WO2013106910A1

WO2013106910A1 - Atomizing nozzle for slurries that prevents solids build-up and method of using

Info

Publication number: WO2013106910A1
Application number: PCT/CA2013/000035
Authority: WO
Inventors: Gordon P. Janes
Original assignee: Turbosonic Inc.
Priority date: 2012-01-17
Filing date: 2013-01-17
Publication date: 2013-07-25

Abstract

An atomizing nozzle is provided for mixing together air and aqueous media, such as lime slurries, comprising a generally cylindrical body having an upstream inlet for the aqueous media and a downstream outlet and a generally cylindrical bore extending from the upstream inlet through a mixing chamber to the downstream outlet to terminate in an unobstructed orifice. A plurality of bores is provided through a wall of the cylindrical body into fluid flow communication with the mixing chamber to convey air from a source thereof to the mixing chamber to mix therein with the aqueous media to form a mixture to be conveyed from the mixing chamber to the orifice. The cylindrical bore has substantially the same diameter from the mixing chamber to the orifice and the ratio of the total cross-sectional areas of the plurality of bores to the cross-sectional area of the orifice is less than 1.

Description

TITLE OF INVENTION

ATOMIZING NOZZLE FOR SLURRIES THAT PREVENTS SOLIDS BUILD-UP

AND METHOD OF USING

REFERENCE TO RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. 119.( e) from US

Provisional Patent Application No. 61/587,263 filed January 17, 2012.

FIELD OF INVENTION

[0002] The present invention is concerned with a design of spray nozzle, sometimes referred to as an "Effervescent Atomizer", where liquid flows through a central passage into a chamber and air is mixed into the water flow through a series of axial holes drilled through the side wall of the chamber, and the combined spray is then ejected from the chamber through an orifice.

BACKGROUND TO THE INVENTION

[0003] When spraying liquids containing slurries, these designs typically experience a small amount of liquid that crosses from the liquid side of the chamber over to the air side of the insert through the air passages or holes, and deposits salts and suspended solids onto these surfaces, eventually restricting the air flow passage and impairing nozzle performance. Such designs often require frequent cleaning of the internal chambers, either by on-line methods or by removing the nozzle from service.

[0004] The mechanism within the insert that creates this problem of cross-over flow is complex, but some aspects of it include:

- Turbulence generated in the side air passages at the interface of air and liquid, that entrains small amounts of liquid into the air chamber;

- Pulsations and back pressure in the mixing chamber caused by downstream injected air bubbles in the mixture;

- Interaction of flow patterns between adjacent air injection passages or injection passages in series in the nozzle.

[0005] While it has been generally recognized that the problem of solids deposition on the side of the air holes is a result of liquid crossover, several attempts at solving the issue have been relatively ineffective. Such approaches include: - Angling of the side air holes in the direction of flow

- Process design to minimize line pulsations (ie: pulsation dampeners on pumps)

- Chemical treatment of the water to minimize scale formation

- Changing hole patterns.

[0006] A search of the prior art has been conducted with respect to the spraying nozzle design provided herein and the following U.S. patents have been located as the closest prior art: Patent Application Nos. US 2009/0071303, 2011/012347 and 2012/02211535 and US Patent Nos. 4,421,787; 4,819,838; 5,025,939; 5,176,325; 5,372,312 and 5,474,435.

SUMMARY OF THE INVENTION

[0007] In accordance with one aspect of the present invention, a modification of the design that successfully and significantly reduces the accumulation of scale or particulate buildup on the air side of the atomizing chamber is made, to include one or more of the following changes:

1 ) Reducing the overall number of air holes drilled;

2) Changing the diameter of the holes so that the ratio of the total area of the air holes to the total area of the orifice is less than about 1.0, preferably less than about 0.8;

3) Reducing the number of rows of holes and offsetting holes in each row

sufficiently such that no air hole is in line with another, nor falls in-line with the flow path generated by the preceding air hole;

4) Reducing the total cross-section of air holes drilled in order to sufficiently increase the velocity of air in the hole passages (air velocity through the holes between about 150 and 750 feet per second);

5) Reducing the total cross-section of air holes drilled in order to sufficiently increase the pressure drop of air flow through the side hole passages,

6) Changing the size of the holes in sequential rows;

7) Changing the shape of the hole to be not round; ie: elongating the air hole drilling; and

8) Increasing the length of the air hole passage by increasing the wall thickness of the insert.

[0008] In accordance with one aspect of the present invention, there is provided an atomizing nozzle for mixing together air and aqueous media including slurries, which comprises: a generally cylindrical body, the cylindrical body having an upstream inlet for said aqueous media and a downstream outlet and a generally cylindrical bore extending from the upstream inlet through a mixing chamber to the downstream outlet to terminate in an unobstructed orifice, and a plurality of bores through a wall of the generally cylindrical body into fluid flow communication with the mixing chamber to convey air from a source thereof to the mixing chamber to mix therein with the aqueous media to form a mixture to be conveyed from the mixing chamber to the orifice, said plurality of bores being circumferentially spaced such that no two bores are radially aligned, the generally cylindrical bore having substantially the same diameter from the mixing chamber to the orifice, the ratio of the total cross-sectional area of the plurality of bores to the cross-sectional area of the orifice being less than about 1.

[0009] The ratio of the total cross-sectional area of the plurality of bores to the cross-sectional area of the orifice is preferably less than about 0.8.

[0010] In the nozzle, the plurality of bores preferably number three or five bores arranged equally circumferentially spaced apart.

[0011] The plurality of bores may be arranged in at least one row of bores. In particular, the plurality of bores may be arranged in two axially-spaced apart rows, for example, two rows of three equally circumferentially spaced apart bores with the bores in the radially-spaced apart rows being circumferentially off-set one from the other. [0012] In accordance with a preferred aspect of the present invention, there is provided an atomizing nozzle for mixing together and spraying air and aqueous media including slurries, which comprises: a generally cylindrical body, the generally cylindrical body having an upstream inlet or the aqueous media and a downstream outlet and a generally cylindrical bore extending from the inlet through a mixing chamber to the outlet to terminate in an unobstructed orifice, a single line of equally circumferentially spaced bores radially extending through a wall of the cylindrical body to fluid flow communicate with the mixing chamber to convey air from a bore thereof to the mixing chamber therein with the aqueous media to form a mixture to be conveyed from the mixing chamber to the orifice, the plurality of bores being circumferentially spaced so that no two bores are radially aligned, the cylindrical bore having substantially the same diameter from the mixing chamber to the orifice, the ratio of the total cross-sectional area of the plurality of bores to the total area of the orifice being less than about 1.

[0013] In this preferred embodiment of the invention, that plurality of bores in the line of bores are number three or five equally circumferentially spaced apart.

[0014] The invention further includes a method of utilizing the nozzles provided herein to reduce the build-up in nozzles used to spray lime slurries, such as lime slurries in SDA plants, so as to increase service time between cleaning operations. Accordingly, in another aspect of the present invention, there is provided a method of utilizing a nozzle to form an atomized spray of slurry, wherein the nozzle comprises: a generally cylindrical body, the cylindrical body having an upstream inlet for said slurry and a downstream outlet and a generally cylindrical bore extending from the upstream inlet through a mixing chamber to the downstream outlet to terminate in an unobstructed orifice, and a plurality of bores through a wall of the generally cylindrical body into fluid flow communication with the mixing chamber to convey air from a source thereof to the mixing chamber to mix therein with the slurry to form a mixture to be conveyed from the mixing chamber to the orifice, the cylindrical bore having substantially the same diameter from mixing chamber to the orifice, the ratio of the total cross-sectional area of the plurality of bores to the cross-sectional area of the orifice being less than about 1 , which comprises feeding said slurry to said mixing chamber at a velocity of about 3 to about 30 ft/sec, feeding the air to said mixing chamber at a velocity of about 150 to about 350 ft/sec, forming in the mixing chamber an atomized mixture of air and slurry having a velocity of about 50 to about 400 ft/sec, and discharging the atomized mixture through the orifice.

[0015] In this method, the slurry preferably is fed to the mixing chamber at a velocity of about 5 to about 20 ft/sec, the air is preferably fed to the mixing chamber at a velocity of about 300 to about 600 ft/sec and the atomized mixture preferably has a velocity of about 120 to about 280 ft/sec.

BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 shows a typical prior-art design of nozzle (Fig. 1 A) and a modified design (Fig. 1 B) in accordance with one embodiment of the invention;

[0017] Figure 2 shows buildup on a typical prior-art nozzle design (Fig. 2A) in comparison to a modified design provided in accordance with one embodiment of the invention (Fig. 2B);

[0018] Figure 3 shows a variety of modified nozzle designs which have been prepared to attempt to alleviate the buildup problem in prior-art nozzle designs; [0019] Figure 4 A is a longitudinal sectional view of a further embodiment of a nozzle according to the invention;

[0020] Figure 4B is a cross-sectional view along line A-A of Figure 4A; and

[0021] Figure 5 shows the build-up, after 24 hours of operation of a typical prior art nozzle design (Figure 5A) in comparison to the modified design of Figures 4A and 4B as provided in accordance with one embodiment of the invention (Figure 5B).

DESCRIPTION OF PREFERRED EMBODIMENT

[0022] In the drawings, Figure 1 A shows a typical prior art design of nozzle in which many openings are employed to achieve mixing of air and liquid and the ratio of the total area of air holes to total area of orifice is greater than 1.0. Figure 2A shows the buildup of lime slurry deposits after 24 hours of operation of the nozzle of Figure 1A.

[0023] As seen therein, the nozzle comprises a substantially cylindrical body with an axial bore extending from an upstream inlet for the liquid, such as a lime slurry, through a mixing chamber to a downstream outlet. A plurality of radial bores through the side wall of the cylindrical body communicate with a source of air to mix with the liquid in the mixing chamber to form an atomized spray which is transported to the downstream orifice.

[0024J As shown schematically in Figure 1 A, slurry cross over into the air chamber causes solids deposits on the bores, gradually blocking the holes.

[0025] Figure IB shows a nozzle design in accordance with one embodiment of the invention, where there are three equally circumferentially spaced bores only provided in a single line and the ratio of the total area of the air holes to the total area of the orifice is less than about 1.0, preferably less than about 0.8. The equal circumferentially spacing of the bores ensure that no two bores are radially aligned. Figure 2B shows the dramatic difference, compared to Figure 2A, in solids buildup of deposits on this nozzle design after 24 hours of operation. [0026] As seen in Figure IB, a nozzle 10 according to an embodiment of the invention utilizes three equally circumferentially-spaced radial bores 12 to convey air to the mixing chamber 14 to mix together with the liquid from inlet 15 to form an atomized spray 16 leaving the orifice 18. The radial bores 12 and the orifice 18 are configured so that the ratio of the total cross-sectional area of the bores 12 and the cross-sectional area of the orifice 18 is about 1.0 or less, preferably less than 0.8.

[0027] Figure 3 illustrates a variety of alternative nozzle designs which have been tested in attempts to alleviate the solids buildup problem when spraying slurries. None of these alternative designs utilized the critical parameter of the ratio of the total area of the air holes to the total area of the orifice is less than about 1.0, preferably less than about 0.8. None of these designs was successful.

[0028] Figures 4A and 4B show respectively longitudinal and cross-sectional views of a further nozzle 10' provided in accordance with another embodiment of the invention. The structure of the nozzle 10' is the same as that shown in Figure IB, except that there are employed five equally circumferentially-spaced radial bores 12' in a single row to permit air to flow to the mixing chamber 14' to form the atomized spray of air and liquid which is discharged from the unobstructed orifice 18'. As in the case of the Figure IB embodiment, the ratio of the cross-sectional area of the radial bores 12' to the cross-sectional area of the unobstructed orifice is about 1.0 or less, preferably less than about 0.8.

[0029] Figure 5 shows the dramatic difference in solids build-up of deposits of the nozzle design of Figures 4A and 4B (Figure 5B) as compared to the conventional nozzle design of Figure 1 (Figure 5A), after 24 hours of operation. EXAMPLES

Example 1 :

[0030] A number of experimental nozzle designs has been tested in commercial

SDA units employing lime slurry atomizing. In each case, the time to plugging of the nozzle, and hence the necessity to engage in a nozzle cleaning operation, was observed. The relevant data is contained in the following Table I:

[0031] As can be seen from this Table, only when the ratio of the total area of the air holes to the total area of the orifice was less than about 1.0 was long term

effectiveness between cleaning cycles observed.

SUMMARY OF THE DISCLOSURE

[0032] In summary of this disclosure, an improved design of nozzle is used to mix air and liquid, particularly lime slurry, with a lesser accumulation of scale or particulate buildup. Modifications are possible within the scope of the invention.

Claims

CLAIMS What I claim is:

1. An atomizing nozzle for mixing together air and aqueous media including slurries, which comprises: a generally cylindrical body, said cylindrical body having an upstream inlet for said aqueous media and a downstream outlet and a generally cylindrical bore extending from said upstream inlet through a mixing chamber to the downstream outlet to terminate in an unobstructed orifice, and a plurality of bores through a wall of said generally cylindrical body into fluid flow communication with said mixing chamber to convey air from a source thereof to said mixing chamber to mix therein with said aqueous media to form a mixture to be conveyed from the mixing chamber to the orifice, said plurality of bores being circumferentially spaced such that no two bores are radially aligned, said generally cylindrical bore having substantially the same diameter from the mixing chamber to the orifice, the ratio of the total cross-sectional area of said plurality of bores to the cross-sectional area of the orifice being less than about 1.

2. The nozzle of claim 1 wherein the ratio of total cross-sectional area of said plurality of bores to the cross-sectional area of the orifice is less than about 0.8.

3. The nozzle of claim 1 wherein said plurality of bores number three or five bores arranged equally circumferentially spaced apart.

4. The nozzle of claim 2 wherein said plurality of bores number three or five bores arranged equally circumferentially spaced apart.

5. The nozzle of claim 1 wherein said plurality of bores are arranged in at least one row of bores.

6. An atomizing nozzle for mixing together and spraying air and aqueous media including slurries, which comprises: a generally cylindrical body, said generally cylindrical body having an upstream inlet for said aqueous media and a downstream outlet and a generally cylindrical bore extending from said inlet through a mixing chamber to the outlet to terminate in an unobstructed orifice, a single line of equally circumferentially spaced bores radially extending through a wall of said cylindrical body into fluid flow communication with the mixing chamber to convey air from a source thereof to said mixing chamber to mix therein with the aqueous media to form a mixture to be conveyed from the mixing chamber to the orifice, said plurality of bores being circumferentially spaced such that no two bores are radially aligned, said cylindrical bore having substantially the same diameter from the mixing chamber to the orifice, the ratio of the total cross-sectional area of the plurality of bores to the total area of the orifice being less than about 1.

7. The nozzle of claim 6 wherein the plurality of bores number three bores equally circumferentially spaced apart.

8. The nozzle of claim 6 wherein the plurality of bores number five bores equally circumferentially spaced apart.

9. A method of utilizing a nozzle to form an atomized spray of slurry, wherein the nozzle comprises a generally cylindrical body, said cylindrical body having an upstream inlet for said slurry and a downstream outlet and a generally cylindrical bore extending from said upstream inlet through a mixing chamber to the downstream outlet to terminate in an unobstructed orifice, and a plurality of bores through a wall of said generally cylindrical body into fluid flow communication with said mixing chamber to convey air from a source thereof to said mixing chamber to mix therein with said slurry to form a mixture to be conveyed from the mixing chamber to the orifice, said cylindrical bore having substantially the same diameter from the mixing chamber to the orifice, the ratio of the total cross-sectional area of said plurality of bores to the cross-sectional area of the orifice being less than about 1 , which comprises feeding said slurry to said mixing chamber at a velocity of about 3 to about 30 ft/sec, feeding said air to said mixing chamber at a velocity of about 150 to about 350 ft/sec, forming in said mixing chamber an atomized mixture of air and slurry having a velocity of about 50 to about 400 ft/sec, and discharging the atomized mixture through said orifice.

10. The method of claim 9, wherein said slurry is fed to the mixing chamber at a velocity of about 5 to about 20 ft/sec, said air is fed to the mixing chamber at a velocity of about 300 to about 600 ft/sec, and said atomized mixture has a velocity of about 120 to about 280 ft/sec .

11. The method of claim 9, wherein said slurry is a lime slurry.