GB2481827A

GB2481827A - Flow Measurement

Info

Publication number: GB2481827A
Application number: GB1011455.1A
Authority: GB
Inventors: Laurie Linnett
Original assignee: BIOS TECHNOLOGIES LLP
Current assignee: BIOS TECHNOLOGIES LLP
Priority date: 2010-07-07
Filing date: 2010-07-07
Publication date: 2012-01-11
Also published as: GB201011455D0

Abstract

A system for determining and/or characterizing constituents of a fluid is described. The system comprises a measurement chamber 10 for receiving a fluid. The chamber is essentially arranged to at least partially separate components of the fluid in at least one separation direction. The system is also provided with a plurality of sensors 105, which are spatially distributed in the separation direction, and which are usable to determine and/or characterize fluid flowing through the chamber. in some cases, the flow path through the chamber is substantially horizontal, such as a horizontal pipeline.

Description

FLOW MEASUREMENT

Field of the Invention

The present invention relates to a device for detecting, measuring and/or characterizing the composition of fluid. In particular, the invention relates to a device for characterizing and/or determining liquid and/or gas phases of a liquid flowing in a pipeline, such as detection and characterization of water and/or oil and/or gas.

Background to the Invention

Detection and/or characterization of multiphase fluid flow is used in a wide range of industrial processes, such as in monitoring of drilling lines in the oil and gas industry, in pipelines of chemical plants and the like. In particular, characterization of oil, water and gas flow in oil field pipes may be used to prevent damage to equipment and/or to characterise actual hydrocarbon production. Various techniques for detecting and/or characterizing the contents of pipelines are known. One method involves passing gamma or x-ray radiation across a pipeline and measuring the intensity of radiation received. Each of oil, gas and water attenuate the radiation by varying amounts, thereby allowing the relative fraction of each constituent in the path of the radiation beam to be determined. However, this method requires use of a radiation source, which may require strict safety controls and whose use may be restricted in certain jurisdictions.

Another example of a known method involves the use of capacitive measurements.

Capacitive techniques generally involve surrounding a pipe with a plurality of electrodes and measuring capacitance between all electrode combinations. The resultant capacitance distribution can then be processed in order to calculate a permittivity distribution of the contents of the pipe, which corresponds to the distribution of materials having differing densities.

Summary of Invention

According to a first aspect of the present invention, there is provided a system for determining and/or characterizing constituents of a fluid, comprising a measurement chamber for receiving the fluid, the chamber being arranged to at least partially separate components of the fluid in at least one separation direction, and a plurality of sensors spatially distributed in the separation direction.

The fluid may comprise a flowing fluid. The measurement chamber may define a flow path.

The flow path may be oriented substantially horizontally. That is, the mean bulk flow may be along a substantially horizontal path. The flow path may be arranged such that at least two components present in the fluid flow at least partially stratify into layers. The flow path may be arranged such that the layers separate out in a generally vertical direction. The flow path may be provided with a substantially horizontal inlet pipe section and/or a separation section between an inlet of the flow path and the transducers, the length of the substantially horizontal inlet pipe section and/or the separation section being selected to permit at least partial separation of at least two components of the fluid flow.

The sensors may be vertically distributed.

In this way, separable components of the flowing fluid separate out and stratify into a vertically stacked series of layers as they pass along the horizontal section of the flow path. By providing a distribution of sensors in the separation direction (for example, vertically off-set from each other), the measurement path of each sensor may be more likely to substantially include only a single component layer of the fluid and reflections from interfaces between components may be minimised.

The sensors may be horizontally distributed. By horizontally distributing (off-setting) the sensors, reflections received by at least some of the sensors may be minimised.

At least one sensor may comprise a signal source and/or receiver, such as sonic or ultrasonic transducer.

The sensors may be provided on at least one side wall of the flow path. At least two sensors may be provided in sensor pairs, which may be a transmitter/receiver pair.

At least one sensor of the sensor pair may be located on a first side wall of the flow path and at least one sensor of the sensor pair may be located on a second side wall of the flow path. At least one sensor may be additionally or alternatively adapted to sense reflected signals.

The system may comprise at least one first sensor and at least one second sensor.

At least one first sensor may comprise a gas sensor adapted to measure properties of one or more gasses. At least one second sensor may comprise a liquid sensor, adapted to measure properties of one or more liquids. At least one first sensor may be arranged to operate at higher frequencies than at least one second sensor.

By providing both gas arid liquid phase sensors, both phases may be accurately determined. By combining multiphase sensing with the separation of phases, more accurate detection and/or characterisation may be achieved, as interference due to liquid or gas respectively in the sensing paths of sensors characterising or detecting the respective gas or liquid phases may be minimised.

The sensors may be arranged such that, in use, they are angled with respect to the direction of fluid flow. The sensors may be adapted to have a sensing path that has at least a component of its direction vector in or against the direction of fluid flow and/or at least a component of its direction vector in a direction across the fluid flow.

The first and/or second sensors may be connected to a controller.

At least one of the first and second sensors may be operable with signals having at least first and second frequency components. The controller may be arranged to determine a time of flight of a signal of the first sensor using the magnitude and/or phase of the first and second frequency components and/or the relative phases of the first and second frequency components.

At least one of the first and second sensors may be arranged to measure magnitude and phase of a signal.

The sensors may be arranged in a sensor array, which may be an integrated sensor array.

The sensors may be distributed over substantially the entire height of the flow path.

In this way, flow of fluid having one or a plurality of components may be detected or characterized over the entire height of the measurement chamber.

The first and/or second sensors may be unevenly distributed in a vertical direction.

A higher density of first sensors may be provided on a section expected to have a particular constituent or phase. For example, a higher density of first sensors may be provided on at least one upper section of the side of the flow path than on at least one lower section of the side of the flow path. As a further example, a higher density of second sensors may be provided on at least one lower section of the side of the flow path than on at least one upper section of the side of the flow path.

In this way, the density of gas sensors may be higher towards an upper region of the flow path, where the gas components are more likely to be located and the density of liquid sensors may be higher towards a lower region of the flow path, where liquid components are more likely to be located. In this way, increased sensing resolution may be provided without a corresponding increase in the cost or complexity of extra sensors.

The number of second sensors may be more or less than the number of first sensors.

The system may comprise at least four first sensors and/or at least eight second sensors. Thus, in systems in which most of the flow is expected to be liquid, more liquid sensors than gas sensors may be provided, thereby maintaining sensing accuracy whilst sensor cost and complexity may be minimised. The converse may apply to systems in which most of the flow is expected to be gaseous.

The flow path may be connected to, or be part of, a pipeline. The flow path may have a cross section in the form of a quadrilateral, such as a square or rectangle. At least part of at least one side of the flow path may be parallel to at least part of an opposing side of the flow path. At least some of the transducers may be located on the parallel parts of the opposing side walls of the flow path.

In this way, the path length between transducers located on opposing walls may be constant for each transducer pair, which may simplify data processing. Furthermore, a quadrilateral cross section may encourage smooth flow and may promote stratification of the constituent parts into layers.

In an optional alternative embodiment, the flow path may have a circular cross section. In this way, the flow path may be made more consistent with common pipe configurations.

The flow path may have a greater cross sectional area than the pipeline. The system may comprise at least one flow conditioner for transitioning flow between the pipeline and the flow path. The flow conditioners may be located at one or both transitions between the flow path and pipeline.

At least one flow conditioner and/or flow path may be arranged to provide, establish, encourage or the like, laminar flow in the flow path.

The system may be provided with a cross-sectional imager, which may be located before the flow path. The cross-sectional imager may be arranged to determine static properties of the fluid in a cross section of the pipeline. The controller may be arranged to combine output from the cross-sectional imager with output from the transducers in order to determine static and dynamic properties of the fluid.

The system may comprise a pressure and/or temperature gauge, which may be provided toward an upper region of, or in a top surface of the flow path.

The controller may be arranged to characterize the material in the measurement path of each transducer by determining the time of flight of a transmitted pulse, such as a sonic pulse across the flow path.

The composition of material in the measurement path may be determined by comparing measured time of flight data with characteristic values. The composition of interfacial layers may be determined by interpolating between known values, for example, if a first transducer was determined to be measuring a layer of oil and a third transducer was determined to be measuring a layer of water, and a second transducer was providing measurements that were intermediate those expected for water and oil, then the intermediate reading may be usable to determine the relative composition of water and oil in the interfacial layer.

The system may be adapted to be retrofitted to a pipeline.

According to a second aspect of the present invention is a method for determining and/or characterizing constituents of a fluid, comprising at least partially separating the constituents in at least one separation direction and taking measurements using a plurality of sensors, the sensors being spatially distributed in the separation direction.

The method may include use of a system according to the first aspect.

According to a third aspect of the present invention, there is provided a system for determining and/or characterizing constituents of a flowing fluid, comprising a measurement chamber and a plurality of sensors, wherein the measurement chamber defines a horizontal fluid flow path and the sensors are vertically distributed on the sides of the flow path.

The measurement chamber may define a fluid flow path. The fluid flow path may be oriented substantially horizontally.

Optional features described in relation to the first aspect may also apply to the third aspect.

According to a fourth aspect of the present invention is a method for determining and/or characterizing constituents of a fluid, comprising providing a horizontal fluid flow path and taking measurements using a plurality of sensors, the sensors being vertically distributed on the sides of the flow path.

The method may include use of a system according to the third aspect.

Description of the Drawings

Various aspects of the invention will now be described by way of example only and with reference to the accompanying drawings, of which: Figure 1 is a side view of a flow cell system; Figure 2 is a cross sectional view of the flow cell system of Figure 1 taken through the axis indicated 2-2 in Figure 1; Figure 3 is a cross section of the flow cell system shown in Figures 1 and 2, taken through an axis indicated 3-3 in Figure 2; Figure 4 is a cross section of the flow cell system shown in Figures 1 to 3, taken through an axis indicated 4-4 in Figure 3; Figure 5 is a perspective view of the system of Figures 1 to 4; and Figure 6 is an exploded perspective view of the system of Figures 1 to 5.

Figure 7 is a top view of an alternate embodiment of a flow cell system; Figure 8 is a cross section of the flow cell system shown in Figure 7, taken through an axis indicated 8-8 in Figure 7; Figure 9 is a cross section of the flow cell system shown in Figures 7 and 8, taken through an axis indicated 9-9 in Figure 8;

Specific Description

Figures 1 to 6 and Figures 7 to 9 respectively show two alternate embodiments of a flow cell system 5 for detecting, measuring and/or characterizing the composition of a flowing fluid. The flow cell system 5 comprises a measurement cell 10 located between an inlet flow transition section 15 and an outlet flow transition section 20.

The inlet section 15 and the outlet section 20 are connectable to a pipeline (not shown) such that, in use, fluid may flow from the pipeline through the inlet transition section 15 to the measurement cell 10, through the measurement cell 10 and out via the outlet transition section 20 into the pipeline.

The inlet transition section 15 comprises a body 25 defining an inlet bore 30 running from a pipe connector 35 to a cell connector 40. The pipe connector 35 is adapted to connect to the pipeline and comprises a flange 45 or other suitable connecting means known in the art, whilst the cell connector 40 is arranged to connect to an optional viewing chamber 50 or an inlet 55 of the measurement cell 10 via a suitable flange or other means known in the art. The inlet bore 30 of the inlet transition section 15 has a circular cross section at the pipe connector end 35 and tapers outwardly, transitioning gradually to a square cross section at the cell connector end 40, such that the cross sectional area of the inlet bore 30 at the cell connector end 40 is larger than the cross sectional area of the inlet bore 30 at the pipe connector end 35.

The optional viewing port 50 is formed from glass or other suitable transparent material and defines a square cross sectioned bore 60 and mounting means 65 for sealably attaching the viewing chamber 50 to the cell connector 40 of the inlet transition section 15 and an inlet connector 55 of the measurement cell 10 such that the bore 30 of the inlet transition section 15 at the cell connector end 40, the bore 60 of the viewing section 50 and a cell bore 70 of the measurement cell 10 form a substantially continuous channel having a constant square cross section.

The measurement cell 10 comprises a cell body 75 having a top 80, bottom 85 and opposing side walls 90, 95, which define the cell bore 70. The cell bore 70 runs from the cell inlet 55 to a cell outlet 100. The cell bore 70 is arranged to have a substantially continuous square cross section along its length. The measurement cell 10 is provided with two sets of sensors 105, 110 on each side wall 90, 95 of the measurement cell 10. Each set of sensors 105, 110 comprises eight ultrasonic transducers 115, 120 located in apertures in a first side wall 90 of the measurement cell 10. The transducers 115, 120 are oriented to face across the cell bore 70 to a corresponding group of eight ultrasonic transducers 125, 130 located in apertures on an opposing side wall 95. Thus the transducers 115, 120 on one side wall 90 may be operable to detect reflected signals originating from those transducers 115, 120 or to detect transmitted signals originating from the transducers 125, 130 on the opposing side wall 95 The transducers 115, 120, 125, 130 are obliquely angled with respect to the direction of fluid flow through the measurement cell 10 in use such that a component of a directional vector of an ultrasonic signal emitted from the transducers 115, 120, 1 25, is either with or against the direction of flow and a component of a directional vector of an ultrasonic signal emitted from the transducers 115, 120, 125, 130 is transverse to the direction of fluid flow. The transducers 115, 120 on each side wall are aligned to face a corresponding transducer 125, 130 on the opposing side wall such that there is a direct line of communication between corresponding transducers and 125 or 120 and 130.

The transducers 115, 120, 125, 130 are arranged to produce ultrasonic pulses having controlled frequencies. The first set 105 of transducers 115, 125 are arranged to operate through gaseous media, such as natural gas, and produce signals having a higher frequency than the transducers 120, 130 of the second set 110. The transducers 115, 125 of the first set 105 are arranged to produce a signal having two frequency components having respective frequencies of 290kHz and 310kHz. The two frequency components can be utilised to more accurately determine the time of flight of the signal, as detailed in PCT/GB2009/001 120, which is dependent on the medium through which the signal passes. In this way, properties such as the composition, velocity and flow rate of the fluid and its constituent layers can be determined. It should be understood, however, that the disclosure of PCT/GB2009/001120 is not essential to the present invention.

The second set 110 of transducers 120, 130 are arranged to produce a signal at a single frequency. The magnitude and phase of the received signal is usable to determine the composition of the medium using techniques known in the art, such as variation of speed of sound or attenuation of the signal.

The measurement chamber 10 is also provided with at least one top and bottom mounted transducer. In one embodiment, only one top and bottom transducer pair oriented transversely of the direction of flow is provided (as shown in Figures 2 to 4). In an alternate embodiment, three top and bottom transducers 140 oriented with the direction of flow are provided, as shown in Figures 6 to 9. One of more of the top and bottom transducers 135, 140 are arranged to function as liquid phase transducers and are operable to provide additional phase characterisation when the fluid is substantially entirely liquid. Additionally or alternately, one or more of the top and bottom transducers 135, 140 are arranged to function as gas phase transducers and are operable to provide additional phase characterisation when the fluid is substantially entirely gas.

Pressure and temperature probes 145, 150 may be provided in the top of the measurement cell 10 in order to provide further data regarding any gas phase present.

The cell outlet 100 of the measurement cell 10 is sealably connected to a cell connector 155 of the outlet transition section 20 via a flange or other suitable connecting means known in the art. The outlet transition section 20 comprises a body 160 defining an outlet bore 165 running from the cell connector 155 of the outlet transition section 20 to a pipe connector 170. The pipe connector 170 is adapted to connect to the pipeline, for example, by a suitable flange or other means known in the art. The outlet bore 165 has a square cross section at the cell connector end 155, which tapers inwardly and transitions gradually to a circular cross section at the pipe connector end 170, such that the cross sectional area of the outlet bore 165 at the pipe connector end 170 is smaller than the cross sectional area of the outlet bore 165 at the cell connector end 155. The outlet bore 165 is sized to match the cell bore at the cell connector end 155 and sized to match the pipeline at the pipe connector end 170.

In use, the flow cell 5 is mounted to the pipeline such that it is oriented substantially horizontally. There may also be a substantially horizontally extending section (not shown) of pipeline connected to the pipe connector 35 of the inlet transition section 15. In this way, as fluid is passed through the pipeline, the speed of the fluid flow is reduced upon entering the inlet transition section 1 5 due to the increase in diameter of the inlet bore 30. Since the flow cell 5 is mounted horizontally, separable components of the fluid, each component having a differing density, separate and stratify into layers as they pass through the horizontal flow cell 5. The length of the inlet transition section 15, the viewing chamber 50 and the section of the measurement cell 10 before the sensors 105, 110 and the length of any horizontal section of pipeline before the flow cell 5 are selected to provide a horizontal path length that affords sufficient time for the separable components to stratify. Upon stratification, the more dense phases, such as oil, will separate out towards the bottom of the measurement cell 10, intermediate density phases, such as water or brine, will separate out above the dense phases and the least dense phases, such as natural gas, will tend toward the upper section of the measurement cell 10.

If more than one separable component is present, particularly if both liquid and gas phases are present, signals passed between top/bottom mounted transducers 135, may suffer from attenuation due to reflections from the interfacial boundaries between component layers or be absorbed by certain components.

However, by having a series of transducers 115, 120, 125, 130 distributed over the direction in which separation occurs, i.e. vertically on the side walls 90, 95 of the measurement cell 10, the signal produced by the transducers 115, 120, 125, 130 passes through the stratified layers generally in the plane of, or generally parallel with, the stratified component layers. In this way, the signal from each transducer 115, 120, 125, 130 is more likely to pass through only one component layer in a multiphase system. In this way reflections from phase boundaries can be minimised and the transducers 115, 120, 125, 130 can be optimised for use with particular phases (for example by selecting appropriate signal frequencies), in order to minimise absorption.

However, it will be appreciated that the signal path of some transducers 115, 120, 125, 130 may include an interface between two phases or a mixed phase. In this case, the signals obtained from the appropriate first 115, 125 and second 120, 130 transducers may be analysed and an estimate of the relative amount of each phase for the measured section of the measurement cell 10 determined.

In order to provide maximum detection flexibility, each of the series of first 105 and second 11 0 sets of transducers 11 5, 1 20, 125, 130 are distributed over the full height of the measurement cell 10. In this way, the system may detect fluid flow in which fewer than a maximum number of phases are present, for example when gas slugs occur, in which gas substantially fills a section of the measurement cell 10 for a short period of time.

The vertical distribution of transducers 11 5, 1 20, 125, 130 also does not necessarily need to be uniform. For example, the density of first transducers 115, 125 may be higher towards the top of the measurement cell 10, where gas phases are more likely to be found relative to the bottom of the measurement cell 10. Similarly, the density of second transducers 120, 130 may be higher towards the bottom of the measurement cell 10 than toward the top, as any liquid phase is more likely to be found toward the bottom of the measurement cell 10. In this way, the accurate phase determination may be obtained whilst minimising the number of sensors required.

The transducers 115, 120, 125, 130 of each set of sensors are offset from each other in the direction of fluid flow. In this way, reflections received by the transducers 115, 120, 125, 130 can be minimised.

The components of the flow cell system 5 such as the measurement cell 10, inlet 15 and outlet 20 transition sections and viewing chamber 50 may be sealably connected using suitable known sealing means such as gasket sealing, interlocking and/or conformable mating surfaces.

In an optional embodiment, a cross sectional analyser (not shown) may be provided between the pipeline and the flow cell system 5. The cross sectional analyser is adapted to determine the composition of a cross section of the fluid flowing through the pipeline. The cross sectional analyser collects static information regarding the composition of the fluid in the cross section at any given time. Thus, by combining the static information determined by the cross-sectional analyser with dynamic information such as flow rates for each of the constituent layers from the flow cell 5, a more complete and accurate characterization of the flow can be carried out. Using the combination of static characterisation by the cross-sectional analyser with dynamic flow data obtained using the flow cell system 5, volumetric flow rates may be determined and monitored. This data is very important in certain industries, for example, it may be used to determine the volume of oil extracted from a well over time and thereby produce an accurate determination of its actual extracted value.

A skilled person will also appreciate that variations of the disclosed arrangements are possible without departing from the invention. For example, whilst the cell bore 70 of the measurement chamber 10 is advantageously presented as having a square cross section, measurement chambers having other cross sectional profiles such as circular, rectangular or the like may be used. In addition, although in the specific embodiments, two sets of sensors 105, 110 are provided, it will be appreciated that other numbers of sets of sensors and/or other sensor configurations or types may be provided. In certain embodiments, eight transducer pairs 115, 120, 125, 130 are provided in each set 105, 110 of sensors. However, it will be appreciated each set of sensors 105, 110 may contain other numbers of transducer pairs 115, 120, 125, 130 and/or that each set 105, 110 may contain the same or different numbers of transducer pairs 115, 120, 125, 130. Although the transducers are describes as discrete transducers, in an alternative embodiment, integrated transducer arrays may be used. It will also be appreciated that the transducers 115, 120, 125, 130 may be selected and/or arranged to operate in a reflection mode, a transmission mode or a combination of both. Furthermore, in an embodiment described above, the transducers 115, 120, 125, 130 are described as operating using a signal having two frequency components at 290kHz and 310kHz. However, it will be appreciated that other signals using different frequencies and having other numbers of frequency components may be used. Accordingly the above description of the specific embodiment is made by way of example only and not for the purposes of limitation.

It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

CLAIMS: 1. A system for determining and/or characterizing constituents of a fluid, comprising a measurement chamber for receiving the fluid, the chamber being arranged to at least partially separate components of the fluid in at least one separation direction, and a plurality of sensors spatially distributed in the separation direction.
2. The system of claim 1, wherein the measurement chamber define a flow path for a flowing fluid.
3. The system of claim 2, wherein the flow path is oriented substantially horizontally such that a mean bulk flow is directed along a substantially horizontal path.
4. The system of claim 2 or 3, wherein the flow path is arranged such that at least two components present in the fluid flow at least partially stratify into layers.
5. The system of claim 4, wherein the flow path is arranged such that the layers separate out in a generally vertical direction.
6. The system of any one of claims 2 to 5, wherein the flow path is provided with a substantially horizontal inlet pipe section and/or a separation section between an inlet of the flow path and the sensors, the length of the substantially horizontal inlet pipe section and/or the separation section being selected to permit at least partial separation of at least two components of the fluid flow.
7. The system of any preceding claim, wherein the sensors are vertically distributed.
8. The system of any preceding claim, wherein the sensors are horizontally distributed.
9. The system of any preceding claim, wherein at least one sensor comprises a signal source and/or receiver.
10. The system of any preceding claim, wherein at least one sensor comprises a sonic-based transducer.
11. The system of any one of claims 2 to 10, wherein at least two sensors are provided in a sensor pair, one sensor of the sensor pair being located on a first side wall of the flow path and the other sensor of the sensor pair being located on a second side wall of the flow path.
12. The system of any preceding claim, comprising at least one first sensor and at least one second sensor, wherein the at least one first sensor comprises a gas sensor adapted to measure properties of one or more gasses, and the at least one second sensor comprises a liquid sensor, adapted to measure properties of one or more liquids.
13. The system of any preceding claim, wherein one or more of the plurality of sensors are arranged such that, in use, they are adapted to have a sensing path that has at least a component of its direction vector in or against the direction of fluid flow and/or at least a component of its direction vector in a direction across the fluid flow.
14. The system of claim 12 or 13, wherein at least one of the first and second sensors is operable with signals having at least first and second frequency components.
15. The system of claim 14, wherein the first and/or second sensors are connected to a controller arranged to determine a time of flight of a signal of the first sensor using the magnitude and/or phase of the first and second frequency components and/or the relative phases of the first and second frequency components.
16. The system of any one of claims 12 to 15, wherein at least one of the first and second sensors is arranged to measure magnitude and phase of a signal.
17. The system of any one of claims 2 to 16, wherein the sensors are distributed over substantially the entire height of the flow path.
18. The system of any one of claims 12 to 17, wherein the first and/or second sensors are unevenly distributed in a vertical direction.
19. The system of any one of claims 2 to 18, wherein the sensors comprise both liquid sensors and gas sensors, wherein a higher density of liquid sensors are provided in a lower region of the flow path, and a higher density of gas sensors are provided in an upper region of the flow path.
20. The system of any one of claims 2 to 19, wherein the flow path is connected to a pipeline.
21. The system of claim 20, wherein the flow path may has a greater cross sectional area than the pipeline.
22. The system of any one of claims 2 to 21, comprising at least one flow conditioner configured for transitioning flow between into the flow path.
23. The system of any one of claims 2 to 22, wherein the flow path defines a cross section in the form of a quadrilateral.
24. The system of any preceding claim, comprising a cross-sectional imager.
25. The system of any preceding claim, comprising a pressure and/or temperature gauge.
26. The system of any preceding claim, comprising a controller arranged to characterize the material in the measurement path of each sensor by determining the time of flight of a transmitted pulse.
27. The system of any preceding claim, wherein the composition of material in the measurement path is determined by comparing measured time of flight data with characteristic values.
28. The system of any preceding claim, adapted to be retrofitted to a pipeline.
29. A method for determining and/or characterizing constituents of a fluid, comprising at least partially separating the constituents in at least one separation direction and taking measurements using a plurality of sensors, the sensors being spatially distributed in the separation direction.