Method for monitoring nitrogen preparation process

Abstract

The invention discloses a method for monitoring a nitrogen preparation process. The method comprises the following steps: step 100, acquiring an inlet temperature parameter, an inlet pressure parameter, an outlet temperature parameter and an outlet pressure parameter of a circulating nitrogen compressor according to a preset time interval; 200, the efficiency change rate of the circulating nitrogen compressor is analyzed based on the inlet temperature parameter, the inlet pressure parameter, the outlet temperature parameter and the outlet pressure parameter of the circulating nitrogen compressor; 300, whether the efficiency change rate of the circulating nitrogen compressor is in a first preset interval or not is judged, and if the efficiency change rate of the circulating nitrogen compressor is in the first preset interval, the running time of the circulating nitrogen compressor, the temperature difference parameter of a main heat exchanger and the inlet pressure parameter of a low-temperature expansion unit are called; 400, the running time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger and the inlet pressure parameter of the low-temperature expansion unit are analyzed, and the scaling risk probability is evaluated; and step 500, sending an online cleaning instruction according to the scaling risk probability.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrogen preparation, and particularly to a monitoring method for the nitrogen preparation process. Background Art

[0002] In modern industrial production, nitrogen, as an important industrial gas, is widely used in many fields such as chemical industry, electronics, food, and medicine. For example, it is used for ammonia synthesis, protective gas, etc. in chemical production; for atmosphere protection in the chip manufacturing process in the electronics industry; as a fresh-keeping gas in food packaging; and for gas protection in the drug production environment in the pharmaceutical field. With the continuous improvement of the requirements for nitrogen purity, output, and stability in various industries, an efficient and reliable nitrogen preparation process has become increasingly crucial.

[0003] Currently, the common nitrogen preparation methods mainly include cryogenic air separation, pressure swing adsorption, and membrane separation. Among them, cryogenic air separation occupies a dominant position in large-scale nitrogen production due to its advantage of being able to produce high-purity nitrogen. However, in the nitrogen preparation process, since it involves multiple complex and interrelated links such as air filtration, compression, cooling, purification, and rectification, any problem in one link may lead to a decline in the quality of nitrogen products, a reduction in production efficiency, and even safety accidents.

[0004] In the prior art, DCS (distributed control system) is used to obtain the relevant parameters of each device in the nitrogen production process, and when a certain parameter is abnormal, a warning is given. However, this monitoring method based on a single-parameter threshold has defects and lacks dynamic correlation analysis of parameters such as the differential pressure of the air filter, the operating state of the air compressor, the efficiency of the cooling system, and the adsorption performance of the molecular sieve. For example, when there is a slight scale formation at the boosting end of the circulating nitrogen compressor, the vibration / axial displacement of the circulating nitrogen compressor monitored alone does not exceed the standard, but it will cause a reduction in the circulating nitrogen flow, leading to an imbalance in the cooling capacity of the main heat exchanger and a decline in the rectification efficiency. Summary of the Invention

[0005] To solve the technical problems existing in the prior art, the present invention provides a monitoring method for the nitrogen preparation process.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A monitoring method for the nitrogen preparation process includes the following steps:

[0008] Step 100: Obtain the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor at a preset time interval.

[0009] Step 200: Analyze the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor.

[0010] Step 300: Determine whether the efficiency change rate of the circulating nitrogen compressor is within a first preset range. If the efficiency change rate of the circulating nitrogen compressor is within the first preset range, retrieve the operating time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit.

[0011] Step 400: Analyze the operating time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit to evaluate the probability of fouling risk.

[0012] Step 500: Send an online cleaning instruction according to the probability of fouling risk.

[0013] Preferably, analyzing the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor includes the following:

[0014] Calculate the first efficiency of the circulating nitrogen compressor corresponding to the first moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment.

[0015] Calculate the second efficiency of the circulating nitrogen compressor corresponding to the second moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the second moment.

[0016] Calculate the efficiency change rate of the circulating nitrogen compressor according to the first efficiency and the second efficiency according to a preset formula.

[0017] Preferably, calculating the first efficiency of the circulating nitrogen compressor corresponding to the first moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment includes the following:

[0018] Calculate the first enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor according to the inlet temperature parameter and inlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment.

[0019] Calculate the second enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the circulating nitrogen compressor according to the inlet temperature parameter, inlet pressure parameter, and first enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor corresponding to the first moment.

[0020] Calculate the third enthalpy value of nitrogen at the outlet of the circulating nitrogen compressor according to the outlet temperature parameter and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment.

[0021] Calculate the first efficiency of the circulating nitrogen compressor at the first moment according to the first enthalpy value, the second enthalpy value, and the third enthalpy value according to a preset calculation formula.

[0022] Preferably, according to the inlet temperature parameter and inlet pressure parameter of the recycle nitrogen compressor corresponding to the second moment, calculate the fourth enthalpy value of nitrogen at the inlet of the recycle nitrogen compressor;

[0023] According to the inlet temperature parameter, inlet pressure parameter, and fourth enthalpy value of nitrogen at the inlet of the recycle nitrogen compressor corresponding to the second moment, calculate the fifth enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the recycle nitrogen compressor;

[0024] Based on the outlet temperature parameter and outlet pressure parameter of the recycle nitrogen compressor corresponding to the second moment, calculate the sixth enthalpy value of nitrogen at the outlet of the recycle nitrogen compressor;

[0025] Based on the fourth enthalpy value, fifth enthalpy value, and sixth enthalpy value, calculate the second efficiency of the recycle nitrogen compressor at the second moment according to a preset calculation formula.

[0026] Preferably, the analysis of the operation time of the recycle nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit to evaluate the fouling risk probability includes the following:

[0027] Perform hierarchical quantization processing on the operation time of the recycle nitrogen compressor, divide the operation time into multiple time intervals, and different time intervals correspond to different first fouling risk coefficients;

[0028] Calculate the difference between the current temperature difference of the main heat exchanger and the standard temperature difference during normal operation, compare this difference with a preset temperature difference threshold, and if the difference exceeds the threshold, determine different second fouling risk coefficients according to the magnitude of the difference;

[0029] Calculate the difference between the current inlet pressure and the standard inlet pressure during normal operation, compare it with a preset pressure threshold, and determine the third fouling risk coefficient according to the magnitude of the pressure exceeding the threshold;

[0030] Perform weighted summation on the first fouling risk coefficient, second fouling risk coefficient, and third fouling risk coefficient to obtain the fouling risk probability.

[0031] Preferably, the online cleaning instruction includes a cleaning cycle and a cleaning intensity parameter, and the cleaning cycle and cleaning intensity parameter are dynamically adjusted according to the fouling risk probability.

[0032] Preferably, the cleaning cycle and cleaning intensity parameter are dynamically adjusted according to the fouling risk probability:

[0033] Pre-set a mapping table of different fouling risk probability intervals and corresponding cleaning cycle and cleaning intensity parameters;

[0034] According to the current fouling risk probability value, look up the corresponding cleaning cycle and cleaning intensity parameter adjustment rules in the mapping table.

[0035] Preferably, after evaluating the probability of fouling risk, it further includes: when the probability of fouling risk exceeds a preset threshold, an alarm signal is sent.

[0036] The beneficial effects of the present invention are as follows: Different from the traditional single-parameter threshold monitoring method, this method constructs a systematic fouling risk assessment model by combining the efficiency change rate of the circulating nitrogen compressor with multi-dimensional parameters such as running time, temperature difference of the main heat exchanger, and inlet pressure of the low-temperature expander, and can predict the fouling risk in advance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The embodiments of the present invention will be described in detail below with reference to the drawings.

[0039] Embodiment

[0040] It should be noted that during the nitrogen preparation process, air successively undergoes a series of treatment steps and finally produces nitrogen products that meet the requirements.

[0041] Air first flows into the self-cleaning air filter. The self-cleaning air filter can remove dust and other various particulate impurities in the air. The preliminarily purified air then enters the main air compressor. The main air compressor adopts a multi-stage compression design. After each stage of compression, the air will be cooled by an inter-stage cooler to reduce the temperature of the compressed air, improve the compression efficiency, and reduce energy consumption. After such multi-stage compression and cooling treatment, the air is sent into the precooling system to reduce its temperature to about 15°C.

[0042] The air undergoes heat and mass exchange with water in the direct contact air cooling tower and is cooled to ~12°C, and then enters the alternately used molecular sieve adsorber. The molecular sieve adsorber is a vertical single-bed layer, which is used to remove moisture, carbon dioxide, and some hydrocarbons in the air, so as to obtain clean and dry air. The air purified by the purification system directly enters the main heat exchanger of the fractionating tower.

[0043] In the main heat exchanger, it exchanges heat with the reflux gas (pure nitrogen, waste nitrogen, etc.) to reach a temperature close to the air liquefaction temperature and enters the lower column. In the lower column, the air is preliminarily separated into nitrogen and oxygen-rich liquid air. The nitrogen at the top is condensed into liquid in the condensing evaporator, and at the same time, the liquid oxygen on the low-pressure side of the main condenser is vaporized. Part of the liquid nitrogen is used as the reflux liquid in the lower column, and the other part of the liquid nitrogen is led out from the top of the lower column, supercooled by nitrogen and waste nitrogen in the subcooler. Part of it is throttled and sent to the condenser of the argon purification column as a cold source, vaporized and then enters the waste nitrogen pipeline. Part of it is throttled and sent to the top of the upper column to participate in rectification, and part of it is sent as a product to the storage system for storage.

[0044] A stream of pressurized nitrogen is withdrawn from the lower column, reheated by air and high-pressure nitrogen in the main heat exchanger, and then sent to the inlet of the circulating nitrogen compressor. After reheating, the pressurized nitrogen and the expanded nitrogen are compressed by the circulating nitrogen compressor and then divided into two parts. One part directly enters the main heat exchanger for cooling, and is drawn out at a certain temperature to the expansion end of the high-temperature expander for adiabatic expansion to produce the cold energy required by the air separation unit, and then returns to the main heat exchanger for reheating and then enters the circulating nitrogen compressor for circulating compression; the other part first goes to the boosting end of the high-temperature turbine expansion unit for boosting, is cooled by the cooler and then enters the boosting end of the low-temperature expansion unit for boosting, is cooled by the cooler and then enters the main heat exchanger to be cooled by the reflux cold gas, and a part is drawn out from the middle to enter the expansion end of the low-temperature expansion unit for adiabatic expansion to produce the cold energy required by the air separation unit. The expanded nitrogen returns to the main heat exchanger for reheating and enters the circulating nitrogen compressor for circulation, and the other part of the nitrogen is discharged from the end of the main heat exchanger, throttled and then sent to the top of the lower column to participate in rectification, and then the qualified nitrogen is rectified and sent to downstream users.

[0045] During the nitrogen preparation process, as the core equipment for cold energy circulation, the operating efficiency of the circulating nitrogen compressor directly affects the stability of the entire air separation system. During the actual operation process, the circulating nitrogen compressor faces the problem of fouling. The existing monitoring methods mainly focus on conventional parameters such as the vibration, temperature, and pressure of the equipment. In the initial stage of fouling of the circulating nitrogen compressor, the changes in these conventional parameters are extremely weak and it is difficult to trigger an early warning. For example, in the multi-stage compression and cooling process of air, the efficiency of the circulating nitrogen compressor begins to slowly decrease due to initial fouling, but the temperature, pressure and other parameter fluctuations of the main air compressor and the inter-stage cooler are within the normal error range and cannot be captured by the existing monitoring means. With the continuous development of fouling, until it has a significant impact on the mechanical structure of the circulating nitrogen compressor and causes abnormal vibration and other situations, it will be detected, but at this time it has had a negative impact on the nitrogen preparation process, such as causing the treatment effect of air in the subsequent cooling, purification and rectification stages to decline, and the purity and output of the product nitrogen are affected.

[0046] To solve the above problems, this embodiment provides a monitoring method for the nitrogen preparation process, as Figure 1 shown, including the following steps:

[0047] Step 100, obtain the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter and outlet pressure parameter of the circulating nitrogen compressor at a preset time interval.

[0048] For reference, in a specific implementation, relevant parameters of the circulating nitrogen compressor are obtained through high-precision temperature sensors and pressure sensors at preset time intervals. At the inlet of the circulating nitrogen compressor, a PT100 type temperature sensor is installed to accurately measure the inlet temperature parameter, and at the same time, a high-precision piezoresistive pressure sensor is equipped to measure the inlet pressure parameter. At the outlet of the circulating nitrogen compressor, sensors of the same type and with the same accuracy are also installed to obtain the outlet temperature parameter and the outlet pressure parameter.

[0049] Step 200, analyze the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor.

[0050] For reference, in a possible implementation, the analysis of the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor includes the following:

[0051] According to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment, calculate the first efficiency of the circulating nitrogen compressor corresponding to the first moment.

[0052] For reference, in a possible implementation, calculating the first efficiency of the circulating nitrogen compressor corresponding to the first moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment includes the following.

[0053] According to the inlet temperature parameter and inlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment, calculate the first enthalpy value of the nitrogen at the inlet of the circulating nitrogen compressor.

[0054] Exemplarily, based on the inlet temperature parameter and inlet pressure parameter at the first moment, combined with the thermodynamic property data of nitrogen, determine the state of the nitrogen at the inlet of the circulating nitrogen compressor at the first moment, and then calculate the first enthalpy value of the nitrogen at the inlet at the first moment.

[0055] According to the inlet temperature parameter, inlet pressure parameter, and the first enthalpy value of the nitrogen at the inlet of the circulating nitrogen compressor corresponding to the first moment, calculate the second enthalpy value of the nitrogen when isentropically compressed to the outlet pressure of the circulating nitrogen compressor.

[0056] Exemplarily, assume that the compression process in the circulating nitrogen compressor at the first moment is an isentropic compression process. Based on the inlet temperature parameter, inlet pressure parameter, and the calculated first enthalpy value at the first moment, combined with physical property parameters such as the isentropic index of nitrogen, calculate the second enthalpy value of the nitrogen when isentropically compressed to the outlet pressure of the circulating nitrogen compressor at the first moment.

[0057] Calculate the third enthalpy value of nitrogen at the outlet of the recycle nitrogen compressor based on the outlet temperature parameter and outlet pressure parameter corresponding to the first moment.

[0058] Exemplarily, based on the outlet temperature parameter and outlet pressure parameter at the first moment, combined with the thermodynamic property data of nitrogen, determine the state of nitrogen at the outlet of the recycle nitrogen compressor at the first moment, and then calculate the third enthalpy value of nitrogen at the outlet at the first moment.

[0059] Calculate the first efficiency of the recycle nitrogen compressor at the first moment according to the preset calculation formula based on the first enthalpy value, second enthalpy value, and third enthalpy value.

[0060] Exemplarily, according to the first enthalpy value, second enthalpy value, and third enthalpy value obtained from the above calculations, according to the formula: Calculate the first efficiency of the recycle nitrogen compressor corresponding to the first moment. Where n1 is the first efficiency, h1 is the first enthalpy value, h2 is the second enthalpy value, and h3 is the third enthalpy value.

[0061] Calculate the second efficiency of the recycle nitrogen compressor corresponding to the second moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the recycle nitrogen compressor corresponding to the second moment.

[0062] Referentially, in a possible implementation manner, calculate the fourth enthalpy value of nitrogen at the inlet of the recycle nitrogen compressor according to the inlet temperature parameter and inlet pressure parameter of the recycle nitrogen compressor corresponding to the second moment.

[0063] Exemplarily, based on the inlet temperature parameter and inlet pressure parameter at the second moment, combined with the thermodynamic property data of nitrogen, determine the state of nitrogen at the inlet of the recycle nitrogen compressor at the second moment, and then calculate the fourth enthalpy value of nitrogen at the inlet at the second moment.

[0064] Calculate the fifth enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the recycle nitrogen compressor according to the inlet temperature parameter, inlet pressure parameter, and fourth enthalpy value of nitrogen at the inlet of the recycle nitrogen compressor corresponding to the second moment.

[0065] Exemplarily, assume that the compression process in the recycle nitrogen compressor at the second moment is an isentropic compression process. Based on the inlet temperature parameter, inlet pressure parameter, and the calculated fourth enthalpy value at the second moment, combined with physical property parameters such as the isentropic index of nitrogen, calculate the fifth enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the recycle nitrogen compressor at the second moment.

[0066] Calculate the sixth enthalpy value of nitrogen at the outlet of the recycle nitrogen compressor based on the outlet temperature parameter and outlet pressure parameter of the recycle nitrogen compressor corresponding to the second moment;

[0067] Exemplarily, based on the outlet temperature parameter and outlet pressure parameter at the second moment, combined with the thermodynamic property data of nitrogen, the state of nitrogen at the outlet of the recycle nitrogen compressor at the second moment is determined, and then the sixth enthalpy value of nitrogen at the outlet at the second moment is calculated.

[0068] Based on the fourth enthalpy value, the fifth enthalpy value, and the sixth enthalpy value, calculate the second efficiency of the recycle nitrogen compressor at the second moment according to a preset calculation formula.

[0069] Exemplarily, according to the fourth enthalpy value, the fifth enthalpy value, and the sixth enthalpy value obtained from the above calculations, calculate the second efficiency of the recycle nitrogen compressor corresponding to the second moment according to the formula, where n2 is the second efficiency, h4 is the fourth enthalpy value, h5 is the fifth enthalpy value, and h6 is the sixth enthalpy value.

[0070] According to the first efficiency and the second efficiency, calculate the efficiency change rate of the recycle nitrogen compressor according to a preset formula.

[0071] Exemplarily, according to the calculated first efficiency and second efficiency, according to the formula calculate the efficiency change rate of the recycle nitrogen compressor, where n3 is the efficiency change rate, n1 is the first efficiency, and n2 is the second efficiency. The time interval between the first moment and the second moment is a preset time interval.

[0072] Step 300, determine whether the efficiency change rate of the recycle nitrogen compressor is within the first preset interval. If the efficiency change rate of the recycle nitrogen compressor is within the first preset interval, then retrieve the running time of the recycle nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit.

[0073] Step 400, analyze the running time of the recycle nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit, and evaluate the scaling risk probability.

[0074] Referentially, in a possible implementation manner, the analyzing the running time of the recycle nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit, and evaluating the scaling risk probability includes the following:

[0075] Perform hierarchical quantization processing on the running time of the recycle nitrogen compressor, divide the running time into multiple time intervals, and different time intervals correspond to different first scaling risk coefficients.

[0076] Exemplarily, in the specific implementation process, according to the historical operation data and experience of the factory, the running time of the recycle nitrogen compressor is divided into the following time intervals:

[0077] Time interval 1: The operating time t ≤ 100 hours, and the corresponding first scaling risk coefficient k1 = 0.1.

[0078] Time interval 2: 100 < t ≤ 300 hours, and the corresponding first scaling risk coefficient k1 = 0.3.

[0079] Time interval 3: 300 < t ≤ 500 hours, and the corresponding first scaling risk coefficient k1 = 0.5.

[0080] Time interval 4: t > 500 hours, and the corresponding first scaling risk coefficient k1 = 0.7.

[0081] Assume that the operating time of the current circulating nitrogen compressor is t = 250 hours. By querying the above classification and quantification table, it can be known that the corresponding first scaling risk coefficient k1 = 0.3.

[0082] Calculate the difference between the current temperature difference of the main heat exchanger and the standard temperature difference during normal operation, and compare this difference with a preset temperature difference threshold. If the difference exceeds the threshold, determine different second structural risk coefficients according to the magnitude of the difference.

[0083] Exemplarily, in a specific implementation process, determine the standard temperature difference △Tstandard during normal operation of the main heat exchanger. According to the design parameters of the factory and the statistical data of long-term operation, △Tstandard = 10 ± 2 °C. Monitor the current temperature difference △Tcurrent of the main heat exchanger in real time. For example, at a certain moment, it is measured that △Tcurrent = 15 °C. Calculate the difference △T between the current temperature difference and the standard temperature difference: △T = △Tcurrent - △Tstandard = 15 - 10 = 5 °C. The preset temperature difference threshold is △Tthreshold = 3 °C. Since △T = 5 °C > △Tthreshold, determine the second scaling risk coefficient k2 according to the magnitude of the difference. When △Tthreshold < △T ≤ 5 °C, k2 = 0.4; when 5 °C < △T ≤ 7 °C, k2 = 0.6; when △T > 7 °C, k2 = 0.8. Since △T = 5 °C, the second scaling risk coefficient k2 = 0.4.

[0084] Calculate the difference between the current inlet pressure and the standard inlet pressure during normal operation, and compare it with a preset pressure threshold. Determine the third scaling risk coefficient according to the magnitude of the pressure exceeding the threshold.

[0085] Exemplarily, determine the standard inlet pressure P standard when the low-temperature expansion unit is operating normally. According to the equipment specifications and operating experience, P standard = 0.5 ± 0.05 MPa. Real-time monitor the current inlet pressure P current of the low-temperature expansion unit. For example, at the same moment, it is measured that P current = 0.58 MPa. Calculate the difference △P between the current inlet pressure and the standard inlet pressure, △P = P current - P standard = 0.58 - 0.5 = 0.08 MPa. The preset pressure threshold is △P threshold = 0.05 MPa. Since △P = 0.08 MPa > △P threshold, determine the third scaling risk coefficient k3 according to the magnitude of the exceeded pressure threshold. When △P threshold < △P ≤ 0.1 MPa, k3 = 0.3; when 0.1 MPa < △P ≤ 0.15 MPa, k3 = 0.5; when △P > 0.15 MPa, k3 = 0.7. Since △P = 0.08 MPa, the third scaling risk coefficient k3 = 0.3.

[0086] Perform a weighted sum of the first structural risk coefficient, the second structural risk coefficient, and the third structural risk coefficient to obtain the scaling risk probability.

[0087] Use the method of weighted sum to calculate the scaling risk probability R, and the formula is: R = w1k1 + w2k2 + w3k3.

[0088] Among them, w1, w2, and w3 are the weights of the first scaling risk coefficient, the second scaling risk coefficient, and the third scaling risk coefficient respectively. According to experience and the analysis of the importance of each parameter, it is set that w1 = 0.4, w2 = 0.4, and w3 = 0.2.

[0089] Step 500, send an online cleaning instruction according to the scaling risk probability.

[0090] In a possible implementation manner, the online cleaning instruction includes a cleaning cycle and a cleaning intensity parameter, and the cleaning cycle and the cleaning intensity parameter are dynamically adjusted according to the scaling risk probability.

[0091] In a possible implementation manner, the cleaning cycle and the cleaning intensity parameter are dynamically adjusted according to the scaling risk probability: preset a mapping table of different scaling risk probability intervals and corresponding cleaning cycle and cleaning intensity parameters; according to the current scaling risk probability value, look up the corresponding cleaning cycle and cleaning intensity parameter adjustment rules in the mapping table.

[0092] In a possible implementation manner, after evaluating the scaling risk probability, it further includes: when the scaling risk probability exceeds the preset threshold, send an alarm signal.

[0093] Exemplarily, in the specific implementation process, in this monitoring method, by analyzing parameters such as the operating time of the circulating nitrogen compressor, the temperature difference of the main heat exchanger, and the inlet pressure of the low-temperature expansion unit, and calculating the fouling risk probability through weighted summation. The preset threshold is determined in advance based on past operating experience, equipment design standards, and research on the degree of fouling influence.

[0094] In summary, by using the calculation method based on the thermodynamic principle, in the initial stage of fouling, even if there are no obvious abnormalities in the mechanical parameters, the subtle changes in the efficiency of the circulating nitrogen compressor can be detected. Compared with the traditional monitoring methods, the trend of efficiency reduction can be discovered in advance. When the efficiency change rate of the circulating nitrogen compressor is within a specific range, multiple parameters such as the operating time, the temperature difference of the main heat exchanger, and the inlet pressure of the low-temperature expansion unit are immediately retrieved for collaborative analysis. The hierarchical quantification of the operating time takes into account the cumulative risk generated by the long-term operation of the equipment; the temperature difference of the main heat exchanger can reflect the influence of fouling on the heat exchange efficiency; the inlet pressure of the low-temperature expansion unit reflects the interference of fouling on gas flow. By calculating the fouling risk probability through weighted summation, compared with the judgment of a single parameter, the comprehensiveness and accuracy of risk assessment are improved.

[0095] The above-described embodiments merely represent the specific implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A monitoring method for the nitrogen preparation process, characterized in that, It includes the following steps: Step 100: Obtain the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor at preset time intervals; Step 200: Analyze the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor; Step 300: Determine whether the efficiency change rate of the circulating nitrogen compressor is within a first preset range. If the efficiency change rate of the circulating nitrogen compressor is within the first preset range, retrieve the operating time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit; Step 400: Analyze the operating time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit to evaluate the probability of fouling risk; Step 500: Send an online cleaning instruction according to the probability of fouling risk.

2. The monitoring method for a nitrogen preparation process according to claim 1, characterized in that, The analysis of the efficiency change rate of the circulating nitrogen compressor based on the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor includes the following: Calculate the first efficiency of the circulating nitrogen compressor corresponding to the first moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment; Calculate the second efficiency of the circulating nitrogen compressor corresponding to the second moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the second moment; Calculate the efficiency change rate of the circulating nitrogen compressor according to the first efficiency and the second efficiency according to a preset formula.

3. The monitoring method for a nitrogen preparation process according to claim 2, characterized in that, Calculating the first efficiency of the circulating nitrogen compressor corresponding to the first moment according to the inlet temperature parameter, inlet pressure parameter, outlet temperature parameter, and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment includes the following: Calculate the first enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor according to the inlet temperature parameter and inlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment; Calculate the second enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the circulating nitrogen compressor according to the inlet temperature parameter, inlet pressure parameter, and the first enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor corresponding to the first moment; Calculate the third enthalpy value of nitrogen at the outlet of the circulating nitrogen compressor according to the outlet temperature parameter and outlet pressure parameter of the circulating nitrogen compressor corresponding to the first moment; Calculate the first efficiency of the circulating nitrogen compressor at the first moment according to the first enthalpy value, the second enthalpy value, and the third enthalpy value according to a preset calculation formula.

4. The monitoring method of a nitrogen preparation process according to claim 3, wherein Calculate the fourth enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor according to the inlet temperature parameter and inlet pressure parameter of the circulating nitrogen compressor corresponding to the second moment; Calculate the fifth enthalpy value of nitrogen when isentropically compressed to the outlet pressure of the circulating nitrogen compressor according to the inlet temperature parameter, inlet pressure parameter, and the fourth enthalpy value of nitrogen at the inlet of the circulating nitrogen compressor corresponding to the second moment; Calculate the sixth enthalpy value of nitrogen at the outlet of the circulating nitrogen compressor according to the outlet temperature parameter and outlet pressure parameter of the circulating nitrogen compressor corresponding to the second moment; Calculate the second efficiency of the circulating nitrogen compressor at the second moment according to the fourth enthalpy value, the fifth enthalpy value, and the sixth enthalpy value according to a preset calculation formula.

5. The monitoring method for a nitrogen preparation process according to claim 4, wherein Analyzing the running time of the circulating nitrogen compressor, the temperature difference parameter of the main heat exchanger, and the inlet pressure parameter of the low-temperature expansion unit, and evaluating the scaling risk probability includes the following: Perform hierarchical quantification on the running time of the circulating nitrogen compressor, divide the running time into multiple time intervals, and different time intervals correspond to different first scaling risk coefficients; Calculate the difference between the current temperature difference of the main heat exchanger and the standard temperature difference during normal operation, compare this difference with a preset temperature difference threshold. If the difference exceeds the threshold, determine different second structural risk coefficients according to the magnitude of the difference; Calculate the difference between the current inlet pressure and the standard inlet pressure during normal operation, and compare it with a preset pressure threshold. Determine the third scaling risk coefficient according to the magnitude of the pressure exceeding the threshold; Perform weighted summation on the first structural risk coefficient, the second structural risk coefficient, and the third structural risk coefficient to obtain the scaling risk probability.

6. The monitoring method for a nitrogen preparation process according to claim 1, characterized in that, The on-line cleaning instruction includes a cleaning cycle and a cleaning intensity parameter, and the cleaning cycle and the cleaning intensity parameter are dynamically adjusted according to the scaling risk probability.

7. The monitoring method for a nitrogen preparation process according to claim 6, wherein, The cleaning cycle and the cleaning intensity parameter are dynamically adjusted according to the scaling risk probability: Pre-set a mapping table of different scaling risk probability intervals and corresponding cleaning cycle and cleaning intensity parameters; According to the current scaling risk probability value, look up the corresponding cleaning cycle and cleaning intensity parameter adjustment rules in the mapping table.

8. A monitoring method for a nitrogen preparation process according to claim 7, characterized in that, After evaluating the scaling risk probability, it also includes: when the scaling risk probability exceeds a preset threshold, send an alarm signal.

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