A method for monitoring surge in a centrifugal compressor

Abstract

The present application relates to a kind of centrifugal compressor surge monitoring method, belong to the control technical field of centrifugal compressor.The centrifugal compressor surge monitoring method includes centrifugal compressor system, the centrifugal compressor system includes centrifugal compressor, frequency converter for controlling the operation of centrifugal compressor, and the pipe network connected with centrifugal compressor;The centrifugal compressor includes inlet guide vane, bypass valve is equipped on the pipe network, and it further includes frequency converter input power detection device.The present application judges whether centrifugal compressor has occurred surge by the standard deviation and correlation coefficient of the change of frequency converter input power, but due to active load change and passive load change, it can also cause the change of power standard deviation and correlation coefficient, in order to avoid system misjudgment, by analyzing the characteristics of active load change and passive load change, it is eliminated in surge change judgment, guarantee the accuracy of surge judgment.

Description

Technical Field

[0001] This invention relates to a method for monitoring surge in a centrifugal compressor, belonging to the field of centrifugal compressor control technology. Background Technology

[0002] The surge phenomenon in centrifugal compressors is caused by excessive pipeline resistance leading to extremely low flow rates in the centrifugal compressor. This causes rotational detachment within the impeller or diffuser, resulting in deteriorated flow and stall. The centrifugal compressor outlet pressure suddenly drops significantly, falling below the pressure in the pipeline. Consequently, gas in the pipeline instantly flows back into the centrifugal compressor. This backflow temporarily alleviates the problem of insufficient flow in the impeller or diffuser, improving flow and causing the centrifugal compressor outlet pressure to rise. However, due to the instantaneous drop in pipeline pressure caused by the backflow, the backflow stops, and the centrifugal compressor resumes supplying gas to the pipeline. Normal gas supply increases pipeline resistance, raising the pressure within the pipeline and reducing the flow rate again. When the flow rate becomes extremely low, the flow in the impeller or diffuser deteriorates again, causing the centrifugal compressor outlet pressure to drop suddenly and significantly once more, and gas in the pipeline flows back into the compressor again. This periodic, low-frequency, large-amplitude airflow oscillation phenomenon within the system is called surge.

[0003] When mild surge occurs, the pulsation and periodic oscillation of airflow will cause large fluctuations in air supply parameters (pressure, flow rate, etc.), which will significantly reduce system stability and the operating efficiency of centrifugal compressors. Severe surge will cause the blades to vibrate strongly, increase noise, and may even cause friction and collision between moving and stationary parts, causing the compressor shaft to bend and deform, resulting in serious damage to the equipment.

[0004] Existing methods for monitoring surge include: (1) The test personnel rely on listening to the breathing sound to monitor, which requires manual supervision and does not meet the characteristics of automatic operation of the equipment; (2) Install a vibration sensor on the centrifugal compressor, but this will increase the equipment cost; (3) Monitoring the current and judging by the number of times the current fluctuation exceeds the limit cannot accurately characterize the surge characteristics and is prone to false alarms and missed alarms. When false alarms occur, the equipment will stop without reason, which can cause significant losses to production in special cases. When missed alarms occur, the surge can cause irreversible significant losses to the equipment. In addition, the current is not only affected by the load size, but also by the output voltage regulation of the frequency converter. Therefore, the standard deviation of the current may sometimes be too large when the load is stable. Summary of the Invention

[0005] The purpose of this invention is to provide a new technical solution to improve or solve the technical problems existing in the prior art as described above.

[0006] The technical solution provided by this invention is as follows: A method for monitoring surge in a centrifugal compressor, comprising a centrifugal compressor system, the centrifugal compressor system comprising a centrifugal compressor, a frequency converter for controlling the operation of the centrifugal compressor, and a pipeline network connected to the centrifugal compressor; the centrifugal compressor comprises an inlet guide vane, the pipeline network is provided with a bypass valve, and the method further comprises a frequency converter input power detection device, the monitoring method of which is as follows; S1. Continuously measure the input power of the frequency converter within a set period using an input power detection device. , where i is a positive integer greater than or equal to 1, calculate the standard deviation s of the power change, if the absolute value of the standard deviation s within one cycle is less than or equal to the surge judgment setting value Q, then continue to detect the input power of the inverter, if the absolute value of the standard deviation s within one cycle is greater than the surge judgment setting value Q, then continue to execute S2;

[0007] S2. Determine if the issue is caused by changes in active load. If not, proceed to S3. If so, continue execution. S2.1 Determine if the change is caused by a change in the set frequency. If so, execute S1 after the frequency change response time TF. If not, continue to execute S2.2. S2.2 Determine whether the change is caused by the inlet guide vane opening. If so, execute S1 after the inlet guide vane response time TR. If not, execute S2.3. S2.3 is caused by a change in the opening degree of the bypass valve. S1 will be executed after the bypass valve response time Tb. S3. Determine whether the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When the absolute value of the power standard deviation s within a cycle is greater than the surge judgment setting value Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then the centrifugal compressor is judged to have experienced a surge. When the absolute value of the standard deviation s is greater than the surge judgment setting value Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and S1 continues.

[0008] Furthermore, in step S2.1, if the frequency is increasing, the frequency change response time TF is the host acceleration response time, TF=Ta*Ha / Hmax. If the frequency is decreasing, the frequency change response time TF is the host deceleration response time, TF=t+Td*Hd / Hmax, where Hmax is the maximum frequency of the inverter, Ta is the acceleration time, Td is the deceleration time, Ha is the frequency increase, Hd is the frequency decrease, and the duration of power feedback fluctuation caused by frequency change is t.

[0009] Furthermore, in step S2.2, the inlet guide vane response time TR = t1 + T1 * a / 100, where T1 is the full stroke time of the inlet guide vane, a is the change in the opening of the inlet guide vane, and the duration of the power feedback fluctuation caused by the change in the opening of the inlet guide vane is t1.

[0010] Furthermore, in step S2.3, the bypass valve response time Tb = t2 + T2*b / 100, where T2 is the full stroke time of the bypass valve, b is the change in the opening of the bypass valve, and the duration of the power feedback fluctuation caused by the change in the opening of the bypass valve is t2.

[0011] Furthermore, the formula for calculating the standard deviation s is as follows:

[0012] in, Here is the number of samples, and the sample mean is: , This is a power sample.

[0013] Furthermore, the formula for calculating the correlation coefficient r is as follows:

[0014] in, for The time sample corresponding to the power sample, and .

[0015] Furthermore, when surge is detected, the frequency of the inverter and the ratio of the intake pressure to the exhaust pressure of the centrifugal compressor are recorded.

[0016] Compared with the prior art, the technical solution provided by this invention has the following beneficial effects: This invention uses the standard deviation and correlation coefficient of the variable frequency drive input power to determine whether a centrifugal compressor has experienced surge. However, since changes in active load and passive load can also cause changes in the power standard deviation and correlation coefficient, in order to avoid system misjudgment, the characteristics of active load and passive load changes are analyzed and eliminated in the surge change judgment to ensure the accuracy of surge judgment. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1This is a flowchart of the centrifugal compressor surge monitoring method of the present invention. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0020] like Figure 1 As shown, a method for monitoring surge in a centrifugal compressor includes a centrifugal compressor system, which comprises a centrifugal compressor, a frequency converter for controlling the operation of the centrifugal compressor, and a piping network connected to the centrifugal compressor. The centrifugal compressor includes inlet guide vanes, and a bypass valve is provided on the piping network. The method also includes a frequency converter input power detection device, and the monitoring method is as follows: S1. Continuously measure the input power of the frequency converter within a set period using an input power detection device. Where i is a positive integer greater than or equal to 1, calculate the standard deviation s of the power change. If the absolute value of the standard deviation s within one cycle is less than or equal to the surge judgment setpoint Q, then continue to detect the input power of the frequency converter. If the absolute value of the standard deviation s within one cycle is greater than the surge judgment setpoint Q, then continue to execute S2.

[0021] S2. Determine if the issue is caused by changes in the active load. Changes in the active load include changes in the inverter frequency, the inlet guide vane opening, and the bypass valve opening. If not, proceed to S3; otherwise, continue to the next step. S2.1 Determine if the change is caused by a change in the set frequency. If so, execute S1 after the frequency change response time TF. If the frequency is increasing, the frequency change response time TF is the main unit's acceleration response time, TF = Ta * Ha / Hmax. If the frequency is decreasing, the frequency change response time TF is the main unit's deceleration response time, TF = t + Td * Hd / Hmax, where Hmax is the inverter's maximum frequency, Ta is the acceleration time, Td is the deceleration time, Ha is the frequency increase, Hd is the frequency decrease, and the duration of the power feedback fluctuation caused by the frequency change is t. If the change is not caused by a change in the set frequency, continue executing S2.2. S2.2 Determine if the change is caused by the inlet guide vane opening. If so, execute S1 after the inlet guide vane response time TR. The inlet guide vane response time TR = t1 + T1 * a / 100, where T1 is the full stroke time of the inlet guide vane, a is the change in the inlet guide vane opening, and the duration of the power feedback fluctuation caused by the change in the inlet guide vane opening is t1. If not, execute S2.3. S2.3 is caused by the change in the bypass valve opening. S1 will be executed after the bypass valve response time Tb. The bypass valve response time Tb = t2 + T2 * b / 100, where T2 is the full stroke time of the bypass valve and b is the change in the bypass valve opening. The duration of the power feedback fluctuation caused by the change in the bypass valve opening is t2.

[0022] It should be noted that since changes in the frequency of the inverter, the opening of the inlet guide vane, and the opening of the bypass valve can also cause power feedback fluctuations, when the system experiences the above-mentioned active load changes, power feedback monitoring should be performed after a certain response time to determine whether surge has occurred, so as to avoid false alarms from the equipment.

[0023] S3. Determine if the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When a centrifugal compressor experiences surge, the inverter's input power will change periodically. If the absolute value of the power standard deviation s within one cycle is greater than the surge judgment setting value Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then it is determined that the centrifugal compressor has experienced a surge. Record the inverter's frequency and the ratio of the centrifugal compressor's suction pressure to discharge pressure during the surge, and then continue to execute S1 to continuously detect the surge point. If the absolute value of the standard deviation s is greater than the surge judgment setting value Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and continue to execute S1.

[0024] During surge, the power characteristics of the inverter fluctuate periodically, with the periodicity and power standard deviation varying with the severity of the surge. Mild surges have longer surge cycles and smaller power standard deviations, while severe surges have shorter surge cycles and larger power standard deviations. Therefore, the surge intensity judgment in this invention is determined by the standard deviation and the surge cycle. A strong correlation coefficient that is initially negative and then positive indicates surge. If this pattern is not observed, it is considered to be caused by passive load. Passive load-induced surges may only show a positive or negative correlation coefficient, and the correlation coefficient may not reach 0.8. Therefore, the standard deviation will be greater than the set value. As long as the initial negative-then-positive pattern is not observed, it is considered to be caused by passive load changes.

[0025] Furthermore, when the load remains constant, it will not cause changes in the power standard deviation and correlation coefficient, thus avoiding false surge predictions. The speed of active load adjustment is determined by the setter and may be very fast, adjusting every few seconds or tens of seconds; however, passive load fluctuations in the system will not be as frequent.

[0026] The formula for calculating the standard deviation s is as follows:

[0027] in, Here is the number of samples, and the sample mean is: , This is a power sample.

[0028] The formula for calculating the correlation coefficient r is as follows:

[0029] in, for The time sample corresponding to the power sample, and .

[0030] The correlation coefficient changes from -1 to +1, when This indicates that the two variables are positively correlated, meaning that the larger the value of one variable is, the larger the value of the other variable will also be. This indicates that the two variables are negatively correlated, meaning that the larger the value of one variable is, the smaller the value of the other variable will be. The larger the absolute value of the coefficient, the stronger the correlation between the two variables. It is generally believed that... There is a significant correlation. Highly correlated The correlation is moderate. Low correlation The relationship is extremely weak; it is considered unrelated.

[0031] This invention uses the standard deviation and correlation coefficient of the inverter input power change to determine whether a centrifugal compressor has experienced surge. However, since changes in active and passive loads can also cause changes in the power standard deviation and correlation coefficient, in order to avoid system misjudgment, the characteristics of active and passive load changes are analyzed and eliminated in the surge change judgment to ensure the accuracy of surge judgment.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surge monitoring method for a centrifugal compressor, comprising a centrifugal compressor system, characterized by, The centrifugal compressor system includes a centrifugal compressor, a frequency converter for controlling the operation of the centrifugal compressor, and a piping network connected to the centrifugal compressor. The centrifugal compressor includes inlet guide vanes, and the piping network is equipped with a bypass valve. It also includes a frequency converter input power detection device, the monitoring method of which is as follows: S1, continuously measuring the input power of the frequency converter in a set period through an input power detection device wherein i is a positive integer greater than or equal to 1, the standard deviation s of the power change is calculated, if the absolute value of the standard deviation s in a period is less than or equal to the surge judgment setting value Q, the input power of the frequency converter is continuously detected, if the absolute value of the standard deviation s in a period is greater than the surge judgment setting value Q, S2 is continuously executed. S2. Determine if the issue is caused by changes in active load. If not, proceed to S3. If so, continue execution. S2.1 Determine if the change is caused by a change in the set frequency. If so, execute S1 after the frequency change response time TF. If not, continue to execute S2.

2. S2.2 Determine whether the change is caused by the inlet guide vane opening. If so, execute S1 after the inlet guide vane response time TR. If not, execute S2.

3. S2.3 is caused by a change in the opening degree of the bypass valve. S1 will be executed after the bypass valve response time Tb. S3. Determine whether the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When the absolute value of the standard deviation s of the power within one cycle is greater than the surge judgment setting value Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then it is determined that the centrifugal compressor has experienced a surge, and S1 continues to be executed; when the absolute value of the standard deviation s is greater than the surge judgment setting value Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and S1 continues to be executed.

2. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, In step S2.1, if the frequency is increasing, the frequency change response time TF is the main unit acceleration response time, TF=Ta*Ha / Hmax. If the frequency is decreasing, the frequency change response time TF is the main unit deceleration response time, TF=t+Td*Hd / Hmax, where Hmax is the maximum frequency of the inverter, Ta is the acceleration time, Td is the deceleration time, Ha is the frequency increase, Hd is the frequency decrease, and the duration of power feedback fluctuation caused by frequency change is t.

3. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, In step S2.2, the inlet guide vane response time TR = t1 + T1*a / 100, where T1 is the full stroke time of the inlet guide vane, a is the change in the opening of the inlet guide vane, and the duration of the power feedback fluctuation caused by the change in the opening of the inlet guide vane is t1.

4. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, In step S2.3, the bypass valve response time Tb = t2 + T2*b / 100, where T2 is the full stroke time of the bypass valve, b is the change in the opening of the bypass valve, and the duration of the power feedback fluctuation caused by the change in the opening of the bypass valve is t2.

5. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, The formula for calculating the standard deviation s is as follows: in, Here is the number of samples, and the sample mean is: , This is a power sample.

6. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, The formula for calculating the correlation coefficient r is as follows: in, for The time sample corresponding to the power sample, and .

7. The method for monitoring surge in a centrifugal compressor according to claim 1, characterized in that, When surge is detected, record the frequency of the inverter and the ratio of the intake pressure to the exhaust pressure of the centrifugal compressor.

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