A method for efficient treatment of spent scr catalysts using a rotary hearth furnace process and the resulting pellets

Abstract

The application discloses a kind of high-efficiency treatment method of waste SCR catalyst using rotary hearth furnace process and obtained briquetting, belong to carbon-containing briquetting field.The application first mixes waste SCR catalyst particles and coke uniformly, waste SCR catalyst particles are used to modify coke;Then, iron-containing raw material, coke, waste SCR catalyst particles, bentonite are mixed uniformly and put into roll pressure ball machine to form carbon-containing briquetting, and carbon-containing briquetting is formed into calcined briquetting after drying and calcination reduction.Carbon-containing briquetting prepared in this way not only strengthens the compressive strength of calcined briquetting, but also effectively recycles waste SCR catalyst, and the metallurgical properties of carbon-containing briquetting are improved after the addition of waste SCR catalyst.

Description

Technical Field

[0001] This invention relates to the field of waste SCR catalyst treatment technology, and more specifically, to a method for efficiently treating waste SCR catalyst using a rotary hearth furnace process and the resulting pellets. Background Technology

[0002] Industrial flue gas emitted during industrial production processes such as waste incineration, thermal power generation, and iron ore sintering contains large amounts of nitrogen oxides (NOx). x To reduce air pollution, industrial flue gas should undergo denitrification treatment before emission. V2O5-WO3 / TiO2 catalyst is currently the most widely used denitrification catalyst in industry. During the use of catalysts, due to the harsh on-site environment, blockage and deactivation can occur, resulting in spent SCR catalysts. Current policies have strict requirements for the disposal of spent SCR catalysts. How to achieve the harmless and resource-efficient utilization and treatment of spent SCR catalysts has become a difficult problem.

[0003] For the treatment and disposal of spent SCR catalysts, existing recycling methods mainly include active regeneration, recovery of valuable elements, and harmless disposal. Active regeneration can often only be performed 2-3 times before the catalyst accumulates too many toxins, necessitating disposal of the spent SCR catalyst. Recovery of valuable elements uses chemical methods, which suffer from problems such as large amounts of acid and alkaline wastewater, long processes, high energy consumption, and serious secondary pollution. Harmless disposal methods such as direct landfilling and melt solidification result in resource waste and potential environmental problems.

[0004] Currently, utilizing existing processes to dispose of solid waste is an emerging harmless treatment method. A search revealed a patent application (application number 2023110619356) that discloses a method for co-processing waste vanadium-tungsten-titanium catalyst from denitrification using a rotary hearth furnace. The waste SCR catalyst is crushed, ground, and added to carbon-containing pellet raw materials in a certain proportion, ultimately fixing it in the roasted pellets to form titanium-containing pellets, which are then used as furnace protectants. The applicant conducted repeated experiments in the laboratory to further study this scheme. They found that when 25% of the waste SCR catalyst was added to the carbon-containing pellet raw materials, the strength of the roasted pellets decreased from 1753 N in the baseline experiment without the addition of waste SCR catalyst to 807 N. This shows that a large proportion of waste SCR catalyst significantly reduces the strength of the roasted pellets. Furthermore, the metallization rate of the roasted pellets also decreased from 90.8% in the baseline experiment to 50.1%. Neither the strength nor the metallization rate of the roasted pellets meets the current requirements for blast furnace smelting, indicating that this design cannot meet practical application needs. Summary of the Invention

[0005] 1. The technical problem that the invention aims to solve

[0006] The purpose of this invention is to address the problem of poor strength of carbon-containing pellets after roasting in rotary hearth furnaces by providing a method for efficiently treating waste SCR catalysts using a rotary hearth furnace process and the resulting pellets. The method of this invention can improve the performance of roasted carbon-containing pellets, enabling them to meet the strength requirements of large blast furnace smelting and increasing their utilization pathways. In addition, it addresses the difficulty in treating waste SCR catalysts generated from flue gas denitrification in steel enterprises, realizing the resource utilization of waste SCR catalysts.

[0007] 2. Technical Solution

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0009] Based on the prior patent application technology of application number 2023110619356, the applicant has conducted long-term and in-depth research. Through extensive verification and analysis, the applicant believes that when a large proportion of waste SCR catalyst is added to the raw materials, the TiO2 contained in the waste SCR catalyst and the iron oxide contained in the raw materials form a large amount of difficult-to-reducible ilmenite FeTi2O4, which significantly reduces the metallization rate of the roasted pellets. In addition, a large amount of unreacted TiO2 is mixed in the iron intercalation crystals, affecting the connection of the iron intercalation crystals and reducing the compressive strength of the roasted pellets. As a result, the roasted pellets cannot meet the current requirements for blast furnace smelting in terms of both strength and metallization rate.

[0010] To avoid the adverse effects of adding spent SCR catalyst, the applicant conducted further experimental research and found that when the proportion of spent SCR catalyst added to the carbon-containing pellets was between 2.5% and 7.5%, the metallization rate of the calcined pellets was not affected compared with the experimental control group without spent SCR catalyst, remaining above 90%, and the compressive strength of the calcined pellets was also significantly improved. For example, when the proportion of spent SCR catalyst was 2.5%, the compressive strength of the calcined pellets increased from 1753 N in the baseline experiment to 1980 N, and when the proportion of spent SCR catalyst was 5.0% and 7.5%, the corresponding strengths of the calcined pellets were further improved to 2202 N and 2350 N, respectively. It is evident that when waste SCR catalyst is added at a ratio of 2.5-7.5%, it not only does not reduce the strength of the roasted pellets, but also significantly improves them. Analysis suggests that the applicant believes the main reason is that the surface of the waste SCR catalyst contains some remaining active sites, which can catalyze the carbon gasification reaction of the fuel added to the carbon-containing pellets, enhancing the reduction capacity and thus ensuring that the metallization rate of the roasted pellets remains unchanged. Simultaneously, it strengthens the bonding of iron crystals, increasing the compressive strength of the roasted pellets. Given the current requirements for large-scale blast furnace development in my country, the strength of pellets entering the furnace is generally required to be higher than 2500 N / piece. Therefore, by optimizing the addition method of waste SCR catalyst and better utilizing its catalytic role in the fuel reduction process, it is expected to further improve the strength of pellets containing waste SCR catalyst, meeting the needs of large-scale blast furnace smelting.

[0011] Accordingly, this invention provides a method for efficiently treating spent SCR catalyst using a rotary hearth furnace. First, spent SCR catalyst particles are uniformly mixed with coke, and the coke is modified using the spent SCR catalyst particles. Then, iron-containing raw materials, modified coke, and bentonite are uniformly mixed and fed into a roller pelletizer to form carbon-containing pellets. These carbon-containing pellets are then dried and calcined to form calcined pellets. The carbon-containing pellets prepared in this way not only enhance the compressive strength of the calcined pellets but also effectively recover the spent SCR catalyst. The addition of the spent SCR catalyst improves the metallurgical properties of the carbon-containing pellets.

[0012] The specific process is as follows:

[0013] Step 1: Preparation of spent SCR catalyst particles: Take spent SCR catalyst, remove the blockages and impurities, crush and grind the spent SCR catalyst, and sieve to obtain spent SCR catalyst particles with a particle size ≤0.074mm.

[0014] Step 2: Raw Material Mixing: Modified coke is prepared by uniformly mixing coke with spent SCR catalyst particles. The spent SCR catalyst can further enhance the high-temperature gasification performance of the modified coke. In practice, a cylindrical mixer can be used. High-pressure nitrogen gas is pressurized to 4-5 atm, and then water (10%-12% of the total mass of coke and spent SCR catalyst) is sprayed in via a sprayer for mixing. The mixing time is 5-10 minutes. After mixing, modified coke is obtained. In practice, the spray water mass ratio can be 10%, 10.5%, 11%, 12%, etc., and the mixing time can be 5 minutes, 6 minutes, 8 minutes, 10 minutes, etc.

[0015] Step 3, Briquetting preparation: Mix the iron-containing raw materials, modified coke, and bentonite evenly, add water, and put them into a roller briquetting machine to briquette carbon-containing pellets; the moisture content of the briquetting raw materials is 12%-16%; in practice, the moisture content can be 12%, 13%, 14%, 15%, 16%, etc.

[0016] Step 4: Preparation of roasted pellets: Take raw pellets, dry and reduce them to obtain roasted pellets.

[0017] Preferably, the percentage of the waste SCR catalyst particles added is 2.5%-7.5% of the total mass of the three raw materials: iron-containing raw materials, coke, and bentonite. In practice, 2.5%, 3%, 4.5%, 5%, 6%, 7.5%, etc. can be used. The waste SCR catalyst particles can be added externally.

[0018] Preferably, bentonite can also be added externally. The mass percentage of bentonite added among the three raw materials—iron-containing raw materials, coke, and bentonite—is 1%-2%, with practical applications including 1%, 1.2%, 1.3%, 1.5%, 1.8%, and 2%. Furthermore, the formulation of the iron-containing raw materials and coke requires controlling the carbon-oxygen ratio in the carbon-containing pellet raw material system to be 1.1-1.2. In practice, the carbon-oxygen ratio can be controlled at 1.1, 1.15, 1.18, and 1.2, etc., meaning the amount of coke added is determined based on the iron oxide and carbon content in the iron-containing raw materials.

[0019] Preferably, the waste SCR catalyst particles are less than 0.074 mm and the coke diameter is less than 1.06 mm.

[0020] In practice, after the roller briquetting machine has finished briquetting, it is necessary to select suitable green balls for green ball performance testing, including green ball drop strength and compressive strength testing. After some green balls are dried, dry ball strength testing is also required.

[0021] Preferably, the drying process in step four is as follows: drying in a forced-air drying oven at 110-120℃ for 4-8 hours. In practice, the drying temperature can be 110℃, 1112℃, 1115℃, 120℃, etc., and the drying time can be 4 hours, 6 hours, 7 hours, 8 hours, etc.

[0022] Preferably, the roasting regime in step four is 1250℃±10℃ for 20-25 minutes. In practice, the roasting temperature can be 1240℃, 1245℃, 1250℃, 1255℃, 1260℃, etc., and the drying time can be 20 minutes, 21 minutes, 22 minutes, 25 minutes, etc.

[0023] The present invention also provides a carbon-containing pellet prepared by the above method.

[0024] 3. Beneficial effects

[0025] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0026] (1) The present invention provides a method for efficiently treating waste SCR catalyst using a rotary hearth furnace process. By modifying the coke added to the carbon-containing pellets, the gasification rate of the coke at high temperature is improved, and the metal iron crystals generated by the reduction of the carbon-containing pellets are more densely connected, thereby improving the mechanical properties of the roasted pellets.

[0027] (2) The present invention adds carbon-containing pellets of waste SCR catalyst to the blast furnace. The Ti element contained therein has a good furnace protection effect on the hearth of the blast furnace. In addition, the V and W elements in the waste SCR catalyst are reduced to elemental substances and enter the molten iron. V and W elements are beneficial elements in the steelmaking process. Remaining in the molten steel can greatly improve the quality of steel, thereby realizing the reduction, harmlessness and resource utilization of waste SCR catalyst. Attached Figure Description

[0028] Figure 1 The coke gasification reaction rate under CO2 atmosphere with 40% waste SCR catalyst;

[0029] Figure 2 Thermogravimetric analysis results of coke mixed with 40% waste SCR catalyst under N2 atmosphere;

[0030] Figure 3 Metallographic images of calcined pellets without the addition of waste SCR catalyst;

[0031] Figure 4 Metallographic images of calcined pellets with added untreated waste SCR catalyst;

[0032] Figure 5 Metallographic images of roasted pellets containing treated waste SCR catalyst;

[0033] Figure 6 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0034] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0035] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] The present invention will be further described below with reference to embodiments.

[0037] Example 1

[0038] This embodiment presents a method for efficiently treating spent SCR catalyst using a rotary hearth furnace. Iron-containing raw materials, spent SCR catalyst particles, coke, and bentonite are used as briquetting raw materials. After being mixed evenly, the mixture is briquetting into green pellets. These green pellets are then dried and calcined to form calcined pellets. This method achieves the harmless and resource-based utilization of spent SCR catalyst. The specific preparation and performance testing process is as follows:

[0039] Step 1: Preparation of spent SCR catalyst particles:

[0040] Take the waste SCR catalyst, remove the impurities from the waste SCR catalyst, crush and grind the waste SCR catalyst body into particles with a particle size ≤200 mesh, and dry it at 110℃ for 3 hours.

[0041] Step 2, Raw material mixing: The coke and waste SCR catalyst are mixed once in a high-pressure mixer. After being pressurized to 4 atm by high-pressure nitrogen, water accounting for 10% of the total mass of coke and waste SCR catalyst is sprayed in through a sprayer to mix evenly. The mixing time can be 5 minutes. After mixing, modified coke is obtained.

[0042] Step 3: Briquetting Preparation: Modified coke, iron-containing raw materials, and bentonite are added to a mixer for secondary mixing. The mixing time can be 3-5 minutes, ensuring the final moisture content of the mixture is controlled at 14%. Then, the mixture is placed into a roller briquetting machine for briquetting. The briquetting parameters can be set as follows: roller linear pressure 2.5 × 10⁻⁶. 4 N / cm, roller speed 6.0 r / min, the pressed carbon-containing pellets are ellipsoidal in shape, with dimensions of length × width × thickness = 32mm × 25mm × 15mm; after pressing, the green pellets are tested for properties such as drop strength and compressive strength. Details are as follows:

[0043] Drop strength test of raw pellets: Select 10 pellets of the same specification and drop each pellet from a height of 0.5m onto a 10mm thick steel plate. Repeat this process until the pellet breaks. The number of times the pellet breaks is the number of drops. After removing extreme values, calculate the average value as the drop strength index. The unit is "drops / 0.5m".

[0044] Compressive strength test of green pellets: Ten pellets from the same batch were selected, and the crushing pressure of each pellet was measured using a JHY-5000 electronic universal pressure testing machine. The pressurization speed was maintained at 10 mm / min. The average value was calculated after removing extreme values ​​to represent the compressive strength, with the unit being "N / pellet".

[0045] Step 4: Preparation of roasted pellets: Take green pellets, dry and reduce roasting them to obtain roasted pellets; specifically: place qualified green pellets in a 110℃ forced-air drying oven for 8 hours; the pellet roasting is carried out in a box type, the roasting temperature is 1250℃, the roasting time is 25 minutes, and nitrogen gas is introduced throughout the roasting process to prevent the roasted pellets from being oxidized by air when they are taken out, thereby reducing the metallization rate.

[0046] Compressive strength test of roasted pellets: Ten roasted pellets from the same batch were selected, and the crushing pressure of each pellet was measured using a JHY-5000 electronic universal pressure testing machine. The pressurization speed was maintained at 10 mm / min. The average value was calculated after removing extreme values ​​to represent the compressive strength, with the unit being "N / pellet".

[0047] Metallurgical performance testing of pellets: Pellet composition testing includes total iron (TFe) analysis and metallic iron (MFe) analysis to calculate the metallization rate. The total iron content of the pellets is determined according to the method specified in GB / T6730.5-2022, and the metallic iron content is determined according to the method specified in GB / T38812.2-2020.

[0048] In this embodiment, the unmodified coke mass percentage of the carbon-containing pellet raw material is 9.0%, the iron-containing raw material mass percentage is 89%, and the bentonite mass percentage is 2.0%, so that the carbon-oxygen ratio in this experiment reaches 1.2. To ensure that the carbon-oxygen ratio in the mixture in this embodiment remains unchanged, the waste SCR catalyst is added to the carbon-containing pellet raw material externally. In this embodiment, the amount of waste SCR catalyst added is 5.0% of the total mass of the iron-containing raw material, coke, and bentonite. After the above raw materials are mixed evenly, water is added to 14% for pelletizing into green pellets, and the performance of the green pellets is tested. The performance of the roasted pellets is also tested, and the experimental results are recorded in Table 1.

[0049] It is necessary to note that the iron-containing raw material used in this embodiment is a mixture of various iron-containing dust and sludge from a domestic steel plant, with TFe ≥ 50.00% in the iron-containing raw material. Specifically, the mass percentage content of its components in this embodiment is as follows: TFe: 56.74%, FeO: 30.36%, CaO: 5.61%, C: 4.66%, SiO2: 2.7%, MgO: 1.83%, ZnO: 1.58%, Al2O3: 0.98%, and the remainder being unavoidable impurities. The fixed carbon content in the coke used is not less than 80% of the total weight of the coke. In this embodiment, the fixed carbon content of the coke is 84.00%. The carbon-oxygen ratio is calculated as follows: (amount of C in the iron-containing raw material + amount of C in the coke) / (amount of oxygen atoms bound to iron in the iron-containing raw material).

[0050] Comparative Example 1

[0051] This comparative example serves as a baseline experiment. The pellet preparation process in this comparative example is the same as in Example 1, except that no coke is treated and no waste SCR catalyst is added. The mass percentages of the dry components of the mixture are as follows: iron-containing raw materials: 89%, coke: 9.0%, and bentonite: 2.0%, achieving a carbon-to-oxygen ratio of 1.2. After the above raw materials are mixed evenly, moisture is added to 14% for pelletizing into green pellets, and the performance of the green pellets is tested. The performance of the roasted pellets is also tested, and the experimental results are recorded in Table 1.

[0052] Comparative Example 2

[0053] The pellet preparation process in this comparative example is the same as in Example 1, except that the spent SCR catalyst particles are directly added to the pelletizing raw material without being mixed with coke for modification. The mass percentages of each component in the dry mixture are: iron-containing raw material: 89%, coke: 9%, and bentonite: 2%, to achieve a carbon-to-oxygen ratio of 1.2 in this experiment. To ensure that the carbon-to-oxygen ratio in the mixture remains constant, the spent SCR catalyst is added externally to the carbon-containing pelletizing raw material. In this example, the amount of spent SCR catalyst added is 5.0% of the total mass of the three raw materials: iron-containing raw material, coke, and bentonite. After the above raw materials are mixed evenly, water is added to 14% and added to the roller briquetting machine to produce pellets. After briquetting, the performance of the green pellets is tested, and the performance of the roasted pellets is measured. The experimental results are recorded in Table 1.

[0054] Comparative Example 3

[0055] The pellet preparation process in this comparative example is the same as in Example 1, except that the particle size of the spent SCR catalyst is greater than 0.074 mm. The mass percentage of each component in the dry mixture is as follows: iron-containing raw material: 89%, coke: 9%, and bentonite: 2%, so that the carbon-oxygen ratio in this experiment reaches 1.2. At the same time, in order to ensure that the carbon-oxygen ratio in the mixture remains unchanged, the spent SCR catalyst is added to the carbon-containing pellet raw material externally. In this example, the amount of spent SCR catalyst added is 5.0% of the total mass of the three raw materials: iron-containing raw material, coke, and bentonite. After the above raw materials are mixed evenly, water is added to 14% and added to the double-roller briquetting machine to produce pellets. After briquetting, the performance of the green pellets is tested, and the performance of the roasted pellets is measured. The experimental results are recorded in Table 1.

[0056] Table 1 Pellet Performance Testing

[0057]

[0058] By comparing and analyzing the green pellet quality indicators and the metallurgical properties of the roasted pellets in Table 1, the following conclusions can be drawn:

[0059] (1) Through the experiments of Example 1 and Comparative Example 1, it can be found that when waste SCR catalyst is mixed with coke for modification, and the modified coke is added to the pelletizing raw material for carbon-containing pellet production, the performance of the pellets is greatly improved. The average drop strength and average compressive strength of green pellets are significantly improved. The metallization rate of roasted pellets remains basically unchanged and is not affected. The compressive strength is significantly improved, meeting the requirements of large blast furnace smelting. This shows that waste SCR catalyst can improve the strength of carbon-containing pellets.

[0060] (2) Through the experiments of Comparative Example 1 and Comparative Example 2, it can be found that without treating the waste SCR catalyst and coke, directly adding them to the pelletizing raw material for carbon-containing pellet production significantly improves the performance of the pellets. The average drop strength and average compressive strength of the green pellets are significantly improved. The metallization rate of the roasted pellets remains basically unchanged and is not affected. However, the increase in the compressive strength of the roasted pellets is small and does not meet the requirements of large blast furnace smelting.

[0061] (3) Through the experiments of Example 1 and Comparative Example 3, it can be found that when the particle size of the waste SCR catalyst is greater than 0.074 mm, the addition of it to the carbon-containing pellets after mixing with coke under atomized water has little effect on improving the strength of the roasted pellets and does not meet the requirements of large blast furnace smelting.

[0062] (4) Through the experiments of Example 1, Comparative Example 1 and Comparative Example 2, it can be found that adding waste SCR catalyst to carbon-containing pellets can improve the pelletizing performance of carbon-containing pellets, but directly adding waste SCR catalyst can only improve the compressive strength of calcined pellets, and waste SCR catalyst needs to be treated.

[0063] Therefore, it can be seen that spent SCR catalyst cannot be directly added to pellet production. It is necessary to combine the strength enhancement mechanism of roasted pellets with the properties of spent SCR catalyst to modify both the spent SCR catalyst and coke, thereby improving the strength performance of carbon-containing pellets used in rotary hearth furnaces. This effectively utilizes spent SCR catalyst in the pellet production process. Simultaneously, the produced titanium-containing pellets are used during blast furnace protection, achieving resource utilization of spent SCR catalyst.

[0064] This invention improves the gasification activity of coke by modifying spent SCR catalyst with coke. Iron-containing raw materials, modified coke, and bentonite are used as briquetting raw materials, mixed evenly, and then briquetting to form green pellets. These green pellets are then dried and roasted to form roasted pellets. The produced roasted pellets have compressive strength meeting blast furnace smelting standards and can be used as titanium-containing furnace protection pellets in the early stages of new blast furnace operation or at the end of blast furnace lifespan. The Ti element effectively protects the blast furnace hearth and extends its service life. Simultaneously, the strong reducing atmosphere of the blast furnace reduces V and W elements in the spent catalyst to elemental form, which enters the molten iron. V and W are beneficial elements in steelmaking; their presence in the molten steel significantly improves steel quality. This invention achieves the harmless and resource-based treatment of spent SCR catalyst.

[0065] This invention, through in-depth analysis of the strength formation mechanism of carbon-containing pellets under high-temperature conditions and combined with extensive experiments conducted by the applicant, reveals that the roasting and reduction process of carbon-containing pellets is accompanied by complex physicochemical changes. When large areas of metallic iron intergrowth crystals are formed inside the pellets, creating an iron skeleton, the pellet strength increases rapidly. The degree of interconnection of the iron intergrowth crystals is a key influencing factor on the improvement of pellet strength. Through analysis of the reduction roasting process of carbon-containing pellets, the applicant found that the limiting factor affecting the formation of iron intergrowth crystals is the carbon gasification rate. The applicant conducted carbon gasification experiments after mixing waste SCR catalyst with coke powder, and the results are as follows... Figure 1 As shown in the figure, the coke with the added spent SCR catalyst exhibits a significantly higher carbon gasification reaction rate at high temperatures compared to coke without the added spent SCR catalyst. The applicant conducted thermogravimetric experiments on coke with the attached spent SCR catalyst under a nitrogen atmosphere, and the results are as follows. Figure 2 As shown, it can be seen that the weight loss rate of coke at high temperature is significantly increased after the addition of waste SCR catalyst. The waste SCR catalyst used in this invention is mainly composed of nano-titanium dioxide, which has a catalytic gasification effect. In addition, the residual active sites on the surface of the waste SCR catalyst have an oxygen supply effect, which enhances the gasification effect of coke.

[0066] Therefore, by mixing the spent SCR catalyst with coke beforehand using atomized water, the spent SCR catalyst, which contains a large number of hydrophilic functional groups on its surface, is adsorbed onto the coke surface through van der Waals forces and capillary forces. Furthermore, the use of spent SCR catalyst with a particle size of less than 0.074 mm results in a larger specific area and a rougher surface, allowing it to be better embedded in the pores of the coke. This promotes the solid-phase structure between particles, which is beneficial for enhancing the carbon gasification reaction of the spent SCR catalyst at high temperatures. This improves the gasification activity of the coke at high temperatures, resulting in better iron crystal bonding in the roasted pellets, enhancing the overall integrity of the pellets, and increasing their compressive strength. Figure 3-5 The images show the metallographic images of calcined pellets without added waste SCR catalyst, calcined pellets with added untreated waste SCR catalyst, and calcined pellets with added treated waste SCR catalyst, respectively. It can be seen that when waste SCR catalyst is directly added to carbon-containing pellets, the iron crystals in the pellets after reduction calcination are more densely packed than those in pellets without added waste SCR catalyst, but there are still many pores. When waste SCR catalyst is premixed with coke and then added to carbon-containing pellets, the iron crystals connect into sheets, forming a skeleton that maintains the strength of the calcined pellets and improves the compressive strength of the pellets.

[0067] Example 2

[0068] The experimental procedure in this embodiment is the same as in Embodiment 1, except that the amount of waste SCR catalyst added in this embodiment is 2.5% of the total mass of the three raw materials: iron-containing raw material, coke, and bentonite. After the modified coke, iron-containing raw material, and bentonite are mixed evenly, water is added to 14% to form green pellets, and the performance of the green pellets is tested. The performance of the roasted pellets is also tested, and the experimental results are recorded in Table 2.

[0069] Example 3

[0070] The experimental procedure in this embodiment is the same as in Embodiment 1, except that the amount of waste SCR catalyst added in this embodiment is 7.5% of the total mass of the three raw materials: iron-containing raw material, coke, and bentonite. After the modified coke, iron-containing raw material, and bentonite are mixed evenly, water is added to 14% to form green pellets, and the performance of the green pellets is tested. The performance of the roasted pellets is also tested, and the experimental results are recorded in Table 2.

[0071] Table 2 Performance testing of spent SCR catalyst pellets with different addition amounts

[0072]

[0073] By comparing the experimental results of Examples 1 to 3, it can be found that when coke and waste SCR catalyst are modified, and the waste SCR catalyst accounts for 2.5% to 7.5% of the total mass of the three raw materials (iron-containing raw materials, coke, and bentonite), the green pellet strength index and the compressive strength of the roasted pellets improve significantly with the increase of catalyst addition, meeting the pellet strength requirements of large blast furnaces. Therefore, it can be added to large blast furnaces as a furnace protector.

[0074] The present invention and its embodiments have been described above illustratively. This description is not restrictive and is merely one embodiment of the present invention, and is not actually limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for efficient treatment of spent SCR catalysts using a rotary hearth furnace process, characterized by: First, waste SCR catalyst particles are mixed evenly with coke, and the waste SCR catalyst particles are used to modify the coke. Then, iron-containing raw materials, modified coke, and bentonite are mixed evenly and put into a roller briquetting machine to form carbon-containing pellets. The carbon-containing pellets are dried, roasted and reduced to form roasted pellets. The percentage of waste SCR catalyst particles added is 2.5%-7.5% of the total mass of the three raw materials: iron-containing raw materials, coke, and bentonite. Among the three raw materials—iron-containing raw materials, coke, and bentonite—the mass percentage of bentonite added is 1%-2%; and the ratio of iron-containing raw materials to coke satisfies the requirement that the carbon-oxygen ratio in the system is 1.1-1.

2. The particle size of the spent SCR catalyst is less than 0.074 mm, and the particle size of the coke is less than 1.06 mm. Coke and spent SCR catalyst particles are mixed in a mixer and then pressurized to 4-5 atm by high-pressure nitrogen gas before being sprayed with water to ensure uniform mixing. The mass of sprayed water accounts for 10%-12% of the total mass of coke and spent SCR catalyst, thereby producing modified coke.

2. A method for efficient treatment of spent SCR catalysts using a rotary hearth furnace process according to claim 1, characterized in that: The moisture content of the raw material for briquetting carbon-containing pellets is 12-16%.

3. The method for efficiently treating waste SCR catalyst using a rotary hearth furnace process according to claim 1, characterized in that: The drying process for carbon-containing pellets is to dry them in a forced-air drying oven at 110-120°C for 4-8 hours.

4. The method for efficiently treating waste SCR catalyst using a rotary hearth furnace process according to claim 1, characterized in that: The carbon-containing pellets were roasted at 1250℃±10℃ for 20-25 minutes.

5. The method for efficiently treating waste SCR catalyst using a rotary hearth furnace process according to claim 1, characterized in that, The specific process is as follows: Step 1: Preparation of spent SCR catalyst particles: Take spent SCR catalyst, remove the blockages and impurities, crush and grind the spent SCR catalyst, and sieve to obtain spent SCR catalyst particles with a particle size ≤0.074mm. Step 2, Raw material mixing: Mix coke and waste SCR catalyst particles evenly to prepare modified coke; Step 3, Briquetting preparation: Mix the iron-containing raw materials, modified coke, and bentonite evenly, add water, and put them into a roller briquetting machine to briquette carbon-containing pellets. Step 4: Preparation of roasted pellets: Take raw pellets, dry and reduce them to obtain roasted pellets.

6. A carbon-containing pellet, characterized in that: It is prepared by the method described in any one of claims 1-5.

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