A production method of adding screen under powder of a pellet to a rotary hearth furnace
Patent Information
- Application Number
- CN202611119090.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-27
- Publication Date
- 2026-09-25
AI Technical Summary
若掺入烧结工序使用，易造成高炉有害元素负荷超标，扰乱炉况稳定顺行；粉料粒度细小，直接送入转炉、电炉冶炼，存在进料难度大、金属回收率偏低、烟尘排放量高等问题
1、实现固废资源化利用，绿色环保：转底炉金属化筛下粉占转底炉产出物料20~30%，传统处置方式仅能厂区堆存或小比例配加烧结，不仅占用大量土地，还存在扬尘、重金属渗漏等环保风险。将其配入球团造球、经焙烧机焙烧回用，可实现该类冶金固废规模化、常态化消纳，彻底杜绝堆存带来的环保隐患，打通冶金尘泥全流程资源化闭环，提升企业固废综合利用率，符合绿色生产与环保管控要求。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of pellet production technology, and in particular to a production method for adding powder from rotary hearth furnace screens to pellets. Background Technology
[0002] Currently, the mainstream process for treating dust generated in the steel industry is to use rotary kilns and rotary hearth furnaces to form metallized pellets from metallurgical dust and sludge. Zinc is then separated and recovered through high-temperature reduction. The dezincified metallized pellets can be reused in blast furnaces and converters for smelting, and the enriched zinc powder can be sold to zinc processing companies.
[0003] During production, approximately 20% to 30% of the metallized pellets are produced as undersize powder. This powder has insufficient reduction in the reaction process, with a zinc content ranging from 1% to 2.5%. If used in the sintering process, it can easily cause excessive harmful element loads in the blast furnace, disrupting stable furnace operation. Furthermore, the fine particle size of the powder makes it difficult to feed directly into converters or electric furnaces, resulting in low metal recovery rates and high dust emissions. Preparing it into cold-pressed pellets results in products with weak mechanical strength, easily crumbling and pulverizing upon entering the furnace. This not only slows the heating rate and increases smelting energy consumption but also increases the safety hazard of molten steel splashing.
[0004] If the undersized powder is sent back to the rotary hearth furnace for recycling, the high proportion of fine material will worsen the permeability of the material layer, resulting in uneven reduction reaction and easy to cause crusting at the furnace bottom, ultimately causing a decline in both equipment capacity and product metallization rate.
[0005] Such undersize powder is difficult to directly adapt to the production requirements of steelmaking processes. Most of it can only be stored on-site or consumed in small proportions with sintering raw materials, which not only occupies space resources but also poses environmental control risks. Given the significant drawbacks of the existing disposal methods, we are exploring the possibility of incorporating rotary hearth furnace undersize powder into the pelletizing mixture and feeding it into a belt roaster for pellet roasting, thereby solving the existing utilization problem. Summary of the Invention
[0006] The purpose of this invention is to provide a production method for adding rotary hearth furnace undersize powder to pellets. By adding the rotary hearth furnace undersize powder to the pelleting mixture and feeding it into a belt roaster for pellet roasting, the method achieves both the resource utilization of solid waste and the stable production of finished pellets.
[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:
[0008] A method for producing pellets by adding rotary hearth furnace undersize powder involves grinding rotary hearth furnace undersize powder and coarse ore in a specific ratio to prepare a self-made refined powder. The self-made refined powder, magnetic refined powder, bentonite, and carbonaceous ash are then uniformly mixed and extruded by a counter roller press and stirred by a high-intensity mixer to form a homogeneous material. The homogeneous material is then pelletized by a disc pelletizer to prepare green pellets. The green pellets are then sequentially fed into a belt roaster and roasted through a forced-air drying section, an exhaust drying section, a preheating section, a roasting section, a cooling section 1, and a cooling section 2 to finally produce finished pellets containing rotary hearth furnace undersize powder.
[0009] Preferably, the Zn content in the powder under the rotary hearth furnace screen is controlled at 1-2%.
[0010] Preferably, the mass fraction of the powder passing through the rotary hearth furnace in the self-made refined powder is 1-3%, with the remainder being coarse ore, which is selected from one or more of limonite, goethite, or hematite.
[0011] Preferably, the self-made refined powder contains 61-64% TFe, 0.5-10% FeO, 5-8.5% SiO2, 1-3% CaO, 0.5-2% MgO, 1-1.8% Al2O3, has a -200 mesh particle size ratio of not less than 80%, and a specific surface area of not less than 1500 cm². 2 / kg.
[0012] Preferably, the carbon-containing ash contains at least 25% C, at least 6% SiO2, at least 0.8% MgO, and at least 4% Al2O3, with at least 95% of the particles having a size of less than 0.5 mm and a specific surface area of at least 2000 m². 2 / kg.
[0013] Preferably, the mixture contains ≥55% self-made refined powder, ≤1% bentonite, ≤3% carbon ash, and the remainder is magnetic refined powder.
[0014] Preferably, the proportion of green pellets with a particle size range of 10~16mm is more than 92%, the green pellet drop intensity is controlled at 5 times / 0.5m, and the pelletizing disc rotation speed of the disc pelletizing machine is 36~38r / min.
[0015] Preferably, the mixed material contains 62-66% TFe, 10-30% FeO, 3-7% SiO2, 1-3% CaO, 0.1-1% MgO, 0.5-1.5% Al2O3, and 0-0.1% Zn, and the specific surface area of the mixed material is controlled at 1800-2100 cm². 2 / g, the moisture content of the mixed material is controlled at 8.5~9.5%.
[0016] Preferably, the temperature of the blower drying section is 200℃~260℃, and the machine speed is 2.02m / min, which dries the green pellets and promotes the evaporation of moisture on the surface of the green pellets; The temperature of the exhaust drying section is 290℃~310℃, and the machine speed is 2.5m / min. The green pellets are dried again by exhaust to remove the moisture inside the green pellets. The preheating section has a temperature of 950℃~1100℃ and a machine speed of 2.5m / min. It preheats the green pellets to increase their temperature and prepare them for the subsequent roasting section. The roasting section has a temperature of 1100℃~1260℃ and a machine speed of 2.5m / min, during which the green pellets are roasted and a chemical reaction occurs. The first cooling section has a temperature of 380℃~400℃ and a machine speed of 2.5m / min, which pre-cools the green balls to prevent cracking or deformation of the product caused by rapid cooling. The second cooling stage has a temperature of 160℃~200℃ and a machine speed of 2.5m / min, which cools the green balls again.
[0017] Preferably, the finished pellets have a CaO / SiO2 ratio ≤0.3, a compressive strength greater than 2400 N / P, a Zn content <0.1%, a reduction expansion of less than 15%, and a reducibility greater than 65%.
[0018] In summary, the present invention has the following beneficial effects: 1. Achieving resource utilization of solid waste in a green and environmentally friendly manner: Metallized screen powder from rotary hearth furnaces accounts for 20-30% of the output material. Traditional disposal methods only allow for storage on-site or small-scale addition to sintering, which not only occupies a large amount of land but also poses environmental risks such as dust and heavy metal leakage. By adding it to pelletizing and roasting it in a roasting machine for reuse, this type of metallurgical solid waste can be disposed of on a large scale and on a regular basis, completely eliminating the environmental hazards caused by storage, opening up a closed loop for the resource utilization of metallurgical dust and sludge, improving the comprehensive utilization rate of solid waste in enterprises, and meeting the requirements of green production and environmental protection management.
[0019] 2. Avoiding the drawbacks of traditional processes and stabilizing production conditions: This production method overcomes many defects of existing recycling technologies and solves the problems of poor material permeability, uneven reduction, furnace bottom crusting, and reduced capacity caused by returning undersize powder to the rotary hearth furnace. At the same time, it avoids the defects of low strength, easy pulverization, high smelting energy consumption, and high risk of splashing of cold-pressed briquettes, as well as the defects of zinc alkali enrichment and blast furnace condition fluctuation caused by sintering addition, effectively ensuring stable and smooth production throughout the entire process.
[0020] 3. Effective control of harmful elements and reduction of blast furnace smelting load: The zinc content in undersize powder is as high as 1%~2.5%. Traditional sintering addition methods can lead to the accumulation of zinc in the blast furnace, causing problems such as furnace wall erosion, nodule formation, and deterioration of the permeability of the charge column when the zinc content exceeds the limit. Under the high-temperature oxidizing atmosphere of pellet roasting, some harmful elements such as zinc and alkali metals in the undersize powder can be volatilized and removed in advance, significantly reducing the content of harmful elements in the finished pellets. This reduces the zinc and alkali loads entering the furnace from the source, avoids the vicious cycle of harmful element accumulation in the blast furnace, significantly improves the smooth operation of the blast furnace, and reduces the blast furnace operation and maintenance costs and production risks.
[0021] 4. Cost Reduction and Efficiency Improvement: This production method can utilize large quantities of waste undersize powder, reducing the costs of solid waste treatment, transportation, and storage. It also replaces some iron concentrate, lowering raw material procurement costs. Compared to traditional cold-pressing briquetting, it eliminates the need for large amounts of expensive binders. The finished briquettes, formed through high-temperature solidification, exhibit high strength, low powder return rate, and high furnace recovery rate, reducing smelting energy consumption and auxiliary material losses, avoiding equipment reduction and abnormal shutdowns, and significantly improving the overall production efficiency of the ironmaking system. Detailed Implementation
[0022] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.
[0023] Example 1 The undersize powder from the rotary hearth furnace is ground in a proportion with other mineral powders, including the first, second, third, fourth, fifth, and sixth coarse ore, to obtain a self-made concentrate. This self-made concentrate, along with the first, second, and third magnetic concentrates, bentonite, and carbonaceous ash, is then mixed and processed through a counter-roller press and a high-intensity mixer to obtain a homogenized mixture. The specific surface area of this homogenized mixture is controlled to be between 1800 and 2100 cm². 2 / g, the moisture content of the mixed material is controlled at 8.5%~9.5%, and green balls are obtained by pelletizing through a disc pelletizer. The number of green balls falling is 6.7 times / 0.5m, and the green ball particle size is required to be 10~16mm, accounting for 92%.
[0024] The green pellets are sequentially fed into a belt calciner. The temperature of the blast drying section is controlled at 190℃~250℃, the temperature of the exhaust drying section is controlled at 290℃~310℃, the temperature of the preheating section is controlled at 950℃~1100℃, the temperature of the calcining section is controlled at 1100℃~1250℃, the temperature of the first cooling section is controlled at 380℃~400℃, and the temperature of the second cooling section is controlled at 160℃~200℃. The final product pellets are obtained from the rotary hearth furnace undersize screen, with CaO / SiO2 controlled at ≤0.25, compressive strength of 2984 N / P, reduction expansion of 14.6%, and reducibility of 66.2%, meeting the requirements of blast furnace production.
[0025] The group allocation examples in this embodiment 1 are shown in Table 1 below: Table 1: Material proportions in Example 1
[0026] Example 2 The powder undersize from the rotary hearth furnace is ground in a proportion with the first, second, third, fourth, fifth, and sixth coarse minerals from other mineral powders to obtain a self-made concentrate. The self-made concentrate, first magnetic concentrate, second magnetic concentrate, third magnetic concentrate, bentonite, and carbonaceous ash are then batched and processed through a counter-roll press and a high-intensity mixer to obtain a homogenized mixture. The specific surface area of the homogenized mixture is controlled between 1800 and 2100 cm². 2 / g, the moisture content of the mixed material is controlled at 8.5%~9.5%, and green balls are obtained by pelletizing through a disc pelletizer. The number of green balls falling is 6.9 times / 0.5m, and the green ball particle size is required to be 10~16mm, accounting for 92%.
[0027] The green pellets are sequentially fed into a belt calciner. The temperature of the blast drying section is controlled at 200℃~240℃, the temperature of the exhaust drying section is controlled at 290℃~310℃, the temperature of the preheating section is controlled at 950℃~1100℃, the temperature of the calcining section is controlled at 1160℃~1250℃, the temperature of the first cooling section is controlled at 380℃~400℃, and the temperature of the second cooling section is controlled at 160℃~200℃. The final product pellets are obtained from the rotary hearth furnace undersize screen, with CaO / SiO2 controlled at ≤0.27, compressive strength of 3053 N / P, reduction expansion of 14.4%, and reducibility of 65.2%, meeting the requirements of blast furnace production.
[0028] The group allocation examples in this embodiment 2 are shown in Table 2 below: Table 2: Material proportions in Example 2
[0029] Comparative Example 1 The first, second, third, fourth, fifth, and sixth coarse ores are ground to obtain a self-made concentrate. This self-made concentrate, along with the first, second, and third magnetic concentrates, rotary hearth furnace undersize powder, bentonite, and carbonaceous ash, are then mixed using a counter-roll press and a high-intensity mixer to obtain a homogenized mixture. The specific surface area of this homogenized mixture is controlled to be between 1800 and 2100 cm². 2 / g, the moisture content of the mixed material is controlled at 8.5%~9.5%, and green balls are obtained by pelletizing through a disc pelletizer. The green balls fall 4 times / 0.5m, and the green ball particle size is required to be 10~16mm, accounting for 92%.
[0030] The green pellets are sequentially fed into a belt calciner. The temperature of the forced-air drying section is controlled at 190℃~250℃, the temperature of the exhaust drying section is controlled at 290℃~310℃, the temperature of the preheating section is controlled at 950℃~1100℃, the temperature of the calcination section is controlled at 1200℃~1300℃, the temperature of the first cooling section is controlled at 380℃~400℃, and the temperature of the second cooling section is controlled at 160℃~200℃. The final product pellets are obtained by passing through the rotary hearth furnace sieve, with CaO / SiO2 controlled at ≤0.25, compressive strength of 2354 N / P, reduction expansion of 17.8%, and reducibility of 62.66%.
[0031] The difference between Comparative Example 1 and Example 1 is that the powder sieved from the rotary hearth furnace is not ground and is directly added to the mixture for pelletizing. This reduces the number of green pellets falling, allows for timely increases in the roasting temperature, and results in a decrease in the compressive strength of the finished pellets, an increase in reducing expansion, and a decrease in reducibility.
[0032] The group assignments in Comparative Example 1 are shown in Table 3 below: Table 3: Material proportions in Comparative Example 1
[0033] The method of this invention can dispose of waste undersize powder in large quantities, reducing the costs of solid waste treatment, transportation, and storage, while also replacing some iron concentrate, thus lowering raw material procurement costs. Compared to the traditional cold-pressing briquetting process, it eliminates the need for adding large amounts of expensive binders. The finished briquettes, formed by high-temperature solidification, have high strength, low powder return rate, and high furnace recovery rate, reducing smelting energy consumption and auxiliary material losses, avoiding equipment production reduction and abnormal shutdowns, and significantly improving the overall production efficiency of the ironmaking system.
[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.
Claims
1. A method for producing pellets by adding powder from a rotary hearth furnace sieve, characterized in that, The powder undersize from the rotary hearth furnace and coarse ore are ground to prepare a self-made fine powder. The self-made fine powder, magnetic fine powder, bentonite and carbonaceous ash are then uniformly mixed and extruded by a counter roller press and stirred by a high-power mixer to form a homogeneous material. The homogeneous material is then pelletized by a disc pelletizer to prepare green pellets. The green pellets are then fed into a belt roaster and roasted through a forced-air drying section, an exhaust drying section, a preheating section, a roasting section, a cooling section 1, and a cooling section 2 to finally produce pellets containing powder undersize from the rotary hearth furnace.
2. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The Zn content in the powder passing through the rotary hearth furnace screen is controlled at 1-2%.
3. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The mass fraction of the powder passing through the rotary hearth furnace in the self-made refined powder is 1-3%, and the remainder is crude ore. The crude ore is selected from one or more of limonite, goethite, or hematite.
4. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The self-made refined powder contains 61-64% TFe, 0.5-10% FeO, 5-8.5% SiO2, 1-3% CaO, 0.5-2% MgO, 1-1.8% Al2O3, with a particle size of -200 mesh not less than 80% and a specific surface area of not less than 1500 cm². 2 / kg.
5. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The carbon-containing ash shall contain no less than 25% C, no more than 6% SiO2, no less than 0.8% MgO, and no more than 4% Al2O3. The particle size of 0.5mm or smaller shall account for no less than 95%, and the specific surface area shall be no less than 2000 m². 2 / kg.
6. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The mixture contains ≥55% self-made refined powder, ≤1% bentonite, ≤3% carbon ash, and the remainder is magnetic refined powder.
7. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The proportion of green pellets with a particle size range of 10~16mm reaches more than 92%, the green pellet drop intensity is controlled at 5 times / 0.5m, and the pelletizing disc rotation speed of the disc pelletizer is 36~38r / min.
8. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The homogenized material contains 62-66% TFe, 10-30% FeO, 3-7% SiO2, 1-3% CaO, 0.1-1% MgO, 0.5-1.5% Al2O3, and 0-0.1% Zn. The specific surface area of the homogenized material is controlled at 1800-2100 cm². 2 / g, the moisture content of the mixed material is controlled at 8.5~9.5%.
9. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The temperature of the blower drying section is 200℃~260℃, and the machine speed is 2.02m / min; The temperature of the exhaust drying section is 290℃~310℃, and the machine speed is 2.5m / min; The preheating section has a temperature of 950℃~1100℃ and a machine speed of 2.5m / min; The temperature of the roasting section is 1100℃~1260℃, and the machine speed is 2.5m / min; The temperature of the first cooling section is 380℃~400℃, and the machine speed is 2.5m / min; The temperature of the two cooling sections is 160℃~200℃, and the machine speed is 2.5m / min.
10. The production method of pellets with powder from rotary hearth furnace sieves according to claim 1, characterized in that: The finished pellets contain CaO / SiO2 ≤ 0.3, compressive strength > 2400 N / P, Zn content < 0.1%, reduction expansion < 15%, and reducibility > 65%.