Method for controlling ring formation of kiln body of metallurgical dust and mud roasting rotary kiln

Abstract

The invention relates to the technical field of metallurgical dust and mud roasting, in particular to a method for controlling ring formation of a kiln body of a metallurgical dust and mud roasting rotary kiln, which comprises the following steps: firstly, carrying out three-stage washing desalination and dechlorination on metallurgical dust and mud raw materials, and then adding high bauxite or magnesium oxide to prepare a mixture with a specific proportion; the roasting operation is divided into three stages of feeding preheating, high-temperature roasting regulation and control and cooling and discharging, and parameters such as the feeding speed and the preheating temperature are controlled during feeding preheating; alternate air blowing is adopted for high-temperature roasting regulation and control; and materials are cooled through a quenching section and a slow cooling section in the cooling and discharging stages. Through three-stage washing desalination and dechlorination, the contents of Cl <->, Na < + > and K < + > in the raw materials are greatly reduced, ring formation is inhibited from the source, the proportion and the content of magnesium oxide and aluminum oxide in the mixture are accurately adjusted, generation of a high-melting-point mineral phase is promoted, a low-melting-point glass phase is reduced, the ring formation resistance is enhanced, and the environment in the kiln is stabilized by accurately controlling parameters of all stages of roasting, so that the ring formation resistance is improved. And local overheating and melt aggregation are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical dust and sludge roasting, and specifically to a method for controlling the ring formation on the kiln body of a rotary kiln for metallurgical dust and sludge roasting. Background Art

[0002] In the metallurgical industry, for the large-scale treatment of metallurgical dust and sludge solid wastes (such as dry ash, electric furnace ash, zinc-containing sludge, etc.), the rotary kiln process has become an important choice in industrial production due to its advantages of large processing capacity and high operating efficiency. However, the problem of ring formation on the kiln body, which has long plagued this process, seriously affects its stability and economic benefits.

[0003] The phenomenon of ring formation refers to the formation of a ring-shaped hard deposition layer on the inner wall of the kiln due to the melting and adhesion of materials. This problem will cause a series of hazards. On the one hand, ring formation causes uneven material distribution, blocks the gas flow channels in the kiln, and greatly increases the system resistance; the effective reaction cross-sectional area is reduced, the heat transfer efficiency is lowered, and the unit energy consumption rises; at the same time, the thermal regime in the kiln is unbalanced, the product qualification rate drops, and the service life of the kiln lining refractory material will also be shortened. On the other hand, after ring formation occurs, the kiln must be stopped urgently. After cooling, workers enter the kiln manually for high-intensity mechanical ring cleaning, and then the kiln is reheated and raised in temperature. During this period, the production line is completely stagnant. Each single treatment not only directly results in a loss of thousands of tons of production capacity, but also indirectly causes the supply interruption of upstream and downstream processes. Restarting the system also requires additional consumption of a large amount of fuel and manpower; frequent kiln stoppages further exacerbate equipment wear and tear, resulting in a significant increase in annual maintenance costs.

[0004] Currently, although there are related patented technologies attempting to solve the problem of rotary kiln ring formation, they all have certain limitations. For example, the Chinese patent with the publication number CN115558783B proposes to mix metallurgical zinc-containing dust and magnesium-containing materials in a certain proportion (the amount of magnesium-containing materials does not exceed 5%), and send them into the rotary kiln for drying, preheating, heating up, and calcining, so that the MgO content is greater than 40% after the high-temperature decomposition of the magnesium-containing materials in the rotary kiln, thereby increasing the melting point of the eutectic from 1200°C to 1400°C, avoiding the melting and adhesion of the eutectic to the kiln wall, and thus controlling the problem of ring formation and extending the stable operation period of the rotary kiln. However, this method only has good effects on dust and sludge with relatively low chlorine and alkali metal (such as K, Na) contents. For dust and sludge with relatively high chlorine and alkali metal contents, low-melting salts (such as KCl, NaCl) may still melt and adhere to the kiln wall, and the removal effect is not good.

[0005] For another example, a Chinese patent with the publication number CN102146510B discloses a method for cracking and shedding the build-up rings on the inner wall of a rotary kiln by determining two near-roasting points and far-roasting points that are 3-5 m apart in the rotary kiln body. The near-roasting point uses a thick diameter and short spiral flame for roasting, and the far-roasting point uses a thin diameter and long direct current flame for roasting. In theory, this method can effectively avoid build-up rings, but in actual production, due to problems such as high operation difficulty, it is difficult to achieve the expected effect.

[0006] It can be seen from this that the existing methods for suppressing build-up rings in rotary kilns cannot meet the actual production requirements. There is an urgent need for a more efficient and comprehensive method to solve the problem of build-up rings in the rotary kiln body for metallurgical dust and sludge roasting, so as to improve the overall performance and economic benefits of the rotary kiln process. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method for controlling build-up rings in the rotary kiln body for metallurgical dust and sludge roasting. The present invention greatly reduces the Cl - , Na + and K + contents in the raw materials through three-stage water washing for desalination and dechlorination, inhibits build-up rings from the source, promotes the formation of high-melting-point mineral phases, reduces low-melting-point glass phases, and enhances the anti-build-up ring ability by accurately adjusting the ratio and content of magnesium oxide and alumina in the mixed materials. By precisely controlling the parameters in each roasting stage, such as the relevant parameters of feed preheating, high-temperature roasting, and cooling and discharging, the internal environment of the kiln is stabilized, and local overheating and aggregation of molten substances are avoided.

[0008] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for controlling build-up rings in the rotary kiln body for metallurgical dust and sludge roasting, the method comprising the following steps: Raw material pretreatment: Perform three-stage water washing for desalination and dechlorination on the metallurgical dust and sludge raw materials to obtain pretreated raw materials; add bauxite, magnesium oxide or both to the pretreated raw materials. When only bauxite is added, the ratio requirements are met by the alumina in the bauxite and the small amount of magnesium oxide contained in the raw materials; when only magnesium oxide is added, the ratio requirements are met by the alumina that may be contained in the raw materials and the added magnesium oxide; when both are added, the ratio requirements are met through the synergistic effect of the two to make a mixed material, control the mass ratio of magnesium oxide and alumina in the mixed material to be less than 0.5, and the sum of the masses of magnesium oxide and alumina accounts for more than 8% of the total mass of the mixed material; Roasting operation: including feed preheating, high-temperature roasting control, and cooling and discharging; Feed and preheating: Continuously feed bulk materials, and set up a negative pressure suction preheating system at the inlet section of the rotary kiln; High-temperature roasting control: Adopt alternating air blowing in the high-temperature section of the rotary kiln; Cooling and discharging: The materials after high-temperature roasting pass through the rapid cooling section and the slow cooling section in sequence.

[0009] Further, after the three-stage water washing for desalination and dechlorination, the Cl content in the pretreated raw materials is less than 1%, and the contents of Na and K are both less than 0.5%. - + and +

[0010] Even further, the three-stage water washing for desalination and dechlorination specifically includes: First-stage water washing: Mix the metallurgical dust raw materials with water at 80 - 90 °C at a liquid-solid ratio of 5:1, and stir at 80 - 120 rpm for 30 min; Second-stage water washing: Add a sodium carbonate solution with a mass fraction of 0.5% - 1% to the materials after the first-stage water washing, control the solid-liquid ratio to be 3:1, and stir at 80 - 120 rpm for 30 min; Third-stage water washing: Use 40 kHz ultrasonic wave-assisted cleaning for 20 - 30 min, and then perform centrifugal dehydration and drying.

[0011] Even further, the bauxite is of the second-class first-grade, with an Al2O3 content of 70 - 80%, a CaO content lower than 0.8%, and an Fe2O3 content lower than 3.0%.

[0012] Even further, the carbon content of the mixed materials accounts for 2% by mass fraction, and the calorific value of the mixed materials is 1300 Kcal.

[0013] Even further, the feeding speed of the negative-pressure suction preheating system is 8 - 12 t / h, the preheating temperature is controlled at 300 - 800 °C, the pressure of the negative-pressure suction preheating system is -0.03 MPa to -0.02 MPa, and the heating rate is 50 °C / min. Among them, the pressure of the negative-pressure suction preheating system is preferably -0.025 MPa.

[0014] Even further, the blowing cycle of the alternating blowing is 5 - 10 minutes, the switching blowing azimuth angle is ±30°, the wind speed is 15 - 20 m / s, the volume fraction of oxygen is controlled at 8% - 12%, the high-temperature roasting time is 30 - 60 min, and the temperature is 1250 - 1300 °C. The alternating blowing uses a conical nozzle array to implement the azimuth angle switching, and the nozzle outlet diameter is inversely proportional to the wind speed.

[0015] Even further, the rapid cooling section and the slow cooling section for the cooling and discharging are specifically as follows: In the rapid cooling section, the temperature is reduced to below 800 °C, and the cooling rate is 60 °C / min; in the slow cooling section, the temperature is reduced to below 200 °C, and the cooling rate is 35 °C / min. The rapid cooling section adopts the nitrogen curtain cooling method, and the nitrogen purity ≥ 99.5%.

[0016] ​​Furthermore, a multi-stage stepped heat exchanger is provided in the slow cooling section, and the temperature difference gradient between adjacent heat exchangers is ≤ 50°C.

[0017] Furthermore, the particle size of the pretreated raw material is controlled within 0.05 - 0.5 mm, and the moisture content is ≤ 5%.

[0018] Adopting the technical solution provided by the present invention, compared with the known public technology, it has the following beneficial effects: 1. The present invention conducts three-stage water washing on the raw material to remove harmful elements. Cl - , Na + , K + and other elements will form low-melting-point compounds with FeO, SiO2, etc. at high temperatures, reducing the ash melting point. Through three-stage water washing (high-temperature water dissolution, sodium carbonate replacement, ultrasonic-assisted cleaning), the Cl - content can be reduced to less than 1%, and the Na + , K + content can be reduced to less than 0.5%. From the source, the generation of low-melting-point liquid phase is reduced. Combining with the physical stripping effect of ultrasonic waves, the salts adsorbed on the particle surface are further destroyed, the removal efficiency is improved, and the reaction of alkali metals with acidic oxides to form viscous liquid phase is avoided.

[0019] 2. The present invention optimizes the MgO / Al2O3 ratio. After adding bauxite or magnesia, the contents of Al2O3 and MgO in the mixture are increased, which can increase the ash melting point. Al2O3 reacts with FeO to form high-melting-point calcium iron aluminum silicate, while MgO reacts with SiO2 to form forsterite, inhibiting the formation of low-melting-point phases such as fayalite. Controlling the MgO / Al2O3 mass ratio < 0.5% can avoid the competitive reaction of excessive MgO and Al2O3 to form low-melting-point substances and maintain the high-temperature stability of the mixture.

[0020] 3. When feeding in the present invention, continuous feeding of bulk materials is adopted. Continuous feeding can avoid local high temperature caused by material accumulation, reduce the excessive generation of FeO, and combined with the negative pressure induced draft preheating system, the temperature is raised to 300 - 800°C, promoting the formation of a dense oxide layer on the material surface and inhibiting the early reaction of FeO with other substances.

[0021] 4. In the high-temperature roasting section of the present invention, an alternating air blowing method is adopted and the oxygen concentration is controlled to form a weak oxidation atmosphere, which can inhibit the generation of FeO. At the same time, maintaining sufficient oxygen potential promotes the stable existence of Fe2O3, reducing the eutectic reaction of FeO and SiO2. The carbon content of the mixture is 2% (calorific value 1300 Kcal), ensuring that carbon reacts with oxygen to form CO2 preferentially in the high-temperature section rather than overly reducing Fe2O3 to form FeO. The alternating air blowing breaks the laminar flow of the gas flow in the kiln, evenly distributes the temperature in the kiln, and avoids local overheating leading to the secondary reaction of Al2O3 or MgO with FeO to form low-melting-point phases.

[0022] In summary, through dechlorination, dealkalization, composition optimization, and atmosphere control, the present invention inhibits the formation of low-melting eutectics. The high Al2O3 and MgO contents increase the liquid-phase viscosity, reduce the adhesion force between particles, avoid the thickening of kiln skins, maintain the thermodynamic balance in the kiln through continuous feeding and alternating air blowing, and reduce the repeated melting-solidification of the liquid phase caused by temperature fluctuations, thereby inhibiting the formation of the layered structure of the coating layer. Specific Embodiments

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0024] The following further describes the present invention in conjunction with embodiments.

[0025] It should be noted that the high-aluminum bauxite and magnesium oxide selected in the present invention are both obtained through external procurement. Among them, the high-aluminum bauxite is of the second-class first-grade, with an Al2O3 content of 70-80%, a CaO content of less than 0.8%, and an Fe2O3 content of less than 3.0%. The typical component contents of the metallurgical dust and sludge raw materials used in each embodiment are shown in the following table, which cover working conditions with different chlorine, alkali metal, and aluminum and magnesium contents to verify the universality of the method of the present invention: Example <![CDATA[Cl - Content (%)]]> <![CDATA[Sodium + Content (%)]]> <![CDATA[K + Content (%)]]> <![CDATA[Al2O3 content (%)]]> MgO content (%) 1 1.5 0.8 0.7 3.2 0.6 2 1.2 0.6 0.5 2.8 0.5 3 1.0 0.4 0.3 4.0 0.9 4 1.8 1.0 0.9 3.5 0.7 Example 1

[0026] Raw Material Pretreatment: Three-stage water washing for desalination and dechlorination: In the first-stage water washing, the metallurgical dust and sludge raw material and hot water at 85°C are mixed at a liquid-solid ratio of 5:1 and continuously stirred at a stirring speed of 100 rpm for 30 minutes. Under such high-temperature and high liquid-solid ratio conditions, most of the soluble Cl - (such as NaCl, KCl, etc.) in the raw material can be fully dissolved, greatly reducing the possibility of subsequent coating formation. Entering the second-stage water washing, a sodium carbonate solution with a mass fraction of 0.8% is added, the solid-liquid ratio is controlled at 3:1, and it is still stirred at a speed of 100 rpm for 30 minutes. The chemical conversion effect of the sodium carbonate solution is used to reduce the concentration of water-soluble chlorides, and the ultrasonic wave's peeling effect on salts is enhanced through the alkaline environment to further reduce the alkali metal content. Finally, in the third-stage water washing, ultrasonic assistance with a frequency of 40 kHz is used for cleaning for 25 minutes. After the cleaning, centrifugal dehydration and drying treatments are carried out. After detection, the Cl - content in the treated raw material is 0.9%, and the K + and Na +The content of both is 0.5%, fully meeting the index requirements of pretreatment.

[0027] Ingredient mixing: Add bauxite and magnesia to the pretreated raw materials that have completed water washing, and precisely adjust the mass ratio of MgO to Al2O3 in the mixed material to be 0.49, and make the total mass of the two account for 12% of the total mass of the mixed material. Such a ratio design can promote the generation of high-melting-point mineral phases, reduce low-melting-point glass phases, and thus effectively prevent the occurrence of kiln wall adhesion.

[0028] Roasting stage: Feeding and preheating: Adopt the method of continuous feeding of bulk materials, and set the feeding speed to 10 t / h. Set up a negative pressure air extraction system with a pressure of -0.03 MPa at the inlet section of the rotary kiln, and preheat the materials to 300 °C at a heating rate of 50 °C / min. Negative pressure air extraction can evenly disperse the materials, and rapid heating can avoid local overheating, effectively reducing the risk of ring formation in the preheating section.

[0029] High-temperature roasting control: Control the temperature in the high-temperature section at 1250 - 1255 °C, and use the alternating air blowing technology. Set the air blowing cycle to switch the air blowing azimuth angle by ±30° every 5 minutes, keep the wind speed at 15 m / s, and at the same time control the volume fraction of oxygen at 8 - 9%. This alternating air blowing method can cause air flow disturbance in the kiln, make the heat evenly distributed, and prevent the aggregation of molten materials caused by local high temperature. The carbon content of the mixed material is set to 2% (mass fraction), and its calorific value is 1300 Kcal. Reasonably controlling the carbon content can ensure the stability of the combustion process, maintain the heat balance in the high-temperature section, and avoid ring formation caused by temperature fluctuations. During roasting, through real-time monitoring and regulation, prevent the material from overheating and melting due to too high temperature, and can also use inert gas to inhibit exothermic oxidation, ensuring the stability of the temperature.

[0030] Cooling and discharging: The materials after high-temperature roasting enter the rapid cooling section and the slow cooling section in sequence. In the rapid cooling section, cool the materials to below 800 °C at a rate of 60 °C / min. Rapid cooling can quickly solidify the mineral phases and prevent the precipitation of secondary low-melting-point phases. The slow cooling section cools the materials to below 200 °C at a rate of 35 °C / min. Slow cooling helps to reduce the internal stress of the materials and avoid the pulverization of the finished products.

[0031] Example 2

[0032] Raw material pretreatment: Three-stage water washing for desalination and dechlorination: In the first-stage water washing, mix the metallurgical dust and sludge raw materials with 90 °C hot water at a liquid-solid ratio of 5:1, and stir at 80 rpm for 30 minutes. In the second-stage water washing, add a sodium carbonate solution with a mass fraction of 0.5%, with a solid-liquid ratio of 3:1, and stir at 80 rpm for 30 minutes to make K + 、Na +The content is reduced to 0.5%. For the three-stage water washing, ultrasonic assistance at 40 kHz is used for 20 minutes. After centrifugal dehydration and drying, the Cl - content is 1%, and the K + and Na + content is 0.4%.

[0033] Ingredient mixing: High-aluminum bauxite and magnesia are added to the pretreated raw materials, and the mass ratio of MgO to Al2O3 is controlled at 0.2, with a total proportion of 8.5%.

[0034] Roasting stage: Feeding and preheating: The continuous feeding speed is 8 t / h, the pressure of the negative pressure air extraction system in the inlet section is -0.025 MPa, and the temperature is raised to 400 °C at a rate of 50 °C / min.

[0035] High-temperature roasting control: The temperature is controlled at 1255 - 1260 °C, the blast azimuth angle is switched by ±30° every 6 minutes, the wind speed is 16 m / s, the oxygen concentration is 9 - 10%, the carbon content of the mixture is 2% (mass fraction), and the calorific value is 1300 Kcal.

[0036] Cooling and discharging: In the rapid cooling section, the temperature is decreased to below 800 °C at a rate of 60 °C / min, and in the slow cooling section, the temperature is decreased to below 200 °C at a rate of 35 °C / min.

[0037] Example 3

[0038] Raw material pretreatment: Three-stage water washing for desalination and dechlorination: In the first-stage water washing, the raw materials are mixed with hot water at 80 °C at a liquid-solid ratio of 5:1 and stirred at 110 rpm for 30 minutes. In the second-stage water washing, a sodium carbonate solution with a mass fraction of 1% is added, the solid-liquid ratio is 3:1, and it is stirred at 110 rpm for 30 minutes. In the third-stage water washing, ultrasonic assistance at 40 kHz is used for 25 minutes. After centrifugal dehydration and drying, the Cl - content is 0.5%, and the K + and Na + content is 0.2%.

[0039] Ingredient mixing: High-aluminum bauxite and magnesia are added, and the mass ratio of MgO to Al2O3 is controlled at 0.1, with a total proportion of 10%.

[0040] Roasting stage: Feeding and preheating: The continuous feeding speed is 11 t / h, the pressure of the negative pressure air extraction system in the inlet section is -0.02 MPa, and the temperature is raised to 600 °C at a rate of 50 °C / min.

[0041] High-temperature roasting control: The temperature is 1260 - 1280 °C, the blast azimuth angle is switched by ±30° every 8 minutes, the wind speed is 18 m / s, the oxygen concentration is 10 - 11%, the carbon content of the mixture is 2% (mass fraction), and the calorific value is 1300 Kcal.

[0042] Cooling and discharging: Rapid cooling section cools down to below 800°C at a rate of 60°C / min, and slow cooling section cools down to below 200°C at a rate of 35°C / min.

[0043] Example 4

[0044] Raw material pretreatment: Three-stage water washing for desalination and dechlorination: In the first-stage water washing, the raw material is mixed with hot water at 87°C at a liquid-solid ratio of 5:1 and stirred at 120 rpm for 30 minutes. In the second-stage water washing, a sodium carbonate solution with a mass fraction of 0.9% is added, with a solid-liquid ratio of 3:1, and stirred at 120 rpm for 30 minutes. In the third-stage water washing, ultrasonic cleaning at 40 kHz is assisted for 30 minutes. After centrifugal dehydration and drying, the Cl - content is 0.6%, and the K + and Na + content is 0.5%.

[0045] Batching and mixing: Add high-aluminum bauxite and magnesia, and control the mass ratio of MgO to Al2O3 to be 0.45, with a total proportion of 11%.

[0046] Roasting stage: Feeding and preheating: The continuous feeding speed is 12 t / h, the pressure of the negative pressure air extraction system in the inlet section is -0.03 MPa, and it is heated to 800°C at a rate of 50°C / min.

[0047] High-temperature roasting control: The temperature is 1280 - 1300°C, the blast azimuth angle is switched by ±30° every 10 minutes, the wind speed is 20 m / s, the oxygen concentration is 11 - 12%, the carbon content of the mixed material is 2% (mass fraction), and the calorific value is 1300 Kcal.

[0048] Cooling and discharging: Rapid cooling section cools down to below 800°C at a rate of 60°C / min, and slow cooling section cools down to below 200°C at a rate of 35°C / min.

[0049] Comparative example 1 The main difference between this comparative example and Example 1 is that the second-stage and third-stage water washings are not carried out.

[0050] In actual operation, only the first-stage water washing is carried out, that is, the metallurgical dust and sludge raw material is mixed with hot water at 85°C at a liquid-solid ratio of 5:1 and stirred at 100 rpm for 30 minutes. Subsequently, batching and mixing are directly carried out. High-aluminum bauxite and magnesia are added to the raw material that has undergone the first-stage water washing, and the mass ratio of MgO to Al2O3 in the mixed material is controlled to be 0.49, and the total proportion of the two is 12%. The parameter settings of feeding and preheating, high-temperature roasting control, and cooling and discharging in the roasting stage are the same as those in Example 1. Due to the lack of the second-stage and third-stage water washings, the Cl - and alkali metal contents in the raw material may be relatively high. Even after the first-stage water washing, the residual K + , Na + and Cl -Low-melting salts may still form at high temperatures, which may further promote the occurrence of ring formation.

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass ratio of MgO to Al2O3 is 1.

[0052] In the raw material pretreatment stage, the three-stage water washing for desalination and dechlorination steps are the same as those in Example 1, that is, in the first-stage water washing, the metallurgical dust and sludge raw materials are mixed with 85°C hot water at a liquid-solid ratio of 5:1, stirred at 100 rpm for 30 minutes; in the second-stage water washing, a sodium carbonate solution with a mass fraction of 0.8% is added, the solid-liquid ratio is 3:1, and stirred at 100 rpm for 30 minutes; in the third-stage water washing, 40 kHz ultrasonic wave is used for assisted cleaning for 25 minutes, and then centrifuged, dehydrated and dried. However, when mixing the ingredients, the mass ratio of MgO to Al2O3 is adjusted to 1, and the total proportion of the two is 12%. The parameter settings in the roasting stage are the same as those in Example 1. The change in the mass ratio of MgO to Al2O3 may affect the formation of mineral phases. When the content of MgO is too high, sufficient high-melting-point spinel may not be formed, and even other low-melting-point compounds may be formed, which is not conducive to suppressing ring formation.

[0053] Comparative Example 3 The difference between this comparative example and Example 1 is that the total proportion of MgO and Al2O3 is only 5%.

[0054] The three-stage water washing for desalination and dechlorination steps in the raw material pretreatment are the same as those in Example 1. When mixing the ingredients, the mass ratio of MgO to Al2O3 is controlled at 0.49, but the total proportion of the two is only 5%. The parameters of feeding, preheating, high-temperature roasting control and cooling and discharging in the roasting stage are all set with reference to Example 1. Since the total proportion of MgO and Al2O3 is relatively low, the total amount of high-melting-point mineral phases is correspondingly reduced, and the formation of low-melting-point glass phases cannot be effectively inhibited. When the contents of Al2O3 and MgO in the system are insufficient, the proportion of low-melting-point components relatively increases, which will accelerate the speed of ring formation.

[0055] After actual tests, in Examples 1-4 using the method of the present invention, the ring formation cycle of the rotary kiln was extended from one month to about 5 months compared with the traditional process. However, due to the differences in the key technical links and parameter settings between Comparative Examples 1-3 and the present invention, serious ring formation occurred within 2-3 months. This fully proves that the technical means such as three-stage water washing for desalination and dechlorination, and precisely controlling the ratio and content of MgO and Al2O3 in the present invention have a significant effect on suppressing ring formation in the rotary kiln body. In actual production applications, the parameters in each example can be reasonably adjusted according to specific raw material characteristics and production conditions to achieve the best ring formation control effect and production efficiency.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, characterized in that, The method includes the following steps: Raw material pretreatment: Perform three-stage water washing to desalt and dechlorinate the metallurgical dust raw material to obtain a pretreated raw material; add bauxite, magnesia or both to the pretreated raw material. When only bauxite is added, the proportion requirements are met by the alumina in the bauxite and the small amount of magnesia contained in the raw material; when only magnesia is added, the proportion requirements are met by the alumina that may be contained in the raw material and the added magnesia; when both are added, the proportion requirements are met by their synergistic effect to make a mixed material. Control the mass ratio of magnesia to alumina in the mixed material to be less than 0.5, and the sum of the masses of magnesia and alumina accounts for more than 8% of the total mass of the mixed material. Roasting operation: It includes feeding and preheating, high-temperature roasting control, cooling and discharging. Feeding and preheating: Use continuous feeding of bulk materials and set up a negative pressure suction preheating system at the inlet section of the rotary kiln. High-temperature roasting control: Adopt alternating air blowing in the high-temperature section of the rotary kiln. Cooling and discharging: The materials after high-temperature roasting pass through the rapid cooling section and the slow cooling section in sequence.

2. A method for controlling the formation of rings in the metallurgical dust and sludge roasting rotary kiln body according to claim 1, characterized in that: After the three-stage water washing for desalination and dechlorination, the Cl - content in the pretreated raw material is less than 1%, and the Na + and K + contents are both less than 0.5%.

3. A method for controlling the ring formation of the metallurgical dust and sludge roasting rotary kiln body according to claim 1, characterized in that: The specific three-stage water washing for desalting and dechlorinating includes: First-stage water washing: Mix the metallurgical dust raw material with water at 80 - 90 °C at a liquid-solid ratio of 5:1, and stir at 80 - 120 rpm for 30 min. Second-stage water washing: Add a sodium carbonate solution with a mass fraction of 0.5% - 1% to the materials after the first-stage water washing, control the solid-liquid ratio to be 3:1, and stir at 80 - 120 rpm for 30 min. Third-stage water washing: Use 40 kHz ultrasonic-assisted cleaning for 20 - 30 min, and then centrifuge and dry.

4. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, according to claim 1, characterized in that: The bauxite is of the second-class first-grade, with an Al2O3 content of 70 - 80%, a CaO content of less than 0.8%, and an Fe2O3 content of less than 3.0%.

5. A method for controlling the ring formation of the metallurgical dust and sludge roasting rotary kiln body according to claim 1, characterized in that: The carbon content of the mixed material accounts for 2% by mass fraction, and the calorific value of the mixed material is 1300 Kcal.

6. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, according to claim 1, characterized in that: The feeding speed of the negative pressure suction preheating system is 8 - 12 t / h, the preheating temperature is controlled at 300 - 800 °C, the pressure of the negative pressure suction preheating system is -0.03 MPa to -0.02 MPa, and the heating rate is 50 °C / min.

7. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, according to claim 1, characterized in that: The air blowing cycle of the alternating air blowing is 5 - 10 minutes, the switching azimuth angle of the air blowing is ±30°, the wind speed is 15 - 20 m / s, the volume fraction of oxygen is controlled at 8% - 12%, the high-temperature roasting time is 30 - 60 min, and the temperature is 1250 - 1300 °C. The alternating air blowing adopts a conical nozzle array to implement the azimuth angle switching, and the nozzle outlet diameter is inversely proportional to the wind speed.

8. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, according to claim 1, characterized in that: The specific rapid cooling section and slow cooling section for cooling and discharging are as follows: Cool down to below 800 °C in the rapid cooling section, with a cooling rate of 60 °C / min; cool down to below 200 °C in the slow cooling section, with a cooling rate of 35 °C / min. The rapid cooling section adopts the nitrogen curtain cooling method, and the nitrogen purity ≥ 99.5%.

9. A method for controlling the formation of rings in the rotary kiln body of metallurgical dust and sludge roasting, according to claim 1, characterized in that: A multi-stage stepped heat exchanger is set in the slow cooling section, and the temperature difference gradient between adjacent heat exchangers ≤ 50 °C.

10. A method for controlling the formation of rings in the metallurgical dust and sludge roasting rotary kiln body according to claim 1, characterized in that: The particle size of the pretreated raw material is controlled at 0.05 - 0.5 mm, and the moisture content ≤ 5%.