EP2598755B1 - Method for operating a compressor - Google Patents

Description

• a) Saugdruckmessung, b) Enddruckmessung, c) Durchsatzmessung, wobei in einem Normalbetrieb, während dessen die Messungen fehlerfrei ablaufen, mittels eines ersten Regelungskennfeldes aus zweien der gemessenen Größen ein Sollwert für einen Pumpgrenzregler ermittelt wird, welcher diesen Sollwert mit der dritten Messgröße direkt oder indirekt vergleicht, wobei der Pumpgrenzregler bei einem Unterschreiten oder einem Überschreiten des dritten Messwertes oder einer Anwandlung des dritten Messwertes im Vergleich mit dem Sollwert ein Bypassventil öffnet, so dass der Enddruck abgesenkt wird.

The invention relates to a method for operating a compressor with the installed measurements:

• a) suction pressure measurement, b) final pressure measurement, c) throughput measurement, wherein in a normal operation, during which the measurements proceed without error, a setpoint for a surge limit controller is determined by means of a first control characteristic of two of the measured quantities, which directly or indirectly compares, wherein the surge limit opens a bypass valve when falling below or exceeding the third measured value or an application of the third measured value in comparison with the setpoint, so that the final pressure is lowered.

When operating a compressor, care must be taken to ensure that the ratio of the discharge pressure to the inlet pressure does not become so high that the throughput through the compressor falls below a certain minimum level. This lower barrier is defined essentially by strongly increasing vibrations of the machine, which are caused among other things by so-called pump surges. The experts call the boundary between the regular operation and this so-called pumping as the surge limit. This surge limit depends essentially on the ratio between inlet pressure and final pressure. For the surge limit control of turbocompressors algorithms are used, which continuously determine the distance to the surge limit on the basis of several measured values. If this is too low, the controller opens a bypass valve and thus ensures a minimum distance to the pumping limit, in which the final pressure is lowered and, accordingly, the required flow rate, mass flow or volume flow is restored. During undisturbed normal operation, the so-called surge limit control protects the control of the Bypass valve the compressor from damage that would be caused by the pump, and in case of failure of any of the measuring signals involved, the protection of the machine must be guaranteed against this damage.

One possibility for reacting to a signal failure at the measuring points is the replacement of the disturbed measured value by the worst-case possible measured value-that is, a value which is closer to the surge limit than is actually the case. Thus, the machine is still protected against pump surges, but it is possibly the most often designed as a control valve bypass valve opened unnecessarily, so that the efficiency of the system deteriorates. In the worst case, the valve opens so far that the throughput through the compressor is reduced to an unacceptable minimum and so the usually connected by the compression process connected process can no longer be maintained.

In addition to the possibility described above, it is also known that the surge regulator generates a constant output signal in the event of a fault, which opens the valve so far that under any circumstances, a pump can occur. This also leads to a negative influence on the connected process.

As a rule, the measured values measured also include a measurement of the throughput through the compressor. In this connection, it is also known, in the event of a fault, which does not relate to the measurement of the flow rate, to regulate the compressor to the throughput of a minimum amount at which pumping is precluded.

Another known way of dealing with an accident in the measurements is the specification that the pressure ratio is assumed to be constant and corresponding to the largest expected, which also results in a large distance from the surge line. One Failure of the suction pressure can not be controlled in this way.

From the US 2009/274565 A1 is a method of operating a compressor known with measurements of suction pressure, discharge pressure and throughput. If the setpoint range for a surge limit controller is undershot or exceeded, a bypass valve is opened to lower the final pressure.

EP 0 676 545 A2 suggests a procedure for the case of a "transmitter failure" on a similar arrangement.

Based on the problems of the prior art, the invention has the object to develop a fallback strategy in case of failure of one of the aforementioned measurements for the operation of a compressor of the type mentioned, which ensures an acceptable efficiency in continued operation despite a maximum of safety ,

To solve the problem of the invention, a method of the type mentioned is proposed with the features of the characterizing part of claim 1.

The invention understands the measured values of a suction pressure measurement or final pressure measurement both the measured parameters in a unit characteristic of the physical parameter and a modification of this measured value by normalization, in particular normalization, which renders this measured value dimensionless. This is expedient, for example, in the suction pressure and the final pressure, if these are normalized to the suction pressure. The throughput is measured regularly by means of a differential pressure measurement via a metering orifice and can accordingly also be specified in the physical unit of a pressure and accordingly modified in the same way, particularly dimensionless, as the suction pressure and the final pressure. Basically, but also a different kind Quantity measurement possible and the implementation of the invention with non-normalized or dimensioned measured sizes. The decisive difference from the method known hitherto in the prior art is that a substantially constant assumption is not simply made with regard to the failed measured variable, but that, on the one hand, an already existing other measured variable is used to compare it with the remaining intact measured quantities a spare control algorithm or replacement control map to implement a setpoint for the surge limit controller. This difference leads to a much better utilization of the possible operating range with simultaneously improved efficiency compared to conventional methods for operating compressors in the event of failure of one of the measuring points, which have an influence on the surge limit control.

A preferred embodiment of the invention provides that in normal operation from the Saugdruckmessung and the final pressure measurement by means of the first control map, a target value for the surge limit is determined, which corresponds to a minimum value for the throughput. Preferred as the further measurement of the other physical size of the compression process, the measurement of the angle of attack Eintrittsleitapparates or the speed. The variation of the angle of the Eintrittsleitapparates or the speed is particularly suitable for the substitute control with failed measurement of the final pressure or the inlet pressure. In this case, a maximum ratio of end pressure to inlet pressure can be assigned to a specific position of the inlet guide apparatus. The same applies to the speed. In this way, each results in a particularly good approximation to the surge line for the replacement control. Appropriately, the implementation of the relationship between the maximum ratio between the final pressure and inlet pressure and the angle of the Eintrittsleitapparates or the speed by means of an additional map that in the event of a fault in the measurement of Enddrucks or the inlet pressure of the surge regulator for the implementation of the sizes is used together.
If the measurement of the final pressure should have failed, a good approximation for the pressure ratio, from which the quantity setpoint is formed, results from: $$\frac{p_e}{p_A}\le \frac{p_e}{p_A}{|}_{\mathrm{Max}}=f\left(\alpha \right)\mathrm{,}$$

Eine Abschätzung ohne Verwendung des Saugdrucks kann z.B. durch folgende Formel gegeben werden: $$\frac{\mathrm{\Delta }p}{p_A}\le \frac{\mathrm{\Delta }p}{p_E}*\frac{p_E}{p_A}{|}_{\min }$$

The additional map can also be used if there should be a failure of the suction pressure measurement. The minimum quantity setpoint is then formed according to the above approximation for the maximum pressure ratio. The formula for the calculation of the actual values often contains the suction pressure, eg in the form $\dot{V}\approx \sqrt{\frac{\mathrm{\Delta }p}{PaA}}\mathrm{,}$

An estimation without using the suction pressure can be given for example by the following formula: $$\frac{\mathrm{\Delta }p}{p_A}\le \frac{\mathrm{\Delta }p}{p_e}*\frac{p_e}{p_A}{|}_{\min }$$

Should the measurement of the throughput, in particular the measurement of the differential pressure, fail over an orifice plate, it is expedient in the development of the invention if the following equation is implemented by the surge limit regulator: $$\frac{p_e}{p_A}\le S*\frac{p_e}{p_A}{|}_{\min }=f\left(\alpha \right)\mathit{or\; f}\left(\mathit{n}\right)\mathit{where\; S}<\mathit{1}\left(\mathit{safety\; factor}\right)$$

Figur 1

eine schematische Darstellung der einzelnen Komponenten eines Verdichters, wie er mittels des Verfahrens nach der Erfindung geregelt wird,

Figur 2

die Darstellung eines Regellinie aus dem Linienzug im Regelungskennfeld für einen Pumpgrenzregler im normalen Betrieb,

Figur 3

die Darstellung eines zusätzlichen Kennfeldes für den Pumpgrenzregler,

Figur 4

ein Flussdiagramm des erfindungsgemäßen Verfahrens.

In the present, the invention is described with reference to a specific embodiment with reference to drawings for better understanding, with the skilled person in particular from any combination of the claims further embodiments of the invention. Show it:

FIG. 1

a schematic representation of the individual components of a compressor, as regulated by the method according to the invention,

FIG. 2

the representation of a control line from the line in the control diagram for a surge limit controller in normal operation,

FIG. 3

the representation of an additional characteristic diagram for the surge limit regulator,

FIG. 4

a flow chart of the method according to the invention.

FIG. 1 shows a compressor CO with the associated auxiliary systems and a drive T, which is designed here in the manner of a Heißgasexpanders. The compressor CO receives process fluid PF on a suction line SL at an inlet pressure PA and compresses it to a final pressure PE while delivering it to a pressure line PL. The compressed process fluid PF is cooled after the compressor CO in a heat exchanger CL. On the inlet side on the suction line SL of the compressor CO, an input temperature TE is measured by means of a temperature measuring point TT, a volume flow VF is measured by means of a volume measuring point FE via a pressure difference ΔP of a local measuring diaphragm and the input pressure PA by means of a simple pressure measuring point PAE. Immediately before entering the impeller of the compressor CO is still a Eintrittsleitapparat ELA, which is set to the angle of attack α. Suitably, either the drive T is variable speed or an inlet guide ELA provided. A quantity regulator MCTR controls the setting angle α of the inlet guide apparatus ELA by specifying a setpoint value αS for the setting angle α. The actual value αC for the angle of attack α is transmitted to the quantity controller MCTR by a position transmitter ZT.

On the pressure line, the final pressure PE is measured behind the heat exchanger CL by means of a pressure measuring point PEE. The results of all measurements are from a control CTR detected, with part of this scheme is a surge limit control PCTR. Decisive for the surge limit control is the activation of a bypass valve BV, which is designed as a control valve and controls the opening of a bypass BP, which closes the pressure line PL with the suction line SL via a defined opening short when the compressor CO threatens to the state of the pumping to reach.

FIG. 2 shows an operating point OP and a control line CTRL as an extract from the not completely shown control map CTFE. The Y coordinate of the illustrated graph represents the ratio of end pressure PE to input pressure PA and the X coordinate represents the ratio of the differential pressure ΔP at the flow rate measurement to the input pressure PA. The measured ratio of the final pressure PE to the input pressure PA is the basis for determining the setpoint value TV of the surge limit controller PCTR. The actual value ΔV at the operating point OP is formed via the ratio of the differential pressure ΔP in relation to the input pressure PA. The diagram shown essentially expresses a ratio of the compaction power on the Y-coordinate and the flow rate through the compressor CO on the X-coordinate. The surge limit control PCTR opens the bypass valve BV when the operating point OP with respect to the flow rate reaches the target value TV or the surge limit line CTRL.

zusätzlich den Temperatureinfluss am Verdichtereingang berücksichtgt mit $\frac{\mathrm{\Delta }p*TE}{p_A}\mathrm{.}$

Die Regelung sieht nicht voraus, dass der Eingangsdruck PA konstant ist. Figur 3 zeigt ein Zusammenhang zwischen dem Anstellwinkel α als Eingangsgröße und minimalen sowie maximalen Verhältnissen zwischen Enddrücken PE und Eingangsdrücken PA dargestellt in einem Ersatzregelungskennfeld SCTFE, welches von der Pumpgrenzregelung PCTR umgesetzt wird, wenn die Messung des Eingangsdrucks oder des Enddrucks oder der Menge ausfällt. Anhand der Messung des Anstellwinkels α lassen sich diese minimalen und maximalen Druckverhältnisse zwischen Eingang und Ausgang ermitteln und gemäß der in Figur 4 dargestellten Abfolge in dem erfindungsgemäßen Verfahren umsetzen.The precision of the control can be further improved if the X coordinate of the control characteristic CTFE instead $\frac{\mathrm{\Delta }p}{p_A}$

additionally takes into account the temperature influence at the compressor inlet with $\frac{\mathrm{\Delta }p*Te}{p_A}\mathrm{,}$

The control does not foresee that the input pressure PA is constant. FIG. 3 shows a relationship between the angle of attack α as an input variable and minimum and maximum ratios between final pressures PE and input pressures PA shown in a replacement control map SCTFE, which is implemented by the surge limit control PCTR when the measurement of the input pressure or the final pressure or the amount fails. Based on the measurement of the angle of attack α, these minimum and maximum pressure ratios between input and output can be determined and according to the in FIG. 4 implement the sequence shown in the method according to the invention.

FIG. 4 shows a flowchart of the method according to the invention. In the flowchart of FIG. 4 the method according to the invention is subdivided into four successive steps, wherein in a first step at least three measurements take place, in this case the inlet pressure PA, the final pressure PE and a differential pressure measurement ΔP carried out to determine the throughput. If these measurements are less than 1) trouble-free (Y), the method goes to step 2), during which the operating point OP is determined by means of a control characteristic diagram CTFE and a nominal value TF based on the difference to the control line CTRL. In the subsequent step 3), the setpoint value TV is compared with the pressure difference ΔP, wherein at a larger value of ΔP compared to TV in a fourth step, the bypass valve BV remains closed and is otherwise opened. If a fault of one of the measurements is present in method step 1), a further measurement d) is used for the evaluation in a replacement control characteristic field SCTFE for determining a substitute setpoint value ETV. In the subsequent step 3a), a comparison is made in the same way as in step 3), here between the final pressure PE and the substitute setpoint TVE. If the final pressure PE is greater, a closing of the bypass valve BV takes place in method step 4), otherwise an opening.

Claims (10)

1. Method for operating a compressor (CO), comprising the installed measurements of:

   a) suction pressure measurement (PA),

   b) final pressure measurement (PE),

   c) throughput measurement (ΔP),

   wherein, in normal operation, during which the measurements proceed faultlessly, a target value for a surge limiter (PCTR) is determined from one or two of the measured variables by means of a first control characteristic map (CTFE) and the surge limiter compares this target value with the third measured variable directly or indirectly, wherein the surge limiter (PCTR) opens a bypass valve (BV) if the third measured value falls below or exceeds the target value (TV), with the result that the final pressure (PE) is lowered or the flow through the compressor is increased,
   characterized in that,
   in the event of failure of at least one of the measurements

   a) suction pressure measurement (PA),

   b) final pressure measurement (PE) or

   c) throughput measurement (ΔP), a further measurement of another physical variable of the compression process, together with a measured variable of the remaining measurements or a modification of this measured variable on the basis of a supplementary characteristic map, is an input variable for a substitute control characteristic map (SCTFE), from which a maximum value or a minimum value of the fault-affected measured variable is determined and is used to form the target value in the first control characteristic map (CTFE) or, itself as a substitute target value (TV), is an input variable for the surge limiter (PCTR).
2. Method according to Claim 1, wherein, in normal operation, the target value (TV) for the surge limiter (PCTR), which corresponds to a minimum value for the throughput, is determined from the suction pressure (PA) and the final pressure (PE) by means of the first control characteristic map (CTFE), wherein the surge limiter opens the bypass valve (BV) if the throughput falls below the minimum value for the throughput.
3. Method according to Claim 1 or 2, wherein the further measurement is the measurement of the setting angle (α) of an intake guiding apparatus (ELA).
4. Method according to Claim 1 or 2, wherein the further measurement is the measurement of the rotational speed (n) of the drive (T).
5. Method according to Claim 3, wherein, in the event of a failure of the measurement of the suction pressure (PA) or the measurement of the final pressure (PE), the further measurement of the other physical variable is the measurement of the setting angle (α) of the intake guiding apparatus (ELA) and the maximum final pressure (PE) or the maximum ratio of the suction pressure (PA) to the final pressure (PE) is obtained from the input of the setting angle (α) into the supplementary characteristic map.
6. Method according to Claim 4, wherein, in the event of a failure of the measurement of the suction pressure (PA) or the measurement of the final pressure (PE), the further measurement of the other physical variable is the measurement of the rotational speed (n) of the drive (T) and the maximum final pressure (PE) or the maximum ratio of the suction pressure (PA) to the final pressure (PE) is obtained from the input of the rotational speed (n) into the supplementary characteristic map.
7. Method according to at least one of Claims 1 to 4, wherein the suction pressure (PA) and/or the final pressure (PE) and/or the throughput (ΔP) as the input variable of a characteristic map are normalized to a process variable, in particular the suction pressure (PA).
8. Method according to one of Claims 3 to 5, wherein, in the event of a failure of the measurement of the final pressure (PE) or the suction pressure (PA), the following applies: $$\frac{p_E}{p_A}\le \frac{p_E}{p_A}{|}_{\max }=f\left(\alpha \right)\mathrm{or}\frac{p_E}{p_A}\le \frac{p_E}{p_A}{|}_{\max }=\mathit{f}\left(\mathit{n}\right)$$

   

   
   where:

   α = setting angle of the intake guiding apparatus (ELA)

   n = rotational speed of the drive (T).
9. Method according to Claim 6, wherein, in the event of a failure of the measurement of the suction pressure (PA), the following also applies:

   
10. Method according to at least one of Claims 3 to 5, wherein, in the event of a failure of the measurement of the throughput (Δp), the pressure ratio is limited by the limiter according to:

    

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