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Title:
AN AIR PURIFIER MODULE, AN AIR PURIFICATION SYSTEM, AN AIR HANDLING UNIT, USE OF AN AIR PURIFIER MODULE, AND A METHOD OF PURIFYING AIR
Document Type and Number:
WIPO Patent Application WO/2020/245508
Kind Code:
A1
Abstract:
An air purifier module comprising at least one air cleaning unit comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow, wherein all creepage distances (220, 260, 270) in the module are at least 2 mm/kV, preferably at least 3mm/kV.

Inventors:
RANTANEN PEKKA (FI)
LIPPOJOKI ISMO (FI)
Application Number:
FI2020/050396
Publication Date:
December 10, 2020
Filing Date:
June 05, 2020
Export Citation:
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Assignee:
AAVI TECH LTD (FI)
International Classes:
B03C3/02; B03C3/41; B03C3/78
Foreign References:
JP2009082901A2009-04-23
US4240809A1980-12-23
US4496375A1985-01-29
US4643745A1987-02-17
US5330559A1994-07-19
EP2535115A12012-12-19
EP3552710A12019-10-16
Attorney, Agent or Firm:
LAINE IP OY (FI)
Download PDF:
Claims:
CLAIMS:

1. An air purifier module, comprising:

- at least one air cleaning unit, comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow;

wherein all creepage distances in the module are at least 2 mm/kV, preferably at least 3 mm/kV.

2. The air purifier module according to claim 1, wherein the voltage between the collector plates is less than 60 kV, preferably in the range from 10 to 20 kV.

3. The air purifier module according to claim 1, wherein the voltage between the collector plates is in the range from 10 to 20 kV, and all creepage distances in the module are in the range from 20 to 60 mm.

4. The air purifier module according to any of the preceding claims, wherein all creepage distances in the module are at least 5 mm/kV, preferably at least 10 mm/kV, such as 10 to 20 mm/kV, and the material of the metal parts of the ionizer is stainless steel.

5. The air purifier module according to any of the preceding claims, wherein:

- the ionizer comprises a net of electrodes having a general shape of a needle or a cylinder or a cone;

- at least 90 % of the lateral surface of said electrodes, preferably substantially the entire lateral surface of said electrodes, is coated with an electrical insulator material; and

- the tips of the electrodes are not coated with an electrical insulator material.

6. The air purifier module according to any of the preceding claims, wherein:

- the ionizer comprises a net of electrodes having an elongated overall shape,

- each electrode comprises a body part and a tip part extending from said body part and being thinner than said body part, - the tip part comprises or consists of a metal wire that has been partially coated with an electrically insulating material so that only a distal end of said tip part exhibits a bare uncoated metal surface.

7. The air purifier module according to claim 6, wherein the thickness of the metal wire is less than 1 mm, preferably less than 0.2 mm.

8. The air purifier module according to any of claims 6 to 7, wherein the tip part is connected to the body part via a spring, and said spring comprises or consists of a coiled metal wire that has been coated with an electrically insulating material.

9. The air purifier module according to any of claims 6 to 8, wherein the material of the metal wire is stainless steel.

10. The air purifier module according to any of the preceding claims, wherein the ionizer comprises:

- a set of ionizer tubes forming a honeycomb cell structure; and

- a net of electrodes having an overall elongated shape, each of the electrodes being at least partially inserted in the middle of one of the ionizer tubes in the honeycomb cell structure.

11. The air purifier module according to any of the preceding claims, further comprising a washing system integrated into each air purifier module and comprising at least one nozzle that is configured to jet a cleansing solution towards said at least one air cleaning unit with a pressure that is larger than 50 bars, preferably larger than 80 bars.

12. The air purifier module according to any of the preceding claims, wherein the material of the metal parts of the ionizer and the collector plates is stainless steel.

13. The air purifier module according to any of the preceding claims, further comprising means for parallel and/or serial assembly with further air purifier modules.

14. An air purification system, comprising several air purifier modules according to any of the claims 1 to 13 arranged in parallel and/or in series.

15. The air purification system according to claim 14, wherein a high voltage source has been connected to the ionizer and the collector by means of insulated tubes, such as metal tubes, wherein the insulated tubes, or insulated metal tubes, have been slid inside insulated connector parts of the air cleaning unit in particular so as to form a water tight connection, and wherein spring loaded connectors secure the connection.

16. An air handling unit, comprising:

- an air purification system according to claim 14 or 15;

- a blower configured to blow air through the air handling unit; and

- a heating element and/or a cooling element configured to heat and/or cool the air.

17. Use of the air purifier module according to any of claims 1 to 13 for purifying air originating from a building site or a construction site.

18. The use according to claim 17, wherein said air comprises oil droplets as impurities.

19. A method of purifying air, wherein the air purifier module according to any of claims 1 to 13 is used.

Description:
TITLE

An air purifier module, an air purification system, an air handling unit, use of an air purifier module, and a method of purifying air

FIELD

[0001] The present invention concerns an air purification system that can be affixed to an air handling unit (AHU) in order to replace conventional mechanical filters. Particularly, the present invention relates to an air purifier module comprising an electrostatic precipitator.

BACKGROUND

[0002] An air purifier is a device that is used in order to clean the air in a room from dust and other contaminants. Air purifiers can be based on various kinds of collection principles of contamination, such as mechanical filtration, precipitation, activated carbon, gravitation, and centrifugation. Commercial air purifiers can operate either as small stand alone units, especially in individual rooms and households, or as larger units that can be affixed, as one of the major components, to an air handling unit (AHU). An air handling unit is usually a large compartment containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Large air purifiers are used especially on an industrial scale, but also in AHU’s serving whole buildings.

[0003] Air that is supplied to buildings is processed in an air handling unit (AHU) to meet the requirements set for intake air. Lresh air from the outside is filtered, and at least most of the particles and aerosols are removed from the air. In some cases even small particles, odours, and toxic gases are removed. Liltration targets are defined in local standards or building codes. Lresh air might be mixed with recirculating air, which must be cleaned as well. Air can be heated or cooled to have a desired temperature. In most cases filtering is performed by mechanical filters made from a fibre fabric or a similar material. Such filters are a simple and inexpensive solution for removing small amounts of dust or particles from air. [0004] When the quality of outdoor air is very low and the particle load to the filters is high, the maintenance interval, i.e. the time between changing of filters, is very short. This means high annual and lifetime costs for a user. If regular maintenance is neglected, air flow will drop. If the output flow is not regulated, negative pressure is created in the building and dirty air will come through the construction.

[0005] In electrostatic purification some ozone is produced. Ozone is harmful to humans even in very small concentrations and therefore it is necessary to minimize ozone production in air purifiers. The amount of ozone produced is a function of the voltages and currents used in electrostatic purification and the construction of the purifier.

[0006] An electrostatic precipitator (ESP), or an electrostatic air purifier, is a device that removes fine particles, like dust and smoke, from a flowing gas by electrostatic attraction. However, it does not work on odours. An ESP includes an ionizer which ionizes, or electrically charges, particles of the incoming air. The charged particles are then attracted to and trapped by collector plates that are oppositely charged. The trapped particles stick to the plates until they are removed. Collector plates are usually formed as an assembly of parallel conductive plates or nested cylinders.

[0007] Particles accumulated on a collector must be regularly removed in order to maintain good purification efficiency. Depending on the method by which particles are removed from the collector plates, ESPs may be divided into two categories: dry and wet. The dry variant is the most abundantly used, basic form of an ESP. In industrial- scale dry ESPs the removal of accumulated dust can be accomplished by using rappers: the dirt and dust is shaken loose by vibration.

[0008] In wet precipitators, a continuous supply of water is used for forming a wet layer on the surfaces of the collector to remove the dirt therefrom.

[0009] It is known to use washing devices for removing accumulated dust from collector surfaces.

[0010] JP 2002035641 A discloses a washing device for an electrostatic dust collector in which a plurality of dust-collecting plates is arranged parallel to each other. The washing device consists of a multistage cylinder in which cylinders having smaller diameters are housed and to which a pressure is applied by compressed air. Water washing nozzles are fitted to the front end of the multistage cylinder so as to be rotatable clockwise and counterclockwise and used for jetting high-pressure water. A wire-drum type winch is used for controlling the extension speed of the multistage cylinder.

[0011] US 4240809 discloses an electrostatic air cleaner intended for commercial and industrial air cleaning applications. The air cleaner includes a number of precipitator cells having spaced parallel plates for collecting dirt particles, and a vertically disposed traversing pipe-like spray header containing a number of spray nozzles for directing a spray of wash or rinse fluid onto the collecting plates in order to remove collected particles. The header is traversed horizontally across the precipitator cells by means of a trolley.

[0012] KR 101436381 discloses an electrostatic precipitator which can automatically clean hazardous materials collected on a surface of a dust collecting electrode during the operation of the electrostatic precipitator by periodically and alternately driving two dust collecting parts. The hazardous materials are continuously collected by using one dust collecting part when the other collecting part is subject to the cleaning operation.

[0013] US 3156547 discloses an electronic air cleaner containing a wash manifold. During the washing operation, the manifold is moved from one side of the electronic air cleaner to the opposite side. During the movement of the wash manifold, one of various liquids is applied to the cells from manifold. The liquids are supplied to manifold as it moves back and forth through a hose.

[0014] There is a need for an improved air purifier that can be affixed to an air handling unit in demanding environments with high levels of airborne particles. Examples of such demanding environments include construction sites, factories, and industrial facilities. Air impurities originating from construction or renovation work are particularly difficult to handle as they tend to form stubborn calcium deposits on the collection surfaces.

[0015] Manual maintenance and cleaning of the collector plates of an electrostatic air purifier is not always possible due to lack of know-how, personnel or facilities. Thus, there is a further need for developing an air purifier that better tolerates accumulation of dust on its surfaces without any substantive deterioration of purification efficiency.

[0016] There is a need to make the cleaning and washing of an electrostatic precipitator easier and to increase the maintenance intervals. [0017] At least some embodiments of the present invention are intended to overcome at least some of the above discussed disadvantages and restrictions of the known air purifiers.

SUMMARY OF THE INVENTION

[0018] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0019] According to a first aspect of the present invention, there is provided an air purifier module, comprising: at least one air cleaning unit, comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow; wherein all creepage distances in the module are at least 2 mm/kV, preferably at least 3 mm/kV.

• Various embodiments of the first aspect may comprise at least one feature from the following bulleted list:

• All creepage distances in the module are in the range 2 to 5 mm/kV.

The voltage between the collector plates is less than 60 kV, preferably in the range from 10 to 20 kV.

• The voltage between the collector plates is in the range from 10 to 20 kV, and all creepage distances in the module are in the range from 20 to 60 mm. · All creepage distances in the module are at least 5 mm/kV, preferably at least 10 mm/kV, such as 10 to 20 mm/kV, and the material of the metal parts of the ionizer is stainless steel.

The ionizer comprises a net of electrodes having a general shape of a needle or a cylinder or a cone. · At least 90 % of the lateral surface of said electrodes, preferably substantially the entire lateral surface of said electrodes, is coated with an electrical insulator material.

The tips of the electrodes are not coated with an electrical insulator material. • The ionizer comprises a net of electrodes having an elongated overall shape.

• Each electrode comprises a body part and a tip part extending from said body part and being thinner than said body part.

• The tip part comprises or consists of a metal wire that has been partially coated with an electrically insulating material so that only a distal end of said tip part exhibits a bare uncoated metal surface.

• The thickness of the metal wire is less than 1 mm, preferably less than 0.2 mm.

• The tip part is connected to the body part via a spring, and said spring comprises or consists of a coiled metal wire that has been coated with an electrically insulating material.

The material of the metal wire is stainless steel.

• The ionizer comprises: a set of ionizer tubes forming a honeycomb cell structure; and a net of electrodes having an overall elongated shape, each of the electrodes being at least partially inserted in the middle of one of the ionizer tubes in the honeycomb cell structure.

• The air purifier module further comprises a washing system integrated into each air purifier module and comprising at least one nozzle that is configured to jet a cleansing solution towards said at least one air cleaning unit with a pressure that is larger than 50 bars, preferably larger than 80 bars. · The material of the metal parts of the ionizer and the collector plates is stainless steel.

• The air purifier module further comprises means for parallel and/or serial assembly with further air purifier modules.

[0020] According to a second aspect of the present invention, there is provided an air purification system, comprising several air purifier modules according to the first aspect arranged in parallel and/or in series.

[0021] Various embodiments of the second aspect may comprise at least one feature from the following bulleted list: • A high voltage source has been connected to the ionizer and the collector by means of insulated tubes, such as metal tubes, wherein the insulated tubes, or insulated metal tubes, have been slid inside insulated connector parts of the air cleaning unit in particular so as to form a water tight connection, and wherein spring loaded connectors secure the connection.

[0022] According to a third aspect of the present invention, there is provided an air handling unit, comprising: the air purification system according to the second aspect; a blower configured to blow air through the air handling unit; and a heating element and/or a cooling element configured to heat and/or cool the air. [0023] According to a fourth aspect of the present invention, there is provided use of the air purifier module according to the first aspect for purifying air originating from a building site or a construction site.

[0024] Various embodiments of the fourth aspect may comprise at least one feature from the following bulleted list: · Said air comprises oil droplets as impurities.

[0025] According to a fifth aspect of the present invention, there is provided a method of purifying air, wherein the air purifier module according to the first aspect is used.

[0026] At least some embodiments of the present invention provide significant advantages. The present air purifier module can replace mechanical filters in an air handling unit. In some embodiments, size of the present module is comparable to the size of a mechanical filter with the same air flow capacity. High purification efficiency can be reached even on days when air quality is at a low level and particle mass concentrations are high. [0027] At least some embodiments of the present invention provide advantages on markets where the quality of outdoor air is poor and the use of mechanical fibre filters is challenging. In developing countries the operation and maintenance culture is not as developed as in western countries, and there is a demand for purifiers not requiring frequent manual maintenance. [0028] At least some embodiments of the present invention provide lower lifetime costs, continuous high purification efficiency and ease of use.

[0029] At least some embodiments of the present invention provide better tolerance with regard to accumulation of dust on the collector plates and other parts of the system. [0030] In at least some embodiments of the present invention, ozone production is reduced.

DESCRIPTION OF THE DRAWINGS

[0031] FIGURE 1 illustrates an air cleaning unit comprising an ionizer and a collector according to an embodiment of the present invention.

[0032] FIGURE 2 illustrates in more detail an air cleaning unit comprising an ionizer, a collector and electrical insulation of support rods.

[0033] FIGURE 3 illustrates in more detail an air cleaning unit comprising an ionizer and a collector. The head (tip) of each ionization needle is non- isolated. The sidewalls of the ionization needles have been coated by an electrical insulator material. The needles are located inside ionization pipes 360.

[0034] FIGURE 4 illustrates in more detail a high voltage connector according to an embodiment of the present invention.

[0035] FIGURE 5 illustrates air cleaning units connected to each other (in series) with high voltage connections.

[0036] FIGURE 6 illustrates air cleaning units connected to each other (in series) with high voltage connections in more detail.

[0037] FIGURE 7 shows two embodiments of an ionization net comprising ionization needles, and an ionization cell structure of an ionizer according to an embodiment of the present invention. The ionization needle net is inserted into the cells in order to form the ionizer.

[0038] FIGURE 8 illustrates a collector in which the distance between adjacent collector cells is 5.5 mm. [0039] FIGURE 9 illustrates an air purification system capable of holding six air cleaning units and three washing systems. Four air cleaning units and one washing system are shown. The ready system will comprise three air purifier modules in parallel, on top of each other. [0040] FIGURE 10 illustrates a partly assembled air handling unit comprising two air cleaning units (consecutively in series) and a filter (in the left end of the unit).

[0041] FIGURE 11 is the air handling unit of FIGURE 10 with a washing system assembled between the two air cleaning units.

[0042] FIGURE 12 illustrates a large air purification system capable of holding four air purifier modules (three are shown), in a parallel matrix arrangement to provide a large face area. Each air purifier module comprises two air cleaning units and a washing system between them.

[0043] FIGURE 13 illustrates as a side view two air purifier modules with two air cleaning units in each module. [0044] FIGURE 14 illustrates four air purifier modules with two air cleaning units in each module and a washing system on both sides of the air cleaning units.

[0045] FIGURE 15 illustrates four air cleaning units and a washing system.

[0046] FIGURE 16 illustrates an ionization net according to an embodiment of the present invention. [0047] FIGURE 17 illustrates an individual ionization electrode according to an embodiment of the present invention.

[0048] FIGURE 18 illustrates a spring-shaped tip of an ionization electrode according to an embodiment of the present invention.

EMBODIMENTS

[0049] DEFINITIONS [0050] In the present context, the term“air cleaning unit” refers to a unit comprising an ionizer and a collector. The term“collector” refers to one or more collector surfaces, for example a set of parallel collector plates.

[0051] In the present context, the term“air purifier module” refers to a module comprising two air cleaning units and, optionally, a washing system between the two units.

Examples are shown in FIGS. 10 and 11.

[0052] In the present context, the term “air purification system” refers to an assembly of several air purifier modules. In such an assembly, individual modules are arranged in parallel to form a matrix with a larger face area (examples of parallel arrangements are shown in FIGS. 9 and 12) and/or in series. In a serial configuration, outlet air coming from the frontmost air purifier module is lead to an inlet of the subsequent air purifier module for further purification.

[0053] In the present context, the term“air handling unit” refers to a unit comprising an air purification system, which system comprises at least one air purifier module, and further functionalities for transferring and treating air. Examples of such additional functionalities include blowers, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Exemplary embodiments comprising a filter (such as 1130) are shown in FIGS. 10 to 12.

[0054] In the present context, the term“creepage distance” means the shortest distance along the surface of a solid insulating material between two conductive parts.

[0055] The invention provides a modular air purification system with an improved structure and versatility.

[0056] The air purification system of the present invention is based on electrostatic precipitators. [0057] The air purification system of the present invention comprises one or more air purifier modules. In one embodiment, the module comprises two air cleaning units, each having an ionizer and subsequently a plurality of collector plates having walls and forming channels between them for receiving an air flow. Air flow can be horizontal or vertical as well. [0058] In one embodiment, there is a washing system 920, 1120 in between said two air cleaning units (as shown in FIGS. 9, 11 and 12), the washing system comprising a nozzle that is configured to jet a cleansing solution towards one or both of the air cleaning units. Preferably, there is a washing system integrated into each air purifier module. In one embodiment, the nozzle that is configured to jet a cleansing solution towards the air cleaning (or each air cleaning unit) is capable of achieving a pressure that is larger than 50 bars, in particular larger than 80 bars.

[0059] The air purifier module preferably comprises means for parallel and/or serial assembly with further similar air purifier modules.

[0060] In one embodiment, in an air purifier module the ionizer comprises a net of electrodes having a general shape of a needle or a cylinder or a cone; at least 90 % of the lateral surface of said electrodes, preferably substantially the entire lateral surface of said electrodes, is coated with an electrical insulator material; and the tips of the electrodes are not coated with an electrical insulator material.

[0061] In one embodiment, rails are used for sliding air purifier modules sideways to place inside an air purification system. High voltage is supplied to the modules by connecting the modules to each other by connecting rods. When the modules are slid to place, the respective rods are slid into the connection points in the modules. The connection of the outermost modules (the first module and the last module in a row of modules) to high voltage is realized by means of connecting rods located outside the casing.

[0062] In one embodiment, air cleaning units slide on rails from side. High voltage is connected between units by means of connecting rods which slide into the connectors in the air cleaning units preferably to form a water tight connection when the units are slid together. High voltage to the last units is connected by rods located outside the casing. The connecting rods comprise an insulated metal tube. The connectors in the air cleaning units comprise a banana plug.

[0063] One embodiment comprises connecting rods having an insulated metal tube and connectors in purifier units which have a banana plug.

[0064] If the system comprises several modules, they can be assembled in series, i.e. consecutively in the direction of air flow, to achieve higher purification efficiency. The modules can also be assembled in parallel (to a matrix) to form an air purification system with a face area that is larger than a face area of a single air purifier module. They can even be assembled by using both serial and parallel configurations.

[0065] Preferably, each air purifier module comprises a washing system and one or more air cleaning units on one or both sides of the washing system. In one embodiment, there is one air cleaning unit on each side of a washing system. In another embodiment, there is a matrix of air cleaning units, e.g. a 2 x 2 matrix or a 1 x 2 matrix, on each side of a washing system.

[0066] An air cleaning unit of the present invention comprises an ionizer and a collector. The ionizer is located in front of the collector in order to charge the particles and to enable the collector to trap those particles. The ionizer comprises charged electronic surfaces or needles, which generate electrically charged air or gas ions which attach to airborne particles. The collector includes electrostatic collector plates.

[0067] FIGURE 7 shows two embodiments of an ionization net comprising ionization needles, and an ionization cell structure of an ionizer according to an embodiment of the present invention. The ionization needle net is inserted into the cells in order to form the ionizer.

[0068] In FIG. 7, the ionization net 710, version 1, is manufactured by a laser cutting method, and comprises a grid of bars with sharp edges. The ionization net 720, version 2, comprises a grid of bars with a rounded shape, which is advantageous in terms of reduce ozone production. The ionization cell structure 730 shown in FIG. 7 (upper right) is a honeycomb structure. Each cell of the honeycomb is a tube into which an individual ionization electrode (the tip part of it) is placed. The honeycomb structure is advantageous as it provides a maximally large open area for air flow, which enables a slow flow rate and and thus an improved purification result.

[0069] FIGURE 16 illustrates an ionization net 160 according to an embodiment of the present invention. The net comprises a grid consisting of two sets of bars. The bars 161 are perpendicular to the bars 162. The electrodes 163 are attached to the bars. The tips of the needle-formed ionization electrodes 163 are configured to be located in the middle of the tubes (cells) of a honeycomb cell structure, such as the honeycomb cell structure 730 shown in FIG. 7 (the upper right figure). The bars 161, 162 are rounded and do not comprise any sharp edges. Preferably the bars have been manufactured by using a welding method and not for example a laser cutting based method. Sharp edges would increase ozone production and therefore shall be avoided.

[0070] FIGURE 17 illustrates an individual ionization electrode 170 according to an embodiment of the present invention. The electrode comprises an electrode body 171 and a spring part 172. The electrode body 171 is connected to a bar 174 of the grid. The spring part 172 comprises a tip part 173. The spring part is made of a thin metal wire, which preferably is made of stainless steel. The thickness of the wire is for example 0.1 to 0.5 mm. The tip part 173 is retained in place by means of spring force. Once the entire ionization net has been assembled and the electrodes attached, the net is coated by an insulating coating layer. The distal ends of the tip parts are exposed by cutting the wires, whereby the cross-section of the wire and a bare metal surface is exposed.

[0071] In one embodiment, a wire comprising a thin tip part may be attached to an electrode body by welding.

[0072] Preferably, the spring part folds around the body part and they have a common central (longitudinal) axis.

[0073] FIGURE 18 illustrates a spring part 182 of an ionization electrode according to an embodiment of the present invention. The spring part 182 comprises a spring 184, and a thin tip part 183. The distal end 186 of the tip part 183 comprises or consists of a bare metal surface while all other surfaces of the spring part 182 are coated by an electrical insulation material.

[0074] In a particularly advantageous embodiment of the present invention, the ionization electrodes comprise a thin tip part made of metal wire. The metal wire is coated by an insulating coating except for its distal end cross-sectional surface, which is a bare uncoated metal surface. Preferably the diameter of the wire is less than 0.5 mm. Preferably, the exposed bare metal surface has an area of less than 0.2 mm 2 .

[0075] In one embodiment, the ionizer comprises a honeycomb made of 66 mm hexagonal tubes. There is one ionization needle in the middle of each tube. Thus, the distance or gap from the tube wall to the needle is 32 mm. Preferably, the nominal voltage is 14 kV and the maximum voltage is 16 kV. [0076] In one embodiment, the ionization current is in the range 4 to 9 mA.

[0077] In one embodiment, the ionization voltage is in the range 12 to 16 kV.

[0078] In one embodiment, electrode needles 330 of the ionizer are insulated 350 except their tips 340 to minimize ozone production. Such an embodiment is illustrated in FIG. 3.

[0079] In one embodiment, the tip of each ionization electrode is formed by a metal wire which, as a first step, has been entirely coated by an insulating coating and thereafter, as a second step, the end of the wire has been cut to expose a bare metal surface, i.e. the cross-section of the wire. [0080] Preferably, the thickness of the wire is less than 2 mm, for example less than

0.5 mm.

[0081] In one embodiment, the collector plate package is designed to have a separation of 5.5 mm, a voltage of 6 kV and thus a collection efficiency of 95 %.

[0082] The separation of the collector plates is preferably 4 mm to 6 mm, more preferably 5 mm to 6 mm, even more preferably at least 5.5 mm. The advantage of having a separation of at least 5.5 mm is that water droplets are not trapped between the plates during washing, and liquid bridges are not formed.

[0083] The voltage between the collector plates is preferably less than 60 kV, more preferably less than 50 kV, for example 5 to 10 kV. [0084] In one embodiment, all creepage distances in the air purifier module, or at least in a collector of the air purifier module, are at least 2 mm/kV, preferably at least 3 mm/kV, such as 4 to 10 mm/kV.

[0085] In one embodiment, all creepage distances in the air purifier module, or at least in a collector of the air purifier module, are at least 4 mm/kV, preferably at least 10 mm/kV. A creepage distance of at least 10 mm/kV is advantageous when the air to be purified comprises a high concentration of impurities.

[0086] In one embodiment, all creepage distances in the air purifier module, or at least in a collector of the air purifier module, are at least 5 mm/kV, such as 5 to 20 mm/kV. [0087] In one embodiment, the voltage between the collector plates is less than 50 kV, and creepage distances are at least 2 mm/kV.

[0088] In one embodiment, the voltage between the collector plates is less than 60 kV, preferably it is in the range from 10 to 20 kV. Preferably all creepage distances in the module are in the range from about 20 to about 60 mm.

[0089] Collector and ionizer parts must be washable and regularly washed, because coal-based dust and impurities conduct electricity.

[0090] The ratio between effective channel length and distance between the collector plates shall be preferably at least 10, more preferably at least 15.

[0091] The material of the collector plates may be any suitable conducting material, for example a metal or an electrically conductive plastic or an electrically conductive polymer. Suitable electrically conductive polymers include polyfluorenes, polyphenylenes, polypyrenes, polyazulenes, polynaphthalenes, polypyrroles, polycarbazoles, polyindoles, polyazepines, polyanilines, polythiophenes, poly(3,4-ethylenedioxythiophene), poly(p- phenylene sulphide), polyacetylenes, poly(p-phenylene vinylene). Suitable metals include stainless steel and aluminium in any suitable form, such as a plate or a grid.

[0092] Preferably, the material of the collector plates is stainless steel, preferably stainless steel EN 1.4307 or better. This material enables the use of a high pressure, e.g. larger than 50 bars, for spraying a cleansing liquid onto the collector plates and ionizer surfaces. It also makes it possible to use strong detergents, e.g. acidic detergents that are capable of removing calcium deposits, or alkaline detergents.

[0093] In an air cleaning unit, preferably all such metal parts and metal surfaces of the collector and/or the ionizer which are exposed to the air to be purified are made of stainless steel. The advantage is that strong detergents can be used for cleaning said surfaces of the air cleaning unit.

[0094] In an air handling unit, preferably all inner metal parts inside a casing of the air handling unit are made of a same material, most preferably of stainless steel.

[0095] In some embodiments, dispensing of the cleansing solution is performed by applying high pressure. Preferably, the pressure is larger than 50 bars, for example 60 to 90 bars, more preferably larger than 80 bars, for example from 85 to 100 bars. [0096] According to one embodiment, the air handling unit does not contain any active carbon filter so that the pressure drop across the air purification system remains small, preferably below 40 Pa, more preferably below 30 Pa, for example 10 to 25 Pa.

[0097] In some embodiments, the air handling unit receives circulated air.

[0098] In the embodiments in which air circulation is used, ozone removal is preferably applied. Ozone can be removed by using an active carbon filter or a catalyst.

[0099] In some embodiments, the present air purification system is a modular part of an air handling unit. An air handling unit according to the present invention may be further equipped with a mixing chamber, means for recirculating air, and means for reducing ozone concentration.

[00100] In one embodiment, the air purifier module comprising means for parallel and/or serial assembly with further air purifier modules.

[00101] One embodiment provides an air purification system, comprising several air purifier modules as discussed above. They can be arranged in parallel and/or in serial arrangement. Further, in an air purification system, a high voltage source can be connected to the ionizer and the collector by means of insulated metal tubes. Such insulated metal tubes can be slid inside insulated connector parts of the air cleaning unit. To secure the connection, there can be one or more spring loaded connectors.

[00102] One embodiment provides an air handling unit, which comprises an air purification system for example as discussed above with a blower configured to blow air through the air handling unit; and a heating element and/or a cooling element configured to heat and/or cool the air.

[00103] In an air handling unit, the volumetric air flow is preferably in the range 0.5 to 20 m 3 /s, for example 0.7 to 14 m 3 /s. Air velocity is preferably in the range 1.0 to 3.0 m/s, for example 2.0 to 2.5 m/s.

[00104] If the volumetric air flow is in the range 0.7 to 14 m 3 /s, it is preferable to use at least 12, more preferably 16 air purifier modules. 16 air purifier modules (each for example 600 mm x 600 mm) can be arranged so that 4 modules are laid to a 2x2 matrix, and 4 such matrices are then laid in series. In such an arrangement, the face area is 2400 mm x 2400 mm. [00105] According to an embodiment, the flow rate of air is in the range 1200 to 3200 m 3 /h.

[00106] The dimensions of the face area of an air purifier module can be for example: 600 mm (length) x 600 mm (width), or 300 mm x 600 mm, or 600 mm x 300 mm. The depth of an air purifier module can vary in the range 300 mm to 750 mm.

[00107] Preferably, the length of an air purifier module is equal to or less than 600 mm.

[00108] Preferably, the width of an air purifier module is equal to or less than 300 mm. [00109] The mechanical parts of the ionizer and the collector plates should preferably have no sharp edges to minimize ozone production and thus to avoid the use of an active carbon filter.

[00110] The present invention is applicable for purifying indoor air or outside air both in new buildings and in existing buildings. In the latter case, mechanical fibre filters can be replaced by the present technology. Preferably, mechanical fibre filters are not used in an air handling unit according to the present invention.

[00111] The present invention is also applicable for purifying air and process gases at construction sites and manufacturing sites.

[00112] According to an embodiment, the air to be purified contains impurity particles or droplets with a diameter smaller than 1 pm.

[00113] Example

[00114] In this example we used an air purification system comprising two air purifier modules in series. Each module contained an ionizer and a collector. The air to be purified originated from an aerosol generator and contained oil droplets with a diameter smaller than 1 pm as impurities. The ionization voltage was in the range 12 to 16 kV. The ionization current was in the range 4.2 to 8.4 mA. The flow rate of air was in the range 1271 to 3167 m 3 /h. The results are shown in Table 1 below. The purification efficiency was very good: more than 90 % of the impurities were removed. The ozone yields stayed on low levels, below 40 ppb. Table 1. Results

[00115] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[00116] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[00117] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[00118] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[00119] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below. [00120] The verbs“to comprise” and“to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of“a” or“an”, i.e. a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[00121] The present invention can be industrially applied in the field of air purification in centralized ventilation systems, industrial buildings, construction and building sites, commercial buildings and office buildings.

ACRONYMS LIST

AHU air handling unit

ESP electrostatic precipitator

REFERENCE SIGNS

210 electrical insulator 220 creepage distance 230 electrical insulator 240 O-rings

250 plastic nut 260 creepage distance 270 creepage distance 310 ionisating pipes 320 collector plates 330 ionisating needle

340 open head

350 electrical insulator 360 ionisating pipes 370 collector plates

410 plug

420 electrical insulator 430 O-ring

440 electrical conductor 450 O-ring

460 electrical conductor

500 end plug

501 O-ring

502 electrical conductor 503 O-ring

504 electrical insulator

505 O-ring

506 plug

507 electrical insulator 508 electrical conductor

509 electrical conductor

510 plug

511 power supply 710 ionization net, version 1

720 ionization net, version 2

730 ionization cell

910a, 910b, 910c, 91 Od air cleaning units

920 washing system

1110a, 1110b air cleaning units

1120 washing system

1130 filter

CITATION LIST

Patent Literature

JP 2002035641 A

US 4240809

KR 101436381

US 3156547