A method and system for treating zinc-containing solid waste sludge

Abstract

The application discloses a kind of zinc-containing solid waste dust sludge treatment method and system, by controlling the carbon-oxygen ratio in raw material, the different physicochemical properties of raw material are utilized, the on-site production digestion process is optimized by granulation and pelletizing process, and the properties of high viscosity of OG mud are fully utilized, the binder is saved, the cost is greatly reduced, then the pellets prepared by granulation and pelletizing process are subjected to direct reduction reaction and indirect reduction reaction respectively at high temperature, the utilization efficiency of carbon in blast furnace secondary ash is improved, and carbon emission is reduced.

Description

A method and system for treating zinc-containing solid waste dust and sludge Technical Field

[0001] This invention belongs to the field of metallurgical dust and sludge resource utilization, and relates to a method and system for treating zinc-containing solid waste dust and sludge. Background Technology

[0002] The steel industry is a crucial foundation for my country's economic development and a major contributor to solid waste emissions. The smelting process generates substantial amounts of metallurgical dust and sludge. Statistics show that steel companies typically generate 8% to 15% of all dust produced, with zinc-containing dust accounting for approximately 20% to 30%. Based on 2022 data, steel companies generate over 20 million tons of zinc-containing dust annually. Without proper treatment, this would cause environmental pollution and resource waste. Therefore, the rational disposal of metallurgical dust and sludge has become a critical issue for the sustainable development of the steel industry.

[0003] To build a resource recycling system and strengthen the comprehensive utilization of bulk solid waste, the iron and steel metallurgical industry promotes the "solid waste not leaving the factory" policy. By utilizing advanced technologies and strengthening full-scale utilization, carbon dioxide emissions can be effectively reduced, contributing to China's goal of "carbon peaking and carbon neutrality".

[0004] Currently, among the methods for treating metallurgical dust and sludge, the rotary hearth furnace process has significant application value due to its good adaptability, high reliability, ease of operation and maintenance, and relatively low environmental pollution, making it more suitable for the process-oriented production of steel enterprises. In conventional rotary hearth furnace processes, metallurgical dust, sludge, binders, and water are usually mixed evenly, then pressed into pellets or granulated, dried, and fed into the rotary hearth furnace for reduction dezincification; the carbon-to-oxygen ratio of the raw materials used is controlled above 0.9. Electric arc furnace ash and LT ash, which are dry dust from steelmaking processes, are the main raw materials in metallurgical dust and sludge. These often contain a large amount of free calcium oxide. If pelletizing is carried out directly without pre-treatment or with low degree of pre-treatment, the f-CaO in the electric arc furnace ash and LT ash hydrates into Ca(OH)2 in the mixture, leading to pellet volume expansion, strength deterioration, and pulverization. A large amount of binder needs to be added to ensure pellet strength. Therefore, optimizing the on-site production digestion and pelletizing process is of great practical significance for improving rotary hearth furnace output and product quality, reducing production costs, and reducing carbon emissions. Summary of the Invention

[0005] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a method and system for treating zinc-containing solid waste dust and sludge. By controlling the carbon-oxygen ratio in the raw materials and utilizing their different physicochemical properties, the on-site production digestion process is optimized through granulation and pelletizing processes. Furthermore, the high viscosity of OG sludge is fully utilized, eliminating the need for binders and significantly reducing costs. Subsequently, the pellets prepared by the granulation and pelletizing processes are subjected to direct and indirect reduction reactions at high temperatures, respectively, thereby improving the carbon utilization efficiency in blast furnace secondary ash and reducing carbon emissions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a method for treating zinc-containing solid waste sludge, comprising the following steps:

[0008] S1, granulation: Zinc-containing solid waste dust and sludge are mixed and granulated with blast furnace secondary ash in a cylindrical granulator to obtain carbon-containing pellets; during the granulation process, water is added to the cylindrical granulator to promote the decomposition of free calcium in the zinc-containing solid waste dust and sludge.

[0009] S2, pelletizing: The carbon-containing small pellets enter the disc pelletizer and undergo secondary pelletizing with OG sludge to obtain secondary pellets; during the pelletizing process, water is added to the disc pelletizer to promote the further decomposition of free calcium in the zinc-containing solid waste dust and sludge.

[0010] S3, Drying, drying the secondary pellets to obtain dried pellets;

[0011] S4, Rotary hearth furnace reduction: The dried pellets are fed into the rotary hearth furnace. After being preheated in the heating zone of the rotary hearth furnace, the dried pellets enter the reduction zone of the rotary hearth furnace for reduction to obtain metallized pellets. During the reduction process, the carbon-containing small pellets in the OG mud coating layer of the dried pellets undergo a direct reduction reaction. The CO generated during the direct reduction reaction undergoes an indirect reduction reaction with the iron oxide and zinc oxide in the OG mud layer of the dried pellets.

[0012] Preferably, in step S1:

[0013] The zinc-containing solid waste sludge has an iron content of 42-48%, a zinc content of 2-5%, and a free calcium content of 3-4.5%, wherein the iron exists in the form of iron oxide and the zinc exists in the form of zinc oxide; and / or

[0014] The zinc-containing solid waste sludge includes one or more of electric furnace ash, LT ash, and converter secondary ash; and / or

[0015] The carbon content in the secondary blast furnace ash is 18-25%; and / or

[0016] The secondary blast furnace ash and zinc-containing solid waste dust are mixed and granulated at a carbon-to-oxygen ratio of 0.6 to 0.7.

[0017] Preferably, in step S1:

[0018] The carbon-containing pellets have a moisture content of 9–13 wt%; and / or

[0019] The carbon-containing microspheres have a particle size of 4–6 mm.

[0020] Preferably, in step S2:

[0021] The OG sludge is wet dust removal sludge produced during converter steelmaking, with a moisture content of 30-35%. Before entering the disc pelletizer, the OG sludge is dried to below 5 wt% and crushed to below 200 mesh by a crusher; and / or

[0022] The ratio of the OG mud to the carbon-containing pellets is 3-3.5:2; and / or

[0023] The diameter of the secondary pellets is 10–13 mm; and / or

[0024] The moisture content of the secondary pellets is 9–13 wt%; and / or

[0025] The digestion rate of free calcium in the secondary pellets reaches over 50%.

[0026] Preferably, in step S3, the drop intensity of the dried pellets at 0.5m is greater than 10 times.

[0027] Preferably, in step S4:

[0028] During the rotary hearth furnace reduction process, the temperature of the rotary hearth furnace is 1150–1280℃; and / or

[0029] During the rotary hearth furnace reduction process, a reducing atmosphere is used inside the furnace, and the concentration of CO in the reducing atmosphere is 15-25%; and / or

[0030] The rotary hearth furnace takes 20 to 28 minutes to complete one revolution.

[0031] Preferably, in step S4:

[0032] During the direct reduction reaction, iron oxide in the carbon-containing pellets is reduced to metallic iron and CO, and zinc oxide in the carbon-containing pellets is reduced to zinc vapor and CO.

[0033] In the indirect reduction reaction, the CO generated in the direct reduction reaction reduces the iron oxide in the carbon-containing pellets to metallic iron and CO2, and the CO generated in the direct reduction reaction reduces the zinc oxide in the carbon-containing pellets to zinc vapor and CO2.

[0034] Preferably, in step S4, the iron metallization rate of the metallized pellets is >80%; and / or

[0035] The dezincification rate of the dried pellets is >90%.

[0036] A second aspect of the present invention provides a zinc-containing solid waste sludge treatment system for performing the zinc-containing solid waste sludge treatment method as described in the first aspect of the present invention, comprising:

[0037] A cylindrical granulator is used to mix and granulate zinc-containing solid waste dust and blast furnace secondary ash, and to promote the decomposition of free calcium in the zinc-containing solid waste dust. The cylindrical granulator is equipped with a metallurgical dust silo and a blast furnace secondary ash silo, and is connected to a water tank.

[0038] OG mud treatment device for drying and crushing OG mud; the OG mud treatment device includes an OG mud silo, a drying cylinder connected to the OG mud silo, and a crusher connected to the drying cylinder;

[0039] A disc pelletizer is used to perform secondary pelletizing of carbon-containing small pellets prepared by the cylindrical pelletizer and OG sludge obtained by the crusher, and to further promote the decomposition of free calcium in zinc-containing solid waste dust and sludge; the disc pelletizer is connected to the discharge port of the cylindrical pelletizer and the outlet of the crusher respectively; the disc pelletizer is provided with a water inlet connected to a water tank;

[0040] A drying device is used to dry the secondary pellets prepared by the disc pelletizer; the drying device is connected to the discharge port of the disc pelletizer.

[0041] A rotary hearth furnace is used to reduce the dried pellets obtained from the drying device. The rotary hearth furnace is provided with a heating zone, a reduction zone and a discharge zone in sequence, and partition walls are provided between the heating zone, the reduction zone and the discharge zone.

[0042] Preferably, the time for the rotary hearth furnace to complete one revolution is 20 to 28 minutes.

[0043] The zinc-containing solid waste dust and sludge treatment method and system provided by this invention also have the following beneficial effects:

[0044] 1. The zinc-containing solid waste dust and sludge treatment method and system of the present invention improves the carbon utilization efficiency in blast furnace secondary ash and reduces carbon emissions by controlling the carbon-oxygen ratio of the raw materials and using a combination of direct reduction and indirect reduction.

[0045] 2. The zinc-containing solid waste dust and sludge treatment method and system of the present invention fully dissolves free calcium online through granulation and pelletizing processes, so that the free calcium dissolution rate in zinc-containing solid waste dust and sludge reaches more than 50%, which solves the problem of separate dissolution of free calcium in zinc-containing solid waste dust and sludge, and at the same time eliminates the influence of free calcium reaction with water on the strength of the pellets.

[0046] 3. The zinc-containing solid waste dust and sludge treatment method and system of the present invention fully utilizes the high viscosity of OG sludge by preparing secondary pellets through granulation and pelletizing processes, and eliminates the need for external binders by using OG sludge coating method, which greatly reduces production costs.

[0047] 4. The zinc-containing solid waste dust and sludge treatment method and system of the present invention can effectively reduce the carbon emissions in the zinc-containing solid waste dust and sludge process. For every ton of zinc-containing solid waste dust and sludge treated, the carbon emissions are reduced by 95-143 kg. Using the technology of the present invention, a rotary hearth furnace production line with a disposal capacity of 250,000 tons can reduce carbon emissions by 2,300-3,500 tons per year and save 8,500 tons of binder. Attached Figure Description

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

[0049] Figure 1 is a schematic diagram of the zinc-containing solid waste dust and sludge treatment system of the present invention. Detailed Implementation

[0050] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0051] Referring to Figure 1, the present invention provides a method for treating zinc-containing solid waste sludge, comprising the following steps:

[0052] S1, granulation: Zinc-containing solid waste dust and sludge are mixed and granulated with secondary blast furnace ash in a cylindrical granulator 1 to obtain carbon-containing pellets; during the granulation process, water is added to the cylindrical granulator 1 to promote the dissolution of free calcium in the zinc-containing solid waste dust and sludge.

[0053] Specifically, blast furnace secondary ash and zinc-containing solid waste sludge are first mixed and granulated in a cylindrical granulator 1 at a carbon-oxygen ratio of 0.6 to 0.7, with the moisture content controlled at 9 to 13 wt%. During the granulation process, as the free calcium in the zinc-containing solid waste sludge absorbs water through decomposition, water needs to be continuously added to the cylindrical granulator 1 to promote the decomposition of free calcium in the zinc-containing solid waste sludge. The particles that come out of the cylindrical granulator 1 are carbon-containing small pellets with a particle size of 4 to 6 mm and a moisture content of 9 to 13 wt%.

[0054] The iron content of zinc-containing solid waste sludge is 42-48%, the zinc content is 2-5%, and the free calcium content is 3-4.5%, with iron and zinc mainly existing in the form of iron oxide and zinc oxide. Zinc-containing solid waste sludge includes one or more dry-process ashes containing free calcium, such as electric furnace ash, LT ash, and converter secondary ash.

[0055] The carbon content in secondary blast furnace ash is 18-25%.

[0056] S2, pelletizing: Carbon-containing small pellets enter the disc pelletizer 4 and undergo secondary pelletizing with OG sludge to obtain secondary pellets; During the pelletizing process, water is added to the disc pelletizer 4 to promote the further decomposition of free calcium in zinc-containing solid waste dust and sludge;

[0057] Specifically, the carbon-containing pellets from the cylindrical pelletizer 1 enter the disc pelletizer 4 for secondary pelletizing with OG sludge to obtain secondary pellets. During the pelletizing process, water needs to be continuously added to the cylindrical pelletizer 1 to further replenish the water absorbed by the free calcium during the pelletizing process, so as to promote the further dissolution of free calcium in the zinc-containing solid waste dust and sludge. The diameter of the secondary pellets from the disc pelletizer 4 is 10-13 mm, the moisture content is 9-13 wt%, and the dissolution rate of free calcium in the secondary pellets reaches more than 50%.

[0058] OG sludge is a wet dust removal sludge produced during the converter steelmaking process. This material contains a large amount of flocculant and has strong viscosity. It adheres to the small pellets coming out of the disc pelletizer 4 and the cylindrical pelletizer 1, forming a coating layer on the outside of the small pellets. This coating layer improves the strength of the pellets and replaces the binder. The moisture content of OG sludge is 30-35%. Therefore, before entering the disc pelletizer 4, OG sludge needs to be dried and crushed to a moisture content of less than 5 wt%, and then crushed to less than 200 mesh by the crusher 3. In a specific embodiment, the ratio of OG sludge to carbon-containing small pellets is 3-3.5:2.

[0059] S3, Drying, drying the secondary pellets to obtain dried pellets;

[0060] Specifically, the secondary pellets from the disc granulator are dried in the drying device 5 to obtain dried pellets with a moisture content of less than 5 wt%. The dried pellets have a drop strength of more than 10 times at 0.5 m, which fully meets the production requirements of the rotary hearth furnace 6.

[0061] S4, Rotary hearth furnace 6 reduction: The dried pellets are fed into the rotary hearth furnace 6 and preheated in heating zone A of the rotary hearth furnace 6 before entering the reduction zone B of the rotary hearth furnace 6 for reduction to obtain metallized pellets; During the reduction process, the carbon-containing small pellets in the OG mud coating layer of the dried pellets undergo a direct reduction reaction, and the CO generated during the direct reduction reaction undergoes an indirect reduction reaction with the iron oxide and zinc oxide in the OG mud layer of the dried pellets.

[0062] Specifically, the dried pellets are fed into a rotary hearth furnace 6. In heating zone A of the furnace 6, the pellets are preheated and their water of crystallization is removed. The pores formed during the evaporation of the water of crystallization facilitate the subsequent diffusion of carbon monoxide. The preheated pellets then enter reduction zone B of the furnace 6 for reduction. During reduction, the temperature of the furnace 6 is 1150–1280°C, and the furnace rotates once every 20–28 minutes. The furnace 6 is divided into heating zone A, reduction zone B, and discharge zone C. The pellets spend 2–3 minutes in heating zone A and 2–3 minutes in discharge zone C. The temperature in heating zone A is approximately 1150°C.

[0063] Dry pellets are reduced under high-temperature conditions to obtain metallized pellets. During this process, carbon-containing small pellets within the OG sludge coating of the dried pellets undergo a direct reduction reaction. Iron oxide in the zinc-containing solid waste dust is reduced to metallic iron and CO, and zinc oxide is reduced to zinc vapor and CO. The specific reactions are as follows:

[0064] Fe₂O₃ + 3C = 3CO↑ + 2Fe

[0065] ZnO + C = CO + Zn↑

[0066] During the direct reduction reaction, the CO generated reacts indirectly with iron oxide and zinc oxide in the dried pellet OG sludge layer during its escape. The iron oxide in the OG sludge layer is reduced to metallic iron and CO2, while the zinc oxide is reduced to zinc vapor and CO2. The specific reactions are as follows:

[0067] Fe₂O₃ + 3CO → 3CO₂↑ + 2Fe

[0068] ZnO + CO = CO2 + Zn↑

[0069] During the reduction process, the upper part of the dried pellets is in a reducing atmosphere with a CO concentration of 15-25%. This reducing atmosphere ensures the reduction of iron and zinc oxides (iron oxide and zinc oxide) in the OG mud layer of the secondary pellets.

[0070] The metallized pellets obtained after the above-mentioned dried pellets are reduced by rotary hearth furnace 6 have an iron metallization rate of >80% and a dezincification rate of >90%.

[0071] Referring to Figure 1, the present invention also provides a zinc-containing solid waste dust and sludge treatment system for performing the above-mentioned zinc-containing solid waste dust and sludge treatment method. Specifically, the zinc-containing solid waste dust and sludge treatment system of the present invention includes a cylindrical granulator 1, an OG sludge treatment device, a disc pelletizer 4, a drying device 5, and a rotary hearth furnace 6. The cylindrical granulator 1 is used to mix and granulate the zinc-containing solid waste dust and sludge with blast furnace secondary ash, and to promote the dissolution of free calcium in the zinc-containing solid waste dust and sludge. The cylindrical granulator 1 is equipped with a metallurgical dust and sludge silo 11 and a blast furnace secondary ash silo 12, and is connected to a water tank 13. The metallurgical dust and sludge silo 11 is used to hold the zinc-containing solid waste dust and sludge, and the blast furnace secondary ash silo 12 is used to hold the blast furnace secondary ash. The OG sludge treatment unit is used to dry and crush OG sludge to meet the requirements for subsequent pelletizing. This unit includes an OG sludge silo 14, a drying cylinder 2 connected to the silo 14, and a crusher 3 connected to the drying cylinder 2. A disc pelletizer 4 is used to perform secondary pelletizing of the carbon-containing pellets prepared by the cylindrical granulator 1 and the OG sludge obtained from the crusher 3, further promoting the dissolution of free calcium in the zinc-containing solid waste dust. The disc pelletizer 4 is connected to the discharge port of the cylindrical granulator 1 and the outlet of the crusher 3. The disc pelletizer has an inlet connected to a water tank 13. A drying unit 5 is used to dry the secondary pellets prepared by the disc pelletizer 4; this drying unit 5 is connected to the discharge port of the disc pelletizer. The rotary hearth furnace 6 is used to reduce the dried pellets obtained by the drying device 5. The rotary hearth furnace 6 is provided with heating zone A, reduction zone B and discharge zone C in sequence, and partition walls are provided between heating zone A, reduction zone B and discharge zone C.

[0072] In a specific embodiment, the time for the rotary hearth furnace 6 to complete one revolution is 20 to 28 minutes.

[0073] In conventional rotary hearth furnace 6 processes, the carbon-to-oxygen ratio is around 0.9. The carbon emissions from the reducing agent reach 0.43 tons when treating 1 ton of zinc-containing solid waste sludge. The zinc-containing solid waste sludge treatment method and system of this invention directly utilizes a combination of direct and indirect reduction methods to control the carbon-to-oxygen ratio at 0.6–0.7, reducing carbon emissions by 95–143 kg per ton of solid waste treated. Simultaneously, by employing a novel OG sludge-wrapping and secondary molding method, external binders are eliminated. Granulation and secondary pelletizing processes enable rapid decomposition of free calcium, saving costs. Using this technology, a 250,000-ton capacity rotary hearth furnace 6 production line can reduce carbon emissions by 0.23–0.35 tons annually and save 0.85 tons of binder.

[0074] The following describes a zinc-containing solid waste dust and sludge treatment method and system of the present invention in further detail with specific examples;

[0075] Example 1

[0076] The method for treating zinc-containing solid waste dust and sludge in this embodiment is as follows:

[0077] The zinc-containing solid waste dust and sludge are made from dry ash and other solid waste from steel plants with an iron content of 42%, a zinc content of 2%, and a free calcium content of 3%, and secondary blast furnace ash with a carbon content of 18%. The secondary blast furnace ash and zinc-containing solid waste dust and sludge are mixed and granulated at a carbon-oxygen ratio of 0.6, with the moisture content controlled at 9%. The granulation results in carbon-containing pellets of 4mm to 6mm that come out of the cylindrical granulator.

[0078] The small pellets from the cylindrical pelletizer enter the disc pelletizer and OG mud for secondary pelletizing. The OG mud has a moisture content of 30-35%, which needs to be pre-dried to below 5% and crushed to below 200 mesh. The secondary pellets obtained after secondary pelletizing have a diameter of 10-13 mm, a moisture content of 10%, and a free calcium dissolution rate of over 50%.

[0079] After being dried in a drying device, the secondary pellets are sent to a rotary hearth furnace for reduction. The dried pellets undergo a 0.5m drop test with a strength of 15 cycles. The furnace temperature is 1150–1280℃, and one revolution takes 28 minutes. During reduction, the upper part of the dried pellets is exposed to a reducing atmosphere with a CO concentration of 15–25%. This reducing atmosphere ensures the reduction of iron and zinc oxides in the OG sludge layer. After reduction in the rotary hearth furnace, the dried pellets are metallized, with a metallization rate of 81% and a dezincification rate of 90.5%.

[0080] Example 2

[0081] The method for treating zinc-containing solid waste dust and sludge in this embodiment is as follows:

[0082] The zinc-containing solid waste dust and sludge are made from dry ash and other solid waste from steel plants with an iron content of 45%, a zinc content of 3%, and a free calcium content of 3.8%, and secondary blast furnace ash with a carbon content of 22%. The secondary blast furnace ash and zinc-containing solid waste dust and sludge are mixed and granulated at a carbon-oxygen ratio of 0.65, with the moisture content controlled at 11%. The granulation results in carbon-containing pellets of 4mm to 6mm from the cylindrical granulator.

[0083] The small pellets from the cylindrical pelletizer enter the disc pelletizer and OG mud for secondary pelletizing. The OG mud has a moisture content of 30-35%, which needs to be pre-dried to below 5% and crushed to below 200 mesh. The secondary pellets obtained after secondary pelletizing have a diameter of 10-13 mm, a moisture content of 11%, and a free calcium dissolution rate of over 50%.

[0084] After being dried in a drying device, the secondary pellets are sent to a rotary hearth furnace for reduction. The dried pellets have a drop strength of 13.5 times from 0.5m, the furnace temperature is 1150–1280℃, and one revolution takes 28 minutes. During the reduction process, the upper part of the dried pellets is exposed to a reducing atmosphere with a CO concentration of 15–25%, which ensures the reduction of iron and zinc oxides in the OG sludge layer. After reduction in the rotary hearth furnace, the dried pellets are metallized, with a metallization rate of 83.2% and a dezincification rate of 91.4%.

[0085] Example 3

[0086] The method for treating zinc-containing solid waste dust and sludge in this embodiment is as follows:

[0087] The zinc-containing solid waste dust and sludge are made from dry ash and other solid waste from steel plants with an iron content of 48%, a zinc content of 5%, and a free calcium content of 4.5%, and secondary blast furnace ash with a carbon content of 24%. The secondary blast furnace ash and zinc-containing solid waste dust and sludge are mixed and granulated at a carbon-oxygen ratio of 0.7, with the moisture content controlled at 13%. The granulation results in carbon-containing pellets of 4mm to 6mm from the cylindrical granulator.

[0088] The small pellets from the cylindrical pelletizer enter the disc pelletizer and OG mud for secondary pelletizing. The OG mud has a moisture content of 30-35%, which needs to be pre-dried to below 5% and crushed to below 200 mesh. The secondary pellets obtained after secondary pelletizing have a diameter of 10-13 mm, a moisture content of 13%, and a free calcium dissolution rate of over 50%.

[0089] After being dried in a drying device, the secondary pellets are sent to a rotary hearth furnace for reduction. The dried pellets have a drop strength of 11.3 times from 0.5m, the furnace temperature is 1150–1280℃, and one revolution takes 28 minutes. During the reduction process, the upper part of the pellets is exposed to a reducing atmosphere with a CO concentration of 15–25%, which ensures the reduction of iron and zinc oxides in the OG sludge layer. After reduction in the rotary hearth furnace, the dried pellets are metallized, with a metallization rate of 85.1% and a dezincification rate of 92.7%.

[0090] In summary, the zinc-containing solid waste dust and sludge treatment method and system of the present invention fully utilizes the high viscosity of OG sludge through the secondary pellets produced by granulation and pelletizing processes, eliminating the need for binders and greatly reducing costs. Furthermore, the granulation and pelletizing processes achieve a free calcium dissipation rate of over 50% in the zinc-containing solid waste dust and sludge, eliminating the impact of free calcium reaction with water on pellet strength. In addition, the secondary pellets produced by granulation and pelletizing processes are fed into a rotary hearth furnace where direct and indirect reduction reactions are carried out separately under high-temperature conditions, improving the carbon utilization efficiency in the secondary blast furnace ash, reducing the carbon-oxygen ratio of the raw materials, and decreasing carbon emissions.

[0091] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for treating zinc-containing solid waste dust and sludge, characterized in that, Includes the following steps: S1, Granulation: Zinc-containing solid waste dust and blast furnace secondary ash are mixed and granulated in a cylindrical granulator to obtain carbon-containing pellets; during the granulation process, water is added to the cylindrical granulator to promote the dissolution of free calcium in the zinc-containing solid waste dust; the blast furnace secondary ash and zinc-containing solid waste dust are mixed and granulated at a carbon-to-oxygen ratio of 0.6-0.7; the carbon content in the blast furnace secondary ash is 18-25%; the particle size of the carbon-containing pellets exiting the cylindrical granulator is 4-6 mm, and the moisture content is 9-13 wt%; S2, Pelletizing... The carbon-containing small pellets are fed into a disc pelletizer and undergo secondary pelletizing with OG sludge to obtain secondary pellets. During the pelletizing process, water is added to the disc pelletizer to further promote the dissolution of free calcium in the zinc-containing solid waste dust. The ratio of OG sludge to carbon-containing small pellets is 3–3.5:

2. The secondary pellets exiting the disc pelletizer have a diameter of 10–13 mm and a moisture content of 9–13 wt%. The dissolution rate of free calcium in the secondary pellets reaches over 50%. S3, drying: The secondary pellets are dried to obtain dried pellets. The dried pellets have a drop strength of more than 10 times at 0.5m; S4, rotary hearth furnace reduction: the dried pellets are fed into the rotary hearth furnace, and after preheating in the heating zone of the rotary hearth furnace, they enter the reduction zone of the rotary hearth furnace for reduction to obtain metallized pellets; during the rotary hearth furnace reduction process, the carbon-containing small pellets in the OG mud coating layer of the dried pellets undergo a direct reduction reaction, and the CO generated in the direct reduction reaction undergoes an indirect reduction reaction with the iron oxide and zinc oxide in the OG mud coating layer of the dried pellets. During the direct reduction reaction, the iron oxide in the carbon-containing small pellets is reduced to metallic iron and CO, and the zinc oxide in the carbon-containing small pellets is reduced to zinc vapor and CO; during the indirect reduction reaction, the CO generated in the direct reduction reaction reduces the iron oxide in the carbon-containing small pellets to metallic iron and CO2, and the CO generated in the direct reduction reaction reduces the zinc oxide in the carbon-containing small pellets to zinc vapor and CO2; the iron metallization rate of the metallized pellets is >80%; the dezincification rate of the dried pellets is >90%.

2. The method for treating zinc-containing solid waste dust and sludge according to claim 1, characterized in that, In step S1: the zinc-containing solid waste sludge has an iron content of 42-48%, a zinc content of 2-5%, and a free calcium content of 3-4.5%, wherein the iron exists in the form of iron oxide and the zinc exists in the form of zinc oxide; and / or the zinc-containing solid waste sludge includes one or more of electric furnace ash, LT ash, and converter secondary ash.

3. The method for treating zinc-containing solid waste dust and sludge according to claim 1, characterized in that, In step S2: the OG sludge is wet dust removal sludge produced during the converter steelmaking process, with a moisture content of 30-35%; before the OG sludge enters the disc pelletizer, its moisture content is dried to below 5wt% and crushed to below 200 mesh by a crusher.

4. The method for treating zinc-containing solid waste dust and sludge according to claim 1, characterized in that, In step S4: during the rotary hearth furnace reduction process, the temperature of the rotary hearth furnace is 1150–1280°C; and / or during the rotary hearth furnace reduction process, a reducing atmosphere is used inside the rotary hearth furnace, and the concentration of CO in the reducing atmosphere is 15–25%; and / or the time for the rotary hearth furnace to rotate one revolution is 20–28 minutes.

5. A zinc-containing solid waste dust and sludge treatment system for performing the zinc-containing solid waste dust and sludge treatment method as described in any one of claims 1 to 4, characterized in that, The system includes a cylindrical granulator for mixing and granulating zinc-containing solid waste dust and blast furnace secondary ash, and promoting the dissolution of free calcium in the zinc-containing solid waste dust; the cylindrical granulator is equipped with a metallurgical dust silo and a blast furnace secondary ash silo, and is connected to a water tank; an OG sludge treatment device for drying and crushing OG sludge; the OG sludge treatment device includes an OG sludge silo, a drying cylinder connected to the OG sludge silo, and a crusher connected to the drying cylinder; and a disc pelletizer. This device is used to perform secondary pelletizing of carbon-containing small pellets prepared by the cylindrical pelletizer and OG sludge obtained by the crusher, and to further promote the decomposition of free calcium in zinc-containing solid waste dust and sludge; the disc pelletizer is connected to the discharge port of the cylindrical pelletizer and the outlet of the crusher; the disc pelletizer is provided with a water inlet connected to a water tank; a drying device is used to dry the secondary pellets prepared by the disc pelletizer; the drying device is connected to the discharge port of the disc pelletizer; A rotary hearth furnace is used to reduce the dried pellets obtained from the drying device. The rotary hearth furnace is provided with a heating zone, a reduction zone and a discharge zone in sequence, and partition walls are provided between the heating zone, the reduction zone and the discharge zone.

6. The zinc-containing solid waste dust and sludge treatment system according to claim 5, characterized in that, The rotary hearth furnace takes 20 to 28 minutes to complete one revolution.

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