A structure for strengthening heat exchange in a preheating section of a kaolin suspension kiln and a gradient preheating system

Abstract

The application discloses a kind of kaolin suspension kiln preheating section heat transfer enhancement structure and gradient preheating system, including preheater, the upper end of the preheater is fixedly connected with the upper end of preheating pipeline, the lower end of preheating pipeline is closed, and the bottom of preheating pipeline is fixedly connected with fan inside, preheating pipeline is fixedly connected with spoiler bracket above fan, spoiler bracket is rotatably connected with spoiler, the lower end of preheater is fixedly connected with discharging pipeline.This application uses variable-diameter preheating pipeline structure, combined with gradient preheating method, makes hot air flow speed gradually increase along the flow direction in the pipeline, effectively enhances the relative motion of hot air flow and kaolin powder, and at the same time, cooperates with the temperature gradient gradually increasing from top to bottom, so that the powder can complete the preheating process according to the phase change rule.Secondly, with the help of the spoiler rotatably connected in the preheating pipeline, it can effectively destroy the thermal boundary layer between the hot air flow and the inner wall of the preheating pipeline under the action of hot air flow.

Description

Technical Field

[0001] This invention relates to the field of kaolin calcination technology, specifically to an enhanced heat exchange structure and gradient preheating system for the preheating section of a kaolin suspension kiln. Background Technology

[0002] In the kaolin suspension calcination process, the preheating section is a core component determining product quality and energy consumption. Its main function is to preheat the kaolin raw material powder to the dehydroxylation temperature, removing free and adsorbed water and laying the foundation for subsequent calcination processes. Currently, existing kaolin suspension kilns generally suffer from low heat exchange efficiency, uneven material preheating, and problems such as material adhering to the walls and accumulating, which seriously affect the preheating effect and production continuity.

[0003] In existing preheating structures, preheating pipes mostly adopt a constant diameter design. The hot airflow velocity inside the pipe is stable, making it difficult to form strong turbulence. This results in insufficient gas-solid contact, low heat exchange efficiency, and increased energy consumption in subsequent calcination processes. At the same time, the preheating pipes do not have effective turbulence structures. When the hot airflow flows through the inner wall of the pipe, a stable thermal boundary layer is easily formed. This not only hinders the heat exchange process but also causes kaolin powder to adhere to the inner wall of the pipe due to uneven heat exchange. Long-term accumulation can cause pipe blockage and affect continuous production.

[0004] In addition, existing feeding methods mostly adopt continuous feeding, with a large amount of powder entering the preheating pipe at once. This makes it easy for the powder to accumulate and agglomerate inside the pipe, preventing it from fully contacting the hot airflow. This results in some powder being under-preheated and some being over-preheated, which in turn affects key indicators such as whiteness and activity of the kaolin products after calcination, making it difficult to meet the needs of large-scale, high-quality production.

[0005] To address the aforementioned technical issues, there is an urgent need for an enhanced heat exchange structure and corresponding preheating method that can improve heat exchange efficiency, prevent material from adhering to the wall and accumulating, and achieve uniform gradient preheating. This would overcome the shortcomings of existing technologies, reduce production energy consumption, and improve product quality stability. Summary of the Invention

[0006] The purpose of this invention is to provide an enhanced heat exchange structure and gradient preheating system for the preheating section of a kaolin suspension kiln, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an enhanced heat exchange structure for the preheating section of a kaolin suspension kiln, comprising a combination of multiple preheaters in a vertical direction, wherein one side of the upper end of the preheater is connected to the upper end of a preheating pipe, and the lower end of the preheater is fixedly connected to a feeding pipe, the lower end of the preheating pipe is closed, and a fan is provided at the bottom position inside it, and a baffle plate for disturbing the airflow is provided above the fan, the baffle plate is rotatably connected to a baffle plate support, and is mounted inside the preheating pipe through the baffle plate support, the disturbed airflow is forced to compress and flow to the upper end along the bottom of the preheating pipe; The preheating pipe is fixedly connected to a dispersing bracket in the middle, and the dispersing bracket is rotatably connected with dispersing blades for dispersing the powder so that it can fully contact the hot airflow. The preheating pipe adopts a smooth variable diameter structure, and the pipe diameter gradually decreases along the direction of hot air flow, so that the flow velocity of the hot air gradually increases during the flow process, enhancing the relative movement between the hot air and the kaolin powder and improving the gas-solid heat exchange efficiency.

[0008] Preferably, the preheating pipe has a larger diameter at the end closer to the fan and a smaller diameter at the end closer to the preheater, with the ratio of the maximum to the minimum diameter being 2:1.

[0009] Preferably, multiple preheaters are provided and arranged vertically. Each preheater is connected to a preheating pipe with a discharge hole. The discharge pipe connected to the upper preheater extends into the discharge hole of the preheating pipe connected to the lower adjacent preheater.

[0010] Preferably, the uppermost preheating pipe is provided with a discharge hole, into which a feeding pipe is inserted. A feeding valve is installed on the feeding pipe. A disintegration bracket is fixedly connected inside the preheating pipe. The disintegration bracket is located at the end of the preheating pipe with a smaller diameter, near the preheater.

[0011] Preferably, the lowermost feeding pipe is fixedly connected to one end of the rotary kiln, and the other end of the rotary kiln is fixedly connected to the discharge pipe.

[0012] Another aspect of the present invention provides a gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln, comprising a sensing and detection unit, an execution and control unit, and a distributed control unit; The sensing and detection unit includes a temperature sensor group, an airflow parameter sensor group, a material state sensor group, and a mechanism speed sensor. The temperature sensor group is respectively arranged in the air inlet and outlet sections of each stage of the preheating pipe, the inner cavity of the preheater, and the axial inner wall of the preheating pipe. The airflow parameter sensor group is located on the air inlet side of each stage of the preheating pipe. The material state sensor group is located in the feed pipe and the discharge pipes of each stage. The mechanism speed sensor is matched with the deflating blades and the baffles. The execution control unit includes a variable frequency fan unit, a staged independent heating unit, an electrically controlled intermittent feeding valve, and a variable frequency dispersing drive mechanism; the fan at the bottom of each stage preheating pipe is a pulse-adjustable variable frequency fan; each stage preheater cavity is independently arranged with controllable heating components; the feeding valve is an electrically controlled proportional intermittent valve; the dispersing blades are equipped with variable frequency speed-adjustable motors; The distributed control unit includes a central controller and various levels of sub-control stations. The central controller has built-in phase change gradient temperature control algorithm, pulsating flow heat transfer enhancement algorithm, and multi-mechanism linkage adaptive control program. Each level of sub-control station collects sensor data at its level and independently controls all execution components at its level in a closed loop. When the gradient preheating control system is running, the main controller sends gradient temperature, fan speed, feeding cycle, and dispersing speed setpoints to each level of sub-control station according to the phase transformation law of kaolin. The independent heating units at each level form a gradient temperature field that gradually increases from top to bottom in each level of preheater. The variable frequency fan unit outputs an adjustable airflow with periodic pulsation, which, together with the variable diameter preheating pipe speed increase and the disturbance of the baffle plate, continuously destroys the thermal boundary layer of the pipe wall. The control system links the feeding, dispersing, and fan mechanisms to achieve full heat exchange of powder dispersion and suspension, thereby improving the gas-solid heat exchange efficiency.

[0013] Preferably, the graded independent heating unit divides multiple preheaters vertically into a low-temperature dehumidification section, a medium-temperature dehydration section, and a high-temperature dehydroxylation section. Each preheater uses a dual closed-loop temperature control logic of air temperature feedforward and material discharge temperature feedback to adjust the power of the heating components.

[0014] Preferably, the temperature of the hot airflow in the multiple preheating pipes increases gradually from top to bottom. Combined with the hot airflow velocity brought by the variable diameter structure of the preheating pipes, the disturbance effect of the baffles, and the intermittent feeding method, the powder can sequentially complete the removal of free water, the removal of adsorbed water and interlayer water, the deep dehydroxylation, and the preliminary crystal transformation in the preheating pipes from top to bottom, thereby realizing the gradient preheating of the powder.

[0015] Preferably, the variable frequency fan unit adopts a graded reference wind speed superimposed with a periodic pulsating speed control strategy; the reference wind speed of each preheating pipeline is increased step by step from top to bottom; the control system adjusts the fan reference speed in real time according to the concentration of material in the pipeline, and the fan speed is increased when the powder concentration increases.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: By employing a variable-diameter preheating pipe structure combined with a gradient preheating method, the flow velocity of the hot airflow gradually increases along the flow direction within the pipe, effectively enhancing the relative motion between the hot airflow and the kaolin powder, significantly improving gas-solid heat exchange efficiency, and reducing energy consumption in the preheating process. Simultaneously, the gradually increasing temperature gradient from top to bottom allows the powder to complete the preheating process according to the phase change law, ensuring sufficient and uniform preheating. Secondly, the rotating baffles connected within the preheating pipe achieve autonomous rotation under the action of the hot airflow, effectively disrupting the thermal boundary layer between the hot airflow and the inner wall of the preheating pipe, reducing heat exchange resistance, enhancing the heat exchange effect, and preventing powder from adhering to the inner wall of the pipe, thus preventing pipe blockage, ensuring continuous production, reducing powder waste, and lowering equipment maintenance costs.

[0017] By using an intermittent feeding method of "feeding-stopping feeding-feeding again-stopping feeding again" through the feed valve, the accumulation and agglomeration of powder in the preheating pipe is effectively avoided. This ensures that the powder entering the feed pipe is dispersed, and that each batch of powder can fully contact the hot airflow, further improving the uniformity of preheating and avoiding local underheating or overheating, thus ensuring the stability of the quality of kaolin products after subsequent calcination.

[0018] The layout design of preheating pipes and preheaters at each level, combined with variable diameter structures, baffle plate disturbances, and intermittent material discharge, forms a synergistic gradient preheating system. This allows the powder to sequentially complete processes such as free water removal, adsorbed water and interlayer water removal, and deep dehydroxylation within the preheating pipes at each level. This achieves precise matching between preheating and the powder phase change process, further enhancing the stability of product activity and whiteness. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the overall process of the present invention. Figure 3 This is a partial cross-sectional view of the present invention at the location of the material feeding pipe; Figure 4 This is a cross-sectional view of the invention at the location of the preheating pipe; Figure 5 for Figure 4 A magnified view of a portion of point A in the middle; Figure 6 This is a cross-sectional view of the invention at the location of the spoiler; Figure 7 This is a cross-sectional view of the present invention at the location of the disintegrating blades; Figure 8 This is a schematic diagram of the spoiler structure of the present invention; Figure 9 This is a schematic diagram of the disintegrating blade structure of the present invention.

[0020] In the diagram: 101, feed pipe; 102, feed valve; 103, dispersing blades; 104, dispersing support; 201, preheater; 202, preheating pipe; 203, discharge pipe; 204, fan; 205, baffle plate; 206, baffle plate support; 207, discharge hole; 301, rotary kiln; 302, discharge pipe. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1-9 To address the common problems in the preheating section of existing kaolin suspension kilns, such as low heat exchange efficiency, uneven material preheating, and easy material adhesion and accumulation, the preheating pipe 202 adopts a variable diameter structure to increase the hot air flow velocity and enhance the heat exchange effect. With the help of baffles 205, it achieves autonomous rotation under the action of the hot air flow, effectively breaking down the thermal boundary layer between the hot air flow and the inner wall of the preheating pipe 202, reducing heat exchange resistance, and enhancing the heat exchange effect. Simultaneously, the gradually increasing temperature gradient from top to bottom allows the powder to complete the preheating process according to the phase change law. Furthermore, the feed valve 102 adopts an intermittent discharge method, allowing the incoming material to... The powder in the feed pipe 101 is dispersed, ensuring that each batch of powder can fully contact the hot airflow. The present invention provides a technical solution: an enhanced heat exchange structure for the preheating section of a kaolin suspension kiln, including a preheater 201. The upper end of the preheater 201 is fixedly connected to the upper end of the preheating pipe 202. The lower end of the preheating pipe 202 is closed, and a fan 204 is fixedly connected to the bottom of the preheating pipe 202. A baffle bracket 206 is fixedly connected above the fan 204 in the preheating pipe 202. Baffles 205 are rotatably connected to the baffle bracket 206. The lower end of the preheater 201 is fixedly connected to the feed pipe 203.

[0023] The preheating pipe 202 has a larger diameter at the end near the fan 204 and a smaller diameter at the end near the preheater 201. The pipe diameter of the preheating pipe 202 is smooth.

[0024] Multiple preheaters 201 are provided and arranged vertically. Each preheater 201 is connected to a preheating pipe 202 with a discharge hole 207. The discharge pipe 203 connected to the upper preheater 201 extends into the discharge hole 207 of the preheating pipe 202 connected to the lower adjacent preheater 201.

[0025] The uppermost preheating pipe 202 is provided with a discharge hole 207, into which a feed pipe 101 is inserted. A feed valve 102 is installed on the feed pipe 101. A dispersing bracket 104 is fixedly connected inside the preheating pipe 202. The dispersing bracket 104 is located at the smaller end of the preheating pipe 202, near the preheater 201. Dispersing blades 103 are rotatably connected to the dispersing bracket 104.

[0026] The bottom feed pipe 203 is fixedly connected to one end of the rotary kiln 301, and the other end of the rotary kiln 301 is fixedly connected to the discharge pipe 302.

[0027] When preheating kaolin powder, the kaolin powder first enters the feed pipe 101. The feed valve 102 controls the discharge frequency of the kaolin powder using a "discharge-stop discharge-discharge-stop discharge" method, ensuring that the kaolin powder enters the uppermost preheating pipe 202 at the specified frequency. Please refer to [link / reference]. Figure 5 The lower end of the preheating pipe 202 is closed, but an air inlet is provided on the side of the preheating pipe 202 at the position of the fan. Therefore, the fan 204 generates hot air, and the baffle 205 starts to rotate freely on the baffle support 206 under the push of the hot air. At the same time, the baffle 205 changes the flow mode of the hot air, thereby breaking the thermal boundary layer between the hot air and the inner wall of the pipe, enhancing the heat exchange effect, improving the heat exchange efficiency, and ensuring that the kaolin powder is in uniform contact with the hot air and that the preheating of the kaolin powder is uniform. Hot air blows kaolin powder into the uppermost preheating pipe 202, which moves along a decreasing diameter path. The kaolin powder is agitated within the pipe, contacting the dispersing blades 103. A motor is built into the dispersing support 104, which autonomously drives the dispersing blades 103 to rotate. The blades 103 disperse the accumulated kaolin powder, increasing its contact area with the air. The kaolin powder then enters the uppermost preheater 201, where it is subjected to... Under the influence of gravity, the kaolin powder begins to settle. After preliminary preheating, it enters the uppermost feed pipe 203 and then flows into the next preheating pipe 202. Except for the uppermost preheating pipe 202, the other preheating pipes 202 do not have dispersing blades 103 or dispersing supports 104. Therefore, the kaolin powder in the remaining preheating pipes 202 is only subjected to the hot air passing through the baffles 205. The temperature in the preheating pipes 202 gradually increases from top to bottom, allowing the powder to complete the preheating process according to the phase change law, ensuring sufficient and uniform preheating. After the preheated kaolin powder enters the lowermost feed pipe 203, it continues to move into the rotary kiln 301 and is discharged from the discharge pipe 302, completing the full kaolin preheating process.

[0028] A gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln includes a sensing and detection unit, an execution and control unit, and a distributed control unit. The sensing and detection unit is used to collect real-time data on temperature, airflow, materials, and actuator operation in each level of the preheating unit. All sensor signals are connected to the corresponding level of the hierarchical sub-control station, and the specific arrangement is as follows: (1) Temperature sensor group: A K-type high temperature thermocouple is fixed in the air inlet section and air outlet section of each preheating pipe 202; an integrated material-gas mixing temperature sensor is installed in the center of the inner cavity of each preheater 201; four patch wall temperature sensors are uniformly fixed axially in a single preheating pipe 202 to monitor the material accumulation and adhesion status of the pipe wall. (2) Airflow parameter sensor group: An integrated wind speed and air pressure transmitter is installed at the air outlet of the 202 fan in each stage of preheating pipeline to synchronously collect the real-time airflow velocity and pressure difference inside the pipeline. The pressure difference value is used as the basis for determining the risk of pipeline blockage. (3) Material status sensor group: A powder solid flow meter is installed on the feed pipe section 101 to collect the instantaneous feed flow in real time; an infrared material temperature probe is installed at the outlet of each stage discharge pipe 203 to provide real-time feedback on the preheating discharge temperature of the kaolin powder in this stage. (4) Mechanism speed sensor: A Hall speed sensor is installed on the output shaft of the drive motor of the decomposing blade 103; a miniature photoelectric speed sensor is installed at the end of the deflector bracket 206 to collect the passive rotation speed of the deflector in real time and indirectly provide feedback on the intensity of airflow disturbance in the pipeline.

[0029] The execution control unit receives control commands from the staged sub-control station and completes precise adjustments to temperature, air volume, feeding, and dispersing mechanisms. (1) Variable frequency fan unit: The fan is a three-phase variable frequency centrifugal fan. Each fan is equipped with an independent frequency converter. The frequency converter receives speed control commands through analog signals and adjusts the speed. (2) Staged independent heating unit: The inner wall of each preheater 201 is surrounded by a silicon molybdenum rod electric heating array. Each heating array is equipped with an independent thyristor power regulator, which is controlled by the stage sub-control station. The three preheaters are divided into a low temperature dehumidification section, a medium temperature dehydration section, and a high temperature dehydroxylation section from top to bottom. The temperature control range of the low temperature dehumidification section is 80-120℃; the temperature control range of the medium temperature dehydration section is 220-350℃; and the temperature control range of the high temperature dehydroxylation section is 450-650℃. (3) Electrically controlled intermittent feeding valve: The feeding valve 102 is an electrically controlled powder proportional gate valve, equipped with a pulse control module, which can freely set the single feeding time and intermittent shutdown time; (4) Variable frequency dispersing drive mechanism: The dispersing bracket 104 has a built-in variable frequency reduction motor to drive the dispersing blade 103 to rotate. It receives the speed adjustment signal from the classifier control station and can switch between high-speed dispersing and low-speed maintenance according to the feeding stage.

[0030] The distributed control unit consists of one main controller and three hierarchical sub-control stations. The main controller communicates bidirectionally with each hierarchical sub-control station via an industrial Profinet bus. (1) The main controller is an industrial PLC master station. The human-machine interface screen is integrated into the main controller cabinet. The main controller receives the working condition data uploaded by all hierarchical sub-control stations in real time, issues unified gradient constraint instructions, and receives and summarizes signals at all levels. (2) The graded sub-control station is a small independent PLC, and each group of preheating units is matched with one graded sub-control station. The graded sub-control station independently collects all sensor detection data of its own level, independently controls the variable frequency fan, preheater heating array and dispersion drive motor of its own level in closed loop, and uploads real-time temperature, wind speed, material and mechanism speed data to the main controller, and receives temperature and air volume set values ​​issued by the main controller.

[0031] The system operates as follows: Heating and standby: The control system starts up, and the independent heating units of each preheater heat up according to the gradient set value. The variable frequency fan runs at low speed and no load. After the temperature of each stage stabilizes, it enters standby mode. Intermittent feeding heat exchange: The electrically controlled feeding valve feeds kaolin powder in three-stage cycles, the dispersing blades break up the agglomerated powder at high speed, and the variable frequency fan outputs pulsating airflow to carry the powder in suspension and flow in the variable diameter preheating pipe; Gradient heat treatment: The powder enters the lower preheating pipe through the feeding pipe. Each level of preheater independently controls the temperature to complete the corresponding phase change reaction. The suspension heat exchange and sedimentation feeding process is repeated until the bottom preheating unit. Real-time adaptive control: The sensing unit continuously collects parameters throughout the entire process, and the main controller dynamically corrects the heating power, fan pulsation speed, feeding cycle, and dispersing speed through built-in algorithms; when the risk of wall blockage is triggered, airflow flushing intervention is automatically executed; Discharge shutdown: The preheated powder is sent to the rotary kiln for calcination; the shutdown procedure is to first stop feeding, then have the blowers at all levels continuously blow for 5-10 minutes to remove residual material from the pipes, and then shut down the heating unit, blowers, and dispersing mechanism step by step.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A heat exchange enhancement structure for the preheating section of a kaolin suspension kiln, characterized in that: The system includes a combination of multiple preheaters (201) in a vertical direction. The upper end of the preheater (201) is connected to the upper end of the preheating pipe (202), and the lower end of the preheater (201) is fixedly connected to the feeding pipe (203). The lower end of the preheating pipe (202) is closed, and a fan (204) is provided at the bottom of the pipe. A baffle (205) for disturbing the airflow is provided above the fan (204). The baffle (205) is rotatably connected to the baffle bracket (206) and is mounted in the preheating pipe (202) through the baffle bracket (206). The disturbed airflow is forced to compress and flow to the upper end along the bottom of the preheating pipe (202). The preheating pipe (202) is fixedly connected to a dispersing bracket (104) in the middle, and a dispersing blade (103) for dispersing the powder to make it fully contact the hot airflow is rotatably connected on the dispersing bracket (104). The preheating pipe (202) adopts a smooth variable diameter structure. The diameter of the preheating pipe (202) gradually decreases along the direction of hot air flow, so that the flow velocity of the hot air gradually increases during the flow process, enhances the relative movement between the hot air and the kaolin powder, and improves the gas-solid heat exchange efficiency.

2. The enhanced heat exchange structure for the preheating section of a kaolin suspension kiln according to claim 1, characterized in that: The preheating pipe (202) has a larger diameter at the end near the fan (204) and a smaller diameter at the end near the preheater (201), with the ratio of the maximum to the minimum diameter being 2:

1.

3. The enhanced heat exchange structure for the preheating section of a kaolin suspension kiln according to claim 2, characterized in that: Multiple preheaters (201) are provided and arranged in a vertical direction. Each preheater (201) is connected to a preheating pipe (202) with a discharge hole (207). The discharge pipe (203) connected to the upper preheater (201) extends into the discharge hole (207) of the preheating pipe (202) connected to the lower adjacent preheater (201).

4. The enhanced heat exchange structure for the preheating section of a kaolin suspension kiln according to claim 3, characterized in that: The uppermost preheating pipe (202) is provided with a discharge hole (207), into which a feed pipe (101) is inserted. A feed valve (102) is installed on the feed pipe (101). A disintegration bracket (104) is fixedly connected inside the preheating pipe (202). The disintegration bracket (104) is located at the end of the preheating pipe (202) with a smaller diameter, near the preheater (201).

5. The enhanced heat exchange structure for the preheating section of a kaolin suspension kiln according to claim 4, characterized in that: The bottommost feeding pipe (203) is fixedly connected to one end of the rotary kiln (301), and the other end of the rotary kiln (301) is fixedly connected to the discharge pipe (302).

6. A gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln according to any one of claims 1-5, characterized in that: It includes a sensing and detection unit, an execution and control unit, and a distributed control unit; The sensing and detection unit includes a temperature sensor group, an airflow parameter sensor group, a material state sensor group, and a mechanism speed sensor. The temperature sensor group is respectively arranged in the air inlet and outlet sections of each stage preheating pipe (202), the inner cavity of the preheater (201), and the axial inner wall of the preheating pipe (202). The airflow parameter sensor group is located on the air inlet side of each stage preheating pipe (202). The material state sensor group is located in the feed pipe (101) and the discharge pipes (203) of each stage. The mechanism speed sensor is matched with the dispersing blade (103) and the baffle (205). The execution control unit includes a variable frequency fan unit, a staged independent heating unit, an electrically controlled intermittent feeding valve, and a variable frequency dispersing drive mechanism; the fan (204) at the bottom of each stage preheating pipe (202) is a pulse-adjustable variable frequency fan; each stage preheater (201) has an independently arranged controllable heating component in its inner cavity; the feeding valve (102) is an electrically controlled proportional intermittent valve; the dispersing blades (103) are equipped with a variable frequency speed-adjustable motor; The distributed control unit includes a central controller and various levels of sub-control stations. The central controller has built-in phase change gradient temperature control algorithm, pulsating flow heat transfer enhancement algorithm, and multi-mechanism linkage adaptive control program. Each level of sub-control station collects sensor data at its level and independently controls all execution components at its level in a closed loop. When the gradient preheating control system is running, the main controller sends gradient temperature, fan speed, feeding cycle and dispersing speed settings to each level of sub-control station according to the phase change law of kaolin. The graded independent heating unit forms a gradient temperature field that increases from top to bottom in each level of preheater (201). The variable frequency fan unit outputs an adjustable airflow with periodic pulsation, which, together with the variable diameter preheating pipe (202) speeding up and the turbulence plate (205) disturbing the pipe wall thermal boundary layer, the control system links the feeding, dispersing and fan mechanisms to achieve full heat exchange of powder dispersion and suspension, and improve gas-solid heat exchange efficiency.

7. The gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln according to claim 6, characterized in that: The graded independent heating unit divides multiple preheaters vertically into a low-temperature dehumidification section, a medium-temperature dehydration section, and a high-temperature dehydroxylation section. Each preheater uses a dual closed-loop temperature control logic of air temperature feedforward and material discharge temperature feedback to adjust the power of the heating components.

8. The gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln according to claim 7, characterized in that: The temperature of the hot airflow in the multiple preheating pipes (202) increases gradually from top to bottom. Combined with the hot airflow velocity brought by the variable diameter structure of the preheating pipes (202), the disturbance effect of the baffles (205), and the intermittent feeding method, the powder material completes the removal of free water, the removal of adsorbed water and interlayer water, the deep dehydroxylation and the initial crystal transformation in the preheating pipes (202) from top to bottom, thereby realizing the gradient preheating of the powder material.

9. The gradient preheating system with enhanced heat exchange structure in the preheating section of a kaolin suspension kiln according to claim 8, characterized in that: The variable frequency fan unit adopts a graded reference wind speed superimposed with a periodic pulsating speed control strategy; the reference wind speed of each level of preheating pipeline is increased from top to bottom; the control system adjusts the reference speed of the fan in real time according to the concentration of the material in the pipeline, and the fan speed is increased when the concentration of powder increases.

Images