AU728871B2 - Oxygen dissolver for pipelines or pipe outlets - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

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ORIGINAL

Name of Applicant: Actual Inventors: Address of Service: Invention Title: BOC Gases Australia Limited Edwin Paul Archbold and Stephen Paul Vaughan SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 "OXYGEN DISSOLVER FOR PIPELINES OR PIPE

OUTLETS"

Details of Associated Provisional Application No. PO 1290 dated 26 July 1996 The following statement is a full description of this invention, including the best method of performing it known to me/us:- -2- TECHNICAL FIELD The present invention relates generally to pipelines and more particularly to an apparatus and method for dissolving gases such as oxygen in pipelines or pipe outlets.

BACKGROUND ART In various applications involving chemical process engineering, water treatment, sewerage treatment, mineral separation and the like, it is desirable to dissolve gases such as oxygen, nitrogen, C0 2

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2 air and admixtures thereof into a fluid stream within a pipeline or pipe outlet. Numerous techniques involving injectors and other devices have been developed for this purpose. However, these suffer various disadvantages. For example, most known injectors produce excessively large oxygen bubbles within the fluid stream because of the tendency for the bubbles simply to expand adjacent the :°•eoo injection nozzles. Larger bubbles are not readily dissolved due to the relative decrease in total surface area for a given volume and so diminish the efficiency of the process.

Another disadvantage is that known oxygen injection and dissolution devices are prone to rapid wear, particularly in applications involving abrasive slurries or corrosive fluids.

This results in excessive downtime and increased expense for maintenance and repair operations. Some known injectors are also prone to clogging and are generally unserviceable without specialist equipment and expertise.

It is an object of the present invention to overcome or substantially ameliorate at least some of these disadvantages of the prior art.

DISCLOSURE OF THE INVENTION Accordingly, the invention as presently contemplated provides an apparatus for dispersing a gas into a fluid stream, said apparatus comprising a generally annular body -3disposed to define an orifice in the fluid stream, a plurality of inwardly depending apertures formed in the body for fluid communication with a supply of pressurised gas, each of said apertures defining a localised injection point for dispersion of the pressurised gas into the fluid stream, said orifice including a restricted throat section adapted progressively to reduce the effective cross-sectional flow area of the fluid downstream of said apertures, such that resultant velocity and pressure differentials enhance dissolution of the gas in the fluid.

Preferably, the body includes an annular retainer adapted to be clamped between complementary radial flanges formed on adjacent sections of a fluid pipeline.

Preferably also, the restricted throat section of the orifice is generally frustoconical in shape, converging to a neck region of minimum diameter, downstream of the .oq gas injection points. The orifice preferably diverges outwardly downstream of the neck region to the nominal inner diameter of the pipeline, either through a smooth transition section of substantially uniform curvature or a smooth frusto-conical section.

In one embodiment, the retainer is formed from stainless steel, whilst the inner surface of the throat section is formed as a replaceable ceramic insert for enhanced wear resistance and ease of replacement or repair. Alternatively, the body including the throat section, neck and transition section may be entirely constructed of a ceramic material.

The apertures are preferably defined by an array of radial passages formed in the ceramic insert, and fed from a surrounding annular manifold region formed in the stainless steel retainer. Each of the passages is between 0.5 and 5 mm and preferably around 1 mm in diameter. The spacing between the bores is preferably between 4 and 15 mm at the zone -4of largest diameter and between 2 and 10 mm at the zone of smallest diameter in the throat section.

In another aspect, the present invention provides a method for dispersing a gas into a fluid stream comprising passing said stream through conduit into an orifice having a restricted throat section which progressively reduces the effective cross-sectional flow area of the fluid from the cross-sectional area of the conduit to the cross-sectional area of a restricted neck portion downstream of said throat section and subsequently allowing said fluid to pass through said neck portion, gas being supplied to the fluid stream in said o• throat portion upstream of said neck portion by means of a plurality of localised injection 10 points wherein the resultant velocity and pressure differentials upstream and downstream of said neck portion enhance the dissolution of the gas in the fluid.

:**.Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an •inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense o 15 of "including, but not limited to".

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 is a cross-sectional side elevation showing a gas dispersing apparatus according to a first embodiment of the present invention; Figure 2 is a plan view showing the ceramic insert defining the throat section of the apparatus of Figure 1; Figure 3 is a cross-sectional side elevation of the ceramic insert of Figure 2; 4a- Figure 4 is an enlarged cross-sectional side elevation of the ceramic insert of Figures 2 and 3; Figure 5 is a cross-sectional view showing the apparatus of Figures 1 to 4, operatively positioned in a fluid pipeline; e Se o eo

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Figure 6 is a cross-sectional side elevation of a gas dispersing apparatus according to a second embodiment of the present invention; Figure 7 is an enlarged cross-sectional side elevation of section A namely the throat and neck portion of the ceramic body of Figures 6; Figure 8 is a cross-sectional side elevation of a gas dispersing apparatus of Figure 6 operatively positioned in a pipeline.

Figure 9 is a plan view showing the throat section of the ceramic body of the apparatus of Figure 6; and Figure 10 is a cross-sectional view showing the apparatus of Figures 6 to 9 operatively positioned in a fluid pipe discharge into a tank.

MODES FOR CARRYING OUT THE INVENTION Referring to Figures 1-5 of the drawings, wherein corresponding features are denoted by corresponding reference numerals, the invention provides an apparatus 1 for dissolving a gas such as oxygen into a fluid stream 2 within a pipeline 3. The apparatus comprises a main body in the form of a generally annular stainless steel retainer defining a restricted orifice 6 in the fluid stream. As best seen in Figure 5, the retainer is adapted to be clamped between complementary radial flanges 7 formed on adjacent sections 8 of the pipeline.

The orifice 6 is defined in part by a generally frusto-conical throat section 11, formed by a replaceable ceramic insert 12. The ceramic insert includes a series of radial passages 13 defining a corresponding series of inwardly depending apertures 14. These passages are fed from a surrounding annular manifold region 15 formed in the retainer The manifold region in turn is in fluid communication with a supply of pressurised oxygen, via inlet port 16 and appropriate pressurised supply lines. In this way, each aperture 14 defines a localised injection point for dispersion of the pressurised gas into the fluid stream within the throat section 11 of the orifice 6.

The converging configuration of the throat section is adapted progressively to reduce the effective cross-sectional flow area of the fluid passage toward an intermediate restricted neck region 18 of minimum diameter, downstream of the injection points.

Thereafter, the orifice diverges outwardly from the neck region through a downstream transition section 20 to the nominal inner diameter of the pipe. The transition section is generally frusto-toroidal or bell-mouthed in shape and as such defines a substantially oooo 10 uniform curvature between the neck region of the orifice and the downstream section of

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the pipe.

In the preferred embodiment, each of the passages 13 formed in the ceramic insert 12 is approximately 1 mm in diameter. The frusto-conical array of apertures is formed in 67 columns and 6 rows, giving an approximate injector spacing of5.5 mm at the largest diameter, and around 4.0 mm at the smallest diameter of the throat. The outer diameter of the throat section is preferably around 155 mm, converging to around 85 mm at the neck. It will be appreciated, however, that the apparatus may be produced in any size appropriate to the pipeline in which it is to be used.

The invention enables a high quantity of small gas bubbles to be introduced into the fluid upstream of the restricted orifice. Through the restriction, the fluid velocity increases and in accordance with the Bernoulli relationship, there is a corresponding pressure drop. This allows the small gas bubbles to expand and shear the fluid in a zone of turbulence created within the transition section 20 and downstream of the device.

This mechanism has been found to significantly enhance the rate at which gas is dissolved in the fluid stream. Furthermore, because the apertures 14 are disposed directly in the fluid path, the gas bubbles are stripped from the injection points immediately upon creation, thereby preventing the formation of excessively large bubbles. The resultant creation of a larger number of relatively small bubbles maximises the total surface area of the gas-liquid interface and thereby further enhances the rate at which the oxygen is dissolved.

*:eee Additionally, the disposition of the gas apertures on the upstream face of the restricting orifice provides a gas cushion against the slurry flow and thus reduces 10 component wear. This upstream zone is also a region of relatively high pressure, which favours gas dissolution. It will further be noted that the device makes use of positive gas supply pressure rather than inducing gas flow at atmospheric pressure. This arrangement thus makes use of the energy of compression already inherent in various sources of compressed industrial gas, to increase the rate of gas dissolution. By providing axial as distinct from centrifugal flow, the invention reduces the number and relative size of high :wear points which leads in turn to longer component life. In preferred applications, the device is not completely submerged in the process fluids and as such, allows easier access for inspection and maintenance. Furthermore, this arrangement simplifies the selection of materials and surface preparations for the external body of the device.

Finally, the use of a high wear resistant material such as ceramic for the restricting orifice provides the benefit of allowing relatively complex shapes to be manufactured with a relatively long wear life, compared for example with machined metals.

Referring now the second embodiment shown in Figures 6-9, in this embodiment the apparatus 100 is positioned in a pipeline 300 for dissolving a gas such as oxygen in a fluid stream 200 passing through the pipeline. The apparatus comprises a main replaceable ceramic body 112 which defines a frusto-conical throat section 111, a transition section 120 which is also generally frusto-conical in shape and a restricted neck region 118 therebetween. The ceramic body 112 includes a series of radial passages 113 defining a corresponding series of inwardly depending apertures 114.

These passages are fed from a surrounding annular retainer ring 116 and appropriate pressurised gas supply lines (not shown). In this way, as with the embodiment shown in Figures 1-5, each aperture 114 defines a localised injection point for dispersion of the pressurised gas into the fluid stream 200 within the throat section 111 and upstream of neck region 118.

The embodiment shown in Figures 6-9 differs from the embodiment of Figures in that the ceramic body 112 includes both the upstream frusto-conical throat section 111 and downstream transition section 120. It is also preferred that this downstream transition section 120 is extended further down the pipeline 300 to provide a more gradual divergence from the effective cross-sectional flow area of neck region 118 to the effective cross-sectional flow area of the conduit 300. In this way the transition section 120 defines a smooth gradual expansion thereby reducing cavitation and turbulence downstream of the neck region 118.

As will be understood by persons skilled in the art, the long tapered walls of transition section 120 also serve to provide support for throat section 111. To explain, there is considerable force applied by the fluid stream to the throat section 111. The applicant has found that the ceramic throat section 111 may fail if it is not provided with sufficient support. Not only does transition section 120 provide a smoother divergent section for the fluid stream and dissolved gas, thereby reducing turbulence, it also serves to provide a more reliable support for throat section 111.

In the embodiment shown in Figures 1-5, 6 rows and 67 columns of apertures were provided in the throat section 111. In the embodiment shown in Figures 6-10, 3 rows with 36 columns are provided with an approximate injector spacing with 10 mm at the largest diameter and 8 mm at the smallest diameter of the throat section 111. Each of the passages 113 formed in the ceramic body 112 is approximately 1 mm in diameter. The 6•co outer diameter of the throat section 111 is preferably around 140 mm converging to around 85 mm at the neck. The transition section 120 is approximately 300 mm long and the throat section 111 approximately 50 mm. Once again, however, as discussed in regard to the embodiment of Figures 1-5 the apparatus may be produced in any size appropriate to the pipeline in which it is used.

00015 The ceramic body 112 may be attached to the pipeline 300 by any appropriate mechanism. The pipeline flange 310 serves to position an attached throat section in the pipeline. An appropriate gasket 311 is preferably positioned between the flange 310 and the retainer ring 116. Glue or similar 320 may be used to fix transition section 120 to the interior wall of the pipe 300.

If desired, to further reduce wear on the interior wall of pipeline 300, a wear-resistant lining 330 may be included in the pipeline. This lining, which may be produced from rubber for example, is particularly useful where the fluid stream is highly erosive and corrosive.

As discussed above, the present invention is particularly suitable for use in pipeline but may also be used with a pipeline discharge. Figure 10 shows inventive apparatus 100 installed adjacent a pipe discharge 350. This discharge 350 may, for example, feed the fluid stream after it has been dosed with the appropriate quantity of gas into an open tank (not shown). The pressure drop in the fluid stream between the inventive apparatus 100 and the tank, which would be at atmospheric pressure, will cause the gas to come out of the solution in the form of fine bubbles thereby increasing the agitation and oeooo mixing in the tank as well as increasing the surface contact area between the gas and slurry.

Preferably, the pipe discharge 350 includes a flow constriction means 360. In the embodiment shown this flow constriction means 360 is provided by another restricted throat section which reduces the effective cross-sectional flow area at the pipe discharge •350. This constriction means serves two purposes. Firstly, by reducing the effective cross-sectional flow area it maintains the slurry/gaseous mixture at an elevated pressure 15 in the pipeline 300 such that once the mixture leaves the pipeline discharge 350 the pressure is substantially reduced and the gas comes out of solution.

The applicants have found, however, that the flow constriction means 360 also serves to reduce vibration of the pipe discharge 350. To explain, the section of pipe 300 downstream of the inventive apparatus 100 tends to vibrate or oscillate in response to the speed and pressure of the fluid flowing therethrough. The applicants have found that by providing a flow constriction means at the pipe discharge 350, the pipe 300 does not vibrate to such a great extent. The constriction means 360 may be the simple throat -11section shown in Figure 10 or alternatively a valve arrangement for controlling flow of the fluid through the pipe discharge 350.

As mentioned above, the embodiment shown in Figure 10 may be used to feed a fluid such as a slurry to a tank. Generally such tanks contain an impeller and in a particularly preferred embodiment the pipe discharge 350 is positioned at approximately of the radius of the tank impeller to thereby take advantage of the maximum downdraft from the impeller.

*oooo S. •The applicants have noted a substantial increase in the dissolved gas content of the fluid in the tank using the fluid discharge configuration shown in Figure 10 For example, using the inventive apparatus for dissolving oxygen in an ore slurry, the inventive apparatus uses 0.05-0.1 m 3 of oxygen per tonne of ore to achieve a dissolved oxygen level of 20 ppm. This can be compared with previous consumption °••using conventional lances, normally in the form of 4 x 2 mm nozzles, which uses 0.3 m 3 of oxygen per tonne of ore to achieve a dissolved oxygen content of 19 ppm.

15 Other advantages of the invention include a cheaper capital cost as compared with prior art devices, reduced wear, less maintenance, easier serviceability, more efficient mixing, and a greater resistance to blockages. Moreover, the invention is adaptable to a wide range of applications including mineral extraction, water treatment, sewerage treatment, slurry pumping and the like. Accordingly, the invention represents a commercially significant improvement over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (14)

1. An apparatus for dispersing a gas into a fluid stream flowing through a conduit comprising a generally annular body disposed to define an orifice in the fluid stream, said orifice including a restricted throat section adapted to progressively reduce the effective cross-sectional flow area of the fluid from the cross-sectional area of the conduit to the cross-sectional area of a neck portion downstream of said throat section, and a plurality of inwardly depending apertures formed in said throat section in fluid communication with a supply of pressurised gas, each of said apertures defining a localised injection point for dispersion of the pressurised gas into the fluid S. stream upstream of said neck portion, whereby the resultant velocity and pressure differentials in the fluid upstream and downstream of said neck portion enhance dissolution of the gas therein. S• 2. An apparatus according to claim 1, wherein the body includes an annular °00oo retainer adapted for clamping between complementary radial flanges formed on l: adjacent sections of a fluid pipe line.

3. An apparatus according to claim 1 or claim 2, wherein the restricted throat section of the orifice is generally frusto-conical in shape, converging to a neck region of minimum diameter, downstream of the gas injection points.

4. An apparatus according to any one of the preceding claims, wherein the orifice diverges outwardly downstream of the neck region to a nominal inner diameter of the pipe line through a generally smooth transition section of substantially uniform curvature in cross-sectional profile. An apparatus according to any one of the preceding claims, wherein the inner surface of the throat section is defined by a replaceable wear resistant insert. -13

6. An apparatus according to claim 5, wherein the retainer is formed from stainless steel, and/or the replaceable insert is formed from a ceramic material.

7. An apparatus as claimed in any one of claims 1-6 wherein the orifice diverges outwardly downstream of the neck region to the nominal inner-diameter of the pipeline through a generally smooth frusto-conical transition section.

8. An apparatus as claimed in any one of the previous claim wherein the throat section, neck and transition section are all formed from a ceramic material.

9. An apparatus according to any one of the previous claims wherein said apertures are defined by an array of radial passages formed in the throat section.

10. An apparatus according to claim 9, wherein each of said passages is between 0.5 mm and around 5 mm in diameter. S: 11. An apparatus according to claim 10, wherein each of said passages is around 1 mm in diameter. o: •o12. An apparatus according to claim 11, wherein the spacing between the radial o. passages is between 4 and 15 mm at a zone of largest diameter and between 2 and mm at a zone of smallest diameter in the throat section.

13. A method for dispersing a gas into a fluid stream comprising passing said stream through conduit into an orifice having a restricted throat section which progressively reduces the effective cross-sectional flow area of the fluid from the cross-sectional area of the conduit to the cross-sectional area of a restricted neck portion downstream of said throat section and subsequently allowing said fluid to pass through said neck portion, gas being supplied to the fluid stream in said throat portion upstream of said neck portion by means of a plurality of localised injection -14- points wherein the resultant velocity and pressure differentials upstream and downstream of said neck portion enhance the dissolution of the gas in the fluid.

14. A method as claimed in claim 1 wherein directly downstream of said neck portion, said fluid stream is passed through a divergent portion which diverges outwardly to increase the effective cross-sectional flow area of the fluid from the cross-sectional area of the neck portion to said conduit cross-sectional area. A method as claimed in claim 13 or 14 wherein gas is supplied to said localised injection points under pressure.

16. A method as claimed in any one of claims 13-15 wherein said fluid is maintained at an elevated pressure after it passes through said neck portion to retain said gas in solution.

17. A method as claimed in claim 16 wherein said pressure is maintained in said conduit downstream of said neck portion by means of a flow restriction device a- downstream of said neck portion.

18. An apparatus for dispersing a gas into a fluid stream substantially as herein before described with reference to the accompanying drawings.

19. A method for dispersing a gas into a fluid stream substantially as herein before described with reference to the accompanying drawings. Dated this 8th day of November 2000 BOC GASES AUSTRALIA LIMITED Attorney: PAUL G. HARRISON Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS