Method for generating compressor surge signal

Abstract

FIELD: compressor engineering.SUBSTANCE: invention can be used in compressor surge protection systems. The method for generating a compressor surge signal includes measuring at least two dynamic parameters of compressor operation, calculating the rate of their change using a fifth-order digital differentiator filter with a sampling interval of 100 ms, and comparing the calculated rate with positive and negative threshold values. When the thresholds are exceeded on both sides within a specified time interval of 1 to 2 seconds, a parameter oscillation indicator is generated. The Surge output signal is generated based on majority logic, provided that an oscillation indicator is recorded simultaneously for two or more dynamic parameters, which include the pressure at the suction or discharge of the compressor sections, the pressure drops on the flow-metering devices of the compressor or turbine, the stator current of the drive electric motor, or the rotational speed of the rotors of the compressor or turbine.EFFECT: increasing the reliability and noise immunity of surge detection.4 cl, 4 dwg

Description

[0001] The invention relates to the field of compressor engineering and compressor operation, in particular to systems for determining the presence of surge in a compressor and to systems for protecting against compressor surge, and can be used in various industries.

[0002] There are various known methods for detecting and protecting a compressor from surge.

[0003] For example, a method is known according to patent No. 2453733 for an invention called "METHOD FOR PROTECTING A COMPRESSOR AGAINST SURGE" (IPC: F04D 27 / 02). The method for protecting a compressor from surge by measuring the gas pressure behind the compressor, the gas pressure before the compressor, the pressure drop at the inlet orifice (confuser), the speed of its rotor, the pressure drop at the confuser, comparing the current values ​​of these parameters with the recorded values, characterized in that the rate of change of the flow through the compressor or the rate of change of the pressure drop at the inlet orifice (confuser) and the acceleration of the compressor rotor speed are determined, if the acceleration of the compressor rotor speed exceeds the predetermined and / or the rate of flow drop through the compressor with the opposite sign greater than the predetermined A "Pre-Surge" signal is generated, after which the surge signal countdown and pre-surge signal holddown time are started. If a new "Pre-Surge" signal is received during the "Pre-Surge" signal holddown time, the holddown time is restarted. If the pre-surge signal holddown time has not yet been reached by the end of the "Surge" signal countdown, a "Surge" signal is generated. The disadvantage of this method is that the "Surge" signal is generated with a time delay relative to the onset of the surge, caused by the need to receive multiple "Pre-Surge" signals, which will correspond to several surge cycles. The time delay required to generate the "Surge" signal reduces the effectiveness of the control action that must be generated to bring the compressor out of surge mode.

[0004] The closest analogue to the claimed invention in terms of the set of existing features (prototype) is the "METHOD FOR GENERATING A TURBOCHARGER SURGE SIGNAL" according to invention patent No. 2263234 (IPC: F04D 27 / 02). A method for generating a turbocharger surge signal, including measuring compressor parameters, determining the sign and calculating the magnitude of the time derivatives of these parameters, comparing each derivative with its threshold value and generating discrete signals of excess of the derivatives of the parameters over their threshold values, characterized in that all discrete signals of excess of the derivatives of the parameters over their threshold values ​​are delayed and a surge signal is generated in the presence of two or more delayed discrete signals simultaneously on excess of the derivatives of the parameters over their threshold values.The disadvantages of this method include the requirement for correct and high-quality operation of at least two of the three measurement channels used for the majority indicator to function, which requires the simultaneous presence of signals from several channels. The presence of poor signal quality (noise, filtering, and fluctuations) in even one of the signals can lead to a missed or delayed signal indicating the presence of actual surge.

[0005] The developer of the new compressor surge signal generation method set a goal of increasing the reliability of surge detection. The technical result achieved in solving this problem is increased reliability and noise immunity of surge detection.

[0006] This technical result is achieved through the use of majority logic based on the presence of a two-way change (oscillation) of dynamic parameters that respond to the surge of the compressor being used.

[0007] The essence of the invention is that the method for generating a compressor surge signal includes measuring at least two dynamic parameters of its operation, calculating the rate of change for each measured dynamic parameter, comparing each calculated rate of change with a threshold value and generating an output discrete surge signal, characterized in that the following actions are performed simultaneously for each of the dynamic parameters of the compressor:

[0008] - calculates the rate of change of the dynamic parameter of the compressor;

[0009] - the calculated rate of change is compared with both positive and negative threshold values;

[0010] - when the rate of change exceeds the positive threshold value, a sign of exceeding the rate of change in the positive direction is generated;

[0011] - when the rate of change exceeds (in absolute value) the negative threshold value, a sign is generated that the rate of change has exceeded the negative value;

[0012] - generates an oscillation indicator for a dynamic parameter if, within a specified time interval, indicators of both positive and negative rate-of-change exceeding are generated. The "Surge" output signal is then generated provided that an oscillation indicator is generated over a specified time interval for at least two compressor dynamic parameters. The dynamic parameter's rate of change is calculated using a fifth-order digital differentiator filter operating on a sequence of unfiltered samples of the dynamic parameter's value with a sampling interval of 100 ms.The following parameters are also used as dynamic compressor parameters: suction pressure of each compressor section and / or discharge pressure of each compressor section, and / or gas pressure drop across the compressor flow meter, and / or pressure drop across the turbine flow meter, and / or stator current of the drive electric motor, and / or compressor rotor speed, and / or turbine rotor speed. Furthermore, the specified time interval for generating the dynamic parameter oscillation flag and the "Surge" flag is from 1 to 2 seconds.

[0013] The invention is explained graphically, showing:

[0014] in Fig. 1 – an example of a trend of the result of the operation of filters-differentiators according to the parameters of air pressure at the entrance to the 1st, 2nd, 3rd sections of the compressor Pn1, Pn2, Pn3 at the moment of surge for an air track-section compressor;

[0015] in Fig. 2 – an example of a trend of the result of the operation of filters-differentiators according to the parameters of air pressure at the outlet of the 1st, 2nd, 3rd sections of the compressor Pk1, Pk2, Pk3 at the moment of surge for an air track-section compressor;

[0016] in Fig. 3 – an example of a trend of the result of the operation of filters-differentiators based on the parameters of gas pressure at the compressor inlet Pn, gas pressure, pressure drop across the measuring diaphragm ∆p, current i and power n of the drive electric motor at the moment of surge of a single-section compressor;

[0017] in Fig. 4 – an example of a trend of the result of the operation of filters-differentiators based on the parameters of gas pressure at the compressor outlet Pk, pressure drop on the measuring diaphragm ∆p, current i and power n of the drive electric motor at the moment of surge of a single-section compressor;

[0018] The compressor surge signal generation method involves detecting sudden parameter fluctuations. A surge is characterized by a sharp change in the compressor's dynamic parameters. Moreover, the parameter changes in both directions—either increasing or decreasing. In other words, a surge causes a parameter fluctuation. Previously proposed methods used derivative analysis in one direction—either increasing or decreasing the parameter. The proposed method, however, specifically analyzes the detection of sudden parameter fluctuations. The set of analyzed dynamic parameters includes compressor and drive parameters (pressure, flow rate, frequency, and current) to the maximum extent. If at least two analyzed parameters from the entire sample of dynamic parameters fluctuate within a specified time interval, a surge flag is triggered. To solve this problem, the following improved solutions are proposed:

[0019] a. Formation of a parameter oscillation indicator for a measuring channel.

[0020] b. Formation of a surge indicator using majority logic across several measurement channels with an oscillation presence indicator, i.e., using "2 out of 4", "2 out of 5" logic.

[0021] c. The following are used as dynamic measuring channels:

[0022] i. Pressure drop across the orifice (gas flow rate).

[0023] ii. Stage suction pressure

[0024] iii. Stage discharge pressure.

[0025] iv. Electric motor stator current.

[0026] v. Pressure drop across the orifice (steam flow).

[0027] vi. Rotor speed.

[0028] The sensors measuring the above parameters are configured with a filter time constant of zero to minimize potential dynamic delays. 3.9. The use of a sufficiently large number of independently processed variables ensures high reliability of the protection function and immunity to single-point failures. The formation of a parameter fluctuation indicator along the measuring channel is performed as follows:

[0029] 1) Calculate the rate of change of a parameter using a fifth-order differentiator filter on five consecutive samples of the unfiltered input signal. The basic cycle is a 100 ms cycle;

[0030] 2) Comparison of the rate of change of the parameter on the current scan with a positive threshold value;

[0031] 3) Comparison of the rate of change of the parameter on the current scan with a negative threshold value;

[0032] 4) A variable that tracks the presence of a speed limit indicator above a positive threshold, recording the indicator each scan with a consistent time shift;

[0033] 5) A variable that tracks the presence of a speed limit indicator above a negative threshold, recording the indicator each scan with a sequential time shift;

[0034] 6) The oscillation flag for the measuring channel is set if, during the same specified time interval (base time – two seconds), the speed is exceeded above the positive threshold and the speed is exceeded above the negative threshold.

[0035] Each of the measured parameters is independently fed to the input of the fifth-order differentiator filter:

[0036] Yn=A1*Xn+A2* Xn-1 + A3* Xn-2 + A4* Xn-3 + A5* Xn-4

[0037] The values ​​of Yn, Xn, Xn-1, Xn-2, Xn-3, Xn-4 counts correspond to the values ​​on the current and previous controller scan.

[0038] The controller scan is set to 100 ms. The 100 ms scan value is determined by the typical update time of the pressure and differential pressure sensors. The Yn filter result for each parameter is compared with the permissible positive and negative limits over a specified time interval. Three conditions must be met to generate the "Significant dynamic two-sided parameter jump (sign of oscillation)" flag:

[0039] - Within a 1 second time window;

[0040] - There was a significant jump in the parameter in the positive direction (large derivative with a plus sign);

[0041] - There was a significant jump in the parameter in the negative direction (large derivative with a minus sign).

[0042] These flags are generated independently for each parameter. The surge detection indicator is generated using a majority sample of the type "two out of five" or "three out of seven." If the "Compressor Surge" flag is set, the detection circuit opens the recirculation line or the relief line. The recirculation valve opening value is set to 25%. After issuing a command to open the valve on a given scan, the next opening (if the "Compressor Surge" flag remains present) should occur after a 1-second interval. This circuit significantly facilitates surge tests, which identify the actual surge limit. To determine the limit, the parametric anti-surge protection and control circuit is disabled, and the surge detector remains operational. The tester loads the compressor by closing the gas discharge to the atmosphere (or recirculation) until the surge detector is triggered, which brings the machine out of the dangerous surge mode.Furthermore, the surge detector plays an important role in periodically checking the performance of the anti-surge protection and control circuit. To verify the correctness of the parametric calculations of the pre-surge margin, a surge test is performed, during which the pre-surge margin value corresponding to the surge limit is recorded. The normal value of this parameter at the surge limit is minus 8% to 14%.

[0043] Examples of trends in the results of the operation of differentiating filters at the moment of surge, responsible for the analysis of the dynamic properties of the process.

[0044] The graphs presented in Figures 1-4 show graphs of changes in the performance of the differentiating filters for several measured variables during compressor surge. Values ​​were calculated in the compressor controller (ControlLogix L55), and the parameter change graphs were recorded using specialized RSLogix5000 engineering software. The differentiating filters operated on a 100 ms scan. The parameters used for the calculations were the air pressure drop across the compressor end diaphragm, the air pressure at the compressor section inlet, and the air pressure at the compressor section outlet. Surge mode was achieved by gradually closing the air bleed valve to the atmosphere for the air compressor and by gradually closing the recirculation valve for the ethylene compressor.

[0045] Fig. 1 and Fig. 2 show an example of the trend of the filter-differentiators operation result based on the air pressure parameters at the inlet of the 1st, 2nd, 3rd compressor sections Pn1, Pn2, Pn3, and the air pressure at the outlet of the 1st, 2nd, 3rd compressor sections Pk1, Pk2, Pk3 at the moment of surge for the K-250-61-1 air track-section compressor of the Severnaya Glubokaya turbocompressor shaft of the Pechenganikel combine of JSC Kola MMC. The graphs show a sharp change in the output values ​​of the filter-differentiators both upward (in the positive direction) and downward (in the negative direction), which allows us to confidently determine the presence of parameter fluctuations and set a surge presence flag.

[0046] Fig. 3 and Fig. 4 show an example of the trend of the filter-differentiator operation results based on the parameters of gas pressure at the compressor inlet Pn, gas pressure at the compressor outlet Pk, pressure drop across the measuring diaphragm ∆p, current i, and power n of the drive electric motor at the moment of surge of a single-section ethylene compressor of the N-50-32-1M type at the Kazanorgsintez JSC workshop. The graphs show a sharp change in the output values ​​of the filter-differentiators, both upward (positive) and downward (negative), which allows one to confidently determine the presence of parameter fluctuations and set a surge indicator.

Claims

1. A method for generating a compressor surge signal, including measuring at least two dynamic parameters of its operation, calculating the rate of change for each measured dynamic parameter, comparing each calculated rate of change with a threshold value and generating an output discrete surge signal, characterized in that the following actions are performed simultaneously for each of the compressor dynamic parameters: calculate the rate of change of the dynamic parameter of the compressor operation, the calculated rate of change is compared with both positive and negative threshold values, when the rate of change exceeds the positive threshold value, a sign of excess of the rate of change in the positive direction is generated, when the absolute value of the rate of change exceeds the negative threshold value, a sign of excess of the rate of change in the negative direction is generated, form a sign of oscillation for a dynamic parameter in the event that during a given time interval, signs of exceeding the rate of change were formed in both the positive and negative direction, after which the output signal “Surge” is generated under the condition that the oscillation indicator is formed over a given time interval for at least two dynamic parameters of the compressor.

2. A method for generating a surge signal according to paragraph 1, characterized in that the calculation of the rate of change of the dynamic parameter is carried out using a fifth-order digital differentiator filter operating on a sequence of unfiltered readings of the value of the dynamic parameter with a sampling interval of 100 ms.

3. The method for generating a surge signal according to paragraph 1, characterized in that the following parameters are used as dynamic parameters of the compressor: the suction pressure of each section of the compressor and / or the discharge pressure of each section of the compressor, and / or the gas pressure drop on the compressor flow meter, and / or the pressure drop on the turbine flow meter, and / or the stator current of the drive electric motor, and / or the compressor rotor speed, and / or the turbine rotor speed.

4. The method for generating a surge signal according to paragraph 1, characterized in that the specified time interval for generating the dynamic parameter oscillation indicator and the “Surge” indicator is from 1 to 2 seconds.

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