SE543755C2 - Particle eliminator - Google Patents

Abstract

A particle elimination system (1) comprises an ion emitting unit (10), and a collection unit (50). The ion emitting unit is configured for emission of negatively charged ions into a gas volume (2) having particles therein. Thereby, the negatively charged ions, when encountering the particles, charge the particles to form negatively charged particles (4). The collection unit is aimed for collection of the negatively charged particles. The ion emitting unit comprises a multitude of sharp ion-emission points (30) and a high-voltage source (40) connected to the multitude of sharp ion-emission points. The collection unit comprises a collection structure of metal, electrically connected to a zero or positive voltage. Each of the sharp ion-emission points is isolated from each other and, as the only electrical connection, is connected to the high-voltage source by a respective feed connection.

Description

lO PARTKHJBELUMNATOR TECHNK%LFElD The present technology relates in general to particle elimination arrangements and in particular to such arrangements based on emission of ions.

BACKGROUND Air quality inside buildings has often been discussed during many years. Ahigh concentration of particles and/ or viruses / bacteria in the indoorenvironment may cause many problems. There is thus a need to clean theindoor air in many places. This is particularly important e. g. in hospitals or in indoor environments Where many people pass.

One prior-art approach is to use so-called air cleaners based on ionization. Anionizer emits a stream of negative ions into the air volume to be cleaned. Thenumber of ions may be extremely high. These negative ions Will reach particlesin the air and thereby charge these particles. The particles may range from afew nanometres up to visible sizes. The charged particles are typicallyagglomerated into larger particles and Will eventually settle down at a surface, preferably a positively charged surface.

Many of the prior-art air cleaners have different kinds of problems. Particlesmay settle on the ionizer tips causing short-circuiting of the high voltageprovided to the ionizer tips. Positively charged surfaces positioned in thevicinity of the ionizer may disturb the spreading of the negative ions in theroom and/ or give an inefficient collection of charged particles. The need for more stable and efficient arrangements is large. lO SUMMARY A general object of the present technology is to provide a stable and efficient arrangement for particle elimination in a room.

The above object is achieved by methods and devices according to the independent claims. Preferred embodiments are defined in dependent claims.

In general Words, a particle elimination system comprises an ion emitting unit,and a collection unit. The ion emitting unit is configured for emission ofnegatively charged ions into a gas volume having particles therein. Thereby,the negatively charged ions, When encountering the particles, charge theparticles to form negatively charged particles. The collection unit is aimed forcollection of the negatively charged particles. The ion emitting unit comprisesa multitude of sharp ion-emission points and a high-voltage source connectedto the multitude of sharp ion-emission points. The collection unit comprises acollection structure of metal, electrically connected to a zero or positivevoltage. Each of the sharp ion-emission points is isolated from each other and,as the only electrical connection, is connected to the high-voltage source by a respective feed connection.

One advantage With the proposed technology is that a stable and efficientelimination of particles is enabled. Other advantages Will be appreciated When reading the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, together With further objects and advantages thereof, may bestbe understood by making reference to the following description taken togetherWith the accompanying draWings, in Which: FIG. 1 schematically illustrates a prior art ion emitting unit; FIG. 2 schematically illustrates an embodiment of an ion emitting unit having separate high-voltage connections; FIG. 3 schematically illustrates an embodiment of a particle eliminationsystem arranged in a room; andFIGS. 4A-B schematically illustrates two view of an embodiment of a collection unit.

DETAILED DESCRIPTION Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

For a better understanding of the proposed technology, it may be useful tobegin with a brief overview of a corona discharge. An electrode provided withan electrical potential will create an electrical field in the surroundings,typically in air. When the potential gradient, i.e. the electrical field is largeenough, the air may ionize. If a charged object has a sharp point, the electricfield strength around that point will be enhanced. Corona discharge inatmospheric pressure air typically occurs at 30 kilovolts per centimeter. Atvery sharp points, corona discharge can start at potentials of 2 - 6 kV. In mostcorona discharge ionizers, negative potentials are used, thus producing negative ions escaping from the sharp points.

In many prior art ionizers 100, the sharp points 110 are provided attached toa common base 111, as schematically illustrated in Figure 1. The commonbase 1 1 1 is connected by a common connection 1 12 to the high voltage supply 113. The sharp points 110 are typically provided in holes 114 in a casing 115.

During operation, particles may settle down on the sharp points 110,potentially causing a contact between the casing 115 and the sharp points.This may e.g. be the case if positively charged particles are present in thevicinity of the ionizer and the sharp points are provided with a negative voltage.Such short-circuiting of one sharp point 110 will influence the operation of allsharp points 110 and the arrangement is thereby sensitive for such contamination particles.

Figure 2 schematically illustrates an embodiment of an ion emitting unit 10.The ion emitting unit 10 is configured for emission of negatively charged ions5 (illustrated by the arrows 5) into a gas volume 2 having particles 3 therein.The negatively charged ions 5, When encountering the particles 3, charge the particles to form negatively charged particles 4.

The ion emitting unit 10 comprises a multitude of sharp ion-emission points30 and a high-voltage source 40 connected to the multitude of sharp ion-emission points 30. Each of the sharp ion-emission points 30 is isolated fromeach other and, as the only electrical connection, being connected to said high-voltage 40 source by a respective feed connection 42A-42J. Preferably, each ofsaid feed connections 42A-J has an individual electrical resistance 44A-J ofat least 1 MQ from the high voltage potential. The high-voltage source 40 is furthermore connected to ground 48 by a ground connection 46.

This configuration Will result in that even if one of the sharp emission points30 Will be short-circuited, only that specific sharp emission point 30 Will beseverely affected. The remaining sharp emission points 30 Will essentiallyremain undisturbed and Will continue to deliver a stream of ions as requested.Cleaning of the ion emitting unit 10 can thereby Wait for some time Withoutharming the efficiency considerably. The cleaning can instead be scheduled totimes When such activities are more appropriate and may even be scheduledin advance in a regular manner, regardless of any existing short-circuiting. Incase of one defect or clogged sharp emission point, 90% of the unit performance is still available.

The ion emitting unit 10 has in this embodiment a casing 20 With holes 22.Each of the sharp ion-emission points 30 is positioned in or just inside arespective one of the holes 22. In other Words, a casing outer plane, illustratedby the dotted line 29, is situated outside, With reference to the interior of thecasing 20, a tip plane, illustrated by the dotted line 39, comprising the tips of the sharp ion-emission points 30. lO Conducting casings are not to recommend due to the high risk of short-circuiting with the sharp ion-emission points 30, either by physical to thecasing or sharp ion-emission points 30 or by contaminating particles. It istherefore preferred if at least the part of the casing 20 presenting the holes 22has a low electrical conductivity. Preferably, the casing 20 has an electricalconductivity of less than 1O'4 S/ m, and even more preferably less than 10-8 S/m.

However, highly electrically isolating materials also have the tendency tocharge up, presenting a static surface charge. Such static charge can distorta local electrical field just in front of the casing, which may alter the electricalfield in which the ions are supposed to move. Therefore, in one embodiment,the casing has an electrical conductivity of more than 10-12 S/ m. In aparticular embodiment, the casing is made of wood. Wood, especially withsurface treatment to avoid humidity, is known to be electrically isolating, but will not build up any static surface charge.

As mentioned above, by using a very sharp ion-emission point 30, ions caneff1ciently be produced already around a potential of 2 kV. An even moreefficient ion production is achieved if the voltage is increased, e.g. above 2.4 kV.

In other words, in one embodiment, the high-voltage source provides a voltage to the feed connections of at least 2.4 kV.

When a corona discharge takes place, the molecules in the gas in the vicinityof the sharp ion-emission points 30 achieve an extra electron and becomes anegatively charged ion. If this corona discharge takes place in air, the twomain components present are nitrogen gas and oxygen gas. If oXygen gasbecomes a negatively charged oXygen ion, such an ion may pick up anadditional oXygen atom from another oXygen gas molecule, forming ozone.

Ozone is a gas having a high oXidizing effect. This oXidizing effect is sometimes utilized for sanitizing or deodorizing actions. However, since the sameoxidizing effect also causes damages to the respiratory organs in humans, highconcentrations of ozone has to be avoided in rooms where humans are intended to be present.

The amount of production of ozone is dependent on the strength of the appliedelectrical field. The corona discharge first appearing at relatively low voltages,such as 2 kV mainly affects the nitrogen gas in the air. The production ofozone, however, occurs at higher applied voltages. Ozon is not created withlower voltages than BkV when the surrounding material is isolated and cannot create arcs or plasma creeping.

In order to avoid ozone production, the voltage has been found to be keptbelow 3 kV. In other words, in one embodiment, the high-voltage source provides a voltage to the feed connections of at most 3 kV.

Figure 3 illustrates schematically an embodiment of a particle eliminationsystem 1. The, particle elimination system 1 is installed in a room 6, enclosinga gas volume 2. In other words, in one embodiment, the gas volume 2 iscomprised in a room 6 of a building. The particle elimination system 1comprises an ion emitting unit 10, configured as described above. The particleelimination system 1 also comprises a collection unit 50 for collection of thenegatively charged particles 4. The collection unit comprises a collectionstructure of metal, electrically connected to a zero or positive voltage. This will be described more in detail below.

The sharp ion-emission points 30 of the ion emitting unit 10, having a negativepotential, and the positive-potential collection unit 50 creates an electricalfield within the room 6. This is schematically illustrated by field lines 7. Thenegatively charged particles 4 are influenced by the electrical field and isdrawn towards the collection unit 50. The collection of the negatively chargedparticles 4 is most efficient if the electrical field is a stationary and stable field.

In order to assure that this electrical field is created and is reasonably stable, it is therefore preferred if the electrical systems of the ion emitting unit 10 andthe collection unit 50 are interconnected. In other words, in one embodiment,the high-voltage source 40 of the ion emitting unit 10 and the collection unit 50 are connected to a same ground potential.

In order to achieve an efficient removal of particles within the gas volume 2,The stream of negatively charged ions from the ion emitting unit 10 ispreferably spread over an as large volume as possible. Such a spreading isfacilitated if the collection unit 50 is positioned relatively far from the emitting unit 10.

In the embodiment illustrated in Figure 3, the ion emitting unit 10 and thecollection unit 50 are situated at opposite walls 9 of the room 6. In such away, most of the gas volume will be penetrated by the electrical field and an efficient particle removal is expected.

However, in some applications, such arrangements may be difficult to achieve.However, it is still advantageous to separate the ion emitting unit 10 and thecollection unit 50. In some simple tests, it has been shown that a distancebetween these two components preferably should exceed 2m, in particular in larger rooms.

Another measure that can be used for finding advantageous distances is touse a relative distance measure. If a room has a smallest distance betweenopposite walls, it has been found that an advantageous operation of thearrangement is achieved if the separation between the ion emitting unit 10and the collection unit 50 is at least half this smallest distance. Even if theion emitting unit 10 and the collection unit 50 in such a configuration do notenclose the entire gas volume in the room 6, regular convection within the gasvolume 2 will typically be sufficient to achieve particle removal of the entire space.

In other words, in one embodiment, a distance between the ion emitting unit10 and said collection unit 50 is at least larger than 2 m and/ or larger than half the distance between two walls 9, facing each other, of the room 6.

In the illustration, the ion emitting unit 10 and said collection unit 50 are bothprovided at the walls 9 of the room 6. However, other mounting places mayalso be utilized, i.e. one or both of the components may be placed on a floor or in a ceiling.

The separation of the ion emitting unit 10 and said collection unit 50 and thepreference to have a same ground potential may cause the need for providingof long cables between these two positions. In many applications, however,already existing power grids provided to the room can be utilized. This isschematically illustrated in Figure 3 by the electrical sockets 60 and the powergrid connection 62. In other words, in one embodiment the same groundpotential is zero potential or ground potential of an electrical power grid installed in connection to the gas volume 2.

Figures 4A and 4B illustrate schematically one embodiment of a collectionunit 50 of a particle elimination system. Figure 4A is a side cross-sectionalview and Figure 4B is a front view. The collection unit 50 comprises acollection structure 53 of metal, electrically connected to a zero or positivevoltage via a cable 51 and connection piece 52. In this particular embodiment,the collection structure 53 comprises a mesh 54 of thin metal plates. The mesh54 presents large open areas in the front direction, thus allowing air to passthrough the mesh 54. In this embodiment, the collection unit 50 furthercomprises a fan 55 configured for sucking gas from the gas volume 2 in front of the collection unit 50 through the mesh 54.

The main collection of particles by the mesh 54 is caused by the electrostaticattraction of the neutral or positive-potential mesh with the negatively chargedparticles. The fan 55 is believed to be responsible only for a minor part of the direction of particles. lO When the particles meet the mesh 54, they typically settle down at the frontsurface of the mesh 54. This means that during operation, particles aregathering on the collection structure 53, and the collection structure 53 therefore has to be cleaned regularly.

In areas Where bacteria or viruses are present, such hazardous particles arealso charged and collected by the collection structure 53. The front of thecollection structure 53 thereby achieves large amounts of infection particles.In one embodiment, particularly advantageous for avoiding spreading ofviruses and bacteria, the collection unit 50 is further equipped With a UV lightsource 70. In such an embodiment, the UV light source 70 is mounted in sucha Way that the beam 71 of UV light covers the entire front area of the collectionstructure 53. Preferably, a screen 72 is provided, Which prohibits any UV lightto escape from the UV light source 70 in any other directions, that may reachany human beings. The irradiation by UV light 71 is intended to destroy the bacteria and viruses collected at the collection structure 53.

The operation of the UV light source 70 can be configured in different Ways.One alternative is to have a continuous illumination of UV light. In suchapplications, in particular if the system is installed in areas Where humanbeings are present, the design of the screen 72 is important for avoiding anyaccidental UV radiation to the human beings. In another approach, theoperation of the UV light source 70 could be intermittent, i.e. the collectionstructure 53 is only irradiated during some time periods. In such cases, suchirradiation periods may be synchronized With time periods When there is asmall risk of human beings being present in the vicinity. This could e.g. beused in an office or a Waiting room, Which is intended to be empty during nights, When the UV radiation can take place.

In other Words, in one embodiment, the collection unit 50 further comprisesa UV light source 70, configured for continuously or intermittently illuminating the collection structure 53. lO The embodiments described above are to be understood as a few illustrativeexamples of the present invention. It Will be understood by those skilled in theart that various modifications, combinations and changes may be made to theembodiments Without departing from the scope of the present invention. Inparticular, different part solutions in the different embodiments can becombined in other configurations, Where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims (9)

1. A particle elimination system (1), comprising: - an ion emitting unit (10), configured for emission of negativelycharged ions (5) into a gas volume (2) having particles (3) therein, wherebysaid negatively charged ions (5), when encountering said particles (3), chargesaid particles (3) to form negatively charged particles (4); and a collection unit (50) for collection of said negatively charged particles(4); said ion emitting unit (10) comprising a multitude of sharp ion-emission points (30) and a high-voltage source (40) connected to saidmultitude of sharp ion-emission points (30); said collection unit (50) comprising a collection structure (53) of metal,electrically connected to a zero or positive voltage; each of said sharp ion-emission points (30) is isolated from each otherand, as the only electrical connection, being connected to said high-voltagesource (40) by a respective feed connection (42A-J),characterized in that said gas volume (2) is comprised in a room (6) of abuilding, and that a distance between said ion emitting unit (10) and saidcollection unit (50) is at least one of: larger than 2 m; and larger than half the distance between two Walls of said room (6) facing each other.

2. The particle elimination system according to claim 1, characterized inthat each of said feed connections (42A~J) has an individual electrical resistance (44A-J) of at least 1 MQ from the high voltage potential.

3. The particle elimination system according to claim l or 2,characterized in that said high-voltage source (40) provides a voltage to saidfeed connections (42A-J) of at. least 2.4 kV. lO

4. The particle elimination system according to any of the claims 1 to 3,characterized in that said high-voltage source (40) and said collection unit (50) are connected to a same ground potential.

5. The particle elimination system according to claim 4, characterized inthat said same ground potential is zero potential or ground potential of an electrical power grid installed in connection to said gas volume (2).

6. The particle elimination system according to any of the claims 1-5,characterized in that said collection structure (53) comprises a mesh (54); and said collection unit (50) further comprises a fan (55) conñgured for sucking gas from said gas volume (2) through said mesh (54).

7. The particle elimination system according to any of the claims 1-6,characterized in that said collection unit (50) further comprises a UV lightsource (70), configured for continuously or intermittently illuminating saidcollection structure (53) to destroy hazardous content of the collected particles.

8. The particle elimination system according to any of the claims 1-7,characterized in that ion emitting unit (10) has a casing (20) With holes (22);whereby each of said sharp ion-emission points (30) is positioned in or justinside a respective one of said holes (22); and whereby said casing (20) has an electrical conductivity of less than 10* S/ m, preferably less than 1043 S/ m.

9. The particle elimination system according to claim 8, characterized in that said casing (20) has an electrical conductivity of more than lO“12 S /m.