GB2558637A

GB2558637A - Sterilisation apparatus with anti-fouling

Info

Publication number: GB2558637A
Application number: GB1700588.5A
Authority: GB
Inventors: Cherry Richard
Original assignee: Alpha Cure Ltd
Current assignee: Alpha Cure Ltd
Priority date: 2017-01-13
Filing date: 2017-01-13
Publication date: 2018-07-18
Also published as: GB201700588D0

Abstract

A sterilisation apparatus comprising: a chamber H having an internal wall; an inlet I and outlet O formed through the internal wall; a UV light source L disposed within the chamber; and a UV-transparent wall T disposed between the UV light source and the internal wall such that fluid flowing between the inlet and outlet is directed around and/or past the UV-transparent wall. The invention comprises an anti-fouling layer disposed upon the UV-transparent wall for reducing the deposit of contaminants from the fluid thereon. Also claimed is a sleeve incorporating the UV-transparent wall with anti-fouling layer for use in the sterilisation apparatus and a method of improving a UV sterilisation apparatus by applying an anti-fouling layer to a UV transparent wall surround a UV light source. Preferably, the anti-fouling layer is formed from a fluoropolymer such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and/or perfluoroalkoxy alkane (PFA). Furthermore, the anti-fouling layer may be less than 0.05mm thick so as to minimise any adverse effect on UV transmission. In some embodiments the anti-fouling layer is applied as a heat shrink sleeve or powder coating. The apparatus may be used to sterilise water.

Description

(54) Title of the Invention: Sterilisation apparatus with anti-fouling

Abstract Title: Sterilisation apparatus comprising a UV light source and an anti-fouling layer (57) A sterilisation apparatus comprising: a chamber H having an internal wall; an inlet I and outlet O formed through the internal wall; a UV light source L disposed within the chamber; and a UV-transparent wall T disposed between the UV light source and the internal wall such that fluid flowing between the inlet and outlet is directed around and/or past the UV-transparent wall. The invention comprises an anti-fouling layer disposed upon the UV-transparent wall for reducing the deposit of contaminants from the fluid thereon. Also claimed is a sleeve incorporating the UVtransparent wall with anti-fouling layer for use in the sterilisation apparatus and a method of improving a UV sterilisation apparatus by applying an anti-fouling layer to a UV transparent wall surround a UV light source. Preferably, the anti-fouling layer is formed from a fluoropolymer such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and/or perfluoroalkoxy alkane (PFA). Furthermore, the anti-fouling layer may be less than 0.05mm thick so as to minimise any adverse effect on UV transmission. In some embodiments the anti-fouling layer is applied as a heat shrink sleeve or powder coating. The apparatus may be used to sterilise water.

I

1004 18

Wavelength [nm]

2/2

1004 18

Fig. 4

Sterilisation Apparatus with Anti-Fouling

The present invention relates to an anti-fouling covering layer as applied to parts of an apparatus, in the field of UV water sterilisation.

Background to the Invention

UV lamps are used for the treatment of water in many applications. One of the primary reasons this is done is to reduce the level of microorganisms present in the water, such as bacteria and viruses, to a level where it is effectively 'sterilised'. Exposure to the UV radiation produced by the lamp causes disruption to the DNA in the microorganism and renders it incapable of reproduction by a process which is termed 'inactivation'.

A typical water sterilisation system, e.g. as illustrated by Figure 1, consists of a cylindrical stainless steel housing H with a cylindrical quartz tube T or sleeve on a central axis that houses the UV lamp L and separates it from the water to be treated, i.e. so that the water is not in direct contact with the lamp. The housing's water inlet I and outlet O are arranged to allow access to the electrical connections at the ends E of the lamp and so that water flows in the annular gap between the housing inner wall and the sleeve outer wall. In this way the lamp can be run in air and the UV radiation R passes through the quartz sleeve into the water to be treated.

The level of UV irradiation of the water has to be strictly controlled to ensure there is sufficient exposure to achieve the sterilising effect required. The level of exposure is controlled by both the UV lamp output (which can be monitored by a sensor S through a window W in the housing H) and the ability of the system to transmit that radiation to the media to be treated. Transmittance of the radiation is affected by the raw water quality as well as the sleeve T that separates the lamp L from the water. Both the lamp and the sleeve are normally made of quartz as this is a material that can transmit the wavelengths of radiation necessary for a germicidal affect. However, one of the major problems with these systems is that the wet side of tube T containing the lamp can be fouled as materials carried by the water are deposited on to it. This effectively blocks radiation from the lamp from reaching the water to be treated.

To achieve the required radiation exposure over prolonged periods, regular system maintenance is essential. The inner sleeve T has to be manually or chemically cleaned, which can only be achieved when the system is shut down and drained. Where there are high throughput demands, a parallel system would be required to carry the load during maintenance periods. To alleviate down time and increase effectiveness some systems employ a mechanical 'wiper' assembly. This consists of a cylindrical or annular wiper element suitably housed and driven longitudinally up and down the lamp sleeve to remove the debris. It will be apparent that such a wiper system adds complexity to the overall machine and is another component that requires its own maintenance.

Summary of the Invention

The present invention was prompted by the realisation that, if there was a means to reduce fouling of a lamp sleeve that does not require a mechanical wiper, then complexity and cost would be reduced. It is further understood that any reduction of fouling will, in any case, reduce the requirement for system maintenance and so reduce the associated costs and system down time. Similarly any improvement to the UV transmission over the service life would improve the system efficiency and this would easily translate to energy savings with suitable monitoring.

In a broad aspect the invention provides a sterilisation apparatus with anti-fouling, e.g. a layer according to claim 1. Particularly, the covering layer is a coating applied to UV water sterilisation equipment, such as on the water-contacting surface of a sleeve surrounding a UV lamp, the lamp itself if operating conditions allow and/or the inside of the housing.

Brief Description of the Drawings

Figure 1 illustrates a UV water sterilisation apparatus that is generally known, but it is also useful for demonstrating components utilised with the present invention;

Figure 2 shows a graphical representation plotting overall transmission (in percentage terms) to wavelength;

Figure 3 shows a graphical representation overlaying spectrums for coated and uncoated surfaces from the output of a medium pressure UV lamp; and Figure 4 shows a graphical representation of single powder coated tube transmission, both grit and non-grit blasted.

Detailed Description of the Invention

The invention relates to application of a 'non-stick' coating/covering layer to a lamp sleeve in a water sterilisation apparatus in order to reduce fouling thereon. Unfortunately, most practical materials are opaque to both visible and UV radiation wavelengths so would be useless in the proposed application. However, there are fluoropolymers that are highly transmissive to UV, available in several forms, that would allow them to be readily applied to a quartz tube T (referring to Figure 1).

In sheet form the layer material could be simply wrapped around the sleeve T with a suitable fixing for the loose edge, however, this may be problematic in terms of operation as it could be removed by a high water flow rate. A better method of using preformed material would be to apply it as a seamless tube heat shrunk into place. Alternatively materials are available in a powder form that can be sprayed directly on the tube and treated to be fixed in place (e.g. powder-coating).

There are several fluoropolymers available that would be suitable in this application; e.g. PTFE, FEP and PFA. Further investigation may yield alternative or optimum configurations.

The UV transmission of all the coating materials is significantly affected by thickness, e.g. for a heat shrink method the thickness of the material is somewhat limited by availability. In general as thin as currently available (0.05mm) gives good strength and uniformity however this material does detract from the total transmission properties. Thinner materials will be tested as they become available and it is felt will better fulfil the requirements of the invention, i.e. minimal disruption to UV transmission. It would generally be desirable for an anti-fouling layer according to the invention to be less than 0.05mm.

Powder coating methods involve electrostatically wet spraying with a coating in the form of a liquid dispersion containing the fluoropolymer, resin and other ingredients. This is then oven baked to give a dry film in the region of 0.015mm per coat. Multiple layers can be applied typically up to a total thickness of 0.035mm. UV transmission can be optimised with a single coat but the finish is not very uniform and somewhat patchy. The addition of a second coat yields a more useful coverage but also a corresponding reduction in UV transmission.

For powder coated material, adhering the layer to the surface of the quartz also causes an issue that is not present for heat shrink methods. Without pre-treating the quartz tube prior to application the powder coated layers do not adhere to the surface sufficiently well which leaves the layer extremely susceptible to peeling off. In all instances degreasing is required prior to the application of the material but a further pre-treatment is to grit blast the surface of the quartz. This greatly increase adhesion but has an adverse effect on transmission as the radiation is blocked by the roughened surface of the quartz. Figure 4 shows a comparison of single powder coated tubes, both grit and non-grit blasted. In future iterations, improved and controlled grit blasting may be possible with a view to minimising transmission losses.

It has been found that there is a close correlation between the respective transmission of the materials involved and the overall transmission of the coated product, e.g. if the quartz has a transmission of 90% and the coating is 90% then the overall effect will be a transmission of 81% (multiplication of the two values). This allows a good level of prediction in the development stages when selecting materials without having to actually coat quartz tubes. This is especially useful as each coating material has a differing transmission characteristic so understanding the combined effect at each wavelength is helpful in selecting the best material for the application.

Figure 2 illustrates a transmission comparison (denoted %T on the y-axis) as measured on a spectrometer of an uncoated quartz tube and one coated with FEP as applied by powder coating. Although a 20% drop off is observed, this is only due to the measuring method. The surface of the FEP coating diffracts the beam of light used for the analysis and hence not all of it falls on the spectrometer detector which shows as a net reduction in transmission. The important information to be noted from Figure 2 is that the shape of the curves are similar (parallel), therefore showing that the coating is not absorbing radiation at different wavelengths to the quartz tube alone and it is only the overall reduction in signal caused by the scattering effect. Any marginal loss in UV transmittance is offset by its reduced requirement for maintenance and associated downtime.

Figure 3 illustrates overlaid spectrums for the output of a medium pressure UV lamp as measured on a spectrophotometer. The same lamp was run with both a coated and uncoated tube and the data overlaid on the same graph. This clearly shows there are insignificant differences in the output of an uncoated system and a coated system according to the invention; i.e. the FEP coating is detracting very little from the total UV radiation available for the process.

Accordingly, when employing a suitable coating method to apply an anti-fouling layer (somewhat dependent on the application in which it is to be used) the fluoropolymer coating has little or acceptable negative effect on the system output. Such a material is known to be non-stick rather than having inherent germicidal properties (which may be a more obvious choice for an anti-fouling purpose). Therefore, a layer according to the invention can be used to reduce the build-up of waterborne contaminants on the lamp sleeve, because they are prevented from adhering and sterilised contaminants are simply carried away by water movement through the system. Although UV transmission is slightly reduced, the apparatus is operational for a much longer period hence making the output over time significantly improved.

Claims

Claims:

1. A sterilisation apparatus including:

a chamber having an internal wall;

an inlet and outlet formed through the internal wall, for directing fluid to flow through the chamber;

a UV light source disposed within the chamber;

a UV-transparent wall, disposed between the UV light source and the internal wall, such that fluid flowing between the inlet and outlet is directed around and/or past the UV-transparent wall; wherein an anti-fouling layer is disposed upon the UV-transparent wall, for reducing the deposit of contaminants from the fluid thereon.

2. The sterilisation apparatus of claim 1 wherein the anti-fouling layer is formed from a fluoropolymer or blend thereof.

3. The sterilisation apparatus of claim 2 wherein the fluoropolymer is selected from: PTFE, FEP and/or PFA.

4. The sterilisation apparatus of any preceding claim wherein the anti-fouling layer is less than 0.05mm thick.

5. The sterilisation apparatus of any preceding claim wherein the anti-fouling layer is applied as a heat shrink sleeve or powder-coating.

6. The sterilisation apparatus of any preceding claim wherein a further anti-fouling layer is applied to the internal wall of the chamber.

7. The sterilisation apparatus of any preceding claim wherein the UV transparent wall is in the form of a cylindrical sleeve surrounding the UV light source.

8. The sterilisation apparatus of any preceding claim wherein the UV light source is housed in a lamp.

9. A sleeve incorporating the UV-transparent wall with anti-fouling layer, for use in a

5 sterilisation apparatus according to any preceding claim.

10. A method of improving a UV sterilisation apparatus, including the step of applying an anti-fouling layer to a UV transparent wall surrounding a UV light source.

10

11. The method of claim 10 wherein the anti-fouling layer is formed from a fluoropolymer or blend thereof.

12. The method of claim 11 wherein the fluoropolymer is selected from: PTFE, FEP and/or PFA.

13. The method of any of claims 8 to 10 wherein the anti-fouling layer is applied either:

in sheet form;

as a heat shrinkable tube; or sprayed directly onto the UV transparent wall (e.g. powder-coating).

14. The method of any claim 10 to 13 wherein the anti-fouling layer is less than 0.05mm thick.

15. The method of any of claims 10 to 14 wherein the UV-transparent wall is a sleeve

25 surrounding a UV lamp containing the UV light source.

16. The method of claim 15 wherein the sleeve is degreased prior to application of the anti-fouling layer.

30

17. The method of claim 15 or 16 wherein the sleeve is grit blasted.

Intellectual

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Application No: GB1700588.5 Examiner: Helen Yard