A method for preparing sintered magnesite-chrome sand by using a table tile circulation service

Abstract

The present application belongs to the technical field of waste refractory recycling and high-temperature sintering process control, and discloses a method for preparing sintered magnesia-chrome sand by recycling service of table bricks. The waste magnesia-chrome table bricks are cleaned, crushed, ground, classified, dehydrated and dried to obtain regenerated powder, the dry basis batch quality data and the mass fraction of magnesium oxide and chromium trioxide are collected, the compensation batching, feeding mixing, continuous re-measuring and component convergence judgment are performed to obtain the corrected mixed powder and the corrected component state quantity; the spherical green body is formed by double-source binder compounding, granulation and drying, the carbon monoxide target volume concentration sequence of the batch is generated according to the corrected component state quantity and the sintering temperature rise gradient, and the carbon monoxide gas supply regulating valve is feedback controlled according to the actual carbon monoxide volume concentration and the sintering temperature rise gradient, so that the spherical green body completes high-temperature solid-phase sintering. The present application provides technical means for controlling the formation conditions of magnesia-chrome spinel main crystal phase and the sintering body densification process.

Description

Technical Field

[0001] This invention relates to the field of waste refractory material recycling and high-temperature sintering process control technology, specifically to a method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service. Background Technology

[0002] Magnesia-chrome refractories combine the alkali resistance of magnesia with the high-temperature stability of the magnesia-chrome spinel structure, making them suitable for use in steel refining furnaces, non-ferrous metal smelting furnaces, and other industrial furnaces subjected to high-temperature erosion and thermal cycling. Regular maintenance of high-temperature equipment and replacement of refractory linings generate waste magnesia-chrome lining bricks. After high-temperature service, slag erosion, localized penetration, and thermal cycling, the magnesium oxide content, chromium trioxide content, and impurity composition of these waste magnesia-chrome lining bricks vary depending on the furnace type, service location, and replacement batch. However, some waste magnesia-chrome lining bricks still retain usable magnesia and chromium components, providing a basis for reuse as recycled refractory raw materials.

[0003] Existing recycling routes for waste refractory materials typically involve processes such as sorting, crushing, screening, fixed-ratio blending, molding, and heat treatment. For raw materials with stable composition sources, a fixed formula can meet basic production requirements. However, the residual components of waste magnesia-chrome countertop tiles are affected by their service history. When magnesia or chrome raw materials are added in a fixed ratio at once, batch-to-batch variations in raw materials will translate into deviations in the actual mass ratio of magnesia to chromium trioxide in the mixture. If only the incoming material is tested and not retested after feeding and mixing, it is impossible to confirm whether measurement errors, deviations in the effective components of the raw materials, and the mixing state have been corrected.

[0004] On the other hand, high-temperature sintering processes typically operate according to a fixed temperature rise regime and a fixed atmosphere setpoint. For natural mineral raw materials or standard raw materials with stable composition, a fixed regime can maintain continuous process operation. However, for recycled powder formed from waste magnesia-chrome countertop tiles, even if the mass ratio of magnesium oxide to chromium trioxide is adjusted to the target range through compensating batching, the corrected chromium trioxide mass fraction and impurity background may still vary within acceptable limits between different batches. If the component adjustment process and the sintering control process are independent of each other, the corrected component state obtained upstream cannot continue to participate in downstream atmosphere control, and the sintering atmosphere can only operate according to a fixed target value, unable to respond to changes in the state of the recycled raw material batch and the sintering temperature rise.

[0005] When the sintered body moves from the high-temperature sintering zone to the cooling zone, the surface temperature change is affected by the charge amount, particle size, degree of sintering, cooling airflow, and ambient heat exchange conditions. When a fixed cooling fan frequency is used, different batches may experience different cooling processes. Excessive cooling rate may increase thermal stress, while insufficient cooling rate may prolong the production cycle. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing sintered magnesia-chromium sand using cyclic service of countertop tiles, in order to solve the technical problems of inconsistent batch composition of waste magnesia-chromium countertop tiles, the inability to confirm the results of a single batching, the disconnect between the composition state and sintering control, and the inability of a fixed cooling intensity to respond to the actual cooling state of the sintered body.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] This invention discloses a method for preparing sintered magnesium chromium sand using countertop tiles in cyclic service. The method includes raw material classification and cleaning, crushing and grinding, slurry grading, dehydration and drying, dry basis component detection, compensation batching, mixing and retesting and component convergence determination, dual-source binder compounding, granulation and drying, temperature-gas coupled high-temperature sintering, feedback cooling, crushing and screening and quality detection.

[0009] Waste magnesia-chrome countertop bricks are classified according to the furnace type and service batch, and surface slag, refractory fibers, metal inclusions, and obvious loose powdery layers are removed. The cleaned waste magnesia-chrome countertop bricks are then crushed into coarse particles suitable for grinding.

[0010] Coarse particles are fed into a wet ball mill for grinding to obtain a recycled slurry. The recycled slurry is then classified by a classifier. Coarse particles that do not meet the target particle size are returned to the wet ball mill for further grinding. The recycled slurry that meets the target particle size is then dewatered and dried to form recycled powder.

[0011] In this invention, the batch mass, magnesium oxide mass fraction, and chromium trioxide mass fraction of the recycled powder are all measured and expressed on a dry basis. A batch weighing device obtains the dry-basis batch mass of the recycled powder, and a component detection unit obtains the dry-basis magnesium oxide mass fraction and dry-basis chromium trioxide mass fraction of the recycled powder.

[0012] Mass conservation compensation calculations were performed based on the dry batch mass of the recycled powder, the dry magnesium oxide mass fraction, the dry chromium trioxide mass fraction, and the content of the effective components of the adjusting components.

[0013] ;

[0014] in, This indicates the mass of magnesium-modifying components added. This indicates the mass of chromium-modifying components added. This indicates the mass ratio of the target magnesium oxide to chromium trioxide. This indicates the dry basis mass fraction of magnesium oxide in the recycled powder. This indicates the dry basis mass fraction of chromium trioxide in the recycled powder. This indicates the dry basis batch weight of the recycled powder. This indicates the effective magnesium oxide mass fraction of the magnesium-modifying component. Indicates the effective chromium trioxide mass fraction of the chromium-modifying component; subscript Indicates the magnesium-regulated branch, subscript Indicates the chromium regulation branch, subscript Indicates the target state, subscript Indicates batch status.

[0015] When the actual mass ratio of magnesium oxide to chromium trioxide in the recycled powder is lower than the target mass ratio of magnesium oxide to chromium trioxide, the process controller generates a magnesium conditioning batching execution command; when the actual mass ratio of magnesium oxide to chromium trioxide in the recycled powder is higher than the target mass ratio of magnesium oxide to chromium trioxide, the process controller generates a chromium conditioning batching execution command.

[0016] The magnesium-based adjusting component can be one or more of light-burned magnesia powder, magnesite powder, or dolomite powder. The chromium-based adjusting component can be one or more of industrial chromium oxide powder or chromite powder. The effective magnesia mass fraction and effective chromium trioxide mass fraction included in the compensation calculation are based on the actual measured values ​​of the corresponding adjusting components, and are not replaced by the theoretical purity corresponding to the material name.

[0017] The metering and feeding equipment completes the feeding according to the batching execution command. After the mixing equipment completes the predetermined mixing process, the component detection unit re-obtains the mass fraction of magnesium oxide and chromium trioxide in the mixed powder.

[0018] When the absolute deviation of the actual mass ratio of magnesium oxide to chromium trioxide from the target mass ratio of magnesium oxide to chromium trioxide exceeds the proportioning error threshold, the batching execution instruction is regenerated based on the latest test data.

[0019] The absolute deviation of the actual magnesium oxide to chromium trioxide mass ratio does not exceed the proportioning error threshold, and the absolute difference between two consecutive measurements of the magnesium oxide mass fraction and the absolute difference between two consecutive measurements of the chromium trioxide mass fraction do not exceed the state change threshold. When three consecutive valid measurements meet the above conditions, the process controller determines that the component state has converged. The proportioning error threshold is determined based on the allowable deviation of the target magnesium oxide to chromium trioxide mass ratio and the accuracy of the metering equipment, and is set to 0.02 in some embodiments. The state change threshold is determined based on the repeatability accuracy of the component detection unit and the process stability requirements, and is set to 0.20 percentage points in some embodiments.

[0020] After the component states converge, a corrected mixed powder and a corrected component state quantity are formed. The corrected component state quantity includes at least the corrected magnesium oxide mass fraction, the corrected chromium trioxide mass fraction, and the actual magnesium oxide to chromium trioxide mass ratio formed by continuous and effective detection.

[0021] The chromium trioxide mass fraction is corrected and the process continues into the high-temperature sintering control process, without stopping use after the compensation batching is completed.

[0022] Organic and inorganic binders are added to the corrected mixed powder. The organic binder is used to improve the molding retention ability during the granulation and low-temperature drying stages, while the inorganic binder is used to maintain the spherical green body structure after the gradual thermal decomposition of the organic binder.

[0023] Organic binders can be polyvinyl alcohol solutions or dextrin solutions, while inorganic binders can be sodium silicate solutions or phosphate solutions. The total amount of organic and inorganic binders added should be controlled between 1% and 3% of the corrected mixed powder mass.

[0024] The material with the binder compounded is fed into a granulation device to form spherical green bodies. The spherical green bodies are dried at 80°C to 150°C until the residual moisture content is no higher than 0.5%.

[0025] Spherical green billets enter the high-temperature sintering kiln. The process controller establishes the correspondence between the current batch of spherical green billets and the sintering control zone.

[0026] When using a tunnel kiln, the sintering control zone of the current batch of spherical green billets is determined based on the kiln car batch identifier, the kiln entry time, and the kiln car's running position. In some embodiments, the tunnel kiln is equipped with a kiln car position encoder or proximity switch, and the process controller receives the position signal and establishes a mapping table with the kiln car batch identifier.

[0027] When using a rotary kiln, the control time window corresponding to the current batch of materials is determined based on the feeding time window, the rotary kiln speed, the rotary kiln tilt angle, and the average residence time obtained during equipment debugging.

[0028] The temperature acquisition unit collects the furnace temperature of the sintering control zone corresponding to the current material batch. Multiple temperature detection locations are set in the same sintering control zone. After filtering out communication interruptions and data that are outside the effective measurement range of the equipment, the process controller generates a temperature sequence for the sintering control zone based on the effective temperature detection results.

[0029] The process controller obtains the sintering temperature rise gradient based on the temperature change in the sintering control zone between adjacent control cycles and the time interval between control cycles.

[0030] The process controller uses the corrected chromium trioxide mass fraction after component state convergence and the sintering temperature rise gradient together to calculate the target volume concentration of carbon monoxide in the batch:

[0031] ;

[0032] in, Indicates the first The target volume concentration of carbon monoxide for each control cycle. This indicates the lower limit of the target volume concentration for carbon monoxide. This indicates the upper limit of the target volume concentration of carbon monoxide. Indicates the baseline carbon monoxide volume concentration. Represents the component coupling coefficient. This represents the corrected chromium trioxide mass fraction after the component states have converged. This indicates the reference chromium trioxide mass fraction. Represents the temperature gradient coupling coefficient. Indicates the first The sintering temperature rise gradient for each control cycle, Indicates the reference sintering temperature rise gradient. Indicates the control cycle number; This indicates that the calculation results are limited to a range between the lower limit and the upper limit of the target volume concentration of carbon monoxide. This indicates taking the maximum value among the values ​​within the parentheses, indicated by the subscript. Indicates carbon monoxide, superscript Indicates the target value, subscript Indicates reference status, subscript Indicates the lower limit, subscript Indicates the upper limit, subscript Indicates the temperature status.

[0033] It should be noted that the subscripts in the compensation calculation formula... The subscript in the above formula indicates the chromium-modifying branch. Both indicate the atmospheric concentration state and are used within the independent definition range of each formula.

[0034] During the calculation, the volume concentration is entered as a volume fraction decimal. For example, 1% is calculated as 0.01, and 5% is calculated as 0.05.

[0035] The baseline carbon monoxide volume concentration was obtained from kiln commissioning data under standard composition conditions and reference sintering temperature rise gradient.

[0036] The component coupling coefficients were obtained by fitting multiple calibration points corresponding to the stable carbon monoxide target volume concentration at the corrected chromium trioxide mass fraction state. The numerical values ​​and positive / negative directions of the component coupling coefficients are based on the calibration results.

[0037] The temperature rise gradient coupling coefficient is obtained by fitting the target concentration compensation amount corresponding to different sintering temperature rise gradient states.

[0038] In one embodiment, with a reference chromium trioxide mass fraction of 0.15 and a sintering temperature rise gradient of 5°C / min, the corresponding calibrated target carbon monoxide volume concentrations for calibrated chromium trioxide mass fractions of 0.15, 0.17, and 0.19 are 0.025, 0.033, and 0.041, respectively. Based on the above calibration points, the component coupling coefficient is 0.4.

[0039] When the chromium trioxide mass fraction is maintained at the reference state, the target volume concentrations after target concentration compensation are 0.025, 0.027 and 0.029 when the sintering temperature rise gradient is 5℃ / min, 6℃ / min and 7℃ / min, respectively. Based on the above calibration points, the temperature rise gradient coupling coefficient is 0.002℃⁻¹·min.

[0040] The furnace gas sampling location of the atmosphere analysis unit is set downstream of the carbon monoxide process gas inlet in the corresponding sintering control zone and upstream of the total flue gas collection point. The atmosphere analysis unit outputs the actual carbon monoxide volume concentration sequence for the current sintering control zone.

[0041] The process controller generates the carbon monoxide supply regulating valve opening command based on the target carbon monoxide volume concentration, the actual carbon monoxide volume concentration, and the sintering temperature rise gradient.

[0042] ;

[0043] in, Indicates the first Normalized carbon monoxide supply regulating valve opening command for each control cycle This indicates the normalized carbon monoxide supply regulating valve opening. This represents the proportional gain of the atmosphere concentration error. Indicates the first The atmospheric concentration error is obtained by subtracting the actual carbon monoxide volume concentration from the target carbon monoxide volume concentration for each control cycle. This represents the integral gain of the atmosphere concentration error. Indicates the sequence number of the integral summation. Indicates the control cycle number. Indicates the control cycle time interval. This represents the gain for temperature gradient error compensation. Indicates the first The temperature rise gradient error is obtained by subtracting the reference sintering temperature rise gradient from the sintering temperature rise gradient of each control cycle. This indicates a limiting operation that restricts the normalized carbon monoxide supply valve opening command to between zero and one; subscript Indicates the baseline state, subscript Indicates proportional effect, subscript Indicates the integral action, subscript Indicates the effect of temperature gradient compensation, subscript Indicates the state of atmospheric concentration.

[0044] The proportional gain of the atmosphere concentration error, the integral gain of the atmosphere concentration error, and the gain for compensating for the temperature rise gradient error are tuned based on the step response of the carbon monoxide supply system.

[0045] During the tuning process, the opening of the carbon monoxide supply regulating valve is changed within the allowable carbon monoxide volume concentration range. The response time, steady-state deviation, and response process required for the actual carbon monoxide volume concentration to reach a new stable state are recorded. The gain combination that does not produce continuous oscillations and can enter the error band within the allowable time of the process is selected.

[0046] In one implementation, the control cycle time interval is set to 60 seconds. When the absolute deviation between the actual carbon monoxide volume concentration and the batch target carbon monoxide volume concentration does not exceed 0.2 percentage points, and the absolute deviation between the sintering temperature rise gradient and the reference sintering temperature rise gradient does not exceed 0.5 °C / min, and these conditions are met for five consecutive control cycles, the process controller enters a hold control state. In the hold control state, the process controller continues to collect temperature and atmosphere concentration data and performs closed-loop correction after limiting, stopping the integral accumulation of atmosphere concentration error until the deviation exceeds the set conditions again.

[0047] The sintering temperature is controlled between 1650℃ and 1800℃, the holding time is controlled between 2h and 6h, and the volume fraction of carbon monoxide in the weakly reducing atmosphere is controlled between 1% and 5%.

[0048] Under high temperature conditions, magnesium oxide and chromium trioxide undergo a solid-state reaction:

[0049] ;

[0050] in, It represents magnesium oxide. It represents chromium trioxide. It represents magnesium chromium spinel.

[0051] The atmosphere control objective of this invention is to adjust the target volume concentration of carbon monoxide in the controlled sintering zone according to the composition state and the sintering temperature rise state, and to limit the deviation between the target state and the actual state through actual atmosphere feedback, so as to provide controlled process conditions for the formation of the main crystal phase of magnesium chromium spinel and the densification of the sintered body.

[0052] After sintering, the sintered body enters the cooling equipment. Multiple surface temperature detection positions are set along the cooling direction of the sintered body, and the temperature acquisition unit obtains the surface temperature sequence of the sintered body.

[0053] The surface cooling rate represents the positive value of the temperature drop on the surface of the sintered body per unit time.

[0054] When the surface cooling rate exceeds the upper limit of the cooling rate, the process controller sends a control command to the cooling fan inverter to reduce the frequency. The frequency reduction step is determined based on the rated frequency range of the cooling fan and the extent of the cooling rate exceeding the limit. In some embodiments, the rated frequency is reduced by 1% to 3% each time. When the surface cooling rate is below the lower limit of the cooling rate, the process controller sends a control command to the cooling fan inverter to increase the frequency. The frequency increase step is determined based on the rated frequency range of the cooling fan and the extent of the cooling rate deficiency. In some embodiments, the rated frequency is increased by 1% to 3% each time. When the surface cooling rate is within the cooling target range, the cooling fan frequency is maintained.

[0055] After cooling, the sintered body enters the sintered body crushing equipment and vibrating screen equipment. The sintered body can be crushed in two stages to form particles suitable for screening, and then separated into coarse-grained sintered magnesia-chromium sand, medium-grained sintered magnesia-chromium sand, and fine-grained sintered magnesia-chromium sand according to the particle size requirements.

[0056] The quality testing of sintered magnesia-chrome sand includes chemical composition analysis, crystal phase analysis, apparent porosity analysis, bulk density analysis, and compressive strength analysis. Chemical composition is determined using X-ray fluorescence spectrometry. The main crystalline phase of magnesia-chrome spinel is quantitatively analyzed using X-ray diffraction combined with Rietveld full-spectrum fitting; the proportion of the main crystalline phase mass to the total mass of the crystalline phase is defined as the main crystalline phase content. Apparent porosity and bulk density are determined using the immersion method. Compressive strength is tested using material pressure testing equipment.

[0057] Furthermore, when the component detection unit outputs a fault status, repeat detection differences exceed the allowable error of the equipment, or data communication is interrupted, the corresponding component detection data is marked as invalid data.

[0058] Invalid component detection data will not be included in the compensation calculation. The process controller will stop automatic feeding and output resampling and retesting instructions.

[0059] When the atmosphere analysis unit malfunctions or fails to generate valid data for two consecutive control cycles, the process controller stops the integral accumulation of atmosphere concentration error, maintains the opening of the carbon monoxide supply regulating valve that has been confirmed to be in a safe state the most recently, and triggers the safety interlock procedure of the high-temperature sintering kiln.

[0060] If a single abnormal measurement point exists in the temperature acquisition unit, the abnormal measurement point is removed, and the remaining valid measurement points are used to form the temperature sequence of the sintering control zone. When the number of valid temperature measurement points is lower than the control requirement, the process controller stops automatic temperature-gas coupling control and enters a safety control state.

[0061] The present invention also discloses a linkage control system for recycling waste magnesia-chromium countertop bricks to prepare sintered magnesia-chromium sand, including raw material cleaning equipment, crushing equipment, wet ball milling equipment, grading equipment, dehydration equipment, drying equipment, batch weighing equipment, component detection unit, process controller, metering and feeding equipment, mixing equipment, granulation equipment, high-temperature sintering kiln, temperature acquisition unit, atmosphere analysis unit, carbon monoxide supply regulating valve, cooling equipment, cooling fan, cooling fan frequency converter, sintered body crushing equipment, and vibrating screening equipment;

[0062] The raw material cleaning equipment, crushing equipment, wet ball milling equipment, classification equipment, dewatering equipment and drying equipment sequentially form a material handling path from waste magnesia-chrome countertop bricks to recycled powder. The batch weighing equipment sends the dry basis batch mass data of the recycled powder to the process controller, and the component detection unit sends the component detection data of the recycled powder or mixed powder to the process controller.

[0063] The process controller generates a batching execution instruction based on dry batch quality data and component detection data, and sends the batching execution instruction to the metering and feeding equipment. The metering and feeding equipment delivers magnesium or chromium conditioning components to the mixing equipment. The mixed powder output by the mixing equipment returns to the component detection unit to form a component compensation closed loop.

[0064] After the components converge, the corrected mixed powder is sequentially fed into the granulation equipment and the drying equipment to form spherical green bodies. The high-temperature sintering kiln receives the spherical green bodies. The temperature acquisition unit sends the temperature sequence of the sintering control zone to the process controller. The atmosphere analysis unit sends the actual carbon monoxide volume concentration sequence to the process controller. The process controller receives the corrected component state quantity, the sintering control zone temperature sequence and the actual carbon monoxide volume concentration sequence, and sends an opening command to the carbon monoxide gas supply regulating valve.

[0065] The sintered material output from the high-temperature sintering kiln enters the cooling equipment. The temperature acquisition unit sends the surface temperature sequence of the sintered material to the process controller. The process controller sends a frequency control command to the frequency converter of the cooling fan according to the surface temperature sequence of the sintered material. The frequency converter of the cooling fan controls the cooling fan to provide cooling airflow to the cooling equipment. The cooled sintered material enters the sintered material crushing equipment and the vibrating screening equipment in sequence to form sintered magnesium chromium sand.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] This invention forms a continuous technology chain through closed-loop component compensation, cross-process component state transfer, temperature-gas coupled sintering control, and surface cooling rate feedback. The component compensation stage does not perform only one component detection and one feeding; instead, it re-detects the mixed powder after feeding and mixing, simultaneously checking the actual mass ratio deviation, the continuous change in magnesium oxide mass fraction, and the continuous change in chromium trioxide mass fraction. Only after three consecutive valid detections satisfying the convergence condition is the corrected component state value allowed to be generated, reducing control errors caused by directly equating theoretical feeding results with the actual mixing state. The corrected component state value continues into the high-temperature sintering control process. The corrected chromium trioxide mass fraction, together with the sintering temperature rise gradient, forms the batch carbon monoxide target volume concentration sequence; therefore, the raw material state data continues to participate in subsequent process control after batching, forming a data dependency between preceding and following processes. During the cooling stage, the cooling fan frequency is adjusted according to the actual surface cooling rate of the sintered body, enabling the cooling process to respond to the actual cooling state and providing process control conditions to limit excessively rapid cooling and shorten unnecessary low-intensity cooling time. Attached Figure Description

[0068] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0069] Figure 1 This is a flowchart of the main method for preparing sintered magnesia-chromium sand using countertop tiles in the present invention.

[0070] Figure 2 This is a flowchart of the compensation ingredient calculation and instruction generation process of the present invention.

[0071] Figure 3 This is a flowchart of the raw material pretreatment and recycled powder acquisition process of the present invention.

[0072] Figure 4 This is a partial flowchart of the binder compounding, granulation and sintering control of the present invention.

[0073] Figure 5 This is a flowchart of the sub-process for generating the opening command of the carbon monoxide supply regulating valve in this invention. Detailed Implementation

[0074] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0075] See Figures 1-5 This invention begins with waste magnesia-chrome countertop tiles, which are then sorted, cleaned, crushed, wet-ground, graded, dehydrated, and dried to form recycled powder. After dry-basis weighing and dry-basis component analysis, the recycled powder enters a component compensation closed-loop process.

[0076] The component compensation closed-loop calculation calculates the feed mass based on the mass fractions of magnesium oxide and chromium trioxide, batch mass, target mass ratio, and the effective component content of the adjusting components. After feed replenishment, the mixture is remixed and retested. Continuous testing until the convergence condition is met yields the corrected mixed powder and the state quantity of the corrected components.

[0077] The corrected mixed powder enters the dual-source binder compounding, granulation and drying process to form spherical green bodies.

[0078] The corrected chromium trioxide mass fraction in the corrected component state quantity continues to be incorporated into the sintering control. The process controller generates a batch carbon monoxide target volume concentration sequence based on the corrected chromium trioxide mass fraction and the sintering temperature rise gradient, and then adjusts the carbon monoxide supply regulating valve according to the actual carbon monoxide volume concentration and the sintering temperature rise gradient.

[0079] After the sintered body enters the cooling equipment, the surface temperature sequence of the sintered body is used to calculate the surface cooling rate, which is then used to control the frequency of the cooling fan. The cooled sintered body is then crushed, screened, and subjected to quality testing to obtain sintered magnesia-chromium sand.

[0080] Waste magnesia-chromium countertop tiles are derived from replacement parts of steel refining furnaces or non-ferrous metal smelting furnaces.

[0081] During the collection process, the furnaces are stored separately according to their source furnace type, service batch, and replacement area. Each batch is assigned a batch identifier, which must be associated with at least the original furnace type, replacement time, and raw material quality information.

[0082] During the cleaning process, slag, refractory fibers, metal inclusions, and loose powdery layers can be separated from the surface of the waste magnesia-chromium countertop tiles.

[0083] Waste magnesia-chrome countertop tiles with cracks but whose main body can still stably enter the mechanical crushing process are not automatically excluded based on cracks. Waste magnesia-chrome countertop tiles that cannot be stably conveyed or contain large metal foreign objects are further disassembled and foreign objects removed before entering the crushing process.

[0084] The cleaned-up waste magnesia-chrome countertop tiles are fed into a jaw crusher for coarse crushing.

[0085] In one embodiment, the particle size of the coarse crushed output is controlled between 20 mm and 50 mm.

[0086] Coarsely crushed particles are fed into the wet ball mill. During wet ball milling, the slurry concentration is controlled within the range of 60% to 75%. The wet ball mill uses wear-resistant grinding media, and the filling state of the grinding media and the rotation speed of the wet ball mill are determined according to the equipment manufacturing parameters and the target particle size.

[0087] The recycled slurry obtained from wet ball milling enters the classification equipment. Coarse particles that do not meet the target particle size are returned to the wet ball mill for further grinding, while the recycled slurry that meets the target particle size meets the dewatering equipment.

[0088] The dehydrated wet material is fed into a drying device to form recycled powder. The drying process ensures that the quality and chemical composition of subsequent batches can be consistently expressed on a dry basis.

[0089] In one embodiment, the median particle size of the recycled powder is controlled between 5 μm and 20 μm, and the specific surface area is controlled between 300 m² / kg and 800 m² / kg.

[0090] In the examples, the batch mass of the recycled powder refers to the dry basis batch mass, and the mass fractions of magnesium oxide and chromium trioxide are dry basis test values.

[0091] Batch weighing equipment obtains the dry basis batch mass of the current recycled powder.

[0092] When the component detection unit uses an X-ray fluorescence spectrometer, multiple incremental samples are obtained from different sampling times of the batch of powder. These multiple incremental samples are then mixed, reduced, and prepared for detection.

[0093] When the component detection unit uses an online elemental analysis device, the recycled powder passes through the controlled detection area, and the component detection unit outputs component detection data associated with the current batch identifier.

[0094] The process controller only initiates compensation calculations when the batch quality data, magnesium oxide mass fraction, and chromium trioxide mass fraction are all valid data.

[0095] The compensation calculation uses:

[0096] ;

[0097] in, This indicates the mass of magnesium-modifying components added. This indicates the mass of chromium-modifying components added. This indicates the mass ratio of the target magnesium oxide to chromium trioxide. This indicates the dry basis mass fraction of magnesium oxide in the recycled powder. This indicates the dry basis mass fraction of chromium trioxide in the recycled powder. This indicates the dry basis batch weight of the recycled powder. This indicates the effective magnesium oxide mass fraction of the magnesium-modifying component. Indicates the effective chromium trioxide mass fraction of the chromium-modifying component; subscript Indicates the magnesium-regulated branch, subscript Indicates the chromium regulation branch, subscript Indicates the target state, subscript Indicates batch status.

[0098] After the calculation is completed, the process controller converts the material replenishment quality into a batching execution command.

[0099] The metering and feeding equipment performs material feeding and returns the cumulative feed mass to the process controller. Once the cumulative feed mass reaches the target value, the process controller stops the corresponding metering and feeding equipment.

[0100] The mixing equipment performs the mixing. After mixing is complete, a new sample is taken and the components are analyzed.

[0101] In one implementation, the proportioning error threshold is set to 0.02, and the state change threshold is set to 0.20 percentage points.

[0102] When the absolute deviation of the actual magnesium oxide to chromium trioxide mass ratio obtained from three consecutive valid tests relative to the target value does not exceed 0.02, and the absolute difference between two consecutive tests of magnesium oxide mass fraction and two consecutive tests of chromium trioxide mass fraction does not exceed 0.20 percentage points, the process controller determines that the component state has converged.

[0103] After the component states converge, the final detection data from the three valid detections form the corrected component state quantity for the current batch.

[0104] The corrected mixed powder is fed into a mixing device for binder compounding. The organic binder is a polyvinyl alcohol solution or dextrin solution. The inorganic binder is a sodium silicate solution or phosphate solution. The total amount of organic and inorganic binders added is controlled between 1% and 3% of the mass of the corrected mixed powder.

[0105] In one embodiment, the amount of organic binder added is 1.2% of the corrected mixed powder mass, the amount of inorganic binder added is 0.8% of the corrected mixed powder mass, and the total amount added is 2.0%.

[0106] The mixture with the binder compounded is fed into a disc granulator to form spherical green bodies of 5mm to 12mm.

[0107] The spherical green bodies are fed into a drying equipment and dried at 120°C until the residual moisture content is no higher than 0.5%.

[0108] When using a tunnel kiln, each kiln car is associated with the current batch identifier of the spherical green billets. The process controller determines the sintering control zone of the current batch based on the kiln car's entry time and running position. In some embodiments, the tunnel kiln is equipped with a kiln car position encoder or proximity switch, and the process controller receives the position signal and establishes a mapping table with the kiln car batch identifier.

[0109] The detection data from the temperature acquisition unit and atmosphere analysis unit are supplemented with sintering control zone identifiers. The process controller correlates the corrected component state quantity with the temperature and atmosphere data of the same sintering control zone based on the kiln car position.

[0110] When using a rotary kiln, the process controller establishes a batch time identifier based on the feed time window, and estimates the control time window corresponding to the current batch based on the rotary kiln speed, inclination angle, and average residence time obtained during equipment commissioning. Atmosphere control utilizes the calibration component state variables and process detection data within the aforementioned control time window.

[0111] The temperature acquisition unit obtains the temperature sequence of the sintering control zone. The process controller obtains the sintering temperature rise gradient based on the temperature changes in the sintering control zone between adjacent control cycles and the time interval between control cycles.

[0112] The target volume concentration of carbon monoxide in a batch is obtained according to the following formula:

[0113] ;

[0114] in, Indicates the first The target volume concentration of carbon monoxide for each control cycle. This indicates the lower limit of the target volume concentration for carbon monoxide. This indicates the upper limit of the target volume concentration of carbon monoxide. Indicates the baseline carbon monoxide volume concentration. Represents the component coupling coefficient. This represents the corrected chromium trioxide mass fraction after the component states have converged. This indicates the reference chromium trioxide mass fraction. Represents the temperature gradient coupling coefficient. Indicates the first The sintering temperature rise gradient for each control cycle, Indicates the reference sintering temperature rise gradient. Indicates the control cycle number; This indicates that the calculation results are limited to a range between the lower limit and the upper limit of the target volume concentration of carbon monoxide. This indicates taking the maximum value among the values ​​within the parentheses, indicated by the subscript. Indicates carbon monoxide, superscript Indicates the target value, subscript Indicates reference status, subscript Indicates the lower limit, subscript Indicates the upper limit, subscript Indicates the temperature status.

[0115] The lower and upper limits of the target volume concentration of carbon monoxide are set based on the safe operating conditions of the high-temperature sintering kiln and the sintering process window. Within the scope of the process implementation of this invention, the target volume concentration of carbon monoxide is limited to 1% to 5%.

[0116] The atmosphere analysis unit continuously acquires the actual carbon monoxide volume concentration in the current sintering control zone.

[0117] The process controller uses the following formula to calculate the opening degree of the carbon monoxide supply regulating valve:

[0118] ;

[0119] in, Indicates the first Normalized carbon monoxide supply regulating valve opening command for each control cycle This indicates the normalized carbon monoxide supply regulating valve opening. This represents the proportional gain of the atmosphere concentration error. Indicates the first The atmospheric concentration error is obtained by subtracting the actual carbon monoxide volume concentration from the target carbon monoxide volume concentration for each control cycle. This represents the integral gain of the atmosphere concentration error. Indicates the sequence number of the integral summation. Indicates the control cycle number. Indicates the control cycle time interval. This represents the gain for temperature gradient error compensation. Indicates the first The temperature rise gradient error is obtained by subtracting the reference sintering temperature rise gradient from the sintering temperature rise gradient of each control cycle. This indicates a limiting operation that restricts the normalized carbon monoxide supply valve opening command to between zero and one; subscript Indicates the baseline state, subscript Indicates proportional effect, subscript Indicates the integral action, subscript Indicates the effect of temperature gradient compensation, subscript Indicates the state of atmospheric concentration.

[0120] In one controller tuning implementation, the control cycle time interval is set to 1 min, the reference normalized carbon monoxide supply regulating valve opening is set to 0.40, the atmosphere concentration error proportional gain is set to 5, the atmosphere concentration error integral gain is set to 0.5 min⁻¹, and the temperature rise gradient error compensation gain is set to 0.01℃⁻¹·min.

[0121] The above parameters are used to explain the controller implementation method. Before using the high-temperature sintering kiln, the parameters should be readjusted according to the actual gas supply pipeline and the step response of the carbon monoxide gas supply regulating valve.

[0122] The spherical green billets undergo heating and heat preservation in a high-temperature sintering kiln.

[0123] In one embodiment, the heating rate from room temperature to 600°C is 2°C / min to 5°C / min to gradually remove residual moisture and organic binder decomposition products from the spherical green body. The heating rate from 600°C to 1200°C is 3°C / min to 8°C / min. The heating rate from 1200°C to the maximum sintering temperature is 5°C / min to 10°C / min. The sintering temperature is 1650°C to 1800°C, and the holding time is 2 hours to 6 hours. Under these high-temperature conditions, the spherical green body forms a magnesium chromium spinel main crystalline phase and undergoes sintering densification.

[0124] Furthermore, after the sintered body enters the cooling equipment, the temperature acquisition unit continuously acquires the surface temperature of the sintered body. The process controller calculates the positive value of the temperature drop of the sintered body surface per unit time to obtain the surface cooling rate.

[0125] In one embodiment, the target surface cooling rate range for the 1800°C to 1200°C stage is set to 5°C / min to 10°C / min, and the target surface cooling rate range for the 1200°C to 600°C stage is set to 3°C / min to 5°C / min.

[0126] When the surface cooling rate exceeds the upper limit of the cooling rate for the corresponding stage, the process controller reduces the frequency of the cooling fan. The frequency reduction step is determined based on the rated frequency range of the cooling fan and the extent of the cooling rate exceeding the limit. In some embodiments, the rated frequency is reduced by 1% to 3% each time.

[0127] When the surface cooling rate is lower than the lower limit of the cooling rate for the corresponding stage, the process controller increases the frequency of the cooling fan. The frequency increase step is determined based on the rated frequency range of the cooling fan and the extent of insufficient cooling rate. In some embodiments, the rated frequency is increased by 1% to 3% each time.

[0128] When the surface cooling rate is within the target range, maintain the current cooling fan frequency.

[0129] The cooled sintered body enters the sintered body crushing equipment.

[0130] In one embodiment, a two-stage crushing process is employed. The first stage crushes the large sintered body to below 50 mm, while the second stage further breaks it down into particles suitable for processing by a vibrating screen. The vibrating screen separates the sintered magnesia-chrome sand into coarse particles (10 mm to 20 mm), medium particles (3 mm to 10 mm), and fine particles (0 mm to 3 mm). Quality testing includes at least chemical composition, crystal phase composition, apparent porosity, bulk density, and compressive strength.

[0131] One product determination criterion of the present invention is that the apparent porosity is less than 15%, the bulk density is greater than 3.3 g / cm³, and the compressive strength is greater than 50 MPa.

[0132] To facilitate a better understanding of the present invention by those skilled in the art, the present invention will be further described below with reference to specific embodiments.

[0133] Example 1: This example uses waste magnesia-chrome countertop tiles generated from the dismantling of steel smelting refining furnaces. After sorting and surface cleaning, the waste magnesia-chrome countertop tiles are crushed to less than 30mm.

[0134] Coarsely crushed particles are fed into a wet ball mill, with the slurry concentration controlled at 65%. The recycled slurry is then classified, with the coarse particles returned to the wet ball mill for further grinding. The recycled slurry that meets the particle size requirements is dewatered and dried to form recycled powder.

[0135] The median particle size of the recycled powder was 12 μm, and the specific surface area was 520 m² / kg.

[0136] The batch weighing equipment yielded a dry basis batch weight of 1000 kg of recycled powder.

[0137] The component detection unit yielded a dry-basis magnesium oxide mass fraction of 67.5% and a dry-basis chromium trioxide mass fraction of 14.8%.

[0138] The target magnesium oxide to chromium trioxide mass ratio was set to 3.8.

[0139] The initial mass ratio of magnesium oxide to chromium trioxide is: The initial mass ratio is higher than the target mass ratio, therefore chromium conditioning component compensation is performed. The effective chromium trioxide mass fraction of the chromium conditioning component is 95%. According to the law of conservation of mass, the mass of chromium conditioning component added is:

[0140]

[0141] The process controller sends a chromium conditioning batch dispensing instruction of 31.1911 kg to the metering and feeding equipment.

[0142] After the metering and feeding equipment completes the feeding, the mixing equipment performs the mixing.

[0143] After mixing, perform continuous component detection.

[0144] The first valid test result was 65.40% magnesium oxide and 17.15% chromium trioxide. The actual mass ratio was calculated as follows:

[0145] The second valid test result was 65.38% magnesium oxide and 17.16% chromium trioxide. The actual mass ratio calculation result was:

[0146] The third valid test result was 65.39% magnesium oxide and 17.16% chromium trioxide. The actual mass ratio calculation result was:

[0147] The absolute deviations of the three actual mass ratios from the target value of 3.8 are approximately 0.0134, 0.0100 and 0.0106, respectively, all not exceeding 0.02.

[0148] In continuous monitoring, the adjacent changes in the mass fractions of magnesium oxide and chromium trioxide were both less than 0.20 percentage points, therefore the process controller determined that the component states had converged.

[0149] The final corrected chromium trioxide mass fraction for the current batch was 17.16% based on the third valid test result.

[0150] Polyvinyl alcohol solution and sodium silicate solution were added to the correcting mixed powder, with the total amount added being 2% of the mass of the correcting mixed powder.

[0151] After mixing and disc granulation, spherical green bodies of 5 mm to 12 mm are formed.

[0152] The spherical green body was dried at 120°C, with a residual moisture content of 0.3%.

[0153] Spherical green billets enter a high-temperature tunnel kiln.

[0154] The high-temperature tunnel kiln uses kiln car batch identification for location mapping. The temperature acquisition unit collects temperature data of the sintering control zone where the current kiln car is located, and the atmosphere analysis unit collects the actual carbon monoxide volume concentration in the same sintering control zone.

[0155] This embodiment uses a sintering temperature of 1750℃ and a holding time of 4 hours. The reference carbon monoxide volume concentration is 2.5%, the reference chromium trioxide mass fraction is 15%, the component coupling coefficient is 0.4, the temperature rise gradient coupling coefficient is 0.002℃⁻¹·min, and the reference sintering temperature rise gradient is 5℃ / min.

[0156] When the current sintering temperature rise gradient is 6℃ / min, the target volume concentration of carbon monoxide in the batch is calculated as follows:

[0157] When the actual carbon monoxide volume concentration is 2.9%, the atmosphere concentration error is 0.00664.

[0158] The control cycle is 1 min, the reference normalized carbon monoxide supply regulating valve opening is 0.40, the atmosphere concentration error proportional gain is 5, the atmosphere concentration error integral gain is 0.5 min⁻¹, the current integral accumulation stage only includes the current control cycle error, and the temperature rise gradient error compensation gain is 0.01℃⁻¹·min.

[0159] The current calculation for the opening degree of the carbon monoxide supply regulating valve is as follows:

[0160] The process controller outputs a normalized opening command of 0.44652 to the carbon monoxide supply regulating valve.

[0161] In the next control cycle, the actual carbon monoxide volume concentration and sintering control zone temperature sequence are re-acquired, and feedback control continues. After sintering, the sintered body enters the cooling equipment. The process controller adjusts the cooling fan frequency according to the surface cooling rate. After cooling, two-stage crushing and vibrating screening are performed.

[0162] In the test records of this embodiment, the apparent porosity was 11.2%, the bulk density was 3.42 g / cm³, and the compressive strength was 62 MPa. Quantitative analysis of the crystal phase was performed using X-ray diffraction combined with Rietveld full-spectrum fitting. The main crystalline phase content of magnesium chromium spinel was 94%, and the grain size was mainly distributed in the range of 8 μm to 20 μm.

[0163] Example 2: This example further illustrates the magnesium adjustment branch, continuous component retesting, parameter calibration, and cooling feedback process in the system implementation layer based on Example 1.

[0164] In this embodiment, a batch of 1000 kg of recycled powder was selected on a dry basis.

[0165] The component detection unit detected a magnesium oxide mass fraction of 60.0% and a chromium trioxide mass fraction of 20.0%.

[0166] The target magnesium oxide to chromium trioxide mass ratio was set to 3.25.

[0167] The initial mass ratio is:

[0168] Since the initial mass ratio was below 3.25, magnesium adjustment component compensation was performed.

[0169] The effective magnesium oxide mass fraction of the magnesium-modifying component is 90%.

[0170] The mass of magnesium-modifying components added is calculated as follows:

[0171] The process controller outputs a 55.5556 kg magnesium conditioning batch dispensing command to the metering and feeding equipment.

[0172] After feeding and mixing are completed, three consecutive tests are performed.

[0173] The first test yielded 61.55% magnesium oxide and 18.94% chromium trioxide, with an actual mass ratio of 3.2497.

[0174] The second test yielded 61.54% magnesium oxide and 18.94% chromium trioxide, with an actual mass ratio of 3.2492.

[0175] The third test yielded 61.55% magnesium oxide and 18.95% chromium trioxide, with an actual mass ratio of 3.2480.

[0176] All three test results met the ratio error condition and state change condition, and the process controller output a component state convergence indicator.

[0177] In this embodiment, polyvinyl alcohol solution is used as the organic binder, and sodium silicate solution is used as the inorganic binder. The amount of polyvinyl alcohol solution added is 1.2% of the corrected mixed powder mass, and the amount of sodium silicate solution added is 0.8% of the corrected mixed powder mass.

[0178] After mixing, a disc granulator is used to form spherical green bodies of 5mm to 12mm, which are then dried at 120℃ until the residual moisture content is no higher than 0.5%.

[0179] This embodiment uses a sintering temperature of 1750℃ and a holding time of 4 hours.

[0180] During the equipment commissioning phase, with the sintering temperature rise gradient maintained at 5℃ / min, the target carbon monoxide volume concentrations corresponding to the corrected chromium trioxide mass fractions of 15%, 17%, and 19% were calibrated to 2.5%, 3.3%, and 4.1%, respectively, and the component coupling coefficient was obtained by fitting.

[0181] With the chromium trioxide mass fraction maintained at 15%, the target carbon monoxide volume concentrations corresponding to sintering temperature rise gradients of 5℃ / min, 6℃ / min, and 7℃ / min were calibrated to 2.5%, 2.7%, and 2.9%, respectively, and the temperature rise gradient coupling coefficient was obtained as 0.002℃⁻¹·min.

[0182] The carbon monoxide supply system is tuned to a step response. The normalized carbon monoxide supply regulating valve opening is set to 0.40, the proportional gain for atmosphere concentration error is set to 5, the integral gain for atmosphere concentration error is set to 0.5 min⁻¹, and the temperature rise gradient error compensation gain is set to 0.01℃⁻¹·min.

[0183] After sintering is completed, the temperature acquisition unit detects the surface temperature of the sintered body. The surface cooling rate is controlled at 5℃ / min to 10℃ / min during the 1800℃ to 1200℃ stage, and at 3℃ / min to 5℃ / min during the 1200℃ to 600℃ stage.

[0184] When the surface cooling rate exceeds the upper limit of the corresponding stage, the process controller reduces the cooling fan frequency; when it falls below the lower limit of the corresponding stage, the cooling fan frequency is increased.

[0185] Example 3: This example illustrates the method for disposing of waste magnesia-chromium countertop tiles generated during the dismantling of a non-ferrous metal smelting furnace.

[0186] Waste magnesia-chrome countertop tiles are classified according to the type of furnace from which they originated and the batch from which they were replaced.

[0187] The cleaning process removes surface-adhered metal and slag. Controlled cleaning is performed when surface deposits that are difficult to remove mechanically are present. After cleaning, dehydration and drying are completed before the material enters the crushing process.

[0188] The cleaned-up waste magnesia-chrome countertop tiles were broken to less than 40mm.

[0189] Coarsely crushed particles are fed into a wet ball mill to form a recycled slurry.

[0190] After magnetic separation to remove impurities, the recycled slurry enters the classification process. Coarse particles that do not reach the target particle size are returned to the wet ball mill, while the recycled slurry that reaches the target particle size undergoes dewatering and drying to form recycled powder.

[0191] Magnetic separation for impurity removal must be completed before component compensation calculation. The component compensation calculation uses the batch quality and component test results of the recycled powder after magnetic separation for impurity removal; data from before magnetic separation for impurity removal cannot be used as a substitute.

[0192] Assume the dry batch weight of the recycled powder after magnetic separation is 1000 kg, the mass fraction of magnesium oxide is 58.0%, the mass fraction of chromium trioxide is 20.0%, and the target mass ratio of magnesium oxide to chromium trioxide is 3.25.

[0193] The initial actual mass ratio is:

[0194] A magnesium-based adjusting component with an effective magnesium oxide mass fraction of 90% was added, calculated by mass:

[0195] After completing feeding, mixing, and continuous retesting, the process controller confirms that the component states have converged.

[0196] After the corrected mixed powder is compounded with dual-source binder, granulated and dried, it enters the high-temperature sintering kiln.

[0197] In this embodiment, a sintering temperature of 1780℃ and a holding time of 5h are used. The target volume concentration of carbon monoxide in the batch is dynamically generated based on the converged corrected chromium trioxide mass fraction and the actual sintering temperature rise gradient.

[0198] After sintering and feedback cooling are completed, the material is crushed, screened, and quality tested.

[0199] In the test record of this embodiment, the apparent porosity is 13.5%, the bulk density is 3.38 g / cm³, and the compressive strength is 55 MPa, which meets the qualified batch judgment conditions set by the present invention.

[0200] Comparative Example 1: This comparative example uses the same waste magnesia-chromium countertop tile source, cleaning method, crushing method, grinding method, initial batch mass of recycled powder, initial magnesium oxide mass fraction, initial chromium trioxide mass fraction, granulation conditions, drying conditions, sintering conditions, cooling conditions, crushing conditions, and sieving conditions as Example 1.

[0201] The only technical change in this comparative example is the elimination of continuous retesting and component convergence determination after component compensation calculation, and the adoption of a fixed feed amount.

[0202] The initial recycled powder dry basis batch weight is 1000 kg, the mass fraction of magnesium oxide is 67.5%, the mass fraction of chromium trioxide is 14.8%, and the target mass ratio of magnesium oxide to chromium trioxide is 3.8.

[0203] This comparative example has a fixed addition of 25 kg of a chromium-modifying component with an effective chromium trioxide mass fraction of 95%.

[0204] The theoretical mass of chromium trioxide after addition is:

[0205] The theoretical mass ratio of magnesium oxide to chromium trioxide after addition is:

[0206] The absolute deviation is 0.1301 relative to the target quality ratio of 3.8.

[0207] In Example 1, the mass ratios of three consecutive effective detections were 3.8134, 3.8100, and 3.8106, with deviations from the target values ​​of 0.0134, 0.0100, and 0.0106.

[0208] When the closest continuous test result to the target value (0.0100) is used as the comparison value, the mass ratio deviation of this comparative example is approximately 13 times that of Example 1; when the first effective test deviation of Example 1 (0.0134) is used as the comparison value, the mass ratio deviation of this comparative example is approximately 9.7 times that of Example 1. The above comparisons are used to demonstrate the role of compensation calculations and continuous retest convergence in controlling the proportioning error, and the above calculation results are not directly interpreted as year-on-year changes in compressive strength, apparent porosity, or bulk density.

[0209] Comparative Example 2: This comparative example uses the same waste magnesia-chromium countertop tile source, cleaning, crushing, grinding, component detection, mass conservation compensation, feeding, mixing, continuous retesting, component convergence, dual-source binder compounding, granulation, drying, sintering temperature, holding time, actual atmosphere concentration detection, cooling, crushing and sieving processes as Example 1.

[0210] The only technical change in this comparative example is the elimination of the correction for the effect of chromium trioxide mass fraction on the target volume concentration of carbon monoxide in the batch, and the consistent use of a fixed target volume concentration of 2.5% for carbon monoxide.

[0211] The final test result for Example 1 showed a corrected chromium trioxide mass fraction of 17.16%.

[0212] Under the conditions of a baseline carbon monoxide volume concentration of 2.5%, a reference chromium trioxide mass fraction of 15%, a component coupling coefficient of 0.4, a current sintering temperature rise gradient of 6 °C / min, a reference sintering temperature rise gradient of 5 °C / min, and a temperature rise gradient coupling coefficient of 0.002 °C⁻¹·min, Example 1 yielded a batch carbon monoxide target volume concentration of 3.564%.

[0213] The target volume concentration in this comparative example was fixed at 2.5%.

[0214] The difference between the fixed target volume concentration and the current batch coupled target volume concentration is:

[0215] Therefore, this comparative example has a batch target adaptation bias of 1.064 percentage points. This comparative example is only used to demonstrate that after the correction component state quantity is cancelled and transferred across processes, the fixed target cannot respond to the change in the state of the correction component in the current batch, and is not used to fabricate specific material performance degradation values.

[0216] In a preferred embodiment, waste magnesia-chromium tabletop tiles from a batch of steel refining furnaces, after being sorted and surface-cleaned, enter the crushing process. The coarsely crushed particles are then wet-milled, graded, dehydrated, and dried to form 1000 kg of dry-basis recycled powder. The component analysis unit determined that the magnesium oxide mass fraction was 67.5%, the chromium trioxide mass fraction was 14.8%, the target magnesium oxide to chromium trioxide mass ratio was set to 3.8, and the effective chromium trioxide mass fraction of the chromium-modifying component was 95%.

[0217] The initial mass ratio was 4.5608, higher than the target value of 3.8. The mass of the chromium-modifying component added was calculated using pure numerical substitution relationships:

[0218]

[0219] Therefore, the process controller sends a 31.1911 kg chromium conditioning group dispensing command to the metering and feeding equipment.

[0220] After feeding and mixing, three effective tests were performed. The mass ratios of the three tests were 3.8134, 3.8100, and 3.8106, all of which met the proportioning error threshold of 0.02. The changes in the mass fractions of adjacent magnesium oxide and chromium trioxide did not exceed 0.20 percentage points. Therefore, the process controller output a component status convergence indicator and used 17.16% as the corrected chromium trioxide mass fraction for the current batch sintering control.

[0221] After the spherical green billets enter the high-temperature sintering kiln, the current sintering temperature rise gradient is 6℃ / min. The reference carbon monoxide volume concentration is 0.025, the component coupling coefficient is 0.4, the reference chromium trioxide mass fraction is 0.15, the temperature rise gradient coupling coefficient is 0.002℃⁻¹·min, and the reference sintering temperature rise gradient is 5℃ / min. The batch target carbon monoxide volume concentration is calculated as follows:

[0222]

[0223] The calculated value is 3.564%, which is within the allowable range of 1% to 5%.

[0224] The current actual carbon monoxide volume concentration is 2.9%, and the atmosphere concentration error is 0.00664. The reference normalized carbon monoxide supply regulating valve opening is 0.40, the atmosphere concentration error proportional gain is 5, the atmosphere concentration error integral gain is 0.5 min⁻¹, the current control cycle time interval is 1 min, the temperature rise gradient error is 1℃ / min, and the temperature rise gradient error compensation gain is 0.01℃⁻¹·min. The carbon monoxide supply regulating valve opening for the first control cycle is calculated as follows:

[0225]

[0226] The process controller outputs a normalized carbon monoxide supply regulating valve opening command of 0.44652.

[0227] In the next control cycle, the temperature acquisition unit and atmosphere analysis unit re-output the sintering control zone temperature data and actual carbon monoxide volume concentration data. The process controller regenerates the batch target carbon monoxide volume concentration and recalculates the opening of the carbon monoxide supply regulating valve. The absolute deviation between the actual carbon monoxide volume concentration and the target volume concentration does not exceed 0.2 percentage points, and the absolute deviation between the sintering temperature rise gradient and the reference sintering temperature rise gradient does not exceed 0.5℃ / min. After meeting these conditions for five consecutive control cycles, the process controller enters a hold control state. In the hold control state, the process controller continues to acquire temperature and atmosphere concentration data and performs closed-loop correction after limiting, stopping the integral accumulation of atmosphere concentration error until the deviation exceeds the set conditions again.

[0228] After sintering at 1750℃ and holding for 4 hours, the sintered body enters the cooling equipment. The temperature acquisition unit continuously collects the surface temperature of the sintered body, and the process controller adjusts the frequency of the cooling fan according to the surface cooling rate. After cooling, the sintered body undergoes two stages of crushing, vibrating screening, and quality testing to form sintered magnesia-chromium sand that meets the corresponding particle size grade and quality indicators.

[0229] All data objects that play a technical role in this invention have clear sources and downstream applications. Dry-basis batch mass and component detection data of recycled powder are used for component compensation; batching execution instructions are used to control metering and feeding equipment; continuous retest data are used for component convergence determination; the corrected chromium trioxide mass fraction is used to generate the batch carbon monoxide target volume concentration; the sintering control zone temperature sequence is used to obtain the sintering temperature rise gradient; the actual carbon monoxide volume concentration is used for gas supply feedback control; and the sintered body surface temperature sequence is used for cooling fan frequency control.

[0230] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0231] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements 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 preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, characterized in that, include: Waste magnesia-chromium countertop tiles are sorted, cleaned, crushed and ground. The recycled slurry obtained from wet grinding is graded, dehydrated and dried to obtain recycled powder. Obtain the dry basis batch mass data, dry basis magnesium oxide mass fraction, and dry basis chromium trioxide mass fraction of the recycled powder. Generate magnesium-adjusted component distribution execution instructions or chromium-adjusted component distribution execution instructions based on the target component constraints. After completing the feeding and mixing, re-obtain the component detection data of the mixed powder. Perform re-compensation or component convergence determination based on the actual mass ratio deviation and continuous component detection status changes to obtain the corrected mixed powder and the corrected component status quantity. Organic and inorganic binders are added to the corrected mixed powder, and the mixture is then mixed, granulated, and dried to form spherical green bodies. The spherical green billet is fed into a high-temperature sintering kiln. Based on the corrected chromium trioxide mass fraction in the corrected component state quantity and the sintering temperature rise gradient obtained from the sintering control zone temperature sequence, a batch carbon monoxide target volume concentration sequence is generated. The actual carbon monoxide volume concentration sequence is collected. Based on the deviation between the batch carbon monoxide target volume concentration and the actual carbon monoxide volume concentration, as well as the deviation between the sintering temperature rise gradient and the reference sintering temperature rise gradient, a carbon monoxide gas supply regulating valve opening command is generated, so that the spherical green billet completes solid-phase sintering in a weak carbon monoxide reducing atmosphere to obtain a sintered body. The surface temperature sequence during the cooling process of the sintered body is collected to obtain the surface cooling rate and the frequency of the cooling fan is adjusted. After cooling, the sintered magnesium chromium sand is obtained by crushing and screening.

2. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 1, is characterized in that... Based on the dry-basis batch mass data of the recycled powder, the dry-basis magnesium oxide mass fraction, the dry-basis chromium trioxide mass fraction, the effective magnesium oxide mass fraction of the magnesium conditioning component, and the effective chromium trioxide mass fraction of the chromium conditioning component, the added mass of the magnesium conditioning component and the added mass of the chromium conditioning component are calculated. The calculation relationship is as follows: ； in, This indicates the mass of magnesium-modifying components added. This indicates the mass of chromium-modifying components added. This indicates the mass ratio of the target magnesium oxide to chromium trioxide. This indicates the dry basis mass fraction of magnesium oxide in the recycled powder. This indicates the dry basis mass fraction of chromium trioxide in the recycled powder. This indicates the dry basis batch weight of the recycled powder. This indicates the effective magnesium oxide mass fraction of the magnesium-modifying component. Indicates the effective chromium trioxide mass fraction of the chromium-modifying component; subscript Indicates the magnesium-regulated branch, subscript Indicates the chromium regulation branch, subscript Indicates the target state, subscript Indicates batch status.

3. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 2, is characterized in that... After the magnesium or chromium conditioning components are fed and mixed, the mass fraction of magnesium oxide and chromium trioxide in the mixed powder are retested, and the actual mass ratio of magnesium oxide to chromium trioxide is obtained based on the retest results. When the absolute deviation of the actual magnesium oxide to chromium trioxide mass ratio from the target magnesium oxide to chromium trioxide mass ratio exceeds the proportioning error threshold, the batching execution instruction is regenerated; when the absolute deviation of the actual magnesium oxide to chromium trioxide mass ratio does not exceed the proportioning error threshold, and the absolute difference between two consecutive detections of magnesium oxide mass fraction and two consecutive detections of chromium trioxide mass fraction does not exceed the state change threshold, and the conditions are met for three consecutive detections, the component state is determined to have converged.

4. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 3, is characterized in that... The batch weighing equipment acquires the dry basis batch mass data of the recycled powder and sends it to the process controller. The component detection unit acquires the dry basis magnesium oxide mass fraction and dry basis chromium trioxide mass fraction of the recycled powder and sends them to the process controller. The process controller generates a batching execution command and sends it to the metering and feeding equipment connected to the magnesium conditioning component silo and the chromium conditioning component silo, respectively. After the metering and feeding equipment completes the feeding, the mixed powder output by the mixing equipment is re-detected by the component detection unit. The component detection data obtained from the re-detection is returned to the process controller to form a component compensation closed loop.

5. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 3, is characterized in that... The corrected chromium trioxide mass fraction obtained after component convergence, together with the sintering temperature rise gradient, is used to calculate the target volume concentration of carbon monoxide for the corresponding control period. The calculation relationship is as follows: in, Indicates the first The target volume concentration of carbon monoxide for each control cycle. This indicates the lower limit of the target volume concentration for carbon monoxide. This indicates the upper limit of the target volume concentration of carbon monoxide. Indicates the baseline carbon monoxide volume concentration. Represents the component coupling coefficient. This represents the corrected chromium trioxide mass fraction after the component states have converged. This indicates the reference chromium trioxide mass fraction. Represents the temperature gradient coupling coefficient. Indicates the first The sintering temperature rise gradient for each control cycle, Indicates the reference sintering temperature rise gradient. Indicates the control cycle number; This indicates that the calculation results are limited to a range between the lower limit and the upper limit of the target volume concentration of carbon monoxide. This indicates taking the maximum value among the values ​​within the parentheses, indicated by the subscript. Indicates carbon monoxide, superscript Indicates the target value, subscript Indicates reference status, subscript Indicates the lower limit, subscript Indicates the upper limit, subscript Indicates the temperature status.

6. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 5, is characterized in that... The carbon monoxide supply regulating valve opening command is generated based on the target volume concentration of carbon monoxide, the actual volume concentration of carbon monoxide, and the sintering temperature rise gradient. The calculation relationship is as follows: ； in, Indicates the first Normalized carbon monoxide supply regulating valve opening command for each control cycle This indicates the normalized carbon monoxide supply regulating valve opening. This represents the proportional gain of the atmosphere concentration error. Indicates the first The atmospheric concentration error is obtained by subtracting the actual carbon monoxide volume concentration from the target carbon monoxide volume concentration for each control cycle. This represents the integral gain of the atmosphere concentration error. Indicates the sequence number of the integral summation. Indicates the control cycle number. Indicates the control cycle time interval. This represents the gain for temperature gradient error compensation. Indicates the first The temperature rise gradient error is obtained by subtracting the reference sintering temperature rise gradient from the sintering temperature rise gradient of each control cycle. This indicates a limiting operation that restricts the normalized carbon monoxide supply valve opening command to between zero and one; subscript Indicates the baseline state, subscript Indicates proportional effect, subscript Indicates the integral action, subscript Indicates the effect of temperature gradient compensation, subscript Indicates the concentration state of the atmosphere.

7. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 6, is characterized in that... After the sintered body enters the cooling equipment, the surface temperature sequence of the sintered body is collected by multiple surface temperature detection positions set along the cooling direction. The surface cooling rate is obtained based on the temperature drop value at adjacent detection times and the detection time interval. When the surface cooling rate is higher than the upper limit of the cooling rate, the frequency of the cooling fan is reduced; when the surface cooling rate is lower than the lower limit of the cooling rate, the frequency of the cooling fan is increased; and when the surface cooling rate is within the target cooling range, the frequency of the cooling fan is maintained.

8. The method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 4, is characterized in that... The organic binder is a polyvinyl alcohol solution or dextrin solution, and the inorganic binder is a sodium silicate solution or phosphate solution. The total amount of organic and inorganic binders added is 1% to 3% of the mass of the corrected mixed powder. The spherical green body formed by granulation is dried at 80°C to 150°C until the residual moisture of the spherical green body is not higher than 0.5%.

9. A method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 4, is characterized in that... Waste magnesia-chromium countertop tiles are crushed and then wet-milled. The recycled slurry obtained from the wet-milling is classified. Coarse particles that do not meet the target particle size are returned to the wet-milling path. The recycled slurry that meets the target particle size is dewatered and dried to form recycled powder. The median particle size of the recycled powder is 5μm to 20μm, and the specific surface area is 300 m² / kg to 800 m² / kg.

10. A method for preparing sintered magnesia-chromium sand using countertop tiles in cyclic service, as described in claim 7, is characterized in that... The waste magnesia-chromium countertop tiles are derived from the dismantling and replacement parts of steel smelting refining furnaces. They are stored in batches according to the service batch and furnace type. The cleaning process removes the slag, refractory fiber and metal inclusions attached to the surface. The sintering temperature is 1650℃ to 1800℃, the holding time is 2h to 6h, and the volume fraction of carbon monoxide in the weakly reducing carbon monoxide atmosphere is 1% to 5%.

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