DE102008055032B4 - Arrangement and method for multiphase flow measurement - Google Patents

Abstract

Arrangement for multiphase flow measurement, consisting of a channel body (2) introduced within a flow channel (1), characterized in that a. A differential pressure sensor (5) is arranged above the channel body (2) or in front of and behind the channel body (2) a pressure sensor (7), from which the differential pressure of the two pressure sensors (7) is determined; b. the channel body (2) consists of a plurality of continuous channels (3) running in the direction of flow and having a small hydraulic diameter; c. on each of the channels (3) at least two phase sensors (4) for identifying the material phase are arranged one behind the other in the direction of flow; d. all phase sensors (4) are connected in terms of signaling to associated measuring electronics which simultaneously record the phase indicator signals from the phase sensors (4) and the measured value from the differential pressure sensor (5) at a high sampling rate; e. a microcontroller or computer integrated in the measurement electronics or connected downstream of the latter calculates the partial volume flows in the channels (3) and the mean partial volume flows of the entire cross section of the flow channel (1) from the recorded measured values; and f. each volume flow element has to pass the channel body (2) through one of the channels (3).

Description

The invention relates to an arrangement for inline measurement of the partial volume flows of multiphase mixtures in a flow channel.

In many industries, such as petroleum extraction, chemical, biotechnology, pharmaceutical, environmental and energy process engineering, mixtures of substances are to be measured in terms of their quantitative composition. If it is mixtures with difficult or immiscible substances, it is called multi-phase flows. The measurement of the partial volume or partial mass flows of the phases of a multiphase mixture is the task of the multiphase flow measurement. For single-phase flows, there are currently a large number of measuring devices for determining the volume or mass flow. These include vane anemometers, variable area flowmeters, differential pressure meters, electromagnetic flowmeters, ultrasonic flowmeters, and Coriolis mass flowmeters. These meters are not suitable for multi-phase flow measurement due to their physical operating principles.

Multiphase flow measurement represents a very demanding and complex metrological problem. Currently known methods for multiphase flow measurement are subdivided in principle into those with separation of the mixtures and those for inline flow measurement in flow channels. An example of methods with separation is the in WO 2006/000771 A2 disclosed arrangement. Separation measuring methods are often unsuitable or not optimal for use in the process industry. The reasons for this are the space required for additional separation vessels, the increased complexity of the measuring devices due to the necessary shut-off valves and partial stream extraction, as well as the limited real-time capability due to the long time constant for the mixture separation. Inline measurement techniques can overcome these disadvantages. The method described here belongs to the group of in-line multiphase flow measurement methods.

Currently known arrangements for inline multiphase flow measurement usually consist of a plurality of measuring instruments, which simultaneously detect different parameters of the mixture flow within a flow channel, and from a downstream data processing unit which calculates partial volume flows or partial mass flows of the mixture from the measured values of the individual instruments. For most in-line multiphase flow measuring methods, the mixture speed and the phase composition of the mixture are recorded and calculated virtually simultaneously. With homogeneous phase distribution and slip-free movement of the phases, the corresponding partial volume flows can be easily determined from these measured values. With an additional density measurement for the phases, the corresponding partial mass flows also result.

The measurement of the mixture speed can be carried out, for example, with anvil anemometer ( CA 2 492 522 A1 ), Differential pressure measurement ( US 20050268702 A1 ), Coriolis mass flow measurement ( WO 2006 127 527 A1 ) or cross-correlation of sensor signals ( JP 08271309 A ) respectively. Radiation measuring methods ( US Pat. No. 6,993,979 B2 ), electrical ( CA 2 492 522 A1 ) or acoustic ( US 20050268702 A1 ) Measuring method suitable. Furthermore, many of the known arrangements have additional instrumentation for detecting the temperature of the phases or of the pressure in the mixture. These additional measures allow an accurate determination of the density of the phases involved, which is generally temperature and pressure dependent. The density can be used to convert partial mass flow values into partial volume flow values and vice versa, as required.

An alternative in-line measuring arrangement for a two-phase mixture is disclosed in US Pat US 20070124091 A1 disclosed. Here, the presence of a ring flow of a gas and one or more liquids is assumed in the flow channel. The mixture composition is measured by means of electromagnetic sensors, the mixture speed by means of cross-correlation of the signals of several electromagnetic sensors and the mixture density by means of gamma densitometry or Venturi tube.

The WO 2008/117024 A2 describes a system and method for the local measurement of the mixture composition and the volume or mass flows of a multiphase flow by means of a sampling system.

The US 5,861,556 A describes a flow meter with a plurality of flow velocity sensors, which are arranged at different positions in the same flow cross-section of a gas flow, wherein the mean value of the flow velocity detected and used to measure the flow.

The US Pat. No. 6,655,221 B1 describes an arrangement and a method for characterizing a multi-phase flow in a pipe by means of cross-correlation involving electrical measurements.

Disadvantage of all known inline measuring methods is their explicit dependence on the flow structure. In US 20070124091 A1 this is evident by the requirement for a ring flow. In the abovementioned arrangements, at least one of the measuring methods involved (for example, the mixture velocity measurement by Venturi tube, the capacitive phase component measurement or the mixture density measurement by means of single-jet gamma densitometer) requires a completely homogeneous (for example homogeneously finely dispersed) mixture composition. It is obvious that this ideal state can not be achieved in any technical system, since the aspiration to separate phases of different densities under the influence of always existing forces (gravitation, centrifugal forces, flow forces) is a universal property of multiphase mixtures and inevitably deviates from them result in an ideally presupposed phase mixing. With the partly strong dependence of the measurement result on the flow shape, considerable measurement uncertainties are associated. In principle, this problem could be solved by suitable metrological detection of the flow structure and a corresponding adjustment of the parameter calculation. However, to solve this problem, there are currently hardly any sufficiently inexpensive and inline-suitable measuring methods for detecting the flow structure (for example imaging methods). Furthermore, there is currently no closed theory that provides a sufficiently accurate quantitative description of the dependence of flow characteristics for phase mixtures on the flow structure.

The object of the present invention was therefore to specify an arrangement and a method for measuring the partial volume flows in a flow channel, which overcomes the abovementioned disadvantages of known solutions and which is suitable for a wide range of applications, in particular with regard to flow regimes and mixture compositions.

• – Die Strömung wird mittels eines Kanalkörpers in wenige, messtechnisch gut unterscheidbare, Strömungsstrukturen (Einphasenströmung, Kolbenströmung) gezwungen.
• – Die im Allgemeinen übliche getrennte Messung von Gemischgeschwindigkeit und Gemischzusammensetzung mit unterschiedlichen Messverfahren wird durch eine zeit- und ortsaufgelöste Phasenindikatormessung an einer Vielzahl von Messpunkten im Kanalkörper mit einem einzigen Messverfahren realisiert.

The object is achieved by the arrangement according to claim 1 and the method according to claim 9. Advantageous embodiments of the invention are set forth in the subclaims. The invention overcomes the disadvantages of known solutions by the following features:

• - The flow is forced by means of a channel body in a few metrologically well distinguishable flow structures (single-phase flow, piston flow).
• The generally customary separate measurement of mixture velocity and mixture composition with different measurement methods is realized by a time and spatially resolved phase indicator measurement at a plurality of measurement points in the channel body with a single measurement method.

By these features, a very accurate Partialvolumenstrommessung with comparatively low technical complexity and complexity of the meter is achieved. The required phase indicator measurement at a plurality of measuring points can be advantageously realized by grid-shaped phase sensor arrangements.

The invention will be explained below with reference to exemplary embodiments. In the accompanying drawings show:

1 : Longitudinal section of an arrangement according to the invention

2 : View of a duct body according to the invention ( 2 )

3 : Schematic representation of the signal curve of the phase sensors ( 4 ) of a channel ( 3 )

The arrangement consists of a segment of a flow channel ( 1 ) of any cross-sectional shape in which a channel body ( 2 ) is installed. This channel body ( 2 ) is of a plurality of flow channels ( 3 ) with a small hydraulic diameter. The width of the channels should be chosen so that a single-phase or piston flow is formed at the expected mixture velocities in the channels. The information required for such a design is easily taken from a corresponding flow chart. The arrangement of the channels ( 3 ) in cross section may be regular, for example in the form of a square lattice, or irregular. At each of the channels ( 3 ) are at least two in the axial direction one behind the other arranged phase sensors ( 4 ), which are capable of detecting the respective phase sensor ( 4 ) to identify the surrounding material phase of the mixture (the phase indicator) at a high sampling rate. The phase sensors ( 4 ) can be found inside the channels ( 3 ), on its inner surface or at the inlet and outlet of the channels ( 3 ) on the channel body ( 2 ) are located. The Phase sensors ( 4 ) can operate according to an optical (reflection, transmission), electrical (capacitive, inductive, conductive, electromagnetic), acoustic (sound echo, sound transmission), electromechanical (surface waves, vibrational resonance), radiometric or other measuring principle.

Also is an arrangement of the phase sensors ( 4 ) inside the channel body ( 2 ) or at the inlet and outlet of the channels ( 3 ) on the channel body ( 2 ) in the form of a grid sensor DE 10 2006 019 178 A1 conceivable.

The principle of operation of the measuring method is explained below with reference to the example of a two-phase flow of a gas and a liquid, wherein it is noted that an extension to more than two phases without restrictions is possible, provided that the phase sensors ( 4 ) are able to distinguish these phases from each other.

If the flow channel is flowed through by a two-phase mixture, it comes at the channel body ( 2 ) to a splitting of the flow to the individual channels ( 3 ). It turns within a single channel ( 3 ) either a single-phase flow (passage of a larger volume of liquid or gas) or a piston flow (intermittent passage of gas or liquid droplets covering the entire cross section of the channel ( 3 ). The formation of a ring flow, which is possible at high gas phase velocities, is intended by appropriate design of the channel body ( 2 ) are excluded. It should be noted, however, that the case of a ring flow can also be treated in principle with this arrangement. Either this is achieved by the fact that the phase sensors ( 4 ) are designed to be capable of controlling the film thickness of the liquid film on the wall of each channel ( 3 ) or that the occurrence of a ring flow from the signals of the differential pressure sensor ( 5 ) and the flow of the two phases is derived from corresponding empirical formulas or tables.

With the help of in the channels ( 3 ) arranged phase sensors ( 4 ) as well as an associated measuring electronics, the high-temporal resolution at each of the phase sensors ( 4 ) currently applied phase determined. It follows in accordance 3 for each channel ( 3 ) a waveform that indicates the presence of the gas or liquid phase in binary form. It denotes S _{A, i} (t) the phase indicator signal of the upstream phase sensor A ( 4 ) of the i-th channel ( 3 ) and S _{B, i} (t) the phase indicator signal of the downstream phase sensor B ( 4 ) of the i-th channel ( 3 ).

berechnen. Es bezeichnet i die Nummer des betrachteten Kanals (3), T₁, T₂ den Start und Endzeitpunkt des gewählten Messintervalls, d den Abstand der Phasensensoren (4) und ΔT die mittlere Zeitdifferenz der Passage von Grenzflächen an den Phasensensoren (4). Fernerhin sei X ∈ {A, B}. Es sei dahingestellt, ob die mittlere Zeitdifferenz ΔT direkt oder mittels eines zeitlich mittelnden Kreuzkorrelationsverfahrens computertechnisch aus dem Signalverlauf extrahiert wird. Aus den ermittelten Werten für Gasgehalt und Phasengrenzflächengeschwindigkeit ergeben sich die Partialvolumenströme für Gas und Flüssigkeit im Kanal (3) zu V ._gas,i = ε_iAν_i V ._liq,i = (1 –ε_i)Aν_i' (2) wobei A die Kanalquerschnittsfläche bezeichnet.In the case of the expression of a piston flow, the slip between the phases is negligible, since the plugs of one phase occupy almost the entire channel cross-section. Thus, the velocity of the phase boundary is a measure of the velocity of the gas phase and the liquid phase in the channel ( 3 ). 3 schematically shows the waveform for the two phase sensors ( 4 ) within a channel ( 3 ) for a piston flow. The presence of the gas phase is coded by the signal value 1, the presence of the liquid phase by the signal value 0. As can be seen, from the phase indicator signals, the gas content and the phase velocity v within a channel ( 3 ) according to

to calculate. I denotes the number of the considered channel ( 3 ), T ₁ , T ₂ the start and end time of the selected measurement interval, d the distance of the phase sensors ( 4 ) and ΔT the mean time difference of the passage of interfaces on the phase sensors ( 4 ). Furthermore, let X ∈ {A, B}. It is an open question whether the mean time difference .DELTA.T is extracted from the signal curve, either directly or by means of a time-averaging cross-correlation method. From the determined values for gas content and phase interface velocity, the partial volume flows for gas and liquid in the channel ( 3 ) too V. _{gas, i} = ε _i A v _i V. _{liq, i} = (1 -ε _i ) Aν _i '(2) where A denotes the channel cross-sectional area.

mit dem Durchmesser D und der Länge L des Kanals (3), der Fluiddichte ρ und dem als bekannt vorausgesetzten Rohrreibungskoeffizienten λ. Die Fluiddichte ρ und der Rohrreibungskoeffizient λ sind phasenabhängig. Die entsprechenden Volumenströme ergeben sich wieder nach Gl. (2). Show the phase sensors ( 4 ), that there is only one phase in the channel for a period of time which exceeds the average residence time of a phase boundary in the channel, the velocity of the relevant phase can be determined directly via the pressure loss at the channel body ( 2 ). This is done by a differential pressure sensor ( 5 ). With the pressure loss Δp, the phase velocity v results from the relationship

with the diameter D and the length L of the channel ( 3 ), the fluid density ρ and the assumed assumed pipe friction coefficient λ. The fluid density ρ and the pipe friction coefficient λ are phase-dependent. The corresponding volume flows are again given in Eq. (2).

The integral partial volume flows of the entire flow channel ( 1 ) result accordingly from the averaging

According to the above description of the calculation method, the measuring electronics associated with the arrangement are designed such that they realize a detection of the phase indicator on each of the 2 × N phase sensors with a sufficiently high sampling rate. In addition, with a sufficiently high sampling rate, the differential pressure at the channel body ( 2 ) capture. A microprocessor or computer integrated in the measurement electronics or computer accordingly performs the calculation of the phase velocities or partial volume flows from the detected phase indicator signals S _{A, i} or S _{B, i of} each channel ( 3 ) according to Eq. 1 to 3 and the subsequent averaging according to Eq. 4 numerically.

Additionally, in front of or behind the channel body ( 2 ) a temperature sensor ( 6 ) are arranged in the flow to compensate for the temperature dependence of measured variables with the measured mixture temperature.

Additionally, in front of or behind the channel body ( 2 ) an absolute pressure sensor ( 7 ) can be arranged to measure the pressure-dependent density of the gas phase and to be taken into account in the calculation of mass flows.

Instead of a differential pressure sensor over the channel body can in each case before and behind the channel body ( 2 ) an absolute pressure sensor ( 7 ) can be arranged to simultaneously the pressure-dependent density of the gas phase and the differential pressure at the channel body ( 2 ) to eat.

The determination of partial mass flows from the partial volume flows is by appropriate conversion over the density of the phases according to the equations m. _gas = ρ _gas V. _gas m. _liq = ρ _liq V. _liq (5) possible. To determine the density of the phases, an additional measuring instrument can be integrated into the arrangement, which measures the density of the phases.

LIST OF REFERENCE NUMBERS

1

flow channel

2

channel body

3

channel

4

phase sensor

5

Differential Pressure Sensor

6

temperature sensor

7

Absolute pressure sensor

Claims (11)

Arrangement for multiphase flow measurement, consisting of one within a flow channel ( 1 ) introduced channel body ( 2 ), characterized in that a. above the channel body ( 2 ) a differential pressure sensor ( 5 ) or in front of and behind the channel body ( 2 ) each a pressure sensor ( 7 ) is arranged, from which the differential pressure of the two pressure sensors ( 7 ) is determined; b. the channel body ( 2 ) from a plurality of flow-through continuous channels ( 3 ) consists of a small hydraulic diameter; c. at each of the channels ( 3 ) at least two phase sensors ( 4 ) are arranged one behind the other for identification of the material phase in the flow direction; d. all phase sensors ( 4 ) are signal-technically connected to an associated measuring electronics, which simultaneously monitor the phase indicator signals of the phase sensors ( 4 ) as well as the measured value of the differential pressure sensor ( 5 ) detected at a high sampling rate; e. an integrated in the measuring electronics or downstream of this microcontroller or computer, the partial flow rates in the channels ( 3 ) and the mean partial flow rates of the entire cross-section of the flow channel ( 1 ) calculated from the measured values; and f. each volume flow element the channel body ( 2 ) through one of the channels ( 3 ) must happen. Arrangement according to claim 1, characterized in that the phase sensors ( 4 ) inside the channels ( 3 ) are arranged. Arrangement according to claim 1, characterized in that the phase sensors ( 4 ) on the inner surface of the channels ( 3 ) are arranged. Arrangement according to claim 1, characterized in that the phase sensors ( 4 ) at the entrance and exit of the channels ( 3 ) at the end faces of the channel body ( 2 ) are arranged. Arrangement according to claim 1, characterized in that the phase sensors ( 4 ) are realized in the form of two regular electrode grids lying transversely to the flow plane, wherein each electrode grid is constructed so that in each case one crossing point of each electrode grating within a channel ( 3 ) or at its inlet or outlet opening at the end faces of the channel body ( 2 ), the intersecting electrodes have a small distance from one another and the electrical impedance of each intersection point is measured as a phase indicator signal by an associated measuring electronics. Arrangement according to claim 1, characterized in that in the flow direction in front of or behind the channel body ( 2 ) a temperature sensor ( 6 ) is mounted, whose signals are additionally sampled by the associated measuring electronics and used to correct temperature effects on the measured variables. Arrangement according to claim 1, characterized in that in the flow direction in front of or behind the channel body ( 2 ) a pressure sensor ( 7 ) is mounted, whose signals are additionally sampled by the associated measuring electronics and used to determine the gas phase density for further signal processing. Arrangement according to claim 1, characterized in that in the flow direction in front of or behind the channel body ( 2 ) further measuring instruments are mounted, which measure the density of individual phases of the flowing mixture. Method for multi-phase flow measurement with an arrangement according to one of claims 1 to 8, characterized in that by means of the phase sensors ( 4 ) of a channel the volume fractions (ε _k ) and the phase velocities (v _k ) of the material phases present in the mixture within the channel are determined. Process according to Claim 9, characterized in that the partial volume flows of the phases within the individual channels are determined from the volume fractions (ε _k ) and the phase velocities (v _k ) of the material phases present in the mixture. A method according to claim 10, characterized in that the integral partial flow rates of the phases are determined from the arithmetic mean of the partial volume flows of the phases within the individual channels.

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