FR2484862A1 - Injector for contacting gas with liq. to form emulsion - injects high speed gas co-current at low angle of incidence - Google Patents

Abstract

The flow passage for liq. is designed so that liq. pressure is reduced as the liq. approaches the gas injection zone. Here, gas is injected at a very high speed, e.g. several hundred metres per second. The injection of gas is cocurrent with the flow of liq. and at an angle of incidence which is very low, pref. below 10 deg., w.r.t. the axis of flow of the liq. The mixt. advances through an expansion zone of the passage to form a fine emulsion. The pressure in the liq. is then raised to a level which remains lower than the pressure at which liq. is admitted to the mixer. Pref. the mixer passage converges in cross-section as it approaches the injection zone. Immediately downstream of the injection zone the passage is non-convergent where a confluence of fluids takes place. The confluence zone is followed by a divergent length of passage leading to a chamber where undissolved gas is recovered and from which it can be recycled. The mixer can be used for a wide range of gas/liq. contacting applications, e.g. oxygenation of waste water, carbonating drinks, introducing chlorine and ozone for disinfection. Also in the pharmaceutical industry for injecting gas into biological reactions. Very short contacting time reduces energy requirements. Minimal wastage of undissolved gas.

Description

 The present invention relates to a device for the transfer of gas in a liquid.

There are currently three main types of gas transfer devices in a liquid namely
devices of the bubble injection type by compressed air or superpressure which provide large bubbles by means of injection rods or fine bubbles by dispersion using porous elements or even so-called laminated bubbles by means of devices combining the injection of bubbles and a mechanical action allowing a deformation and an elongation of the path of the bubbles.

 - The devices causing a mixing of the liquid surface by means of either turbines or brushes; and devices of the venturi type enabling the creation of an emulsion.

 However, these devices are all characterized by the achievement of a mixture at low relative speed of the two fluids brought into contact resulting in a low shear rate because the difference in velocities does not exceed a few meters per second. This results in a low rate of liquid renewal in the vicinity of the gas bubbles and the consequences of which are the need for a long contact time between the two fluids, a low operating efficiency and a relatively high energy expenditure of where devices and devices bulky and unprofitable.

 However, the present invention provides a method and a device for obtaining a transfer of gas in a liquid with both a very short contact time between the two fluids, a reduced energy expenditure and an increased depletion of the gas to dissolve. injected gas.

 It is already known to obtain a short contact time between a liquid and a gas with the formation of a liquid-gas emulsion by injecting the gas at very high speed and at low incidence into the liquid.

 This is indeed the case for example in the case of the "jet propulsion jet for naval propulsion" described in French Patent No. 7406639 filed February 27, 1974 by the Company "The Modern Engine". Such a thruster fixed to a floating body comprises a diverging inlet diffuser in which the admitted water is compressed and slowed down, at least one injection stage of short length following the diffuser and comprising said means for introducing the reaction gas. at very high speed and under a low incidence and finally a non-convergent relaxation stage.

 Due to the high speed of the gas, the interpenetration of the two fluids, taking place rapidly, causes, in said non-convergent zone, a liquid-gas emulsion of very interesting characteristics.

 Such characteristics are due to the very high initial shear rate resulting from the difference in speed, at the injection of the gas, of several tens of meters per second. The consequences are a strong renewal of gas in the vicinity of the liquid and, therefore, a very fast energy exchange and high efficiency and a relatively low energy expenditure.

 All the conditions for a good gas transfer are therefore met.

However, if such a "propeller" was used as such in the field of gas-liquid transfers, it would have, among others, the following drawbacks:
- ejection at the outlet of a highly emulsified liquid and it would result in the loss of a large amount of undissolved gas
- a general energy level that is too high since the "propulsive" aspect loses its priority in the field considered.

 However, the present invention obviates these drawbacks and provides a method and a device implementing the gas introduction means used previously to allow to inject the latter at a very high speed and at a low incidence and a non-expansion stage. converge in combination with means provided upstream and downstream of these elements to achieve an assembly operating in a global vacuum cycle incorporating a partial pressure cycle. In which the maximum value of the pressure remains lower than the high value of the pressure in the overall cycle.

 The method according to the invention is thus essen so characterized by the fact that it consists in lowering the pressure of the liquid intended to come into contact with the gas in question, to admit the latter at very high speed and at low incidence, to bring about both fluids under conditions of expansion to achieve a fine emulsion and then resume said emulsion and raise the pressure while maintaining the resulting pressure at a level below that corresponding to the initial pressure of the liquid admitted.

 The invention also covers a device for carrying out this method, essentially characterized by the fact that it comprises, from upstream to downstream, (a) a convergent duct for feeding the liquid, (b) a gas injection stage producing a gas injection at very high speed and at low incidence, (C) a non-convergent enclosure in which the confluence of the two fluids and the production of a fine emulsion and (d) a divergent duct take place opening into a chamber arranged to allow total or partial recovery of undissolved gas and / or recycling in (b).

 The means (a), (b) and (c) of the device thus designed allow the realization of a vacuum cycle while the means (d) makes it possible to raise the average pressure level of the total cycle, the assembly constituting always a depression cycle.

As indicated above, such a device has the following advantages
very short contact time between the two fluids: for example the concentration of dissolved oxygen in a water can be brought from 0 to 50% of the saturation concentration under the same conditions in less than 0.2 seconds.

- reduced energy expenditure
- Increased depletion of gas to dissolve.

 This results in a compact device, inexpensive use and great interest when it comes to recovering and / or recycle an expensive gas. Furthermore, this device, without any moving parts, does not present a risk of clogging, the constituent materials to be chosen by taking into account the possibly aggressive characters of the treated gas or liquid.

 The downstream device (d) for optimum operation is advantageously arranged so as to allow regulation in pressure and / or gas concentration to dissolve.

Other characteristics and advantages of the invention will emerge more clearly from the following description given with reference to the accompanying drawings in which:
- Figure 1 is a schematic longitudinal sectional view of a device according to the invention;
FIG. 2 is a view on a larger scale of a detail of FIG. 1;
FIG. 3 is a graph showing the variations of the pressure throughout the device of FIG. 1; and
FIG. 4 is a diagram illustrating the gas transfer obtained according to the invention compared to the transfer obtained according to known methods.

 Referring to these figures, the device according to the invention comprises, from upstream to downstream, a convergent duct 1 for supplying the liquid, a gas injection stage 2 (shown on a larger scale in FIG. 2 ), stage in which is introduced the gas from a conduit 3. The successive sections of this injection stage are a function of the pressure created in the pipe 3 so that the gas is injected at a very high speed, for example to a speed of the order of one or a few hundred meters per second and under a relatively low incidence of the order of ten degrees.

 The injection stage is immediately followed by a so-called expansion stage 4 consisting of an enclosure whose walls are non-convergent, which chamber opens into a clearly diverging zone 5 in communication with a chamber 6 for recovery and / or recycling. This chamber 6 can be made according to the recovery rate and / or the recycling of gas diaspout.

 Upon examination of such a constitution, it is immediately realized by following the graph of FIG. 3 that it implements the method of the invention, that is to say that in zone AB the the pressure of the liquid to be treated is substantially constant, that this pressure is lowered in the first upstream means 1 of the device according to the invention, the liquid passing through the zone BC, the created depression substantially keeps its value following CD in the zone of injection of the gas 2, the pressure continues to decrease according to DE in the so-called expansion zone 4 and finally, the pressure rises according to EF in the zone 6 while reaching a stabilized value according to FG remaining always lower than the value initial AB of the liquid introduced into the system.

The general cycle thus remains a vacuum cycle, which makes it possible in the case where it is desired to recycle the undissolved gas that is released in zone 6 to re-introduce it into zone 2 via line 3 without providing additional energy. zone 2 necessarily being in depression (CD in FIG. 3) with respect to zone 6 (FG in FIG. 3).

 It can be seen that, in proceeding in this way and with the device according to the invention, on the one hand, a high gas transfer efficiency is obtained in a liquid, in particular under the pressure conditions of the gas to be transferred, for which the hitherto known processes prove to be ineffective and, on the other hand, a possibility of recovery and recycling of the undissolved gas without additional energy input.

 The comparative diagram of FIG. 4 makes it possible to demonstrate the superiority of the invention.

In this diagram, on which the average pressure of the liquid medium (P) has been plotted on the abscissa, and on the ordinate, the transfer capacity (Q)
the shape of curve I corresponds to the case of injection of bubbles
- The shape of the curve It corresponds to the case of a mixing of the surface of the liquid or to that of the formation of an emulsion such as that resulting from the application of a thruster of the type of that of the French patent Na 7406 639 involving a pressure-relax cycle and finally
the shape of curve III corresponds to the case of the device according to the invention.

 In case I (curve I), we see that when the pressure increases, the process used is more and more effective. However, for an increased capacity of gas transfer, the optimal working area (zone A) is at a pressure P greater than P2 (P2 being commonly of the order of 4.104 Pascal).

In case II (curve II), it is found that when the pressure decreases, the system quickly loses its effectiveness. The optimal working area (B) is then for P greater than P1 and preferably for P between
P1 and P2 (P1 being of the order of 2.104 Pascal).

 Finally, in case III (curve IIIX), we see that the transfer capacity is only slightly influenced by the lowering of the average pressure of the medium and it keeps a significant value for values of the pressure below P2 and above all at P1, values for which the other devices lose more and more their efficiency (zone C).

It follows that, according to the invention, the integration of a pressure cycle in a global vacuum cycle makes it possible to supply the gas again with the differential pressure that was previously provided by the compression and consequently that the transfer efficiency is maintained in areas deemed inaccessible such as, for example, those corresponding to very low head. On the other hand, it should be noted that in the areas of high pressure the apparatus according to the invention is less advantageous compared with apparatuses implementing the known methods.

The method and the device of the invention have multiple applications. Thus, because of the simplicity of realization, the low cost price and efficiency, they can be applied
- for the treatment of water with air or oxygen for the oxygenation of basins, in particular basins at low and very shallow depths (fish farming, aquaculture); the oxygenation of water and sludge in transport pipelines; oxygenation of sewage; the deodorization of charged water and sludge oxygen supply complements in the purification devices, in particular biological doping of the stations); the oxidation of reductive water sulphurous calves ..)
- for the treatment of water, by means of various gases in the case of degassing of water and by extension of liquid food by nitrogen; the use of C62 in certain food liquids and for the treatment of effluents; the use of C1 O3 or its derivatives in the field of disinfection;
- in biotechnology (pharmaceutical or food industry) for 0 supply of gas for biological reactions; sterilization of media, especially for continuous fermentations; sterilization of the speakers; ;
- in the chemical industry for the introduction of reaction gases into liquids, hydrogenation, etc.
for the treatment of gases, in particular for their washing, deodorization or purification, etc.

 and in general in all cases where the transfer of a gas into a liquid is sought.

 It goes without saying that the present invention has been described only as a purely explanatory and non-limiting and that any useful modification can be made without departing from its scope as defined by the claims below.

Claims (6)

 A method for the transfer of gas into a liquid, characterized in that it consists in lowering the pressure of the liquid intended to come into contact with the gas considered to admit it at very high speed and at low incidence, to make confluent the two fluids under conditions of relaxation to achieve a fine emulsion then to resume said emulsion and to raise the pressure while maintaining the resulting pressure to a level less than that corresponding to the initial pressure of the liquid admitted.  2. Device for carrying out the method according to claim 1, characterized in that it comprises, from upstream to downstream, (a) a convergent duct for feeding the liquid, (b) an injection stage of gas producing an injection of gas at very high speed and low incidence, () a non-onvergente enclosure in which the influence of the two fluids and the production of a fine emulsion and <d) a divergent duct opening in an enclosure designed for allow total or partial recovery of the undissolved gas and / or its recycling in (b)  3.Dispositif transfer according to claim 2, characterized in that the successive sections of the passage of the liquid and the emulsion perform a sub-cycle pressure in a cy-le global vacuum.  4. Transfer device according to claim 2 or 3, characterized in that the downstream means is organized to allow regulation in pressure and / or concentration of gas to dissolve.  5. Application of the process according to claim 1 to the treatment of water, in biology, in the chemical industry, and all other industries involving a transfer of gas into a liquid.  6. Application of the device according to any one of claims 2 to 4 to water treatment, in biotechnology, in the chemical industry and all other industries involving a transfer of gas in a liquid.