Jet Aeration and Mixing Nozzle

Field of the invention

[001] The present invention relates to an improved jet nozzle suitable for aspirating or mixing multi-component substances.

Background of the invention

[002] Waste liquid streams including, but not limited to, industrial waste, contaminated waste water and sewage are commonly treated before discharge into the environment. In many cases, this treatment involves placing the liquid into pondage or tanks to allow the consumption of the organic material by aerobic bacteria. For the aerobic bacteria to live in this liquid body, it is often necessary to introduce oxygen into the liquid by aeration. If there is insufficient oxygen in the liquid, then anaerobic bacteria may develop leading to unwanted odours.

[003] One method of aeration uses surface mounted mechanical aerators that physically mix liquid and air at the free surface. The disadvantages of mechanical aerators include that they typically only provide aeration at the free surface limiting the gas enrichment of the liquid body, and they use moving parts, reducing their reliability and increasing susceptibility to wear and tear.

[004] It is preferable to provide aeration of the liquid at the bottom of the liquid body as it allows longer contact of the introduced air with the liquid, increasing the amount of oxygen which is dissolved into the liquid and available to the bacteria. This has been achieved in the prior art by supplying air under pressure to a porous medium or to jet aeration nozzles. US patent no 2,479,403 describes an early jet aeration system.

[005] Jet aeration is considered generally to be more energy efficient than diffusion or surface aeration. Jet aeration systems operate by pumping the waste water through submerged nozzles or tubes with openings through which air or other gas is entrained or pumped into the tubes to create turbulent mixing with the waste water by means of the Venturi principle. This aspirating technology simultaneously moves large volumes of high kinetic energy liquid and air through one or more jet nozzles. The high velocity liquid exits the inner, primary jet and rapidly mixes with the incoming air in the outer jet. This intense mixing and the high degree of turbulence in the gas/liquid cloud that travels outward from the jet along the basin floor leads to significant amounts of oxygen being dissolved into the liquid prior to the vertical rise of the gas bubble column to the liquid surface.

[006] US patent no 4,210,534 (Molvar) describes an improved system for mixing a gas such as oxygen or air with waste water in a body of waste water. Molvar describes a multiple stage nozzle system that increases the amount of gas dissolved into the liquid stream with little increase in the power increasing the efficiency of the overall system.

[007] Despite the increase in efficiency afforded by multiple stage nozzle systems, such as Molvar, the prior art jet aeration systems require the aeration gas to be supplied under pressure in order to overcome the static pressure of the liquid being aerated. Supplying gas to the nozzle under pressure necessitates the provision of an aeration pump or blower which increases both the capital and operating cost of the installation.

[008] Furthermore, the more efficient aeration systems maximise the time the aerating gas is in contact with the liquid so that the deeper the placement of the aeration system in the vessel, the more efficient the system. However, increasing the depth of the aeration system in the liquid vessel has a significant impact on the cost and power of the aeration pump or blower supplying the aerating gas, that is, the deeper the system, the larger the pump required. Accordingly, there is a need for a jet aeration system which minimises its reliance on an aeration pump or blower or reduces the size of the pump required.

[009] In addition to dealing with waste water, industry often needs to mix large quantities of liquids in order to maintain their homogeneity. Examples include paint, milk and other multi-component substances. Traditionally, the homogeneity of these liquids is maintained through the use of mechanical agitators, that is, impellers driven by some form of rotary drive including electric motors, to overcome stratification or settling of the component phases. The use of mechanical agitators increases energy and maintenance costs. There are mixing systems which use jet nozzles but these systems rely on Venturi geometry to mix the liquid locally by introducing a turbulent jet and entrainment of local fluids. These jet nozzle systems do not mix liquids from different levels in the tank. There is also a need for a system which reduces the energy and maintenance costs involved in mixing large quantities of liquids.

Summary of the Invention

[010] The present invention relates to an improved jet nozzle suitable for the purpose of aspirating and/or mixing multi-component substances. For example, by introducing gas or liquid sampled at the free surface or any other depth of the liquid body intermediate the surface and the nozzle and combining it with liquid at the nozzle depth. Surprisingly, the nozzle of the invention, depending on the application, is not reliant on an aeration pump or blower (ie is self-aspirating) or is able to achieve similar results to existing systems using a smaller pump than that used in existing systems.

[011 | According to one aspect of the invention, there is provided a multiple stage jet nozzle comprising:

(a) an outer housing;

(b) a first nozzle-shaped stage comprising a convergent outlet which discharges a first fluid, wherein the convergent outlet has an internal taper in the range of from 15 to 20 degrees with a reduction of cross-sectional area over the taper of between 40 and 60%;

(c) a second nozzle-shaped stage located coaxially with the first nozzle-shaped stage, wherein the second nozzle-shaped stage has a tapered inlet and a substantially parallel bore of a diameter substantially equivalent to the exit diameter of the convergent outlet of the first nozzle-shaped stage;

(i) wherein the inlet tapers so that the parallel bore of the second nozzle- shaped stage commences at a distance from the outlet of the first nozzle-shaped stage which is between 1 and 2 times the exit diameter of the convergent outlet of the first nozzle-shaped stage; and

(ii) wherein the parallel bore of the second nozzle-shaped stage extends downstream for a distance which is between 2 and 3 times the exit diameter of the convergent outlet of the first nozzle-shaped stage; (d) a mixing chamber formed within the outer housing pipe between the outlet of the first nozzle-shaped stage and the inlet of the second nozzle-shaped stage; and

(e) a convergent annular passage formed between the outer housing pipe and an exterior surface of the first nozzle-shaped stage enabling entry of a second fluid into the mixing chamber.

[012] The multiple stage jet nozzle is suitable for use in aspiration systems and systems for mixing a multi-component substance to maintain or improve its homogeneity (eg liquids and suspended solids).

[013] According to a further aspect of the invention, there is provided a system for aspirating a first fluid body with a second fluid, eg ambient air, the system comprising at least one multiple stage jet nozzle according to the invention.

[014] According to a further aspect of the invention, there is provided a system for mixing a multi-component substance to maintain or improve its homogeneity, the system comprising at least one multiple stage jet nozzle according to the invention.

[015] According to a further aspect of the invention, there is provided a system for perfusing a first fluid body with a second fluid, the system comprising at least one multiple stage jet nozzle according to the invention.

[016] In a preferred embodiment, the system comprises a plurality of multiple stage jet nozzles according to the invention.

[017] In a preferred embodiment, the exit diameter is in the range of 10mm to 20mm. Preferably, the exit diameter is 14mm.

[018] The geometry of a preferred embodiment of present invention enables the multiple stage jet nozzle to operate without the need for a pump to introduce the second fluid (gas or another liquid mixture) into the nozzle under pressure. The second fluid enters the multiple stage jet nozzle by means of a connecting pipe terminating at a fixed point above or floating on the free surface for aeration systems, or terminating at a point in connection with the second liquid mixture for mixing systems. [019] As the first fluid is forced through the first nozzle-shaped stage (using a pump), the velocity of the first fluid is accelerated, lowering the pressure, and creating a zone of low pressure in the mixing chamber. The low pressure zone causes the second fluid to be drawn down through the annular passage into the mixing chamber. In the mixing chamber, the first fluid and second fluid are combined into a liquid jet (containing fine bubbles in the case of aeration) which shoots through the second nozzle-shaped stage. This drawing of a second fluid (whether gas or liquid) by suction into a vessel containing a first fluid is referred to as "aspiration".

[020] The advantage of this invention over the prior art is that it allows the use of a smaller pump for the second fluid, and in some embodiments elimination of the pump (or blower) entirely, with a reduction in capital cost and reduced system complexity. For example,

• in typical waste water circumstances, with the nozzle placed at a depth of 3 to 4 metres, a system comprising nozzles according to the invention would usually be self-aspirating;

• where an increased rate of aspiration is desired, a blower or pump may be used which would be smaller and at a lower cost than the pumps required to achieve the same rate of aspiration in a prior art system. The blower or smaller pump can also allow for easier maintenance and replacement compared with the larger pumps required for use with prior art systems; and

• if a system comprising nozzles according to the invention was to be used at a depth greater than 4.5 metres, then a blower or smaller pump may be used to increase the air flow rate, which would be smaller and at a lower cost than the pumps required to operate a prior art system at the same depth.

[021] By minimizing or eliminating the pump, it is possible to reduce capital costs, operational expenses and assist maintenance, as well as allowing the use to realise significant energy savings. The pressure pump used in the prior art systems needs to provide sufficient air pressure to overcome the hydrostatic pressure of the water to achieve the desired level of aeration. In contrast, any use of a blower or pump in a system using a nozzle according to the invention is directed to increasing air flow, not pressure.

[022] The system according to the invention when mixing multi-component substances enables the mixing of fluid from different levels of the fluid body (including the free surface). This is in contrast to the prior art systems which only provide mixing at the nozzle level.

Brief description of the drawings

[023] Figure 1 shows a representation of an aspirating system according to the prior art.

[024] Figure 2 shows a sectional view of a multi stage jet nozzle according to one embodiment of the present invention.

[025] Figure 3 shows a perspective view of a multi stage jet nozzle according to an embodiment of the present invention.

[026] Figure 4 shows a second view of the multi stage jet nozzle of Figure 3.

[027] Figure 5 shows a tank containing an aeration system that includes a number multi stage jet nozzles according to an embodiment of the present invention.

[028] Figure 6 shows a top view of the tank of Figure 5.

[029] Figure 7 shows a side view of the tank of Figure 5.

Detailed Description of an Embodiment

Comparative example

[030] Nozzle configurations in the prior art, such as that shown in Figure 1, may appear similar to the present invention in structure, but to date none has proven to be self-aspirating and they all necessarily require a pump, fan, or blower to supply air under pressure to the nozzle assembly. A nozzle was prepared according to the description in Molvar and was determined to not be self-aspirating. To be used in an aspirating system, a nozzle according to Molvar needs to be used with a pump for the second fluid which is similar to pumps used in existing systems.

Example according to the invention

[031] Figure 2 shows a sectional view of a preferred embodiment of a multistage self- aspirating nozzle of the present invention.

[032] The nozzle 20 in Figure 2 comprises a first nozzle-shaped stage 13 and a second nozzle-shaped stage 16 mounted inside an outer housing 14. The first nozzle-shaped stage 13 comprises a substantially parallel bore terminating in a convergent outlet 11 having an exit diameter D. The taper of the convergent outlet 11 of the first nozzle-shaped stage is typically in the range of 15 to 20 degrees to reduce the cross-sectional diameter from 2D to the exit diameter D over a streamwise distance of 2D. The wall thickness of the first nozzle- shaped stage 13 is such that both the internal and external diameters of the nozzle taper concurrently.

[033] The placement of the first nozzle-shaped stage 13 and second nozzle-shaped stage 16 is such that each is coaxial with the streamwise axis of the assembly. The relative diameters of the outer housing 14 and the first nozzle-shaped stage 13 are such that they form a divergent annular duct 15 becoming thereafter parallel at the exit of the convergent outlet 11 until the inlet to the second nozzle-shaped stage 16 is encountered. The second nozzle- shaped stage 16 has a tapered inlet with a typical included angle of 110 degrees, and a substantially parallel bore having an internal diameter substantially equivalent to D, with a length ranging from 2 to 3 times D but typically about 2.5D. The exit diameter of the first nozzle-shaped stage 13 and the internal bore of the second nozzle-shaped stage 16 are typically of substantially the same diameter D.

[034] In combination with the second nozzle-shaped stage 16 having a tapered entrance and the outer housing 14, the first nozzle-shaped stage 13 creates a convergent mixing chamber 17. The separation of the exit from the first nozzle-shaped stage 13 to the entrance to the substantially parallel bore of the second nozzle-shaped stage 16 is between 1 and 2 times the exit diameter D, typically about 1.5D. [035] A primary fluid A to be aerated or mixed is supplied under pressure (for example, using a pump (not shown) to the first nozzle-shaped stage 13 through the inlet 10 and then passes through the convergent outlet 11 at an increased velocity (compared with its entry velocity). The accelerated velocity of primary fluid A creates a low pressure zone (reduced static pressure) in mixing chamber 17. This low pressure zone draws the second fluid B into the mixing chamber 17 via the annular duct 15 (and inlet 12) and mixing of the two fluid streams entails. This second fluid B will be drawn into the mixing chamber 17 by entrainment (ie drawn in due to the low pressure zone), or supplied under pressure by means including but not limited to a pump, blower or fan.

[036] Turbulent mixing results in dispersion of second fluid B in the primary fluid A stream. The resulting fluid jet enters the second nozzle-shaped stage 16 where further turbulent mixing and shearing of the fluid boundaries occurs enabling more complete mixing in the case of two liquids, and a greater dispersion of smaller bubbles where the secondary fluid is a gas. The mixed fluid then exits the nozzle through outlet 18.

[037] Preferred embodiments of the present invention are also shown in Figures 3 and 4.

[038] Diameter D is generally in the range of 10mm to 20mm. In a preferred embodiment, D is 14mm. The particular relative proportions of the present invention, as shown in Figure 2 in relation to a preferred embodiment, are important to achieve the self-aspiration of the present invention, which is absent from similar nozzles such as those disclosed in Molvar.

[039] The nozzle according to the invention may be located at any level in the primary fluid but for reasons of optimising the interaction between the primary fluid and secondary fluid would commonly be located at the bottom of the tank, as shown in Figures 5 and 7. Due to the self-aspirating nature of a preferred embodiment, the supply of secondary fluid may be drawn via a pipe connected to the inlet 12 with the distal, sampling end located at any desired location in the fluid, above the fluid, or at the free surface acting as a skimmer. When located at the free surface, common practice would be to suspend the sampling point on the free surface by means of a floatation device.

[040] When used in an aeration system, in order to effect the maximum exchange of gases (commonly oxygen), it is desirable to have the smallest possible bubbles entrained and to maximize the time the bubbles are in contact with the liquid. It is therefore desirable to have a deep vessel with bubbles released at the bottom. Maximising the depth of the vessel increases the residence time of the bubbles but has the effect that the pump supplying the air must overcome significant pressure, increasing its size and cost.

[041] By minimizing, or in some instances eliminating, the pump for the second fluid, it is possible to reduce the capital cost and operational expenses, more easily maintain the system, realize significant energy savings.

[042] As shown in Figures 5 to 7, in use multiple nozzles 20 are attached to an aeration system 21 in a tank 22 in a preferred embodiment of the present invention. The primary fluid A is drawn into the aeration system 21 via system inlet 23, which may be above or below the level of fluid in the tank 22. The nozzles 20 may alternatively be used in any self-aspirating system.

[043] The word 'comprising' and forms of the word 'comprising' as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.

[044] Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.

[045] In this specification where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date publicly available, known to the public, part of the common general knowledge or known to be relevant to an attempt to solve any problem with which this specification is concerned.