Gas cleaning apparatus and method of cleaning gas

Abstract

Cleaning device cleaning gas or air, comprising a cleaning room having a gas inlet and outlet. The cleaning room comprises elongated or flat photocatalytic interaction bodies of light guiding, trans-lucent or transparent material, where the pc bodies extend in the gas flow area or areas between said gas inlet and gas outlet that the gas is allowed or forced to flow along, to touch and to interact with the surfaces of the pc bodies. The pc bodies are coated with a photocatalytically active, light guiding, translucent or transparent coating e.g. of dispersed nanoparticles of TiO2. The cleaning room comprises UV light sources, radiating light into each pc body and / or along their coated surfaces, thus activating the coating's gas cleaning activity.

Description

[0001] GAS CLEANING APPARATUS AND METHOD OF CLEANING GAS

[0002] DESCRIPTION

[0003] The invention relates to a gas cleaning apparatus, for instance for cleaning air. In particular, the invention relates to an enhanced photo catalytic ultraviolet lighting arrangement in such an air cleaning apparatus, which can for instance be incorporated or implemented in HVAC devices, heat exchangers, or can be applied to electrical fans, air conditioners and other air conditioning apparatus. The apparatus described herein can also be applied to reduce serious harmful environmental greenhouse gasses like Hydrogen Sulphide (H2S), Ammonia (NH3), Methane (CH4) and other.

[0004] Presented is a proposed solution for reduction of Volatile or smell and harmful gasses and particular matter by PCO. PCO (Photo Catalytic Oxidation) is a photo chemical process which at least partially eliminates harmful organic and inorganic particles from our environment. This presentation shows a practical approach of implementing practical solutions of this technology, for instance for reducing indoor and environmental air or sewage gas problems.

[0005] Scientific reports studies present PCO efficiencies of H2S reduction in the gas phase over Ti©2 between 64% to 89%. However, a practical solution and implementation is non-existing.

[0006] In the past five decades since Ti©2 photo catalysis was discovered in 1972, a wide range of photo catalytic materials came to the market. TiO2, often doped with other materials, has been used as a catalyst, sized from micron to nano scale in various forms of coating and plating on a catalyser surface. Current air cleaning apparatus have ultraviolet (UV) fluorescent tubes or LEDs radiating ultraviolet light on the catalytic surface (in other words the active surface). The air cleaning efficiency thus obtained is a result of the total released electrons from the photo catalytic surface initiated by UV radiation. Most currently available or described systems consist of a confined box (in other words a cleaning chamber), with airflow inlet and airflow outlet (in other words a gas inlet and a gas outlet), with UV lamps illuminating photo catalytic coated laminated plates, fiberglass cloth (such as in U.S. Pat. No. 6,135,838), a coated mesh or photo catalytic impregnated porous filter (WO 2017 / 055094 Al). Effective perpendicular UV illumination on such catalytic surfaces is limited when catalytic plates or filters are stacked, since the stacked configuration causes incident light to graze over the catalytic surfaces, thereby reducing the effective UVa radiated power per unit area, measured in mW / cm2, to e.g. less than 5% compared with perpendicular light on a surface, or to not reach a particular part of the catalytic surface at all. An atempt has been made in US 6558639 to alleviate this problem to some extent, by providing transparent carriers for the photoactive surface, so that the photoactive light can pass through one or more of the carriers. However, a need to improve the efficiency remains.

[0007] The present invention therefore aims to improve the photocatalytic process, i.e. increase the efficiency of an apparatus used therefore, for instance by providing an improved and longer coupling path between ultraviolet light and the photo catalytic surface.

[0008] This improvement can be achieved by the features described in claim 1. Inventive technical features of the air cleaning apparatus create optimal conditions for maximal ‘in situ’ elimination of harmful volatile organic compounds (VOC’s) and pathogens. This elimination results from a chain of reactions initiated by the release of electrons from a photocatalytic reaction. The released electrons immediately create free radicals like hydroxyl and super-oxides from surrounding hydrogen and oxygen molecules. The hydroxyl radical has a very short in vivo half-life of approximately 10-9 seconds and a very high reactivity to harmful organisms and VOC’s. Humans, animals and plants have evolved to coexist with hydroxyl radicals, and hydroxyl radicals cannot enter the blood stream or tissues within the body. Hydroxyl is, in contrast to ozone, therefore relative harmless for health risks.

[0009] The invention can be applied to expose a polluted and / or contaminated polluted airflow during a maximum time in contact to the photo catalytic surface to facilitate a long lateral photo chemical path within the air cleaning apparatus with a minimum of pressure drop.

[0010] Achieving the aforementioned objects of the air cleaning apparatus of the present invention a preferred embodiment may comprise a housing, for instance forming the cleaning chamber, that has at least one gas inlet opening and one gas outlet thereon, at least one translucent photocatalytic coated device, i.e. the photocatalytic element(s) therein and at least one ultraviolet irradiator disposed in such a way that it preferably radiates the ultraviolet radiation at a distance from the active surface, for instance on another face of the photoactive element. The light could thus be introduced into the photocatalytic element in a preferably uncoated area or face of the element, and exit the element at a coated area or face. In general, it is advantageous if the radiation is introduced in a smooth and / or uncoated entry surface of the element. A source of radiation may be provided directly against the entry surface, so that no (air) gap is in between, thereby increase the coupling into the element.

[0011] In particular, if the photocatalytic element substantially extends in two directions to define main surfaces, and has thickness that is limited in comparison to the dimensions in the other two directions, e.g. the element is plate-like, the entry surface may be a side face, i.e. a face at a nonzero angle with regards to the main surfaces. Such a configuration could be called a head-on irradiation, as the irradiation is introduced into the end-face.

[0012] It is therefore preferred if the irradiation is provided, preferably substantially or exclusively, into the end face of such an element. The entry surface may thus correspond to the end face. Of course, the same principle can be applied to different shapes of elements, as long as they have a longitudinal direction and an end face, where the main surface, which may be coated, extends in the longitudinal direction.

[0013] In particular, the end face extends perpendicular to the main surface. Preferably, the element is plate shaped.

[0014] The irradiation source may be e.g. LED’s of a suitable type provided at the entry surface, e.g. at the end surface of the photocatalytic elements.

[0015] Another arrangement that allows irradiating an end surface, comprises providing an aperture in the main surface (i.e. the at least one active surface) and arranging the one or more light sources in the aperture. Is an example, a UV tube may extend through an aperture in a plate-shaped element. The end surface into which radiation is introduced, is formed in that case by an end face delimiting the aperture. The other end surfaces, around the periphery of the plate, may be reflective. The main surface may be coated to form active surfaces.

[0016] Throughout this application, the main surfaces may be the at least one active surface.

[0017] In addition, the ultra violet light of air cleaning systems currently known are mostly based on fluorescent tubes with 254 nm UVc radiation or UVc Light Emitting Diodes. Such UVc driven systems like in (WO 2014 / 022355 Al) should be blocked for visual and physical exposure and include a light shield configured to eliminate line-of-site access to block the harmful ultraviolet light from an outlet of the air purification system. Besides UVc radiation being harmful when human cells are exposed to it, health can also be affected by the ozone typically generated by UVc light. Applying UVc for photo catalysis is a waste of energy. The band gap of a most suitable photocatalytic material like TiCE is approximately 3.2 eV, which can be bridged by the photon energy of UVc radiation - yet this requires almost two times more electrical energy. Due to Stokes-shift, no further electrons will be freed even though UVc radiation exceeds the band gap considerably. As a result, using UVc radiation is inefficient. Another object of the invention is therefore to increase efficiency.

[0018] The applicant has found that the photon energy of UVa at 365 nm of > 3.2 eV is sufficient to kick an electron out of the TiCf catalyst. Thus, it is favourable to apply UVa (herein also referred to as UV-A, sometimes referred to as UVA) radiation instead of the known UVc (sometimes referred to as UV-C or UVC) radiation. Therefore, an air cleaning apparatus with multiple UVa translucent pc (Photo Catalytic) coated elements, such as plates stacked with sufficient distance to enable free airflow between the plates with minimal pressure drop in a labyrinth or lateral configuration is provided. The long air path facilitates complete elimination of the VOC’s and facilitates a chain reaction of the pc process because the residue elements of the pc process being mainly CO2 and H2O will improve ambient humidity in the apparatus, supporting further cleaning of the air on its way out of the apparatus and actively providing an effective air cleaning effect rapidly to indoor and local spaces.

[0019] According to the invention the air cleaning apparatus is provided with the ultraviolet irradiator, or any other light source, attached on the head sides of the pc coated PMMA (e.g. Plexiglas, Perspex etc.) laminates (plates). Of course other shapes and materials could be used, as long as they are transparent or translucent to the radiation involved. Due to the refractive index the radiation, e.g. UVa light, will be trapped and transmitted within the plates as is seen in fiber optic light guides. Guiding light in this manner is also a known technology in UED flat panel illumination and TV flatscreen backlighting (cf. WO2020 / 221448 Al).

[0020] The translucent PMMA pc coated plates, or elements of another material or shape, can contain fluorescent or quantum dot particles to allow or promote trapped UV light or radiation to escape from the pc surface. A micro structured (i.e. having structures that have characteristic size in the range of tenths of millimeters, such as 0,01 - 0,5 mm. The surface may e.g. be carved or laser scribed, which will also enhance i.e. promote the light extraction from the PMMA plates or elements, and at the same time increase the virtual surface of the pc active surface. The size of the nano particle pc coating may increase the virtual surface by multiples of its actual geometric size. Micro structured surface or scribing will even further enhance the virtual pc active surface while enhancing the light extraction from the translucent or transparent plates / elements.

[0021] In a particularly effective embodiment, one or more, preferably all end faces of the element which are not directly used for introducing radiation into the element, are reflective to the radiation introduced in the element. This avoids a radiation exiting through the end surfaces, and thereby increases efficiency. A reflective surface may be obtained by a surface finish, by providing a reflective film, a coating or otherwise.

[0022] The advantage of this method of radiation distribution is that the irradiated intensity will be uniformly distributed over the whole surface of all plates and the emitted electrons from the pc coating will be optimal over the whole surface. The irradiation distribution of this method results in a relatively high photo catalytic efficiency and may provide optimal evenly distributed self-cleaning properties of the catalyser plates at the lowest energy requirements. At mentioned high efficiency the pc plates can be configured lateral in the direction of the airflow which will minimize the pressure fall and air resistance while still performing optimal air cleaning. In other words, the airflow may be locally parallel to a longitudinal direction of the photocatalytic elements, i.e. parallel to the local active surface thereof.

[0023] Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention. The invention is therefore defined by the claims, in which subclaims define preferred embodiments.

[0024] Hereinafter the invention will be elucidated more in detail with reference to the figures, in which: Figure 1 schematically shows a cross sectional view of a gas cleaning device, and Figure 2 schematically shows a perspective view of a gas cleaning device.

[0025] Figures 1 and 2 show exemplary embodiments of a cleaning device 1 according to the invention, in 2D and 3D representation respectively.

[0026] The devices of figures 1 and 2 are arranged for cleaning a gas or air, hereinafter called gas and represented in figures 1 and 2 as a gas flow 2, the cleaning device 1 being in particular arranged for eliminating volatile organic compounds, inorganic pollutants, pathogens etc. from the air in the gas / air flow 2.

[0027] The device 1 shown in figures 1 and 2 comprises a cleaning room 3 having a gas inlet 4 and a gas outlet 5 and I arranged to allow the gas (2) to be cleaned to flow through the cleaning room from said gas inlet 4 toward said gas outlet 5. The cleaning room 1 comprises mainly elongated or flat photocatalytic interaction bodies, which are of geometric prism shape having two opposing ends, e.g. in the form of bars, profiles or -as in the embodiment of figures 1 and 2- plates, hereinafter called pc bodies 6, made of a UV, in particular UV-A, light guiding, translucent or transparent material like in particular PMMA. The pc bodies 6 extend within the gas flow area or areas (or gas flow channels) 3a between said gas inlet 4 and gas outlet 5, allowing the gas to flow (turbulently) along, to touch and to interact with the surfaces of the pc bodies 6.

[0028] The (surfaces of the) pc bodies 6 are coated with a photocatalytically active UV, in particular UV- A, light guiding, translucent or transparent coating 6b, in particular comprising dispersed nanoparticles of TiO2.

[0029] The cleaning device 1, moreover, comprises UV light sources 8, arranged so that the UV light of said UV light sources 8 is radiated into the pc bodies and optionally along or upon their coated surfaces via or from at least one side face 6c of those pc bodies 6. The light thus enters the pc body through the at least one side face, and exits through the active surface, thereby interacting with the coating and enabling photocatalysis. The side face substantially corresponds to the base of the geometric prism shape of the respective pc body, and may be arranged at a non-zero angle of e.g. 90 degrees with respect to the active surfaces extending in the longitudinal direction of the respective pc body.

[0030] Although figure 1 does not show light sources, they can be arranged similar to those of figure 2, e.g. on the end surfaces, radiation light in the side surfaces of the pc bodies 6, e.g. in the view direction of figure 1.

[0031] In the exemplary embodiments of figures 1 and 2 the gas inlet 4 and gas outlet 5 are located in opposite locations of the cleaning room 3. The pc bodies 6 may be made from polymethylmethac- rylaat (PMMA).

[0032] The UV light sources may comprise UV, preferably UV-A light emitting UEDs, arranged so that the UV light of the UV light sources is radiated into the pc bodies and / or along or upon their coated surfaces via or from at least one side edge of those pc bodies, mainly in the direction of de pc body's main axis or main plane respectively. The photocatalytically active, UV, in particular UV-A, light guiding, translucent or transparent coating may comprise dispersed nanoparticles of TiO2. Figure 1 shows the incoming airflow splitting in four channels 7. Each channel comprises a meandering path, of twists and turns around the pc bodies 6 which extend into the channel 7 altemat- ingly from opposing sides. Accordingly, airflow around the pc bodies 6 is turbulent, as indicated by chaotic curved lines representing airflow in the right of figure 1. Each pc body 6 is plateshaped, and defines active surfaces 6b parallel to their extension direction 6a. The pc bodies 6 all comprise an aperture (although more could be provided) through which a UV tube 8 runs. The UV tubes 8 thus introduce radiation into the end surfaces defining the aperture. The other end surfaces 6c, which are free end surfaces, are reflective. The active surfaces 6b are coated. The entry surface, where radiation is introduced is not coated and lies directly against the UV tubes, and is preferably smooth. The active surfaces 6b comprise a microstructure, provided by scribing the surface 6b.

[0033] Figure 2 specifically shows that the cleaning chamber has outer walls which are transparent, so that sunlight can enter for providing (additional) UV light. However, figure 2 also shows radiation sources 8 in the form of LEDs 8. The LEDs are provided on the end surfaces 6c of the pc bodies 6. End surfaces 6c not provided with LEDs are reflective, whereas end surfaces 6c with LEDs allow light introduction, by being smooth and by lying directly against the LEDs preferably. Light from the LEDs exits the pc bodies 6 at their main surfaces, i.e. their active surfaces 6b, to interact with a coating in order to perform photocatalysis.

[0034] The present invention could be summarized by next points:

[0035] 1. Cleaning device (1) arranged for cleaning a gas or air, hereinafter called gas (2), the device comprising a cleaning room (3) having a gas inlet (4) and a gas outlet (5) and arranged to allow the gas to be cleaned to flow through the cleaning room from said gas inlet toward said gas outlet; wherein the cleaning room comprises one or more mainly elongated or flat photocatalytic interaction bodies (also referred to as photocatalytic elements), e.g. in the form of bars, profiles or plates, hereinafter called pc bodies (6), made of a UV, in particular UV-A, light guiding, translucent or transparent material, the pc bodies extending in the gas flow area or areas (3a) between said gas inlet and gas outlet so that the gas is allowed or forced to flow along, to touch and to interact with the surfaces of the pc bodies; the pc bodies having an active surface, for instance from being coated with a photocatalyti- cally active, UV, in particular UV-A, light guiding, translucent or transparent coating (6b); wherein the cleaning device, moreover, comprises one or more -internal or external, artificial or natural- UV light sources (8,8a), arranged so that the UV light of said one or more UV light sources is radiated into the pc bodies and / or along or upon their active surfaces via or from at least one second surface, such as a side edge (6c) (or a side face) of those pc bodies.

[0036] 2. Device according to point 1, wherein said gas inlet and said gas outlet are located in opposite locations of said cleaning room.

[0037] 3. Device according to point 1 or 2, said pc bodies being made from polymethyhnethacrylaat (PMMA).

[0038] 4. Device according to any preceding point, wherein said one or more UV light sources comprise UV, preferably UV-A light emitting LEDs.

[0039] 5. Device according to any preceding point, wherein said photocatalytically active coating comprises dispersed nanoparticles of TiCL.

[0040] Finally, the following additional notes could be made:

[0041] The efficiency of a Photo Catalytic (PC) process depends on the catalyst type (such as TiCh). the virtual surface of the coating on the catalytic plates and the intensity of the irradiated ultraviolet irradiation per unit area (e.g. in mW / cm2) incident the transparent Photo Catalytic coating. Perpendicular light on the pc surface may result in the strongest and most efficient air cleaning.

[0042] The airflow is fast and the longer the pc path the better the air will be cleaned from Volatile Organic Compounds (VOC’s). The first concept is therefore to use UVa translucent PMMA material which is coated with completely transparent TiO2 as pc body. The TiO2 coating will be applied on both sides of the PMMA material. It is preferable to provide a labyrinth with a long air path for enhanced air cleaning to provide the right residence time to eliminate pathogens, VOC’s and harmful organic and inorganic particle matter.

[0043] The air path through the labyrinth is long and the translucency of the catalyst improves pc activity. Turbulence of the airflow in the labyrinth will facilitate long contact times of the polluted air with the catalyst surface for optimal air cleaning. A negative effect on the air turbulence and long path is a substantial air resistance and pressure drop in the device. Current air cleaner systems use multiple photo catalytic coated mesh layers or coated (Hepa) filters and non-transparent Photo Catalytic (PC) plates, limiting optimal UV irradiation on the pc active surface. Mesh layers, coated filters or pc coated laminates cause a substantial pressure drop in the air cleaning channel. Afore mentioned photo catalytic objects will accumulate dirt, dust and pc Oxidation residues which requires regular cleaning and maintenance. Applying pc coated transparent / translu- cent material such as PMMA facilitates an operational advantage. The pc process exhibits selfcleaning properties on the pc surface. The surface of the pc coated PMMA material will remain relatively clean.

[0044] A second advantage of the presented invention is the long air path which will provide maximal oxidation of the pollutants. The residue of the pc process is mainly CO2 and H2O (water). The water molecules as a result of the oxidation process provide a pc chain reaction maintaining high humidity, causing the best condition for the pc process.

[0045] Finally it is noted that the UV light source of the cleaning device can be formed by any external UV light source like the sun 8a or means which are arranged for receiving UV light from the sun and guiding it toward the pc bodies. To allow the sun radiation to enter into the cleaning room 3, the cleaning room's wall should at least partially be made of any UV light guiding, translucent or transparent material, e.g. made from PMMA. This advantage can be achieved regardless of characterizing portion of claim 1, as long as the cleaning chamber has outer walls which are transparent or translucent.

Claims

Claims1. Gas cleaning apparatus for cleaning a gaseous substance including contaminants, such as air containing e.g. volatile organic compounds, wherein the gas cleaning apparatus comprises- a cleaning chamber with a gas inlet and a gas outlet which is otherwise sealed, so that the gaseous substance may be flown into the gas inlet through the cleaning chamber to the gas outlet; and- one or more photocatalytic elements disposed inside the cleaning chamber, each photocatalytic element having at least one active surface which is photocatalytic, wherein each photocatalytic is arranged such that a flow of gaseous substance from the gas inlet to the gas outlet of the cleaning chamber passes the active surface of the one or more photocatalytic elements, such that the contaminants may be subjected to photocatalysis under the influence of the at least one active surface,- one or more light sources configured to produce radiation of a predetermined spectral distribution, and configured to irradiate the at least one active surface, characterized in that the photocatalytic elements are substantially transparent or translucent to light of the predetermined spectral distribution, and in that the one or more light sources are arranged to introduce the radiation into a second surface of each of the one or more photocatalytic elements, the second surface being a different surface than the at least one active surface, so that the radiation travels through the photocatalytic element and reaches the active surface from the inside of the photocatalytic element.

2. Gas cleaning apparatus according to the previous claim, wherein the second surface is located on a different face of the respective photocatalytic element than the active surface, preferably and end face.

3. Gas cleaning apparatus according to the previous claim, wherein the one or more photocatalytic elements are shaped substantially like a geometric prism formed by a base translated along a longitudinal direction between two end surfaces, wherein the at least one active surface extends along the longitudinal direction and the second surface is an end surface.

4. Gas cleaning apparatus according to any of the preceding claims, the one or more photocatalytic elements defining a or the longitudinal direction, wherein the one or more photocatalytic elements are arranged such that a local direction of flow of gas from the gas inlet to the gas inlet close toeach photocatalytic element is substantially perpendicular to the longitudinal direction of the respective photocatalytic element.

5. Gas cleaning apparatus according to any of the preceding claims, wherein the at least one active surface comprise a coating of a photocatalytic material.

6. Gas cleaning apparatus according to the previous claim, wherein the coating, in particular the photocatalytic material is transparent or translucent for light of the predetermined spectral distribution.

7. Gas cleaning apparatus according to any one of claims 5 - 6, wherein the coating comprises or consists of dispersed particles.

8. Gas cleaning apparatus according to any one of claims 5 - 7, wherein the photocatalytic material comprises or is titanium dioxide.

9. Gas cleaning apparatus according to any of the preceding claims, wherein the one or more photoactive elements comprise light extraction promoting means, such as a microstructure surface or fluorescent or quantum dot particles in the elements, or a roughened surface including scratches, carves, or scribes.

10. Gas cleaning apparatus according to any of the preceding claims, wherein the predetermined spectral distribution comprises UV-light, preferably UV-A light, or wherein the spectral distribution comprises substantially exclusively UV-light, preferably UV-A light.

11. Gas cleaning apparatus according to the previous claim, wherein the light sources comprise UV UEDs, preferably UV-A EEDs.

12. Gas cleaning apparatus according to the previous claim, wherein the photocatalytic elements are manufactured from poly(methyl methacrylate).

13. Gas cleaning apparatus according to any of the preceding claims, wherein the gas inlet and the gas inlet are arranged opposite each other.

14. Gas cleaning apparatus according to any of the preceding claims, including multiple photoactive elements arranged so as to define collectively a path from the gas inlet to the gas inletthat has multiple bends and / or turns and travels along multiple of the photoactive elements, in particular in a labyrinth-like manner.

15. Gas cleaning apparatus according to any of the preceding claims, wherein the cleaning chamber is transparent to allow external UV radiation to enter, in particular wherein the cleaning chamber comprises outside walls of a transparent or translucent material, preferably PMMA.

16. Gas cleaning apparatus according to any of the preceding claims, the photocatalytic elements being substantially plate shaped.

17. Gas cleaning apparatus according to any of the preceding claims, wherein the photocatalytic elements comprise one or more third surfaces separate from the main surfaces and the second surface, wherein the one or more third surfaces are reflective.

18. Method of cleaning a gas including contaminants, such as air comprising e.g. volatile organic compounds, for instance using a gas cleaning apparatus according to one of the preceding claims, comprising: a) having the gas flow into contact with an active surface of a photoactive element; b) irradiating the active surface with radiation; characterized in that- the photoactive element is substantially transparent or translucent to the radiation;- step b) is performed by introducing radiation into the photoactive element preferably exclusively at least initially remote from the active surface, such as on a different face than the active surface.

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