Rotary kiln calcining method based on annular air curtain sealing

Abstract

The invention relates to the technical field of rotary kiln calcining equipment, in particular to a rotary kiln calcining method based on annular air curtain sealing, which comprises the following steps: S1, dynamic gap three-dimensional modeling: collecting a radial gap value between a kiln body flange end face and a static housing in real time through radial distance sensor groups uniformly distributed on the circumference; synchronously obtaining the axial displacement of the kiln body; constructing a dynamic gap three-dimensional topology model based on the angle distribution data of the radial gap value and the axial play vector; s2, generating a double-layer vortex air curtain; s3, dynamically regulating and controlling air curtain parameters; and S4, sealing efficiency closed-loop control is conducted, specifically, the escape dust concentration of the outer wall of the static housing is detected, and when the concentration exceeds the standard, the compensation coefficient of the reference flow velocity is increased according to the gradient, and the step S2 is executed again. The sealing effect of the rotary kiln is greatly improved by adopting a double-layer vortex air curtain sealing technology, dynamic gap modeling, air curtain parameter dynamic regulation and control and sealing efficiency closed-loop control.

Description

Technical Field

[0001] The invention relates to the technical field of rotary kiln calcining equipment, in particular to a rotary kiln calcining method based on annular air curtain sealing. Background Art

[0002] In rotary kiln calcining processes in industries such as cement and metallurgy, the sealing performance of the dynamic and static interfaces at the kiln head and kiln tail directly affects production efficiency and environmental performance. The current mainstream technology uses a single-layer annular air curtain seal, which injects air between the stationary cover and the rotating kiln body to prevent dust from escaping. This has the following drawbacks:

[0003] During calcination, the kiln temperature in a rotary kiln can reach over 800°C. This creates a non-uniform radial gap between the kiln flange and the stationary cover due to differences in the thermal expansion coefficients of the materials. This gap distribution changes periodically as the kiln rotates. This problem, determined by the thermodynamic properties of the materials, cannot be eliminated through mechanical design. Consequently, a single-layer air curtain experiences blind spots in the gap peak region.

[0004] The kiln body, supported by rollers, inevitably experiences axial movement, with the amount of movement reaching ±30mm. The Bernoulli effect creates low-pressure vortices in the region of sudden movement caused by the constant velocity air curtain. These vortices draw external dust back into the kiln, disrupting the calcining atmosphere. This phenomenon is governed by the principles of fluid dynamics and is unavoidable under axial movement.

[0005] Therefore, there is an urgent need for a rotary kiln sealing method that can simultaneously solve dynamic gap leakage and dust backflow. Summary of the Invention

[0006] Based on the above purpose, the present invention provides a rotary kiln calcining method based on annular air curtain sealing, comprising the following steps:

[0007] S1: Dynamic gap 3D modeling:

[0008] The radial clearance value between the kiln flange end face and the stationary cover is collected in real time by a group of radial distance sensors evenly distributed around the circumference, and the axial movement of the kiln body is simultaneously obtained. Based on the angular distribution data of the radial clearance value and the axial movement vector, a dynamic clearance three-dimensional topological model is constructed.

[0009] S2: Double-layer vortex air curtain generation:

[0010] A primary air curtain layer is formed by jetting air at a first inclination angle toward the front side of the kiln body in the direction of rotation through the annular main air chamber, and a secondary air curtain layer is formed by jetting air at a second inclination angle toward the rear side of the kiln body in the direction of rotation through the annular secondary air chamber; a reference flow velocity of the primary air curtain layer is calculated based on the maximum radial gap value in the three-dimensional topological model, and a flow velocity of the secondary air curtain layer is generated in proportion to the flow velocity of the primary air curtain layer; and the primary and secondary air curtain layers are caused to collide in the dynamic gap to form a closed vortex ring;

[0011] S3: Dynamic control of air curtain parameters:

[0012] Determining a vortex stability factor based on the rate of change of the axial movement, and dynamically adjusting the ratio based on the factor; adjusting the reference flow rate based on the degree of deviation of the maximum radial clearance value from the design reference clearance;

[0013] S4: Sealing efficiency closed-loop control:

[0014] Detect the escaping dust concentration on the outer wall of the static cover. When the concentration exceeds the standard, increase the compensation coefficient of the reference flow rate according to the gradient and return to S2 for execution.

[0015] Preferably, the process of constructing the dynamic gap three-dimensional topological model in S1 includes:

[0016] The radial gap values ​​collected at equal angles in the circumferential direction are mapped into a gap angle distribution curve in polar coordinates. The density of the curve sampling points is determined by the spatial resolution algorithm according to the kiln diameter.

[0017] The axial movement is decomposed into plane vector components perpendicular to the axis of the kiln body, and the decomposition direction is determined according to the position of the kiln body support roller;

[0018] The vector components are superimposed on the gap angle distribution curve according to the installation position of the axial displacement sensor to generate a three-dimensional gap topology map with the axial position as the Z-axis coordinate. The update frequency of the topology map is positively correlated with the kiln body rotation speed.

[0019] Preferably, the method for determining the first inclination angle and the second inclination angle in S2 includes:

[0020] The first inclination angle is determined by the vector synthesis experiment of kiln body rotation speed and air flow velocity: on the rotary kiln simulation platform, the air jet inclination angle is adjusted until the main air curtain layer completely covers the side edge of the kiln body in the dynamic gap;

[0021] The second inclination angle is determined by vortex collision test: under the condition of fixed main air curtain layer inclination angle, the inclination angle of the secondary air curtain layer is adjusted so that the high-speed camera can capture the complete annular vortex;

[0022] The inclination correction value is dynamically compensated according to the thermal expansion coefficient of the kiln body.

[0023] Preferably, the calculation logic of the reference flow velocity of the main air curtain layer in S2 includes:

[0024] Establish a mapping model between the maximum radial gap value and the critical sealing flow velocity: Under different kiln body movement phases, measure the minimum airflow velocity when dust escapes, and generate a gap-flow velocity compensation curve through piecewise linear regression;

[0025] The initial value of the reference flow velocity is obtained by interpolating the compensation curve according to the real-time maximum radial clearance value;

[0026] The correction amount for the negative pressure fluctuation at the kiln tail is superimposed and calculated based on the sliding average of the historical data of the pressure sensor.

[0027] Preferably, the process of obtaining the vortex stability factor in S3 includes:

[0028] Construct a time series database of the change rate of axial movement, and the change rate is calculated based on the range of movement per unit time;

[0029] Through gas-solid two-phase flow simulation, the lower limit of the secondary / main flow rate ratio to maintain vortex stability under different change rates is calibrated;

[0030] Quantifying the lower limit of the ratio as a vortex stability factor and establishing a change rate-stability factor lookup table;

[0031] When the real-time fluctuation rate exceeds the range of the table, the value is obtained by extrapolation from the closest table entry.

[0032] Preferably, the execution rules of the compensation coefficient for increasing the reference flow rate according to the gradient in S4 include:

[0033] Set three levels of fugitive dust concentration thresholds, with each level increasing proportionally according to the emission standards;

[0034] Every time the concentration exceeds the first threshold, the compensation coefficient is increased by a fixed percentage step. The step value is determined by the step response test based on the critical increase of the reference flow rate;

[0035] When the concentration drops below the threshold and remains below the preset time, the compensation coefficient is decreased by 50% of the step size until it reaches the initial value;

[0036] When the concentration does not decrease after three consecutive increases, the air curtain inclination angle calibration process is triggered.

[0037] Preferably, the spatial resolution algorithm is implemented by:

[0038] Taking the circumference of the kiln flange end face as the benchmark, calculate the minimum number of sensors according to the principle of equal arc length;

[0039] Determine the density of axial sensors based on the maximum deflection angle of the kiln body to ensure that the overlap rate of adjacent probe measurement areas is not lower than the set value;

[0040] Dynamically adjust the sampling frequency: when the kiln speed increases, the sampling frequency is increased by a multiple of the square root of the speed.

[0041] Preferably, the specific steps of the vortex collision test include:

[0042] A particle generator is arranged in a transparent sealed test chamber to simulate a dust environment;

[0043] Laser Doppler velocimeter is used to calibrate the velocity distribution in the air curtain intersection area;

[0044] The trajectory of the tracer particles is captured by a high-speed camera, and the criterion for identifying vortex closure is that the particles complete closed-loop motion within the annular region and have no radial escape path.

[0045] The qualified condition for the inclination angle of the secondary air curtain layer is: under the highest speed operating condition of the kiln body, the vortex closure rate continues to meet the standard.

[0046] Preferably, the implementation rules of the extrapolation method include:

[0047] When the rate of change of the drift is higher than the maximum value in the table, the stability factor is calculated by linear extrapolation of the slopes of the two items at the end of the table;

[0048] When the change rate of the oscillation is lower than the minimum value in the table, 90% of the stability factor value of the first item in the table is taken as the output;

[0049] When the extrapolation result exceeds the physically feasible region, the emergency braking protocol is initiated and an alarm is issued.

[0050] Preferably, the execution process of the step response test includes:

[0051] Under stable operating conditions, the flow rate of the main air curtain layer is increased stepwise and the dust concentration change curve is recorded;

[0052] The critical increase is defined as the flow rate increment when the concentration decrease rate reaches the peak value;

[0053] The critical increase value was averaged through three repeated tests, and 10% of the average value was set as the compensation coefficient step size;

[0054] The test process excludes the interference of kiln body movement and is only carried out during the stable period of axial displacement.

[0055] Beneficial effects of the present invention:

[0056] 1. The present invention adopts double-layer vortex air curtain generation technology and uses the collision of the main and auxiliary air curtain layers to form a closed vortex ring, which can effectively fill the blind spots covered by the airflow and ensure a uniform airflow sealing effect under any working conditions, greatly improving the sealing performance of the rotary kiln and reducing dust overflow.

[0057] 2. The present invention accurately controls the vortex stability factor and dynamically adjusts the ratio of the flow rates of the primary and secondary air curtain layers based on the rate of change of the axial movement, ensuring that the air curtain layer remains stable during the movement change process, thereby avoiding the generation of low-pressure vortexes, effectively maintaining the stability of the atmosphere in the kiln, and preventing the reverse inhalation of external dust.

[0058] 3. The present invention uses dynamic gap three-dimensional modeling technology to collect the radial gap value between the kiln flange end face and the static cover in real time, and calculates the flow rate and angular distribution of the air curtain layer based on the model, ensuring that the air curtain flow rate and distribution can be adjusted with the dynamic changes of the kiln body, thereby providing real-time and accurate sealing protection.

[0059] 4. This invention utilizes closed-loop sealing efficiency control technology to detect the concentration of fugitive dust on the outer wall of the stationary housing and dynamically adjusts the compensation coefficient of the baseline flow rate based on concentration changes, creating a self-regulating mechanism. This closed-loop control system rapidly responds to changes in fugitive dust, ensuring a consistently effective seal during actual operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0061] Figure 1 is a flow chart of the steps of the method of the present invention;

[0062] Figure 2 A flowchart of the steps for implementing the spatial resolution algorithm of the method of the present invention;

[0063] Figure 3 The present invention provides a flowchart of the steps of executing the step response test. DETAILED DESCRIPTION

[0064] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It is also noted that, to provide a more detailed description, the following embodiments are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing certain known technologies. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0065] See Figure 1-Figure 3, an embodiment of the present invention provides a rotary kiln calcining method based on annular air curtain sealing. In the production process of the rotary kiln, step 1 first collects the radial clearance value between the kiln body flange end face and the stationary cover shell in real time through a group of circumferentially evenly distributed radial distance sensors installed around the kiln body. These sensors can accurately record the radial changes of the kiln body during rotation. At the same time, the system synchronously obtains the axial movement of the kiln body and captures the axial displacement of the kiln body during operation. Combined with these data, a dynamic gap three-dimensional topological model is constructed through a high-precision algorithm to accurately reflect the real-time spatial distribution and dynamic changes between the kiln body and the cover shell. The model can be updated in real time to provide necessary data support for subsequent air curtain control.

[0066] In step 2, based on the constructed three-dimensional topological model of the dynamic gap, airflow is injected at different angles from the front and rear of the kiln body through the annular main and auxiliary air chambers. The injection angles and flow rates of the main and auxiliary air curtain layers are precisely calculated based on the maximum radial gap value, ensuring that the airflow evenly covers the entire space between the kiln flange and the cover. When the two airflow layers collide in the dynamic gap, they form a closed vortex ring, providing a strong airflow barrier. This double-layer vortex air curtain effectively avoids the coverage blind spots of a single-layer air curtain, improving the overall efficiency of the air curtain.

[0067] In step 3, the axial motion of the kiln body changes over time during the operation of the rotary kiln. Therefore, a vortex stability factor is calculated based on the rate of change of the axial motion. This factor dynamically adjusts the flow rate ratio between the primary and secondary air curtain layers to maintain the stability of the air curtain. Furthermore, the baseline flow rate of the primary air curtain is adjusted based on the deviation of the maximum radial clearance from the design baseline clearance. This dynamic control mechanism ensures that the air curtain remains efficient and stable under all operating conditions, avoiding uneven airflow caused by kiln body movement.

[0068] During actual production, the escape of external dust can cause environmental pollution. To address this, in step 4, a dust concentration sensor is installed on the outer wall of the stationary housing to monitor dust concentration in real time. If the concentration exceeds the specified value, the system automatically increases the compensation factor for the baseline flow rate and returns to step S2 for readjustment. This closed-loop control system rapidly responds to changes in actual operation, ensuring that the rotary kiln's air curtain sealing system maintains optimal operating conditions at all times, minimizing dust escape and ensuring environmentally friendly production practices.

[0069] By utilizing double-layer vortex air curtain sealing technology, dynamic gap modeling, dynamic air curtain parameter control, and closed-loop control of sealing efficiency, the rotary kiln's sealing effectiveness has been significantly improved. Compared with existing technologies, this system effectively eliminates airflow coverage blind spots, prevents the reverse suction of dust by low-pressure vortices, and ensures a stable kiln atmosphere. Furthermore, the ability to dynamically adjust the air curtain flow rate and compensation coefficient enables the sealing system to adapt to varying kiln operating conditions, reducing energy waste and minimizing environmental pollution caused by dust spillage, thereby improving production efficiency and environmental performance.

[0070] In one possible implementation, during the operation of the rotary kiln, a set of radial distance sensors positioned at equal angles around the circumference periodically collects radial clearance values ​​between the kiln flange end face and the stationary cover at preset angular intervals. To more accurately describe this data, the collected radial clearance values ​​are mapped to a polar coordinate system to form a "gap angle distribution curve." The density of sampling points in this curve is adjusted based on the kiln diameter. Specifically, a spatial resolution algorithm is used to optimally allocate the number of sampling points based on the kiln diameter, ensuring that the gap distribution covers the entire area of ​​the rotary kiln flange and ensuring sampling accuracy.

[0071] During kiln operation, the kiln body inevitably experiences a certain degree of axial movement due to the support rollers. To accurately quantify the impact of this movement, the system decomposes the axial movement into planar vector components perpendicular to the kiln axis. The direction of this decomposition is determined by the position of the kiln support rollers, ensuring that the decomposition of the movement accurately reflects the changes in the kiln body at different support positions. This decomposition process helps to clarify the axial displacement of the kiln body and ensure that this data can be effectively applied in subsequent models.

[0072] By combining the vector components of the aforementioned axial motion with the radial clearance value, the system overlays this information onto the gap angle distribution curve. Specifically, based on the installation position of the axial displacement sensor, the axial motion is overlaid onto the radial clearance angle distribution curve according to the displacement position. This creates a three-dimensional gap topology map with the axial position as the Z-axis coordinate, describing the dynamic changes in the gap between the kiln flange and the stationary cover over time and space. This topology map is regularly updated to ensure the timeliness and accuracy of its data. The update frequency is positively correlated with the rotary kiln's rotational speed, ensuring synchronization with the dynamic changes of the kiln body.

[0073] This invention accurately and in real time depicts the dynamic gap changes between the flange and the cover during rotary kiln operation. The use of a polar coordinate system allows for a more efficient description of the radial gap distribution, reducing errors in data processing. Furthermore, by combining axial motion with radial gap values, the resulting three-dimensional topological map accurately reflects the various influences on the kiln during operation. This not only improves the adaptability and accuracy of the sealing system but also provides real-time data support for subsequent double-layer air curtain generation and control, thereby ensuring the rotary kiln's sealing effectiveness and production efficiency.

[0074] In one possible implementation, the first inclination angle is determined through vector synthesis experiments comparing kiln rotation speed and airflow velocity. On a rotary kiln simulation platform, the inclination angle of the air jets is first adjusted, gradually changing the direction of the main air curtain until it completely covers the side edges of the kiln's dynamic gap. This process involves coordinated regulation of the kiln rotation speed and the air jet velocity, ensuring that the airflow angle synchronizes with changes in kiln rotation speed, thus avoiding unstable sealing due to inaccurate airflow direction. Through repeated experiments, the first inclination angle of the main air curtain layer is precisely determined, ensuring that it stably covers the gap during kiln operation and preventing air leakage.

[0075] Furthermore, the second inclination angle is determined through a vortex collision test. In an embodiment of the present invention, the first inclination angle is maintained unchanged, and the injection inclination angle of the secondary air curtain layer is adjusted so that it collides with the airflow of the primary air curtain layer and forms a stable vortex structure. The process of the secondary air curtain layer's airflow colliding with the primary air curtain layer's airflow is captured by a high-speed camera to observe and confirm whether the vortex is complete and stable. The ideal second inclination angle enables the two layers of air curtain to form a closed vortex ring, effectively preventing dust leakage and enhancing the air curtain's sealing ability.

[0076] Considering the potential for thermal expansion in rotary kilns at high temperatures, changes in kiln body dimensions can affect the airflow angle. Therefore, the system dynamically compensates for the airflow angle based on the kiln's thermal expansion coefficient. As the kiln temperature fluctuates, the system adjusts the airflow angle in real time to ensure that the airflow accurately covers the dynamic gap and forms a stable vortex. This compensation process relies on the real-time temperature changes of the kiln body. Sensors monitor the kiln temperature and calculate the corresponding angle correction, ensuring a stable airflow seal regardless of temperature fluctuations.

[0077] The present invention effectively solves the problem of unstable sealing caused by kiln body rotation speed, air flow velocity and thermal expansion during the calcination process of the rotary kiln. The experimental determination of the first inclination angle ensures that the main air curtain layer can cover the edge of the kiln body with a dynamic gap, thereby avoiding airflow leakage. The second inclination angle is optimized through vortex collision tests to ensure effective collision of the airflow and vortex stability, thereby further improving the sealing effect. In addition, the dynamic compensation function of the inclination angle enables the system to adapt to changes in kiln body temperature, avoids the airflow from deviating from the original design path due to thermal expansion, and ensures the stable operation of the rotary kiln under different working conditions. This technical solution not only improves the sealing effect of the kiln body, but also improves production efficiency and reduces energy waste, while reducing the pollution of dust overflow to the environment.

[0078] In one possible implementation, the critical sealing flow rate is first determined by measuring the minimum airflow velocity at zero dust escape under different phases of the rotary kiln. This flow rate represents the airflow velocity just sufficient to prevent dust from escaping the kiln. To accurately describe the required airflow velocity for different radial gaps, the system analyzes multiple measured data points through piecewise linear regression to generate a gap-flow rate compensation curve. This curve reflects the corresponding relationship between different radial gap values ​​and corresponding airflow velocities, providing a theoretical basis for subsequent baseline flow rate calculations.

[0079] During rotary kiln operation, the maximum radial clearance within the kiln is measured in real time. Based on this real-time maximum radial clearance, the previously established gap-flow rate compensation curve is used for interpolation calculation to determine the initial reference flow rate. This method allows for real-time acquisition of a reference flow rate that meets the current kiln operating conditions, ensuring that the airflow velocity accurately matches the dynamic changes in the kiln body.

[0080] Because negative pressure fluctuations may occur at the tail of a rotary kiln, causing variations in airflow pressure and velocity, the system calculates a correction for these fluctuations using a sliding average algorithm based on historical data collected by the pressure sensor. This correction reflects the impact of negative pressure fluctuations on airflow and modifies the baseline flow rate based on the magnitude of the fluctuation. By adding this correction to the initial baseline flow rate, the system ensures stable airflow even in the presence of fluctuating negative pressure at the tail, thereby optimizing the air curtain sealing effect.

[0081] This calculation logic allows the rotary kiln to accurately adjust the baseline flow rate of the main air curtain layer in real time, ensuring that the airflow effectively covers and seals the dynamic gap under different operating conditions, preventing dust leakage. The greatest advantage of this method is that it combines real-time monitoring and dynamic adjustment, ensuring that it can maintain a stable sealing effect despite changes in kiln temperature, pressure, speed, and other operating conditions.

[0082] Furthermore, the combined correction of the gap-flow rate compensation curve based on piecewise linear regression and the negative pressure fluctuation correction factor ensures that this method not only has high accuracy but also provides flexibility to adapt to the actual operating conditions of the kiln. In particular, under complex negative pressure fluctuations and kiln temperature variations, the airflow velocity can be corrected in real time to avoid a decrease in sealing effectiveness. This technology can significantly improve the airtightness of the rotary kiln during calcination, reduce energy consumption, minimize pollution, and increase production efficiency, with significant economic and environmental benefits.

[0083] In one possible implementation, first, by measuring the rate of change of the axial flow of the airflow in the rotary kiln, a corresponding time series database is constructed. The calculation method of the rate of change is based on the range of the flow per unit time. The flow refers to the change in the kinetic energy of the airflow in the axial direction, and this change reflects the degree of disturbance of the airflow. The larger the range, the stronger the airflow disturbance, so the rate of change of the flow is an important indicator for measuring the stability of the airflow. By recording the rate of change of the flow under different working conditions, data support can be provided for subsequent stability analysis.

[0084] Through gas-solid two-phase flow simulations, the effects of the secondary flow to primary flow ratio on vortex stability at different rates of change are simulated. Gas-solid two-phase flow simulations accurately reflect the interaction between airflow and solid materials, as well as the influence of airflow velocity on vortex structure stability. During the simulations, the lower limit of the secondary flow to primary flow ratio under different rates of change was calibrated—the minimum ratio that ensures vortex structure stability. This calibration process was performed using both experimental data and simulation results to determine the minimum ratio that maintains vortex stability under different operating conditions.

[0085] The lower limit of the secondary / primary velocity ratio, obtained through gas-solid two-phase flow simulations, is quantified as the vortex stability factor. This numerical indicator represents the minimum velocity ratio required to maintain a stable vortex structure under a given rate of change in axial motion. This factor reflects airflow stability and serves as a guiding parameter for subsequent operations. By establishing a relationship between the rate of change and the stability factor, a rate-of-change-stability-factor lookup table is created, facilitating real-time calculation and adjustment.

[0086] In actual operation, if the real-time monitored rate of change of the turbulence exceeds the range of the lookup table, the system uses the closest extrapolation method to calculate the vortex stability factor. Extrapolation is based on the closest data point in the lookup table, and the trend of these points is used to perform linear or nonlinear extrapolation to obtain the out-of-range stability factor value. This ensures that the vortex stability factor can be adjusted promptly under any changing conditions, thereby maintaining airflow stability.

[0087] By obtaining the vortex stability factor, the present invention can effectively adjust the ratio of the primary and secondary airflow velocities in the rotary kiln in real time, ensuring the stability of the vortex structure of the airflow, thereby improving the sealing effect of the annular air curtain. The stability of the vortex structure is crucial for sealing dust. A stable vortex can prevent dust from escaping, avoid environmental pollution, and improve the operating efficiency of the rotary kiln.

[0088] Furthermore, the calculation logic for the vortex stabilization factor combines gas-solid two-phase flow simulation, real-time data acquisition, and extrapolation to form a dynamic and precise airflow regulation mechanism. Even under significant fluctuations in kiln operating conditions, the system can rapidly respond and adjust the vortex stabilization factor, thereby maintaining efficient operation of the sealing system. This approach not only improves rotary kiln sealing, reduces energy consumption and dust pollution, but also enhances the safety and stability of the production process, possessing significant practical significance and long-term application value for industrial production.

[0089] In one possible implementation, three dust concentration thresholds are set based on environmental emission standards and process requirements. Each threshold corresponds to a different degree of dust escape, and these thresholds increase proportionally. The first threshold represents the lowest allowable dust concentration, while the second and third levels represent increasingly stringent emission standards. The purpose of setting these thresholds is to enable rapid response and appropriate adjustments when monitoring dust concentration in real time.

[0090] Whenever the fugitive dust concentration exceeds the first threshold, the system automatically increases the compensation factor to raise the baseline flow rate, enhancing the air curtain's sealing effectiveness. This increase is adjusted in fixed percentage steps, determined through step-response testing. These tests optimize the step size by analyzing the critical increase in the baseline flow rate (i.e., the change in dust concentration at different airflow rates). This ensures that the airflow regulation responds quickly to concentration changes without overshooting.

[0091] When the dust concentration drops below the threshold and remains below that threshold for a set period (predetermined duration), the system begins decreasing the compensation factor by 50% of the initial value until it returns to its initial value. This design ensures adaptive system adjustment, allowing it to not only respond to sudden changes in dust concentration but also gradually return to a normal sealing state once the concentration returns to normal, avoiding wasted resources caused by over-adjustment of the air curtain.

[0092] If the dust concentration remains above the set threshold after three consecutive increases in the compensation factor, the system automatically triggers an air curtain angle calibration process. The air curtain angle is a crucial factor influencing airflow distribution and sealing effectiveness; even small adjustments can significantly impact the seal. By triggering an air curtain angle calibration, the air curtain's physical structure can be adjusted to suit varying operating conditions, even if airflow velocity adjustments are ineffective.

[0093] While improving the efficiency of the rotary kiln calcining process, the method also meets environmental protection requirements, reduces energy waste, and ensures stable production over a long period of time.

[0094] In one possible implementation, the minimum number of sensors is first calculated based on the circumference of the kiln flange end face. This calculation is based on the principle of equal arc length, assuming that the kiln circumference is equally divided by the sensors, and that each sensor covers an area of ​​equal arc length. This ensures that the sensors are evenly distributed, with no overlapping or excessive gaps in their measurement areas. This uniform arrangement maximizes the spatial resolution of the sensors, ensuring accurate acquisition of airflow information from every part of the annular air curtain seal.

[0095] Rotary kilns may experience yaw during operation, meaning the kiln's central axis may shift or bend irregularly. To ensure accurate measurements, the density of axial sensors needs to be adjusted based on the kiln's maximum yaw angle. During design, the influence of yaw angle can be considered, increasing the density of axial sensors to ensure sufficient overlap between adjacent sensor measurement areas, thus preventing measurement blind spots during yaw. By setting a minimum overlap ratio, airflow data from each area can be effectively captured and compared.

[0096] During rotary kiln operation, the kiln speed varies with operating conditions. To ensure sensor data accuracy, the sampling frequency needs to be increased as the kiln speed increases. Specifically, the sampling frequency increases proportionally to the square root of the speed. This algorithm captures more sampled data at higher speeds, improving data timeliness and accuracy. Conversely, at lower speeds, the sampling frequency is appropriately reduced, reducing the system's computational burden and data redundancy.

[0097] Through sophisticated sensor arrangement and dynamic frequency adjustment, the monitoring accuracy, efficiency and system adaptability of the rotary kiln calcining process have been significantly improved, ensuring that the rotary kiln can maintain optimal airflow control and sealing effects under different operating conditions, thereby improving production efficiency and reducing environmental pollution.

[0098] In one possible implementation, a particle generator is placed within a transparent, sealed test chamber. By controlling the particle size, concentration, and distribution, the dust environment within a rotary kiln is simulated. This step is crucial for recreating the dust distribution within the rotary kiln as realistically as possible, ensuring that the test conditions align with actual production conditions, thereby providing reliable data support for subsequent testing.

[0099] A laser Doppler anemometry (LDA) is used to precisely calibrate the velocity distribution in the air curtain's intersection area. Laser Doppler anemometry uses the scattering effect between the laser beam and particles to measure the speed and direction of the airflow in real time, thereby accurately obtaining velocity data in the air curtain's intersection area. This step reveals the flow state and changing characteristics of the airflow, which is essential for ensuring the stability of the air curtain.

[0100] High-speed cameras are used to capture the trajectory of tracer particles in the airflow. By recording the particle movement, the system can analyze the stability and vortex characteristics of the airflow. The particle trajectory provides detailed information about the airflow pattern, clearly indicating whether the airflow can form a stable vortex structure, and thus providing intuitive evidence for sealing effectiveness.

[0101] By analyzing the captured particle motion trajectories, we determine the criteria for vortex closure. Vortex closure refers to the ability of particles to complete a closed-loop motion within the annular region, with no radial escape paths. This criterion ensures the airflow is contained within the annular region, thereby verifying the sealing effectiveness of the air curtain. A well-closed vortex indicates that the air curtain is effectively suppressing dust escape and ensuring a stable kiln environment.

[0102] With the kiln at its highest speed, measure the vortex closure rate and ensure it consistently meets the specified standards. The inclination of the secondary air curtain layer is a crucial factor influencing airflow stability. A qualified inclination ensures that the air curtain maintains a good seal under varying operating conditions. Ensuring the inclination of the secondary air curtain layer meets the specified requirements is crucial during this step, as the effectiveness of the air curtain is directly related to its physical structure and angle.

[0103] By simulating real-world operating conditions and accurately analyzing airflow characteristics, the vortex impact test provides a reliable method for verifying the annular air curtain seal of a rotary kiln. This technology ensures the airflow seal effectiveness of the rotary kiln under various operating conditions, improving production stability and environmental friendliness, and possessing significant economic and environmental value.

[0104] In one possible implementation, during rotary kiln operation, the rate of change refers to the rate of change of the airflow or material velocity within the kiln. If this rate of change exceeds the maximum value in the table (i.e., exceeds the range of the table data), an extrapolation method is used to estimate the stability factor. This extrapolation method calculates the slope of the last two terms in the table data and linearly extrapolates to a higher rate of change range. This extrapolation method can predict changes in the stability factor based on trends, helping to adjust system parameters and avoid unexpected operational anomalies.

[0105] When the rate of change is below the minimum value in the table, indicating a relatively stable or low-variability state, the stability factor calculation adopts a more conservative strategy. In this case, the output stability factor value is 90% of the stability factor value in the first entry in the table. This conservative setting prevents the system from overly optimistically estimating stability, ensuring a sufficient safety margin even with minimal fluctuations, preventing excessive airflow from compromising the air curtain's sealing effectiveness.

[0106] If the stability factor calculated by extrapolation exceeds the physically feasible region (i.e., cannot be achieved or does not meet actual operating conditions), the system will initiate an emergency braking protocol and issue an alarm. This is to ensure the safety of the rotary kiln, preventing kiln failure or airflow seal failure caused by operations outside the physically feasible range, and ensuring stability and safety during production.

[0107] The extrapolation method, through dynamic adjustment of the stability factor and combined with an emergency braking protocol and alarm mechanism, has significantly improved rotary kiln stability, optimized system response, and ensured production safety. This approach not only responds to various operating conditions but also effectively prevents equipment failures, improving the efficiency and safety of rotary kiln operations.

[0108] In one possible implementation, while the rotary kiln is operating at a stable level, the flow rate of the main air curtain layer is gradually increased in steps. This means the air velocity increases in predetermined steps rather than continuously. After each flow rate increase, the system records the change in dust concentration. This continuous monitoring accurately captures the dust concentration response at different flow rates, providing data support for analyzing the air curtain's sealing effectiveness.

[0109] After recording the dust concentration curve, we analyze the rate of concentration decrease and define the critical increase as the flow rate increment at which the dust concentration decrease rate reaches its peak. This critical increase is a key parameter, indicating that increasing the air curtain flow rate effectively affects the change in dust concentration. Specifically, when the air flow rate reaches a certain critical value, the rate of dust concentration decreases at its maximum, indicating that the air curtain sealing effect is optimal.

[0110] To ensure the reliability of the test results, the step response test is repeated three times, and the critical increase obtained from each test is averaged. This average value reflects the stability and reliability of the airflow under different test conditions, ensuring the accuracy and representativeness of the data.

[0111] After taking the average of the critical increase, 10% of this average is set as the compensation coefficient step size. This compensation coefficient step size is used as a reference value for compensating and optimizing airflow velocity during subsequent air curtain adjustments, ensuring airflow regulation accuracy and the continued stability of the airflow seal within the rotary kiln.

[0112] During the test, it was necessary to eliminate interference from kiln movement, as this would affect the stability of the airflow and the measurement of dust concentration. To ensure the accuracy of the experimental data, the test was only conducted during the stage of stable axial displacement to avoid errors caused by kiln instability.

[0113] The step response test can not only optimize the air curtain sealing effect through precise flow rate regulation and dust concentration change monitoring, but also improve the operational stability and environmental performance of the rotary kiln, thereby achieving the goal of improving production efficiency and reducing environmental pollution.

[0114] The following is a detailed explanation using examples:

[0115] The present invention is applied to the production process of rotary kilns, especially in the fields of steel smelting, building materials and fertilizer production. It aims to control the dust concentration in the kiln by optimizing the rotary kiln airflow sealing system, thereby improving production efficiency and environmental quality.

[0116] First, the initial airflow is set to 4000m³ / h. The airflow can be adjusted from 3000-8000m³ / h.

[0117] The initial dust concentration is 80mg / m³, and the target concentration is controlled below 40mg / m³.

[0118] According to experimental data and equipment characteristics, the stability factor is initially set to 0.95.

[0119] Extrapolation and step response test algorithms are used to dynamically adjust the airflow and air curtain pressure.

[0120] Furthermore, dust concentration data at different air flow speeds are collected in real time through sensors.

[0121] Assume that the relationship between dust concentration C and air velocity V is linear:

[0122] ;

[0123] Two data points were measured through experiments: When the dust concentration , at air flow speed When the dust concentration .

[0124] The linear relationship between air flow velocity and dust concentration is calculated by extrapolation:

[0125] ;

[0126] ;

[0127] Therefore, the relationship between dust concentration and air flow velocity is:

[0128] ;

[0129] By adjusting the air flow speed and observing the changes in dust concentration.

[0130] Set the test values ​​at different air flow velocities and test the dust concentration when the air flow velocity is 3000m³ / h, 4000m³ / h, 5000m³ / h and 6000m³ / h.

[0131] The dust concentrations measured at different speeds are shown in the following table:

[0132] Air flow velocity V (m³ / h) Dust concentration C (mg / m³) 3000 70 4000 60 5000 50 6000 40

[0133] Based on the test results, the stability factor was set to 0.95 and dynamically adjusted. The system automatically adjusts to ensure that the airflow speed remains within the appropriate range during different time periods.

[0134] The PLC control system monitors sensor data in real time and automatically adjusts the air flow speed and air curtain pressure.

[0135] When the dust concentration exceeds 50mg / m³, the system automatically increases the airflow to 5000m³ / h.

[0136] If the dust concentration reaches the predetermined target of 40mg / m³, the system adjusts the airflow to 4000m³ / h.

[0137] Extrapolation formula:

[0138] ;

[0139] Where C is the dust concentration, V is the air velocity, a=−0.01, and b=100.

[0140] Stability factor: 0.95, adjusted according to experimental data to ensure stable operation of the system.

[0141] Air flow velocity range: 3000m³ / h to 8000m³ / h, suitable for production adjustment under different load conditions.

[0142] Comparison 1: Traditional system vs. this invention

[0143] Traditional system: There is no real-time adjustment of airflow and air curtain pressure, and the dust concentration fluctuates greatly, ranging from about 70-80mg / m³.

[0144] The system of the present invention: through extrapolation method and step response test, the airflow and air curtain pressure are adjusted in real time, and the dust concentration is stabilized below 40mg / m³.

[0145] System Type Air flow rate (m³ / h) Dust concentration (mg / m³) Traditional control systems 4000 75 Control system of the present invention 4000 40

[0146] From the comparison results, it can be seen that the present invention can significantly reduce the dust concentration and improve the cleanliness of the kiln environment.

[0147] Comparison 2: Changes in dust concentration at different airflow velocities

[0148] Air flow rate (m³ / h) Dust concentration in traditional system (mg / m³) Dust concentration of the system of the present invention (mg / m³) 3000 80 70 4000 75 60 5000 72 50 6000 70 40

[0149] By comparison, it can be seen that the present invention can more effectively control the dust concentration within an ideal range, avoiding the problem of excessively high dust concentration in traditional systems.

[0150] This invention combines extrapolation with a step-response test algorithm to adjust airflow velocity and air curtain pressure in real time, significantly reducing dust concentration in rotary kilns. This improves production efficiency and reduces environmental pollution. Compared to traditional control systems, this invention offers significant advantages, including greater stability and control accuracy, enabling optimal dust concentration control under varying operating conditions.

[0151] The present invention encompasses any alternatives, modifications, equivalents, and solutions that fall within the spirit and scope of the present invention. To provide a thorough understanding of the present invention, specific details are described in detail below in connection with the preferred embodiments of the present invention, but those skilled in the art will be able to fully understand the present invention without these detailed descriptions. Furthermore, to avoid unnecessary confusion regarding the essence of the present invention, well-known methods, processes, procedures, components, and circuits have not been described in detail.

[0152] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A rotary kiln calcining method based on annular air curtain sealing, characterized in that: The following steps are involved: S1: Dynamic gap 3D modeling: The radial clearance value between the kiln flange end face and the stationary cover is collected in real time by a group of radial distance sensors evenly distributed around the circumference, and the axial movement of the kiln body is simultaneously obtained. Based on the angular distribution data of the radial clearance value and the axial movement vector, a dynamic clearance three-dimensional topological model is constructed. S2: Double-layer vortex air curtain generation: A primary air curtain layer is formed by jetting air at a first inclination angle toward the front side of the kiln body in the direction of rotation through the annular main air chamber, and a secondary air curtain layer is formed by jetting air at a second inclination angle toward the rear side of the kiln body in the direction of rotation through the annular secondary air chamber; a reference flow velocity of the primary air curtain layer is calculated based on the maximum radial gap value in the three-dimensional topological model, and a flow velocity of the secondary air curtain layer is generated in proportion to the flow velocity of the primary air curtain layer; and the primary and secondary air curtain layers are caused to collide in the dynamic gap to form a closed vortex ring; S3: Dynamic control of air curtain parameters: Determining a vortex stability factor based on the rate of change of the axial movement, and dynamically adjusting the ratio based on the factor; adjusting the reference flow rate based on the degree of deviation of the maximum radial clearance value from the design reference clearance; S4: Sealing efficiency closed-loop control: Detect the escaping dust concentration on the outer wall of the static cover. When the concentration exceeds the standard, increase the compensation coefficient of the reference flow rate according to the gradient and return to S2 for execution.

2. A rotary kiln calcining method based on annular air curtain sealing according to claim 1, characterized in that: The construction process of the dynamic gap 3D topology model in S1 includes: The radial gap values ​​collected at equal angles in the circumferential direction are mapped into a gap angle distribution curve in polar coordinates. The density of the curve sampling points is determined by the spatial resolution algorithm according to the kiln diameter. The axial movement is decomposed into plane vector components perpendicular to the axis of the kiln body, and the decomposition direction is determined according to the position of the kiln body support roller; The vector components are superimposed on the gap angle distribution curve according to the installation position of the axial displacement sensor to generate a three-dimensional gap topology map with the axial position as the Z-axis coordinate. The update frequency of the topology map is positively correlated with the kiln body rotation speed.

3. The rotary kiln calcining method based on annular air curtain sealing according to claim 1, characterized in that: The method for determining the first inclination angle and the second inclination angle in S2 includes: The first inclination angle is determined by the vector synthesis experiment of kiln body rotation speed and air flow velocity: on the rotary kiln simulation platform, the air jet inclination angle is adjusted until the main air curtain layer completely covers the side edge of the kiln body in the dynamic gap; The second inclination angle is determined by vortex collision test: under the condition of fixed main air curtain layer inclination angle, the inclination angle of the secondary air curtain layer is adjusted so that the high-speed camera can capture the complete annular vortex; The inclination correction value is dynamically compensated according to the thermal expansion coefficient of the kiln body.

4. The rotary kiln calcining method based on annular air curtain sealing according to claim 1, characterized in that: The calculation logic of the reference velocity of the main air curtain layer in S2 includes: Establish a mapping model between the maximum radial gap value and the critical sealing flow velocity: Under different kiln body movement phases, measure the minimum airflow velocity when dust escapes, and generate a gap-flow velocity compensation curve through piecewise linear regression; The initial value of the reference flow velocity is obtained by interpolating the compensation curve according to the real-time maximum radial clearance value; The correction amount for the negative pressure fluctuation at the kiln tail is superimposed and calculated based on the sliding average of the historical data of the pressure sensor.

5. The rotary kiln calcining method based on annular air curtain sealing according to claim 1, characterized in that: The process of obtaining the vortex stability factor in S3 includes: Construct a time series database of the change rate of axial movement, and the change rate is calculated based on the range of movement per unit time; Through gas-solid two-phase flow simulation, the lower limit of the secondary / main flow rate ratio to maintain vortex stability under different change rates is calibrated; Quantifying the lower limit of the ratio as a vortex stability factor and establishing a change rate-stability factor lookup table; When the real-time fluctuation rate exceeds the range of the table, the value is obtained by extrapolation from the closest table entry.

6. The rotary kiln calcining method based on annular air curtain sealing according to claim 1, characterized in that: The execution rules of the compensation coefficient for increasing the reference flow rate according to the gradient in S4 include: Set three levels of fugitive dust concentration thresholds, with each level increasing proportionally according to the emission standards; Every time the concentration exceeds the first threshold, the compensation coefficient is increased by a fixed percentage step. The step value is determined by the step response test based on the critical increase of the reference flow rate; When the concentration drops below the threshold and remains below the preset time, the compensation coefficient is decreased by 50% of the step size until it reaches the initial value; When the concentration does not decrease after three consecutive increases, the air curtain inclination angle calibration process is triggered.

7. The rotary kiln calcining method based on annular air curtain sealing according to claim 2, characterized in that: The implementation of the spatial resolution algorithm includes: Taking the circumference of the kiln flange end face as the benchmark, calculate the minimum number of sensors according to the principle of equal arc length; Determine the density of axial sensors based on the maximum deflection angle of the kiln body to ensure that the overlap rate of adjacent probe measurement areas is not lower than the set value; Dynamically adjust the sampling frequency: when the kiln speed increases, the sampling frequency is increased by a multiple of the square root of the speed.

8. The rotary kiln calcining method based on annular air curtain sealing according to claim 3, characterized in that: The specific steps of the vortex collision test include: A particle generator is arranged in a transparent sealed test chamber to simulate a dust environment; Laser Doppler velocimeter is used to calibrate the velocity distribution in the air curtain intersection area; The trajectory of the tracer particles is captured by a high-speed camera, and the criterion for identifying vortex closure is that the particles complete closed-loop motion within the annular region and have no radial escape path. The qualified condition for the inclination angle of the secondary air curtain layer is: under the highest speed operating condition of the kiln body, the vortex closure rate continues to meet the standard.

9. The rotary kiln calcining method based on annular air curtain sealing according to claim 5, characterized in that: The implementation rules of the extrapolation method include: When the rate of change of the drift is higher than the maximum value in the table, the stability factor is calculated by linear extrapolation of the slopes of the two items at the end of the table; When the change rate of the oscillation is lower than the minimum value in the table, 90% of the stability factor value of the first item in the table is taken as the output; When the extrapolation result exceeds the physically feasible region, the emergency braking protocol is initiated and an alarm is issued.

10. The rotary kiln calcining method based on annular air curtain sealing according to claim 6, characterized in that: The execution process of the step response test includes: Under stable operating conditions, the flow rate of the main air curtain layer is increased stepwise and the dust concentration change curve is recorded; The critical increase is defined as the flow rate increment when the concentration decrease rate reaches the peak value; The critical increase value was averaged through three repeated tests, and 10% of the average value was set as the compensation coefficient step size; The test process excludes the interference of kiln body movement and is only carried out during the stable period of axial displacement.

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