 2 to 5 mm.

6. The pelletizing method according to claim 1, characterized in that: The final ball making includes two stages: a mother ball growth stage and a compact ball agglomeration stage; wherein, under the condition of maintaining a rotation speed of 10 to 25 r / min, the mother ball growth stage lasts for 3 to 8 minutes, and the compact ball agglomeration stage lasts for 2 to 6 minutes; and green balls with a particle size of 10 to 13 mm are obtained.

7. The pelletizing method according to claim 1, characterized in that: In the process of making the mother ball, water is added by dripping; in the final ball making process, water is added by spraying; and finally the water content of the obtained raw ball is controlled at 7-9wt%.

8. The pelletizing method according to claim 1, characterized in that: The iron ore powder is iron ore concentrate.

9. The pelletizing method according to any one of claims 1 to 8, characterized in that: The green pellets are used for low-carbon ironmaking.

Images