GB2597361A - An air purification apparatus and method - Google Patents

Abstract

An air purification apparatus (Fig. 1, 10) comprising: a pump (Fig. 1, 12) or fan to generating an air stream; a filter (Fig. 1, 18); a light source 20 for producing ultraviolet (UV) light in the UVC range (200 to 260 nm); and a helical air pathway around the light source. There may be a tubular member 24 around the light source 20, comprising a quartz glass tube, wherein the external surface of the tubular member 24 and the internal surface of a sheath 26 located thereupon forms the helix pathway. The sheath 26 may comprise a rubber material. The apparatus 10 may further include a cooling device (Fig. 1, 34). The filter 18 may remove particles greater than 0.3 μm/microns and may comprise a HEPA filter. The light source 20 may be a UVC light generating tube 22. Also claimed is a method of purifying air. The advantage of the invention is that the air stream passes along a spiral pathway, thus maximising exposure to the light source and decontaminating the air stream. The apparatus is capable of deactivating viruses that are not captured by the filter.

Description

An Air Purification Apparatus and Method The present invention relates to an air purification apparatus and to a method of purifying air and relates particularly, but not exclusively, to air purification for the disinfection of air by the deactivation of viruses in confined spaces.

Various processes for the disinfection of air by the deactivation or removal of viruses are known and include: filtration; ionising purifiers; ozone purifiers; absorbent purifiers; and UV-light on photocatalytic surface treatment. However, the safe disinfection of air in a small scale compact unit is difficult to achieve.

Filtration (HEPA) -In part, the density of the filter 15 material limits the size of the particles that pass through, very dense filters have smaller gaps, allowing it to catch small particles. Pleated filters work best because of the increased surface area for catching particles. HEPA (High Efficiency Particulate Air) filters meet a Department of Energy standard for removing particles from the air. The filter can consist of any material if it meets this standard, that is, penetration of less than 0.03 percent of particles 0.3pm in size or larger. The filter must also allow a specific amount of air to flow through, which varies by the size of the filter. However, airborne viruses are on their own smaller than 0.3um and can stick to particles or cluster together in particles smaller than the smallest size removed by the filter.

Ionizing Purifiers -These air purifiers use a method called corona discharge to create charged molecules called ions.

The corona discharge is a small but intense electrical field. Molecules passing through it will pick up an additional electron, giving the molecule a negative charge, or it may have -2 -an electron knocked off it, giving it a positive charge. Larger particles in the air, such as dust or other contaminants, are more likely to be ionized because they make larger targets for the electrons as they pass through the corona discharge.

Once a particle is charged, it will be attracted to anything with the opposite charge. Two metal plates within the purifier are charged (one negative, one positive) to attract these particles. Also, particles in the air will be drawn to each other if they have opposite charges. As the particles clump together, they get heavier and eventually they settle out of the air.

There is evidence of this type of air sterilizer working with 100% efficiency towards the influenza virus, Hagbom et al., conducted studies using a modified ionizer device described as an effective prevention of airborne transmitted influenza A (strain Panama 99) virus infection between animals and inactivation of virus (>97%). Active ionizer prevented 100% (4/4) of guinea pigs from infection. Moreover, the device effectively captured airborne transmitted calicivirus, 20 rotavirus and influenza virus, with recovery rates up to 21% after 40min in a 19m3 room. The ionizer generates negative ions, rendering airborne particles/aerosol droplets negatively charged and electrostatically attracts them to a positively charged collector plate. Trapped viruses are then identified by reverse transcription quantitative real-time PCR. The device enables unique possibilities for rapid and simple removal of virus from air and offers possibilities to simultaneously identify and prevent airborne transmission of viruses. [M. Haghom, J.Nordgren, R. Nybom, Scientific reports, 2015, 5, 1- 10] However, only viruses attached to a particle will be removed from the airstream. The charged particle is attracted to a plate but not deactivated. Consequently, the virus remains -3 -active on the displaced dust particle which in turn becomes a secondary source of infection.

Ozone purifiers -An ozone generator works much like an ionizing purifier, but it is designed to alter molecules of 5 oxygen and turn them into ozone, a molecule made up of three oxygen atoms. Oxygen in the atmosphere exists as dioxygen, a molecule made up of two oxygen atoms. When these molecules are exposed to a corona discharge or UV light, some of the dioxygen molecules split into separate oxygen atoms (free oxygen). While 10 most of this oxygen recombines into dioxygen, some of the atoms form ozone. Manufacturers of these devices claim that the ozone deodorizes and disinfects the air. Many also claim other health benefits from the presence of ozone. However, there is strong evidence that ozone does not accomplish air purification. Ozone is also known to be a toxic gas. It is not a very stable molecule and it reacts readily with other chemicals that may be in the air, forming new compounds that can be more dangerous than the ozone itself. Ozone also oxidizes metals and causes corrosion. The same process that creates ozone also creates nitrogen oxides, leading to further reactions with compounds present in the air and with ozone itself. As a result, Ozone purifiers generate air which is not suitable for breathing.

Adsorbents -Many purifiers incorporate an adsorbent material to take care of odours, fumes and chemicals in the air.

The most common adsorbent is activated charcoal, which is extremely porous and has many microscopic "nooks and crannies" to trap passing molecules. Larger particles are simply stuck in the many pores in the charcoal. Electrostatic attraction draws some substances into the pores. Certain substances react 30 chemically with the charcoal and bond to it. The high surface area of the charcoal gives it lots of bonding places. The process used to make the charcoal can affect which compounds it is better at adsorbing. Furthermore, the activated charcoal -4 -requires regular replacement to ensure it is operating effectively. As with ionizing purifiers, a virus attached to the charcoal is not deactivated leaving the contaminated charcoal as a secondary source of infection.

UV-light on Photocatalytic Surfaces -Ultraviolet radiation renders certain micro-organisms sterile (and harmless). Some air purifiers feature a UV light that bathes the air as it passes through, eliminating the potential harm of airborne bacteria and viruses. Although many studies on the photocatalytic inactivation of bacteria have been reported, few studies have addressed virus inactivation. Nakano et al., concluded that Titanium dioxide (1102) under ultraviolet (UV) light produces a strong oxidative effect and may therefore be used as a photocatalytic disinfectant. Schmidt et al, demonstrated the inactivation of influenza virus through TiO2 photocatalysis using TiO2 nanoparticles immobilized on a glass plate. The influences of the UV intensity, UV irradiation time and bovine serum albumin (BSA) concentration in the viral suspensions on the inactivation kinetics were investigated. [S. Schmidt, J. Hauling, Chem. Eng. Technol. 2007, 30, 945-950]. The European Chemical Agency's (ECHA) Committee for Risk Assessment (RAC) has given a proposal that titanium dioxide (Ti02) be classed as a category 2 carcinogen through inhalation under REACH Regulation. This decision follows the French Agency ANSES' original proposal to class the substance as a class lb carcinogen.

Preferred embodiments of the present invention seek to overcome or alleviate the above described disadvantages of the prior art to provide a compact air purification apparatus to disinfect air in particular of viruses.

According to an aspect of the present invention there is provided an air purification apparatus comprising: a pump to generate an air stream; -5 -a filter for substantially removing particles from the air stream to a predetermined maximum size; an elongate light source producing light including wavelengths in the range 200 -260 nm; and a helical pathway for directing the air stream around said light source.

By creating a helical pathway passing around a light source producing light in the PVC range, the advantage is provided that the air stream is given maximum exposure to the light source providing the best opportunity for exposure of any particles within the air stream, which were not captured by the filter, to be exposed to the virus deactivating light. The filter traps particles to a predetermined small size ensuring that only small particles pass through which will then be exposed to the deactivating PVC light. Because the particle size is small the light is able to penetrate into the particles to deactivate any viruses contained therein. In particular, the helical pathway generates Dean vortices ensuring that the air stream mixes significantly as it passes along the pathway in turn ensuring that all services of any particles contained within the airstream are exposed to the UVC light source for sufficient time to deactivate viruses. The apparatus described above is effective in efficiently ensuring almost complete deactivation of viruses by the use of UVC light in a device which is compact and therefore easily adapted to retrofitting to existing environment, locations and apparatus.

The apparaLus may furLher comprise aL leasL one sheaLh located on a tubular member such that an external surface of said tubular member and at least one internal surface of said 30 sheath together form said helical pathway.

Using a sheath to generate the helical pathway provides the advantage that a simple structure can be added to a tube (either a quartz glass tube or an external surface of the light source -6 -itself) to create the required helical passage. As a result, the sheath is the only bespoke component to be manufactured.

In a preferred embodiment the tubular member comprises a quartz glass tube.

In a preferred embodiment the tubular member comprises an external surface of said elongate light source.

In a preferred embodiment the sheath comprises at least one rubberised material, preferably a fluorinated material such as a synthetic fluoropolymer of tetrafluoroethylene.

The apparatus may further comprise at least one cooling device for cooling the air stream.

In a preferred embodiment the cooling device is located downstream of said light source.

In a preferred embodiment the filter removes particles 15 having a major dimension greater than 0.3pm.

In a preferred embodiment the filter comprises a HEPA filter.

In a preferred embodiment the elongate light source comprises a UVC light generating tube.

Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense with reference to the accompanying drawings in which:-Figure 1 is a schematic representation of an apparatus of the present invention; and Figure 2 is a partial sectional view of a component of the apparatus of figure 1.

Referring initially to figure 1, an air purification apparatus 10 is provided to remove large particles from an air stream and to substantially sterilise the remaining airstream and any particles therein. In particular, this sterilisation is the deactivation of viruses. The apparatus 10 includes a pump 12 which generates an air stream which passes between an inlet 14 and an outlet 16. A filter 18 is provided downstream of the inlet 14 and acts to remove larger particles from the air stream. The filter 18 is preferably a HEPA filter with pleated filter members contained therein which are capable of removing particles down to those which have a major dimension less than 0.3m. For example, for a substantially spherical particle the diameter of the particle is 0.3pm.

Downstream of the filter 18 is provided one or more sterilisation devices 20 which use a light source, in particular a UVC generating light source, to deactivate viruses contained within the airstream. With additional reference to figure 2, the sterilisation device 20 includes an elongate light source for producing light including wavelengths in the range 200- 260nm, in the form of UV tube 22. Sizes for these UV tubes typically range from 2 inches (5cm) to 85 inches (2.1m). A suitably sized UV tube 22 is 1 inch (2.5cm) diameter and 18 inches (45cm) long. The UV tube 22 delivers sufficient energy (1.5 to 2.1mJ/cm2) to deactivate a virus of the Corona family of viruses. Using a wavelength greater than 185nm ensures that the UV light does not generate ozone in the air passing next to the light source. The UV tube 22 is contained within a quartz glass tube 24 which allows transmission of the vast majority of the light generated in the wavelength 200-260 nm. Surrounding the quartz glass tube 24 is a sheath 26 which is preferably formed from a rubberised and fluorinated material such as a synthetic fluoropolymer of tetrafluoroethylene. The sheath 26 has an inlet tube 28 and an outlet tube 30 between which a plurality of ribs 32 form spaces with the quartz glass tube 24 to create a helical pathway passing from the inlet tube 28 to the outlet tube 30 along the quartz glass tube 24. As a result, an airstream entering the inlet tube 28 passes along a helical pathway around the UV tube 22. Alternatively, the sheath 26 can form the whole of the tubular pathway. This is achieved by wrapping a flexible tube around a larger tube both formed from a material that is transparent to the UV wavelength in question. An example of such a material is fluorinated ethylene propylene (FEP) although other similar rubberised materials and more rigid 5 plastic which are UV transparent could be used.

Downstream of the sterilisation devices 20 is an airstream cooler 34, for example a refrigeration device, which reduces the temperature of the air stream which will have been heated as it passes down the helical pathway of the sterilisation devices 20.

The apparatus is contained within a housing which, in addition to the sheath 28 surrounding the UV tube 22, creates a sealed system ensuring that no UVC light, which is potentially harmful, can escape.

Non-sterilised air entering the inlet 14 passes through the 15 filter 18 which removes large particles. The air stream, which now contains only gases and particles smaller than 0.3 pm is then directed to enter the inlet tube 26 of one of the sterilisation devices 20. The air stream passes along the helical pathway which generate Dean vortices ensuring effective mixing of the airstream and that any particles contained within the airstream are caused to tumble exposing all sides of the particle to the UV light generated by the UV tube 22. Viruses contained within the airstream, whether on particles or not, are exposed to sufficient light in the UVC range to deactivate them thereby substantially sterilising the air exhausting through the outlet 30. The substantially sterilised air is then cooled in the cooling devices 34 to a required temperature (typically room temperature or the temperature of the air entering the device) before passing through the pump 12 to the outlet 16. This sterilised and cooled air is then suitable for breathing.

An apparatus of the type described above is suitable for use in many situations. In particular, this device can be produced in a compact form making it suitable for generating _ 9 _ sterilised air streams for people working in enclosed or semi-enclosed environments where they may be exposed to virus contaminated air entering that enclosed environment. For example, bus drivers work in an enclosed area but are exposed to air entering from the remainder of the vehicle. Likewise, in some retail and banking environments customers are separated from employees by a transparent barrier thereby creating an enclosed space for the workers. As a result, if the air entering the enclosed area can be sterilised this can assist in preventing employees from coming into contact with an airborne virus. Similarly, hospital patients can be protected from airborne viruses by applying a sterile laminar airflow over a patient's bed thereby providing them with sterile air to breathe and preventing air which is not passed through the sterilisation apparatus from coming into contact with the patient. Also, in a medical situation, staff dealing with patients suffering from an airborne viral infection can be protected by carrying a portable air sterilisation device which provides sterilised air for them to breathe. Furthermore, this can be provided in the form of a laminar airflow mask which creates an air barrier using sterilised air thereby removing the need for physical barriers such as Perspex masks. Larger devices can be used to sterilise the air in whole rooms.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the protection which is defined by the appended claims.

Claims (11)

1. -10 -Claims 1. An air purification apparatus comprising: a pump to generate an air stream; a filter for substantially removing particles from the air 5 stream to a predetermined maximum size; an elongate light source producing light including wavelengths in the range 200 -260 nm; and a helical pathway for directing the air stream around said light source.
2. 2. An apparatus according to claim 1, further comprising at least one sheath located on a tubular member such that an external surface of said tubular member and at least one internal surface of said sheath together form said helical pathway.
3. 3. An apparatus according to claim 2, wherein said tubular 15 member comprises a quartz glass tube.
4. 4. An apparatus according to claim 2, wherein said tubular member comprises an external surface of said elongate light source.
5. S. An apparatus according to any of claims 2 to 4, wherein said sheath comprises at least one rubberised material, preferably a fluorinated material such as a synthetic fluoropolymer of tetrafluoroethylene.
6. 6. An apparatus according to any preceding claim, further comprising at least one cooling device for cooling the air 25 stream.
7. 7. An apparatus according to claim 6 wherein said cooling device is located downstream of said light source.
8. 8. An apparatus according to any preceding claim wherein said filter removes particles having a major dimension greater than 30 0.3pm.
9. 9. An apparatus according to any preceding claim wherein said filter comprises a HEPA filter.
10. 10. An apparatus according to any preceding claim wherein said elongate light source comprises a UVC light generating tube.
11. 11. A method of purifying air comprising: using a pump to generate an air stream; passing said air stream through a filter to substantially remove particles to a predetermined maximum size; passing said air stream along a helical pathway around an 10 elongate light source producing light including wavelengths in the range 200 -260 nm so as to expose said air stream to said light source.