Method for setting surge line of axial flow compressor with inlet pressure as variable

Abstract

The invention relates to an axial flow compressor, and provides an axial flow compressor surge line setting method with inlet pressure as a variable in order to solve the technical problem that the safe operation boundary of a compressor cannot be accurately confirmed under the working condition that the inlet pressure of the compressor is changed in a large range in an existing compressor surge line. Comprising the following steps that a two-dimensional coordinate system is established, the abscissa of a surge line setting curve is set as the reduced flow m'of a surge line, and the ordinate is set as the pressure ratio; the axial flow compressor is adjusted to be in a stable working condition, and after the working condition is kept for a certain time, a surge line setting curve coefficient Y1 is calculated; related parameters of each surge point of the axial flow compressor are recorded through a surge test experiment, and the reduced flow corresponding to each surge point is calculated according to the coefficient Y1 obtained through calculation; and according to the calculated reduced flow of each surge point and the measured pressure ratio, a surge curve schematic diagram is drawn and formed.

Description

Technical Field

[0001] The invention relates to an axial flow compressor, and in particular to a method for setting a surge line of an axial flow compressor with a variable inlet pressure. Background Art

[0002] The surge line of an axial compressor is a critical benchmark parameter for the operation of the unit. It is determined by parameters such as pressure ratio and flow rate. Its formation mechanism is closely related to airflow separation and pipe network resonance. When the joint operating point enters the surge limit line, the surge phenomenon is triggered.

[0003] The most common method for setting the surge line of an existing axial compressor is as follows: Figure 1 As shown, the coordinate variable of the X axis in the two-dimensional coordinate system is set to the throat differential pressure value, referred to as throat difference, represented by Δp, and the coordinate variable of the Y axis is set to absolute pressure or pressure ratio;

[0004] When the pressure at the compressor inlet is within a constantly changing range, such as when the inlet pressure changes from 99 kPa to 10 kPa, the density of the working fluid naturally decreases due to the decrease in inlet pressure, and the throat differential pressure also tends to decrease. If the throat differential pressure is still used as the coordinate variable of the X-axis, the system will mistakenly determine that the compressor has entered a surge condition and shut down due to the decrease in throat differential pressure. In fact, the compressor has not entered a surge condition. Therefore, this setting method cannot accurately confirm the safe operating boundary of the compressor when the compressor inlet pressure fluctuates within a large range, resulting in abnormal operation of the compressor and affecting the safe operation of the compressor. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that the existing compressor surge line cannot accurately confirm the safe operating boundary of the compressor when the compressor inlet pressure fluctuates within a large range, and to propose a method for setting the surge line of an axial flow compressor with a variable inlet pressure.

[0006] To achieve the above objectives, the technical solutions proposed by the present invention are:

[0007] A method for setting a surge line of an axial flow compressor with a variable inlet pressure is characterized in that it includes the following steps:

[0008] S1. Establish a two-dimensional coordinate system, set the horizontal coordinate of the surge line setting curve to the equivalent flow rate m' of the surge line, and the vertical coordinate to the pressure ratio; the pressure ratio is the ratio of the compressor outlet pressure to the inlet pressure;

[0009] S2. Adjust the axial flow compressor to a stable operating condition and maintain it at this condition for a certain period of time. Then collect the voltage and current of the compressor drive motor, the inlet temperature, outlet temperature, inlet pressure, outlet pressure, and throat pressure of the compressor, and calculate the coefficient Y1 using the following formula;

[0010]

[0011] Where U is the voltage of the compressor drive motor, I is the current of the compressor drive motor, T1 is the inlet temperature, T2 is the outlet temperature, p1 is the inlet pressure, ΔP is the throat pressure difference, and Cp is the constant pressure specific heat capacity of the working fluid;

[0012] S3. Record the throat pressure difference ΔP, inlet pressure p1, and outlet pressure p3 of each surge point of the axial flow compressor through a surge test experiment. Calculate the equivalent flow rate m′ corresponding to each surge point using the following formula based on the coefficient Y1 calculated in step S2.

[0013]

[0014] S4. Draw a surge line curve diagram based on the calculated equivalent flow rate m' of each surge point and the measured pressure ratio ε.

[0015] Furthermore, in step S2, the axial flow compressor is adjusted to a stable operating condition and maintained for at least 40 minutes.

[0016] Furthermore, in step S2, the throat pressure difference ΔP is calculated by the following formula:

[0017] ΔP=P2-P1

[0018] Among them, P2 is the compressor throat pressure.

[0019] Furthermore, in step S4, the pressure ratio ε satisfies the following formula:

[0020]

[0021] Among them, P3 is the outlet pressure of the compressor.

[0022] Beneficial effects of the present invention:

[0023] [1] The present invention provides a method for setting the surge line of an axial flow compressor with a variable inlet pressure. The horizontal coordinate of the surge line is set to the equivalent flow rate, and the vertical coordinate is set to the pressure ratio. This method can effectively solve the problem of compressor operation safety when the inlet pressure of the compressor is in a wide range of fluctuation conditions, effectively reduce the probability of system misjudgment, and ensure that the compressor always maintains a stable, safe, and sustainable operating state.

[0024] [2] The compressor surge line setting method provided by the present invention uses actual test values ​​to more accurately draw the surge line curve, effectively improving the accuracy and effectiveness of the calculated compressor surge line and improving the operating stability of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The invention relates to a method for setting a surge line of an existing axial flow compressor in the background technology of the invention;

[0026] Figure 2 This is a schematic diagram of a surge line curve according to an embodiment of a method for setting a surge line for an axial flow compressor with a variable inlet pressure. DETAILED DESCRIPTION

[0027] A method for setting a surge line of an axial flow compressor with a variable inlet pressure comprises the following steps:

[0028] S1. Establish a two-dimensional coordinate system, set the horizontal coordinate of the surge line setting curve to the equivalent flow rate m' of the surge line, and the vertical coordinate to the pressure ratio; the pressure ratio is the ratio of the compressor outlet pressure to the inlet pressure;

[0029] S2. Select a certain stator blade opening for the compressor and adjust the axial flow compressor to a stable operating condition. After maintaining this operating condition for at least 40 minutes, collect the voltage and current of the compressor drive motor, the compressor inlet temperature, outlet temperature, inlet pressure, and throat pressure, and calculate the coefficient Y1 using the following formula:

[0030]

[0031] Where U is the voltage of the compressor drive motor, I is the current of the compressor drive motor, T1 is the inlet temperature, T2 is the outlet temperature, P1 is the inlet pressure, ΔP is the throat pressure difference, and Cp is the constant pressure specific heat capacity of the working fluid;

[0032] S3. Record the throat pressure difference and inlet pressure of each surge point of the axial flow compressor through a surge test experiment. Calculate the equivalent flow rate m′ corresponding to each surge point using the following formula based on the coefficient Y1 calculated in step S2;

[0033]

[0034] S4. Draw a surge line curve diagram based on the calculated equivalent flow rate m' of each surge point and the measured pressure ratio ε.

[0035] The value of Y1 is calculated according to the following formula:

[0036]

[0037] The mass flow rate m is:

[0038]

[0039] The formula for the reduced flow rate m′ is derived as follows:

[0040]

[0041] Will Denoted as coefficient Y1, then:

[0042] Where: A1 is the compressor inlet cross-sectional area, C1 is the compressor inlet flow rate, A2 is the compressor throat cross-sectional area, C2 is the compressor throat flow rate, α1 is the flow coefficient, and R is the working fluid gas constant.

[0043] Since Y1 is a parameter related to the actual working conditions, it is more accurate to use the actual test value; select a certain stator blade opening for the compressor, adjust the axial flow compressor to a stable working condition, and maintain this working condition for at least 40 minutes, then collect the voltage and current of the compressor drive motor, the compressor inlet temperature, outlet temperature, inlet pressure and throat pressure difference;

[0044] According to the motor power

[0045] Compressor power P 压 =m·Cp·(T2-T1), combined to obtain:

[0046]

[0047] The specific derivation process of the equivalent flow rate m′ is as follows:

[0048]

[0049] The formula and Simultaneous calculations yield

[0050] The compressor surge line obtained through the above calculation can effectively ensure that the compressor can always maintain a safe operating state.

[0051] According to the above calculation method, the compressor surge line is calculated based on the measurement parameters in the following table: Figure 2 As shown:

[0052] Speed r / min 1840 2040 2240 2440 2630 Throat pain kpa 1.22 1.17 1.15 1.30 1.48 Inlet pressure kpa 40.37 30.34 23.67 19.77 17.98 Inlet temperature ℃ 16 16 16 16 16 Pressure ratio / 2.571 3.433 4.424 5.321 5.907 Throat difference / inlet pressure 0.03016 0.03843 0.04876 0.06582 0.08242 Equivalent flow m' 0.03141 0.03546 0.03994 0.04641 0.05193

Claims

1. A method for setting the surge line of an axial flow compressor with a variable inlet pressure, characterized in that: The following steps are involved: S1. Establish a two-dimensional coordinate system and set the horizontal coordinate of the surge line setting curve to the equivalent flow rate m of the surge line. ′ , the vertical axis is the pressure ratio; the pressure ratio is the ratio of the compressor outlet pressure to the inlet pressure; S2. Adjust the axial flow compressor to a stable operating condition and maintain it at this condition for a certain period of time. Then collect the voltage and current of the compressor drive motor, the inlet temperature, the outlet temperature, the inlet pressure, and the throat pressure of the compressor, and calculate the coefficient Y1 using the following formula; Where U is the voltage of the compressor drive motor, I is the current of the compressor drive motor, T1 is the inlet temperature, T2 is the outlet temperature, p1 is the inlet pressure, ΔP is the throat pressure difference, and Cp is the constant pressure specific heat capacity of the working fluid; S3. Record the throat pressure difference ΔP, inlet pressure p1, and outlet pressure p3 of each surge point of the axial flow compressor through the surge test experiment. According to the coefficient Y1 calculated in step S2, calculate the equivalent flow rate m corresponding to each surge point by the following formula ′ ; S4, the equivalent flow rate m of each surge point obtained by calculation ′ , and the measured pressure ratio ε are plotted to form a surge line curve diagram.

2. The method for setting a surge line of an axial flow compressor with a variable inlet pressure according to claim 1, characterized in that: In step S2, the axial flow compressor is adjusted to a stable operating condition and maintained for at least 40 minutes.

3. The method for setting a surge line of an axial flow compressor with a variable inlet pressure according to claim 2, characterized in that: In step S2, the throat pressure difference ΔP is calculated by the following formula: ΔP=P2-P1 Among them, P2 is the compressor throat pressure.

4. The method for setting a surge line of an axial flow compressor with a variable inlet pressure according to claim 3, characterized in that: In step S4, the pressure ratio ε satisfies the following formula: Among them, P3 is the outlet pressure of the compressor.

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