EP4076698A1

EP4076698A1 - Method for degassing a fluid

Info

Publication number: EP4076698A1
Application number: EP20829889.3A
Authority: EP
Inventors: Damien COLOMBET; Frédéric Ayela
Original assignee: Centre National de la Recherche Scientifique CNRS; Institut Polytechnique de Grenoble; Universite Grenoble Alpes
Current assignee: Centre National de la Recherche Scientifique CNRS; Institut Polytechnique de Grenoble; Universite Grenoble Alpes
Priority date: 2019-12-17
Filing date: 2020-12-16
Publication date: 2022-10-26
Also published as: US20230017163A1; WO2021122769A1; FR3104450B1; FR3104450A1

Abstract

The invention relates to a method for degassing a fluid comprising the following steps: supplying, at the inlet of a reactor comprising at least one microfluidic pipe, a fluid that can comprise at least one dissolved gas; then making the fluid flow through the reactor, the at least one pipe comprising a portion having a smaller hydraulic diameter, and the flow being parameterised such that bubbles are generated by micro-cavitation, the fluid then comprising a liquid phase and a gas phase; then allowing the at least partial transfer of the at least one dissolved gas present in the fluid from the liquid phase to the gas phase; separating the liquid phase and the gas phase; and recovering the liquid phase in order to obtain the degassed fluid, the method not involving the application of ultrasound to the fluid between the step in which the fluid is supplied to the reactor and the step of separating the liquid phase and the gas phase.

Description

l Process for degassing a fluid TECHNICAL FIELD

The present invention relates to the field of processes for degassing a fluid, and more particularly to the field of processes for degassing a fluid by cavitation. It finds a particularly advantageous application in the extraction of gas dissolved in the fluid, and more particularly a liquid. STATE OF THE ART

The at least partial extraction of the gases dissolved in a fluid, also called degassing, is a common practice, first of all in order to prevent these gases from reacting with other compounds dissolved in the fluid. For example, dissolved dioxygen can be extracted from a solvent when other compounds intended to be dissolved in that solvent are sensitive to dioxygen. The dissolved gases can also be extracted from a fluid, upstream of certain technological steps for treating the fluid, in order to avoid the formation of bubbles which may be problematic during these technological steps. For example, the formation of gas bubbles when a fluid is solidified may be undesirable. There are several solutions for degassing a fluid. First, the degassing of a fluid can be achieved through the use of a chemical phase reaction liquid. In the food industry, one can cite as an example the elimination of dioxygen dissolved in wine by chemical reaction with sulphite salts. This process however involves the addition of chemical reagents in the fluid to be degassed.

It is also possible to degas a liquid by substitution with another gas. However, this process is more akin to replacing dissolved gases than to degassing.

Several degassing processes aim to transfer the gases dissolved in a liquid phase to a gas phase, the liquid phase being able to be separated from the gas phase to obtain the degassed fluid. Such a transfer is linked to a phenomenon that can be modeled by Henry's law. More particularly, the solubility of a gas can obey Henry's law, i.e. the equilibrium between the quantity of gas dissolved in the liquid phase and the quantity of gas in the gas phase, in contact with the gas. liquid phase, is controlled by the following relation, for a given gas: x ₌ H Xi P with x _g the molar fraction of gases in gas phase, X _| the molar fraction of the gases dissolved in the liquid phase, H the Henry's constant of the gas considered, in Pa, and P the pressure in the gas phase in Pa.

Henry's law thus reflects the fact that in order to decrease the molar fraction in liquid phase of dissolved gases X _|, it is possible to increase Henry's constant and / or to decrease the total pressure of the fluid. Several methods exist which exploit the aforementioned phenomenon, among which are the methods described below.

A first type of known degassing process is vacuum degassing. The degassing of a fluid can be achieved by reducing the pressure in a sealed tank containing the fluid to be degassed. This process operates on the lowering of the partial pressure of the gases in a gas phase present in the tank. This reduction in the partial pressure causes a reduction in the molar fraction of the gases in the gaseous phase. Through Henry's law, it appears that, at the gas-liquid interface, an imbalance is created which generates the transfer of dissolved gases from the liquid phase to the gas phase. For example, document US Pat. No. 6,119,484 (A) relates to a device for degassing molten glass by degassing under vacuum. The main disadvantage of this type of process is that it is generally carried out batchwise.

A second type of degassing process used is degassing by boiling the fluid. In general, the solubility of gases dissolved in a liquid phase decreases with temperature. This process is based on the fact that the solubility of a gas dissolved in liquid phase decreases with a rise in temperature to reach its minimum value when the Henry's constant of the gas is maximum. One example is the degassing of water used in electricity production plants in contact with steam turbines, the degassing of a fluid in a heat pipe described by document CN 1510386 (A) or the degassing of coolant described in document US Pat. No. 3,789,577 (A). The main disadvantage of this type of process is that it requires a significant increase in the temperature of the fluid. This temperature rise can lead to the degradation of compounds present in the fluid, or even the degradation of the fluid itself. For example, undesirable chemical reactions can occur in gas and / or liquid phase, such as oxidation of a dissolved compound in liquid phase, self-decomposition of compounds in gas phase.

There is another type of degassing process exploiting the aforementioned phenomenon, which is characterized by a step in which the fluid is treated by cavitation. More particularly, the fluid is subjected to a vacuum so that the pressure of the fluid becomes lower than its saturated vapor pressure. Therefore, vapor bubbles are likely to be generated and form a gas phase, to which a transfer of dissolved gases from the liquid phase can be subsequently carried out, commonly referred to as the phenomenon of desorption.

It is known in particular from the document Z. Yang et al., A prototype of ultrasonic micro-degassing device for portable dialysis System, Sensors and Actuators A: Physical, 95, 274-280, 2002, a microfluidic device for degassing a fluid by acoustic cavitation. The fluid to be degassed is subjected to an acoustic wave, here ultrasound, in order to allow its cavitation. For this, the degassing device comprises a degassing chamber and a piezo-transducer module for the emission of ultrasound. Acoustic cavitation and the elimination of gas bubbles are carried out in the degassing chamber. The elimination of gas bubbles is carried out by hydrophobic channels distributed all along the degassing chamber. However, the use of ultrasound can induce an uncontrolled rise in the temperature of the fluid. Here again, this temperature rise can lead to the degradation of compounds present in the fluid, or even the degradation of the fluid itself.

It is also known from document US Pat. No. 3,853,500 (A), a process for degassing viscous fluids. This method comprises a step in which the fluid is passed through a perforated partition to degas it and form bubbles therein and a subsequent step in which the fluid is stirred by subjecting it to ultrasound. Here still, the use of ultrasound can induce an uncontrolled rise in the temperature of the fluid.

An object of the present invention is therefore to provide a process for degassing by cavitation making it possible to improve the degassing of a fluid. Another object of the invention may be to increase the efficiency of the process for degassing by cavitation of a fluid. Another object of the invention may be to improve the elimination by cavitation of at least one gas dissolved in a fluid while limiting the risk of degradation of compounds possibly present in the fluid, or even the risk of degradation of the fluid therein. - even, during degassing. More particularly, an object of the invention is to limit the rise in the temperature of the fluid during the process so as to avoid the degradation of compounds possibly present in the fluid, or even the degradation of the fluid itself.

The other objects, features and advantages of the present invention will become apparent on examination of the following description and the accompanying drawings. It is understood that other advantages can be incorporated.

ABSTRACT

To achieve this objective, according to one embodiment there is provided a process for degassing a fluid comprising the following steps:

- supplying, at the inlet of a reactor, a fluid which may include at least one dissolved gas; then

- causing the fluid to flow through the reactor, the reactor comprising at least one fluidic conduit, the at least one fluidic conduit comprising a first portion, a second portion and a third portion, the second portion being disposed between the first portion and the third portion, the second portion having a reduced hydraulic diameter with respect to the first portion and the third portion, and the flow being configured so that bubbles are generated by cavitation, the fluid then comprising a liquid phase and a gas phase, then

- allow at least partial transfer of at least one dissolved gas present, or even remaining, in the liquid phase to the gas phase; - separating the liquid phase and the gas phase; and

- recover the liquid phase to obtain the degassed fluid.

Advantageously, the method is exempt from the application of ultrasound to the fluid between the step in which the fluid is supplied at the inlet of the reactor and the step of separating the liquid phase and the gas phase. Thus, the method implements degassing of a fluid by hydrodynamic cavitation. By hydrodynamic cavitation, degassing is carried out by applying a continuous pressure drop in the fluid as it flows through the at least one reactor. Therefore, the degassing process can be implemented continuously.

In addition, since the method does not require the application of ultrasound to the fluid, the method makes it possible to limit or even avoid an uncontrolled rise in the temperature of the fluid. Thus, the fluid can be substantially at ambient temperature, for example to avoid the degradation of compounds dissolved in the fluid, or even the degradation of the fluid itself. The fluid can further be at a controlled temperature.

Preferably, the liquid phase and the gas phase are separated at the outlet of the reactor.

Optionally, the method may further exhibit at least any one of the following characteristics, optionally used in combination or alternatively.

The at least one fluidic conduit can be a microfluidic conduit. The use of a microfluidic duct makes it possible to induce micro-cavitation of the fluid. Due to this small hydraulic diameter, a dense dispersion of bubbles of millimeter or even micrometric size can be created. These bubbles are then characterized by an interfacial area per unit of volume which may be greater than 3000 m ¹ . The phase transfer of dissolved gases is thus facilitated, increasing the efficiency of the degassing process. Preferably the reduced hydraulic diameter is less than 1 mm, preferably 800 μm, preferably less than 300 μm, preferably less than 150 μm, even more preferably less than 100 μm.

The liquid phase and the gas phase can be separated at the outlet of the reactor, the third portion having a length chosen to temporally dissociate the generation of bubbles by cavitation and the separation of the liquid phase and the gas phase. The process thus allows the fluid to flow into the third portion so as to promote the phase transfer of the dissolved gases.

The first portion, the second portion and the third portion are preferably adjoining. The at least one duct of the reactor can comprise at least one of a diaphragm, even a micro-diaphragm, a Venturi, even a micro-Venturi and a step, or even a micro-step. The step may also have a protruding edge.

The second portion may have a cross section to a longitudinal axis of the duct, with an aspect ratio greater than or equal to 3. Alternatively or complementarily, the first portion may have a cross section of area. A1, and the second portion may have a cross section of area A2, the cross sections being perpendicular to a longitudinal axis (x) of the duct, so that the ratio A1 / A2 is greater than or equal to 3.

The fluid may have a viscosity of less than 5 mPa.s (10 ³ Pa.s) at the operating temperature of the process, preferably the viscosity of the fluid being between 0.5 mPa.s and 5 mPa.s at the temperature of 20 ° C.

The flow of the fluid in the at least one reactor can be configured so as to be turbulent at least downstream of the second portion. A turbulent regime makes it possible to promote the mixing of the dissolved gases in the liquid phase. According to one example, the flow speed of the fluid in the at least one reactor is set so that the flow is turbulent at least downstream of the second portion. The turbulent regime is reached when the Reynolds number of the flow is greater than 2300, the Reynolds number being defined as: pUD Re = - m with U the flow speed of the fluid (in ms ¹ ), D the diameter hydraulic (in m), p the density of the liquid (in kg.m ³ ), and m its viscosity (in Pa.s). Thus the diffusion of dissolved gases from the liquid phase to the liquid-gas interface, on the surface of the bubbles, is accelerated. The efficiency of the degassing process is thus further increased. In addition, the total interfacial area per unit volume of the bubbles generated is thus very large, which, in synergy with the turbulent nature of the flow of the fluid, makes it possible to intensify the transfer of dissolved gases and helps to improve the flow. efficiency of the process.

When the fluid flows into the third portion, the fluid may be at a pressure lower than the pressure of the fluid in the first portion, and for example lower than ambient pressure. Preferably, said pressure is less than the saturation pressure of the at least one dissolved gas, at the temperature of the fluid entering the reactor.

When the fluid flows into the third portion, the pressure in the third portion is preferably less than ambient pressure, by substantially 1 bar.

When the fluid flows in the third portion, or even until the liquid phase and the gas phase are separated from one another, the fluid can be at a temperature between room temperature and the boiling temperature of the fluid. The fluid can be at a temperature between the solidification temperature of the fluid, for example 0 ° C for water at 1 bar, and its boiling temperature, for example 100 ° C for water at 1 bar. When the fluid flows in the third portion, or even until the liquid phase and the gas phase are separated from each other, the fluid can be at a temperature chosen so as to maximize the Henry's constant of at least a dissolved gas. When the fluid flows in the third portion, or even until the liquid phase and the gas phase are separated from each other, the fluid is at a temperature chosen so as to minimize the solubility of the at least one dissolved gas .

When the fluid flows in the third portion, or even until the liquid phase and the gas phase are separated from each other, the fluid comprising a plurality of dissolved gases, the temperature can be chosen so as to maximize the constant of Henry of a gas from among the plurality of dissolved gases, in order to allow selectivity of the degassing with respect to a dissolved gas in particular.

When the fluid flows in the third portion, or even in the reactor, or even until the liquid phase and the gas phase are separated from each other, the fluid comprising a plurality of dissolved gases, the fluid can be at a temperature chosen so as to promote the degassing of a gas from among the plurality of dissolved gases, and in particular the at least partial transfer of the at least one dissolved gas.

The temperature of the fluid can be controlled by a heating device.

Furthermore, the reactor can include a plurality of conduits. Preferably the conduits are arranged in parallel. BRIEF DESCRIPTION OF THE FIGURES

The aims, objects, as well as the characteristics and advantages of the invention will become more apparent from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

Figure 1 shows the steps of the degassing process according to one embodiment of the invention.

Figure 2 shows a diagram of the experimental setup of the degassing process according to one embodiment of the invention.

FIG. 3 shows the change in the hydraulic diameter D of the portions of the conduit during the flow of the fluid, according to one embodiment of the invention. Figure 4 shows the change in the flow velocity F of the fluid during the flow of the fluid, according to the embodiment illustrated in Figure 3.

Figure 5 shows the change in pressure P during the flow of the fluid, according to the embodiment illustrated in Figure 3.

Figure 6 shows the change in the volume fraction a of the gas phase during the flow of the fluid, according to the embodiment illustrated in Figure 3.

FIG. 7 represents a conduit of the reactor according to an embodiment of invention.

Figure 8 shows a reactor conduit according to another embodiment of the invention.

Figure 9 shows a reactor conduit according to another embodiment of the invention.

Figure 10 shows examples of flow (from right to left) observed in the degassing process according to one embodiment of the invention, the conduit comprising a micro-step.

Figure 11 shows an example of flow (from right to left) observed in the degassing process according to one embodiment of the invention, the conduit comprising a micro-diaphragm.

The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily on the scale of practical applications.

DETAILED DESCRIPTION

It is specified that in the context of the present invention, the term degassing designates the at least partial extraction of the gases dissolved in a fluid, also known under the name of desorption. Equivalently, degassing consists in reducing the concentration of gas dissolved in a liquid phase. Thus, in the context of the present invention, a distinction is made between degassing and debubbling or deaeration, which consists in eliminating bubbles initially present in a liquid phase by a simple mechanical separation of a gas phase and a liquid phase. . The degassing carried out during the implementation of the process may, however, be accompanied by debubbling.

The term "gas" is understood to mean a set formed by compounds in the gaseous state under ambient temperature and pressure conditions, and volatile organic compounds. By way of non-limiting example, these gases can include oxygen, nitrogen, carbon dioxide, carbon monoxide, argon, nitrous oxide, and methane.

These gases can be qualified as "incondensable", that is to say that, under the operating conditions of the process, they do not undergo a phase change from the gaseous state to the liquid state and vice versa. These gases dissolve in a fluid and can undergo transfer from a liquid phase in which they are dissolved to a gas phase.

The fluid can be qualified as "condensable", that is to say that, in operating conditions of the process, it can at least partially undergo a phase change from the gaseous state, which can also be signed as vapor, in the liquid state and vice versa. For example, the condensable is water which can be in the form of a liquid or a vapor.

By viscosity is meant the dynamic viscosity of the fluid in Pa.s.

The pressure is given in bar, corresponding to 1000 hPa in the international system of units.

The “hydraulic diameter” D is a quantity commonly used for the calculation of the flows in a duct of cross section to the longitudinal axis x of the duct, the cross section being of any shape. It can be determined according to the following relation.

A being the area of the cross section at the longitudinal x axis of the duct, and Pw being the wetted perimeter of that section.

By a “micro-” geometry is meant, in a known and common way in the field of microfluidics, a geometry having at least one dimension substantially less than 1 mm.

The longitudinal axis of the fluidic conduit can be locally defined as the main flow direction of the fluid in the conduit. Thus, the longitudinal axis of the fluidic conduit is not necessarily a straight line, but can accommodate a curvature of the fluidic conduit.

A particular embodiment of the degassing process 1 is now described. By way of example, Method 1 is illustrated in Figure 1, where variants of Method 1 are indicated by parallel paths and optional steps are indicated by dotted lines. By way of example, the elements of the experimental setup of the degassing process are illustrated in Figure 2.

The fluid to be degassed is supplied 10 at the inlet of a reactor 2. It is specified that the fluid can comprise a gas phase G mixed with a liquid phase L, or a liquid phase L only, when it is supplied 10 at the inlet of the reactor. reactor 2. In fact, the gaseous phase allowing the desorption of the dissolved gases being generated by cavitation, it is not necessary for the fluid to include a gaseous phase when it is introduced into the reactor 2. In the following, and as illustrated by FIG. 2, the embodiment of the method in which the fluid initially comprises only a liquid phase L is described. It is understood that the characteristics described can also be applied to a fluid initially comprising a phase gas G mixed with a liquid phase L. The fluid is capable of comprising at least one dissolved gas, ie the solution may initially comprise at least one dissolved gas, the concentration of which in the liquid phase is desired to be minimized.

The reactor 2 comprises at least one pipe 20, this pipe 20 comprising a first portion 21 of hydraulic diameter D1, a second portion 22 of hydraulic diameter D2, and a third portion 23 of hydraulic diameter D3, as illustrated in Figures 7 and 8 The second portion 22 more particularly has a reduced hydraulic diameter D2 with respect to those of the first portion 21 and of the third portion 23.

The reduction of the hydraulic diameter D2 of the second portion 22 allows the local lowering of the pressure during the flow 11 of the fluid through the reactor 2, to result in the cavitation of the fluid. This phenomenon is explained with reference to FIGS. 3 to 6. The hydraulic diameter D decreases at the level of the second portion 22 of the reactor 2, relative to the hydraulic diameters of the first portion 21 and of the second portion 23, as illustrated by FIG. 3. The decrease in the hydraulic diameter D leads to an increase in the speed F of the fluid, as illustrated in FIG. 4. Thus, the speed F of the fluid increases during the flow 11b of the fluid through the second portion 22. This increase in the speed F of the fluid induces a decrease in the static pressure P of the fluid, which can reach pressures equal or even lower than the saturation pressure of the liquid P _sat , as illustrated in figure 5. For example, P _sat is equal to 23 mbar for water at room temperature. Note that, if the reduction of the hydraulic diameter D2 of the second portion 22 induces a singular pressure drop when the fluid flows 11b through the second portion 22, the pressure decreases by linear pressure losses during the flow 11a , 11c of the fluid in the first portion 21 and in the third portion 23.

The decrease in static pressure with the reduction of the hydraulic diameter depends on many parameters such as the viscosity of the fluid, its flow speed, the dimensions of the hydraulic diameter and the magnitude of the reduction of the hydraulic diameter, these parameters can be combined between them in many ways to result in cavitation. It is clear that a person skilled in the art will be able to adapt either of these parameters to induce cavitation of the fluid.

In a perfectly common way in the field of fluidics of microfluidics, the person skilled in the art indeed knows how to adapt the various parameters of a fluid and of a conduit in which the fluid circulates in order to generate cavitation. Cavitation is obtained by adapting these different parameters so that the number of cavitations is less than 1 (o <1). The number of cavitation o can be defined as the ratio between the pressure drop inducing cavitation on the pressure drop generated by the flow, according to the following mathematical formula, with p the density of the fluid and U the velocity of the fluid in the second portion 22. P - P _S at 0.5 pU ²

These various parameters are for example taken from the flow speed, the geometry of the duct, and in particular the reduction in the areas of the cross sections of the portions of the duct in a direction substantially perpendicular to the flow. Cavitation can be detected by various techniques, for example by identifying the presence of bubbles. This presence of bubbles can for example be identified using an optical bubble sensor and / or using a camera and / or a binocular and / or a microscope.

When the static pressure of the fluid becomes lower than the saturation pressure of the liquid P _sat under the conditions for implementing method 1, a phase change of the fluid is induced. At least part of the liquid phase L of the fluid passes to the vapor state by generation 12 of bubbles by cavitation. Depending on the temperature and pressure conditions, these bubbles can also assemble in a cavitation pocket.

FIG. 6 illustrates the evolution of the volume fraction a of the gas phase G when the fluid flows 11 through the reactor 2. The volume fraction a of the gas phase G can initially be substantially zero, the fluid initially comprising only a liquid phase, according to the example illustrated. When the fluid flows 11b through the second portion 22, the cavitation induces an increase in the volume fraction of the gas phase G. When the fluid flows 11c through the third portion 23, the volume fraction of the gas phase G may continue to increase because of the linear pressure losses, or even because of the imposition of a low pressure downstream of the second portion 22.

During the generation 12 of the bubbles by cavitation, the gaseous phase mainly comprises the fluid in its vapor form. The liquid-vapor equilibrium can be translated by Raoult's law which links the mole fraction of the gas phase of the fluid Xc _(fiuid) to the molar fraction in liquid phase of the fluid Xi_ _(fiUid) (generally substantially equal to 1) such que: xg {fluid) Psat

- ^x g (fluid) ^~

XlÇfluid with P _sat the saturating vapor pressure of the fluid in Pa and P the gas phase pressure in Pa.

The appearance of these bubbles or pockets initially filled with vapor induces a phase transfer 13 of the gases dissolved in the liquid phase to the gas phase, this transfer being able to be translated by Henry's law for an incondensable gas /. with Xg _(i ) the mole fraction of gas / in gas phase, X | _(i) the mole fraction of the gas / dissolved in the liquid phase, H the Henry's constant of the gas /, in Pa, and P the gas phase pressure in Pa.

This transfer 13 of the non-condensable gases more particularly comprises the diffusion of the non-condensable gases at the liquid-gas interface, from the liquid phase to the gas phase. Thus the gaseous phase G can become charged with non-condensable gases initially dissolved in the liquid phase of the fluid to be degassed.

At the outlet of the reactor, the fluid comprises a liquid phase L and a gas phase G. The gas phase G has a proportion of non-condensable gases initially dissolved in the fluid to be degassed, which is more or less significant depending on the efficiency of the degassing.

The liquid phase L and the gas phase G are then separated 14. For this, a separation device 4, as shown diagrammatically in FIG. 2, can be used. For example, the separation device 4 can comprise a membrane 41, permeable to gases, in an enclosure 40 and a reservoir 42. According to this example, the fluid, comprising the liquid phase L and the gas phase G, can be supplied in the gas phase. first gas / liquid separation enclosure 40. The gas phase G can pass through the permeable membrane 41 to be discharged through the conduit 44. As an alternative, any process for separating a gas phase G and a liquid phase L can be envisaged.

The liquid phase and the gas phase can be separated directly at the outlet of the reactor 2. As an alternative, a connecting pipe 45 can connect the reactor 2 to the separation chamber 4.

After the separation 14 of the liquid phase L and the gas phase G, the degassed liquid phase is recovered 15. For this, the separation device 4 can for example comprise a reservoir 42 comprising a membrane non-permeable to gases defining a configured volume. to accommodate the liquid phase L. The reservoir 42 can be connected to a gas pump 5 ′ communicating with the outside of this volume in order to maintain the reservoir 42 in depression. The tank 42, and more particularly the volume configured to accommodate the liquid phase L, can be connected to an evacuation duct 43 of the liquid phase, connected to the reservoir 42, the duct 43 possibly comprising a pump 5 making it possible to withdraw the degassed fluid in the state liquid. In addition, the gas phase G can be recovered 19. For this, the separation device 4 can further comprise an evacuation duct 44 of the gas phase, connected to the first chamber 40, the duct 44 possibly comprising a pump for gas 5 '.

Process 1 is free from the application of ultrasound to the fluid, at least between the step in which the fluid is supplied to the reactor 2 and the step 14 of separating the liquid phase L and the gas phase G. The process thus makes it possible to degas a fluid while avoiding an uncontrolled increase in its temperature. The fluid can include compounds, other than non-condensable gases, which can be altered or even degrade beyond a certain temperature. For example, the fluid can include biomolecules such as proteins, carbohydrates or lipids. Advantageously, a fluid comprising these compounds can thus be degassed, while avoiding their deterioration, or even their degradation.

In method 1, the degassing of the fluid being carried out by applying a continuous pressure reduction to it during its flow 11 in the reactor 2, the degassing of the fluid can be carried out continuously. It is understood that the fluid can be supplied continuously to the reactor 2. The fluid can be supplied directly to the reactor 2. According to the example used in FIG. 2, the fluid can be supplied to the reactor by a reservoir 3, this reservoir 3 being able to be connected to the reactor 2 by a connecting pipe 30. The reservoir may also comprise a device 31 for measuring the mass flow rate of the fluid.

An example of reactor 2 is described with reference to FIGS. 7 to 9. According to this example, the reactor comprises a pipe 20 as described above. The first portion 21 may have a hydraulic diameter D1, and the third portion may have a hydraulic diameter D3. At least one of the first portion 21 and the second portion 23 may have a constant hydraulic diameter along the longitudinal axis of the conduit 20. The conduit 20 may more particularly comprise a diaphragm, or even a micro-diaphragm, as illustrated. by Figures 7 and 11.

At least one of the first portion 21 and the second portion 23 may have a variable hydraulic diameter along the longitudinal axis of the duct 20. According to one example, at least one of the hydraulic diameter D1 of the first portion 21 and the hydraulic diameter D3 of the third portion can vary greatly monotonic along the longitudinal axis of the duct 20. According to this example, the second portion 22 can be of a specific length along the longitudinal axis of the duct 20. The duct 20 can more particularly comprise a Venturi, or Venturi tube , or even a micro-Venturi, as illustrated in figure 8.

At least one of the first portion 21 and the second portion 23 may have a variable hydraulic diameter over part of the portion, along the longitudinal axis of the duct 20, as the example illustrated in FIG. 9. According to In this example, the second portion 22 may be of a specific length along the longitudinal axis of the duct 20. The duct 20 can more particularly comprise a step, or even a micro-step as illustrated in FIG. 10. The step may furthermore present a protruding edge so as to improve the cavitation of the fluid.

It should be noted that any geometry of the duct 20 allowing cavitation of the fluid can be envisaged. Any pressure-reducing geometry, configured to induce cavitation of the fluid, can more particularly be considered.

The efficiency of the degassing by method 1 can be optimized so that a proportion of non-condensable gases in the gas phase G is as high as possible. Several solutions are possible and can be used in a complementary or alternative manner. These solutions are detailed below.

The reactor can be a microfluidic reactor. The use of a microfluidic duct makes it possible to induce micro-cavitation of the fluid. Micro-cavitation can cause the generation of a dense dispersion of bubbles with a size substantially less than 1 mm, or even substantially less than 100 μm. Micro-cavitation is therefore distinguished from the most common cavitation carried out at a macro-scale, that is to say at a scale of at least a centimeter. These bubbles are then characterized by a very large interfacial surface per unit volume, in a very small volume of liquid. For example, the interfacial surface per unit volume of the bubbles may be greater than 1000 m ¹ for a volume of the fluid less than 0.55 mm ³ . This dense dispersion of bubbles can form a cavitation pocket, of micrometric size in a direction substantially perpendicular to the direction of the flow, and micrometric to millimeter in a direction substantially parallel to the direction of the flow. At least one of the first portion 21, the second portion 22 and the third portion 23 has at least one dimension of its cross section to the longitudinal axis of the duct 20, less than 1 mm, or even less than 500 μm. Preferably, the entire duct 20 has at least one dimension of its cross section to its longitudinal axis, less than 1 mm, or even less than 500 μm. The reduced hydraulic diameter D2 can more particularly be appreciably less than 1 mm, preferably less than 800 μm, preferably less than 300 μm, preferably less than 150 μm, even more preferably less than 90 μm. The more the hydraulic diameter is reduced, the more the interfacial surface of the bubbles per unit of volume is increased and the more the phenomenon of micro-cavitation is improved.

The second portion 22 may have a cross section to the longitudinal axis x of the duct, with an aspect ratio greater than or equal to 3. In a known and common way in the field, the aspect ratio, also called aspect ratio, denotes the ratio between the longest dimension and the shortest dimension of the cross section, for example between one of its length and width, and the other of its length and width. According to an alternative or complementary example, the second portion 22 may have a cross section of area A1, substantially perpendicular to the longitudinal axis x of the duct, and the first portion 21 may have a cross section of area A2, substantially perpendicular to the longitudinal axis x of the duct, so that the fluid passage area ratio A1 / A2 is substantially greater than or equal to 3. An aspect ratio greater than or equal to 3, and / or a passage area ratio fluid greater than or equal to 3, makes it possible to confine the fluid in at least one dimension, relative to the dimensions of the cross section of the first portion 21. This confinement makes it possible to increase the flow speed 11b of the fluid at the level of the second portion 22. The increase in the flow speed of the fluid makes it possible to lower the local pressure and thus to generate cavitation, and preferably to achieve a turbulent flow regime. In addition, the reactor 2 can thus comprise a plurality of conduits 20, for example arranged in parallel, while remaining of a limited volume.

The reactor 2 can in fact comprise a plurality of conduits 20 arranged in parallel. A larger quantity of fluid can thus be degassed in parallel. For example, each of the conduits 20 can open out into the same separation chamber 4. Each of the conduits 20 can be connected to the same tank 3.

The flow 11c of the fluid can be turbulent downstream of the second portion 22, and in particular in the third portion 23. The flow can in particular have a Reynolds number greater than 2300. A turbulent flow makes it possible, on the one hand, to promote a stirring of the liquid phase of the fluid, and in particular to promote the mixing of bubbles and dissolved species, such as non-condensable gases, in the liquid phase of the fluid. Thus, the diffusion of the dissolved gases from the liquid phase to the liquid-gas interface, on the surface of the bubbles formed 12 by cavitation, can be accelerated. In addition, a turbulent flow makes it possible to avoid the presence of dead volume in the reactor 2. As is clear from the foregoing description, the Fluid flow velocity can be set so that the fluid flow is turbulent, having a Reynolds number greater than 2300, downstream of the second portion 22.

In addition, the turbulent flow of the fluid, in synergy with the use of a microfluidic conduit 20 and therefore the generation12 of a dispersion of bubbles with a high interfacial area, allows the intensification of the phase transfer 13 of the dissolved gases. Thus the proportion in the gas phase of the non-condensable gases can more quickly reach its equilibrium value given by Henry's law.

Furthermore, so that the proportion in the gas phase of the non-condensable gases can reach its equilibrium value according to Henry's law under the temperature and pressure conditions of the process, the third portion 23, or the third portion 23 plus a pipe connection 45 connecting the reactor 2 to the separation chamber 4, may have a length chosen to temporally dissociate the generation 12 of the bubbles by cavitation and the separation 14 of the liquid phase L and the gas phase G.

This temporal dissociation makes it possible to promote the establishment of the mass transfer equilibrium. Since the bubbles initially mainly comprise the fluid in its vapor form, the molar fraction of the non-condensable gases in the gas phase can thus be controlled, or even increased before the step of separating the liquid phase L and the gas phase G. In addition, Additional head losses can be induced during the flow 11c of the fluid in the third portion 23, the longer the third portion 23 is.

In order to optimize the efficiency of the degassing by method 1, the pressure and the temperature of the experimental set-up can be adjusted. The pressure P3 downstream of the second portion 22, and preferably up to the separation 14 of the liquid phase L and the gas phase G, can be chosen 16 so as to avoid redissolution of the gases in the liquid phase L. furthermore, maintaining 16 a low downstream pressure P3 induces additional pressure drops of the fluid during its flow 11c in the third portion 23 and therefore promotes the creation of a larger gas phase G.

The pressure P2 in the second portion 22 and the pressure P3 downstream of the second portion 22, and in particular in the third portion 23, are preferably less than the saturated vapor pressure (P _sat ) of the fluid at the temperature of the fluid in reactor inlet. According to Henry's law, the proportion at equilibrium of non-condensable gases in the gas phase G depends in part on the pressure conditions applied to the fluid. Maintaining a low pressure P3 of the fluid downstream of the second portion 22 makes it possible to promote the phase transfer of the non-condensable gases. During the development of method 1, the tests have shown that the lower the pressure P3 downstream of the second portion 22, the more efficient the degassing. In particular, a concentration of gas dissolved in the degassed liquid phase of less than 1 mg / L can be reached. The concentration of gas dissolved in the liquid phase can be measured by gas concentration probes 7, arranged upstream and / or downstream of the reactor 2. More particularly the pressure P3 downstream of the second portion 22 can be less than the ambient pressure, approximately 1 bar.

The flow rate and the pressure P3 in the third portion 23 can be adjusted in order to generate a flow having a cavitation number o less than 1 or even as low as possible in order to optimize the degassing. The cavitation number o is here defined as the ratio between the pressure drop inducing cavitation on the pressure drop generated by the flow, according to the following mathematical formula, with p the density of the fluid and U the speed of the fluid in the second portion 22. P - P _S at 0.5 pU ²

The pressure P3 downstream of the second portion 22 can be controlled 16 by a vacuum pump 5 connected to the separation chamber 4. The force of the vacuum applied by the vacuum pump 5 can for example be regulated as a function of the measurement of the pressure P3 by a pressure sensor 8 arranged downstream of the second portion 2, or even downstream of the reactor 2, as illustrated in FIG. 2.

According to Henry's law, the proportion at equilibrium of non-condensable gases in the gas phase G also depends on the temperature conditions applied to the fluid. The fluid can be 18 at a temperature between the solidification temperature and the boiling temperature of the fluid. Preferably, the fluid is maintained at a temperature within this range. Temperature control makes it possible to promote the flow 11 of the fluid in the reactor 2 and to promote the transfer of dissolved gases. In this temperature range, the higher the temperature, the more the viscosity of the fluid can be reduced. By controlling the temperature, the process allows a compromise between promoting the transfer of dissolved gases and limiting the risk of degrading compounds that may be present in the fluid, or even the fluid itself. Preferably, when the fluid is water, the fluid can be maintained at a temperature between 0 and 100 ° C.

The closer the temperature downstream of the second portion 22 is to that corresponding to the solubility of the dissolved gases, the lower, that is to say to a high Henry's constant, the more efficient the degassing. When the fluid flows 11 in the third portion 23, or even until the liquid phase L and the gas phase G are separated 15, the fluid can be at a temperature chosen so as to maximize Henry's constant, or in an equivalent manner so as to minimize the solubility of the gases dissolved in the liquid phase.

The temperature of the fluid can be controlled 18 by a heating device, preferably making it possible to maintain the reactor 2 at the desired temperature, or even the entire experimental set-up. For example, one can use a heat exchanger or a thermostatically controlled enclosure. Temperature sensors 6 can also be placed upstream and downstream of the reactor 2 in order to measure the temperature of the fluid, as illustrated in FIG. 2.

In order to optimize the efficiency of the degassing by method 1, the fluid may also have a viscosity of less than 5 mPa.s (10 ³ Pa.s) at the temperature of the implementation of the method. The fluid can more particularly have a viscosity of less than 2 mPa.s when the fluid is at a temperature of 20 ° C. Thus, the fluid can be sufficiently low viscous to facilitate its flow in the reactor 2, and thus facilitate its cavitation. When the conduit is a microfluidic conduit, the viscosity of the fluid may preferably be between 0.5 mPa.s and 5 mPa.s at the temperature for carrying out the process, and preferably between 0.5 mPa.s and 2 mPa.s, in order to facilitate its flow through this duct. The fluid can more particularly be water.

Depending on the choice of the pressures applied to the fluid and the temperature of the fluid, the method can be configured to remove a particular gas from among a plurality of non-condensable gases. For this, the temperature of the fluid, at least downstream of the second portion 22 of the conduit 20, can be chosen 18 as that corresponding to the lowest solubility of the target gas. Equivalently, this temperature can be chosen so as to maximize the Henry's constant of the target gas. The Henry's constant of a gas is generally maximum when the solubility of that gas is minimum. For example, the Henry's constant of oxygen, nitrogen, carbon dioxide in water is maximum at a temperature substantially between 100 and 130 ° C. Typically, an increase in the temperature of the fluid promotes degassing. For example, Henry's constant in water is maximum at T = 100 ° C for oxygen 0 ₂ and dinitrogen N ₂ but not for C0 ₂ for which Henry's constant is maximum T = 130 ° C. Thus, if the fluid is water under cavitation at a temperature of approximately 130 ° C, the degassing carried out by the process will be more selective towards the C0 ₂ than _{towards N 2} and 0 _2. A temperature close to 100 ° C may be more appropriate to maximize the degassing of N ₂ and 0 _2.

The temperature downstream of the second portion 22 can be chosen so as to promote the liquid phase diffusion of a gas among the plurality of dissolved gases. Since the temperature influences the rate of diffusion of the gases in the liquid phase, a more or less rapid degassing of the various dissolved gases can thus be obtained. Thus the degassing of the fluid can be made more selective for a particular dissolved gas.

The invention is not limited to the embodiments described above and extends to all the embodiments covered by the claims.

For example, provision can be made for the method to include the successive flow of the fluid through a plurality of reactors, before the step 14 of separating the liquid phase G and the gas phase.

Provision can also be made for the at least one duct to have a succession of geometries configured to generate bubbles in the fluid by cavitation. More particularly, each of these geometries can comprise the three portions described above, the third portion of a of these geometries playing, for example, the role of the first portion of the following configuration.

LIST OF NUMERICAL REFERENCES

1 process

10 Supply a fluid at the inlet of a reactor 11 Allow the fluid to flow through the reactor

11a Fluid flow in the first portion 11b Fluid flow through the second portion 11c Fluid flow in the third portion 12 Generation of bubbles by cavitation 13 Phase transfer of dissolved gases

14 Separate the liquid phase and the gas phase

15 Recover the liquid phase

16 The fluid is under pressure P3

17 The fluid is under a pressure P1 18 The fluid is at a temperature T

19 Recover the gas phase

2 Reactor

20 Led

21 First portion 22 Second portion

23 Third portion

3 Tank

30 Connection duct

31 Mass flow measuring device 4 Separating device

40 First speaker

41 Permeable membrane

42 Tank

43 Liquid phase discharge pipe 44 Gas phase discharge pipe

45 Connection duct

5 Pump

5 ’Gas pump

6 Temperature sensor 7 Dissolved gas concentration probe

8 Pressure sensor D1 Hydraulic diameter of the first portion D2 Reduced hydraulic diameter D3 Hydraulic diameter of the third portion L Liquid phase G Gas phase

P1 Pressure in the first portion P2 Pressure in the second portion P3 Pressure in the third portion

Claims

1. Process (1) for degassing a fluid comprising the following steps:

• supply (10), at the inlet of a reactor (2), a fluid comprising at least one dissolved gas; then

• making the fluid flow (11) through the reactor (2), the reactor comprising at least one microfluidic duct (20), the at least one microfluidic duct (20) comprising a first portion (21), a second portion (22) and a third portion (23), the second portion (22) being disposed between the first portion (21) and the third portion (23), the second portion having a reduced hydraulic diameter (D2) with respect to the first portion and in the third portion, the reduced hydraulic diameter (D2) being less than 1 mm, and the flow being configured so that bubbles are generated (12) by micro-cavitation, the fluid then comprising a liquid phase ( L) and a gas phase (G), then

• allow at least partial transfer (13) of at least one dissolved gas present in the liquid phase (L) to the gas phase (G);

• separating (14) the liquid phase and the gas phase;

• recover (15) the liquid phase to obtain the degassed fluid, the process (1) being free from the application of ultrasound to the fluid between the stage in which the fluid is supplied (10) at the inlet of the reactor (2) and the step of separating (14) the liquid phase (L) and the gas phase (G).

2. Method (1) according to the preceding claim, wherein the reduced hydraulic diameter (D2) is less than 300 pm, preferably less than 150 pm, even more preferably less than 100 pm.

3. Method (1) according to any one of the preceding claims, wherein the liquid phase and the gas phase are separated at the outlet of the reactor, the third portion (23) having a length chosen to temporally dissociate the generation (12) of the bubbles by cavitation and the separation (14) of the liquid phase (L) and the gas phase (G).

4. Method (1) according to any one of the preceding claims, wherein the at least one duct (20) comprises one of a diaphragm, or even a micro diaphragm, a Venturi, or even a micro-Venturi and a step. , even a micro step.

5. Method (1) according to any one of the preceding claims, wherein the second portion (22) has a cross section to a longitudinal axis (x) of the duct, with an aspect ratio greater than or equal to 3.

6. Method (1) according to any one of the preceding claims, wherein the first portion (21) has a cross section of area A1, and the second portion (22) has a cross section of area A2, the sections transverse being perpendicular to a longitudinal axis (x) of the duct, the ratio A1 / A2 being greater than or equal to 3.

7. Method (1) according to any one of the preceding claims, wherein the fluid has a viscosity of less than 5 mPa.s at an implementation temperature of the method, preferably the viscosity of the fluid being between 0.5 mPa.s and 5 mPa.s at a temperature of 20 ° C.

8. A method (1) according to any preceding claim, wherein the flow rate (11) of the fluid in the at least one reactor (2) is set so that the flow is turbulent at least in downstream of the second portion (22).

9. A method (1) according to any preceding claim, wherein when the fluid flows (11c) in the third portion (23), the fluid is (16) at a pressure (P3) lower than the pressure (P1) of the fluid in the first portion (21).

10. A method (1) according to any preceding claim, wherein the pressure (P3) in the third portion (23) is less than ambient pressure.

11. Method (1) according to any one of the preceding claims, wherein, when the fluid flows (11c) in the third portion (23), or even until the liquid phase (L) and the phase. gas (G) are separated (15) from each other, the fluid is (18) at a temperature between the solidification temperature of the fluid and the boiling temperature of the fluid, the temperature of the fluid being controlled by a heating device.

12. Method (1) according to any one of the preceding claims, wherein, when the fluid flows (11c) in the third portion (23), or even until the liquid phase (L) and the phase. gas (G) are separated (15) from each other, the fluid is (18) at a temperature chosen so as to maximize the Henry's constant of the at least one dissolved gas, the temperature of the fluid being controlled by a heating device.

13. Method (1) according to any one of the preceding claims, wherein, when the fluid flows (11c) in the third portion (23), or even until the liquid phase (L) and the gas phase (G) are separated (15) from each other, the fluid comprising a plurality of dissolved gases, the temperature is chosen (18) so as to maximize the Henry constant of one gas among the plurality of dissolved gases, the temperature of the fluid being controlled by a heating device.

14. Method (1) according to any one of the preceding claims, wherein, when the fluid flows (11c) in the third portion (23), or even in the reactor (2), or even until the liquid phase (L) and gas phase (G) are separated (15) from each other, the fluid comprising a plurality of dissolved gases, the fluid is (18) at a temperature chosen so as to promote the transfer (13) at least partial of at least one dissolved gas, the temperature of the fluid being controlled by a heating device.

15. Method (1) according to any one of the preceding claims, wherein the reactor (2) comprises a plurality of conduits (20), preferably arranged in parallel.