FR2558071A1 - METHOD AND DEVICE FOR MIXING AT LEAST TWO GASES AND APPLICATION TO THE DILUTION IN THE AIR OF A GAS BEFORE REJECTING IT TO THE ATMOSPHERE - Google Patents

Abstract

1. A method of diluting a gas or a mixture of gases with air before discharge to atmosphere, by means of a device comprising a shaped body (20) forming a venturi which is open to the atmosphere at both ends, said gas or mixture of gases being injected under pressure at the upstream end thereof, method characterised in that said gas or mixture of gases is injected into said body in the form of a layer of annular cross-section by means of at least one set of injection tubes (21), the circular orifices (24) of which are arranged in a ring at the upstream part of said body (20) forming a venturi.

Description

Method and device for mixing at least two gases and application to

  the dilution in the air of a gas before its rejection to the atmosphere. The present invention relates to a method and a device for mixing at least two gases. It also relates to the application of this method and this device to the dilution in air of a

  gas or a gaseous mixture, before being discharged into the atmosphere.

  In many technical fields, it is necessary to intimately mix two gases. This is particularly the case when it is desired to release into the atmosphere hazardous or combustible residual gases, which must be diluted in the air, before their release, to a sufficiently low concentration so that the mixture result is no longer dangerous or is below the threshold

of gas impermeability.

  The present invention aims to propose in this patent a process that is easy to implement, even when the amounts of gas to be treated are important. It also aims to propose a device for the implementation of this method, which is simple and

  easy maintenance during use.

  For this purpose, the subject of the invention is a process for mixing a first and a second gas, according to which said second gas is injected at the upstream end of a profiled body forming a venturi, in which said first gas is circulated, said method being characterized in that the injection of said second gas takes place in said next body at least one sheet of rectangular cross-section. In a preferred embodiment of this process, said second gas will be injected into said body along a plurality of annular cross-section plies offset from upstream to downstream, the plies

  successive ones with increasing sections from upstream to downstream.

  The invention also relates to a device for mixing first tn and at least one second gas, comprising tun profiled body forming venturi, wherein said first gas flows, and at least one means for injecting under pressure said second gas at the upstream end of said body, this device being characterized in that said injection means is such that said second gas is

  injected in the form of a sheet of annular cross-section.

  Advantageously, the device will comprise several injection means offset from upstream to downstream, said means being such that the successive layers of said second gas produced by said means

  have increasing cross-sections from upstream to downstream.

  Preferably, said venturi body and said one or more injection means will have a symmetry of revolution around a

Same axis.

  Said injection means may be constituted by an injector

with annular orifice.

  It may also include a jet of injectors whose circular holes are arranged in a ring at the upstream end.

said venturi forming body.

  For the mixing of very large quantities of gas, use will preferably be made of a plurality of devices according to the invention, the venturi bodies of which will be open at their two ends and which will be arranged in parallel inside a tubular structure in which will circulate said first gas. In addition to the mixtures made by the elementary devices, an additional mixing effect will be obtained inside said tubular structure. In order to increase this effect, this structure will preferably form venturi and said devices will preferably be

arranged at its upstream part.

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  This combination of a plurality of devices according to the invention also has the advantage that it is possible to disassemble one of the devices for maintenance operations

  without immobilizing all the equipment.

  In its application to the air dilution of dangerous or flammable gases, said first gas will be constituted by the ambient air and the venturi body of the device will be open at both ends. In this application, it will be preferable to use a plurality of injection means offset from upstream to downstream and with an annular section increasing from upstream to downstream, and the injection pressures of said second gas may be different at each injector and even be zero, in order to obtain the optimum dilution effect

during each injection.

  Advantageously, additional air inlets may be provided laterally in the downstream portion of said body forming

  venturi, in order to increase the dilution effect of the second gas.

  When it comprises one or more combustible gases, the dilution in the air before discharge into the atmosphere shall be such that it is outside the flammability limits for its constituents, in particular for hydrogen and methane, which is most commonly found in residual gases released to the atmosphere. The accompanying drawings illustrate various embodiments of the invention which will be described hereinafter. In this

  description, reference is made to the dilution in the air of a gas

  before it is released to the atmosphere, but it is clear that

  the invention is not limited to this application.

  In the drawings: FIG. 1 is a schematic sectional view of a device

2558071.

  according to the invention; FIG. 2 is a partial section of the upstream part of a device comprising a plurality of offset annular injectors; FIG. 3 is a partial section similar to FIG. 2 in which each injection means comprises a plurality of circular orifice injectors disposed in FIG. 4 is a diagrammatic section of a set of several devices according to the invention, assembled in parallel within a tubular structure

venturi.

  The device shown in FIG. 1 comprises a venturi body having three essential parts - an air inlet chamber 1 open to the atmosphere with a convergent profile, possibly frustoconical, disposed upstream in the direction of flow of the gas - a cylindrical chamber 2, connected to the chamber 1; - A divergent 3, extending the chamber 2, of frustoconical shape or flaring regularly downstream in the manner

a trumpet.

  The divergent 3 leads to the atmosphere, either directly or

  through unrepresented subsidiary bodies.

  The arrival of the gas to be diluted before discharge to the atmosphere is effected by a nozzle with an annular section 6, coaxial with the inlet chamber

  1 and provided with an annular section injector.

  The nozzle 6 is pierced along its axis with a conduit 8, open at both ends and which communicates with the atmosphere at its downstream end. This duct 8 forms a second air inlet, which is added to that defined by the outer walls of the nozzle 6 and the

internal walls of the chamber 1.

  Dilution in the air is carried out by air entrainment

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  by the gas to be diluted, which acts as a driving agent, this gas being injected under pressure, in the form of a cylindrical or conical sheet, in contact with the air as well by its external part as by its internal part, a diffusion and a mixture with the air occurring very rapidly, with a minimum of pressure loss in contact with the walls. The energy exchange between the two gaseous flows, the motor flow of gas to be diluted, on the one hand, and the induced air flow, on the other hand, firstly in the chamber 2, then in the divergent 3, leads to

  a homogeneous mixture at the downstream end of the divergent.

  Advantageously, as shown, the diverging portion 3 will be pierced laterally with orifices 4, near its downstream end, so that

  to increase the rate of dilution of the gas in the air.

  FIG. 2 illustrates a preferred embodiment of the invention in which the gas to be diluted in air is injected at the downstream end of a body 10 forming venturi by three successive nozzles with annular injectors offset by upstream downstream, respectively 11,12 and 13, and of increasing section from upstream to downstream. Preferably, as shown, each nozzle will open in the upstream part, open to the atmosphere, of the next nozzle. This will result in a dilution effect and air entrainment

considerably increased.

  As indicated above, in this case, the injection pressures at each injector may be different and even zero, each pressure being chosen so as to obtain the effect

  optimum dilution in the air for the injector considered.

  The invention is not limited to the use of annular orifice injection nozzles and any equivalent means can of course be used. Thus, as shown in Figure 3, can be used to inject the gas to be diluted in the body forming

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  venturi 20, a plurality of tubes 21 carried by a plate 22 and fed by a manifold 23, the discharge ports 24 being disposed in the upstream portion of the body 20 so as to form a ring. In this case too, as shown, it will preferably use several successive injection means offset amoent downstream and able to form gas sheets of increasing section from upstream to downstream. The tubes 25 arranged upstream and carried by the plate 26, will be supplied with gas by the collector 27 and will lead preferably to the downstream end, open to the atmosphere, a venturi 28, while the downstream tubes 21 will disposed substantially in the extension of the downstream portion of the venturi 27. The side walls of the downstream portion of the venturi may be advantageously pierced with air inlets

additional 29.

  In the case where it is desired to dilute in the air very large quantities of gas, before their discharge to the atmosphere, it will be advantageous to use, as shown schematically in FIG. 4, a plurality of devices according to the invention disposed in parallel inside a tubular structure forming venturi 30, open to the atmosphere. Each device will comprise a body 31 forming venturi, open at both ends, and at least one injector 32 disposed at the upstream end of said body for injecting the gas to be diluted in the form of a sheet of annular section. For simplicity, the supports of the devices and the gas supply means of the injectors 31

  have not been represented on the drawing.

  With such an assembly, which is another object of the present invention, additional air is induced in the tubular structure and an increased effect of gas dilution in the air is achieved. In addition, each of the basic devices can be disassembled individually for maintenance or repair without interrupting the operation of the device.

  1 'together for a period longer than that of disassembly.

  The invention therefore provides a method and a device that are simple and easy to implement for mixing at least two gases and, more particularly, for diluting a gas in the ambient air.

  or a mixture of gases before being released to the atmosphere.

$ 5580 7i

Claims (11)

  1. A process for mixing a first and at least a second gas, wherein said second gas is injected at the anont end of a profiled body (1,2,3) forming a venturi, in which circulates said second gas, said method being characterized in that the injection of said second gas takes place in said next body at   minus a sheet of annular cross-section.   2. A process according to claim 1, characterized in that said second gas is injected into said body (10) along a plurality of annular cross-section plies offset from upstream to downstream, the successive plies having ascending sections of upstream downstream. 3.- Device for mixing a first and at least a second gas, comprising a profiled body (1,2,3) forming venturi, wherein said first gas flows, and at least one means (6) for injecting under pressure said second gas at the upstream end of said body, this device being characterized in that said injection means is such that said second gas is injected in the form   a sheet with an annular cross-section.   4.- Device according to claim 3, characterized in that it comprises a plurality of injection means (11,12,13) offset from upstream to downstream, said means being such that the successive layers of said second gas produced by said means have   increasing cross sections from anont downstream.   5.- Device according to one of claims 3 and 4,   characterized in that said body (1,2,3; 10) and said one or more injection means (6; 11,12,13) have a symmetry of revolution around the same axis.   6.- Device according to one of claims 3 to 5,   characterized in that the one or more injection means (6; 11,12,13) comprise an annular injector.   7.- Device according to claims 4 and 6 in combination,   characterized in that said injection means comprise a central duct open at both ends, in the upstream portion of which opens the annular injector of the injection means arranged immediately upstream.   8.- Device according to one of claims 3 to 5,   characterized in that the or said injection means comprise a plurality of tubes (21) whose circular holes (24) are arranged in a ring at the downstream portion of said body (20) forming venturi.   9.- Device according to claims 4 and 8 in combination,   characterized in that each injection means opens into the upstream part of a tubular structure (28) forming venturi and in that the conduits (21) of the injection means arranged downstream of this tubular structure (28) are substantially in the extension of it.   10.- Set of devices (31,32) according to one of   Claims 3 to 9, arranged in parallel within a   tubular structure (30) in which said first gas flows.   1il.- Application of a device according to one of the claims   3 to 9 or an assembly according to claim 10 to the dilution in air of a gas or a gaseous mixture before its discharge to the atmosphere, characterized in that said venturi body of said device and said structure tubular are in communication with the atmosphere at both ends and in that said gas or   gaseous mixture to be diluted feeds said injection means.   12. Application according to claim 11, in the case where each device comprises a plurality of injection means offset from upstream to downstream, characterized in that the pressure 25580 71   injection of the gas to be diluted will be chosen such that, at each injection means, optimum dilution is obtained for each injection.   13.- Application according to one of claims 11 and 12 to the   dilution in air of a flammable gas before its discharge to the atmosphere, characterized in that said dilution is such that it is below the flammability threshold of the various constituents of said gas.