A method and device for graded reduction of steel smelting zinc-containing dust

Abstract

This invention discloses a method and equipment for graded reduction of zinc-containing dust from iron and steel smelting, belonging to the field of zinc extraction technology from metallurgical waste. The zinc-containing dust is mixed with a carbon reducing agent to form pellets, which are then fed into a multi-stage reduction furnace. The pellets undergo graded gradient carbothermic reduction through three reduction stages, utilizing the difference in carbothermic reduction temperature between zinc oxide and zinc ferrite to achieve selective reduction and extraction. The composition of the flue gas is monitored in real time at the flue gas outlet of each stage, and the zinc reduction progress index is calculated. A proportional-integral control algorithm is used to dynamically adjust the temperature of each stage, achieving adaptive closed-loop control. The zinc-containing flue gas from each stage is introduced into independent condensation and collection channels for separate collection, obtaining secondary zinc oxide products of different grades. The supporting equipment includes a feeding and pelletizing unit, a multi-stage reduction furnace, a graded flue gas condensation and collection unit, and an online monitoring and intelligent control unit. This invention improves the stability of zinc recovery rate, enhances product grade, and reduces energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of zinc extraction technology from metallurgical waste, specifically relating to a method and equipment for the graded reduction of zinc-containing dust from iron and steel smelting. Background Technology

[0002] In the iron and steel smelting process, blast furnaces, converters, and electric arc furnaces generate a large amount of zinc-containing dust during operation. The zinc in this dust exists primarily in two phases: zinc oxide and zinc ferrite. Zinc oxide is a simple oxide with a relatively low thermodynamic onset temperature for carbothermic reduction; while zinc ferrite is a spinel-type complex oxide with a much higher lattice energy than zinc oxide, requiring a higher temperature for carbothermic reduction to effectively break down its spinel structure and release zinc. Direct storage of zinc-containing dust without effective treatment not only wastes zinc resources but also pollutes soil and water bodies due to the heavy metals it contains. Therefore, efficiently extracting zinc from zinc-containing dust and simultaneously recovering and utilizing iron resources is both economically valuable and environmentally significant.

[0003] Existing pyrometallurgical zinc extraction technologies mainly include rotary kiln and rotary hearth furnace processes, which generally employ a single high-temperature reduction strategy, subjecting the material to a one-time carbothermal reduction at a high temperature. Although the concept of staged reduction, which separates dezincification and iron reduction into different temperature zones, has emerged in recent years, several prominent technical problems remain at the engineering implementation level. First, the process control methods of existing staged reduction processes are relatively crude. The temperature of each reduction zone is usually maintained at a fixed, pre-set value, lacking real-time sensing and dynamic control of the actual reduction progress within the furnace. However, in actual production, the zinc content and phase composition of different batches of raw materials often fluctuate significantly. The constant-temperature operation cannot automatically adjust the temperature according to changes in the material's state, resulting in substantial fluctuations in zinc recovery rates between batches. When the zinc content of the material is high, a fixed temperature may lead to overly vigorous reduction, causing iron oxides to be excessively reduced to metallic iron and triggering ring formation within the kiln; when the zinc content of the material is low, a fixed temperature may result in insufficient reduction, leading to a decrease in zinc recovery rates. Meanwhile, due to the lack of real-time assessment of reduction completion, a conservative high-temperature strategy is generally adopted to ensure reduction effectiveness. Actual operating temperatures often exceed the necessary temperatures, resulting in unnecessary energy waste. Secondly, existing technologies generally employ a mixed collection method in the zinc product collection stage, where zinc-containing flue gas from each reduction stage is combined and introduced into the same condensation and collection system. However, the zinc-containing flue gas produced at different reduction stages exhibits significant differences in zinc vapor purity and impurity composition. The zinc vapor produced in the zinc oxide reduction stage has high purity and extremely low iron vapor and iron-containing particle content; while the flue gas produced in the zinc ferrite decomposition and reduction stage contains not only zinc vapor but also a significant amount of iron vapor, volatile chlorides, and alkali metal compounds. Mixing these two flue gases with significantly different purities and then condensing and collecting them together dilutes the high-purity zinc vapor with the low-purity flue gas, ultimately resulting in a lower overall grade of the secondary zinc oxide product. This increases the impurity removal burden and cost of downstream hydrometallurgical zinc refining processes.

[0004] Therefore, designing a method and supporting equipment for real-time dynamic control of the reduction process and simultaneous fractional collection of zinc products to solve the above problems is of great significance. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a method for graded reduction of zinc-containing dust from iron and steel smelting, comprising the following steps:

[0006] S1. Batching and pelletizing: Zinc-containing dust collector ash is mixed with carbon reducing agent and then pelletized to prepare green pellets;

[0007] S2, graded gradient reduction: The green pellets are continuously fed into a multi-stage reduction furnace and undergo graded carbothermic reduction in sequence through the first reduction stage, the second reduction stage and the third reduction stage;

[0008] S3. Online monitoring and dynamic temperature control of flue gas: The volume concentration of carbon monoxide, the volume concentration of carbon dioxide, and the mass concentration of zinc vapor in the flue gas are detected in real time at the flue gas outlet of each reduction section. The zinc reduction progress index of each section is calculated based on the detection data. The heat supply of the burner in each section is dynamically adjusted according to the deviation between the zinc reduction progress index and the preset target value using a proportional-integral control algorithm.

[0009] S4. Staged condensation and separate collection: The zinc-containing flue gas produced in each reduction section is introduced into three independent condensation and collection channels for condensation and dust removal, and high-grade secondary zinc oxide, medium-grade secondary zinc oxide and low-grade zinc-containing dust are collected respectively. The low-grade zinc-containing dust is returned to step S1 to participate in the batching.

[0010] S5. Residue discharge: The solid material after three-stage reduction is discharged from the discharge end of the multi-stage reduction furnace.

[0011] 2. The method according to claim 1, wherein step S2 comprises:

[0012] S21, Reduction in the first reduction stage: The green pellets enter the first reduction stage and undergo carbothermic reduction under the following conditions. The zinc vapor is reduced to zinc vapor and volatilizes into the flue gas in this section. Because its spinel lattice energy is higher than However, under these temperature conditions, it was not effectively decomposed, and the iron oxides were essentially not reduced; this step achieves... The selective preferential reduction of the phase results in low iron vapor and iron-containing particle content in the zinc-containing flue gas.

[0013] S22, Second Reduction Stage: The material processed in the first reduction stage passes through the first baffle ring and enters the second reduction stage, where it undergoes carbothermic reduction at a higher temperature. The spinel structure is destroyed, zinc is reduced to zinc vapor and volatilizes into the flue gas in this section, and iron is reduced to zinc vapor. Form remains in the solid phase; realization Reduction extraction of zinc from the phase;

[0014] S23, Reduction in Section III: The material processed in Section II passes through the second baffle ring and enters Section III, where the zinc-containing phases remaining in the first two sections are deeply reduced at the highest temperature to obtain a reduction slag with low zinc content.

[0015] In a preferred embodiment, step S3 includes:

[0016] S31. Online Flue Gas Detection and Filtering: At the flue gas outlets of each of the first, second, and third reduction sections, an infrared gas analyzer is used to detect... volume concentration and Volume concentration is determined by detecting the mass concentration of zinc vapor using a laser-induced breakdown spectroscopy device. The detection data is transmitted to the central controller in real time, and the central controller performs moving average filtering on each detection signal. This step obtains the real-time flue gas composition data of each segment after filtering.

[0017] S32. Calculate the zinc reduction progress index: Based on the filtered data obtained in step S31, the central controller calculates the zinc reduction progress index for each segment at the current time using the following formula:

[0018] ;in, For the first Level restoration segment in Zinc reduction progress index at any given time (dimensionless). For the first Level restoration segment in Zinc vapor mass concentration (mg / m³) after filtering at any given time 3 ); For the first The theoretical maximum zinc vapor concentration in the first reduction stage (mg / m³) 3 The value is determined by dividing the theoretically reducible zinc mass by the product of the flue gas volumetric flow rate and the material residence time. For the first Level restoration segment in Time after filtering Volume concentration (%) For the first Level restoration segment in Time after filtering Volume concentration (%) The restored segment number can be I, II, or III; The detection time (min);

[0019] Obtain comprehensive indicators to characterize the progress of zinc volatilization completion and the adequacy of the reducing atmosphere;

[0020] S33, Dynamic temperature control: The central controller will calculate the temperature in step S32. Compared with the preset zinc reduction progress target value of each section Compare the values ​​and calculate the temperature adjustment for each segment using the proportional-integral control algorithm. ,Will Superimposed on the reference set temperature of each segment The actual target temperature of each segment is obtained. The output is then sent to the corresponding burner group controller; this step enables adaptive dynamic adjustment of the temperature of each segment based on the actual reduction state.

[0021] Calculate the temperature adjustment amount and determine the actual target temperature using the following formula:

[0022] ;

[0023] ;in, For the first Level restoration segment in The temperature adjustment amount (°C) at any given time; a positive value indicates a temperature increase, and a negative value indicates a temperature decrease. For the first The proportional gain coefficient (°C) of the first-stage reduction section; For the first The preset target value for zinc reduction progress in the first reduction stage (dimensionless). For the first Level restoration segment in Zinc reduction progress index at any given time (dimensionless). For the first Integral gain coefficient of the first stage of reduction (°C / min), subscript Indicates integration; For the summation operation, for the first to the second... The deviation within each control cycle is accumulated cycle by cycle; For the first Level restoration segment in the first Each control cycle time Zinc reduction progress index (dimensionless). To control the cycle duration (min); As of The total number of control cycles that have been executed at any given time; For the first Level restoration segment in The actual target temperature at any given time (°C); For the first The reference set temperature (°C) for the first stage of reduction; real-time closed-loop temperature control based on the deviation of the zinc reduction progress index.

[0024] In a preferred embodiment, step S4 includes: S41, Stage I condensation and collection: The zinc-containing flue gas discharged from the outlet of the first reduction stage is introduced into the stage I condensation and collection channel, cooled by a quench tower, and then collected sequentially by a cyclone separator and a bag filter to obtain a high-grade secondary zinc oxide product; since the first reduction stage only reduces... In this phase, iron oxides do not participate in the reaction, and the product obtained in this step has low iron impurities and high grade;

[0025] S42, Stage II Condensation and Collection: The zinc-containing flue gas discharged from the outlet of the Stage II reduction section is introduced into the Stage II condensation and collection channel. After being cooled by a quench tower, it is collected sequentially by a cyclone separator and a bag filter to obtain a medium-grade secondary zinc oxide product; due to the decomposition of the Stage II reduction section... Iron oxides participate in the reaction simultaneously, and the product obtained in this step has a lower grade than the Grade I product.

[0026] S43, Stage III Condensation and Collection: The zinc-containing flue gas discharged from the flue gas outlet of the Stage III reduction section is introduced into the Stage III condensation and collection channel. After being deeply cooled by the quench tower, low-grade zinc-containing dust is collected by the cyclone separator and bag filter. The dust is then sent back to step S1 via the return material conveying device to participate in the batching process. This achieves the capture and recovery of residual zinc and avoids zinc loss.

[0027] In the preferred embodiment, the quenching temperatures of the three sets of condensation collection channels in steps S41 to S43 are set to decrease sequentially from stage I to stage III according to the following principles:

[0028] S411, the quench tower of the first-stage condensation and collection channel cools the flue gas to a higher temperature range below the boiling point of zinc, causing the zinc vapor to condense into fine zinc oxide powder; alkali metal chlorides, due to their condensation temperature being lower than that of zinc, mostly enter the downstream dust removal process with the tail gas, achieving the initial separation of zinc products from alkali metal impurities.

[0029] S412, the quench tower of the second-stage condensation collection channel cools the flue gas to a temperature range lower than the first-stage quench temperature, promoting the full condensation and sedimentation of iron vapor and volatile heavy metal impurities, and reducing their mixing with the secondary zinc oxide product.

[0030] The quench tower in the S413 and third-stage condensation collection channel cools the flue gas to the lowest temperature range in the three stages to fully capture the residual low-concentration zinc vapor; the specific value of the third-stage quench temperature is determined through optimization tests during the commissioning phase.

[0031] The present invention also provides a zinc-containing dust removal and ash classification and reduction device for steel smelting, characterized in that it comprises:

[0032] The feeding and pelletizing unit is used to mix zinc-containing dust and carbon reducing agent and pelletize them. The discharge port is connected to the feed end of the multi-stage reduction furnace.

[0033] The multi-stage reduction furnace has three stages: reduction stage I, reduction stage II, and reduction stage III, arranged sequentially along the length of the furnace body. Each reduction stage is equipped with an independent burner group. A refractory heat-insulating baffle ring fixed to the inner wall of the furnace body is provided between adjacent reduction stages. Each reduction stage has an independent flue gas outlet at the end of each stage.

[0034] The staged flue gas condensation and collection unit includes three independent condensation and collection channels, which are respectively connected to the flue gas outlets of the first reduction section, the second reduction section, and the third reduction section. Each condensation and collection channel includes a quench tower, a cyclone separator, and a bag filter in sequence along the flue gas flow direction. The powder outlet of each bag filter is connected to an independent product silo. The product silo corresponding to the third reduction section is connected to the feeding and pelletizing unit through a return material conveying device.

[0035] The online monitoring and intelligent control unit includes an infrared gas analyzer, a laser-induced breakdown spectroscopy device, and a central controller. The infrared gas analyzer is used to detect gases in each section of the flue gas. volume concentration and Volume concentration: The laser-induced breakdown spectroscopy device is used to detect the mass concentration of zinc vapor in each section of flue gas, and one set of both is installed at the flue gas outlet of each reduction section; The central controller is connected to the signal output terminal of each analytical instrument and the signal input terminal of each burner group controller, and has built-in detection signal filtering program, zinc reduction progress index calculation program and proportional-integral temperature control program.

[0036] In a preferred embodiment, the central controller adopts a hierarchical architecture of a programmable logic controller (PLC) and an industrial computer. The PLC is directly connected to each infrared gas analyzer, each laser-induced breakdown spectroscopy device, and each burner group controller, and is responsible for high-frequency execution of the detection signal filtering program, the zinc reduction progress index calculation program, and the proportional-integral temperature control program. The industrial computer is connected to the PLC via a communication bus and is responsible for the operation parameter self-tuning program, the online correction program for the theoretical maximum zinc vapor concentration, and historical data recording. The industrial computer is connected to a human-machine interface terminal for real-time display of temperature, flue gas composition, and zinc reduction progress index for each segment, and allows operators to set and modify target values ​​and control parameters for each segment.

[0037] The beneficial effects achieved by this invention are as follows:

[0038] First, this invention decouples the traditional single high-temperature one-step carbothermal reduction process into a multi-stage gradient reduction process targeting different zinc-containing phases. By utilizing the temperature difference between zinc oxide and zinc ferrite in the thermodynamics of carbothermal reduction, selective reduction is performed at different temperature ranges. This changes the crude operation method of indiscriminately performing a one-time high-temperature reduction on all zinc-containing phases in the prior art. Each reduction stage can set appropriate temperature conditions for its corresponding target zinc-containing phase, avoiding the kiln ring formation problem caused by excessive reduction of iron oxide due to excessive temperature. It also avoids the loss of zinc recovery rate caused by insufficient reduction of some zinc-containing phases due to insufficient temperature, laying the technological foundation for subsequent dynamic temperature control and fractional collection.

[0039] Secondly, this invention installs online gas analysis devices at the flue gas outlets of each reduction section to monitor the concentrations of carbon monoxide, carbon dioxide, and zinc vapor in the flue gas in real time. Based on this, a zinc reduction progress index, comprehensively representing the completion of zinc volatilization and the sufficiency of the reducing atmosphere, is calculated. The deviation between this index and a preset target value is used as a feedback signal, and the heat supply of each burner is dynamically adjusted through a proportional-integral control algorithm, establishing a closed-loop feedback control loop from flue gas composition detection to temperature regulation output. This dynamic temperature control method allows the temperature of each reduction section to be adaptively adjusted in real time according to the actual zinc content and phase composition of the material. Even under conditions of large fluctuations in raw material composition between batches, the zinc recovery rate can still be maintained at a high and stable level, significantly reducing the batch-to-batch fluctuation range of zinc recovery rate. At the same time, unnecessary high-temperature heating is avoided when the zinc content of the material is low, effectively reducing the overall energy consumption per ton of ash. In addition, the proportional-integral control algorithm, combined with safety measures such as integral limiting and temperature regulation limiting, effectively prevents temperature overshoot and integral saturation while ensuring control response speed, maintaining long-term stable operation of the kiln.

[0040] Third, this invention introduces the zinc-containing flue gas produced in each reduction stage into independent condensation and collection channels for graded collection. Utilizing the natural differences in zinc purity between the zinc-containing flue gas produced in different reduction stages due to the different reduction targets, it achieves source-level graded collection of secondary zinc oxide products. Since the first reduction stage only reduces the zinc oxide phase, iron oxides are essentially not involved in the reaction at this temperature. The flue gas in this stage has high zinc vapor purity and extremely low iron vapor and iron-containing particle content. After independent collection through the first-stage condensation channel, high-grade secondary zinc oxide products can be directly obtained, serving as a high-quality raw material for hydrometallurgical zinc refining and reducing the complexity and reagent consumption of downstream iron removal processes. In the second reduction stage, iron oxides participate simultaneously in the decomposition and reduction of zinc ferrite. The flue gas in this stage has a relatively high impurity content. After collection through the second-stage condensation channel, a medium-grade product is obtained. The low-grade zinc-containing dust collected in the third-stage condensation channel is returned to the batching stage for reprocessing via a return conveyor device, preventing the loss of residual zinc. The staged condensation collection avoids the problem of high-purity zinc vapor being diluted by low-purity flue gas in traditional mixed collection, which significantly improves the overall grade of zinc oxide products and the proportion of high-grade products. At the same time, the condensation channels of each stage adopt a gradient quenching temperature set from high to low, and the difference in condensation temperature of different components is used to achieve selective separation of volatile heavy metal impurities such as alkali metal chlorides and lead, which reduces the impurity removal pressure of downstream wet process.

[0041] Fourth, the two core technical features of this invention, dynamic temperature control and staged condensation and fractional collection, work synergistically to achieve refined control of the reduction process and fractional collection of zinc products at the source within the framework of staged reduction. Dynamic temperature control, through closed-loop feedback, allows the temperature of each stage to adaptively match the actual material state, primarily contributing to improved zinc recovery rate and recovery stability. Staged condensation and collection utilizes the natural differences in zinc purity in each stage of flue gas, primarily contributing to the acquisition of high-grade products and the improvement of overall grade. The combined application of these two technologies enables both the total zinc recovery rate and the proportion of high-grade products to reach optimal levels, achieving synergistic efficiency. Attached Figure Description

[0042] Figure 1 This is a comparison chart of the PI dynamic temperature control response characteristics of Example 1 and Comparative Example 1, in which... Figure 1 (a) shows the restoration progress of the second restoration stage. Track the response comparison curve. Figure 1 (b) represents the temperature regulation value of the PI controller. Curve graph showing changes over time;

[0043] Figure 2 This is a comparison chart of the contents of four components, Zn, Fe, Pb, and Cl, in the various levels of condensation products of Examples 1-3 and Comparative Examples 2-3;

[0044] Figure 3 It is the second-level condensation temperature adjustment coefficient of Example 1. Comparison chart of the relationship between product Zn grade and zinc capture rate;

[0045] Figure 4 This is a comparison chart of the comprehensive zinc recovery indicators of Examples 1-3 and Comparative Examples 1-3, in which... Figure 4 (a) is a bar chart comparing the total zinc recovery rate. Figure 4 (b) is a bar chart comparing the proportion of high-grade products in the first-level channel.

[0046] Figure 5 This is a flowchart of a method for classifying and reducing zinc-containing dust in steel smelting according to the present invention. Detailed Implementation

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] The present invention provides a graded reduction method for zinc-containing dust from steel smelting, decoupling the traditional single high-temperature one-step carbothermal reduction process into a multi-stage gradient reduction process targeting different zinc-containing phases. Zinc in steel smelting dust mainly exists in two phases: zinc oxide. and zinc ferrite . It belongs to simple oxides, and its thermodynamic onset temperature for carbothermic reduction is relatively low; while It belongs to the spinel-type composite oxide, and its lattice energy is much higher than that of spinel. Carbothermic reduction requires higher temperatures to effectively break down its spinel structure and release zinc. This invention utilizes the temperature difference in the carbothermic reduction thermodynamics of the two zinc-containing phases to selectively reduce them at different temperature ranges. Simultaneously, real-time flue gas analysis feedback enables dynamic adaptive control of the temperature in each range. Furthermore, the zinc-containing flue gas produced in each range is introduced into independent condensation channels for separate collection, thereby improving the stability of zinc recovery and obtaining secondary zinc oxide products of different grades.

[0049] The method for graded reduction of zinc-containing dust in steel smelting provided by this invention is implemented through the following equipment: including four main components: a feeding and pelletizing unit, a multi-stage reduction furnace, a graded flue gas condensation and collection unit, and an online monitoring and intelligent control unit.

[0050] The feeding and pelletizing unit is located upstream of the entire equipment. Its function is to uniformly mix zinc-containing dust and carbon reducing agent in a set ratio and then pelletize them. The discharge port of this unit is connected to the feed end of the multi-stage reduction furnace. After the mixed material is processed into green pellets of a certain particle size by the pelletizer, it is continuously fed into the multi-stage reduction furnace through the feeding device. The purpose of pelletizing is to ensure that the material has appropriate particle size and mechanical strength, guaranteeing its permeability and structural integrity during its movement in the furnace, and avoiding problems such as dust generation, flue gas short-circuiting, and uneven reduction caused by direct feeding of powder into the furnace.

[0051] A multi-stage reduction furnace is the core equipment for achieving graded gradient reduction. In one embodiment of the present invention, the reduction furnace adopts a multi-stage continuous rotary kiln structure. The furnace body is an inclined cylindrical shell, and the material moves continuously from the feed end to the discharge end by gravity and the rotation of the kiln body. Along the length of the furnace body, the internal space of the kiln is divided into three independent temperature-controlled zones: reduction zone I, reduction zone II, and reduction zone III. Each of the three reduction zones is equipped with an independent burner group, and the gas flow rate and combustion air flow rate of each burner group can be independently adjusted, so that the furnace temperature of each reduction zone can be independently controlled. At the junction of two adjacent reduction zones, i.e., between reduction zone I and reduction zone II, and between reduction zone II and reduction zone III, a refractory heat-insulating baffle ring is provided. The baffle ring is fixed to the inner wall of the kiln body and protrudes inward at a certain height along the radial direction of the kiln body. The baffle ring performs three functions in the present invention. First, the baffle ring obstructs the axial flow of the material, forcing it to accumulate upstream of the baffle ring until a certain level is reached before it can pass through and enter the next section, thus controlling the residence time of the material in each section. Second, the baffle ring axially divides the kiln space into relatively independent areas, reducing cross-mixing of atmospheres between adjacent sections and allowing each section to maintain its required reducing atmosphere and temperature conditions. Third, the zinc-containing flue gas produced in each section is mainly discharged from the annular gap between the baffle ring and the kiln wall, as well as from the flue gas outlet at the end of that section, achieving directional diversion of the flue gas from each section. At the end of each of the three reduction sections, there are independent flue gas outlets, each connected to a corresponding condensation collection channel via a flue, ensuring that the zinc-containing flue gas from each section is drawn out separately without mixing.

[0052] The staged flue gas condensation and collection unit is located downstream of the multi-stage reduction furnace. This unit includes three independent condensation and collection channels, each connected to the flue gas outlets of the first, second, and third reduction stages, respectively. Each condensation and collection channel, along the flue gas flow direction, includes a quench tower, a cyclone separator, and a bag filter. The quench tower rapidly cools the high-temperature zinc-containing flue gas, causing the zinc vapor in the flue gas to quickly condense into fine zinc oxide powder. The cyclone separator uses centrifugal force to separate larger particles from the airflow. The bag filter further collects fine dust particles, ensuring the exhaust gas meets environmental protection requirements. The powder outlet of each bag filter is connected to an independent product silo, enabling separate storage of products at each stage. Specifically, the product silo of the third-stage condensation and collection channel, corresponding to the third reduction stage, is connected to the feeding and pelletizing unit via a return conveyor, allowing the low-grade zinc-containing dust collected in this channel to be returned to the batching stage for reprocessing, thus preventing the loss of residual zinc.

[0053] The online monitoring and intelligent control unit is the hardware foundation for realizing the dynamic temperature control method of this invention. This unit includes three core components: an infrared gas analyzer, a laser-induced breakdown spectroscopy device, and a central controller. At the flue gas outlets of each of the first, second, and third reduction stages, one infrared gas analyzer and one laser-induced breakdown spectroscopy device are installed, for a total of six analytical instruments. The infrared gas analyzer employs the non-dispersive infrared principle, i.e., the NDIR principle, to detect gases in the flue gas... and The volume concentration of two substances is determined by the absorption intensity of molecules at specific infrared wavelengths. NDIR analyzers are widely used online gas analysis technologies in the metallurgical and chemical industries, characterized by fast response, strong anti-interference capabilities, and low maintenance. Laser-induced breakdown spectroscopy (LIBS) devices focus high-energy pulsed lasers into flue gas to form plasma, collecting the atomic characteristic spectra emitted during plasma cooling to quantitatively analyze the mass concentration of zinc in the flue gas. LIBS technology is a new detection method that has been widely applied in the field of online metallurgical analysis in recent years, suitable for harsh working environments with high temperatures and high dust content. Each infrared gas analyzer and each laser-induced breakdown spectroscopy device is connected to the data input terminal of the central controller via signal lines, transmitting real-time detection data to the central controller. The control output terminal of the central controller is connected to the burner group controllers of the three reduction sections, issuing temperature adjustment commands to each burner group. The central controller has built-in signal filtering, zinc reduction progress calculation, and proportional-integral temperature control programs. After receiving data from each analysis device, it automatically completes the entire process of signal filtering, index calculation, deviation comparison, adjustment calculation, and command output. In one embodiment of the invention, the central controller adopts a layered architecture of a programmable logic controller (PLC) and an industrial computer. The PLC is directly connected to the signal output terminals of each sensor and the signal input terminals of each burner group controller. It is responsible for high-frequency execution of signal filtering, real-time calculation of zinc reduction progress, and proportional-integral temperature control operations, and converts the calculation results into control signals for output to each burner group. The industrial computer is connected to the PLC via a communication bus and is responsible for running lower-frequency auxiliary programs, including self-tuning programs for control parameters, online correction programs for the theoretical maximum zinc vapor concentration, and historical data recording programs. The industrial computer is also connected to a human-machine interface (HMI) terminal, used to display the temperature and flue gas concentration of each segment in real time in the form of digital instruments and trend curves. Concentration and The system provides information on zinc concentration, zinc vapor concentration in each section, and zinc reduction progress indicators for each section, allowing operators to set and modify target values ​​and control parameters for each section.

[0054] The graded reduction method of the present invention will be described below in sequence according to the method steps. Before formally entering the reduction process, step S01, namely the material detection step, is performed first. A quantitative phase analysis is conducted on the zinc-containing dust to be fed into the furnace to determine the content of zinc in the material. and The mass fractions of each phase were determined. Quantitative phase analysis could be performed using X-ray diffraction with the Rietveld refinement method, or indirectly using chemical analysis combined with selective dissolution to obtain the content of the two zinc-containing phases. Based on the analytical results, the content of each phase in the material was calculated. The quality of zinc contained and The mass of zinc it contains. Specifically, for The phase, whose zinc content is equal to the amount of zinc in the material. Mass multiplied by zinc The mass fraction in the latter is equal to the atomic weight of zinc, 65.38, divided by... The molar mass is 81.38, or 0.8034. For The phase, whose zinc content is equal to the amount of zinc in the material. Mass multiplied by zinc The mass fraction in, the latter equals 65.38 divided by The molar mass is 241.06, or 0.2712. The calculated data is transmitted to the central controller, providing material baseline data for calculating the theoretical maximum zinc vapor concentration in each segment in subsequent step S3. During continuous production, when the raw material batch changes, it is necessary to perform quantitative phase analysis again and update the baseline data in the central controller. Step S01 enables the subsequent dynamic temperature control algorithm to adaptively adjust to the material composition of different batches, rather than relying on fixed empirical parameters.

[0055] Reference Figure 5 Step S1 involves batching and pelletizing. Zinc-containing dust and carbon reducing agent are mixed evenly in the feeding and pelletizing unit to produce green pellets. The carbon reducing agent can be carbon-containing materials such as coke powder, anthracite powder, or graphite. The amount of carbon reducing agent added is determined based on the stoichiometric requirements of the zinc-containing phase in the material and the carbon content of the material itself, while also considering the participation of carbon in the Boudouard reaction at high temperatures. The consumption of raw pellets is limited. Pelletizing can be done using a disc pelletizer or a pellet press. The selection of green pellet size must consider both air permeability and heat transfer efficiency within the furnace. Excessively large particle size will prolong the solid-phase diffusion path between the reducing agent and the zinc-containing phase, reducing reduction efficiency; excessively small particle size will increase the flow resistance of the material, affecting gas flow within the furnace. During pelletizing, an appropriate amount of water or binder can be added to ensure that the green pellets have sufficient drop strength, preventing premature crushing after entering the furnace.

[0056] Step S2 is a graded reduction. The green pellets prepared in step S1 are continuously fed into the feed end of a multi-stage reduction furnace through a feeding device. The green pellets pass through the first reduction stage, the second reduction stage, and the third reduction stage in sequence in the furnace to complete the graded carbothermic reduction.

[0057] Step S21 is the reduction stage I. After the green pellets enter the reduction stage I, a carbothermic reduction reaction occurs under the temperature conditions of this stage. The temperature setting principle for this stage is to ensure... The carbothermic reduction reaction can proceed effectively, and Because of the high thermal stability of its spinel structure, it cannot be effectively decomposed at this temperature. The main carbothermic reduction reaction is The standard Gibbs free energy change of the reaction The value becomes negative around 900°C, indicating that the reaction can proceed spontaneously above this temperature from a thermodynamic perspective. The zinc produced in the reaction escapes from the solid phase as vapor and enters the flue gas in this section. Meanwhile, The carbothermal reduction requires first overcoming the binding energy of its spinel lattice to remove zinc from... The tetrahedral sites are released, and then the released zinc oxide is reduced. This process requires temperatures much higher than [the required temperature]. The direct reduction temperature. Therefore, under the temperature conditions of the first reduction stage, It largely retains its spinel structure, with zinc still locked within the crystal lattice. Iron oxides are mainly... and At this temperature, it is not significantly reduced to metallic iron, but rather remains in oxide form or is only partially reduced to... Therefore, step S21 is achieved. Selective preferential volatilization of zinc phase, while maintaining The phase composition of the iron oxide remains essentially unchanged. Since the iron oxide does not participate in the reaction, the content of iron vapor and iron particles in the zinc-containing flue gas produced in the first reduction stage is extremely low, and the purity of the zinc vapor is relatively high.

[0058] Step S22 is the reduction stage II. The material processed in the first reduction stage passes the first baffle ring and enters the second reduction stage. The temperature in the second reduction stage is higher than that in the first reduction stage; the setting principle is to ensure... The spinel structure was effectively destroyed under carbothermic reduction conditions. The carbothermic decomposition and reduction can be summarized as the following overall reaction: The reaction proceeds in two microscopic stages: firstly... Under the influence of carbon, structural decomposition occurs, with zinc being released from the spinel tetrahedral sites and reduced to zinc vapor; simultaneously, iron transforms from the octahedral sites... Under the temperature conditions of the second reduction stage, the above reaction can proceed completely, and the material... Most of the zinc it contains is reduced to zinc vapor and volatilizes into this section of the flue gas. Because... The decomposition process inevitably involves the structural transformation of iron oxides. This stage of the flue gas will carry a small amount of iron vapor and iron-containing particles. Simultaneously, some volatile impurities in the material, such as alkali metal chlorides, lead, and cadmium, also enter the gas phase at this temperature. Therefore, the purity of zinc vapor in the flue gas of the second reduction stage is lower than that of the first reduction stage. The key control point for step S22 is to ensure... While ensuring the zinc is fully reduced and volatilized, it's crucial to avoid excessive reduction of iron oxides to metallic iron. The formation of metallic iron can cause materials to adhere to the kiln walls, forming rings and disrupting continuous equipment operation. Iron content should be controlled within... This condition ensures both effective zinc release and reduces the risk of ring formation within the kiln.

[0059] Step S23 is the reduction stage III. The material processed in the reduction stage II passes through the second baffle ring and enters the reduction stage III. The temperature in the reduction stage III is the highest of the three stages, and its purpose is to deeply reduce the small amount of zinc-containing phase remaining in the material after the first two stages of reduction. These residual zinc-containing phases may include those not completely reduced in the first two stages. and gangue minerals such as silicates Under the high-temperature conditions of the third reduction stage, the kinetic rate of the carbothermic reduction reaction accelerates, allowing the aforementioned difficult-to-reduce zinc-containing phases to be further reduced. After the third reduction stage, the residual zinc content in the material is reduced to a low level, forming a reduction slag mainly composed of iron oxides.

[0060] Step S3 involves online monitoring and dynamic temperature control of the flue gas. This step is one of the core technical features of this invention. Its essence is to establish a closed-loop feedback control circuit from flue gas composition detection to temperature adjustment output, enabling the temperature of each reduction section to be adaptively adjusted in real time according to the actual reduction progress.

[0061] Step S31 involves online flue gas detection. At the flue gas outlets of each of the first, second, and third reduction stages, an infrared gas analyzer continuously monitors the flue gas concentration in that stage. volume concentration and The volume concentration of zinc vapor in the flue gas is measured in real time using a laser-induced breakdown spectroscopy device. Each measured value is transmitted to the central controller in real time via signal lines. At this point, the central controller obtains real-time flue gas composition data for each of the three sections, including the individual volume concentrations of each section. concentration, Nine real-time parameters, including concentration and zinc vapor concentration.

[0062] Step S312 involves filtering the detection signal. The central controller processes the signals obtained in step S31. Volume concentration, The raw detection signals for volume concentration and zinc vapor mass concentration are respectively processed by moving average filtering. The specific implementation of moving average filtering is as follows: for the signal from any detection channel, the central controller continuously stores the most recent consecutive... The detection value of each sampling period is taken. The arithmetic mean of the detected values ​​is used as the filtered output value at the current time. Whenever a new sample value arrives, the oldest sample value is removed from the storage window, the new sample value is added to the window, and the arithmetic mean is recalculated. is the width of the filter window, which is a positive integer. The value of needs to balance the filtering effect and the real-time performance of signal tracking. If the value is too large, the response of the filtered signal to changes in the material state will be delayed, which may affect the timeliness of the PI controller's adjustment. If the value is too small, the filtering effect will be insufficient, and residual noise may still interfere with the control operation. In one embodiment of the present invention, The value ranges from 3 to 10, and the specific value is determined during the commissioning phase based on the signal-to-noise ratio characteristics of each detection channel. The purpose of introducing moving average filtering is twofold. First, to eliminate random measurement noise generated by online detection instruments under high temperature and high dust conditions, thereby improving the data quality input to the control algorithm. Second, because the response time characteristics of infrared gas analyzers and laser-induced breakdown spectroscopy devices differ, Concentration signal There may be a phase difference between the concentration signal and the zinc vapor concentration signal. Applying a moving average filter with the same window width to these three signals can partially cancel out the asynchrony between the signals, reduce the interference of the phase difference on the subsequent multiplication calculation of the zinc reduction progress index, and improve the stability of the closed-loop control system. This is used in subsequent step S32. , and All values ​​are the result of filtering in this step.

[0063] Step S32 involves calculating the zinc reduction progress indicators. Based on the filtered real-time flue gas data obtained in step S312, the central controller calculates the zinc reduction progress indicators for the three reduction stages at the current moment using the following formula:

[0064] ;

[0065] in, For the first Level restoration segment in The zinc reduction progress index at any given time is a dimensionless quantity with a value ranging from 0 to 1; For the first Level restoration segment in Zinc vapor mass concentration (mg / m³) after filtering at any given time3 ); For the first The theoretical maximum zinc vapor concentration (mg / m³) in the primary reduction stage under current feed conditions 3 The method for determining this is described in step S321; For the first Level restoration segment in Time after filtering Volume concentration (%) For the first Level restoration segment in Time after filtering Volume concentration (%) The restored segment number can be I, II, or III; The detection time (min).

[0066] The above formula consists of the product of two ratio terms. The first ratio term... This is the ratio of the actual detected zinc vapor concentration to the theoretical maximum concentration, directly reflecting the degree to which the actual zinc volatilization in this segment is close to the theoretical upper limit. When this value is close to 1, it indicates that the reducible zinc in this segment has almost completely volatilized; when this value is low, it indicates that the reduction is not yet sufficient. (Second ratio item) In the flue gas exist and The proportion of carbon in the total volume. In carbothermic reduction metallurgy, this ratio is a commonly used indicator of the sufficiency of the reducing atmosphere. When the reduction reaction is active, carbon reducing agent is continuously generated. , The proportion is relatively high; when carbon is insufficient or the temperature is too low, causing the reduction reaction to weaken, As the proportion increases, the ratio decreases. Multiplying the two terms results in a composite index that approaches a high value only when both effective zinc volatilization and a sufficient reducing atmosphere are present. If zinc volatilization is nearly complete but the reducing atmosphere remains sufficient, the first term approaches 1 while the second term remains relatively high. A high value may indicate a risk of excessively high temperature. If the reducing atmosphere is insufficient but there is still room for zinc to volatilize, the decrease in the second parameter will pull down the overall temperature. The value indicates that the amount of carbon added needs to be checked or the temperature should be increased appropriately. Therefore, this indicator integrates multi-dimensional flue gas detection information into a single dimensionless quantity, providing a unified control basis for subsequent automatic temperature regulation.

[0067] Step S321 is the theoretical maximum zinc vapor concentration The determination is based on the quantitative analysis data of the material phase obtained in step S01. The mass of zinc contained in the phase is assigned to the corresponding value in the first reduction stage. ,Will The mass of zinc contained in the phase is assigned to the corresponding value in the second reduction stage. The estimated mass of residual unreduced zinc in the first two stages under the designed dezincification rate is assigned to the corresponding value of the third reduction stage. .in, A certain percentage of the sum of the theoretically reducible zinc masses from the first two stages can be used as an estimate. This percentage is determined based on the measured zinc removal rates from the first two stages during the equipment commissioning phase. The theoretical maximum zinc vapor concentration for each stage is calculated using the following formula:

[0068] ;

[0069] in, For the first The theoretical maximum zinc vapor concentration in the first reduction stage (mg / m³) 3 ); For the first The theoretical mass (kg) of zinc that can be reduced in the first reduction stage; For conversion factors from kilogram to milligram; For the first Flue gas volumetric flow rate (m³) in the first stage of reduction 3 ( / min), this value is determined by the combined amount of gas and combustion air input of the burner section and the amount of gas produced by the reduction reaction, and can be obtained by actual measurement with a gas flow meter or by combustion calculation; For materials in the first The residence time (in minutes) in the first reduction stage is determined by the kiln's geometry, tilt angle, rotational speed, and baffle ring height, and can be measured and calibrated during commissioning. The physical meaning of this formula is: assuming the first... If all the reducible zinc in the flue gas evaporates uniformly into the flue gas during the material's residence time, then the theoretical upper limit of the zinc vapor concentration in the flue gas is... This value is used in step S32. The normalization benchmark of the formula makes the schedule indicators comparable under different production volumes and material conditions.

[0070] It should be pointed out that, and In actual continuous operation, these are not strictly constant values; both will drift with changes in operating parameters such as material filling rate, kiln speed, and burner load. If the initial values ​​calibrated during the commissioning phase are used without correction for an extended period, [the situation will worsen]. As a normalization benchmark, it will gradually become inaccurate, thereby affecting... Accurate reflection of the restoration progress. To this end, the present invention sets up a central controller... The online correction function is implemented. During continuous operation, the industrial control computer executes the online correction program for the theoretical maximum zinc vapor concentration at a low cycle frequency. The execution logic of this program is as follows: For The measured volumetric flow rate of flue gas was collected using gas flow meters installed at the outlets of each flue gas section. The time average of the flow rate data during the most recent period of stable operation was taken as the mean. The updated value. For Online soft measurement is performed based on the material mass balance relationship. Specifically, It can be estimated indirectly through the following relationship: equal to the The material holding capacity of each section under steady-state operation is divided by the mass flow rate of the material. The mass flow rate of the material can be obtained from the metering data of the feeding device, while the material holding capacity of each section can be estimated using empirical formulas based on geometric and operating parameters such as kiln rotation speed, tilt angle, and baffle ring height, or through soft measurement using a regression model established by tracer experiments during calibration periods. The industrial control computer utilizes the updated... and Recalculate each segment The updated value is then written into the programmable logic controller for subsequent processing. Real-time calculation. The online correction procedure only executes when the system is in a stable operating state. When a drastic fluctuation is detected in temperature, flow rate, or progress indicators, the correction is paused to avoid introducing erroneous update values ​​due to transient disturbances. This online correction function ensures... It can adaptively adjust to changes in operating conditions during long-term operation, thereby maintaining... The accuracy of reflecting the restoration progress.

[0071] Step S33 is dynamic temperature adjustment. The central controller will process the temperature ranges calculated in step S32. Compared with the preset zinc reduction progress target value for this section The temperature regulation is calculated by comparing the values ​​and using the proportional-integral (PI) control algorithm. PI control is a classic feedback control algorithm widely used in process control engineering. Its parameter tuning method was systematically proposed by Swedish engineer Ziegler and American engineer Nichols in 1942. A PI controller consists of two components: a proportional term and an integral term. The proportional term provides an immediate corrective response to the current deviation, and its response amplitude is proportional to the deviation value. The integral term integrates the historical accumulated deviation to eliminate steady-state errors that proportional control cannot completely eliminate. In this invention, the PI control algorithm adopts a positional implementation, meaning the controller's output is... The output is determined directly by the sum of the cumulative values ​​of the current proportional and integral terms. The output of the positional PI control represents the absolute value of the temperature regulation in each control cycle, facilitating its coordination with the integral limiting measure in step S331 and the temperature regulation limiting measure in step S332. The PI control algorithm is executed according to the following formula:

[0072] ;

[0073] in, For the first Level restoration segment in The temperature adjustment amount (°C) at any given time; a positive value indicates that the temperature needs to be increased, and a negative value indicates that the temperature needs to be decreased. For the first The proportional gain coefficient (°C) of the primary reduction stage determines the instantaneous response of the temperature adjustment to the current deviation. For the first The target value for zinc reduction progress in the first stage of reduction is a dimensionless quantity. The first one calculated in step S32 Level restoration segment in Indicators of zinc reduction progress at any given time; For the first The integral gain coefficient (°C / min) of the primary reduction stage determines the rate at which the temperature adjustment eliminates the accumulated deviation. From the first control cycle to the second Summation operation for each control cycle; For the first Level restoration segment in the first Each control cycle time The zinc reduction progress indicator; The control cycle duration (min) is the time interval between two adjacent control operations; As of The total number of control cycles that have been executed at any given time.

[0074] In the above formula, square brackets This represents the deviation value at the current moment. When Below the target value When the deviation is positive, it indicates that the reduction progress in this segment has not reached the expected level, and the temperature needs to be increased to promote the reduction reaction; at this time When the value is positive, the central controller sends a command to that section of the burner group to increase the heating output. When the deviation is higher than the target value, it is negative, indicating that the reduction in this segment may be too intense, posing a risk of excessive iron reduction or high energy consumption; at this time... If the value is negative, the central controller instructs a reduction in heat supply to save energy and maintain stable kiln conditions. Stacked up to the first Reference set temperature of the primary reduction stage The actual target temperature of that segment is obtained from the above. and will The temperature setpoint is sent to the corresponding burner group controller for execution.

[0075] It should be noted that in the above formula The physical meaning of is the integral gain coefficient, with dimensions of °C / min, compared to the deviation (dimensionless) and the control cycle duration. Multiplying by (min) yields the integral component (°C) of the temperature regulation. In actual programming implementation, the positional formula above should be strictly followed. Define and write the calculation logic for the integral term to avoid conflict with another common form of the PI algorithm, namely... Integral time The definition is confusing. In this invention, With integration time The relationship is ,in This is the integration time. The time obtained in step S334 is determined by the Ziegler-Nichols method or the relay feedback self-tuning method. That is, it is calculated according to this definition.

[0076] In actual industrial process control, the integral term of a PI controller may experience integral saturation if the deviation persists for an extended period. This means the accumulated value of the integral term continuously increases, causing the controller output to deviate abnormally from the reasonable range, and ultimately resulting in severe temperature overshoot after the deviation reverses. To prevent integral saturation, this invention incorporates an integral limiting measure in step S331. During the execution of the proportional-integral control algorithm, the central controller continuously monitors the integral term. The cumulative value. When the absolute value of this integral term reaches the preset integral limit threshold. At this point, the accumulation of deviations is paused; that is, newly generated deviations are no longer included in the summation term. (To be continued) When the sign reverses, it indicates that the system has begun to regress towards the target value, at which point accumulation resumes. Integral limit threshold. During the commissioning and debugging phase, the value is determined based on the thermal inertia characteristics of each section. It should be large enough to ensure that the integral term is not limited within the normal fluctuation range, while being small enough to effectively truncate when abnormal deviations accumulate.

[0077] Furthermore, the present invention includes a temperature regulation amount limiting measure in step S332. The temperature regulation amount calculated in step S33 is... The absolute value is limited to ensure that it does not exceed the preset maximum allowable adjustment range. When the calculation result Exceed At that time, Cut off as or The value depends on its sign. The purpose of this measure is to prevent the burner assembly from receiving excessively large temperature regulation commands within a single control cycle, even in the event of abnormal sensor signals or extreme fluctuations in material composition. This protects the refractory materials inside the kiln from thermal shock damage and maintains overall kiln stability. Maximum permissible adjustment range. The value is determined based on the allowable temperature change rate of each section of refractory material and the maximum adjustment capability of the burner assembly.

[0078] The present invention also provides two parameter tuning methods for selection: the Ziegler-Nichols critical proportional method and the relay feedback self-tuning method.

[0079] The first method is the Ziegler-Nichols critical proportional gain method. Proposed by J.G. Ziegler and NB. Nichols, this method remains one of the most widely used PI / PID parameter tuning methods in industrial process control. Its basic principle is to experimentally determine the critical steady state of the controlled object under pure proportional control, and then deduce the parameters of the PI or PID controller. The specific operational steps are as follows: During the commissioning phase, first adjust the integral gain coefficient... Setting it to 0 makes the controller perform only proportional control. From a smaller value... Starting with a value, gradually increasing After each increase, observe the zinc reduction progress index. For target value The tracking response. With The increase, The response speed to deviations increases, but the oscillation tendency also strengthens. Continued increase... Until A sustained constant-amplitude oscillation occurs, meaning the response curve neither converges nor diverges but maintains a constant amplitude periodic oscillation. Record this value as the critical proportional gain. The period of the constant-amplitude oscillation is recorded as the critical oscillation period. Then calculate the final proportional gain coefficient and integral gain coefficient using the following formulas:

[0080] ;

[0081] in, For the first The final proportional gain coefficient (°C) used in the stage reduction section; 0.45 is the tuning coefficient of the proportional gain of the PI controller in the Ziegler-Nichols critical proportional gain method, which comes from the optimal parameter tuning table of the PI controller given in the aforementioned paper by Ziegler and Nichols. For the first The critical proportional gain (°C) of the stage reduction section was obtained by actual measurement through the above debugging process. For the first The final integral gain coefficient (°C / min) used in the stage reduction section; 0.83 is the proportionality coefficient between the integral time and the critical oscillation period in the Ziegler-Nichols method, which also comes from the parameter tuning table of the PI controller in the aforementioned paper, and its original form is integral time. Converted to ,Right now 0.83 in the middle equals ; For the first The critical oscillation period (min) of the stage reduction segment was measured.

[0082] It is important to note that the Ziegler-Nichols critical proportionality method requires the controlled system to be pushed towards the critical stability boundary, during which the system will undergo constant-amplitude oscillations. For large industrial furnaces, constant-amplitude oscillations mean that the temperature of each section will fluctuate periodically around the target value. If the oscillation amplitude is too large or the duration is too long, it may cause thermal fatigue damage to the refractory materials in the kiln, or lead to overheating of the material and ring formation in the kiln. Therefore, when using this method for parameter tuning, it must be carried out under strict safety monitoring conditions and should meet the following requirements: the critical oscillation experiment should be performed during the commissioning phase or after major equipment overhaul and renovation, and should not be carried out during normal production; during the experiment, the operator should continuously monitor the real-time temperature and progress indicators of each section through the human-machine interface terminal, set the upper limit alarm value of the safe temperature, and once the temperature exceeds the safe threshold, immediately switch back to the fixed temperature control mode and terminate the experiment; each increase The amplitude should be controlled in small increments to ensure that the system smoothly approaches the critical state rather than suddenly jumping into violent oscillations; the duration of the critical oscillation experiment should be limited to the point where the constant amplitude oscillation is confirmed and at least 3 complete oscillation cycles are recorded, and should not be extended.

[0083] The second method is the relay feedback self-tuning method, which can serve as an alternative or supplement to the Ziegler-Nichols critical proportional gain method. Unlike the Ziegler-Nichols method, which requires operators to manually increase the proportional gain step by step until the system reaches critical oscillation, the relay feedback self-tuning method introduces a relay-type nonlinear control automatic excitation system to generate limit cycle oscillations. Based on this, the central controller automatically extracts the critical parameters. The entire process requires no manual intervention, making operation safer and more automated. The specific implementation steps are as follows: when parameter tuning is required, the operator issues a self-tuning command through the human-machine interface terminal, and the central controller automatically extracts the critical parameters. The segment's PI controller switches to relay control mode. In relay control mode, the central controller applies relay-type switching control to the deviation signal: when the deviation... When the actual progress is below the target value, the controller outputs a preset positive temperature adjustment range. (°C) increases the heat output of the burner assembly by a fixed amount; when the deviation is negative, meaning the actual progress exceeds the target value, the controller outputs a preset negative temperature adjustment range. This reduces the heat output of the burner assembly by the same amount. Under this relay switching control, At the target value A stable limiting cycle oscillation is generated nearby. The central controller records the amplitude of this limiting cycle oscillation. (Pick Half the difference between the positive and negative peak values ​​of the oscillation and the oscillation period. According to the relay feedback self-tuning theory, the equivalent critical proportional gain of the system in the limiting cycle oscillation state is... and critical oscillation period It can be calculated using the following formula:

[0084] ;

[0085] in, The preset relay control output amplitude (°C); Pi; In the limit cycle oscillation The amplitude of the wave (dimensionless). denoted as the period (min) of the limit cycle oscillation. The value of should be small enough to ensure that the amplitude of the limiting cycle oscillation generated by the system is mild and does not cause significant disturbance to the kiln condition. Generally, it can be taken as the maximum allowable temperature adjustment range of each section. A certain proportion. Obtained and Then, the tuning formula of the Ziegler-Nichols method is still followed. and Calculate the final proportional gain and integral gain coefficients. The advantage of the relay feedback self-tuning method compared to the Ziegler-Nichols critical proportional gain method is that the operator does not need to manually increase the proportional gain step by step, avoiding the risk of sudden and severe oscillations in the system due to improper step selection; the amplitude of the relay control output... The parameters are preset and limited, and the oscillation amplitude is controllable. The entire process can be automatically completed by the central controller for parameter extraction and calculation, resulting in a high degree of automation. This method is particularly suitable for scenarios where parameters need to be readjusted due to significant changes in raw material conditions during normal production.

[0086] Because the thermal inertia, material state, and reaction characteristics of the three reduction stages are different, each stage needs to undergo the above tuning process independently to obtain its own suitable results. and Value. In actual operation, if the raw material conditions change significantly or the equipment has undergone maintenance or modification, it is recommended to re-perform parameter tuning. Furthermore, a control performance evaluation module can be set up in the industrial control computer; this module continuously monitors each stage. Relative to target value The module measures parameters such as deviation variance and overshoot. When performance indicators continue to deteriorate beyond preset thresholds, the module sends parameter optimization prompts to the operator via the human-machine interface terminal, suggesting that the relay feedback self-tuning program be started to readjust the parameters to ensure that the control effect remains at a good level.

[0087] Regarding the target values ​​for each segment The method for determining this is proposed in this invention: during the commissioning and production phase, reduction tests are conducted on actual materials in each stage, and the results are recorded at a fixed temperature. Observe the curve showing the change over time, and identify the asymptotic value as the reduction nears completion. This asymptotic value represents the upper limit of the achievable progress for that segment at that temperature. Setting the level slightly below this asymptotic value ensures that the PI controller has a margin of adjustment within the normal fluctuation range and does not remain in a state of deviation. For the first reduction stage, since... It is relatively easy to reduce and the zinc in this section of flue gas is of high purity, which can... Set at a relatively high level to ensure The complete restoration. For the second restoration segment, due to... The reduction is quite difficult and requires careful control of the oxidation state of iron. It is advisable to set it to a medium level. For the third reduction stage, due to the low amount of residual zinc, It can be set to a lower level.

[0088] Through the dynamic temperature control in step S3, the temperature of each section is no longer a fixed constant temperature operation, but rather adaptively adjusted based on real-time flue gas composition feedback. When the zinc content of a certain section of material is higher than the average level, Initially, the temperature will be higher than the target value; the PI controller will appropriately reduce the temperature to save energy. When the zinc content of the material is low... If the temperature is too low, the PI controller automatically raises the temperature to maintain reduction efficiency. This closed-loop feedback mechanism enables the present invention to maintain the zinc recovery rate within a narrow fluctuation range even when the raw material composition fluctuates widely.

[0089] Step S4 is staged condensation and fractional collection. This step is another core technical feature of the present invention. Its principle is to utilize the natural differences in zinc purity of the zinc-containing flue gas produced in the three reduction sections due to the different reduction targets, and to achieve source fractional collection of secondary zinc oxide products through independent condensation channels.

[0090] Step S41 is the first-stage flue gas condensation and collection. The zinc-containing flue gas discharged from the flue gas outlet of the first reduction stage is introduced into the first-stage condensation and collection channel. As mentioned above, the first reduction stage only reduces... In this phase, iron oxides are largely unaffected by the reaction at this temperature, resulting in high purity zinc vapor and extremely low levels of iron vapor and iron-containing particles in the flue gas. The flue gas is rapidly cooled upon entering the first-stage quench tower. The quench tower achieves rapid cooling by injecting cold air into the flue gas or by circulating cooling. During quenching, zinc vapor undergoes uniform nucleation and condensation, forming fine zinc oxide powder. The quenching rate must be controlled at a high level because if the cooling rate is too slow, the zinc vapor will remain at high temperatures for an extended period during condensation, easily forming a dense oxide layer on the particle surface or growing into larger particles, affecting the solubility in subsequent wet leaching. The flue gas, condensed in the quench tower, carrying zinc oxide particles, passes sequentially through a cyclone separator and a bag filter, where the zinc oxide particles are separated and collected. Due to the low iron impurity content in the raw flue gas, the collected secondary zinc oxide product has a high grade and can be used as a high-quality raw material for wet zinc smelting, reducing the complexity of downstream iron removal processes and reagent consumption.

[0091] Step S42 involves the condensation and collection of the second-stage flue gas. The zinc-containing flue gas discharged from the outlet of the second reduction stage is introduced into the second-stage condensation and collection channel. This is due to the decomposition and reduction in the second reduction stage. During the process, iron oxides undergo simultaneous structural transformation. In addition to zinc vapor, the flue gas in this section also contains small amounts of iron vapor, iron-containing particles, and alkali metal chlorides and heavy metal impurities such as lead and cadmium that volatilize at this temperature. The flue gas is cooled to a temperature level lower than that of the first-stage quench tower in the second-stage quench tower to promote the full condensation and sedimentation of iron vapor and heavy metal impurities. After collection by a cyclone separator and bag filter, a medium-grade secondary zinc oxide product is obtained. The zinc grade of this product is lower than that of the first-stage product, but it can still be sold as a conventional secondary zinc oxide product or, after simple washing and purification, enter the wet process.

[0092] Step S43 involves the condensation and collection of the third-stage flue gas. The flue gas discharged from the outlet of the third reduction stage is introduced into the third-stage condensation and collection channel. Since the third reduction stage is a deep reduction stage, the residual zinc content in the material is already low, and the concentration of zinc vapor in the flue gas of this stage is much lower than in the previous two stages, while the relative content of impurities is higher. The third-stage quench tower cools the flue gas to the lowest temperature level among the three stages to capture as much of the remaining low-concentration zinc vapor as possible. After collection by a cyclone separator and a bag filter, low-grade zinc-containing dust is obtained. This dust is sent back to the feeding and pelletizing unit via a return conveyor, mixed with fresh dust, and then reintroduced into the furnace for processing. This return circulation mechanism avoids the loss of residual zinc.

[0093] Steps S411 to S413 further explain the setting principles for the quenching temperatures of the three condensation collection channels. The quenching temperatures of the three channels are set in descending order from stage I to stage III. The quenching tower of the stage I condensation collection channel cools the flue gas to a higher temperature range below the boiling point of zinc. Within this temperature range, zinc vapor can be effectively condensed into fine-particle zinc oxide, while alkali metal chlorides... and The condensation temperature of the flue gas is lower than that of zinc, and most of it remains in gaseous form, entering the downstream process with the exhaust gas, thus achieving initial separation of zinc products from alkali metal impurities. The quench tower in the second-stage condensation collection channel cools the flue gas to a temperature range lower than that of the first stage. This deeper cooling helps to fully condense and settle iron vapors and volatile heavy metal impurities in the flue gas, reducing their entry into the secondary zinc oxide product. The quench tower in the third-stage condensation collection channel cools the flue gas to the lowest temperature range of the three stages to address the low zinc vapor concentration in this section, ensuring maximum capture of residual zinc. The specific values ​​of the three-stage quenching temperatures are determined through optimization experiments on the grade of each product and the zinc capture rate during the commissioning phase. Experimental methods can employ single-factor stepwise optimization or orthogonal experimental design.

[0094] Step S5 is the discharge of residue. After staged carbothermic reduction in stages I, II, and III, most of the zinc in the material has been reduced, volatilized, and collected as secondary zinc oxide. The remaining solid material forms reduction slag. The reduction slag is discharged from the outlet of the multi-stage reduction furnace, and its main component is iron oxide (in the form of...). and The reducing slag contains a high iron content and a small amount of gangue components. It can be recycled as an iron-containing raw material in sintering or steelmaking processes, thus realizing the recycling of iron resources in the material.

[0095] In summary, this invention, through the synergistic combination of two core technical features—dynamic temperature control in step S3 and graded condensation and quality-differentiated collection in step S4—achieves refined control of the reduction process and source-level quality differentiation of zinc products within the framework of graded reduction. The closed-loop feedback control in step S3 enables the temperature of each stage to adaptively match the actual material state, maintaining the stability of the zinc recovery rate under fluctuating raw material composition. The independent condensation channel in step S4 utilizes the natural differences in zinc purity in the flue gas from each reduction stage, avoiding the problem of high-purity zinc vapor being diluted by low-purity flue gas in traditional mixed collection, thus improving the overall grade of the secondary zinc oxide product.

[0096] Example 1: In this example, a steel plant uses the mixed dust from the present invention for graded reduction zinc extraction. The specific implementation process is as follows:

[0097] Step S01 was performed to conduct quantitative phase analysis on the zinc-containing dust collected in the furnace. The raw material was a mixture of 60% blast furnace bag filter ash and 40% converter ash from a steel plant. X-ray diffraction analysis combined with the Rietveld refinement method was used for quantitative phase analysis. The results were: TFe 35.2%, Zn 6.8% (of which... The zinc content accounts for 58% of the total zinc content. (Contains 42% zinc of the total zinc content), C 8.5%, 4.3%, 5.1%, Pb 0.4%, Cl 0.8%. The phase analysis data is transmitted to the central controller.

[0098] Perform step S1, material preparation and pelletizing. Coke powder is selected as the carbon reducing agent, and it is added at 12% of the total carbon content, including the carbon contained in the material itself. Green pellets with a diameter of 8-12mm are prepared using a disc pelletizer, and the green pellet drop strength is ≥4 times / 0.5m.

[0099] Step S2 is executed, involving graded gradient reduction. The equipment employs a multi-stage continuous rotary kiln with an inner diameter of 3.0m, a length-to-diameter ratio of 15:1, a total length of 45m, an inclination angle of 3.5°, and a rotational speed of 0.8 r / min. The height of the baffle ring is 12% of the kiln's inner diameter, i.e., 360mm, and it is made of high-alumina refractory castable. The first reduction stage accounts for 30% of the effective length of the kiln, the second reduction stage accounts for 45%, and the third reduction stage accounts for 25%.

[0100] Step S21, the green pellets enter the first reduction stage, reference temperature. At 940°C, at this temperature It is reduced by carbon to zinc vapor, which then volatilizes and enters the flue gas. The spinel phase was not effectively decomposed, and the iron oxides were basically not reduced.

[0101] Step S22: The material passes the first retaining ring and enters the second reduction section, with a reference temperature. It is 1140°C. The spinel structure is destroyed, zinc is reduced and volatilized, and iron is released. The solid phase remains in the form of the form.

[0102] Step S23: The material passes the second retaining ring and enters the third reduction section, at the reference temperature. =1200°C, to deeply reduce the first two residual zinc-containing phases.

[0103] Perform step S3: online monitoring and dynamic temperature control of flue gas.

[0104] Step S31: Install one NDIR infrared gas analyzer (range 0–30%, response time ≤ 3s) and one LIBS online zinc vapor detector (range 0–50000 mg / m³) at each of the three reduction section flue gas outlets. 3 Response time ≤ 5s.

[0105] Step S312, Detection signal filtering processing, filtering window width =5, sampling period =0.5min.

[0106] Steps S32 and S321 calculate the zinc reduction progress index for each stage. Based on the phase data from step S01, the theoretically reducible zinc mass in stage I is... correspond Zinc content in phase II, reduction stage correspond Zinc content in phase III, reduction stage We take 8% of the sum of the theoretically reducible zinc mass from the first two sections as the estimate. Flue gas flow rate for each section. and length of stay Determined based on measured calibration data. The central controller is determined according to the formula. Calculate the zinc reduction progress indicators for each stage in real time.

[0107] Step S33, dynamic temperature adjustment. The PI control parameters for each segment are set as follows: Segment I =0.78, =30°C, =1.0°C / min; Section II =0.65, =45°C, =1.5°C / min; Section III =0.50, =25°C, =0.8°C / min. The central controller operates according to the formula... The temperature adjustment is calculated, superimposed on the reference temperature, and then output to each burner group.

[0108] Step S331, Integral limiting threshold: =25°C, =40°C, =20°C.

[0109] Step S332, Temperature adjustment range limit: =40°C, =60°C, =35°C.

[0110] Step S334, PI parameter tuning adopts the Ziegler-Nichols critical proportional gain method. Taking the first reduction stage as an example, during the commissioning phase... Set to 0, from =From 10°C, gradually increase, until =67°C A sustained constant-amplitude oscillation occurs; the critical proportional gain is recorded. =67°C, critical oscillation period =6.2min. According to the formula =0.45×67≈30°C =30 / (0.83×6.2)≈5.8°C / min, actual value taken =1.0°C / min for a smoother control effect. The parameters for sections II and III are tuned in the same way.

[0111] Execute step S4 for staged condensation and separate collection. The condensation temperature adjustment coefficients for the three independent condensation collection channels are as follows. =1.0, =1.4, =2.0.

[0112] Step S41: The first-stage condensation channel is quenched at 810°C to collect high-grade secondary zinc oxide.

[0113] Step S42: The quenching temperature of the second-stage condensation channel is 567°C, and medium-grade secondary zinc oxide is collected.

[0114] In step S43, the quench temperature of the third-stage condensation channel is 520°C. Low-grade zinc-containing dust is collected and returned to step S1 for batching. The cooling rate of each quench tower is ≥200°C / s.

[0115] In step S5, the reducing slag is discharged from the outlet. The TFe content of the reducing slag is 48.3%, and the metallization rate is 72.1%, which is used as iron-containing raw material for recovery. The central controller adopts a hierarchical architecture of PLC and industrial computer. The PLC control cycle is 0.5s, and the industrial computer has a self-tuning program for operating parameters. Online correction program. The HMI terminal displays real-time temperature, flue gas composition, and... value.

[0116] Key results after 30 days of continuous operation: Total zinc recovery rate 95.3%, batch-to-batch standard deviation of zinc recovery rate 1.3%, Grade I zinc oxide 67.2% (based on Zn), Grade II 54.8%, Overall grade 61.5%, Grade I channel product proportion 48%, Comprehensive energy consumption per ton of ash 498 MJ, Economic benefit per ton of ash product 335 yuan, PI controller automatically adjusted 15-25 times per day, Steady-state deviation... <0.03.

[0117] Example 2, the raw material is dust from a steelmaking process in an electric arc furnace, Zn 18.5% ( The zinc content accounts for 62% of the total zinc content. (38%), TFe 24.3%, C 2.1%, Pb 2.8%, Cl 3.5%, 3.8%, 2.9%. Carbon reducing agent is added externally at 18% of the total carbon content using anthracite powder. Green pellet diameter is 10–15 mm.

[0118] Equipment parameters: Kiln inner diameter 3.5m, length-to-diameter ratio 16:1, total length 56m, inclination angle 3.0°, rotation speed 0.6r / min. The height of the baffle ring is 10% of the kiln inner diameter.

[0119] PI control parameters: Segment I =0.82, =35°C, =1.2°C / min; Section II =0.68, =50°C, =1.8°C / min; Section III =0.55, =28°C =0.9°C / min. Integral limiting threshold. =28°C =38°C =22°C. Temperature regulation range limit. =45°C, =55°C, =38°C. Filter window width. =8. Reference temperature: =960°C, =1160°C, =1220°C.

[0120] Condensation temperature adjustment coefficient =0.9, =1.6, =2.3. The quench temperature of the first-stage condensation channel is 859°C, the second-stage is 502°C, and the third-stage is 485°C. The PI parameter tuning adopts the relay feedback self-tuning method. Taking the first reduction stage as an example, the relay control output amplitude is set... At 15°C, the system produces a limiting cycle oscillation, and the amplitude is measured. =0.052, oscillation period =5.8min. According to the formula =4×15 / (π×0.052)≈367°C, =5.8min, =0.45×367≈165°C, to obtain a suitable damping ratio, the actual value is taken as... =35°C. Sections II and III are tuned in the same way.

[0121] Example 3: The raw material in this example is blast furnace gas ash from a steel plant, with a Zn content of 12.3%. The zinc content accounts for 55% of the total zinc content. It accounted for 45%, TFe 29.8%, and C 5.6%. 5.1%, 6.2% carbon, 1.2% phosphorus, 1.5% phosphorus (Pb), 1.5% coke powder. Carbon reducing agent is added to the coke powder at 15% of the total carbon content. Green pellet diameter is 9–13 mm. Equipment parameters: kiln inner diameter 4.0 m, length-to-diameter ratio 14:1 (total length 56 m), inclination angle 4.0°, rotation speed 1.0 r / min. The height of the baffle ring is 14% of the kiln inner diameter.

[0122] PI control parameters: Segment I =0.75, =25°C, =0.8°C / min; Section II =0.60, =40°C, =1.2°C / min; Section III =0.45, =22°C, =0.6°C / min. Integral limiting threshold. =22°C, =35°C, =18°C. Temperature regulation range limit. =38°C =58°C, =32°C. Filter window width. =6. Reference temperature: =950°C, =1130°C, =1190°C. Condensation temperature adjustment coefficient. =1.1, =1.5, =2.2. The first-stage quenching temperature is 860°C, the second-stage temperature is 572°C, and the third-stage temperature is 505°C. The PI parameter is tuned using the Ziegler-Nichols critical proportionality method.

[0123] Comparative Example 1 uses a combination of constant temperature control and staged condensation collection to process the same raw materials as in Example 1. The equipment parameters, condensation channel structure, and condensation temperature adjustment coefficient are all the same as in Example 1. The difference from Example 1 is that the dynamic temperature control function in step S3 is not enabled; the temperature of each reduction stage remains constant throughout the entire operation: stage I is constant at 940°C, stage II at 1140°C, and stage III at 1200°C; and online flue gas monitoring and PI control are not performed.

[0124] Comparative Example 2 uses a dynamic temperature control combined with a single-channel flue gas mixing and collection method to process the same raw materials as in Example 1. The equipment parameters and PI control parameters are the same as in Example 1. The difference from Example 1 is that instead of setting up three independent condensation and collection channels, the zinc-containing flue gas from the three reduction sections is combined and introduced into a single condensation and collection channel. A quench tower, cyclone separator, and bag filter are used for mixed condensation and collection, with a quench temperature of 650°C.

[0125] Comparative Example 3 uses a traditional constant temperature control combined with a single-channel flue gas mixing and collection method to process the same raw materials as in Example 1. The equipment parameters are the same as in Example 1. The difference from Example 1 is that dynamic temperature control is not enabled, nor is staged condensation collection set up; the temperature of each section is constant as in Comparative Example 1, and the flue gas mixing and collection is the same as in Comparative Example 2.

[0126] Experiment 1: Verification of the Response Characteristics of Dynamic Temperature Control PI Algorithm; The response characteristics of the dynamic temperature control PI algorithm were tested using the method and equipment of Example 1, and compared with the constant temperature control of Comparative Example 1. The test method was as follows: Under continuous stable operation, at the 40-minute mark, a batch of material with a high zinc content was manually switched, with Zn abruptly changing from 6.8% to 8.5%, and the zinc reduction progress index of the second reduction stage was recorded. The real-time changes in the material before and after disturbance, and the temperature regulation output of the PI controller. The process of change over time. Comparative Example 1 records under the same disturbance conditions. The data changes. Each data point is automatically recorded by the central controller at 0.5-minute intervals.

[0127] Experimental results are as follows Figure 1 As shown. Figure 1 (a) shows the second reduction stage of Example 1 and Comparative Example 1 under material disturbance. The tracking response comparison curve over time, with the X-axis representing time (min) and the Y-axis representing... In the figure, the solid blue line represents the PI dynamic temperature control of Example 1, the dashed red line represents the constant temperature control of Comparative Example 1, and the dotted black line represents the target value. =0.65, with the green dotted line marking the time when the material disturbance occurred. Figure 1 (b) shows the temperature regulation output of the PI controller in Example 1 under this disturbance. The curve shows the change over time, with the X-axis representing time (min) and the Y-axis representing... The values ​​(°C) are shown in the graph. The solid blue line represents the temperature adjustment amount, the dashed red line represents the limit value of ±60°C, and the green dotted line marks the time when the material disturbance occurs.

[0128] from Figure 1 As can be seen in (a), after adopting PI dynamic temperature control in Example 1, The material disturbance returned to the target value within approximately 8–12 minutes after the deviation occurred. With a value around 0.65, overshoot ≤5%, and steady-state deviation <0.03, it exhibits good tracking response characteristics. Comparative Example 1, under isothermal control, After material disturbance, the deviation from the target value persists and cannot automatically return to normal, with the deviation exceeding 0.12 and remaining there for an extended period. Figure 1 As can be seen in (b), the PI controller quickly outputs a negative temperature regulation after the disturbance occurs, due to the high zinc content of the material. Too high, deviation = - <0, therefore When the value is negative, a cooling command is issued, with a maximum adjustment range of approximately -35°C. The temperature adjustment then gradually converges to around 0, and the adjustment amount never exceeds the limit. =60°C. This indicates that step S3 of the present invention and the zinc reduction progress index are... The feasibility and effectiveness of the feedback-based PI dynamic temperature control method. The PI controller monitors the flue gas composition in real time and calculates... It can sense changes in the state of materials and automatically adjust the temperature, so that the reduction progress tracks the target value, while constant temperature control cannot cope with material fluctuations due to the lack of a feedback mechanism.

[0129] Experiment Example 2: Comparative Verification of the Composition of Staged Condensation Products; Examples 1, 2, and 3 were all conducted using dynamic temperature control + staged collection; Comparative Example 2 used dynamic temperature control + mixed collection; and Comparative Example 3 used constant temperature + mixed collection. The chemical composition of the zinc oxide products collected under each method was analyzed. The experimental results are as follows: Figure 2 As shown. Figure 2Grouped bar charts were created to collect the Zn, Fe, Pb, and Cl contents of the products from each scheme. The X-axis represents each scheme and its product level: Example 1 Level I, Example 1 Level II, Example 2 Level I, Example 2 Level II, Example 3 Level I, Example 3 Level II, Comparative Example 2 Mixed Product, and Comparative Example 3 Mixed Product. The Y-axis represents the mass fraction (%) of each component. In the chart, blue bars represent Zn content, red bars represent Fe content, yellow bars represent Pb content, and green bars represent Cl content.

[0130] from Figure 2 It can be seen that in Examples 1, 2, and 3, which adopted staged condensation and collection, the Zn grade of the first-stage product reached 67.2%, 69.5%, and 68.1%, respectively, all higher than 65%, and far higher than the comparative examples 248.5% and 347.3% of the mixed collection. Meanwhile, the Fe content of the first-stage product in all three examples was ≤2.1%, Pb content was ≤0.3%, and Cl content was ≤0.5%, significantly lower than the corresponding 8.2%–8.8%, 1.5%–1.6%, and 2.8%–3.0% of the mixed product. Although the Pb and Cl content of the electric arc furnace ash raw material in Example 2 was much higher than the Pb content of 2.8% and Cl content of 3.5% in Examples 1 and 3, the Pb and Cl content of the first-stage product after staged collection was still controlled at a low level of 0.3% and 0.5%, respectively, indicating that the staged condensation channel has a good impurity separation effect on different raw materials. The above results are related to S4 of the present invention and the staged condensation and fractional collection method. Since the first reduction stage only reduces... In this section, the content of iron vapor and heavy metal impurities in the flue gas is naturally low. High-grade products can be obtained directly by collecting the flue gas through an independent condensation channel, avoiding the dilution of grade caused by mixing with the iron- and lead-containing flue gas in the second reduction section.

[0131] Experiment Example 3: Optimization and Verification of Condensation Temperature Adjustment Coefficient; This experiment uses the equipment and raw materials from Example 1, and fixes the reference temperature of the second reduction stage. =1140°C and PI control parameters remain unchanged, only the condensing temperature adjustment coefficient of the second-stage condensing channel is changed. Values, respectively Ten levels were established: 0.5, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.5. After running continuously for 3 days at each level, samples were taken for analysis of the Zn grade and zinc capture rate of the Level II product. The Level II condensation temperature was determined using the formula... = - ×( - ) calculate, where =907°C, actual measurement =1150°C. Zn grade was determined by EDTA complexometric titration; zinc capture rate was calculated by mass balance method, i.e., the mass of zinc in the stage II collected product divided by the total amount of zinc in the flue gas of stage II reduction.

[0132] Experimental results are as follows Figure 3 As shown. Figure 3 The condensing temperature adjustment coefficient for the second-stage condensing channel. The relationship curves between product Zn grade and zinc capture rate are plotted using a dual Y-axis. The X-axis represents... The value is also labeled at the top of the graph by the formula. =907- The corresponding condensation temperature is calculated using ×(1150-907). The left Y-axis represents the product Zn grade (%), indicated by a blue circular marker line, and the right Y-axis represents the zinc capture rate (%), indicated by a red square marker line. The light blue shaded area in the figure indicates Level II. The preferred range is 1.0 to 1.8, and the preferred operating point of Example 1 is marked with a black pentagram. =1.4.

[0133] from Figure 3 It can be seen that, with Increasing the condensation temperature lowers the zinc capture rate; the red square marker line rises monotonically, but the rate of increase gradually decreases, while the blue circular marker line for Zn grade shows a trend of first rising and then falling. The grade reaches its peak value within the range of 1.2-1.6. When When the condensation temperature is too low and too high, the zinc vapor condenses insufficiently, and some zinc escapes with the exhaust gas, leading to a decrease in the capture rate. Simultaneously, insufficient condensation results in poor separation of impurities from the zinc vapor, leading to a lower grade. When the condensation temperature is too high and too low, although the capture rate is close to the upper limit, excessive cooling causes impurities such as alkali metal chlorides and iron vapors to condense simultaneously in the quench tower and mix into the zinc product, resulting in a decrease in grade. In this invention... Within the light blue shaded area of ​​the =1.01.8 range graph, the Zn grade consistently remained above 52.7%, significantly better than values ​​outside this range, while the capture rate also reached a relatively high level of 95.3% to 96.8%. At a concentration of 1.4, the optimal balance between grade and capture rate is achieved, corresponding to the black pentagram mark in the preferred operating point diagram of Example 1. This verifies the formula of the present invention. = - ×( - The validity of the condensation temperature setting as a basis. The condensation temperature is determined by... The adjustment coefficient is controlled within an appropriate range below the boiling point of zinc, which ensures the full condensation of zinc vapor and utilizes the difference in condensation temperature of different components to achieve selective separation of impurities.

[0134] Experiment Example 4: Comparison and Verification of Total Zinc Recovery Rate and Proportion of Products from the First-Stage Channel; The results of 30 days of continuous operation of Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were summarized, and a comprehensive comparison was made between the total zinc recovery rate and the percentage of product mass collected in the first-stage condensation channel relative to the total product mass of all channels. The zinc recovery rate was calculated based on the mass balance of the zinc mass entering the furnace and the zinc mass collected from each stage of the product. The proportion of products from the first-stage channel was calculated by weighing the cumulative output mass of each stage of the product bins. Comparative Examples 2 and 3 did not have a graded collection system, so there were no products from the first-stage channel, and their proportion was recorded as 0%.

[0135] Experimental results are as follows Figure 4 As shown. Figure 4 The middle section (a) is a bar chart comparing the total zinc recovery rates of each scheme. The X-axis represents the name of each scheme, and the Y-axis represents the total zinc recovery rate (%). The examples are represented by blue bars, and the comparative examples are represented by red bars. Figure 4 (b) is a bar chart comparing the proportion of products in the Level I channel for each scheme. The X-axis represents the name of each scheme, and the Y-axis represents the proportion of products in the Level I channel (%). The color marking method is the same as above. Figure 4 (a).

[0136] from Figure 4 As shown in Figure (a), the total zinc recovery rates of Examples 1-3 were all above 95%, significantly higher than those of Comparative Example 1 (90.5%) and Comparative Example 3 (388.2%). Comparative Example 2, which employed dynamic temperature control, achieved a recovery rate of 95.0%, close to that of Examples 1, indicating that dynamic temperature control is a key technology for improving zinc recovery. Although Comparative Example 1 involved staged collection, the constant temperature control resulted in insufficient reduction in some batches, resulting in a recovery rate of only 90.5%. Comparative Example 3, lacking both dynamic temperature control and staged collection, had the lowest recovery rate of 88.2%, a difference of 7.1 percentage points from Example 1.

[0137] from Figure 4 As can be seen in (b), the proportion of products from the first-stage channel in Examples 1-3 is 48%-52%, meaning nearly half of the products come from the first-stage channel, with grades of 67.2%, 69.5%, and 68.1% respectively, all ≥65%, allowing them to directly enter the hydrometallurgical zinc smelting process. Although Comparative Example 1 involved graded collection, the reduction precision in each stage was insufficient due to constant temperature control, resulting in insufficient reduction in the first reduction stage. The selective reduction efficiency was low, with the product output of the first-stage channel accounting for only 43%, and the product grade of this channel being only 63.5%. Comparative Examples 2 and 3, lacking a staged condensation channel, collected all products together, with no first-stage channel product, resulting in a 0% proportion in both cases. This indicates that the dynamic temperature control of this invention primarily contributes to the improvement of zinc recovery rate, compared to 95.3% in Example 1 and 90.5% in Comparative Example 1. Staged condensation collection primarily contributes to the acquisition of high-grade first-stage products, compared to 48% in Example 1 and 0% in Comparative Example 2. The combined application of both methods optimizes both the recovery rate and the proportion of first-stage products.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for graded reduction of zinc-containing dust from iron and steel smelting, characterized in that, Includes the following steps: S1. Batching and pelletizing: Zinc-containing dust collector ash is mixed with carbon reducing agent and then pelletized to prepare green pellets; S2, graded gradient reduction: The green pellets are continuously fed into a multi-stage reduction furnace and undergo graded carbothermic reduction in sequence through the first reduction stage, the second reduction stage and the third reduction stage; S3. Online monitoring and dynamic temperature control of flue gas: The volume concentration of carbon monoxide, the volume concentration of carbon dioxide, and the mass concentration of zinc vapor in the flue gas are detected in real time at the flue gas outlet of each reduction section. The zinc reduction progress index of each section is calculated based on the detection data. The heat supply of the burner in each section is dynamically adjusted according to the deviation between the zinc reduction progress index and the preset target value using a proportional-integral control algorithm. S4. Staged condensation and separate collection: The zinc-containing flue gas produced in each reduction section is introduced into three independent condensation and collection channels for condensation and dust removal, and high-grade secondary zinc oxide, medium-grade secondary zinc oxide and low-grade zinc-containing dust are collected respectively. The low-grade zinc-containing dust is returned to step S1 to participate in the batching. S5. Residue discharge: The solid material after three-stage reduction is discharged from the discharge end of the multi-stage reduction furnace.

2. The method according to claim 1, characterized in that, Step S2 includes: S21, Reduction in the first reduction stage: The green pellets enter the first reduction stage and undergo carbothermic reduction under the following conditions. The zinc vapor is reduced to zinc vapor and volatilizes into the flue gas in this section. Because its spinel lattice energy is higher than However, under these temperature conditions, it was not effectively decomposed, and the iron oxides were essentially not reduced; this step achieves... The selective preferential reduction of the phase results in low iron vapor and iron-containing particle content in the zinc-containing flue gas. S22, Second Reduction Stage: The material processed in the first reduction stage passes through the first baffle ring and enters the second reduction stage, where it undergoes carbothermic reduction at a higher temperature. The spinel structure is destroyed, zinc is reduced to zinc vapor and volatilizes into the flue gas in this section, and iron is reduced to zinc vapor. Form remains in the solid phase; realization Reduction extraction of zinc from the phase; S23, Reduction in Section III: The material processed in Section II passes through the second baffle ring and enters Section III, where the zinc-containing phases remaining in the first two sections are deeply reduced at the highest temperature to obtain a reduction slag with low zinc content.

3. The method according to claim 1, characterized in that, Step S3 includes: S31. Online Flue Gas Detection and Filtering: At the flue gas outlets of each of the first, second, and third reduction sections, an infrared gas analyzer is used to detect... volume concentration and Volume concentration is determined by detecting the mass concentration of zinc vapor using a laser-induced breakdown spectroscopy device. The detection data is transmitted to the central controller in real time, and the central controller performs moving average filtering on each detection signal. This step obtains the real-time flue gas composition data of each segment after filtering. S32. Calculate the zinc reduction progress index: Based on the filtered data obtained in step S31, the central controller calculates the zinc reduction progress index for each segment at the current time using the following formula: ;in, For the first Level restoration segment in Indicators of zinc reduction progress at any given time; For the first Level restoration segment in The mass concentration of zinc vapor after filtering at any given time; For the first The theoretical maximum zinc vapor concentration in the reduction stage is determined by dividing the theoretically reducible zinc mass of that stage by the product of the flue gas volume flow rate and the material residence time. For the first Level restoration segment in Time after filtering Volume concentration; For the first Level restoration segment in Time after filtering Volume concentration; The restored segment number can be I, II, or III; For the detection time; Obtain comprehensive indicators to characterize the progress of zinc volatilization completion and the adequacy of the reducing atmosphere; S33, Dynamic temperature control: The central controller will calculate the temperature in step S32. Compared with the preset zinc reduction progress target value of each section Compare the values ​​and calculate the temperature adjustment for each segment using the proportional-integral control algorithm. ,Will Superimposed on the reference set temperature of each segment The actual target temperature of each segment is obtained. The output is then sent to the corresponding burner group controller; this step enables adaptive dynamic adjustment of the temperature of each segment based on the actual reduction state. Calculate the temperature adjustment amount and determine the actual target temperature using the following formula: ； ;in, For the first Level restoration segment in The temperature adjustment value at any given time; a positive value indicates a temperature increase, and a negative value indicates a temperature decrease. For the first The proportional gain coefficient of the first-stage reduction section; For the first The preset target value for zinc reduction progress in the first stage of reduction; For the first Level restoration segment in Indicators of zinc reduction progress at any given time; For the first Integral gain coefficient of the first-stage reduction section, subscript Indicates the integral; For the summation operation, for the first to the second... The deviation within each control cycle is accumulated cycle by cycle; For the first Level restoration segment in the first Each control cycle time The zinc reduction progress indicator; To control cycle duration; As of The total number of control cycles that have been executed at any given time; For the first Level restoration segment in The actual target temperature at any given time; For the first The reference set temperature for the first stage of reduction; real-time closed-loop temperature control based on the deviation of the zinc reduction progress index.

4. The method according to claim 1, characterized in that, Step S4 includes: S41, Stage I condensation and collection: The zinc-containing flue gas discharged from the outlet of the first reduction stage is introduced into the stage I condensation and collection channel, cooled by a quench tower, and then collected sequentially by a cyclone separator and a bag filter to obtain a high-grade secondary zinc oxide product; since the first reduction stage only reduces... In this phase, iron oxides do not participate in the reaction, and the product obtained in this step has low iron impurities and high grade; S42, Stage II Condensation and Collection: The zinc-containing flue gas discharged from the outlet of the Stage II reduction section is introduced into the Stage II condensation and collection channel. After being cooled by a quench tower, it is collected sequentially by a cyclone separator and a bag filter to obtain a medium-grade secondary zinc oxide product; due to the decomposition of the Stage II reduction section... Iron oxides participate in the reaction simultaneously, and the product obtained in this step has a lower grade than the Grade I product. S43, Stage III Condensation and Collection: The zinc-containing flue gas discharged from the flue gas outlet of the Stage III reduction section is introduced into the Stage III condensation and collection channel. After being deeply cooled by the quench tower, low-grade zinc-containing dust is collected by the cyclone separator and bag filter. The dust is then sent back to step S1 via the return material conveying device to participate in the batching process. This achieves the capture and recovery of residual zinc and avoids zinc loss.

5. The method according to claim 4, characterized in that, The quenching temperatures of the three sets of condensation collection channels in steps S41 to S43 are set to decrease sequentially from stage I to stage III according to the following principles: S411, the quench tower of the first-stage condensation and collection channel cools the flue gas to a higher temperature range below the boiling point of zinc, causing the zinc vapor to condense into fine zinc oxide powder; alkali metal chlorides, due to their condensation temperature being lower than that of zinc, mostly enter the downstream dust removal process with the tail gas, achieving the initial separation of zinc products from alkali metal impurities. S412, the quench tower of the second-stage condensation collection channel cools the flue gas to a temperature range lower than the first-stage quench temperature, promoting the full condensation and sedimentation of iron vapor and volatile heavy metal impurities, and reducing their mixing with the secondary zinc oxide product. The quench tower in the S413 and third-stage condensation collection channel cools the flue gas to the lowest temperature range in the three stages to fully capture the residual low-concentration zinc vapor; the specific value of the third-stage quench temperature is determined through optimization tests during the commissioning phase.

6. A grading and reduction device for zinc-containing dust in iron and steel smelting, implementing the method of any one of claims 1 to 5, characterized in that, include: The feeding and pelletizing unit is used to mix zinc-containing dust and carbon reducing agent and pelletize them. The discharge port is connected to the feed end of the multi-stage reduction furnace. The multi-stage reduction furnace has three stages: reduction stage I, reduction stage II, and reduction stage III, arranged sequentially along the length of the furnace body. Each reduction stage is equipped with an independent burner group. A refractory heat-insulating baffle ring fixed to the inner wall of the furnace body is provided between adjacent reduction stages. Each reduction stage has an independent flue gas outlet at the end of each stage. The staged flue gas condensation and collection unit includes three independent condensation and collection channels, which are respectively connected to the flue gas outlets of the first reduction section, the second reduction section, and the third reduction section. Each condensation and collection channel includes a quench tower, a cyclone separator, and a bag filter in sequence along the flue gas flow direction. The powder outlet of each bag filter is connected to an independent product silo. The product silo corresponding to the third reduction section is connected to the feeding and pelletizing unit through a return material conveying device. The online monitoring and intelligent control unit includes an infrared gas analyzer, a laser-induced breakdown spectroscopy device, and a central controller. The infrared gas analyzer is used to detect gases in each section of the flue gas. volume concentration and Volume concentration: The laser-induced breakdown spectroscopy device is used to detect the mass concentration of zinc vapor in each section of flue gas, and one set of both is installed at the flue gas outlet of each reduction section; The central controller is connected to the signal output terminal of each analytical instrument and the signal input terminal of each burner group controller, and has built-in detection signal filtering program, zinc reduction progress index calculation program and proportional-integral temperature control program.

7. The device according to claim 6, characterized in that, The central controller adopts a hierarchical architecture of programmable logic controller (PLC) and industrial computer. The PLC is directly connected to each infrared gas analyzer, each laser-induced breakdown spectroscopy device, and each burner group controller, and is responsible for high-frequency execution of the detection signal filtering program, the zinc reduction progress index calculation program, and the proportional-integral temperature control program. The industrial computer is connected to the PLC via a communication bus and is responsible for the operation parameter self-tuning program, the online correction program for the theoretical maximum zinc vapor concentration, and historical data recording. The industrial computer is connected to a human-machine interface terminal for real-time display of temperature, flue gas composition, and zinc reduction progress index for each segment, and allows operators to set and modify target values ​​and control parameters for each segment.

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