FR3047910A1 - REGENERABLE FILTER, PROCESS FOR REGENERATING SAID FILTER AND USE THEREOF - Google Patents

Abstract

The present invention relates to a regenerable filter, preferably a regenerable air filter, comprising: a filtering matrix, adapted to allow the circulation of a flow of fluid therein, from an inlet to an outlet of said filtering matrix, in order to filter said fluid, and - at least one heating element comprising at least a first and second electrode, positioned at a defined distance from one another and connected to each other via a conductive material, said conductive material being a positive temperature coefficient material, adapted to function as a heating resistor and allow the electrical connection between said first and second electrodes to be cut off when the temperature of said conductive material reaches a threshold temperature.

Description

REGENERABLE FILTER, PROCESS FOR REGENERATING SAID FILTER AND

USE OF SAID METHOD

Field of the invention

The present invention relates to the field of filters, more particularly regenerable filters (ie having the capacity to be regenerated). More specifically, the invention relates to an air filter adapted for use within an electrical system of a motor vehicle for filtering air entering a fuel cell membrane proton exchange (whose acronym is "PEMFC" for: "Proton Exchange Membrane Fuel Cell".

State of the art

A proton exchange membrane fuel cell can be used for the production of electricity for a motor vehicle, more particularly for an electric or hybrid type vehicle, in order to have a source of electrical energy. within said motor vehicle.

A proton exchange membrane fuel cell is an electrochemical reactor producing electricity and heat by reacting: - on the one hand hydrogen, at the anode, which will have the effect of to release electrons in the circuit and to generate H + ions which will cross the electrolyte, consisting of a non-conductive membrane, - on the other hand of air, at the cathode; the oxygen contained in this air recombines with the aforementioned H + ions and electrons brought by the circuit to produce water and heat.

The electrochemical reaction between the oxygen of the air and the H + ions takes place at a multitude of catalyst-activated reaction sites, generally in the form of platinum particles dispersed on a porous substrate.

To ensure optimum performance and maximum life of these reaction sites, the presence of any particulate or gaseous pollutants in the air should be minimized.

Particulate pollutants can clog the porous medium that diffuses oxygen to the reaction sites.

Gaseous pollutants, especially sulfur dioxides (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs: benzene, toluene, formaldehyde) compete with the oxygen of the air, reacting or fixing on reaction sites which are then neutralized.

Some pollutants may also migrate within the electrolyte membrane and reduce its ionic conductivity and electrical insulation qualities. The impact of certain pollutants is irreversible, especially S02, accelerating the aging of the battery and reducing its life. Some pollutants may be partially discharged by rinsing the battery with "new" air or by performing transient operating cycles, particularly Open Circuit Voltage (OCV) pulses, which regenerate the catalytic sites.

Various studies highlight the fact that the maintenance of a low drift in the operation of the cell requires good filtration of the air at admission, in particular to ensure on average less than a few ppb (parts per billion) of SO 2 to the input, and less than a few tens of ppb of NOx. This depends strongly on the use environment, knowing for example that the SO 2 contents in the atmosphere can vary from around ppb in the absence of pollution to more than 100 ppb in polluting conditions, for example in urban or industrial areas.

Advances in the design of proton exchange membrane cells, and more particularly their electrodes and reaction sites, are leading to a reduction in the amount of catalyst used to reduce the cost of the system. For example, the platinum catalyst (chemical symbol: Pt) represents a significant cost in first generation batteries, with more than 100g of platinum needed for a battery that delivers 80 kW peak. The reduction of the amount of platinum generates a greater sensitivity of the battery to the pollutants present in the air and increases the importance and the stake of a good filtration of the gases with the intake of air.

In order to limit the impact of the particulate and / or gaseous pollutants mentioned above, filters have been developed in the prior art to protect PEMFC cells. In order to guarantee efficient and durable filtration, the most severe operating conditions make it necessary to provide a high dosage of absorbent material or adsorbents in the filter matrix of the filters used. In order to increase the life of these filters, preserve their maximum efficiency and increase the operating time before their replacement (and thus reduce the cost of maintenance), it is interesting to consider the possibility of regenerating these filters in situ, namely directly on vehicle, so as to regenerate their filtering properties without having to replace them.

The simplest method for regenerating a filter is to "warm up" it, beyond typical ambient conditions (ie> 50 ° C), while rinsing with fresh air with little or no pollution. It is thus possible to "desorb" the pollutants from the filter matrix (typically activated carbon) and thus "clean" the filter by giving it properties similar to those of a new filter.

Fuel cells for Full Power FCEV vehicles require the use of an air compressor that is powerful enough to pressurize the air in the fuel cell to a minimum. pressure up to 2 or 3 bars, which increases the peak power density without increasing the number of cells. It will be noted that at the most heavily loaded operating points, particularly in summer (during which the temperatures are generally high), the temperature of the air at the outlet of the compressor can easily exceed 100 ° C, or even go up to 150 / 200 ° C on the most dimensioning points. It is disadvised to dispose the filter just downstream of the compressor, it would indeed lose its filtering qualities and could desorb pollutants at high temperature that would then pour into the pile, affecting de facto its life and performance as indicated above. In addition, such temperatures are likely to affect the proper operation of the filter and its durability over time.

It is also not recommended to dispose the filter just downstream of the air cooler arranged after the compressor. Indeed, the "CAC" ("Charge Air Cooler", in English language, which can be translated into French as: "Chiller Air Supercharging") aims to control an air temperature in the vicinity of that of the battery, to ensure that it is included, as a rule, between 60 and 90 ° C, which temperature is, despite everything, also too high to ensure proper and durable operation of the filter. Taking into account these constraints, the most technically advisable arrangement of the air filter on a fuel cell is to dispose it upstream of the inlet line, namely upstream of the compressor. air.

In view of the problems described above, the object of the invention is notably the development of a regenerable filter, more particularly adapted to fulfill the function of an air filter in a power generation system comprising a battery. fuel, such as a PEMFC; said filter having a very good performance and a very satisfactory durability over time, without resorting to technical solutions too expensive.

Presentation of the invention

Consequently, the invention relates to a regenerable filter, preferably a regenerable air filter, comprising: a filtering matrix, adapted to allow the circulation of a flow of fluid within it, from an inlet to an outlet of said matrix filter, so as to filter said fluid, and - at least one heating element comprising at least a first and second electrode, positioned at a defined distance from one another and connected to each other by the intermediate of a conductive material, said conductive material being a positive temperature coefficient material, adapted to function as a heating resistor and allow the electrical connection between said first and second electrodes to be cut off when the temperature of said conductive material reaches a threshold temperature . The invention therefore relates to a filter adapted to be regenerated after a specific use. For the purpose of the present invention, the term "regenerate" is intended to clean the filter by removing it from the pollutants absorbed or adsorbed within said filter, so that the latter finds identical, similar or similar properties or, at all the least, approaching these original properties. The invention more particularly relates to the regeneration of a regenerable fluid filter by using a heat source for increasing the temperature of the filter matrix of said regenerable filter. As soon as the filtering matrix reaches a predetermined temperature, or during the heating stage of said filtering matrix, an unpolluted fluid (for example, a flow of air) is conducted in the direction of the said filtering matrix in order to eliminate (For example, desorbing) the pollutants of said filter matrix. Increasing the temperature of the filter matrix makes it easier to remove the pollutants with the aid of said unpolluted fluid.

Particularly preferably, the aforementioned at least one heating element is adapted to heat, by means of an electric current, said filter matrix and / or said fluid stream so as to regenerate partially or completely said filter matrix.

According to a first embodiment of the invention, the heating element is connected to the filtering matrix.

Advantageously, according to this first embodiment of the invention, the filter comprises a first and a second heating element, said filter matrix being positioned "sandwiched" between said first and second heating elements.

According to a second embodiment of the invention, the heating element is positioned upstream of the inlet of the filtering matrix.

Advantageously, and whatever the embodiment of the invention in question, said at least first and second electrodes each comprise a plurality of conductive elements, connected together like the teeth of a comb, said conductive elements of said first electrode being positioned head-to-tail relative to the conductive elements of said second electrode.

Advantageously, and whatever the embodiment of the invention in question, the filtering matrix is folded, preferably zigzag, so as to increase the surface of said filter matrix. The effect of this measure is to grow the filter medium and thus increase its performance while reducing the loss of load of the whole.

Advantageously, and whatever the embodiment of the invention in question, the filter matrix comprises an adsorbent. Advantageously, the filter matrix comprises activated carbon or consists essentially of activated carbon, or even consists of activated carbon.

Advantageously, and whatever the embodiment of the invention in question, the first and second electrodes, the distance between them and / or the conductive material are selected so that the electrical connection between said first and second electrodes and the second electrode is cut off, the temperature of said conductive material reaches a threshold temperature of at least about 50 ° C, preferably between about 50 and about 110 ° C, preferably between about 60 and about 100 ° C.

Advantageously, and whatever the embodiment of the invention in question, said first and second electrodes are fixed on a non-conductive support. Preferably, said non-conductive support comprises a woven or non-woven polymer. The invention also relates to a heating element as defined above.

Another subject of the invention relates to a system for producing electricity comprising a fuel cell, such as a proton exchange membrane fuel cell, and an air supply, adapted to supply said battery with electricity. fuel in air, wherein said air supply comprises a filter according to the invention, as defined above. The invention also relates to a motor vehicle, preferably electric or hybrid, comprising the aforementioned system.

Another subject of the invention relates to a method for regenerating a filter according to the invention, as defined above, said method comprising the following steps: a) allowing the circulation of a flow of fluid within said filter matrix, the inlet of said filter matrix to the output of said filter matrix, b) heating said filter matrix and / or said fluid flow so as to regenerate partially or completely said filter matrix, c) leave the heating step of said matrix heating and / or said fluid flow b) continue until the temperature of the conductive material reaches a threshold temperature, temperature at which the heating of said conductive material is stopped automatically by increasing the electrical resistance of the conductive material .

According to a preferred embodiment, the step of heating said heating matrix and / or said fluid stream b) is implemented by means of said at least one heating element. The invention also relates to the use of the method mentioned above to partially or completely regenerate said filter matrix, wherein said method is triggered at the end of use of said motor vehicle, for example after the parking of said motor vehicle.

Brief descriptions of the drawings

The purpose (s), object (s) and advantages (s) of the present invention will appear more clearly on reading the description which follows, made with reference to the drawings, in which: FIG. 1 shows, schematically, a first and a second electrode positioned at a distance from each other and connected by means of a conductive material, said material being adapted to behave as a heating resistor; - Figure 2 represents a heating element in which these first and second electrodes - remotely positioned and connected by means of the conductive material adapted to behave as a heating resistor - are fixed on a support; - FIG. 3 shows a filtering matrix positioned between a first and a second element of heating, said heating elements and said filtering matrix together forming a "sandwich"; - FIG. 4 represents a stack formed of a first, a second and a third heating element and a first and second filter matrix, together forming a filter; - Figure 5 shows a folded filter matrix ("zigzag") comprising a heating element located on each its upper and lower ends, and - Figure 6 shows a filter matrix and a heating element for heating a fluid flow upstream of said filter matrix.

detailed description

The purpose of the following detailed description is to explain the invention in a sufficiently clear and complete manner, particularly by way of examples, but should not be considered as limiting the scope of protection to particular embodiments. and the examples presented below.

Figure 1 shows, schematically, a first electrode 10 and a second electrode 20 positioned at a determined distance from each other. The first electrode 10 is provided with conductive elements 11, 12, 13, 14, 15 and 16 connected together like the teeth of a comb. Similarly, the second electrode is also provided with conductive elements 21, 22, 23, 24, 25 and 26, also connected to each other like the teeth of a comb. The various conductive elements 11-16 of said first electrode 10 are positioned "head to tail" with respect to the conductive elements 21-26 of said second electrode 20.

It should be noted that in the example illustrated in FIG. 1, the first electrode 10 and the second electrode 20 each have six conductive elements. A quantity of conductive elements more or less important can also be considered as needed.

The first electrode 10 and the second electrode 20 are remotely positioned but connected with a conductive material 30. This conductive material 30 has the ability to function as a heating resistor. This means that said material 30 is adapted to allow the flow of an electric current between said first electrode 10 and said second electrode 20. The electric current thus obtained induces an increase in the temperature of the conductive material 30. According to the invention, the Conductive material 30 is selected from conductive materials whose resistance increases with increasing temperature. A material of this type is referred to as a "CTP property material" (for: positive temperature coefficient). In English, the name used for this type of material is: "positive temperature coefficient" (whose acronym is "PTC").

The operating principle of the assembly shown in Figure 1 is based on the fact that: the presence of the conductive material 30 allows the passage of the electric current between the first electrode 10 and the second electrode 20 until the temperature of the material conductor 30 reaches a predetermined threshold, - the electrical resistance of the conductive material 30, resulting from the presence of the electric current, increases by increasing the temperature of the conductive material 30, and - the flow of the current between the first electrode 10 and the second electrode 20 stops when the electrical resistance - related to the temperature of the conductive material 30 - reaches a predetermined threshold.

In other words, when the electric current passes between the first electrode 10 and the second electrode 20, the temperature of the conductive material 30 increases to a predetermined threshold temperature, at which the heating of said conductive material 30 is stopped because of the increased resistance of the conductive material 30.

This operating principle can be exploited, particularly advantageously, in the context of a process for regenerating a regenerable fluid filter (for example a regenerable air filter), the temperature of said filter being increased - in order to regenerate / cleaning the regenerable filter - up to a predetermined maximum level (predetermined temperature threshold value), in order to preserve the integrity of said regenerative filter and, in doing so, ensure correct operation of said filter and guarantee very good durability over time of it.

Based on the aforesaid principle of operation, a first aspect of the invention comprises the integration, within the filter matrix of a regenerable fluid filter, or in the vicinity thereof, of an element having a first electrode 10, a second electrode 20 and a conductive material 30 as shown in Figure 1. This is particularly of interest in the development of a CTP sensor (positive temperature coefficient). In other words, even in the embodiment according to which the filtering matrix is not directly heated by the current flowing between the first and second electrodes 10, 20 (said filtering matrix being able to be heated by any other type of heat source). heat, for example by a "conventional" resistance a sensor provided with elements such as shown in Figure 1 can be used: - to indicate to the user and / or a control / control system that the threshold temperature determined a has been reached at the level of the filtering matrix of the regenerable fluid filter according to the invention, and possibly - stopping the heating of said filter matrix after said threshold temperature has been reached.

A PTC sensor may be used if the filter matrix comprises a conductive material and a current capable of passing from a first end to a second end of said filter matrix, thereby increasing its temperature. Such an option is possible in the case of a filter matrix comprising activated carbon.

Still based on the operating principle described above, a second aspect of the invention comprises integrating the elements shown in Figure 1 in an electric circuit used to heat the filter matrix of a regenerable fluid filter. Thus, when the threshold temperature is reached at the level of the filtering matrix, the electric circuit used to heat the filtering matrix of said filter is automatically cut off, thus preserving the integrity of said regenerable fluid filter and, thereby, ensuring correct operation of said filtering filter. filter and guaranteeing very good durability over time. According to this second aspect of the invention, the elements shown in FIG. 1 can be used to produce a heating element that can be used to heat either the filter matrix of a regenerable fluid filter (first embodiment of the second aspect of the invention). invention), or the flow of a fluid before it reaches said filter matrix (second embodiment of the second aspect of the invention). Both variants are described with reference to Figures 3, 4, 5 and 6.

FIG. 2 shows a heating element 40, said heating element comprising a first electrode 10 and a second electrode 20 integrated with a predetermined quantity of a conductive material 30. The assembly composed of the first electrode 10, the second electrode 20 and conductive material 30 is positioned on a support 35. The assembly as shown in FIG. 2 forms a structural entity, said structural entity being able to be used for heating a filter matrix as shown in FIGS. 5.

The support 35 may comprise (or consist essentially of, or even consist of) a polymer, such as a woven or nonwoven polymer. The support 35 can also close (or, preferably, seal) a sealed element, in order to prevent the passage of the fluid to be filtered through said support 35.

According to another embodiment, the heating element 40 is adapted to heat an air flow upstream of the inlet of the filtering matrix, in order to indirectly heat said filter matrix using the air flow of which the temperature has been increased by means of the heating element 40. An example of this type of configuration is illustrated in FIG.

Figure 3 illustrates a first use of the heating element 40 shown in Figure 2, for heating the filter matrix 50 of a regenerable fluid filter. A first heating element 40 is positioned against the upper end of the filtering matrix 50 and a second heating element 40 is, for its part, positioned against the lower end of said filtering matrix 50. During normal use of the filter, a flow of fluid, for example a flow of air, can flow through the filter matrix 50, an inlet 51 towards an outlet 52. The path of the fluid flow is illustrated using arrows 60 and 61; the arrow 60 thus making it possible to convey the flow of said fluid to the inlet 51 of the filter matrix 50, and the arrow 61 making it possible to materialize the fluid at the outlet of said matrix 50.

In "normal" use, the heating elements 40 are not used. The matrix 50 is used at a temperature determined by the environment of said filtering matrix 50, as well as by the temperature of the fluid flowing through said filtering matrix 50, from the inlet 51 to the outlet 52. It is found that the filter matrix 50 needs to be regenerated, the heating elements 40 are used in order to increase the temperature of said filter matrix 50 and thereby desorb the pollutants. During the regeneration process, the path of the fluid flowing through the filter matrix 50 differs from the fluid path during "normal" use (see above). Indeed, during a "normal" use, the fluid emitted at the outlet of the filtering matrix 50, through the outlet 52, travels towards a part of the system where said fluid is necessary, for example towards a fuel cell, such as a PEMFC fuel cell. Conversely, during the regeneration step of the filter matrix 50, the latter is heated to desorb the pollutants and evacuate them. In order to preserve the device (s) which are positioned downstream of said filter matrix 50, the fluid comprising the pollutants desorbed by heat can not be sent to this device (s). Therefore, during the aforesaid step of the regeneration of said filter matrix 50, said fluid leaving said filter matrix 50 (materialized by the arrow 61) - and including the desorbed pollutants - is led to an evacuation where the fluid used to clean the filter matrix can be rejected / evacuated.

In the embodiment shown in FIG. 4, the first, second and third heating elements 40 are used to heat first and second filter matrices 50. According to the embodiment illustrated in FIG. 4, the three heating elements 40 are adapted to efficiently heat the first and second filter matrices 50.

In the embodiment illustrated in FIG. 5, the filtering matrix 55, provided with two ends 56, 57, is advantageously in the form of a "zigzag". In other words, the filtering matrix 55 is folded to increase its developed area, without requiring an increase in the size of the filter. On each of the two upper and lower faces of the filtering matrix 55 is arranged a heating element 45, whose shape matches that of each of said upper and lower faces of the filtering matrix 55.

In the embodiment illustrated in FIG. 6, a filtering matrix 155 is used in combination with a heating element 140. The heating element 140, used to heat a fluid to be filtered (for example an airflow), is positioned upstream of the filtering matrix 155. The path of the fluid that moves towards the heating element 140 and the filtering matrix 155 is embodied by means of the arrow 160. The heating element 140 may, by for example, having the form of a grid to allow the passage of a determined volume and / or flow rate (s) of fluid (consisting, for example, of a flow of air) to the filter matrix 155. When the fluid reaches and passes through the heating element 140, it is heated before coming into contact with the filter matrix 155. The temperature of said fluid is thus adjusted / controlled, which also makes it possible to adjust / control the temperature of said filter matrix 155 through which the fluid will flow. In the "normal" use of the filter, the heating element 140 is not used. The fluid passes through the heating element 140 without heat exchange between said fluid and the heating element 140. On the other hand, when the filter matrix has to be regenerated, the heating element 140 is used to heat the fluid which is The invention as described above, with reference to Figs. 1-6, is particularly suitable for use as a regenerable air filter (i.e., the filter matrix of which can be regenerated). In this context, a preferred embodiment of the invention relates to the use of an air filter according to the invention upstream of the air supply of a fuel cell, in particular from a fuel cell. PEMFC fuel. Indeed, the use of a fuel cell, in particular a PEMFC fuel cell, requires efficient filtration of the air for supplying the fuel cell. This is all the more important as the air intended for the fuel cell is the ambient air, coming from the environment in which the motor vehicle is used, which environment generally has particulate and / or gaseous pollution ( often both) particularly important.

When using a motor vehicle (in particular an FCEV) provided with a filter according to the invention, different possibilities exist to regenerate the filter matrix of this filter. A first possibility is to regenerate the filter at fixed intervals. In this regard, the filter according to the invention can be connected to a control / control system which controls, for example, one or more parameters inherent to the use of this motor vehicle. In this case, the command / control system is adapted to trigger the regeneration of the filter matrix of a filter after a determined number of kilometers traveled by the motor vehicle in which the filter is used.

An alternative is to correlate the regeneration of the filter according to the invention to a certain period of use of the motor vehicle.

Particularly advantageously, the regeneration process of the filter according to the invention can be parameterized to occur at the least untimely time possible, for example after parking the motor vehicle (and, generally, at the end of a use of the motor vehicle). This means that the filter regeneration process can occur without the knowledge of the user and without causing any particular discomfort.

Claims (14)

1. Regenerable filter, preferably a regenerable air filter, comprising: - a filter matrix (50, 55, 155), adapted to allow the circulation of a flow of fluid therein, of an inlet (51, 56) to an outlet (52, 57) of said filter matrix (50, 55, 155), for filtering said fluid, and - at least one heating element (40, 45, 140) comprising at least a first (10) and second (20) electrodes, positioned at a defined distance from each other and connected to each other via a conductive material (30), said conductive material (30) being a material with a positive temperature coefficient, adapted to function as a heating resistor and to allow the electrical connection between said first (10) and second (20) electrodes to be cut off when the temperature of said conductive material (30) reaches a threshold temperature. 2. The filter of claim 1, wherein said at least one heating element (40, 45, 140) is adapted to heat, by means of an electric current, said filter matrix (50, 55) and / or said flow fluid to partially or completely regenerate said filter matrix (50, 55, 155). The filter of claim 1 or 2, wherein the heating element (40,45) is connected to the filter matrix (50,55). 4. Filter according to one of the preceding claims, said filter comprising a first and a second heating element (40, 45), wherein said filter matrix (50, 55) is sandwiched between said first and second heating elements. (40, 45). The filter of claim 1 or 2, wherein the heating element (140) is positioned upstream of the inlet of the filter matrix (155). 6. Filter according to one of the preceding claims, wherein said at least one first (10) and second (20) electrodes each comprise a plurality of conductive elements (11-16, 21-26) connected together like the teeth of a comb, said conductive elements (11-16) of said first electrode (10) being positioned head-to-tail with respect to the conductive elements (21-26) of said second electrode (20). 7. Filter according to one of the preceding claims, wherein the filter matrix (55) is folded, preferably zigzag, so as to increase the surface of said filter matrix (55). 8. Filter according to one of the preceding claims, wherein the filter matrix (50, 55, 155) comprises an absorbent such as activated carbon. 9. The filter according to one of the preceding claims, wherein the first (10) and the second (20) electrodes, the distance between them and / or the conductive material (30) are selected (s) so that the electrical connection between said first (10) and second (20) electrodes is cut, the temperature of said conductive material reaches a threshold temperature of at least about 50 ° C, preferably between about 50 and about 110 ° C, preferably between about 60 and about 100 ° C. 10. Filter according to one of the preceding claims, wherein said first (10) and the second (20) electrodes are fixed on a support (35) non-conductive. The filter of claim 10, wherein said non-conductive carrier (35) comprises a woven or non-woven polymer. 12. Process for regenerating a filter as defined in one of claims 1 to 11, said method comprising the following steps: a) allowing the circulation of a fluid flow within said filter matrix (50, 55, 155 ), from the inlet (51, 56) of said filter matrix to the outlet (51, 56) of said filter matrix (50, 55, 155), b) heating said filter matrix (50, 55, 155) and / or said fluid stream so as to partially or completely regenerate said filter matrix (50, 55, 155), c) leave the heating step of said heating matrix (50, 55, 155) and / or said fluid flow b ) continue until the temperature of the conductive material (30) reaches a threshold temperature, at which temperature the heating of said conductive material (30) is stopped automatically by increasing the electrical resistance of the conductive material (30) 13. The method of claim 12, wherein the step of heating said heating matrix (50, 55, 155) and / or said fluid stream b) is implemented by means of said at least one heating element (40). , 45, 155). 14. Use of the method according to claim 12 or 13 for regenerating partially or completely said filter matrix (40, 55, 155), wherein said method is triggered at the end of use of said motor vehicle, for example after the parking of said motor vehicle .