Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CHOKE FLOW BEAN
This invention pertains to a novel choke
flow bean and a choke nipple assembly containing an
adaptor and the choke flow bean.
More particularly, the choke flow bean of
the invention is unusually effective in reducing the
pressure of fluids flowing through it and is also
capable of handling fluids having entrained particu-
late solids.
A wide variety of mechanical devices have
been used to control the flow of fluids (liguids
and/or gases) through a pipe. The various engineers
handbooks describe various orifices, nozzles, and
short tubes as means for reducing pressure of a fluid.
See, for example, Chemical Enqineers Handbook, 5th
Edition, by R. H. Perry et al., McGraw-Hill Book
Company (1973) and Unit ODerations of Chemical
Enqineerinq, 3rd Edition, by W. L. McCabe et al.,
McGraw-Hill, Inc. (1976).
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_ These handbooks show or describe a variety
of "Venturi nozzles" where the fluid passes through
a converging truncated cone into usually a short,
straight-walled tube from which it is discharged
into a diverging truncated cone, often called a dif-
fuser. See, for example, the disclosure by McCabe
et al., supra, at pages 203,212.
In other instances, simple flow nozzles have
been used to regulate the flow of fluids. Nozzles with
a well-rounded throat generally have a higher average
coefficient of discharge than orifices having a square
edge or a thin plate with a sharp edge. Flow measure-
ments through such nozzles are described in Chapter 14
of the text, "Mechanical Measurements", by T. G. Beck-
with et al., Addison-Wesley Publishing Company (1973),
at pages 417-419.
The flow of fluids through convergent-
-divergent nozzles (DeLaval nozzles) has also been
studied and is reported, for example, by R. H. Perry,
supra, at pages 5-29 et seq. None of the DeLaval-
-type nozzles have been used, so far as the applicant
know~, as a choke flow bean capable of handling
fluids with entrained particulate solids.
The choke flow bean of the invention5 comprises:
a housing having a first end and second end
defining a bore of generally circular cross section
which extends, along with its axis of generation, from
the first end to the second end,
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the bore being of varying diameter along
its axis of generation with regions of large diameter
adjacent the first and second ends of the housing and
a region of minimum diameter, d, intermediate the first
and second ends,
the bore having a general configuration
approximating that of a trumpet bell between the
first end and the region of minimum diameter, and
the bore having a frustoconical configura-
tion between the first end and the region of minimumdiameter with a tota' included angle of from 4 to
8 and having a length along the axis of generation
of up to about 9d between the region of minimum dia-
meter and the second end.
Figure l shows a side schematic cross-
-sectional view of the choke flow bean.
Figure 2 shows a side schematic cross-
-sectional view of a choke nipple containing a
choke adapter which in turn contains the choke
flow bean.
In Figure l, the choke flow bean is shown
as a housing having a generally cylindrical shape
with a bore traversing from a first end to a second
end. The bore is of generally circular cross-section
and has an axis of generation from the first to the
second end. The bore of varying diameter along its
axis with regions of large diameter adjacent the
first and the second ends. The throat portion of
the bore has a general configuration approximating
that of a trumpet bell (lO) between the first end
and the region of minimum diameter (ll) having a
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diameter, d. The bore has a frustoconical configu-
ration (12) between the second end and the region
of minimum diameter with a total included angle, ~,
of from about 4~ to about 8~ (preferably from about
5 to about 7; more preferably, about 5) and
having a length, 1, along the axis of generation of
up to about 9 d. When 1 is less than about 9 d, the
pressure in the fluid is not reduced as much as it
might be as it passes through the choke flow bean.
If 1 is greater than about 9 d, the fluid passing
through the choke flow bean experiences considerable
turbulance as the fluid begins to fall away from the
sides of the choke flow bean.
The choke flow bean may be prepared from
substantially any material of construction, but
because it is exposed generally to high pressures
during conditions of use, it is normally constructed
of metal (usually steel) and in most instances it
is prepared from materials noted for their toughness
and abrasion resistance (e.g., tungsten carbide or
carburized steel). The throat portion (10) is more
subject to abrasion than the frustoconical portion
(12). It is, therefore, convenient and usually
preferred to construct the throat separately from
the remainder of choke flow and to include an
insert in the bean which contains the throat portion.
This embodiment is illustrated in Figure 2. The use
of an insert permits the skilled artisan to use
materials of construction which may be more critical
to the particular application and also permits the
artisan to more effectively utilize the metallurgy
of the two different types of metals. For example,
the throat portion could be an insert of tungsten
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carbide and the remainder of the choke flow bean
could be of carburized steel which is far less
expensive and easier to machine.
The radius of curvature of the throat
portion (lO) can be varied but is usually at least
about 0.5 d (preferably from about 0.5 d to about
l.0 d) when circular or eliptical in shape. This
well-rounded opening at the throat permits maximum
flow through the choke flow bean and eliminates the
formation of a vena contracta. This is important
because as the choke flow bean flows full, the void
spaces associated with a vena contracta do not form
and cause the fluids passing through the choke flow
bean to "hammer" and cavitate the surface of the
throat portion.
The throat portion passes through the
region of minimum diameter (ll) and opens smoothly
and directly into the portion of frustoconical
configuration (12). The total included angle in
the frusto(;onical configuration, as noted above,
is most preferably about 5, and its length (l)
is most preferably about 9 d.
The outer surface of the choke flow bean
can be varied to convenience but is generally
cylindrical in shape with external threads (17)
fashioned at the discharge end (B). These external
threads are adapted to engage a choke adapter 13
which holds the choke flow bean in place during
conditions of use. The inlet end (A) of the choke
flow bean usually has a hexagonal configuration 16
(not specifically illustrated) adapting it to
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removal or emplacement within the choke adapter (13)
using a conventional open-ended wrench (i.e., a wrench-
engaging fitting).
The choke adapter (13) is also usually of
cylindrical shape, although it could take on different
configurations, and has internal threads ~18) to
engage the choke flow bean, and external threads (19)
to engage a choke nipple (14). The choke adapter
is primarily a convenient spacing device that holds
the choke flow bean firmly within the bore of the
choke nipple. The choke adapter usually has a
wrench-engaging fitting (20) at the inlet end and a
hollow cylindrical bore (21) at the discharge end
to receive depressurized fluids passing through the
flow bean. The choke adapter can be of various
materials of construction, but it is usually metal
(generally steel).
The choke nipple (14) is provided with
internal threads within its bore for threadedly
engaging the choke adapter. The hollow bore (20)
discharges fluids discharged from the choke flow
bean/choke adapter and also includes means at the
inlet end for fixedly engaging it in fluid communi-
cation with a source of pressurized fluid. The
choke nipple may be of various materials of con-
struction, but it is usually designed to withstand
high pressure and is normally metal (e.g., steel).
Fluid sealing means (15), such as elasto-
meric "o-rings" are desirable in many instances, and
are depicted in Figure 2.
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The choke flow bean illustrated in Figure 1
was embodied in a choke nipple as illustrated in
Figure 2 and used in the choke assembly described by
Zingg et al. in a commonly owned, copending patent
application submitted even date herewith (Attorney
Docket No. 29,071-F) attached to a slurry concentrator
described by Zingg in copending Canadian patent appli-
cation Serial No. 391,517, filed December 4, 1981,
during the high pressure fracturing of a well. The
throat of the choke flow bean was a tungsten carbide
insert and the remainder of the choke flow bean was
carburized steel. The choke flow bean showed little
or no signs of wear after 8 hours of use in which the
fluid was pressurized through the choke flow bean
at over 700 Kg/cm2 (10,000 psi). When the choke
flow bean of the instant invention was replaced
with a conventional commercial choke flow bean of
ceramic construction, the ceramic choke flow bean
destructed in less than 20 minutes.
In another instance, a well had been
hydraulically fractured using a foam fracturing
fluid and was highly pressurized with gaseous
nitrogen and gases within the well. The well was
valved off, the choke nipple containing the choke
adapter and choke flow bean was attached, and the
valve to the well reopened. The gases emitted from
the well were at several thousand psi and would
normally have destroyed ceramic choke flow beans
within a matter of minutes but the choke flow bean
~as detailed above) showed little or no signs of wear
during the course of bleeding off the well pressure.
The gases and li~uids emitted from the well were safely
discharged into conventional piping without undue erosion.
