Apparatus for dissolving gas in a liquid

Abstract: A nozzle 20 for use in apparatus for dissolving gas in a volume of liquid comprises a through passageway 26 for the liquid having a first convergent portion 28, a second parallel portion 30 and a third divergent portion 32. A gas passage 44 is in communication with the passageway 26 at a location along the second parallel portion 20. An advantage of the nozzle 20 is that it obviates the need of a separate venturi.

Description: 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, there is described a method of treating a large volume of liquid contained in a sewage 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 are a plurality of conduits each conduit having located at its upper end a venturi. Each venturi has an inlet for gaseous oxygen. At the lower 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 sewage treatment tank. Each venturi creates a restriction in its associate conduit whereby turbulence is imparted to the liquid flowing 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 sheer 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 an 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 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, said gas passage being 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 sewage 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 4 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 therein. Each 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 sheer 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 surfaces 36, 38 of the inner part 24 and 40, 42 of the outer part 22 defined 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 will be 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 e.g. 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.

Claims: An apparatus for dissolving a gas in a volume of liquid comprising a pump (2) for passing the liquid through a plurality of conduits (6), each conduit (6) terminating in a nozzle (20), each nozzle (20) having a passageway (26) for the flow therethrough of a stream of said liquid, said passageway (26) comprising a first convergent portion (28), a second parallel portion (30) downstream of the first portion (28) and a third divergent portion (32) downstream of the second portion (30) and means defining an annular gas passage (44) communicating with the passageway (26) at a location along the second parallel portion (30), said gas passage (44) being located at or adjacent the root of the third divergent portion (32). An apparatus as claimed in Claim 1, characterised in that the nozzle (20) comprises first and second parts, an outer first part (22) which defines the third divergent portion and a inner second part (24) secured within the outer first part (22) and which defines the first convergent and second parallel portions (28, 30). An apparatus as claimed in Claim 2, characterised in that the passage (44) is defined, at least in part, by opposed, spaced surfaces (36, 40, 38, 42) of the first and second parts (22, 24). An apparatus as claimed in Claim 2 or 3, characterised in that each part (22, 24) is made of moulded plastics material.

Inventors: GARRETT MICHAEL ERNEST, GARRETT, MICHAEL ERNEST
Applicants: BOC GROUP PLC, THE BOC GROUP PLC
Application year: 1993
Main classification: B01F1
IPC codes: B01F5, B01F3