NL2001650C2 - Filter device for use in separation screen for filtering gas stream, has filter including movable filter body and cylindrical filter chamber, which is arranged between inlet and outlet - Google Patents

Abstract

The filter device has a filter including a movable filter body and a cylindrical filter chamber (1), which is arranged between an inlet (4) and an outlet (5). The filter body has a maximum dimension between 2 mm and 5 mm, and comprises an electrically insulating composition. The filter body is made of plastic e.g. polystyrene and polyurethane. The filter chamber has a dense wall (2) and a hexagonal cross-section and is placed in a honeycomb structure.

Description

Filter device and filter for use therein as well as a separation screen for placement along a traffic road.

The present invention relates to a filter device for a gas stream comprising a filter at least one filter chamber between an inlet and an outlet for passing the gas stream therethrough and a filter medium in the filter chamber to feed particles, in particular fine dust, to the gas stream to withdraw. The invention also relates to a filter for use in such a device and to a separating screen for placement along a traffic road with at least one hollow space for receiving an airflow escaping from the traffic road therein.

In many places, air quality does not meet the standards set by the government, with all the associated risks for public health. In particular along traffic roads, local residents experience harmful consequences due to the presence of fine solid particles in the air that come from the rushing traffic.

These particles are collectively referred to as particulate matter and are of different nature and composition, but have in common that they are so small that they are simply entrained by an air stream. Particulate matter is always and everywhere. Problems arise when the concentration of particulate matter becomes so high that it is harmful to health. Values have been set by the European Union that may not be exceeded by more than 40 days per year. However, data from different measuring stations show that at the location of the so-called liot spots, where the air problems are greatest, the values determined for particulate matter are exceeded for an average of no less than no less than sixty days. With the increasing crowds on the roads, it is feared that this number will only increase if the number of hot spots, if not intervened.

One possibility to reduce the concentration of fine dust in the air is to place filter devices with one or more filters through which air is passed through to capture fine dust. Such filters usually include fine pore mats or meshes that are impermeable to particulate matter. As smaller fractions of particulate matter, such as those designated as PM2.5 and PM10, also have to be captured, such filters will have to be finer-meshed. As a result, the LA08.1388NL.nI.ttpd -2-filter resistance of the known filters will generally increase with a decrease in particle size to be captured. For cleaning outside air, moreover, a relatively large amount of air must be passed through the filter - compared to industrial filters - with a low pollution concentration. With traditional filtering techniques, this means that a relatively large amount of energy is required to pass sufficient air through the filtering device.

The present invention has for its object, inter alia, to provide a filtering device which at least substantially mitigates one or more of these and other drawbacks and which can at least partly be used as a result in a separation screen for a traffic road.

In order to achieve the intended object, a filter device of the type described in the preamble according to the invention has the feature that the filter medium comprises a quantity of filter bodies freely movable in the filter chamber of an electrically insulating composition which are capable and adapted during operation by the gas stream to be stirred and thereby assume an electrostatic charge. During operation, the polluted gas stream, whether forced or not, carries the filter bodies into the polluted gas, in particular polluted ambient air.

Because the filter bodies are relatively light, the filter bodies are entrained relatively easily with the gas stream without requiring much energy for this. In this range, the contaminating particles can settle on the filter bodies. In addition, the filter bodies set in motion will become electrostatically charged due to mutual collision and friction with the walls of the filter chamber. The filter bodies thus electrostatically charged attract contaminating particles to them, thus actively extracting them from the gas stream. A significant reduction in the proportion of small particles in a gas stream can thus be achieved, such as, for example, a flow of ambient air at a traffic route or other hot spot.

The filter bodies can for instance be of hollow design to achieve a relatively low total weight, but it is also possible to start from bodies with a full core and thereby choose a material with a sufficiently low density. A special embodiment of the filter device according to the invention is characterized in this connection in that the bodies comprise monolithic foam bodies with a substantially full core. Such foam bodies can be manufactured relatively easily on an industrial scale at relatively low costs and thus lend themselves perfectly for use in the filter device according to the invention. A pressing, or density of the foam material can thereby be adjusted to an optimal mobility in the gas stream.

10 Contaminated filter bodies can be cleaned or totally recycled for reuse or continued use. Partly in view of this latter possibility, a further preferred embodiment of the filter device according to the invention has the feature that the bodies are foamed from a single plastic, in particular from a plastic from a group comprising polystyrene and polyurethane.

Thus, a recycling process only needs to be tailored to a single plastic and no mixing of different plastics occurs.

A particularly good mobility of the bodies and homogeneous electrostatic charge distribution thereon is achieved with a further preferred embodiment of the filter device according to the invention, which is characterized in that the filter bodies are at least substantially granular, in particular spherical. A particularly uniform filtering effect is thus achieved by the filter bodies.

Particularly satisfactory results have been achieved in practice with a special embodiment of the filter device according to the invention, characterized in that the filter bodies are at least substantially identical with a maximum dimension of between 1 and 10 millimeters, in particular between 2 and 5 millimeters. By thus starting from bodies with relatively modest dimensions, an adequate mobility thereof in the gas stream is achieved, while nevertheless the total active filtering surface remains large.

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The total active area can be increased by increasing a degree of filling of the filter chamber. However, this ultimately comes at the expense of the free mobility of the filter bodies in the same filter chamber. A correct balance is achieved in a further particular embodiment of the refurbishing device according to the invention, which is characterized in that the filter chamber has a filling degree of filter bodies of at most 50 volume percent, and in particular a filling degree of about 30 volume percent

The filter bodies will be driven to the outlet during operation under the influence of the gas flow. In order to prevent a continuous accumulation of filter bodies taking place there, a further preferred embodiment of the filter device according to the invention has the feature that the filter chamber is placed at a slope to the inlet. The filter bodies will thus fall back to the inlet side again under the influence of gravity, in particular in the event of a temporary loss of the gas flow, so that it can subsequently be carried away again by the gas flow.

In order to promote the mobility of the filter bodies in the filter chamber, a further special embodiment of the filter device according to the invention has the feature that an inner wall of the filter chamber is structured on a side facing the filter bodies. The walls thus structured will give rise to turbulence of the flowing gas stream, which will thereby cause more agitation to the bodies.

A further preferred embodiment of the filter device according to the invention is characterized in that an inner wall of the filter chamber comprises a friction layer on a side facing the filter bodies. Such a friction layer aims at promoting an electrostatic charge of the filter bodies, which are partly brought into contact therewith along the same and which, for the remainder, take over electrostatic charge from other filter bodies. The effectiveness of the filter can thus be increased.

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As soon as the filter bodies become too saturated to properly fulfill their filtering action, they can be removed, possibly removed from the fine dust in a regeneration process, and replaced. In a particularly practical embodiment, the filter device according to the invention is characterized in this respect in that the filter comprises a removable filter unit with the filter bodies therein, the filter unit having an open structure on an inlet side and outlet side that allows an at least substantially unhindered gas flow but for the filter bodies are at least substantially impermeable. Thus, a contaminated filter unit can simply be taken out as a whole to be exchanged for a fresh one. The filtering device does not need to be put out of operation, or hardly so.

Although in principle it is sufficient for the filtering effect that the filtering unit on the inlet side and outlet side is sufficiently open to allow the gas flow to pass through, a further special embodiment of the filter device has the feature that the filtering unit 15 has an open structure on all sides, and in particular a basket or bag, and that the filter unit is suitably accommodated in a filter housing. Such a structure that is open on all sides offers optimum accessibility of the filter bodies enclosed within it in a regeneration process in which, for example, the filter bodies are cleaned in a liquid bath after becoming too saturated. The filter bodies 20 thus do not need to be removed from the filter unit for this purpose, while also a possible drying step via the open structure can be particularly effective and therefore relatively short.

The filter unit can itself be manufactured from various materials, but a special embodiment of the filter device according to the invention is preferred, which is characterized in that the filter unit comprises an electrically insulating wall on all sides. Such insulating walls avoid compromising the electrostatic charge on the filter bodies.

The filter can cover one or a few relatively large filter chambers, but can also be distributed over a relatively large number of smaller filter chambers. In this regard, a further particular embodiment of the filter device according to the invention has the feature that the filter comprises a collision of filter chambers separated by intermediate walls. Thus an excessive accumulation of filter bodies in the filter is avoided because fractions thereof are each enclosed in their own filter chamber, which benefits their mobility.

A particularly practical embodiment of the filter device according to the invention is characterized in that the filter chambers have a polygonal, in particular hexagonal, cross-section with intermediate walls shared between adjacent filter chambers. Such polygonal filter chambers can be arranged adjacent to each other, whereby a special high packing density of filter chambers operating parallel to each other can be achieved. The intermediate walls between adjacent filter chambers are relatively thin and therefore have little or no influence on the packing density, but on the other hand do promote a free mobility of the filter bodies. A further preferred embodiment of the filter device according to the invention is herein characterized in that the intermediate walls are permeable to the gas flow, but confine the filter bodies in the filter chambers. The intermediate walls thus open to the gas stream process transverse flows in the filter which are turbulent during operation and additionally touch the filter bodies. Moreover, such open intermediate walls offer additional access to the filter chambers for a cleaning medium in order to be able to regenerate and revitalize saturated filter bodies to a greater or lesser extent.

The filter device according to the invention, although not exclusively, is eminently suitable for cleaning, for example, fine dust from an air flow with a relatively low flow but large volume, such as, for example, an air flow escaping from a traffic route. The invention therefore also relates to a separation screen of the type described in the preamble which is characterized according to the invention in that the at least one hollow space is provided with a filter device according to one or more of the preceding claims. The filtering device can herein be placed both in, and in front of or behind the hollow space in such a way that the air flow is passed through it.

The invention also relates to a filter for use in the above-described filter device according to the invention and will now be further elucidated on the basis of a number of exemplary embodiments and an associated drawing. In the drawing: figure 1 shows a cross-section and operating principle of a first exemplary embodiment of a filter device according to the invention; Figure 2 shows a cross section and operating principle of a second exemplary embodiment of a filter device according to the invention; figure 3 shows a cross section and operating principle of a first exemplary embodiment of a separation screen according to the invention with the filter device of figure 1 for placement along a traffic route; Figure 4 shows a cross section and operating principle of a second exemplary embodiment of a separation screen according to the invention with the filter device of figure 1 for placement along a traffic route; figure 5 is a perspective view of a third exemplary embodiment of a filter device according to the invention; Figure 6 shows a cross section and operating principle of the filter device of figure 5; Figure 7 is a front view of the filter device of Figure 5; Fig. 8 shows a cross section and operating principle of a third exemplary embodiment of a separation screen according to the invention with the filter device of Fig. 5 for placement in a central reservation of a traffic road; figure 9 shows a cross-section and operating principle of a fourth exemplary embodiment of a separation screen according to the invention with the filter device of figure 5 for placement along a traffic route; Figure 10 shows a cross-section and operating principle of a fifth exemplary embodiment of a separation screen according to the invention with the filter device of Figure 5 for placement along a traffic road. The figures are purely schematic and not drawn to scale. In particular, for the sake of clarity, some dimensions are exaggerated to a greater or lesser extent. Corresponding parts are designated in the figures with the same reference numeral.

The filter device shown in Figure 1 comprises a substantially cylindrical filter chamber 1 which is bounded by a closed longitudinal wall 2 and a pair of gas-permeable end walls 4,5 schematically indicated by arrows 3,3 '. The longitudinal wall 2 is, for example, made of a suitable plastic such as polyethylene, polypropylene or polystyrene and extends around the filter chamber 1. For example, a mesh, cloth or grid 6 is provided on the ends 4.5 to form an inlet 15 and an outlet of the filter chamber, respectively, which are sufficiently open to allow a virtually unhindered gas flow.

In the filter chamber 1 there is a filter medium in the form of a large quantity of individual filter bodies 7. The filter chamber is filled with such filter bodies approximately for 30% by volume so that the filter bodies retain sufficient space and freedom therein to be free to move. The filter bodies 7 are so light in relation to their size that they are susceptible to being entrained by the gas stream. In this example, the filter bodies are based on substantially identical foamed granules or beads with a diameter of typically between 1 and 10 millimeters, with a diameter of around 4 millimeters being chosen in this example. A mesh size or pore size in the inlet and outlet 4.5 is chosen such that the filter cooling rings are locked up, but also the inlet and outlet nevertheless open enough air with little or no air resistance. The filter bodies can therefore at least substantially not leave the filter chamber.

30-9

The filter bodies are based on an electrically insulating material, such as in this case polystyrene foam, which has the capacity to accept an electrostatic charge under the influence of mutual collisions and friction along the walls 2,4,5 of the filter chamber. During operation, the fender bodies brought by the gas stream 3 into agitation 5 will thus charge electrostatically static.

The filter bodies first of all have a passive filtering effect because fine dust, or other microscopic solid particles, can adhere to the filtering bodies in the event of an accidental collision. In addition, the electrostatically charged filter bodies in the filter according to the invention will also actively attract and bind fine particles, such as particulate matter in particular, from the gas stream. The result is a significant reduction in the concentration of solid contamination in the gas stream, which is indicated by the lighter colored arrow on the outlet side.

The filtering device shown is, for example, applicable for filtering fine dust from an air stream escaping from a traffic route. Figure 3 gives an example of this in which the filtering device 1 is applied in a partition screen 12 which is placed, for example, as a noise barrier along a traffic road 10 behind a guide path 13. To this end, the partition screen 12 comprises a spout-shaped extension 14 with a hollow space 15 at a top thereof. wherein the filter device 1 of Figure 1 is interchangeably arranged as a detachable filter unit, for example in the form of a filter cartridge. A wing 16 formed on the roadside directs and concentrates an air flow 11 through the filter and thus increases the efficiency of the device.

The air flow 11 is in practice the result of a locally prevailing wind in connection with a driving wind of the passing traffic. In addition, a fan or turbine can optionally be provided in or near the screen to generate a forced air flow if desired, for example if there is insufficient wind. The air stream 11, whether or not mechanically forced, carries the loose polystyrene granules 7 in the filter chamber into the polluted air. Because the material of the grains 7 is particularly light, the grains 7 are easily carried along with the wind without this costing much energy. In this range, the fine dust can settle on the grains. The chamber 1 is positioned under a slope to the inlet side so that the pellets can fall out again to be taken back into the air stream again. The upwardly directed outflow opening also ensures dispersion and dilution of air pollution in the air that has not passed through the filter.

A second aspect of the filter is that due to the collision and friction, both of the grains themselves and against the walls of the filter chamber 1, the grains become electrostatically charged. The electrostatically charged grains ensure that the deposition rate of particulate matter to the material of the grains is greater than the speed along the material. In other words, the charged polystyrene beads also attract fine particulate matter that will adhere to them. Before the pellets become completely saturated with particulate matter, the filter cassette 1 is taken out of the cavity 15 to be exchanged for a fresh copy and / or to remove the saturated particulate matter from a collected copy or to recycle it completely.

All separate parts of the filter device of this example are 'mono materials', which means: consisting of one type of material, making them ideally suited for recycling. After cleaning, the used granules are also suitable for reuse or as a raw material for new products. The materialization of the components into which the filter device is fitted is tailored to the situation on site. The design and color scheme can also vary.

When mounting the filter device on an existing separation screen along a traffic road, it is important to use materials that are light and yet sufficiently strong to guarantee the required durability. Polystyrene (EPS) is ideally suited for this. Especially because the material can be made in any desired shape with the help of a mold. The required durability can be achieved by using EPS with a high rigidity. By providing EPS with a coating, a hard, smooth surface is created. The coating can be applied by means of a paint sprayer and colored by adding pigments.

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Figure 2 shows, as a variation on the filter device shown in Figure 1, a second exemplary embodiment of a filter device according to the invention. The device is largely similar to that of Fig. 1, although a funnel-shaped outlet 8 is provided here on an outflow side to collect rain 9, for example, during rain, and to pass it through the filter chamber 1. Thus, the filter granules 7 will be wholly or partially rinsed, which will prolong their operating cycle. Moreover, the longitudinal wall 2 is coated on the inside with a coarse friction material to promote electrostatic interaction with the grains 7 and provided with a structure that causes more turbulence in the air stream 3 to better move the grains 7.

The filter device according to the invention can, in addition to or on an existing sound screen, also be ideally used within a partition screen 20 with an internal cavity 21 as a hollow space, as is shown, for example, in Figure 4. Such a screen is described in more detail in current Dutch patent application no. 1034614, the content of which is to be considered herein and incorporated by reference.

The cavity 21 here forms a number of consecutive shafts in which in each case a filter unit 1 according to the invention is placed. On a side facing away from the road 10, a supply opening 22 provides access to such a shaft for an airflow 11 that is out of the way, and the shaft thereby provides extra draft through the filter 1 through which a particularly effective airflow takes place therethrough. At a top, the separation screen 20 in each case provides a discharge opening 23 per shaft 21, through which at least partially purified air can escape and is mixed with ambient air. Such a double-walled set-up 25 of a partition screen 20 offers in practice a particularly effective and efficient interaction with air flow 11.

Instead of a single relatively large filter chamber, a filter device according to the invention can also comprise a concatenation of a large number of smaller filter chambers. An example of this is shown in Figs. 5 to 7. Fig. 5 shows a structure of the filter 10 used in the device with individual filter chambers 1. The filter chambers 1 each have a hexagonal section and are close to a honeycomb structure. placed apart, only separated by intermediate walls 2. The intermediate walls 2 can be closed, but can also have an open structure and be air-permeable to allow mutual communication between neighboring filter chambers 1. Each chamber is 20 to 30 percent filled with filter bodies in the form of foamed polystyrene beads or foamed polyurethane beads with a diameter of the order of 3 millimeters.

As can be seen clearly in the cross-section of Figure 6, the filter chambers 1 are placed at an incline towards the inlet side in order to promote a relapse of granules 7 once carried by a gas stream to the inlet side. On the inlet side 4 and outlet side 5, an open grid or cloth 6 ensures that the granules 7 cannot leave the chambers, but that nevertheless a practically undisturbed air flow through them is possible. The filter 10 is included in a form-retaining frame or frame 31 which completely surrounds the filter 10 and gives it rigidity. For the frame 31, as well as for the walls 2 of the filter itself, extruded polystyrene (EPS) can be used as starting material. A filter unit 41 is thus obtained which can be used as a removable cassette 32 or can be placed in a fixed arrangement.

20

In particular, an elongated filter screen 30 can be constructed from a number of such filter cassettes 32, as is shown in front view in Figure 7. Such a screen 30 can be used, for example, in the manner indicated in Figure 8, in a central reservation of a traffic road 19. The screen 40 comprises a concatenation of filter cassettes 32 which are each slid between uprights 33 arranged on either side. The cassettes are fully removable and interchangeable for quick and easy maintenance.

With such an arrangement directly along a guide rail 13 of a traffic route, polystyrene is also a particularly suitable material. By designing the entire housing in polystyrene, it has no negative effect on the operation of the guide rail. In the event of a collision, the guide wheel will continue to do its work while the housing of filtering device does not resist and is pulverized. The defective parts can easily be replaced with new ones. The polystyrene is preferably designed to be fire-retardant. By incorporating a fire-retardant into the structure of the material during the chemical process of polymerization, the fire-retardant properties are also guaranteed over the years.

The cassettes 32 of Figure 6 can also be stacked vertically or made higher to be placed completely in front of an existing separation screen 40 of a traffic road 10. This is shown in Figure 9. Such a separation screen 40 typically has a height of approximately 4 meters and is generally used as a noise-limiting measure for buildings present behind it. By thus placing a filter screen 30 according to the invention in front of it, additional functionality can be added to it in a relatively simple manner. The filter screen itself is, due to the use of relatively light materials such as the aforementioned polystyrene, relatively light and can therefore be applied without problem to an existing foundation of such a sound screen.

In addition, filter cassettes 30 of the type shown in Figure 6 can be used as an inlet filter in a supply opening 22 of a double-walled separation screen 22, as shown in Figure 10. The separation screen 22 is otherwise substantially identical to that of figure 4.

The invention thus offers a particularly practical solution for filtering solid particles from a gas stream, in particular particulate matter from ambient air, which can be used in many forms and situations. Although the invention has been further elucidated on the basis of merely a number of exemplary embodiments and application possibilities, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and forms of appearance are still possible for an average person skilled in the art within the scope of the invention.

Claims (17)

CLAIMS 1. Filter device for a gas stream comprising a filter at least one filter chamber between an inlet and an outlet for passing the gas stream and a filter medium through the filter chamber to extract particles, in particular fine dust, from the gas stream, characterized in that the filter medium comprises an amount of filter bodies freely movable in the filter chamber of an electrically insulating composition that are capable and arranged to be agitated by the gas stream during operation and thereby assume an electrostatic charge. 10 A filter device according to claim 1, characterized in that the bodies comprise monolithic foam bodies with a substantially full core. 3. Filtering device as claimed in claim 2, characterized in that the bodies are foamed from a single plastic, in particular from a plastic from a group comprising polystyrene and polyurethane. A filter device according to claim 1, 2 or 3, characterized in that the filter bodies are at least substantially granular, in particular spherical. 20 Filter device according to one or more of the preceding claims, characterized in that the filter bodies are at least substantially identical with a maximum dimension of between 1 and 10 millimeters, in particular between 2 and 5 millimeters. Filter device according to one or more of the preceding claims, characterized in that the filter chamber has a filling degree of filter bodies of at most 50 volume percent, and in particular a filling degree of about 30 volume percent. 7. Filtering device as claimed in one or more of the foregoing claims, characterized in that the filter chamber is placed at a slope towards the inlet. -15- A filter device according to one or more of the preceding claims, characterized in that an inner wall of the filter chamber is structured on a side facing the filter bodies. 9. Filtering device as claimed in one or more of the foregoing claims, characterized in that an inner wall of the filter chamber comprises a friction layer on a side facing the filter bodies. A filter device according to any one or more of the preceding claims, characterized in that the filter comprises a removable filter unit with the filter bodies therein, the filter unit having an open structure on an inlet side and outlet side that allows an at least substantially unhindered gas flow but at least for the filter bodies substantially impermeable. A filter device according to claim 10, characterized in that the filter unit has an open structure on all sides, and in particular comprises a basket or bag, and that the filter unit is suitably accommodated in a filter housing. A filter device according to claim 10 or 11, characterized in that the filter unit 20 comprises an electrically insulating wall on all sides. A filter device according to one or more of the preceding claims, characterized in that the filter comprises an arrangement of filter chambers separated by intermediate walls. 25 A filter device according to claim 13, characterized in that the filter chambers have a polygonal, in particular hexagonal, cross-section with intermediate walls shared between adjacent filter chambers. A filter device according to claim 14, characterized in that the intermediate walls are permeable to the gas flow, but confine the filter bodies in the filter chambers. -16- A partition screen for placement along a traffic route with at least one cavity for receiving therein an air flow evading from the traffic route, characterized in that the at least one cavity is provided with a filter device according to one or more of the preceding claims. 5 A filter for use in the filter device according to one or more of claims 1 to 15.