Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02478364 2004-08-02
I
MULTI-STAGE EDUCTOR APPARATUS
Related Application Data
This application claims the benefits of U.S. Provisional Patent Application
Serial Number
60/492,084, filed August I, 2003, and titled Multi-Stage Eductor Apparatus.
Field Of The Invention
S The present invention generally relates to venturi-type suction devices and
apparatus, and
in its preferred embodiments more specifically relates to suction and mixing
eductor devices and
apparatus utilizing a plurality of longitudinally aligned stages.
Background Of The Invention
The venturi tube, which invented by Giovanni Venturi, basically comprises two
tapered
sections of pipe joined by a narrow throat. This convergent-divergent shape is
commonly
referred to as a diffuser when used in venturi tubes. As a fluid flows through
the venturi tube
structure the fluid velocity in the throat is increased and the pressure is
reduced, in keeping with
the principles of conservation of energy and with Bernoulli's Theory, which
states, "At any point
in a pipe through which a fluid is flowing the sum of the pressure energy, the
kinetic energy, and
the potential energy of a given mass of the fluid is constant "
Over time it was realized that the reduced pressure section of the venturi
structure
provided suction capabilities that could be put to use. Thus, a solid, liquid
or gas could be
moved, aerated, pumped, mixed, entrained, reacted, transferred, conveyed,
agitated, sheared, or
blended with a venturi tube incorporating an opening at the point of greatest
suction or vacuum.
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The absence of any moving parts in the venturi-based suction device provides
significant
advantages in reliability and operation as compared to, e.g., mechanical
pumps.
There are many names for venturi tubes that incorporate a suction port. For
example, if
the motive or driving fluid is a liquid, it is normally referred to as an
eductor. If the motive or
driving fluid is a gas such as steam, the venturi tube is commonly referred to
as an ejector. Two
other common names are aspirator and siphon pump or siphon. However, the
venturi tube with a
suction port is almost universally referred to as a jet pump or venturi jet.
For the sake of brevity
and consistency, the remainder of the disclosure of the present invention will
utilize the term
eductor, and it is to be understood that the term "eductor" as used herein
shall refer to any
venturi structure regardless of the motive fluid used or the purpose for which
the suction is
utilized.
When an eductor is used to produce a suction for material transport, mixing,
etc., the
motive fluid is typically injected at or just before the narrowed throat of
the venturi structure, so
that the motive fluid will increase in velocity as it flows through the
venturi throat, reducing
pressure and creating a suction. Since the motive fluid is injected
tangentially, the longitudinal
path into the throat is available for the free flow of other material in
response to the suction
created by the device. That material then becomes mixed with and entrained by
the driving fluid
in the throat of the venturi structure.
Various designs for the injection of the motive fluid have been developed. In
one design,
manufactured by the Derbyshire Machine and Tool Company of Philadelphia,
Pennsylvania,
nozzles are located on the periphery of the inlet to the diffuser. Derbyshire
refers to its design as
the Peri-Jet~ Eductor. As another example, an eductor with a lobed shape jet
nozzle is
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manufactured by Vortex Ventures, Inc. of Houston, Texas. Vortex Ventures
refers to its eductor
as the LobeStarC~ Mixing Eductor. This nozzle is disclosed in U.S. patent
number 5,664,733, to
Gerald Lott.
There are several drawbacks associated with eductors known in the prior art.
First, an
eductor has a specific geometry with respect to the jet nozzle diameter, the
throat, the diffuser,
the suction inlet and the discharge outlet. The geometry or diameter of the
jet nozzle determines
the mass flow rate of the driving fluid. The throat diameter of the diffuser
section determines the
velocity of the combined streams which are the driving fluid and the entrained
material. The
geometry of the divergent section of the diffuser determines the pressure
recovery capabilities of
the eductor.
Specific geometries can be referred to as fixed geometries. Quite simply,
eductors
operate with pump curves based upon flow rate through the jet nozzle at a
specified pressure.
Some eductors, such as waterwell eductors, are designed to operate at low
pressures, ranging
froml0 to 50 psig. Eductors used for firefighting purposes normally operate at
a medium
pressure range, between 140 psig to 185 prig. Chemical ejection eductors used
with high
pressure sprayers must operate at high pressures, ranging from 1000 to greater
than 4000 psig.
As pressure increases, flow through a jet or orifice increases. For example, a
one inch diameter
nozzle will flow 200 gallons per minute (gpm) at a pressure of 45 psig. At a
pressure of 180
psig, the flow will double to 400 gpm through the same nozzle.
Eductors are designed to operate effectively within a relatively narrow range
of driving
fluid pressures and flow rates, and deviation from the design range typically
results in
substantially reduced performance. For example, a prior art eductor designed
to operate with a
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driving fluid pressure of 150 psig at a flowrate of 277 gpm will lift a column
of water 20 feet
when operated at those parameters. However, when that eductor is operated with
a reduced
pressure of 50 psig, with a corresponding flow rate of 162 gpm, the eductor is
capable of lifting a
column of water about 2 feet.
Summary Of The Invention
The present invention provides an eductor apparatus that overcomes the
drawbacks
inherent in fixed ratio eductors,and which can be effectively used over a wide
range of pressures
and flow rates. The mufti-stage eductor apparatus of the invention includes a
first eductor stage
directly coupled with at least one additional eductor stage to form a material
flow passageway
through the paired eductor units. In the preferred embodiment of the invention
each eductor
includes a venturi throat and diffuser section, a material inlet and outlet,
and a drive fluid inlet
feeding nozzles directing drive fluid into the venture throat to create a low
pressure zone
resulting in suction of material into the eductor. With the closely coupled
eductor stages the
material outlet from the first eductor stage is within the low pressure, or
drafting zone created by
the second eductor, moving both driving fluid and entrained material through
the passageway
with lower friction and increased efficiency, and increasing the suction at
the material inlet to the
mufti-stage apparatus.
The structure and features of the eductor apparatus of the invention will be
described in
more detail with reference to the accompanying drawing figures.
Brief Description Of The Drawings
Figure 1 is a side elevation schematic illustration of a first embodiment of
the mufti-stage
eductor of the invention.
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Figure 2 is a side elevation schematic illustration of a second embodiment of
the multi-
stage eductor of the invention.
Figure 3 is a graph showing a comparison between the performance of an eductor
of the
invention and a prior art eductor through a wide range of driving fluid
pressures.
Figure 4 is a side elevation schematic illustration of a third embodiment of
the multi-
stage eductor of the invention.
Description Of The Invention
The mufti-stage eductor of the invention, generally identified by reference
number 10,
comprises a first stage venturi-type eductor 11, with a venturi throat section
12 and a diffuser
section 13, and a second stage venturi-type eductor 14 with a venturi throat
section 15 and a
diffuser section 16, connected in series with the first stage. The first stage
eductor has an inlet 17
and an outlet 18, and the second stage eductor has an inlet 19 and an outlet
20. The inlet of the
second stage structure connected to the outlet of the first stage so that the
longitudinal axes of the
first and second stages are in coaxial alignment. The flow of material into
the mufti-stage
eductor apparatus is indicated as "A", and the flow of material from the mufti-
stage eductor
apparatus is indicated as "B". The dashed line through the structure
represents the longitudinal
axis of the mufti-stage eductor, as well as the center line of the flow path
of material drawn into
and through the eductor.
The first stage eductor 11 has a driving fluid inlet 21 for the introduction
of a flow of
driving fluid indicated as "C", and the second stage eductor 14 has a driving
fluid inlet 22 for the
introduction of a driving fluid "D" to the second stage. The driving fluid(s),
or motive fluid(s), is
introduced, under pressure, to the respective first and second stage eductors
through the
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CA 02478364 2004-08-02
respective inlet and is emitted into the interior of that stage through first
stage inlet nozzle or
nozzles 23 and second stage inlet nozzle or nozzles 24, upstream of the
venturi throat of the
respective stage. The inlet nozzles are disposed to direct the driving fluid
toward the venturi
throat at an angle relative to the longitudinal axis of the stage, thereby
creating a zone of reduced
pressure behind, or upstream from, the inlet nozzles in the region of the
suction inlet and
inducing material flow into the suction inlet.
The mufti-stage eductor of the invention has been demonstrated to provide a
dramatic
enhancement in eductor effectiveness, measured in terms of the suction, or
partial vacuum
developed by an eductor apparatus at a selected driving fluid pressure and
flow rate. In a
controlled comparison test, one of the stages of a mufti-stage eductor as
illustrated in Figure 1
was operated at various driving fluid pressures, and the suction created by
the single stage during
operation at the various pressures was measured. The second stage was then
connected to form
the two-stage eductor illustrated in Figure l, and the suction created by that
mufti-stage eductor
at various driving fluid pressures was measured and recorded. The comparative
results are
shown in the following table and graphically illustrated in Figure 3:
Pressure (psig) 30 40 50 75 100 150
Single Stage Eductor ~ ~ 1, 4" ~ ~ 11" ~ 15"
Mufti-Stage Eductor ~ 17" ~ 24" ~ 25" ~ 27" ~ 27"
The vacuum produced was measured, and is shown in the table, in inches of
mercury. Fields in
the table for which no data was collected are left blank.
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As can be readily seem from the table and the graphical representation, the
performance
provided by the mufti-stage eductor is a dramatic improvement over the
performance of a single
eductor stage, and is unprecedented in the prior art.
A test of the apparatus of Figure 1 for the mixing of drilling "mud" was
performed to
evaluate the performance of the apparatus in a practical application. The
apparatus was used to
educt AquaGel° dry drilling mud (essentially a bentonite) and mix the
dry material with water,
which was also used as a driving fluid for the eductor apparatus. Not only did
the apparatus of
the invention perform more effectively than a conventional eductor in
vacuuming the dry
material, the shear and mixing of the dry material with water to produce a
homogenous drilling
mud fluid was highly effective as well. The mud fluid was thoroughly mixed
with no clumps of
dry material ("fisheyes"), and after a two week period of observation there
was no visually
detectable precipitation of bentonite particles from the fluid. To determine
whether discharging
from the mufti-stage eductor apparatus of the invention against a static head
would effect
performance, the apparatus of Figure 1 was then set up to discharge mixed
drilling mud against a
10 foot head, and the results were compared to results obtained without the
head. The head
pressure or back pressure on the mufti-stage eductor had no detrimental
effect.
Without limitation to any particular theory or to any particular mechanism of
action, it is
contemplated that the unprecedented improvement can be attributed to a
"drafting effect",
similar to that experienced by a vehicle closely following another in the
slipstream created by the
leading vehicle. It is known that as a single vehicle, e.g., a race car,
travels through the air it
creates a zone, or bubble, of high-density air in front of it and a zone of
low-density air behind.
The difference in the pressure between these two zones of air creates drag,
the force that impedes
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motion. This drag force limits the top speed the car can attain. However, when
a second car
pulls up behind the first, the slipstreams created by the two merge, so that
the first car losses its
aft bubble and the second car loses its front bubble. This effect reduces the
drag force each car
experiences and both are able to travel slightly faster.
The same principle can apply to moving fluids. Again, without limitation as to
any
particular theory or mechanism, it is contemplated that the fluid discharging
from the first stage
driving fluid nozzles does not readily give up energy to form a boundary layer
on the inner
surface of the venturi throat and diffuser. It is contemplated that the
driving fluid discharging
from the second stage, or downstream, inlet nozzles forms a boundary layer on
the inner surface
of the second stage venturi and diffuser. The friction, and consequent drag
associated with the
creation of a boundary layer in the first stage is reduced, if not eliminated
entirely.
Returning to the vehicle analogy; if the trailing vehicle drops back out of
the low pressure
zone behind the leading vehicle, the drafting effect is lost. Likewise, in the
case of the multi-
stage eductor of the invention, it is contemplated that if the stages are
placed too far apart, the
first stage cannot draft on the second stage. Although in that instance the
second, downstream,
stage will reduce head pressure for the first, upstream, stage, the advantage
of the drafting affect
would be lost. Hence, the stages should be disposed in sufficiently close
proximity to take
advantage of drafting on each subsequent stage. The close proximity and the
drafting effect
achieved by the present invention distinguishes it from simply placing
separated eductors in
series in the flow stream, as has been on occasion done in the prior art.
Separated eductors, even
though piped in series, do not achieve the drafting effect or the dramatic
improvement in
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effectiveness of the mufti-stage eductor of the present invention, and the
practice of simply
placing eductors in series is not comparable or material prior art to the
present invention.
Figure 2 illustrates a modified version, or second embodiment, of the
apparatus shown in
Figure 1. In the apparatus of Figure 2 the diffuser section 13 of the first
stage 11 is removed to
enhance velocity and take full advantage of the drafting affect of the fluid
entering into the
second stage 14. In addition, this configuration places the driving fluid
inlet nozzles 23 of the
first stage closer to the inlet nozzles 24 of the second stage. The diffuser
section 16 of the
second stage is retained in order to reduce the velocity of the fluid, thus
recovering pressure.
The more compact structure of the embodiment of Figure 2 also provides the
advantages of
reduced size and weight.
Although the mufti-stage eductor of the invention is shown in the drawing
figures with
two stages, it is to be understood that the invention is not limited with
regard to the number of
stages. A third stage and/or further additional stages may be added to the
apparatus, and the
scope of the invention is to be considered to include any number of stages.
The mufti-stage eductor apparatus of the invention provide the capability of
utilizing
different driving, or motive fluids in the different stages. For example,
referring to either Figure
1 or Figure 2, a first motive supply fluid C, is used to provide a suction for
entraining a material
A in the first stage 10a. A second motive fluid D supplied to the second stage
lOb provides
drafting affects for entraining and mixing fluids C and D, and material A. The
product is
discharged through the diffuser 16 of the second stage as a final product B.
This capability
substantially expands the range of possible uses for an eductor apparatus
beyond anything
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contemplated or possible using prior art apparatus. For example, the mufti-
stage eductor of the
invention is ideally suited for emulsifying a hydrophobic liquid and water
with a surfactant.
A further variation, or alternative embodiment of the mufti-stage eductor of
the invention
is illustrated in Figure 4, in which the motive fluid C for the first stage is
introduced through a jet
nozzle disposed with its axis in alignment with the longitudinal axes of the
first and second
eductor stages, to create a drafting envelope as generally indicated in the
figure. As material A is
introduced into the first stage it is entrained in the motive fluid through
the first stage of the
apparatus and into the second stage. The embodiment of Figure 4 provides the
same capabilities
and advantages as the previously described embodiments, and is susceptible to
the same wide
range of uses.
Another ideal application for the present invention is for emulsifying super
absorbent
polymers (SAP) into water. Super absorbent polymers, which readily absorb
liquids, are used in
baby diapers, as well as many other uses. The typical SAP is the chemical
polyacrylamide, which
is normally supplied in a prehydrated form. Thus, prehydrated or prehydrolyzed
polyacrylamide
is given the acrynom PHPA. Polymers are coiled when in the prehydrated state.
Thus, the
polymer must be uncoiled and aged to be highly effective. The mufti-stage
eductor allows for
pneumatic conveying PHPA into the first stage for uncoiling purposes, followed
by thorough
mixing and blending in the second stage. The PHPA emulsion can then be used
for water
treatment purposes, as a drilling fluid additive or as a firefighting agent.
The mufti-stage eductor can also be utilized as an effective firefighting
tool. Aqueous
film forming foam (AFFF) is utilized to suppress Class B fires: AFFF is
educted into the
firefighting water and sprayed on top of the pool of burning fuel. Also, it
may be sprayed on a
CA 02478364 2004-08-02
pool of spilled fuel to prevent a fire or to prevent reflash of a fire. The
benefit of the mufti-stage
eductor is that is can supply high pressure water similar to a firefighting
monitor, while
simultaneously educting in the AFFF.
Another application for the mufti-stage eductor can be found in the wastewater
treatment
industry. Aerators are used to supply dissolved oxygen to aeration lagoons,
ponds or tanks.
Aerators range from propeller type systems to low pressure roots blowers to
ineffective
conventional eductor systems. The mufti-stage eductor is very well suited for
a wastewater
treatment plant for several reasons. First, it can be used to entrain air and
discharge the mixture
to the bottom of the lagoon. This agitates the lagoon and prevents settling of
solids. Second,
since the mufti-stage eductor will pull a high vacuum, a suction hose can be
attached to the
mufti-stage eductor. This allows for operating the eductor of the invention as
a mini-dredge.
Thus, solids can be removed from the bottom of the lagoon for cleaning
purposes with a multi-
stage eductor that can also be used as an aerator.
Another potential use for the mufti-stage eductor of the present invention
involves the
capture and recovery of volatile organic compounds (VOCs); a use to which
conventional
eductors have never been put. With the mufti-stage eductor of the invention a
deep vacuum can
be drawn on, for example, a glycol recovery boiler condenser in order to
recover VOCs. The
vacuum and the flow rate of VOCs can be controlled by operating each stage
independently of
one another. For example, if the motive fluid is natural gas and line pressure
drops due to
unforeseen equipment failures, another stage can be brought online to maintain
a constant
vacuum and flowrate.
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CA 02478364 2004-08-02
Yet another application for the mufti-stage eductor is using it as a venturi
scrubber. The
variable vacuum and flow rate capabilities of the mufti-stage eductor, coupled
with its ability to
thoroughly shear and mix fluids with micron sized particles, makes it a highly
effective gas
scrubber. Themulti-stage eductor would be ideally suited for scrubbing
particulate matter
smaller than 2.5 microns (PM 2.5) from diesel emissions and power plant flue
gas.
Another application can be found in the medical industry. Vacuum pumps are
used
throughout the medical industry for providing a vacuum for many different
uses. One
application in particular requires the use of an expensive desk size vacuum
pump to provide a
vacuum for a small size tube of 1 to 3 millimeters in diameter. When an ear is
impacted, for
example, a physician will utilize a suction tube to withdraw the material away
from the eardrum.
A small mufti-stage eductor can easily be fabricated to operate with water
supplied from a
lavatory or common kitchen faucet. Typically, most cities control the water
pressure between 30
and 60 psig. This allows for a cost effective vacuum pump that is
intrinsically safe in that
operation does not require electricity.
It is contemplated that many more uses and benefits of the mufti-stage eductor
will be
identified by those of skill in the various arts in which the new apparatus
may offer improvement
over conventional devices and methods.
The foregoing description of the structure and features, and potential methods
of use, of
the mufti-stage eductor is intended to be illustrative and not for purposes of
limitation. The
apparatus is susceptible to variations and further alternative embodiments in
addition to those
discussed above, all within the scope of the invention as described above and
set forth in the
following claims.
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