A device and method for converting zinc-containing dust sludge into high value-added products using joule heat

Abstract

The application provides a device and method for converting zinc-containing dust sludge into high-value-added products by using Joule heat, relates to the technical field of zinc-containing dust sludge treatment, and aims to solve the problems of low treatment efficiency and poor product purity of traditional zinc-containing dust sludge treatment. By using the Joule heat method, the zinc in the zinc-containing dust sludge is removed, and metal iron and zinc products are simultaneously prepared by adjusting parameters such as voltage, current and reaction time. The process has high zinc removal efficiency, and the obtained metal products have excellent purity. Moreover, the process has the advantages of short time consumption, simple process, higher efficiency and environmental protection compared with traditional methods, and can realize high-value resource recycling of the zinc-containing dust sludge.

Description

Technical Field

[0001] This invention relates to the field of zinc-containing dust and sludge treatment technology, specifically to an apparatus and method for converting zinc-containing dust and sludge into high-value-added products using Joules. Background Technology

[0002] As a fundamental industry supporting national economic development, the steel industry plays an indispensable role in numerous fields such as construction, machinery manufacturing, and transportation. During various stages of steelmaking, such as blast furnace ironmaking, converter steelmaking, and electric arc furnace steelmaking, a large amount of industrial dust and sludge is generated, with zinc-containing dust and sludge being a prime example. This type of zinc-containing dust and sludge not only has a considerable annual output but also contains a high proportion of iron and zinc. From a resource perspective, zinc-containing dust and sludge is a recyclable secondary resource. However, due to the presence of zinc, existing production processes within steel companies make it difficult to directly recycle and reuse it, resulting in large quantities of zinc-containing dust and sludge being stockpiled for extended periods. This not only occupies valuable land resources but also poses a serious threat to the ecological environment due to factors such as rainwater runoff and wind dispersion, causing soil, water, and air pollution. Therefore, developing efficient, economical, and environmentally friendly zinc-containing dust and sludge treatment technologies to achieve its resource recovery and harmless disposal is of crucial practical significance for promoting the green and low-carbon development of the steel industry and improving resource utilization efficiency.

[0003] Currently, the mainstream technology for treating zinc-containing dust and sludge in industry is pyrometallurgical processes, with rotary kiln and rotary hearth furnace processes being the most widely used. The rotary kiln process, with its mature technology, holds a certain market share in zinc-containing dust and sludge treatment. This process typically involves mixing zinc-containing dust and sludge with appropriate amounts of reducing agents and fluxes, then feeding it into a rotary kiln for high-temperature roasting and reduction. During the reduction process, the zinc element in the dust and sludge volatilizes as zinc vapor, which is then collected and recovered through a collection system. The remaining iron-containing material can be returned to the blast furnace as raw material for ironmaking. However, the rotary kiln process is not only extremely energy-intensive, but the resulting iron-containing product generally has a low degree of metallization, making it difficult to meet the raw material quality requirements of subsequent blast furnace ironmaking. More importantly, rotary kilns often experience ring formation during operation, where a hard, adhered layer forms on the inner wall of the kiln. This not only reduces the effective space inside the kiln and decreases processing capacity, but also increases equipment energy consumption and may even require shutdown for cleaning, severely affecting the continuity and stability of production. Rotary hearth furnace technology, as another mainstream pyrometallurgical process, has seen increasing application in the resource utilization of zinc-containing dust and sludge in recent years. The core of this process involves mixing zinc-containing dust and sludge with reducing agents and binders to form green pellets. These green pellets are then dried and fed into the rotary hearth furnace, where a reduction reaction is completed under high-temperature conditions, achieving the recovery of zinc volatilization and the metallization of iron. While the rotary hearth furnace process offers advantages such as relatively wide raw material adaptability and short processing cycles, it also suffers from several insurmountable drawbacks. Firstly, the rotary hearth furnace uses gas or pulverized coal combustion for heating, with heat transferred to the material inside the furnace through furnace wall radiation and flue gas convection. This indirect heating method results in significant heat loss with flue gas emissions, leading to substantial heat loss and generally low energy utilization. Secondly, to ensure uniform heating, the material inside the rotary hearth furnace is typically laid in a single layer or a few layers, resulting in insufficient utilization of the furnace space and low space utilization. Furthermore, the large-scale use of traditional energy sources and their high carbon emissions are also major drawbacks.

[0004] To address the problems existing in rotary hearth furnace processes, the industry has conducted relevant research and improvements. For example, Chinese patent publication CN113073198A discloses a method for efficiently treating zinc-containing dust and sludge. This relates to methods for dust and sludge recycling in the metallurgical industry, particularly a method for treating zinc-containing dust and sludge. It boasts low unit energy consumption and high dust and sludge recycling rate. However, this method is still based on the traditional indirect heating principle and fails to fundamentally change the problem of low heat transfer efficiency, resulting in limited improvement in energy utilization in practical applications. Another example is Chinese patent publication CN110788113A, which discloses a space optimization device for rotary hearth furnaces. This device aims to improve space utilization by setting up multi-layer material-bearing structures inside the furnace. However, the multi-layer structure design makes the airflow distribution and temperature field control inside the furnace more complex, easily leading to uneven heating of materials in different layers, which in turn affects product quality.

[0005] Overall, both rotary kiln and rotary hearth furnace processes, as existing pyrometallurgical processes, generally suffer from a series of common problems. In terms of cost, pyrometallurgical processes rely heavily on fossil fuels such as coal and natural gas, resulting in high fuel costs. Furthermore, production costs are difficult to control effectively due to fluctuations in energy prices. Regarding energy consumption, indirect heating methods lead to high heat transfer energy consumption. Combined with heat loss from flue gas and cooling wastewater, this results in significant heat loss and persistently high energy consumption per unit of product. In terms of space utilization, limitations in heating methods and material handling requirements lead to dispersed equipment layouts, insufficient space integration, large land footprints, and increased land use costs and infrastructure investment. In terms of environmental protection, the large-scale combustion of fossil fuels produces substantial amounts of carbon dioxide, resulting in high carbon emissions. This contradicts the current national "dual carbon" goals and fails to meet the requirements for green and low-carbon development in the steel industry. These shortcomings severely restrict the efficient, economical, and environmentally friendly application of pyrometallurgical processes in the treatment of zinc-containing dust and sludge, prompting the industry to urgently seek a new technology to overcome the bottlenecks of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to provide an apparatus and method for converting zinc-containing dust into high-value-added products using Joules, so as to solve the problems mentioned in the background art.

[0007] This invention provides the following technical solution: a method for converting zinc-containing dust into high-value-added products using Joules, comprising the following steps:

[0008] S1 Preparation of carbon-based conductive reducing agent: Biochar is obtained by roasting biomass and mixed with industrial coke powder and coal powder in proportion;

[0009] S2 raw material drying and mixing: Zinc-containing dust and conductive reducing agent are dried to a moisture content of ≤2% and then mixed evenly;

[0010] S3 Joule self-terminating reaction: The mixed raw materials are fed into the reaction zone via a chain drive, mechanical load is applied to form a reaction body, and green electricity is passed through in an inert atmosphere to trigger the Joule effect. The reaction ends after a certain period of time.

[0011] S4 Crushing and Separation: The product is crushed and screened to obtain metallic iron particles and carbon-rich slag phase;

[0012] S5 Zinc Recovery: Zinc vapor is cooled and recovered to obtain high-purity metallic zinc.

[0013] Preferably, in step S1, biomass is crushed and calcined at 700-900℃ in an inert atmosphere for 30 minutes to prepare the conductive reducing agent. The mass percentages of each component are 10%-50% biochar, 30%-100% industrial coke powder, and 0%-20% coal powder.

[0014] Preferably, in step S2, the zinc-containing dust has a particle size of < 0.1 mm and a moisture content of < 6%, and the ratio of zinc-containing dust to conductive reducing agent is 70~100:20~40.

[0015] The present invention also provides a device for the Joule heat treatment of zinc-containing dust and sludge, specifically including a chain drive system, a Joule heat heating drive system, a sample reaction tank, a zinc cooling and recovery device, a crusher and a screening machine, with each component linked together in sequence to form a complete process operation link;

[0016] The chain drive system is used to realize the continuous transmission of raw materials from feeding to the output of post-reaction products;

[0017] The Joule heating drive system includes a DC power supply, a controllable current source, and a fixed electrode. The fixed electrode is set in relation to the sample reaction cell and is used to apply pulse impact to the raw material in the reaction cell and trigger the Joule effect.

[0018] The sample reaction cell is equipped with an upper static load input structure, and uses a hydraulic device to provide mechanical pressure load. The lower part of the cell has an integrated zinc product output port.

[0019] The zinc cooling and recovery device is connected to the lower outlet of the sample reaction cell and is used to receive zinc vapor carried by the inert gas flow and achieve rapid cooling and condensation.

[0020] The crusher and screening machine are connected in sequence to dissociate and classify the reaction products for recovery.

[0021] Preferably, the sample reaction cell adopts a closed furnace structure, and the inner cavity of the furnace is an inert atmosphere cavity to ensure that there is no oxidation interference during the reaction process.

[0022] Preferably, the zinc cooling and recovery device has a built-in condensation airflow channel, and a collection well is set at the channel outlet to collect the condensed zinc particles by gravity-driven sedimentation.

[0023] Preferably, the chain drive system includes a feeder, a transmission and conveying unit, and a discharge mechanism. Multiple independent sample reaction tanks are evenly distributed on the transmission and conveying unit to achieve continuous batch processing.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. Existing technologies generally rely on indirect heat transfer methods, which inevitably involve energy losses during thermal radiation, thermal conduction, or thermal convection, resulting in low energy utilization efficiency. This application innovatively utilizes the Joule effect to directly conduct current through zinc-containing dust and sludge, thereby realizing the conversion of electrical energy into heat energy. This method completely breaks free from the constraints of traditional heat transfer paths, fundamentally eliminating energy losses from indirect heat transfer and significantly improving energy utilization efficiency.

[0026] 2. Existing technologies have large equipment footprints and dispersed system layouts, requiring significant factory space. However, this application is based on the principle of direct heating, which eliminates the need for excessively large spatial structures. The raw material space is the reaction space, achieving a compact heating layout, significantly improving factory space utilization, and reducing the company's site construction and operating costs.

[0027] 3. Existing zinc-containing dust and sludge treatment technologies are prone to introducing impurities into the products due to limitations in heating methods and process paths, which affects the purity of the products and thus limits their subsequent high-value-added utilization. However, this application uses direct heating based on the Joule effect and green clean energy to avoid the introduction of external impurities, resulting in a significant improvement in the purity of the zinc- and iron-containing products, greatly enhancing the added value of the products and creating higher economic benefits for enterprises.

[0028] 4. This application clearly states that green electricity can be used as a heating energy source, which greatly reduces carbon emissions caused by heating and is in line with the national green and low-carbon industry development direction. Attached Figure Description

[0029] Figure 1 Bar graphs showing the zinc removal efficiency of comparative examples 1, 2, and 3;

[0030] Figure 2 Bar graphs showing the zinc removal efficiency of comparative examples 6, 5, 4, and 3;

[0031] Figure 3 Bar graphs showing the zinc removal efficiency of Comparative Examples 5, 7, 8 and Example 1;

[0032] Figure 4 Bar graphs showing the zinc and iron purity of Example 1 and Comparative Example 11;

[0033] Figure 5 (a) A physical image of the metallic iron product obtained by the method of the present invention; Figure 5 (b) is a photograph of a metallic iron product obtained by conventional methods;

[0034] Figure 6 SEM image of zinc obtained by the method of this invention;

[0035] Figure 7 This is a photograph of the zinc obtained by the method of the present invention.

[0036] Figure 8 This is a diagram of a device for Joule heat treatment of zinc-containing dust and sludge. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The technical solution adopted in this invention is as follows:

[0039] Step 1: Preparation of conductive reducing agent

[0040] A biomass (such as corn stalks or wheat stalks) is crushed and calcined at 700-900℃ in an inert atmosphere for 30 minutes to prepare biochar. 10%-50% of the biochar, 30%-100% of the industrial coke powder, and 0%-20% of the coal powder are uniformly mixed to prepare a carbon-based conductive reducing agent.

[0041] Step 2: Drying and Mixing

[0042] Prepare the raw materials by selecting a conductive reducing agent and zinc-containing dust and drying them in an oven. Then, mix the conductive reducing agent and zinc-containing dust evenly for later use.

[0043] Of the above raw materials,

[0044] Zinc-containing dust and sludge: Various iron-containing and zinc-containing dust and sludge from metallurgical production processes can be used, with dust particle size <0.1mm and moisture content <6%;

[0045] This article takes electric arc furnace ash as an example, containing 70-100 parts of ash and 20-40 parts of conductive reducing agent;

[0046] The moisture content of each raw material is reduced to below 2% by using a dryer, and then they are mixed evenly according to the above proportions.

[0047] Step 3

[0048] The dried raw materials are uniformly mixed in a mixer. The uniformly mixed materials are then loaded into a feeder, which feeds them into each unit reaction tank of the transmission device. The transmission device carries the materials into the Joule heating zone. Upon reaching the reaction zone, mechanical pressure is applied by a hydraulic device to tightly bind the raw material particles, forming a reaction body with resistance parameters meeting the process requirements. Subsequently, voltage and current parameters are set, and a continuous load is input through the hydraulic device. At this time, pulse impacts are applied to both ends of the reaction body to trigger the Joule effect. The reaction ends after a certain period of time. An inert atmosphere should be maintained throughout the entire reaction process to provide a stable environment for the reaction.

[0049] Step Four

[0050] The products in the reaction tank are fed into the ore crusher by the transmission device. The crushed material then enters the screening machine. After the screening process, high-grade metallic iron particles and carbon-rich slag phase can be obtained.

[0051] Step 5

[0052] In step three, the zinc vapor is cooled and recovered by a zinc cooling and recovery device. The cooled metallic zinc can be used as a high-zinc product; the metallic iron particles can be used as raw materials for electric arc furnace short-process steelmaking; and the slag phase can be recycled.

[0053] The transmission device in the above steps is a chain drive system, a Joule heating zone with a Joule heating drive system, and a sample reaction cell. The chain drive structure is responsible for transporting the reaction raw materials; it includes a feeder and a transmission and conveying unit. The transmission and conveying unit includes a conveyor belt and multiple independent sample reaction cells evenly distributed above the conveyor belt to achieve continuous batch processing. The feeder transports the raw materials into the sample reaction cells.

[0054] The Joule heating drive system mainly consists of a power supply module equipped with a DC power supply and a controllable current source. The sample reaction cell is electrically connected to the Joule heating drive system through electrodes. The electrodes are fixed to the main body of the reaction cell, and the mechanical pressure load is provided by the hydraulic device above. The reaction cell between the two electrodes is a sealed furnace body.

[0055] The zinc cooling and recovery device mainly consists of an airflow channel and a collection well. After the zinc vapor evaporates through the device, it escapes downwards, comes into contact with the inert airflow, and is rapidly cooled, transforming the zinc phase from a gaseous phase into fine solid particles. The inert airflow further carries the fine zinc particles into the collection well, where the particles settle under the influence of gravity and are efficiently recovered. The remaining gas is smoothly discharged through the airflow channel at the top of the collection well.

[0056] The remaining reaction products are fed into an ore crusher via a conveyor belt for crushing, and then screened by a screening machine.

[0057] To help you understand the above technical solutions, the following specific embodiments and comparative examples are provided.

[0058] Example 1

[0059] The raw material composition of this comparative example was: 30% conductive reducing agent (10% corn stalks, 5% coal powder, 85% coke powder) and 70% electric arc furnace ash. The parameters of the Joule heating device used were set as follows: voltage 36V, current 15A, reaction time 40s. After the reaction, the dezincification rate was tested. At this time, the dezincification rate under these conditions was 96.95%.

[0060] Comparative Example 1

[0061] The raw material composition of this comparative example was: 30% conductive reducing agent (same as in Example 1) and 70% electric arc furnace ash. The parameters of the Joule heating device used were set as follows: voltage 24V, current 25A, reaction time 30s, and the dezincification rate was detected after the reaction. At this time, the dezincification rate under these conditions was 71.55%.

[0062] Comparative Example 2

[0063] The raw material composition of this comparative example was: 30% conductive reducing agent and 70% electric arc furnace ash. The parameters of the Joule heating device used were set as follows: voltage 30V, current 25A, reaction time 30s, and the dezincification rate was tested after the reaction. At this time, the dezincification rate under these conditions was 97.64%.

[0064] Comparative Example 3

[0065] The raw material composition of this comparative example was: 30% conductive reducing agent and 70% electric arc furnace ash. The parameters of the Joule heating device used were set as follows: voltage 36V, current 25A, reaction time 30s, and the dezincification rate was tested after the reaction. At this time, the dezincification rate under these conditions was 99.41%.

[0066] Comparative Examples 4, 5, and 6

[0067] Comparative Examples 4, 5, 6 and 3 differ only in their current settings, which are 20A, 15A and 10A respectively.

[0068] Comparative Examples 7 and 8

[0069] The only difference between Comparative Examples 7, 8 and 5 is the setting time.

[0070] The relevant data of Example 1 and Comparative Examples 1 to 8 are summarized in Table 1.

[0071]

[0072] Based on the data analysis in Table 1, the following conclusions can be drawn:

[0073] Comparative Examples 1, 2, and 3 constitute a set of parallel control experiments. Figure 1 The data shows that as the voltage gradually increases, the zinc removal rate is significantly improved, but excessively high temperatures cause excessive damage to the reactor.

[0074] Comparative Examples 3, 4, 5, and 6 form a group of control experiments under different current conditions. According to... Figure 2 Data analysis showed that the dezincification rate increased significantly with increasing current, with Comparative Example 3 showing particularly outstanding dezincification effect, reaching 99.41%. However, a current of 15A was more suitable for the overall temperature, but the dezincification rate still did not meet the requirements. Therefore, the time was increased to improve the dezincification rate.

[0075] Comparative Examples 5, 7, and 8, together with Example 1, constitute a set of control experiments with different reaction times. Combined with... Figure 3 Data analysis shows that when the reaction time in Example 1 is 40 seconds, a zinc removal rate of 96.95% can be achieved, and the peak temperature is only 1744℃.

[0076] Comparative Examples 9 and 10

[0077] Comparative Examples 9 and 10 are the results of experiments conducted using a tubular furnace to simulate the traditional rotary hearth furnace process: their data are recorded in Table 2. When the reaction proceeded for 15 minutes, the dezincification rate reached 85.67%; after the reaction continued for 30 minutes, the dezincification rate further increased to 98.63%.

[0078]

[0079] In summary, a comparison of the data in Tables 1 and 2 clearly shows that the direct heating method based on the Joule effect has a much shorter reaction time than the traditional rotary hearth furnace process, significantly shortening the reaction cycle and resulting in significantly higher reaction efficiency. Furthermore, the use of resistance heating and green electricity achieves higher energy utilization and lower carbon emissions.

[0080] pass Figure 5 It can be seen that 'a' is the metallic iron product of the new method, with obvious iron granular structure, and its purity can reach over 90% according to the test. Figure 4 ), while b is a product of the traditional method, exhibiting a loose structure and obviously low purity; through Figure 6 Compared to zinc, the new method can achieve a zinc purity of over 95%.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for converting zinc-containing dust into high-value-added products using Joule heating, characterized in that: Includes the following steps: S1 Preparation of carbon-based conductive reducing agent: Biochar is obtained by roasting biomass and mixed with industrial coke powder and coal powder in proportion; S2 raw material drying and mixing: Zinc-containing dust and conductive reducing agent are dried to a moisture content of ≤2% and then mixed evenly; S3 Joule reaction: The mixed raw materials are fed into the reaction zone via a chain drive, mechanical load is applied to form a reaction body, and the Joule effect is triggered by passing green electricity under an inert atmosphere. The reaction ends after a certain time. S4 Crushing and Separation: The product is crushed and screened to obtain metallic iron particles and carbon-rich slag phase; S5 Zinc Recovery: Zinc vapor is cooled and recovered to obtain high-purity metallic zinc.

2. The method for converting zinc-containing dust and sludge into high-value-added products using Joule heating according to claim 1, characterized in that: In step S1, biomass is crushed and calcined at 700-900℃ in an inert atmosphere for 30 minutes to prepare the conductive reducing agent. The mass percentages of each component are 10%-50% biochar, 30%-100% industrial coke powder, and 0%-20% coal powder.

3. The method for converting zinc-containing dust and sludge into high-value-added products using Joule heating according to claim 1, characterized in that: In step S2, the zinc-containing dust particles are < 0.1 mm in diameter and < 6% in moisture content. The ratio of zinc-containing dust to conductive reducing agent is 70~100:20~40.

4. A device for Joule heat treatment of zinc-containing dust and sludge to implement the method of claim 1, characterized in that: It includes a chain drive system, a Joule heating drive system, a sample reaction cell, a zinc cooling and recovery device, a crusher and a screening machine, with each component linked together to form a complete process chain; The chain drive system is used to realize the continuous transmission of raw materials from feeding to the output of post-reaction products; The Joule heating drive system includes a DC power supply, a controllable current source, and a fixed electrode. The fixed electrode is set in relation to the sample reaction cell and is used to apply pulse impact to the raw material in the reaction cell and trigger the Joule effect. The sample reaction cell is equipped with an upper static load input structure, and uses a hydraulic device to provide mechanical pressure load. The lower part of the cell has an integrated zinc product output port. The zinc cooling and recovery device is connected to the lower outlet of the sample reaction cell and is used to receive zinc vapor carried by the inert gas flow and achieve rapid cooling and condensation. The crusher and screening machine are connected in sequence to dissociate and classify the reaction products for recovery.

5. The Joule heat treatment apparatus for zinc-containing dust and sludge according to claim 4, characterized in that: The sample reaction cell adopts a closed furnace structure, and the inner cavity of the furnace is an inert atmosphere cavity.

6. The Joule heat treatment apparatus for zinc-containing dust and sludge according to claim 4, characterized in that: The zinc cooling and recovery device has a built-in condensation airflow channel, and a collection well is set at the channel outlet. Gravity drives the condensed zinc particles to settle and be collected.

7. The Joule heat treatment apparatus for zinc-containing dust and sludge according to claim 4, characterized in that: The chain drive system includes a feeder and a transmission and conveying unit. Multiple independent sample reaction tanks are evenly distributed on the transmission and conveying unit to achieve continuous batch processing.

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