Treatment of liquids

Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...

Reexamination Certificate

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C422S186070, C204S164000

Reexamination Certificate

active

06558638

ABSTRACT:

This application claims the priority of United Kingdom Application No. 9805419.0 filed Mar. 14, 1998, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to the treatment of liquids, and more particularly to the treatment thereof so as to improve them through processing, e.g. inactivation or decomposition, of materials dissolved or suspended therein.
Electrical discharge is widely known in gases with various practical applications e.g. for lighting, cutting through metals etc. It is also known in principle that such an electrical discharge can be obtained inside a liquid. To date though this has not found any significant practical application due to inter alia the very short working life of the electrodes in the devices used.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid or reduce one or more of the above disadvantages.
The present invention provides an apparatus suitable for use in the treatment of a liquid, said apparatus comprising a high voltage electric discharge device with a first electrode and a second electrode spaced apart from said first electrode, said discharge device including electrical power supply control means formed and arranged for applying a series of high voltage pulses across said first and second electrodes in use of the apparatus with said device connected to an electrical power supply so as to produce, in use of the apparatus, an extended area electrical discharge in an electric discharge zone extending between first and second electrodes, said apparatus including a gas delivery means formed and arranged for feeding a series of bubbles of gas into a body of liquid in said electric discharge zone in use of said apparatus.
Thus with an apparatus of the present invention it is possible to generate an electrical discharge inside a liquid for treatment of the liquid, with a relatively low voltage electrical power supply and in a way which results in substantially increased working life of the discharge device, with associated economy of construction, etc. Without in any way wishing to restrict the scope of the present invention, it is believed that a significant factor in the reduced voltage threshold required to establish the electrical discharge within the liquid in use of apparatus of the present invention is the generation of electrical discharge within the bubbles of gas passing between the electrodes.
The generation of a pulsed electrical discharge inside a liquid can induce various different and more or less powerful effects in the liquid depending on the form and type of apparatus of the invention used, which can have a strong effect on various materials present in the liquid. In general, within the immediate vicinity of the plasma discharge there are generated various more or less active species such as hydrated electrons, ions, excited atoms, and free radicals, which can react with materials present in the liquid. Zones of liquid extending beyond the immediate vicinity of the plasma discharge can be affected by UV-radiation. In the case of water containing trace amounts of material such as may be encountered in water being treated for domestic consumption, such zones may extend up to 6 cms or more. The extent of such zones will naturally depend on various factors such as the intensity of the plasma discharge which in turn may depend to a greater or lesser extent on such factors as the voltage of the pulses used for the electrical discharge; and on the OD (optical density or absorbance of the liquid and any material dissolved or suspended in it). Acoustic and shock waves may also be generated by the plasma discharge. By using suitable geometric arrangements of secondary electrodes e.g. generally toroidal, it is possible to combine and concentrate such shock waves for even greater cumulative effect. It will moreover be appreciated that unlike with conventional UV-irradiation apparatus, various embodiments of the apparatus of the present invention will have significantly more powerful effect from the UV-irradiation alone due to the avoidance of any barriers to UV-transmission between the source and the liquid being treated. Even quartz glass which has above average UV-transmission characteristics, substantially attenuates UV-radiation with a wavelength of less than 200 nm. In addition, in at least some forms, the present invention can provide more or less significant synergistic effects through the combination of the UV-radiation, acoustic/shock waves generated, and plasma-chemical and photo-chemical reactions. This may be particularly significant in the treatment of liquids containing micro-organisms such as bacteria, so as to kill or inactivate these in order effectively to sterilise the liquid. The apparatus of the present invention may also be used to treat particular resistant infectious agents such as protozoal oocysts and prions.
Various liquids may be treated by use of the present invention, but the apparatus of the present invention is especially useful for the treatment of water contaminated with various different kinds of materials in order to improve the quality of the water, reduce environmental pollution etc. Thus the present invention may be used by public utility companies for the treatment of water supplied for consumption and running pools, and other uses, and for the treatment of waste water. Other liquids that may be mentioned as suitable for treatment include oils, for example used or waste transformer oil containing more or less toxic additives (e.g. PCBs—polychlorinated biphenyls) required for improving its performance, which require to be neutralised to facilitate safe disposal of the oil. Thus the present invention may also be used to decompose hazardous or toxic organo-chemicals into more or less safe and/or easily biodegradable substances. Other organochemicals which may be mentioned as suitable for neutralisation to a greater or lesser extent by means of the present invention include alkanols e.g. methanol; aldehydes e.g. formaldehyde; phenol and substituted phenols e.g. para-chlorophenol; etc. Other applications of the present invention which may be mentioned include activation of oils and generation of ultrasound for medical purposes.
It will be appreciated that various configurations and geometries of electric discharge device and of the electrodes used therein may be used in accordance with the present invention. In a first preferred form of the invention, the first and second electrodes are substantially spaced apart and there is provided a multiplicity of spaced apart secondary electrodes distributed between opposed portions of said first and second electrodes. Conveniently there is used a device form which has a generally annular electric discharge zone, which may be defined by an internal or external cylindrical surface, and having a longitudinal axis which may be substantially rectilinear, or arcuate to a greater or lesser extent e.g. circular (corresponding to a toroidal discharge surface) or helical, and extending between generally annular opposed portions of the first and second electrodes. With such non-rectilinear axis electric discharge zones it will be appreciated that there may be obtained a degree of interaction between shock or acoustic waves generated by the electric discharge, for example, to produce a more focused and intense cumulative effect.
In the above described first form of the invention, the first electrode may also have an elongate portion extending generally parallel to the electric discharge surface and insulated therefrom by a suitable solid insulator dielectric. Thus, for example, with an external electric discharge surface, said first electrode elongate portion could be in the form of a conductor extending generally along the central longitudinal axis of the electric discharge surface. Conveniently the electric discharge surface is provided on the outside of a tubular insulator with an internal passage extending therealong, which is conveniently used as a gas supply passage, inside which extends said conducto

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