Self-adaptive control method and system for sealing pressure of lithium iron phosphate rotary kiln

Abstract

The invention relates to the technical field of industrial automation control, in particular to a lithium iron phosphate rotary kiln sealing pressure self-adaptive control method and system, and aims to solve the technical problems of sealing gap fluctuation caused by cylinder thermal creep and gravity bending in the prior art and leakage and abrasion caused by feedback control lag in the prior art. The method comprises the following steps: acquiring operation data of the rotary kiln; based on the current effective value and the accumulated operation time, constructing a thermogravity coupling deformation index; constructing a target sealing pressure feedforward model, and calculating a theoretical optimal sealing pressure set value at the current moment; and calculating the control quantity finally output to the execution mechanism. According to the invention, the wear rate of the sealing element can be reduced, and continuous sintering of high-quality materials is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of industrial automation control technology, and more specifically, to an adaptive control method and system for the sealing pressure of a lithium iron phosphate rotary kiln. Background Technology

[0002] In the production of lithium-ion battery cathode materials, especially lithium iron phosphate (LFP), high-temperature solid-state sintering is a critical process affecting material performance. This process typically employs an electrically heated rotary kiln, maintaining a slightly positive pressure nitrogen protective atmosphere within the kiln to prevent oxidation. Therefore, the dynamic and static sealing performance at the kiln head and tail is crucial. Currently, the industry commonly uses a composite sealing structure combining mechanical contact and a gas barrier, applying pressure to force the sealing ring to adhere to the cylinder flange.

[0003] However, the rotary kiln shell undergoes thermal creep under high-temperature electric heating, resulting in a decrease in yield strength. Combined with the weight of the shell itself and the material load, the suspended section will experience irreversible sagging deformation. This deformation causes the sealing end face to exhibit eccentric jumping during rotation, resulting in violent fluctuations in the sealing gap within the rotation cycle.

[0004] Existing control technologies primarily rely on pressure sensors within the sealed cavity for PID feedback regulation. However, due to the compressibility of the gas medium and the actuator's lag, this hysteretic feedback mechanism cannot adapt to rapidly changing gaps. When the gap widens, untimely pressure compensation leads to oxygen infiltration; when the gap narrows, untimely pressure release causes severe friction between the sealing ring and the cylinder. This dual failure problem of leakage and wear not only increases maintenance costs but also severely affects the sintering consistency of the product. Summary of the Invention

[0005] To address the problems of sealing gap fluctuations caused by thermal creep and gravitational bending of the cylinder in the prior art, as well as leakage and wear caused by the lag in existing feedback control, the present invention provides solutions in the following aspects.

[0006] In a first aspect, the present invention provides an adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln, comprising: The operating data of the rotary kiln is collected, including the original value of heating current, cumulative operating time, real-time rotation angle and pressure feedback value of the sealed cavity. The original value of heating current is processed by sliding window root mean square to obtain the effective value of current. Based on the effective value of the current and the cumulative running time, a thermogravity coupling deformation index is constructed. The thermogravity coupling deformation index is used to characterize the degree of deformation of the suspended section of the cylinder bending downward. Its value is positively correlated with the heat input power represented by the effective value of the current, and shows a nonlinear increase with the increase of the cumulative running time. Using the thermogravity coupling deformation index as the amplitude modulation parameter and combining it with the real-time rotation angle, a target sealing pressure feedforward model is constructed to calculate the theoretical optimal sealing pressure setting value at the current moment. The theoretical optimal sealing pressure setting value fluctuates periodically with the rotation angle. Based on the deviation between the theoretically optimal sealing pressure setting value and the pressure feedback value of the sealing cavity, and combined with the dynamic adjustment of the controller sensitivity by the thermogravimetric coupling deformation index, the control quantity finally output to the actuator is calculated to adaptively adjust the rotary kiln sealing pressure.

[0007] This invention changes the traditional passive feedback control mode. By using the deformation index constructed from current and time data, it can predict the deformation trend before the physical gap changes and generate dynamic pressure commands that change with the angle. The feedforward mechanism of this invention eliminates control lag and ensures that the sealing pressure is always synchronized with the eccentric jump of the cylinder.

[0008] Furthermore, the sliding window root mean square processing of the original value of the heating current includes: setting the number of data points corresponding to the time length of the sliding window to N, and calculating the root mean square value of the data within the sliding window as the effective value of the current, so as to filter out high-frequency noise introduced by power grid fluctuations and thyristor voltage regulation.

[0009] By processing the root mean square (RMS) data, electrical interference can be eliminated, and a current index that truly reflects the thermal energy density can be obtained, providing an accurate data basis for subsequent thermal expansion calculations.

[0010] Furthermore, the formula for calculating the thermogravimetric coupling deformation index is as follows: ; In the formula, for The thermogravimetric coupling deformation index at any given moment; From the current moment Push forward The effective value of the current at each sampling time; To calculate the length of the time window; The cumulative high-temperature operating time of the rotary kiln; The coefficient of thermal expansion. The creep aging coefficient; It is the natural logarithm function.

[0011] This formula mathematically integrates the instantaneous thermal expansion represented by the square term of the current and the long-term creep aging represented by the logarithmic time term, and evaluates the actual sagging degree of the rotary kiln shell under complex working conditions, solving the problem of deformation assessment that cannot be observed by the naked eye.

[0012] Furthermore, the first term in the thermogravimetric coupling deformation index calculation formula represents the square root of the mean square of the current over a period of time, used to assess the current average heat input power; the second term uses the natural logarithm function to simulate the creep characteristics of metallic materials at high temperatures, characterizing the saturation effect of deformation accumulating over time but with a gradually slowing growth rate.

[0013] Furthermore, the calculation formula for the target sealing pressure feedforward model is as follows: ; In the formula, for The theoretical optimal sealing pressure setting value at any given time; The set value for the basic sealing pressure when the equipment is cold and stationary; for The thermogravimetric coupling deformation index at any given moment; The basic gain coefficient; This is the amplitude coefficient of the wave. This refers to the real-time rotational speed angular frequency of the rotary kiln. This is the initial phase angle.

[0014] By using the deformation index as the amplitude modulation parameter, the pressure command generated by the system is no longer a constant value, but a sine wave. The system will automatically reduce pressure when the rotary kiln body is pressed downward and automatically increase pressure when the rotary kiln body is deflected upward.

[0015] Furthermore, the initial phase angle corresponds to the lowest point of the bending geometry of the rotary kiln shell, and is the angle at which the rotary kiln shell exerts the most downward pressure on the sealing ring; when the cosine value is positive, the actuator applies pressure in advance to seal the enlarged gap; when the cosine value is negative, the actuator releases pressure in advance, using the weight of the shell to maintain the seal.

[0016] Phase alignment avoids the vicious superposition of actuator pressure and rotary kiln weight, reduces mechanical friction and wear of the sealing ring, and extends its service life.

[0017] Furthermore, the formula for calculating the final control quantity output to the actuator is: ; In the formula, For the current moment The control quantity output to the actuator; This is the output value of the previous control cycle; The basic proportional gain coefficient; for The thermogravimetric coupling deformation index at any given moment; This is the maximum allowable design deformation limit constant for the equipment; for The theoretical optimal sealing pressure setting value at any given time; This is the pressure feedback value for the sealed cavity.

[0018] By introducing an adaptive gain factor based on the degree of deformation. When equipment ages or experiences severe thermal shock leading to increased deformation, the controller's sensitivity will automatically increase, enabling it to quickly correct severe pressure instability and ensure response speed under extreme operating conditions.

[0019] Furthermore, in the formula As an adaptive gain factor, when the thermo-gravity coupling deformation index approaches the maximum design deformation limit constant allowed by the equipment, the adaptive gain factor increases, causing the controller to output a larger adjustment range to correct pressure instability.

[0020] Furthermore, the adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln also includes a boundary constraint step: if the calculated... If the value is greater than 100%, then the value is taken as 100%; if the calculated value is... If it is less than 0%, then the value is 0.

[0021] Secondly, the present invention provides an adaptive control system for the sealing pressure of a lithium iron phosphate rotary kiln, comprising a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, the aforementioned adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln is implemented.

[0022] The beneficial effects are as follows: This invention constructs a thermo-gravity coupling model reflecting the physical state of the cylinder by deeply analyzing electrothermal data, and implements feedforward adaptive control accordingly, which solves the long-standing problem of control lag in the field of rotary kiln sealing, eliminates the risk of instantaneous oxygen infiltration, reduces the wear rate of the seals, and provides a guarantee for the continuous sintering of high-quality materials. Attached Figure Description

[0023] Figure 1 This is a comparison diagram of the dynamic control effect of rotation angle and sealing pressure in this invention; Figure 2 This is a comparison chart showing the evolution of seal wear and leakage risk between the present invention and existing technologies under long-term operation. Detailed Implementation

[0024] This invention discloses an adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln, the method comprising the following steps: Step S1: Collect the operating data of the rotary kiln, including the original value of the heating current, the cumulative operating time, the real-time rotation angle, and the pressure feedback value of the sealed cavity. Then, perform root mean square processing on the original value of the heating current through a sliding window to obtain the effective value of the current.

[0025] Specifically, during the production and operation of the rotary kiln, multi-dimensional data is collected at high frequency through an industrial fieldbus (such as a PLC or DCS system). This includes: acquiring the real-time raw value of the heating current through a Hall current sensor installed in the main circuit of the electric heater at a sampling frequency of not less than 10Hz; recording the cumulative effective operating time of the rotary kiln above a set high temperature threshold through the system's non-volatile timer (for example, the set high temperature threshold is 300℃); obtaining the current real-time rotation angle and real-time speed of the rotary kiln cylinder through an absolute encoder installed on the motor shaft or transmission gear; and acquiring the pressure feedback value of the sealed cavity through a pressure transmitter.

[0026] For the raw heating current values ​​collected, high-frequency noise is introduced due to power grid fluctuations and SCR voltage regulation, necessitating root mean square (RMS) processing via a sliding window. The sliding window time is set to... , where N is the number of data points; calculate the effective value of the current within the sliding window. For example, if the sampling frequency is 10Hz and the sliding window length is set to 10 points (i.e., 1 second), then the square root of the square mean of these 10 original heating current values ​​is calculated as the effective value of the current at that moment.

[0027] By collecting multidimensional data and processing the root mean square of the sliding window, the thermal energy density input to the metal material of the rotary kiln cylinder can be accurately reflected, eliminating electrical interference and providing an accurate basis for subsequent thermal expansion calculations.

[0028] Step S2: Based on the effective value of the current and the cumulative running time, construct a thermo-gravity coupling deformation index. The thermo-gravity coupling deformation index is used to characterize the degree of deformation of the suspended section of the cylinder bending downward. Its value is positively correlated with the heat input power represented by the effective value of the current, and shows a non-linear increase with the increase of the cumulative running time.

[0029] Specifically, based on the principles of materials mechanics, the sagging deformation of the rotary kiln shell is the result of the combined effects of instantaneous thermal expansion and long-term high-temperature creep. Using the effective current value and cumulative operating time obtained in step S1, a thermogravimetric coupling deformation index is constructed to quantitatively characterize the current stiffness decay and sagging degree of the rotary kiln shell. Its calculation formula is as follows: ; In the formula, for The thermogravimetric coupling deformation index at time t, its unit is mm or normalized dimensionless value; From the current moment Push forward The effective value of the heating current at each sampling time; To calculate the length of the time window; The cumulative high-temperature operating time of the rotary kiln is expressed in hours (h). This is the coefficient of thermal expansion, and its unit is mm / A; The creep aging coefficient is expressed in mm. It is the natural logarithm function.

[0030] For example, setting , , Assuming the current time... The effective current value was stable at 500A for the first 100 moments, and the cumulative operating time was 1000 hours.

[0031] The first term in the calculation formula is the thermal expansion term, and its calculation result is: .

[0032] The second term in the calculation formula is the creep term, and its calculation result is as follows: .

[0033] This value is an evaluation indicator; the larger the value, the greater the downward deflection of the suspended section of the rotary kiln cylinder.

[0034] By constructing a thermo-gravity coupled deformation index, the invisible physical deformation of the cylinder can be assessed, and the instantaneous thermal expansion and long-term creep effects are quantitatively superimposed, providing forward-looking state parameters for subsequent control.

[0035] Step S3: Using the thermogravity coupling deformation index as the amplitude modulation parameter, combined with the real-time rotation angle, construct the target sealing pressure feedforward model, calculate the theoretical optimal sealing pressure setting value at the current moment, and the theoretical optimal sealing pressure setting value fluctuates periodically with the rotation angle.

[0036] Specifically, due to the bending of the rotary kiln shell, the sealing flange surface exhibits eccentric vibration. Using the thermogravimetric coupling deformation index calculated in step S2 as the amplitude modulation parameter, and combining it with the real-time rotation angle, a feedforward model for the target sealing pressure is constructed. The calculation formula is as follows: ; In the formula, for The theoretical optimal sealing pressure setting value at any given time, in kPa; The set value for the basic sealing pressure when the equipment is cold and stationary; This is the real-time rotational speed angular frequency of the rotary kiln, and its unit is rad / s; The initial phase angle, in rad, corresponds to the position where the rotary kiln shell is squeezed downwards most severely; The basic gain coefficient; This represents the amplitude coefficient of the wave.

[0037] For example, setting kPa, , , Assume the thermogravimetric coupling deformation index is 0.6 at the current moment.

[0038] When the speed corresponds At that time, the rotary kiln cylinder deflects upward, and the gap increases. At this point, the dynamic term in the formula is... , kPa. It should be noted that the definition of the phase angle assumes that the pressure increases as the gap increases, and the specific sign orientation needs to be adjusted according to the actual calibration. Only the calculation logic is shown here.

[0039] If in At that time, the rotary kiln cylinder is squeezed downwards. The dynamic item is... , kPa.

[0040] The above calculations show that the target pressure fluctuates between 2.3 kPa and 2.9 kPa. In practical applications, when the rotary kiln shell is pressed downwards, the gap decreases, and the actively applied pressure should be reduced, utilizing gravity sealing. When the rotary kiln shell is pressed upwards, the gap increases, requiring an increase in pressure. The phase angle values ​​and signs in the formulas can be calibrated according to the actual physical installation location.

[0041] By generating dynamic pressure commands that vary with the rotation angle, the system achieves synchronous compensation for changes in the sealing gap, preventing leakage and reducing wear.

[0042] Step S4: Based on the deviation between the theoretical optimal sealing pressure setting value and the pressure feedback value of the sealing cavity, and combined with the dynamic adjustment of the controller sensitivity by the thermogravimetric coupling deformation index, calculate the final control quantity output to the actuator, and adaptively adjust the rotary kiln sealing pressure.

[0043] The theoretically optimal sealing pressure setpoint calculated in step S3 is combined with the sealing cavity pressure feedback value from the sensor to calculate the final control quantity output to the actuator. To prevent delayed response under severe deformation, an adaptive gain is introduced, calculated as follows: ; In the formula, This is the control quantity output to the actuator at the current moment; This is the output value of the previous control cycle; The basic proportional gain coefficient; This is the maximum allowable design deformation limit constant for the equipment; This is the pressure feedback value for the sealed cavity.

[0044] For example, the output of the previous cycle , , Assuming the current deformation is severe, The theoretically optimal sealing pressure setting is... kPa, the pressure feedback value of the sealed cavity is kPa.

[0045] Adaptive gain factor for: .

[0046] Pressure deviation for: kPa.

[0047] but .

[0048] In another comparative example, if A gain factor of only 0.2 indicates that the deformation of the rotary kiln cylinder is very small. At this time, the gain factor is only 1.1, and the output adjustment is smaller and the control is smoother for the same deviation.

[0049] If the calculated result of the control quantity is greater than 100%, then take 100%; if it is less than 0%, then take 0%.

[0050] In an optional embodiment, such as Figure 1 As shown, the red solid line represents the sealing pressure curve generated by this invention, which exhibits a sinusoidal wave pattern that closely matches the actual clearance requirement represented by the black dashed line. Compared to the existing constant pressure control represented by the gray solid line, this invention actively reduces the pressure at the troughs (corresponding to the downward extrusion of the rotary kiln cylinder), avoiding the excessive wear risk area shown in the orange area; and actively increases the pressure at the peaks (corresponding to the widening of the clearance), avoiding the gas leakage risk area shown in the cyan area.

[0051] like Figure 2 As shown, with the extension of the production cycle, the equipment of the present invention, represented by the bright green broken line, maintains a consistently low cumulative leakage index in its sealed cavity, and the wear depth of the seals, represented by the dark green bars, increases extremely slowly; while the prior art, represented by the red broken line and gray bars, shows an exponential increase in the risk of seal wear and cumulative leakage in the sealed cavity over time, demonstrating the significant advantages of the present invention in extending equipment life and ensuring sealing performance.

[0052] By introducing a deformation index to adjust the control gain, the system can output a stronger adjustment force when the rotary kiln body is severely deformed, ensuring the response speed under extreme conditions and avoiding pressure instability caused by untimely adjustment.

[0053] This invention also discloses an adaptive control system for the sealing pressure of a lithium iron phosphate rotary kiln, including a processor and a memory. The memory stores computer program instructions, and when the computer program instructions are executed by the processor, the aforementioned adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln is implemented.

[0054] The system also includes other components well known to those skilled in the art, such as communication buses and communication interfaces, the settings and functions of which are known in the art and will not be described in detail here.

[0055] In addition, in the description of this specification, "multiple" means at least two, such as two, three or more, etc., unless otherwise expressly and specifically defined.

Claims

1. An adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln, characterized in that, include: The operating data of the rotary kiln is collected, including the original value of heating current, cumulative operating time, real-time rotation angle and pressure feedback value of the sealed cavity. The original value of heating current is processed by sliding window root mean square to obtain the effective value of current. Based on the effective value of the current and the cumulative running time, a thermogravity coupling deformation index is constructed. The thermogravity coupling deformation index is used to characterize the degree of deformation of the suspended section of the cylinder bending downward. Its value is positively correlated with the heat input power represented by the effective value of the current, and shows a nonlinear increase with the increase of the cumulative running time. Using the thermogravity coupling deformation index as the amplitude modulation parameter and combining it with the real-time rotation angle, a target sealing pressure feedforward model is constructed to calculate the theoretical optimal sealing pressure setting value at the current moment. The theoretical optimal sealing pressure setting value fluctuates periodically with the rotation angle. Based on the deviation between the theoretically optimal sealing pressure setting value and the pressure feedback value of the sealing cavity, and combined with the dynamic adjustment of the controller sensitivity by the thermogravimetric coupling deformation index, the control quantity finally output to the actuator is calculated to adaptively adjust the rotary kiln sealing pressure.

2. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 1, characterized in that, The sliding window root mean square processing of the original value of the heating current includes: setting the number of data points corresponding to the time length of the sliding window to N, and calculating the root mean square value of the data within the sliding window as the effective value of the current, so as to filter out high-frequency noise introduced by power grid fluctuations and thyristor voltage regulation.

3. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 1, characterized in that, The formula for calculating the thermogravimetric coupling deformation index is as follows: ； In the formula, for The thermogravimetric coupling deformation index at any given moment; From the current moment Push forward The effective value of the current at each sampling time; To calculate the length of the time window; The cumulative high-temperature operating time of the rotary kiln; The coefficient of thermal expansion. The creep aging coefficient; It is the natural logarithm function.

4. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 3, characterized in that, The first term in the thermogravity coupling deformation index calculation formula represents the square root of the mean square of the current over a period of time, which is used to assess the current average thermal input power. The second term uses the natural logarithm function to simulate the creep characteristics of metallic materials at high temperatures, characterizing the saturation effect where deformation accumulates over time but the growth rate gradually slows down.

5. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 1, characterized in that, The calculation formula for the target sealing pressure feedforward model is as follows: ； In the formula, for The theoretical optimal sealing pressure setting value at any given time; The set value for the basic sealing pressure when the equipment is cold and stationary; for The thermogravimetric coupling deformation index at any given moment; The basic gain coefficient; This is the amplitude coefficient of the wave. This refers to the real-time rotational speed angular frequency of the rotary kiln. This is the initial phase angle.

6. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 5, characterized in that, The initial phase angle corresponds to the lowest point of the bending geometry of the rotary kiln shell, and is the angle when the rotary kiln shell is pressing the sealing ring downwards most severely; when the cosine value is positive, the actuator applies pressure in advance to seal the enlarged gap; when the cosine value is negative, the actuator releases pressure in advance and uses the weight of the shell to maintain the seal.

7. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 1, characterized in that, The formula for calculating the final control quantity output to the actuator is: ； In the formula, For the current moment The control quantity output to the actuator; This is the output value of the previous control cycle; The basic proportional gain coefficient; for The thermogravimetric coupling deformation index at any given moment; This is the maximum allowable design deformation limit constant for the equipment; for The theoretical optimal sealing pressure setting value at any given time; This is the pressure feedback value for the sealed cavity.

8. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 7, characterized in that, In the formula As an adaptive gain factor, when the thermo-gravity coupling deformation index approaches the maximum design deformation limit constant allowed by the equipment, the adaptive gain factor increases, causing the controller to output a larger adjustment range to correct pressure instability.

9. The adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to claim 7, characterized in that, The adaptive control method for the sealing pressure of a lithium iron phosphate rotary kiln also includes a boundary constraint step: if the calculated... If the value is greater than 100%, then the value is taken as 100%; if the calculated value is... If it is less than 0%, then the value is 0.

10. An adaptive control system for the sealing pressure of a lithium iron phosphate rotary kiln, characterized in that, It includes a processor and a memory, the memory storing computer program instructions that, when executed by the processor, implement the adaptive control method for sealing pressure of a lithium iron phosphate rotary kiln according to any one of claims 1-9.

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