WO1990009580A1 - Appareil et procede d'utilisation de radiations micro-ondes pour mesurer la teneur en eau d'un liquide - Google Patents

Appareil et procede d'utilisation de radiations micro-ondes pour mesurer la teneur en eau d'un liquide Download PDF

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Publication number
WO1990009580A1
WO1990009580A1 PCT/GB1989/000153 GB8900153W WO9009580A1 WO 1990009580 A1 WO1990009580 A1 WO 1990009580A1 GB 8900153 W GB8900153 W GB 8900153W WO 9009580 A1 WO9009580 A1 WO 9009580A1
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WIPO (PCT)
Prior art keywords
fluid
frequency
microwave
mixture
volume
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PCT/GB1989/000153
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English (en)
Inventor
Claude V. Swanson
Original Assignee
Chettle, Adrian, John
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 Chettle, Adrian, John filed Critical Chettle, Adrian, John
Priority to PCT/GB1989/000153 priority Critical patent/WO1990009580A1/fr
Publication of WO1990009580A1 publication Critical patent/WO1990009580A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N22/00—Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more
    • G01N22/04—Investigating moisture content

Definitions

  • the present invention relates to method and apparatus for using microwave radiation to measure the volume fraction and/or spatial distribution of a first fluid in a mixture of that fluid and a second fluid such as an oil-water mixture. It is especially useful for measuring water infiltration in a crude oil pipeline.
  • a multitude of devices are used to measure the water content of oil or other organic fluids, with special attention being paid to the measurement of the water content of crude oil. These devices find special utility when used as monitors on oil pipelines or oil loading pipes used for loading oil tankers. In general, they measure water content by measuring the attenuation due to absorption of a single microwave beam transmitted across a conduit carrying the oil. They are intended to detect and measure water which is dispersed in the oil in the form of a homogenous distribution of fine droplets.
  • the present invention is preferably embodied in a device having a microwave generator which generates microwave beams in the frequency range between 1 and 200 GHz.
  • the device measures the attenuation of the beams as they propagate through the fluid.
  • One embodiment of the device comprises first means, on one side of a volume of the fluid, for generating first and second microwave beams; second means, arranged across the volume from the first means, for receiving the first and second generated microwave beams after they have been attenuated at least in part by the water in the fluid and for generating at least one signal indica tive of degree of attenuation of the first and second microwave beams; and third means, electrically connected to the second means and responsive to the at least one signal, for computing a volume fraction of wafer in the fluid based on the at least one signal.
  • the two microwave beams differ from each other in at least one
  • This device can be generalized to include a plurality of microwave generators and corresponding microwave transmitters arranged in co-extensive linear
  • said apparatus comprising:
  • first means arranged on one side of a volume of said mixture, for generating a microwave beam having an initial energy E o and a frequency ⁇ which varies within said predetermined range;
  • second means arranged across said volume from said first means, for receiving said generated microwave beam after it has passed through the mixture, and for generating signals E h indicative of attenuation of the initial energy of said microwave beam in said mixture as said frequency varies;
  • third means coupled to said second means and
  • the invention also provides apparatus for measuring a volume fraction of a first fluid in a mixture of said first fluid and a second fluid, one of said fluids having a microwave energy absorptivity greater than that of the other, said apparatus comprising:
  • first means arranged on one side of a volume of said mixture, for generating a microwave beam having a frequency which varies with time;
  • second means arranged across said volume from said first means, for receiving said generated microwave beam after it has passed through the mixture, and for generating signals indicative of attenuation of said microwave beam in said mixture as said frequency varies;
  • third means electrically connected to said second means and responsive to said signals, for calculating said volume fraction of said first fluid in said mixture based on said signals; wherein said first means varies its power with frequency according to exp ( ⁇ ( ⁇ ) ), wherein ⁇ ( ⁇ ) is a
  • apparatus for measuring a volume fraction of a first fluid in a mixture of said first fluid and a second fluid, one of said fluids having a microwave energy
  • said apparatus comprising:
  • first means arranged on one side of a volume of said mixture, for generating a microwave beam having a frequency which varies with time;
  • second means arranged across said volume from said first means, for receiving said generated microwave beam after it has passed through the mixture, and for generating signals indicative of attenuation of said microwave beam in said mixture as said frequency varies;
  • third means electrically connected to said second means and responsive to said signals, for calculating said volume fraction of said first fluid in said mixture based on said signals:
  • said first means includes means for varying output power with frequency in accordance with a first function
  • said third means includes means for storing data indicative of said first function and for performing calculations based at least in part on said data such that with measurement of received power, absorption can be measured as of a function of frequency.
  • the invention also provides a method for measuring a total volume of a first fluid having a first frequency dependent microwave energy absorption characteristic ⁇ ( ⁇ ) within a predetermined frequency range in a mixture of said first fluid and a second fluid, said second fluid having a microwave energy absorption characteristic lower than that of said first fluid within said frequency range, said mixture comprising values of said first fluid in various sizes, said method comprising the steps of:
  • the invention provides a method for measuring the volume fraction of a first fluid in a mixture of said first fluid
  • step (a) comprises varying the power of said microwave beam according to exp ( ⁇ ( ⁇ ) ), wherein ⁇ ( ⁇ ) describes said absorptivity of microwave energy of said first fluid as a function of time.
  • the invention provides a method for measuring the volume fraction of a first fluid in a mixture of said first fluid and a second fluid, one of said fluids having a microwave energy absorptivity greater than that of the other, said method comprising the steps of:
  • the water content of crude oil or other materials is measured by sweeping the microwave frequency quickly and continuously or in many small steps over a wide range of frequencies, from frequencies below 10 GHz to frequencies above 20 GHz.
  • this is known as "chirping" the signal.
  • the attenuation across the beam volume is measured continuously as a function of frequency during the "chirp” and a mathematical process based on the Laplace inverse transform is used to analyze the attenuation and compute the water volume directly in the beam.
  • a chirp would be done quickly, in less than one second, and possibly as fast as one millisecond. The cycle would be repeated continuously.
  • mixture will be applied to any sharing of a given volume by two fluids which maintain their respective physical and chemical identities.
  • the term is intended to encompass terms sach as “suspension'' or "sol”. It is also intended to cover circumstances wherein a substantially continuous interface exists between the two fluids, e.g., an interface between two fluids completely filling their respect segments of a pipeline.
  • Figure 1 is a partially schematic block diagram of a first exemplary embodiment of a fluid content measurement device according to the invention
  • Figure 2 is a partially schematic block diagram of a fluid distribution measurement device according to a seeond embodiment of the present invention
  • Figure 3 is a partially schematic block diagram of a fluid distribution measurement device according to a third embodiment of the present invention
  • Figure 4 is a partially schematic block diagram of a fluid content/distribution measurement device according to a fourth embodiment of the present invention
  • Figure 5 is a partially schematic block diagram of a fluid content/distribution measurement device according to a- fifth embodiment of the present invention.
  • Figure 6 is a graphical representation of a desirable variation of frequency with respect to time in a device as shown in Figure 5.
  • Figure 1 is a partially schematic end-on view of an arrangement for measuring the volume fraction of a first fluid in a mixture (as defined above) of that fluid with another fluid, such as an oil-water mixture, according to the present invention.
  • a mixture as defined above
  • another fluid such as an oil-water mixture
  • the volume of oil-water mixture the water content of which is instantaneously being measured in Figure 1 is designated by numeral 10.
  • first means for generating first and second microwave beams M 1 and M 2 comprising a microwave transmitter 20 and a transmit horn 30.
  • These means comprise a microwave receiver 40 and a receive horn 50.
  • Beams M 1 and M 2 each have a wavefront parallel to line 60. These wavefronts propagate transverse to the flow of the oil-water mixture 10 and are
  • First and second microwave beams M 1 and M 2 as attenuated in the oil-water mixture 10 are preferably combined with a reference signal R also originating in microwave transmitter 20.
  • Microwave receiver 40 then generates a signal S indicative of the degree of attenuation of beam M 1 and beam M 2 as compared to reference signal R.
  • Signal S is fed to a computer 70 where it is processed to provide an on-line measurement of the volume fraction of water in oil-water mixture 10.
  • the receiver measures the received power, from which it is possible to calculate the power absorbed by the mixture in the pipe in a fashion which will now be described.
  • the microwave absorption will be measured at each frequency propagated.
  • the average absorption of the fluid is:
  • the water content can be measured by measuring this value at more than one frequency, and taking advantage of the high absorption of water at about 23 GHz, the so-called "water absorption line.”
  • water absorption line the so-called "water absorption line.”
  • three measurements are made, one may be made at the water absorption line frequency and the other measurements can be made at frequencies differing from this frequency by the same amount.
  • the results can then be combined algebraically to derive the volume fraction of water. For example, let the frequency of the water absorption line be denoted by , and the other two frequencies by
  • the advantages of this technique derive from the realization that variations in the absorption of oil will not affect the accuracy of the measurement as long as the variation is smooth. Additional measurements at additional frequencies will provide a more accurate value for water content.
  • the computations can be controlled by a small microcomputer, which calculates and reads out the results instantaneously.
  • the computer can also be easily programmed to integrate the water volume to compute the total water volume passing through the pipe in a given time interval.
  • the apparatus in Figure 2 also includes a microwave transmitter 20 and a microwave receive 40 as well as a computer 70.
  • Transmit horn 30 has, however, been replaced with a linear array 80 of transmit horns.
  • receive horn 50 has been replaced by a linear array 90 of receive horns.
  • each receiver acts as a sensor and measures absorption along one path through the volume. When a large globule of water crosses some of these paths the measured absorption of those paths will increase many tens of decibels.
  • the dimension of the blob in the direction of the array is obtained from the number of sensors which detect this absorp tion, i.e., the number of sensors which are in the "shadow.”
  • the amount of absorption provides an indicator of the blob thickness in the beam direction.
  • the length of time the absorption persists multiplied by flow speed in the pipe (measured by flow meter 110 in Figure 2) provides an approximate measure of the third dimension of the blob.
  • the volume of the blob can be calculated by a small microcomputer attached to the output. This shadowing technique may be made more accurate by using multiple sensors in both the horizontal and vertical axes of the cross plane of the pipe. This is shown in Figure 3.
  • an additional microwave transmitter 25 and an additional microwave receiver 45, with associated horn arrays 85 and 95, respectively, have been added.
  • These additional components obtain the projection or shadow of water globule 100 in a direction perpendicular to the projection obtained by microwave transmitter 20 and microwave receiver 40.
  • the details of adaptation to this two-dimensional system are straightforward and will be apparent to one having ordinary skill in the art.
  • the embodiment shown in Figure 4 has both a broad-beam transmitter 20 transmitting two beams M 1 and M 2 as well as a linear array 97 of receive horns receiving a broad beam transmitted by transmitter 27 through antenna 32.
  • the combination of components 20, 30, 50, 40 defines an apparatus such as that described in connection with Figure 1 which provides data on the volume fraction of water in mixture 10.
  • the combination of components 27, 32, 97, and 70 defines an apparatus giving information on the existence and location of large globules of water.
  • Figure 4 thus provides comprehensive data on the amount and distribution of water in mixture 10. It will be apparent to one having ordinary skill that the two combinations can be arranged so that their beams are parallel rather than transverse as shown in Figure 4.
  • the chirp rate would be would be determined 'by the flow rate in the pipe, the width of the microwave beam, and by processing requirements.
  • the non-linear absorption which occurs in large-globules or "slugs" of water, as discussed above, can be accounted for, and the water volume computed accurately even if there are many large globules of water or an irregular spectrum of sizes of water droplets suspended in the fluid.
  • the instantaneous water content is computed by an on-line numerical processor, and is combined with information on flow rate in the pipe to compute the total volume of water carried through the pipe during some time interval.
  • the flow rate in the pipe can be measured by a variety of conventional, well known, methods. One method is to place an orifice constriction downstream of the microwave device, and measure the pressure drop in the fluid upstsream and downstream of the orifice, using simple pressure sensors. A second, more sophisticated method of measuring fluid flow velocity would utilize acoustic waves transmitted across the pipe at an angle, and measuring the travel time and doppler shift of the waves to compute average flow veolcity in the pipe.
  • the flow rate can be measured. It is the purpose of the devices described above to measure the instantaneous fractional water volume of the fluid, and to combine this with the flow rate measurement to compute the total integrated water volume passing the measuring device.
  • the direction across the pipe in the beam direction will be x
  • the vertical direction across the pipe will be y
  • the axis down the pipe will be z.
  • n the number of droplets having a specific set of dimensions.
  • n the number of droplets having a specific set of dimensions.
  • the microwave absorption caused by the droplets and globules of various sizes can be added, by summing over the spectrum of droplets sizes, given by n.. Then the microwave energy E h received by the microwave receiver can be related to the emitted microwave energy E o by
  • the sum is over all of the droplets in the beam, and this can be subdivided into droplets of various sizes, such that the thickness of the droplets in the x direction is the same for all droplets of the ith type.
  • Equation (4) The variation of received microwave power with a small change in microwave frequency can be calculated by differentiating Equation (4) with respect to frequency, resulting in:
  • the independent parameter in the continuous formulation is the x-dimension, or T .
  • Equation (7) may be written in the simpler form:
  • ⁇ ( ⁇ ) is just the Laplace transform of the volume spectral function .
  • the quantity of interest for the oil-water monitor is the integral of the volume spectral function over . This is the total water volume Q in the beam, and is given by:
  • the water volume Q is the parameter of interest for the oil-water monitor. That parameter can be computed from Equation (9) by using the inverse Laplace transform to invert Equation (9) to solve for then integrating this function over to
  • the Laplace transform can be converted into the Fourier transform by a simple change of variables, so the transformations described below can be converted to equivalent Fourier transforms, which are identical from the mathematical viewpoint, However, the Laplace transform is more closely relatsd to the form of the equations, and so is used here for the purposes of explanation. As is well known, if the Laplace transform is specified as in Equation (9), then the transform can be inverted to obtain See, for example, Morse et al., Methods of Theoretical
  • Equation (10) the total volume Q, as defined in Equation (10), can be related to by:
  • the volume of water Q in the microwave beam is computed using the received microwave power E h and the emitted microwave power E o , both of which may be functions of microwave frequency ⁇ .
  • the expression also requires the area A of the microwave beam, and the function ⁇ ( ⁇ ), which describes the absorption rate of microwave energy in water as a function of frequency. This is a well-known relationship, and if it were not known it could be measured easily using this device.
  • ⁇ ( ⁇ ) the microwave energy absorved by the receiver will depend on other factors besides the water volume in the beam. The most important of these other factors will be resonances which occur at certain frequencies.
  • w(t) For a "linear" chirp, w(t) would be given as the product of t and a constant, the constant corresponding to the slope of the slanted portions of the waveform in Figure 6.
  • the transmitter would be set up to maintain constant microwave power as it varies its frequency over the range from the minimum frequency ⁇ 1 to the upper frequency ⁇ 2 .
  • the function ⁇ ( ⁇ ) which embodies the damping rate of m ⁇ crowaves in water, as well as possible impedance mismatch or coupling factors, is implemented entirely in the software of the microcomputer which analyzes the measured power.
  • the frequency derivative dE h /d ⁇ can be computed by comparing the received power levels at two nearby times, for which the frequency will be different because of the chirp. If the chirp is linear with time, then the frequency difference will be simply proportional to time difference within the chirp period.
  • the transmitter would be set up to vary its power with frequency according to e ⁇ ( ⁇ ) .
  • the frequency is varied linearly with time.
  • the receiver employs a time delay circuit and a subtractor, or differential amplifier, which has the effect of computing the derivative dE h /d ⁇ by an analog technique. Then the receiver need only to integrate and time average this signal to generate a signal proportional to the water content in the beam. This is an analog technique which requires minimal digital processing to compute the water volume.
  • two duplicate embodiments of the device are installed across the pipe, one having a beam in the horizontal, or x direction, and the second having a beam in the vertical, or y direction.
  • the computed water volumes measured by the two systems can be compared by the computer to improve the accuracy of the measurement.
  • the microwave transmission system has three facets.
  • the first uses at least two broad and coincident microwave beams of different frequencies.
  • the second uses multiple narrow beams.
  • the third uses a single broad, "chirped" beam.
  • the broad beams measure the average water content in the pipe, so that the device using them is most accurate when the water is dispersed in fine droplets, i.e., where the droplets are on the order of half a centimeter or so.
  • the narrow beam system computes a microwave absorption along each of many paths. Mis- identification of the broad beams as the spatially-differentiated narrow beams is avoided by assigning frequencies to the broad beams which are different from frequencies assigned to the narrow beams. Misidentification can also be avoided by pulsing the broad and narrow beams out of phase with each other.
  • the narrow beams may be differentiated by focusing antennae.
  • a device such as that shown in Figure 4 would be flexible enough to measure water and air content in oil pipelines in a variety of applications in which it is not possible to do so now.
  • the present invention will be very useful in the measurement and detection of multiphase flow in pipelines.
  • Such a situation commonly occurs in pipelines in which water, oil, air, and/or other fluids occur in globules or strata.
  • monitors are not capable of measuring the fluid properties correctly.
  • a device constructed according to the present invention would not have this disadvantage.
  • Other applications might include use in nuclear power plants or in other pressure steam systems in which two phase flow occurs involving steam and condensed water.
  • a device would be used in those situations requiring an extremely accurate measurement of water content/distribution. For example, during in tanker on-loading, real-time measurement of the oil, water, and air content of the oil could be made while the oil is being loaded into the tanker. This would eliminate any need for settling time of the water and eliminate legal disputes over excess water content in the oil. In refinery monitoring, real-time measurement of water content and refinery oil can be made, thus permitting warning or automatic shut-off of downstream processes which would otherwise be harmed by large slugs of water occurring the pipelines.
  • Another application would be as a furnace monitor. It is known that oil-burning furnaces can explode if a globule of water is injected while the furnace is burning. The cost of repair to such a system is many times the cost of oil monitor warning system according to the present invention.
  • Transcontinental pipelines transmit a variety of fluids in the same pipeline by loading first one fluid and then another in a sequential manner. It is very important to be able, at a downstream pumping or switching station, to measure when these interfaces occur, and to determine over what distance mixing and contamination of the fluids has occurred.

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Abstract

Système à micro-ondes permettant de déterminer la teneur en eau d'un fluide. Dans le mode de réalisation envisagé, le fluide en question est du pétrole brut et ledit système sert à déterminer la quantité d'eau contenue dans le pétrole brut. Un rayon à micro-ondes, dont la fréquence varie avec le temps, passe à travers le liquide et permet ainsi de calculer les pertes d'absorption, à partir desquelles on détermine la teneur en eau du liquide.
PCT/GB1989/000153 1989-02-16 1989-02-16 Appareil et procede d'utilisation de radiations micro-ondes pour mesurer la teneur en eau d'un liquide WO1990009580A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/GB1989/000153 WO1990009580A1 (fr) 1989-02-16 1989-02-16 Appareil et procede d'utilisation de radiations micro-ondes pour mesurer la teneur en eau d'un liquide

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/GB1989/000153 WO1990009580A1 (fr) 1989-02-16 1989-02-16 Appareil et procede d'utilisation de radiations micro-ondes pour mesurer la teneur en eau d'un liquide

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WO1990009580A1 true WO1990009580A1 (fr) 1990-08-23

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0607558A1 (fr) * 1993-01-18 1994-07-27 Elpatronic Ag Procédé pour détecter des substances liquides dans un conteneur

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2797388A (en) * 1956-05-07 1957-06-25 Paul C Maybury Apparatus for measuring attenuation
US3498112A (en) * 1968-04-30 1970-03-03 Us Navy Microwave system for determining water content in fuel oil
US4289020A (en) * 1979-12-26 1981-09-15 Texaco Inc. Microwave-gamma ray water in crude monitor
US4301400A (en) * 1979-12-26 1981-11-17 Texaco Inc. Microwave water in crude monitor
SU1015287A1 (ru) * 1980-06-06 1983-04-30 Ордена Трудового Красного Знамени Институт Радиотехники И Электроники Ан Ссср Способ определени влагосодержани нефти
SE449138B (sv) * 1984-06-27 1987-04-06 Stiftelsen Inst Mikrovags Forfarande jemte anordning for bestemning av mikrovagors dempning och/eller fasvridning vid transmission genom ett material

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2797388A (en) * 1956-05-07 1957-06-25 Paul C Maybury Apparatus for measuring attenuation
US3498112A (en) * 1968-04-30 1970-03-03 Us Navy Microwave system for determining water content in fuel oil
US4289020A (en) * 1979-12-26 1981-09-15 Texaco Inc. Microwave-gamma ray water in crude monitor
US4301400A (en) * 1979-12-26 1981-11-17 Texaco Inc. Microwave water in crude monitor
SU1015287A1 (ru) * 1980-06-06 1983-04-30 Ордена Трудового Красного Знамени Институт Радиотехники И Электроники Ан Ссср Способ определени влагосодержани нефти
SE449138B (sv) * 1984-06-27 1987-04-06 Stiftelsen Inst Mikrovags Forfarande jemte anordning for bestemning av mikrovagors dempning och/eller fasvridning vid transmission genom ett material

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DERWENT'S ABSTRACT, No. 84-48505/08; & SU,A,1 015 287, Publ. Week 8408. *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0607558A1 (fr) * 1993-01-18 1994-07-27 Elpatronic Ag Procédé pour détecter des substances liquides dans un conteneur

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