Method and control unit for operating a compressor

Abstract

Method for operating a compressor (10) which serves to compress a process gas, wherein a volume flow of the process gas through the compressor (10) or a variable corresponding to the volume flow is determined, wherein a delivery head of the compressor (10) or a variable corresponding to the delivery head is determined as a function of a measured inlet pressure of the compressor (10) and as a function of a measured outlet pressure of the compressor (10), wherein a surge limit controller (20) determines a control variable for an actuator (17) cooperating with the compressor (10) as a function of the volume flow or the variable corresponding to the volume flow and as a function of the delivery head or the variable corresponding to the delivery head, such that the compressor (10) is operated along a control line (RL) which has a defined distance from the surge limit (PG) of the compressor (10),wherein a water vapor content of the process gas or a value corresponding to the water vapor content is determined, and wherein the control line (RL) along which the compressor (10) is operated is adjusted depending on the water vapor content or the value corresponding to the water vapor content. Fig. 1,

Description

[0001] The invention relates to a method for operating a compressor and a control device for operating a compressor.

[0002] In practice, it is known to operate a compressor using a surge limit controller so that the compressor is operated along a control line that is a defined distance from the surge limit of the compressor. It is known that the surge limit depends on the composition of the process gas to be compressed by the compressor. In practice, the composition of a process gas to be compressed is therefore determined using a gas chromatograph or a comparable gas analysis system in order to adjust the control line for the surge limit controller depending on the composition of the process gas determined by the gas chromatograph. However, gas analysis using a gas chromatograph takes a relatively long time, so a rapid response of the surge limit controller to a changing composition of the process gas to be compressed cannot be guaranteed. Furthermore, the use of gas chromatographs is expensive.

[0003] DE 35 44 822 A1, DE 195 28 253 C2 and DE 103 04 063 A1 each disclose methods for operating a compressor with a surge limit control.

[0004] There is a need for a method and a control device for operating a compressor that make it possible to react to a changing composition of a process gas to be compressed within a very short time, in particular in the range of less than one second, and thus to ensure stable operation of the compressor along a control line that is always at a defined distance from the surge limit of the compressor.

[0005] Based on this, the present invention is based on the object of creating a novel method for operating a compressor and a control device for operating a compressor.

[0006] This object is achieved by a method for operating a compressor according to claim 1 and by a control device according to claim 7. According to the invention, a water vapor content of the process gas or a variable corresponding to the water vapor content is determined, wherein the control line along which the compressor is operated is adapted depending on the water vapor content or the variable corresponding to the water vapor content.

[0007] The present invention proposes, for the first time, determining the water vapor content of the process gas or a value corresponding to the water vapor content and adapting the control characteristic along which the compressor operates based on this. A compressor used to compress a process gas with a dynamically changing water vapor content can thus always operate stably. The invention is particularly suitable for compressing carbon dioxide as a process gas with a dynamically changing water vapor content.

[0008] Preferably, the dew point of the process gas is measured, in particular using a dew point mirror hygrometer, and the water vapor content is determined depending on the dew point, in particular based on a characteristic map or characteristic curve. Using a dew point seal hygrometer, the dew point of the process gas and, depending on the dew point, the water vapor content can be determined very quickly with little effort and therefore low cost. The water vapor content can be determined in a timescale of less than one second, in particular in the order of 50 milliseconds, in order to then adjust the control characteristic of the surge limit controller with the same dynamic response.

[0009] Preferably, a temperature of the process gas upstream of the compressor is also measured, wherein the control line along which the compressor is operated is also adjusted depending on the temperature of the process gas upstream of the compressor, in particular depending on the characteristic map or characteristic curve. If the temperature of the process gas upstream of the compressor is additionally measured and the control characteristic curve is adjusted not only depending on the water vapor content but also on the temperature of the process gas, in particular depending on the characteristic map or characteristic curve, the operation of the surge limit controller can be further improved in order to always operate the compressor within a stable operating range, i.e., with sufficient distance from the surge limit.

[0010] Preferably, a gas constant of the process gas is determined depending on the water vapor content or the quantity corresponding to the water vapor content. The control curve along which the compression is carried out is adjusted depending on the gas constant of the process gas and thus depending on the water vapor content or the quantity corresponding to the water vapor content, in particular depending on the characteristic map or characteristic curve. This procedure is particularly preferred. The gas constant of the process gas to be compressed is determined depending on the water vapor content, in order to then adjust the control characteristic curve depending on the gas constant of the process gas to be compressed.

[0011] Preferred developments of the invention will become apparent from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1 shows a schematic block diagram of a first compressor; Fig. 2 shows a schematic block diagram of a second compressor; Fig. 3 shows a first volume flow-discharge head characteristic map; Fig. 4 shows a second volume flow-discharge head characteristic map.

[0012] Fig. 1 shows a highly schematic view of a compressor 10 for compressing a process gas, wherein process gas to be compressed is fed to the compressor 10 via a supply line 11, and wherein compressed process gas is discharged from the compressor 10 via a discharge line 12.

[0013] The operation of the compressor 10 is controlled by a control unit 13, wherein a surge limit controller 20 is a component of the control unit 13.

[0014] Various input variables are provided to the control unit 13, such as the input variable of a so-called differential pressure sensor 14.

[0015] The differential pressure sensor 14 measures a pressure difference in the supply line 11 upstream of the compressor 10, as a function of which the control unit 13, in particular the surge limit controller 20 thereof, determines a volume flow of the process gas through the compressor 10 or a variable corresponding to this volume flow, in particular in a map-dependent or characteristic-curve-dependent manner.

[0016] The volume flow of the process gas through the compressor (10) or a value corresponding to the volume flow is determined depending on a pressure difference in the supply line upstream of the compressor.

[0017] As an alternative to a differential pressure sensor, other measuring methods such as temperature-based measuring methods (hot wire anemometers), Coreolis flow measurements, ultrasonic flow meters, laser Doppler anemometers can be used to determine the volume flow.

[0018] Fig. 1 further shows a pressure sensor 15 in the area of ​​the supply line 11 and a pressure sensor 16 in the area of ​​the discharge line 12, wherein the pressure sensor 15 measures a suction pressure and thus an inlet pressure of the compressor 10 and the pressure sensor 16 measures an outlet pressure of the compressor 10 and provides it to the control unit 13. Depending on the inlet pressure of the compressor 10 and depending on the outlet pressure of the compressor 10, a so-called delivery head of the compressor 10 or a variable corresponding to the delivery head can be determined by the control unit 13, in particular by the surge limit controller, in particular in a map-dependent or characteristic-curve-dependent manner.

[0019] Fig. 3 shows an exemplary volume flow-head characteristic map of the compressor 10, where Fig. 3 The delivery head FH is plotted against the volume flow VS through the compressor 10. Fig. 3 shows a so-called surge limit PG, which separates the stable operating range from the unstable operating range of the compressor 10. The surge limit controller 20 of the control unit 13 operates the compressor 10 along the Fig. 3 shown control line RL with sufficient distance from the surge limit PG to operate the compressor 10 in the stable operating range.

[0020] The surge limit controller 20 or the control unit 13 acts on a valve 17. In Fig. 1 This valve 17 is designed as a relief valve. If the surge limit controller 20 determines, depending on the volume flow VS or the value corresponding to the volume flow VS as well as depending on the discharge head FH or the value corresponding to the discharge head FH, that the compressor 10 is no longer operating along the control line RL but with too little distance to the surge limit PG, the control unit 13 or the surge limit controller 20 thereof outputs a control variable for the valve 17 serving as the actuator in order to blow off part of the compressed process gas. In contrast, Fig. 2 an embodiment of the invention in which the valve 17 is not designed as a relief valve, but as a return valve in order to return a part of the compressed process gas in the direction of the supply line 11 of the compressor 10.

[0021] If the process gas to be compressed is a gas with a dynamically changing water vapor content, the characteristic map of the compressor 10 and thus also its surge limit PG will change depending on the water vapor content. Fig. 4 a volume flow-head characteristic map analogous to the Fig. 3 , but with a higher water vapor content of the process gas to be compressed. If the volume flow-head characteristic map of the Fig. 4 the surge limit controller the control line RL of the Fig. 3 this could lead to unstable operation of the compressor 10.

[0022] Therefore, according to the invention, the water vapor content of the process gas or a value corresponding to the water vapor content is determined. This is done according to Fig. 1, 2 using a dew point mirror hygrometer 18, which measures the dew point of the process gas to be compressed and provides the measured dew point to the control unit 13 as an input variable.

[0023] The control unit 13 can then determine the water vapor content of the process gas to be compressed depending on the measured dew point, in particular depending on the characteristic map or characteristic curve.

[0024] However, it is also possible for a dew point mirror hygrometer 18 to directly determine the water vapor content of the process gas to be compressed as an output variable and to provide it to the control unit 13.

[0025] The control unit 13 adjusts the control characteristic curve depending on the water vapor content or the size corresponding to the water vapor content RL of the surge limit controller, in particular in a map-dependent or characteristic-dependent manner, in order to always ensure stable operation of the compressor 10 depending on the water vapor content of the process gas. The control unit 13 can adapt the control line RL in such a way that it determines a gas constant of the process gas depending on the water vapor content or the variable corresponding to the water vapor content, for example, in a map-dependent or characteristic-dependent manner. From the gas constant determined as a function of the water vapor content, the control line RL can then be adapted, in particular in a map-dependent or characteristic-dependent manner.

[0026] The control line RL of the surge limit controller is adjusted depending on the gas constant and thus depending on the water vapor content or the quantity corresponding to the water vapor content.

[0027] In Fig. 1 und 2It is further provided to measure the temperature of the process gas to be compressed upstream of the compressor 10 using a temperature sensor 19 and to provide a corresponding temperature measurement value to the control unit 13. In this development of the invention, it is provided that the control unit 13 adapts the control line RL depending on the water vapor content on the one hand and on the temperature of the process gas on the other hand, in particular depending on the characteristic map or characteristic curve.

[0028] The invention further relates to the control unit 13 with the surge limit controller 20, which is configured to automatically execute the method described above on the control side. For this purpose, the control unit 13 has data interfaces for exchanging data with the components involved in implementing the method according to the invention, such as the differential pressure sensor 14, the pressure sensors 15, 16, the dew point mirror hygrometer 18, and the temperature sensor 19. All of these components provide input data to the control unit 13. The control unit 13 outputs operating parameters for the compressor 10 and the valve 17 as output data.

[0029] The control unit 13 is configured to adapt the control line RL of the surge limit controller thereof depending on the water vapor content of the process gas or the variable corresponding to the water vapor content and preferably also depending on the temperature of the process gas to be compressed, in particular depending on the characteristic map or characteristic curve.

[0030] The invention allows the control line RL of a surge limit controller to be adjusted highly dynamically, within a time range of less than one second, particularly on the order of 50 milliseconds, depending on the water vapor content of the process gas to be compressed. The solution according to the invention is fast and cost-effective. List of reference symbols

[0031] 10Compressor 11Supply line 12Discharge line 13Control unit 14Diffusive pressure sensor 15Pressure sensor 16Pressure sensor 17Valve 18Dew point mirror hygrometer 19Temperature sensor 20Surge limit controller

Claims

1. A method for operating a compressor (10) which serves to compress a process gas, wherein a volume flow of the process gas through the compressor (10) or a variable corresponding to the volume flow is determined, wherein a delivery head of the compressor (10) or a variable corresponding to the delivery head is determined as a function of a measured inlet pressure of the compressor (10) and as a function of a measured outlet pressure of the compressor (10), wherein a surge limit controller (20) determines a control variable for an actuator (17) cooperating with the compressor (10) as a function of the volume flow or the variable corresponding to the volume flow and as a function of the delivery head or the variable corresponding to the delivery head, such that the compressor (10) is operated along a control line (RL) which has a defined distance from the surge limit (PG) of the compressor (10), characterized in thata water vapor content of the process gas or a variable corresponding to the water vapor content is determined, the control line (RL) along which the compressor (10) is operated is adjusted depending on the water vapor content or the variable corresponding to the water vapor content.

2. Method according to claim 1, characterized in that the water vapor content of the process gas is measured.

3. Method according to claim 1, characterized in that the dew point of the process gas is measured and the water vapor content is determined depending on the dew point.

4. Method according to claim 3, characterized in that the dew point of the process gas is measured using a dew point mirror hygrometer (18).

5. Method according to one of claims 1 to 4, characterized in thatfurthermore, a temperature of the process gas upstream of the compressor (10) is measured, wherein the control line (RL) along which the compressor is operated is also adjusted depending on the temperature of the process gas upstream of the compressor (10).

6. Method according to one of claims 1 to 5, characterized in that a gas constant of the process gas is determined depending on the water vapor content or the quantity corresponding to the water vapor content, wherein the control line (RL) along which the compression (10) is operated is adapted depending on the gas constant of the process gas and thus depending on the water vapor content or the quantity corresponding to the water vapor content.

7. A control device (13) for operating a compressor (10) which serves to compress a process gas, wherein the control device (13) determines a volume flow of the process gas through the compressor (10) or a variable corresponding to the volume flow, wherein the control device (13) determines a delivery head of the compressor (10) or a variable corresponding to the delivery head depending on a measured inlet pressure of the compressor (10) and depending on a measured outlet pressure of the compressor (10), wherein a surge limit controller (20) of the control device (13) determines a control variable for an actuator (27) cooperating with the compressor (10) depending on the volume flow or the variable corresponding to the volume flow and depending on the delivery head or the variable corresponding to the delivery head such that the compressor (10) is operated along a control line (RL) which has a defined distance from the surge limit (PG) of the compressor (10), characterized in that, the control unit (13) adapts the control line (RL) along which the compressor (10) is operated, depending on a water vapor content of the process gas or the size corresponding to the water vapor content.

8. Control device (13) according to claim 7, characterized in that the same is configured to carry out the method according to one of claims 1 to 6 on the control side.

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