FILTER ELEMENT AND GAS PURIFICATION DEVICE COMRPISING A FILTER ELEMENT

Abstract

A filter element (1) for use in a gas purification device (100) is disclosed. It comprises a substrate (10) and a filter layer (20) covering an exterior surface of the substrate (10). The substrate (10) comprises material for containing chemicals (30) effective to remove gas pollutants from a gas. The material of the filter layer (20) is hydrophilic to adsorb liquid solution adsorbents effective in removing gas pollutants from a gas, and the exterior surface of the substrate (10) covered by the filter layer (20) is hydrophobic.

Claims

1. Filter element for use in a gas purification device, comprising a substrate and a filter layer covering an exterior surface of the substrate, wherein the substrate comprises material for containing chemicals effective to remove gas pollutants from a gas, wherein the material of the filter layer is hydrophilic to adsorb liquid solution adsorbents effective in removing gas pollutants from a gas, and wherein the exterior surface of the substrate covered by the filter layer is hydrophobic.

2. Filter element according to claim 1, wherein the substrate comprises a plurality of channels, and wherein the filter layer covers at least a portion of the exterior surface of the substrate in the channels.

3. Filter element according to claim 2, wherein the substrate has a honeycomb appearance by virtue of at least a portion of the channels having a hexagonal outline.

4. Filter element according to claim 2, wherein the channels are non-straight channels, i.e. channels different from straight channels extending in a single longitudinal direction.

5. Filter element according to claim 1, wherein the substrate comprises a hydrophilic material such that only its exterior surface is hydrophobic.

6. Filter element according to claim 1, wherein the substrate is entirely made of hydrophobic material.

7. Device for purifying a gas such as air, comprising a filter element according to claim 1, and means for realizing a flow of the gas along the filter layer of the filter element during operation.

8. Device according to claim 7, further comprising indication means for indicating to a user information regarding the effective lifetime of the filter layer of the filter element.

9. Device (100) according to claim 7, wherein the filter element is removably arranged in the device.

10. Device according to claim 7, further comprising a spraying arrangement for spraying a liquid on at least a portion of the filter layer of the filter element.

11. Device according to claim 10, further comprising a tank for containing liquid chemicals, wherein the spraying arrangement is connected to the tank.

12. Device according to claim 10, further comprising a timer for activating the spraying arrangement at a predetermined interval frequency.

13. Device according to claim 10, further comprising detecting and controlling means which are adapted to check the effectiveness of the gas purifying process, and to activate the spraying arrangement in case the effectiveness appears to be below a predetermined reference value.

14. Filter element according to claim 1, wherein the material of the filter layer comprises Tris(hydroxylmethyl)amino-methane.

15. Filter element according to claim 1, wherein the filter layer comprises a hydrophilic polymer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will now be explained in greater detail with reference to the figures, in which equal or similar parts are indicated by the same reference signs, and in which:

[0017] FIG. 1 diagrammatically shows a practical embodiment of a filter element according to the invention; and

[0018] FIG. 2 diagrammatically shows components of an air purifier including the filter element.

DETAILED DESCRIPTION OF EMBODIMENTS

[0019] FIG. 1 diagrammatically shows a practical embodiment of a filter element 1 according to the invention. The filter element 1 comprises a substrate 10 and a filter layer 20 in the form of a thin layer of hydrophilic coating applied to an area 11 which is a portion of the exterior surface 12 of the substrate 10, i.e. a portion of the surface of the substrate 10 which is accessible from outside of the substrate 10, which includes the surface which is accessible in pores, holes, channels etc. as may be present in the substrate 10. In the diagrammatic representation of FIG. 1, the thickness of the filter layer 20 is depicted in an exorbitant large fashion with respect to the thickness of the substrate 10, for the sake of illustration of the presence of the filter layer 20 on the covered area 11 of the substrate 10.

[0020] In the shown example, the substrate 10 comprises a plurality of channels 13 for allowing gas to be purified to flow through the filter element 1. In order to have a most effective filter element 1, the exterior surface 12 of the substrate 10 is covered by the filter layer 20 in each of the channels 13. The exterior surface 12 of the substrate 10 is liquid-resistant in order to obtain effects as will be explained below. To this end, an outer layer of the substrate 10 may comprise one or more liquid-resistant materials such as glass, metal, plastic or ceramics, or the entire substrate 10 may be made of such materials.

[0021] The channels 13 may have any suitable outline. In the shown example, a number of channels 13 have a hexagonal outline, so that the substrate 10 has a honeycomb appearance. It is a well-known fact that a honeycomb structure is advantageous when it comes to having both a relatively large surface and a relatively small pressure drop. All channels 13 can have a hexagonal outline in order to obtain the honeycomb structure, but it is also possible to have a combination of hexagonal channels 13a and diamond-shaped channels 13b as shown. The channels 13 may be straight channels, but channels 13 comprising curves are also feasible within the framework of the invention.

[0022] The filter element 1 is suitable to be applied in a device which is intended to be used for purifying air or another gas. In such a device, a fan or the like is used for driving the gas to be purified through the filter element 1, for contacting the filter layer 20 of the filter element 1. Due to its hydrophilic property, the filter layer 20 is capable of adsorbing liquid solution adsorbents which are effective in removing gas pollutants from the gas flowing along the filter layer 20 during operation of the gas purification device. The filtering function of the filter element 1 is based on the fact that pollutants are entrained in the filter layer 20 and are reacted with the chemicals as present in the filter layer 20. As long as not all chemicals have been reacted, it is achieved that an outgoing gas flow of the filter element 1 contains less gas contaminants than an ingoing gas flow of the filter element 1. The liquid solution adsorbents stay on top of the exterior surface 12 of the substrate 10 in the form of a thin film, wherein, due to the liquid-resistant property of the substrate 10, it is avoided that the liquid solution adsorbents penetrate deeper into the substrate 10. Hence, the quantity of liquid solution adsorbents needed to have a functional state of the filter element 1 is considerably less than in case the substrate 10 would be hydrophilic as known in the art.

[0023] In order to reach satisfactory removal efficiency of the filter element 1, pore size of the filter element 1, which is determined by the cross-sectional size of the channels 13, is a very important factor. Small pore size filter elements will have better removal efficiency, but a larger pressure drop is obtained. On the other hand, filter elements with larger pore size will benefit in smaller pressure drop, but their removal efficiency will be decreased because the gas will not have full contact to the filter element. Therefore, the selection of a suitable pore size which involves satisfactory removal efficiency and an acceptable pressure drop is important.

[0024] In the following, a way of determining a suitable pore size is explained. As an example of an actual situation of purifying air in a room by means of a suitable device, i.e. an air purifier, it is assumed that the volume of the room is 50 m.sup.3, and that the air purifier is able to clean the air in the room five times every hour, so that the flow rate of the filter element 1 needs to be 250 m.sup.3/h. The size of a face area of the filter element 1 is assumed to be 0.1 m.sup.2, while the thickness of the filter element 1 is assumed to be 30 mm. The air velocity is calculated to be 0.69 m/s (250÷0.1÷3600=0.69 m/s). Using the following formula, the residence time t of the gas molecules within the filter element 1 can be calculated, wherein c represents the porosity of the filter element 1 and is assumed to be 0.5, L represents the thickness of the filter element 1, and ν represents the air velocity:

t=εL/ν=0.5×0.03/0.69=0.02 s

[0025] The diffusion path Δ of the gas molecules is calculated by means of the following formula, wherein D represents the gas diffusion coefficient, which is assumed to be applicable to formaldehyde in this example, D.sub.HCOH=1×10.sup.−5 m.sup.2/s:

Δ=(4Dt).sup.1/2=(4×10.sup.−5×0.02).sup.1/2=0.9 mm

[0026] According to the calculation result, if the shape of the channels 13 of the filter element 1 is straight, then the ideal diameter of the channels 13, i.e. the ideal pore size, is 0.9 mm. If the channels 13 of the filter element 1 are not straight, the increased complexity of the air pathway allows larger pore size as long as the open pore of the filter element 1 extending all the way from one side of the filter element 1 to another is smaller than 0.9 mm.

[0027] An important issue in the field of filter elements for purifying air or another gas is the lifetime of the filter element. The filter element 1 according to the invention can be regenerated by supplying chemicals to the filter layer 20, which may be done in any suitable manner, for example, through spraying. In the following, it is explained how a regeneration interval can be calculated. As an example, it is assumed that the composition of the chemical adsorbent to be included in the filter layer 20 is 10% w/w KHCO.sub.3/5% w/w K.sub.2CO.sub.3/10% w/w KHCO.sub.2/25% w/w Tris-hydroxymethyl-amino-methane/50% w/w H.sub.2O. In that case, the Tris supplied to the filter layer 20 is 12.5 g (ca. 0.1 mol) when the filter layer 20 is assumed to adsorb 50 g chemical adsorbent. On the basis of the fact that each NH.sub.2 group helps to combine two formaldehyde gas molecules, it is found that 0.1 mol Tris adsorbs 0.2 mol (6000 mg) formaldehyde. This implies that in a 50 m.sup.3 size room, in which the formaldehyde concentration is 0.1 mg/m.sup.3, the filter element 1 is able to clean 60000 m.sup.3 polluted air. Assuming that the air purifier is capable of emitting 200 m.sup.3/h clean air, this means that the filter element 1 can be used for 300 hours. When the pollution reaches a double level (0.2 mg/m.sup.3), the effective lifetime of the filter element 1 is 150 hours. Based on this exemplary calculation, regeneration of the filter element 1 needs to take place every week or every two weeks, which is a practical and reasonable time interval.

[0028] In the example as described in the foregoing, the functional group to remove formaldehyde is NH.sub.2. It is noted that other types of amine with NH groups are also suitable for formaldehyde removal.

[0029] It is beneficial to the effectiveness of the filter element 1 if a periodic regeneration system is provided with the filter element 1. A lifetime cycle of the filter element 1 is started by loading the hydrophilic filter layer 20 with functional gas removal adsorbents. After a predetermined period of time or on the basis of sensor feedback, a new dose of the adsorbents can be supplied to the filter layer 20 to start a new lifetime cycle and to keep the effectiveness at which the removal of gas pollutants takes place at a predetermined level throughout the entire lifetime of the filter element 1. On the basis of the fact that the design of the filter element 1 according to the invention allows for regeneration, problems associated with known filter elements, such as short lifetime and limited efficiency of removal of gas pollutants are effectively alleviated.

[0030] FIG. 2 diagrammatically shows components of an air purifier 100 including the filter element 1 as described in the foregoing. In particular, besides the filter element 1, the air purifier 100 comprises a fan 101 for generating a flow of air through the filter element 1, a tank 102 for containing liquid solution adsorbents 30, a pump 103 with a control valve 104, a nozzle 105 to spray liquid solution adsorbents 30 on the filter element 1, and tubing 106 having a first section 106a for enabling the pump 103 with the control valve 104 to take liquid solution adsorbents 30 from the tank 102, and a second section 106b for enabling the pump 103 with the control valve 104 to supply liquid solution adsorbents 30 to the filter element 1 through the nozzle 105. According to this design, the air purifier 100 comprises a regeneration system which is adapted to regenerate the filter element 1 by taking liquid solution adsorbents 30 from the tank 102 and spraying those on the filter element 1, wherein the liquid solution adsorbents 30 are adsorbed by the filter layer 20 of the filter element 1 and form a thin film on the exterior surface 12 of the substrate 10 of the filter element 1 as explained in the foregoing. In FIG. 2, a spray of liquid solution adsorbents 30 is diagrammatically depicted by means of a group of dashed lines.

[0031] In the air purifier 100 as shown, regeneration of the filter element 1 takes place by activating the pump 103 with the control valve 104, assuming that the tank 102 is filled with liquid solution adsorbents 30. According to one feasible option, the pump 103 with the control valve 104 are activated manually by a user of the air purifier 100. To that end, the air purifier 100 may comprise a suitable button or the like, for operation by the user. In a basic embodiment of the air purifier 100, it is up to the user to the decide when regeneration of the filter element 1 should take place, namely by sensing the quality of the air in the surroundings of the air purifier 100 and/or taking into account a certain time interval. In a more sophisticated embodiment of the air purifier 100, an indicator 107 is provided for warning the user that it is time to have a regeneration action. The indicator 107 may be operated by means of a timer (not shown), or the air purifier 100 may be equipped with a controller 108 and at least one sensor 109 for checking whether the filter element 1 is effective to a predetermined extent and activating the indicator 107 when this appears not to be the case. The checking process as mentioned may take place in any suitable manner, and may involve detecting the content of gas pollutants in the outgoing flow of air and comparing the value as found to a threshold value, or detecting the content of gas pollutants in both the incoming flow and the outgoing flow of air and comparing a difference value as found to a threshold value. In an automatic embodiment, which is also feasible within the concept of the regeneration system as shown, the indicator 107 may be omitted. Instead of being adapted to provide a signal to the user, the controller 108 may be adapted to directly activate the pump 103 with the control valve 104 as soon as regeneration appears to be necessary on the basis of information relating to the effectiveness of the filter element 1 as received through the sensor 109.

[0032] Although it is preferred to allow for regeneration of the filter element 1 in a convenient manner, it is not necessary for an air purifier comprising the filter element 1 to comprise a regeneration system. As an alternative, the user can act to regenerate the filter element 1, namely by removing the filter element 1 from the air purifier, spraying the filter element 1 with liquid solution adsorbents 30 from a suitable spray can or the like, and putting the filter element 1 which is regenerated in this manner back in place in the air purifier. In respect of this alternative, the air purifier may be equipped with an indicator for helping a user with determining the right time for a regeneration action.

[0033] It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims. While the invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive. The invention is not limited to the disclosed embodiments.

[0034] Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the figures, the description and the attached claims. In the claims, the word “comprising” does not exclude other steps or elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

[0035] In short, the invention relates to a filter element 1 for use in a device for purifying a gas, which filter element 1 comprises a substrate 10 and a filter layer 20 covering an area 11 of the substrate 10 which is at least a portion of an exterior surface 12 of the substrate 10. The filter layer 20 comprises material for containing chemicals effective to remove gas pollutants from a gas such as air. The material of the filter layer 20 is hydrophilic, while at least a portion of the area 11 of the substrate 10 as covered by the filter layer 20 is liquid-resistant. When a drop of liquid solution adsorbents 30 is applied to the filter element 1, the liquid drop will quickly spread out in the filter layer 20, forming a very thin liquid layer, so that all of the chemicals can be effectively used and regeneration of the filter element 1 is possible by supplying liquid solution adsorbents 30 to at least a portion of the filter layer 20 of the filter element 1.