A rotary hearth furnace treatment method and system for metallurgical dust and sludge

Abstract

The present invention discloses a rotary hearth furnace treatment method and system for metallurgical dust sludge, which changes the traditional raw material pretreatment method. The metallurgical dust sludge is treated by ball mill grinding, disc pelletizing machine pelletizing and rotary hearth furnace reduction. The physical properties of the raw material are improved by grinding. Sodium silicate and water are added during the grinding process. Under the action of water, the sodium silicate acts as a binder to obtain metallurgical dust sludge pellets with higher strength, thereby eliminating the need for a pellet drying device. The pellets are then dehydrated and pre-reduced in a rotary hearth furnace, thereby solving the problems of large binder usage, high cost and high pulverization rate in the conventional rotary hearth furnace process.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and energy, and relates to a rotary hearth furnace treatment method and system for metallurgical dust and sludge. Background Art

[0002] The steel industry, a crucial foundation for my country's economic development, is also a major emitter of solid waste. The smelting process generates significant amounts of metallurgical dust and sludge. Statistics show that the total amount of various dusts generated by steel companies generally accounts for 8% to 15% of steel production, with zinc-containing dust accounting for approximately 20% to 30%. In 2021, China's crude steel output exceeded 1.03 billion tons. Based on this, it is estimated that zinc-containing dust generated in 2021 exceeded 20 million tons. Therefore, the proper disposal of metallurgical dust and sludge has become crucial for the sustainable development of the steel industry.

[0003] Among the current methods of treating metallurgical dust and sludge, the rotary hearth furnace process has great application value due to its good adaptability, high reliability, easy operation and maintenance, and relatively small pollution to the environment. It is more suitable for the process production of steel enterprises. However, it also has certain defects. Due to the complex types of raw materials, the raw materials need to be pretreated, and a large amount of binder needs to be added in the molding process. The quality of the pellets is poor. At the same time, the pellet pulverization rate is high during the reduction process, reaching more than 20%, and a large amount of undersize powder is produced, which ultimately leads to a significant increase in the production cost of the rotary hearth furnace and a decrease in production efficiency.

[0004] Chinese patent application number CN201810482560.3 discloses a method for treating solid waste in a rotary hearth furnace, which belongs to the technical field of solid waste treatment in steel mills and solves the problems of low grade of recovered zinc oxide powder and high pulverization rate of finished metallized pellets in the prior art. The method for treating solid waste in a rotary hearth furnace comprises the following steps: pelletizing, reduction and recovery of zinc-containing powder, and also includes a drying stage between pelletizing and reduction. The technology belongs to the conventional process of rotary hearth furnace production, which requires the consumption of a large amount of binder and produces undersize powder with a high pulverization rate.

[0005] Chinese patent application number CN202010622128.7 discloses a cold pressed block for a converter and a preparation method thereof. The cold pressed block for a converter is composed of OG mud, metallized pellet undersize powder and a binder. The weight ratio of the OG mud to the metallized pellet undersize powder is 70-90:10-30, and the ratio of the weight of the binder to the sum of the weight of the OG mud and the metallized pellet undersize powder is 2-2.5%. The particle size of the OG mud is 0-5 μm, and the metallized pellet undersize powder is 0-10 μm. The particle size of the pellet undersize powder is 0.02 to 5 mm; the particle size of the metallized pellet undersize powder is significantly larger than the particle size of the OG mud. The metallized pellet undersize powder with a larger particle size structure can provide a skeleton material for the cold-pressed blocks for the converter, and can increase the primary strength of the cold-pressed blocks for the converter with a smaller amount of binder, and reduce the return rate of the cold-pressed blocks for the converter during the processing; however, this technology only provides a method for processing the undersize powder of the rotary hearth furnace, and does not fundamentally suppress the generation of undersize powder.

[0006] Chinese patent application number CN202010765310.8 discloses an organic binder and its application, which comprises at least 60-80 parts of pregelatinized starch, 5-5 parts of polyacrylamide, 5-20 parts of white dextrin, and 5-15 parts of cellulose derivatives by weight. The organic binder provided by the present invention has a long shelf life and can be used as an intermediate for the utilization of solid waste, which can significantly reduce production costs and shorten production cycles. The amount of addition is 2.5% of the mass of the iron-containing solid waste in the steel plant. After being rolled with a 95 kg pressure ball, the wet ball strength can reach more than 300N. After drying at 200°C (assisted by 400°C strong hot air) for 25 minutes, the moisture content is controlled within 2%, and the strength of the ball can reach more than 420N. After high-temperature reduction at 1280°C in the terminal rotary hearth furnace, the ball output rate of the metallized pellets can be increased, the pulverization rate can be effectively reduced, and the pellet strength can reach more than 1800N. However, in this technology, the cost of the binder is relatively high, and the pulverization rate is reduced only by increasing the strength of the green balls, which has limited effect and high cost.

[0007] In view of the above situation, it is urgent to develop a new method for treating metallurgical dust and mud, which can solve the problems of large amount of binder, high cost and high pulverization rate in the conventional rotary hearth furnace process. Summary of the Invention

[0008] In view of the above-mentioned defects in the prior art, the purpose of the present invention is to provide a rotary hearth furnace treatment method and system for metallurgical dust sludge, which treats the metallurgical dust sludge through ball mill grinding, disc pelletizing machine pelletizing and rotary hearth furnace reduction, utilizes grinding to improve the physical properties of the raw materials, and adds sodium silicate and water during the grinding process. Under the action of water, sodium silicate acts as a binder to obtain metallurgical dust sludge pellets with higher strength, thereby eliminating the need for a pellet drying device and utilizing a rotary hearth furnace to achieve dehydration and pre-reduction of the pellets, thereby solving the problems of large binder usage, high cost and high pulverization rate in conventional rotary hearth furnace processes.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A first aspect of the present invention provides a method for treating metallurgical dust and sludge in a rotary hearth furnace, comprising the following steps:

[0011] S1, adding metallurgical dust into a ball mill for wet grinding, and adding sodium silicate and water into the ball mill during the wet grinding process to obtain a mixture;

[0012] S2, pelletizing the mixture using a disc pelletizer to obtain metallurgical dust pellets;

[0013] S3, sending the metallurgical dust pellets into a rotary hearth furnace for reduction. During the rotation of the furnace bottom of the rotary hearth furnace, the metallurgical dust pellets pass through a dehydration zone, a pre-reduction zone, a deep reduction zone and a discharge zone in sequence to obtain metallized pellets.

[0014] Preferably, in step S1:

[0015] The metallurgical dust comprises 45-50 wt% iron, 2-4 wt% zinc, 9-11 wt% carbon, 5-8 wt% water, 3-4 wt% silicon dioxide, 8-11 wt% calcium oxide, and 2.5-3.5 wt% free calcium oxide; and / or

[0016] The particle size of the metallurgical dust is 0.074 mm to 3 mm; and / or

[0017] The metallurgical dust sludge is selected from one or more of LT ash, steelmaking sludge, blast furnace dry process ash, gas mud, electric furnace ash, and converter secondary ash generated in steel plants.

[0018] Preferably, the binary basicity of the metallurgical dust is 2.6 to 3.2.

[0019] Preferably, in step S1:

[0020] The mass ratio of the metallurgical dust and sodium silicate is 100:2.5-3.5; and / or

[0021] The modulus N of the sodium silicate is 1.8 to 3.0; and / or

[0022] The metallurgical dust to which the sodium silicate is added has a binary basicity of 1.4 to 1.9; and / or

[0023] The moisture content of the mixture is 8-11 wt %.

[0024] Preferably, in step S1:

[0025] During the grinding process, the grinding time is 1.2 to 1.8 hours; and / or

[0026] The particle size of the mixture is less than 0.0325 mm, and the specific surface area is 4000-5000 cm 2 / g, binary alkalinity is 1.6-1.8, and the digestion rate of free calcium is ≥80%.

[0027] Preferably, in step S2, the 0.5 m drop strength of the metallurgical dust pellets is greater than 20 times, and the compressive strength is greater than 100N.

[0028] Preferably, in step S3:

[0029] The temperature of the dehydration zone is 400-500°C, and the pellets are kept in the dehydration zone for 5-10 minutes;

[0030] The temperature of the pre-reduction zone is 800-1000°C, and the pellets are kept in the pre-reduction zone for 4-8 minutes;

[0031] The temperature of the deep reduction zone is 1260-1280°C, and the pelletizing time in the deep reduction zone is 8-15 minutes;

[0032] The temperature of the discharging zone is 900-1000° C., and the pellets are kept in the discharging zone for 3-5 minutes.

[0033] Preferably, the compressive strength of the metallized pellets is greater than 2000N, the metallization rate is greater than 80%, the zinc removal rate is greater than or equal to 90%, and the pulverization rate is less than 5%.

[0034] Preferably, the process further comprises S4, wherein the high-temperature flue gas from the rotary hearth furnace is subjected to waste heat recovery and dust removal treatment to obtain zinc-containing dust, and the flue gas after dust removal treatment is discharged through a chimney.

[0035] A second aspect of the present invention provides a rotary hearth furnace treatment system for metallurgical dust sludge for performing the rotary hearth furnace treatment method for metallurgical dust sludge according to the first aspect of the present invention, comprising a metallurgical dust sludge bin, a sodium silicate bin, a water storage tank, a ball mill, a disc pelletizer, and a rotary hearth furnace;

[0036] The ball mill is connected to the metallurgical dust sludge bin, the sodium silicate bin and the water storage tank respectively, and is used to grind the metallurgical dust sludge, the sodium silicate and water to obtain a mixture;

[0037] The disc pelletizing machine is connected to the ball mill via a belt, and is used to pelletize the mixed material to obtain metallurgical dust pellets;

[0038] The rotary hearth furnace is connected to the disc pelletizing machine through a belt to reduce the metallurgical dust pellets; the interior of the rotary hearth furnace is provided with a dehydration zone, a pre-reduction zone, a deep reduction zone and a discharge zone in sequence; a flue gas duct is provided above the dehydration zone.

[0039] Preferably, it further comprises a waste heat boiler, a dust collector and a chimney connected to the flue gas duct of the rotary hearth furnace; the waste heat boiler, dust collector and chimney are connected by pipelines.

[0040] The rotary hearth furnace treatment method and system for metallurgical dust and sludge provided by the present invention also have the following beneficial effects:

[0041] 1. The method of the present invention changes the traditional raw material pretreatment method. Metallurgical dust is added to a ball mill and the physical properties of the metallurgical dust are improved by wet grinding, so that free calcium is quickly digested. The particle size of the mixed material after wet grinding is uniform, which is conducive to molding. In addition, the reducing agent carbon (reducing agent carbon is the carbon in the metallurgical dust) can be evenly dispersed in the material, increasing the contact between carbon and iron and zinc oxides, which is conducive to the rapid progress of the reduction reaction.

[0042] 2. The method of the present invention adds water and sodium silicate during the ball milling process. Sodium silicate acts as a binder under the action of water, replacing the conventional starch binder, greatly reducing production costs and solving the problems of large binder dosage and high cost in conventional rotary hearth furnace processes.

[0043] 3. The method of the present invention can solve the problems of slow free calcium digestion, large amount of binder and high cost in conventional rotary hearth furnace process;

[0044] 4. The method of the present invention improves material properties through moist grinding, and selects a suitable additive, sodium silicate, which acts as a binder and inhibits pulverization, thereby reducing the cost of traditional binders, eliminating the pellet drying process, effectively reducing the pulverization rate, improving production efficiency, and significantly increasing economic benefits;

[0045] 5. The method of the present invention can solve the problem of high pulverization rate in rotary hearth furnaces. The method of the present invention reduces the output of undersize powder by 75% and reduces the pulverization rate to below 5%.

[0046] 6. The present invention improves material properties and pellet strength by moist grinding and adding sodium silicate, eliminating the conventional starch binder and drying process. Digestion and mixing are achieved through a ball mill, while reducing reduction pulverization. The raw material production process of the rotary hearth furnace is changed. A small amount of sodium silicate additive acts as a binder and also reduces pulverization.

[0047] 7. The rotary hearth furnace treatment system for metallurgical dust and sludge of the present invention improves the properties of metallurgical dust and sludge by grinding in a ball mill, thereby increasing the strength of the pellets, thereby eliminating the need for a drying device. In addition, a dehydration zone, a pre-reduction zone, a deep reduction zone, and a treatment zone are provided in the rotary hearth furnace, thereby achieving dehydration and reduction of the pellets in the rotary hearth furnace, thereby saving energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0049] Figure 1 Schematic diagram of the process of the rotary hearth furnace treatment method of metallurgical dust and sludge according to the present invention;

[0050] Figure 2 The figure is a schematic structural diagram of the rotary hearth furnace treatment system for metallurgical dust and sludge according to the present invention. DETAILED DESCRIPTION

[0051] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0052] Combine Figure 1 As shown, the present invention provides a method for treating metallurgical dust and sludge in a rotary hearth furnace, comprising the following steps:

[0053] S1, adding metallurgical dust into a ball mill for wet grinding, and adding sodium silicate and water into the ball mill during the wet grinding process to obtain a mixture;

[0054] Specifically, the raw material is metallurgical dust from a steel mill. The composition of the metallurgical dust is 45-50 wt% iron, 2-4 wt% zinc, 9-11 wt% carbon, 5-8 wt% moisture, 3-4 wt% silicon dioxide, 8-11 wt% calcium oxide, and 2.5-3.5 wt% free calcium oxide. The metallurgical dust is selected from a mixture of one or more of the following: LT ash, steelmaking sludge, blast furnace dry process ash, gas sludge, electric furnace ash, and converter secondary ash. The particle size of the metallurgical dust is 0.074 mm to 3 mm, and the binary basicity is 2.6-3.2.

[0055] The metallurgical dust is first added into a ball mill for grinding. During the grinding process, sodium silicate is added according to a mass ratio of metallurgical dust to sodium silicate of 100:2.5-3.5. At the same time, a certain amount of water is added into the ball mill to obtain a mixture with a moisture content of 8-11wt%. The sodium silicate is added in solid form, the modulus N of the sodium silicate is 1.8-3.0, and the binary alkalinity of the metallurgical dust to which sodium silicate is added is 1.4-1.9. During the grinding process, the grinding time is controlled at 1.2-1.8h. The specific surface area can be increased by the grinding process, and the specific surface area of ​​the metallurgical dust can be increased from 1919 to 3200cm 2 / g increased to 4000~5000cm 2 / g, thereby improving the activity of the mixture, making the free calcium in it quickly dissipate, and the mixing uniformity reaches 99%. The solid sodium silicate is in close contact with the metallurgical dust and mud, and the bonding effect is high. After the above-mentioned grinding, the obtained mixture has a particle size of less than 0.0325mm and a specific surface area of ​​4000-5000cm 2 / g, binary alkalinity is 1.6-1.8, and the digestion rate of free calcium is ≥80%.

[0056] During the above-mentioned grinding process, the free calcium in the metallurgical dust is rapidly degraded, and the degrading reaction is as follows: CaO+H2O=Ca(OH)2.

[0057] S2, using a disc pelletizer to pelletize the mixed material to obtain metallurgical dust pellets;

[0058] Specifically, the mixture discharged from the ball mill is pelletized using a disc pelletizer, in which sodium silicate plays a bonding role, eliminating the step of externally preparing starch binder, thereby obtaining metallurgical dust pellets. The 0.5m drop strength of the metallurgical dust pellets is greater than 20 times, which is more than 4 times higher than that of conventional processes (the 0.5m drop strength of pellets using conventional binders is less than 5 times), and the compressive strength is greater than 100N, which is more than 2 times higher than that of wet balls prepared by conventional processes. The pelletizing cost is reduced by 20% compared with the conventional pelletizing process.

[0059] S3, the metallurgical dust pellets are sent to a rotary hearth furnace for reduction. During the rotation of the furnace bottom of the rotary hearth furnace, the metallurgical dust pellets pass through a dehydration zone, a pre-reduction zone, a deep reduction zone and a discharge zone in sequence to obtain metallized pellets.

[0060] Specifically, due to the high strength of the pellets prepared by the damp grinding process, the drying device can be omitted, and the metallurgical dust pellets are directly sent to the rotary hearth furnace for reduction. The rotary hearth furnace is divided into a dehydration zone, a pre-reduction zone, a deep reduction zone and a discharge zone. During the production process, the walls and upper part of the rotary hearth furnace are stationary, and the pellets rotate with the land and pass through each zone in turn. During the rotation of the rotary hearth furnace, the metallurgical dust pellets pass through the dehydration zone, pre-reduction zone, deep reduction zone and discharge zone in turn, and finally obtain metallized pellets.

[0061] During the reduction process in the rotary hearth furnace, the dehydration zone is heated to 400-500°C, and the dust pellets remain in the dehydration zone for 5-10 minutes. This temperature effectively prevents the pellets from bursting due to excessive vapor pressure from the dewatering process. The pre-reduction zone is heated to 800-1000°C, and the dehydrated dust pellets remain in the pre-reduction zone for 4-8 minutes. In this zone, zinc is initially removed from the pellets, while the iron oxide in the pellets is pre-reduced to ferrous oxide. Some of the ferrous oxide reacts with sodium silicate and silica in the dust to form ferric silicate. At this temperature, the ferric silicate is in a semi-liquid phase, binding the pellet particles together and preventing them from breaking and pulverizing. The temperature in the deep reduction zone is 1260-1280°C, and the pre-reduced metallurgical dust pellets remain in the deep reduction zone for 8-15 minutes. Once in this zone, under high-temperature conditions, ferrous oxide and ferric silicate are rapidly reduced to metallic iron by carbon and CO. Silicon dioxide and calcium oxide further react to produce dicalcium silicate and tricalcium silicate phases, which help enhance the strength of the metallized pellets and further remove residual zinc. The temperature in the discharge zone is 900-1000°C, and the reduced metallized pellets remain in this zone for 3-5 minutes before being discharged from the discharge zone.

[0062] The mixing uniformity of the ordinary mixing process does not exceed 80%. Due to the use of the moist grinding process in this method, the mixing uniformity of the mixture reaches more than 99%, which can make the reducing agent carbon more evenly dispersed in the material system, thereby promoting the rapid reduction reaction and avoiding the powdering phenomenon caused by uneven carbon and incomplete local reduction.

[0063] The compressive strength of the metallized pellets prepared above is greater than 2000N, the metallization rate is greater than 80%, the zinc removal rate is ≥90%, and the pulverization rate is less than 5%. The pulverization rate of this method is reduced by more than 75% compared with the conventional process, and is reduced to a pulverization rate of less than 5%.

[0064] The above method further includes S4, wherein the high-temperature flue gas from the rotary hearth furnace is subjected to waste heat recovery and dust removal treatment to obtain zinc-containing dust, and the dust-removed flue gas is discharged from a chimney.

[0065] Combine Figure 2As shown, the present invention also provides a rotary hearth furnace treatment system for metallurgical dust sludge, which is used to implement the above-mentioned rotary hearth furnace treatment method for metallurgical dust sludge. The system comprises a metallurgical dust sludge bin 1, a sodium silicate bin 2, a water storage tank 3, a ball mill 4, a disc pelletizer 5, and a rotary hearth furnace 6. The ball mill 4 is connected to the metallurgical dust sludge bin 1, the sodium silicate bin 2, and the water storage tank 3, respectively. The ball mill 4 is used to grind the metallurgical dust sludge, sodium silicate, and water to produce a mixture. The disc pelletizer 5 is connected to the ball mill 4 via a belt and is used to pelletize the mixture into metallurgical dust pellets. The rotary hearth furnace 6 is connected to the disc pelletizer 5 via a belt and is used to reduce the metallurgical dust pellets. The rotary hearth furnace 6 is sequentially provided with a dehydration zone, a pre-reduction zone, a deep reduction zone, and a discharge zone. A flue gas duct is provided above the dehydration zone.

[0066] Combine Figure 2 As shown, the rotary hearth furnace treatment system for metallurgical dust and sludge further includes a waste heat boiler 7, a dust collector 8 and a chimney 9 connected to the flue gas duct of the rotary hearth furnace 6; the waste heat boiler 7, the dust collector 8 and the chimney 9 are connected by pipelines.

[0067] The following further describes the rotary hearth furnace treatment method and system for metallurgical dust and sludge of the present invention with reference to specific examples.

[0068] Example 1

[0069] The rotary hearth furnace treatment method for metallurgical dust and sludge in this embodiment includes the following steps:

[0070] (1) Metallurgical dust sludge is made from dry ash from steel mill blast furnaces, steelmaking sludge, electric furnace ash, gas sludge, and secondary converter ash. Its composition is as follows: iron content is 45%, zinc content is 2.3%, carbon content is 9.5%, moisture content is 5%, calcium oxide content is 8.5%, silicon dioxide content is 3%, binary basicity is 2.8, and free calcium content is 2.7%. The particle size of the metallurgical dust sludge ranges from 3mm to 0.074mm.

[0071] (2) Metallurgical dust and sodium silicate were milled in a ball mill at a mass ratio of 100:3.5. A certain amount of water was added during the milling process. The milling time was 1.8 h. The modulus of sodium silicate was N=1.8. The moisture content of the mixture obtained after milling was 8.8%, the binary alkalinity was 1.6, and the particle size of the mixture after milling was <0.0325 mm. The specific surface area was increased from 3000 cm before milling to 1.5 cm. 2 Increased to 4900cm 2 , the free calcium digestion rate reaches 80%.

[0072] (3) The mixture discharged from the ball mill is pelletized using a disc pelletizer, and the metallurgical dust pellets obtained have a 0.5 m drop strength of 21.5 times and a compressive strength of 102 N;

[0073] (4) The metallurgical dust pellets enter the rotary hearth furnace for reduction. The temperature of the dehydration zone of the rotary hearth furnace is controlled at 400°C, and the pellets stay in the dehydration zone for 9.5 minutes. The temperature of the pre-reduction zone is controlled at 850°C, and the pellets stay in the pre-reduction zone for 7.5 minutes. The temperature of the deep reduction zone is controlled at 1280°C, and the pellets stay in the deep reduction zone for 8 minutes. The temperature of the discharge zone is controlled at 1000°C, and the pellets stay in the discharge zone for 5 minutes. The metallized pellets are discharged from the discharge zone of the rotary hearth furnace. The high-temperature flue gas of the rotary hearth furnace is recovered by the waste heat boiler and then enters the dust collector for dust removal. After meeting the standards, it is discharged through the chimney.

[0074] The compressive strength of the metallized pellets prepared in this example is 2580 N, the metallization rate is 85%, the zinc removal rate is 92%, and the pulverization rate is 4.7%.

[0075] Example 2

[0076] The rotary hearth furnace treatment method for metallurgical dust and sludge in this embodiment includes the following steps:

[0077] (1) Metallurgical dust sludge is made from dry ash from steel mill blast furnaces, steelmaking sludge, LT ash, gas sludge, and secondary converter ash. Its composition is as follows: iron content is 47%, zinc content is 3.2%, carbon content is 10.2%, moisture content is 6.4%, calcium oxide content is 10.3%, silicon dioxide content is 3.3%, binary basicity is 3.13, and free calcium content is 3.3%. The particle size of the metallurgical dust sludge ranges from 3 mm to 0.074 mm.

[0078] (2) Metallurgical dust and sodium silicate were milled in a ball mill at a mass ratio of 100:3. A certain amount of water was added during the milling process. The milling time was 1.5 h. The modulus of sodium silicate was N = 2.4. The moisture content of the mixture obtained after milling was 9.7%, the binary alkalinity was 1.8, the particle size of the mixture after milling was <0.0325 mm, and the specific surface area was increased from 2500 cm before milling to 1.500 cm. 2 Increased to 4500cm 2 , the free calcium digestion rate reached 82%.

[0079] (3) The mixed material discharged from the ball mill was pelletized using a disc pelletizer, and the obtained metallurgical dust pellets had a 0.5 m drop strength of 23.6 times and a compressive strength of 104 N;

[0080] (4) The metallurgical dust pellets enter the rotary hearth furnace for reduction. The temperature of the dehydration zone of the rotary hearth furnace is controlled at 450°C, and the pellets stay in the dehydration zone for 7 minutes. The temperature of the pre-reduction zone is controlled at 930°C, and the pellets stay in the pre-reduction zone for 6 minutes. The temperature of the deep reduction zone is controlled at 1270°C, and the pellets stay in the deep reduction zone for 12 minutes. The temperature of the discharge zone is controlled at 980°C, and the pellets stay in the discharge zone for 4 minutes. The metallized pellets are discharged from the discharge zone of the rotary hearth furnace. The high-temperature flue gas of the rotary hearth furnace is recovered by the waste heat boiler and then enters the dust collector for dust removal. After meeting the standards, it is discharged through the chimney.

[0081] The compressive strength of the metallized pellets prepared in this example is 2560 N, the metallization rate is 83%, the zinc removal rate is 91%, and the pulverization rate is 4.5%.

[0082] Example 3

[0083] The rotary hearth furnace treatment method for metallurgical dust and sludge in this embodiment includes the following steps:

[0084] (1) Metallurgical dust sludge is made from dry ash from steel mill blast furnaces, steelmaking sludge, LT ash, and gas sludge. Its composition is as follows: iron content is 49%, zinc content is 3.8%, carbon content is 11%, moisture content is 8%, calcium oxide content is 11%, silicon dioxide content is 3.9%, binary basicity is 3.13, and free calcium content is 3%. The particle size of the metallurgical dust sludge ranges from 3mm to 0.074mm.

[0085] (2) Metallurgical dust and sodium silicate were milled in a ball mill at a mass ratio of 100:2.5. A certain amount of water was added during the milling process. The milling time was 1.2 h. The sodium silicate modulus N was 3. The moisture content of the mixture obtained after milling was 11.5%, the binary alkalinity was 1.8, the particle size of the mixture after milling was <0.0325 mm, and the specific surface area was increased from 2000 cm before milling to 1.50 cm. 2 Increased to 4200cm 2 , the free calcium digestion rate reaches 85%.

[0086] (3) The mixed material discharged from the ball mill is pelletized using a disc pelletizer, and the obtained metallurgical dust pellets have a 0.5 m drop strength of 24 times and a compressive strength of 112 N;

[0087] (4) The metallurgical dust pellets enter the rotary hearth furnace for reduction. The temperature of the dehydration zone of the rotary hearth furnace is controlled at 500°C, and the pellets stay in the dehydration zone for 5 minutes. The temperature of the pre-reduction zone is controlled at 1000°C, and the pellets stay in the pre-reduction zone for 4.5 minutes. The temperature of the deep reduction zone is controlled at 1260°C, and the pellets stay in the deep reduction zone for 15 minutes. The temperature of the discharge zone is controlled at 900°C, and the pellets stay in the discharge zone for 3 minutes. The metallized pellets are discharged from the discharge zone of the rotary hearth furnace. The high-temperature flue gas of the rotary hearth furnace is recovered by the waste heat boiler and then enters the dust collector for dust removal. After meeting the standards, it is discharged through the chimney.

[0088] The metallized pellets prepared in this example had a compressive strength of 242 N, a metallization rate of 81%, a zinc removal rate of 90%, and a pulverization rate of 3.9%.

[0089] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for treating metallurgical dust and sludge in a rotary hearth furnace, characterized in that: The following steps are involved: S1, adding metallurgical dust into a ball mill for wet grinding, and adding sodium silicate and water into the ball mill during the wet grinding process to obtain a mixture; The metallurgical dust has an iron content of 45-50 wt%, a zinc content of 2-4 wt%, a carbon content of 9-11 wt%, a moisture content of 5-8 wt%, a silicon dioxide content of 3-4 wt%, a calcium oxide content of 8-11 wt%, and a free calcium oxide content of 2.5-3.5 wt%; The mass ratio of the metallurgical dust and sodium silicate is 100:2.5-3.5; The modulus N of the sodium silicate is 1.8 to 3.0; The dibasic basicity of the metallurgical dust to which the sodium silicate is added is 1.4 to 1.9; The moisture content of the mixture is 8-11 wt%; During the grinding process, the grinding time is 1.2 to 1.8 hours; The particle size of the mixture is less than 0.0325 mm, and the specific surface area is 4000-5000 cm 2 / g, binary alkalinity is 1.6-1.8, and the digestion rate of free calcium is ≥80%; S2, pelletizing the mixture using a disc pelletizer to obtain metallurgical dust pellets; S3, feeding the metallurgical dust pellets into a rotary hearth furnace for reduction. During the rotation of the furnace bottom of the rotary hearth furnace, the metallurgical dust pellets sequentially pass through a dehydration zone, a pre-reduction zone, a deep reduction zone, and a discharge zone to obtain metallized pellets; The temperature of the dehydration zone is 400-500°C, and the pellets are kept in the dehydration zone for 5-10 minutes; The temperature of the pre-reduction zone is 800-1000°C, and the pellets are kept in the pre-reduction zone for 4-8 minutes; The temperature of the deep reduction zone is 1260-1280°C, and the pelletizing time in the deep reduction zone is 8-15 minutes; The temperature of the discharge zone is 900-1000°C, and the pellets are kept in the discharge zone for 3-5 minutes; The compressive strength of the metallized pellets is greater than 2000N, the metallization rate is greater than 80%, the zinc removal rate is greater than or equal to 90%, and the pulverization rate is less than 5%.

2. The rotary hearth furnace treatment method for metallurgical dust and sludge according to claim 1, characterized in that: In the step S1: The particle size of the metallurgical dust is 0.074 mm to 3 mm; The metallurgical dust sludge is selected from one or more of LT ash, steelmaking sludge, blast furnace dry process ash, gas mud, electric furnace ash, and converter secondary ash generated in steel plants.

3. The rotary hearth furnace treatment method for metallurgical dust and sludge according to claim 2, characterized in that: The binary basicity of the metallurgical dust is 2.6 to 3.

2.

4. The rotary hearth furnace treatment method for metallurgical dust and sludge according to claim 1, characterized in that: In the step S2, the metallurgical dust pellets have a 0.5 m drop strength greater than 20 times and a compressive strength greater than 100N.

5. The rotary hearth furnace treatment method for metallurgical dust and sludge according to claim 1, characterized in that: The process further comprises S4, wherein the high-temperature flue gas from the rotary hearth furnace is subjected to waste heat recovery and dust removal treatment to obtain zinc-containing dust, and the flue gas after the dust removal treatment is discharged through a chimney.

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