WO1997033631A1

WO1997033631A1 - Uv radiation sterilisation system for fluids

Info

Publication number: WO1997033631A1
Application number: PCT/GB1997/000712
Authority: WO
Inventors: James Edward Mcalpine; Peter Phillip Oakes
Original assignee: Mcalpine & Company Limited
Priority date: 1996-03-13
Filing date: 1997-03-13
Publication date: 1997-09-18
Also published as: AU2166297A; GB9605311D0

Abstract

A UV radiation sterilisation system (10; 10a) includes a container (12) for a fluid to be sterilised and a UV lamp (14) positioned within the container such that the fluid to be sterilised contacts the lamp surface. The UV lamp (14) has ends defining electrical connections (28, 29), and the ends of the lamp may be isolated from a fluid containing portion of the container (12) by resilient annular seals (30, 31) located between the lamp surface and the container. The system (14) is operated using a low voltage supply of less than 110 volts, typically at a voltage of 12 volts.

Description

UV RADIATION STERILISATION SYSTEM FOR FLUIDS

This invention relates to a sterilisation system, and in particular to a sterilisation system in which ultra¬ violet (UV) radiation is utilised to sterilise a fluid, typically water. It is known to sterilise water and other fluids using

UV radiation, and UV sterilisation systems have been used, for example, in ships and laboratories since at least the 1950s. Proposals have also been made for large scale UV- based purification systems for public water supplies and sewage treatment plants, however such systems have not come into common use. The UV radiation is produced by appropriate lamps (typically in the form of tubes) and the water to be treated may be contained in shallow trays beneath the lamps or passed through UV transparent tubes located around the lamps, as disclosed in US Patent No 3,814,680. The efficiency of these systems is relatively low, and the systems occupy a relatively large volume, making them unsuitable for many applications. In other arrangements UV tubes are sealed within quartz sleeves which may then be immersed in the liquid to be sterilised. Quartz is substantially transparent to UV radiation and the isolating sleeves allow the UV tubes to be maintained at a relatively high temperature, for increased efficiency. Such systems are relatively efficient for sterilising liquids, but the quartz tubes are only available from a limited number of sources, in a limited number of sizes and configurations, and are also expensive. Further, the electrical supply connections for the UV tubes must be isolated from the liquid and this requires provision of sealed "boxes" on the ends of the tubes. Each box is sealed relative to the quartz sleeve with an O-ring or similar gland which fits over the respective end of the quartz sleeve. These seals provide a potential point of weakness in the systems, particularly if the seals are disturbed by, for example, replacing the UV tube. It is among the objects of the embodiments of the present invention to obviate or mitigate these disadvantages .

According to a first aspect of the present invention there is provided a UV radiation sterilisation system including an enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure such that the fluid to be sterilised contacts the lamp surface.

According to another aspect of the present invention there is provided a method of sterilising fluid comprising passing fluid through an enclosure having a UV lamp therein such that the fluid comes into contact with the lamp surface .

Allowing the fluid to come into direct contact with the lamp surface increases the efficiency of UV transmission into the fluid and the absence of a quartz sleeve reduces the cost of the system when compared to existing systems. The invention may be utilised in the sterilisation of a wide range of fluids, including air, water and other gasses and liquids.

Preferably, the system is operable with a relatively low voltage supply, preferably less than 110 volts and more preferably less than 50 volts. In the preferred embodiment the system is operable with 12 of 24 volts supply. The use of a relatively low voltage supply minimises the risks involved in placing the UV lamp in direct contact with conductive or semi-conductive liquids, including water. Further, the system may be installed in vehicles, for example trucks transporting live seafood, and powered directly from the vehicle's existing 12 volt electrical system. It has been found that a conventional 240 volt lamp system may be operated at such low voltages without difficulty. Of course, the system will include means for providing the lamp with an initial higher voltage boost (for example 400 volts for 29 ms) to initiate lamp burn, and the energised lamp may then operate at a slightly higher voltage (for example 50 - 60 volts) than the supply. Preferably also, the UV lamp is operated at relatively high frequency, preferably over 20 kHz, more preferably over 30 kHz, and most preferably over 40 kHz. In the preferred embodiment of the invention the lamp operates at a frequency in the region of 52 kHz. It has been found that the use of such relatively high frequencies, compared to normal "mains" frequency as utilised in most conventional systems (50 - 60 Hz) , minimises any loss of efficiency due to the cooling effect of the fluid in direct contact with the tube. It has also been found that use of higher frequencies prolongs lamp life; it is believed this is due, in part, to the less pronounced temperature cycling that the lamp experiences at higher frequencies. Conventional 50 - 60 Hz UV lamps have been found to be capable of operating at these higher frequencies without difficulty.

Preferably also, the UV lamp is elongate, typically in the form of a "tube", and the enclosure includes a fluid containing portion in the form of a conduit. Most preferably, the lamp is located substantially concentrically within a tubular conduit, such that the fluid to be sterilised passes through an annulus defined by the lamp surface and the conduit. Preferably also, insulated conductors providing electrical communication between the lamp end electrical connectors pass through the annulus. Most preferably, the insulation on the conductors is a sterilisable material which does not degrade with exposure to UV radiation. In the preferred embodiment the insulation is PTFE, which also offers the advantage of being relatively thin and thus minimises "shading", that is the insulated conductors cast only a small shadow and do not hinder the sterilising effect to any significant degree.

In low voltage systems, it may not be necessary to isolate the electrical connections within the system from the fluid to be sterilised. However, the ends of the UV lamp, which define electrical connections, may be isolated from a fluid containing portion of the enclosure by resilient annular seals. Most preferably, conductors extending between the connections pass directly through the seals; it has been found that an effective seal may be achieved between the conductors and the seals simply by threading the conductors through the seals using an appropriately sized needle. This obviates the need to provide additional O-ring seals and the like. This arrangement for providing sealing between the lamp and the container facilitates assembly of the system and also facilitates replacement of lamps: in the preferred arrangement it is merely necessary to expose the lamp ends, disconnect the wiring from the lamps, and remove the seals over the lamp ends to permit removal of a defective lamp. Preferably also, the system is provided in the form of an elongate unit aligned with a main fluid containing conduit or vessel, with a fluid inlet and a fluid outlet for connection to appropriate inlet and outlet conduits. The ends of the UV lamp may be located within appropriate end fittings secured to the main conduit, and if necessary the interiors of the fittings may be isolated from the fluid-containing portion of the conduit. In one embodiment, one of the fittings may also accommodate a unit, of conventional construction, for converting mains electricity supply to an appropriate high frequency, low voltage supply, which modified supply is passed through an appropriate ballast unit to the lamp. In other embodiments, this unit may be positioned remotely of the lamp. This latter arrangement is useful is situations where the UV lamp is to be located, for example, in a domestic garden for sterilising water in a garden pond and is powered from an existing mains socket within a house; all of the electrical connections and cabling located outside the house will be low voltage, facilitating installation of the system and minimising the risk of electric shock from the householder, for example, accidentally cutting through the external wiring with a lawn mower. The use of a low voltage supply may also remove the requirement to install the system under IEE, or equivalent local, regulations.

Preferably also, the systems includes means for creating a magnetic field in the vicinity of the lamp. Most preferably, said means creates a magnetic field which is normal to the direction of fluid flow through the system. Conveniently, said means is in the form of ulti- polar or annular magnets. It has been found that, in certain circumstances, such a magnetic field will reduce limescale deposition on the lamp. According to a further aspect of the present invention there is provided a UV radiation sterilisation system including an enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure and having ends defining electrical connections, the ends of the lamp being isolated from a fluid containing portion of the enclosure by resilient seals located between the lamp surface and the enclosure .

According to a still further aspect of the present invention there is provided a UV radiation sterilisation system including a enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure, the system being operable at a voltage of less than 110 volts. These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of a UV radiation sterilisation system, in accordance with a first embodiment of the present invention; and

Figure 2 is an illustration of a UV radiation sterilisation system in accordance with a second embodiment of the present invention.

Reference is first made to Figure 1 of the drawings, which illustrates a system 10 comprising an opaque conduit in the form of a length of pipe 12 with a conventional UV tube 14 mounted concentrically therein. The pipe 12 includes inlet and outlet fittings 16, 17 such that the pipe 12 may form part of a water supply or circulation system. As indicated by the arrows 18, water flows through the inlet 16, along an annulus 20 defined between the tube

14 and the pipe 12, and then through the outlet 17. The water is thus exposed to ultra-violet radiation as it passes through the pipe 12 and is sterile on leaving the outlet 17.

The UV tube 14 is of conventional construction, that is the tube is of the type which is supplied for operation at conventional mains voltage and frequency, that is 240 volts AC and 50 Hz. However, the system 10 includes a pulse generator and converter unit 22 which modifies the mains electricity supply from power cable 24 to a 12 volts 52 kHz supply. The unit 22 is "potted" within an end fitting 26 mounted on an end of the pipe 12.

The ends of the UV tube 14 include electrical connections 28, 29 and these are isolated from the water in the annulus 20 by respective resilient annular seals 30, 31 located over the tube ends . The seals may each form part of a respective end cap extending over the end of the tube. One end of the tube 14 extends into the end fitting 26 while the other end of the tube extends into a further end fitting 32. The ends of the pipe 12 and the end fittings 26, 32 define appropriate flanges to engage portions of the respective seals 30, 31. Conventional threaded collars

(not shown) are provided to retain the end fittings 26, 32 on the tube 14 and compress the seals between the flanges.

The electrical connection between the unit 22 and the tube end connections 29 is achieved by means of fine insulated wires 34 which extend through the annulus 20. The wires are provided with PTFE insulation which is sterilisable and is not degraded by exposure to UV radiation. The wires are threaded through the seals 30, 31 and it has been found that an effective seal may be obtained between the wires 34 and seals 30, 31 simply by threading the wires through the seals using a needle of appropriate diameter.

Mounted in the inlet 16 is a multi-polar magnet 36 which create a magnetic field at right angles to the flow of water through the inlet 16. It has been found that the magnetic field minimises limescale deposition on the tube 14 and pipe 12 in "hard" water areas, reducing the frequency of cleaning required.

In use, water is passed through the pipe 12 while the tube 14 is energised, via the pulse generator and conversion unit 22. As the water flows through the annulus 20 surrounding the tube 14 the UV radiation is effective to sterilise the water, the flow rate being selected such that the water is exposed to UV radiation for an appropriate period.

Reference is now made to Figure 2 of the drawings, which illustrates a UV radiation sterilisation system 10a in accordance with a second embodiment of the present invention. The system is similar to the system described above, however the pulse generator and converter unit 22a which modifies the mains electricity supply from mains power cable 24a to a 12 volts 52 kHz supply is located remotely (for example 10 metres away) from the remainder of the system. The system will include a fluorescent tube inverter unit 22b to apply a relatively high voltage (400 volts) to the lamp to initiate firing and then apply a voltage of 50 - 60 volts to operate the lamp. The unit 22b is a two transistor push pull resonant design similar to a "Royer oscillator". Such a system is useful in, for example, domestic applications such as sterilising the water in a garden pond. In such an application the power supply will be the existing mains supply within the dwelling house. The householder simply plugs the unit into an appropriate socket within his house, and then routes the connecting wires to the system 10a. As the connecting wires will only carry a 12 volt supply it is not essential to employ a qualified electrician to install the system as IEE or equivalent local regulations are unlikely to apply, and the use of low voltages minimises the dangers normally associated with outdoor electrical installations. It will be clear to those of skill in the art that the systems 10, 10a may be constructed of easily available and relatively inexpensive materials and is easily assembled. It will also be clear to those of skill in the art that the above-described embodiment is merely exemplary of the present invention, and that various modifications and improvements may be made thereto without departing from the scope of the present invention. In other embodiments of the invention, it has been found that the seals 30, 31 may be omitted; in the low voltage systems as described above, successful operation may be possible with the tube end connections 28, 29 in direct contact with the fluid to be sterilised. Further, in systems provided to handle larger flow rates, a multiplicity of UV lamps may be provided. The lamps may be provided within a single vessel or container, or a number of systems 10, 10a as described above may be used in series or in parallel. In addition, systems in accordance with the present invention may be used in the sterilisation of air and other gasses . For these applications fans may be provided for circulating air past the UV lamp, or the enclosure may be open and include a reflector, such that larger areas may be exposed to the UV radiation. Of course embodiments of the invention may be provided for use with a twin-ended UV tube as described above, or with single-ended tubes, that is tubes in which the electrical connections for the tube are provided in a single fitting.

Claims

CLAIMS ;

1. A UV radiation sterilisation system including an enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure such that the fluid to be sterilised contacts the lamp surface.

2. The system of claim 1, wherein the system is operable using a supply voltage of less than 110 volts.

3. A UV radiation sterilisation system including an enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure, the system being operable using a supply voltage of less than 110 volts.

4. The system of any of the preceding claims, wherein the UV lamp has an end defining an electrical connection, the end of the lamp being isolated from a fluid containing portion of the enclosure by a resilient annular seal located between the lamp surface and the container.

5. A UV radiation sterilisation system including an enclosure for a fluid to be sterilised and a UV lamp positioned within the enclosure and having an end defining electrical connections, the end of the lamp being isolated from a fluid containing portion of the enclosure by a removable resilient seal located between the lamp surface and the enclosure.

6. The system of any of the preceding claims wherein the system is provided in conjunction with step-down means for reducing the voltage of a power supply to a lower voltage supply for the system, said step-down means being located remotely from the lamp and being connected thereto by low voltage wiring.

7. The system of any of the preceding claims, wherein the system is operable using a supply voltage of 24 volts or less.

8. The system of claim 7, wherein the system is operable using a supply voltage of 12 volts.

9. The system of any of the preceding claims, wherein the UV lamp is operable at a frequency of over 20 kHz.

10. The system of claim 10, wherein the lamp is operable at a frequency of over 40 kHz.

11. The system of claim 10, wherein the lamp is operable at a frequency of over 50 kHz.

12. The system of any of the preceding claims, wherein the UV lamp is elongate and the enclosure includes a fluid containing portion in the form of a tubular conduit, the lamp being located substantially concentrically within the conduit, such that fluid to be sterilised may pass through an annulus defined by the lamp surface and the conduit .

13. The system of any of the preceding claims, wherein conductors providing electrical communication between a lamp end and a power source pass through the fluid containing portion of the enclosure.

14. The system of claim 13, wherein the conductors are threaded through seals provided between the lamp and enclosure which isolate the lamp ends from the fluid.

15. The system of claim 13 or 14, wherein the conductors are insulated by a sterilisable material which does not degrade with exposure to UV radiation.

16. The system of claim 15, wherein the insulation material is PTFE.

17. The system of any of the preceding claims, in combination with a device for converting a mains electricity supply to a high frequency, low voltage supply for the system.

18. The system of any of the preceding claims including means for creating a magnetic field in or adjacent the enclosure .

19. The system of claim 18 wherein said means for creating a magnetic field creates a field at right angles to the direction of fluid flow.

20. A method of sterilising fluid comprising passing fluid through an enclosure having a UV lamp therein such that the fluid comes into contact with the lamp surface.

21. The method as claimed in claim 20, in which the fluid is water.

22. The method as claimed in claim 20, in which the fluid is a gas.

23. The method as claimed in claim 22, in which the fluid is air.

24. The method of any of claims 20 to 23, wherein the lamp forms part of a system operating at a supply voltage of less than 110 volts.

25. A method of sterilising fluid comprising passing fluid through an enclosure having a UV lamp forming part of a system operating with a supply voltage of less than 110 volts .

26. A UV sterilising method comprising exposing material to be sterilised to a UV lamp forming part of a system operating with a supply voltage of less than 110 volts.

27. The method of any of claims 20 to 26 wherein the UV lamp forms part of a system operating with a supply voltage of 24 volts or less.

28. The method of claim 27, wherein the system is operated with a supply voltage of 12 volts.

29. The method of any of claims 20 to 28, wherein the UV lamp is operated at a frequency of over 20 kHz.

30. The method of claim 29, wherein the lamp is operated at a frequency of over 40 kHz.

31. The method of claim 30, wherein the lamp is operated at a frequency of over 50 kHz.

32. The method of any of claims 20 to 31, including creating a magnetic field in the container.