CA2116709A1 - Apparatus for and method of accelerating fluidized particulate matter - Google Patents

Abstract

An apparatus and method for transporting or discharging fluidized particulate matter at varying pressures and velocities utilize actual and effective nozzles for increasing velocities and pressures, and for energy transfer between an incoming fluidized stream and a blast medium. Series of nozzle throats are formed by both static flow path structures and an effectively solid boundary formed by a shock wave or flow front, which are combined with the inductive action of the blast medium delivered through an co-axial with a flow passage for the particulate matter, to inner blast nozzle, facilitate sizing, and boosting or discharge of the fluidized particulate matter. A discharge nozzle provides an improved high energy density and even blast pattern which promotes kinetic energy transfer between the blast medium and particulate matter, thereby creating the discharge velocities requisite for applications such as blast cleaning.

Description

92PlCA

This invention relates to an apparatus for and a method of accelerating a fluidized 5 stream of particulate matter for the purposes, for example, of duct transport over long distances and the discharge of the fluidized streams at high velocities.

In abrasive blast cleaning, such as with sand, grit or shot particles, velocity is imparted to particles which are directed against a surface to be cleaned, depainted, 10 radioactively decont~min~ted or otherwise modified. The dynamic particle energy is converted into destructive forces which mechanically abrade or deform surface coatings.
This methodology results in residual particulate matter of the blast stream, blast media and the material removed as the blasting strips off the coating of the target surface, creating a high dust environment that may be hazardous to health, equipment and 15 surrounding property. The cost of removing such matter may be excessive as well.

In addition, these blast particles are destructive when used for the treatment of fragile surfaces such as thin sheets, carbon and plastic.

Recently, less aggressive particulate matter such as dry ice and ice has been utilized as blast particulate matter to avoid these problems, but not without limitations relating to transport and discharge. First, ice is not free flowing and must be "fluidized"
with a gas, liquified gas or liquid in order to be transported to the target surface. Second, ice is not effective if discharged at low velocities. Third, ice is friable and heat sensitive and high velocity transport will generate considerable friction and heat and cause melting and breakdown of the ice particles. That said, the aim has been to achieve low transport and high discharge velocities within an apparatus that can handle all types and sizes of particulate matter, including ice particles, and to control the sizing of particulate matter.

Previous practice of transporting or discharging fluidized particulate matter athigh pressures, high velocities or both has involved the use of costly mechanical positive displacement pumps, which are volume dependent, complicated and do not mix or disperse or accelerate a fluidized stream well. Blowers, fans, and air jet and liquid jet pumps have also been used, but are only capable of generating small pressure increases and low velocities.

The use of single venturi nozzles as described in United States Patents Nos.
4,038,786 and 4,707,951, in "Foundations of Aerodynamics" (A.M. Kuethe and J.D.
Schetzer) and the "Mechanical Engineers' Handbook" (T. Baumeister and L.S. Marks) is ineffective for increasing pressure as can be achieved by induced flow created by 10injectors using either gas or liquid. Single venturi nozzles create increased velocity by gas expansion through falling pressures.

Amplifiers, such as taught by United States Patent No. 4,389,820, have been usedwith limited success to induce flow in signific~nt volumes, but unfortunately are able to 15only generate minim~l pressure differentials and small increases in velocity. This is due to several inherent problems. First, the induction effect is dependent upon the boundary layer formation of a very thin high speed air film which is destroyed by the bombardment of particulate matter. Second, since the induction is via boundary layer shear viscous forces, there is minim~l mixing and therefore little energy transfer to the bulk of the 20induced stream. Third, acceleration by usage of conduit restrictions will greatly affect or destroy the inductive effect, thereby placing a limitation on the effective increase in velocity that may be achieved. Fourth, air amplifiers, as the name implies, use a small amount of high velocity air to form a boundary layer to induce flow of a much larger amount of air and therefore there is little energy available to be Ir~l~relled either for 25pressure or velocity increase. Finally, the foregoing limitations in mixing, velocity, available energy and pressure all preclude the possibility for effective high velocity discharge.

Oblique injectors of the form utilized in United States Patents Nos. 4,555,872 and 305,203,794, where air or liquid is introduced via an opening in a main conduit after or 211~7~9 before the entry of a particulate stream into the main conduit, have the chief advantage of providing for m~xim~l turbulence and good mixing. However, these effects disturb the natural flow pattern of any incoming particulate stream, thereby preventing the possibility of forming an efficient nozzle. Because of this loss of efficiency, more energy and 5 significant expense are required to achieve optimal pressures and velocities. The disturbance of the natural flow also results in regions of different velocities, thereby c~ ing particulate deposition and plugging.

As a variation of these injectors, gas or liquid injectors embodied within nozzles 10 that extend into the main conduit thereby creating a multi-nozzle system have been practised in the art (United States Patents Nos. 998,762, 4,806,171, 4,817,342). In terms of discharge effectiveness, these systems use inefficient non-venturi converging nozzles, which release an uncontrolled expanded blast pattern. This pattern tends to concentrate the bulk of the particulate matter in a central region and consequently are not suitable 15 for targeting large blast areas. The same may be said of component attachments such as are described in United States Patent No. 4,843,770, which attempt to create a wider blast area using an uncontrolled expanded blast pattern. In addition, these systems tend to plug easily due to the use of non-fluid path defining nozzle body profiles, which create regions of different velocities and depositions.
Accordingly, it is a general object of the present invention to provide a methodand apparatus for an efficient and free-flowing pressure transport of fluidized particulate streams.

It is a further object to provide a method and apparatus for an efficient and free-flowing high velocity discharge of fluidized particulate streams that produces an evenly distributed blast pattern with high energy density.

The present invention provides a fluid jet accelerator/pressurizer apparatus andmethod for efficiently and effectively accelerating and further fluidizing a fluidized stream of particulate material, e.g. ice particles and air. A discharge nozzle may be attached in series for further accelerating, concen~lalillg, or discharging the pressurized and accelerated fluidized stream against a target surface to achieve m~im~l blasting.

The fluid jet accelerator/pressurizer operates on the basis of a reduced pressure at the inlet of a main conduit in order to promote the feeding of the fluidized stream into the fluid jet accelerator/pressurizer and an increased pres~ure on the outlet side in order to compensate for subsequent transport duct resistance or to provide for increased acceleration and velocity through expansion in the high energy blast embodiment. The structures and associated functions within the fluid jet accelerator/pressurizer are designed to create differential pres~lres and diLrerelltial velocities which entrain, disperse and establish conditions for m~im~l energy transfer between the incoming fluidized stream and the blast medium, which may comprise gas, such as air, or liquifièd gas, such as liquitïed air.
The fluid jet accelerator/pressurizer comprises the main conduit and an inner blast nozzle. The inner blast nozzle is profiled to provide an aerodynamic and hydrodynamic profile. The main conduit is internally profiled to provide a first venturi nozzle prior to contact between the fluidized stream and the inner blast nozzle. The inner blast nozzle is secured by means of a fairing to the main conduit, which fairing together with the external profile of the inner blast nozzle provide a guided free-flowing flow path free of velocity dirLelelltials and plugging. A divergence and acceleration region is later created by the discontinuance of the fairing within the main conduit space. Finally, at some distance downslleam from the outlet of the inner blast nozzle, the internal profile of the main conduit is shaped to form a second venturi nozzle and acceleration region.

High pressure blast medium is delivered to the main conduit through the inner blast nozzle at sonic or greater speeds. As a result of decolllpression of the blast medium following its discharge from the inner blast nozzle, a conical flow front is formed, which extends into the second venturi nozzle, thus forming a powerful effective nozzle.

For discharge, the discharge nozzle facilitates a controlled expansion of the fluidized stream, thereby creating a more even blast pattern and promoting better kinetic 5 energy transfer between the blast medium and particulate matter and thus, promoting greater particulate discharge velocities. Without the discharge nozzle, the fluid jet accelerator/pressurizer can be used to convey and boost the fluidized stream to overcome subsequent transport duct resistance over long distances until the fluidized stream is finally discharged against the target surface.
In terms of constriction, all conduits may be built from standard pressure ratedfittings common in the refrigeration industry. The inner blast nozzle may be made from cast or m~chined metal such as brass. The fairing, external body and discharge nozzle may be cast of a variety of pourable or injectable plastic materials to provide a 15 lightweight, rigid and low thermal conduction constriction or alternatively a combination of non, and electrically conducting materials capable of neutralizing or enh:~ncing electrostatic charges of the fluidized stream.

The invention will be apparent from the following description of an embodiment 20 thereof with reference to the accompanying drawings, in which:

FIGURE 1 is a flow diagram of a particle blast cleaning and treating system, according to the present invention, wherein a wide variety of particulate matter and blast media may be used;
FIGURE 2 is a lateral sectional view of a fluid jet accelerator/pressurizer forming part of the system of Figure 1;

FIGURE 3 is an end sectional view of the fluid jet accelerator/pressurizer of Figure 2;
30 and FIGURE 4 is a fragmentary perspective view of the discharge nozzle connected in series to the fluid jet accelerator/pressurizer of Figures 2 and 3.

Referring to the drawings and in particular to Figure 1, there is illustrated a 5 particle blast cleaning and treating system designated generally by referellce numeral 1, comprising a tank 2 for m~king and/or storing blast particulate matter 3, a particle sizer 4, a particle meterer 5, a particle fluidizer 6, a fluidizing and high pressure blast medium source 7 for pre~uli~ing a blast media and supplying the blast media through a conduit 9 for fluidizing the blast particulate matter, a conduit 8 for transporting the fluidized 10 particulate stream to two fluid jet accelerator/pressurizers 19 attached in series to a discharge nozzle 50, control valves 10, and a deadman switch 11 for turning off and on the particle blast cleaning and treating system 1.

The blast particulate matter 3 is made, in the case of water ice or dry ice, or 15 stored, in the case of sand, grit or shot particles, in the particulate tank 2. This particulate matter 3 may either be delivered to the particle fluidizer 6 directly or may be sized by the particulate sizer 4 for even metering by the particle meterer 5 and then fluidized for transport. Fluidization occurs by introduction of the fluidizing blast media, which may be gas, liquified gas or liquid at a controlled pressure from the conduit 9. If 20 the fluidized particulate stream must be transported over a long distance to a target surface 18, then it is preferable that one or more fluid jet accelerator/~uressuri~er 19 be placed at one or more intermediate positions along conduit 8 to provide boost, as shown in Figure 1. Otherwise, conveyance to the final delivery outlet is f~cilit~qted by the combined action of the particle fluidizer 6 and one fluid jet accelerator/pres~uri;~er 19.
25 In any case, at the final delivery outlet of the particle blast cleaning and treating system 1, one of the fluid jet accelerator/pressurizers 19 is attached in series to a discharge nozzle 50 to allow for the delivery of an evenly di~l-il~uted large blast pattern against the target surface 18.

Figures 2 and 3 show in greater detail one of the fluid jet accelerator/pressurizers 211~709 19. The conduit 8, preferably a flexible hose, is coupled at an inlet end 21 to a main conduit forming a flow passage 22 extending through a fluid jet accelerator/pressurizer nozzle housing 20, which contains an inner blast nozzle 40. The external surface 41 of the inner blast nozzle 40 is of an efficient fusiform shape. This fusiform shape has the 5 shape of a torpedo with a "tapered tail" end facing inlet 21 and a "head" end facing outlet end 28 of the main conduit 22. A fairing 23 secures the inner blast nozzle 40 to the main conduit's inner surface 24.

The cross-sectional area of the inner surface 24 preferably converges slightly or 10 remains unchanged from the inlet 21 to an initial collvergenl-div~;lgent region or first constriction in the form of a venturi nozzle throat 25 located just before the inner blast nozzle 40. The flow passage 22 is then gradually enlarged in size to accommodate the inner blast nozzle 40 and, more importantly, to a provide a first acceleration region 26.
Further, the flow passage 22 is contoured to provide an intermediate region of constant 15 cross-sectional area between the inner surface 24 and the inner blast nozzle's external fusiform surface 41 and the fairing 23 until a point 27 prior to an outlet 44 of the inner blast nozzle 40. After this point 27, the inner blast nozzle 40 projects unsupported by any fairing towards the outlet 28 of the flow passage 22. Because the diameter of the flow passage 22 is unchanged during this projection, the cross-sectional area of space 20 between the inner surface 24 and the blast nozzle surface 41 is greater downstream from the point 27 than it is upstream from the point 27. This enlargement provides for a second divergence, and in the case of a gaseous or liquified gaseous fluidizing blast media, i.e. a compressible blast media capable of expansion, an acceleration region 29 in the flow passage 22. This arrangement creates a three-dimensional varying flow path 25 to avoid plugging and provide acceleration, mixing and even di~ ulion for a co-axial flow and system pressure. Specifically, the minimum distance between inner surface 24 of the flow passage and the outer surface of the inner blast nozzle and fairing is based on the specific particle size and the characteristics of the fluidized stream being treated, where the minilllulll preferred distance is 1.5 to 2.0 times the mean particle size 30 diameter.

There is a high pressure blast medium tube 42 which penetrates the flow passage 22 and comm~lnic~tes with a conduit 43 of the inner blast nozzle 40. The conduit 43 is co-axial with the flow passage 22. The blast media, indicated by reference numeral 48 and in gaseous or liquified gaseous form, capable of partial or whole expansion upon 5 discharge from the inner blast nozzle, is directed through the tube 42 from fluidizing media source 7. The inner blast nozzle conduit 43 is constant in diameter from the end of blast media tube 42 to a nozzle throat 45 upstream from the outlet 44 of the inner blast nozzle 40, which is followed by a liv~;lgence region in the present embodiment or, alternatively by a region of constant cross-section region (not shown). This arrangement 10 creates a venturi acceleration region or constriction 46 within the inner blast nozzle. At some distance downstream from the inner blast nozzle outlet 44, the surface 24 of passage 22 converges to a venturi nozzle throat or second constriction 30 and then diverges, forming an acceleration region 31 of the passage 22. Preferably, the blast medium 48 is forced through the nozzle throat 45 at sonic or greater speeds such that 15 supersonic speeds are achieved, thus creating an impenetrable flow front 47. Between this flow front 47 and the walls of the nozzle throat 30, an effective nozzle and a powerful induction region are formed, which serve to accelerate the fluidized particulate stream and may also reduce the size of friable particles to improve acceleration and blast impact.
The cross-sectional area of the flow passage between the main surface 41, downstream of the point 27, is greater than the ~nn~ r cross-sectional passage area defined by the wall of the second constriction 30 and the flow front 47.

Figure 4 depicts a perspective view of the discharge nozzle 50 connected in series to one of the fluid jet accelerator/pres~uliGers 19. With the discharge nozzle 50 attached in series to the fluid jet accelerator/pressurizer 19 and sufficient pressure of all flows at or after the effective nozzle there is a further e~r~n~ion and fluidic energy transfer and acceleration. This effective energy transfer from the blast medium 48 to the particles in the fluidized stream in the form of velocity assists in producing a linear strip or fan g pattern having a high and even concentration of particles for imp~ct In such an arrangement, the duct profile after initial mixing in the main conduit makes a transition from a diverging annular flow to a transversely elongate, diverging rectangular form 51.
The discharge nozzle 50 may have alternative forms, e.g. a circular, oblong or square 5 form. In this way, the flow may be accelerated to sonic or supersonic speeds with an optimum pattern. For such an expansion to occur, it is necessary that the stream speed through the effective nozzle throat is sonic, and the upstream pressures are balanced as is described below in the example for water ice. Further, the transitional nozzle profile must consider maintaining even multi-phase distribution, mixing for particle acceleration, 10 and dimensional criteria for plugging and pressure control.

A more complete understanding of the present invention can be obtained by referring to the following example of water ice or dry ice blasting of surfaces, which example is not intended to be limitative of the invention. In a conventional environment 15 of ice blasting apparatus and methodology, col~lp~ising meçh~ni~m~ for ice m:~king, ice particle sizing, metering and fluidizing or ice m~king, ice particle sizing and flu;~li7ing using high quality pres~uli~ed air (20% cold and dry air, 80% ambient air), fluid jet accelerator/pressurizers 19 are used to transport a fluidized ice particle stream over long distances to a final delivery and discharge point, and also to discharge the fluidized 20 stream against a target surface.

In the ice blasting context, from the nozzle throat 25 there is slight acceleration of the incoming fluidized stream of ice particles and air, which is fed in the range from a moderate vacuum to 15-25 psig. The resulting fluid stream is then directed along the 25 body of the inner blast nozzle 40 and the fairing 23 as a partial ~nm~l~r flow.

At the next acceleration region 29, the fluidized stream becomes a full annular flow and is again slightly accelerated. The partial and full annular flows are designed to minimi~e plugging and m~ximi7e energy transfer from the blast medium stream. The30 fairing 23 prevents the formation of velocity differentials that cause deposition and plugging.

The blast medium 48, which in this case consists of low quality cool dry air, isintroduced through the blast medium tube 42 and the inner blast nozzle conduit 43 at S 100-450 psig. At the inner blast nozzle throat 45, the air is forced to reach sonic speed.
Following this point, the blast medium decolllpres~es re~ching a supersonic speed and forms the effective nozzle. The annular fluidized stream, travelling at subsonic speed, is unable to penetrate the flow front 47 and, due to the shear and inductive forces of the flow front 47 moving at a high speed and the convergence of the surface 24 of the passage n at the nozzle throat 30, the annular fluidized stream is significantlyaccelerated and its pressure is boosted up to 15 psig or greater. The configuration of this effective nozzle is dependent upon the pro~ y of the inner blast nozzle outlet 44 to the convergence of the passage 22 at nozzle throat 31, the velocities and flows of the blast medium 48 and the fluidized stream. The ratio between the pressures and volumes of the incoming fluidized stream and the blast medium are set at a range of 1:7 to 1:35 for the pressures and 1:7 to 1:14 for the volumes. It is preferable but not necessary that the ratio of these pressures remain in this range. A low ratio will result in choking at the nozzle throat 30, a rise in upstream pressure and consequently an interference with upstream fluidization. If the ratio is too high, the inductive effect of the blast medium will be weak and excessive volumes of fluidized flow may also result in choking.
It will be understood from the foregoing description and apparent that various modifications and alterations may be made in the form, constriction and arrangement of the parts thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form herein described being merely preferred embodiments thereof.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fluid jet accelerator/pressurizer apparatus for accelerating and pressurizing a fluidized stream of particulate matter and comprising:

a nozzle housing defining a main conduit;

said main conduit forming a passage for the flow of the fluidized stream throughsaid nozzle housing;

said main conduit having, in succession in the direction of flow of the fluidized stream, an inlet end, a first constriction formed by a convergent-divergent region of said main conduit for effecting an initial acceleration of the fluidized stream, an intermediate region, a second constriction for effecting a further acceleration of the fluidized stream and an outlet end; and an inner blast nozzle in said main conduit for discharging a blast media at highspeeds through said second constriction towards said outlet end of said main conduit; said inner blast nozzle including a fairing.

2. A fluid jet accelerator/pressurizer apparatus as set forth in claim 1, in which;

said inner blast nozzle has an outlet end portion spaced from the wall of said main conduit; and said intermediate region has a cross-sectional passage area, defined by said nozzle housing, said inner blast nozzle and said fairing, which is constant along the length of said intermediate region;

said main conduit including a further passage region beyond said intermediate region and extending along said outlet end portion of said inner blast nozzle; and said further region having a greater cross-sectional passage area than the annular cross-sectional passage area defined by the wall of the second constriction and the flow front.

3. A fluid jet accelerator/pressurizer apparatus as set forth in claim 2, in which said inner blast nozzle comprises:

an external body profile of a fusiform shape for efficient guidance of the flow path of the fluidized stream; and an internal inner blast nozzle conduit for the delivery of the blast media to said main conduit in a co-axial flow, said internal inner blast nozzle conduit having an outlet and an internal convergent region along the direction of travel of the blast media and located at said outlet of said inner blast nozzle for high speed discharge of the blast media to generate a flow front impenetrable by the fluidized stream and capable of sizing friable particular matter;

said apparatus further comprising an internal blast media tube for delivery of said blast media to the inner blast nozzle conduit.

4. A fluid jet accelerator/pressurizer apparatus as set forth in claim 1, further comprising a discharge nozzle for controlling and enhancing the acceleration andexit of said fluidized stream from said main conduit towards a target surface, said discharge nozzle having a receiving end defining an opening communicating with said main conduit, a discharging end defining a transversely elongate opening, and a conduit portion connecting said receiving and discharging ends.

5. A fluid jet accelerator/pressurizer apparatus as set forth in claim 3, further comprising a discharge nozzle for controlling and enhancing the acceleration andexit of said fluidized stream from said main conduit towards a target surface, said discharge nozzle having a receiving end defining an opening communicating with said main conduit, a discharging end defining an opening, and a conduit portion connecting said receiving and discharging ends.

6. A process for accelerating and pressurizing a fluidized stream of particulate matter, comprising the steps of:

accelerating and pressurizing a fluidized stream of particulate matter through afirst passage constriction;

discharging into the accelerated fluidized stream a flow of blast media having avelocity sufficient to form, between the blast media and the fluidized stream, aflow front which is impenetrable by the fluidized stream and capable of sizing friable particulate matter; and combining a second passage constriction region with said impenetrable flow frontto produce therebetween an effective nozzle and induction region for acceleration and pressurization of said fluidized stream of particulate matter.

7. A process for accelerating and pressurizing a fluidized stream of particulatematter as set forth in claim 6, which includes passing the fluidized stream through a passage region having a cross-sectional area greater than the annular cross-sectional area defined by a wall of second constriction and the flow front.

8. A process for accelerating and pressurizing fluidized streams of particulate matter as set forth in claim 6, further comprising the step of controlling and enhancing the acceleration and exit of the fluidized stream, beyond said effective nozzle, by forming the fluidized stream into a further accelerated and evenly distributed blast pattern.

9. A process for accelerating and pressurizing fluidized streams of particulate matter as set forth in claim 8, in which said particulate matter comprises water ice.

10. A process for accelerating and pressurizing fluidized streams of particulate matter as set forth in claim 8, in which said particulate matter comprises dry ice.