Patent Application
20180369767
Some embodiments are directed to micro-fluidics, and in particular, to devices and methods for the continuous emulsification of immiscible fluids, in particular in order to carry out emulsions of the water-in-oil (W/O) type intended for immediate use and calling into play flow rates compatible with industrial applications.
More particularly, some embodiments relate to the continuous emulsion of a percentage of substantially aqueous fluid (less than or equal to 20% by volume of the final emulsion formed) in a lipid fluid (for example a recovered vegetable oil or heavy fuel oil, or an animal fat), in order to form in-situ an emulsion for the purpose of the direct combustion thereof in a boiler, a furnace, a turbine or an engine.
Some embodiments provide an emulsification system that is especially dedicated to the carrying out of continuous emulsions of two immiscible liquids, and in particular emulsions of the water-in-oil (W/O) type.
The applications targeted by these embodiments relate to the field of energy conversion, such as turbines, boilers, furnaces or internal combustion engines in general. Work has shown that the presence of a small fraction of finely emulsified water (droplets of about 5 to 10 μm) in the liquid fuel makes it possible to lower the combustion temperature and as such decrease the emissions of polluting gases and of particles resulting from poor combustion. The continuous phase can be of a diverse nature such as conventional diesel, heavy fuel oil or lipid waste (used vegetable oils, animal fats).
The constraints linked to the applications under consideration are numerous, whether in terms of the nature of the fluids to be emulsified, the volume ratio of the fluids in the emulsion, or the need to design a compact method that makes it possible to process the flows that may be required for the operation of internal combustion engines.
Generally, the devices operate discontinuously (for example tanks in continuous or “batch” mode) are currently favoured. They are based on the use of suitable agitation blades (of the rotor-stator type for example) and are relatively energy-hungry. The stability over time of these emulsions is, in such devices, generally provided by adding surfactants.
As this entails producing an emulsion continuously, those of ordinary skill in the art know various systems that operate in continuous mode, such as static mixers (for example those of the commercial name SMX SULZER), membranes, high-pressure nozzles, and micro-channels. However, membranes have the disadvantage of not being able to process substantial flow rates (i.e. of about a few μl/h to a few ml/h). Moreover, static mixers do not make it possible to obtain very fine granulometries, unless models that have very small hydraulic diameters are used.
The research in the field of micro-fluidics has been very active for two decades now and shows in particular an interest in the development of methods of continuous emulsification[1], [2]. A substantial number of studies are known to those of ordinary skill in the art that treat methods of emulsification substantially applied to mixtures of the oil in water type (O/W)[3], [4]. This type of dispersion is considered to be less demanding in emulsification energy, this due to the use of an aqueous phase (low viscosity) as continuous phase. Undeniably, the water in oil emulsification (W/O) which is more particularly targeted in some embodiments due to the applications targeted may require an optimisation from an energy standpoint for two main reasons:
With regards more particularly to the continuous emulsification methods of two immiscible fluids, the devices known to those of ordinary skill in the art are micro-mixers with streams with confined impinging. A first study covered the use of impinging streams for the purpose of carrying out a liquid-liquid dispersion of immiscible fluids[8], [9]. This work is based on the principle of emulsification by the impact of two sprayed streams (or “sprays”). These streams are produced by two injectors arranged facing each other inside the same chamber[8], [9].
In what follows, we find the use of impinging streams in confined systems based on the use of micro-channels with high fluid delivery speeds[10], [11].
The first studies conducted on the subject concerned the mixture of miscible fluids. The results obtained then encouraged those of ordinary skill in the art to take interest in splitting immiscible fluids, here sunflower oil and water in order to form water-in-oil emulsions (W/O), while still keeping this configuration of the flow of impinging streams confined in a micro-channel[12], [13].
Then, based on these first studies, the applicant realised a microsystem for a continuous emulsification device, which is shown in
Such a device including the micro-system shown in
However, such a device has the disadvantage that the filament formed in the output micro-channels is not split enough, which does not allow for its immediate use as fuel in internal combustion engines, turbines, boilers and furnaces.
Some embodiments therefore address or overcome all or a portion of the disadvantages of related art, by the setting in place in the device of at least one singularity able to destabilise the interfaces between the two liquids and as such further split the filament formed in the output micro-channels.
More particularly, some embodiments are directed to a device for carrying out a continuous emulsion of two immiscible fluids, the device including:
The first microsystem further includes at least one singularity capable of destabilizing the interfaces between the fluids in the pre-emulsion.
The term immiscible fluids, in terms of some embodiments, means a hydrophilic liquid and a hydrophobic liquid.
With regards to the nature of the fluids flowing in the device according to some embodiments, it is possible in particular to use a hydrophilic fluid (more advantageously or preferably aqueous) and a hydrophobic fluid (advantageously or preferably a lipid or hydrocarbon fluid).
The term microsystem, in terms of some embodiments, means a system with millimetric or submillimetric dimensions, including an intersection formed by channels of submillimetric dimensions.
The term micro-channels, in terms of some embodiments, means channels with a submillimetric hydraulic diameter, i.e. less than a millimetre.
In the microsystem of the device according to some embodiments, at least two intake micro-channels with respective difference sections S1 and S2 face each other along a central intake axis A and having an offset, linked to their difference in section, in a direction different from the central intake axis. However, these channels are not necessarily arranged symmetrically in relation to this central intake axis (as is shown in
In addition to the intake micro-channels, the microsystem of the device according to some embodiments furthermore includes at least two micro-channels for the output from the device of the emulsion once formed, and an intersection area wherein the intake and output micro-channels intersect.
Advantageously, the first microsystem can include a supply and collection system, and a part wherein the micro-channels and the singularity or singularities are etched.
Advantageously, the output micro-channels can be arranged in the microsystem of the device according to some embodiments, in such a way as to face each other along a central output axis that is different from the central intake axis, and more advantageously or preferably symmetrically, in relation to the central intake axis. More advantageously or preferably, the output micro-channels can be arranged perpendicularly to the intake axis by facing each other along the central output axis.
The device according to some embodiments further includes at least one singularity able to destabilise the interfaces between the two liquids in the pre-emulsion (or offset impinging stream), with these interfaces being created in the intersection area of the microsystem and being completed by the singularity or singularities. These singularities are etched within output micro-channels.
The intersection area of the microsystem according to some embodiments allows for the propulsion and the impact of the two fluids to be emulsified at relative substantial speeds. From these impacts, a pre-emulsion of the two fluids in the intersection area is created. This pre-emulsion has the form of a swirl structure, including an entanglement of filaments and of droplets of fluid of the dispersed phase surrounded by fluid of the continuous phase. This structure starts to be split in the intersection area, in order to reach an emulsion at the outlet of the output channels. The slitting is continued and is refined during the passage of the pre-emulsion in the singularity or singularities (in particular the bend or bends). These speeds are of about 1 to 3 metres per second, which is largely above the fluid speeds usually observed in micro-channels.
The device according to some embodiments is therefore particular suited to emulsifying a fluid with a low viscosity flowing in an intake micro-channel (for example water), in a fluid with a much higher viscosity (for example a lipid or hydrocarbon fluid) flowing in a second intake micro-channel. Furthermore, the device according to some embodiments has the advantage of being compact and offers the possibility of continuously producing and on demand an emulsion in-situ by overcoming the use of surfactant. This has a considerable interest in the case of an emulsion intended to be used as a fuel, given that the use of surfactant in a fuel worsens the carbon and economic content of the method.
According to a first advantageous embodiment, the singularity can be a bend formed in each output micro-channel of the microsystem.
In this first embodiment, the device according to some embodiments can include two to six bends formed in each output micro-channel of the microsystem.
According to a second advantageous embodiment, the singularity can be an abrupt enlargement or a narrowing formed in each output micro-channel of the microsystem.
According to a third embodiment, the device according to some embodiments can furthermore include a second microsystem in series or in parallel including:
Advantageously or preferably, in this third embodiment, it is possible to use as a second microsystem, a microsystem identical to the first microsystem.
Advantageously, regardless of the embodiment, the intake and output micro-channels have a square or rectangular section S1, S2, and of which the hydraulic diameter can advantageously be between 100 and 800 micrometres.
Some embodiments are directed to a method for carrying out a continuous emulsion of two immiscible liquids implementing the device disclosed above, the method including:
The flow rate of the continuous phase is between 8.3.10−7 m3/s to 20.10−7 m3/s (i.e. between 50 and 200 ml/min), and the fluid of the dispersed phase represents between 3 and 20% by volume of the continuous phase.
of the method further includes splitting of the pre-emulsion between the steps 3 and 4, in order to obtain an emulsion with an average diameter of the drops of the dispersed phase between 5 and 20 micrometres.
Advantageously, the fluid of the dispersed phase represents between 5 and 10% by volume of the continuous phase.
Advantageously, the flow rate of the continuous phase is between 8.3.10−7 m3/s to 12.10−7 m3/s (i.e. between 50 and 120 ml/min).
Advantageously, the fluids to be emulsified include a hydrophilic fluid, which is advantageously or preferably an aqueous phase, and a hydrophobic fluid, advantageously or preferably a lipid or hydrocarbon fluid.
Advantageously or preferably, the hydrophilic fluid is a salt-free aqueous phase and the lipid or hydrocarbon fluid is free of surfactant.
Some embodiments are directed to using the emulsion able to be obtained by the method disclosed above as a fuel for internal combustion engines, turbines, furnaces and boilers, if the hydrophilic fluid is a salt-free aqueous phase and the lipid or hydrocarbon fluid is free of surfactant.
As such, the device and the method according to some embodiments therefore operate on principles for the emulsification of two non-miscible fluids, which are different from those known in related art, for the main application targeted: realisation of emulsified fuel, in particular intended to be used in internal combustion engines. Thanks to the device and to the method disclosed above, a better combustion of the fuel is obtained by a micro-explosion effect. The microsystems of the device disclosed above associate an impinging stream (frontal collision of the intake fluids intended to be emulsified) generated by the intersection of the microsystem and the offset intake channels in depth (in such a way as to form a step) and the singularity or singularities (for example the bends in the output channels). The straight length of the channels can be dimensioned with the objective of reducing or minimising drops in pressure in the microsystem. Moreover, the various geometries of the singularities that can be implemented in the device disclosed above are used to favour the flow effects favourable to the fluid/fluid splitting: in particular, the formation of a winding on the step (offset in the depth between the intake channels) increases the stresses undergone by the pre-emulsion. The number and position of the singularity or singularities in the output micro-channels make it possible to optimise the splitting. Thanks to these various mechanisms, it is possible to produce a continuous emulsion without additives (in particular surfactant).
Other advantages and particularities of some embodiments shall result from the following description, provided as a non-limiting example and in reference to the following examples and to the corresponding accompanying figures:
d are commented in the description of related art.
The microsystem 2 of the device according to some embodiments is differentiated from the one shown in
This emulsification bench 1 was developed and used (cf. example hereinafter) to test in emulsification conditions corresponding to the targeted applications (properties of the fluids and flow rates called into play) the microsystems according to some embodiments such as shown in
This emulsification bench forms a device 1 according to some embodiments, wherein the microsystem 2 includes two plates made of transparent PMMA (for example of PMMA marketed under the registered trademark PLEXIGLAS®) in order to facilitate the optical investigations. The micro-channels are etched using a micro-mill on one of these plates.
The microsystem 2 of the emulsification bench shown in
The emulsification bench 1 of
The following example shows some embodiments without however limiting the scope thereof.
The emulsification bench described hereinabove and shown in
During these tests, using the emulsification bench shown in
Water was used as aqueous phase in small quantities, not exceeding 20% by volume, compared to sunflower oil which represents the continuous phase therefore the major phase. Sunflower oil was chosen in order to operate according to the principle of a cold model. The viscosity of this oil, at ambient temperature, corresponds to the temperature of heavy fuel oil preheated in an engine. The characteristics of the various fluids used are gathered together in the table 1 hereinafter.
γ
e/h [mN/m]
All of the emulsification tests were conducted at a temperature of 25° C. Due to the friction effects of the fluids, the emulsion at the outlet of the emulsification circuit experienced heating of about +5° C. in relation to the intake temperature.
For all of the tests carried out, the flow rate Qh of the oily phase in an intake micro-channel was set to about 60 ml/min, for three flow rates of water Qe tested (about 5 ml/min, 10 ml/min and 15 ml/min).
The properties of the pre-emulsion formed after the impact (frontal collision) are studied at the intersection between the stream of water and that of the sunflower oil in the intersection area 27 of the microsystem 2 (via high-frequency view of the flow in the output micro-channels), as well as via measurement of the diameter d10 of the droplets formed in the emulsion at the outlet of the micro-channels (bar chart shown in
Entailing flows of the two-phase type characterised by substantial flow speeds and implemented in complex geometries, it cannot be considered to carry out numerical simulations.
The views at high frequency are therefore indispensable for following the splitting of the fluids in the bend or bends present in the emulsion channel. The objective of these views makes it possible to show the favoured located of the splitting, and also the areas where the coalescence of the droplets can possibly be produced.
This bar chart makes it possible to judge the pertinence of adding one or several additional bends. The letters a, b and c represent the three ranges of flow rates of the dispersed phase. The data shows the interest in placing two bends in series and in provoking two impacts in the microsystem (configuration shown in
The purpose of the presence of the bends is to generate, in addition to the viscous forces of which the role is preponderant on the splitting[15], with additional stresses used to fragment the filament of water initially formed (see
| Number | Date | Country | Kind |
|---|---|---|---|
| 1562682 | Dec 2015 | FR | national |
This application is a national phase filing under 35 C.F.R. § 371 of and claims priority to PCT Patent Application No. PCT/FR2016/053458, filed on Dec. 15, 2016, which claims the priority benefit under 35 U.S.C. § 119 of French Patent Application No. 1562682, filed on Dec. 17, 2015, the contents of each of which are hereby incorporated in their entireties by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2016/053458 | 12/15/2016 | WO | 00 |
