Dynamic estimation control method and system for ammonia synthesis purge gas

Abstract

The application provides a dynamic estimation control method and system for synthetic ammonia purge gas, and belongs to the technical field of synthetic ammonia. The method comprises the following steps: obtaining process data in a current control period of a synthetic ammonia circulation system; calculating an inert gas accumulation rate soft measurement index based on the process data; comparing the inert gas accumulation rate soft measurement index with a preset target interval, calculating a purge control correction amount according to a comparison result and a deviation, and generating a new purge control set value for dynamic control. The application effectively eliminates the interference of ammonia production load and pressure fluctuation, accurately matches the purge amount and the real inert accumulation state, significantly reduces the effective gas loss on the premise of preventing inert control from being out of control and enriching, and improves the stability and economy of device operation.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis technology, specifically relating to a dynamic prediction and control method and system for ammonia synthesis off-gas. Background Technology

[0002] Ammonia synthesis typically employs a recirculation loop to return unreacted gases to the synthesis tower for further reaction. In this loop, the fresh gas, in addition to effective components such as hydrogen and nitrogen, usually contains small amounts of inert components such as methane and argon. These inert components cannot be consumed within the synthesis tower and gradually accumulate as the system operates, reducing the partial pressure of the effective components and affecting the synthesis reaction efficiency and liquid ammonia yield. To control the accumulation of inert components, industrial processes usually include a venting branch to discharge a portion of the recirculated gas.

[0003] In existing technologies, relaxation control often relies on fixed valve positions, manual adjustment based on experience, or correction based on a single parameter such as circulating pressure. These methods struggle to accurately reflect the true accumulation state of inert components in the circulating system, easily leading to insufficient or excessive relaxation. Insufficient relaxation results in the continuous enrichment of inert components, affecting system stability; excessive relaxation causes the loss of valuable components such as hydrogen and nitrogen, reducing the economic efficiency of the equipment. Therefore, it is necessary to provide a control method that can more accurately characterize the accumulation trend of inert components and dynamically adjust relaxation accordingly. Summary of the Invention

[0004] In view of the above situation and to overcome the defects of the prior art, the purpose of the present invention is to provide a dynamic prediction and control method and system for synthetic ammonia purge gas, so as to at least partially solve the problems mentioned in the background art.

[0005] The technical solution adopted in this invention is as follows: The first aspect of this invention proposes a method for dynamic prediction and control of ammonia synthesis off-gas, comprising the following steps: Acquire process data for the current control cycle of the synthetic ammonia cycle system. The process data includes at least inert input related data for determining inert input characteristic quantities, purge discharge related data for determining purge discharge characteristic quantities, effective component reaction consumption related data for determining liquid ammonia production correction characteristic quantities, and system inventory change related data for determining system inventory change correction characteristic quantities. Based on the process data, the inert input characteristic quantity, the purge discharge characteristic quantity, the liquid ammonia production correction characteristic quantity, and the system inventory change correction characteristic quantity are determined, and the inert gas accumulation rate soft measurement index is calculated according to the preset weighting relationship. The inert gas accumulation rate soft measurement index is used to quantitatively characterize the net accumulation trend of inert components in the circulation system within the current control cycle. The inert gas accumulation rate soft measurement index is compared with a preset target range to determine the current accumulation trend of the inert component; Based on the judgment result of the cumulative trend and the deviation of the inert gas accumulation rate soft measurement index from the target center value, the relaxation control correction is calculated; wherein, the target center value is the center reference value of the preset target interval; A new relaxation control setpoint is generated based on the relaxation control correction and output to the actuator to dynamically adjust the relaxation amount.

[0006] In some embodiments of the present invention, the process data specifically includes: The inert input-related data includes the total fresh gas flow rate and the content of inert components in the fresh gas, and is used to calculate the inert input amount; The data related to venting and venting includes venting gas flow rate; when the venting gas flow rate is not directly obtained, the data related to venting and venting includes venting valve opening, pressure difference across the venting branch, and preset valve flow coefficient, and is used to estimate the venting gas flow rate. The relevant data on the reaction consumption of the effective components include liquid ammonia production or equivalent liquid ammonia generation. The system inventory change related data includes the circulating loop pressure of the current control cycle and the previous control cycle; when the pressure change of the circulating system is characterized by the synthesis tower inlet pressure, the system inventory change related data includes the synthesis tower inlet pressure of the current control cycle and the previous control cycle.

[0007] In some embodiments of the present invention, the step of calculating the soft-measure index of the inert gas accumulation rate includes: The inert input characteristic quantity is determined based on the total fresh air flow rate and the inert component content in the fresh air; The purge discharge characteristic quantity is determined based on the purge gas flow rate. When the purge gas flow rate is not directly obtained, the purge gas flow rate is estimated based on the purge valve opening, the pressure difference before and after the purge branch, and the preset valve flow coefficient, and the purge discharge characteristic quantity is determined accordingly. The liquid ammonia production correction characteristic quantity is determined based on the liquid ammonia production or equivalent liquid ammonia generation. The system inventory change correction characteristic quantity is determined based on the pressure change of the current control cycle and the previous control cycle. Based on the inert input characteristic, the purge discharge characteristic, the liquid ammonia production correction characteristic, and the system inventory change correction characteristic, a soft measurement index for the inert gas accumulation rate is constructed.

[0008] In some embodiments of the present invention, the inert gas accumulation rate is a soft-measurement index. The calculation expression is: in, For lazy input features, For the characteristic quantity of relaxation discharge, Correction characteristic for liquid ammonia production. Correct characteristic quantities for changes in system stock; , These are the corresponding weighting coefficients.

[0009] In some embodiments of the present invention, the preset target interval includes an upper threshold and a lower threshold; the step of determining the current accumulation trend of inert components includes: When the control cycle of the inert gas accumulation rate soft measurement index is greater than the upper limit threshold for a preset number of consecutive cycles, it is determined that the inert component is in a state of net rapid accumulation under the current operating conditions. When the control period of the inert gas accumulation rate soft measurement index is less than the lower limit threshold for a consecutive preset number of control cycles, it is determined that the current release is too strong and there is a tendency for excessive loss of effective gas. When the soft measurement index of the inert gas accumulation rate is within the preset target range, it is determined that the current relaxation level is basically matched with the inert gas introduction level. The judgment step also includes a hysteresis judgment rule and / or a continuous boundary crossing judgment rule.

[0010] In some embodiments of the present invention, the step of calculating the relaxation control correction includes: Calculate the deviation between the soft-measurement index of the inert gas accumulation rate and the target center value; When the absolute value of the deviation is greater than the set dead zone boundary, the relaxation control correction amount is calculated using a segmented proportional method; when using stepped logic, the corresponding relaxation control correction amount is determined according to the deviation interval in which the deviation is located; wherein, a single-cycle change rate limit is set for the relaxation control correction amount, and upper and lower limits are set for the relaxation control set value.

[0011] In some embodiments of the present invention, the method further includes an abnormal operating condition handling step: Real-time monitoring of the validity of the process data and the system operating status; When critical data fails, the circulating pressure exceeds the set safety limit, or the system enters a major operating condition disturbance phase, control based on the soft measurement index of the inert gas accumulation rate is stopped, and the system switches to degraded control mode. The degradation control mode includes any of the following: maintaining the effective release control setting value of the previous cycle, switching to the preset fixed release control setting value, or performing pressure auxiliary control based on the pressure deviation.

[0012] A second aspect of this invention provides a dynamic prediction and control system for ammonia synthesis off-gas, comprising: The data acquisition module is used to acquire process data within the current control cycle of the ammonia synthesis cycle system; The soft measurement module is used to calculate the soft measurement index of inert gas accumulation rate based on the process data; The trend determination module is used to compare the soft measurement index of the inert gas accumulation rate with a preset target range to determine the current accumulation trend of the inert component. The deviation control calculation module is used to calculate the relaxation control correction amount based on the judgment result of the cumulative trend and the deviation of the soft measurement index of the inert gas accumulation rate relative to the target center value. The output execution module is used to generate a new relaxation control setpoint based on the relaxation control correction amount and output it to the actuator.

[0013] In some embodiments of the present invention, a data preprocessing module is also included, which is used to perform time synchronization, filtering and smoothing, and outlier removal on the process data.

[0014] In some embodiments of the present invention, an abnormal switching module is also included. The abnormal switching module is used to stop controlling based on the soft measurement index of the inert gas accumulation rate and switch the system to a degraded control mode when critical data fails, the circulating pressure is higher than the set safety limit, or the system enters a major operating condition disturbance stage. The degradation control mode includes maintaining the effective release control setting value of the previous cycle, switching to the preset fixed release control setting value, or performing pressure auxiliary control based on the pressure deviation.

[0015] The beneficial effects achieved by this invention are as follows: This invention constructs a soft-sensor index for the accumulation rate of inert gas based on process data, and dynamically adjusts the purge amount of the ammonia synthesis cycle system according to the soft-sensor index. This can more accurately reflect the net accumulation trend of inert components in the cycle system, avoiding problems of insufficient or excessive purge caused by fixed valve position control, manual experience adjustment, or adjustment based on a single parameter. Thus, while suppressing the continuous enrichment of inert components, it reduces the loss of effective components and improves the operational stability and economy of the ammonia synthesis cycle loop. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this invention.

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] In response to the problems mentioned in the background art, the first aspect of the present invention proposes a dynamic prediction and control method for ammonia synthesis purge gas, which is applied to an ammonia synthesis unit equipped with a circulation loop and a purge branch.

[0020] Acquire process data for the current control cycle of the synthetic ammonia cycle system. The process data includes at least inert input related data for determining inert input characteristic quantities, purge discharge related data for determining purge discharge characteristic quantities, effective component reaction consumption related data for determining liquid ammonia production correction characteristic quantities, and system inventory change related data for determining system inventory change correction characteristic quantities. Based on the process data, the inert input characteristic quantity, the purge discharge characteristic quantity, the liquid ammonia production correction characteristic quantity, and the system inventory change correction characteristic quantity are determined, and the inert gas accumulation rate soft measurement index is calculated according to the preset weighting relationship. The inert gas accumulation rate soft measurement index is used to quantitatively characterize the net accumulation trend of inert components in the circulation system within the current control cycle. The inert gas accumulation rate soft measurement index is compared with a preset target range to determine the current accumulation trend of the inert component; Based on the judgment result of the cumulative trend and the deviation of the inert gas accumulation rate soft measurement index from the target center value, the relaxation control correction is calculated; wherein, the target center value is the center reference value of the preset target interval; A new relaxation control setpoint is generated based on the relaxation control correction and output to the actuator to dynamically adjust the relaxation amount.

[0021] The process involves several steps. First, acquiring process data provides the input basis for subsequent soft sensor index calculations. Then, calculating these soft sensor indices based on the process data transforms various dispersed process information into unified representations that can directly participate in control decisions. Next, comparing these soft sensor indices with a preset target range determines whether the inert component is currently in a net accumulation, near-equilibrium, or net release state. Finally, based on the trend analysis and deviation, a relaxation control correction is calculated, further converting the soft sensor results into executable control actions. Finally, a new relaxation control setpoint is generated based on the correction and output to the actuator, thereby achieving dynamic adjustment of the relaxation amount in the field. By repeating this process in subsequent control cycles, the relaxation control setpoint can be continuously corrected according to changes in operating conditions, thus forming a closed-loop control.

[0022] Optionally, the control cycle can be set according to the signal refresh rate of the device, the response speed of the actuator, and the system inertia, preferably from 10 to 120 seconds, more preferably 30 or 60 seconds. The control cycle should not be too short, otherwise it will amplify measurement noise and cause the control actions to be too frequent; the control cycle should also not be too long, otherwise it will reduce the timeliness of response to changes in operating conditions. By reasonably setting the control cycle, both control sensitivity and control stability can be taken into account.

[0023] In some embodiments, the process data specifically includes: The inert input-related data includes the total fresh gas flow rate and the content of inert components in the fresh gas, and is used to calculate the inert input amount; The data related to venting and venting includes venting gas flow rate; when the venting gas flow rate is not directly obtained, the data related to venting and venting includes venting valve opening, pressure difference across the venting branch, and preset valve flow coefficient, and is used to estimate the venting gas flow rate. The relevant data on the reaction consumption of the effective components include liquid ammonia production or equivalent liquid ammonia generation. The system inventory change related data includes the circulating loop pressure of the current control cycle and the previous control cycle; when the pressure change of the circulating system is characterized by the synthesis tower inlet pressure, the system inventory change related data includes the synthesis tower inlet pressure of the current control cycle and the previous control cycle.

[0024] The accumulation of inert components in a circulating system is not determined by a single factor, but is simultaneously influenced by inert input, purge discharge, removal of effective components, and changes in the overall system state. For example, a higher fresh gas flow rate and higher inert component content result in more inert components being introduced; a stronger purge branch discharge capacity leads to a more pronounced inert component discharge trend; higher liquid ammonia production results in faster removal of effective reactants from the gas phase, typically leading to a more pronounced relative enrichment trend of inert components in the remaining circulating gas; changes in the overall state of the circulating system also affect the assessment of the net accumulation trend of inert components. Therefore, acquiring multiple types of process data simultaneously, rather than relying solely on a single parameter such as circulating pressure, allows subsequent soft sensing results to more closely approximate actual operating conditions.

[0025] Optionally, to improve the availability of the process data, preprocessing is performed on the process data in each control cycle. This preprocessing may include time synchronization, filtering and smoothing, and outlier handling. For signals that update rapidly, such as pressure, valve position, and flow rate, the latest effective value of the current control cycle can be used; for signals that update slowly, such as liquid ammonia production and inert component analysis values, the most recent effective value can be used in conjunction with smoothing from the previous few control cycles; for outliers that significantly exceed the physically reasonable range, the effective value of the previous cycle, the average value of adjacent cycles, or a limited substitution value can be used in the calculation. Through this preprocessing, the interference of abnormal measuring points and short-term fluctuations on the calculation results of subsequent soft-sensor indicators can be reduced, thereby improving the stability of the control output.

[0026] In some embodiments, the step of calculating the soft-sensor index of the inert gas accumulation rate includes: The inert input characteristic quantity is determined based on the total fresh air flow rate and the inert component content in the fresh air; The purge discharge characteristic quantity is determined based on the purge gas flow rate. When the purge gas flow rate is not directly obtained, the purge gas flow rate is estimated based on the purge valve opening, the pressure difference before and after the purge branch, and the preset valve flow coefficient, and the purge discharge characteristic quantity is determined accordingly. The liquid ammonia production correction characteristic quantity is determined based on the liquid ammonia production or equivalent liquid ammonia generation. The system inventory change correction characteristic quantity is determined based on the pressure change of the current control cycle and the previous control cycle. Based on the inert input characteristic, the purge discharge characteristic, the liquid ammonia production correction characteristic, and the system inventory change correction characteristic, a soft-measure index for the inert gas accumulation rate is constructed. Specifically, the inert input characteristic characterizes the intensity of inert components introduced by fresh gas; the purge discharge characteristic characterizes the discharge capacity of the purge branch within the current control cycle; the liquid ammonia production correction characteristic reflects the increased relative enrichment trend of inert components after the effective reactants are removed from the gas phase during continuous liquid ammonia generation; and the system inventory change correction characteristic corrects the impact of changes in the overall gas phase retention of the circulating system on inert gas accumulation assessment. By comprehensively incorporating these factors into a single index, multiple interrelated process influencing factors from different sources can be uniformly converted into a comprehensive index usable for control assessment. Thus, without relying on new large-scale online analysis equipment or requiring the establishment of complex and complete thermodynamic models, existing process data can be used to characterize the net accumulation trend of inert components online, providing a basis for subsequent trend assessment and purge control correction.

[0027] Specifically, the inertial input characteristic quantity can be determined by the total fresh gas flow rate and the inert component content in the fresh gas; when the methane and argon contents are measured separately on-site, they can be summed before being included in the calculation. The purge discharge characteristic quantity can be directly determined by the purge gas flow rate; when the purge gas flow rate cannot be directly obtained on-site, it can be estimated based on the purge valve opening, the pressure difference before and after the purge branch, and the empirical flow coefficient. The liquid ammonia production correction characteristic quantity can be determined by the liquid ammonia production and the corresponding correction coefficient. The system inventory change correction characteristic quantity can be determined by the change in circulation loop pressure between adjacent control cycles, or it can be jointly characterized by the circulation gas flow rate or the circulation machine load. By setting the above different implementation methods, the present invention can be adapted to the measurement point configuration and on-site conditions of different devices, improving its engineering applicability.

[0028] In some embodiments, the inert gas accumulation rate soft measurement index The calculation expression is: in, For lazy input features, For the characteristic quantity of relaxation discharge, Correction characteristic for liquid ammonia production. Correct characteristic quantities for changes in system stock; , These are the corresponding weighting coefficients.

[0029] The net accumulation trend of inert components in a circulating system is essentially influenced by four factors: increased input, decreased discharge, relative enrichment due to the removal of effective components, and changes in the overall system state. By combining the inert input characteristic, the purge discharge characteristic, the liquid ammonia production correction characteristic, and the system stock change correction characteristic into a comprehensive index, the dispersed process influencing factors can be unified under a single criterion. Specifically, the inert input characteristic and the liquid ammonia production correction characteristic typically have a positive effect on the net accumulation trend of inert components, while the purge discharge characteristic typically has a negative effect. The system stock change correction characteristic is used to correct for the impact of overall system state fluctuations on the judgment result. This allows soft sensor indices to more systematically reflect actual operating conditions.

[0030] The weighting coefficients can be set based on historical operating data, empirical tuning results, or trial operation calibration results. In other words, different units can adjust the degree of influence of each factor based on their own fresh gas composition, circulation system volume, purge branch characteristics, and ammonia production level. By setting weighting coefficients, the matching degree between soft sensor indicators and the actual operating state of specific units can be improved, thereby enhancing the effectiveness of subsequent trend judgment and control correction. It should be noted that the soft sensor indicators are not limited to absolute quantities with strict physical dimensions; they can also be dimensionless indicators after normalization, as long as they can stably characterize the net accumulation trend of inert components.

[0031] In some embodiments, the preset target range includes an upper threshold and a lower threshold; the step of determining the current accumulation trend of inert components includes: When the control cycle of the inert gas accumulation rate soft measurement index is greater than the upper limit threshold for a preset number of consecutive cycles, it is determined that the inert component is in a state of net rapid accumulation under the current operating conditions. When the control period of the inert gas accumulation rate soft measurement index is less than the lower limit threshold for a consecutive preset number of control cycles, it is determined that the current release is too strong and there is a tendency for excessive loss of effective gas. When the soft-measurement index of the inert gas accumulation rate is within the preset target range, it is determined that the current venting level is basically matched with the inert gas introduction level. Soft sensor parameters within a single control cycle can be affected by measurement fluctuations, signal refresh delays, or short-term operational disturbances. If control actions are based solely on single-cycle results, frequent adjustments to the actuator can easily occur. Therefore, this implementation combines target range and continuous cycle determination: when the soft sensor parameter consistently exceeds the upper threshold, it indicates that the current relaxation level is consistently below the level required by the net accumulation trend of the inert component, and the relaxation intensity should be increased; when the soft sensor parameter consistently falls below the lower threshold, it indicates that the current relaxation is consistently too strong, and the relaxation intensity should be decreased; when the soft sensor parameter is within the target range, the current control can be considered basically reasonable. Continuous cycle determination reduces erroneous actions and improves control stability.

[0032] In a preferred embodiment, the preset quantity can be set according to the system inertia and signal stability of the field device, preferably 2 to 5 control cycles.

[0033] Furthermore, the judgment step can also include hysteresis judgment rules and / or continuous boundary crossing judgment rules. That is, different thresholds can be used when entering and exiting the increased relaxation state, and different thresholds can also be used when entering and exiting the decreased relaxation state, to form a hysteresis band. By introducing a hysteresis band, frequent control state switching can be avoided when soft measurement indicators fluctuate near the interval boundaries, thereby further improving the stability of field operation.

[0034] In some embodiments, the step of calculating the relaxation control correction includes: calculating the deviation between the soft measurement index of the inert gas accumulation rate and the target center value; when the absolute value of the deviation is greater than the set dead zone boundary, calculating the relaxation control correction using a segmented proportional method; when using stepped logic, determining the corresponding relaxation control correction based on the deviation interval in which the deviation is located; wherein, a single-cycle change rate limit is set for the relaxation control correction, and upper and lower limit constraints are set for the relaxation control setpoint.

[0035] The dead zone boundary is an allowable deviation boundary set around the target center value, used to limit the deviation range that does not require relaxation correction under the current control state. In other words, when the deviation between the soft-measurement index of the inert gas accumulation rate and the target center value is within the range defined by the dead zone boundary, it can be considered that the current net accumulation trend of the inert component is basically consistent with the control target, or although there is a certain deviation, it is not enough to trigger a control action. In this case, the current relaxation control setpoint is maintained basically unchanged. This reduces frequent fine-tuning caused by measurement noise, short-term disturbances, or signal fluctuations, improving control stability.

[0036] Calculating the deviation between the soft sensor index and the target center value quantifies the degree of deviation of the current net accumulation trend of the inert component from the control target. A positive deviation indicates a strong accumulation trend of the inert component and insufficient relaxation level, requiring an increase in relaxation intensity. A negative deviation indicates strong relaxation, requiring an appropriate decrease in relaxation intensity. Only when the absolute value of the deviation exceeds the dead zone boundary is the current deviation considered to have reached a level requiring control correction, and the relaxation control correction amount is further calculated based on the deviation magnitude. By introducing the dead zone boundary, subsequent control corrections can consider not only the direction and magnitude of the deviation but also the disturbance rejection capability during the field control process, thereby improving the stability of industrial operation.

[0037] In some embodiments, the dead zone boundary can be set as a symmetrical boundary on both sides of the target center value; in other embodiments, the dead zone boundary can also be set as an asymmetrical boundary according to different control requirements of increasing and decreasing the relaxation.

[0038] In one embodiment, a segmented proportional method is used to calculate the relaxation control correction to maintain a good correspondence between the control correction and the magnitude of the deviation, thereby achieving a smoother adjustment process. In another embodiment, a stepped logic method is used to calculate the relaxation control correction to facilitate stepped adjustment in industrial control systems. Regardless of the method used, setting a single-cycle change rate limit for the relaxation control correction is to prevent the actuator from making excessive movements in a short period of time, reducing the impact on the stable operation of the cyclic system. Setting upper and lower limits for the relaxation control setpoint is to prevent excessive relaxation from causing a large loss of effective components, and to prevent insufficient relaxation from causing inert components to lose their basic discharge channels, respectively. Through the above settings, both control sensitivity and industrial operation safety can be balanced.

[0039] In some embodiments, the method further includes an abnormal operating condition handling step: Real-time monitoring of the validity of the process data and the system operating status; When critical data fails, the circulating pressure exceeds the set safety limit, or the system enters a major operating condition disturbance phase, control based on the soft measurement index of the inert gas accumulation rate is stopped, and the system switches to degraded control mode. The degradation control mode includes any of the following: maintaining the effective release control setting value of the previous cycle, switching to the preset fixed release control setting value, or performing pressure auxiliary control based on the pressure deviation.

[0040] The soft sensor indexes are based on the premise that process data is valid and operating conditions are basically controllable. When critical data fails, the system enters start-up / shutdown or major disturbance phases, continuing to perform closed-loop corrections based on normal soft sensor results may lead to distorted control outputs, thereby affecting system operational safety. Therefore, when an abnormal situation is detected, it is preferable to suspend dynamic corrections based on soft sensor indexes and switch to a more conservative degraded control mode. By maintaining the valid setpoint of the previous cycle, switching to a preset fixed setpoint, or performing auxiliary control based on pressure deviation, the system's operational safety and basic stability can be prioritized under abnormal operating conditions. After the abnormal state is eliminated, closed-loop control based on the soft sensor indexes is resumed. This improves the reliability of the invention in industrial settings.

[0041] As a specific example, the control system can operate in 30-second control cycles. Within each control cycle, the total fresh gas flow rate, the total methane and argon content in the fresh gas, the opening degree of the venting valve, the pressure difference across the venting branch, the liquid ammonia production, and the circulation loop pressure are acquired. The data is then time-synchronized, filtered, smoothed, and anomaly-handled. Subsequently, a soft-sensor index for the inert gas accumulation rate is constructed using the aforementioned method. When the soft-sensor index is higher than the upper threshold for three consecutive control cycles, the inert component is determined to be in a state of net rapid accumulation, and a positive venting control correction is calculated. When the soft-sensor index is lower than the lower threshold for three consecutive control cycles, the current venting is determined to be strong, and a negative venting control correction is calculated. When the soft-sensor index is within the target range, the current venting control setpoint remains essentially unchanged. Subsequently, the venting control correction is superimposed on the venting control setpoint of the previous cycle to generate a new venting control setpoint, which is then output to the actuator after being constrained by upper and lower limits. If critical data failure or circulation pressure exceeding the safety limit is detected, the closed-loop correction is paused and the system switches to a preset degraded control mode. This method enables dynamic rolling adjustment of the purge rate in the ammonia synthesis cycle system.

[0042] A second aspect of this invention provides a dynamic prediction and control system for ammonia synthesis off-gas, comprising: The data acquisition module is used to acquire process data within the current control cycle of the ammonia synthesis cycle system; The soft measurement module is used to calculate the soft measurement index of inert gas accumulation rate based on the process data; The trend determination module is used to compare the soft measurement index of the inert gas accumulation rate with a preset target range to determine the current accumulation trend of the inert component. The deviation control calculation module is used to calculate the relaxation control correction amount based on the judgment result of the cumulative trend and the deviation of the soft measurement index of the inert gas accumulation rate relative to the target center value. The output execution module is used to generate a new relaxation control setpoint based on the relaxation control correction amount and output it to the actuator.

[0043] The system repeatedly executes the above control process in subsequent control cycles to achieve rolling closed-loop control of the ammonia synthesis cycle purge. A data acquisition module is set up to uniformly acquire process data related to inert input, purge discharge, effective component reaction consumption, and system inventory changes, providing a basic input for subsequent soft sensing and control calculations. A soft sensing module is set up to convert various types of process data into a comprehensive index that can characterize the net accumulation trend of inert components. A trend determination module is set up to determine whether there is excessively rapid accumulation of inert components or excessively strong purge under the current operating conditions based on the comprehensive index. A deviation control calculation module is set up to generate an executable correction amount based on the determination result and the magnitude of the deviation. An output execution module is set up to implement the correction amount into on-site control actions. Through the coordinated work of these modules, the control logic based on the net accumulation trend of inert components can be modularly implemented, making it easy to deploy in existing DCS, APC, PLC, or industrial computer control platforms, improving engineering convenience.

[0044] In some examples, the data acquisition module, soft measurement module, trend determination module, deviation control calculation module, and output execution module can be implemented as software functional modules and integrated into the same controller, industrial computer, or host computer system. In another example, these modules can also be configured in different control units and interact with each other through communication interfaces. By adopting a modular structure, the system can be flexibly configured according to the automation foundation of different devices, thereby improving its adaptability.

[0045] In some embodiments, the system further includes a data preprocessing module, which is used to perform time synchronization, filtering and smoothing, and outlier removal on the process data.

[0046] The reason for including a data preprocessing module is that the refresh frequency, sampling time, and transmission delay of different process measurement points may vary. Directly inputting raw data into the soft measurement module could lead to inconsistent operating conditions corresponding to different data points within the same control cycle, thus affecting the accuracy of the soft measurement results. Therefore, the data preprocessing module preferably first synchronizes the time of each process data point to ensure that the data used in the calculation correspond to the same operating condition as much as possible; then it filters and smooths rapidly fluctuating signals such as pressure, flow rate, and valve position to reduce short-term noise interference; and it identifies and removes outliers that clearly exceed the physically reasonable range or do not conform to the equipment's operating rules. By setting up this data preprocessing module, the quality of the input data can be improved, thereby enhancing the stability of the soft measurement index calculation results and subsequent control outputs.

[0047] In some examples, for signals that update rapidly, such as pressure, valve position, and flow rate, the data preprocessing module can use the latest effective value at the end of the current control cycle; for signals that update slowly, such as liquid ammonia production and inert component analysis values, the most recent effective value can be used, combined with smoothing from the previous few control cycles; for outliers, the effective value from the previous cycle, the average value of adjacent cycles, or a limited substitute value can be used in the calculation. Through these processing methods, the impact of a single abnormal measurement point or short-term fluctuation on the overall control behavior of the system can be reduced, thereby lowering the risk of malfunction.

[0048] In some embodiments, the system further includes an abnormal switching module, which is used to stop controlling the system based on the soft measurement index of the inert gas accumulation rate and switch the system to a degraded control mode when critical data fails, the cyclic pressure exceeds the set safety limit, or the system enters a major operating condition disturbance phase. The degraded control mode includes maintaining the effective relaxation control setting value of the previous cycle, switching to a preset fixed relaxation control setting value, or performing pressure-assisted control based on the pressure deviation.

[0049] The reason for including the anomaly switching module is that the validity of the soft measurement indicators is based on the premise that key process data can be obtained normally and the operating conditions are within a controllable range. When key data fails, system pressure rises abnormally, or the unit is in a major disturbance phase such as start-up, shutdown, or gas cut-off, continuing to perform closed-loop correction based on normal soft measurement results may cause the control output to deviate from actual needs, thereby affecting the safe and stable operation of the system. Therefore, when the anomaly switching module detects abnormal conditions, it preferentially suspends normal closed-loop control based on soft measurement indicators and switches to a more conservative degraded control mode. In this way, the safety and basic stability of system operation can be prioritized under abnormal operating conditions.

[0050] In some examples, when the anomaly duration is short, the anomaly switching module can control the output execution module to maintain the effective relaxation control setpoint of the previous cycle, thus avoiding frequent switching of control strategies due to short-term fluctuations. When the anomaly duration is long or critical data cannot be recovered, it can switch to a preset fixed relaxation control setpoint to ensure the system retains its basic relaxation capability. When the circulating pressure deviates significantly, it can also temporarily switch to auxiliary control based on the pressure deviation to prevent uncontrolled accumulation of inert components. After the abnormal state is eliminated, the anomaly switching module can switch the system back to the closed-loop control mode based on the soft measurement index of the inert gas accumulation rate. Through the above settings, the reliability and continuous operation capability of this invention in industrial field applications can be improved.

[0051] In some specific embodiments, the data acquisition module, data preprocessing module, soft measurement module, trend determination module, deviation control calculation module, output execution module, and anomaly switching module can be integrated into the existing control platform of the ammonia synthesis unit. During operation, the data acquisition module first acquires process data such as the total fresh gas flow rate, inert component content, venting valve opening, pressure difference across the venting branch, liquid ammonia production, and circulation loop pressure within the current control cycle. The data preprocessing module performs time synchronization, filtering, smoothing, and outlier processing on the data. The soft measurement module constructs a soft measurement index for the inert gas accumulation rate based on this data. The trend determination module determines the current accumulation trend of the inert component based on the positional relationship between the soft measurement index and the target interval. The deviation control calculation module calculates the venting control correction amount based on the trend judgment result and the magnitude of the deviation. The output execution module generates a new venting control setpoint and outputs it to the actuator. If the anomaly switching module detects that critical data is invalid or the circulation pressure exceeds the safety limit, it suspends normal closed-loop correction and switches to a degraded control mode. Through the coordinated operation of the above modules, dynamic rolling adjustment of the venting amount in the ammonia synthesis circulation system can be achieved.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A dynamic prediction control method for synthesis ammonia purge gas, characterized in that, Includes the following steps: Acquire process data for the current control cycle of the synthetic ammonia cycle system. The process data includes at least inert input related data for determining inert input characteristic quantities, purge discharge related data for determining purge discharge characteristic quantities, effective component reaction consumption related data for determining liquid ammonia production correction characteristic quantities, and system inventory change related data for determining system inventory change correction characteristic quantities. Based on the process data, the inert input characteristic quantity, the purge discharge characteristic quantity, the liquid ammonia production correction characteristic quantity, and the system inventory change correction characteristic quantity are determined, and the inert gas accumulation rate soft measurement index is calculated according to the preset weighting relationship. The inert gas accumulation rate soft measurement index is used to quantitatively characterize the net accumulation trend of inert components in the circulation system within the current control cycle. The inert gas accumulation rate soft measurement index is compared with a preset target range to determine the current accumulation trend of the inert component; Based on the judgment result of the cumulative trend and the deviation of the inert gas accumulation rate soft measurement index from the target center value, the relaxation control correction is calculated; wherein, the target center value is the center reference value of the preset target interval; A new relaxation control setpoint is generated based on the relaxation control correction and output to the actuator to dynamically adjust the relaxation amount.

2. The method of claim 1, wherein, The process data specifically includes: The inert input-related data includes the total fresh gas flow rate and the content of inert components in the fresh gas, and is used to calculate the inert input amount; The data related to venting and venting includes venting gas flow rate; when the venting gas flow rate is not directly obtained, the data related to venting and venting includes venting valve opening, pressure difference across the venting branch, and preset valve flow coefficient, and is used to estimate the venting gas flow rate. The relevant data on the reaction consumption of the effective components include liquid ammonia production or equivalent liquid ammonia generation. The system inventory change related data includes the circulating loop pressure of the current control cycle and the previous control cycle; when the pressure change of the circulating system is characterized by the synthesis tower inlet pressure, the system inventory change related data includes the synthesis tower inlet pressure of the current control cycle and the previous control cycle.

3. The method of claim 2, wherein, The steps for calculating the soft-sensor index of inert gas accumulation rate include: The inert input characteristic quantity is determined based on the total fresh air flow rate and the inert component content in the fresh air; The purge discharge characteristic quantity is determined based on the purge gas flow rate. When the purge gas flow rate is not directly obtained, the purge gas flow rate is estimated based on the purge valve opening, the pressure difference before and after the purge branch, and the preset valve flow coefficient, and the purge discharge characteristic quantity is determined accordingly. The liquid ammonia production correction characteristic quantity is determined based on the liquid ammonia production or equivalent liquid ammonia generation. The system stock change correction characteristic quantity is determined based on the pressure change of the circulating loop in the current control cycle and the previous control cycle; when the pressure change of the circulating system is characterized by the inlet pressure of the synthesis tower, the system stock change correction characteristic quantity is determined based on the pressure change of the inlet pressure of the synthesis tower in the current control cycle and the previous control cycle. Based on the inert input characteristic, the purge discharge characteristic, the liquid ammonia production correction characteristic, and the system inventory change correction characteristic, a soft measurement index for the inert gas accumulation rate is constructed.

4. The method according to claim 3, characterized in that, The inert gas accumulation rate soft measurement index The calculation expression is: wherein, is an inert input characteristic, is a blowdown discharge characteristic, is an ammonia production correction characteristic, is a system inventory change correction characteristic; , are respective weight coefficients.

5. The method of claim 1, wherein, The preset target range includes an upper threshold and a lower threshold; The steps for determining the current accumulation trend of inert components include: When the control cycle of the inert gas accumulation rate soft measurement index is greater than the upper limit threshold for a preset number of consecutive cycles, it is determined that the inert component is in a state of net rapid accumulation under the current operating conditions. When the control period of the inert gas accumulation rate soft measurement index is less than the lower limit threshold for a consecutive preset number of control cycles, it is determined that the current release is too strong and there is a tendency for excessive loss of effective gas. When the soft measurement index of the inert gas accumulation rate is within the preset target range, it is determined that the current release level is basically matched with the inert gas carryover level. The judgment step also includes a hysteresis judgment rule and / or a continuous boundary crossing judgment rule.

6. The method according to claim 1, characterized in that, The step of calculating the relaxation control correction includes: Calculate the deviation between the soft-measurement index of the inert gas accumulation rate and the target center value; When the absolute value of the deviation is greater than the set dead zone boundary, the relaxation control correction amount is calculated using a segmented proportional method; when using stepped logic, the corresponding relaxation control correction amount is determined according to the deviation range in which the deviation is located. Specifically, a single-cycle change rate limit is set for the relaxation control correction amount, and upper and lower limits are set for the relaxation control setpoint.

7. The method according to claim 1, characterized in that, The method also includes abnormal operating condition handling steps: Real-time monitoring of the validity of the process data and the system operating status; When critical data fails, the circulating pressure exceeds the set safety limit, or the system enters a major operating condition disturbance phase, control based on the soft measurement index of the inert gas accumulation rate is stopped, and the system switches to degraded control mode. The degradation control mode includes any of the following: maintaining the effective release control setting value of the previous cycle, switching to the preset fixed release control setting value, or performing pressure auxiliary control based on the pressure deviation.

8. A dynamic prediction and control system for ammonia synthesis off-gas, characterized in that, include: The data acquisition module is used to acquire process data within the current control cycle of the ammonia synthesis cycle system; The soft measurement module is used to calculate the soft measurement index of inert gas accumulation rate based on the process data; The trend determination module is used to compare the soft measurement index of the inert gas accumulation rate with a preset target range to determine the current accumulation trend of the inert component. The deviation control calculation module is used to calculate the relaxation control correction amount based on the judgment result of the cumulative trend and the deviation of the soft measurement index of the inert gas accumulation rate relative to the target center value. The output execution module is used to generate a new relaxation control setpoint based on the relaxation control correction amount and output it to the actuator.

9. The system according to claim 8, characterized in that, It also includes a data preprocessing module, which is used to perform time synchronization, filtering and smoothing, and outlier removal on the process data.

10. The system according to claim 8 or 9, characterized in that, It also includes an abnormal switching module, which is used to stop control based on the soft measurement index of the inert gas accumulation rate and switch the system to a degraded control mode when critical data fails, the circulating pressure exceeds the set safety limit, or the system enters a major operating condition disturbance stage. The degradation control mode includes maintaining the effective release control setting value of the previous cycle, switching to the preset fixed release control setting value, or performing pressure auxiliary control based on the pressure deviation.