Membrane separation nitrogen production plant control method

Abstract

The application provides a membrane separation nitrogen production equipment control method. The method introduces adsorption memory risk level judgment, conditional purging, first compliance anti-rebound verification and gas supply delay release control mechanism during the start-up of the membrane separation nitrogen production equipment, so that the product gas does not immediately enter the user gas supply channel after first reaching the oxygen content threshold, but continues to maintain the emptying or recycling state, and the oxygen content peak, change rate, cumulative empty air volume and water desorption state are comprehensively verified, thereby effectively identifying and filtering the oxygen content rebound process that may occur during the start-up stage. Further, it can avoid misjudging the local low-oxygen valley value in the start-up stage as a stable qualified state, reduce the risk of the first batch of oxygen-containing nitrogen entering the user system, improve the gas supply reliability of the membrane separation nitrogen production equipment under complex working conditions such as high humidity, long downtime, low temperature membrane shell and intermittent operation, and reduce gas waste and offline reinspection frequency caused by excessive fixed purging.

Description

Technical Field

[0001] This application relates to data processing technology, and more particularly to a control method for a membrane separation nitrogen generation device. Background Technology

[0002] Membrane separation nitrogen generators typically utilize hollow fiber membranes to selectively separate oxygen and nitrogen from the air to obtain product nitrogen that meets process requirements. They are now widely used in food packaging, lithium battery material protection, pharmaceutical packaging, grain inerting, and powder explosion protection.

[0003] Existing membrane separation nitrogen generation equipment typically adopts a control method of supplying gas immediately after the oxygen content reaches a set threshold during startup. That is, after the equipment starts up, the oxygen content of the product gas is detected by an oxygen analyzer. When the oxygen content is lower than the target upper limit and maintained for a preset time, the product gas is controlled to enter the user's gas supply system.

[0004] However, existing technologies typically assume that the oxygen content of membrane separation nitrogen generators decreases monotonically during the start-up phase. They lack identification and control mechanisms for issues such as wet memory within the membrane module, residual gas retention, and dynamic separation performance drift after prolonged shutdowns. Therefore, under cold start or long-term shutdown and restart conditions, the oxygen content of the product gas may briefly meet the standard before rebounding and exceeding the limit again, resulting in substandard nitrogen entering the user's end. Summary of the Invention

[0005] This application provides a control method for a membrane separation nitrogen generator, which can identify the adsorption memory state of the membrane module, suppress oxygen content rebound, and accurately determine the timing of gas supply during the start-up phase.

[0006] This application provides a control method for a membrane separation nitrogen generator. By acquiring parameters such as shutdown duration, inlet dew point, membrane shell temperature, ambient dew point, and shutdown sealing status, the method classifies the risk of wet adsorption memory formed during membrane module shutdown. Based on different risk levels, it controls the exhaust air volume, purging time, product gas recovery rate, and membrane shell temperature adjustment during the purging process to gradually release adsorbed moisture and retained oxygen inside the membrane module and reduce the impact of wet plasticization of the membrane material. After the oxygen content of the product gas first falls below the release threshold, the controller continues to keep the user gas supply channel closed and continuously monitors the peak oxygen content and change rate within the verification window. Alternatively, it actively induces potential oxygen rebound by applying disturbances to product flow rate, product back pressure, and inlet pressure to confirm whether the membrane module has returned to a stable separation state. At the same time, it judges whether the dead cavity on the product side and the water decomposition and adsorption front in the membrane have been replaced by combining the cumulative exhaust air volume and dew point change trend. Only after confirming that the oxygen content of the product gas will not rebound beyond the limit again is the product gas allowed to enter the user gas supply channel, thereby effectively suppressing the dynamic purity risk during the start-up phase. Attached Figure Description

[0007] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0008] Figure 1 This is a schematic flowchart illustrating a membrane separation nitrogen generator control method according to an example embodiment of this application;

[0009] Figure 2 This is a schematic flowchart illustrating a membrane separation nitrogen generator control method according to an example embodiment of this application;

[0010] Figure 3 This is a schematic flowchart of S400 according to an example embodiment of this application;

[0011] Figure 4 This is a schematic flowchart of S600 according to an example embodiment of this application.

[0012] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0013] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0014] Membrane separation nitrogen generation equipment typically utilizes hollow fiber polymer membranes to selectively separate oxygen, nitrogen, and water vapor from compressed air to obtain product nitrogen that meets process purity requirements. Existing membrane separation nitrogen generation systems generally include an air compressor, drying unit, filtration unit, membrane module, product gas pressure regulating structure, oxygen-enriched exhaust gas emission structure, and oxygen analysis and control system. Air, after compression and drying, enters the membrane module. Under the influence of the partial pressure difference across the membrane, rapidly permeating components such as oxygen, water vapor, and carbon dioxide preferentially permeate through the membrane wall, while nitrogen, as a relatively slow-permeating component, accumulates on the stagnant side of the membrane module, thus forming product nitrogen.

[0015] Membrane separation processes typically follow the "dissolution-diffusion" mechanism in polymer membrane gas separation, for gaseous components. Its permeation flux through the membrane can be expressed as:

[0016]

[0017] in: Indicates components Through flux; Indicates components The permeability coefficient; Indicates the effective thickness of the membrane; Indicates the partial pressure of components on the inlet side of the membrane; This indicates the partial pressure of the components on the membrane permeate side.

[0018] Furthermore, the permeability coefficient It is usually determined by both the diffusion coefficient and the solubility coefficient, that is:

[0019]

[0020] in: Indicates components Diffusion coefficient in membrane materials; Indicates components Solubility coefficient in membrane materials.

[0021] Because oxygen, water vapor, and carbon dioxide diffuse at higher rates and dissolve at higher rates than nitrogen in most polymer membranes, these components typically exhibit higher permeation rates. The ability of a membrane module to separate oxygen and nitrogen is usually expressed using an oxygen-nitrogen selectivity parameter.

[0022]

[0023] in: Indicates oxygen and nitrogen osmotic selectivity; Indicates the oxygen permeability coefficient; This represents the nitrogen permeability coefficient.

[0024] Under steady-state, dry, and continuous operating conditions, the internal temperature and humidity of the membrane module remain relatively stable, and the oxygen-nitrogen selectivity varies little. Therefore, the oxygen content in the product gas typically decreases gradually with increasing purging time and eventually stabilizes. Based on this operating principle, existing membrane separation nitrogen generation equipment generally adopts the following control logic:

[0025] (1) Equipment startup;

[0026] (2) Establish the inlet pressure of the membrane module;

[0027] (3) Detect the oxygen content of the product;

[0028] (4) When the oxygen content is lower than the set threshold and remains so for a preset time, open the gas supply valve;

[0029] (5) Supply gas to users.

[0030] However, existing control logic typically assumes that the oxygen content change during the membrane module startup phase is a monotonically decreasing process, i.e., the default is:

[0031]

[0032] in: Indicates the oxygen content of the product; This indicates the rate of change in oxygen content.

[0033] In other words, existing technologies generally assume that when the oxygen content of the product gas is already below the process limit at a certain moment, the oxygen content will not increase significantly again in the future.

[0034] However, in practice, long-term engineering experience has shown that under conditions of cold start, long shutdown and restart, high humidity, or low temperature of the membrane housing, the oxygen content in the product does not necessarily show a monotonically decreasing trend, but may instead exhibit the following:

[0035]

[0036] Then it was satisfied again:

[0037]

[0038] in: Indicates the upper limit of the oxygen content allowed by the process; Indicates the moment when the target was first achieved; This indicates the moment when oxygen rebounds.

[0039] This means that the oxygen content of the product exhibits a non-monotonic dynamic change phenomenon, where "after initially meeting the standard, it rebounds and exceeds the limit again."

[0040] Since existing control systems typically only supply gas based on the initial compliance status, under the above conditions, the local low oxygen trough during the startup phase may be misjudged as a stable gas supply state, leading to excess oxygen entering the user system during the subsequent rebound phase. This can affect process safety in scenarios such as food packaging, lithium battery material protection, pharmaceutical encapsulation, and inerting explosion protection.

[0041] It is worth noting that further research has revealed that the technical problem of oxygen content initially reaching the target and then rebounding is not due to insufficient steady-state separation performance of the membrane module, but mainly due to the wet adsorption memory effect, gas retention effect, and dynamic selective drift effect formed during the shutdown of the membrane module.

[0042] Specifically, during long-term shutdown, the hollow fiber membrane module is not in the ideal state of "completely dry and completely reset", but retains the temperature and humidity history and residual gas state formed in the previous operating cycle.

[0043] On the one hand, when the equipment is shut down, humid air, oxygen, and some nitrogen from the product may remain inside the membrane module. This is especially true under the following conditions: high inlet dew point; dew point rises after the dryer stops operating; membrane shell temperature is lower than the ambient dew point; equipment is stored in a high-humidity environment for a long time; and drying, sealing, and purging are not performed on the product side or the exhaust gas side.

[0044] Water vapor readily adsorbs and can even condense locally on membrane surfaces, in free volume regions, in end-capped structures, and in dead cavities within pipelines. For water vapor, the dew point and condensation conditions typically satisfy the following relationship:

[0045]

[0046] in: Indicates the temperature of the membrane housing; Indicates the ambient air dew point.

[0047] When the temperature of the membrane housing is lower than the ambient dew point, water vapor in the air will condense and adhere to the surface of the internal structure of the membrane module.

[0048] On the other hand, polymer membrane materials contain a large number of nanoscale free volume structures. When water molecules enter the membrane material, they alter the polymer chain segment spacing and local free volume distribution, leading to a short-term plasticization effect. After plasticization, both the diffusion coefficient and solubility coefficient of the membrane material change, i.e.:

[0049]

[0050]

[0051] This further leads to:

[0052]

[0053] Because oxygen and nitrogen are affected by humidity to different degrees, the oxygen and nitrogen selectivity of the membrane module will drift:

[0054]

[0055] in: Indicates wet transient selectivity; This indicates dry-state steady-state selectivity.

[0056] The drift process is not an instantaneous recovery, but has a certain time constant:

[0057]

[0058] in: Indicates time Dynamic selectivity; Indicates wet selectivity during the initial startup phase; Indicates steady-state and dry-state selectivity; This represents the wet recovery time constant of the membrane material.

[0059] Therefore, in the initial stage of equipment startup, even with the same air intake conditions, the actual separation performance of the membrane module will still deviate from the steady-state characteristics at the factory calibration.

[0060] Furthermore, during shutdown, oxygen can diffuse, leak, and exchange with the environment into the product-side piping, sampling piping, and detection chamber, creating a residual high-oxygen gas area. Meanwhile, the oxygen analyzer itself also experiences sampling delays.

[0061] The oxygen content actually measured by an oxygen analyzer typically meets the following requirements:

[0062]

[0063] in: Indicates the detected value; Indicates the actual oxygen content; This indicates a delay in the sampling system.

[0064] This delay time can be further approximated as:

[0065]

[0066] in: Indicates the volume of the sampling pipeline and the detection chamber; This represents the sampling flow rate.

[0067] Therefore, in the initial startup phase, the oxygen content data actually received by the controller may correspond to the gas state several seconds or even tens of seconds ago.

[0068] Under the combined influence of the above factors, the change in oxygen content during the start-up process of a membrane nitrogen generator typically exhibits the following dynamic process:

[0069] In the first stage, residual low oxygen gas on the product side and sampling delay caused the oxygen analyzer to show that the oxygen content had reached the standard in a short time.

[0070] In the second stage, as compressed air continues to enter the membrane module, the moisture and oxygen adsorbed in the membrane material are gradually desorbed, and the selective transient drift of the membrane material causes the oxygen content of the product gas to increase again.

[0071] In the third stage, after continuous drying and purging, the internal wet state of the membrane module is gradually eliminated, the membrane material regains stable dry selectivity, and the oxygen content of the product gas decreases again and tends to stabilize.

[0072] Therefore, the actual oxygen content curve of the product exhibits a non-monotonic change process with local minima and subsequent rebound peaks, rather than the monotonically decreasing process assumed by traditional control logic. Existing technologies lack identification and control mechanisms for the membrane module's wet adsorption memory, water decomposition and adsorption state, and dynamic rebound process, making it difficult to accurately determine the true stable gas supply timing.

[0073] To address the aforementioned issues, the embodiments provided in this application propose a control mechanism for dynamic risks during the start-up phase of a membrane separation nitrogen generator. This control mechanism does not simply extend the purging time, but rather establishes a dynamic judgment model around the recovery process of the internal state of the membrane module, thereby enabling proactive identification and control of the oxygen content rebound problem after the initial achievement of standards.

[0074] Unlike existing technologies that rely solely on instantaneous oxygen content thresholds for gas supply determination, this application treats the membrane module startup process as a non-steady-state recovery process that evolves over time, and uses changes in oxygen content, the degree of wet recovery, the degree of gas replacement, and disturbance stability as the criteria for gas supply determination.

[0075] Because membrane modules develop varying degrees of wet adsorption during shutdown, the startup risk differs depending on the shutdown conditions. Research has revealed a coupling relationship between the amount of water adsorbed inside the membrane module and shutdown time, ambient humidity, and dew point conditions. This is combined with the aforementioned moisture adsorption model:

[0076]

[0077] It can be known that: when the downtime As the pressure increases, the amount of water adsorbed inside the membrane module increases; when the ambient water vapor partial pressure... As the pressure increases, the adsorption driving force increases; when the membrane material reaches equilibrium water vapor partial pressure... At lower levels, wet accumulation is more likely to occur.

[0078] Therefore, this application does not adopt a uniform fixed start-up strategy, but instead generates a corresponding adsorption memory risk level based on one or more parameters among shutdown duration, ambient dew point, inlet dew point, membrane housing temperature, and product-side residual pressure. Its technical essence lies in using externally detectable parameters to reflect the unobservable wet-state history within the membrane module. This mechanism can solve the following technical problems:

[0079] Traditional equipment cannot distinguish between slightly damp conditions after a short-term shutdown and severely damp conditions after a long-term high-humidity shutdown, which leads to premature gas supply in some operating conditions due to the fixed purging strategy.

[0080] By establishing a risk level mechanism, the recovery process can be dynamically adjusted based on different wetland risks, thereby reducing the probability of oxygen content rebound.

[0081] Furthermore, existing technologies typically employ a fixed-time purging method:

[0082]

[0083] That is, the gas supply is only allowed based on a preset time.

[0084] However, based on the aforementioned wet recovery model:

[0085]

[0086] It can be seen that the residual moisture level inside the membrane module is not only related to time, but also to the initial adsorbed water content. ; sweeping flow Desorption coefficient Directly related.

[0087] Therefore, even if the purging time is the same:

[0088]

[0089] It may still exist under different working conditions:

[0090]

[0091] in: This indicates the safe residual moisture level when a stable gas supply is allowed.

[0092] This means that purging at fixed intervals cannot guarantee that the membrane module will truly return to a stable state.

[0093] Based on the above mechanism, this application constrains the degree of gas replacement by accumulating the amount of vented air:

[0094]

[0095] in: Indicates the cumulative amount of air discharged; Indicates the dead cavity volume on the membrane module and product side; Indicates the safety permutation factor.

[0096] Its technical significance lies in using the actual amount of gas replacement completed, rather than simply the time parameter, to determine whether the residual high-oxygen gas and humid air inside the system have been fully discharged.

[0097] Therefore, the embodiments of this application can avoid the problem of incorrectly opening the gas supply simply because a fixed purging time has been reached under low purging flow or high humidity shutdown conditions.

[0098] Furthermore, the aforementioned analysis has shown that the product's oxygen content curve is not a stable, monotonically decreasing curve, but may exhibit the following:

[0099]

[0100] Subsequently:

[0101]

[0102] Therefore, achieving the standard for the first time does not equate to consistently achieving it.

[0103] Further research revealed that local low-oxygen troughs during the start-up phase typically originate from: residual low-oxygen nitrogen on the product side; sampling system delays; local transient pressure equilibrium; and incomplete release of wet desorption.

[0104] Especially when sampling delay exists:

[0105]

[0106] Therefore, the oxygen content signal received by the controller is delayed.

[0107] In this case, even if the detection value meets the following requirements: The actual oxygen content may continue to change.

[0108] Based on the above mechanism, this embodiment does not immediately supply gas after the initial compliance, but continues to perform anti-rebound verification. Further testing is conducted during the verification process:

[0109]

[0110] in: This represents the threshold for the allowable rate of change in oxygen content.

[0111] Its technical significance lies in the fact that it not only detects the oxygen content value itself, but also whether the oxygen content has entered a stable convergence state. Furthermore, the embodiments of this application also incorporate: Limit the peak oxygen content during the validation phase.

[0112] Therefore, even if there are localized rebound peaks, they can be identified and blocked before the formal gas supply. This mechanism can solve the technical problem that traditional systems easily misjudge instantaneous low oxygen levels as a stable state, leading to subsequent rebound oxygen entering the user end.

[0113] Furthermore, research revealed that even if the membrane module has stabilized during the static purging phase, the system may still experience new oxygen content fluctuations due to load changes after the gas supply valve is opened. This is because the oxygen content of the product gas is related to the product flow rate. Transmembrane pressure difference and the dynamic selectivity of membrane modules There is a coupling relationship:

[0114]

[0115] When the user's gas supply valve is suddenly opened: the product flow rate changes abruptly; the product side back pressure is redistributed; the transmembrane pressure difference changes; and consequently, the gas transmission state inside the membrane module is readjusted.

[0116] Therefore, even if the oxygen content is within acceptable limits during the static testing phase, fluctuations in oxygen content may still occur during the actual gas supply.

[0117] Based on the above mechanism, this application actively applies the following to the user's gas supply channel before formally connecting the gas supply channel: flow disturbance; pressure disturbance; back pressure disturbance; and continues to maintain product gas venting or isolation during the disturbance phase.

[0118] Its essence lies in: exposing potential dynamic rebound risks in advance without supplying gas to users.

[0119] If the condition is still met after the perturbation: This indicates that the membrane module has entered a truly stable operating state.

[0120] Therefore, the embodiments of this application can avoid the problem of direct gas supply in the case of static compliance but dynamic instability in the prior art.

[0121] In summary, this application's embodiments introduce adsorption memory risk level determination, conditional purging, anti-rebound verification after initial compliance, and delayed gas release control mechanisms during the startup process of the membrane separation nitrogen generator. This ensures that the product gas does not immediately enter the user's gas supply channel after initially reaching the oxygen content threshold, but continues to be vented or recovered. Furthermore, it comprehensively verifies the peak oxygen content, rate of change, cumulative vented air volume, and water decomposition and adsorption status, effectively identifying and filtering potential oxygen content rebound processes during startup. This technical solution avoids misjudging localized low-oxygen troughs during startup as stable and qualified states, reducing the risk of the first batch of oxygen-exceeding nitrogen entering the user's system. It also improves the gas supply reliability of the membrane separation nitrogen generator under complex operating conditions such as high humidity, long shutdowns, low-temperature membrane housings, and intermittent operation, while reducing gas waste caused by excessive fixed purging and the frequency of offline re-inspection. Ultimately, this improves the safety and purity stability of gas supply in food packaging, lithium battery material protection, pharmaceutical packaging, and inerting explosion-proof scenarios.

[0122] Figure 1 This is a schematic diagram illustrating an application scenario of the membrane separation nitrogen generator control method according to an example embodiment of this application. For example... Figure 1As shown, the membrane separation nitrogen generation equipment control method provided in this application is applied to pipelines including membrane modules, inlet pipelines, product gas main pipelines, oxygen-enriched waste gas pipelines, product gas three-way valves, venting channels, recovery channels, user gas supply channels, initial gas buffer tanks, membrane housing heating units, product gas back pressure regulating valves, oxygen analyzers, dew point sensors, pressure sensors, flow sensors, memory, and processors.

[0123] The system includes an inlet pipe connected to the inlet end of the membrane module for supplying dry compressed air. The membrane module includes a product gas outlet and an oxygen-enriched exhaust gas outlet, which is connected to the external environment via an oxygen-enriched exhaust gas pipe. The product gas outlet is connected to a product gas three-way valve via a main product gas pipe. This three-way valve is connected to the user's gas supply channel, an venting channel, and a recovery channel, allowing the processor to control the product gas to enter either the venting or recovery channel during startup and to control it to enter the user's gas supply channel once the supply conditions are met. The recovery channel is connected to the first-phase gas buffer tank for oxygen content detection. An oxygen analyzer is installed on the main product gas pipe to obtain the oxygen content of the product gas. A dew point sensor is installed at least one of the inlet pipe, the main product gas pipe, and the oxygen-enriched exhaust gas pipe to obtain the inlet dew point, the product gas side dew point, and / or the oxygen-enriched exhaust gas side dew point. A pressure sensor is installed on the inlet pipe and / or the main product gas pipe to obtain the inlet pressure and / or the product gas pressure. A flow sensor is installed on the main product gas line to obtain the product gas flow rate. A product gas back pressure regulating valve is installed on the main product gas line, located between the membrane module and the product gas three-way valve, to regulate the product gas back pressure. A membrane housing heating unit is located on the outside of the membrane module to regulate the membrane housing temperature.

[0124] It is worth noting that the above Figure 1 The piping shown only illustrates a portion of the piping structure for implementing the method in the embodiments of this application. For connection parts not shown, connections can be made via pipes. Furthermore, the above... Figure 1 This is merely an illustrative diagram. In practical applications, the positions of various components and pipe connections can be adapted based on this diagram.

[0125] The processor is electrically connected to the product gas three-way valve, oxygen analyzer, dew point sensor, pressure sensor, flow sensor, initial gas buffer tank, membrane housing heating unit, and product gas back pressure regulating valve. A memory coupled to the processor stores the control program, enabling the processor to execute the membrane separation nitrogen generator control method provided in this application embodiment.

[0126] Figure 2 This is a schematic flowchart illustrating a membrane separation nitrogen generator control method according to an example embodiment of this application. Figure 2 As shown, the method provided in this embodiment includes:

[0127] S100: After the control membrane separation nitrogen generator enters the start-up state, disconnect the product gas outlet from the user's gas supply channel and allow the product gas to enter the venting channel or recovery channel.

[0128] After receiving the start command, the controller of the membrane nitrogen generator first reads the status of the switching valve at the product gas outlet and the status of the corresponding gas supply valve in the user gas supply channel. If the user gas supply channel is in the open state, the controller outputs a valve closing control signal to close the user gas supply valve, thereby cutting off the connection between the product gas and the user gas supply channel. Simultaneously, the controller controls the three-way switching valve on the product gas outlet side to switch to either the venting channel side or the recovery channel side, ensuring that the initial product gas generated by the membrane module does not enter the user gas supply channel, but instead flows to the venting or recovery pipeline. During the switching process, the controller continuously acquires the product gas outlet pressure and the user gas supply channel pressure, and keeps the user gas supply valve closed if the product gas outlet pressure is lower than the user gas supply channel pressure, to prevent backflow of gas from the user side into the membrane module.

[0129] When product gas enters the venting channel, the controller opens the venting valve and controls the venting regulating valve to maintain the venting flow rate, ensuring continuous discharge of product gas. During venting, the controller continuously monitors the oxygen content of the product gas and maintains the venting state until the oxygen content reaches the subsequent verification conditions, so that residual high-oxygen gas inside the membrane module and gases trapped during shutdown are gradually discharged.

[0130] When the product gas enters the recovery channel, the controller activates the recovery switching valve, allowing the product gas to enter the first-stage gas buffer tank. After entering the first-stage gas buffer tank, the product gas undergoes pressure stabilization through the buffer volume, and its oxygen content is continuously monitored by an oxygen analyzer installed on the first-stage gas buffer tank. During the recovery process, the controller keeps the user's gas supply channel closed, isolating the product gas, which has not yet been confirmed to be stable during the startup phase, from the user's gas supply system.

[0131] Specifically, the controller opens the recovery switching valve located between the product gas outlet and the first-stage gas buffer tank, and also opens the inlet valve of the first-stage gas buffer tank, allowing the product gas to enter the first-stage gas buffer tank via the recovery channel. Upon entering the buffer tank, the product gas first undergoes pressure equalization within the buffer volume to reduce the impact of product gas flow fluctuations during membrane module startup on oxygen content detection results. During the product gas entry process, the controller continuously monitors the pressure inside the first-stage gas buffer tank and closes the recovery switching valve when the buffer tank pressure reaches the upper limit of the allowable pressure to prevent overpressure in the buffer tank.

[0132] An oxygen analyzer installed on the initial gas buffer tank continuously samples and detects the gas inside the tank. The controller acquires the oxygen content signal output by the oxygen analyzer and simultaneously acquires the corresponding sampling flow rate and sampling pressure. When the sampling flow rate reaches the detection flow rate condition and the sampling pressure is within the allowable detection range, the controller determines the corresponding oxygen content signal as valid oxygen content data; when the sampling flow rate is insufficient or the sampling pressure is abnormal, the controller maintains the current recovery state and prohibits subsequent gas release operations.

[0133] The controller continuously compares the oxygen content in the initial gas buffer tank with the upper limit of the allowable oxygen content for auxiliary gas. When the oxygen content in the initial gas buffer tank is lower than the upper limit of the allowable oxygen content for auxiliary gas, and the corresponding oxygen content does not show an upward trend during the continuous monitoring period, the controller controls the auxiliary gas supply valve to open and controls the outlet valve of the initial gas buffer tank to open, connecting the initial gas buffer tank with the auxiliary gas branch. The auxiliary gas branch can be a purge branch for equipment, a low-level protective gas branch, or a non-critical process gas branch, thereby realizing the graded utilization of product gas during the start-up phase.

[0134] When the controller detects that the oxygen content in the first batch of gas buffer tanks exceeds the upper limit of the allowable oxygen content for auxiliary gas, the controller keeps the auxiliary gas supply valve closed and controls the buffer tank vent valve to open, allowing gas inside the buffer tank to enter the vent pipeline. During the venting process, the controller continuously monitors the buffer tank pressure and closes the vent valve once the pressure drops to the venting completion pressure. Subsequently, the controller continues to control the subsequent product gas to enter the first batch of gas buffer tanks to re-execute oxygen content detection and gas diversion control.

[0135] S200: Obtain the shutdown status parameters of the membrane separation nitrogen generator.

[0136] During the shutdown period of the membrane separation nitrogen generator, the controller continuously records the shutdown time corresponding to the equipment stopping operation, and reads the current time when the equipment receives a restart command. The controller determines the shutdown duration based on the time difference between the current time and the shutdown time, and stores the shutdown duration as a shutdown status parameter.

[0137] Before the membrane separation nitrogen generator is shut down, the controller acquires the inlet dew point signal from the dew point meter installed on the inlet pipeline and determines the last stable inlet dew point collected before shutdown as the pre-shutdown dew point. Stable collection includes situations where the dew point variation is within the allowable fluctuation range during continuous collection cycles, to avoid distortion of shutdown status parameters due to instantaneous fluctuations.

[0138] The controller acquires the oxygen content signal of the product gas output from the oxygen analyzer at the product gas outlet and records the last effective oxygen content data before shutdown as the product gas oxygen content before shutdown. Simultaneously, the controller acquires the sampling flow rate and sampling pressure corresponding to the oxygen analyzer, and determines the corresponding oxygen content data as the effective oxygen content data when the sampling flow rate reaches the detection flow rate condition and the sampling pressure is within the allowable detection range.

[0139] After the membrane nitrogen generator is shut down, the controller receives the output signal from the temperature sensor located on the outer wall or inside the membrane housing and determines the membrane housing temperature based on the sensor output signal. During the shutdown period, the controller continuously records the membrane housing temperature changes at time intervals to reflect the risk of condensation inside the membrane module and changes in the moisture adsorption state.

[0140] The controller acquires the output signal from the pressure sensor installed on the gas-side pipeline of the product and determines the residual pressure on the product side based on the pressure sensor output signal. When the residual pressure on the product side is higher than the ambient pressure, the controller determines that there is still residual gas trapped on the product side and records the corresponding pressure value as a shutdown status parameter.

[0141] The controller acquires the output signal from the environmental dew point detection device located in the equipment installation environment and determines the environmental dew point based on the output signal. When the environmental dew point is close to or higher than the membrane housing temperature, the controller determines that there is a risk of external condensation on the membrane module and records the corresponding environmental dew point data.

[0142] During the shutdown process of the membrane separation nitrogen generator, the controller acquires the valve action records and purging control records corresponding to the shutdown procedure. Based on these records, the controller determines whether a drying and sealing purging was performed before shutdown. If the shutdown procedure includes a record of dry gas being introduced into the membrane module and the venting channel remaining open, the controller determines that a drying and sealing purging has been performed.

[0143] After the membrane separation nitrogen generator restarts, the controller reads the historical operating records corresponding to the previous startup process and determines whether an oxygen content rebound occurred during the previous startup based on the oxygen content change curve in the historical operating records. When the oxygen content of the product gas rises again after initially falling below the release threshold and exceeds the upper limit of oxygen content, the controller determines that an oxygen content rebound occurred during the previous startup process.

[0144] S300. Determine the adsorption memory risk level of the membrane module based on the shutdown status parameters.

[0145] After the membrane separation nitrogen generator receives a restart command, the controller reads the shutdown time from the equipment shutdown record and obtains the current system time. The controller determines the shutdown duration based on the time difference between the current system time and the shutdown time. The shutdown duration is recorded in minutes or hours to characterize the duration during which the membrane module is in a static state.

[0146] After the membrane separation nitrogen generator enters the start-up preparation stage, the controller acquires the output signal from the dew point meter located on the main intake pipe and determines the current intake dew point based on the output signal. To avoid the impact of instantaneous fluctuations in compressed air on the detection results, the controller continuously acquires dew point data over multiple sampling cycles. If the dew point fluctuation amplitude over multiple consecutive sampling cycles is less than the allowable fluctuation range, the corresponding dew point value is determined as the current intake dew point.

[0147] The controller acquires the output signal from the temperature sensor located on the outer wall or inside the membrane housing, and determines the current membrane housing temperature based on the output signal. Specifically, the controller continuously acquires membrane housing temperature data according to a sampling period, and if the temperature change is less than the allowable fluctuation range within multiple consecutive sampling periods, the corresponding temperature value is determined as the current membrane housing temperature.

[0148] The controller calculates the temperature difference between the current membrane housing temperature and the current inlet dew point, and defines this temperature difference as the temperature margin. A decrease in the temperature margin indicates an increased likelihood of condensation or enhanced moisture adsorption inside the membrane module.

[0149] After obtaining the downtime and temperature margin, the controller determines the adsorption memory risk level based on the risk conditions corresponding to the downtime and temperature margin ranges. Specifically, the longer the downtime and the smaller the temperature margin, the higher the corresponding adsorption memory risk level.

[0150] When the downtime is less than the first duration range and the temperature margin is greater than the first temperature range, the controller determines the adsorption memory risk level to be low, indicating that there is less residual moisture inside the membrane module and the oxygen content stabilizes quickly after startup.

[0151] When the downtime is within the second duration range and the temperature margin is within the second temperature range, the controller determines the adsorption memory risk level to be medium risk, indicating that there is some residual adsorption of moisture inside the membrane module, and short-term fluctuations in oxygen content may occur during startup.

[0152] When the downtime exceeds the third duration range and the temperature margin is less than the third temperature range, the controller determines the adsorption memory risk level to be high, indicating that there is significant wet adsorption residue inside the membrane module, and oxygen content rebound is likely to occur during the startup phase.

[0153] When the current inlet dew point is higher than the current membrane housing temperature, or the temperature margin is less than the condensation temperature difference range, the controller determines the adsorption memory risk level to be the condensation risk level, indicating that there are conditions for condensation formation inside the membrane module, and it is necessary to extend the purging time and restrict the release of product gas.

[0154] S400, Under the start-up control conditions corresponding to the adsorption memory risk level, perform conditional purging on the membrane module.

[0155] It is worth noting that during shutdown of membrane separation nitrogen generation equipment, significant wet adsorption and accumulation occur inside the membrane module. Because hollow fiber membrane materials have a strong adsorption capacity for water molecules, when the internal pressure of the membrane module decreases, the temperature drops, or the ambient humidity increases after shutdown, some moisture will form an adsorption layer or even a localized condensate film on the surface of the membrane fibers and in the microporous areas. This adsorption layer alters the diffusion channels and permeation rates of oxygen and nitrogen in the membrane material, causing the membrane module to exhibit unstable separation characteristics in the initial restart phase.

[0156] Furthermore, during the start-up phase, after the dry compressed air enters the membrane module, the adsorbed moisture is not instantly desorbed, but rather forms a water desorption front that gradually moves along the length of the membrane module. During this desorption process, the oxygen and nitrogen permeability varies across different regions of the membrane module, resulting in a time lag effect and dynamic rebound in the oxygen content of the product gas. Especially when the membrane shell temperature is close to or below the inlet dew point, condensation zones are more likely to form inside the membrane module, further reducing local gas separation selectivity and creating short-term high-oxygen permeation channels within the membrane module. Therefore, relying solely on a fixed purging time or a single oxygen content threshold to determine the timing of air supply cannot accurately reflect whether the membrane module has returned to a stable selectivity state.

[0157] Furthermore, residual gases inside the membrane module, dead spaces on the product side, and humid gases accumulated during shutdown are gradually released during the startup phase. When the purge flow rate, exhaust air volume, or purge duration is insufficient, residual high-oxygen gases inside the membrane module cannot be fully replaced, causing the oxygen content in the product gas to rise again after initially meeting the standard. Therefore, the membrane module startup process is essentially a non-steady-state mass transfer recovery process with wet adsorption memory, dynamic desorption migration, and temperature-dew point coupled condensation characteristics.

[0158] In response, Figure 3 This is a schematic flowchart of S400 according to an example embodiment of this application. Figure 3 As shown, the above S400 includes:

[0159] S410, Control the intake of dry compressed air into the membrane module.

[0160] After the membrane nitrogen generator enters the start-up phase, the controller controls the air compressor to operate and opens the intake solenoid valve on the main intake pipe, allowing compressed air to pass sequentially through the refrigerated dryer, adsorption dryer, and precision filter before entering the membrane module. The controller acquires the output signals from the pressure sensor and dew point meter on the main intake pipe and determines whether the compressed air entering the membrane module meets the start-up purging conditions based on the corresponding detection results. When the intake pressure reaches the start-up pressure range and the intake dew point is lower than the allowable dew point range, the controller maintains the intake solenoid valve open to continuously supply dry compressed air to the membrane module.

[0161] S420. With the product gas outlet disconnected from the user's gas supply channel, allow the product gas to enter the venting channel or the recovery channel.

[0162] After the membrane module begins producing gas, the controller keeps the gas supply shut-off valve on the user's gas supply channel closed and opens either the vent control valve on the vent channel or the recovery switching valve on the recovery channel, allowing the product gas output from the membrane module to enter the vent or recovery channel. Specifically, when the oxygen content of the product gas is higher than the release threshold, the controller keeps the gas supply shut-off valve closed to prevent fluctuating oxygen levels during startup from entering the user's gas system.

[0163] S430. Based on the adsorption memory risk level, adjust at least one of the following: product gas venting flow rate, product gas recovery rate, cumulative venting volume, and purging duration.

[0164] Based on the determined adsorption memory risk level, the controller adjusts the openings of the vent control valve, the recovery switching valve, and the inlet regulating valve. When the adsorption memory risk level increases, the controller increases the opening of the vent control valve to increase the product gas venting flow rate and decrease the product gas recovery rate, thereby increasing the gas replacement rate inside the membrane module. Simultaneously, the controller extends the purging duration and increases the control requirements corresponding to the cumulative venting air volume to enhance the removal of residual oxygen and adsorbed moisture inside the membrane module.

[0165] When the adsorption memory risk level is low, the controller controls the product gas to enter the venting channel or recovery channel at a lower venting flow rate, and enters the anti-rebound verification stage after the cumulative venting air volume reaches the lower replacement requirement.

[0166] When the adsorption memory risk level is medium risk, the controller increases the product gas venting flow rate and extends the purging duration to improve the gas renewal efficiency of the dead cavity area inside the membrane module.

[0167] When the adsorption memory risk level is high or the condensation risk level, the controller controls the product gas to maintain a high venting flow rate and limits the proportion of product gas entering the recovery channel. At the same time, it continuously performs high-flow purging to accelerate the decomposition of adsorbed water inside the membrane module and the discharge of residual oxygen.

[0168] S440, obtain membrane housing temperature and inlet dew point.

[0169] The controller acquires the output signal from the temperature sensor located on the outer wall of the membrane housing and determines the membrane housing temperature based on the output signal. Simultaneously, the controller acquires the output signal from the dew point meter located on the main intake air line and determines the intake dew point based on the output signal. To reduce the impact of instantaneous fluctuations, the controller continuously acquires temperature and dew point data over multiple sampling periods, and when the corresponding data changes are within acceptable limits, uses the corresponding detection results as the current membrane housing temperature and the current intake dew point.

[0170] S450: Control the operation of the diaphragm heating unit based on the temperature margin between the diaphragm temperature and the inlet dew point.

[0171] The controller calculates the difference between the membrane housing temperature and the inlet dew point, defining this difference as the temperature margin. When the temperature margin decreases to the condensation risk range, the controller activates the membrane housing heating unit to heat the outer wall of the membrane module. As the membrane housing temperature rises, the controller continuously acquires the membrane housing temperature and inlet dew point, adjusting the operating status of the membrane housing heating unit based on the corresponding changes to improve the temperature margin and reduce the probability of condensation formation inside the membrane module.

[0172] S460. After the temperature margin reaches the preset value, continue to perform conditional purging.

[0173] Once the temperature margin reaches the condensation relief range, the controller continues to control the intake of dry compressed air into the membrane module and maintains the vent control valve open to continuously perform conditional purging. During this process, the controller continuously acquires the product gas oxygen content, membrane shell temperature, and inlet dew point. After the product gas oxygen content meets the release conditions and the oxygen content change tends to stabilize, the anti-rebound verification stage begins.

[0174] pass Figure 3 The embodiment shown treats the start-up phase of the membrane separation nitrogen generator as a dynamic recovery process of the membrane module's separation selectivity, and performs graded conditional control of the start-up purging process based on the wet adsorption state, temperature state, and residual gas state of the membrane module after shutdown.

[0175] Specifically, when the membrane module is shut down, a transient low-selectivity region forms inside due to moisture adsorption and localized condensation. During startup, dry compressed air enters the membrane module and, under the influence of the pressure gradient, gradually desorbs the adsorbed moisture, forming a water desorption front moving along the airflow direction. As purging continues, the thickness of the adsorbed layer inside the membrane material gradually decreases, and the diffusion coefficients of oxygen and nitrogen in the membrane material gradually return to stability, thereby gradually restoring the overall separation selectivity of the membrane module to normal.

[0176] Figure 3 The illustrated embodiment dynamically adjusts the venting flow rate, recovery ratio, and purging duration based on the adsorption memory risk level to improve the gas replacement rate and wet zone removal efficiency inside the membrane module, enabling the water decomposition adsorption front to pass through the key mass transfer region inside the membrane module more quickly. Simultaneously, by controlling the membrane housing heating unit to increase the temperature margin between the membrane housing temperature and the inlet dew point, the probability of the membrane module reaching saturated condensation conditions can be reduced, thereby inhibiting the formation of new liquid water and preventing localized deterioration of the membrane material's permeability.

[0177] Under the combined effect of the above control mechanisms, the gas mass transfer state inside the membrane module gradually recovers from the unsteady wet transport state to the stable dry selective separation state, thereby achieving stable control of the product gas oxygen content during the start-up phase and reducing the risk of subsequent oxygen content rebound.

[0178] S500: During the conditional purging process, the oxygen content of the product gas is obtained.

[0179] During the conditional purging process of the membrane separation nitrogen generator, the controller continuously reads the detection signals from the sampling flow sensor and sampling pressure sensor located on the sampling branch of the oxygen analyzer to obtain the current sampling flow rate and sampling pressure of the oxygen analyzer. One end of the sampling branch is connected to the product gas pipeline, and the other end is connected to the detection inlet of the oxygen analyzer. The sampling branch is equipped with a sampling flow restrictor, a sampling shut-off valve, a sampling flow sensor, and a sampling pressure sensor. By synchronously acquiring the sampling flow rate and sampling pressure, it can be determined whether the current product gas is stably entering the internal detection chamber of the oxygen analyzer, and to avoid oxygen content detection distortion caused by sampling gas flow interruption, excessively low sampling pressure, or sampling flow fluctuations. In practice, the controller cyclically reads the data corresponding to the sampling flow sensor and sampling pressure sensor at time intervals, and stores the corresponding detection results in a time-correlated manner with the oxygen content detection data for subsequent validity assessment and delay compensation processing.

[0180] After acquiring the sampling flow rate and sampling pressure, the controller determines whether the sampling flow rate is within the stable sampling flow rate range corresponding to the oxygen analyzer, and whether the sampling pressure is within the stable operating pressure range corresponding to the oxygen analyzer. When the sampling flow rate is consistently lower than the minimum detection flow rate of the oxygen analyzer, the controller determines that the product gas has not effectively entered the detection chamber of the oxygen analyzer; when the sampling pressure is lower than the stable detection pressure of the oxygen analyzer, the controller determines that there is insufficient pressure in the detection gas path inside the oxygen analyzer; when the sampling flow rate fluctuates periodically or the sampling pressure pulsates, the controller determines that the oxygen analyzer is in an unstable detection state. If the sampling flow rate meets the stable flow rate condition and the sampling pressure meets the stable pressure condition, the controller determines that the oxygen analyzer is in an effective operating state and allows the corresponding oxygen content data to participate in subsequent anti-rebound verification processing. If the oxygen analyzer is not in an effective operating state, the controller keeps the user gas supply channel closed and continues to perform conditional purging.

[0181] Because the product gas needs a certain transmission time to flow from the membrane module outlet through the sampling branch and into the oxygen analyzer detection chamber, there is a time delay between the oxygen content signal output by the oxygen analyzer and the actual oxygen content at the membrane module outlet. To improve the accuracy of oxygen content rebound identification during the startup phase, the controller performs delay compensation processing on the oxygen content signal after the oxygen analyzer is in an effective working state. Specifically, the controller calculates the gas transmission time corresponding to the product gas entering the oxygen analyzer detection position from the product gas pipeline based on the sampling branch length, sampling branch inner diameter, sampling flow rate, and oxygen analyzer detection chamber volume. Subsequently, the controller backtracks and corrects the oxygen content detection time based on the gas transmission time to ensure that the oxygen content data output by the oxygen analyzer corresponds to the actual gas production time at the membrane module outlet. In practical implementation, the controller can also perform time series smoothing processing on continuously acquired oxygen content data to reduce the impact of sampling pulsations and transient flow fluctuations on the oxygen content change rate judgment results, thereby improving the accuracy of oxygen content stability judgment during the anti-rebound verification phase.

[0182] S600: After the oxygen content of the product gas falls below the release threshold for the first time, keep the user's gas supply channel closed and perform anti-rebound verification.

[0183] The fundamental reason for the oxygen content rebound during the startup phase of membrane separation nitrogen generators lies in the significant dynamic and unsteady mass transfer process within the membrane module. During shutdown, the membrane material and shell adsorb moisture, oxygen, and some residual gases. Upon restart, compressed air enters the membrane module, but the adsorbates on the membrane fiber surface and in the pores do not desorb instantly; instead, a desorption front forms over time. Due to the different permeation rates of oxygen, water vapor, and nitrogen in the membrane material, a localized selective temporary recovery occurs in the initial startup phase, causing the oxygen content in the product gas to drop briefly and reach the release threshold for the first time. However, as adsorbed moisture continues to desorb, the pressure field within the membrane redistributes, and residual oxygen-enriched gas in the dead cavity on the product side is re-entrained, the oxygen content at the membrane module outlet rises again, resulting in the oxygen content rebound phenomenon. Furthermore, existing control methods typically only collect oxygen content values ​​at a single moment, failing to identify trends and transient peak changes in oxygen content. Therefore, it is easy to misjudge that the membrane module has entered a stable separation state.

[0184] In response, Figure 4 This is a schematic flowchart of S600 according to an example embodiment of this application. Figure 4 As shown, the above-mentioned S600 includes:

[0185] S610 Record the first time that the product's oxygen content falls below the release threshold.

[0186] During conditional purging in the membrane separation nitrogen generator, the controller continuously receives product gas oxygen content data from the oxygen analyzer and records it continuously according to a fixed sampling period. When the product gas oxygen content is below the release threshold for multiple consecutive sampling periods, the controller determines that the product gas oxygen content has met the release conditions for the first time and records the sampling time corresponding to the first meeting of the release conditions as the first time the conditions are met. To avoid misjudgment caused by instantaneous fluctuations in the oxygen analyzer, a moving average processing can be performed on the oxygen content sampling data before recording the first time the conditions are met, and the first time the conditions are met can only be recorded after the oxygen content has been continuously and stably below the release threshold.

[0187] S620. Continuously acquire the oxygen content of the product within the verification window.

[0188] After recording the initial time of compliance, the controller establishes a verification window corresponding to that time and keeps the product gas outlet disconnected from the user's gas supply channel during the verification window. During the verification window, the oxygen analyzer continuously outputs product gas oxygen content data at a fixed sampling frequency. The controller stores the product gas oxygen content at each sampling time in chronological order to form an oxygen content time series within the verification window. To improve the accuracy of oxygen content acquisition, the oxygen analyzer's sampling flow rate can be kept stable during the verification window, and the sampling pressure can be maintained within a stable range, thereby reducing the impact of sampling fluctuations on the oxygen content detection results.

[0189] S630. Based on the oxygen content of the product, determine the peak oxygen content and the rate of change of oxygen content within the verification window.

[0190] The controller compares the oxygen content of the continuously collected product gas within the verification window point by point, and determines the maximum oxygen content within the verification window as the peak oxygen content. Simultaneously, the controller calculates the oxygen content change rate based on the change in oxygen content between adjacent sampling times and the corresponding time interval. In practice, the instantaneous oxygen content change rate can be obtained by dividing the difference between two adjacent sampling points by the sampling time interval, and further averaging multiple continuous change rates to reduce the impact of local noise fluctuations on the calculation results. When the oxygen content change rate continuously decreases and tends to stabilize, it can be determined that the mass transfer state inside the membrane module is gradually stabilizing.

[0191] S640. Based on the peak oxygen content and the rate of change of oxygen content, determine whether there is an oxygen content rebound.

[0192] The controller compares the peak oxygen content with the upper limit of oxygen content and simultaneously determines whether the rate of change of oxygen content remains consistently higher than the rate of change threshold. When the peak oxygen content within the verification window rises again and exceeds the upper limit of oxygen content, the controller determines that an oxygen content rebound has occurred; or, when the oxygen content does not exceed the upper limit of oxygen content, but the rate of change of oxygen content continues to rise and exceeds the rate of change threshold, the controller determines that an unstable desorption migration process still exists inside the membrane module and continues to determine that there is a risk of oxygen content rebound. After determining that an oxygen content rebound has occurred, the controller keeps the user's gas supply channel closed and continues to perform conditional purging until the peak oxygen content and the rate of change of oxygen content meet the gas supply determination conditions again.

[0193] Although continuous purging under fixed operating conditions can temporarily reduce the oxygen content of the product gas to the target range, there may still be areas of high oxygen that have not been completely released and areas of wet membrane that have not yet returned to stability inside the membrane module. When the product gas flow rate suddenly increases, the local flow velocity increase will accelerate the migration of high oxygen retention areas towards the product side; when the product gas back pressure changes, it will change the partial pressure difference across the membrane, thereby changing the permeation flux of oxygen and nitrogen; when the inlet pressure fluctuates, it will cause changes in the transmembrane driving force within the membrane, causing the unstable mass transfer state to be reactivated. Therefore, the stable oxygen content state achieved by the membrane module under static conditions is not equivalent to the stable selectivity state under dynamic disturbance conditions, which is the fundamental reason why secondary oxygen rebound is prone to occur after gas supply in the existing technology.

[0194] In response, based on the S610-S640, Figure 4 The illustrated embodiment further includes:

[0195] S650. Within the verification window, a perturbation is applied to at least one of the product air flow rate, product air back pressure, and inlet pressure.

[0196] After the verification window begins, the controller keeps the user gas supply channel closed and controls the product gas to continue entering the venting channel or recovery channel. Subsequently, the controller controls the opening of the product gas regulating valve to change the product gas flow rate; and / or controls the opening of the back pressure regulating valve to change the product gas back pressure; and / or controls the opening of the inlet pressure regulating valve to change the membrane module inlet pressure. During the execution of each disturbance, the oxygen content of the product gas is continuously acquired to cause the mass transfer state inside the membrane module to redistribute under different boundary conditions, thereby exposing the potential risk of oxygen content rebound.

[0197] Optionally, the product gas flow rate can be controlled to change in a preset step change manner. Specifically, the controller controls the opening of the product gas regulating valve to increase or decrease rapidly according to the current product gas flow rate, so that the product gas flow rate switches between a first flow rate value and a second flow rate value; during the flow rate switching process, the oxygen content of the product gas is continuously acquired, and the oxygen content response corresponding to the flow rate change is recorded to determine the stability of the membrane module under flow disturbance conditions.

[0198] Optionally, the product gas back pressure can be controlled to switch to a preset back pressure value. Specifically, the controller controls the back pressure regulating valve located on the product gas outlet side to increase or decrease the product gas outlet pressure; during the back pressure switching process, the oxygen content of the product gas is continuously acquired, and the oxygen content change corresponding to the back pressure change is recorded; if the oxygen content increases significantly after the back pressure change, it is determined that the mass transfer state inside the membrane module has not yet stabilized.

[0199] Optionally, the intake pressure can be controlled to switch to a preset pressure value. Specifically, the controller controls the intake pressure regulating valve to increase or decrease the compressed air pressure entering the membrane module; after the intake pressure is switched, the oxygen content of the product gas is continuously acquired, and the oxygen content change corresponding to the intake pressure change is recorded; if the oxygen content fluctuation increases after the intake pressure change, it is determined that there is still an unstable wet region inside the membrane module.

[0200] S660, Obtain the oxygen content of the product after disturbance.

[0201] After the disturbance is applied, the controller continuously acquires the oxygen content signal of the product gas output by the oxygen analyzer and records the baseline oxygen content value corresponding to the start of the disturbance. Subsequently, the oxygen content change data during the disturbance is continuously recorded in chronological order. After the oxygen analyzer completes the sampling gas update, the oxygen content change curve during the disturbance is continuously tracked to obtain the change of product gas oxygen content after the disturbance.

[0202] S670. Based on the peak oxygen content of the product gas after disturbance, determine whether the product gas meets the gas supply conditions.

[0203] After the disturbance is completed, the controller counts the peak oxygen content during the disturbance period and compares the peak oxygen content with the allowable fluctuation range corresponding to the release threshold. If the peak oxygen content after the disturbance is consistently lower than the upper limit of the allowable oxygen content, it is determined that the membrane module maintains a stable selectivity state under dynamic operating conditions and that the product gas meets the gas supply conditions. If the peak oxygen content after the disturbance exceeds the upper limit of the allowable oxygen content, it is determined that there is still an unstable region inside the membrane module and that the product gas does not meet the gas supply conditions.

[0204] For S650-S670, external operating condition disturbances are used to actively stimulate the unstable unsteady-state mass transfer process inside the membrane module, and the oxygen content response after disturbance is used to inversely determine whether the membrane module has reached a stable selective state. When the product gas flow rate changes abruptly, the flow field distribution and residence time inside the membrane module change, and the high-oxygen retained gas hidden inside the membrane fibers will be re-exposed. When the product gas back pressure changes, the gas partial pressure difference across the membrane changes, thereby altering the oxygen permeation rate and nitrogen enrichment efficiency. When the inlet pressure changes, the transmembrane driving force is redistributed, which can further expose the unstable permeation behavior of the wet membrane region. If there are still incomplete water desorption regions or unrestored membrane fiber selectivity regions inside the membrane module, the oxygen content of the product gas will increase again or fluctuate more under disturbance. Conversely, if the membrane module has returned to a stable dry mass transfer state, the oxygen content of the product gas can remain stable even under disturbance conditions. Therefore, the above steps actually make the hidden unsteady mass transfer state inside the membrane module explicit by using the coupling relationship between dynamic disturbance and oxygen content response, thereby achieving accurate determination of the true stable gas supply timing.

[0205] Furthermore, when the equipment restarts, as compressed air flows through the membrane module, the moisture originally adsorbed inside and on the membrane material gradually desorbs, forming a dynamic migration front along the axial and radial directions of the membrane fibers. Because water vapor molecules have high diffusion capacity, their migration rate inside the membrane is not consistent with that of oxygen and nitrogen, thus causing changes in the instantaneous permeation characteristics of localized areas of the membrane module. Particularly between the product gas side and the oxygen-enriched waste gas side, moisture migration causes a redistribution of local permeation driving forces, resulting in phased fluctuations in oxygen permeation behavior. This process exhibits a significant time lag; even if the oxygen content in the product gas has temporarily decreased below the release threshold, there may still be wet regions inside the membrane module that have not yet completed desorption, leading to a re-increase in oxygen content during subsequent operation. Existing technologies, lacking dynamic monitoring of dew point changes, cannot effectively identify this type of hidden unsteady-state mass transfer process.

[0206] In response, based on the S610-S640, Figure 4 The illustrated embodiment further includes:

[0207] S680. Obtain the dew point on the oxygen-enriched exhaust gas side and / or the dew point on the product gas side, and determine the water decomposition and adsorption state based on the dew point on the oxygen-enriched exhaust gas side and / or the dew point on the product gas side.

[0208] During the anti-rebound verification process of the membrane separation nitrogen generator, a first dew point sensor is installed on the oxygen-enriched exhaust gas emission pipeline, and a second dew point sensor is installed on the product gas output pipeline. The controller continuously acquires the dew point data of the oxygen-enriched exhaust gas side corresponding to the first dew point sensor and / or the dew point data of the product gas side corresponding to the second dew point sensor according to the sampling cycle. In order to reduce the influence of residual condensate in the pipeline on the detection results, before acquiring the dew point data, the corresponding detection branch is controlled to perform continuous flow guidance so that the gas inside the detection branch reaches a stable flow state. If the fluctuation amplitude of the dew point data in multiple consecutive sampling cycles is less than the allowable fluctuation range, the corresponding dew point data is determined as valid dew point data.

[0209] The controller stores continuously collected dew point data in chronological order and calculates the dew point change between adjacent sampling times. When the dew point change continues to decrease, it indicates that the water migration rate inside the membrane module is decreasing. When the dew point change approaches stability and maintains a slow change in the same direction over multiple consecutive sampling cycles, it indicates that the main water decomposition and adsorption process inside the membrane module is nearing completion. When the dew point data shows a phased increase followed by a decrease, it indicates that there is a localized release of retained water inside the membrane module. Based on the direction of dew point change, the duration of dew point change, and the magnitude of dew point change, the current water decomposition and adsorption state of the membrane module is comprehensively determined.

[0210] Specifically, the controller calculates the dew point change rate based on the dew point data corresponding to two consecutive sampling times and the sampling time interval; where the dew point change rate is the amount of dew point change per unit time; the controller continuously records the dew point change rate corresponding to multiple consecutive sampling periods and generates a dew point change trend sequence; in order to reduce the impact of instantaneous fluctuations, the dew point change rate corresponding to multiple consecutive sampling periods is averaged and then used as the current dew point change rate.

[0211] After obtaining the current dew point change rate, the controller continuously determines whether the dew point change rate is lower than the corresponding allowable change range. When the dew point change rate remains low for multiple consecutive sampling cycles and the corresponding time length reaches the continuous judgment duration, it is determined that the main water migration process inside the membrane module has ended. At this time, it is determined that the water decomposition and adsorption front has passed through the main mass transfer region of the membrane module. After determining that the water decomposition and adsorption front has passed, this determination result is allowed to be used as one of the criteria for determining that the membrane module has reached a stable selective state.

[0212] S690. Based on the water desorption state, determine whether the membrane module has reached a stable selectivity state.

[0213] After determining the current water decomposition and adsorption state of the membrane module, the controller further acquires the changes in product oxygen content over the corresponding time period. If the dew point change rate continues to decrease and the product oxygen content change rate decreases simultaneously, it is determined that the wet migration process inside the membrane module is nearing its end. If the dew point change rate remains stable and the product oxygen content remains continuously below the release threshold, it is determined that the membrane module has reached a stable selectivity state. If the dew point change rate increases again or the product oxygen content rises again, it is determined that the membrane module has not reached a stable selectivity state, and conditional purging continues.

[0214] For S680-S690 above, after the membrane module restarts, if significant water decomposition and adsorption still exist inside the membrane, the dew point on the oxygen-enriched waste gas side or the product gas side will continuously change over time. When water decomposition and adsorption inside the membrane module is not yet complete, the water vapor concentration continuously redistributes along the airflow direction, causing the dew point parameter to exhibit a continuous drift state; as the desorption process gradually ends, the residual moisture inside the membrane tends to stabilize, and the dew point change rate gradually decreases and enters a stable range. Therefore, the dew point change rate can indirectly characterize the movement state of the moisture migration front inside the membrane module. When the dew point change rate remains below the corresponding threshold for a certain period of time, it indicates that the main water decomposition and adsorption process inside the membrane module has been completed, the membrane material gradually recovers its stable dry-state transport characteristics, and the separation selectivity of oxygen and nitrogen tends to stabilize. Based on this mechanism, the above steps use the dew point change rate as the criterion for determining the stable state of the membrane module, realizing the explicit identification of the hidden wet mass transfer process, thereby improving the accuracy of stable gas supply judgment during the start-up phase.

[0215] Furthermore, based on the above embodiments, it is worth noting that after maintenance, airtightness testing, or pressure testing, existing membrane separation nitrogen generation equipment typically uses high-purity nitrogen to maintain pressure on the membrane shell, product-side pipelines, buffer tanks, and sampling branches. When the equipment restarts, the control system generally decides whether to supply gas to the user side based solely on whether the oxygen content of the product gas is below the release threshold. However, the high-purity nitrogen remaining in the product-side space during maintenance can cause the oxygen analyzer to quickly detect extremely low oxygen content at the initial startup stage, creating a false impression of premature compliance. In this case, although the oxygen analyzer shows that the product gas meets the purity requirements, the actual separation process inside the membrane module has not yet established a stable mass transfer state. Subsequently, as the residual air in the dead space region, oxygen-rich side region, and inside the membrane fibers is gradually released, the oxygen content of the product gas will rise again, leading to a rebound in the purity of the supplied gas, failure of purity on the user side, and even failure of the inerting protection.

[0216] Existing technologies typically assume: This means the system has reached a stable gas supply condition, where: Indicates time The oxygen content of the product; This indicates the oxygen content threshold for product gas release.

[0217] However, existing technologies assume that low-oxygen gas must come from the real-time membrane separation process and do not consider the effect of residual nitrogen from historical pressure tests on the oxygen content detection results, thus failing to identify false compliance conditions.

[0218] Specifically, after maintenance, a non-uniform initial gas distribution will form inside the membrane separation nitrogen generator. Under normal start-up conditions, the initial oxygen concentration at various locations in the system typically approximates the following:

[0219]

[0220] in: Indicates the position at the moment of startup Oxygen concentration at that location; This indicates the spatial location of the membrane module, product pipeline, buffer tank, and sampling branch.

[0221] At this point, as the membrane separation process is gradually established, the oxygen content of the product gas will gradually decrease and tend to stabilize.

[0222] However, after pressurizing with high-purity nitrogen, the initial oxygen concentration in different regions of the system becomes:

[0223]

[0224] Some areas meet the following criteria:

[0225]

[0226] The other part of the region still meets the following requirements:

[0227]

[0228] This results in a spatially stratified gas distribution.

[0229] Furthermore, after the equipment restarts, the oxygen content at the system outlet is not solely determined by the real-time membrane separation capacity, but rather by the combined effect of the gas flows released from each region:

[0230]

[0231] in: Indicates time The oxygen content at the outlet; Indicates the first Each region at time Release traffic; Indicates the first Each region corresponds to a specific gas oxygen concentration; This indicates the number of regions within the system that are involved in the release.

[0232] The derivation principle of the above formula is as follows:

[0233] The total amount of oxygen contributed to the outlet by each region per unit time is:

[0234]

[0235] The total outbound flow of the system is:

[0236]

[0237] Therefore, the outlet oxygen concentration is equal to the ratio of the total oxygen flow rate to the total gas flow rate.

[0238] During the initial startup phase, because the high-purity nitrogen residue areas in the product pipelines, buffer tanks, and sampling branches are preferentially purged out, therefore:

[0239]

[0240] During subsequent operation, residual air inside the membrane fibers, in the dead space region, and on the oxygen-enriched side is gradually released, therefore: This results in a dynamic phenomenon where the oxygen content first reaches the target quickly and then rebounds.

[0241] Further analysis reveals that the actual degree of replacement of residual nitrogen gas during pressure testing within the system satisfies a volume replacement relationship with the cumulative vented air volume:

[0242]

[0243] in, Indicates time The replacement completion rate; Indicates the cumulative amount of air discharged; This indicates the effective volume on the product side.

[0244] The above relationship derives from a continuous mixing and displacement process. Assuming the gases inside the system are in a state of continuous and complete mixing, the change in the residual proportion per unit time satisfies:

[0245]

[0246] in: Indicates time The proportion of residual gas; This indicates the drainage flow rate.

[0247] The integral yields:

[0248]

[0249] Therefore, the replacement completion rate is:

[0250]

[0251] This indicates that if the cumulative air venting volume is insufficient, the residual nitrogen from the historical pressure test has not been truly vented, and the low oxygen state detected by the system may still originate from the residual gas from the historical test rather than from the real-time stable nitrogen production process.

[0252] To address this, before performing anti-rebound verification, maintenance operation records during the shutdown period can be obtained. Based on these records, it can be determined whether at least one high-purity nitrogen pressure holding operation was performed during the shutdown, including product-side pressure holding tests, membrane housing pressure holding tests, buffer tank pressure holding tests, and sampling branch pressure holding tests. If a high-purity nitrogen pressure holding operation was performed during the shutdown, the membrane separation nitrogen generator is confirmed to be in a residual gas testing condition. Under this condition, even if the oxygen content of the product gas falls below the release threshold for the first time, the user gas supply channel remains closed, and conditional purging continues. Then, the cumulative vented air volume is obtained. Based on the correspondence between the cumulative vented air volume and the effective volume on the product side, it is determined whether the residual test gas on the product side has been completely replaced. After confirming that the residual test gas on the product side has been completely replaced, anti-rebound verification is performed.

[0253] Specifically, through the above steps, instantaneous hypoxia is no longer directly equated with the completion of stable nitrogen production. Instead, the start-up phase is viewed as a dynamic competitive process of gradual replacement of historical residual gases and gradual establishment of real-time membrane-separated gases. Specifically:

[0254] First, by obtaining maintenance operation records, we can identify whether the system has a history of high-purity nitrogen pressure holding, thereby identifying possible residual gas conditions during pressure testing.

[0255] Secondly, by keeping the user's gas supply channel closed and continuing to perform conditional purging, the historical residual low-oxygen gas inside the system is continuously discharged, thereby preventing the first low-oxygen detection value from directly entering the user side.

[0256] Furthermore, by analyzing the correlation between the cumulative vented air volume and the effective volume on the product side, it can be determined whether the residual nitrogen from the historical pressure test has been fully replaced.

[0257] When the following conditions are met: When this time, it indicates that the system has completed at least Volume replacement, where: Indicates the permutation factor.

[0258] Under these circumstances, the impact of historical residual test nitrogen on the outlet oxygen content is significantly reduced.

[0259] Subsequently, we will continue to observe through anti-rebound verification:

[0260]

[0261] When the following conditions are met:

[0262]

[0263] If the temperature remains stable, it indicates that no new sources of air release have appeared within the system.

[0264] Furthermore, by changing operating conditions such as flow rate, back pressure, or intake pressure, the internal flow field of the system is actively disturbed, forcibly releasing the residual air hidden in the dead cavity.

[0265] If the following conditions are still met after the disturbance:

[0266]

[0267] This indicates that the current low-oxygen state originates from a real, stable membrane separation process, rather than from residual test gas from the past.

[0268] Therefore, the above steps establish a multi-stage dynamic judgment mechanism that includes historical residual gas identification, cumulative replacement and elimination, dynamic disturbance verification, and stable gas supply confirmation, thereby effectively suppressing the risk of false compliance during the startup phase.

[0269] It is evident that by identifying high-purity nitrogen pressure holding conditions during the startup phase, restricting immediate release upon first compliance, establishing a cumulative venting volume judgment mechanism, and implementing anti-rebound verification, the problem of misjudging the product's oxygen content prematurely meeting the standard due to historical residual test pressure nitrogen can be avoided. This can improve the gas supply safety in scenarios such as food packaging, lithium battery protection, inerting explosion protection, and electronic gas protection, and reduce the risk of product contamination, process interruption, and safety accidents caused by erroneous release.

[0270] S700. Based on the verification results of the anti-rebound verification, determine whether the product gas meets the gas supply conditions.

[0271] After the membrane separation nitrogen generator completes the anti-rebound verification, the controller continuously acquires the product gas oxygen content at the end of the verification window, the peak oxygen content within the verification window, the oxygen content change rate, the product gas dew point, and the stabilization time after disturbance recovery. Among them, the stabilization time after disturbance recovery is the duration corresponding to the product gas oxygen content returning to the stable range after changes in product gas flow rate, product gas back pressure, or inlet pressure.

[0272] The controller compares multiple consecutive sampling cycles after the verification window ends. If the oxygen content of the product gas is lower than the release threshold in multiple consecutive sampling cycles, and the rate of change of oxygen content continues to decrease, while the stabilization time after disturbance recovery gradually shortens and the change amplitude of dew point on the product gas side continues to decrease, then it is determined that the moisture migration process inside the membrane module has basically stabilized and the membrane module has reached a stable selectivity state. Under this condition, it is determined that the product gas meets the gas supply conditions.

[0273] If, after the verification window ends, the oxygen content of the product gas increases again, the rate of change of oxygen content increases, the dew point on the product gas side rises again, or the stabilization time after the disturbance is restored is prolonged, it is determined that there is still a wet region inside the membrane module that has not been fully released; in this case, it is determined that the product gas does not meet the gas supply conditions.

[0274] It is worth noting that the product-side piping, analyzer sampling branch, valve body cavity, buffer tank interface, and low-flow-rate area in a membrane separation nitrogen generator collectively constitute a dead-cavity region of a certain volume on the product side. During equipment shutdown, the gas diffusion rate in this region is slow, and due to the lack of continuous flow drive, residual high-oxygen gas tends to remain for a long time. After the equipment restarts, even if the membrane module outlet has obtained the required low-oxygen product gas, the low-oxygen product gas still needs to push and displace the residual high-oxygen gas in the dead-cavity region before entering the user's gas supply channel. However, due to flow fluctuations, uneven flow field distribution, and local backmixing effects during the startup phase, the displacement process in the dead-cavity region is significantly delayed. Therefore, simply detecting the oxygen content at the membrane module outlet cannot accurately reflect the actual purity of the gas supplied to the user, resulting in a mismatch where the detected purity meets the standard but the actual gas supply does not.

[0275] In this regard, the S700 may also include: acquiring the cumulative air venting volume, determining whether the dead cavity on the product side has been replaced based on the relationship between the cumulative air venting volume and the preset replacement volume, and determining that the product gas meets the gas supply conditions if the dead cavity on the product side has been replaced.

[0276] Specifically, when the cumulative vented air volume is less than the actual volume to be replaced on the product side, residual high-oxygen gas that has not been completely expelled still exists inside the dead cavity. As the cumulative vented air volume continues to increase, low-oxygen product gas gradually replaces the original stagnant gas and pushes the high-oxygen gas out along the venting channel. When the cumulative vented air volume reaches or exceeds the volume to be replaced on the product side, the main dead cavity area on the product side completes gas replacement. At this time, the gas composition received by the user side will gradually approach the actual product gas composition at the membrane module outlet. Therefore, the above steps, which use the cumulative vented air volume to determine the dead cavity replacement status on the product side, essentially utilize the gas volume replacement law to explicitly characterize the hidden residual gas status during the start-up phase, thereby achieving accurate control of the gas supply switching timing.

[0277] S810. If the product gas meets the gas supply conditions, control the product gas outlet to connect with the user's gas supply channel.

[0278] After confirming that the product gas meets the supply conditions, the controller controls the product gas switching valve to switch from the venting channel side to the user supply channel side, so that the product gas outlet is connected to the user supply channel. During the switching process, the controller controls the product gas flow rate to gradually increase and simultaneously monitors the changes in the oxygen content of the product gas to reduce the impact of pressure fluctuations at the moment of switching on the separation state of the membrane module.

[0279] After the product gas outlet is connected to the user's gas supply channel, the controller continues to monitor the product gas oxygen content, product gas dew point, and product gas flow rate. If the product gas oxygen content remains stable during continuous operation, the current gas supply status is maintained. If the product gas oxygen content continues to rise, the product gas outlet is disconnected from the user's gas supply channel, and the product gas is re-entered into the venting channel or recovery channel.

[0280] It is worth noting that even if a membrane separation nitrogen generator passes the initial compliance test and anti-rebound verification during the start-up phase, some wet mass transfer regions may still exist within the membrane module that have not yet fully recovered to a stable state. These regions may remain temporarily stable under low-disturbance conditions, but once the equipment enters actual gas supply mode, changes in user-side flow rate, back pressure switching, inlet pressure fluctuations, and redistribution of the flow field within the membrane can cause localized stagnant moisture to migrate again, leading to renewed fluctuations in the oxygen-nitrogen separation selectivity of the membrane module. When these fluctuations are superimposed on the product gas output, the oxygen content in the product gas will increase again, resulting in a secondary rebound phenomenon. Therefore, relying solely on a single stability assessment during the start-up phase cannot fully guarantee the true stability during subsequent continuous gas supply.

[0281] In response, after S810, it is necessary to continuously obtain the oxygen content of the product gas. Based on the trend of the change in the oxygen content of the product gas, it is necessary to determine whether a secondary rebound has occurred. If a secondary rebound occurs, the product gas outlet should be disconnected from the user's gas supply channel, and the product gas should be re-entered into the venting channel or the recovery channel.

[0282] Specifically, after initial stabilization during the start-up phase, some localized areas may still retain adsorbed moisture that has not been completely released. When the system's gas supply changes, the internal pressure distribution, flow rate distribution, and gas partial pressure gradient of the membrane module alter, causing localized moisture to migrate again and changing the membrane material's instantaneous permeability to oxygen and nitrogen. This process leads to a resurgence of oxygen content in the product gas within a certain timeframe. Based on this, the above steps dynamically and explicitly identify the hidden unsteady-state mass transfer release process within the membrane module by continuously monitoring the trend of oxygen content changes in the product gas. When an abnormal rise in oxygen content is detected, the gas supply is immediately disconnected and the system is evacuated, thereby using real-time closed-loop control to block abnormal gas output and achieve dynamic purity protection during the continuous gas supply phase.

[0283] S820. If the product gas does not meet the gas supply conditions, continue to perform conditional purging.

[0284] After determining that the product gas does not meet the gas supply conditions, the controller maintains the disconnection between the product gas outlet and the user's gas supply channel, and continues to allow the product gas to enter the venting channel or the recovery channel; at the same time, the controller continues to input dry compressed air into the membrane module to maintain the water decomposition and adsorption process inside the membrane module.

[0285] Based on the purging requirements corresponding to the current adsorption memory risk level, the controller continues to adjust the product gas venting flow rate, cumulative venting volume, product gas recovery rate, and purging duration. During the continued conditional purging, the controller continuously acquires the product gas oxygen content and product gas dew point, and re-enters the anti-rebound verification process until the product gas meets the gas supply conditions.

[0286] Among them, the above-mentioned conditional purging can include at least one of the following purging methods: forward drying high displacement purging; product-side dry nitrogen reverse purging; membrane shell temperature-dew point margin control purging; deep drying start-up purging.

[0287] Specifically, for forward drying high-displacement purging, after the membrane separation nitrogen generator enters the start-up phase, the dry compressed air is controlled to enter the membrane module from the inlet end and continuously vented from the product gas outlet side. During the purging process, the inlet pressure is gradually increased to the start-up working pressure range, while keeping the product gas outlet disconnected from the user's gas supply channel. The cumulative vented air volume, product gas oxygen content, and product gas dew point are continuously acquired. When the cumulative vented air volume reaches multiple times the replacement volume corresponding to the effective internal volume of the membrane module, and the product gas oxygen content continues to decrease and tends to stabilize, and the product gas dew point continues to decrease, it is determined that the residual oxygen-enriched gas and adsorbed moisture inside the membrane module have been largely replaced. Then, the anti-rebound verification stage begins.

[0288] For product-side dry nitrogen reverse purging, after the membrane separation nitrogen generator is shut down or before it is restarted, dry nitrogen is controlled to enter the membrane module from the product gas outlet side and exit from the oxygen-enriched waste gas side. During the reverse purging process, the pressure on the product side is controlled to be higher than the pressure on the oxygen-enriched waste gas side, so that the dry nitrogen flows in the reverse direction along the mass transfer direction inside the membrane module. The dew point and oxygen content on the oxygen-enriched waste gas side are continuously measured. When the dew point on the oxygen-enriched waste gas side continues to decrease and stabilizes, and the oxygen content on the oxygen-enriched waste gas side decreases to a stable range, it is determined that the adsorbed moisture and residual oxygen inside the membrane module have completed the reverse migration. Then, the reverse purging is stopped and the normal startup process begins.

[0289] For membrane housing temperature-dew point margin control purging, during conditional purging, the membrane housing temperature and inlet dew point are continuously acquired, and the temperature difference between the membrane housing temperature and the inlet dew point is calculated. When the temperature difference decreases, the membrane housing heating unit is controlled to increase the membrane housing temperature, and the inlet air drying unit is controlled to decrease the inlet dew point. During purging, the product gas-side dew point and the oxygen-enriched exhaust gas-side dew point are continuously acquired. When the temperature difference between the membrane housing temperature and the inlet dew point remains stable, and both the product gas-side dew point and the oxygen-enriched exhaust gas-side dew point tend to stabilize, it is determined that there is no risk of condensation inside the membrane module. Then, the current purging state is maintained to enter the anti-rebound verification stage.

[0290] For deep drying start-up purging, the membrane separation nitrogen generator can be controlled to enter deep drying start-up purging state when a long shutdown period, increased ambient humidity, or membrane shell temperature is detected as being lower than the ambient temperature. In this state, low dew point drying compressed air is controlled to enter the membrane module at a low flow rate, and the purging duration is extended. During the purging process, the product gas side exhaust flow rate and the oxygen-enriched waste gas side exhaust flow rate are periodically switched to change the internal flow field distribution of the membrane module. The oxygen content of the product gas, the dew point of the product gas side, the dew point of the oxygen-enriched waste gas side, and the membrane shell temperature are continuously acquired. When both the product gas side dew point and the oxygen-enriched waste gas side dew point continue to decrease and stabilize, and the product gas oxygen content remains stable within the continuous detection cycle, it is determined that the deep adsorbed moisture inside the membrane module has been basically released. Then, the deep drying start-up purging ends and the gas supply determination process begins.

[0291] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A control method for a membrane separation nitrogen generator, characterized in that, include: After the membrane separation nitrogen generator enters the start-up state, the product gas outlet is disconnected from the user's gas supply channel, and the product gas enters the venting channel or the recovery channel. The adsorption memory risk level of the membrane module is determined based on the shutdown status parameters of the membrane separation nitrogen generator. Under the start-up control conditions corresponding to the adsorption memory risk level, conditional purging is performed on the membrane module; During the conditional purging process, the oxygen content of the product gas is obtained, and after the oxygen content of the product gas first falls below the release threshold, the user gas supply channel is kept closed, and anti-rebound verification is performed. Based on the verification results of the anti-rebound verification, determine whether to continue performing the conditional purging.

2. The control method for membrane separation nitrogen generation equipment according to claim 1, characterized in that, Based on the shutdown status parameters, the adsorption memory risk level of the membrane module is determined, including: Obtain the downtime, current intake dew point, and current diaphragm temperature; The adsorption memory risk level is determined based on the correspondence between the downtime, the current inlet dew point, the current membrane temperature, and the preset risk assessment conditions.

3. The control method for membrane separation nitrogen generator according to claim 1, characterized in that, The conditional purging of the membrane module includes: Control the entry of dry compressed air into the membrane module; With the product gas outlet disconnected from the user gas supply channel, the product gas is allowed to enter the venting channel or the recovery channel; Based on the adsorption memory risk level, adjust at least one of the following: product gas venting flow rate, product gas recovery rate, cumulative venting volume, and purging duration.

4. The control method for membrane separation nitrogen generation equipment according to claim 3, characterized in that, The conditional purging of the membrane module further includes: Obtain the membrane housing temperature and inlet dew point; The operation of the membrane heating unit is controlled according to the temperature margin between the membrane temperature and the inlet dew point. After the temperature margin reaches the preset value, the conditional purging continues.

5. The control method for a membrane separation nitrogen generator according to claim 1, characterized in that, During the conditional purging process, the oxygen content of the product gas is obtained, including: Obtain the sampling flow rate and sampling pressure corresponding to the oxygen analyzer; Based on the sampling flow rate and the sampling pressure, determine whether the oxygen analyzer is in an effective working state; When the oxygen analyzer is in working condition, delay compensation processing is performed on the oxygen content signal.

6. The control method for a membrane separation nitrogen generator according to claim 1, characterized in that, After the oxygen content of the product gas first falls below the release threshold, the user gas supply channel remains closed, and anti-rebound verification is performed, including: Record the first time when the product's oxygen content first falls below the release threshold, corresponding to the first time the product meets the standard. Continuously acquire the product's gaseous oxygen content within the verification window; Based on the oxygen content of the product gas, determine the peak oxygen content and the rate of change of oxygen content within the verification window; Based on the peak oxygen content and the rate of change of oxygen content, determine whether there is an oxygen content rebound.

7. The control method for a membrane separation nitrogen generator according to claim 6, characterized in that, Based on the verification results of the anti-rebound verification, determine whether the product gas meets the gas supply conditions, including: If the peak oxygen content within the verification window does not exceed the upper limit of oxygen content and the rate of change of oxygen content is less than the rate of change threshold, then the product gas is determined to meet the gas supply conditions. If the peak oxygen content within the verification window exceeds the upper limit of oxygen content, it is determined that the product gas does not meet the gas supply conditions.

8. The control method for a membrane separation nitrogen generator according to claim 6, characterized in that, The process of performing anti-rebound verification also includes: Within the verification window, at least one of the product gas flow rate, product gas back pressure, and inlet pressure is perturbed. Obtain the oxygen content of the product after disturbance; Based on the peak oxygen content of the product gas after disturbance, determine whether the product gas meets the gas supply conditions.

9. The control method for a membrane separation nitrogen generator according to any one of claims 6-8, characterized in that, Prior to performing the anti-bounce verification, the following is also included: Under the condition of residual gas during pressure testing, the cumulative air venting volume is obtained, and based on the correspondence between the cumulative air venting volume and the effective volume on the product side, it is determined whether the residual gas during pressure testing on the product side has been completely replaced.

10. The control method for a membrane separation nitrogen generator according to claim 8, characterized in that, Perturbation is applied to at least one of the product gas flow rate, product gas back pressure, and inlet pressure, including: Control the product gas flow rate to change according to a preset step change pattern; and / or, Control the product's back pressure to switch to a preset back pressure value; and / or, Control the intake pressure to switch to the preset pressure value.

11. The control method for a membrane separation nitrogen generator according to claim 1, characterized in that, The product gas enters the recovery channel, including: Control the product gas to enter the first batch gas buffer tank; Obtain the oxygen content in the first batch of gas buffer tanks; If the oxygen content in the first batch of gas buffer tanks meets the preset conditions, then the first batch of gas buffer tanks is connected to the auxiliary gas branch. If the oxygen content in the first batch of gas buffer tanks does not meet the preset conditions, then the first batch of gas buffer tanks will be emptied.

12. The control method for a membrane separation nitrogen generator according to claim 1, characterized in that, The step of determining whether the product gas meets the gas supply conditions based on the verification results of the anti-rebound verification further includes: Obtain the cumulative air discharge volume; Based on the relationship between the cumulative air discharge volume and the preset replacement volume, it is determined whether the dead cavity on the product side has been replaced. Once the dead cavity on the product side has been replaced, it is determined that the product gas meets the gas supply requirements.

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