NZ245677A

NZ245677A - Apparatus for dissolving a gas in a liquid, using mixing nozzles with integral venturis

Info

Publication number: NZ245677A
Application number: NZ245677A
Authority: NZ
Inventors: Michael Ernest Garrett
Original assignee: Boc Group Plc
Priority date: 1992-01-21
Filing date: 1993-01-14
Publication date: 1994-06-27
Also published as: PL169306B1; DE69306923D1; GB9201193D0; EP0602762A1; AU3034392A; PL297470A1; DE69306923T2; AU657021B2; ZA93348B; EP0602762B1

Description

<div id="description" class="application article clearfix"> 24 5 6 7 7 Patents Form 5 Conipi'wiw L, r i:. .lb'!'.% rt^. jjpjF.8l*i*\. #9( Publicotron Dc* . .2.7 J.UN M P.O. Jourru.!, No: ...... J3?.l NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION TREATMENT OF LIQUIDS We, THE BOC GROUP PLC., an English Company of Chertsey Road, Windlesham, Surrey, GU20 6HJ, England do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- -1 - (Followed by 1A) - 1 A- TREATMENT OF LIQUIDS The present invention relates to apparatus for dissolving gas in a volume of liquid and more particularly to nozzles for use in such apparatus. For the avoidance of doubt, throughout this specification the term "gas" is intended to include gas mixtures. In our European Patent Application, Publication No. 0389230 (corresponding to NZ 2 32 944), there is described a method of treating a large volume of liquid contained in a sevage treatment tank. A sewage pump forms a stream of the waste liquid and passes said liquid through a ring main. Depending vertically from the ring main is a plurality of conduits each conduit having located at its upper end a venturi. Each venturi has an inlet for gaseous oxygen. At the lover end of each conduit downstream of the venturi is a T-piece pipe in which is received one or more outlet nozzles for passing a liquid-gas mixture into the main volume of liquid in the sevage treatment tank. Each venturi creates a restriction in its associated conduit whereby turbulence is imparted to the liquid floving therethrough. The flow of oxygen to the turbulent region from the inlet of the venturi breaks the oxygen into small bubbles. The liquid-gas mixture passes down the conduit and through a nozzle which has an outlet diameter much smaller than that of the diameter of the associated conduit such that the liquid-gas mixture leaves the nozzle at a relatively high velocity thereby creating turbulence and helping further to break up or shear- bubbles in the liquid-gas mixture to even smaller bubbles that are readily dissolved in the main body of liquid in the sewage treatment tank. It is an aim of the present invention to provide sin improved nozzle for use in apparatus of the type described in European Publication No. 0389230 which avoids the need for an independent venturi. According to the present invention, an apparatus for dissolving a gas in a volume of liquid comprises a pump for passing the liquid through a plurality of conduits, each conduit terminating in a nozzle, each nozzle /> v 2 6 APP:994' 24 5 6 7 7 paDlOQj'gSj'MJ ■ - 2 - having a passageway for the flow therethrough of a stream of said liquid, in which said passageway comprises a first convergent portion, a second parallel portion downstream of the first portion and a third divergent portion downstream of the second portion and means defining an annular gas passage communicating with the passageway at a location along the second parallel portion. Preferably, the gas passage is located at or adjacent to the root of the third divergent portion. In a preferred embodiment the nozzle comprises two parts, an outer part which defines the third divergent portion and an inner part secured within the outer part which defines the first convergent and second parallel portions. Each part may be made of moulded plastics material. An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying diagrammatic drawings in which: Figure 1 is a schematic drawing, partly in perspective of an oxygenation apparatus as described in European Patent Application Publication No. 0389230; and Figure 2 is a vertical cross-section through a nozzle of the present invention for use in an apparatus of the type as described in European Publication No. 0389230. Referring first to Figure 1, the illustrated apparatus may be located wholly within a large volume of liquid, for example, liquid contained within a sevage treatment tank. A sewage pump 2 having a suction inlet forms a stream of waste water which enters a ring main 4. The ring main A is adapted to feed the liquid to a plurality of conduits 6 which depend generally vertically therefrom. Each conduit 6 has a venturi 8 disposed 3 therein. Bach venturi 8 has an inlet 10 for gaseous oxygen. Each conduit 6 has a downstream T-piece pipe 13 at its bottom end in which is received one or more outlet nozzles 12 for passing a liquid gas mixture into the main volume of liquid in which the ring main is immersed. As explained in European Patent Application Publication No. 0389230, each venturi 8 creates a restriction in its associated conduit 6 such that turbulence is imparted to the liquid flowing through the conduit 6. The flow of oxygen to the turbulent region from the inlet 10 breaks the oxygen into bubbles. Each nozzle 12 has an outlet diameter much smaller than the diameter of the associated conduit 6 such that the liquid-gas mixture leaves the nozzle 12 at a relatively high velocity thereby creating turbulence, helping further to break up or shear bubbles in the mixture into even smaller bubbles that are readily dissolved in the main body of liquid. It will be evident that the apparatus described in European Publication No. 0389230 requires with each conduit 6 a separate venturi 8 and one or more nozzles 12. Referring now to Figure 2, this illustrates a nozzle 20 which is intended for use in an apparatus for dissolving gas in a volume of liquid of the type described in European Patent Publication No. 0389230 and which obviates the need of a venturi. The nozzle 20 comprises an outer part 22 within which is securely attached an inner part 24. Both parts 22, 24 may,be made of moulded plastics material. The nozzle 20 has a central passageway 26 for the flow therethrough of a stream of liquid from left to right (as shown). The passageway 26 comprises a first convergent portion 28 and downstream therefrom a second parallel portion 30 both defined by the inner part 24; and a third divergent portion 32 downstream of the second parallel portion 30 said portion 32 being defined by the outer part 22. The outer part 22 is formed with an inlet 34 for gas, for example, oxygen and opposing v 2 6APRP94 - 4 - surfaces 36, 38 of the inner part 24 and 40, 42 of the outer part 22 define between them means in the form of an annular passage 44 which communicates with the passageway 26 at a location along the second parallel portion 30 adjacent the root of the third divergent portion 32. It will be apparent, that the nozzle 20 is intended for attachment either directly to a conduit 6 or a T-piece pipe 13 of the type illustrated in Figure 1. In use, oxygen passes through inlet 34 and annular passage 44 and is injected into the liquid passing through passageway 26 near the root of the third divergent section 32 and the liquid-oxygen mixture leaves the nozzle 20 at a velocity which exceeds the sonic velocity for the mixture thereby creating shock waves in the main body of liquid. Use of the nozzle 20 in an apparatus of the type as illustrated in Figure 1 avoids the need, cost and pressure drop associated with a venturi and since conduit 6 no longer conveys a gas-liquid mixture the velocity of the liquid can be reduced resulting in the pressure drop associated with the conduit being reduced by 25% when compared with the apparatus as illustrated in Figure 1. The net benefit is to halve the power consumption required to operate the apparatus illustrated in Figure 1. Modifications can be made to the embodiment illustrated in Figure 2 in that the passage 44 need not communicate with the passageway 26 immediately adjacent the third divergent portion 32 but may be located anywhere along the second parallel portion 30. I Furthermore, a plurality of shallow vanes can be formed on the surface of the third divergent portion 32 to impart a rotating motion to the liquid-oxygen mixture leaving the nozzle 20. The vanes can be moulded as a spiral or long pitch thread to the surface of the divergent portion 32. Rotary motion of the liquid-oxygen mixture as it leaves the nozzle 20 helps with dispersion and mixing. /A'1; , ■f v ^2 6A?m-74 </div>

Claims

<div id="claims" class="application article clearfix printTableText"> WHAT WE CLAIM IS:

1. An apparatus for dissolving a gas in a volume of liquid comprising a pump for passing the liquid through a plurality of conduits, each conduit terminating in a nozzle, each nozzle having a passageway for the flow therethrough of a stream of said liquid, in which said passageway comprises a first convergent portion, a second parallel portion downstream of the first portion and a third divergent portion downstream of the second portion and means defining an annular gas passage communicating with the passageway at a location along the second parallel portion.

2. An apparatus as claimed in Claim 1, in which the gas passage is located at or adjacent the root of third divergent portion.

3. An apparatus as claimed in Claim 1 or 2, in which the nozzle comprises an outer first part which defines the third divergent portion and a inner second part secured within the outer first part and which defines the first convergent and second parallel portions.

4. An apparatus as claimed in Claim 3, in which the passage is defined, at least in part, by opposed, spaced surfaces of the first and second

5. An apparatus as claimed in Claim 3 or 4, in which each part is made of moulded plastics material.

6. In an apparatus for dissolving a gas in a volume of liquid, a nozzle constructed and arranged substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings. parts By Their Attorneys HENRY HUGHES LTD THE BOC GROUP PLC T3 A ♦- \ 2 6 APR 1994 </div>