System for filtering an airflow

Abstract

The invention relates to a filtration system (1) for filtering an airflow (2) containing particles (3), the system comprising: - a support (10); - an active layer (11) arranged on the support (10), the active layer (11) being impermeable and not traversed by the airflow (2); and - means (12) for directing the airflow onto a surface (S) of the active layer (11); the active layer being formed from a material comprising a polymer and at least one plasticizer for the polymer, and comprising, on the surface of the active layer, a film of the plasticizer allowing the particles to be trapped.

Description

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

[0003] PM10 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." PM10 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 PM1 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). 3) 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: classes “ISO Coarse”, “ePM10”, “ePM2.5” and “ePM1” (according to ISO 16890) for coarse, medium and fine air filters; and classes “E” (E10, E11, E12), “H” (H13, H14) and “U” (U15, U16, U17) (according to 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 offer 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 ensure a minimum airflow. Therefore, they are 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 filters, are complex and generally bulky devices that use an electrostatic force to extract highly charged particles 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 are less efficient than HEPA filters and require very high voltages to generate the strong electric field needed to attract the particles. SUMMARY OF THE INVENTION

[0009] We observe that there is a need to provide an airflow filtration system that offers a good compromise between efficiency and pressure drop, and that 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:

[0011] a support; an active layer disposed on the support, the active layer being airtight and not traversed by said airflow; 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 of the polymer, and having on the surface of the active layer a film of said plasticizer.

[0012] Since plasticizers are by nature slightly sticky or tacky, the plasticizer film is able to trap particles on the surface of the active layer.

[0013] Indeed, the surface of the active layer is electrically charged by the effect of the plasticizer molecules, thus trapping particles in the airflow, which naturally carry partial charges. The bonds created by these partial charges are weak but nonetheless sufficient to trap the particles. Furthermore, since the active layer is airtight, it does not create resistance to the airflow.

[0014] Furthermore, even if all or part of the plasticizer film on the surface of the active layer is removed during cleaning, the plasticizer contained within the material forming the active layer is inherently capable of migrating to the surface and advantageously reconstituting the plasticizer film on the surface of the active layer over time, thus continuing to trap particles. The lifespan of the filtration system is therefore increased.

[0015] 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).

[0016] Compared to conventional filtration systems relying 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 multiple times, unlike a mechanical filter which must be replaced periodically.

[0017] In a first embodiment, the filtration system is without a mechanical filter.

[0018] In a second embodiment, the filtration system further includes an air filter of class "ISO Coarse", "ePM10", 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, achieves a filtration efficiency close to that of very high-efficiency air filters (class "H" filters or HEPA filters) but with a significantly lower pressure drop.

[0019] 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.

[0020] In addition to the characteristics mentioned in the preceding paragraphs, the filtration system according to the invention may have one or more of the following complementary characteristics, considered individually or in all technically possible combinations: the polymer is poly(vinyl chloride); the active layer material comprises 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 further comprises an airflow circulation device; the filtration system further comprises a housing containing the active layer, the airflow circulation device, and the means for directing the airflow; the housing comprises: an upstream compartment in which the airflow circulation device is disposed;a downstream compartment in which the active layer is located; 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 velocity 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 at an angle of incidence between 0° and 20° in absolute value; the surface area of ​​the active layer is between 5 mm 2 and 1 m 2; 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 device for circulating the airflow is integrated with the device for measuring the concentration of particles in the airflow. BRIEF DESCRIPTION OF THE FIGURES

[0021] 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: Figure 1 shows, in schematic cross-section, an airflow filtration system according to a first embodiment of the invention; Figure 2 shows the filtration system of Figure 1 in operation; and Figure 3 shows, in schematic cross-section, an airflow filtration system according to a second embodiment of the invention.

[0022] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DETAILED DESCRIPTION

[0023] 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 active layer 11.

[0024] The active layer 11 is formed from 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. This plasticizer film is a thin layer of plasticizer. It imparts to the surface S of the active layer 11 the 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.

[0025] The polymer is preferably polyvinyl chloride, or PVC. The plasticizer (or each of the plasticizers in the case of multiple plasticizers) can be any substance conventionally used to plasticize PVC. However, plasticizers with a molecular weight between 750 and 1250, such as chain-locked polypropylene glycol adipate or 1,3-butanediol azelate, are preferable due to their low volatility.

[0026] Patent GB1475366A describes an example of plasticized PVC that can be used to form the active layer 11. This plasticized PVC is used by Dycem® to manufacture floor mats that suppress dust and bacteria carried on shoes and trolley wheels. These floor mats are used, for example, at the entrance to cleanrooms and other controlled environments.

[0027] 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.

[0028] Primary or fully compatible plasticizers are tightly bound to the polymer and can only migrate slowly into the polymer mass.

[0029] Secondary or partially compatible plasticizers are less tightly bound and therefore migrate more easily through the polymer mass, from an area of ​​high plasticizer concentration to an area of ​​low plasticizer concentration. They can thus exude onto the surface of the polymer layer.

[0030] The extenders are weakly bound and can migrate freely within the mass, and exude to the surface to a large extent.

[0031] 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.

[0032] Such regeneration does not occur as easily with a primary plasticizer, and an extender would tend to exude in unacceptable proportions.

[0033] Esters and polyesters, such as glycolic esters of straight-chain dibasic acids, or monomeric esters of straight-chain dibasic acids and monohydric C4 to Ci4 alcohols, for example monomeric adipates, or modified polyester plasticizers, are examples of suitable secondary plasticizers.

[0034] 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.

[0035] 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 for rapid and numerous regeneration of the plasticizer film on the surface S of the active layer 11. The active layer 11 thus benefits from a long service life.

[0036] 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.

[0037] The active layer 11 may be part of a multilayer stack comprising a reinforcing layer and an intermediate layer, which is positioned between the reinforcing layer and the active layer 11 and is made of a polymer material that reduces 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. Furthermore, the intermediate layer and the reinforcing layer protect the surface of the substrate 10 from damage by the plasticizer.

[0038] The intermediate layer is made of a material that can be bonded to both the active layer 11 and the reinforcing layer. This material can be PVC containing a lower proportion of plasticizer than that contained in the active layer 11, although the plasticizer is not necessarily 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 can also be considered.

[0039] 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.

[0040] An adhesive can be applied to the back of the reinforcement layer to fix the multi-layer stack to support 10.

[0041] Examples of multilayer stacking are described in patent FR2429101B1.

[0042] The contamination control mats marketed by Dycem® under the name "CleanZone" can notably be used in filtration system 1.

[0043] The active layer 11 is impermeable to the airflow 2. Thus, when the airflow 2 reaches the surface S of the active layer 11, it bounces off this surface S, shedding 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.

[0044] 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.

[0045] Referring to Figures 1 and 2, the filtration system 1 may also include an airflow circulation device 13, such as a fan or 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.

[0046] 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 therefore has very low power consumption.

[0047] 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 recirculation 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.

[0048] 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.

[0049] The housing 14 can be compartmentalized. In the example shown in Figures 1 and 2, it includes: a first compartment 141 called "upstream compartment" (with respect to the direction of airflow 2) in which the circulation device 13 is disposed; and a second compartment 142 called "downstream compartment" in which the active layer 11 is disposed.

[0050] 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.

[0051] The housing 14 may also include a third compartment 143 in which is placed a battery used to power the circulation device 13.

[0052] The surface S of the active layer 11 advantageously has an area greater than or equal to the section of the opening 121, in order to maximize the trapping of particles 3.

[0053] Finally, the filtration system 1 may include, upstream of the active layer 11 in the direction of 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.

[0054] 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.

[0055] 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.

[0056] Similar to the particle sensor described in patent EP3625549B1, the measuring device 15 may include an internal channel through which the flow air 2. This internal channel may constitute all or part of the means 12 for directing the air flow 2.

[0057] In the first embodiment shown in Figures 1 and 2, the filtration system 1 has no mechanical filter. The pressure drop in the filtration system 1 is therefore zero.

[0058] Figure 3 shows a second embodiment of the filtration system 1, which differs from the first only in that the filtration system 1 also includes 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 significantly increases the filtration efficiency of the system 1, but in return 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 H EPA filters), while the pressure drop in the filtration system 1 is much lower than that generated by the same high-efficiency filters.

[0059] 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 larger than 0.3 pm in diameter can be achieved, with a pressure drop of only about 10 Pa. Without the air filter 16, an efficiency of approximately 70% (for particles larger than 0.3 pm in diameter) 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.

[0060] 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).

[0061] In a variant 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.

[0062] 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 area of ​​the surface S of the active layer 11; the type of air filter 16 used (where applicable); and the distance d between the air filter 16 and the surface S of the active layer 11 (see Fig. 3).

[0063] The preferred values ​​for the parameters "flow direction", "flow velocity", "active layer area" and "filter-active layer distance" are respectively: an airflow 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 mm 2 and 1 m 2 ; 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.

[0064] 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 speed 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 with an angle of incidence between 0° and 20° in absolute value (i.e., perpendicular or substantially perpendicular to the surface S); and / or by dimensioning the active layer 11 so that its surface S has an area between 5 mm 2 and 1 m 2 ; 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.

[0065] 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).

[0066] Many variations and modifications of the filtration system will become apparent to a person skilled in the art.

[0067] The material of the active layer 11 may include a polymer (plasticized) other than PVC.

[0068] The support 10 on which the active layer 11 is placed may not be flat, but for example concave.

[0069] The airflow 2 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.

[0070] An airflow 2 whose flow is turbulent can be directed so that it flows 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.

[0071] 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

1. DEMANDS

1. A filtration system (1) for an air stream (2) containing particles (3), comprising: - a support (10); - an active layer (11) disposed on the support (10), the active layer (11) being airtight against the airflow (2) and not traversed by said airflow; 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, and comprising on the surface (S) of the active layer (11) a film of said plasticizer.

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. [Claims] System (1) according to any one of claims 1 to 4, further comprising an air filter (16) of class “ISO Coarse”, “ePM10” 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. [Claims] 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, wherein the housing (14) comprises: - an upstream compartment (141) in which the airflow circulation device (13) is located (2); - 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' 1 .

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 (1) has an area between 5 mm 2 and 1 m 2 .

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 measuring device (15) for the concentration of particles (3) in the airflow (2).

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