Apparatus for treatment of liquids

Abstract

An apparatus for applying a pulsed voltage to a comestible liquid (pulsed electric field sterilisation). The apparatus comprises an electrically insulating plate 14 with a slot 16. Two electrodes 20 o

Description

Field of the invention The invention relates to apparatus for the treatment of comestible liquids, such as milk or orange juice, by application of a pulsed voltage across the liquid while flowing through a treatment chamber. Background It is known to apply high voltage pulses to comestible liquids, while flowing through a treatment chamber, for the purpose of sterilisation and prolonging of shelflife. Object of the invention The aim of the present invention is to design a treatment chamber that allows the required voltage gradient across the liquid to be achieved using relatively low voltage pulses, while permitting an acceptably high liquid flow rate through the chamber. Summary of the invention According to the present invention, there is provided an apparatus as hereinafter set forth in claim 1 of the appended claims. Desirable features of embodiments of the invention are set forth in the dependent claims. Embodiments of the invention also offer the important advantage of providing a treatment chamber design that has a minimal volume of stagnation zones in the flow, thus preventing the build-up of chamber contamination. Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a first embodiment of the invention, with a section through a central plane of symmetry, Fig. 2 is an exploded view of the embodiment of Figure 1, Fig. 3 is a view similar to that of Fig. 1 of a second embodiment of the invention, and Fig. 4 is an exploded view of the embodiment of Figure 3. Detailed description of the drawings The embodiment of the Figs. 1 and 2 comprises a main housing 10 in the form of a cylinder of an electrically insulating material having two diametrically opposed cutouts 12 that are separated from one another by a thin plate 14. The remainder of the cylinder defines two end caps 10a and 10b and two side walls 10c and lOd that surround the plate 14 on all sides. The plate 14 is formed with a slot 16 that extends through the plate between its upper and lower surfaces. Each of the cutouts receives, in sequence, a seal 18, an electrically conductive electrode 20 and a electrically conductive retainer 22. The electrodes 20 are formed of a material, for example based on graphite, that is safe to bring into contact with the comestible liquid to be treated. Each seal 18 can be in the form of a gasket, of an O-ring, or, as illustrates, of a combination of the two, i.e. a sheet gasket with thickened regions 18a to act as O-rings. If a seal is formed as an O-ring, or incorporate an O-ring, then a continuous groove 16a surrounding the slot 16 may be machined in adjoining surfaces the plate 14 and the electrode 20 to accommodate the O-ring 18a. The incorporation of O-ring 18a into a gasket 18 ensures correct alignment of the seal with the grooves 16a formed in the plate 14 and the electrode 20. All the above components are clamped together by means of three locking rings 28 each formed of two separate halves that are secured to one another by means of bolts (not shown). The locking rings in some embodiments are made of, or coated with, an electrically insulating material. It is however alternatively possible for the locking rings 28 to be made of an electrically conductive material. In such embodiments, insulating washers may be placed around the bolts ensure that they do not make electrical contact with the halves of the locking rings 28, so that each half is electrically isolated from the other half but electrically connected to a respective one of the retainers 22 and electrodes 20. When clamped together in this way, a sealed chamber for treatment of a light is defined within the slot 16 that has the electrodes as its upper and lower walls and the edge of the slot 16 as its side walls. The lower of the two electrodes 20 and of the two retainers 22, as viewed, are each formed with two holes for receiving and sealing against inlet and outlet connectors 24, 26 to allow liquid to enter and be discharged from the treatment chamber. The connectors 24, 26 may be electrically isolated from the electrode 20 but if the lower of the two electrodes is connected as a ground electrode, then electrical isolation of the connectors 24, 26 from the electrode is not essential. In use, while the lower electrode 20 is connected to ground and the upper electrode 20 is connected to received high voltage pulses, liquid is caused to flow through the treatment chamber, so that any volume of liquid will be subjective to a desired number of pulses during its passage through the treatment chamber. For the treatment, the important parameter- is not the total voltage difference between the electrodes, but voltage drop per unit distance. If the plate 14 thickness is reduced, voltage pulses having a reduced peak voltage will suffice for effective treatment. Reducing the plate thickness will however also reduce the volume flow rate but the width of the slot can be increased to maintain the desired flow rate. Thus, in embodiments of the invention, the ratio of the width of the chamber as measured in a direction transverse to the direction of flow to the thickness of the plate 14 is at least 2:1, or 3:1, or 5:1 or 10:1. It will be noted from Figure 2 that the slot 16 has rounded ends that are aligned with the mouths of the connectors 24, 26. There are therefore no comers 16 in the slot to act as stagnation point. The embodiment of Figs 3 and 4 differ from the that of Figs 1 and 2 in its geometry and in the design of the clamping arrangement. To avoid unnecessary repetition, components serving the same function as in the embodiment of Figs land 2 have been allocated reference numerals with the same two least significant digits but in the 100 series. Instead of the main housing 110 being based on a cylinder, in this embodiment it has rectangular faces. It is nevertheless formed with two opposed cutouts 112 separated by a plate 114 formed with a slot 116. The plate is again surrounded by two end caps 110a and 110b and two side walls 110c and 1 lOd. As with the embodiment of Figs 1 and 2, gaskets or seals 118 and electrodes 120 are received in the cutouts 112 and the lower electrode 120 is formed with holes for receiving inlet and outlet connectors 124, 126. The clamping arrangement in this embodiment comprises retainer plates 122a and 122b 5 that are not received within the cutouts 112 but overlie the side walls 110c and 1 lOde and the end caps 110a and 110b defined by the rectangular housing 10. Bolts 130 pass through the retainer plates 122a and 122b to clamp the electrodes 120 against the plate 116. The retainer plates 122a and 122 may be of an insulating material, but if they are electrically conductive then washers may be used to isolate the bolts 130 from the retainer plates 122a io and 122b to avoid short circuiting the electrodes. In the illustrated embodiment, the retainer plates 122a and 122b serve additionally to press electrical connectors 132 and 134 against the respective electrodes 120.

Claims

1. Apparatus for applying a pulsed voltage to a liquid flowing therethrough, comprising a plate of electrically insulating material having opposite planar surfaces and formed with a slot extending therethrough between the opposite surfaces, two electrodes of conductive material overlying the opposite surfaces of the plate and covering the slot to define within the slot a treatment chamber, an arrangement for clamping the electrodes onto the plate, seals for sealing between the plate and the respective electrodes to prevent fluid leakage from the treatment chamber and inlet and outlet connectors in fluid communication with the treatment chamber, wherein the inlet and outlet connectors are sealingly engaged in spaced holes formed in one of the two electrodes, such that liquid flows through the connectors in a direction transverse to the flow through the treatment chamber.

2. Apparatus as claimed in claim 1, wherein one of the electrodes is a ground electrode, the connectors being engaged in holes in the ground electrode.

3. Apparatus as claimed in claim 1 or claim 2, wherein the arrangement for clamping the electrodes onto the plate comprises two part-cylindrical electrically conductive retainers for urging the respective electrodes against the plate of insulating material, the retainers being surrounded by annular locking rings that serve to clamp the retainers, the electrodes and the insulating plate against one another.

4. Apparatus as claimed in claim 3, wherein the locking rings are formed of, or coated with, an electrically insulating material.

5. Apparatus as claimed in claim 3, wherein each locking ring is composed of two electrically conductive semi-circular halves that are bolted to one another but electrically isolated from one another, each half being electrically connected to a respective one of the retainers and the electrodes.

6. Apparatus as claimed in claim 3, 4 or 5, wherein the insulating plate separating the two electrodes is formed integrally with two cylindrical end caps that limit lateral movement of the electrodes and of the retainers.

7. Apparatus as claimed in Claim 1 or 2, wherein the arrangement for clamping the electrodes onto the plate comprises two retainer plates for urging the respective electrodes06 12 24against the plate of insulating material, and bolts for bolting the retainer plates to one another.

8. Apparatus as claimed in claim 7, wherein the insulating plate separating the two5 electrodes is formed integrally with two cylindrical end caps that limit lateral movement of the electrodes and of the retainer, the bolts passing through holes in the end caps.

9. Apparatus as claimed in any preceding claim, wherein the ratio of the width of the treatment chamber as measured in a direction transverse to the direction of flow to the10 thickness of the plate 14 is at least 2:1, or 3:1, or 5:1 or 10:1.

10. Apparatus as claimed in any preceding claim, wherein the electrodes comprise graphite.15 11. Apparatus as claimed in any preceding claim, where the seals comprise, or consistof, O-rings, and wherein the adjoining surfaces of the plate and the electrodes are formed with grooves for receiving the O-rings.

12. Apparatus as claimed in any preceding claim, wherein the edges of the inlet and2 o outlet connectors align with ends of the slot so as to avoid any flow stagnation points in the treatment chamber,

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