A method and system for preheating and calcining high purity alumina

Abstract

The application discloses a high-purity alumina preheating calcining method and system and belongs to the field of high-purity alumina heat treatment and calcining energy-saving control. The method realizes controlled temperature rise and controlled moisture content of the precursor before entering a high-temperature calcining section through tail gas heat exchange, heat exchange of heat residual of finished alumina, three-stage preheating, three-index predictive control and graded dust collection and powder recovery, and reduces the risk of metal impurity introduction through a ceramic contact layer.

Description

Technical Field

[0001] This invention relates to the field of heat treatment and energy-saving control of high-purity alumina calcination, and particularly to a method and system for preheating and calcining high-purity alumina. Background Technology

[0002] High-purity alumina precursors typically require a gradual temperature increase from a cold state to a high-temperature calcination state during the calcination process. In existing processes, when the precursors directly enter the high-temperature calcination section, the material heating rate is prone to sudden changes, resulting in concentrated short-term heat loads. This leads to high peak energy consumption in the calcination system and may cause agglomeration, clumping, or localized adhesion of moist or low-flowability materials.

[0003] Existing preheating structures mostly rely on waste heat from calcination exhaust gas or a single heat exchange branch for preheating. However, it is difficult to maintain a match between the available heat from the exhaust gas, the waste heat release from the hot finished product, and the actual heat absorption requirements of the feed. When the temperature, humidity, and dust load in the preheating section are not controlled in a coordinated manner, the dust entrained in the exhaust gas is prone to back-mixing between different temperature zones, and the return of wet powder may also exacerbate condensation and agglomeration. On the other hand, if high-purity materials are in prolonged contact with metal shells, elbows, or valves during preheating, conveying, and powder return, they are also prone to the introduction of metal wear impurities or external contamination.

[0004] Therefore, there is a need for a high-purity alumina preheating and calcination method and system that can overcome the shortcomings of the existing technology. Summary of the Invention

[0005] One objective of this invention is to propose a method and system for preheating and calcining high-purity alumina. Addressing the problems in existing technologies such as abrupt temperature rise of the cold precursor, mismatch between waste heat supply and demand, difficulty in coordinating the control of temperature, humidity, and dust recirculation in the preheating stage, and susceptibility of high-purity materials to metal contamination, this invention proposes a technical solution involving dual heat sources (tail gas and hot finished product) for staged preheating, graded dust collection and recovery, and coordinated predictive control of three indicators. This enables a continuous and controllable processing chain for precursor preheating, dust recovery, and subsequent calcination.

[0006] This invention provides a method for preheating and calcining high-purity alumina, comprising: S1, feeding a cold high-purity alumina precursor into a low-temperature dehumidification preheating section via a ceramic-lined metering chamber and a closed metering conveyor, collecting the feed rate, initial temperature, and initial moisture content to form feed heat load data; S2, performing ceramic dust removal and heat exchange on the calcination exhaust gas to obtain the available heat of the exhaust gas, and distributing the available heat of the exhaust gas to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section; S3, passing the hot finished alumina through a ceramic heat exchange branch isolated from the material to obtain the finished product waste heat supply, supplying the finished product waste heat released by the hot finished alumina to the high-temperature pre-decomposition preheating section via the ceramic heat exchange branch, and supplying the finished product waste heat to the... The quantity is used as the calculation input for step S4; S4, based on the feed heat load data, available heat of tail gas, waste heat supply of finished product, temperature of each preheating section, humidity of tail gas, pressure difference of dust removal unit and dust concentration of tail gas, calculate the heat gap, dew point margin and dust load of each stage, and generate tail gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position; S5, control the three-stage preheating, graded dust collection and return dust and subsequent calcination according to the tail gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position, so that the precursor enters the high temperature calcination section at the set heating rate, and the recovered dust returns to the corresponding preheating section according to temperature and humidity.

[0007] Optionally, S1 includes: The precursor is isolated from the metal shell in a closed metering conveyor. The inner wall, metering blades and discharge elbow of the closed metering conveyor are all provided with a high-purity alumina ceramic contact layer. The feed rate, initial temperature, initial moisture content, and target outlet temperature of the low-temperature dehumidification preheating section are used together as inputs for generating feed heat load data. The feed heat load data is used to determine the heat deficit at each stage.

[0008] Optionally, S2 includes: The calcination exhaust gas is passed sequentially through a ceramic cyclone separator, a high-purity ceramic filter element, and an exhaust gas heat exchanger. The amount of heat that can be supplied by the exhaust gas is determined based on the exhaust gas inlet temperature, exhaust gas outlet temperature, exhaust gas flow rate, and exhaust gas humidity. The coarse powder separated by the ceramic cyclone separator and the fine powder separated by the high-purity ceramic filter element are respectively sent to independent dust return branches, which are used to classify and return dust according to its state.

[0009] Optionally, S4 includes: The dew point margin is determined by the temperature difference between the gas phase temperature of each preheating stage and the corresponding exhaust gas dew point temperature. The exhaust gas dew point temperature is calculated based on the exhaust gas humidity and the exhaust gas pressure collected by the exhaust gas channel pressure detection point. When the temperature difference is less than the set dew point threshold, the corresponding preheating section is marked as a dew point-limited section; The dew point restricted section is used to limit the return powder valve position and correct the supplementary heating power and fluidizing air volume; Furthermore, the dust load is determined based on the dust concentration at the inlet of the ceramic cyclone separator, the pressure difference of the high-purity ceramic filter element, and the dust mass flow rate of the return dust branch. The heat gaps at each level are determined based on the feed heat load data, the available heat from the exhaust gas, and the waste heat supply from the finished product. The dust load, the dew point margin, and the heat gaps at each level are input into the control mapping table to generate the exhaust gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time, and return dust valve position. Furthermore, when any heat gap at any level exceeds the set heat replenishment start threshold, the clean heat replenisher is controlled to supply supplementary heat to the corresponding preheating section. When the dew point margin is less than the set dew point threshold, the clean heat exchanger preferentially supplies dry hot gas to the dew point restricted section. The dry hot gas supply is determined by the heat exchange power and the fluidizing air volume, and the dry hot gas supply and the dust return valve position are used together for graded dust return control.

[0010] Optionally, S5 includes: The coarse powder separated by the ceramic cyclone separator is returned to the high-temperature pre-decomposition preheating section or the medium-temperature dehydration preheating section according to the coarse powder temperature. The fine powder separated from the high-purity ceramic filter element is returned to the low-temperature dehumidification preheating section or the medium-temperature dehydration preheating section according to the moisture content of the fine powder. When the corresponding preheating section is marked as a dew point restricted section, the return powder valve position of the preheating section is lowered, and the dry hot gas supply determined by the supplementary heating power and fluidizing air volume is increased or the material residence time is extended. Furthermore, when the pressure difference of the high-purity ceramic filter element is greater than the set pressure difference threshold or the dust load is greater than the set dust threshold, the fine powder independent return branch corresponding to the high-purity ceramic filter element is switched to the fine powder temporary storage bin. After the dew point margin in the low-temperature dehumidification preheating section is not less than the set dew point threshold, the fine powder in the fine powder temporary storage bin is sent back to the low-temperature dehumidification preheating section or the medium-temperature dehydration preheating section. Furthermore, the ceramic contact layer is also provided in the low-temperature dehumidification preheating section, the medium-temperature dehydration preheating section, the high-temperature pre-decomposition preheating section, the ceramic heat exchange branch, the powder return branch for graded powder return, the powder return valve core corresponding to the powder return valve position, and the material contact surface of the discharge elbow or material turning elbow. Replaceable ceramic bushings are installed at the return powder valve core, discharge elbow or material turning elbow, and metal impurity detection points are installed on the preheating discharge side. The detection results of the metal impurity detection points are used to switch the material conveying path from the main ceramic conveying channel to the backup ceramic conveying channel connected in parallel with the main ceramic conveying channel.

[0011] On the other hand, the present invention also provides a high-purity alumina preheating and calcining system, comprising: The system includes the following modules: a feed preheating module for executing step S1 and generating feed heat load data; a tail gas heat exchange module for executing step S2 and generating available tail gas heat; a finished product waste heat exchange module for executing step S3 and generating finished product waste heat supply; a three-index prediction and control module for executing step S4 and generating tail gas bypass ratio, finished product heat exchange ratio, supplementary heating power, fluidizing air volume, residence time, and return powder valve position; a graded dust collection and return powder module for executing step S5 and returning the recovered dust to the corresponding preheating section according to temperature and humidity; a clean supplementary heating module for supplying supplementary heat or dry heat gas to the corresponding preheating section; a temporary storage switching module for switching the independent fine powder return branch to the fine powder temporary storage bin; a ceramic anti-pollution and impurity detection module, including a ceramic contact layer set on the material contact surface, a metal impurity detection point set on the preheated discharge side, and a backup ceramic conveying channel connected in parallel with the main ceramic conveying channel; and a high-temperature calcination module for receiving the high-purity alumina precursor after three-stage preheating and calcining it.

[0012] The beneficial effects of this invention are: 1. By making the calcination tail gas and the hot finished alumina into tail gas available heat supply and finished product waste heat supply respectively, and using the two together with the feed heat load data for heat gap calculation, the preheating heat supply and the feed heat absorption demand can be made to correspond, thereby alleviating the sudden temperature rise and concentrated energy consumption peak caused by cold materials directly entering the high temperature calcination section.

[0013] 2. By generating the exhaust gas bypass ratio, supplementary heating power, fluidizing air volume, residence time, and return powder valve position based on dew point margin, dust load, and heat gap, and returning coarse and fine powder to the corresponding preheating section according to temperature and moisture content, the risks of condensation entrainment, wet powder back-mixing, and agglomeration can be reduced.

[0014] 3. By configuring a ceramic contact layer, a replaceable ceramic bushing, a metal impurity detection point, and a spare ceramic conveying channel on the material contact surface, the risk of metal wear contamination and abnormal path contamination of high-purity alumina precursor during preheating, conveying, and powder return processes can be reduced. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Fig. 1 This is a flowchart illustrating the overall control process of a high-purity alumina preheating and calcination method.

[0016] Fig. 2 This is a flowchart of the three-index prediction and control process in step S4 of the present invention. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0018] refer to Figs. 1-2 A method for preheating and calcining high-purity alumina includes: S1, feeding a cold high-purity alumina precursor into a low-temperature dehumidification preheating section via a ceramic-lined metering chamber and a closed metering conveyor, collecting the feed rate, initial temperature, and initial moisture content to form feed heat load data; S2, performing ceramic dust removal and heat exchange on the calcination exhaust gas to obtain available heat from the exhaust gas, and distributing the available heat from the exhaust gas to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section; S3, passing the hot finished alumina through a ceramic heat exchange branch isolated from the material to obtain the finished product waste heat supply, supplying the finished product waste heat released by the hot finished alumina to the high-temperature pre-decomposition preheating section via the ceramic heat exchange branch, and processing the finished product waste heat supply as... The calculation input for step S4 is as follows: S4. Based on the feed heat load data, available heat of tail gas, waste heat supply of finished product, temperature of each preheating section, humidity of tail gas, pressure difference of dust removal unit and dust concentration of tail gas, calculate the heat gap, dew point margin and dust load of each stage, and generate tail gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position; S5. Control the three-stage preheating, graded dust collection and return dust and subsequent calcination according to the tail gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position, so that the precursor enters the high-temperature calcination section at the set heating rate, and the recovered dust returns to the corresponding preheating section according to the temperature and humidity state.

[0019] In this specific embodiment, S1 includes: The cold high-purity alumina precursor first enters a ceramic-lined metering chamber. A high-purity alumina ceramic liner is fixedly laid on the inner surface of the chamber wall, and the alumina mass fraction of the high-purity alumina ceramic liner is not less than [amount missing]. The liner thickness is set to 5mm, and the full-coverage structure prevents the stress contact surface of the precursor in the metering chamber from directly contacting the metal substrate in order to suppress the introduction of metal wear impurities. A closed metering conveyor is installed below the metering chamber. The closed metering conveyor adopts a closed structure with metering blades. The material contact surface of its inner wall, metering blades and discharge elbow is provided with a high-purity alumina ceramic contact layer. The high-purity alumina ceramic contact layer and the metal shell adopt a continuous temperature-resistant isolation structure and a temperature-resistant sealing gasket is provided at the connection to keep the closed metering conveyor airtight during the conveying process and to isolate the material from the metal shell. The discharge end of the sealed metering conveyor is sealed to the inlet of the low-temperature dehumidification and preheating section, and an air extraction port is provided. This ensures that the material is in a controlled, sealed conveying environment before entering the low-temperature dehumidification and preheating section, thus preventing the subsequent dehumidification and preheating control from being affected by external air intrusion. The feed rate is collected and recorded as a mass flow rate. The weight loss value of the weighing sensor in the metering chamber during the control cycle and the length of the control cycle are used to characterize the mass of the precursor entering the low-temperature dehumidification and preheating section per unit time. The initial temperature is denoted as The initial temperature of the material is collected by a temperature detection element located at the ceramic discharge bend of the closed metering conveyor and the temperature of the ceramic temperature measuring sleeve in contact with the material is taken as the initial temperature of the material. The initial moisture content is denoted as The output is provided by an online moisture content analyzer installed at the discharge end of a closed metering conveyor and expressed as a mass fraction. The output of the online moisture content analyzer is directly corresponding to the output after factory calibration. And its range is set to to and with Resolution output; The target outlet temperature of the low-temperature dehumidification preheating section is denoted as The process recipe is set and written into the controller, and in this embodiment, it is set as follows: ; Will and Together, they serve as the input for generating feed heat load data, and the theoretical heat absorption power of the feed is calculated in the controller using the following formula and recorded as: The Used for determining the heat gap at each stage in subsequent steps: ; in, This represents the theoretical heat absorption power required for the precursor to heat up from its initial temperature to the target outlet temperature of the low-temperature dehumidification preheating section, expressed in units of... This indicates the precursor feed mass flow rate, in units of... This represents the isobaric specific heat capacity of the moist precursor, in units of... The parameters were constructed using the controller's built-in parameters according to the "linear weighting of solid specific heat and water specific heat by mass fraction" and adopted. As a dry-based precursor, solid-phase heat, using As the specific heat of water and As a weighting coefficient; This indicates the target outlet temperature of the low-temperature dehumidification preheating section, in units of... ; Indicates the initial temperature of the precursor, in units of ; The controller will and The combined feed heat load data, after being timestamped, is sent to the subsequent three-index prediction and control module as input for heat gap calculation.

[0020] In this specific embodiment, S2 includes: The calcination exhaust gas from the high-temperature calcination module enters the exhaust gas heat exchange module through a closed pipeline and passes through a ceramic cyclone separator, a high-purity ceramic filter element, and an exhaust gas heat exchanger in sequence to achieve the process of "dust removal before heat exchange". The shell and lining of the ceramic cyclone separator are both made of high-purity alumina ceramic and use a tangential air inlet to create a rotating flow field, which cuts off the particle size. The cyclone cone is equipped with a sealed coarse powder discharge port and the discharge port is sealed to the independent coarse powder return branch. The independent coarse powder return branch is equipped with a return valve core with a high-purity alumina ceramic contact layer on the material contact surface, so that the coarse powder obtained by cyclone separation is stably sent out without contacting the metal matrix and serves as the source of coarse powder for subsequent classification and return. The exhaust gas from the cyclone outlet enters the high-purity ceramic filter element filtration unit. The high-purity ceramic filter element is made of heat-resistant porous ceramic material and... The nominal filtration accuracy is used to capture fine powder. Differential pressure detection points are set at both ends of the filter element to collect the differential pressure of the high-purity ceramic filter element and send the differential pressure signal to the subsequent control module. At the same time, a sealed fine powder discharge port is set at the bottom of the filter element and is sealed to the independent fine powder return branch. The independent fine powder return branch is also equipped with a return valve core with a high-purity alumina ceramic contact layer to ensure that the fine powder is transported in the independent channel and used for subsequent classification and return of powder according to dust status. After dust removal, the exhaust gas enters the exhaust gas heat exchanger, which uses a ceramic heat exchange channel and is isolated from the heat exchange medium channel of the preheating section. Exhaust gas inlet temperature detection points are arranged at the exhaust gas inlet and outlet to collect the exhaust gas inlet temperature. And exhaust outlet temperature detection point to collect exhaust outlet temperature A mass flow meter is installed on the exhaust gas main pipe to collect the exhaust gas mass flow rate. High-temperature humidity detection points are installed at the inlet of the exhaust gas heat exchanger to collect exhaust gas humidity data. ,in Defined as the mass of water vapor per unit mass of exhaust gas, with units of . ; Controller based on and Calculate the heat that the exhaust gas can provide and record it as . The As input for subsequent steps to calculate the heat gap at each level, and the The calculation is performed using a sensible heat model that does not involve condensation heat transfer, and the result is determined by the following formula: ; in, This represents the amount of heat that the exhaust gas can release to the preheating system within the exhaust gas heat exchanger, and the unit is 1. Represents the exhaust gas mass flow rate and its unit is . This represents the isobaric specific heat capacity of dry exhaust gas and takes... Indicates exhaust gas humidity and the unit is This represents the isobaric specific heat capacity of water vapor, and takes... Indicates the exhaust gas inlet temperature and the unit is . Indicates the exhaust outlet temperature and the unit is . ; The exhaust gas heat exchanger outlet is equipped with an exhaust gas distribution manifold, which is connected to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section through two closed gas supply branches. Both gas supply branches are equipped with ceramic-lined regulating valves and flow detection points. The controller converts the exhaust gas bypass ratio generated in subsequent steps into the valve opening of the two gas supply branches to distribute the available heat from the exhaust gas to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section. At the same time, the coarse powder separated by the ceramic cyclone separator and the fine powder separated by the high-purity ceramic filter element are maintained in their respective independent return powder branches to form a material source for graded return powder according to dust state and to avoid back mixing of coarse and fine powder in the exhaust gas heat exchange module.

[0021] In this specific embodiment, S3 includes: The hot finished alumina from the high-temperature calcination module enters the finished waste heat exchange module from the calcination discharge end and is introduced into the ceramic heat exchange branch. The ceramic heat exchange branch adopts a fully enclosed material channel, and the material contact surfaces of the straight pipe section, elbow section and distribution tee of the material channel are all high-purity alumina ceramic structures, so that the hot finished alumina only contacts the high-purity alumina ceramic and does not contact the metal substrate during the heat exchange process. The ceramic heat exchange branch and the heat exchange medium gas channel used to transport waste heat adopt an isolated heat exchanger structure. The two sides of the isolated heat exchanger are separated by a dense ceramic heat exchange wall and are gas-tightly packaged to prevent the hot finished alumina from mixing with the heat exchange medium gas, thereby realizing the waste heat recovery that is "isolated from the material". The heat exchange medium is dry nitrogen gas in a closed loop, driven by a circulating fan. The nitrogen inlet dew point is set to be no higher than [the specified value]. After absorbing the heat released by the finished alumina in the isolation heat exchanger, the nitrogen gas is transported to the gas phase inlet of the high-temperature pre-decomposition and preheating section through the heat-resistant and heat-insulated pipeline to serve as the heat source input for this section. At the same time, the nitrogen gas that has released heat in the high-temperature pre-decomposition and preheating section returns to the finished waste heat exchange module to form a closed loop. A finished product mass flow rate detection point is set before the hot finished alumina enters the ceramic heat exchanger branch to collect and record the mass flow rate of the hot finished alumina. The The output is continuously weighed and metered at the discharge end, and synchronized with the controller. Temperature detection points of ceramic protective sleeves are set at the inlet and outlet of the ceramic heat exchange branch to collect the inlet temperature of the hot finished alumina. With respect to the outlet temperature of the hot finished alumina and with and The difference characterizes the temperature drop of the hot finished alumina in the ceramic heat exchange branch; The controller calculates the waste heat supply of the finished product based on the sensible heat release model and records it as follows: The As the calculation input for step S4 and determined by the following formula: ; in, This indicates the amount of waste heat supplied by the hot finished alumina product to the high-temperature pre-decomposition preheating section through the ceramic heat exchanger branch, with units of [unit missing]. Indicates the mass flow rate of the hot-finished alumina, with units of This represents the isobaric specific heat capacity of hot-finished alumina, with units of 1. In this embodiment, a fixed value is taken. For use in control calculations; This indicates the inlet temperature of the hot-finished alumina entering the ceramic heat exchanger branch, and the unit is 1. ; This indicates the outlet temperature of the hot finished alumina when it leaves the ceramic heat exchanger branch, and the unit is 1. ; A finished product diversion switching valve is installed at the inlet of the ceramic heat exchange branch and connected in parallel with the bypass direct discharge channel. The controller adjusts the opening of the finished product diversion switching valve according to the finished product heat exchange ratio generated in subsequent steps to determine the proportion of hot finished alumina entering the ceramic heat exchange branch, and displays the calculated ratio in real time. The waste heat supply data frame, along with the finished product heat exchange ratio, is written into the finished product waste heat supply data frame and then sent to the three-indicator prediction and control module.

[0022] In this specific embodiment, S4 includes: The three-indicator prediction and control module controls the cycle. Run and complete the closed-loop calculation of "acquisition-calculation-mapping-output" in each control cycle; The three-index prediction and control module reads the feed heat load data and extracts the theoretical heat absorption power of the feed within the current control cycle. and feed mass flow rate Initial temperature Compared with initial moisture content Read the heat that can be generated from the exhaust gas and exhaust gas humidity Read the waste heat supply of finished products ; The three-indicator prediction and control module simultaneously collects the gas phase temperature of the low-temperature dehumidification preheating section. Gas phase temperature of the medium-temperature dehydration preheating section Gas phase temperature of the high-temperature pre-decomposition and preheating section The absolute pressure of the exhaust gas output from the pressure detection point in the exhaust gas passage is collected. The inlet dust concentration is collected from the online dust concentration meter at the inlet of the ceramic cyclone separator. The differential pressure of the high-purity ceramic filter element is collected from the differential pressure detection point. The dust mass flow rates of the coarse powder independent return branch and the fine powder independent return branch were collected and recorded as follows: and ; The three-indicator prediction and control module is based on and Calculate the exhaust gas dew point temperature and record it as . and the gas phase temperature of each preheating section is compared with The difference is used as a dew point margin to identify dew point-limited segments. The calculation model for back-calculation of water vapor saturation pressure under constant pressure is adopted, and in this embodiment, the Magnus correlation is used and the following formula is used for calculation: , ; in, This represents the partial pressure of water vapor in the exhaust gas, and the unit is 1. The exhaust gas humidity is expressed as the mass of water vapor per unit mass of exhaust gas, expressed as follows: Unit; The absolute pressure of the exhaust gas is expressed in Pa; the constant 0.62198 represents the ratio of the gas constant of water vapor to that of dry air and is used for the conversion between humidity ratio and partial pressure. This represents the exhaust gas dew point temperature, and the unit is . ; The reference pressure constant representing the correlation of saturated water vapor pressure is taken as follows: Denotes the dimensionless coefficients of the correlation of saturated water vapor pressure and takes The temperature constant representing the correlation of saturated water vapor pressure is taken as follows: Represent the natural logarithm function; The dew point margin is as follows and Calculate and set the dew point threshold separately. In comparison, when the dew point margin corresponding to any preheating section is less than When this happens, the preheating section is marked as a dew point-limited section and the mark is written into the control status word of this cycle for subsequent powder return valve position limitation and reheat correction; The dust load is constructed using a normalized weighted model and denoted as . Its construction method is to... Reference value Normalization, Reference value Normalization is the sum of the dust mass flow rates of the return dust branches. Reference value Normalize, then sort by weight Summation yields and with Determined to have low dust load, Determined as medium dust load, with Determined to be a high dust load; The heat gaps at each level are respectively denoted as and The theoretical heat demand at each level follows the sensible heat model and specific heat model from step S1. Furthermore, the target outlet temperature of the low-temperature dehumidification preheating section is fixed at [temperature value missing]. The target outlet temperature of the medium-temperature dehydration preheating section is fixed at [temperature value missing]. The target outlet temperature of the high-temperature pre-decomposition and preheating section is fixed at [temperature value]. and within this control cycle and The theoretical heat demand corresponding to the three-stage preheating was calculated. The available heating power at each level is estimated by multiplying the available heat from the heat source by the distribution ratio, with the actuator feedback value at the beginning of the current control cycle used as the distribution ratio input. The exhaust gas side uses the exhaust gas bypass ratio. Characterize the distribution relationship of exhaust gas heating in the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section, and according to Distribute to the low-temperature dehumidification preheating section and according to Distributed to the medium-temperature dehydration preheating section, the finished product side adopts the finished product heat exchange ratio. Characterizing the proportion of hot finished alumina entering the ceramic heat exchanger branch and using The available heating power input serves as the high-temperature pre-decomposition and preheating section; The three-index prediction and control module uses the difference between the theoretical heat demand and the available heat supply at each level as the heat gap at each level. Negative values ​​are truncated to zero to represent "no gap"; The dust load Dew point limiting segment markings and heat gaps at various levels Common input control mapping table to generate exhaust bypass ratio Finished product heat exchange ratio Heating power Fluidized air volume Duration of stay With powder return valve position The control mapping table is stored as a discrete rule matrix and executed in the order of "heat gap priority, dew point limitation correction, and dust load suppression": when When the value is greater than zero and the low-temperature dehumidification preheating section is not marked as a dew point-limited section, set To increase the proportion of exhaust gas used for heating allocated to the low-temperature dehumidification and preheating section, when the low-temperature dehumidification and preheating section is marked as a dew point-limited section, the following settings are implemented: To reduce the proportion of exhaust gas entering the low-temperature dehumidification and preheating section and limit the return powder valve position corresponding to the low-temperature dehumidification and preheating section to... And simultaneously correct the fluidization air volume of the low-temperature dehumidification preheating section to To improve the dry heat gas replacement capacity; when Setting when greater than zero To increase the heat input of the waste heat from the finished product to the high-temperature pre-decomposition and preheating section; when When a section is identified as having a high dust load and the corresponding preheating section is not marked as a dew-point-limited section, the dust return valve position of that preheating section will be further reduced based on the current calculated value. The fluidization air volume of the preheating section will be further reduced based on the current calculated value. To suppress dust entrainment and return load; When the heat shortage is at level one or Greater than the set heating start threshold At that time, control the clean heat exchanger to start and set the heat exchange power to [value]. Furthermore, the control mapping table prioritizes the allocation of heat replenishment to the dew-point-limited section, and the amount of dry hot gas supplied by the clean heat replenisher to the dew-point-limited section is determined by the heat replenishment power. Corresponding fluidized air volume of the preheating section or Together determine and match the corresponding preheating section return powder valve position or The linkage is used for graded powder return control, and when a dew point-restricted section exists, the residence time of that section is set to... or or And by adjusting the discharge actuator of this section to maintain the material bed height, a closed-loop stability of the residence time is achieved, ultimately... and As the output of this control cycle, it is written into the execution instruction frame and sent to the three-level preheating, graded dust collection and powder return and cleanroom heating module to enter S5 for execution.

[0023] In this specific embodiment, S5 includes: The three-stage preheating, graded dust collection and powder recovery, and subsequent calcination are executed in a closed-loop linkage according to the execution instruction frame, which includes the exhaust gas bypass ratio. Finished product heat exchange ratio Heating power Fluidization air volume in each section Duration of stay in each segment and the corresponding powder return valve position ,in This indicates the distribution control quantity of exhaust gas between the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section. This indicates the proportion of hot finished alumina entering the ceramic heat exchanger branch. This indicates the set power of the cleanroom heater. This represents the mass flow rate of the fluidizing gas entering the low-temperature dehumidification preheating section, the medium-temperature dehydration preheating section, and the high-temperature pre-decomposition preheating section, respectively. This indicates the target average residence time of the material in the corresponding preheating section. This indicates the valve opening setting value for the coarse powder independent return branch and the fine powder independent return branch returning powder to the corresponding preheating section; During the three-stage preheating process, the exhaust gas distribution manifold at the outlet of the exhaust gas heat exchange module supplies gas to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section via two closed gas supply branches. The controller will... Converted to the opening of the ceramic-lined regulating valves in two branches, the flow rate of each branch is kept stable through a closed-loop feedback mechanism. This ensures that the moisture content of the material at the outlet of the low-temperature dehumidification preheating section is controlled, and the dehydration load of the medium-temperature dehydration preheating section remains continuous and stable. The finished product diversion switching valve at the finished product waste heat exchange module is based on... Adjust the proportion of hot finished alumina entering the ceramic heat exchanger branch and allow the heat exchange medium gas to input the waste heat into the high-temperature pre-decomposition preheating section. The fluidizing air volume of each preheating section is as follows The flow rate is given by the mass flow controller and adjusted through a closed-loop flow feedback mechanism. The residence time of each preheating section is determined according to... The bed height is maintained by a closed-loop discharge actuator. The discharge actuator uses a sealed ceramic-lined star-shaped discharge valve and uses an external motor to drive the speed as the adjustment amount to ensure that the residence time adjustment does not introduce external air. During the graded dust collection and recovery process, the coarse powder separated by the ceramic cyclone separator enters the independent coarse powder recovery branch through the coarse powder discharge port. Temperature detection points are installed on the independent coarse powder recovery branch to collect the coarse powder temperature. ,in This indicates the material temperature when the coarse powder enters the return powder branch, and the unit is 1. Based on this, the controller selects the coarse powder return target section according to fixed rules and executes the distribution valve switching. The coarse powder is then fed into the high-temperature pre-decomposition and preheating section. The coarse powder is fed into the medium-temperature dehydration and preheating section. The amount of coarse powder returned to the target preheating section is determined by the return powder valve position corresponding to that target section. or Closed-loop regulation; The fine powder separated by the high-purity ceramic filter element enters the independent fine powder return branch through the fine powder discharge port. The independent fine powder return branch is equipped with an online moisture content analyzer to collect the moisture content of the fine powder. ,in This indicates the mass fraction of moisture in the fine powder, and the unit is 1. The controller is based on The fine powder return target section is selected according to fixed rules and the distribution valve is switched. The fine powder is then fed into the low-temperature dehumidification preheating section. The fine powder is fed into the medium-temperature dehydration preheating section. The amount of fine powder returned to the target preheating section is determined by the return powder valve position corresponding to that target section. or Closed-loop regulation; When step S4 marks a preheating section as a dew point-limited section, step S5 executes the dew point-limited linkage strategy and forcibly limits the powder return valve position of that preheating section to its upper limit. And the dry hot gas output from the clean heat exchanger is... Corresponding The set value is preferentially supplied to this dew-point-limited section to increase the gas phase temperature and enhance the displacement dehumidification capacity, while the target residence time of this dew-point-limited section is set to... And by implementing a closed-loop discharge mechanism, the risk of condensation and agglomeration caused by wet powder recirculation is reduced. This indicates the preheating section number marked as a dew point-limited section and ; When the pressure difference of the high-purity ceramic filter element Greater than the set differential pressure threshold or dust load Dust levels greater than the set threshold When the controller performs the fine powder temporary storage switch and switches the fine powder independent return branch to the fine powder temporary storage bin, the fine powder temporary storage bin adopts a closed structure and uses dry nitrogen to maintain a slight positive pressure to suppress moisture absorption and agglomeration. The temporary storage bin is equipped with a level gauge to prevent full filling and an arch-breaking air hammer to ensure continuous unloading. When the dew point margin of the low-temperature dehumidification preheating section Not less than the set dew point threshold The temporary storage and return are executed at the same time, among which This indicates the gas phase temperature of the low-temperature dehumidification preheating section, and the unit is . This represents the exhaust gas dew point temperature, and the unit is . Indicates the dew point threshold in K. The controller opens the discharge valve of the fine powder temporary storage bin and discharges according to the moisture content of the fine powder. The powder can be returned to the low-temperature dehumidification preheating section or the medium-temperature dehydration preheating section, and the amount returned continues to be controlled by the corresponding powder return valve position in a closed loop. To reduce the risk of metal contamination, high-purity alumina ceramic contact layers are installed on the material contact surfaces of the low-temperature dehumidification preheating section, the medium-temperature dehydration preheating section, the high-temperature pre-decomposition preheating section, the ceramic heat exchange branch, the coarse powder independent return powder branch, the fine powder independent return powder branch, as well as the return powder valve core, the discharge elbow and the material turning elbow corresponding to the return powder valve position. Replaceable ceramic bushings are installed at the return powder valve core, the discharge elbow and the material turning elbow to replace the ceramic parts in high-wear areas in a modular manner and maintain the continuity of the ceramic contact layer. A metal impurity detection point is set on the preheating discharge side. The metal impurity detection point uses an automatic sampler to sample at a 10-minute cycle and an online inductively coupled plasma atomic emission spectrometer to detect the total metal impurity mass fraction of iron, nickel, and chromium. When the detected value is greater than the set metal impurity threshold of 5 ppm, the controller drives the switching valve to switch the material conveying path from the main ceramic conveying channel to a backup ceramic conveying channel connected in parallel with the main ceramic conveying channel and maintain the closed conveying state of the channel after the switch. At the same time, the main ceramic conveying channel is locked in a maintenance state to avoid the continuous introduction of metal impurities from abnormally worn parts. Finally, the precursor after three-stage preheating enters the high-temperature calcination section with a controlled heating rate and controlled humidity, and the recovered dust returns to the corresponding preheating section according to the temperature and humidity to complete continuous and stable operation.

[0024] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0025] This invention incorporates feed heat load data, available heat from exhaust gas, waste heat supply of finished product, as well as temperature and humidity in the preheating section, dust removal pressure difference, and dust concentration into the control chain. This creates a continuous input, processing, control output, and execution relationship between the three-stage preheating, graded dust collection and return, and subsequent calcination. As a result, waste heat utilization, dew point control, and dust return regulation can be implemented synergistically around the same preheating and calcination process.

[0026] This invention employs predictive control based on three indicators: heat gap, dew point margin, and dust load. It also uses the return powder valve position, supplementary heating power, fluidizing air volume, and residence time as linkage control variables. This allows the system to adjust the preheating and return powder positions according to the limitations of dew point, the increase in dust load, or the change in heat gap. This makes it more suitable for low-pollution, low-backmixing, and low-agglomeration preheating and calcination scenarios for high-purity alumina precursors.

Claims

1. A method for preheating and calcining high-purity alumina, characterized in that, include: S1. The cold high-purity alumina precursor is fed into the low-temperature dehumidification preheating section through a ceramic-lined metering chamber and a closed metering conveyor. The feed rate, initial temperature, and initial moisture content are collected to form the feed heat load data. S2. The calcination exhaust gas is subjected to ceramic dust removal and heat exchange to obtain the available heat of the exhaust gas. This available heat is then distributed to the low-temperature dehumidification preheating section and the medium-temperature dehydration preheating section. S3. The hot finished alumina is passed through a ceramic heat exchange branch isolated from the material to obtain the finished product waste heat supply. The waste heat released by the hot finished alumina is supplied to the high-temperature pre-decomposition preheating section through the ceramic heat exchange branch. S4. Based on the feed heat load... Data, exhaust gas available heat, finished product waste heat supply, temperature of each preheating section, exhaust gas humidity, dust removal unit pressure difference and exhaust gas dust concentration, calculate the heat gap, dew point margin and dust load of each stage, and generate exhaust gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position; S5, control the three-stage preheating, graded dust collection and return dust and subsequent calcination according to the exhaust gas bypass ratio, finished product heat exchange ratio, supplementary heat power, fluidizing air volume, residence time and return dust valve position, so that the precursor enters the high-temperature calcination section at the set heating rate, and the recovered dust returns to the corresponding preheating section according to temperature and moisture content.

2. The method according to claim 1, characterized in that, S1 includes: The precursor is isolated from the metal shell in a closed metering conveyor. The inner wall, metering blades and discharge elbow of the closed metering conveyor are all provided with a high-purity alumina ceramic contact layer. The feed rate, initial temperature, initial moisture content and target outlet temperature of the low-temperature dehumidification preheating section are used as inputs to generate feed heat load data. The feed heat load data is used to determine the heat gap at each stage.

3. The method according to claim 2, characterized in that, S2 includes: The calcination exhaust gas is sequentially passed through a ceramic cyclone separator, a high-purity ceramic filter element, and an exhaust gas heat exchanger. The available heat of the exhaust gas is determined based on the exhaust gas inlet temperature, exhaust gas outlet temperature, exhaust gas flow rate, and exhaust gas humidity. The coarse powder separated by the ceramic cyclone separator and the fine powder separated by the high-purity ceramic filter element are respectively sent to independent dust return branches, which are used for graded dust return according to dust state.

4. The method according to claim 3, characterized in that, In step S4, the dew point margin is determined by the temperature difference between the gas phase temperature of each preheating section and the corresponding exhaust gas dew point temperature. The exhaust gas dew point temperature is calculated based on the exhaust gas humidity and the exhaust gas pressure collected by the exhaust gas channel pressure detection point. When the temperature difference is less than the set dew point threshold, the corresponding preheating section is marked as a dew point restricted section. The dew point restricted section is used to limit the return powder valve position and correct the supplementary heating power and fluidizing air volume.

5. The method according to claim 4, characterized in that, In step S4, the dust load is determined based on the dust concentration at the inlet of the ceramic cyclone separator, the pressure difference of the high-purity ceramic filter element, and the dust mass flow rate of the return dust branch; the heat gap at each stage is determined based on the feed heat load data, the available heat of the exhaust gas, and the waste heat supply of the finished product; the dust load, the dew point margin, and the heat gap at each stage are input into the control mapping table to generate the exhaust gas bypass ratio, the finished product heat exchange ratio, the supplementary heat power, the fluidizing air volume, the residence time, and the return dust valve position.

6. The method according to claim 5, characterized in that, S5 include: The coarse powder separated by the ceramic cyclone separator is returned to the high-temperature pre-decomposition preheating section or the medium-temperature dehydration preheating section according to the coarse powder temperature; the fine powder separated by the high-purity ceramic filter element is returned to the low-temperature dehumidification preheating section or the medium-temperature dehydration preheating section according to the fine powder moisture content; when the corresponding preheating section is marked as a dew point restricted section, the powder return valve position of the preheating section is lowered, and the dry hot gas supply amount determined by the supplementary heating power and fluidizing air volume is increased or the material residence time is extended.

7. The method according to claim 6, characterized in that, In step S5, when the pressure difference of the high-purity ceramic filter element is greater than the set pressure difference threshold or the dust load is greater than the set dust threshold, the fine powder independent return branch corresponding to the high-purity ceramic filter element is switched to the fine powder temporary storage bin. After the dew point margin in the low-temperature dehumidification preheating section is not less than the set dew point threshold, the fine powder in the fine powder temporary storage bin is sent back to the low-temperature dehumidification preheating section or the medium-temperature dehydration preheating section.

8. The method according to claim 6, characterized in that, The ceramic contact layer is also provided in the low-temperature dehumidification preheating section, the medium-temperature dehydration preheating section, the high-temperature pre-decomposition preheating section, the ceramic heat exchange branch, the powder return branch for graded powder return, the powder return valve core corresponding to the powder return valve position, and the material contact surface of the discharge elbow or material turning elbow; a replaceable ceramic bushing is provided at the powder return valve core, the discharge elbow or the material turning elbow, and a metal impurity detection point is provided on the preheating discharge side. The detection result of the metal impurity detection point is used to switch the material conveying path from the main ceramic conveying channel to the backup ceramic conveying channel connected in parallel with the main ceramic conveying channel.

9. The method according to claim 5, characterized in that, In step S4, when any heat gap in each heat gap level is greater than the set heat replenishment start threshold, the clean heat replenisher is controlled to supply supplementary heat to the corresponding preheating section; when the dew point margin is less than the set dew point threshold, the clean heat replenisher preferentially supplies dry hot gas to the dew point restricted section. The dry hot gas supply is determined by the heat replenishment power and the fluidizing air volume, and the dry hot gas supply and the dust return valve position are used together for graded dust return control.

10. A high-purity alumina preheating and calcining system for performing the method according to any one of claims 1 to 9, characterized in that, include: The feed preheating module is used to execute step S1 and generate feed heat load data; the exhaust gas heat exchange module is used to execute step S2 and generate exhaust gas available heat. The system includes: a finished product waste heat exchange module for executing step S3 and generating the finished product waste heat supply; a three-index prediction and control module for executing step S4 and generating the tail gas bypass ratio, finished product heat exchange ratio, supplementary heating power, fluidizing air volume, residence time, and return powder valve position; a graded dust collection and return powder module for executing step S5 and returning the recovered dust to the corresponding preheating section according to temperature and humidity; a clean supplementary heating module for supplying supplementary heat or dry heat gas to the corresponding preheating section; a temporary storage and switching module for switching the independent return powder branch of fine powder to the fine powder temporary storage bin; a ceramic anti-pollution and impurity detection module, including a ceramic contact layer set on the material contact surface, a metal impurity detection point set on the preheating discharge side, and a spare ceramic conveying channel connected in parallel with the main ceramic conveying channel; and a high-temperature calcination module for receiving the high-purity alumina precursor after three-stage preheating and calcining it.

Images