Abstrict An apparatus for determining the relative flows of a two phase
flow using differential pressure to obtain mass flow having a bend
portion for concentrating the dense phase toward an outside of the
bend; a perforated plate downstream of the bend for passing the
portion of the light phase; a nozzle for channelling the portion
of the flow having high density phase toward the center of a venturi
throat which is positioned downstream of the perforated plate; and
four pressure sensors strategically located for measuring pressure
differences at various points in the flow meter.
Claims I claim:
1. An apparatus for determining the relative flows of a two phase
flow through a pipe having a longitudinal axis, an upstream end
and a downstream end, and means for providing a two phase flow to
the upstream end of the pipe, comprising:
means for substantially separating the two phase fluid flow into
a dense phase and a light phase inside the pipe adjacent the upstream
end;
first means for transporting the dense phase separately through
a first section of the pipe to a second section of the pipe downstream
of the first section;
second means for transporting the light phase separately through
the first section of the pipe to the second section of the pipe
downstream of the first section;
means for thoroughly mixing the dense phase and the light phase
in the second section of the pipe; and
four pressure measurement devices connected to at least four different
points within said pipe to obtain four different pressure measurements
which can be used to determine the rate of flow of each of the dense
phase and light phase through the sections of the pipe.
2. An apparatus according to claim 1 wherein the means for separating
the two phase fluid flow comprises a bend in the pipe, oriented
to be capable of taking advantage of centrifugal forces to force
the dense phase toward an external wall of the pipe and allow the
light phase to continue freely through the bend; and
a plate having a multiplicity of perforations sized to provide
sufficient pressure drop to induce the dense flow to flow forward
through a bypass nozzle, said plate being perpendicular to the longitudinal
axis of the pipe, and located adjacent the first transporting means,
and being of a size and shape so not to obstruct the first transporting
means for the dense phase.
3. An apparatus according to claim 2 wherein the first transporting
means comprises an elongated nozzle defining a hollow channel for
transporting the dense phase from adjacent the external wall to
a nozzle outlet substantially on the longitudinal axis of the pipe
in the second section of the pipe.
4. An apparatus according to claim 3 wherein the mixing means
comprises a Venturi tube having a longitudinal axis oriented parallel
to the longitudinal axis of the pipe, located within the second
section of the pipe, said nozzle outlet being located along the
center line of the Venturi tube.
5. An apparatus according to claim 4 wherein the four pressure
measurement points are located one point at the upstream end of
the pipe essentially adjacent the bend, the second point substantially
adjacent the nozzle outlet, the third point in the interior of the
Venturi tube, and the fourth point adjacent the downstream end of
the pipe.
6. An apparatus according to claim 1 wherein the first transporting
means comprises an elongated nozzle defining a hollow channel for
transporting the dense phase to a nozzle outlet substantially on
the longitudinal axis of the pipe in the second section of the pipe.
7. A two phase flow meter according to claim 6 wherein the mixing
means comprises a Venturi tube having a longitudinal axis oriented
parallel to the longitudinal axis of the pipe, located within the
second section of the pipe, said nozzle outlet being located along
the center line of the Venturi tube.
8. A two phase flow meter according to claim 7 wherein the means
for separating the two phase fluid flow comprises a bend in the
pipe, oriented to be capable of taking advantage of centrifical
forces to force the dense phase toward the external wall of the
pipe bend and allow the light phase to continue freely through the
bend; and
a plate having a multiplicity of perforations sized to provide
sufficient pressure drop to induce the dense flow to flow forward
through a bypass nozzle, said plate being perpendicular to the longitudinal
axis of the pipe, and located adjacent the first transporting means,
and being of a size and shape so not to obstruct the first transporting
means for the dense phase.
9. A two phase flow meter according to claim 8 wherein the four
pressure measurement points are located one point at the upstream
end of the pipe essentially adjacent the bend, the second point
substantially adjacent the nozzle outlet, the third point in the
interior of the Venturi tube, and the fourth point adjacent the
downstream end.
10. An apparatus according to claim 9 wherein the dense phase
comprises a powdered solid or liquid.
11. An apparatus according to claim 10 wherein the light phase
comprises a gas or liquid.
12. An apparatus according to claim 9 wherein the dense phase
is pulverized coal and the light phase is air.
13. An apparatus according to claim 12 wherein the dense phase
is petroleum liquids and the light phase is natural gas.
14. An apparatus according to claim 13 wherein the dense phase
is sand and the light phase is water.
15. A two phase flow meter according to claim 1 wherein four of
the pressure measurement points are located one point at the upstream
end of the pipe, a second point substantially adjacent the first
means for transporting, a third point in the second section of the
pipe, and a fourth point adjacent the downstream end of the pipe.
16. An apparatus according to claim 15 wherein the dense phase
comprises a powdered solid or heavy liquid.
17. An apparatus according to claim 16 wherein the light phase
comprises a gas or light liquid.
18. An apparatus according to claim 17 wherein the dense phase
is pulverized coal and the light phase is air.
19. An apparatus according to claim 17 wherein the dense phase
is petroleum liquids and the light phase is natural gas.
20. An apparatus according to claim 17 wherein the dense phase
is sand and the light phase is water.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a fluid flow measurement
arrangement and, more particularly, to an arrangement for measuring
a two phase flow.
2. Description of the Related Art
The ability to accurately measure a two phase fluid flow is hampered
by problems related to the homogeneity or non-homogeneity of the
two phase mixture and the resulting combined density of the mixture.
Unsatisfactory attempts to measure two phase flow have been made
with magnetic flux meters, pneumatic orifices, ultrasonics and electromagnetic
wave instruments.
A flow measuring apparatus having a bend along its conduit is disclosed
in U.S. Pat. No. 2628086 to Cutler, however no particles in suspension
are contemplated as part of the fluid flow. FIG. 2 in U.S. Pat.
No. 2703013 also shows a bend in a flow conduit, and further,
the use of pressure measurements to calculate flow. The use of tapping
fluid from one location is described in U.S. Pat. No. 3689833
the second location being in the throat of a venturi. The use of
curved conduit and flow meter, specifically for taking advantage
of centrifugal flow for a multi-phase fluid flow meter is disclosed
in U.S. Pat. No. 4144754.
The taking of measurements at multiple locations along a flow stream
in a flow meter is disclosed in the U.S. Pat. No. 4231262.
U.S. Pat. No. 4261196 also utilizes a bend in a conduit for multi-phase
fluid.
The mass stream of a dusty solid fuel can be measured according
to U.S. Pat. No. 4501156. This patent also teaches the use of
a bend in the conduit of the measuring apparatus as well as the
taking of measurements at multiple locations along the flow stream.
U.S. Pat. No. 4559835 discloses the use of a partitioned section
of a flow conduit in a flow measuring probe.
Presently, there is no known flow meter that can measure the solid
phase flow in a two phase (gas and powdered solids, gas and liquid,
or liquid and fine solids) medium.
SUMMARY OF THE INVENTION
It is a primary object of the invention to provide a two phase
flow meter which is particularly suited for measuring pulverized
coal flowing in gas along a conduit or for measuring liquid flowing
in gas along a conduit.
In accordance with the invention, a bend is provided in a conduit,
a perforated plate downstream of the bend spans the conduit and
passes predominately gas having a low concentration of particles
or liquid so that through the action of centrifugal force, the particles
or liquid become concentrated at the outside of the bend. A nozzle
having an inlet end, proximate to the outer portion of the conduit,
receives the high particulate or liquid concentration and channels
it radially inwardly and in a downstream direction toward a venturi
throat. No portion of the perforated plate extends into the nozzle
so that the high concentration of dense phase material is injected
into the center of the venturi throat. Four pressure sensors are
strategically located along the conduit for taking differential
pressure measurements which can be used to measure the relative
flow of gas and the solid or liquid phase material.
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this disclosure. For a better understanding of
the invention, its operating advantages and specific objects attained
by its uses, reference is made to the accompanying drawings and
descriptive matter which a preferred embodiment of the invention
is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a schematic view illustrating the present invention;
FIG. 2 is an elevational sectional view of the invention;
FIG. 3 is an end view taken along line 3--3 of FIG. 2
FIG. 4 is an end view taken along line 4--4 of FIG. 2;
FIG. 5 is a top sectional view; and
FIG. 6 is a graphic representation of the relative pressure measurements
with respect to each other.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning to the drawings wherein like reference numerals are used
to indicate the same or similar features throughout the several
views, FIG. 1 shows an enlarged section of pipe generally designated
10. A two phase fluid flow 50 enters the pipe 10 at the upstream
end and passes through a bend 40. The two phase fluid is essentially
separated into two distinct phases, a dense or solid (liquid) phase
flow 52 and a light or fluid gas phase flow 54. The dense phase
flow 52 separates to the external side of the bend 40 in the pipe
10 due to centrifugal forces while the light phase flow 54 continues
through the pipe near the inside of the bend 40.
Once the flows 52 and 54 pass bend 40 a pressure measurement is
taken at an upstream measurement point 12 by a pressure gauge (not
shown). Located adjacent the bend 40 is perforated plate 22 having
a plurality of perforations 24 therethrough and which is situated
on top of nozzle 26 inside the pipe 10. Nozzle 26 has nozzle inlet
28 through which the dense phase flow 52 is directed. Perforated
plate 22 is designed to provide sufficient pressure drop to induce
the dense phase flow 52 flow forward through nozzle 26. The light
phase flow 54 passes through the multiplicity of perforations 24
of perforated plate 22.
The two flows 52 and 54 then pass into the next section of pipe
10 by two different means. Dense phase flow 52 passes through nozzle
26 to nozzle outlet 30 which is located advantageously along the
center line of a venturi tube 20. A second pressure gauge (not shown)
connected to nozzle measurement point 14 measures the pressure adjacent
the nozzle outlet 30 while venturi pressure point 16 has a third
pressure gauge (not shown) connected to it to measure the pressure
at the high velocity throat. The effect of the venturi tube 20 is
to cause a thorough mixing of the separated phase flows 52 and 54
with a minimum amount of resistance into a mixed two phase flow
60 at the exit of the venturi tube 20. The mixed two phase flow
60 then passes by downstream measurement point 18 at which time
the fourth pressure measurement is taken with a fourth pressure
gauge (not shown).
In FIG. 2 a smaller section of pipe 10 is shown. In this view,
the nozzle 26 is shown having an arcuate shape. The nozzle 26 defines
a path from the bottom or outside wall of pipe 10 to approximately
the center of venturi 20. The nozzle 26 slopes inward from nozzle
inlet 28 in an S-shaped curve to a central location at the entrance
to venturi 20 and ends at nozzle outlet 30. The locations of the
pressure measurement points 12 14 16 18 are shown relative to
the nozzle 26 and venturi 20. The perforated plate 22 is positioned
slightly to the downstream side of nozzle inlet 28. The plate 22
surrounds nozzle 26 and is securely connected to the walls of pipe
10 leaving only nozzle inlet 28 and perforations 24 as openings
to the downstream sections of the pipe 10.
FIG. 3 shows the location of the perforated plate 22 with a multiplicity
of perforations 24 around nozzle 26 in more detail. The plate 22
surrounds nozzle 26 and is securely connected to the walls of pipe
10 leaving only nozzle inlet 28 and perforations 24 as openings
to the downstream sections of the pipe 10.
FIG. 4 shows the location of nozzle outlet 30 located in the center
of the venturi 20. The nozzle 26 tapers from wide opening at nozzle
inlet 28 to a smaller diameter opening at nozzle outlet 30.
FIG. 5 shows the taper of the nozzle 26 from the top. Nozzle measurement
point 14 is located advantageously inside the nozzle 26 where the
flow velocity is maximized by the taper. Venturi measurement point
16 is placed adjacent the nozzle outlet 30 inside venturi 20 where
some mixing of the separated flows 52 54 occurs.
Additionally, perforated plate 22 can be seen spanning the width
of pipe 10 over nozzle 26. Upstream measurement point 12 is located
in close proximity to plate 22 and nozzle inlet 28 for obtaining
a pressure measurement of the recently separated flows 52 54.
FIG. 6 is a graphical representation showing the relationship of
the different flows to each other based on the pressure measurements
taken within the pipe 10. The mass flow is calculated from the pressure
measurements in the following way. The natural static pressure changes
through the venturi create pressure differentials that are proportional
to the square of the velocity which allow a calculation of mass
flow. Static pressure differentials across the venturi nozzle and
solid phase nozzle have a compound correlative relationship proportionate
to the apparent density of the dense phase flow stream. The stream
relationship of the differentials can be plotted as shown in the
graph to show a dense phase and light phase flow relationship. By
calibrating these differentials against known mass flow quantities
they can subsequentially be used to obtain a relative flow measurement
of each of the separate phase flows. Referring to the graph shown
in FIG. 6 the venturi differential down-stream pressure reading
minus venturi tube pressure reading would be calibrated to represent
the light phase flow. The differential upstream pressure measurement
minus the nozzle pressure measurement would represent gas and solid
phase flow. Then by plotting the venturi differential against the
nozzle differential, a relative index of solid phase flow may be
established.
This arrangement of pressure measurement points and components
within the pipe are especially useful for determining the phase
flows when the two phases 52 54 are a gas and a powdered solid
or gas and liquid.
The invention can be used in conventional furnaces utilizing pulverized
coal for fuel. The pipe 10 represents one of the pulverized coal
fuel pipes that supply burners. The fuel pipes use primary air to
convey pulverized coal to the burners.
This invention can also be used in natural occuring petroleum feed
staoks when gas and liquid phase flow together.
In pipe 10 the bend 40 and plate 22 separate the combined flow
of primary air and coal into light and dense phases 54 52 respectively.
The two phases then flow through their respective paths and are
recombined in the venturi 20 to continue on to the burner as combined
flow 60.
While the primary air and pulverized coal flow through pipe section
10 the four pressure measurements are taken at measurement points
12 14 16 18 by connected gauges. Using the four measurements,
the relative flow of coal through the pipes can be determined, allowing
better control of the system.
Also, the present invention may be easily retrofit in existing
supply lines having a 90 degree bend by adding flanges to the pipe
section shown in FIGS. 2 and 5. The flanges are fastened to mating
flanges in a pipe or supply line that has a section removed. Alternatively,
the pipe section shown in FIGS. 2 and 5 may be welded in place without
flanges in a line that has a portion removed downstream a 90 degree
bend.
While a specific embodiment of the invention has been shown and
described in detail to illustrate the application of the principles
of the invention, it will be understood that the invention may be
embodied otherwise without departing from such principles.
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