Note: Descriptions are shown in the official language in which they were submitted.
CA 02228928 1998-04-07
FLOW CONDITIONER PROFILE PLATE FOR MORE
ACCURATE MEASUREMENT OF FLUID FLOW
This is a divisional application of co-pending Canadian
Patent Application Serial No. 2,138,686, that was filed on
December 21, 1994.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an improved flow conditioner
used in tubular conduits carrying single phase fluids. In
particular, the invention minimizes metering errors by
producing fully developed velocity profile, fully developed
turbulence structure, and substantially eliminating swirl of
fluids flowing in a conduit.
2. Description of the Related Art
The North American natural gas industry produces,
transports and distributes approximately 700 billion cubic
meters of gas each year (25 trillion standard cubic feet).
The Western European market transports and distributes
250 billion cubic meters of gas each year (9 trillion
standard cubic feet). Because of the importance of gas
measurement for industry operations and fiscal
accountability, it is essential that metering be accurate,
reliable, and cost efficient over a range of conditions.
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All of this gas is measured at least once, and
most of it several times, in meter sizes ranging from
25 - 900 mm (1-36 inches), at pressures from below
atmospheric to 14 MPa (2,000 psi), at temperatures from
5 0 - 100~C (32 - 212~F), with several types of meters.
Large volume metering stations utilize either
concentric, square-edged, flange-tapped orifice meters
or gas turbine meters.
For over sixty years, the concentric orifice meter
has remained the predominant meter of choice for
natural gas production, large volume gas flow and
chemical metering applications. In fact, it is
currently estimated that over 600,000 orifice meters
are being used for fiscal measurement applications
associated with the petroleum, chemical and gas
industries in North America.
All flowmeters are subject to the effects of
velocity profile, swirl and turbulence structure of the
flowing fluid being measured. Meter calibration
factors or empirical discharge coefficients are valid
onlY if geometric and dynamic similarity exists between
the metering and calibration conditions or between the
metering and empirical data base conditions (i.e.,
fully developed flow conditions exist). In fluid
2~ mechanics, this is commonly referred to as the Law of
Similarity.
The classical definition for fully developed
turbulent flow is stated by Hinze as follows:
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For the fully developed turbulent
flow in the pipe the mean-flow
conditions are independent of the
axial coordinate, x and
axisymmetric, assuming a uniform
wall condition.
From a practical standpoint, fully developed flow
implies the existence of a swirl-free, axisymmetric
time average velocity profile in accordance with the
Power Law or Law of the Wall prediction. However,
fully developed turbulent flow requires equilibrium of
forces to maintain the random "cyclic" motions of
turbulent flow. This in turn requires that the
velocity profile, turbulence intensity, turbulent shear
stress, Reynolds stresses, etc., are constant with
respect to the axial position.
Unfortunately, fully developed pipe flow is only
achievable after considerable effort in a research
laboratory. To bridge the gap between research and
industrial applications, reference is made to the term
pseudo-fully developed flow defined as:
a swirl-free, axisymmetric flow
with time average velocity profile
and turbulence structure having
values approximating those found in
fully developed flow and
independent of the axial
coordinate.
Stated another way, Pseudo-fully developed flow exists
when the slope of the orifice meter's discharge
coefficient deviation asymptotically approaches zero as
the axial distance from the orifice meter to the
upstream flow conditioner increases. Of course, this
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assumes that the empirical discharge coefficient
baseline was conducted under fully developed flow
conditions.
In the industrial environment, multiple piping
configurations are often assembled in series generating
complex problems for organizations that write standards
and flow metering engineers. The challenge is to
minimize the difference between actual or "real" flow
conditions in a pipeline and the vertical or research-
achievable "fully developed" flow conditions, on aselected metering device's performance to minimize
error. One of the standard error minimization methods
is to install a flow conditioner in combination with
upstream straight lengths of pipe to "isolate" the
meter from upstream piping disturbances. Present
domestic and international measurement standards
provide specifications for upstream straight pipe
lengths and flow conditioners upstream of orifice
meters. See, e.g., American National Standard
Institute (ANSI) (ANSI 2530) and International
Standards Organization (ISO) (ISO 5167).
Unfortunately, there is considerable disagreement over
straight length requirements between ANSI and ISO.
With respect to installation effects and the near
term flow field, the correlating parameters which
affect similarity vary with meter type and design.
However, it is generally accepted that a concentric,
square-edged, flange-tapped orifice meter exhibits a
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high sensitivity to time average velocity profile,
turbulence structure, bulk swirl and tap location.
In North America, current design practices utilize
short upstream piping lengths with a specific flow
conditioner, American Gas Association (A.G.A.) tube
bundles, to provide "pseudo-fully developed" flow in
accordance with the applicable measurement standard
(ANSI 2530/A.G.A. Report No. 3/API (American Petroleum
Institute) MPMS Chapter 14.3). Most North American
installations consist of 90 degree elbows or complex
header configurations upstream of the orifice meter.
Tube bundles in combination with piping lengths of
seventeen pipe diameters (17*D) have been installed in
an effort to eliminate both swirl and distorted
velocity profiles. Ten diameters (lO*D) of straight
pipe is required between the upstream piping fitting
and the exit of the tube bundle, and seven diameters
(7*D) of straight pipe is required between the exit of
the tube bundle and the orifice meter.
In Western Europe, two design practices are
currently employed to provide "pseudo-fully developed"
flow in accordance with the applicable measurement
standard (ISO 5167) - long upstream piping lengths with
or without flow conditioners. Most Western European
installations consist of complex header configurations
upstream of the orifice meter. Piping lengths of one
hundred pipe diameters (lOO*D) without flow
conditioners or piping lengths of forty-two pipe
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diameters (42*D) in combination with flow conditioners
have been installed in an effort to eliminate both
swirl and distorted velocity profiles.
Three types of flow conditioners have been
generally utilized in Western Europe - tube bundles,
Zanker and Sprenkle designs. Twenty diameters (20*D)
of straight pipe is required between the upstream
piping fitting and the flow conditioner, and twenty-two
diameters (22*D) of straight pipe is required between
the flow conditioner and the orifice meter.
The optimal flow conditioner should achieve a
range of design objectives including: a minimal
deviation of empirical discharge coefficient (or meter
calibration factor) for both long and short pipe
lengths; low permanent pressure loss across the flow
conditioner (i.e., low "head ratio"); a low fouling
rate or a low sensitivity to accumulation of foulants;
elimination of swirl; and flexibility for use in both
short and long straight lengths of pipe. The latter
objective can be achieved by a flow conditioner that
produces an axisymmetric, pseudo-fully developed time
average velocity profile and turbulence structure.
Additionally, it is also desirable that the flow
conditioner should be subject to rigorous mechanical
design and have a moderate cost of construction.
In the specification and claims, when the swirl
angle is less than 2~ as conventionally measured by
using pitot tube devices, swirl is regarded as
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substantially eliminated. Further, when the empirical
discharge coefficient or meter calibration deviation
for both short and long piping lengths is about 1/10 of
1% it is assumed to be at a "minimum".
The IS0 and A.G.A. designs, shown in Figures lA
and lB respectively, are intended to eliminate swirl.
Both designs include a bundle of tubes having the same
length and diameter. For the A.G.A. design (Figure
lB), the length of the bundle must be at least ten
times the tube diameter. For meter runs larger than 75
mm (3 inches) the bundle typically consists of nineteen
tubes arranged in a circular pattern with a bundle
length of two to about three pipe diameters. For
smaller meter runs, the bundle consists of seven tubes
arranged in a circular pattern with a bundle length of
three pipe diameters. For both the IS0 and A.G.A.
designs, permanent pressure loss is low, mechanical
design is rigorous, cost of construction is low,
fouling rate is low, and swirl is eliminated. However,
the performance of these devices for minimal deviation
from the empirical discharge coefficient for both short
and long piping lengths is unacceptable. Also,
velocity profile and turbulence structure measurements
have shown that both A.G.A. and IS0 designs cannot
produce pseudo-fully developed flow conditions within
reasonable distances due to their high porosity and
constant radial resistance. This is shown by the
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instability in the coefficient performance graphs,
Figures 19 and 21.
The Sens ~ Teule flow condition as shown in Figure
2 is designed to isolate piping disturbances from flow
meters. The design consists of a bundle of tubes of
different lengths and diameters arranged in a circular
array. Permanent pressure loss is high, cost of
construction is high, and prototype designs are
rigorous and complex. While swirl is eliminated, the
fouling rate of this design is unknown. It has been
reported that the device exhibits pseudo-fully
developed time average velocity profile and turbulence
structure for short piping lengths. Geometric scaling
of the device is a problem, when considering a range of
pipe sizes.
Figures 3 and 4, respectively, show the Etoile and
Air Moving and Conditioning Association (AMCA) vane-
type of swirl eliminator. The Etoile design consists
of three flat plates of equal length and width
assembled in a star-shaped pattern around a central
hub. While these designs eliminate swirl, it is known
that the Etoile design does not produce pseudo-fully
developed flow conditions in reasonable distances.
Similarly, the AMCA design (Figure 4) was not intended
to produce a pseudo-fully developed flow.
Figure 5 shows an example of screens or wire gauze
assembled in an egg-crate fashion within a pipeline.
Fine mesh screens are impractical in an industrial
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environment due to high permanent pressure loss, non-
rigorous mechanical construction, and high fouling
rates.
Perforated plates, such as the Sprenkle design,
shown in Figure 6, were designed to isolate piping
disturbances from flow meters for measuring steam flow.
The design consists of three perforated plates spaced
one diameter apart and connected by rods. Each plate
has a porosity of about fifty percent with regularly
distributed perforations in a specified hexagonal
pattern. The size of the perforations is about five
percent of the pipe diameter. While the designs
eliminate swirl, cost of construction is high, design
is rigorous and complex, permanent pressure loss is
very high, and fouling rate is moderate. Further,
performance for minimal coefficient deviation for short
piping lengths is unacceptable. Finally, the design is
thought to not produce pseudo-fully developed flow
conditions for short piping lengths due to its almost
constant radial resistance.
The Bellinga design, shown in Figure 7, is a
modified Sprenkle design that suffers much the same
shortcomings as Sprenkle.
The Zanker design, shown in Figure 8, was designed
to isolate piping disturbances for the purpose of pump
efficiency testing. The device consists of a
perforated plate connected to a downstream grid or egg
crate construction. The plate includes 32 holes of
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five different diameters, each hole having a specified
location. Permanent pressure loss for this device is
high as is cost of construction. While the design
eliminates swirl, the design does not provide minimum
deviation from empirical discharge coefficient for both
short and long piping lengths. Therefore, the design
is thought to not produce pseudo-fully developed flow
conditions for all piping configurations.
The Akashi design, sometimes referred to as the
Mitsubishi design, as shown in Figure 9, consists of a
single perforated plate with 35 holes. The hole size
is 13 percent of the pipe diameter and the perforated
plate thickness is equal to the hole diameter. The
plate has a porosity of approximately 59 percent. Hole
distribution is dense toward the (center of the pipe)
and sparse around the periphery (pipe wall). The
upstream inlets of the holes are beveled. While the
device produces a low permanent pressure loss and
mechanical design is rigorous and simple, performance
for minimal deviation from empirical discharge
coefficient for both and short and long piping lengths
are unacceptable since the design calls for almost
constant radial resistance. The design is further
thought to not produce pseudo-fully developed flow
conditions for all piping configurations because it
does not provide minimal deviation from the empirical
discharge coefficient for both short and long pipe
lengths.
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The Laws device, shown in Figure 10, is also a
single perforated plate, but with 21 holes. The plate
thickness is approximately 12 percent of the pipe
diameter (D) and the plate has a porosity of about 51
5 percent. The holes are arranged in circular spaced
arrays around a central hole. The first and second
arrays have 7 and 13 holes respectively. Hole size is
largest in the middle of the pipe, 0.1924*D, and
decreases in size to the first circular array,
0.1693*D, and further in size to the second array,
0.1462*D. The pitch circle diameter for the first and
second array are about 46 and 84 percent of the pipe
diameter respectively. Upstream inlets of the holes
may be beveled. Once again, the performance for
minimal deviation from the empirical discharge
coefficient for short piping lengths is unacceptable,
but acceptable for long piping lengths. The design can
produce axisymmetric, pseudo-fully developed conditions
only for long piping lengths.
A further development of a device shown in U.S.
Patent 5,255,716 to Wilcox is the K-Labs Mark V. The
patent shows a flow conditioner comprising tubular
passages with the area between specific tubes blocked.
While permanent pressure loss is low and mechanical
design is rigorous and simple, and swirl is eliminated
from most piping configurations, the performance for
minimal deviation from the empirical discharge
coefficient for short piping lengths is unacceptable.
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Therefore, the design is thought to not produce pseudo-
fully developed flow conditions for all piping
configurations.
What is yet required is a flow conditioner for use
with flow meters to provide measurements that are
sufficiently accurate for industrial and fiscal
applications. The flow conditioner should achieve all
the design criteria stated above including elimination
of swirl, and achievement of a minimal deviation from
the empirical discharge coefficient or meter
calibration factor for both short and long straight
lengths of pipes by the production of a pseudo-fully
developed time average velocity profile and turbulence
structure. Further, the device should have a low
permanent pressure loss (head ratio) across the flow
conditioner, low fouling rate or insensitivity to
foulant accumulation. Finally, the device should be
subject to a rigorous mechanical design and should have
a relatively moderate cost of construction.
SUMMARY OF THE INVENTION
The flow conditioner according to the invention
isolates flow meters from piping-induced disturbances
and thereby allows more accurate metering of fluids
flowing in pipelines. The invention achieves optimal
flow conditioner objectives and maintains pseudo-fully
developed flow in a pipeline with respect to the axial
direction. Random cyclic forces generated by the
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conditioner produce a self-stabilizing mechanism for
the velocity profile and turbulence structure within a
short axial distance.
The invention device produces pseudo-fully
developed flow conditions for both short and long
piping lengths, as shown by the stability in the
coefficient performance graphs. Further, and
importantly, the deviation of the empirical discharge
coefficient or meter calibration factor, for both short
and long piping lengths, is at an acceptable minimum.
The flow conditioner according to the invention
exhibits a low permanent pressure loss and has a
rigorous, simple mechanical design. Fouling rate is
low and swirl is essentially eliminated. Manufacturing
cost is moderate and retrofitting of existing
installations is readily accomplished.
To achieve its objectives, the preferred device
according to the invention comprises three sections:
an anti-swirl device, a settling chamber, and a flow
profile device; each mounted sequentially in a specific
order and at specific distances from each other in the
pipeline carrying the fluid to be measured. In certain
instances, when the fluid flow pattern does not
necessitate anti-swirl measures, then only the
equivalent of a settling chamber and the profile device
is needed, according to the invention.
In sharp contrast to the prior art, which has
promoted the use of anti-swirl devices downstream of
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14
profile devices for more than 30 years, the present
invention teaches the use of an anti-swirl device
located upstream of the profile device.
The flow conditioner of the invention may be
preassembled into a unit or module that is then
installed into a pipeline at a predetermined distance
upstream of a flow meter and beyond a predetermined
distance downstream of the nearest source of flow
disturbance (valve, elbow, complex pipe configuration)
upstream of the flow meter. The flow conditioner is
oriented in the pipeline such that the anti-swirl
device is farther upstream, followed by a downstream
settling chamber, and a further downstream profile
device or plate.
The anti-swirl device according to the invention
reduces swirl to less than 2~ at its exit. Further,
the anti-swirl device generates a slight distortion to
allow the profile device to generate pseudo-fully
developed flow conditions. According to the invention,
a tube bundle anti-swirl device design is preferred.
This design eliminates geometric similarity concerns
and provides an opportunity for low manufacturing
costs. Further, the design generates reproducible
turbulence intensities and turbulence shear stresses,
regardless of the upstream piping disturbance.
Further, the design provides a constant radial
resistance and low blockage factor. Finally, this
design provides an assurance of swirl elimination.
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Immediately downstream from the anti-swirl device
is the settling chamber. This chamber is required to
eliminate or minimize interaction between the anti-
swirl device and profile device. Further, the chamber
also allows uniformity of the turbulence structure to
develop prior to inlet to the profile device.
Essentially, the settling chamber is a section of
constriction-free pipe between the anti-swirl device
and the profile device of sufficient length to achieve
these objections.
Downstream of the settling chamber is the profile
device, which generates a pseudo-fully developed flow
within five to ten nominal downstream pipe diameters.
According to the invention, a radially-graded plate of
specific design is regarded as the optimal profile
device. This profile plate according to the invention
combines radially graded resistance with an appropriate
plate porosity to produce a pseudo-fully developed flow
profile. Radially graded resistance is achieved by
shaping the device through an uneven hole distribution
as a function of its radial position. The placement of
circular arrays, along with the size and number of
holes in the respective arrays, are critical. The size
of the holes contribute to turbulence intensity and
mixing downstream of the plate. Further, the placement
of the circular arrays contribute to the time average
velocity profile and turbulent mixing downstream of the
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16
plate. As a result, interaction of porosity, hole location
and hole diameter are critical.
Downstream of the profile device is the measuring
device. The distance X between the profile device and the
measuring device is critical. The invention provides for X
as low as D or 3D, depending upon the type of measuring
device used. This short distance is important, especially
in retrofitting short meter pipe lengths or in fitting new
meter pipes in an area where space is restricted. Thus, the
invention provides a significant advantage over the art in
that the devices are both compact and provide superior flow
conditioning so that the minimum deviation (0.1~) from the
empirical coefficient of discharge or meter calibration
factor is readily achieved.
In accordance with one aspect of the present invention
there is provided a profile plate for inducing pseudo-fully
developed in fluid flowing under turbulent flow conditions
in a pipeline of circular cross-section, the plate
comprising a circular plate body having a center, an
upstream face, and a downstream face, said body including:
a central array of through bores having a porosity (P1) of
from about 3.0 to about 5.0~, the through bores in said
array having diameters dl, where:
~_ -05'
(nl*l 00)
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16a
and nl is the number of through bores in the array; a second
array of through bores centered on the locus of a second
circle of diameter pcd2, where:
pcd2=max {[0.4990-0.0065*(P3-P2)],0.4500}
the porosity (P2) of the second array ranging from about
19.0 to about 21.0~, and the hole size d2 of the through
bores of the second array, where:
~_ -05'
(n2*100) and
where n2 is the number of through bores in the second array;
and a third array having a porosity (P3):
P3 =PT- (Pl +P2)
with through bores located on the locus of a circle, having
a diameter pcd3, where:
pcd3= [O . 8575-0.0041* (P3-P2) ]
each of the through bores in said third array having a
diameter d3, where: .
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16b
,_ -05'
_(n3*100)
wherein n3 is the number of through bores in the third
array, and pcd2, pcd3, dl, d2, and d3 are dimensionless.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention, taken in conjunction with the
invention described in co-pending Canadian Patent
Application Serial No. 2,138,686, filed on December 21,
1994, will be described in detail hereinbelow with the aid
of the accompanying drawings, in which:
Figure lA is a schematic representation of the ISO
design swirl eliminator;
Figure lB is a schematic representation of the A.G.A.
design swirl eliminator;
Figure 2 is a schematic of the Sens & Teule swirl
eliminator design;
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Figure 3 is a schematic representation of the
Etoile vane-type swirl eliminator;
Figure 4 is a schematic representation of the AMCA
vane-type swirl eliminator;
Figure 5 is an example of a screen or wire gauze
assembled in egg-crate design for use within a
plpellne;
Figure 6 is a schematic of the Sprenkle flow
condition design showing three perforated plates spaced
one diameter apart interconnected with rods;
Figure 7 is a schematic of the Bellinga design;
Figure 8 is a schematic of the Zanker design
showing a perforated plate connected to downstream
grate or egg-crate construction;
Figure 8B shows the orientation and distribution
of holes on the Zanker perforated plate;
Figure 9 is a schematic of the Akashi perforated
plate design;
Figure 10 is a schematic of the Laws perforated
plate design;
Figure llA is a side view of an embodiment of the
flow conditioner according to the present invention;
Figure llB is an end view B showing the tubes
making up the anti-swirl device of an embodiment of a
flow condition according to the present invention;
Figure llC is an end view C showing the
distribution of holes on a profile plate of a flow
conditioner according to the present invention;
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Figure 12 is an embodiment of a flow conditioner
according to the present invention showing an anti-
swirl device equipped with flanges and a profile plate
equipped with flanges for fitting into a pipeline;
Figure 13 is a schematic diagram, not to scale,
showing the installation of an embodiment of the
invention flow conditioner in a pipe line;
Figures 14A and B show an embodiment of a profile
plate according to the invention with three arrays of
holes or perforations;
Figures 15A and B show an embodiment of a profile
plate according to the invention with four arrays of
holes or perforations;
Figures 16A and B show an embodiment of a profile
plate according to the invention with four arrays of
holes or perforations;
Figures 17A and B show an embodiment of a profile
plate according to the invention with five arrays of
holes or perforations;
Figure 18 shows a schematic of a test loop used to
compare flow conditioners of the invention with other
devices;
Figure 19 summarizes the results obtained when an
AGA tube bundle was utilized in 17D, 45D, and lOOD long
test pipes with an orifice plate of ~ = 0.75 in the
apparatus of Figure 18;
Figure 20 summarizes empirical coefficient of
discharge deviation data for Laws flow conditioner in a
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17D long test pipe used with an orifice plate of B =
0.67 and a tee in place of the elbow of Figure 18;
Figure 21 summarizes data for an AGA tube bundle
tested in a 17D long test pipe with an orifice plate of
B = 0.67 and a tee instead of the elbow of Figure 18;
Figure 22 summarizes empirical coefficient of
discharge deviation obtained using a Mark V flow
conditioner in a 17D long test pipe with an orifice
plate having a ~ of 0.67 and a tee instead of the elbow
of Figure 18;
Figure 23 summarizes empirical coefficient of
discharge deviation obtained when an embodiment of the
flow conditioner according to the invention was used
under the same conditions as in Figures 20-22; and
Figure 24 summarizes empirical coefficient of
discharge deviation obtained when an embodiment of the
the flow conditioner according to the invention was
used, under the same conditions as in Figure 23, except
that for points shown by a square, the B factor was
0.75 and the flow disturbance was caused by an elbow,
and for data points shown by a triangle, the B was 0.67
and the disturbance was caused by an elbow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The flow conditioner according to the present
invention preferably comprises three parts: an anti-
swirl device, a settling chamber, and a profile device,
arranged in a specific order and at specific distances
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relative to each other to isolate piping-induced
disturbances from a flow meter and thereby allow more
accurate metering of fluids flowing in pipelines. More
specifically, the flow conditioner of the invention
eliminates swirl (reduces swirl to less than or equal
to 2~) and provides pseudo-fully developed time
averaged velocity profiles and turbulence structure so
that any deviation from empirical discharge coefficient
or meter calibration factor is less than 1/10 of 1%.
In certain circumstances, an anti-swirl device is
not necessary because of the nature of the type of
fluid flow (i.e., swirl-free or low swirl). In this
event, according to the invention, only an equivalent
to the settling chamber and the profile device is
needed.
In order to more fully appreciate the present
invention, reference is made to embodiments shown in
Figures 11-12 and 15-17 which illustrate flow
conditioners according to the invention but which do
not limit the invention as disclosed herein and claimed
below. For installation into a pipeline, anti-swirl
device 14 may be coupled to profile device 32 by
spacers 18, as detailed in Figure llA, to produce a
unitary structure. Anti-swirl device 14, as shown in
Figure llB, preferably comprises a bundle of nineteen
tubes each having a nominal tube diameter that is
approximately 1/5 of the diameter of the pipe within
which the flow conditioner is to be fitted (D).
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Preferably, the tubes are arranged as shown in Figure
llB: a central tube 20 surrounded by two arrays of
tubes of equal diameter. Preferably, all the tubes are
of the same length L1, ranging from about 0.2*D to
about l*D, most preferably, about 0.5*D, where D is the
internal diameter of the pipe.
Whereas the above description is of the preferred
anti-swirl device according to the invention, other
anti-swirl devices may also be used. Thus, the anti-
swirl device could be of a vane or honey comb design.The vane design presents certain limitations with
respect to retrofitting existing installation. The
honey comb design represents certain geometric
limitations when considering variations in pipe
diameter and honey comb size that may be encountered in
practice. Thus, the preference for the tube bundle
design shown in Figure llB, is not limiting of the type
of anti-swirl devices that may be utilized according to
the invention.
Downstream of the anti-swirl device 14 is a
settling chamber 30. The length of the settling
chamber L2 can be adjusted by selection of the length
of spacers 18. Alternatively, L2 can be determined by
otherwise affixing the anti-swirl device 14 and the
profile device 32 in the pipeline, at a selected
distance apart, without the use of spacers. The
selection of settling chamber length is critical and
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must be sufficient to effectively decouple anti-swirl
effects from the profile device 32 and thus length
varies depending upon jetting velocity the fluid being
measured. Based on test results, L2 ranges from about
l*D to about 20*D, preferably 2*D to 5*D, and most
preferably is about 3*D.
In Figure 13, the profile device 32, according to
the invention, is located at a distance L4 from the
measuring device 52 that is sufficient to decouple the
measuring device 52 from effects of the profile device
32. This distance will vary depending upon several
factors, including the type of measuring device. For
instance, if the measuring device is a turbine meter,
then the profile plate may be located as close to the
meter as feasible or less than about 0.5D from the
inlet side or the upstream face of the turbine meter.
On the other hand, if the measuring device is an
orifice plate, then the downstream face of the profile
device should preferably be located at a distance L4 of
equal to or greater than about 3*D from the orifice
plate.
In general, in any meter run, the critical
dimensions and distances according to the invention are
the length of the settling chamber L2 and the distance
of the profile device from the measuring device L4.
For example, in a typical orifice plate meter run,
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using preferred dimensions, the entire length taken up
by the flow conditioner of the invention may be:
L1+ L2+ L3 + L4 = 0-5D + 3D + 0.125D + 3D = 6.6D
Thus, for a 4-inch inside diameter pipe, the
distance is only 26.4 inches.
In the event that flow conditions in the pipeline
indicate that an anti-swirl device is not necessary,
then the "settling chamber" length L5 extends from the
nearest flow disturbance (elbow, tee, valve, etc.)
located upstream from the flow meter to the profile
device. In this instance, the "equivalent settling
chamber" length is from about l*D to about 20*D, and
preferably about 2*D to about 5*D; most preferably at
least about 3*D.
Downstream from the settling chamber 30, is the
profile device 32. The profile device is a radially
graded perforated plate of thickness L3 where L3 is
preferably in the range about O.lO*D to 0.5*D, most
preferably about 0.125*D.
Radially and axially graded plates have been
considered as alternative profile devices, but the cost
of testing these plates rigorously is prohibitive.
Nevertheless, it is believed that they will operate as
suitable profile devices in conjunction with the anti-
swirl device and settling chamber. Radially graded
tube bundles and radially and axially graded tube
CA 02228928 1998-04-07
24
bundles were also considered and rejected for various
reasons.
As shown in Figure llC, profile device 32
preferably has three radially spaced circular arrays of
holes or through bores spaced around the center of the
plate. Other designs are shown in Figures 14-17.
In the first or central array of through bores or
holes in profile device 32, centered on the loci of the
circle of diameter pcd1, there are preferably three
holes of diameter dl. In the second array, at locus of
a circle of diameter pcd2, there are preferably eight
holes of diameter d2. In the third and final,
peripheral array, at locus of a circle of diameter
pcd3, there are preferably sixteen holes of diameter
d3. (The "dimensions" dD and pcdn are actual
dimensions divided by the pipe internal diameter D to
obtain a "dimensionless" number.) In sum, the porosity
of the profile plate preferably ranges from about 40 to
about 60%. The holes in each circular array are
equally spaced apart around the center of the plate.
The upstream inlets of the holes are preferably beveled
or contoured to reduce permanent pressure loss.
However, all downstream edges of the holes are
preferably square and sharp to minimize adverse
reaction with the flow profile.
In the central array centered on the loci of the
circle of diameter pcd1, it is preferred that the
CA 02228928 1998-04-07
porosity (P1) should range from about 3.0 to about
5.0%, most preferably 3.8%. The "size" of the holes
expressed in dimensionless terms (i.e., as a fraction
of D), dl, is based on the following equation:
dl = {[ Pl ]0'5}
where nl is the number of holes in the central array,
range from two to five, but preferably three holes.
The porosity of the second array (P2) centered on
the loci of the circle of diameter pcd2 should
preferably range from about 19.0 to about 21.0%, most
preferably about 20%. The hole size for the second
array d2 is based on the following equation:
[ (n2*100)]
where n2 is the number of holes in the second array,
range from five to eleven, but preferably eight holes.
Preferably, the pitch circle diameter of the first
array expressed in dimensionless terms is given as:
pcd1 = 0.1125
Further, the pitch circle diameter for the second
circular array (pcd2) expressed in dimensionless terms
may be determined by the following equation:
pcd2 = max~[0.4990-0.0065*(P3-P2)],0.4500)
CA 02228928 1998-04-07
26
The porosity for the third array is selected as
the residual of the total plate porosity (Pt) minus the
porosities for the central (P1) and second (P2) arrays.
Thus, the porosity for the third array is found from
the equation:
P3 = Pt - (P1 + P2)
Further, the hole size for the third array, d3,
expressed in dimensionless terms, may be found from the
equation:
~3 {[ (n3*100)] }
where n3 is the number of holes in the third array,
ranges from about eleven to about twenty-one, but is
preferably sixteen holes.
Finally, the pitch circle diameter for the third
circular array (pcd3), expressed in dimensionless
terms, is based on the following equation:
pcd3 = [0.8575-0.0041*(P3-P2)]
Dam height is defined as the minimum solid
distance on the profile plates between the through
bores or holes that form the circular arrays. Within
the desired limits of plate porosity and limiting the
permanent head loss, it is further preferable that the
dam heights (dhl, dh2, dh3) expressed in dimensionless
terms, between circular arrays should preferably be
greater or equal to the following criteria:
CA 02228928 1998-04-07
dhl 2 0.0100
dh2 2 0.0100
dh3 2 0.0200
The dam heights expressed in dimensionless terms
may be calculated using the following equations:
dhl = [ pCd2- ( dl +d2+pcdl ) ]
dh2 = [pCd3- (d2+d3+pCdl ) ]
dh3 = [1.0000-( d3 +pcd3 ) ]
In order to convert the dimensionless terms used
to actual dimensions, they should be multiplied by the
internal pipe diameter (D).
Clearly, a person having ordinary skill in the
art, having read the above disclosure and being
familiar with the state of the art, will appreciate
certain changes and modifications that are considered
to be a part of the invention. Some of these
modifications include modifying the number of holes in
all three circular arrays as long as the equivalent
porosity for a respective array approximates the values
and/or equations stated above. Further, the number of
circular arrays may be increased by replacing the
second circular array with two tightly packed circular
arrays which have a combined equivalent porosity
approximating that of the second circular array, as
CA 02228928 1998-04-07
28
described above. Likewise, the third circular array
may be replaced with two tightly packed circular arrays
having a combined porosity equivalent to that of the
single third circular array, described above.
A profile plate, according to the invention and as
shown in Figures 15A and B, having four arrays of holes
or through bores, may be designed by modifying the
equations used for the three-array design. Thus, for
instance, the second array may be separated into two
arrays having a porosity equivalent to the second array
of a three-array plate. The pitch circle diameters of
these two replacement arrays expressed in dimensionless
terms are given by:
pcd21 = 0.86*pcd2
pcd22 = 1.22*pcd2
The through bore diameters, d21 and d22, expressed in
dimensionless terms, are preferably about equal to
0.112.
Alternatively, as shown in Figures 16A and B, a
four-array profile plate according to the invention may
be produced by replacing the third array of a three-
array plate with two arrays. In this instance, the sum
of the porosities of the two replacement arrays is
approximately equal to the porosity of the replaced
third array. Also, the pitch circle diameters
expressed in dimensionless terms, are as follows:
pcd31 = 0.917*pcd3
CA 02228928 1998-04-07
pcd32 = 1.047*pcd3
The diameters of the holes in the two replacement
arrays, expressed in dimensionless terms, are
approximately 0.112.
Similar principles apply in the development of the
five-array profile plate according to the invention, as
shown in Figures 17A and B. In this instance, both the
third and second arrays are each replaced with two
arrays.
Figure 13 is a schematic cross section of a
pipeline 50 of diameter D with a flow conditioner
according to the invention installed upstream of a
metering device 52. The direction of fluid flow is
shown by arrow A. A disturbance, not shown, may be an
elbow, tee, bend, valve, or other pipe restriction
located upstream from the metering device 52 at a
length L. Typically, L is selected to allow the fluid
to stabilize after passing through the disturbance so
as to minimize the effects of fluid flow irregularities
on measurements taken at measuring device 52.
According to the invention, the flow conditioner is
interposed between the disturbance and metering device
52. Anti-swirl device 14 (shown as a bundle of tubes,
but which may be of other configurations) is located a
distance Lc from the disturbance. In the event that
the anti-swirl device comprises a bundle of tubes, then
the length of these tubes is L1. Immediately
CA 02228928 1998-04-07
downstream from the anti-swirl device is settling
chamber 30 having a length L2. The settling chamber
terminates at the profile device 32, shown as a
perforated plate, with thickness L3. Downstream of the
S profile device 32, at a distance L4, is the metering
device 52, shown as an orifice plate, although other
measuring devices may be used.
As indicated above, under certain circumstances,
fluid conditions in the pipeline may be such that the
anti-swirl device 14 could be eliminated. Under these
circumstances, the profile device according to the
invention is located at a distance Ls downstream from
the disturbance and L4 upstream from the metering
device 52. Thus, the volume within the pipeline
defined by the length Ls serves as a settling chamber
30. The profile device according to the invention is
of unique design and, unlike prior art devices,
produces pseudo-fully developed flow that is swirl-
free, and axisymmetric with a time average velocity
profile and turbulent structure having values
approximating those found in fully developed turbulent
flow, and that are independent of axial coordinate.
Embodiments of the preferred profile plates
according to the invention are shown in Figures 14A and
B, 15A and B, 16A and B, and 17A and B. These Figures
show the location and size of holes or perforations on
the profile plates for designs ranging from those
CA 02228928 l998-04-07
31
having three arrays of holes (Figures 14A and B) to
those having five arrays of holes (Figures 16A and B).
Further, on the upstream side of the profile plate, the
holes are chamferred to reduce permanent head loss, as
shown. On the downstream side, however, the edges of
the holes are preferably perpendicular to the plate, as
shown.
Figure 14A shows the downstream face 31 of an
embodiment of a profile plate 32 according to the
invention, having a disk-like body 36 of diameter D,
with three arrays 33, 34, and 35 of through bores. The
array 33 shown has 3 through bores, array 34 has 8, and
35 has 16. The through bores in each array are sized
as shown and may be derived from calculations shown
above. From Figure 14B, upstream face 37 that faces
the incoming fluid may have chamfered edges 39 on each
of the through bore inlets. Typical chamfers are at
45~. However, the outlet ends of the through bores on
downstream 31 have sharp edges. The profile plate body
36 iS surrounded by a flange 38 of diameter about 1.5D
and thickness L6 to allow for fitting the plate 32
between two pipe flanges.
Figures 15A and B show an embodiment of a profile
plate 32 with four arrays 41, 42, 43, and 44 of through
2 5 bores. Array 41 has 3 bores of diameter dl, array 42
has 8 bores of diameter d2, array 43 has 8 bores of
diameter d22(=d21), and array 44 has 16 bores of
CA 02228928 1998-04-07
diameter d3. The calculation of these bore sizes is
shown above.
Figures 16A and B show an embodiment of a profile
plate with four arrays: 45, 46, 47, and 48. In this
instance, the third array (array 35) of Figure 14 has
been replaced with two arrays. Thus, array 45 has 3
through bores, 46 has 8 through bores, 47 has 16
through bores, and 48 has 16 through bores. The
diameters of these through bores may each be
calculated, as explained above.
Figures 17A and B show an embodiment of a five
array profile plate 32. The first array 54 has 3
through bores of diameter dl, the next array 56 has 8
through bores of diameter d22, as does array 57. The
two outer arrays, 58 and 59, each have 16 through bores
of diameter d31 and d32, respectively. As shown, d31 =
d32 .
The following comparative examples and referenced
Figures are illustrative of the invention and do not in
any way limit the scope of the invention as described
above and claimed below.
EXAMPLES
The flow conditioner according to the invention
was tested by an outside research laboratory and
compared with commercially available devices. During
this test, a test loop, shown in Figure 18, was used.
Gas enters a stagnation bottle 100 and flows to a
CA 02228928 1998-04-07
33
straight section of pipe 102 of internal diameter D
with a length 12D, as shown. The pipe then bends in an
elbow 104 that has a length of 2.2D as measured from
the center of the pipeline to the center of a flange at
the end of the elbow, as shown in Figure 18. From the -
elbow 104, gas flows into a length of pipeline 106 (the
test pipe length) of length L (which is converted to
dimensionless terms by dividing by D) that extends from
the elbow to an orifice plate 108. The flow
conditioners to be tested were positioned within the
pipe length 106 at various distances X from the
measuring device 110. To obtain dimensionless terms,
the distance X was divided by the internal diameter D
of pipe 106.
For each of the measurements taken, the internal
diameter of the pipeline D was 4.027 inches and the
length of pipe 106 was 17D texcept for AGA tube bundle
tests which also used 45D and lOOD lengths). The flow
disturbance was created by either a 90~ elbow (such as
104) or a tee installed upstream from the test pipe
length 106.
By way of explanation, the designation Cd
deviation (%) refers to the percentage deviation of
empirical coefficient of discharge or flow calibration
factor measured from fully developed flow experienced
by a flow meter due to the influence of the flow
conditioner and piping disturbance. Desirably, this
deviation should be as near to zero as possible. As
CA 02228928 1998-04-07
34
explained before, a "minimal deviation" from empirical
meter coefficient (Cd) is regarded as plus or minus
O . 1% .
Further, the B factor is the ratio of the orifice
plate bore diameter (~O) to the internal diameter of
the pipeline in which the fluid flows (i.e., ~o/D).
Figure 19 summarizes the results obtained when an
AGA tube bundle was utilized in the apparatus of Figure
18 with test pipe lengths 106 of 17D, 45D, and lOOD.
Within these pipe lengths, the AGA tube bundle was
moved, relative to the orifice plate (of ~ = 0.75) so
that its distance X from the plate could be expressed
as a fraction of the pipe diameter, i.e., as X/D. The
Reynolds number characterizing the flow in the pipeline
was 900,000. As can be seen from Figure 19, the AGA
tube bundle is unsuitable for conditioning flow and
only has minimal meter coefficient deviation when:
L1 = 17D; and X/D = 12-15
L1 = 45D; and X/D = 8-9
L1 = lOOD; and X/D > about 45
Similarly, Figure 20 demonstrates that for a 17D
long test pipe, the Laws flow conditioner is only
useful at distances of X/D that are greater than about
12. The ~ factor for the Laws conditioner tests was
0.67, the Reynolds number of the flowing fluid was
900,000, and the disturbance was a tee upstream from
the meter tube.
CA 02228928 1998-04-07
Figure 21 shows the results obtained when an AGA
tube bundle is used in a 17D long test pipe, downstream
from a disturbance that is a tee. None of the data
points show an acceptable or "minimal" deviation, since
all are greater than 0.2%. The B factor for the
orifice meter was 0.67 and the flow Reynolds number was
900, 000.
Figure 22 is a summary of the results obtained
using a Mark V flow conditioner in a 17D long test pipe
with an orifice plate having a B of 0.67 and flow
Reynolds number of 90o,000. The upstream disturbance
was a tee in the pipeline. As can be seen from the
results, minimal deviation from meter coefficient was
only obtained when distance from the orifice meter
(X/D) was in the range 7-8.
In sharp contrast, in Figure 23, a flow
conditioner according to the invention, under the same
conditions (a 17D long meter tube, orifice plate
B = 0.67, upstream disturbance a tee, and Reynolds
number of 900,000) shows an acceptable minimal percent
deviation from meter coefficient when X/D exceeds as
little as about 5.5.
Figure 24 reflects the results obtained when a
flow conditioner according to the invention was used
under the same conditions as in Figure 23, except that
for data points shown by squares, the B was 0.67 and
the disturbance was an elbow; and for data points shown
by triangles, the B factor was 0.75 and the disturbance
CA 02228928 1998-04-07
36
was an elbow. Based upon the results, it is clear that
when X/D exceeds as little as about 3-4, the percentage
meter coefficient deviation is acceptable and conforms
to the minimum required (i.e., is less than 0.1%).
The above tests conclusively demonstrate the
superiority of the invention flow conditioner that
achieves minimum percent deviation from meter
coefficient at distances of X/D far less than the AGA,
Laws, or Mark V flow conditioners. Most importantly,
the minimum percent deviation, when achieved, is stable
so that reliable measurements can be taken as long as
the minimum X/D is met.
Although the invention has been described with
reference to its preferred embodiments, those of
ordinary skill in the art may, upon reading this
disclosure, appreciate changes and modifications which
may be made and which do not depart from the scope and
spirit of the invention as described above and claimed
below.
