Method for reducing the pulverization rate of metallurgical sludge briquettes before entering the rotary hearth furnace

Abstract

The application provides a method for reducing the pulverization rate of metallurgical sludge briquetting before entering a rotary hearth furnace, comprising the following steps: step one: digesting high-calcium metallurgical sludge, mixing the digested high-calcium metallurgical sludge with low-calcium metallurgical sludge, and drying and scattering; step two: dosing the dried and scattered metallurgical sludge with dedusting coke powder and a binder, and mixing after dosing; step three: conveying the mixed material to a briquetting buffer bin, and then briquetting by a ball press to obtain wet briquetting; step four: screening the wet briquetting, returning the undersize part to step two, and feeding the oversize part to step five; step five: three-stage drying of the wet briquetting in the oversize part, with the drying temperature of each stage being increased in sequence, to obtain dry briquetting; step six: screening the dry briquetting, returning the undersize part to step two, and feeding the oversize part, which is qualified dry briquetting, to the rotary hearth furnace. The application reduces the pulverization rate of metallurgical sludge briquetting by digesting calcium oxide and three-stage drying.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgical sintering pellet, and particularly relates to a method for reducing the powdering rate of metallurgical dust and sludge briquettes before entering the rotary hearth furnace. BACKGROUND

[0002] In the process of steel production, a large amount of dust and sludge is generated, and more than 100 kg of metallurgical dust and sludge is generated per ton of steel. The dust and sludge contains harmful elements such as zinc, potassium, sodium, lead and chlorine, and direct reuse will cause great harm to steel production. Therefore, these harmful impurities need to be removed before returning to the steel production process. The rotary hearth furnace process is a process that has attracted much attention in the treatment of metallurgical dust and sludge. It can effectively remove harmful elements such as zinc, potassium, sodium, lead and chlorine in the dust and sludge. The DRI (direct reduced iron) produced is returned to the steel production process, and the zinc powder produced is used as a raw material for zinc smelting, thereby achieving comprehensive utilization of metallurgical dust and sludge.

[0003] The rotary hearth furnace process is a process in which metallurgical dust and sludge are briquetted and then sent to the rotary hearth furnace for high-temperature reduction. The briquettes will break during the transfer process and the high-temperature process, affecting production efficiency. The document "Jin Yonglong, Sun Yukia, Wang Qian. Industrial test and production practice of rotary hearth furnace disposal of zinc-containing solid waste. Hebei Metallurgy, 2022(005):000." points out that there are two main briquetting processes for rotary hearth furnaces. One is disc pelletizing, and the other is roller press briquetting. Practice shows that disc pelletizing has low cost, but the quality of the wet pellets and DRI (direct reduced iron) produced is poor. Roller press briquetting has high cost, but the quality of the wet briquettes and DRI produced is good, and the production efficiency is high. Therefore, the current production process is mainly roller press briquetting. Based on the briquetting process of the rotary hearth furnace process, the main ways to reduce the powdering rate and improve production efficiency are to increase the strength of the wet briquettes, reduce the explosive powdering of the briquettes during the water removal process, and reduce the powdering during the reduction process in 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 Pellets, 2023, 48(4):59-64." shows that drying the wet briquettes before entering the rotary hearth furnace can greatly improve the strength of the DRI and greatly reduce the powdering caused by explosive cracking during the reduction process in the rotary hearth furnace. However, 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 briquette powdering rate during the drying process. Therefore, the current DRI production process flow of the rotary hearth furnace is mainly roller press briquetting-drying-reduction in the rotary hearth furnace, but there is still a problem of high powdering rate of the briquettes before entering the rotary hearth furnace. SUMMARY

[0005] The present application aims at the defects of the prior art, and provides a method for reducing the powdering rate of metallurgical dust and sludge before entering a rotary hearth furnace, which reduces the calcium oxide content by using water to digest the metallurgical dust and sludge in advance, reduces the powdering rate of the wet briquetting in the subsequent drying process by gradually increasing the temperature in the three-stage drying process, and reduces the powdering rate of the briquetting in the drying process, thereby achieving the purpose of reducing the powdering rate of the metallurgical dust and sludge before entering the rotary hearth furnace.

[0006] The present application provides a method for reducing the powdering rate of metallurgical dust and sludge before entering a rotary hearth furnace, which comprises the following steps:

[0007] Step one: according to the calcium oxide content standard, the metallurgical dust and sludge are divided into high-calcium metallurgical dust and low-calcium metallurgical dust, the high-calcium metallurgical dust is subjected to digestion treatment, and the high-calcium metallurgical dust after digestion is mixed with the low-calcium metallurgical dust and then dried and scattered;

[0008] Step two: the metallurgical dust and sludge after drying and scattering are mixed with dedusting coke powder and a binder, and the mixture is uniformly mixed after mixing;

[0009] Step three: the mixture after uniform mixing is transported to a briquetting buffer bin, and then is subjected to briquetting by using a ball press machine to obtain wet briquetting;

[0010] Step four: the wet briquetting is screened, the undersize part is returned to step two, and the oversize part of the wet briquetting enters step five;

[0011] Step five: the wet briquetting of the oversize part is subjected to three-stage drying with the temperature of each stage being increased in turn to obtain dry briquetting;

[0012] Step six: the dry briquetting is screened, the undersize part is returned to step two, and the oversize part is qualified dry briquetting, and the qualified dry briquetting enters the rotary hearth furnace.

[0013] Further, in step one, the calcium oxide content standard is 1%wt, the calcium oxide content in the high-calcium metallurgical dust is >1%wt, and the calcium oxide content in the low-calcium metallurgical dust is ≤1%wt.

[0014] Further, in step one, the specific method for digesting the high-calcium metallurgical dust is to mix the high-calcium metallurgical dust with water to complete digestion, and the free calcium oxide content in the high-calcium metallurgical dust after digestion is ≤1%wt.

[0015] Further, in step one, the moisture content of the high-calcium metallurgical dust after mixing with the low-calcium metallurgical dust and then drying and scattering is not higher than 7%, and the particle size of particles less than 3mm is ≥90%.

[0016] Further, in step two, the bulk density of the mixture after uniform mixing is increased by 5% or more than 5% compared with the bulk density before uniform mixing, and the porosity of the mixture after natural piling is ≤65%.

[0017] Further, in step three, the mixed material in the briquetting buffer bin has a pile height greater than or equal to 70% of the height of the buffer bin.

[0018] Further, in step four, the screening uses a vibrating screen with a 8mm mesh, and the screening principle is: the vibration frequency is less than or equal to 3 times per second, the vibrating screen inclination is less than or equal to 45°, and the number of layers of dry briquettes and wet briquettes laid on the vibrating screen is less than or equal to 3 layers.

[0019] Further, in step five, the first segment of the three-segment drying uses normal temperature natural standing. Further, in step five, the specific method of the three-segment drying is: the first segment uses normal temperature natural standing, the natural standing time is 10min-20min; the second segment uses 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 segment uses 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 application are:

[0021] 1. The high calcium metallurgical dust and water are mixed and extruded to digest CaO in the high calcium dust before briquetting, so that the volume expansion caused by CaO digestion after briquetting is avoided, and the briquettes are dried in three segments before entering the converter, so that the water evaporation speed is controlled, the too fast overflow of water vapor is avoided to cause the briquette to break, and the pulverization rate of the metallurgical dust briquette before entering the rotary hearth furnace is reduced.

[0022] 2. The drying and dispersion of the low calcium metallurgical dust control the particle size and dispersion degree of the dust, and improve the uniformity of the particle distribution after briquetting.

[0023] 3. The mixed material is mixed after batching to control the bulk density and porosity of the mixed material, so that more material per unit volume is pressed during briquetting, the extrusion is tighter, and the briquette strength is better.

[0024] 4. The height of the mixed material in the briquetting buffer bin is controlled to improve the tightness of the mixed material at the discharge port, so that more material per unit volume is pressed during briquetting, and the briquette strength is improved.

[0025] 5. In the three-segment drying step before entering the converter, the first segment is normal temperature natural standing, which can improve the strength of the briquette before water evaporation, so that the briquette can withstand higher pressure when water vapor overflows. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The flow chart of the method for reducing the pulverization rate of the metallurgical dust briquette before entering the rotary hearth furnace. DETAILED DESCRIPTION

[0027] The method of the present application is further described in detail below in conjunction with the accompanying drawings and specific examples:

[0028] Reference Figure 1 The present application provides a method for reducing the pulverization rate of metallurgical sludge briquetting before entering the rotary hearth furnace, comprising the following steps:

[0029] Step one: according to the calcium oxide content standard, the metallurgical sludge is divided into high calcium metallurgical sludge and low calcium metallurgical sludge, the high calcium metallurgical sludge is subjected to digestion treatment, and the high calcium metallurgical sludge after digestion is mixed with the low calcium metallurgical sludge and dried and scattered. Preferably, the calcium oxide content standard is 1%wt, the calcium oxide content in the high calcium metallurgical sludge is >1%wt, and the calcium oxide content in the low calcium metallurgical sludge is ≤1%wt. Preferably, the specific method for digestion treatment of the high calcium metallurgical sludge is to mix the high calcium metallurgical sludge with water and then complete the digestion, and the free calcium oxide in the high calcium metallurgical sludge after digestion is ≤1%wt. The high calcium metallurgical sludge is mixed and extruded with water to digest the CaO in the high calcium sludge before briquetting, so as to avoid the volume expansion and rupture caused by digestion of CaO after briquetting. Preferably, the moisture content of the high calcium metallurgical sludge after mixing, drying and scattering is not higher than 7%, and the particle size of the particles less than 3mm is ≥90%. The drying process in this step has no specific requirements, and as a preferred solution, only the moisture content after drying is required to be not higher than 7%.

[0030] Step two: the dried and scattered metallurgical sludge is mixed with dedusting coke powder and binder, and the mixture is uniformly mixed after mixing. Preferably, 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 accumulation after mixing is ≤65%. By increasing the bulk density and reducing the porosity, the strength of the briquette can be effectively improved.

[0031] Step three: the mixed material after mixing is transported to the briquetting buffer bin, and then the briquetting machine is used for briquetting to obtain wet briquettes. Preferably, the accumulation height of the mixed material in the briquetting buffer bin is greater than or equal to 70% of the height of the buffer bin, which improves the tightness of the mixed material at the discharge port, so that more material per unit volume is obtained during briquetting, thereby improving the briquetting strength.

[0032] Step four: the wet briquettes are screened, the undersize part is returned to step two, and the oversize wet briquettes are subjected to step five.

[0033] Step five: the wet briquetting of the oversize fraction is subjected to three-stage drying with the temperature of each stage being raised successively to obtain dry briquetting. Preferably, the three-stage drying is carried out in the following manner: the first stage is natural standing at room temperature for 10-20 minutes; the second stage is heated by hot flue gas with the wind speed of the flue gas being controlled at 0.4-1.2 m / s and the temperature being controlled at 150-200 DEG C for 10-20 minutes; and the third stage is heated by hot flue gas with the wind speed of the flue gas being controlled at 0.4-1.2 m / s and the temperature being controlled at 200-300 DEG C for 10-20 minutes. The natural standing at room temperature can increase the strength of the briquetting before water evaporation so that the briquetting can withstand higher pressure when water vapor overflows.

[0034] Step six: the dry briquetting is screened, and the undersize fraction is returned to step two, and the oversize fraction is qualified dry briquetting which is fed into the rotary hearth furnace.

[0035] Preferably, in step four, the screening is carried out by using a vibrating screen with a sieve hole of 8 mm, and the screening principle is that the vibrating frequency is less than or equal to 3 times per second, the vibrating screen inclination is less than or equal to 45 DEG, and the number of layers of the dry and wet briquetting laid on the vibrating screen is less than or equal to 3.

[0036] The application will be further illustrated by the following specific examples and comparative examples.

[0037] Example 1

[0038] 1) raw material pretreatment: the high calcium metallurgical sludge is mixed with water and extruded for digestion, and the free calcium oxide after digestion is controlled at 0.96%; the high calcium metallurgical sludge after digestion is dried and scattered together with low calcium metallurgical sludge, and the moisture after drying is 6.4%; and the particle size of the scattered particles is less than 3 mm, and the percentage of the particles is 91.3%;

[0039] 2) batching and mixing: the pretreated metallurgical sludge, dedusting coke powder and binder are batched, the bulk density of the batched mixture is detected, and the bulk density is calculated as ρq=1.2539 g / cm 3 ; and the batched mixture is mixed by using a powerful mixer, the bulk density of the mixed mixture and the porosity of the mixture when naturally stacked are detected, the bulk density of the mixed mixture is calculated as ρh=1.3592 g / cm 3 , and the porosity of the mixed mixture when naturally stacked is calculated as K=62.96%. The bulk density of the mixed mixture after mixing ρh is increased by 8.40% compared with the bulk density of the mixed mixture before mixing ρq, and the porosity of the mixed mixture when naturally stacked K is less than or equal to 65%;

[0040] 3) briquetting: the mixed mixture after mixing is conveyed to a briquetting buffer bin, the height of the mixed mixture is 84.36% of the height of the buffer bin, the height of the mixed mixture accumulated in the buffer bin is greater than 92% of the height of the buffer bin, and then the briquetting is carried out by using a ball press machine;

[0041] 4) Wet briquetting screening: after the total amount of wet briquetting is weighed (counted as MS = 43.61 t / h), screening is performed, the screening uses a vibrating screen with a 8 mm screen hole, the screening principle is: the vibration frequency is ≤3 times per 1 second, the vibrating screen inclination is ≤45°, the dry briquetting and the wet briquetting are laid in 3 layers on the vibrating screen; after the screened part is weighed (counted as MSS = 6.11 t / h), it returns to step 2), the wet briquetting pulverization rate = MSS / MS*100wt% = 6.11 / 43.61*100wt% = 14.01wt%, the screened part is sent to the drying process;

[0042] 5) Drying: the drying is divided into three stages, the first stage is natural standing at room temperature, the natural standing time is 16 min; the second stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 0.8 m / s, the heating temperature is controlled at 191℃, the heating time is 19 min; the third stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 0.9 m / s, the heating temperature is controlled at 237℃, the heating time is 18 min;

[0043] 6) Dry briquetting screening: after the total amount of dry briquetting after drying is weighed (counted as MG = 32.94 / h), screening is performed, the screened part is weighed (counted as MGS = 5.11 / h) and returned to step 2), the screened part is qualified dry briquetting, which enters the rotary hearth furnace, and the drying process pulverization rate = MGS / MG*100wt% = 65.11 / 32.94*100wt% = 15.51%.

[0044] Example 2

[0045] 1) Raw material pretreatment: the high calcium metallurgical sludge is mixed with water and extruded for digestion, the free calcium oxide after digestion is controlled at 0.89%; the high calcium metallurgical sludge after digestion is dried and scattered together with the low calcium metallurgical sludge, the moisture after drying is 5.7%; the particle size after scattering is less than 3 mm, accounting for 92.4%;

[0046] 2) Proportioning and mixing: the pretreated metallurgical sludge, dedusting coke powder and binder are proportioned with the same proportioning ratio and raw materials as in example 1, the bulk density of the mixed material after proportioning is detected, counted as ρq = 1.2475 g / cm 3 ; and the bulk density and the natural porosity of the mixed material after mixing are detected, the bulk density of the mixed material is counted as ρh = 1.3138 g / cm 3 , and the natural porosity of the mixed material is counted as K = 64.20%. The bulk density of the mixed material after mixing ρh is increased by 5.31% compared with the bulk density of the mixed material before mixing ρq, and the natural porosity of the mixed material K is not more than 65%;

[0047] 3) briquetting: the mixed material after mixing is transported to a briquetting buffer bin, the height of the mixed material pile is 84.36% of the height of the buffer bin, the height of the mixed material pile in the buffer bin is greater than 70% of the height of the buffer bin, and then a ball press is used for briquetting;

[0048] 4) wet briquetting screening: after the total amount of wet briquetting is weighed (counted as MS = 45.72 t / h), screening is performed, the screening uses a vibrating screen with a 8 mm sieve hole, and the screening principle is that the vibration frequency is ≤ 3 times per second, the vibrating screen inclination is ≤ 45°, and the number of layers of dry briquetting and wet briquetting laid on the vibrating screen is ≤ 3 layers; after the under-screen part is weighed (counted as MSS = 7.49 t / h), it returns to step 2), the wet briquetting pulverization rate = MSS / MS*100wt% = 7.49 / 45.72*100wt% = 16.38wt%, and the over-screen part of the wet briquetting is sent to the drying process;

[0049] 5) drying: drying is performed in three stages, the first stage is natural standing at room temperature, the natural standing time is 10 min; the second stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 1.0 m / s, the heating temperature is controlled at 169℃, and the heating time is 17 min; the third stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 0.8 m / s, the heating temperature is controlled at 257℃, and the heating time is 18 min;

[0050] 6) dry briquetting screening: after the total amount of dry briquetting after drying is weighed (counted as MG = 34.07 t / h), screening is performed, the under-screen part is weighed (counted as MGS = 6.29 / h) and returned to step 2), and the over-screen part is qualified dry briquetting, which enters the rotary hearth furnace, and the drying process pulverization rate = MGS / MG*100wt% = 6.29 / 34.07*100wt% = 18.46%.

[0051] Example 3

[0052] 1) raw material pretreatment: the high calcium metallurgical sludge is mixed with water and extruded for digestion, and the free calcium oxide after digestion is controlled to be 0.91%; the high calcium metallurgical sludge after digestion is dried and scattered together with low calcium metallurgical sludge, and the moisture after drying is 6.1%; the particle size after scattering is less than 3 mm, and the particles of 90.7% are obtained;

[0053] 2) batching and mixing: the pretreated metallurgical sludge, dedusting coke powder and binder are batched with the same batching ratio and raw materials as in example 1, the bulk density of the mixed material after batching is detected, and is counted as ρq=1.2391 g / cm 3 ; and a strong mixer is used for mixing, the bulk density of the mixed material after mixing and the porosity when naturally stacking are detected, and the bulk density of the mixed material is counted as ρh=1.3078 g / cm 3, the natural bulk porosity of the mixture is K=64.37%. After mixing, the bulk density of the mixed material ρh is increased by 5.54% compared to the bulk density of the mixed material ρq before mixing, and the natural bulk porosity of the mixture K is not more than 65%;

[0054] 3) Briquetting: After mixing, the mixed material is transported to the briquetting buffer bin, the mixed material pile height is 75.6% of the height of the buffer bin, the mixed material pile height in the buffer bin is greater than 70% of the height of the buffer bin, and then a ball press is used for briquetting;

[0055] 4) Wet briquetting screening: After weighing the total amount of wet briquetting (counted as MS=44.67t / h), screening is carried out using an 8mm sieve vibrating screen, the screening principle is: the vibration frequency is ≤3 times per second, the vibrating screen inclination is ≤45°, and the number of layers of dry briquetting and wet briquetting laid on the vibrating screen is ≤3 layers; After weighing the under-screen part (counted as MSS=7.68t / h), return to step 2), calculate the wet briquetting pulverization rate = MSS / MS*100wt% = 7.67 / 44.67*100wt% = 17.19wt%, and the over-screen wet briquetting is sent to the drying process;

[0056] 5) Drying: Drying is divided into three stages, the first stage is natural standing at room temperature, the natural standing time is 13min; the second stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 0.9m / s, the heating temperature is controlled at 173℃, and the heating time is 14min; the third stage uses hot flue gas heating, the heating flue gas wind speed is controlled at 0.9m / s, the heating temperature is controlled at 227℃, and the heating time is 19min;

[0057] 6) Dry briquetting screening: After weighing the total amount of dry briquetting after drying (counted as MG=33.15t / h), screening is carried out, the under-screen part is weighed (counted as MGS=6.37 / h) and returned to step 2), and the over-screen part is qualified dry briquetting. The qualified dry briquetting enters the rotary hearth furnace, and the drying process pulverization rate is calculated = MGS / MG*100wt% = 6.37 / 33.15*100wt% = 19.22%.

[0058] Comparative Example

[0059] 1) Raw material pretreatment: After stacking, the high calcium metallurgical sludge is dried and dispersed together with the low calcium metallurgical sludge, the moisture after drying is controlled at 6.3%, and the particle content of the particle size less than 3mm after dispersion is 77%;

[0060] 2) batching and mixing: the pretreated metallurgical sludge, dedusting coke powder and binder are batched in the same batching ratio and raw materials as in Example 1. The bulk density of the batched mixture is detected and recorded as ρq=1.2344 g / cm3. The batched mixture is mixed by using a strong mixer. The bulk density of the mixed mixture is detected and recorded as ρh=1.2567 g / cm3. The porosity of the mixed mixture is detected and recorded as K=66.68%. The bulk density of the mixed mixture after mixing ρh is increased by 1.81% compared with the bulk density of the batched mixture before mixing ρq;

[0061] 3) briquetting: the mixed mixture after mixing is transported to a briquetting buffer bin, the height of the buffer bin is not controlled, and then a ball press is used for briquetting;

[0062] 4) wet briquette screening: the total amount of wet briquettes is weighed (recorded as MS=43.72 t / h) and then screened. The screening uses a vibrating screen with a sieve hole of 8 mm. The screening principle is that the vibration frequency is ≤3 times per second, the vibrating screen inclination is ≤45°, and the number of layers of dry briquettes and wet briquettes laid on the vibrating screen is ≤3 layers. The screened undersize is weighed (recorded as MSS=9.45 t / h) and returned to step 2). The powdering rate of wet briquettes is calculated as MSS / MS*100wt%=9.45 / 43.72*100wt%=21.61wt%, and the screened oversize is sent to the drying process;

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

[0064] 6) dry briquette screening: the total amount of dry briquettes after drying is weighed (recorded as MG=30.81 t / h) and then screened. The screened undersize is weighed (recorded as MGS=6.93 t / h) and returned to step 2). The screened oversize is qualified dry briquettes, which are sent to the rotary hearth furnace. The powdering rate during the drying process is calculated as MGS / MG*100wt%=7.31 / 32.51*100wt%=22.49wt%.

[0065] It can be seen that the comparative examples have higher wet briquetting dusting rate and drying process dusting rate than the examples 1, 2 and 3, because in the comparative examples 1, 2 and 3, the high calcium metallurgical dust and sludge are mixed and extruded before briquetting to avoid the volume expansion and breakage caused by digestion after briquetting, and secondly, the uniform mixing stage uses a strong mixer to mix and optimize the parameters, fully dispersing the mixed material and reducing the edges and corners of the particles, reducing the voids when the mixed material is stacked, so that the unit volume of material is more when briquetting, the extrusion is tighter when pressing, the briquetting strength is better, the height of the mixed material in the briquetting buffer bin is also improved to increase the tightness of the mixed material at the discharge port, so that the unit volume of material is more when briquetting, thereby improving the briquetting strength, and the three-stage drying of the briquetting before entering the converter is to control the water evaporation speed and avoid the too fast overflow of water vapor causing the briquetting to break. Compared with the comparative examples, the first stage of natural standing at room temperature in examples 1, 2 and 3 can improve the strength of the briquetting before water evaporation, so that the briquetting can withstand higher pressure when water vapor overflows. And in examples 1, 2 and 3, the longer the drying time, the lower the heating flue gas wind speed and the lower the drying temperature in the three-stage drying stage, which can achieve the effect of lower drying process dusting rate. In summary, the dust and sludge briquetting in examples 1, 2 and 3 has lower dusting rate than the comparative examples before entering the rotary hearth furnace.

[0066] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the examples of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for reducing the pulverization rate of metallurgical dust clumps before entering a rotary hearth furnace, characterized in that, Includes the following steps: Step 1: Based on the calcium oxide content standard, metallurgical dust is divided into high-calcium metallurgical dust and low-calcium metallurgical dust. The calcium oxide content standard is 1%wt. High-calcium metallurgical dust contains >1%wt, while low-calcium metallurgical dust contains ≤1%wt. The high-calcium metallurgical dust is then digested. The digested high-calcium metallurgical dust is mixed with the low-calcium metallurgical dust, dried, and dispersed. The moisture content after drying and dispersing is not higher than 7%, and the particle size of particles smaller than 3mm is ≥90%. Step 2: Mix the dried and dispersed metallurgical dust and sludge with dust removal coke powder and binder. After mixing, the bulk density of the mixture should be 5% or more higher than that before mixing, and the porosity of the mixture under natural stacking should be ≤65%. Step 3: The mixed material is conveyed to the briquetting silo. The height of the mixed material in the briquetting silo is greater than or equal to 70% of the height of the silo. Then, the mixture is briquetting machine to obtain wet briquettes. Step 4: Screen the wet compressed lumps. The undersized portion is returned to Step 2, and the oversized portion of the wet compressed lumps is sent to Step 5. Step 5: The wet pressed briquette on the sieve is dried in three stages with the drying temperature increasing in each stage to obtain dry pressed briquette; The specific method for the three-stage drying is as follows: the first stage involves natural resting at room temperature for 10-20 minutes; the second stage involves heating at 150-200℃ for 10-20 minutes; and the third stage involves heating at 200-300℃ for 10-20 minutes. The second stage uses hot flue gas heating with a wind speed controlled at 0.4 m / s-1.2 m / s; the third stage also uses hot flue gas heating with a wind speed controlled at 0.4 m / s-1.2 m / s. Step 6: Screen the dry-pressed briquettes. The undersize portion is returned to Step 2, while the oversize portion is the qualified dry-pressed briquettes, which then enter the rotary hearth furnace.

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

3. The method for reducing the pulverization rate of metallurgical dust clumps before entering the rotary hearth furnace according to claim 1, characterized in that: In step four, the screening uses a vibrating screen with an 8mm mesh size. The screening principles are: the vibration frequency is ≤3 times per second, the inclination angle of the vibrating screen is ≤45°, and the number of layers of dry and wet compressed briquettes laid on the vibrating screen is ≤3.

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