GB2354075A

GB2354075A - Determining fluid flow rate in a pipe

Info

Publication number: GB2354075A
Application number: GB9921118A
Authority: GB
Inventors: Andrew Godley; Stephen Lindsay Russell
Original assignee: WRC PLC
Current assignee: WRC PLC
Priority date: 1999-09-07
Filing date: 1999-09-07
Publication date: 2001-03-14
Anticipated expiration: 2019-09-07
Also published as: GB9921118D0; GB2354075B

Abstract

A method of determining the flowrate of a fluid in a pipe (12), comprising: feeding a sensor (600) on a carrier (56) through an aperture (36) in the pipe (12) and moving the sensor (600) downstream along the pipe (12) to a location remote from the aperture (36); injecting a tracer, which can be detected by the sensor (600), into the pipe (12) upstream of the position of the sensor (600); detecting the tracer with the sensor (600); determining the fluid flow from measurements relating to the tracer made by the sensor (600).

Description

2354075 METHOD AND APPARATUS FOR DETERMINING FLUID FLOW RATE IN A PIPE

This invention relates a method and apparatus for determining fluid flow rate in 5 a pipe.

The measurement of the flow of fluid in pipe is a common requirement. Where continuous flow measurement is needed, a permanent flowmeter is generally installed, for example the electromagnetic type. There is often a requirement for occasional measurement of pipeline fluid flow, for example to determine flows for the sizing of tanks, or in planning changes to pipeline systems. A common application for occasional flow measurement is in the calibration of existing flowmeters.

Flowmeters for closed pipelines are usually calibrated on flow test rigs at manufacture; if the calibration has to be repeated or checked later, the flowmeters are removed and calibrated using a flow test rig. Methods for calibrating flowmeters in-situ are available but are generally expensive and offer reduced accuracy compared with the test rig method. Some flowmeters are installed in close proximity to flow disturbances such as bends or valves and these can affect the calibration such that the test rig calibration is significantly in error. In these situations, in- situ calibration potentially offers superior accuracy to a test rig calibration.

Flow measurement using dilution gauging of tracers of various kinds is well established and the subject of several standards (see BS 3680 Pt 2A: 1995 ISO 9555-3 1994, Measurement of liquid flow in open channels, Dilution methods. 2A General; and BS 3680 Pt 2C: 1993 ISO 9555-1 1992, Measurement of I iquid flow in open channels, Dilution methods. 2C Methods of measurement using chemical tracers). It is most often used on open channels and natural watercourses, but it can also be applied to closed pipes. In the closed pipe situation it has previously been too expensive to carry out routinely, since in its traditional form it requires access to the pipe at two points and uses laboratory analysis for the tracer in samples taken, leading to delays and great care being needed to avoid contamination of the samples by the tracer concentrate. It is thus labour intensive and requires a high skill level.

Another approach to occasional flow measurement in closed pipes is to measure the flow velocity at a number of positions across a pipe using an insertion flowmeter, and to measure the pipe cross sectional area by mechanical means. This technique is also an intensive user of skilled labour, and may not be able to provide sufficient accuracy for some requirements.

We have now found a method for measuring fluid flow in-situ in closed pipes which is economical, provides a direct volumetric flow result at the time of measurement, and is capable of the accuracy required for most calibration requirements. Our method involves deploying the sensor in the pipe through an aperture which is the same as, or close to, the aperture through which the tracer is to be injected, then moving the sensor downstream prior to injection, so that the sensor senses the tracer after it is thoroughly mixed with the fluid in the pipe.

According to one aspect of the invention there is provided a method of determining the flowrate of a fluid in a pipe, comprising: feeding a sensor on a carrier through an aperture in the pipe and moving the sensor downstream along the pipe to a location remote from the aperture; injecting a tracer, which can be detected by the sensor, into the pipe upstream of the position of the sensor; detecting the tracer with the sensor; and determining the fluid flow from measurements relating to the tracer made by the sensor.

It is not essential that the tracer is injected through the same aperture as the sensQr, but it is a particular advantage and feature of the present invention that the tracer can be injected through the same aperture as the sensor. Obviously, if a particular pipe happens to have two nearby apertures, then it may be desirable to feed the sensor through one aperture and to inject the tracer through the other aperture. However, it is necessary that the tracer is injected sufficiently remotely from the downstream position of the sensor that the volumetric fluid flowrate can be determined accurately - in general, this means that the tracer needs to have travelled far enough to be well mixed with the f luid. It is not possible to specify precisely howfar downstream the sensor needs to be moved as this will depend upon a number of factors, including the size and shape of the pipe, the turbulence of the fluid flow etc. However, the determination of a suitable distance is easily accomplished by the skilled person using trial and error and the techniques described in the standards described above.

Typically, we have found that the sensor needs to be moved downstream by a distance of at least 10 pipe diameters, more usually at least 50 pipe diameters, and most usually at least 100 pipe diameters. The important point is to make sure that the sensor is moved a sufficient distance to make sure that the tracer has mixed sufficiently to 5 provide an accurate reading of flowrate.

The sensor can be deployed in the pipe using the apparatus and method described in our copending UK patent application of even date entitled "Deployment of Equipment into Fluid Containers and Conduits". The sensor may be sensitive to any desired condition in the pipe fluid, e.g., changes in conductivity, changes in temperature, changes in fluorescence, changes in radioactivity, or combinations thereof.

According to another aspect of the invention there is provided apparatus for determining the flowrate of a fluid in a pipe, comprising: a sensor which is sensitive to a tracer; deployment means for deploying the sensor through an aperture in the pipe and moving the sensor along the pipe downstream of the aperture; and injection means for injecting the tracer into the pipe.

Although the invention can be used to determine fluid flowrate in any pipe, it is particularly useful for determining fluid flowrate in closed pipes where pipe access may be severely restricted. With the present invention it is not necessary to interrupt the fluid flow in order to deploy the sensor in the pipe, i.e., the sensor can be deployed without any depressurisation in the pipe.

Reference is now made to Figure 1 which is a schematic representation of an apparatus according to the invention.

A sensor 600 is deployed into a pipe 12 using a deployment apparatus 10. The deployment apparatus 10 is described in more detail in our copending UK patent application of even date entitled "Deployment of Equipment into Fluid Containers and Conduits". The apparatus 10 includes, inter alia, a fluid housing 14, a guide tube 16, a winch apparatus 200, a drogue 400 and a cable drum 512. The sensor 600 is deployed in the pipe 12 on a carrier 56 which may be any suitable form of cable or tube. A cable counter 208 is provided for measuring the distance travelled by the cable 56.

A slip ring is provided on the cable drum 512 to enable signals from the sensor 600 to be fed to a line 602 which leads to a signal conditioning unit and amplifier 604 and a control computer 606 which contains signal processing equipment and a display 614.

The control computer 606 is also connected to the cable counter 208 and to a dosing pump 608 which can pump tracer from a reservoir 610 through an injection tube 612 into the pipe 12. There are various ways by which the mixing of the tracer can be improved at the point of entry for example using an injection tube with numerous outlets across the pipe section, or by using an additional pump to take some of the pipe flow out, add the tracer from the dosing pump and pump it back into the main at a high velocity to provide the energy for rapid mixing. By these means it is possible to reduce the downstream distance by which it is necessary to move the sensor 600 to obtain good mixing.

It will be noted that the injection tube 612 and the sensor 600 extend through a single aperture 36 in the pipe 12. A suitable adaptor can be provided to allow the deployment apparatus 10 and the injection tube 612 to be attached to the pipe 12 in the region of the pipe aperture 36. The injection tube 612 and the deployment apparatus 10 are adapted to be inserted through a conventional pre-existing tapping or other pipe access. For example, 50 mm tappings are commonly provided at intervals along water mains. The sensor 600 and the injection tube 612 can be inserted through the pipe 12 without any interrupting of the pipe flow, i.e., it is not necessary to depressurise the pipe.

The apparatus is used as follows. First, the sensor 600 is deployed in the pipe 12 using the deployment apparatus 10 in conjunction with the winch apparatus 200.

The deployment technique is described in,greater detail in our copending UK patent application of even date entitled "Deployment of Equipment into Fluid Containers and Conduits". The sensor 600 is fed into the pipe 12, in a downstream direction, i.e., in the direction A of fluid flow, until the tracer is well mixed - this would normally entail feeding the sensor into the pipe 12 until it is at least 100 pipe diameters downstream of the aperture 36. The distance travelled is monitored using the cable counter 208.

At this point the readings of the sensor 600 are logged. The pump 11 then pumps the tracer into the pipe 12 using the selected dilution gauging method, either the constant rate method, or the integration (sudden injection) method. The sensor 600 records the effect of the injected flow of tracer on the unknown pipe flow, and the volume flowrate in the pipe 12 is calculated according to the standard methods (BS 3680 Pt 2A, referred to above) from the known concentration of the tracer in the reservoir 610, the injected flowrate (and the time for which the pump operated in the case of the integration method) and the sensor readings recorded by the control computer 606. Normal practice would be to repeat the measurement a number of times, and for calibration at a number of different flowrates.

The choice of tracer and sensor 600 will depend upon the fluid and its use, for example for drinking water sodium chloride may be used as a tracer with a conductivity and temperature sensor; alternatively a fluorescent dye could be used with a fluorescence sensor or a radioactive tracer could be used with a radiation sensor. The control computer 606 may be used to automate the flow measurement process by providing instructions to the operators and making decisions on the number of repeat runs needed to obtain the required level of accuracy. In some situations there may be some doubt as to precisely how the tracer material reacts with the pipe fluid, in which case a sample of the fluid may be withdrawn from the pipe 12 and mixed with the tracer in precisely measured proportions and the effect on the sensor 600 or an identical sensor measured. This checking process is also readily automated and is used routinely where high accuracy is needed.

It will be appreciated that the invention described above may be modified.

Claims

CLAIMS:

1. A method of determining the flowrate of a fluid in a pipe, comprising: feeding a sensor on a carrier through an aperture in the pipe and moving the sensor downstream along the pipe to a location remote from the aperture; injecting a tracer, which can be detected by the sensor, into the pipe upstream of the position of the sensor; detecting the tracerwith the sensor; determining the fluid flowfrom measurements relating to the tracer made by the sensor.

2. A method according to claim 1, wherein the tracer is injected through the same aperture in the pipe through which the sensor is deployed.

3. A method according to claim 1 or 2, wherein the sensor is moved downstream a sufficient distance to enable the tracer to be mixed sufficiently with the fluid in the pipe to enable the flowrate to be determined.

4. A method according to claim 1 or 2, wherein the sensor is moved downstream by a distance of at least 10 pipe diameters.

5. A method according to claim 1 or 2, wherein the sensor is moved downstream by a distance of at least 100 pipe diameters.

6. Apparatus for determining the flowrate of a fluid in a pipe, comprising: a sensor which is sensitive to a tracer; deployment means for deploying the sensor through an aperture in the pipe and moving the sensor along the pipe downstream of the aperture; and injection means for injecting the tracer into the pipe.

7. Apparatus according to claim 6, wherein the deployment apparatus and the injection means are adapted to deploy the sensor and inject the tracer through a single aperture in the pipe.

8. Apparatus according to claim 6 or 7, further comprising a computer for controlling movement of sensor along the pipe, and for processing data measured by the sensor.

9. Apparatus according to claim 8, wherein the injection means comprises an injection pump for injecting the tracer into the pipe, and wherein the computer controls operation of the injection pump.

10. A method substantially as herein described with reference to and as shown in 10 the accompanying drawing.

11. Apparatus substantially as herein described with reference to and as shown in the accompanying drawing.