Patent Description:
Bipolar ion generators have become most commonly used for air disinfection of manned premises. Typical examples are disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

The principle of operation of such generators is based on generating a corona discharge area between ionizing electrodes of opposite polarity through which either the entire air-flow containing water molecules (moisture) or a part of it is passed. In known devices the air-flow is either parallel to the axis of the ionizing electrodes and occurs from the non-ionizing part of the electrodes to the ionizing tip thereof (see for example to <CIT>) or is perpendicular to the axes of the electrodes, (see <CIT>).

In the corona discharge area two processes occur concurrently owing to decomposition of the oxygen molecule O<NUM> into two oxygen atoms O+O i.e. conversion of water molecules H<NUM>O into hydrogen peroxide H<NUM>O<NUM> and also ozone O<NUM> generation, i.e.:.

Hence the air-flow at the outlet of a bipolar ion generator contains concurrently hydrogen peroxide, ozone and positive and negative ions captured by the air-flow from the corona discharge area. Molecules of H<NUM>O<NUM> used as liquid disinfectant provide longer contact time with bacteria and viruses and spores as compared to gaseous ozone.

A significant drawback of bipolar ionizers is their low disinfection efficiency which is limited by the maximum permitted ozone concentration in manned premises which is equal to <NUM> ppb.

As noted above H<NUM>O<NUM> and O<NUM> are generated as a result of two concurrent processes in corona discharge. The process of O<NUM> generation is much more efficient than that of H<NUM>O<NUM>. Indeed, using current state-of-the-art corona discharge techniques the electrical energy needed to produce <NUM> of ozone is <NUM>-<NUM> kW/h as against <NUM> kW/h needed to produce <NUM> of H<NUM>O<NUM>. However, the maximum permitted ozone concentration in manned premises is only <NUM> ppb, which establishes a maximum permitted discharge current. In practice this means that taking into account the respective chemical reactions (<NUM>) and (<NUM>) that produce H<NUM>O<NUM> and O<NUM> by corona discharge, at an energy consumption providing an ozone concentration of <NUM> ppb, the concentration of H<NUM>O<NUM> is about 7ppb whereas the maximum permitted concentration of H<NUM>O<NUM> in manned premises is <NUM> ppb or <NUM> ppm.

<CIT> discloses an ionizer device, which reduces the emission of ozone that is produced simultaneously with the ionization process. The device includes a split housing having front and rear sections separated by an active carbon filter and defining front and rear openings. An ionizing electrode is located in the front section and has a tip that faces axially forward toward the front opening surrounding which is an annular non-ionizing electrode. High voltage DC is applied between the two electrodes creates a corona discharge between the tip of the ionizing electrode and the non-ionizing electrode, thus generating a stream of ions and ozone together. An extractor fan located in the rear section applies negative pressure to the interior of the housing, which sucks ozone toward the rear opening, where it is neutralized by the active carbon filter, while allowing the ions to exit through the front opening only.

While the device disclosed in <CIT> separates ozone flow from the ion stream and neutralizes the ozone so that only ions are released, it does not separate hydrogen peroxide from the ozone. Therefore any hydrogen peroxide that is produced in the corona discharge zone will likewise be drawn toward the rear opening by the extractor fan and neutralized by the active carbon filter without exiting through the rear opening into the atmosphere. Document <CIT> discloses a device according to the preamble of claim <NUM>.

Furthermore, most ions created in the corona discharge zone are likewise drawn toward the rear opening under the influence of the extractor fan whose pull exceeds the force of the ion wind directing the escape of ions through the front opening. But in any case, any ions that do escape from the corona discharge area toward the front opening do not form molecules of H<NUM>O<NUM> owing to the absence of secondary emission, which exists only inside the electric field of the corona discharge. So there will be no generation of hydrogen peroxide downstream of the ionizing electrode and the only hydrogen peroxide that is generated will be carried upstream by the extractor fan and neutralized.

Consequently, only a very small number of ions are released into the atmosphere and the device is therefore inefficient as an ion generator and cannot be used at all as a disinfector.

A principal objective of the present invention is to remove the ozone generated in the corona discharge zone so as to prevent its release into an enclosed atmosphere in order to substantially increase the corona discharge current and increase the disinfection efficiency using ion generators, H<NUM>O<NUM> generators and electrostatic filters by more than <NUM> times.

The invention achieves this objecting using a "tip plane" type corona discharge, wherein according to known corona discharge theory, the corona discharge area consists of a plasma ionizing area which is an irradiant space close to the tip of the ionizing electrode, and a dark area between the ionizing electrode i.e. "the tip" and the non-ionizing electrode i.e. "the plane" where the secondary ion emission occurs in the electrical field of the corona discharge. It should be understood that the principle also applies to the corona discharge and the wire-plane system.

Molecules of water are converted into molecules of H<NUM>O<NUM> during both plasma ionization and the secondary emission processes, i.e. in the entire corona discharge area constituted by both the plasma ionizing area and the dark area, whereas actually the entire amount of ozone is formed in the plasma ionizing area which occupies a very small volume (<NUM>-<NUM><NUM>) as compared to the entire ozone discharge area.

However owing to the high velocity of the ions in the electrical field of the corona discharge, neutral ozone molecules generated in the plasma ionization region are attracted by the ordered movement of ions along the electric field lines and reach the dark area of the corona discharge. This phenomenon is called ionic wind the speed of which is <NUM>-<NUM>/s depending on the velocity of the corona discharge current, which is itself a function of the magnitude of the corona discharge current.

The essence of the invention is based on separating the H<NUM>O<NUM> molecules from the molecules of O<NUM> in the corona discharge followed by ozone removal or destruction.

The objective of the invention is achieved by a method and device having the features of the respective independent claims.

The principle of the invention resides in dividing the air-flow entering the corona discharge area into two streams, the first being passed through the plasma area of the corona discharge and an ozone filter while the second is passed through the dark area thereof.

For efficient separation between molecules of H<NUM>O<NUM> and O<NUM> the ionic wind effect should be neutralized, so one of the requirements for implementation of the method that the velocity of the air-flow passed through the plasma area of the corona discharge be higher than the ionic wind velocity.

In an embodiment of the invention, this requirement is fulfilled by mounting the ionizing electrode in a specific location inside the entire air-flow.

According to the invention, the air-flow passing through the corona discharge area is parallel to the axis of the ionizing electrode, but is directed from the tip of the ionizing electrode to its non-ionizing part. This leads to a decrease in the ion wind velocity owing to the opposing directions of the vectors of the ion wind and the air-flow, and as a result to a decrease in the required value of the negative pressure gradient required to separate the flow. In practice, this means that a low power suction device can be used.

Since the ionic wind velocity is in direct proportion to the magnitude of the corona discharge current and in inverse proportion to the volume of the corona discharge area, the second requirement for efficient separation between H<NUM>O<NUM> and O<NUM> is to increase the volume of the corona discharge area.

To comply with this requirement, the non-ionizing electrode is formed as a hollow cylinder with air-flow inlet and outlet apertures inside and the ionizing electrode mounted inside it with its axis coaxial with the geometrical axis of the cylinder.

This solution provides maximum possible volume of the corona discharge area and consequently minimum possible ionic wind velocity.

The method can be applied also to generate both a unipolar negative or positive corona discharge using a single ionizing electrode and to generate a bipolar corona discharge using two ionizing electrodes of opposite polarity. In the latter case the corona discharge will have two plasma corona discharge areas from which to remove ozone.

A disinfector according to the invention is based on the proposed method contains the following elements: a non-ionizing cylindrical electrode with air-flow inlet and outlet apertures, an ionizing electrode, whose axis is coaxial with the geometrical axis of the non-ionizing electrode, a high voltage generator configured to generate a corona discharge area between the electrodes, a suction device having inlet and outlet air channels to generate a negative pressure gradient area in order to form an air-flow passing through the plasma area of the corona discharge and an ozone filter for preventing the escape of ozone.

The inlet aperture of the inlet air-channel of the suction device is positioned close to the ionizing tip of the ionizing electrode, whereas the outlet air channel of the device is connected to the inlet of the ozone filter.

At the same time the high voltage output of the high voltage generator is connected to the ionizing electrode and the low voltage output thereof is connected to the non-ionizing electrode.

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
<FIG> is a schematic representation of a device according to the invention.

<FIG> shows schematically a disinfector <NUM> comprising a generally hollow cylindrical chamber <NUM> having an electrically conductive inner wall <NUM>. The cylinder <NUM> defines least one air inlet aperture <NUM> at its lower end <NUM> and an air outlet aperture <NUM> at its upper end <NUM>. An ionizing electrode <NUM> is supported by a non-ionizing part <NUM> at the upper end <NUM> of the chamber so that its tip protrudes inside the chamber.

A high voltage generator <NUM> has supply terminals <NUM> for connecting to a voltage source such as a main electricity supply and has high voltage output terminals <NUM>, <NUM>' respectively connected to the ionizing electrode <NUM> and the inner wall <NUM> of the chamber <NUM>, which serves as a non-ionizing electrode. The application of high voltage across the two electrodes forms a corona discharge area between them, consisting of a plasma corona discharge area <NUM> and a dark corona discharge area <NUM>. A hollow air-channel <NUM> is mounted in spatial relationship with the chamber <NUM> in axial alignment with the ionizing electrode <NUM> and is dimensioned to cover the whole area of the plasma corona discharge area <NUM>. It is to be understood that the figure is schematic and is intended to demonstrate the principles of the invention. The air-channel <NUM> may be supported in a lid (not shown) of the chamber that is attached to a rim of the chamber but which is perforated to allow the free flow of air other than the air which passes through the hollow air-channel <NUM>. Alternatively, the chamber <NUM> and the hollow air-channel <NUM> may both be supported in proper spatial alignment within an outer structure (not shown). Also, while the device is depicted in the figure as symmetrical with the hollow chamber <NUM> coaxial with the longitudinal axis of the chamber <NUM>, this is not a requirement. The only requirement is that the ionizing electrode be coaxial with the hollow air-channel <NUM>. Likewise, although the chamber <NUM> is described as circularly cylindrical, its cross-section can be of any other polygonal shape.

A suction device <NUM> having power supply input terminals <NUM> is mounted on top of the air-channel <NUM> in fluid communication therewith and is likewise coupled via a channel <NUM> to a filter <NUM>, which is typically an activated carbon (AC) filter. The suction device <NUM> may be a centrifugal fan or a compressor that creates a negative pressure gradient whereby air in the plasma corona discharge area <NUM> is drawn through the air-channel <NUM> into the filter <NUM>. The magnitude of the negative pressure gradient required to remove the ozone may be determined experimentally by measuring the maximum possible concentration of ozone when the corona discharge current is at its maximum and the speed of undivided air flow is at its minimum. The maximum desired corona discharge current is selected based on the use of the device i.e. whether its primary use is to emit hydrogen peroxide and, if so, at what desired concentration; or whether the device is an electrostatic filter or ionizer. Once the maximum desired corona discharge current is established, the air flow is increased and the ozone concentration is measured. The air flow is then increased slightly and the ozone concentration is measured again. This is repeated until the ozone concentration no longer increases. Increasing the air flow beyond this value is to no further benefit and establishes the optimum air flow for the prescribed corona discharge current wherein the velocity of the air flowing through the plasma area of the corona discharge is higher than the ion wind velocity for the preset corona discharge current.

Operation of the disinfector <NUM> is as follows:
As voltage is applied to the terminals <NUM> of the high voltage source <NUM>, a corona discharge area is generated between the ionizing electrode <NUM> and the non-ionizing electrode constituted by the inner wall <NUM> of the chamber <NUM>. Plasma corona discharge <NUM> is generated close to the tip of the ionizing electrode <NUM>, while the remaining volume of the corona discharge constitutes the dark corona discharge area <NUM>. At the same time, power is applied to the supply terminals <NUM> of the suction device <NUM>, thus generating a negative pressure gradient in the air-channel <NUM>, which draws ozone formed in the plasma corona discharge area <NUM> through the channel <NUM> to the filter <NUM> where it is neutralized. Ozone-free air now exits from the ozone filter and reaches the air to be disinfected.

In the air flowing through the dark area of the corona discharge <NUM> some of the water molecules are converted to hydrogen peroxide molecules due to the interaction with ions in the corona discharge electric field and also reach the environment with the air flowing via the outlet aperture <NUM> in the lid <NUM> as shown by arrows A.

As a result, the ozone is separated from most of the hydrogen peroxide, of which a small amount will also pass through the air channels <NUM> and <NUM> and will be neutralized by the filter <NUM>. However, the majority of the hydrogen peroxide passes through the outlet aperture <NUM> into the atmosphere, which is therefore disinfected, while ozone-free air passes into the atmosphere from the filter outlet. Since the ozone is prevented by the filter from escaping into an enclosed atmosphere, the corona discharge current can be safely increased to a level which generates a much higher quantity of hydrogen peroxide as evidenced by Table <NUM> below showing the technical specification of a disinfector manufactured and tested according to the invention.

The filter <NUM> in effect neutralizes the ozone in order that the concentration of ozone released into an enclosed atmosphere in which the device is deployed will be below the permitted maximum. However, the same objective can be achieved without the filter by conveying the ozone out of the enclosed atmosphere through an exit tube or pipe that may simply be envisaged as an extension of the channel <NUM>.

The following devices were used to measure the H<NUM>O<NUM> and O<NUM> concentration:.

Although the invention has been described with particular reference to a disinfection device and method, it will be appreciated that the principles of the invention are equally applicable for other devices based on corona discharge where the maximum permissible concentration of ozone limits the efficiency. Thus, the same principles may also be applied to electrostatic filters and ionizers.

Claim 1:
A method for separating components in a corona discharge zone, said method including:
(a) passing an air stream containing water molecules between at least one ionizing electrode (<NUM>) and at least one non-ionizing electrode (<NUM>);
(b) applying high voltage to said electrodes to create a corona discharge zone consisting of a plasma region wherein ozone is formed and a dark region where predominantly hydrogen peroxide is formed;
(c) dividing the air flow entering the corona discharge zone into two separate air flows, a first of which passes through the corona discharge plasma region, and a second of which passes through the dark corona discharge region; and
(d) applying a negative pressure gradient to the plasma region only so as to remove the ozone and thereby prevent escape of the ozone in the first air flow into an enclosed atmosphere;
characterized by:
(e) supporting the ionizing electrode (<NUM>) at the upper end of a chamber (<NUM>) whose inner wall surface serves as the non-ionizing electrode (<NUM>) with a non-ionizing part (<NUM>) of the ionizing electrode (<NUM>) in coaxial alignment with a hollow air-channel (<NUM>) dimensioned to cover the whole area of the plasma region (<NUM>) so that a tip of the ionizing electrode (<NUM>) protrudes out of an open lower end of the air-channel (<NUM>) into the chamber, and
(f) applying a unipolar negative or positive corona discharge between the ionizing electrode (<NUM>) and the non-ionizing electrode (<NUM>).