Air purification system and method

Abstract

The present invention relates to an air purification system comprising air suction means, a device for filtering the air flow from said suction means, and means for distributing the filtered air flow from said filtration device within said space, in which said filtration device is crossed by the entire flow of sucked air and said filtration device comprises at least one magnetic retention means comprising one or more magnets and at least one granular bed, said magnetic retention means being arranged upstream of said granular bed in the direction of circulation of the air flow. The invention also relates to an air purification method implementing said system. Figure 1 to be published

Description

Title of the invention: Air purification system and method Technical field

[0001] The present invention relates to the field of air treatment, in particular in confined or semi-confined spaces, such as a public transport station, in particular in the case of underground transport networks of the rail type (for example: metro, RER for “Réseau Express Régional” of Île-de-France) or underground bus stations.

[0002] In the case of transport networks, these confined or semi-confined spaces include stations, corridors, trains, tunnels, commercial premises, technical premises and train repair centres.

[0003] Generally speaking, these spaces can be frequented by a transient population, users, and / or by a more or less permanent population, such as operating personnel or traders.

[0004] The particles present in the atmosphere or ambient air can have many origins and / or result from complex evolution processes involving large-scale transport phenomena and photochemical transformation in particular. In particular, particles suspended in the air can also come from the wear of tires or vehicle braking components, or quite simply from the degradation of road or railway surfaces (dust). Their small size, of the order of a few microns, explains why they remain suspended in the air. For underground railway enclosures (EFS), the major constituents identified are different materials including iron, elemental carbon and organic carbon. Terrigenic dust, particularly composed of silica, linked to soil erosion, can also be added.

[0005] Furthermore, if the means of transport are driven by heat engines, the combustion of fuel in these heat engines is a significant source of particle emissions, such as fine particles rich in PAHs (polycyclic aromatic hydrocarbons), but also soot particles, metal particles, particles resulting from nucleation processes from several types of volatile chemical species, or even a combination of these different types of particles. These particles can have sizes ranging from nanometers to several hundred nanometers, or even exceeding one micron.

[0006] These particles, the sources of which are very numerous, present a very large variability in size, ranging from nanometers to several tens of microns, and a very large variability in composition which can be organic and / or inorganic. In particular, fine particles represent one of the main risk factors, linked to the Urban air pollution can lead to cancer. Fine particles can be particularly toxic because they penetrate deep into the lungs and bronchial tree.

[0007] In these various confined or semi-confined places, ventilation and extraction and / or air supply systems are generally installed, the aim of which is to improve the quality of the air, by renewing it with blown-in “fresh” air taken from outside and / or by extracting and rejecting stale air outside. In certain cases, decontamination of the stale air is carried out in so-called “bypass” installations, the air being extracted, decontaminated, then reinjected.

[0008] However, these systems are insufficient to guarantee correct air quality in these confined spaces. For example, for metro-type rail networks, urban outdoor air is taken to renew the air. However, urban air can already present a significant level of pollution, particularly in terms of fine particles but also in terms of gaseous pollutants (such as NOx, VOCs, or sulfur derivatives such as sulfur oxides SOx), in particular due to car traffic, urban heating, or nearby industrial activities.

[0009] There is therefore a real need to purify the air arriving in and / or extracted from these confined or semi-confined spaces, to improve the quality of the air in these spaces, and / or the air in their vicinity. Prior art

[0010] Several technologies have been developed to treat the air in these confined or semi-confined spaces.

[0011] Patent application FR 3117375 (WO2022 / 122463) relates to a device and method for depolluting the air of confined or semi-confined environments by means of an improved TFP filter ("Turbulent Flow Precipitator" in English, and "Précipitateur à Flux Turbulent" in French). Such a system requires creating turbulence in the gas flow, and means for trapping particles. In the system, the air flow circulates parallel to the filter, therefore, filtration is not maximum. In addition, this patent application does not provide for a specific arrangement of the particle capture system in an underground public transport station.

[0012] Patent application FR3046663 relates to a method for collecting fine particles generated during the braking of a train. The method comprises steps of suction, purification, and distribution of the filtered air. This document provides for the implementation of a HEPA filter (high-efficiency particulate air filter). However, such a filter requires a specific installation within the underground transport station, while space is limited. For example, the installation may hinder the movement of users on the platform, which which has an impact on safety and the fluidity of transport. Furthermore, once the filter is clogged, it cannot be reused and must be replaced. Summary of the invention

[0013] The aim of the invention is to filter the air and capture air particles, particularly in a confined or semi-confined space, by means of an efficient, robust, economical and easy-to-implement system.

[0014] For this purpose, the present invention relates to a system and a method for purifying air in a polluted space.

[0015] The invention relates to an air purification system comprising polluting particles within a space to be depolluted, said system comprising means for sucking in the air present within said space, a device for filtering the air flow from said suction means, and means for distributing the filtered air flow from said filtration device within said space, in which said filtration device is crossed by the entire flow of sucked air and said filtration device comprises at least one magnetic retention means comprising one or more magnets and at least one granular bed, said magnetic retention means being arranged upstream of said granular bed in the direction of circulation of the air flow.

[0016] Said suction means may comprise a fan, preferably a tangential fan or a centrifugal fan.

[0017] Said magnetic retention means may be a magnetic filter.

[0018] Said magnetic filter may comprise a set of parallel and spaced magnets, arranged in a plane perpendicular to the air flow in the purification device, preferably in the form of a grid.

[0019] The spacing between the magnets may be between 1 mm and 10 mm, preferably between 2 mm and 6 mm.

[0020] The system may comprise at least one pressure drop sensor for determining the fouling of said filtration device.

[0021] Said granular bed may comprise a gravity drain opening and / or a gravity fill opening.

[0022] Said granular bed may comprise solid mineral, organic, zeolitic or metallic particles having a size between 0.5 mm and 5 mm, and a roughness between 1 and 100 pm.

[0023] Said granular bed may have a thickness of between 1.5 and 10 cm, preferably between 2 and 6 cm.

[0024] Said granular bed or granular beds may be made up of particles of variable sizes, decreasing from upstream to downstream of the granular bed or of all the granular beds, in the direction of circulation of the air flow.

[0025] The invention relates to a method for purifying air comprising polluting particles within a space to be depolluted by means of a system according to any one of the variants described in which: - a flow of polluted air present within said space is sucked in; - the entire flow of sucked air is passed through said magnetic retention means comprising one or more magnets to retain at least a portion of said polluting particles on said means and obtain a flow of treated air; - the entirety of said treated air flow is passed through said at least one granular bed located downstream of said magnetic retention means in the direction of circulation of the air flow to retain in said granular bed(s) at least a portion of said polluting particles contained in said treated air flow and obtain a purified air flow; - said flow of purified air is distributed in said space.

[0026] Said magnetic retention means comprising polluting particles can be cleaned to obtain a cleaned magnetic retention means and / or said at least one granular bed comprising polluting particles can be regenerated to obtain a regenerated granular bed.

[0027] In one embodiment, the pressure drop in the magnetic retention means and / or the granular bed can be measured by means of a sensor, a pressure drop threshold value corresponding to fouling can be determined, and cleaning and / or regeneration can be carried out when the threshold value is reached.

[0028] The polluting particles may be between 10 nm and 100 pm in size and may consist entirely or partly of organic matter, crystalline silica, ionic species, elemental carbon, iron, copper, calcium, zinc, aluminum, other metals, alone or in a mixture.

[0029] The space to be decontaminated may be a confined or semi-confined space.

[0030] Other features and advantages of the system and method according to the invention, ap will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below. List of figures

[0031] [Fig.l]

[0032] [Fig.l] schematically illustrates an air purification system according to the invention in sectional view.

[0033] [Fig.2]

[0034] [Fig.2] represents the distribution in number of particles per cm3 of air as a function of the particle size (number distribution) between the inlet and the outlet of the air purification system according to the invention used in the example.

[0035] [Fig.3]

[0036] [Fig. 3] represents the mass distribution of particles per cm3 of air as a function of the particle size (mass distribution) between the inlet and the outlet of the air purification system according to the invention used in the example. Description of the embodiments

[0037] The present invention relates to an air purification system and method for removing at least part of the polluting particles from a gas flow comprising mainly air, in particular originating from the air present within a polluted space, or within a confined or semi-confined space, for example a public transport station, in particular an underground one, for example for rail transport. For example, it may be a metro or RER station (for “Réseau Express Régional” in Île-de-France) or any equivalent transport. Type of particles captured

[0038] By particles is meant any solid or liquid body with a dimension of less than 100 μm. In the context of the invention, the polluting particles may optionally contain a volatile phase (for example of the hydrocarbon type) which can be adsorbed on a solid phase.In a non-limiting manner, the particles according to the invention may correspond to soot particles which are fine particles rich in PAHs (polycyclic aromatic hydrocarbons), but also particles originating from the abrasion of parts such as metal particles from brake pads, rails, particles originating from the abrasion of tires, but also pollens, PMi0 particles, which group together particles with a diameter of less than 10 pm, which cause an alteration of respiratory health, PM25 fine particles (particles with a diameter of less than or equal to 2.5 pm, consisting of a mixture of different chemical compounds, emitted mainly during combustion phenomena or formed by chemical reactions from precursor gases present in the atmosphere) which also alter cardiovascular health, or even very fine PMi particles (particles with a diameter of less than or equal to 1 pm).

[0039] Suspended particle sizes range from a few nanometers to several pm, but most air quality data focus on PM10 and PM2>5 particles. Historically, these have been the two benchmark metrics for air quality, as in the ANSES report, [Fig.l] (ANSES, 2015), which targets these particles and studies their toxicity.

[0040] The different emission sources will produce in different proportions metallic polluting particles, in particular metallic iron and iron oxides (hematite Fe2O3 and magnetite Fe3O4), mineral polluting particles, in particular crystalline silica (sand) and organic polluting particles: Polycyclic Aromatic Hydrocarbons (PAH), volatile organic compounds (VOC), carbonyl compounds, carbon soot (BC, Black Carbon according to the English name), elemental carbon (EC), organic carbon (OC), nitrogen oxides (Nox) and carbon monoxide (CO).

[0041] More particularly, the elements emitted outdoors or in a semi-confined or confined space such as an underground station mainly belong to the following categories: - Organic matter, - Ionic species, - Elemental carbon, - Iron, - Copper, - Calcium, - Zinc, - Aluminum, - Other metals.

[0042] For the purposes of the invention, the term “polluting particles” therefore means particles with a size between 10 nm and 100 pm, the nature of which belongs to the following categories: - Organic matter, - Crystalline silica, - Ionic species, - Elemental carbon, - Iron, - Copper, - Calcium, - Zinc, - Aluminum, - Other metals.

[0043] The air purification system according to the invention makes it possible to retain particles of different sizes and natures, in particular micrometric particles (PMb PM2j5 and PMio) targeted for air quality.

[0044] The purification system comprises suction means, a means for magnetically retaining particles by magnetization, a means for filtration on a granular bed, and means for distributing the filtered air.

[0045] [Fig.l] illustrates, schematically and in a non-limiting manner, the filtration device 1 of the air purification system according to one embodiment of the invention. [Fig.l] is a sectional view. The air suction and distribution means are not shown. Only the air flow is shown by arrows, in the direction of circulation of the flow.

[0046] The filtration device 1 comprises a magnetic filter 2 (also called magnetic retention means), located upstream of the granular beds (two granular beds of the same thickness in this example), in the direction of circulation of the air flow. The assembly of magnetic filter 2 and granular beds 3 forms the filtration device 1.

[0047] For this embodiment, in [Fig.l], the air circulates in the suction means, and enters from the bottom (according to the plane of the figure) of the filtration device into the magnetic filter 2, then into the granular beds 3, and comes out at the top (according to the plane of the figure) of the filtration device, filtered by the distribution means.

[0048] As goes without saying, the invention is not limited to the embodiments described above as examples; on the contrary, it encompasses all variant embodiments.

[0049] The filtration device of the air purification system according to the invention comprises at least one magnetic retention means and at least one granular bed filtration means. The combination of the magnetic retention means and the granular bed filtration means makes it possible to form an efficient, robust, economical, and easy-to-implement air purification system.

[0050] Advantageously, said magnetic retention means comprises magnets which may be permanent magnets or electromagnets.

[0051] The magnets can be arranged in a staggered pattern or in rows of the same number of magnets.

[0052] According to an embodiment option, the magnetic retention means may be a magnetic filter which may comprise a set of parallel and spaced magnets. This set of magnets is arranged in a plane perpendicular to the air flow in the filtration device. This set of magnets may be formed for example by connected magnetized rods or plates, thus forming a grid. This grid may be mounted in a slide, allowing it to be extracted from the filtration device for cleaning.

[0053] According to an alternative embodiment, the spacing between the magnets can be between 1 mm and 10 mm, preferably between 2 mm and 6 mm. These value ranges allow capture of ferromagnetic particles, without having too significant an impact on the pressure losses.

[0054] This magnetic retention means makes it possible in particular to filter magnetic ferrous particles, for example those resulting from brake or rail wear. These particles may be larger than the particles filtered by the granular bed, but also of different shapes. Indeed, agglomerates of magnetic ferrous particles may form. For this purpose, the magnetic retention means, for example the magnetic filter, is arranged upstream of the particle bed in the direction of the air flow, the purification device being configured so that the entire airflow passes through the magnetic filter.

[0055] The granular bed filtration means comprises at least one granular bed. In the case where several granular beds are present, the thickness of the beds may be identical, or different.

[0056] Similarly, the size of the beads forming a granular bed may be identical within the same bed. The size of the beads may be identical in all of the beds. The size of the beads may be variable within the same bed. The size of the beads may be different in each of the beds.

[0057] In one embodiment, it is possible to use balls of variable size, in particular of decreasing size from upstream to downstream of the granular bed, in the direction of circulation of the air flow.

[0058] In another embodiment, granular beds with different bead sizes can be used, the bead size of the beds decreasing from upstream to downstream of all the granular beds, in the direction of circulation of the air flow.

[0059] In a variant, these embodiments can be combined, the average size of balls in the downstream bed being smaller than the average size of balls in the upstream bed, in the direction of circulation of the air flow.

[0060] The decreasing size configuration of the beads of these two embodiments makes it possible to filter the air with beads of decreasing size in the direction of circulation of the air flow in order to capture the smallest particles at the end.

[0061] In addition, the means of filtration on a granular bed and / or the means of magnetic retention of particles by magnetization can be integrated into an existing infrastructure (for example a wall, or a door support or a structure integrated into the architecture of the place to be decontaminated). Filtration or retention by magnetization makes it possible to eliminate magnetizable particles (iron in particular) as a priority, while filtration by a granular bed allows robust and effective filtration of other particles.

[0062] The invention also relates to a filtration method comprising the following steps: - Suction of polluted air loaded with polluting particles from the space to be depolluted; - Treatment of polluted air in a first retention means which retains by magnetization the magnetizable polluting particles (in particular particles containing iron); - Filtration of the air from the treatment step by magnetization, by passage through a second filtration means comprising at least one granular bed to obtain filtered air depleted of polluting particles; - The air filtered in the previous step is distributed to the outside of the device, by example in a confined or semi-confined space, preferably in an area distant from the suction area so as not to immediately reprocess purified air to the detriment of a more polluted area.

[0063] The flow of sucked air passes entirely through the first magnetic retention means, then through the second granular bed filtration means. Preferably, the passage of the flow of sucked air is forced into the magnetic retention means, then into the granular bed filtration means.

[0064] Without wishing to be bound by any theory, the capture of polluting particles by the purification system depends largely on three phenomena for polluting particles of nanometric and micrometric size: diffusion for the smallest up to 100 nanometers, interception and impaction taking over for particles approaching the micrometer.

[0065] The purification method according to the invention implements an air purification system which comprises at least: - Means of suction of the air present in the space to be depolluted, for example the polluted air from a transport station, - A means of magnetic retention of magnetizable metal particles connected to the suction means, - A granular bed filtration means connected to the outlet of the magnetic retention means, to filter the particles contained in the air sucked in and treated in the retention means, and - Means for distributing filtered air from the filtration device, to distribute purified clean air within the decontaminated space.

[0066] In the present application, the term "air flow" refers to the air circulating in the air purification system. The air flow may be the polluted air loaded with polluting particles, if it is considered before the air purification system at the suction means, the air flow may be the treated air which leaves the magnetic retention means, and the air flow may be the filtered air, if it is considered after the filtration device, also called "purified air".

[0067] Furthermore, in the present application, the terms “before”, “after”, or “upstream”, “downstream”, or “inlet”, “outlet” are considered in the direction of circulation of the air flow, that is to say from the suction means to the distribution means.

[0068] Further, depending on the relative arrangement of these components, the purification system may include airflow conveying conduits for conveying air from one component to another.

[0069] According to the invention, the filtration device comprises at least one magnetic retention means by magnetization and at least one granular bed.

[0070] The filtration device therefore firstly comprises a means of retention ma- genetic, for example a magnetic filter.

[0071] Advantageously, said magnetic retention means comprises magnets which may be permanent magnets or electromagnets.

[0072] The magnets can be arranged in a staggered pattern or in rows of the same number of magnets.

[0073] According to an embodiment option, the magnetic filter may comprise a set of parallel magnets spaced apart from each other. This set of magnets is arranged in a plane perpendicular to the air flow in the filtration device. This set of magnets may be formed, for example, by connected magnetic rods or plates, thus forming a grid. This grid may be mounted in a slide, allowing it to be extracted from the filtration device for cleaning.

[0074] According to an alternative embodiment, the spacing between the magnets can be between 1 mm and 10 mm, preferably between 2 mm and 6 mm. These value ranges allow capture of ferromagnetic particles, without having too significant an impact on the pressure losses.

[0075] This magnetic retention means makes it possible in particular to filter magnetic ferrous particles, for example those resulting from the wear of brakes or rails. These particles may be larger than the dimensions of the particles filtered by the granular bed, but also of different shapes. Indeed, agglomerates of magnetic ferrous particles may form. The magnetic retention means, for example the magnetic filter, is arranged upstream of the particle bed in the direction of the air flow, the purification device being configured so that the entire air flow passes through the magnetic filter.

[0076] The granular bed is formed of solid particles (or grains). To distinguish, in the present application, the particles of the air to be captured, from the particles of the granular bed, the term "polluting particles" is associated with the particles of the air to be captured, and the terms "solid particles" and "grains" are associated with the granular bed. The granular bed is configured such that the entire air flow passes through the granular bed. In other words, the air flow is forced into the granular bed. Such a granular bed allows efficient and robust filtration of polluting particles, in particular particles of small dimensions, typically down to minimum equivalent diameters ranging from 10 nm to 1 pm, preferably from 200 nm to 1 pm. In addition, the granular bed allows adaptation of the shape and size of the filtration device, which facilitates its implementation, in particular in restricted spaces.

[0077] Furthermore, the complete purification device can be integrated into an existing structure, for example a bus shelter or an underground station structure. An underground station structure is a pre-existing element (before the installation of the air purification system) which serves for the operation or rigidity of the station. underground. This may include a wall, a landing door support, a vault support, or any similar element. This specific installation is permitted in particular by the nature of the filtration device (granular bed and magnets).

[0078] According to one embodiment, the granular bed may be formed of solid particles (or grains) with a size between 0.5 mm and 5 mm, preferably between 0.5 mm and 2 mm, and more preferably between 0.5 mm and 1.8 mm. These value ranges allow effective filtration of the finest particles, for example particles having a size between a hundred nanometers and ten microns. Within the granular bed, the grains may have similar diameters or different diameters. In addition, the granular bed may comprise several layers, each layer comprising a specific grain diameter. For this embodiment, the layers may be arranged in the air flow such that the air flow passes through the layers in decreasing order of grain diameters.

[0079] Advantageously, the grains may have a high surface roughness, i.e. a surface roughness of the grains of between 1 μm and 100 μm. Indeed, these roughnesses promote the attraction of particles, for example particles having a size of between about ten nanometers and about ten micrometers.

[0080] According to one implementation of the invention, the grains may be porous. This porosity may promote the retention of pollutants in the granular bed. The dimensionless porosity expressed as void volume relative to the total pore volume is advantageously between 50 and 70%. For example, for an alumina type material, the total pore volume (i.e. the void volume inside the grains per gram of grain) may be between 0.05 cmVg and 1.5 cmVg. This pore volume allows the retention of polluting particles in the grains of the granular bed, in particular by adsorption in the pores of the grain. Alternatively, the grains may be non-porous.

[0081] According to one implementation, the grains constituting the granular bed may be of mineral, organic, zeolitic or metallic origin. Advantageously, it is possible to use particles of mineral oxides (such as aluminas, silicas, titanium) or products of natural origin resulting from grinding and screening operations (such as sand, natural zeolite, pozzolan, diatoms, etc.) to constitute the granular bed. It is also possible to envisage metallic products such as steel balls, glass or even organic products such as polymer resins. The grains may also be catalyst support balls.

[0082] According to one embodiment option, the granular bed may have a thickness of between 1.5 and 10 cm, preferably between 2 and 5 cm. In other words, the air flow passes through the thickness of the granular bed, which has a dimension of between 1.5 and 10 cm, after passing through the magnetic retention means. Thus, the granular bed is little thick, thus facilitating its integration into an existing structure. However, a thicker granular bed can be considered. However, in this case, the pressure losses are greater, and the footprint becomes larger.

[0083] The granular medium may rest on a support in the form of a grid whose mesh size is smaller than the grain size of the granular bed (of the Johnson grid type for example).

[0084] According to one embodiment, the granular bed can be arranged at human height. Thus, the filling and emptying of the granular bed can be carried out easily. This emptying and filling in particular make it possible to remove the grains for the regeneration of the granular bed, in particular when the latter is clogged.

[0085] According to one aspect of the invention, the granular bed may comprise a gravity drainage opening, so as to be able to ensure an operation of regeneration of the grains of the granular bed. Preferably, the drainage opening may be located in the lowest portion of the granular bed. Alternatively, the granular bed may comprise a suction drainage opening, so as to be able to ensure an operation of regeneration of the grains of the granular bed.

[0086] According to one aspect of the invention, the granular bed may comprise a gravity filling opening, so as to be able to ensure filling for the first use or after an operation of regeneration of the grains of the gravity bed. Preferably, the filling opening may be located in the highest portion of the granular bed.

[0087] According to one implementation of the invention, the air flow can pass through the thickness of the granular bed. Preferably, the air flow can pass through the thickness of the granular bed in a substantially horizontal direction. In this way, the arrangement of the granular bed is simplified, which facilitates its integration into a structure of the underground formation.

[0088] Preferably, the granular bed may be planar as described in [Fig. 1], annular (tubular) or cylindrical, or curved to allow for simplified integration.

[0089] Thus, with the implementation of a magnetic retention means by magnetization upstream of the granular bed(s), the filtration device makes it possible to filter, in a first stage, the magnetic particles, which may be among the largest, in particular when they are agglomerated, thanks to the magnetic filter, and, in a second stage, the other particles thanks to the granular bed(s).

[0090] By passing the entirety of said treated air flow through said at least one granular bed located downstream of said magnetic retention means in the direction of circulation of the air flow, it is possible to retain in said granular bed(s) at least a portion of said polluting particles not retained in said magnetic retention means and still contained in said treated air flow.

[0091] These two filtration means are complementary to improve the capture of polluting particles from the air within a polluted confined or semi-confined space, in particular in an underground transport station. The combination of the two means within the filtration device allows the capture of polluting particles of different nature and size, which makes it possible to improve the purification of the air, while remaining easy to implement.

[0092] Furthermore, the implementation of a means for retaining magnetic particles (for example a magnetic filter) upstream of the granular bed makes it possible to prevent these particles from clogging the granular bed more quickly, which makes it possible to space out the regeneration steps of the granular bed. Regeneration and cleaning

[0093] The purification system must be able to operate autonomously for a certain time without the need for maintenance, for example for a period of a few days to several months. To avoid too significant a drop in particle capture, it is possible in particular to envisage autonomous operation without maintenance for 10 days to 2 months, or for 15 days to 1 month to ensure bi-monthly or monthly maintenance.

[0094] The air purification system can be cleaned or the dirty parts can be changed.

[0095] Regeneration or cleaning can be carried out in situ or off site.

[0096] The magnets can also be removed from the filtration device for cleaning. A cleaning system adapted to the shape of the magnets is provided to allow the elements to be cleaned on site without the risk of particles spreading during handling.

[0097] For the granular bed, it is possible in particular to remove the dirty balls and treat them elsewhere in a secure location where the particles can be recovered. In another embodiment, the system according to the invention can be treated by a mobile cleaning system on site which makes it possible to circulate the dirty balls in the portable cleaning system so as to reinject them directly into the system according to the invention. The removal of the granular bed particles can be carried out by drawing them off from the bottom of the structure, either by suction or by simple gravity depending on its position relative to the ground. It can be filled from the top by gravity.

[0098] To rid the balls of the captured polluting particles, regeneration can consist of a simple flush with counter-current air or solvent or a wash with water, for example with slightly acidic water (pH 5 or 6).

[0099] Advantageously, the air purification system may comprise one or more sensors, in particular a pressure drop sensor (for example by pressure difference), to determine the fouling of the granular bed by polluting particles. This allows us to determine when to regenerate the granular bed or clean the magnetic filter. A sensor can be located at the inlet and outlet of each of the air treatment means: magnetic retention means or granular bed.

[0100] When the pressure drop between the inlet and the outlet of each of the air treatment means exceeds a threshold value determining fouling of said means, a regeneration or cleaning step or a change of the fouled parts can be triggered.

[0101] Implementation of the system and method according to the invention

[0102] According to one feature, the air suction means may comprise a fan, a vacuum pump, a suction turbine, or a compressor. For example, the fan may be a tangential fan or a centrifugal fan. The tangential fan has an elongated shape which favors its integration into an elongated volume. The centrifugal fan has a compact shape which favors its integration into a restricted volume.

[0103] According to one implementation of the invention, the means for distributing the filtered air may comprise an outlet for the filtered air, for example in the form of a ventilation grille, for example under a bus shelter or on the platform of an underground station. Thus, users of public transport can breathe filtered air.

[0104] For this first embodiment, the bed of particles can adapt to the shape of the wall, and can in particular be vertical and / or curved.

[0105] Advantageously, the distribution means may be located directly on the granular bed, on the side of the granular bed directed towards the underground station. Thus, no pipe is necessary between the filtration device and the distribution means. Alternatively, the distribution means may be remote, and connected to the filtration device by a pipe.

[0106] According to one example, the passage section of the granular bed may be between 0.3 and 3 m2, preferably between 0.5 and 1 m2. Indeed, these passage sections make it possible to treat at least one air flow of between 2000 and 7500 m3 / h, to treat a significant quantity of air within the underground station. In addition, the speed of the air flow within the filtration device may be of the order of 5 m / s. According to a non-limiting example, the granular bed may have a height of approximately 1.3 m and a width of approximately 0.5 m and a thickness of 5 cm. The height of 1.3 m also has the advantage of remaining at human height (even if it is slightly raised) to carry out the operations of filling and emptying the granular bed in a simple manner.

[0107] The purification device further comprises a means for magnetically retaining the magnetizable particles, for example in the form of a magnetic filter arranged in upstream of the granular bed. For this, the magnetic filter may comprise a flat box comprising magnets, the box being arranged between the wall and the granular bed. Preferably, the box is not very thick. For this embodiment, the air flow successively passes through the suction means, the magnetic filter box, the granular bed and then the distribution means.

[0108] According to one embodiment of this first embodiment, the suction means may be arranged around the periphery of the plane of the filtration device. For this embodiment, the suction means may comprise at least one tangential fan. For this embodiment, the suction means and the filtration device are located close to each other, which simplifies the capture system.

[0109] Alternatively, the suction means may be arranged on the floor of the confined or semi-confined space to be decontaminated. For this embodiment, the suction means may comprise at least one centrifugal fan. In addition, a pipe may connect the suction means to the filtration device. This variant makes it possible to move the suction away from the distribution, which makes it possible to prevent the sucked air from coming from the air that has just been filtered.

[0110] A preferred variant of this first embodiment comprises at least two suction means located on either side of a filtration device, preferably up to six suction means. This preferred variant ensures a homogeneous distribution of the air flow in the filtration device, in particular in the granular bed(s).

[0111] Advantageously, the distribution means may be located directly on the granular bed within the support, and be directed towards the outside of the system. Thus, no conduit is necessary between the filtration device and the distribution means. Alternatively, the distribution means may be remote, and connected to the filtration device by a conduit.

[0112] The magnetic filter may comprise a cylindrical box comprising magnets, the box being arranged above the granular bed; the air flow successively passes through the suction means, the box of the magnetic filter, the granular bed, then the distribution means.

[0113] The invention also relates more generally to an air purification method for all applications requiring air treatment, implementing an air purification system according to any one of the variants or combinations of variants described above. Examples

[0114] Tests were carried out to show the effectiveness of the polluted air purification system comprising polluting particles according to the invention.

[0115] The filtration device consists of a magnetic filter upstream of a ball filter with a ball bed thickness of 5 cm. The balls are alumina balls with a diameter of approximately 1.8 mm.

[0116] To hold the alumina balls, Johnson type grids are used.

[0117] A representative polluted air is reconstituted by mixing a fine Arizona powder Dust (particles between 500 nm and 25 pm) and iron particles. The powder is dispersed into the incoming air using two SAG-410L particle dispersers, one injecting the Arizona Dust particles, the second injecting only the nano-sized magnetic iron powder.

[0118] The iron particles were characterized by DRX and are pure magnetite and hematite type iron oxides; the Arizona Dust powder is mainly made up of silica and traces of feldspar type aluminosilicate are detected, which is commonly detected with quartz in rocks.

[0119] The tests make it possible to approach the concentration of polluting particles present in the air in a polluted environment such as an underground station and to reproduce an aerosol that is globally representative with regard to the different particle sizes and natures with a realistic speed compared to the real case.

[0120] The particle measuring device is the ELPI™ (Electrical Low Pressure Impactor, Dekati Ltd. Finland) which measures particle size distribution and concentration in real time.

[0121] The measurement of the pressure drop generated by the passage of the filtration device combining a filter formed from a bed of 5 cm thick balls with a magnet upstream gives a pressure drop of the order of 2860 Pa (28.6 mbar) at the start of the test. The pressure drop due to the granular bed of balls alone is of the order of 1460 Pa (14.6 mbar).

[0122] All the tests show, for the configuration of the filtration device combining a filter formed from a bed of 5 cm thick beads with a magnetic filter upstream, a capture in a few minutes of particles from 200 nm to 800 nm of the order of 30% and for particles larger than 1 pm rather of the order of 50%. The curves making it possible to obtain these rates are given [Fig.2] and [Fig.3]. The mass and number of particles are measured at the inlet of the device (tap 1, gray squares for the first test, black squares for the second test) and at the outlet of the device (tap 3, gray diamonds for the first test, black triangles for the second test). For the case considered, with injection of nanometric iron powder and micrometric Arizona Dust in parallel, [Fig.2] gives for two "identical" tests the distribution in number of particles and [Fig.3] the distribution in mass of particles.

Claims

Claims

1. Air purification system comprising polluting particles within a space to be depolluted, said system comprises means for sucking in the air present within said space, a device for filtering the air flow from said suction means, and means for distributing the filtered air flow from said filtration device within said space, characterized in that said filtration device is crossed by the entire flow of sucked air and in that said filtration device comprises at least one magnetic retention means comprising one or more magnets and at least one granular bed, said magnetic retention means being arranged upstream of said granular bed in the direction of circulation of the air flow and in that said granular bed comprises a gravity drain opening and / or a gravity fill opening.

2. An air purification system according to claim 1, wherein said suction means comprises a fan, preferably a tangential fan or a centrifugal fan.

3. An air purification system according to one of the preceding claims wherein said magnetic retention means is a magnetic filter.

4. An air purification system according to claim 3 wherein said magnetic filter comprises a set of parallel and spaced magnets, arranged in a plane perpendicular to the air flow in the purification device, preferably in the form of a grid.

5. Air purification system according to claim 4 wherein the spacing between the magnets is between 1 mm and 10 mm, preferably between 2 mm and 6 mm.

6. Air purification system according to one of the preceding claims comprising at least one pressure drop sensor for determining the fouling of said filtration device.

7. An air purification system according to one of the preceding claims, wherein said granular bed comprises solid mineral, organic, zeolitic or metallic particles having a size between 0.5 mm and 5 mm, and a roughness between 1 and 100 pm.

8. Air purification system according to one of the preceding claims, wherein said granular bed has a thickness of between 1.5 and 10 cm, preferably between 2 and 6 cm.

9. Air purification system according to one of the preceding claims, in which said granular bed or said granular beds is (are) made up of particles of variable sizes, decreasing from upstream to downstream of the granular bed or of the set of granular beds, in the direction of circulation of the air flow.

10. Method for purifying air comprising polluting particles within a space to be depolluted by means of a system according to one of claims 1 to 9, in which: - a polluted air flow present within said space is sucked in; - the entire sucked air flow is passed through said magnetic retention means comprising one or more magnets to retain at least a portion of said polluting particles on said means and obtain a treated air flow; - the entire treated air flow is passed through said at least one granular bed located downstream of said magnetic retention means in the direction of circulation of the air flow to retain in said granular bed(s) at least a portion of said polluting particles contained in said treated air flow and obtain a purified air flow; - said purified air flow is distributed in said space.- said magnetic retention means comprising polluting particles is cleaned to obtain a cleaned magnetic retention means and / or said at least one granular bed comprising polluting particles is regenerated to obtain a regenerated granular bed.

11. Air purification method according to claim 10, in which the pressure drop in the magnetic retention means and / or the granular bed is measured by means of a sensor, a pressure drop threshold value corresponding to the fouling is determined, and cleaning and / or regeneration is carried out when the threshold value is reached.

12. Air purification method according to one of claims 10 to 11 in which the polluting particles are between 10 nm and 100 pm in size and consist entirely or partly of organic matter, crystalline silica, ionic species, elemental carbon, iron, copper, calcium, zinc, aluminum, other metals, alone or in a mixture.

13. Method for purifying air according to one of claims 10 to 12 in which the space to be depolluted is a polluted confined or semi-confined space.

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