Anti-deposition discharge system for low-temperature liquid in cold box of air separation device and control method

Abstract

This invention relates to the field of air separation equipment technology, and discloses a cryogenic liquid anti-deposition discharge system and control method in the cold box of an air separation unit. The system includes a data acquisition module, a control module, and an execution module. The data acquisition module acquires pressure timing signals and impurity concentration signals from the liquid oxygen container; the execution module includes a discharge pipeline connected to the liquid oxygen container and a series-connected regulating valve; the control module calculates a characteristic index based on the acquired signals, and when a set threshold is met, sequentially sends a first alternating command and a second step command to the regulating valve, controlling the regulating valve to perform alternating changes in opening degree and step-closing actions. The regulating valve action induces fluid static pressure fluctuations and reverse pressure waves in the discharge pipeline, destroying the solid deposit layer structure and causing it to peel off from the pipe wall. Simultaneously, the detachment status is quantitatively determined based on the pressure reflection signal, and the valve is controlled to reset. This achieves in-situ physical removal of deposits without adding mechanical components and maintains a stable liquid level in the main condenser evaporator.

Description

Technical Field

[0001] This invention relates to the field of air separation equipment technology, specifically to a cryogenic liquid anti-deposition discharge system and control method in the cold box of an air separation unit. Background Technology

[0002] During the long-term operation of large-scale air separation units, the liquid oxygen container at the bottom of the main condenser-evaporator is used to collect the cryogenically liquefied liquid oxygen. Since the air feedstock inevitably contains trace amounts of carbon dioxide, nitrous oxide, and other components, these components gradually accumulate in the liquid oxygen. To control the impurity concentration within safe limits, the conventional technical solution is to install a discharge pipeline and control valve at the bottom of the main condenser-evaporator, using continuous or intermittent drainage to discharge a portion of the liquid oxygen from the cold box, thereby maintaining the purity of the liquid oxygen system.

[0003] Although conventional drainage operations can remove free impurities, some impurities will still crystallize due to changes in solubility under cryogenic conditions, adhering to the bottom of the liquid oxygen container and the inner walls of the pipes, gradually forming a solid deposit layer with high structural strength. Existing constant-opening drainage methods can only create a smooth fluid flow within the pipes; the shear force generated is insufficient to break up the already formed dense deposits, leading to continuous accumulation of the deposit layer and reduction of the flow channel cross-sectional area. Adding dedicated mechanical scraping or cleaning components inside the cold box would not only compromise the thermal insulation of the cryogenic equipment but also significantly increase the structural complexity and maintenance costs of the bottom of the main condenser-evaporator.

[0004] Existing drainage control logic typically relies solely on unidirectional triggering based on impurity concentration values, failing to accurately perceive the actual adhesion state of solid deposits and lacking quantitative assessment methods for the deposit stripping process. When faced with obstructed pipeline flow, this control method often resorts to extending drainage time or blindly increasing drainage flow rate to attempt unblocking. Prolonged, variable-condition drainage disrupts the liquid level balance of the main condenser-evaporator, directly interfering with the stable operation of the distillation system. Simultaneously, a significant increase in valve opening without controlled boundaries can lead to a sudden drop in local static pressure, easily exceeding the fluid's saturated vapor pressure limit and triggering large-scale phase change and vaporization of liquid oxygen. Therefore, this invention provides a cryogenic liquid anti-deposition drainage system and control method for the cold box of an air separation unit to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-temperature liquid anti-deposition discharge system and control method for the cold box of an air separation unit. This solves the problem that liquid oxygen at the bottom of the main condenser evaporator in the cold box of an existing air separation unit is prone to solid impurity deposition during operation. Conventional constant-opening discharge methods are insufficient to remove deposits already attached to the equipment surface, leading to local enrichment of impurities and obstruction of pipeline flow.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a cryogenic liquid anti-deposition discharge system for a cold box in an air separation unit, applied to a main condenser / evaporator with a liquid oxygen container at the bottom. The system includes a data acquisition module, a control module, and an execution module. The data acquisition module includes a pressure transmitter and a liquid oxygen analyzer; the pressure transmitter acquires a pressure timing signal from the liquid oxygen container, and the liquid oxygen analyzer acquires an impurity concentration signal. The execution module includes a discharge pipeline connected to the liquid oxygen container, with a regulating valve, a buffer chamber, and a flow-limiting orifice plate connected in series on the discharge pipeline. The control module calculates the deposition resistance based on the pressure timing signal and the impurity concentration signal. The hysteresis index and the concentration-time derivative are used to send a first alternating command and a second step command to the regulating valve when both the deposition hysteresis index and the concentration-time derivative are greater than a set threshold. The regulating valve receives the first alternating command and alternately increases and decreases its opening at a set frequency and a set amplitude. The regulating valve receives the second step command and closes its opening to a set base opening and maintains it for a set duration. The control module determines the deposition state based on the pressure timing signal collected by the pressure transmitter within the set duration, and controls the regulating valve to return to the initial opening before receiving the first alternating command when the deposition state meets the stop condition.

[0007] In the above technical solution, the control module outputs a first alternating command to cause the flow cross-sectional area of ​​the regulating valve to change alternately, inducing hydrostatic pressure fluctuations in the discharge pipeline. This pressure wave acts on the surface of the solid deposit layer, inducing local phase change and shear force, thus damaging its structural strength. Subsequently, a second step command closes the regulating valve, generating a counter-propagating pressure wave in the pipeline. The pressure wave enters the pores inside the deposit and generates stress release, causing the deposit to detach from the pipe wall. The system simultaneously acquires the reflection signal of the pressure wave to quantify the adhesion state of the deposit, and stops the valve operation after detachment is completed, reducing the interference of unsteady discharge on the liquid level of the main condenser-evaporator.

[0008] Furthermore, the pressure transmitter is connected to the liquid oxygen container via a pressure-sensing line filled with liquid. The control module stores an acoustic transfer function model, which is then used to perform amplitude compensation and phase delay compensation on the pressure timing signal. The liquid-filled pressure-sensing line eliminates pressure attenuation caused by the gas-liquid interface, and the acoustic transfer function model is used to correct amplitude distortion caused by high-frequency signals propagating in a slender pipe, restoring the pressure timing signal waveform at the bottom.

[0009] Furthermore, the execution module also includes a constriction section pipeline, which is connected in series with the discharge pipeline between the liquid oxygen container and the regulating valve. The flow cross-sectional area of ​​the constriction section pipeline is smaller than the basic flow cross-sectional area of ​​the discharge pipeline. When the fluid flows through the constriction section pipeline, the local flow velocity increases and the static pressure decreases, which, in conjunction with the change in the opening of the regulating valve, increases the fluid excitation force acting on the deposition layer.

[0010] Furthermore, the control module internally stores impurity saturation solubility values ​​and crystal yield strength values. The control module subtracts the impurity concentration signal from the impurity saturation solubility value to obtain a supersaturation difference. The control module multiplies the supersaturation difference by the crystal yield strength value to obtain a priority weight value. The impurity with the highest priority weight value is marked as the dominant impurity component. By converting solubility and structural yield strength into a single evaluation index, the type of impurity with high precipitation volume and high structural strength is identified and used as the basis for subsequent calculations of pressure fluctuation amplitude.

[0011] Furthermore, the step of the control module calculating the pressure setpoint corresponding to the first alternating command includes: extracting the crystal yield strength value, safety factor, and pressure conversion coefficient corresponding to the dominant impurity component; obtaining the liquid oxygen temperature parameter and mapping it to obtain the saturated vapor pressure value; and subtracting the product of the crystal yield strength value, safety factor, and pressure conversion coefficient from the saturated vapor pressure value to obtain the pressure setpoint. This ensures that the set pressure drop meets the mechanical conditions for destroying the crystal structure of the dominant impurity while limiting the lower limit of static pressure to prevent large-scale vaporization of liquid oxygen.

[0012] Furthermore, the first alternating command includes setting an amplitude ratio, setting an oscillation frequency, and setting a duration. The amplitude ratio is configured to be 2% to 5% of the initial opening of the regulating valve before receiving the first alternating command, the oscillation frequency is configured to be 5 Hz to 15 Hz, and the duration is configured to be 3 to 8 seconds. This limits the operating frequency to avoid the mechanical resonance zone of the pipeline, and accumulates stress cycles through the set duration to reach the crystal fatigue failure boundary.

[0013] Furthermore, the second step command includes the target base opening degree, the opening degree change rate, and the pulse duration value. The pulse duration value is configured as twice the length of the discharge pipeline divided by the quotient obtained by the speed of sound of the pressure wave propagating within the discharge pipeline. This provides a time window for the pressure wave to complete its round-trip propagation within the pipeline, avoiding the acquisition of crosstalk reflection signals from subsequent valve actions.

[0014] Furthermore, the control module uses a Fast Fourier Transform algorithm to convert the pressure time-series signal into a frequency domain power spectrum value. The control module extracts the integral value within a set frequency band from the frequency domain power spectrum value and calculates the moving average of the integral value. When the moving average value is less than a set reference threshold for a consecutive set number of times, the control module determines that the deposition state meets the stopping condition. The attenuation of the reflected energy of the pressure wave at the deposition layer interface is calculated through frequency domain integration. Based on the law that the reflected energy decreases as the attachment area decreases, the detachment status of the sediment is determined.

[0015] Furthermore, the flow-limiting orifice plate is fixed to the side of the buffer chamber away from the regulating valve, and the end of the discharge pipeline away from the liquid oxygen container is connected to a discharge unit. The discharge unit includes a vaporization buffer container, an oxygen enrichment detector, and a venting pipeline. The buffer chamber and the flow-limiting orifice plate are connected in series to attenuate the downstream pressure shock generated by the operation of the regulating valve, and the discharge unit is used to vaporize the liquid oxygen mixed with impurities and perform centralized venting.

[0016] A second aspect of the present invention provides a method for preventing the deposition of cryogenic liquid in the cold box of an air separation unit, applied to the aforementioned system for preventing the deposition of cryogenic liquid in the cold box of an air separation unit, comprising the following steps: Extract the reference power spectral density value of the pressure time-series signal under the set reference state; Acquire real-time pressure timing signals and impurity concentration signals of the operating status; The real-time power spectral density value of the pressure time-series signal is calculated, and the deposition retardation index is obtained by subtracting the real-time power spectral density value from the reference power spectral density value. The concentration-time derivative is obtained by calculating the time derivative of the impurity concentration signal; When the deposition retardation index is greater than the first threshold and the concentration-time derivative is greater than the second threshold, the first alternating command is output to the regulating valve to control the regulating valve to alternately increase and decrease the opening at a set frequency and a set amplitude. After the first alternating command is output for a set duration, a second step command is output to the regulating valve to control the regulating valve to reduce its opening to the set base opening and maintain it for a set duration. Extract the pressure time-series signal collected within a set time period and convert it into a frequency domain power spectrum value; The power spectrum value in the frequency domain is integrated over a set frequency band to obtain an integral value. When the integral value is less than a set reference threshold, a recovery command is output to control the regulating valve to return to its initial opening degree before receiving the first alternating command.

[0017] This invention provides a cryogenic liquid anti-deposition discharge system and control method in the cold box of an air separation unit. It has the following beneficial effects: 1. This invention sends a first alternating command and a second step command sequentially to the regulating valve via a control module, causing the valve to perform alternating opening changes and step-closing actions, thereby generating local static pressure fluctuations and counter-propagating pressure waves within the discharge pipeline. These hydrostatic pressure fluctuations and pressure waves directly act on the surface and internal pores of the solid deposit layer, damaging the structural strength of the deposit and causing it to peel off from the equipment pipe wall. This method utilizes the hydrodynamic effect generated by the throttling component to achieve in-situ physical removal of the deposit, eliminating the need for additional mechanical cleaning components inside the cold box and controlling the structural complexity of the bottom of the main condenser-evaporator.

[0018] 2. This invention calculates the deposition retardation index and concentration-time derivative using pressure timing signals and impurity concentration signals acquired by the data acquisition module. This serves as the trigger for the anti-deposition discharge procedure. During the output of the second step command, the system determines the deposition detachment status based on the energy reflection attenuation of the pressure wave in the frequency domain. When the stop condition is met, the system automatically controls the regulating valve to return to its initial opening. This closed-loop control logic provides quantified cleaning start and stop points, reducing blind drainage processes and avoiding interference with the liquid level stability of the main condenser evaporator caused by excessively long-term variable-condition drainage.

[0019] 3. This invention combines the supersaturation difference of impurities with the yield strength of the crystal through a control module to calculate the priority weight and lock in the dominant impurity component. Then, based on the structural and mechanical properties of this dominant impurity and the saturated vapor pressure at the current temperature, it back-calculates the pressure setpoint for the first alternating command. This calculation step sets an accurate execution boundary for the valve's alternating action, ensuring that the pressure drop induced in the pipeline meets the mechanical conditions for destroying dense impurity crystals, while simultaneously limiting the lower limit of static pressure to prevent large-scale phase change and vaporization of liquid oxygen due to excessive local pressure reduction. Attached Figure Description

[0020] Figure 1 This is a system framework diagram of the present invention; Figure 2 This is a flowchart of the method of the present invention; Figure 3 This is a flowchart of the present invention for extracting the reference power spectral density of the pressure signal under pure nucleate boiling state and calibrating the safety boundary parameters of the mechanical structure; Figure 4 This is a flowchart of the present invention for cyclically calculating the deposition retardation index of the pressure signal during operation, simultaneously extracting the time derivative of the macroscopic concentration of impurities, and determining the triggering conditions; Figure 5 This is a flowchart of the present invention, which outputs a critical cavitation-targeted pressure reduction command to the regulating valve and induces local cavitation cavitation fatigue pore formation. Figure 6 The flowchart of the present invention is as follows: issuing step pulse command, inducing reverse compression wave and realizing acoustic impedance mismatch pyrolysis and stripping. Figure 7 This is a flowchart of the present invention for evaluating the sediment stripping state and performing system reversion through acoustic feedback; Figure 8 This is a time-frequency energy distribution diagram of the reflected pressure signal collected during the experiment of this invention; Figure 9 This is an endoscopic image of the inlet section of the discharge pipeline and an identification map of the residual deposition area after the test of this invention.

[0021] Among them, 10 is the main condenser / evaporator; 11 is the liquid oxygen container; 100 is the data acquisition module; 110 is the pressure transmitter; 111 is the pressure tapping line; 120 is the liquid oxygen analyzer; 130 is the pressure sensor before the valve; 140 is the pressure sensor after the valve; 150 is the pressure sensor in the buffer chamber; 160 is the discharge flow meter; 170 is the temperature sensor of the main condenser / evaporator; 180 is the liquid oxygen level gauge; 200 is the control module; 300 is the execution module; 310 is the discharge line; 320 is the regulating valve; 330 is the buffer chamber; 340 is the flow limiting orifice plate; 350 is the cavitation-induced flow contraction section; 360 is the bypass venting branch; and 370 is the cryogenic liquid safety discharge unit. Detailed Implementation

[0022] The technical solutions in 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.

[0023] See attached document Figure 1 This invention provides a cryogenic liquid anti-deposition and discharge system for the cold box of an air separation unit, comprising a data acquisition module 100, a control module 200, and an execution module 300. The system operates based on the main condenser-evaporator 10 of the air separation unit, and a liquid oxygen container 11 for containing the internal cryogenic fluid is provided at the bottom of the main condenser-evaporator 10.

[0024] The data acquisition module 100 includes a pressure transmitter 110, a liquid oxygen analyzer 120, a pre-valve pressure sensor 130, a post-valve pressure sensor 140, a buffer chamber pressure sensor 150, a discharge flow meter 160, a main condenser evaporator temperature sensor 170, and a liquid oxygen level gauge 180.

[0025] The pressure transmitter 110 is installed outside the cold box of the air separation unit and is connected to the standard pressure tap at the bottom of the liquid oxygen container 11 via the pressure tapping line 111. It is used to acquire high-frequency pressure timing signals of the fluid at the bottom of the liquid oxygen container 11. The pressure transmitter 110 is a dynamic pressure transmitter with a response bandwidth of not less than 1kHz and a sampling frequency of not less than 2kHz. The pressure tapping line 111 adopts a full liquid filling structure and is equipped with cold insulation and anti-airlock measures. The length of the pressure tapping line 111 ranges from 0.5m to 5m, and the inner diameter ranges from 3mm to 10mm; its length and inner diameter are determined based on the transmission line acoustic response model to ensure that the original transmission amplitude attenuation in the 100Hz to 500Hz frequency band is not greater than 6dB. The control module 200 incorporates the acoustic transfer function of the pressure tapping line 111 to perform amplitude attenuation compensation and phase delay compensation on the high-frequency pressure timing signal to correct the frequency domain attenuation and phase shift of the signal during transmission inside and outside the cold box.

[0026] The upstream pressure sensor 130 and downstream pressure sensor 140 are used to collect pressure signals on both sides of the critical cavitation control object. When the regulating valve 320 is located near the bottom drain port of the main condenser-evaporator 10 and serves as the main cavitation generation location, the upstream pressure sensor 130 is installed on the inlet side of the regulating valve 320, and the downstream pressure sensor 140 is installed on the outlet side of the regulating valve 320. The control module 200 uses the local static pressure at the constriction section of the regulating valve 320 as the main control object. When the regulating valve 320 is located outside the cold box boundary, the control module 200 uses the local static pressure on the side of the cavitation-induced constriction section 350 near the deposition zone as the main control object. The upstream pressure sensor 130 and downstream pressure sensor 140 are respectively located on the inlet and outlet sides of the cavitation-induced constriction section 350, or the pressure on both sides of the cavitation-induced constriction section 350 is collected through independent pressure measuring points. The regulating valve 320 is used to regulate the pressure difference and discharge flow rate on both sides of the cavitation-induced constriction section 350.

[0027] A buffer chamber pressure sensor 150 is installed in the buffer chamber 330, and a discharge flow meter 160 is installed downstream of the flow-limiting orifice plate 340. These sensors provide feedback to the control module 200 on the pressure difference across the critical cavitation control object, the buffer chamber pressure, and the discharge flow rate. A main condenser-evaporator temperature sensor 170 is installed on the side of the main condenser-evaporator 10 or in the vicinity of the liquid oxygen container 11 to obtain the liquid oxygen temperature. A liquid oxygen level gauge 180 is connected to the liquid oxygen container 11 and provides feedback on the liquid oxygen level to the control module 200. The control module 200 can also read the main condenser-evaporator 10 pressure, heat exchange load, air separation unit load rate, and conventional liquid level control output values ​​from the air separation unit's distributed control system.

[0028] The pressure sensor 130 before the valve, the pressure sensor 140 after the valve, and the pressure sensor 150 in the buffer chamber all use pressure sensing elements suitable for low-temperature oxygen conditions. When the pressure sensing elements are arranged outside the cold box, they are connected to the corresponding measuring points through independent pressure tapping branches, and the independent pressure tapping branches are treated with cold insulation, anti-airlock, and transfer function compensation.

[0029] The liquid oxygen analyzer 120 is connected to the internal liquid phase space of the liquid oxygen container 11 through an independent sampling pipeline to obtain data on the impurity content in the liquid oxygen fluid and continuously output the corresponding macroscopic concentration signal.

[0030] The control module 200 establishes communication connections with the pressure transmitter 110, liquid oxygen analyzer 120, inlet valve pressure sensor 130, outlet valve pressure sensor 140, buffer chamber pressure sensor 150, discharge flow meter 160, main condenser-evaporator temperature sensor 170, and liquid oxygen level gauge 180. The control module 200 integrates a spectrum analysis unit and storage medium for synchronously receiving and processing high-frequency pressure timing signals and macroscopic concentration signals. The control module 200 also receives the pressure of the main condenser-evaporator 10, heat exchange load, and air separation unit load rate output from the distributed control system of the air separation unit, for sedimentation resistance index normalization, safety window determination, and routine level control resetting.

[0031] The control module 200 estimates the local static pressure at the constriction section of the control valve 320 in real time based on the inlet pressure, outlet pressure, buffer chamber pressure, discharge flow rate, control valve opening feedback, and the inherent flow characteristic curve of the control valve 320. This local static pressure is then used as a feedback variable for critical cavitation-targeted pressure reduction control. When the cavitation-induced constriction section 350 is the primary cavitation location near the deposition zone, the control module 200 estimates the local static pressure at the outlet side or pressure recovery zone of the cavitation-induced constriction section 350 in real time based on the pressure on both sides of the cavitation-induced constriction section 350, the discharge flow rate, the flow area of ​​the constriction section, and the liquid oxygen density. This local static pressure is then used as a feedback variable for critical cavitation-targeted pressure reduction control.

[0032] The storage medium of the control module 200 embeds a correlation model between the crystal yield strength and critical cavitation threshold of solid hydrocarbons and nitrous oxide under cryogenic air separation conditions. Based on the macroscopic concentration signal, the control module 200 identifies the dominant impurity component that preferentially precipitates in liquid oxygen and generates a critical cavitation-targeted depressurization command based on the correlation model. The control module 200 also sends an opening adjustment command containing conversion rate constraint parameters to the execution module 300 based on a built-in algorithm model.

[0033] Before sending the critical cavitation targeted pressure reduction command and the opening adjustment command, the control module 200 determines whether the liquid oxygen container 11 level, the main condenser evaporator 10 pressure, the discharge pipeline 310 pressure, the buffer chamber 330 pressure, the opening feedback of the regulating valve 320, the pressure difference across the regulating valve 320 or the pressure difference across the cavitation-induced constriction section 350, the discharge flow rate, and the impurity concentration are within a preset safety window. If any parameter exceeds the preset safety window, the control module 200 prohibits the initiation of the anti-deposition pulse emission program and outputs an alarm signal or switches to the normal safe emission mode.

[0034] The cryogenic thermodynamic database within the storage medium includes at least the saturation solubility curves, supersaturation thresholds, crystal yield strengths, fatigue limits, and corresponding cavitation impact pressure conversion coefficients for carbon dioxide, nitrous oxide, methane, ethane, acetylene, and other hydrocarbons within the liquid oxygen temperature range. The control module 200 calculates the supersaturation based on the difference between the current macroscopic concentration of the impurity and its saturation solubility, and determines the dominant dense-crystalline impurity component by combining the concentration-time derivative. When multiple impurities simultaneously meet the precipitation conditions, the control module 200 calculates a comprehensive priority based on the supersaturation and crystal yield strength, and selects the impurity with the highest comprehensive priority as the priority control target. The comprehensive priority increases with increasing supersaturation and decreases with decreasing crystal yield strength. The control module 200 determines the dominant dense-crystalline impurity component according to the same comprehensive priority rule, avoiding using the maximum supersaturation value or the minimum crystal yield strength as the sole criterion.

[0035] The inlet of the execution module 300 is connected to the drain port at the bottom of the main condenser-evaporator 10, and the execution module 300 extends to the outside of the boundary of the air separation cold box. The execution module 300 includes a discharge pipe 310, on which a regulating valve 320, a buffer chamber 330, and a flow-limiting orifice plate 340 are sequentially connected in series along the fluid flow direction. When the regulating valve 320 cannot be arranged near the deposition zone, a cavitation-induced constriction section 350 is provided in the discharge pipe 310 between the drain port at the bottom of the main condenser-evaporator 10 and the regulating valve 320.

[0036] The execution module 300 also includes a bypass vent branch 360 and a cryogenic liquid safety discharge unit 370. The bypass vent branch 360 is connected downstream of the buffer chamber 330 or the flow-limiting orifice plate 340, and the cryogenic liquid safety discharge unit 370 is connected to the end of the discharge pipe 310. The regulating valve 320 can be arranged inside the cold box near the bottom drain port of the main condenser evaporator 10, or it can be arranged outside the cold box boundary and act on the deposition area near the drain port through the cavitation-induced constriction section 350. The buffer chamber 330 and the flow-limiting orifice plate 340 are arranged inside or outside the cold box in the cryogenic discharge section, depending on the cold box structure.

[0037] The regulating valve 320 is equipped with a high-speed electric positioner or a high-speed servo actuator suitable for low-temperature oxygen conditions. The regulating valve 320 establishes a control signal connection with the control module 200. The regulating valve 320 receives opening adjustment commands and critical cavitation targeted pressure reduction commands, and changes the valve body flow cross-sectional area according to the action rate set by the commands.

[0038] The regulating valve 320 is preferably positioned near the bottom drain port of the main condenser-evaporator 10, so that the alternating low-pressure zone formed by the constriction section of the regulating valve 320 covers the easily deposited areas of the bottom drain port of the main condenser-evaporator 10 and the inlet section of the discharge pipe 310. When the regulating valve 320 cannot be located near the deposition area due to space constraints in the cold box, maintenance requirements, or low-temperature arrangement conditions, a cavitation-induced constriction section 350 is installed between the bottom drain port of the main condenser-evaporator 10 and the regulating valve 320, thereby forming an alternating low-pressure zone near the deposition area.

[0039] The regulating valve 320 uses oxygen-compatible materials and an anti-static structure. Its valve opening feedback resolution is no less than 0.5%, and its closed-loop response frequency is more than three times higher than the target oscillation frequency, enabling it to track micro-amplitude opening oscillations within the range of 5Hz to 15Hz. The control module 200 determines whether the valve has completed the command action based on the opening feedback from the regulating valve 320. When the opening response deviation continuously exceeds a preset threshold, the control module 200 immediately terminates the high-frequency oscillation and step pulse action.

[0040] The inlet of the buffer chamber 330 is connected to the outlet of the regulating valve 320. The buffer chamber 330 forms a partially enlarged space, with an internal cross-sectional area larger than the basic cross-sectional area of ​​the discharge pipe 310. After the liquid oxygen fluid discharged through the regulating valve 320 enters the buffer chamber 330, it undergoes isenthalpic throttling pressure reduction and partial flash evaporation phase change phenomena.

[0041] The flow area of ​​the cavitation-induced constriction section 350 is smaller than the basic cross-sectional area of ​​the discharge pipe 310, and it forms a linkage throttling relationship with the opening change of the regulating valve 320. When the regulating valve 320 performs micro-amplitude high-frequency oscillation, a periodic static pressure drop occurs on the side of the cavitation-induced constriction section 350 adjacent to the deposition zone, causing micro-cavitation bubbles to form and collapse on the surface of the deposition zone. When the cavitation-induced constriction section 350 is the main cavitation occurrence location, the pressure sensor 130 before the valve and the pressure sensor 140 after the valve are respectively arranged on the inlet and outlet sides of the cavitation-induced constriction section 350, or independent pressure measuring points are added on both sides of the cavitation-induced constriction section 350. The control module 200 estimates the local static pressure at the location adjacent to the deposition zone based on the pressure on both sides of the cavitation-induced constriction section 350, the discharge flow rate, and the geometric parameters of the constriction section, and uses this local static pressure as a feedback variable for critical cavitation targeted pressure reduction control.

[0042] The flow-limiting orifice plate 340 is fixed to the drain outlet side of the buffer chamber 330. The flow-limiting orifice plate 340 applies physical damping constraint to the fluid discharge inside the buffer chamber 330 and forms back pressure. Its equivalent flow orifice diameter is determined based on the liquid oxygen phase change expansion parameter. The flow-limiting orifice plate 340 and the regulating valve 320 together define the physical boundary where the fluid state inside the buffer chamber 330 undergoes a transient change.

[0043] The control module 200 adjusts the actuation amplitude of the regulating valve 320 according to the detection value of the buffer chamber pressure sensor 150, so that the pressure in the buffer chamber 330 is maintained within the preset back pressure window. The lower limit of the preset back pressure window is used to prevent uncontrolled flash evaporation of the entire discharge pipeline 310, and the upper limit of the preset back pressure window is used to ensure that the local static pressure at the constriction section of the regulating valve 320 or on the side of the cavitation-induced constriction section 350 near the deposition zone can be reduced to near the critical cavitation target pressure.

[0044] See attached document Figure 2 This invention provides a method for preventing the deposition and discharge of cryogenic liquid in the cold box of an air separation unit, comprising the following steps: S10, extract the reference power spectral density of the pressure signal under pure nucleate boiling state and calibrate the safety boundary parameters of the mechanical structure; S20, calculates the deposition retardation index of the pressure signal during operation and extracts the time derivative of the macroscopic concentration of impurities simultaneously, identifies the dense crystalline impurity components that currently dominate in liquid oxygen, and starts the anti-deposition pulse emission program when the triggering conditions are met; S30 outputs a critical cavitation targeted pressure reduction command to the regulating valve. By utilizing the micro-amplitude high-frequency oscillation of the regulating valve's flow cross-sectional area, the local static pressure of the regulating valve 320 flow contraction section, the cavitation-induced flow contraction section 350, or the flow contraction area adjacent to the deposition zone is instantaneously pulled down to the critical cavitation pressure boundary of liquid oxygen. The steep drop in static pressure induces local flash evaporation of liquid oxygen and the generation of micro-cavitation bubbles on the surface of the solid deposition layer. When the static pressure rises in the downstream pressure recovery zone, the cavitation bubbles collapse. The micro-jet cavitation effect causes material fatigue on the surface of the dense solid deposition layer, inducing micro-pores and mechanical structural defects. S40, after the critical cavitation targeted depressurization command is executed, immediately outputs a step pulse command with limited action rate to the regulating valve and maintains the critical basic opening at the valley value. It uses the acoustic channel maintained in the pipeline to generate a reverse compression wave. When the reverse compression wave travels to the deposition zone, it causes an acoustic impedance mismatch with the micropores generated by cavitation inside the solid deposition layer. At the pore interface, it generates local stress amplification and cracking and peeling effects, and performs physical peeling. S50, calculate the energy attenuation integral of the reflection spectrum of the reverse compression wave, continuously determine the crystallization deposition stripping state based on the moving average value of the energy attenuation integral of the reflection spectrum, and terminate the pulse emission program and smoothly return to normal liquid level control after the determination condition is met.

[0045] The following section will provide a detailed explanation of the specific implementation logic of each step in the above technical solution of this invention, combining relevant algorithmic formulas and physical mechanism models.

[0046] See attached document Figure 3 This invention provides a process for extracting the reference power spectral density of pressure signals under pure nucleate boiling conditions and calibrating the safety boundary parameters of mechanical structures. The process includes the following sub-steps.

[0047] S11, Determine the time window for extracting baseline data.

[0048] The control module 200 determines the real-time operating condition of the main condenser-evaporator 10 based on the operating status parameters of the air separation unit. After the air separation unit completes the bare cooling of the cold box, the initial liquid accumulation reaches the design liquid level, and enters stable load operation, the liquid oxygen fluid in the liquid oxygen container 11 is in the stable pool boiling heat transfer stage. At this time, bubbles continuously form and detach from the bottom heat transfer surface of the liquid oxygen container 11, and the flow field pressure disturbance mainly comes from the nucleation boiling process. Initial precipitation and deposition of solid hydrocarbons and nitrous oxide have not yet occurred inside the liquid oxygen.

[0049] Based on the above operating conditions, the control module 200 defines a preset time period after the equipment completes initial liquid accumulation and stabilizes under load as the benchmark acquisition window for the pure nucleate boiling state. This preset time period is between 24 and 72 hours. Within this time window, the control module 200 acquires high-frequency pressure timing signals and uses the acquired data as an effective data source for subsequently establishing the benchmark power spectral density.

[0050] S12 performs preprocessing on the high-frequency pressure timing signal.

[0051] Within the reference acquisition window, the pressure transmitter 110 continuously acquires the high-frequency pressure timing signal of the fluid at the bottom of the liquid oxygen container 11 through the pressure tapping line 111, and transmits the acquired signal to the control module 200.

[0052] The control module 200 sequentially filters and zero-means-normalizes the high-frequency pressure timing signal. During filtering, the control module 200 employs a bandpass filter to remove low-frequency drift and high-frequency environmental white noise, and a notch filter to remove 50Hz power frequency and its harmonic interference. The low-frequency cutoff frequency of the bandpass filter is lower than the lower limit frequency of the low-frequency broadband boiling region, and the high-frequency cutoff frequency is determined based on the upper limit of the inherent response frequency of the pressure transmitter 110. Removing power frequency interference through notch filtering avoids weakening the low-frequency broadband pressure pulsation characteristics corresponding to the detachment of liquid oxygen nucleus boiling bubbles by simply increasing the low-frequency cutoff frequency.

[0053] After filtering, the control module 200 calculates the average value of the filtered pressure signal and subtracts this average value from the filtered pressure signal to obtain a standard pressure pulsation sequence. This process converts the high-frequency pressure time-series signal containing a static pressure background into sequence data reflecting the amplitude of dynamic pressure pulsations, thereby reducing the impact of sensor static zero-point drift on the spectrum calculation results.

[0054] S13, calculate and divide the reference power spectral density of the pressure signal.

[0055] The spectrum analysis unit inside control module 200 performs a Fast Fourier Transform on the standard pressure pulsation sequence. To reduce the impact of random disturbances on the spectrum estimation results, the spectrum analysis unit uses a periodogram mean algorithm based on overlapping segments to calculate the reference power spectral density under pure nucleate boiling conditions. The discrete mathematical calculation model for the reference power spectral density is as follows: ; In the formula, Represents discrete frequency index The reference power spectral density at that location, The values ​​are 0, 1, ..., N−1; Indicates the length of each data segment; This represents the energy normalization constant of the window function; Indicates the total number of overlapping segments; Indicates the first Standard pressure pulsation sequence values ​​within each segment; This represents the time-domain window function applied to data segmentation. In practice, the Hanning window or Hamming window is used to reduce spectral leakage. This indicates the number of calculation points for the Fast Fourier Transform. It represents the imaginary unit.

[0056] The spectrum analysis unit divides the calculated reference power spectral density into frequency bands based on the hydrodynamic characteristics of the liquid oxygen pool boiling process. The frequency range reflecting bubble formation and detachment characteristics is divided into the low-frequency broadband boiling region, and the frequency range reflecting microscale flow field disturbances is divided into the high-frequency band region. The upper limit of the low-frequency broadband boiling region is determined based on the average detachment frequency of boiling bubbles; frequency ranges below this upper limit are included in the low-frequency broadband boiling region.

[0057] The control module 200 stores the reference power spectral density and the corresponding frequency band division results in the storage medium as a reference for subsequent sedimentation state identification during operation.

[0058] S14, combined with the natural frequency, calibrate the safety boundary parameters of the mechanical structure.

[0059] The control module 200 obtains the natural frequencies of the mechanical structure of the main condenser-evaporator 10 and its connected discharge pipe 310 based on the equipment design specifications. The control module 200 then calibrates the safety boundary parameters of the mechanical structure by combining the reference power spectral density, the natural frequencies of the mechanical structure, and the low-temperature fatigue yield limit parameters of the pipe material.

[0060] Specifically, the control module 200 performs frequency domain integration on the reference power spectral density to obtain the basic broadband energy value of the background flow field. Then, combined with the fatigue yield limit of the pipe material under low-temperature conditions, it assesses the remaining allowable stress margin of the pipe material under basic broadband pressure pulsation, and calculates the maximum permissible dynamic pressure pulsation amplitude accordingly. This maximum dynamic pressure pulsation amplitude is used to limit the fluid excitation energy induced in subsequent anti-deposition control actions, preventing the pipeline and equipment from being subjected to dynamic loads exceeding the permissible range.

[0061] The mechanical structure safety boundary parameters output by the control module 200 include the maximum permissible dynamic pressure pulsation amplitude and the resonant frequency range where operation is prohibited. The resonant frequency range is formed by extending a preset tolerance bandwidth to both sides of the natural mechanical structure frequency of the main condenser-evaporator 10 and the discharge pipeline 310. This tolerance bandwidth is set at ±5% to ±10% of the natural mechanical structure frequency, ensuring that the regulating valve 320 avoids the structural resonant frequency band during subsequent high-frequency oscillation operations, thus guaranteeing that the equipment operates within the acoustically safe operating range.

[0062] See attached document Figure 4 This invention provides a process for cyclically calculating the deposition retardation index of the pressure signal during operation, simultaneously extracting the time derivative of the macroscopic concentration of impurities, and determining triggering conditions. This process is used to identify the currently dominant dense crystalline impurity component in liquid oxygen and initiate an anti-deposition pulse emission procedure when the triggering conditions are met, including the following sub-steps.

[0063] S21, calculate the deposition retardation index of the pressure signal during operation.

[0064] During normal operation of the air separation unit, the pressure transmitter 110 continuously acquires the high-frequency pressure timing signal of the fluid at the bottom of the liquid oxygen container 11 and transmits the signal to the control module 200. The spectrum analysis unit inside the control module 200 performs the same filtering, zero-mean, and fast Fourier transform processing on the high-frequency pressure timing signal during operation as in the reference data extraction stage to obtain the real-time power spectral density.

[0065] As solid impurities gradually precipitate at the bottom of the main condenser-evaporator 10 and on the inner wall of the discharge pipe 310, the surface roughness and thermal resistance of the flow channel change, consequently altering the nucleation sites and detachment states of liquid oxygen bubbles. This change weakens the fluid pressure pulsation energy within the low-frequency broadband boiling region and causes a shift in the bubble detachment frequency. Based on this physical characteristic, the control module 200 extracts the real-time power spectral density integral value within the low-frequency broadband boiling region and calculates the deviation between this value and the reference power spectral density integral value to obtain the deposition resistance index.

[0066] To reduce the impact of load fluctuations on the judgment results, before calculating the deposition retardation index, the control module 200 normalizes the real-time power spectral density based on the heat exchange load of the main condenser-evaporator 10, the liquid oxygen level, the liquid oxygen temperature, the pressure of the liquid oxygen container 11, and the load rate of the air separation unit. When the fluctuation of the heat exchange load, liquid level, or pressure exceeds the preset stability threshold, the control module 200 suspends the deposition retardation index determination to avoid false triggering caused by operating condition disturbances.

[0067] The mathematical model for calculating the depositional retardation index is as follows: ; In the formula, Represents the dimensionless depositional retardation index; and These represent the lower and upper discrete frequency indices of the low-frequency broadband boiling region, respectively. Represents discrete frequency index The reference power spectral density at that location; Represents discrete frequency index The real-time power spectral density at the location. Because the main condenser-evaporator maintains boiling heat transfer during the operation of the air separation system, the integral of the reference power spectral density in the denominator is not zero, thus avoiding the logical dead zone of division by zero in the calculation model.

[0068] S22, extract the time derivative of the macroscopic concentration of impurities.

[0069] The liquid oxygen analyzer 120 simultaneously detects the concentration of trace impurities in the liquid oxygen fluid and outputs a macroscopic concentration signal containing the content of carbon dioxide, nitrous oxide, and various hydrocarbons to the control module 200. The control module 200 discretizes the macroscopic concentration signal sequence to obtain the concentration-time derivative, which is used to characterize the change in the accumulation rate of various impurities in liquid oxygen.

[0070] To suppress the impact of sampling noise on the derivative calculation results, the control module 200 first performs a moving average filter on the macroscopic concentration signal, and then uses a backward difference algorithm to calculate the concentration time derivative. The mathematical calculation model is as follows: ; In the formula, Indicates time The concentration-time derivative; Indicates time Macroscopic concentration of impurities after moving average filtering; Indicates time Macroscopic concentration of impurities after moving average filtering; The discrete sampling time interval for the macroscopic concentration signal is based on the detection cycle of existing online liquid oxygen chromatographs. The value range is configured to be from 2 minutes to 5 minutes.

[0071] S23 identifies the dense crystalline impurity components that currently dominate in liquid oxygen.

[0072] The control module 200 has a built-in cryogenic thermodynamic database in its storage medium, which records the saturation solubility curves of different types of impurities within the cryogenic liquid oxygen temperature range. The control module 200 compares the current macroscopic concentration values ​​of various impurities with the corresponding saturation solubility thresholds in the cryogenic thermodynamic database, and calculates the supersaturation of each impurity based on the difference between the two.

[0073] The control module 200 combines supersaturation and concentration-time derivative to determine the physical state of impurities. When the real-time concentration of an impurity exceeds the corresponding saturation solubility and the corresponding concentration-time derivative is greater than zero, the control module 200 determines that the impurity is in a continuous precipitation and crystallization state.

[0074] When multiple impurities are in a continuous precipitation and crystallization state, the control module 200 calls the crystal yield strength parameter of the corresponding impurity and calculates the comprehensive priority of each impurity according to a preset weight. The comprehensive priority increases with the increase of supersaturation and increases with the decrease of crystal yield strength. The control module 200 locks the impurity with the highest comprehensive priority as the dense crystalline impurity component that is currently dominant in liquid oxygen, and uses it as the target for subsequent anti-deposition control.

[0075] If all impurities do not exceed the saturation solubility, or if they exceed the saturation solubility but the corresponding concentration-time derivative is less than or equal to zero, the control module 200 determines that the system is in a state of no crystallization aggravation and returns to step S21 to continue the cycle monitoring.

[0076] S24, determine the triggering condition and start the anti-deposition pulse emission procedure.

[0077] The control module 200 continuously monitors the deposition retardation index and the concentration-time derivative of the main dense-crystalline impurity component, comparing them with preset threshold conditions. The control module 200 internally sets a deposition retardation index threshold and a concentration derivative threshold. The deposition retardation index threshold, ranging from 0.15 to 0.25, characterizes the maximum flow field energy attenuation ratio the system can withstand. The concentration derivative threshold, calibrated based on a crystallization kinetic model and combined with historical operating data from the air separation unit, characterizes the critical aggregation rate at which impurities transform from a completely dissolved state to a solid crystalline state.

[0078] The control module 200 uses logic AND thresholds as comprehensive triggering conditions. When the deposition retardation index is greater than the deposition retardation index threshold, and the concentration-time derivative of the main dense crystalline impurity component is greater than the concentration derivative threshold, the control module 200 determines that the growth size and density of the bottom deposits have posed a risk of blockage to the conventional drainage function, thus meeting the activation conditions of the anti-deposition pulse discharge procedure.

[0079] Before issuing the start command, the control module 200 further verifies the safety conditions. The verification items include: the liquid oxygen container 11 has a liquid level higher than the minimum safe liquid level, the pressure in the discharge pipeline 310 is lower than the maximum allowable pressure, the pressure in the buffer chamber 330 is within the preset back pressure window, the opening feedback of the regulating valve 320 is normal, the pressure difference across the regulating valve 320 or the pressure difference across the cavitation-induced constriction section 350 is within the controllable range, and the impurity concentration does not exceed the emergency shutdown threshold.

[0080] When all the above safety conditions are met, the control module 200 sends a start command to the execution module 300 to trigger the anti-deposition pulse emission program. If any safety condition is not met, the control module 200 prohibits the program from starting and outputs an alarm. If the deposition retardation index and the concentration-time derivative do not simultaneously meet the trigger conditions, the system maintains its current operating state, and the control module 200 returns to step S21 to continue closed-loop monitoring.

[0081] When the liquid oxygen level in container 11 is below the minimum safe level, the pressure in the main condenser / evaporator 10 exceeds the maximum allowable pressure, the pressure in the discharge pipeline 310 exceeds the maximum allowable pressure, the pressure in the buffer chamber 330 exceeds the preset back pressure window, the opening feedback of the regulating valve 320 fails, the signal from the pressure transmitter 110 fails, the signal from the liquid oxygen analyzer 120 fails, the discharge flow meter 160 detects a risk of blockage in the discharge channel, or the impurity concentration exceeds the emergency shutdown threshold, the control module 200 prohibits the execution of the anti-deposition pulse discharge program. In the prohibited state, the control module 200 maintains normal liquid level control or switches to safe discharge mode and outputs corresponding alarm information.

[0082] See attached document Figure 5This invention provides a process for outputting a critical cavitation-targeted pressure reduction command to a regulating valve and inducing localized cavitation fatigue pore formation. This process utilizes the micro-amplitude high-frequency oscillation of the flow cross-sectional area of ​​the regulating valve 320 to create a controllable localized low pressure and pressure recovery process near the target deposition area, causing micro-cavitation bubbles to form and collapse on the surface of the solid deposition layer, thereby creating fatigue pores in the deposition layer. This process includes the following sub-steps.

[0083] S31, calculates the critical cavitation targeted depressurization command.

[0084] Based on the main dense crystalline impurity components identified in step S20, control module 200 calls the correlation model stored in the storage medium. This correlation model is used to characterize the correspondence between the crystal yield strength of solid hydrocarbons and nitrous oxide and the critical cavitation threshold of liquid oxygen under cryogenic air separation conditions. The correlation model includes at least the impurity type, liquid oxygen temperature range, saturation solubility, crystal yield strength, fatigue limit, cavitation impact pressure conversion coefficient, and allowable low-temperature fatigue stress of the metal pipe.

[0085] The control module 200 calibrates the cavitation impact pressure conversion coefficient using historical operating data, offline cryogenic test data, or fluid dynamics simulation data. Based on the crystal yield strength of the main dense crystalline impurity component, the current liquid oxygen temperature, and the safety boundary of the equipment's mechanical structure, the control module 200 calculates the target static pressure value corresponding to the critical cavitation targeted pressure reduction command. This target static pressure value is used to ensure that the microjets generated by the collapse of cavitation bubbles have the ability to weaken the impurity deposition layer, while avoiding impact loads on the metal pipe wall that exceed the fatigue limit.

[0086] The target static pressure value is constrained by both the mechanical structure safety boundary and the liquid oxygen phase safety boundary. If the calculated target static pressure value is lower than the allowable lower limit of the discharge pipeline 310 and the main condenser-evaporator 10, or exceeds the pressure window through which the regulating valve 320, the cavitation-induced constriction section 350, and the buffer chamber 330 can stably form controllable micro-cavitation, the control module 200 is prohibited from executing the critical cavitation targeted pressure reduction command.

[0087] The mathematical model for calculating the target static pressure value is as follows: ; In the formula, This indicates the local target static pressure value at the constriction section of regulating valve 320, on the side of the cavitation-induced constriction section 350 adjacent to the deposition zone, or in the constriction area adjacent to the deposition zone. Indicates the current liquid oxygen temperature The saturated vapor pressure at the current liquid oxygen temperature The temperature is obtained through the main condenser-evaporator temperature sensor 170; This represents the yield strength of the crystal that primarily causes the dense-crystalline impurity component at the current cryogenic temperature; This represents the material fatigue failure safety factor, with a value ranging from 1.2 to 1.5. The cavitation impact pressure conversion coefficient is obtained by fitting and calibrating the throttling cross-sectional area of ​​the discharge pipeline 310 and the liquid oxygen fluid density through a prior fluid dynamics simulation experiment.

[0088] The control module 200 generates a critical cavitation-targeted pressure reduction command containing a specific pressure target based on the calculation results, and uses it as a quantitative constraint for the operation of the control valve 320. When the control valve 320 is the main cavitation occurrence location, the control module 200 estimates the local static pressure at the constriction section of the control valve 320 in real time based on the upstream pressure, downstream pressure, buffer chamber pressure, discharge flow rate, control valve opening feedback, and the flow characteristic curve of the control valve 320.

[0089] When the cavitation-induced constriction section 350 participates in cavitation control, the control module 200 estimates the local static pressure in the pressure recovery zone adjacent to the deposition zone based on the pressure on both sides of the cavitation-induced constriction section 350, the flow area of ​​the constriction section, and the discharge flow rate. The deviation between the local static pressure and the target static pressure value is used as a closed-loop regulation quantity to correct the micro-oscillation amplitude and basic opening of the regulating valve 320.

[0090] S32 sets the control parameters for the micro-amplitude high-frequency oscillation of the regulating valve.

[0091] When the control module 200 issues a critical cavitation targeted depressurization command, it simultaneously configures the high-frequency oscillation action parameters of the regulating valve 320. These action parameters include amplitude ratio, oscillation frequency, and duration.

[0092] The amplitude ratio is set to ±2% to ±5% of the current basic opening of the regulating valve 320 to limit the overall fluctuation of the discharge flow. The oscillation frequency is set according to the response capability of the high-speed electric positioner or high-speed servo actuator, and in combination with the mechanical structure safety boundary parameters determined in step S10. The value range is 5Hz to 15Hz, while avoiding the structural resonance frequency band of the main condenser evaporator 10 and the discharge pipeline 310.

[0093] The control module 200 determines the tracking status of the oscillation action based on the measured opening feedback of the regulating valve 320. When the measured opening response frequency of the regulating valve 320 is less than three times the target oscillation frequency, or when the opening feedback phase lags by more than a preset phase threshold, the control module 200 reduces the oscillation frequency; if the reduction still cannot meet the closed-loop tracking requirements, the high-frequency oscillation control is terminated.

[0094] The sustaining time is set to 3 to 8 seconds to generate a sufficient number of pressure alternation cycles within a limited time, while reducing the risk of fatigue damage to cryogenic metal pipelines caused by prolonged high-frequency oscillations. The closed-loop control parameters internally track the high-frequency input signal in the high-speed electric positioner or high-speed servo actuator, and can perform step response correction based on the actuator response time, valve opening feedback delay, and valve core inertia.

[0095] S33 induces localized liquid oxygen flash evaporation and microjet cavitation.

[0096] After receiving the critical cavitation targeted pressure reduction command, the regulating valve 320 performs a micro-amplitude high-frequency oscillation action according to the set parameters. When liquid oxygen flows through the constriction section of the regulating valve 320, the flow area decreases periodically, the local flow velocity increases, and the static pressure decreases accordingly. When the regulating valve 320 is arranged outside the cold box boundary and works in conjunction with the cavitation-induced constriction section 350, the regulating valve 320 adjusts the discharge flow rate and the pressure difference on both sides of the constriction section to create a periodic low-pressure zone on the side of the cavitation-induced constriction section 350 adjacent to the deposition zone.

[0097] When the local static pressure at the constriction section of the regulating valve 320, the side of the cavitation-induced constriction section 350 adjacent to the deposition zone, or the constriction area adjacent to the deposition zone decreases to near the target static pressure value, some liquid oxygen in the liquid phase undergoes local flash evaporation, inducing microcavitation bubbles inside the fluid and on the surface of the solid deposition layer. The generation area of ​​microcavitation bubbles covers the bottom drain port of the main condenser evaporator 10, the inlet section of the discharge pipe 310, the area adjacent to the cavitation-induced constriction section 350, or the upstream area adjacent to the deposition zone of the regulating valve 320, so that the microjets generated by the subsequent bubble collapse can act on the surface of the solid deposition layer.

[0098] After leaving the constriction section of the regulating valve 320 or the cavitation-induced constriction section 350, liquid oxygen enters the downstream pressure recovery zone. This pressure recovery zone includes the buffer chamber 330, the local expansion zone, or the expansion section of the discharge pipe after the cavitation-induced constriction section 350. As the flow area increases, the fluid velocity decreases, and the local static pressure rises. After the static pressure rises above the saturated vapor pressure of liquid oxygen, the microcavitation bubbles contract and collapse under the action of the internal and external pressure difference. Because the solid deposition layer wall forms an asymmetric boundary constraint on the bubble collapse process, the bubble collapse generates a microscale liquid jet towards the deposition layer surface and an accompanying pressure shock.

[0099] S34, implement sediment cavitation fatigue pore formation.

[0100] Liquid microjets and accompanying pressure shocks act on the surface of the solid deposit layer at the bottom drain port of the main condenser-evaporator 10, the inlet section of the discharge pipe 310, the area adjacent to the cavitation-induced constriction section 350, and the area adjacent to the regulating valve 320. The micro-amplitude high-frequency oscillation of the regulating valve 320 causes the local static pressure to periodically switch between the cavitation-induced boundary and the pressure recovery boundary, and microcavitation bubbles are repeatedly generated and collapsed accordingly.

[0101] Under this periodic action, the surface of the solid deposit layer is subjected to high-frequency alternating impacts. The control module 200 incorporates the crystal yield strength and fatigue limit of the main dense crystalline impurity components when calculating the target static pressure value, ensuring that the alternating impact intensity is suitable for weakening brittle crystalline deposits such as solid hydrocarbons and nitrous oxide. After 3 to 8 seconds of continuous action, microscopic fatigue cracks are generated on the surface of the dense solid deposit layer. These cracks continue to propagate and interconnect, causing fine granular spalling of the surface material and forming microscopic pores and mechanical structural defects within the deposit layer.

[0102] To protect the metal substrate, the control module 200 continuously monitors the high-frequency pressure pulsation amplitude, the pressure difference across the regulating valve 320, the pressure difference across the cavitation-induced constriction section 350, the buffer chamber pressure, and the regulating valve opening response. When the high-frequency pressure pulsation amplitude exceeds the maximum dynamic pressure pulsation amplitude in the mechanical structure safety boundary parameters, or when either the pressure difference across the regulating valve 320 or the pressure difference across the cavitation-induced constriction section 350 exceeds the preset upper limit of the pressure difference, the control module 200 immediately cancels the high-frequency oscillation command and controls the regulating valve 320 to return to a safe opening.

[0103] Through the aforementioned microporous process, the originally dense and homogeneous solid deposition layer is weakened in advance, and a porous interface that can generate acoustic impedance differences is formed, providing a basis for subsequent reverse compression wave stripping.

[0104] See attached document Figure 6 This invention provides a process for issuing a step pulse command, inducing a reverse compression wave, and achieving acoustic impedance mismatch pyrolysis and stripping. Based on pre-cavitation fatigue pore formation, this process generates an upstream propagating compression pressure wave through a valve step action with a limited actuation rate. This causes acoustic impedance mismatch and localized stress concentration at the pore interface within the deposited layer, thereby promoting the pyrolysis and stripping of the weakened solid deposited layer. The process includes the following sub-steps.

[0105] S41 sets the step pulse command control parameters.

[0106] The control module 200 sends a step pulse command with a limited action rate to the regulating valve 320. This step pulse command includes the step amplitude, the rate of change limit, the pulse duration, and the critical base opening at the valley value.

[0107] The critical base opening at the valley value is determined based on the process requirements of the air separation unit to maintain a minimum discharge rate. Its value range is configured to be 10% to 15% of the valve stroke of regulating valve 320 to avoid the risk of pressure buildup caused by the complete disconnection of discharge line 310. The step amplitude is the difference between the current opening of regulating valve 320 and the critical base opening at the valley value.

[0108] The rate of change limit is determined based on the mechanical strength of the discharge pipe 310 and the transient pressure boundary of the fluid. It is used to limit the pressure peak caused by the closing action of the regulating valve 320, ensuring that this pressure peak is below the yield strength of the pipe material. The mathematical model for calculating the maximum pressure peak is as follows: ; In the formula, This indicates the amount of pressure increase induced by valve operation; This indicates the density of the liquid oxygen fluid; This represents the speed of sound during the propagation of pressure waves in liquid oxygen. This indicates the change in fluid velocity caused by valve operation.

[0109] The control module 200 determines the maximum allowable pressure rise based on the pipe's yield strength and then inversely solves for the maximum allowable fluid velocity change. Subsequently, the control module 200, in conjunction with the inherent flow characteristic curve of the regulating valve 320, maps the maximum allowable fluid velocity change to a limit value for the rate of change of the regulating valve 320's opening.

[0110] The pulse duration is set to be greater than the time it takes for the reverse compression wave to propagate once round trip within the discharge pipe 310, with a value range of 0.5 seconds to 2.0 seconds. By limiting the rate of change of opening and the pulse duration, the control module 200 can reduce the risk of excessive transient loads on the pipes and equipment while inducing effective compression pressure waves.

[0111] The control module 200 also sets the maximum number of pulses for a single anti-deposition pulse emission program. The maximum number of pulses is set based on the number of consecutive judgments N, and is greater than or equal to N, with a value range of 5 to 10 times. When the maximum number of pulses is reached, if the moving average of the integral of the reflection spectrum energy attenuation is still not less than or equal to the reflection energy reference threshold for N consecutive times, the control module 200 stops the pulse emission program, outputs a deposition stripping abnormality alarm, and switches to the normal safe drainage or manual handling mode.

[0112] S42 induces a reverse compression wave that propagates upstream.

[0113] After receiving a step pulse command, the regulating valve 320 closes from its current opening to the critical base opening at the valley value according to the rate of change limit. After the flow cross-sectional area of ​​the regulating valve 320 decreases, the velocity of the liquid oxygen fluid flowing through the throttling section changes in a controlled manner, the fluid kinetic energy decreases, and a compression pressure wave, i.e., a reverse compression wave, is formed at the upstream end of the regulating valve 320 and propagates upstream.

[0114] The reverse compression wave propagates against the direction of liquid oxygen discharge flow at the speed of sound in the liquid oxygen medium, and is transmitted along the discharge pipe 310 to the bottom deposition area of ​​the main condenser-evaporator 10. The control module 200 calculates the time window for the reverse compression wave to reach the deposition area and be reflected back to the pressure transmitter 110 based on the equivalent acoustic distance between the regulating valve 320 and the target deposition area and the speed of sound of liquid oxygen, and sets the start and end times of subsequent reflection spectrum sampling accordingly.

[0115] S43 forms an acoustic impedance mismatch interface reflection.

[0116] After the reverse compression wave propagates to the deposition zone, it interacts with the solid deposit layer attached to the pipe wall. During the pre-pore-forming process in step S30, cavitation micropores have already formed inside the solid deposit layer, weakening its original dense and homogeneous structure. The liquid oxygen fluid, the solid deposit, and the medium inside the micropores have different densities and sound velocities, and therefore each has different acoustic impedances.

[0117] When a reverse compression wave propagates to the interface of micropores, reflection and refraction occur at the interface due to the discontinuity of the acoustic boundary. The mathematical model for calculating the interface reflection coefficient is as follows: ; In the formula, The interface reflection coefficient represents the acoustic interface. This represents the acoustic impedance of the medium on the incident side of the wave; This represents the acoustic impedance of the medium on the wave transmission side.

[0118] The acoustic impedance of the medium inside the micropores is lower than that of the solid deposit, creating a distinct acoustic discontinuity at the pore interface. Reverse compression waves are reflected and superimposed at this boundary, providing the acoustic conditions for subsequent localized stress amplification.

[0119] S44 enables localized stress amplification and pyrolysis / stripping.

[0120] When the reverse compression wave is reflected at the interface of the micropores and superimposed on the incident wave, the local mechanical stress around the pores increases. The macroscopic pressure fluctuation is transformed into local tensile and shear stresses at the micropore boundaries and extends along the pore edges into the surrounding solid crystal structure.

[0121] Since the solid deposit layer has already developed cracks, pores, and mechanically weak areas during the pre-cavitation fatigue pore formation process, the local stress concentration caused by the reverse compression wave can further promote crack propagation and connection. Under the action of local tensile stress, shear stress, and fluid erosion, the solid deposit layer fractures and gradually detaches from the metal pipe wall, completing the physical stripping of solid impurities.

[0122] After maintaining the critical trough opening for a preset pulse duration, the control module 200 controls the regulating valve 320 to open to the pre-pulse opening according to a preset recovery rate, thus releasing the low-level drainage state. The stripped sediment particles are then discharged from the system along with the liquid oxygen fluid through the regulating valve 320, completing a single pulse discharge operation.

[0123] To reduce the risk of valve core jamming caused by the overall shedding of large deposits, the control module 200 limits the amplitude of single step pulses and the maximum pressure peak, causing the stripped particles to tend to be discharged with liquid oxygen at a smaller particle size. To prevent stripped particles from clogging the regulating valve 320, buffer chamber 330, or flow restrictor plate 340, the flow restrictor plate 340 adopts a multi-hole parallel structure or a detachable anti-clogging structure, the buffer chamber 330 is provided with a particle settling zone or a purging interface at the bottom, and the discharge pipeline 310 is provided with a bypass venting branch 360.

[0124] When the discharge flow meter 160 detects that the discharge flow is lower than the minimum allowable flow corresponding to the valve opening, and the pressure difference between the valve and the valve rises abnormally, the control module 200 determines that there is a risk of blockage in the discharge channel, immediately stops the pulse action, and opens the bypass venting branch 360 or outputs a maintenance alarm.

[0125] The end of the discharge line 310 is connected to the cryogenic liquid safety discharge unit 370. The cryogenic liquid safety discharge unit 370 includes a vaporization buffer container, an oxygen enrichment detector, and a safety venting line. After being stripped, solid impurity particles enter the cryogenic liquid safety discharge unit 370 with liquid oxygen, and are discharged after buffering and settling, controlled vaporization, and safety venting.

[0126] An oxygen enrichment detector monitors the oxygen concentration in the emission area in real time. When the oxygen concentration in the emission area exceeds a preset safety threshold, the control module 200 immediately reduces the opening of the regulating valve 320 or stops the pulse emission program. When the liquid oxygen analyzer 120 detects that the concentration of hydrocarbons, acetylene, or nitrous oxide exceeds the emergency shutdown threshold, the control module 200 prohibits the execution of the anti-deposition pulse emission program characterized by cavitation hole formation and compression wave stripping, and switches to the safe emission, load reduction, or shutdown procedure.

[0127] See attached document Figure 7 This invention provides a process for evaluating the deposition stripping status and performing system reset through acoustic feedback. This process is used to determine the stripping effect of the solid deposit layer based on the reflected pressure signal after one or more pulse discharges, and to exit the anti-deposition pulse discharge program when termination or abnormal conditions are met, allowing the regulating valve 320 to smoothly return to the normal liquid level control state. This process includes the following sub-steps.

[0128] Before performing the acoustic feedback closed-loop evaluation, the control module 200 first performs baseline calibration of the reflection spectrum. After the air separation unit completes bare cooling, initial liquid accumulation, and enters a deposition-free healthy operating condition, the control module 200 outputs a test step command to the regulating valve 320. The amplitude of the test step command is lower than the step amplitude in the anti-deposition pulse emission program, and is used to collect the reflection pressure signal when the deposition zone is in a healthy state. The control module 200 calculates the baseline reflection spectrum energy in the 100Hz to 500Hz frequency band based on this reflection pressure signal, and stores this baseline reflection spectrum energy in a storage medium as a reference for subsequent judgment of the completion status of deposition stripping.

[0129] S51, calculate the energy attenuation integral of the reverse compression wave reflection spectrum.

[0130] During the execution of the step pulse command in step S40, the pressure transmitter 110 acquires the transient pressure fluctuation signal reflected back from the acoustic interface. The control module 200 uses the moment when the regulating valve 320 begins its step action as the trigger moment. And based on the equivalent acoustic distance from the regulating valve 320 to the deposition zone Speed ​​of sound of liquid oxygen The sampling time window for the reflected wave return pressure signal is determined by the phase delay compensation amount of the pressure tapping line 111.

[0131] The sampling time window is located at Subsequently, its length is determined based on the lowest frequency of the 100Hz to 500Hz reflection band, covering at least three complete cycles of the 100Hz signal, and less than the time interval between stray reflections from adjacent pipelines entering the sampling window. The control module 200 uses a sampling frequency of not less than 2kHz to acquire the reflected pressure signal to meet the frequency domain analysis requirements of the 100Hz to 500Hz reflection band.

[0132] The control module 200 performs a fast Fourier transform on the transient pressure fluctuation signal within the sampling time window to obtain the transient reflection frequency domain power spectrum. By limiting the sampling time window, the control module 200 can distinguish between the incident wave generated by the action of the regulating valve 320, the reflection wave from the deposition zone interface, and the stray reflection wave from the subsequent pipeline.

[0133] To extract the characteristic energy resulting from the interaction between the reverse compression wave and the solid deposition layer, the control module 200 selects 100Hz to 500Hz as the main reflection frequency band and calculates the energy attenuation integral of the reflection spectrum within this band. The mathematical model for calculating the energy attenuation integral of the reflection spectrum is as follows: ; In the formula, This represents the integral of energy decay in the reflection spectrum; and These represent the lower and upper limits of the preset reflection frequency band, respectively, with specific values ​​corresponding to the configured 100Hz and 500Hz. This represents the transient reflection power spectral density at frequency ff; This represents the discrete frequency resolution. Through numerical processing of frequency domain energy, the control module 200 obtains the state variables that quantify the acoustic reflection intensity.

[0134] S52, determine the state of crystallization deposition and peeling.

[0135] The control module 200 continuously calculates the integral of energy attenuation of the reflection spectrum and evaluates the sediment stripping status based on its changing trend. As solid sediments are gradually stripped from the pipe wall and discharged with the liquid oxygen fluid, the acoustic impedance mismatch interface on the pipe wall surface decreases, the reflection effect of the reverse compression wave at the sedimentation zone interface weakens, and the transmission and dissipation energy increases. Correspondingly, the integral of energy attenuation of the reflection spectrum shows a decreasing trend.

[0136] The control module 200 performs a moving average on the real-time calculated reflectance spectrum energy attenuation integral and compares the moving average with a preset reflectance energy reference threshold. The reflectance energy reference threshold is determined based on acoustic reflectance baseline data collected under deposit-free healthy operating conditions and is corrected using a threshold margin coefficient. The threshold margin coefficient is configured to range from 1.05 to 1.15 to accommodate system noise floor and sensor measurement errors.

[0137] To avoid misjudgments caused by transient noise, the control module 200 does not use the result of a single calculation as the termination criterion. Only when the moving average of the energy attenuation integral of the reflection spectrum is less than or equal to the reflection energy reference threshold N times consecutively can the control module 200 determine that the dense solid deposition layer in the deposition zone has been physically stripped and the program termination condition is met. The value of N ranges from 2 to 5.

[0138] If the moving average of the energy attenuation integral of the reflection spectrum is greater than the reflection energy reference threshold, or if the termination condition of being less than or equal to the reflection energy reference threshold for N consecutive times has not been met, the control module 200 determines that the sediment stripping has not met the expected requirements and triggers step S40 to execute the single pulse emission action again.

[0139] If the program termination condition is not met after the preset maximum number of pulses has been reached, the control module 200 determines that the deposition stripping is abnormal, stops outputting high-frequency oscillation commands and step pulse commands, restores the regulating valve 320 to the safe drainage opening, and outputs a blockage risk alarm or requests manual inspection. The maximum number of pulses is greater than or equal to the number of consecutive judgments N to ensure that the control module 200 can complete at least one consecutive judgment.

[0140] S53, execute command cancellation and action termination.

[0141] After the program termination conditions are met, the control module 200 executes the normal exit sequence of the anti-deposition pulse emission program. If any of the following occurs during operation: the liquid oxygen level is lower than the minimum safe level, the pressure in the emission pipeline 310 exceeds the maximum allowable pressure, the pressure in the buffer chamber 330 exceeds the preset back pressure window, the valve opening feedback is abnormal, the reflection spectrum signal is lost, the emission flow rate is abnormally reduced, or the impurity concentration exceeds the emergency shutdown threshold, the control module 200 executes the abnormal exit sequence.

[0142] Upon exiting, the control module 200 terminates the step pulse command sent to the regulating valve 320 to induce a reverse compression wave, and simultaneously cancels the high-frequency oscillation command used to induce microjet cavitation pore formation. After receiving the stop command, the high-speed electric positioner or high-speed servo actuator of the regulating valve 320 stops its high-frequency response and step action. Subsequently, the control module 200 generates a normal opening positioning command, restoring the regulating valve 320 to its basic opening before the anti-deposition pulse discharge program was triggered, thereby restoring the normal liquid oxygen discharge state at the bottom of the main condenser evaporator 10.

[0143] S54 performs anti-disturbance transition and system smooth return.

[0144] To ensure a smooth transfer of control from the regulating valve 320 to the existing conventional liquid level control system of the air separation unit, the control module 200 implements an anti-disturbance switching strategy.

[0145] During the operation of the anti-deposition pulse discharge program, the proportional-integral-derivative controller of the conventional liquid level control system may accumulate integral due to the continuous deviation between the liquid level measurement value and the set value. To avoid sudden changes in opening degree during control handover, the control module 200 writes the current basic opening degree of the regulating valve 320 into the conventional liquid level control system before handover as the preset output parameter of the controller, and initializes and clears the controller integrator.

[0146] After the conventional liquid level control system regains control of the regulating valve 320, it recalculates the liquid level deviation and performs proportional-integral regulation using the actual liquid level as the control starting point. During the preset transition time after regaining control, the control module 200 limits the rate of change of the opening of the regulating valve 320 and the maximum single change in opening to prevent the liquid level controller from making excessive adjustment movements due to short-term liquid level deviations. The preset transition time ranges from 30 seconds to 180 seconds.

[0147] Through the aforementioned preset output, integrator initialization, and opening change limitation, the regulating valve 320 can smoothly transition from the anti-deposition pulse discharge program to the normal liquid level control state, reducing the disturbance to the liquid level of the main condenser evaporator 10 and the system pipeline pressure during the switching process.

[0148] Through the aforementioned acoustic feedback and regressive control process, the system can determine the stripping state based on the continuous change of the energy attenuation integral of the reflection spectrum after the solid deposit layer has been stripped by cavitation fatigue pore formation and reverse compression wave stripping; and promptly exit the anti-deposition pulse emission program and restore normal liquid level control when termination conditions are met or abnormal conditions occur. This process can reduce the risks of deposit blockage, pipeline resonance, valve malfunction, and discharge channel blockage.

[0149] Specific application examples: The cryogenic liquid anti-deposition discharge system of the present invention is applied in a low-pressure air separation unit. A liquid oxygen container 11 is installed at the bottom of the main condenser / evaporator 10 of the air separation unit. A discharge pipe 310 is connected to the bottom drain port of the liquid oxygen container 11. A regulating valve 320, a buffer chamber 330, and a flow-limiting orifice plate 340 are sequentially installed on the discharge pipe 310. A pressure transmitter 110 is connected to the lower pressure tap of the liquid oxygen container 11 via a fully filled pressure tapping line 111, and is used to collect high-frequency pressure timing signals from the bottom of the liquid oxygen container 11. A pressure sensor 130 before the valve, a pressure sensor 140 after the valve, a pressure sensor 150 in the buffer chamber, and a discharge flow meter 160 are used to collect the pressure difference across the regulating valve 320 or the cavitation-induced constriction section 350, the pressure in the buffer chamber 330, and the discharge flow rate, respectively.

[0150] After the air separation unit completes bare cooling, initial liquid accumulation, and enters stable load operation, the control module 200 selects a sediment-free, healthy operating condition as a baseline acquisition window. Within this window, the liquid oxygen level, the pressure of the main condenser-evaporator 10, and the heat exchange load are all within a stable range. The control module 200 acquires high-frequency pressure timing signals within this window and establishes a baseline power spectral density under pure nucleate boiling conditions. After frequency band division, the control module 200 uses the frequency range reflecting bubble generation and detachment characteristics as the low-frequency broadband boiling region and uses the power spectral integration result within this frequency band as a reference for subsequent sediment identification.

[0151] After the air separation unit has been operating for a period of time, the control module 200 detects that the real-time pressure pulsation energy in the low-frequency broadband boiling zone is lower than the baseline state. The deposition retardation index calculation shows that its value exceeds a preset threshold. Simultaneously, the liquid oxygen analyzer 120 detects that the nitrous oxide concentration in the liquid oxygen is close to and exceeds the saturation solubility threshold at the current liquid oxygen temperature, and the concentration-time derivative is greater than a preset concentration derivative threshold. Other impurities such as methane, ethane, acetylene, and carbon dioxide do not simultaneously meet the conditions for supersaturation and continuous growth. Based on a comprehensive priority calculation using supersaturation and crystal yield strength, the control module 200 identifies nitrous oxide as the currently dominant dense crystalline impurity component in the liquid oxygen.

[0152] Before initiating the anti-deposition pulse emission procedure, the control module 200 performs a safety condition verification. Verification items include the liquid oxygen container 11 level, the main condenser / evaporator 10 pressure, the emission line 310 pressure, the buffer chamber 330 pressure, the regulating valve 320 opening feedback, the pressure difference across the regulating valve 320 or the cavitation-induced constriction section 350 pressure difference, the emission flow rate, and the impurity concentration. When all parameters are within the preset safety window, the control module 200 allows the anti-deposition pulse emission procedure to be executed; if any parameter exceeds the safety window, the control module 200 prohibits the initiation of the procedure and maintains normal liquid level control or switches to a safe emission mode.

[0153] The control module 200 calls the correlation model corresponding to nitrous oxide and, in conjunction with the current liquid oxygen temperature, nitrous oxide crystal yield strength, cavitation impact pressure conversion coefficient, and mechanical structure safety boundary, calculates the target static pressure value corresponding to the critical cavitation targeted pressure reduction command. The calculated target static pressure value is above the equipment's allowable lower safety limit and falls within the pressure window where the regulating valve 320, buffer chamber 330, and discharge pipeline 310 can form controllable micro-cavitation. Therefore, the control module 200 generates the critical cavitation targeted pressure reduction command.

[0154] When executing the critical cavitation targeted depressurization command, the regulating valve 320 oscillates at a small amplitude at a high frequency near its base opening. The oscillation frequency is set within a range that avoids the resonance band of the mechanical structure, the amplitude ratio is controlled within a small range of the base opening, and the duration is on the order of several seconds. The opening feedback of the regulating valve 320 shows that it can track the given oscillation action. The control module 200 estimates the local static pressure at the constriction section of the regulating valve 320 based on the pressure before the valve, the pressure after the valve, the buffer chamber pressure, the discharge flow rate, and the flow characteristic curve of the regulating valve 320, and controls the local static pressure near the target static pressure value. If the regulating valve 320 is located outside the cold box boundary, the control module 200 uses the local static pressure on the side of the cavitation-induced constriction section 350 adjacent to the deposition zone as the control object, and adjusts the pressure difference and discharge flow rate on both sides of the constriction section through the regulating valve 320.

[0155] Under the influence of micro-amplitude high-frequency oscillations, periodic static pressure decreases and recoveries occur near the target deposition area. During the local static pressure decrease phase, liquid oxygen undergoes local flash evaporation in the constriction region, forming microcavitation bubbles. During the pressure recovery phase, these microcavitation bubbles collapse near the surface of the solid deposition layer, generating microjets and pressure shocks facing the deposition layer. This process creates microcracks, pores, and localized mechanically weak areas on the surface of the dense deposition layer, providing an acoustic impedance mismatch interface for subsequent compression wave stripping.

[0156] After achieving critical cavitation-targeted depressurization, the control module 200 sends a step pulse command with a limited action rate to the regulating valve 320. The regulating valve 320 is controlled to close from its current opening to a critical valley opening and maintains this valley opening for a preset time. The critical valley opening meets the minimum discharge requirement, preventing the discharge line 310 from being completely shut off. Based on the mechanical strength of the discharge line 310, the liquid oxygen density, the liquid oxygen sound velocity, and the flow characteristic curve of the regulating valve 320, the control module 200 limits the rate of change of the valve opening, ensuring that the pressure peak induced by the valve action is below the mechanical safety boundary.

[0157] During the closing of regulating valve 320, a compressive pressure wave propagates upstream from the upstream end of regulating valve 320. This reverse compressive wave is transmitted along the discharge pipe 310 to the bottom deposition area of ​​the main condenser-evaporator 10. When the reverse compressive wave reaches the micropore interface formed by the pre-cavitation cavitation, the waveform is reflected and superimposed at the interface due to the acoustic impedance difference between liquid oxygen, solid deposits, and the internal medium of the pores. The macroscopic pressure fluctuation is transformed into local tensile and shear stresses at the pore boundary, causing the weakened solid deposit layer to crack and detach from the metal pipe wall.

[0158] The stripped deposited particles enter the buffer chamber 330 and the downstream side of the flow-limiting orifice plate 340 along with the liquid oxygen fluid. The particle settling zone at the bottom of the buffer chamber 330 is used to retain some particles, and the bypass vent branch 360 is used to provide an alternative venting path when the discharge flow rate is abnormally reduced or the pressure difference is abnormally increased. The end of the discharge pipeline 310 is connected to the cryogenic liquid safety discharge unit 370. After the stripped particles enter the unit with the liquid oxygen, they undergo buffering, settling, controlled vaporization, and safe venting.

[0159] During each step pulse execution, pressure transmitter 110 acquires the transient pressure fluctuation signal reflected back from the acoustic interface of the deposition zone. Control module 200, based on the equivalent acoustic distance from regulating valve 320 to the deposition zone, the liquid oxygen velocity, and the phase compensation of pressure tapping line 111, extracts the reflected wave return time window and calculates the integral of the reflection spectrum energy attenuation within the main reflection frequency band. This integral value characterizes the acoustic reflection intensity of the deposition zone.

[0160] In this embodiment, a pre-calibrated reference threshold for reflection energy is established under the non-deposition healthy operating condition. The control module 200 does not use the result of a single reflection spectrum calculation as the termination criterion, but instead performs a moving average processing on the integral of reflection spectrum energy attenuation after multiple consecutive pulses. When the moving average value continuously meets the condition of being less than or equal to the reference threshold for reflection energy, the control module 200 determines that the deposition layer has been physically stripped and terminates the anti-deposition pulse emission program. If the above condition is not met after reaching the maximum number of pulses, the control module 200 determines that the deposition stripping is abnormal, restores the safe drainage opening, and simultaneously outputs an alarm or requests manual inspection.

[0161] After the program terminates, control module 200 cancels the high-frequency oscillation command and step pulse command, restoring the regulating valve 320 to its basic opening before the anti-deposition pulse discharge program was triggered. Before the conventional level control system takes over control of the regulating valve 320, control module 200 writes the current basic opening as a preset output to the conventional level controller and initializes the integrator. After the conventional level control system takes over, control module 200 limits the rate of change of the regulating valve 320's opening and the maximum single opening change within a preset transition time, allowing the system to smoothly return to the conventional level control state.

[0162] To verify the effectiveness of the above embodiments, a cryogenic test section with dimensions identical to the on-site discharge branch was set up. The test section included a simulated liquid oxygen container section, a discharge pipeline 310, a regulating valve 320, a buffer chamber 330, a flow-limiting orifice plate 340, a cavitation-induced flow-constriction section 350, a bypass discharge branch 360, and a cryogenic liquid safety discharge unit 370. The test medium temperature was maintained within the cryogenic operating range of liquid oxygen, and the discharge pressure, valve operation, and flow conditions were configured as per the application embodiment.

[0163] In the experiment, an oxygen-compatible low-temperature brittle deposition simulation layer was prepared on the inner wall of the inlet section of the discharge pipeline 310. This simulation layer was used to reproduce the adhesion and brittle fracture characteristics of low-temperature crystalline deposits without introducing combustible deposits into the liquid oxygen. Two sets of operating conditions were set up in the experiment: Group A adopted a conventional small-flow continuous discharge method, with the regulating valve 320 maintaining a fixed opening; Group B adopted the anti-deposition pulse discharge method of the present invention, which sequentially performed critical cavitation targeted depressurization, micro-amplitude high-frequency oscillation, step pulse stripping, and reflection spectrum closed-loop determination.

[0164] After each set of experiments, the deposition and ablation status was evaluated by stopping the machine for weighing, observing through the pipeline endoscope, and analyzing changes in reflectance spectrum energy. The comparison results are shown in the table below.

[0165] The test results show that Group A's conventional continuous discharge can remove some loose sediment, but relatively continuous sheet-like sediment residue still exists in the 310 inlet section of the discharge pipe. After Group B implemented anti-deposition pulse discharge, the original continuous sediment layer was broken up and discharged with liquid oxygen, and the residue on the pipe wall was mainly distributed in discrete points. Neither group of tests showed blockage of the discharge channel, but Group B's sediment removal effect was closer to a sediment-free healthy operating condition.

[0166] During the Group B test, the opening feedback of regulating valve 320 was continuously effective, and the pressure difference across regulating valve 320 and the pressure difference across cavitation-induced constriction section 350 did not exceed the preset upper limit of pressure difference. The high-frequency pressure pulsation amplitude collected by pressure transmitter 110 did not exceed the maximum dynamic pressure pulsation amplitude in the mechanical structure safety boundary parameters, and there was no continuous energy amplification within the resonant frequency band. The cryogenic liquid safety discharge unit 370 operated normally, the oxygen enrichment detector did not trigger an over-limit alarm, and the bypass vent branch 360 was not forced to open.

[0167] Time-frequency analysis of the reflected pressure signals collected during the experiment showed that Group B exhibited strong reflected energy within the main reflection frequency band during the initial pulse phase, indicating a significant acoustic impedance mismatch interface in the deposition area. As the number of pulses increased, the energy distribution within the main reflection frequency band gradually weakened and approached the baseline range under healthy, non-depositional conditions. This result is consistent with the results of endoscopic observation during shutdown and weighing of residual sediments, demonstrating that the energy attenuation integral of the reflection spectrum can serve as a feedback criterion for the deposition layer stripping status.

[0168] The above applications and verifications demonstrate that this invention, after identifying deposition risks, utilizes critical cavitation to target and depressurize dense deposits, and then induces the deposition layer to fracture and peel off through reverse compression waves and acoustic impedance mismatch. Compared to conventional continuous emissions, this invention improves the removal efficiency of dense deposits while keeping pressure disturbances within mechanical safety boundaries.

[0169] Reference Appendix Figure 8 . Figure 8 The diagram uses the pulse execution timing as the horizontal expansion direction and the reflection frequency as the vertical expansion direction, with color levels representing the reflected energy intensity. It shows the high-energy region within the main reflection frequency band during the initial pulse phase, and the gradual decrease in reflected energy during subsequent pulse phases. This diagram reflects the changes in the acoustic impedance mismatch interface of the deposition area and corresponds to the process of the control module 200 determining the stripping termination condition.

[0170] Reference Appendix Figure 9 . Figure 9 The images include endoscopic images of the pipe wall after routine continuous discharge (Group A), endoscopic images of the pipe wall after anti-deposition pulse discharge (Group B), and residual deposition area identification results based on image grayscale and texture differences. The residual deposition area is superimposed on the original endoscopic image as a pseudo-color region to show the residual differences of sediment in the circumferential and axial directions of the pipe wall. Figure 9 The results can be corroborated with the results of shutdown weighing to illustrate the stripping effect of the present invention on dense deposited layers.

[0171] 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 cryogenic liquid anti-deposition discharge system for the cold box of an air separation unit, applied to the main condenser-evaporator with a liquid oxygen container at the bottom, characterized in that, It includes a data acquisition module, a control module, and an execution module; The data acquisition module includes a pressure transmitter and a liquid oxygen analyzer. The pressure transmitter acquires the pressure timing signal of the liquid oxygen container, and the liquid oxygen analyzer acquires the impurity concentration signal. The execution module includes a discharge pipeline connected to the liquid oxygen container, and a regulating valve, a buffer chamber and a flow limiting orifice plate are connected in series on the discharge pipeline; The control module calculates the deposition retardation index and concentration-time derivative based on the pressure timing signal and the impurity concentration signal. When both the deposition retardation index and the concentration-time derivative are greater than the set threshold, it sends a first alternating command and a second step command to the regulating valve in sequence. The regulating valve receives a first alternating command and alternately increases and decreases its opening according to a set frequency and a set amplitude. The regulating valve receives a second step command to close its opening to a set base opening and maintains it for a set duration. The control module determines the deposition state based on the pressure timing signal collected by the pressure transmitter within the set time period, and controls the regulating valve to return to the initial opening degree before receiving the first alternating command when the deposition state meets the stop condition.

2. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The pressure transmitter is connected to the liquid oxygen container through a pressure-sensing pipeline filled with liquid. The control module stores an acoustic transfer function model and calls the acoustic transfer function model to perform amplitude compensation and phase delay compensation on the pressure timing signal.

3. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The execution module also includes a flow-constricting section pipeline, which is connected in series with the discharge pipeline between the liquid oxygen container and the regulating valve. The flow cross-sectional area of ​​the flow-constricting section pipeline is smaller than the basic flow cross-sectional area of ​​the discharge pipeline.

4. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The control module stores the impurity saturation solubility value and the crystal yield strength value. The control module subtracts the impurity concentration signal from the impurity saturation solubility value to obtain the supersaturation difference value. The control module multiplies the supersaturation difference value by the crystal yield strength value to obtain the priority weight value. The control module marks the impurity with the first priority weight value as the dominant impurity component.

5. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 4, characterized in that, The steps for the control module to calculate the pressure setpoint corresponding to the first alternating command include: extracting the crystal yield strength value, safety factor, and pressure conversion coefficient corresponding to the dominant impurity component; obtaining the liquid oxygen temperature parameter and mapping it to obtain the saturated vapor pressure value; and subtracting the product of the crystal yield strength value, safety factor, and pressure conversion coefficient from the saturated vapor pressure value to obtain the pressure setpoint.

6. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The first alternating command includes setting an amplitude ratio, setting an oscillation frequency, and setting a duration. The amplitude ratio is configured to be 2% to 5% of the initial opening of the regulating valve before receiving the first alternating command, the oscillation frequency is configured to be 5 Hz to 15 Hz, and the duration is configured to be 3 seconds to 8 seconds.

7. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The second step command includes the target base opening, the opening change rate, and the pulse duration. The pulse duration is configured as twice the length of the discharge pipeline divided by the speed of sound of the pressure wave propagating in the discharge pipeline.

8. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The control module calls the Fast Fourier Transform algorithm to convert the pressure time-series signal into a frequency domain power spectrum value. The control module extracts the integral value within a set frequency band from the frequency domain power spectrum value and calculates the moving average value of the integral value. When the number of consecutive set moving average values ​​is less than a set reference threshold, the control module determines that the deposition state meets the stop condition.

9. The cryogenic liquid anti-deposition discharge system in the cold box of the air separation unit according to claim 1, characterized in that, The flow-limiting orifice plate is fixed to the side of the buffer chamber away from the regulating valve. The end of the discharge pipeline away from the liquid oxygen container is connected to a discharge unit, which includes a vaporization buffer container, an oxygen enrichment detector, and a venting pipeline.

10. A method for preventing the deposition of cryogenic liquid in the cold box of an air separation unit, applied to the cryogenic liquid anti-deposition system in the cold box of an air separation unit as described in any one of claims 1-9, characterized in that, Includes the following steps: Extract the reference power spectral density value of the pressure time-series signal under the set reference state; Acquire real-time pressure timing signals and impurity concentration signals of the operating status; The real-time power spectral density value of the pressure time-series signal is calculated, and the deposition retardation index is obtained by subtracting the real-time power spectral density value from the reference power spectral density value. The concentration-time derivative is obtained by calculating the time derivative of the impurity concentration signal; When the deposition retardation index is greater than the first threshold and the concentration-time derivative is greater than the second threshold, the first alternating command is output to the regulating valve to control the regulating valve to alternately increase and decrease the opening at a set frequency and a set amplitude. After the first alternating command is output for a set duration, a second step command is output to the regulating valve to control the regulating valve to reduce its opening to the set base opening and maintain it for a set duration. Extract the pressure time-series signal collected within a set time period and convert it into a frequency domain power spectrum value; The power spectrum value in the frequency domain is integrated over a set frequency band to obtain an integral value. When the integral value is less than a set reference threshold, a recovery command is output to control the regulating valve to return to its initial opening degree before receiving the first alternating command.

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