DE102009003978A1 - Method for determining e.g. molecular weight, of carrier gas using turbo compressor, involves presetting new value for property of gas based on comparison of mathematical parameter and characteristic field parameter - Google Patents

Abstract

The method involves presetting a value for a property of gas, and selecting a characteristic field based on the value. Parameters e.g. enthalpy difference (deltah) and speed (n), are determined. A characteristic field parameter (Vk) i.e. suction flow rate, is determined based on the parameters and the characteristic field. A mathematical parameter (Vf) is determined. The characteristic field parameter is compared with the mathematical parameter. A new value is preset for the property of the gas based on the comparison of the mathematical parameter and characteristic field parameter. Independent claims are also included for the following: (1) a computer program having a set of instructions to perform a method for determining a property of gas using a turbo-machine (2) a data carrier having a computer program with a set of instructions to perform a method for determining a property of gas using a turbo-machine.

Description

The The invention relates to a method for determining a property a gas by means of a turbomachine.

Turbomachinery can be described by maps provided by the Operating points of the respective machine are clamped. For example arises in a turbocompressor at a certain pressure ratio a certain volume flow. Will the compressor at constant Speed, vane and Saugdrosselstellung at another Operating pressure ratio, extends the operating point to the characteristic. By varying the speed or suction throttling or by adjusting the guide vanes, further characteristics are created, which together span the map.

By Change in the manipulated variable (s) speed, Suction throttling and / or position of the vanes can various operating points are approached in the map. Especially can a surge limit control by appropriate control intervention a Operation with sufficient distance to the surge line of the turbocompressor to ensure.

One Map, however, depends on the properties of the gas, which flows through the turbomachine, for example of its molecular weight or molecular weight, its inlet temperature and his entry pressure. Works the turbomachine with a gas whose properties are of those of the one used Characteristic deviate, this can in particular to a malfunction lead to a scheme based on the map used based.

The DE 35 44 822 A1 therefore proposes for the surge limit control of a turbocompressor to determine the delivery head and the intake volume flow by calculation, whereby the gas constant, the isentropic exponent and the compressibility number are based on values of a normal composition of the delivery gas. From the map for this normal composition, a calculated speed is then determined and compared with the actually measured engine speed. From the difference between the calculated and actually measured machine speed, a correction value for the surge limit controller is determined. Thus, it is deliberately based on a characteristic map that deviates from the actual characteristic diagram, which depends on the inlet temperature, inlet pressure and molecular weight, and adjusts the correction in order to compensate for this.

The EP 1 450 046 B1 and the US 5,195,875 B On the other hand, a surge limit control is based on a universal surge limit line which is suitable for gases with different properties or different characteristic maps.

The US 2002/0062679 A1 Proposes to calculate the molecular weight of a delivery gas as a function of actual and imaginary imaged flow and delivery heights.

The US 4,825,380 proposes an iterative process for determining the molecular weight by approximating it from the ratio between a calculated and a measured discharge pressure.

task It is the object of the present invention to provide a method of determination a property of a gas by means of a turbomachine to provide.

These The object is achieved by a method having the features of the claim 1 solved. The subclaims relate to advantageous Training.

The Invention is based on the recognition that the location of an operating point already uniquely determined in a map by two parameters is, so the system is over-determined by a third parameter is. This over-determination is used to the unknown To determine size. Through the iterative use different maps can the dependence of Map of the sought property of the gas considered become.

at An initialization is initially a start value for the sought property of the gas, for example its molecular weight or the determining this gas composition.

In each iteration run, one of several stored maps is now based on the predetermined value for the property of the gas selected. In this case, the specification of the starting value and / or the selection of the characteristic map in the first iteration step can also be realized by a default assignment of corresponding memory locations. If no characteristic field is stored for a value for the property of the gas, it may be suitable, in particular linear, to interpolate between the two characteristic diagrams. The characteristic diagrams for various values of the property of the gas, for example for different molecular weights, can be stored, for example, as tables, flocks of polygons, functional or relational links or the like, and in particular empirically determined in advance from measurements with gases having the respective property.

In the iteration run is a first parameter, for example an enthalpy difference or head over a turbomachine, and a second parameter, for example a rotational speed of a variable-speed turbomachine, a guide vane position of a turbomachine with adjustable front and / or Nachleitschaufeln, or a position of a Saugdrosselarmatur a turbomachine with suction throttle, which determines an operating point of the turbomachine in the map establish.

oder einer Näherung hierfür.The enthalpy difference .DELTA.h can in particular be based on a, preferably measured, inlet temperature Te into the turbomachine, a preferably measured inlet pressure pe upstream of the turbomachine, a preferably measured outlet pressure pa downstream of the turbomachine, a specific gas constant R, an isentropic exponent κ and / or a compressibility number z, which may depend on the molecular weight, in particular according to the formula:

or an approximation for this.

Now becomes a map parameter, for example an intake flow the turbomachine based on the first and second Parameters determined from the map. Is that due to the first and second parameter defined operating point not on a characteristic curve the stored map, can be suitable, in particular linear be interpolated.

In the iteration run also becomes a calculated value of the map parameter determined and the map parameter with this mathematical parameter compared.

in der c eine Konstante bezeichnet. Nun wird in dem Iterationsdurchlauf ein neuer Wert für die Eigenschaft des Gases auf Basis dieses Vergleichs des rechnerischen und des Kennfeld-Parameters vorgegeben. Beispielsweise kann das gespeicherte Molekulargewicht, das dem ausgewählten Kennfeld sowie bevorzugt auch der verwendeten spezifischen Gaskonstante, Kompressibilitätszahl und/oder des verwendeten Isentropenexponenten zugrundegelegt wurde, um ein vorgegebenes oder von dem Vergleich abhängiges Inkrement erhöht oder verringert werden.If the arithmetic parameter is an intake flow Vf of the turbomachine, then this can be determined on the basis of the inlet temperature in the turbomachine, the inlet pressure upstream of the turbomachine, the specific gas constant, the compressibility factor and a pressure difference Δp over a flow measuring device, in particular a flow meter the formula:

where c denotes a constant. Now, in the iteration run, a new value for the property of the gas is given based on this comparison of the computational and the map parameter. By way of example, the stored molecular weight which was used as the basis for the selected characteristic diagram and preferably also for the specific gas constant, compressibility number and / or isentropic exponent used can be increased or reduced by a predetermined or comparison-dependent increment.

Subsequently is used with this changed value for the property of the gas through which the selected map and Preferably, the first parameter, the second parameter and / or the computational parameter change, a new iteration run carried out.

This can be repeated until the difference between map parameters and computational parameter is less than a given iteration limit or abort value. This iteration is preferred during periodically repeats the operation of the turbomachine, changes in the composition of the gas and thus the determining property of the gas, such as its molecular weight, to recognize.

In a preferred embodiment, the first parameter, the second parameter and / or the map parameter based on a Comparison of a measured and a reference value corrected. A map depends, among other things, on the inlet temperature and the inlet pressure. For example, by the first parameter and the map parameter are each corrected with a correction factor, For example, multiply that for a quotient from a measured inlet temperature or a measured inlet pressure and an inlet temperature or an inlet pressure, for which the map was created is taken from a table, this can be taken into account.

Further Advantages and features emerge from the subclaims and the embodiment. The only one shows

1 Fig. 3 is a flowchart of a method according to an embodiment of the present invention.

1 schematically shows the sequence of a method for determining the molecular weight and thus the composition of a conveying gas by means of a turbo compressor.

to Initialization is in a step (a) a storage space for the molecular weight M is assigned a default or starting value M0.

On Basis of this molecular weight is in a step (b) one of several maps selected as polygons or function generator for various molecular weights M1, M2, M3 are stored. Is for a molecular weight no map stored, can between two stored maps be interpolated.

Prefers are also the values for a specific gas constant R, an isentropic exponent κ and / or a compressibility number z is determined on the basis of the value M for the molecular weight. Can isentropic exponent or compressibility number can be considered approximately constant, here too a fixed, constant value can be used.

Now In steps (c) and (e), the first parameter is an enthalpy difference Δh and an arithmetic parameter corresponding to an intake flow Vf of formulas (1), (2) using the specific gas constant R, the isentropic exponent κ and the compressibility number z, based on the value of M for the molecular weight and inlet temperature readings Te in the turbo compressor, the inlet pressure pe in front of the turbo compressor, the outlet pressure pa after the turbo compressor and the pressure difference Ap over a flow meter determined.

bzw. aus gemessenem Eintrittsdruck pe und einem Referenzdruck p0, bei dem das Kennfeld erstellt wurde:

abgespeichert sind, um den Einfluss des Kennfeldes von Ansaug- bzw. Eintrittstemperatur und -druck zu berücksichtigen.The determined enthalpy difference .DELTA.h is then multiplied by correction factors Kp, KT, which are taken from a table in which correction factors for the respective quotient of measured inlet temperature Te and a reference temperature T0, at which the map was created:

or from measured inlet pressure pe and a reference pressure p0 at which the map was created:

are stored in order to take into account the influence of the map of intake and inlet temperature and pressure.

In a step (d) is now from the thus corrected enthalpy difference Δh and the measured speed n of the turbocompressor as the second parameter in the selected molecular weight map M an intake flow Vk determined as a map parameter. How through the dashed or dotted lines indicated, can Here in the stored in the form of polygons Characteristic map between two characteristic curves for constant speeds n1, n2 are interpolated for the measured speed n.

In a manner analogous to the enthalpy difference .DELTA.h, the intake flow rate Vk determined from the characteristic curve is then multiplied by correction factors Kp ', KT', which are taken from a table in which correction factors for the respective quotient of measured entry and reference temperature T0, or entry and reference pressure p0 are stored in order to take into account the influence of the map of intake or inlet temperature and pressure:

alternative can also be the calculated value Vf for the intake flow be corrected with such correction factors.

In a step (f) is now the map parameter Vk with the computational Parameter Vf compared, and in a step (g) the stored Value M for the molecular weight corresponding to the difference ΔV = Vk - Vf between arithmetic and map parameter incremented by the new value M → M + ΔM (ΔV) stored in the storage space for the molecular weight becomes.

In order to is completed an iteration run, the value M for the molecular weight stored afterwards is closer at the actual value for which in step (f) - except for arithmetical and table inaccuracies - none Deviation would result more.

With this new value M for the molecular weight can subsequently a new iteration run will be started in the first in a step (b) a map is selected on the basis of the new value and preferred, new values for the specific gas constant R, the isentropic exponent κ and the compressibility number z be set.

These Iteration is preferred throughout the operation performed the turbo compressor. This approaching the value M for the molecular weight successively the true value. For example, the molecular weight changes due to a change in the composition of the delivery gas, the value M approaches in the subsequent iterations this new molecular weight, so that, for example, a surge limit regulator always operated on the basis of a correct molecular weight or displayed the molecular weight and so a change in the Gas composition can be detected.

.delta.h

enthalpy head

KT, kp,

KT ' kp '

correction factor

κ

isentropic exponent

M

molecular weight

n

rotation speed

p0

reference pressure

pa

CDP

pe

inlet pressure

Ap

Pressure difference over orifice

R

gas constant

T0

reference temperature

Te

inlet temperature

Vf

arithmetical Parameter (intake flow)

vk

Map parameters (Intake flow)

Z

compressibility

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3544822 A1 [0005]
• - EP 1450046 B1 [0006]
• US 5195875 B [0006]
• US 2002/0062679 A1 [0007]
• - US 4825380 [0008]

Claims (16)

Method for determining a property of a Gas by means of a turbomachine, in particular one Turbocompressors, with the steps: (a) Specification of a value (M) for the property of the gas; (b) selecting a Map based on the default value for the property of the gas; (c) determining a first parameter (Δh) and a second parameter (n) which is an operating point of the Define turbomachine in the map; (d) determining a map parameter (Vk) based on the first and second Parameters (Δh, n) and the map; (e) determining a calculated parameter (Vf); (f) comparing the map parameter (Vk) with the calculated parameter (Vf); (g) specification of a new value (M) for the property of the gas based the comparison of the arithmetic and the map parameter; and To repeat of steps (b) to (g). Method according to claim 1, characterized in that that the first parameter (Δh), the second parameter and / or the arithmetic parameter (Vf) based on one of the property of the gas dependent value (R, κ, z) become. Method according to one of the preceding claims, characterized in that in step (c) the first parameter (Δh) and / or the second parameter, in step (d) of Map parameter (Vk) and / or in step (e) of the arithmetic Parameter (Vf) based on a comparison of a measured and a Reference value (Te / T0, pe / p0) are corrected. Method according to claim 3, characterized that the measured and the reference value is an inlet temperature (Te) in the turbomachine and / or an inlet pressure (PE) before the turbomachine include. Method according to one of the preceding claims, characterized in that the property of the gas is its molecular weight (M), its specific gas constant (R), its isentropic exponent (κ) and / or its compressibility number (z) includes. Method according to one of the preceding claims, characterized in that the first parameter is an enthalpy difference (Δh) via the turbomachine. Method according to Claim 6, characterized the enthalpy difference (Δh) in step (c) is based on an inlet temperature (Te) in the turbomachine, an inlet pressure (pe) upstream of the turbomachine, a discharge pressure (pa) after the turbomachine, a specific gas constant (R), an isentropic exponent (κ) and / or a compressibility number (z) determined becomes. Method according to one of the preceding claims, characterized in that the second parameter is a speed (n), a vane position and / or a position of a Saugdrosselarmatur the turbomachine includes. Method according to one of the preceding claims, characterized in that the map parameter (Vk) and the arithmetic parameters (Vf) an intake flow (V) of the turbomachine includes. Method according to claim 9, characterized in that in that the computational parameter (Vf) in step (e) is based on a Inlet temperature (Te) in the turbomachine, one Inlet pressure (pe) in front of the turbomachine, one specific gas constant (R), a pressure difference (Δp) via a flow measuring device, in particular a flow meter, and / or a compressibility number (z) is determined. Method according to one of the preceding claims, characterized in that steps (b) to (g) are repeated until, in step (f), the difference between map parameters (Vk) and computational parameter (Vf) is smaller than a given one Iterationsgrenzwert. Method according to one of the preceding claims, characterized in that during the Operation of the turbomachine, the steps (b) to (g) are repeated periodically Method according to one of the preceding claims, characterized in that a value, in particular the map parameter (Vk), an isentropic exponent (κ) and / or a compressibility number (z) is determined by interpolation from a table. Method according to one of the preceding claims, characterized in that the map in step (b) by interpolation is determined. Computer program, which is a method according to a of the preceding claims, if it in a computer. Disk on which a computer program is stored according to claim 15.