Abstrict A fluid flow meter for a fluid containing mixed liquid and gas.
It has positive displacement structure that incorporates density
measurement of segments of the mixed liquid and gas, while the linear
velocity of both components is the same. There may be means for
measuring the pressure and temperature of the fluid segments in
order to determine the volume of the gas component.
Claims We claim:
1. Fluid flow meter for continuously measuring the rate of flow
of a mixed fluid having both liquid and gas components, comprising
in combination
positive displacement meter means comprising a housing having a
circular cross section interior with tangential inlet and outlet
passages adjacent to one side thereof,
a rotor eccentrically located in said interior and incorporating
a balanced plurality of radial vanes biased into sealing relation
with said housing interior for dividing said mixed fluid stream
into at least one segment during flow through the meter,
a gamma ray densitometer having a beam directed across said segment
adjacent to the other side of said housing interior for measuring
the density of said mixed fluid in order to determine the percent
of one of said components,
means mounted on said housing for measuring the pressure of said
mixed fluid segment, and
means mounted on said housing for measuring the temperature of
said mixed fluid segment,
all whereby the linear flow rate of both liquid and gas components
of said mixed fluid will be equal during said measurements.
2. Fluid flow meter for continuously measuring rate of flow of
a mixed fluid stream having both liquid and gas components, comprising
in combination
positive displacement meter means for measuring total volume flow
rate of said mixed fluid, comprising (a) a circular housing, and
(b) a rotor incorporating a plurality of radial vanes biased into
sealing relation with said housing for dividing said mixed fluid
stream into at least one segment with fluid tight separation from
the remainder of said stream, (c) said rotor being eccentrically
located relative to said housing,
gamma ray densitometer means directed across said fluid stream
segment for measuring the density of said mixed fluid while maintaining
the linear velocities of said liquid and gas components the same,
and
means for measuring the pressure and temperature of said fluid
stream segment.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns fluid flow measurement, in general. More
specifically, it relates to a multi-phase flow meter that is applicable
to a fluid that includes both liquid and gas components therein.
2. Description of the Prior Art
Heretofore there have been various suggestions for measuring fluids
having more than one phase component, but such phases were both
liquids. There has historically been a major problem in measuring
flow rates of a mixture including gas as well as liquid because
the flow rates of these two components have a great tendency to
be different. Consequently, in the petroleum industry it has been
the practice to have a test separator at a crude oil collection
point for making individual flow measurements of the gas and liquid.
Such procedure could be eliminated by use of a continuous flow multi-phase
meter for both liquid and gas according to this invention.
Examples of prior meter structures for measuring flow rate of multi-phase
fluids that only are applicable to liquid phases are the two U.S.
Pat. Nos. 2936618 to H. S. Milam, May 17 1960 and 3304766 to
L. M. Hubby, Feb. 21 1967. It may be noted that the Milam patent
makes cyclic measurements of the quantity of water in a fluid mixture
of oil and water, while the Hubby patent measures the thermal capacity
of the mixed fluid in order to determine the constituent amounts
of oil and water in the mixture. Neither of these patents makes
provision for measuring the rate of flow of a gas which might be
included in a fluid mixture.
Consequently, it is an object of this invention to provide a fluid
flow meter that makes positive displacement measurements which maintain
the volume flow rate of a mixed fluid while maintaining the linear
velocity of the liquid and gas components thereof the same.
SUMMARY OF THE INVENTION
Briefly, the invention concerns a fluid flow meter for continuously
measuring rate of flow of a mixed fluid having both liquid and gas
components. It comprises in combination positive displacement meter
means for measuring total volume flow rate of said mixed fluid,
and means integral with said positive displacement meter means for
measuring the density of said mixed fluid while maintaining the
linear velocities of said liquid and gas components the same.
Again briefly, the invention concerns a fluid flow meter for continuously
measuring rate of flow of a mixed fluid having both liquid and gas
components. It comprises in combination positive displacement meter
means which means comprises a housing having a circular cross-section
interior with tangential inlet and outlet passages adjacent to one
side thereof. The positive displacement meter means also comprises
a rotor eccentrically located in said interior and the rotor incorporates
a balanced plurality of radial vanes that are biased into sealing
relation with said housing interior, in order to divide the said
mixed fluid stream into a least one segment during flow through
the meter. It also comprises a gamma ray densitometer having a beam
directed across the said segment adjacent to the other side of said
housing interior, for measuring the density of said mixed fluid
in order to determine the percent of one of said components. It
also comprises means mounted on said housing for measuring the pressure
of said mixed fluid segment, and means mounted on said housing for
measuring the temperature of said mixed fluid segment. All of the
combination is such that the linear flow rate of both liquid and
gas components of the said mixed fluid will be equal during the
indicated measurements.
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 side elevation of a meter according to the invention;
FIG. 2 is an exploded perspective, illustrating the meter as shown
in FIG. 1 but somewhat enlarged;
FIG. 3 is an enlarged longitudinal cross-sectional view taken along
the lines 3--3 of FIGS. 1 and 4; and
FIG. 4 is an enlarged view, partly in cross-section, taken along
the lines 4--4 on FIG. 3 and looking in the direction of the arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A fluid flow meter according to this invention is illustrated in
the drawings. It utilizes the principles of a positive displacement
pump which is driven by the fluid to be measured. The fluid is trapped
in a segment, or reservoir of the pump and the rotor turns like
a motor due to the unequal pressure on the vanes.
With reference to the figures of the drawings, it will be observed
that the above indicated positive displacement meter structure has
a housing 11 with a circular (in cross-section) interior 12. There
is a rotor 15 that is eccentrically located relative to the housing
interior 12. And, there are four radially situated vanes 16 that
are symmetrically located and mounted in the rotor 15. These vanes
16 are biased radially outward (in any feasible manner--not shown)
into sealing relation with the interior 12 of the housing 11.
The housing 11 includes a pair of tangenital inlet and outlet passages
19 and 20 respectively, which connect into the interior 12 of the
housing as clearly shown in FIG. 4 of the drawings. It will be appreciated
that the structure is symmetrical so that the inlet and outlet passages
might be reversed which would reverse the direction of rotation
of the rotor 15 when fluid flows through the meter.
It will be noted that as the rotor 15 is driven by reason of the
differential in fluid pressure, the vanes 16 will act to divide
the stream of fluid into segments. For example, there is a segment
23 formed when the vanes 16 are in the position illustrated in FIG.
4. Both the liquid and gas components of the mixed fluid are trapped
in such a segment so that the linear rate of flow through the meter
will be equal for both of these components.
In order to measure the density of the mixed fluid as it flows
through the meter, there is a gamma ray densitometer which is made
up of a gamme ray source (not shown) that may be a small quantity
of cesium 137. That source is embedded in a source collimator 24.
It has an interior passage (not shown) to create a columnar beam
of the gamma rays which is directed across the upper portion of
the interior 12 of the housing 11. Such beam is directed toward
a scintillation detector 28 which may be like a commercial instrument
manufactured by Bicron Corporation of Newbury, Ohio. It includes
a collimator section 29 and a scintillation crystal section 30
as well as a photomultiplier tube 31.
It will be understood that the interior 12 of the housing 11 is
enclosed by face plates 35 and 36. These face plates incorporate
hubs 37 and 38 respectively, to act as bearings for a shaft 41
that supports the rotor 15.
There is a temperature sensor 44 and a pressure sensor 45. These
are located adjacent to one another and extend effectively into
the sector 23. As indicated above, the sector 23 is formed at the
top of the interior 12 when the vanes 16 are in a position such
as that illustrated in FIG. 4.
It will be appreciated that there is an arrangement for measuring
the rotation of the rotor 15 so that the velocity of the fluid flow
may be measured. Of course, any feasible arrangement might be employed
and one example is illustrated. It makes use of a disc 48 that is
mounted on the shaft 41 securely, for rotation therewith. The disc
48 has four radial notches 49 that may act to create signals when
they pass a pair of bifurcated elements 50 and 51 that are mounted
on an arcuate arm 55 and have their bifurcated ends extend over
the outer periphery of the disc 48. There is a hub 56 on the disc
48 that fits on the shaft 41.
In the operation of a meter according to this invention, it may
be noted that the total volume flow rate through the meter, may
be expressed by the following equation:
where
W=the volume of the segment 23 (in barrels);
R=the number of segments;
S=rotation speed of the rotor 15 (revolutions per minute); and
l=conversion constant (minutes per day)=1440.
Then considering the two constituent elements of the fluid, i.e.
the liquid and the gas, the volume flow rate of liquid V.sub.1 which
is flowing in the line can be solved by using the following relationship:
where
.rho.=the fractional percent liquid.
Then the volume flow rate of gas, V.sub.g at standard temperature
and pressure can be determined from the following equation:
where
T=temperature of the fluid within the meter (.degree.K.);
P.sub.g =gauge pressure within the meter (psi);
k=conversion factor to give V.sub.g in cubic feet per day.
It will be understood that the percent liquid fraction may be determined
by using the densitometer measurement. As indicated above, the gamma
ray source may be a few millicurries of cesium 137 or of cobalt
60 and it will be understood that the gamma radiation response
of the detector is biased so that only primary (unscattered) gamma
rays are counted by the detector. The primary gamma radiation count
rate recorded by the detector is given by the equation:
where
C.sub.o =the count rate recorded by the detector when the segment
is filled with gas at operating temperature and pressure;
C=the count rate recorded by the detector when the segment is filled
with the fluid being measured;
x=the effective distance traversed by the gamma radiation;
n=the attenuation coefficient of the primary gamma radiation, and
.rho.=the fractional percent of liquid in the fluid.
Then solving equation (4) for .rho. yields:
The term n is known and the terms C.sub.o and x are measured by
a calibration procedure. It will be clear that such calibration
would involve using only the gas to obtain the count rate C.sub.o
and then using only the liquid for obtaining the count when .rho.
is known to be 1.0. This would provide two known values of .rho.
with corresponding counting rates C. These values are used to solve
equation (4) simultaneously for C.sub.o and x. Then substituting
equation (5) and (1) into equation (2) gives the volume flow rate
of the liquid which may be expressed as follows:
where the terms on the right hand side of the equation are either
measured (c,S) or are known (C.sub.o,w,R,l,n,x).
Then by substituting equations (5) and (1) into equation (3), the
volume flow rate of the gas may be expressed as
It will be understood that the pressure P.sub.g and temperature
T will be measured within the segment 23 of fluid flowing through
the meter, by using the sensors 44 and 45. The speed at which the
rotor 15 is rotating (i.e. S) can, of course, be monitored continuously.
Consequently, the terms of the right hand side of equation (7) are
either measured (P.sub.g, T, C, S) or are known (C.sub.o, n, x,
w, R, l, k). It may be noted that the equations (6) and (7) are
the working equations for the positive displacement flow meter according
to this invention.
It will be appreciated by anyone skilled in the art that various
techniques could be employed to continuously or periodically make
a determination of V.sub.g and V.sub.l which are the quantities
of interest. These determinations would be made in accordance with
the working equations (6) and (7).
It will also be appreciated that it might be necessary to have
a synchronizing device (not shown) to disable the gamma ray beam
as each of the vanes 16 passes.
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. |