AIR FLOW FILTRATION SYSTEM

Abstract

AIR FLOW FILTRATION SYSTEM The invention relates to a filtration system (1) for an airflow (2) containing particles (3), comprising: a support (10); an active layer (11) disposed on the support (10), the active layer (11) being impermeable to the airflow (2); and means (12) for directing the airflow towards a surface (S) of the active layer (11); the active layer (11) being formed of a material comprising a polymer and at least one plasticizer of the polymer capable of migrating towards the surface (S) of the active layer (11) to form a plasticizer film for trapping the particles (3). Figure to be published with the abstract: Figure 2

Description

Title of the invention: AIR FLOW FILTRATION SYSTEM TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of air filtration. The invention relates more particularly to a system for filtering an airflow by trapping particles suspended in the air. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Air quality is an essential parameter for ensuring a good quality of life, particularly in cities and urban areas. Among the causes of air pollution, fine particulate matter (PM) is particularly dangerous for human health. These particles are produced largely by human activities related to industry and transportation. They are responsible for health problems such as impaired lung function and can lead to a reduction in life expectancy.

[0003] PM fine particles are particles with an aerodynamic diameter of less than 10 pm. They are not retained by the upper respiratory tract (nose, mouth) and are therefore "breathable." PM fine particles are often classified according to their size. The designation PM10 is used for particles with an aerodynamic diameter of less than 10 pm; PM2.5 for particles with an aerodynamic diameter of less than 2.5 pm; and PM10 for particles with an aerodynamic diameter of less than 1 pm. The aerodynamic diameter of a particle is an equivalent quantity used to describe the aerodynamic behavior of particles in a gas flow such as an airflow. The aerodynamic diameter of a particle is defined as the diameter of a sphere with a unit density (1 g / cm³) and having the same terminal settling velocity as said particle in a fluid at rest.In the remainder of this application, the term "diameter" will be used to refer to the aerodynamic diameter of a particle.

[0004] Various filtration systems are put in place to improve air quality in buildings (homes, schools, hospitals, offices, shops, etc.), industrial environments, vehicle interiors, etc. These systems generally incorporate a filter (or a combination of several filters) which captures particles suspended in the air as the air circulates through the filter.

[0005] The most common filters are mechanical filters and electrostatic filters.

[0006] Mechanical filters are classified according to their efficiency: • “ISO Coarse”, “ePMIO”, “ePM2.5” and “ePM1” classes (according to ISO 16890) for coarse, medium and fine air filters; and • classes “E” (E10, Eli, E12), “H” (H13, H14) and “U” (U15, U16 U17) (according to standard EN 1822) for high efficiency air filters.

[0007] High-efficiency particulate air (HEPA) filters, classified as H13 or H14, are very common. They are used, for example, in hospitals and in cleanrooms in the microelectronics industry. They have an efficiency greater than 99.95% for particles larger than 0.3 µm in diameter. However, these filters have a significant pressure drop (on the order of several hundred Pa) and require a powerful air circulation system to guarantee a minimum airflow. They are therefore not suitable for low-energy air filtration systems, such as portable and self-contained (battery-powered) air purification systems.

[0008] Electrostatic precipitators, also called "electrostatic precipitators," are complex and generally bulky devices that use an electrostatic force to extract particles (previously highly charged) from the airflow. They are used, for example, in industrial flue gas dust collection systems (thermal power plants, waste incinerators, cement plants, etc.) and in air handling units (AHUs) for commercial buildings. Electrostatic precipitators have a lower efficiency than HEPA filters and require the use of very high voltages to generate the strong electric field needed to attract the particles. Summary of the invention

[0009] It is observed that there is a need to provide an airflow filtration system which offers a good compromise between efficiency and pressure drop and which is simple to manufacture and integrate.

[0010] According to the invention, this need is met by providing a filtration system for an airflow containing particles, this system comprising: • a support; • an active layer deposited on the substrate, the active layer being airtight; and • means for directing the airflow towards a surface of the active layer; the active layer being formed of a material comprising a polymer and at least one plasticizer capable of migrating towards the surface of the active layer to form a plasticizer film capable of trapping particles.

[0011] The surface of the active layer is electrically charged by the effect of the plasticizer molecules, thus trapping particles contained in the airflow, which naturally carry partial charges. The bonds created by these charges The partials are small but nonetheless sufficient to trap particles. Furthermore, since the active layer is airtight, it does not create resistance to airflow.

[0012] The filtration system according to the invention thus presents the same advantages as electrostatic filters, namely a low pressure drop and a long service life, while being simpler to manufacture and integrate (due in particular to the absence of an electronic circuit to manage the electric field).

[0013] Compared to conventional filtration systems based solely on mechanical filters, the filtration system according to the invention offers a better compromise between efficiency and pressure drop. Furthermore, the surface of the active layer can be cleaned and regenerated several times, unlike a mechanical filter which must be replaced periodically.

[0014] In a first embodiment, the filtration system is devoid of a mechanical filter.

[0015] In a second embodiment, the filtration system further comprises an air filter of class “ISO Coarse”, “ePMIO” or “ePM2.5”. This air filter can be located upstream or downstream of the active layer in the direction of airflow. The mechanical filter, combined with the active layer, makes it possible to achieve a filtration efficiency close to that of very high efficiency air filters (class “H” filters or HEPA filters) but with a much lower pressure drop.

[0016] The air filter is preferably separated from the surface of the active layer by a distance greater than 1 mm, more preferably between 10 mm and 50 mm.

[0017] In addition to the characteristics mentioned in the preceding paragraphs, the filtration system according to the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • the polymer is poly(vinyl chloride); • the active layer material includes at least one secondary plasticizer of poly(vinyl chloride); • the active layer material comprises between 15% and 45% by mass of poly(vinyl chloride) and between 55% and 85% by mass of plasticizer; • the filtration system also includes a device for circulating the airflow; • the filtration system further includes a housing containing the active layer, the airflow circulation device and the means for directing the airflow; • The case includes: • an upstream compartment in which the airflow circulation device is located; • a downstream compartment in which the active layer is placed; the upstream and downstream compartments having a common partition in which an opening is provided, the opening being located opposite the active layer; • the airflow circulation device is configured so that the airflow reaches the active layer with a speed between 0.01 ms 1 and 1 ms 1; • the means for directing the airflow are configured so that the airflow reaches the active layer with an angle of incidence between 0° and 20° in absolute value; • the surface of the active layer has an area between 5 mm2 and 1 m2; • The filtration system includes, upstream of the active layer in the direction of airflow, a device for measuring the concentration of particles in the airflow; and • The airflow circulation device is integrated with the device for measuring particle concentration in the airflow. BRIEF DESCRIPTION OF THE FIGURES

[0018] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying figures, among which: • Fig. 1 represents, in schematic cross-section view, an airflow filtration system according to a first embodiment of the invention; • Figure 2 represents the filtration system of Figure 1 in operation; and • Fig. 3 represents, in schematic cross-section view, an airflow filtration system according to a second embodiment of the invention.

[0019] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION

[0020] Figures 1 and 2 schematically represent a filtration system 1 for an airflow 2 containing particles 3, according to a first embodiment of the invention. The filtration system 1 comprises: • a support 10; • an active layer 11 disposed on the support 10; and • means 12 for directing the airflow 2 towards a surface S of the layer active 11.

[0021] The active layer 11 is formed of a material comprising a polymer and one or more polymer plasticizers capable of migrating to the surface S of the active layer 11 to form a plasticizer film. The plasticizer film is a thin layer of plasticizer. It gives the surface S of the active layer 11 properties of attracting and retaining particles. The surface S of the active layer 11 is thus sticky or tacky and has the ability to trap particles 3 from the airflow 2.

[0022] The polymer is preferably poly(vinyl chloride), or PVC. The plasticizer (or each of the plasticizers in the case of a plurality) can be any substance conventionally used for plasticizing PVC. Plasticizers with a molecular weight between 750 and 1250, such as chain-locked poly(propylene glycol adipate) or poly(1,3-butanediol azelate), are, however, preferable due to their low volatility.

[0023] Patent GB1475366A describes an example of plasticized PVC that can be used to form the active layer 11. The plasticized PVC is used by Dycem® to manufacture floor mats that suppress dust and bacteria carried by shoes and trolley wheels. These floor mats are, for example, placed at the entrance to cleanrooms and other controlled environments.

[0024] Plasticizers for PVC can be divided into three classes: 1. Primary or fully compatible plasticizers; 2. Secondary or partially compatible plasticizers; and 3. The extenders.

[0025] Primary or fully compatible plasticizers are closely bound to the polymer and can only migrate slowly into the polymer mass.

[0026] Secondary or partially compatible plasticizers are less tightly bound and therefore migrate more easily within the polymer mass, from an area of ​​high plasticizer concentration to an area of ​​low plasticizer concentration. They can therefore exude onto the surface of the polymer layer.

[0027] The extenders are weakly bound and can migrate freely in the mass, and exude to the surface to a large extent.

[0028] The plasticizer in the active layer material 11, or at least one of the plasticizers, is advantageously a secondary PVC plasticizer. This allows for the rapid regeneration of the plasticizer film on the surface S of the active layer 11 after it has been cleaned. Indeed, cleaning the surface S not only removes the trapped particles 3, but also the plasticizer film. After this cleaning, "new" plasticizer migrates from the interior of the active layer 11 to the surface S to replace the plasticizer film removed by the cleaning.

[0029] Such regeneration does not occur as easily with a primary plasticizer, and an extender would tend to exude in unacceptable proportions.

[0030] Esters and polyesters, such as glycolic esters of straight-chain dibasic acids, or monomeric esters of straight-chain dibasic acids and C4 to CM monohydric alcohols, for example monomeric adipates, or modified polyester plasticizers, are examples of suitable secondary plasticizers.

[0031] Alternatively, the material of the active layer 11 comprises a mixture of primary plasticizer(s) and extender(s) because such a mixture can behave as a secondary plasticizer.

[0032] Preferably, the material of the active layer 11 comprises between 15% and 45% by mass of PVC and between 55% and 85% by mass of plasticizer. This is referred to as "heavily plasticized PVC". This significant proportion of plasticizer allows the plasticizer film on the surface S of the active layer 11 to be regenerated quickly and many times. The active layer 11 thus benefits from a long service life.

[0033] Preferably, the amount of plasticizer in the material is such that the active layer 11 has a tensile strength between 10 N and 20 N.

[0034] The active layer 11 may be part of a multilayer stack further comprising a reinforcing layer and an intermediate layer, which is disposed between the reinforcing layer and the active layer 11 and is made of a polymer material having the property of reducing the migration of the plasticizer(s) from the active layer 11 to the reinforcing layer. The reinforcing layer provides dimensional stability to the active layer 11 and facilitates its attachment (typically by bonding) to the surface of the substrate 10. In addition, the intermediate layer and the reinforcing layer protect the surface of the substrate 10 against any damage by the plasticizer.

[0035] The intermediate layer is made of a material capable of being bonded to both the active layer 11 and the reinforcing layer. This material may be PVC containing a lower proportion of plasticizer than that contained in the active layer 11, the plasticizer not necessarily being the same as that used in the active layer 11. Another possible material for the intermediate layer is polyurethane. This material is compatible with plasticized PVC and is resistant to the plasticizers commonly used for plasticizing PVC. Polychloroprene or modified olefinic polymers may also be considered.

[0036] Preferably, the reinforcing layer is a knitted, woven or non-woven sheet of synthetic or natural fibers, for example, cotton, nylon, polyester, polyolefin, jute or hemp.

[0037] An adhesive can be applied to the back of the reinforcing layer to fix the multilayer stack to the support 10.

[0038] Examples of multilayer stacking are described in patent FR2429101B1.

[0039] Contamination control mats marketed by Dycem® under the name "CleanZone" can notably be used in filtration system 1.

[0040] The active layer 11 is airtight against the airflow 2. Thus, when the airflow 2 reaches the surface S of the active layer 11, it bounces off this surface S, dislodging the particles 3 that remain attached (see [Fig. 2]). Since the airflow 2 does not pass through the active layer 11, the latter is not responsible for any pressure drop.

[0041] The airflow 2 can be directed towards the surface S of the active layer 11 in various ways, for example by a duct (or channel), one or more deflection walls, an opening in a wall... The means for directing the airflow are configured so that the airflow 2 reaches the active layer 11 with an angle of incidence (measured with respect to the normal to the surface S of the active layer 11) between -90° and 90°, i.e. between 0° and 90° in absolute value.

[0042] With further reference to Figures 1 and 2, the filtration system 1 may also include an airflow circulation device 13, such as a fan or a pump. Thus, the filtration system 1 can be independent, meaning it does not need to be integrated into an installation equipped with a ventilation system. It then finds advantageous applications as an indoor air purifier.

[0043] The circulation device 13 can be a low-power fan, typically less than 0.2 W, because the active layer 11 does not cause any pressure drop. The filtration system 1 then has very low power consumption.

[0044] The filtration system 1 may also include a housing 14 containing the active layer 11, the means 12 for directing the airflow 2 and, where applicable, the circulation device 13. The housing 14 has, in particular, the functions of channeling the airflow 2 and protecting the active layer 11. It has one or more air inlets 14a and one or more air outlets 14b.

[0045] The support 10 may include one or more walls of the housing 14. The active layer 11 may in particular be disposed entirely on an internal wall of the housing 14, as illustrated in Figures 1 and 2. Alternatively, the active layer 11 may include several portions, adjacent or separated from each other, disposed on different walls of the housing, for example one or more portions each disposed on a side wall of the housing 14, and a portion disposed on the internal wall.

[0046] The housing 14 can be compartmentalized. In the example of Figures 1 and 2, it comprises: • a first compartment 141 called the "upstream compartment" (with respect to the direction of airflow 2) in which the circulation device 13 is located; and • a second compartment 142 called the “downstream compartment” in which the active layer 11 is located.

[0047] The upstream and downstream compartments 141-142 have a common partition in which an opening 121 is provided. The opening 121 is located opposite the active layer 11 and constitutes, in this particular embodiment, at least part of the means 12 for directing the airflow 2 towards the active layer 11. The active layer 11 is preferably located on the bottom of the second compartment 142.

[0048] The housing 14 may also include a third compartment 143 in which is disposed a battery for powering the circulation device 13.

[0049] The surface S of the active layer 11 advantageously has an area greater than or equal to the cross-section of the opening 121, in order to maximize the trapping of particles 3.

[0050] Finally, the filtration system 1 may include, upstream of the active layer 11 in the direction of the airflow 2, a measuring device 15 for the concentration of particles 3 in the airflow 2. This measuring device 15 provides information on the quality of the air entering the filtration system 1. It is preferably located inside the housing 14, at an air inlet 14a of the housing 14.

[0051] The measuring device 15 can be the particle sensor described in patent EP3625549B1. This particle sensor being particularly compact and requiring no maintenance or cleaning, it is perfectly suited to applications such as indoor air purifiers.

[0052] The airflow circulation device 13 is advantageously integrated into the measuring device 15. The filtration system 1 then advantageously has only one airflow circulation device, which serves for measurement and filtration purposes.

[0053] Like the particle sensor described in patent EP3625549B1, the measuring device 15 may include an internal channel through which the airflow 2 flows. This internal channel may constitute all or part of the means 12 for directing the airflow 2.

[0054] In the first embodiment shown in Figures 1 and 2, the filtration system 1 is without a mechanical filter. The pressure drop in the filtration system 1 is therefore zero.

[0055] Figure 3 represents a second embodiment of the filtration system 1 which differs from the first only in that the filtration system 1 further comprises an air filter 16 of class "ISO Coarse", "ePM10" or "ePM2.5" (in other words, a coarse, medium or fine air filter). This mechanical filter considerably increases The filtration efficiency of system 1 is high, but in return, it generates a pressure drop. The filtration efficiency resulting from the combination of the air filter 16 and the active layer 11 is comparable to that of very high efficiency air filters (class H or HEPA filters), while the pressure drop in filtration system 1 is much lower than that generated by the same high efficiency filters.

[0056] For example, with an air filter 16 of class “ePM2.5” and an active layer 11 of highly plasticized PVC (within a decontamination mat marketed by Dycem®), a filtration efficiency greater than 99.5% for particles with a diameter greater than 0.3 pm can be achieved, with a pressure drop of only about 10 Pa. Without the air filter 16, an efficiency of about 70% (for particles with a diameter greater than 0.3 pm) can be achieved with a pressure drop of 0 Pa. This second efficiency value, although lower than the first obtained with the mechanical filter, is sufficient for certain applications.

[0057] The air filter 16 is preferably located upstream of the active layer 11, for example at the opening 121 (through which the upstream and downstream compartments 141-142 of the housing 14 communicate).

[0058] In an embodiment not shown in the figures, the air filter 16 is arranged downstream of the active layer 11. For example, an air filter 16 is fitted to each air outlet 14b of the filtration system 1.

[0059] The inventors were able to demonstrate that the following parameters significantly influence filtration efficiency: • the composition of the active layer 11, and in particular the nature and proportion of the plasticizer(s) in the active layer 11; • the direction of the airflow 2 at the level of the active layer 11, in particular in the case of an active layer 11 with a flat surface S; • the speed of the airflow 2 at the level of the active layer 11; • the surface area S of the active layer 11; • the type of air filter 16 used (if applicable); and • the distance d between the air filter 16 and the surface S of the active layer 11 (cf. [Fig.3]).

[0060] The preferred values ​​of the parameters "flow direction", "flow velocity", "active layer area" and "filter-active layer distance" are respectively: • an air flow velocity 2 between 0.01 ms 1 and 1 ms 1; • an angle of incidence of the airflow 2 (measured with respect to the normal to the surface S of the active layer 11) between -20° and +20°, i.e. between 0° and 20° in absolute value; • an area of ​​the surface S of the active layer 11 between 5 mm2 and 1 m2; and • a distance d between the air filter 16 and the surface S of the active layer 11 greater than 1 mm, more preferably between 10 mm and 50 mm.

[0061] In other words, the efficiency of the filtration system 1 can be optimized: • by configuring the circulation device 13 so that the airflow 2 reaches the active layer 11 with a velocity between 0.01 ms⁻¹ and 1 ms⁻¹; and / or • by arranging the means 12 to direct the airflow so that the airflow 2 reaches the active layer 11 at an angle of incidence between 0° and 20° in absolute value (i.e., perpendicular or substantially perpendicular to the surface S); and / or • by sizing the active layer 11 so that its surface area S is between 5 mm² and 1 m²; and / or • by separating the air filter 16 from the surface S by a distance d greater than 1 mm, more preferably between 10 mm and 50 mm.

[0062] Thanks to its very low pressure drop, the filtration system 1 according to the invention enables significant energy savings in air quality management in industry, buildings, and transportation. In addition to its application as an indoor air purifier, as already mentioned, the filtration system 1 can be integrated into more complex heating, ventilation, and air conditioning (HVAC) systems, particularly for the automotive sector, and into industrial exhaust filtration systems. It can also serve as an alternative filtration system for air handling units (AHUs).

[0063] Many variations and modifications of the filtration system will be apparent to a person skilled in the art.

[0064] The material of the active layer 11 may in particular comprise a polymer (plasticized) other than PVC.

[0065] The support 10 on which the active layer 11 is disposed may not be flat, but for example concave.

[0066] The airflow circulation device 13 can be arranged (or oriented) so that it directs the airflow 2 directly towards the active layer 11. The means 12 for directing the airflow 2 then include the circulation device 13. In a simplified variant of the filtration system, the means 12 for directing the airflow 2 include only the circulation device 13.

[0067] An airflow 2 whose flow is turbulent can be directed so that it circulates parallel to the active layer 11 (i.e. an angle of incidence of 90°), for example inside a pipe whose inner surface is covered with the active layer 11.

[0068] Finally, the filtration system 1 may include a device for measuring the concentration of particles downstream of the active layer (typically at an air outlet), in addition to or as a replacement for the one located upstream.

Claims

Demands

1. A filtration system (1) for an airflow (2) containing particles (3), comprising: - a support (10); - an active layer (11) disposed on the support (10), the active layer (11) being airtight to the airflow (2); and - means (12) for directing the airflow towards a surface (S) of the active layer (11); the active layer (11) being formed of a material comprising a polymer and at least one plasticizer of the polymer capable of migrating towards the surface (S) of the active layer (11) to form a plasticizer film capable of trapping the particles (3).

2. System (1) according to claim 1, wherein the polymer is poly(vinyl chloride).

3. System (1) according to claim 2, wherein the active layer material comprises at least one secondary plasticizer of poly(vinyl chloride).

4. System (1) according to any one of claims 2 and 3, wherein the active layer material (11) comprises between 15% and 45% by mass of poly(vinyl chloride) and between 55% and 85% by mass of plasticizer.

5. System (1) according to any one of claims 1 to 4, further comprising an air filter (16) of class “ISO Coarse”, “ePMIO” or “ePM2.5”.

6. System (1) according to claim 5, wherein the air filter (16) is located upstream of the active layer (11) in the direction of airflow.

7. System (1) according to claim 5, wherein the air filter (16) is located downstream of the active layer (11) in the direction of airflow.

8. System (1) according to any one of claims 5 to 7, wherein the air filter (16) is separated from the surface (S) of the active layer (11) by a distance (d) between 10 mm and 50 mm.

9. System (1) according to any one of claims 1 to 8, further comprising a device for circulating (13) the airflow (2).

10. System (1) according to claim 9, further comprising a housing (14) containing the active layer (11), the airflow circulation device (13) for the airflow (2) and the means (12) for directing the airflow.

11. System (1) according to claim 10, in which the housing (14) comprises: - an upstream compartment (141) in which the airflow (2) circulation device (13) is disposed; - a downstream compartment (142) in which the active layer (11) is disposed; the upstream and downstream compartments (141, 142) having a common partition in which an opening (121) is provided, the opening being located opposite the active layer (11).

12. System (1) according to any one of claims 9 to 11, wherein the airflow (2) circulation device (13) is configured so that the airflow reaches the active layer (11) with a velocity between 0.01 ms 1 and 1 ms '.

13. System (1) according to any one of claims 1 to 12, wherein the means (12) for directing the airflow (2) are configured so that the airflow reaches the active layer (11) with an angle of incidence between 0° and 20° in absolute value.

14. System (1) according to any one of claims 1 to 13, wherein the surface (S) of the active layer (11) has an area between 5 mm2 and 1 m2.

15. System (1) according to any one of claims 1 to 14, comprising, upstream of the active layer (11) in the direction of airflow, a device for measuring the concentration of particles (3) in the airflow (2).

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