Air pollution mitigation device and system comprising it

Abstract

The invention relates to an air pollution mitigation device and a system comprising it, where the device comprises a sound crystal (10) formed by a set of at least three lines of acoustic diffusers (11) of height h permeable to air currents in their transverse direction, characterized in that the device (10) further comprises a diffusion system (20) for a liquid supported on the sound crystal (10), comprising at least one liquid inlet (21) and at least one liquid outlet (22), connected by a distribution network (24), where the at least one outlet (22) of said liquid is configured to create at least one liquid curtain (23) arranged in a frontal plane covering, totally or partially, the height h of the acoustic diffusers (11).

Description

Air pollution mitigation device and system comprising it Field of invention The invention has applications in the construction sector. Specifically, the solution relates to a device, based on sound crystals, capable of reducing air pollution. The device acts simultaneously as a noise barrier and as a system for capturing respirable-sized particles suspended in the air. State of the art Traditional acoustic barriers, consisting of continuous, high-density panels, are known in the prior art. These barriers are placed between the sound source and the receiver, interrupting the transmission of the sound signal. This interruption, combined with other phenomena such as reflection, absorption, and resonance, are the mechanisms used to attenuate noise. There are some disadvantages associated with the use of traditional acoustic barriers. The most significant disadvantages we can observe are basically related to four aspects: 1. Landscape degradation. These are closed barriers that end up becoming canvases for graffiti, degrading the surrounding landscape and creating physical isolation. 2. Barriers impermeable to air and liquids. They disrupt natural air currents, generating a high thermal gradient. 3. Not efficient for low frequencies. These are barriers that cannot be tuned to the problem they are intended to attenuate; they always function the same regardless of the sound source. 4. Sail effect. By preventing the passage of air, a high overturning moment is generated when the air impacts the continuous medium, which entails the use of large foundations. More recently, acoustic screens made of sound crystals have emerged in the state of the art. Sound crystals are periodic, non-continuous structures composed of a network of acoustic diffusers that allow visibility through them, thus reducing their visual impact on the landscape. These screens add to the noise control mechanisms already mentioned the multiple scattering mechanism, specific to this type of device, which prevents the transmission of acoustic waves through the material itself. These devices consist of arrays of isolated acoustic diffusers of any geometric shape, made of different materials, heights, and diameters, arranged regularly or irregularly, and immersed in air. One of the most interesting characteristics of these screens is their permeability to wind and water, allowing natural airflow to pass through them without obstruction. This prevents a thermal gradient in the installation areas and substantially reduces the need for large foundations. On the other hand, there is currently significant interest in capturing particulate matter suspended in the atmosphere. These respirable particles can be small solids or liquid droplets dispersed in the atmosphere, which can be very harmful to human health. While these particles can be generated naturally, for example, by dust carried by the wind, they are generally produced by anthropogenic activities such as the burning of fossil fuels in vehicles and heating systems. Depending on the size of these suspended particles, we can distinguish between coarse particles (with a diameter less than or equal to 10 micrometers), fine particles (with a size less than or equal to 2.5 micrometers) and ultrafine particles (with a diameter less than 0.1 micrometers) also known as black carbon. Existing solutions such as particulate traps have some disadvantages in the existing devices. Some of these disadvantages are: 1. Low filtration flow rate. Current particle capture systems are point elements that perform surface filtration, and their very small surface area limits the filtration flow rate. 2. High maintenance. Air filters (HEPA or electrostatic capture) are generally used to capture particles. These filters require frequent maintenance and replacement because they become saturated as they capture particles, leading to a loss of effectiveness over time. It is therefore necessary to develop devices that allow action on both pollutants simultaneously. Summary The present solution describes a mitigation device with the ability to simultaneously reduce air pollution in the two aspects most harmful to health: noise and respirable-sized particle pollution. The device is based on a sound crystal formed by an array of at least three lines of acoustic diffusers, each of height h, which allows contaminated air to pass through, thus constituting a volumetric capture system, in contrast to the surface-based devices known in the prior art. In other words, the use of acoustic barriers as particle traps overcomes the existing limitations of filtration flow rates due to the enormous surface area associated with the barrier itself, while also introducing volumetric filtration. The permeability characteristic of sound crystals is the property that enables particle capture. To achieve this, the device also includes a liquid diffusion system—for example, water—supported on the sound crystal structure. In use, this system generates a curtain or mist within the crystal's volume, allowing it to capture particles passing through it. The liquid diffusion system comprises at least one liquid inlet or outlet, and at least one outlet for said liquid, where said outlet is configured to create the curtain within the existing volume of the device. The at least one inlet is connected to the at least one outlet by means of a distribution network. The curtain acts as a filter through the interaction of contaminant particles with the microdroplets of liquid that fall due to gravity. To achieve this, at least one outlet is located in a higher area of ​​the device. The filtration of contaminant particles is due to the fluid properties of surface tension and the Venturi effect, which generate a small pressure change that attracts the contaminant particles. In this way, the suspended particles adhere to the microdroplets of the liquid and precipitate onto the base of the device. In other words, this contact allows the airflow to be filtered and the suspended particles to be captured within it. The liquid diffusion system's outlet is configured so that the curtain can cover all or part of the glass volume, substantially improving particle capture capacity compared to surface capture systems. Furthermore, since the liquid acts as the filter medium, maintenance is quick and easy, and the same liquid can be reused multiple times through closed-loop circulation. In a second aspect, the invention relates to a modular barrier system comprising at least one mitigation device as previously described. Thus, the modular barrier system according to the present invention allows for long-distance coverage. In summary, the advantages of the mitigation device according to the present invention in relation to traditional acoustic barriers are: 1. Low landscape impact. These are open barriers that do not break the visual line, so they do not generate a significant impact at the landscape level. 2. Air and liquid permeable barriers. They do not generate a thermal gradient because they do not eliminate the passage of natural air currents. 3. Reduced overturning moment. By allowing airflow, the "sail effect" is reduced, decreasing the thrust generated by the air and requiring smaller foundations for installation. Furthermore, they allow surface runoff to pass through, so they can be installed in areas with rainwater drainage channels as they do not create a pooling effect. 4. Tunable barriers. These are barriers that can function by attenuating a specific frequency, also covering the low-frequency spectrum. Regarding improvements over existing devices for capturing respirable-sized suspended particles, they are: 1. High filtration flow rate. By combining the particle capture property with a large surface area acoustic barrier, extraordinarily high filtration flow rates are achieved compared to existing point elements. 2. Low maintenance. Traditional capture filters are replaced by fluid properties that capture particles, substantially reducing maintenance. Filter changes are not required; the fluid is simply changed periodically. Therefore, the development of this device results in an improvement that can have a positive environmental and social impact by combining, in a single device, the capacity to mitigate noise and respirable particles, two pollutants that affect human health from different angles. Its use could be of particular interest in environments where significant pollution hotspots are detected, where noise and respirable particulate matter are concentrated, such as port areas, ring roads, or industrial sites. Furthermore, this device allows for the creation of clean perimeter environments, which is especially beneficial in sensitive areas with defined boundaries, such as urban school playgrounds near roads. The same application could be made in other environments, such as gardens at hospitals or senior care facilities. Brief description of the figures Figure 1 shows a perspective of an embodiment of an attenuation device comprising a sound crystal formed by an assembly of three disperser lines and a multi-outlet liquid diffusion system arranged at three height levels and with a collecting base comprising a perforated plate and fluid pumping. Figure 2 shows a perspective of an embodiment of an attenuation device comprising a sound crystal formed by a set of three disperser lines and a multi-outlet liquid diffusion system arranged at three height levels and with a sloping collection base comprising a fluid collection and pumping channel. Figure 3 shows a comparison of insertion losses of equipment without a diffusion system vs. a device like the one described in the present solution comprising a water diffusion system. Figure 4 shows the improvement in insertion loss (IL) provided by the water curtain of a device as described in the present solution comprising a water diffusion system vs. equipment without a water curtain Numerical references for the figures 100. Pollution reduction device 10. Sound Crystal 11. Acoustic diffusers 20. Diffusion System 21. Liquid inlet 22. Liquid outlet 23. Liquid Curtain 24. Liquid distribution network. 30. Collection base 31. Pumping medium 32. Perforated plate 33. Collection channel 34 Collection base spillway 35. Drain of the collection base 36. Foundation ring 37. Storage depot Detailed description The present solution describes a mitigation device (100) for noise attenuation and capture of polluting particles comprising a sound crystal (10) formed by an array of at least three rows of acoustic scatterers (11) of height h. The device (100) is configured as a noise barrier, based on sound crystals (10), acting by means of a multiple scattering mechanism. Sound energy, upon passing through the sound crystal (10), undergoes a wave cancellation process that allows for sound attenuation. The configuration of the acoustic diffusers (11) does not occupy the entire volume of the barrier, leaving empty spaces, which gives the device (100) permeability to fluid currents, whether gases or liquids. In this way, the device (100) is permeable to an air current in its transverse direction, perpendicular to the frontal plane of the device (100). Furthermore, the mitigation device (100) comprises a liquid diffusion system (30). This diffusion system (30) comprises at least one liquid inlet (31) and at least one liquid outlet (32), wherein the at least one outlet is configured to create at least one liquid curtain (23) arranged in the frontal plane between the acoustic diffusers (11), covering, totally or partially, the height h of said acoustic diffusers (11) and thus trapping particles present in the airstream passing through the device (100). The at least one inlet (21) is connected to the at least one outlet (22) by means of a distribution network (24). In summary, in the presented device (100), the sound crystal (1) has two main functions: in addition to acting as a noise barrier, it serves as structural support for the liquid diffusion system (11) capable of capturing polluting particles. The liquid diffusion system (30) creates a liquid curtain (8) within the sound crystal (10), such that when air laden with pollutants passes transversely through the sound crystal (10), the liquid contacts and traps the particulate matter. Figure 1 shows a miniature representation of the airflow direction along the Y-axis, or transverse direction. Thus, the airflow passes perpendicularly through the liquid curtain (23) generated in the frontal plane, or XZ plane, of the device (100). Figure 1 shows a perspective view of an embodiment of a mitigation device (100) comprising a sound crystal (10) formed by three lines of acoustic diffusers (11) and a multi-outlet liquid diffusion system (30) which, in this particular embodiment, is arranged at three height levels. The multi-outlet diffusion system (30) comprises a plurality of outlets (32) such that a curtain (33) can be obtained covering the height h of the acoustic diffusers (11) along the entire length of the sound crystal (10). The liquid outlet lines are positioned at different heights to create a homogeneous liquid sheet or curtain (8) on the frontal plane or XZ plane and perpendicular to the OY axis. The distance between these liquid outlet lines (h1, h2, h3, etc.) is determined by the type of liquid diffuser used. The objective is to achieve total or partial coverage of the height, h, of the acoustic diffusers (11) and, preferably, the entire width of the screen. In one particular embodiment, the device (100) may comprise a liquid collection base (30) arranged at the bottom of the device (100). This collection base (30) includes a collection system and a liquid storage reservoir (37) that may occupy the entire base or be located laterally. Furthermore, the collection and storage of liquid in the collection base (30) may be carried out in several different ways. In a particular embodiment, the collection system may comprise a perforated plate (32), as shown in Figure 1, arranged at the top in connection with the storage tank (37) of the collection base (30), which forms the foundation base of the device itself (100). Alternatively, as shown in Figure 2, the collection base (30) may comprise a foundation ring (36), an upper surface constructed with a slope oriented to direct collected liquid towards at least one collection channel (33) so that the storage of said collected liquid can be carried out in the storage tank (37) arranged on at least one side of the collection base (30). Optionally, the slope of the ring (36) of the collection base (30) may be configured for collection of the liquid with one or more slope orientations. As previously stated, the diffusion system (20) of the device (100) may include a liquid pumping means (31), such that the inlet (21) is configured to use liquid collected and stored by the collection base (30). Thus, the liquid diffusion system (20) comprises a liquid inlet (21) connected to the storage tank (37) of the liquid collection base (30). The liquid is then pumped through the pumping means (31), for example, a pressure pump, to at least one outlet (22) of the liquid diffusion system (20). The operating pressure of the device (100) depends on the height of the barrier and the number of diffuser lines at the liquid outlet (22) to be integrated vertically. In one particular embodiment, the device (100) includes a liquid replenishment system that compensates for potential losses due to various causes, such as leaks in joints, evaporation, or wind drift in the water curtains (8), among others. This replenishment system can detect a decrease in the level of the storage tank (37) in the collection base (30) and allows the addition of the necessary liquid volume for the proper functioning of the pumping unit (31). Similarly, the device (100) may include a spillway (34) to allow the release of excess liquid, for example, from rainwater, as well as a drain (35) from the storage tank (37). When using water as the diffused liquid, the water can be discharged into the stormwater network and replaced with a new volume that restarts the capture cycle. This eliminates the need for treatment or filter replacement, as is the case with current solutions. The result is a reduction in the cost and maintenance of the device (100). Figures 1 and 2 illustrate the specific embodiment of two solutions, where a single inlet (21) of the liquid diffusion system (20), in the form of a vertical liquid intake, feeds a distribution network (24) comprising at least two pipes arranged at different heights. Specifically, the distribution network (24) in this embodiment comprises three double pipes installed at three heights, h1, h2, and h3, where, in turn, a plurality of outlets (22) are provided. The distance between these liquid outlet lines (22) depends on the type of liquid diffuser used. The objective is the total or partial coverage of the height, h, of the acoustic diffusers (11) and the entire width of the screen.In this embodiment, a series or plurality of outlets (22) can be arranged along the distribution network pipes (24), with flat or conical diffusers, generating a curtain (23) of descending liquid onto the perforated plate (32) of the collection base (30), where the liquid is collected and stored. Additionally, in a particular embodiment, the distribution network (24) comprises horizontal pipes, simplifying the configuration of the plurality of outlets (22) and the resulting generation of a homogeneous curtain (23) of liquid. The design of the sound crystal (10) is determined by the type of noise related to the emission. Thus, the acoustic diffusers (11) and their distribution are determined according to the frequency bands to be attenuated. However, the liquid diffusion system (20) can remain constant, being modified independently of the parameters that define the geometry of the sound crystal (10). Furthermore, the configuration of the distribution network (24) is not a limitation of the diffusion system (20), and it can be designed in multiple variations, for example, horizontally in parallel, with an orientation parallel to the lines of acoustic diffusers (11). Unlike current solutions for particle capture, where surface capture elements are used, the proposed system can generate several parallel curtains (23) between the rows of dispersers (11), achieving volumetric filtration and thus increasing the particle capture efficiency per unit of barrier surface. As an alternative to water as the recirculating liquid, other aqueous solutions, such as ionic liquids, could be used. These liquids would allow for the capture of suspended particles and could also capture CO2, making them suitable for use in environments with high levels of CO2 pollution. Secondly, the device (100) can be incorporated into a modular barrier system. This barrier system can be of considerable length, giving it a significantly greater capture capacity compared to any point-action system. In one particular embodiment, each module of the modular barrier system can comprise independent liquid diffusion systems. This allows for more versatile and simplified maintenance, enabling the removal and replacement of a malfunctioning module or rapid assembly and disassembly during construction or in situations involving point-source pollution. However, the liquid diffusion system (20) not only serves to capture contaminants, since the curtain (23) generated in the device (100) provides additional reinforcement to the sound attenuation achieved by the acoustic diffusers (10) of the sound crystal (10). Figure 3 shows how the presence of liquid curtains (23) allows for improved sound attenuation. For the validation of the particle capture capacity of the mitigation device (100) described in the present solution, experimentation has been carried out using a specific embodiment of the device (100). The equipment used for validation consisted of a wind tunnel through which an airflow was directed, passing through an attenuation device (100) according to the present solution. Specifically, a tunnel was designed with 550 x 550 mm square steel elements of varying lengths (1,400 mm, 1,000 mm, and 500 mm) for coupling its different parts. In a central module, housing the dispersers and diffusers, the lids are sealed to ensure the watertightness of the various components. A 120W domestic fan and a regulator for controlling the air velocity are attached to the inlet duct. For the water flow requirements necessary for the tests, a Tornado submersible pump (220V, 0.25A) with a 16 mm outlet for polyethylene distribution is used as the pumping medium (31). Wide-angle, flat-spray PVC nozzles were selected. This wind tunnel will be monitored using PMS5003 sensors to measure both particulate matter (PM) and number of particles. PM (particulate matter) is the particulate matter present in the atmosphere, and its size varies in its chemical and physical composition depending on the emission source and the size of the emitted particle. Particulate matter in the atmosphere is classified into fractions based on the size of each of its constituent particles. These fractions are classified into three groups: • Material with a size less than or equal to 10 micrometers, known as PM10, • material with a particle size less than or equal to 2.5 micrometers known as PM2.5 and • Material with a particle size less than or equal to 1.0 micrometers, known as PM1.0. Additionally, we can talk about coarse particles (PM10-PM2.5), as the set of particles resulting from the subtraction between the PM10 set and the PM2.5 set. The units of PM are referenced to a mass in a given volume (µg / m3). On the other hand, the classification according to the number of particles distinguishes between: P0.3, P0.5, P1.0, P2.5, P5.0 and P10.0, which correspond to the number of particles with a diameter smaller than each of the sizes (0.3, 0.5, 1.0, 2.5, 5.0, 10.0, respectively). They indicate the quantity of particles, without taking into account their nature. Said wind tunnel comprises a device formed by 16 integrated PVC cylindrical dispersers (11), with a 4x4 aligned distribution, with a liquid diffusion system (20) of six outlets (5), arranged in two outlet lines, in the middle part of each disperser of each pair of lines (1-2, 3-4) of acoustic dispersers (11). From an acoustic point of view, as can be seen in Figures 3 and 4, a substantial improvement in the insertion loss (IL) of the device is achieved, practically throughout the entire frequency spectrum. Specifically, Figure 3 shows a comparison of insertion losses (IL) as a function of frequency (Hz) for equipment (M1) without a diffusion system versus a device (MH2O), such as the one described in this solution, which includes a water diffusion system. Figure 4, in turn, shows the improvement in insertion losses (IL) provided by the water curtain (23) in the device (MH2O) as a function of frequency (Hz). This translates into the possibility of simplifying the design of acoustic dispersers (11) towards simple geometries, thus substantially reducing the cost of producing the device (100). From a particle capture perspective, the tests were conducted in a wind tunnel designed for particle capture assessment. The tests were performed at three wind speeds, which are listed in Table 1. Table 1. Wind speeds in measurement tunnel The parameters obtained measured in each of the tests performed are: 1. Number of data points 2. Temperature 3. Humidity 4. Type of particles: PM1, PM2.5 and PM10 5. Number of particles by size: P0.3, P0.5, P1.0, P2.5, P5.0 and P10.0 Additionally, two types of polluted air were used, generated by a gasoline engine (with a higher emission of small particles) and by biomass burning (with a higher number of large particles). The results obtained in the tests carried out are summarized in the following tables, Table 2 and Table 3. Table 2. Combustion engine test results Table 3. Results of the biomass burning trial According to the sensors used, a lower number of particles, such as P0.3, produces saturation of the sensors in the different tests carried out. Thus, the particle retention efficiency of the device decreases with increasing air velocity. A significant reduction is observed at air velocities in the range of 1–2.5 m / s, with the highest particle retention occurring at approximately 1.36 m / s, where an overall reduction in particle count of 25–30% is achieved. The present device (100), comprising a liquid diffusion system (11), is capable of retaining and reducing the quantity of larger particles (PM2.5 and above) more effectively. Overall, we obtain reductions of 10-15% for fine particles, smaller than 1 micrometer, while for coarse particles, larger than 2.5 micrometers, the reduction percentage reaches 40-45%. In general, these percentages represent a substantial improvement compared to other filters currently available on the market. The type of pollutant particle and its composition or characteristics affect the percentage reduction in the amount of particles. In tests using an ENGINE as the pollutant source, we found an overall reduction of 15%; however, for tests using BIOMASS combustion, this overall reduction increases to 25%. Likewise, regarding the different fractions of particulate matter (PM1, PM2.5 and PM10), and taking into account the 2 sources of pollution, we obtain the following Table 4 of reduction percentages: Table 4. Percentage reduction according to particulate matter fractions

Claims

1. An air pollution mitigation device comprising a sound crystal (10) formed by a set of at least three lines of acoustic diffusers (11) of height h permeable to air currents in their transverse direction, characterized in that the device (10) further comprises a diffusion system (20) for a liquid supported on the sound crystal (10), comprising at least one liquid inlet (21) and at least one liquid outlet (22), connected by a distribution network (24), wherein the at least one outlet (22) of said liquid is configured to create at least one liquid curtain (23) arranged in a frontal plane covering, totally or partially, the height h of the acoustic diffusers (11). 2.The device according to claim 1, wherein the liquid diffusion system (20) further comprises a collection base (30) disposed at the bottom of the device (100) comprising a liquid storage tank (37) configured for liquid storage.

3. The device according to claim 2, wherein the fluid collection base (30) comprises a perforated plate (32) connected to the storage tank (37).

4. The device according to claim 2, wherein the fluid collection base (30) comprises at least one foundation ring (36) oriented towards at least one liquid collection channel (33) disposed in connection with the storage tank (37). 5.The device according to any one of claims 2 to 4, wherein the liquid diffusion system (20) further comprises a pumping means (31) connected to the storage tank (37) of the collection base (30) configured to pump collected liquid to at least one outlet (22) of the diffusion system (20).

6. The device according to any one of claims 1 to 5, wherein the distribution network (24) comprises at least two pipes arranged at different heights.

7. The device according to any one of claims 1 to 6, wherein the liquid diffusion system (20) comprises a plurality of outlets (22) arranged on each pipe of the distribution network (24).

8. The device according to any one of claims 1 to 7, wherein the distribution network (24) comprises horizontal pipes.

9. A modular barrier system comprising at least one device (100) according to any one of claims 1 to 8.