Rotary kiln steelmaking dust sludge dezincification process

Abstract

The invention discloses a dezincification process for steelmaking dust sludge of a rotary kiln, and belongs to the technical field of metallurgical solid waste resource utilization. According to the method, Fe2O3 in the dust sludge is preliminarily reduced into Fe3O4 and a small amount of FeO through the coke powder, H2 is generated through lignite pyrolysis to replace part of C for reduction, and efficient reduction and separation of zinc and iron in the dust sludge through carbon-hydrogen compounding in the rotary kiln are achieved. According to the method, the brown coal is excessively added, so that ferric oxide in the raw materials is fully reacted, meanwhile, oxygen is isolated by controlling the state of the kiln head, kiln slag is recycled after being cooled, FeO is prevented from being formed again, the ring forming phenomenon of the rotary kiln is relieved, and then the continuous working time of the rotary kiln is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical solid waste resource utilization technology, specifically relating to a zinc removal process for dust and sludge in rotary kiln steelmaking. Background Technology

[0002] With the continuous increase in steel production, the amount of iron- and zinc-containing dust and sludge generated is increasing year by year. Existing technologies are insufficient for the efficient recycling and utilization of this iron- and zinc-containing dust and sludge, resulting not only in resource waste but also irreparable environmental damage. Targeted and rational recycling of the metals in iron- and zinc-containing dust and sludge could bring considerable economic benefits to enterprises. Therefore, it is necessary to seek reasonable technological processes to effectively treat this iron- and zinc-containing dust and sludge.

[0003] While mature technologies exist both domestically and internationally for extracting zinc from iron- and zinc-containing dust, simultaneous iron recovery remains challenging. A domestic steel company faces the problem of processing large quantities of iron- and zinc-containing dust, characterized by low zinc content but rich iron and carbon resources. After comprehensive consideration, a rotary kiln was chosen for its recovery. The rotary kiln process, a pyrometallurgical method, requires heating at a specific temperature to achieve simultaneous iron and zinc recovery. However, ring formation is a common problem during rotary kiln operation, especially as the temperature increases, raising the likelihood of ring formation.

[0004] Therefore, how to provide a process that can reduce iron and zinc in iron- and zinc-containing dust and alleviate ring formation in rotary kilns has become an urgent problem to be solved. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a zinc removal process for rotary kiln steelmaking dust and sludge. This process utilizes H2 generated from lignite pyrolysis to replace part of the C reduction, achieving efficient reduction and separation of zinc and iron in the dust and sludge through carbon-hydrogen composites within the rotary kiln. By controlling the kiln head state to isolate oxygen and cooling the kiln slag before recycling, the process avoids the formation of FeO, alleviates the ring formation phenomenon in the rotary kiln, and thus extends the continuous operating time of the rotary kiln.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A process for zinc removal from dust and sludge in rotary kiln steelmaking includes the following steps: S1, the dust, coke powder, and binder are mixed with water to form raw materials, and the raw materials are fed into the rotary kiln from the kiln tail. The lignite is fed into the calcination zone of the rotary kiln from the kiln head. The mass ratio of the dust, coke powder, binder and lignite is 100:5-6:4-5:15-20. S2, the raw material is heated to 850-900°C in the drying preheating zone; S3, the raw material is heated to 1000-1300℃ in the calcination zone and maintained for 10-30 minutes to obtain Zn steam and kiln slag; S4, in the calcination zone, Zn vapor is recovered; S5, when the kiln slag enters the recycling zone, the kiln head is sealed; S6, cool the recycling belt for 40-60 minutes, and the temperature of the recycling belt after cooling is ≤120℃; S7, Open the kiln head and remove the kiln slag.

[0007] Based on the above technical solution, the rotary kiln is further provided with a blower at the kiln head and an induced draft fan at the kiln tail, and the lignite is sprayed onto the calcination zone through a spray gun.

[0008] Based on the above technical solution, the kiln tail temperature is further 450-500℃.

[0009] Based on the above technical solution, the raw material is a pellet with a diameter of 25-50mm made by a disc pelletizing method.

[0010] Based on the above technical solution, the Zn vapor is further recovered through a flue gas recovery system, and the Zn vapor is cooled into Zn powder. The Zn powder is then collected after being cooled to 180-200°C.

[0011] Based on the above technical solution, the recycling belt is further cooled by circulating cooling water pipes.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses coke powder to initially reduce Fe2O3 in dust and sludge to Fe3O4 and a small amount of FeO, and then uses H2 generated by the pyrolysis of lignite to replace part of the C reduction, thereby achieving efficient reduction and separation of zinc and iron in dust and sludge by carbon-hydrogen composite in a rotary kiln.

[0013] 2. This invention allows for the full reaction of iron oxide in the raw materials by adding excessive amounts of lignite. At the same time, by controlling the state of the kiln head to isolate oxygen and cooling the kiln slag before recycling, the re-formation of FeO is avoided, thus alleviating the ring formation phenomenon in the rotary kiln and extending the continuous working time of the rotary kiln. Attached Figure Description

[0014] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0015] Figure 1 This is a flowchart illustrating the overall process of this invention. Figure 2 This is a schematic diagram of the rotary kiln structure of the present invention; In the diagram: 1. Kiln tail; 2. Drying zone; 3. Preheating zone; 4. Calcination zone; 5. Recovery zone; 6. Kiln head; 7. Exhaust fan; 8. Blower; 9. Pellet; 10. Lignite; 11. Circulating cooling water pipe; 12. Flue gas recovery system. Detailed Implementation

[0016] This invention provides a process for zinc removal from dust and sludge in rotary kiln steelmaking, such as... Figure 1 As shown, it includes the following steps: S1, the dust, coke powder, binder and water are mixed evenly to make raw materials, the raw materials are sent from the kiln tail to the rotary kiln, and the lignite is sent from the kiln head to the calcination zone of the rotary kiln. The mass ratio of dust, coke powder, binder and lignite is 100:5-6:4-5:15-20. S2, the raw material is heated to 850-900℃ in the drying and preheating zone; S3, the raw material is heated to 1000-1300℃ in the calcination zone and maintained for 10-30 minutes to obtain Zn steam and kiln slag; S4, in the calcination zone, recovers Zn vapor; S5, when kiln slag enters the recycling zone, the kiln head is sealed; S6, cool the recovery belt for 40-60 minutes, and the temperature of the recovery belt after cooling is ≤120℃; S7, open the kiln head and remove the kiln slag.

[0017] In the drying and preheating zone, coke powder acts as a reducing agent to reduce some of the Fe2O3 in the dust and mud to Fe3O4 and a small amount of FeO. At the same time, coke powder also acts as a heating agent to assist in raising the temperature.

[0018] In this process, lignite releases H2 during calcination, which acts as a reducing agent to reduce Fe and Zn in the raw materials.

[0019] The mass ratio of dust and sludge to lignite is 100:15-20, which ensures that the excess lignite can effectively consume the oxygen in the kiln when the kiln head is sealed, thus preventing the metals in the kiln slag from being oxidized.

[0020] The kiln head is sealed when the kiln slag enters the recovery zone and is opened only after the recovery zone cools down to below 120°C. This effectively prevents the metal in the kiln slag from being oxidized, which not only improves the metallization rate of the kiln slag but also alleviates the ring formation phenomenon in the rotary kiln.

[0021] The drying and preheating zone includes a drying zone and a preheating zone. After the raw materials are dried in the drying zone, they enter the preheating zone where they begin to heat up.

[0022] In some embodiments, a blower is provided at the kiln head of the rotary kiln and an induced draft fan is provided at the kiln tail of the rotary kiln, and lignite is sprayed into the calcination zone through a spray gun.

[0023] The blower and induced draft fan work together to assist in the air circulation from the kiln head to the kiln tail, providing sufficient oxygen for the reaction inside the kiln.

[0024] In some embodiments, the kiln tail temperature is 450-500℃.

[0025] In some embodiments, the raw material is pellets with a diameter of 25-50 mm produced by a disc pelletizing method.

[0026] In some embodiments, Zn vapor is recovered through a flue gas recovery system, and the Zn vapor is cooled into Zn powder. The Zn powder is then collected after being cooled to 180-200°C.

[0027] In some embodiments, the recycling belt is cooled by circulating cooling water pipes.

[0028] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0029] Example 1 In this embodiment, zinc removal was performed on sludge with a TFe content of 44.83%, a Zn content of 3.17%, and particle sizes as shown in Table 1. The calcination temperature was controlled at 1000℃, and the metallization rate and dezincification rate of the kiln slag were observed by varying the calcination time.

[0030] Table 1: .

[0031] The dezincification process is as follows: 1. Mix dust, coke powder, and bentonite with water evenly, and make pellets with a diameter of 25mm using a disc pelletizing method. Feed the pellets into the rotary kiln from the kiln tail, and feed lignite into the calcination zone of the rotary kiln from the kiln head. The mass ratio of dust, coke powder, binder and lignite is 100:5:4:15. Among them, coke powder has a fixed carbon content of 83.82% and a volatile matter content of 1.79%; lignite has a fixed carbon content of 38.14% and a volatile matter content of 32.36%.

[0032] 2. The pellets are heated to 900℃ in the drying preheating zone; 3. The raw materials are heated to 1000℃ in the calcination zone and maintained for 5 min, 10 min, 15 min, 20 min, 25 min or 30 min to obtain Zn steam and kiln slag; 4. In the calcination zone, Zn vapor is recovered through a flue gas recovery system, and the Zn vapor is cooled into Zn powder. The Zn powder is then collected after being cooled to 180°C. 5. When the kiln slag enters the recycling zone, the kiln head is sealed; 6. Cool the recycling belt for 40 minutes. After cooling, the temperature of the recycling belt should be ≤120℃. 7. Open the kiln head and remove the kiln slag.

[0033] The amounts of TFe, MFe, Zn, and ZnO in the kiln slag were determined by chemical titration.

[0034] The formula for calculating the metallization rate is shown in formula (1): (1).

[0035] In the formula, η Fe MFe represents the metallization rate, MFe represents the metallic iron content, and TFe represents the total iron content.

[0036] The formula for calculating the zinc removal rate is shown in formula (2): (2).

[0037] In the formula, η Zn m1 represents the zinc removal rate, m2 represents the zinc content of the dust and sludge, and m2 represents the zinc content of the kiln slag.

[0038] Table 2 shows the metallization rate and dezincification rate of the kiln slag. With increasing reduction time, the zinc removal rate rapidly increased from 66.93% to 93.22%, then decreased from 93.22% to 88.36%; the iron metallization rate increased from 90.84% ​​to 96.66%, then decreased from 96.66% to 91.89%, but both remained above 90%.

[0039] Table 2: .

[0040] The results showed that when the calcination time was 10-30 min, the metallization rate and dezincification rate remained at a high level, which could effectively remove and recover Fe and Zn.

[0041] Example 2 In this embodiment, zinc removal was performed on sludge with a TFe content of 44.83%, a Zn content of 3.17%, and particle sizes as shown in Table 1. The calcination time was controlled at 10 minutes, and the metallization rate and dezincification rate of the kiln slag were observed by changing the calcination temperature.

[0042] The dezincification process is as follows: 1. Mix dust, coke powder, and bentonite with water evenly, and make pellets with a diameter of 50mm using a disc pelletizing method. Feed the pellets into the rotary kiln from the kiln tail, and feed lignite into the calcination zone of the rotary kiln from the kiln head. The mass ratio of dust, coke powder, binder and lignite is 100:6:5:20. Among them, coke powder has a fixed carbon content of 83.82% and a volatile matter content of 1.79%; lignite has a fixed carbon content of 38.14% and a volatile matter content of 32.36%.

[0043] 2. The pellets are heated to 850℃ in the drying preheating zone; 3. The raw material is heated to 900℃, 1000℃, 1100℃, 1200℃ or 1300℃ in the calcination zone and maintained for 10 minutes to obtain Zn steam and kiln slag. 4. In the calcination zone, Zn vapor is recovered through a flue gas recovery system, and the Zn vapor is cooled into Zn powder. The Zn powder is then collected after being cooled to 200°C. 5. When the kiln slag enters the recycling zone, the kiln head is sealed; 6. Cool the recycling belt for 40 or 60 minutes, and the temperature of the recycling belt after cooling shall be ≤120℃; 7. Open the kiln head and remove the kiln slag.

[0044] The process for obtaining the metallization rate and dezincification rate of kiln slag is the same as in Example 1, and will not be repeated here.

[0045] The metallization rate and dezincification rate of kiln slag are shown in Table 3. With the increase of temperature, the dezincification rate increased from 58.15% to 95.52%, and then decreased from 95.52% to 95.43%; the metallization rate rapidly increased from 33.67% to 95.52%, and then gradually decreased to 91.62%, but both remained above 90%.

[0046] Table 3: .

[0047] The results show that at calcination temperatures of 1000-1300℃, both the metallization rate and the dezincification rate remain at a high level, which can effectively remove and recover Fe and Zn.

[0048] Example 3 This embodiment evaluates the mitigation effect of the rotary kiln steelmaking dust and sludge dezincification process provided by the present invention on the ring formation phenomenon in rotary kilns by statistically analyzing the continuous operating time of the rotary kiln in this process and the comparative process.

[0049] 1. The difference between this zinc removal process and Example 1 is that the calcination time is fixed at 10 minutes. The rotary kiln ran continuously for 108 days, and obvious ring formation was observed.

[0050] 2. The difference between this zinc removal process and the previous one is that the former did not seal the kiln head or cool the recovery zone. After five days of continuous operation, the rotary kiln showed obvious ring formation.

[0051] The comparison of the two processes shows that the rotary kiln steelmaking dust and sludge dezincification process provided by this invention can effectively alleviate the ring formation phenomenon in the rotary kiln and extend the continuous operation time of the rotary kiln.

[0052] Example 4 This embodiment evaluates the influence of FeO in the slag on the ring formation phenomenon in rotary kilns by statistically analyzing the continuous operating time of rotary kilns in this process and the comparative process.

[0053] 1. The difference between this zinc removal process and Example 1 is that the calcination time is fixed at 10 minutes. The rotary kiln ran continuously for 108 days without significant ring formation.

[0054] 2. The difference between this zinc removal process and the previous one is that the mass ratio of dust to lignite is 100:5. After the rotary kiln ran continuously for 5 days, obvious ring formation was observed.

[0055] The 100:5 mass ratio of dust to lignite prevents the FeO in the dust from being fully reduced, leading to an increase in the FeO content in the kiln slag.

[0056] The comparison of the two processes shows that the reduction of FeO content in the kiln slag alleviates the ring formation phenomenon in the rotary kiln and extends the continuous operation time of the rotary kiln.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A zinc removal process for dust and sludge in rotary kiln steelmaking, characterized in that, Includes the following steps: S1, the dust, coke powder, and binder are mixed with water to form raw materials, and the raw materials are fed into the rotary kiln from the kiln tail. The lignite is fed into the calcination zone of the rotary kiln from the kiln head. The mass ratio of the dust, coke powder, binder and lignite is 100:5-6:4-5:15-20. S2, the raw material is heated to 850-900°C in the drying preheating zone; S3, the raw material is heated to 1000-1300℃ in the calcination zone and maintained for 10-30 minutes to obtain Zn steam and kiln slag; S4, in the calcination zone, Zn vapor is recovered; S5, when the kiln slag enters the recycling zone, the kiln head is sealed; S6, cool the recycling belt for 40-60 minutes, and the temperature of the recycling belt after cooling is ≤120℃; S7, Open the kiln head and remove the kiln slag.

2. The zinc removal process for rotary kiln steelmaking dust and sludge according to claim 1, characterized in that, The rotary kiln is equipped with a blower at the kiln head and an induced draft fan at the kiln tail. The lignite is sprayed into the calcination zone through a spray gun.

3. The zinc removal process for rotary kiln steelmaking dust and sludge according to claim 1, characterized in that, The kiln tail temperature is 450-500℃.

4. The zinc removal process for rotary kiln steelmaking dust and sludge according to claim 1, characterized in that, The raw material is pellets with a diameter of 25-50mm produced by a disc pelletizing method.

5. The zinc removal process for rotary kiln steelmaking dust and sludge according to claim 1, characterized in that, The Zn vapor is recovered through a flue gas recovery system, and the Zn vapor is cooled into Zn powder. The Zn powder is then collected after being cooled to 180-200°C.

6. The zinc removal process for rotary kiln steelmaking dust and sludge according to claim 1, characterized in that, The recycling belt is cooled by circulating cooling water pipes.

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