Abstrict An improved multiphase fluid flow meter for fluid which contains
gas. It has a full circle loop to subject the flowing fluid to centrifugal
force, and it can measure the pressure differentials between the
center and the outside and inside radii of the loop. Also it can
measure the density of the average fluid flowing, plus the density
of a continuous sampling of the gas and of the liquid constituent
of the fluid.
Claims We claim:
1. Improved multiphase fluid flow meter wherein one of said phases
is a gas, comprising
a conduit for said fluid to flow therethrough,
said conduit including a full circle loop for subjecting said fluid
to centrifugal force,
first means for measuring the pressure differential between the
center and outside radii on said loop,
second means for measuring the pressure differential between the
inside and center radii on said loop,
means for measuring the average density taken radially across the
fluid flowing through said loop,
means for measuring the density of said gas phase, and
means for measuring the density of said liquid phase,
all whereby rates of fluid flow including said gas flowing through
said meter may be measured.
2. The invention according to claim 1 wherein
said means for measuring the average density and for measuring
the density of said gas and liquid phases each comprise a gamma
ray densitometer.
3. The invention according to claim 2 wherein
said means for measuring the density of said gas and liquid phases
further comprise chamber means for holding samples of said gas and
liquid phases.
4. The invention according to claim 3 wherein
said means for measuring the density of said gas and liquid also
comprise means for dynamically changing said samples held in said
chamber means.
5. The invention according to claim 4 wherein
said gamma ray densitometers all have a common gamma ray source,
and
each of said densitometers has means for collimating said source,
one of said collimators being directed radially across said loop,
the other collimators being directed across each of said chamber
means respectively to make said gas and liquid measurements.
6. The invention according to claim 5 wherein
said means for dynamically changing said samples comprise siphon
means connected to said chamber means for continuously drawing fresh
samples of said gas and liquid phases.
7. Improved two phase fluid flow meter wherein said phases are
gas and liquid, comprising
a conduit for said fluid to flow therethrough,
said conduit including a full circle loop for subjecting said fluid
to centrifugal force,
first means for measuring the pressure differential between the
center and outside radii on said loop,
second means for measuring the pressure differential between the
inside and center radii on said loop,
a first gamma ray densitometer for measuring the average density
radially across the fluid flowing through said loop,
a second gamma ray densitometer for measuring the density of said
gas phase,
a third gamma ray densitometer for measuring the density of said
liquid phase,
first chamber means for holding a dynamically changing sample of
said gas phase,
second chamber means for holding a dynamically changing sample
of said liquid phase,
a common gamma ray source for said densitometers,
a first means for collimating said gamma ray source directed radially
across said loop to make said average density measurement,
a second means for collimating said gamma ray source directed across
said first chamber means to make said gas phase density measurement,
a third means for collimating said gamma ray source directed across
said second chamber means to make said liquid phase density measurement,
and
first and second siphon means connected to said first and second
chamber means for continuously drawing fresh samples of said gas
and liquid phases.
8. Improved flow meter according to claim 7 wherein
said first chamber means has a capped-off portion,
said first siphon means comprises conduit means for connecting
to said fluid upstream of said loop and to said loop at the inside
radius thereof,
said second chamber means has an inlet and an outlet at the top
thereof, and
said second siphon means comprises conduit means for connecting
said inlet and outlet to said loop at the outside and inside radii
thereof.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a fluid flow meter in general. More specifically,
it relates to an improved fluid flow meter that is particularly
applicable to measuring a fluid having as one of its constituents
a gas.
2. Description of the Prior Art
A multiphase fluid flow meter has been developed which employs
centrifugal force on the flowing fluid. While that meter (which
is described in U.S. Pat. No. 4144754 issued Mar. 20 1979) was
applicable to fluids of unknown density or to fluids having mixed
phases of unknown proportions, it was unable to make accurate measurements
in situations where the rate of flow of a gas constituent differed
from the rate of flow of the liquid constituent or constituents
of a mixture.
Consequently, it is an object of this invention to provide additional
capabilities for a meter that employs centrifical flow and that
measures densities of the fluid flowing therethrough.
Another object of the invention is to provide an instrument which
will allow measurement of gas and liquid flow rates in a common
pipe line, even though these two constituents are moving at different
speeds.
SUMMARY OF THE INVENTION
Briefly, the invention relates to an improved multiphase fluid
flow meter wherein one of the phases is a gas. It comprises a conduit
for said fluid to flow therethrough. The conduit includes a full
circle loop for subjecting said fluid to centrifugal force. It also
comprises first means for measuring the pressure differential between
the center and outside radii on said loop, and second means for
measuring the pressure differential between the inside and center
radii on said loop. It also comprises means for measuring the average
density taken radially across the fluid flowing through said loop,
and means for measuring the density of said gas phase, as well as
means for measuring the density of the liquid phase. All of the
elements are combined so that the rates of fluid flow including
that of the said gas flowing through the meter, may be measured.
Again briefly, the invention concerns an improved two-phase fluid
flow meter, wherein the said phases are gas and liquid. It comprises
a conduit for said fluid to flow therethrough. The said conduit
includes a full circle loop for subjecting said fluid to centrifugal
force. It also comprises first means for measuring the pressure
differential between the center and outside radii on said loop,
and second means for measuring the pressure differential between
the inside and center radii on said loop. It also comprises a first
gamma ray densitometer for measuring the average density radially
across the fluid going through said loop, and a second gamma ray
densitometer for measuring the density of said gas phase. It also
comprises a third gamma ray densitometer for measuring the density
of said liquid phase, and first chamber means for holding a dynamically
changing sample of said gas phase. It also comprises second chamber
means for holding a dynamically changing sample of said liquid phase,
and a common gamma ray source for said densitometers. It also comprises
a first means for collimating said gamma ray source directed radially
across said loop to make said average density measurement, and a
second means for collimating said gamma ray source directed across
said first chamber means to make said gas phase density measurement.
It also comprises a third means for collimating said gamma ray source
directed across said second chamber means to make said liquid phase
density measurement. And, it comprises first and second siphon means
connected to said first and second chamber means for continuously
drawing fresh samples of said gas and liquid phases into said chamber
means.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and benefits of the invention will
be more fully set forth below in connection with the best mode contemplated
by the inventors of carrying out the invention, and in connection
with which there are illustrations provided in the drawings, wherein:
FIG. 1 is a schematic side elevation, illustrating the elements
of a meter according to the invention;
FIG. 2 is an end elevation of the meter illustrated in FIG. 1;
FIG. 3 is a somewhat enlarged fragmentary cross-sectional view
taken along the lines 3--3 of FIG. 1 and looking in the direction
of the arrows;
FIG. 4 is a perspective view of the liquid-sample containing chamber;
FIG. 5 is a perspective view of the gas sample containing chamber;
FIG. 6 is a schematic diagram illustrating the connections that
are employed in making pressure differential measurements from the
center to the top and bottom of the loop; and
FIG. 7 is a schematic diagram which is useful in some of the theoretical
explanations.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated in the above mentioned U.S. Pat. No. 4144754 the
petroleum industry has many applications for multiphase flow meters.
This invention provides for improving a meter according to that
patent so that the fluid flow measurement may include conditions
where the rate of flow of a gas constitutent is different from the
rate of flow of the liquid portion.
The figures of drawing illustrate a meter according to this invention.
It will be observed that the meter includes a conduit 11 for carrying
the fluid through the meter, it has an inlet 12 and an outlet 13.
The conduit 11 includes a full circle loop 16 that connects the
inlet 12 with the outlet 13. It subjects the fluid flowing through
the conduit 11 to centrifugal force.
At the top of the loop 16 there are three pressure taps 17 18
and 19 that are illustrated most clearly in FIGS. 3 and 6. These
are employed for measuring the pressure differential between the
center of the loop (tap 18) and the inside and outside (taps 19
and 17 respectively) measured radially of the loop circle.
The foregoing pressure differential measurements may be carried
out as indicated by FIG. 6 where there is shown schematically the
connections for carrying the pressure from taps 17 18 and 19 to
each of a pair of pressure-differential instruments 22 and 23 respectively.
These may be like an instrument manufactured by Rosemount Inc. of
Minneapolis, Minn. which is designated as its model 1151 DP differential
pressure transmitter.
The pressure at the tap 17 is transmitted via a connection 26 (dashed
line) to the pressure differential instrument 22. The tap 18 is
also connected to the instrument 22 via another pressure connection
27 also indicated by a dashed line.
Similarly, the pressure differential between the center radius
(where tap 18 is located) and the inside radius (where tap 19 is
located) is measured by the other pressure differential instrument
23. It has fluid pressure connections as indicated by dashed lines
30 and 31. The instruments 22 and 23 may have electrical output
signals which are carried over circuit connections 32 and 33 indicated.
The flow meter illustrated includes a first gamma ray densitometer
36 which measures the average density taken radially across the
fluid flowing within the loop 16 at the top of the loop. There is
a second densitometer 37 that measures the density of the gas phase
only of the fluid flowing through the meter. In addition, there
is a third densitometer 38 that measures the density of the liquid
phase. The flow meter includes a short cylindrical block 41 of heavy
metal, e.g., lead. The block 41 is located inside of the loop 16
and centrally located inside the upper portion of the block 41
there is a gamma ray source 42 (FIG. 2). It may be 1.3 millicuries
of cesium 137. The radiation from the source 42 is collimated by
three passages 45 46 and 47 that are indicated by dashed lines
in FIG. 2.
Each of the densitometers 36 37 and 38 are made up of a scintillation
detector 48 (see FIG. 3) which has the input collimated by a lead
sheath 49 that is incorporated in each instrument. Such column is,
of course, in alignment with each of the collimating passages 45
46 and 47 respectively.
It will be observed that the location of densitometer 36 is such
that the radiation path 45 goes directly across the interior of
the loop 16 at the top thereof. And, in the case of the densitometers
37 and 38 the collimating passages 46 and 47 direct rays from the
source 42 across the interior of each of a dynamic sample containing
chamber 50 and 51 respectively.
Each densitometer 36 37 and 38 includes as part thereof a crystal
52 which is coupled to a photomultiplier tube 53 all of these within
the detector portion of the densitometers. A detector of this type
may be one like that manufactured by Bycron Corp. of Newberry, Ohio,
which is designated as a scintillation detector. It will be understood
that the crystal may be a sodium iodide crystal doped with thallium.
And, in its use with this invention, it will be biased to count
only primary (unscattered) gamma radiation that is emitted by the
source 42. Such primary gamma radiation is determined by the count
rate of the detector in each of the densitometers 36-38 and this
count rate will have a direct relationship to the density of the
fluids in the path of the collimated gamma rays in each case.
The gas sample chamber 50 is shown individually in FIG. 5. It will
be noted that there is an inlet conduit connector 54 at the top
and an outlet connector 55 at the bottom. Also, it will be noted
that there is an interior barrier or partition 59 in the chamber
50. It is impervious to both the gas and liquid constituents of
the fluid, and it extends from the top and joins both sides down
close to the bottom but leaving a passageway underneath inside the
chamber.
The other sample chamber 51 is illustrated individually in FIG.
4. It has an inlet connector 60 at the top of the chamber near one
side, and an outlet connector 61 at the top of the connector near
the other side. There is also a drain connector 64 at the bottom
which has a valve 65 included. The latter is ordinarily maintained
closed.
There are siphon means connected to each of the dynamic sample
chambers 50 and 51. These constitute conduits, or tubes that are
connected as indicated in FIG. 2. Thus, the gas sample chamber 50
has its inlet connector 54 connected via a pipe 68 that connects
with a tap or connector 69 at the bottom of the conduit 11 near
the inlet 12 thereof. The outlet connector 55 is connected via a
pipe 72 to a tap 73 (FIG. 3) that is located on one side at the
bottom of the conduit 11 near the top of the loop 16.
The liquid sample chamber 51 has its inlet connector 60 connected
by a pipe 76 to a tap 77 that connects to the interior of the conduit
11 at the other side from tap 73 and at the top of the conduit,
near the top of the loop 16 as clearly indicated in FIG. 3. The
outlet connector 61 is connected via a pipe 80 to a tap 81 that
connects into the conduit 11 near the bottom where the pressure
is reduced by the centrifugal action of the fluid flowing therein.
It may be noted that there are valves 85 86 87 and 88 that are
located in the pipes 68 72 76 and 80 respectively of the siphon
connections just described. These values are ordinarily maintained
open when the system is in operation.
It will be understood that the dynamic action of the sampling chambers
causes continuously renewed samples of the gas and liquid phases
to take place because of the siphoning action that is caused by
the piping connections described above. Thus, in the case of the
gas sample, there is the connection at tap 69 which draws off fluid
near the inlet 12 of the conduit 11 of the flow meter. This sample
of the fluid then goes into the chamber 50 via the inlet connector
54 at the top to one side. The fluid is directed into the chamber
on the one side of the partition 59 and the liquid constituent
tends to flow out through the outlet connector 55 while the gas
constituent tends to separate out and rise into and fill the chamber
50 on the other side of the partition 59. Thus, the liquid portion
of the fluid being drawn into the chamber 50 is carried away through
the pipe 72 into the low pressure side of the conduit 11 at the
top of the loop 16 via the tap 73. This action maintains a continuously
changing sample of the gas constituent of the fluid flowing through
the meter. In the chamber 50 the gas sample is retained where the
densitometer 37 can measure it.
In chamber 51 the liquid constituent sample goes into the chamber
with a continuous change that is caused by the inlet conductor 60
being connected via its pipe 76 to the tap 77 located on one side
near the top of the conduit 11 and at the top of the loop 16. Here
the pressure is higher because of the centrifugal action on the
fluid flowing through the meter. The sample fluid (largely liquid)
settles in the chamber 51. But, it is continuously withdrawn through
the outlet connector 61 and the pipe 80 which leads back to the
tap 81 where it rejoins the fluid flowing through the meter at the
low pressure (largely gas) portion of the stream.
With reference to FIG. 7 it will be understood that centrifugal
force acting upon the fluid as it passes through the loop 16 tends
to separate the liquid phase from the gas phase. The commonly heavier
liquid phase forms a layer of a thickness "h" on the outside
wall of conduit 11 whereas the gaseous phase moves toward the inside
wall of the conduit, as shown in FIG. 7. Densitometer 36 measures
the average density .rho. radially across the flowing fluid. Combining
the densities .rho..sub.L of the liquid phase and .rho..sub.G of
the gaseous phase as determined by densitometers 38 and 37 respectively
with the average density .rho. the thickness h of the liquid layer
can be calculated according to equation
where d is the linear inside dimension. The general theory developed
by Cortelyou and published by J. P. Cortelyou in an article entitled
"Centrifugal Flow Measurement", (published in Instruments
and Control System, Vol 3 February 1960 pp. 276-280) provides
the basis for the expressions which relate the differential pressures
.DELTA.P.sub.u and .DELTA.P.sub.l measured across the pressure tap
pairs 17-18 and 18-19 (FIG. 3) to the volume flow rate of the liquid
phase and to the volume flow rate of the gaseous phase.
The volume rate of the liquid phase Q.sub.L and of the gaseous
phase Q.sub.G are given by the equations ##EQU1## where b and d
are the linear inside dimensions of conduit 11 R is the radius
of loop 16 and h is the thickness of the liquid phase as determined
by equation (1). .intg..sub.L and .intg..sub.G are the angular velocities
with which liquid and gas, respectively, pass through conduit 11.
The angular velocities can be calculated from the pressure differentials
.DELTA.P.sub.u and .DELTA.P.sub.l, conduit and loop dimensions,
layer thickness h and the densities .rho..sub.L and .rho..sub.G,
of liquid and gas, respectively, according to the following equations
and conditions.
If h is calculated from equation (1) to be equal or less than d/2
that is the liquid/gas interface is within the upper half of conduit
11 the following equations (4) and (5) must be used to calculate
.intg..sub.L and .intg..sub.G. ##EQU2##
If h is calculated from equation (1) to be larger than d/2 that
is the liquid/gas interface is within the lower half of conduit
11 the following equations (6) and (7) must be used to calculate
.intg..sub.L and .intg..sub.G ##EQU3##
The terms on the right hand side of equations (4), (5), (6) and
(7) are either known or determined from the density measurements
according to equation (1) and measured differential pressures.
Equations (4) and (5) may be substituted into equations (2) and
(3) which will provide the liquid phase volume rate Q.sub.L and
the gaseous phase volume rate Q.sub.G if .rho. is determined such
that the condition h.ltoreq.d/2 is fulfilled.
Equations (6) and (7) may be substituted into equations (2) and
(3) which will provide Q.sub.L and Q.sub.G if .rho. is determined
such that the condition h>d/2 is fulfilled.
It may be noted that an important advantage of a flow meter according
to this invention, is the ability to measure rate of flow of the
constituents, both gas and liquid, even where the rate of flow of
the gas is different from the rate of flow of the liquid.
It will be appreciated that, in order to make the determinations,
it is useful to include measurements of temperature and a temperature
sensor may be included in a manner similar to that shown and described
in the aforementioned U.S. patent.
While a particular embodiment of the invention has been described
above in considerable detail in accordance with the applicable statutes,
this is not to be taken as in any way limiting the invention, but
merely as being descriptive thereof. |