WO2005052521A1 - Instrument and method for determining flow rate - Google Patents

Instrument and method for determining flow rate Download PDF

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Publication number
WO2005052521A1
WO2005052521A1 PCT/IB2004/003837 IB2004003837W WO2005052521A1 WO 2005052521 A1 WO2005052521 A1 WO 2005052521A1 IB 2004003837 W IB2004003837 W IB 2004003837W WO 2005052521 A1 WO2005052521 A1 WO 2005052521A1
Authority
WO
WIPO (PCT)
Prior art keywords
flow rate
flow passage
instrument
throat
density
Prior art date
Application number
PCT/IB2004/003837
Other languages
French (fr)
Inventor
Robert Cooke
Original Assignee
Robert Cooke
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Cooke filed Critical Robert Cooke
Publication of WO2005052521A1 publication Critical patent/WO2005052521A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/74—Devices for measuring flow of a fluid or flow of a fluent solid material in suspension in another fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
    • G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
    • G01F1/36—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction
    • G01F1/40—Details of construction of the flow constriction devices
    • G01F1/44—Venturi tubes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
    • G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
    • G01F1/88—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure with differential-pressure measurement to determine the volume flow

Definitions

  • THIS INVENTION relates to mass flow meters, especially mass flow meters suitable to be used for measuring mass flow rates of magnetic media.
  • the invention relates to an instrument and a method of determining a flow rate.
  • a mass flow rate of a process flow stream such as a mineral slurry can most conveniently be determined by determining the density of the medium in the flow stream and measuring the volumetric flow rate of the flow stream.
  • the medium density is determined using a nuclear density meter, but these meters often need to be recalibrated to compensate for drifts caused by decay of the nuclear source. The use of these meters is also strictly regulated in many countries, and prohibited in some.
  • the volumetric flow rate of a mineral slurry is usually measured using a magnetic flow meter, but this type of meter can not be used for slurries including a magnetic medium.
  • a magnetic flow meter can not be used for slurries including a magnetic medium.
  • an instrument including a body defining an elongate flow passage including: a density measuring flow passage in which an internal cross-sectional profile of the flow passage remains generally constant for the length of the density measuring flow passage, and which includes pressure sensor receiving formations, at locations spaced apart along the length of the flow passage; and a flow rate measuring flow passage defining a throat, in which the cross-sectional area of the flow passage is smaller than the cross-sectional area of the flow passage axially upstream and downstream of the throat, and which includes a pressure sensor receiving formation in the throat, wherein the density measuring flow passage and the flow rate measuring flow passage are connectable in a common flow passage.
  • the density measuring flow passage and the flow rate measuring flow passage may be directly connected in a co-axial arrangement.
  • the flow rate measuring flow passage may define a venturi- type throat, and may be of standardised dimensions, including frusto- conically tapering parts directly adjacent the throat on upstream and downstream sides.
  • the instrument may include pressure sensors, mounted on the pressure sensor receiving formations, and the instrument may include equipment configured to determine the static pressure inside the flow passage, and/or configured to determine the differential in static pressure between the locations of at least two pressure sensor receiving formations.
  • the instrument may include a pressure sensor disposed at the throat of the venturi, and at least one pressure sensor disposed at a control location, spaced axially from the throat and from the frusto-conically tapering parts.
  • the instrument may include equipment configured to determine the differential static pressure between the throat and the control location.
  • the instrument may be installed with the pressure sensors of the density measuring flow passage disposed at different elevations, and may include equipment configured to determine density, volumetric flow rate, and/or mass flow rate of a medium flowing in the flow passage, using the static pressures measured by the pressure sensors.
  • a method for determining a flow rate said method including: measuring a first differential pressure between different elevations in a flow stream of generally constant cross-sectional area; measuring a second differential pressure at locations in the flow stream with different cross-sectional areas; assuming an initial volumetric flow rate; calculating a density of the medium of the flow stream, using the Bernoulli equation, the first differential pressure, the assumed volumetric flow rate, and taking the difference in elevations at which the pressures were measured, into account; and calculating volumetric flow rate using the calculated medium density and the second differential pressure.
  • the method may be repeated, using the calculated volumetric flow rate as the new assumed volumetric flow rate, until the assumed volumetric flow rate and calculated volumetric flow rate differ by less than a predetermined quantity.
  • the method may include calculating mass flow rate by multiplying the volumetric flow rate with the calculated density.
  • Figure 1 shows a three-dimensional view of an instrument in accordance with the invention
  • Figure 2 shows a sectional side view of the instrument of Figure 1
  • Figure 3 shows a flow diagram of a method of determining mass flow rate, volumetric flow rate, and medium density, in accordance with the invention.
  • an instrument 10 in accordance with the invention is generally indicated by reference numeral 10.
  • the instrument 10 includes an elongate, hollow cylindrical body 12 defining an internal elongate flow passage 14.
  • the flow passage 14 includes a density measuring flow passage or parallel flow passage 16 and a mass flow rate measuring flow passage or venturi flow passage 18, directly connected in a coaxial arrangement.
  • the parallel flow passage 16 has a generally constant internal cross-sectional profile throughout its length, and includes two longitudinally spaced sensor receiving formations 20, on which pressure sensors 22 have been mounted, to measure static pressure.
  • the venturi flow passage 18 defines a cylindrical, internal throat 24 in which the cross-sectional area of the flow passage is smaller than the cross-sectional area of the flow passage axially upstream and downstream of the throat, to form a venturi-type flow meter, including standardised frusto-conically tapering parts 36 between the throat and the adjacent flow passage, upstream and downstream.
  • a sensor receiving formation 26 is provided in a circumferential wall of the throat 24, and a sensor receiving formation 28 is provided in a control location, spaced axially from the throat 24.
  • the sensor receiving formation 26 is located in the flow stream and is spaced axially from the tapering parts, preferably by a distance of at least half the diameter of the flow passage.
  • Pressure sensors 30 are mounted on the sensor receiving formations 26,28, to measure static pressure.
  • the pressure sensors 22,30 are connected via conduits 32 to processing equipment 38, shown schematically in Figure 2 of the drawings, to use the measured pressures in a calculation method as described hereinbelow. It is to be appreciated that the pressure sensors 22,30 can be of a variety of formats, including transducers generating pressure signals that are sent to the processing equipment 38, open tubes or tubes closed by flexible diaphragms, transferring pressure via the conduits 32 to the processing equipment, or the like. It is further to be appreciated that the processing equipment 38 can include a calculator, microprocessor, or the like.
  • the pressure sensors 22 are configured to measure the differential pressure between the two axially spaced sensor receiving formations 20, and similarly the pressure sensors 30 are configured to measure the differential pressure between the throat 24 and the control location. It is to be appreciated that one of the pressure sensors 22 can be used instead of the pressure sensor 30 at the control location, but the control location should preferably be close to one of the tapering parts 36.
  • the instrument 10 is installed in a mineral processing plant or the like, by attaching flanges 34 of the body 12 to adjoining equipment, preferably in an upright orientation.
  • the instrument 10 can be installed at an angle, provided that there is a known difference in elevation between the positions of the pressure sensors 22.
  • the density of the flow stream can be determined from the differential pressures between the sensors 22 in the parallel flow passage 16, provided that the mass flow rate of the flow stream is known. Further, the mass flow rate of the flow stream can be determined from the differential pressure between sensors 30 in the Venturi flow passage 18, provided that the density of the flow stream is known.
  • the mass flow rate, volumetric flow rate and medium density of the flow stream is determined in the processing equipment 38, in accordance with the following iterative method, illustrated in Figure 3 of the drawings: the differential pressures in the parallel flow passage 16 (sensors 22) and the venturi flow passage 18 (sensors 30) are measured as described hereinabove; an initial or trial volumetric flow rate of zero is assumed; a medium density for the flow stream is calculated using the pressure differential in the parallel flow passage 16 and the trial volumetric flow rate, using the Bernoulli equation, taking the different elevations of the pressure sensors 22 into account, and making provision for losses due to pipe friction; a new volumetric flow rate is calculated using the calculated medium density and the differential pressure between pressure sensors 30; the new calculated volumetric flow rate is compared to the previous volumetric flow rate, and if the two flow rates differ by more than a predetermined quantity, the process is repeated in an iterative manner, using the new calculated volumetric flow rate as the trial volumetric
  • the mass flow rate is calculated, using the calculated medium density, and an output of mass flow rate, volumetric flow rate and medium density is provided.
  • the invention illustrated holds the advantage that mass flow rate of a process flow stream can be determined without the use of a nuclear source or magnetic sensing devices.
  • the invention illustrated holds the further advantages of low cost and simplicity of structure and operation.

Abstract

An instrument (10) and a method are provided for determining a flow rate of a medium in a flow passage (14). The instrument (10) includes a parallel flow passage (16) with axially spaced pressure sensors (22), directly connected to a flow measurement flow passage (18) defining a Venturi-type throat (26), and including pressure sensors (30), positioned at the throat (24) and at a control position (28). A trial volumetric flow rate is initially assumed to be zero and a density of the flow stream is calculated using the trial volumetric flow rate and the pressure differential between sensors (20). A new trial volumetric flow rate is calculated using the calculated density and the pressure differential between sensors (30), and the difference between the new trial flow rate and the previous flow rate is determined. The process is repeated using the new trial flow rate, until the difference between the trial flow rate and previous flow rate is small enough.

Description

INSTRUMENT AND METHOD FOR DETERMINING FLOW RATE
FIELD OF THE INVENTION
THIS INVENTION relates to mass flow meters, especially mass flow meters suitable to be used for measuring mass flow rates of magnetic media. In particular, the invention relates to an instrument and a method of determining a flow rate.
BACKGROUND TO THE INVENTION
A mass flow rate of a process flow stream such as a mineral slurry can most conveniently be determined by determining the density of the medium in the flow stream and measuring the volumetric flow rate of the flow stream. In many mineral processing applications, the medium density is determined using a nuclear density meter, but these meters often need to be recalibrated to compensate for drifts caused by decay of the nuclear source. The use of these meters is also strictly regulated in many countries, and prohibited in some.
The volumetric flow rate of a mineral slurry is usually measured using a magnetic flow meter, but this type of meter can not be used for slurries including a magnetic medium. Thus, there is a need for accurate measurement of mass flow rates of mineral slurries including magnetic media, without requiring a nuclear source, when the densities of the slurπes are not known.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided an instrument including a body defining an elongate flow passage including: a density measuring flow passage in which an internal cross-sectional profile of the flow passage remains generally constant for the length of the density measuring flow passage, and which includes pressure sensor receiving formations, at locations spaced apart along the length of the flow passage; and a flow rate measuring flow passage defining a throat, in which the cross-sectional area of the flow passage is smaller than the cross-sectional area of the flow passage axially upstream and downstream of the throat, and which includes a pressure sensor receiving formation in the throat, wherein the density measuring flow passage and the flow rate measuring flow passage are connectable in a common flow passage.
The density measuring flow passage and the flow rate measuring flow passage may be directly connected in a co-axial arrangement. The flow rate measuring flow passage may define a venturi- type throat, and may be of standardised dimensions, including frusto- conically tapering parts directly adjacent the throat on upstream and downstream sides.
The instrument may include pressure sensors, mounted on the pressure sensor receiving formations, and the instrument may include equipment configured to determine the static pressure inside the flow passage, and/or configured to determine the differential in static pressure between the locations of at least two pressure sensor receiving formations.
The instrument may include a pressure sensor disposed at the throat of the venturi, and at least one pressure sensor disposed at a control location, spaced axially from the throat and from the frusto-conically tapering parts. The instrument may include equipment configured to determine the differential static pressure between the throat and the control location.
The instrument may be installed with the pressure sensors of the density measuring flow passage disposed at different elevations, and may include equipment configured to determine density, volumetric flow rate, and/or mass flow rate of a medium flowing in the flow passage, using the static pressures measured by the pressure sensors. According to another aspect of the invention, there is provided a method for determining a flow rate, said method including: measuring a first differential pressure between different elevations in a flow stream of generally constant cross-sectional area; measuring a second differential pressure at locations in the flow stream with different cross-sectional areas; assuming an initial volumetric flow rate; calculating a density of the medium of the flow stream, using the Bernoulli equation, the first differential pressure, the assumed volumetric flow rate, and taking the difference in elevations at which the pressures were measured, into account; and calculating volumetric flow rate using the calculated medium density and the second differential pressure.
The method may be repeated, using the calculated volumetric flow rate as the new assumed volumetric flow rate, until the assumed volumetric flow rate and calculated volumetric flow rate differ by less than a predetermined quantity.
The method may include calculating mass flow rate by multiplying the volumetric flow rate with the calculated density.
The invention will now be described, by way of non-limiting example, with reference to the accompanying diagrammatic drawings. BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings: Figure 1 shows a three-dimensional view of an instrument in accordance with the invention; Figure 2 shows a sectional side view of the instrument of Figure 1 ; and Figure 3 shows a flow diagram of a method of determining mass flow rate, volumetric flow rate, and medium density, in accordance with the invention.
DETAIL DESCRIPTION OF THE DRAWINGS
Referring to the drawings, an instrument 10 in accordance with the invention is generally indicated by reference numeral 10.
The instrument 10 includes an elongate, hollow cylindrical body 12 defining an internal elongate flow passage 14. The flow passage 14 includes a density measuring flow passage or parallel flow passage 16 and a mass flow rate measuring flow passage or venturi flow passage 18, directly connected in a coaxial arrangement. The parallel flow passage 16 has a generally constant internal cross-sectional profile throughout its length, and includes two longitudinally spaced sensor receiving formations 20, on which pressure sensors 22 have been mounted, to measure static pressure.
The venturi flow passage 18 defines a cylindrical, internal throat 24 in which the cross-sectional area of the flow passage is smaller than the cross-sectional area of the flow passage axially upstream and downstream of the throat, to form a venturi-type flow meter, including standardised frusto-conically tapering parts 36 between the throat and the adjacent flow passage, upstream and downstream.
A sensor receiving formation 26 is provided in a circumferential wall of the throat 24, and a sensor receiving formation 28 is provided in a control location, spaced axially from the throat 24. The sensor receiving formation 26 is located in the flow stream and is spaced axially from the tapering parts, preferably by a distance of at least half the diameter of the flow passage. Pressure sensors 30 are mounted on the sensor receiving formations 26,28, to measure static pressure.
The pressure sensors 22,30 are connected via conduits 32 to processing equipment 38, shown schematically in Figure 2 of the drawings, to use the measured pressures in a calculation method as described hereinbelow. It is to be appreciated that the pressure sensors 22,30 can be of a variety of formats, including transducers generating pressure signals that are sent to the processing equipment 38, open tubes or tubes closed by flexible diaphragms, transferring pressure via the conduits 32 to the processing equipment, or the like. It is further to be appreciated that the processing equipment 38 can include a calculator, microprocessor, or the like.
The pressure sensors 22 are configured to measure the differential pressure between the two axially spaced sensor receiving formations 20, and similarly the pressure sensors 30 are configured to measure the differential pressure between the throat 24 and the control location. It is to be appreciated that one of the pressure sensors 22 can be used instead of the pressure sensor 30 at the control location, but the control location should preferably be close to one of the tapering parts 36.
In use, the instrument 10 is installed in a mineral processing plant or the like, by attaching flanges 34 of the body 12 to adjoining equipment, preferably in an upright orientation. The instrument 10 can be installed at an angle, provided that there is a known difference in elevation between the positions of the pressure sensors 22. When a mineral slurry process flow stream flows in the flow passage 14, the density of the flow stream can be determined from the differential pressures between the sensors 22 in the parallel flow passage 16, provided that the mass flow rate of the flow stream is known. Further, the mass flow rate of the flow stream can be determined from the differential pressure between sensors 30 in the Venturi flow passage 18, provided that the density of the flow stream is known. However, in applications where both the density and the volumetric flow rate of the flow stream are not known, the mass flow rate, volumetric flow rate and medium density of the flow stream is determined in the processing equipment 38, in accordance with the following iterative method, illustrated in Figure 3 of the drawings: the differential pressures in the parallel flow passage 16 (sensors 22) and the venturi flow passage 18 (sensors 30) are measured as described hereinabove; an initial or trial volumetric flow rate of zero is assumed; a medium density for the flow stream is calculated using the pressure differential in the parallel flow passage 16 and the trial volumetric flow rate, using the Bernoulli equation, taking the different elevations of the pressure sensors 22 into account, and making provision for losses due to pipe friction; a new volumetric flow rate is calculated using the calculated medium density and the differential pressure between pressure sensors 30; the new calculated volumetric flow rate is compared to the previous volumetric flow rate, and if the two flow rates differ by more than a predetermined quantity, the process is repeated in an iterative manner, using the new calculated volumetric flow rate as the trial volumetric flow rate.
If the new trial flow rate and the previous flow rate differ by a small enough margin, the mass flow rate is calculated, using the calculated medium density, and an output of mass flow rate, volumetric flow rate and medium density is provided.
The invention illustrated holds the advantage that mass flow rate of a process flow stream can be determined without the use of a nuclear source or magnetic sensing devices. The invention illustrated holds the further advantages of low cost and simplicity of structure and operation.

Claims

1. An instrument 10 including a body 12 defining an elongate flow passage 14 including: a density measuring flow passage 16 in which an internal cross- sectional profile of the flow passage 14 remains generally constant for the length of the density measuring flow passage 16, and which includes pressure sensor receiving formations 20, at locations spaced apart along the length of the flow passage 16; and a flow rate measuring flow passage 18 defining a throat 24, in which the cross-sectional area of the flow passage 18 is smaller than the cross- sectional area of the flow passage 18 axially upstream and downstream of the throat 24, and which includes a pressure sensor receiving formation 26 in the throat, characterised in that the density measuring flow passage 16 and the flow rate measuring flow passage 18 are connectable in a common flow passage.
2. An instrument 10 as claimed in Claim 1 , characterised in that the density measuring flow passage 16 and the flow rate measuring flow passage 18 are directly connected in a coaxial arrangement.
3. An instrument 10 as claimed in Claim 1 or Claim 2, characterised in that the flow rate measuring flow passage 18 defines a Venturi-type throat 24 and tapering parts 36 adjacent the throat 24.
4. An instrument 10 as claimed in any one of the preceding claims, characterised in that it includes pressure sensors 22,30, mounted on the pressure sensor receiving formations 20,26, and the instrument 10 includes equipment 32,38 configured to determine the static pressure inside the flow passage 14.
5. An instrument 10 as claimed in any one of Claims 1 to 3, characterised in that it includes pressure sensors 22,30, mounted on the pressure sensor receiving formations 20,26, and the instrument 10 includes equipment 32,38 configured to determine the differential in static pressure between the locations of at least two pressure sensor receiving formations 20,26.
6. An instrument 10 as claimed in Claim 3, characterised in that it includes a pressure sensor 30 disposed in the throat 24 and at least one pressure sensor 30 disposed at a control location 28, spaced axially from the throat 24 and from the tapering parts 36.
7. An instrument 10 as claimed in Claim 6, characterised in that it includes equipment 32,38 configured to determine the differential static pressure between the throat 24 and the control location 28.
8. An instrument 10 as claimed in any one of Claims 4 to 7, characterised in that the instrument 10 is installed with the pressure sensors 22 of the density measuring flow passage 16 disposed at different elevations, and includes equipment 32,38 configured to determine at least one of density, volumetric flow rate, and mass flow rate of a medium flowing in the flow passage 14, using the static pressures measured by the pressure sensors 22.
9. A method for determining a flow rate, said method including: measuring a first differential pressure between different elevations 20 in a flow stream of generally constant cross-sectional area; measuring a second differential pressure at locations 26,28 in the flow stream with different cross-sectional areas; characterised by: assuming an initial volumetric flow rate; calculating a density of the medium of the flow stream, using the Bernoulli equation, the first differential pressure, and the assumed volumetric flow rate, and taking the difference in elevations 20 at which the pressures were measured, into account; and calculating volumetric flow rate using the calculated medium density and the second differential pressure.
10. A method as claimed in Claim 9, characterised in that the method is repeated, using the calculated volumetric flow rate as the new assumed volumetric flow rate, until the assumed volumetric flow rate and calculated volumetric flow rate differ by less than a predetermined quantity.
11. A method as claimed in Claim 9 or Claim 10, characterised by calculating the mass flow rate by multiplying the volumetric flow rate with the calculated density.
PCT/IB2004/003837 2003-11-25 2004-11-24 Instrument and method for determining flow rate WO2005052521A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ZA200309162 2003-11-25
ZA2003/9162 2003-11-25

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WO2005052521A1 true WO2005052521A1 (en) 2005-06-09

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4856344A (en) * 1986-02-21 1989-08-15 Schlumberger Technology Corporation Measuring flow in a pipe
GB2261519A (en) * 1991-11-06 1993-05-19 Exal Reservoir Serv Ltd Hydro-carbon flow rate monitor

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4856344A (en) * 1986-02-21 1989-08-15 Schlumberger Technology Corporation Measuring flow in a pipe
GB2261519A (en) * 1991-11-06 1993-05-19 Exal Reservoir Serv Ltd Hydro-carbon flow rate monitor

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