GB2345917A - Device for introducing biocidal ions into water - Google Patents

Abstract

A device for introducing biocidal ions into flowing water comprises an elongate flow chamber 1 dimensioned and arranged such that, for the desired volumetric flow rate of water therethrough, non-laminar flow occurs therein, the chamber containing a pair of curved metal electrodes 2,3 having a common axis of curvature which extends in the direction of flow through the chamber, the electrodes being spaced apart such that, in use, there is a region of non-laminar flow between them, and a power supply for supplying electric current to the electrodes whereby biocidal metal ions are introduced into the water flow from at least one of the electrodes. The electrodes can be supplied with an alternating current, and when formed of different metals can be supplied with different power levels in the two half-cycles, thereby permitting separate control of the generation of the different metal ions. In a modification the device for introducing biocidal ions into flowing water comprises as a replaceable cartridge a tubular body having flow connection means at each end thereof and containing a pair of spaced metal electrodes each electrically connected to an external terminal on the cartridge. The electrodes may be provided with longitudinal corrugations.

Description

DEVICE FOR INTRODUCING BIOCIDAL IONS INTO WATER Field of the Invention This invention relates to a device for introducing biocidal ions into flowing water to kill bacteria and hence disinfect the water.

Background to the Invention The use of metal ions such as copper and silver to disinfect water for such appli- cations as swimming pools and cooling water for air conditioning and the like is wellknown, and a variety of electrolytic devices have been proposed for injecting the metal ions into flowing water. In such devices, direct current is supplie to a pair of electrodes fabricated from the same metal, for example a copper-silver alloy. Copper and silver ions generated at the anode are attracted towards the cathode, but under certain conditions a proportion of these ions may pass downstream, where they are available for immediate or residual disinfection purposes.

The continued use of direct current of unvarying polarity eventually results in erosion of the anode, together with a build-up of various electrolytic deposits on both electrodes. To prevent these effects, polarity reversal can be employed. Various arrangements have been proposed, with typical reversal times of 30 to 120 seconds. Polarity reversal results in equal wear of the electrodes and decreases the formation of electrode deposits.

A better solution is to supply the electrodes with alternating current derived from the mains supply. This obviates the need first to rectify the AC mains supply and apply polarity reversal, resulting in savings in both electrical components and in installation labour costs. Energy savings arising from increased energy efficiency of the AC sys- tem also decrease running costs. In addition, the use of AC throughout permits greater versatility in design, control and fabrication.

Typical electrode configurations have involved simple spaced plates located in a flow conduit. This type of configuration has disadvantages where the water velocity is to be increased to increase the efficiency of ion introduction for large volumes of water. Increasing the size of the electrodes in order to introduce ions at a greater rate necessitates an increase in the size of the chamber, reducing water velocity over the electrodes, thereby reducing efficiency.

Another problem experienced with prior art electrolytic devices is that, where mixed ions are to be introduced, for example because different organisms which may be present are affected differently by the ions, the balance between the ions can only be controlled by varying the proportions of metals in the alloys used to form the elec- trodes. Thus, if the balance is to be changed, the electrodes need to be changed. This is not only inconvenient, but is does not permit the balance to be varied dynamically in response to variations in the micro-organism concentration or other factors.

Summary of the Invention According to one aspect of the invention, a device for introducing biocidal ions into flowing water comprises an elongate flow chamber dimensioned and arranged such that, for the desired volumetric flow rate of water therethrough, non-laminar flow occurs therein, the chamber containing a pair of curved metal electrodes having a common axis of curvature which extends in the direction of flow through the chamber, the electrodes being spaced apart such that, in use, there is a region of non-laminar flow between them, and a power supply for supplying electric current to the electrodes whereby biocidal metal ions are introduced into the water flow from at least one of the electrodes.

This arrangement permits the velocity of the water to be maximised while ensuring the maximum surface area for the electrodes in contact with the water flow.

Preferably, both electrodes are formed of biocidal metal and the power supply is arranged to supply an alternating current to the electrodes, whereby both electrodes introduce biocidal metal ions into the water flow alternately.

The electrodes are preferably formed of different biocidal metals, for example silver and copper. The flow chamber is preferably formed of a non-conducting material, for example a plastics material.

The electrodes are preferably formed as an electrode assembly comprising a pair of thin metal electrode sheets located one on the other with flexible spacing means between them, the resultant stack then being rolled into generally tubular or cylindrical form. An addition spacing means may be included in the stack to form a layer on the inner electrode surface within the tube, or on the outer electrode surface, or two additional spacing means may be used, one on the inner surface and one on the outer sur face. The or each spacing means may consist of a perforate plastics sheet having longi- tudinal passages in the thickness thereof so that flow can occur between the adjacent electrodes. Alternatively, the longitudinal passages are provided by corrugating the electrode sheets, for example in a sinusoidal or V-shaped form. This arrangement has the advantage of further increasing the surface area of the electrodes so as to maximise ion generation for a given cross-sectional area and water flow rate.

In another embodiment, the electrodes are initially planar and the or each spacing means consists of a perforate plastics sheet having longitudinal corrugations to space adjacent electrodes apart and to provide longitudinal flow passages between the electrodes. The corrugations may take any convenient form, for example sinusoidal or Vshaped.

The provision of the electrode in tubular or cylindrical form with non-laminar flow between the electrodes ensures that the velocity of the water through the flow chamber is maximised while still permitting the desired concentration of biocidal ions to be achieved in the water in a relatively compact size, permitting the chamber to be manufactured as a readily replaceable cartridge, for example.

It will be appreciated that, while reference is made throughout to a pair of elec- trodes, it may be possible to employ more than one pair of electrodes spaced apart radially or axially within the chamber.

Another aspect of the invention provides a device for introducing biocidal ions into flowing water, comprising a flow chamber containing two spaced electrodes of two different biocidal metals, and a power supply for supplying an alternating electric current to the electrodes, whereby metal ions are generated at each electrode in altemate half-cydes.

The alternating electric current is suitably at mains supply frequency, i. e. 50 or 60Hz. The power supply is preferably arranged to control the flow of electricity in each half-cycle independently, whereby the rate of generation of the different metal ions can be controlled independently of each other. For example, a portion of each halfcycle may be clipped to reduce the energy delivered, the degree of clipping in one halfcycle being controlled to be different from that in the other half-cycle. Alternatively, the amplitude (i. e. the voltage) in one half-cycle may differ from that in the other half-ycle.

The control of alternating current waveforms to vary the power selectively is wellunderstood by those skilled in the art, and will not therefore be described in more detail.

Another aspect of the invention provides a device for introducing biocidal ions into flowing water, comprising as a replaceable cartridge a tubular body having flow connection means at each end thereof and containing a pair of spaced metal electrodes each electrically connected to an external electrical terminal on the cartridge.

The terminals may simply comprise conductors in a cable for connection to a power supply, but more conveniently comprises a plug part of a plugand-socket connector. The electrodes are suitably tubular, in accordance with other aspects of the invention, especially of the type formed into a tubular assembly from flat electrode sheets and spacer sheets as hereinbefore defined.

The cartridge preferably has a filter at least at the inlet end thereof. The flow connection means suitably comprise external screw threads for connection to a releasable screw-threaded coupling.

The diameter of the cartridge may be sized to yield the optimum water velocity past the electrode faces, while the length is chosen to yield the required concentrations of biocidal ions, taking into account the conductivity of the water.

The cartridge arrangement permits the replacement of worn electrodes as a cartridge assembly in an operation which does not require skilled labour.

The use of tubular electrodes permits a high water velocity to be used, ensuring that a high rate of water treatment can be achieved from a relatively small device, improving efficiency and reducing installation costs.

The use of different metal electrodes and an alternating current supply permits control of the generation of the different metal ions without requiring special alloy electrodes to be used. Where the power supplie in the two half-cycles is varied independently, precise dosing of the different ions can be achieved, and can be controlled dynamically.

Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the invention and their operation: Figure 1 is a perspective view of a cartridge device in accordance with the invention ; Figure 2 is a perspective view of a part of the electrode assembly from the device of Figure 1, partially disassembled ; Figure 3 is a diagram illustrating one way of controlling the generation of ions independently at two different electrodes ; Figure 4 is an enlarged view of one form of electrode assembly of the general type shown in Figure 2; and Figure 5 is an enlarged end view of an alternative form of electrode assembly.

Detailed Description of the Illustrated Embodiments The cartridge shown in Figure 1 comprises a tubular body 1 formed of an elec- trically insulating material, for example a plastics material, and having a threaded connector 16,17 at each end thereof. A mesh filter 14,15 is installed at each end of the body to trap any particulate or fibrous material which might interfere with the operation of the electrolytic process, and to prevent any material breaking off the electrodes from passing into the water flow leaving the device. A tubular electrode assembly 5, described hereinafter in more detail with reference to Figure 2, is located coaxially within the body 1, with electrical connecting leads passing out of the body through a sealed connector 12 in a side branch piece 13 to a power supply (not shown).

It will be seen that the tubular arrangement of the electrodes ensures that the water flow through the cartridge is disrupted to a minimal extent, enabling the water velocity to be maximised while ensuring a maximum contact area between the elec- trodes and the water. The cartridge can be readily replace when the electrodes have been eroded through use by unscrewing the end connectors and detaching the electrical connector lead from the power supply. Installation of a new cartridge is carried out in a simple reverse of this operation.

The electrode assembly is illustrated in Figure 2. It consists of a pair of thin metal sheets 2 and 3, for example one of silver and the other of copper, and two spacer sheets 6 and 7 of a water-permeable electrically-insulating material initially stacked in a flat state with a first spacer 6 outermost, the first electrode sheet 2 laid on this, followed by the second spacer sheet 7 and the second electrode sheet 3. The stack of sheets is then rolled into a tube with the first spacer sheet 6 outermost. Electrical leads 10 and 11 connect the electrodes 2 and 3 to the power supply. The roll of sheets may form a spiral partially or completely filling the cross-section of the chamber in which it is located. The spacer sheets are such as to allow longitudinal flow of water over the electrodes, carrying away the ions as they are formed into the water leaving the chamber.

Figure 3 illustrates one method of controlling the power supplie to the elec- trodes so as to control the relative rates of generation of the different bioddal metal ions. An alternating current supply is connected to the two electrodes, for example the electrodes 2 and 3 in the arrangement of Figure 2. Figure 3 is a graph of voltage against time for the alternating current supplie to the electrodes. In the positive half of each cycle, the full peak voltage is applied to the first electrode to generate the first type of metal ions (for example), while in the second half of each cycle a reduced peak voltage is applied to generate the other metal ions at the second electrode. In this case, fewer of the second metal ions are generated because of the lower voltage applied. By vary- ing the amplitude of the waveform from one part of the cycle to another the rates of generation of the different ions can be controlled precisely and independently of each other.

Figure 4 shows an enlarged view of an electrode assembly according to a preferred embodiment of the invention. As in the arrangement shown in Figure 2, a stack of alternate electrode sheets and spacer sheets is assemble and then rolled to form a tubular assembly. The spacer sheets 40 and 41 each consist of a flexible polymer sheet having a matrix of apertures 9 therethrough allowing the diffusion of ions away from the electrode faces and into the main flow of water aiong the chamber in which the assembly is located, for example a cartridge as shown in Figure 1. In addition, apertures 42 in the thickness of the sheets 40 and 41 allow rapid, non-laminar longitudinal flow of water parallel to the axis of the electrodes. The grid-like structure of the spacer faces imposes a high resistance path to immediately adjacent areas of the electrode, thereby inhibiting erosion of the electrode sheets in these regions. This results in the electrode sheets retaining a minimum structural integrity throughout the working life of the electrode assembly. As the remaining regions of the electrodes begin to erode significantly, the effective resistance of the assembly starts to increase, and this can be detected and used to signal the need to replace the assembly, or in the case of a cartridge arrangement as shown in Figure 1, the complete cartridge.

Referring now to Figure 5, an alternative electrode assembly comprises first and second corrugated electrodes 50 and 51, separated by a perforated plastics sheet 51.

The corrugations in the electrodes are achieved by a series of creases in the sheets to form longitudinal flow passages along the electrodes and to space the electrodes apart with the spacer sheet between. A second spacer sheet 53 surrounds the outer electrode 50 to separate the turns of the coiled electrode assembly from each other. The flow passages are dimensioned to allow non-iaminar flow therealong at the operating water velocity of the device. Although the electrodes and the spacer are for convenience and clarity illustrated as being rolled only to form one revolution, it will be appreciated that in practice it may be desirable to form a continuos spiral occupying substantially the whole cross-sectional area of the chamber in which the electrode assembly is located.

Claims (18)

1. A device for introducing biocidal ions into flowing water, comprising an elongate flow chamber dimensioned and arranged such that, for the desired volumetric flow rate of water therethrough, non-laminar flow occurs therein, the chamber containing a pair of curved metal electrodes having a common axis of curvature which extends in the direction of flow through the chamber, the electrodes being spaced apart such that, in use, there is a region of non-laminar flow between them, and a power supply for supplying electric current to the electrodes whereby biocidai metal ions are introduced into the water flow from at least one of the electrodes.

2. A device according to Claim 1, wherein both electrodes are formed of biocidal metal and the power supply is arranged to supply an alternating current to the electrodes, whereby both electrodes introduce biocidal metal ions into the water flow alternately.

3. A device according to Claim 2, wherein the electrodes are formed of different biocidal metals.

4. A device according to Claim 3, wherein one electrode comprises silver and the other electrode comprises copper.

5. A device according to any preceding claim, wherein the flow chamber is formed of an electrically non-conducting material.

6. A device according to any preceding claim, wherein the electrodes are formed as an electrode assembly comprising a pair of thin metal electrode sheets located one on the other with flexible spacing means between them, the resultant stack then being rolled into generally tubular or cylindrical form.

7. A device according to Claim 6, wherein at least one of the electrodes is provided with longitudinal corrugations, so that flow can occur between the adjacent electrodes, and the flexible spacing means consists of a perforate plastics sheet.

8. A device according to Claim 7, wherein the rolled electrode assembly substantially fills the cross-sectional area of the chamber.

9. A device for introducing biocidal ions into flowing water, comprising a flow chamber containing two spaced electrodes of two different biocidal metals, and a power supply for supplying an alternating electric current to the electrodes, whereby metal ions are generated at each electrode in alternate half-cycles.

10. A device according to Claim 9, wherein the alternating electric current is at mains supply frequency.

11. A device according to Claim 9 or 10, wherein the power supply is arranged to control the flow of electricity in each half-cycle independently, whereby the rate of generation of the different metal ions can be controlled independently of each other.

12. A device for introducing biocidal ions into flowing water, comprising as a replaceable cartridge a tubular body having flow connection means at each end thereof and containing a pair of spaced metal electrodes each electrically connected to an external electrical terminal on the cartridge.

13. A device according to Claim 12, wherein the terminals comprise conduc- tors in a cable for connection to a power supply.

14. A device according to Claim 12, wherein the terminals comprise a plug part of a plug-and-socket connector.

15. A device according to Claim 12,13 or 14, wherein the electrodes are tubular.

16. A device according to any of Claims 12 to 15, wherein the cartridge has a filter at least at the inlet end thereof.

17. A device according to any of Claims 12 to 16, wherein the flow connection means comprise external screw threads for connection to a releasable screwthreaded coupling.

18. A device for introducing biocidal ions into flowing water, substantially as described with reference to, or as shown in, the drawings.