Method for reducing pulverization rate before metallurgical dust and sludge briquettes enter rotary hearth furnace

Abstract

The invention provides a method for reducing the pulverization rate of metallurgical dust and sludge before briquettes enter a rotary hearth furnace, which comprises the following steps: 1, digesting high-calcium metallurgical dust and sludge, mixing the digested high-calcium metallurgical dust and sludge with low-calcium metallurgical dust and sludge, drying and scattering; 2, the dried and scattered metallurgical dust and mud, dust removal coke powder and a binder are subjected to burdening, and after burdening, the materials are mixed to be uniform; 3, conveying the uniformly mixed mixture to a briquetting buffer bin, and then briquetting by using a ball press machine to obtain wet briquettes; 4, screening the wet briquettes, returning the undersize part to the step 2, and entering the oversize part of the wet briquettes to the step 5; step 5, performing three-section drying on the wet briquettes on the oversize part, wherein the drying temperature of each section is increased in sequence, so as to obtain dry briquettes; and step 6, screening the dry briquettes, returning the undersize part to the step 2, taking the oversize part as qualified dry briquettes, and feeding the qualified dry briquettes into the rotary hearth furnace. According to the invention, calcium oxide is digested and three-stage drying is carried out, so that the pulverization rate of metallurgical dust and sludge briquettes is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of sintering pellets for iron and steel metallurgy, and in particular to a method for reducing the pulverization rate of metallurgical dust and sludge pellets before entering a rotary hearth furnace. Background Art

[0002] A large amount of dust and mud is generated during the steel production process. More than 100 kg of metallurgical dust and mud is generated for every ton of steel produced. Dust and mud contain harmful elements such as zinc, potassium, sodium, lead and chlorine. Direct reuse will bring great harm to steel production. These harmful impurities need to be removed before returning to the steel production process. The rotary hearth furnace process is currently the most popular metallurgical dust and mud treatment process. It can effectively remove harmful elements such as zinc, potassium, sodium, lead and chlorine in dust and mud. The DRI (direct reduced iron) produced is returned to steel production, and the zinc powder produced is used as a zinc smelting raw material to achieve the comprehensive utilization of metallurgical dust and mud.

[0003] The rotary hearth furnace process is a process in which metallurgical dust is agglomerated and then sent into a rotary hearth furnace for high-temperature reduction. After the metallurgical dust is agglomerated, it will crack during the transportation process and high-temperature process, affecting production efficiency. The literature "Jin Yonglong, Sun Yujia, Wang Qian. Industrial test and production practice of rotary hearth furnace for the treatment of zinc-containing solid waste. Hebei Metallurgy, 2022(005):000." points out that there are two mainstream agglomeration processes used in rotary hearth furnaces, one is disc ball making and the other is briquetting by a briquetting machine. Practice shows that disc ball making has low cost, but the quality of wet balls and DRI (direct reduced iron) produced is poor. Roller press briquetting has high cost, produces wet lumps and DRI of better quality, and has higher production efficiency. Therefore, the current production process is mostly roller press briquetting. Based on the briquetting process, the main ways to reduce the pulverization rate and improve production efficiency of the rotary hearth furnace process are: to increase the strength of wet briquetting, reduce the bursting and pulverization of briquetting during water removal, and pulverization during the reduction process of the rotary hearth furnace.

[0004] The document "Guo Xiujian, Luo Baolong, Zhao Zhongyu, et al. Analysis of factors affecting the compressive strength of metallized pellets and resource utilization. Sintering Pelletizing, 2023, 48(4): 59-64." shows that the wet pressed pellets can be dried and then enter the rotary hearth furnace to greatly improve the strength of DRI and greatly reduce the pulverization caused by bursting during the reduction process of the rotary hearth furnace, but the specific drying process parameters have not been studied. The high-temperature drying process adopted in the patent "A method for treating solid waste in a rotary hearth furnace, publication number CN108611458B" does not mention the problem of briquetting pulverization rate during the drying process. Therefore, the current mainstream process flow of DRI production in the rotary hearth furnace is roller press briquetting-drying-rotary hearth furnace reduction, but there is still a problem of high pulverization rate of the pressed pellets before entering the rotary hearth furnace in the rotary hearth furnace process. Summary of the invention

[0005] The purpose of the present invention is to address the defects of the prior art and provide a method for reducing the pulverization rate of metallurgical dust sludge pressed into a pellet before entering a rotary hearth furnace. The metallurgical dust sludge is digested in advance with water to reduce the calcium oxide content, thereby achieving the purpose of reducing the pulverization rate of wet pressed pellets. In the subsequent drying process, a three-stage drying process with gradually increasing temperature is performed to further reduce the pulverization rate of the pressed pellets during the drying process, thereby achieving the purpose of reducing the pulverization rate of the metallurgical dust sludge pressed into a pellet before entering a rotary hearth furnace.

[0006] The present invention provides a method for reducing the pulverization rate of metallurgical dust sludge before it enters a rotary hearth furnace, comprising:

[0007] Step 1: dividing the metallurgical dust into high-calcium metallurgical dust and low-calcium metallurgical dust according to the calcium oxide content standard, digesting the high-calcium metallurgical dust, mixing the digested high-calcium metallurgical dust with the low-calcium metallurgical dust, drying and breaking them up;

[0008] Step 2: Mix the dried and broken metallurgical dust with dust removal coke powder and binder, and mix them evenly;

[0009] Step 3: transport the mixed material to a pelletizing buffer bin, and then use a pelletizing machine to pelletize the material to obtain wet pellets;

[0010] Step 4: Screen the wet pressed mass, the part under the screen is returned to step 2, and the wet pressed mass above the screen is entered into step 5;

[0011] Step 5: drying the wet pressed dough on the sieve in three stages with the drying temperature increasing successively to obtain dry pressed dough;

[0012] Step 6: The dry pressed mass is screened, the part under the screen is returned to step 2, the part above the screen is the qualified dry pressed mass, and the qualified dry pressed mass enters the rotary hearth furnace.

[0013] Furthermore, in step 1, the calcium oxide content standard is 1%wt, the calcium oxide content in high-calcium metallurgical dust is greater than 1%wt, and the calcium oxide content in low-calcium metallurgical dust is ≤1%wt.

[0014] Furthermore, in step 1, the specific method of digesting the high-calcium metallurgical dust is: the high-calcium metallurgical dust is mixed with water to complete digestion, and the free calcium oxide of the high-calcium metallurgical dust after digestion is ≤1%wt.

[0015] Furthermore, in step 1, the high-calcium metallurgical sludge after digestion is mixed with the low-calcium metallurgical sludge, and after drying and breaking up, the moisture content is not higher than 7%, and the particles with a particle size of less than 3 mm are ≥90%.

[0016] Furthermore, in step 2, the bulk density of the mixture after mixing is increased by 5% or more than the bulk density before mixing, and the porosity of the mixture after mixing under natural stacking is ≤65%.

[0017] Furthermore, in step three, the stacking height of the mixed material in the briquetting buffer bin is greater than or equal to 70% of the height of the buffer bin.

[0018] Furthermore, in step 4, a vibrating screen with 8 mm mesh is used for screening, and the screening principle is: the number of vibrations in 1 second is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed masses and wet pressed masses laid on the vibrating screen is ≤3 layers.

[0019] Furthermore, in step 5, the first stage of the three-stage drying adopts natural standing at room temperature. Further, in step 5, the specific method of the three-stage drying is: the first stage adopts natural standing at room temperature, and the natural standing time is 10min-20min; the second stage adopts hot flue gas heating, the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s, the heating temperature is controlled at 150-200℃, and the heating time is 10min-20min; the third stage adopts hot flue gas heating, the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s, the heating temperature is controlled at 200-300℃, and the heating time is 10min-20min.

[0020] The beneficial effects of the present invention are:

[0021] 1. Mix high-calcium metallurgical dust and water for extrusion digestion, so that the CaO in the high-calcium dust can be fully digested before agglomeration, avoiding the volume expansion and rupture caused by the digestion of CaO after agglomeration. The agglomerates are dried in three stages before entering the converter, which can control the evaporation rate of water and avoid the rupture of agglomerates caused by excessive overflow of water vapor, thereby reducing the pulverization rate of metallurgical dust agglomerates before entering the rotary hearth furnace.

[0022] 2. Drying and breaking up the low-calcium metallurgical dust sludge controls the particle size and dispersion of the dust sludge, and improves the uniformity of particle distribution after agglomeration.

[0023] 3. After batching, mix the ingredients evenly to control the bulk density and porosity of the mixture, so that there is more material per unit volume during agglomeration, the material is squeezed tighter during compression, and the agglomeration strength is better.

[0024] 4. Controlling the height of the mixture in the agglomeration buffer bin improves the compactness of the mixture at the discharge port, making more material per unit volume during agglomeration, thereby improving the agglomeration strength.

[0025] 5. Before entering the converter, the pressed agglomerates are dried in three stages, in which the first stage is left to stand naturally at room temperature, which can increase the strength of the agglomerates before the water evaporates, so that the agglomerates can withstand a higher pressure when water vapor overflows. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flow chart of a method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace. DETAILED DESCRIPTION

[0027] The method of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] refer to Figure 1 The present invention provides a method for reducing the pulverization rate of metallurgical dust sludge before it enters a rotary hearth furnace, comprising the following steps:

[0029] Step 1: Divide the metallurgical dust into high-calcium metallurgical dust and low-calcium metallurgical dust according to the calcium oxide content standard, digest the high-calcium metallurgical dust, mix the digested high-calcium metallurgical dust with the low-calcium metallurgical dust, dry and break it up. Preferably, the calcium oxide content standard is 1%wt, the calcium oxide content in the high-calcium metallurgical dust is greater than 1%wt, and the calcium oxide content in the low-calcium metallurgical dust is ≤1%wt. Preferably, the specific method for digesting the high-calcium metallurgical dust is: digestion is completed after the high-calcium metallurgical dust is mixed with water, and the free calcium oxide of the high-calcium metallurgical dust after digestion is ≤1%wt. The high-calcium metallurgical dust and water are mixed and extruded to digest, so that the CaO in the high-calcium dust is fully digested before pressing the mass, so as to avoid the volume expansion and rupture caused by the digestion of CaO after pressing the mass. Preferably, the high-calcium metallurgical sludge and low-calcium metallurgical sludge after digestion are mixed and dried, and the moisture content after breaking up is not higher than 7%, and the particles with a particle size less than 3 mm are ≥ 90%. There is no specific requirement for the drying process in this step. As a preferred solution, it only requires that the moisture content after drying is not higher than 7%.

[0030] Step 2: Mix the dried and broken metallurgical dust with dust removal coke powder and binder, and mix them evenly. Preferably, the bulk density of the mixed material after mixing is 5% or more higher than that before mixing, and the porosity of the mixed material under natural stacking is ≤65%. By increasing the bulk density and reducing the porosity, the strength of the pressed mass can be effectively improved.

[0031] Step 3: The mixed material is transported to a pelletizing buffer bin, and then pelletized using a pelletizing machine to obtain wet pellets. Preferably, the stacking height of the mixed material in the pelletizing buffer bin is greater than or equal to 70% of the buffer bin height, which increases the compactness of the mixed material at the discharge port, so that more material per unit volume is available during pelletizing, thereby increasing pelletizing strength.

[0032] Step 4: Screen the wet pressed mass, return the under-sieve portion to step 2, and enter step 5 for the wet pressed mass above the sieve portion.

[0033] Step 5: Dry the wet pressed mass on the sieve in three stages, with each stage of drying temperature increasing successively, to obtain a dry pressed mass. Preferably, the specific method of the three-stage drying is: the first stage is naturally standing at room temperature, and the natural standing time is 10min-20min; the second stage is heated by hot flue gas, the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s, the heating temperature is controlled at 150-200℃, and the heating time is 10min-20min; the third stage is heated by hot flue gas, the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s, the heating temperature is controlled at 200-300℃, and the heating time is 10min-20min. Natural standing at room temperature can increase the strength of the high-pressure mass under the premise of water evaporation, so that the pressed mass can withstand higher pressure when water vapor overflows.

[0034] Step 6: The dry pressed mass is screened, the part under the screen is returned to step 2, the part above the screen is the qualified dry pressed mass, and the qualified dry pressed mass enters the rotary hearth furnace.

[0035] Preferably, in step 4, a vibrating screen with 8 mm mesh is used for screening, and the screening principle is: the number of vibrations per second is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed masses and wet pressed masses laid on the vibrating screen is ≤3 layers.

[0036] The present invention is further illustrated by several specific examples and comparative examples below.

[0037] Example 1

[0038] 1) Raw material pretreatment: high calcium metallurgical dust mud is fully mixed with water and extruded for digestion, and the free calcium oxide after digestion is controlled to be 0.96%; the high calcium metallurgical dust mud and low calcium metallurgical dust mud after digestion are dried and dispersed together, and the moisture content after drying is 6.4%; after dispersion, the particle size of particles less than 3mm reaches 91.3%;

[0039] 2) Batching and mixing: The pre-treated metallurgical dust, dust removal coke powder and binder are batched, and the bulk density of the mixture after batching is tested, which is calculated as ρq = 1.2539 g / cm 3 ; Use a strong mixer to mix evenly, test the bulk density of the mixed material after mixing and the porosity of natural stacking. The bulk density of the mixed material is ρh = 1.3592g / cm 3 , the natural stacking porosity of the mixture is K = 62.96%. The bulk density ρh of the mixture after mixing is 8.40% higher than the bulk density ρq of the mixture before mixing, and the natural stacking porosity K of the mixture does not exceed 65%;

[0040] 3) Pressing into agglomerates: The mixed material is transported to agglomeration buffer bin, the mixed material pile height is 84.36% of the buffer bin height, and the mixed material accumulation height in the buffer bin is greater than 92% of the buffer bin height, and then agglomerates are pressed into agglomerates using a ball press;

[0041] 4) Screening of wet pressed mass: the total amount of wet pressed mass is weighed (MS=43.61 t / h) and then screened. A vibrating screen with 8 mm mesh is used for screening. The screening principle is: the vibration frequency is ≤3 times per second, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed mass and wet pressed mass laid on the vibrating screen is ≤3 layers; the part under the screen is weighed (MSS=6.11 t / h) and then returns to step 2), and the powdering rate of wet pressed mass is calculated as MSS / MS*100wt%=6.11 / 43.61*100wt%=14.01wt%, and the wet pressed mass on the screen is sent to the drying process;

[0042] 5) Drying: Drying is carried out in three stages. The first stage is natural standing at room temperature for 16 minutes. The second stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 0.8m / s, the heating temperature is controlled at 191°C, and the heating time is 19 minutes. The third stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 0.9m / s, the heating temperature is controlled at 237°C, and the heating time is 18 minutes.

[0043] 6) Screening of dry pressed agglomerates: The total amount of dry pressed agglomerates after drying is weighed (calculated as MG=32.94 / h) and then screened. The part under the screen is weighed (calculated as MGS=5.11 / h) and then returns to step 2). The part above the screen is qualified dry pressed agglomerates. The qualified dry pressed agglomerates enter the rotary hearth furnace, and the powderization rate of the drying process is calculated as MGS / MG*100wt%=65.11 / 32.94*100wt%=15.51%.

[0044] Example 2

[0045] 1) Raw material pretreatment: high calcium metallurgical dust mud is fully mixed with water and extruded for digestion, and the free calcium oxide after digestion is controlled to be 0.89%; the high calcium metallurgical dust mud and low calcium metallurgical dust mud after digestion are dried and dispersed together, and the moisture content after drying is 5.7%; after dispersion, the particle size of particles less than 3mm reaches 92.4%;

[0046] 2) Batching and mixing: The pretreated metallurgical dust, dust removal coke powder, and binder were batched with the same batching ratio and raw materials as in Example 1. The bulk density of the mixed material after batching was measured and calculated to be ρq = 1.2475 g / cm 3 ; Use a strong mixer to mix evenly, test the bulk density of the mixed material after mixing and the porosity of natural stacking. The bulk density of the mixed material is ρh = 1.3138 g / cm 3 , the natural stacking porosity of the mixture is K = 64.20%. The bulk density ρh of the mixture after mixing is 5.31% higher than the bulk density ρq of the mixture before mixing, and the natural stacking porosity K of the mixture does not exceed 65%;

[0047] 3) Pressing into agglomerates: The mixed material is transported to agglomeration buffer bin, the mixed material pile height is 84.36% of the buffer bin height, and the mixed material accumulation height in the buffer bin is greater than 70% of the buffer bin height, and then agglomerates are pressed using a ball press;

[0048] 4) Screening of wet pressed mass: the total amount of wet pressed mass is weighed (calculated as MS=45.72t / h) and then screened. A vibrating screen with 8mm mesh is used for screening. The screening principle is: the vibration frequency is 1 second and the number of vibrations is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed mass and wet pressed mass laid on the vibrating screen is ≤3 layers; the part under the screen is weighed (calculated as MSS=7.49t / h) and then returns to step 2), and the wet pressed mass pulverization rate is calculated as MSS / MS*100wt%=7.49 / 45.72*100wt%=16.38wt%, and the wet pressed mass on the screen is sent to the drying process;

[0049] 5) Drying: Drying is carried out in three stages. The first stage is natural standing at room temperature for 10 minutes. The second stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 1.0m / s, the heating temperature is controlled at 169℃, and the heating time is 17min. The third stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 0.8m / s, the heating temperature is controlled at 257℃, and the heating time is 18min.

[0050] 6) Screening of dry pressed agglomerates: The total amount of dry pressed agglomerates after drying is weighed (calculated as MG=34.07t / h) and then screened. The part under the screen is weighed (calculated as MGS=6.29 / h) and then returns to step 2). The part above the screen is qualified dry pressed agglomerates. The qualified dry pressed agglomerates enter the rotary hearth furnace, and the powderization rate of the drying process is calculated as MGS / MG*100wt%=6.29 / 34.07*100wt%=18.46%.

[0051] Example 3

[0052] 1) Raw material pretreatment: Add water to high-calcium metallurgical dust and sludge, fully mix and squeeze to digest, and control the free calcium oxide content after digestion to 0.91%; dry and disperse the high-calcium metallurgical dust and sludge together with the low-calcium metallurgical dust and sludge after digestion, and the moisture content after drying is 6.1%; after dispersion, the particle size of particles less than 3mm reaches 90.7%;

[0053] 2) Batching and mixing: The pretreated metallurgical dust, dust removal coke powder, and binder were batched with the same batching ratio and raw materials as in Example 1. The bulk density of the mixed material after batching was measured and calculated to be ρq = 1.2391 g / cm 3 ; Use a strong mixer to mix evenly, test the bulk density of the mixed material and the porosity of the natural stacking after mixing, the bulk density of the mixed material is ρh = 1.3078g / cm 3, the natural stacking porosity of the mixture is K = 64.37%. The bulk density ρh of the mixture after mixing is 5.54% higher than the bulk density ρq of the mixture before mixing, and the natural stacking porosity K of the mixture does not exceed 65%;

[0054] 3) Pressing the pellets: The mixed material is transported to the pelletizing buffer bin, the pile height of the mixed material is 75.6% of the buffer bin height, and the pile height of the mixed material in the buffer bin is greater than 70% of the buffer bin height, and then the pelletizing machine is used for pelletizing;

[0055] 4) Screening of wet pressed mass: the total amount of wet pressed mass is weighed (calculated as MS=44.67 t / h) and then screened. A vibrating screen with 8 mm mesh is used for screening. The screening principle is: the vibration frequency is 1 second and the number of vibrations is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed mass and wet pressed mass laid on the vibrating screen is ≤3 layers; the part under the screen is weighed (calculated as MSS=7.68 t / h) and then returns to step 2), and the wet pressed mass pulverization rate is calculated as MSS / MS*100wt%=7.67 / 44.67*100wt%=17.19wt%, and the wet pressed mass on the screen is sent to the drying process;

[0056] 5) Drying: Drying is carried out in three stages. The first stage is natural standing at room temperature for 13 minutes. The second stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 0.9m / s, the heating temperature is controlled at 173℃, and the heating time is 14min. The third stage is heated by hot flue gas, the wind speed of the heating flue gas is controlled at 0.9m / s, the heating temperature is controlled at 227℃, and the heating time is 19min.

[0057] 6) Screening of dry pressed agglomerates: The total amount of dry pressed agglomerates after drying is weighed (calculated as MG=33.15 t / h) and then screened. The part under the screen is weighed (calculated as MGS=6.37 / h) and then returns to step 2). The part above the screen is qualified dry pressed agglomerates, which enter the rotary hearth furnace. The powderization rate of the drying process is calculated as MGS / MG*100wt%=6.37 / 33.15*100wt%=19.22%.

[0058] Comparative Example

[0059] 1) Raw material pretreatment: After the high-calcium metallurgical dust is stored, it is dried and dispersed together with the low-calcium metallurgical dust. The moisture content after drying is controlled to be 6.3%, and the content of particles with a particle size of less than 3 mm after dispersion is 77%;

[0060] 2) Batching and mixing: The pretreated metallurgical dust, dust removal coke powder, and binder were batched with the same batching ratio and raw materials as in Example 1, and the bulk density of the mixture after batching was detected, which was calculated as ρq = 1.2344 g / cm3; and a strong mixer was used to mix the mixture, and the bulk density and porosity of the mixture after mixing were detected. The bulk density of the mixture was calculated as ρh = 1.2567 g / cm3, and the porosity of the mixture during natural stacking was calculated as K = 66.68%. The bulk density ρh of the mixture after mixing was 1.81% higher than the bulk density ρq of the mixture before mixing;

[0061] 3) Pressing the pellets: The mixed material is transported to the pelletizing buffer bin, the height of which is not controlled, and then the pelletizing is performed using a pelletizing machine;

[0062] 4) Screening of wet pressed mass: the total amount of wet pressed mass is weighed (calculated as MS=43.72 t / h) and then screened. A vibrating screen with 8 mm mesh is used for screening. The screening principle is: the vibration frequency is 1 second and the number of vibrations is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed mass and wet pressed mass laid on the vibrating screen is ≤3 layers; the part under the screen is weighed (calculated as MSS=9.45 t / h) and then returns to step 2), and the wet pressed mass pulverization rate is calculated as MSS / MS*100wt%=9.45 / 43.72*100wt%=21.61wt%, and the wet pressed mass on the screen is sent to the drying process;

[0063] 5) Drying: Drying is carried out in two stages. The first stage uses hot flue gas heating, the heating temperature is controlled at 224°C, and the heating time is 17 minutes; the second stage uses hot flue gas heating, the heating temperature is controlled at 331°C, and the heating time is 14 minutes;

[0064] 6) Screening of dry pressed agglomerates: The total amount of dry pressed agglomerates after drying is weighed (calculated as MG=30.81 t / h) and then screened. The part under the screen is weighed (calculated as MGS=6.93 t / h) and then returns to step 2). The part above the screen is qualified dry pressed agglomerates. The qualified dry pressed agglomerates enter the rotary hearth furnace, and the powderization rate of the drying process is calculated as MGS / MG*100wt%=7.31 / 32.51*100wt%=22.49wt%.

[0065] It can be seen that the comparative example is higher than that of Examples 1, 2 and 3 in both the wet pressing and the drying process. This is because in Comparative Examples 1, 2 and 3, the high-calcium metallurgical dust and sludge are mixed, extruded and digested before pressing, so as to avoid the volume expansion and rupture caused by the digestion after pressing. Secondly, a strong mixer is used for mixing in the mixing stage, and its parameters are optimized to fully break up the mixed mixture, reduce the edges and corners of the particles, and reduce the gaps when the mixture is piled up, so that there is more material per unit volume during pressing, the material is squeezed tighter during pressing, and the strength of the pressing is better. Controlling the height of the mixture in the pressing buffer bin also increases the compactness of the mixture at the discharge port, so that there is more material per unit volume during pressing, thereby improving the strength of the pressing. The pressing is dried in three stages before entering the converter in order to control the evaporation rate of water and avoid the rupture of the pressing due to the excessive overflow of water vapor. Compared with the comparative example, the first stage of Examples 1, 2 and 3 is naturally left to stand at room temperature, which can increase the strength of the pressing mass before the water evaporates, so that the pressing mass can withstand a higher pressure when water vapor overflows. In Examples 1, 2, and 3, in the three drying stages, the longer the drying time, the lower the heating flue gas velocity, and the lower the drying temperature, the lower the powdering rate in the drying process can be achieved. In summary, the powdering rate of the gold dust sludge agglomerates in Examples 1, 2, and 3 before entering the rotary hearth furnace is lower than that of the comparative example.

[0066] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for reducing the pulverization rate of metallurgical dust sludge before it enters a rotary hearth furnace. It is characterized in that The steps include: Step 1: dividing the metallurgical dust into high-calcium metallurgical dust and low-calcium metallurgical dust according to the calcium oxide content standard, digesting the high-calcium metallurgical dust, mixing the digested high-calcium metallurgical dust with the low-calcium metallurgical dust, drying and breaking them up; Step 2: Mix the dried and broken metallurgical dust with dust removal coke powder and binder, and mix them evenly; Step 3: transport the mixed material to a pelletizing buffer bin, and then use a pelletizing machine to pelletize the material to obtain wet pellets; Step 4: Screen the wet pressed mass, the part under the screen is returned to step 2, and the wet pressed mass above the screen is entered into step 5; Step 5: drying the wet pressed mass on the sieve in three stages with the drying temperature increasing successively, to obtain a dry pressed mass; Step 6: The dry pressed mass is screened, the part under the screen is returned to step 2, and the part above the screen is the qualified dry pressed mass, which enters the rotary hearth furnace.

2. The method for reducing the pulverization rate of metallurgical dust sludge before entering the rotary hearth furnace according to claim 1, Features: In the step 1, the calcium oxide content standard is 1%wt, the calcium oxide content in high-calcium metallurgical dust is greater than 1%wt, and the calcium oxide content in low-calcium metallurgical dust is ≤1%wt.

3. The method for reducing the pulverization rate of metallurgical dust sludge before entering the rotary hearth furnace according to claim 1, Features: In the step 1, the specific method for digesting the high-calcium metallurgical dust is: the high-calcium metallurgical dust is mixed with water to complete digestion, and the free calcium oxide in the high-calcium metallurgical dust after digestion is ≤1%wt.

4. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 1, Features: In the step 1, the high-calcium metallurgical sludge and the low-calcium metallurgical sludge after digestion are mixed and dried, and the moisture content after dispersion is not higher than 7%, and the particles with a particle size of less than 3 mm are ≥90%.

5. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 1, Features: In the step 2, the bulk density of the mixed material after mixing is increased by 5% or more than the bulk density before mixing, and the porosity of the mixed material under natural stacking is ≤65%.

6. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 1, Features: In the step 3, the stacking height of the mixed material in the briquetting buffer bin is greater than or equal to 70% of the height of the buffer bin.

7. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 1, Features: In the step 4, a vibrating screen with 8 mm mesh is used for screening, and the screening principle is: the number of vibrations in 1 second is ≤3 times, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry pressed masses and wet pressed masses laid on the vibrating screen is ≤3 layers.

8. The method for reducing the pulverization rate of metallurgical dust sludge before entering the rotary hearth furnace according to claim 1, Features: In the step 5, the first stage of the three-stage drying is natural standing at room temperature.

9. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 8, Features: In step 5, the specific method of three-stage drying is: the first stage adopts natural standing at room temperature, and the natural standing time is 10min-20min; the second stage heating temperature is controlled at 150-200℃, and the heating time is 10min-20min; the third stage heating temperature is controlled at 200-300℃, and the heating time is 10min-20min.

10. The method for reducing the pulverization rate of metallurgical dust sludge agglomerates before entering a rotary hearth furnace according to claim 9, Features: The second section adopts hot flue gas heating, and the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s; the third section adopts hot flue gas heating, and the heating flue gas wind speed is controlled at 0.4m / s-1.2m / s.

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