EP1450046A2 - Method for operation of turbocompressors with surge limitation regulation - Google Patents

Abstract

The method involves determining set point and actual value for surge limit control based on delivery head and volume flow plotted in form of predetermined surge limit. A compressor is operated based on determined set point and actual value for surge limit control within minimal distance from surge limit.

Description

The invention relates to a method for the safe operation of Turbo compressors with one surge limit control and one Pump limit control valve, the compressor with gases different composition promotes and Composition of the gas (molecular weight) the map of the Turbo compressor and thus the position of the surge limit in the map affected.

DE 198 28 368 C2 describes a method for operating two or multi-stage compressors known, each of which Compressor stage over between a pressure line a blow-by line and a suction line arranged Pump surge control valve has. That blows in each case Pump limit control valve in the suction line of the associated Compressor stage. There is also a flow calculator to calculate the intake flow and a calculator for the minimum allowable target flow rate provided from the Final pressure or the delivery head is determined.

Furthermore, EP 0 810 358 A2 describes a method for regulating Gas pressures of a regenerator with a gas expansion turbine known in the flue gas pipe with a generator, being a Process controller the inlet fittings of a gas expansion turbine and / or the bypass fittings opens or the bypass fittings throttles. The process controller has several function generators downstream, which are the manipulated variables for the downstream Specify fittings.

In addition, DE 100 12 380 A1 describes a method for Protection of a turbo compressor with a downstream process known an operation in the unstable work area, where a Machine controller is used in addition to a surge limit controller if necessary, a suction pressure regulator, a final pressure regulator and has a bypass controller. From the position of a flow the actuator determining the process is taken into account of possibly other influencing variables, such as Compressor suction pressure and compressor outlet pressure and Compressor intake temperature and the process pressure, a Tax matrix determined. Using the tax matrix, a rapid transient operating point change the required Position of the surge limit control valve and the bypass valve, the Suction pressure control valve and the actuator for the Compressor inlet blades determined directly. The determined The control variable is then the surge limit control valve, the Suction pressure regulator, the final pressure regulator and the bypass regulator directly activated as a manipulated variable.

Furthermore, EP 0 757 180 B1 describes a method for Avoiding controller instabilities in surge limit controls for Protection of a turbocompressor against pumps with a large selection Proportional gain of the surge limit controller by blowing off known via a relief valve. The timing of the The blow-off valve closes at an asymmetrically constructed gradient limiter, whereby in Opening direction no time limit is effective. In However, the closing direction is a parameterizable time Limitation of the closing process of the relief valve is provided.

In the known methods it is assumed that the Location of the surge limit in the map of the compressor is known. The Coordinates of the working point in the map are usually as compression work or enthalpy difference or head plotted against the intake volume flow. The Parameters of the respective sizes can also be known.

The present invention is based on the object Process for safely operating a turbo compressor specify that is able to also gases with different Safe to process composition, in particular with regard to the sizes for the gas constant R and the Isentropic exponent k is not well known.

The underlying task is solved in that the different compositions of the gases with the influence on the location of the surge line and thus also the location of the Surge limit line can be compensated by within the Pump limit control for the detection of delivery head (Enthalpy difference) Δ h and volume flow V predetermined Design values for gas constant R, isentropic exponent k and Compressibility number z are used and in the form of a predetermined surge line (Fig. 2, Fig. 4) within the Pump limit control are mapped, with setpoint and actual value for the surge limit control can be determined from the figure and the compressor with the determined target and actual values for the Pump limit control with a minimum required distance from Pump limit is operated.

It has also proven advantageous that a number of characteristic curves with constant speed or with each constant geometry (guide vane position or position of a Throttle valve) is shown, with a family of curves each with surge limit control lines for a constant speed or constant compressor geometry describes that between interpolated the various curves and the Pump limit control line at any speed or compressor geometry is correctly determined and the surge limit controller with the minimum required distance to the surge line is operated.

It has also proven to be particularly beneficial found that instead of interpolating between different surge limit control lines a single "fictitious" Control line is depicted, the location of which depends on the map and determined by the rightmost pump points becomes.

Alternatively, the procedure for the safe operation of Turbo compressors with one surge limit control and one Pump limit control valve applicable in an advantageous manner, in which the compressor gases with different compositions promotes and the composition of the individual gases (Molecular weight) the map of the turbo compressor and thus leaves the position of the surge line in the map unaffected, whereby within the surge limit regulation for the detection of delivery head Δ h and volume flow V a predetermined design value for Gas constant R, isentropic exponent k and compressibility number z is used and in the form of a predetermined surge line (Fig. 1) is mapped within the surge limit control, wherein the setpoint for the surge limit control from the figure determined and the actual value calculated from the measured variables and the compressor with the determined target and Actual values for the surge limit control with a minimum required distance to the surge line is operated.

One of the most important in the surge limit control Machine protection devices for turbo compressors is manufactured by Location of the surge limit in the map of a compressor made. Within the surge limit control, the Enthalpy difference the minimum permissible flow through the Compressor determined as setpoint for the surge limit controller. at Knowledge of enthalpy difference and volume flow is then one correct surge limit control and thus a safe one Machine protection possible.

und V = K Δp 1 · R · z · T 1 p 1 wobei
R gleich Gaskonstante
k gleich Isentropenexponent
z gleich Kompressibilitätszahl
T₁ gleich Temperatur Saugseite
p₁ gleich Druck auf Saugseite
p₂ gleich Druck auf Druckseite
K gleich Parametrierkonstante für Durchfluß
Δp₁ gleich Differenzdruck über Wirkdrucksensor auf SaugseiteThe formulas for determining the coordinates of the enthalpy difference delta h or Δh and volume flow V are:

and V = K Δ p 1 · R · z · T 1 p 1 in which
R equals gas constant
k is the isentropic exponent
z equals compressibility number
T ₁ is the temperature of the suction side
p ₁ equals pressure on the suction side
p ₂ equals pressure on the pressure side
K is the parameterization constant for flow
Δp ₁ equal to differential pressure via differential pressure sensor on the suction side

The parameters R and k as well as z are of the Gas composition dependent. R is the gas constant, k is the Isentropic exponent and z the compressibility number. Usually the composition is that of the compressor compressed gas known. In most cases only compresses a gas, e.g. Air, nitrogen or a process gas with time-constant composition in one chemical process. The sizes R, k and z are over the whole Operating time of the compressor constant and can therefore be considered Constants in the formulas for calculating the enthalpy difference and volume flow are taken into account. The sizes The enthalpy difference and volume flow are in this case physically correctly recorded.

In some applications, especially chemical Industry, however, are also known processes in which the The composition of the gas can change over time. The sizes R, k and z are then no longer constant, but must be are regarded as a variable that changes over time. Provided the sizes R, k and z are assumed to be known or can be precisely determined at any time, these can be taken into account within the underlying formulas. The enthalpy difference and volume flow are then also in these Cases physically correctly determined. A safe one Machine protection by means of correctly determined values for the setpoint and actual value is possible.

In other applications, compressors are used variable gas composition operated, the composition in the Individual case is not known. Depending on the composition of the gas there is a different course for different compressors the surge limit, which increases within the surge limit control is considered. Without knowing the gas parameters R, k and z is the consideration of a different course of the surge limit however usually not possible.

The present procedure is therefore with the compressors to be used for which the course of the surge limit or the Surge limit control line in the map a dependency of at least a gas composition.

A method is given below with the aid of which it is possible, even if the gas composition is not known the difference between the setpoint and actual value for the surge limit control to determine exactly and thus the compressor optimally in front of you Protect operation in an unstable area.

Fig. 1

die Kennlinie eines Kompressors mit konstanter Drehzahl und feststehender Geometrie;

Fig. 2

Kennlinien eines Kompressors für zwei Gase;

Fig. 3

Kennlinien eines Kompressors für fünf verschiedene Gase;

Fig. 4

Kennlinien eines Kompressors für ähnlich verschiedene Gase wie in Fig. 3;

Fig. 5

Kennlinien eines Kompressors für verschiedene Winkel der verstellbaren Leitschaufeln;

Fig. 6

Kennlinien eines Kompressors bei prozentualer Nenndrehzahl für zwei Gase und

Fig. 7

Regelkennlinien eines Kompressors mit Pumpgrenzen zweier Gase und eine gewählte Regellinie.

The method is described below using exemplary embodiments, the characteristic curves of which are shown in each case. For a better understanding, the method is first described for a compressor with constant speed and constant geometry (fixed guide vanes and without throttle valve). The process is then generalized for any compressor. Show it:

Fig. 1

the characteristic of a compressor with constant speed and fixed geometry;

Fig. 2

Characteristics of a compressor for two gases;

Fig. 3

Characteristic curves of a compressor for five different gases;

Fig. 4

Characteristic curves of a compressor for similarly different gases as in Fig. 3;

Fig. 5

Characteristic curves of a compressor for different angles of the adjustable guide vanes;

Fig. 6

Characteristic curves of a compressor at percentage nominal speed for two gases and

Fig. 7

Control characteristics of a compressor with surge limits of two gases and a selected control line.

Fig. 1 shows the characteristic of a compressor with constant Speed and fixed geometry.

There are compressors in which the map according to FIG. 1 is independent of the gas composition. The characteristic in Map delta h over V is designed such that this has general validity for all extracted gases.

Other compressors are designed in such a way that each Gas composition a different characteristic with another Pump limit point results.

2 shows, for example, the characteristic curve of a compressor, its characteristic curve and thus also the location of the The surge limit depends on the gas composition.

The main difference between the case of FIG. 1 and Fig. 2 now consists in that at a universally valid 1 the characteristic and thus the Pumping limit point only calculated for a gas composition are needed. For the acceptance measurements in the test field, the Characteristic curve to be verified only for one gas.

If for each gas composition, as shown in Fig. 2, one other characteristic is effective is the compressor thermodynamic for all occurring gas compositions or at least for some representative gas compositions interpreted. The characteristic curves are then through in the test field verify corresponding measurements with different gases.

For the method described below is the one shown Difference not of particular importance. The difference will be only mentioned for the sake of completeness.

In the following, a compressor according to FIG be assumed.

To determine the position of the operating point in the map, the exact determination of delivery head delta h and volume flow V required. This allows the location of the current working point relative to the surge limit point. That sets due to the known formulas for the delivery head delta h and the Volume flow V a precise knowledge of the sizes R, k and z ahead. However, these sizes are often not known. Therefore it is assumed that the quantities R, k and z are measured not detectable and not to be used to determine delta h and V are known to be used. When determining the working point can therefore only a single parameter set for R, k and z be used. Different parameter sets can not be used because there is no criterion according to which can be switched between the different parameter sets can.

Usually to switch to different Parameter sets using the data of the gas composition which the compressor is operated most of the time, or it the gas composition values for which the Compressor was designed (hereinafter also design values called). As long as the extracted gas in its composition The position of the working point corresponds exactly to the design also correctly recorded in the map.

However, if the composition of the gas has changed, it can because of the quantities R, k and z which cannot be measured provided computer for determining the delivery head delta h and Volume flow V no longer correctly determine these values. Instead of the computer uses the correct values for R, k and z only incorrectly specified values. It sets in Error, the size of which depends on the deviation of the current gas composition from those in the calculation formulas design values used for delta h and V.

1 can be seen with knowledge of the assumed errors due to the non-measurable Convert sizes of R, k and z into "fictitious" characteristic curves. Then the characteristic curves are created which the surge limit controller under Use of the incorrectly specified values for R, k and z determined.

3 shows the course of the respective compressor characteristics for different gas compositions according to FIG. 1, as the course from a surge limit controller without knowing the actual Gas composition is detected. For every gas mixture it results another characteristic curve with a different surge limit point. From the Pump surge point in Fig. 1 are different surge point, that can be connected by a line. From the Pump limit point in Fig. 1 thus becomes a "fictitious" Surge limit line.

The fictitious can be found within the surge limit control Simulate the surge line and the protection system of the compressor (Surge limit control), a control line according to the "fictitious" Pump limit line can be specified. This will be normal characteristics the surge limit control used. Each surge limit control is e.g. designed a variable speed compressor or variable geometry. Any such compressor will by a map with different speed characteristics or different geometries (guide vane position or Throttle position). Each of the characteristics of one such "normal" compressor ends in a surge limit. The connection of such surge limit points results in Surge limit line. The same applies to a compressor with fixed geometry and fixed speed at variable Gas composition a surge line of the same characteristics. The surge limit controller therefore does not need any additional features in order to also the case of any variable gas composition with fixed Cover geometry and fixed speed.

The process works according to the method that the Control error that occurs in the surge limit controller of a compressor due to the unknown gas composition results in the determination of the "fictitious" surge limit is predetermined. The surge limit controller will errors that inevitably result in advance by the provided computer, in which the occurring Error has been taken into account in advance. The compressor can by taking into account the errors that occur safe when operating a compressor with different gases and be protected precisely, even if the gas composition of the actually extracted gas is not known at all.

The method can also be applied to a compressor, whose characteristic curve is dependent on the 2 has gas composition. For the determination of the Sizes delta h and V for the surge limit controller are intended as examples the data for the gas composition are used with which the compressor is operated frequently. The corresponding Data are those according to the upper characteristic curve in FIG. 2.

In Fig. 4, five characteristics are similar to Fig. 3 applied. The upper characteristic curve corresponds exactly to the upper one Characteristic curve according to FIG. 3. The other characteristic curves are opposite those shifted in Fig. 3. The characteristics became like this converted that instead of the correct values for R, k and z the same values were used as for the others Characteristic curves apply. The representation in FIG. 4 thus corresponds the representation in Fig. 3. In both cases there is a "Fictitious" surge line, which has universal validity, too if the composition of the gas currently being extracted is not is known.

The "fictitious" surge line according to FIGS. 3 and 4 can be used derive a universal control line that the compressor too without knowledge of the gas composition in the entire area of application optimally protects.

It does not matter which parameter set for which Gas composition is used, it is only important that the same parameter set is always used.

The purpose of surge limit control is the compressor always operate as close as possible to the surge line. To becomes a control difference from the minimum permissible flow and current flow and the surge limit controller switched. The fictitious surge limit control line is given by the Formation of a system deviation such a course that the arithmetic errors occurring due to the unknown quantities R, k and z of a gas composition when determining delta h and current volume flow V cancel each other out.

If the surge limit line thus determined is within the Pump limit control is used, the compressor is always adequately protected against operation in the unstable map area, even if the gas composition fluctuates significantly is subject.

The process becomes somewhat more complex if the compressor is used variable speed or with variable geometry (guide vanes, Swirl throttle or throttle valve) and more variable Gas composition is operated. One with compressors such a construction results only with constant Gas composition already a surge line or Surge limit line. As is known, the compressor must never beyond, i.e. to the left of the surge line. In order to this can be ensured, a rule line is to the right of the surge line with a sufficient safety margin positioned that the surge limit controller even under extreme Operating conditions always the compressor outside the Pump limit range can operate.

There are quite a number of turbo compressors, in particular multi-stage machines, in particular the course of the Pump limit line in the map depends on the Gas composition.

With variable geometry or variable speed and variable Gas composition can apply to any gas composition different course of the surge line or the surge line result. From the surge line or the surge line becomes a bevy of surge line and surge line control lines.

Each characteristic of the original map (Fig. 5) is after the previously described procedure for the different Predetermined gas compositions. From the surge limit of Characteristic curve results in a surge line that is only valid for this speed or this throttle valve position or Has guide vane position. An application of this procedure on all characteristics of the original map leads to a family of Surge limit lines. Each of these lines applies to a speed or Guide vane position or throttle valve position. Because speed and position of the throttle valve or guide vane by measurement The surge limit controller can always be easily detected for the respective speed and throttle valve position or Guide vane position valid pump limit line can be specified. Between the characteristic curves can be done via the central computer unit be interpolated so that the default is limited Number of characteristic curves must take place.

Another, simpler approach does not measure Speed and vane position or throttle position. This simplifies the outlay in terms of equipment, and thus that The entire system is cheaper, but the usable one Map area somewhat limited because of this procedure the worst case scenario is always assumed.

One advantage of the simplified approach is that it is a classic one Pump limit control without any modification to protect such Compressors can be used. To do this are preferred the required surge limit points for the different Compressor geometries or speeds and the possible Gas compositions in a common map consider. This results in a surge limit band. The Course of the surge limit line decisive for the surge limit control results from a connection of the farthest right, i.e. with the largest volume flows Surge points. This ensures that independent on the gas composition that is driven but is unknown a sufficient safety distance from the current surge limit consists.

6 shows the two characteristic diagrams of a surge limit control percentage nominal speed for two gases.

7 shows the position of the predetermined "fictitious" Pump limit lines for the two gases and the associated one selected control line, the location of which is at the rightmost oriented surge line.

By changing the gas composition the fictitious surge line or the universal surge line to a map of fictitious surge limit lines or more universal Rule lines.

The maps of fictitious surge limit lines or are shown universal control lines in FIGS. 5 and 6. From the characteristic in Fig. 1 is due to the variable speed or variable geometry the map according to FIG. 5. Each of these Characteristic curves (for solid gas composition) according to FIG. 5 can be into a map (for variable gas composition). Because each of the characteristics is limited by a pump point, in each of the results Maps of a surge line. Since each characteristic curve in FIG. 5 due to a fixed speed and a fixed compressor geometry is marked, each map in Fig. 6 and thus each surge line in Fig. 6 by a fixed speed and a characterized compressor geometry.

Since both speed and compressor geometry (changeable with adjustable guide vanes or throttle fittings) can be easily measured by measuring the Speed and the compressor geometry always the one for the respective Relevant characteristic can be selected.

Operating points can pass through between two characteristic curves numerical interpolation can be determined exactly.

Claims (4)

Method for the safe operation of turbocompressors with a surge limit control and a surge limit control valve, the compressor conveying gases with different compositions and the composition of the gas (molecular weight) influencing the characteristic map of the turbocompressor and thus the position of the surge limit in the characteristic map, characterized in that the different compositions the gases with the influence on the position of the surge line and thus also on the position of the surge line are compensated by using predetermined design values for gas constant R, isentropic exponent k and compressibility number z within the surge limit control for the detection of delivery head Δ h and volume flow V and in Form a predetermined surge line (Fig. 2, Fig. 4) within the surge limit control, setpoint and actual value for the surge limit control are determined from the figure and the compressor with the determined setpoint and actual value s for the surge limit control is operated with a minimum required distance from the surge limit. A method according to claim 1, characterized in that a number of characteristic curves with constant speed or with constant geometry (guide vane position or position of a throttle valve) is mapped, wherein a family of curves is described in each case with surge limit control lines for a constant speed or constant compressor geometry that between the different Curves are interpolated and the surge limit control line is correctly determined at every speed or compressor geometry and the surge limit controller is operated with the minimum required distance to the surge limit. A method according to claim 2, characterized in that instead of the interpolation between different surge limit control lines, a single "fictitious" control line is depicted, the position of which depends on the map and is determined by the pump points on the far right. Method for the safe operation of turbocompressors with a surge limit control and a surge limit control valve, the compressor conveying gases with different compositions and the composition of the individual gases (molecular weight) leaving the map of the turbo compressor and thus the position of the surge limit in the map unaffected, characterized in that within of the surge limit control for the detection of delivery head Δ h and volume flow V, a predetermined design value for gas constant R, isentropic exponent k and compressibility number z is used and is shown in the form of a predetermined surge limit line (FIG. 1) within the surge limit control, the setpoint and actual value for the surge limit control determined from the figure and the compressor is operated with the determined target and actual values for the surge limit control with a minimum required distance from the surge limit.

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