FI129661B - Electrically enhanced air purification - Google Patents

Electrically enhanced air purification Download PDF

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Publication number
FI129661B
FI129661B FI20207172A FI20207172A FI129661B FI 129661 B FI129661 B FI 129661B FI 20207172 A FI20207172 A FI 20207172A FI 20207172 A FI20207172 A FI 20207172A FI 129661 B FI129661 B FI 129661B
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Finland
Prior art keywords
filter
charger
passing
ions
functional
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FI20207172A
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Finnish (fi)
Swedish (sv)
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FI20207172A1 (en
Inventor
Markku Rajala
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Air0 Oy
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Priority to FI20207172A priority Critical patent/FI129661B/en
Priority to PCT/FI2021/000010 priority patent/WO2022084576A1/en
Publication of FI20207172A1 publication Critical patent/FI20207172A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/40—Electrode constructions
    • B03C3/41—Ionising-electrodes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/0027—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours with additional separating or treating functions
    • B01D46/0032—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours with additional separating or treating functions using electrostatic forces to remove particles, e.g. electret filters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/10—Particle separators, e.g. dust precipitators, using filter plates, sheets or pads having plane surfaces
    • B01D46/12—Particle separators, e.g. dust precipitators, using filter plates, sheets or pads having plane surfaces in multiple arrangements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/42—Auxiliary equipment or operation thereof
    • B01D46/44—Auxiliary equipment or operation thereof controlling filtration
    • B01D46/46—Auxiliary equipment or operation thereof controlling filtration automatic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D49/00—Separating dispersed particles from gases, air or vapours by other methods
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/017—Combinations of electrostatic separation with other processes, not otherwise provided for
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/02—Plant or installations having external electricity supply
    • B03C3/04—Plant or installations having external electricity supply dry type
    • B03C3/12—Plant or installations having external electricity supply dry type characterised by separation of ionising and collecting stations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/02—Plant or installations having external electricity supply
    • B03C3/04—Plant or installations having external electricity supply dry type
    • B03C3/14—Plant or installations having external electricity supply dry type characterised by the additional use of mechanical effects, e.g. gravity
    • B03C3/155—Filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/36—Controlling flow of gases or vapour
    • B03C3/368—Controlling flow of gases or vapour by other than static mechanical means, e.g. internal ventilator or recycler
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/38—Particle charging or ionising stations, e.g. using electric discharge, radioactive radiation or flames
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/66—Applications of electricity supply techniques
    • B03C3/68—Control systems therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/82—Housings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/86—Electrode-carrying means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T19/00—Devices providing for corona discharge
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2273/00—Operation of filters specially adapted for separating dispersed particles from gases or vapours
    • B01D2273/30—Means for generating a circulation of a fluid in a filtration system, e.g. using a pump or a fan
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C2201/00—Details of magnetic or electrostatic separation
    • B03C2201/10—Ionising electrode has multiple serrated ends or parts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y02A50/2351—Atmospheric particulate matter [PM], e.g. carbon smoke microparticles, smog, aerosol particles, dust

Abstract

Apparatus (101) for electrically enhanced air purification, the apparatus (101) comprising a frame (103) with intake (105) and outlet (107) and fan (109) for passing air from intake (105) to outlet (107), and a charger (111) for diffusion charging. The apparatus (101) comprises a diffusion chamber (113) and downstream of it, concerning the air flow generated by the fan (109), an electrically essentially non-conducting filter (115) and functional means (125) for controlling ion current escaping from the charger (111) and functional means (123) for controlling rotation speed of the fan (109), and downstream the essentially non-conducting filter (115), an ion trap (119) for removing free ions passing through the filter (115). Method for electrically enhancing air purification. The method uses a ion generator to produce essentially unipolar ions to a space through which particle-ladden air stream flows, which unipolar ions are attached at least to the particles passing through the space, and to the fibers of an electrically essentially non-conducting filter placed downstream of the space, with some unipolar ions passing through the filter, the number of generated ions N being at least 10000 times the number of particles M passing through the space at time t.

Description

ELECTRICALLY ENHANCED AIR PURIFICATION Field of invention The present invention relates to a method and an apparatus for electrically enhanced air cleaning, especially on cleaning with diffusion-charging-based particle-charging and the use of massive amount of free ions produced by the method and by the apparatus.
Background of the invention Using electrical particle charging for improving air cleaning unit efficiency is a well-known technology.
US7 513,933 B2, StrionAir, 17.8.2006, describes a method for operating an air filter assembly including: providing motive force to produce an air flow along a flow pathway, corona precharging particles in the air flow to produce precharged particles, polarizing a fibrous filter to act in symbiosis for enhancement of filtration efficiency by action upon the precharged particles and directing air flow across the fibrous filter including the precharged particles for enhanced removal thereof, wherein the step of polarizing the fibrous filter includes creating a potential difference between an insulated electrode at an upstream position with respect to a downstream conductive electrode, the downstream conductive electrode being in physical contact with the fibrous filter media in plurality of locations evenly distributed over the entire surface of the filter media.
The publication fails to give information in structural details, throw- away distance, CADR or anything similar.
US 6,364,935B1A, Blueair AB, 6.5.1997, describes a device for cleaning of a gaseous fluid from particles present in said fluid, comprising: a permanently positive or permanently negative high o voltage source; a filter spaced apart from said source, said filter comprising a fine filter medium O composed of fibers having a fiber diameter of approximately 1 micron or greater, and an 2 average spacing between said fibers of approximately ten times said fiber diameter, said fibers S being easily polarized when subjected to an electric charge; means for passing a flow of said E 25 fluid past said high voltage source and through said filter; said filter further characterized by an N absence of external charging means other than said particles passing through said filter.
The S invention fails to talk about treatment of free ions downstream the filter and it also fails to talk O about the number of free ions compared to the number of particles.
US 4,624,685, Butrns & McDonnell Engineering Co, 25.11.1986, describes a process for optimizing the power consumption of electrostatic precipitators communicating with a boiler or the like includes a load indexed signal fed forward to a field power controller to approximate the required power levels. An optical transducer is provided in the boiler stack for monitoring the emissions therefrom and feeds back a signal to the controller proportional to the emission from the stack to trim the power level. The controller incrementally adjusts the field power by comparing the opacity generated signal to a continuously optimized limit in order to thereby optimize the power consumption by lowering and raising the field power in response to changes in the opacity. The invention relates to conventional electrostatic precipitators using field charging to charge particles and does not tell about the use of excess free ions. One should note that in a conventional electrostatic precipitator with collection plates, free ions are effectively collected by such collection plates and free ions hardly exist in the apparatus downwards the particle charging unit.
DE3048979 (Al), Thyssen Industrie, 28.10.1982, describes an electrostatic filter which consumes relatively little power and maintains a minimum purity of outgoing waste gas and smoke from smelting processes. The instantaneous concentration of dust in the clean outgoing gas is measured and the filter's high voltage adjusted so as to keep the concentration roughly constant. The voltage is increased if the dust concentration increases and reduced if the concentration reduces. The filter consists of several filtering stages. The invention describes the use of conventional electrostatic precipitation and a key motive for the invention is to avoid breakdown between the filter electrodes. The publication neither talks about free ions nor the number of free ions compared to the number of particles.
Prior-art has technical problems in either not using diffusion charging or understanding the o need for massive ion production and treatment of free ions.
S N Brief description of the invention
O LO The object of the present invention is to provide a method and apparatus so as to overcome or
N r 25 at least alleviate at least some prior art disadvantages. The objects of the present invention are Ao a N achieved with an apparatus according to the characterizing portion of claim 1 and a method . an . .
= according to the characteristic portion of claim 6.
oO
N S The art of collecting charged particles is well-known. Conventional electrostatic purifiers apply field charging which is charging by unipolar ions in the presence of a strong electric field. Such electric field is generated e.g. in a corona charger by the corona electrode and an opposite electrode which is an electrode in the same electrical circuit but in another potential than the corona electrode, being situated a few centimeters from it. The electric field is generated essentially perpendicular to the stream of particle-ladden air to be purified. The ‘another potential’ is most commonly a zero electrical potential.
With the current method the opposite electrode does not work as a collection electrode but soiling of the opposite electrode by particles is avoided as much as possible. lons are produced to a narrow space bertween the first electrode and the second electrode, the first electrode being typically a high-voltage corona electrode, like corona needle, multiple corona needles or corona wire, and the second electrode being at zero potential or at some other electrical potential different from the potential of the first electrode. The first and second electrodes are placed essentially perpendicular to the air stream of the particle-ladden air to be purified. The speed of the air between the electrodes is such that essentially all particles and and a major share of the ions are captured by the air stream and transferred to a diffusion chamber placed downstream the gap formed by the charging electrodes. In the diffusion chamber the particles and ions are effectively mixed and particles form an electric charge. The amount of charge per particle depends on the particle size and in diffusion charging the number of elementary units of charging acquired is shown in Table I.
Table !. Number of elementary units of charges acquired for different particle diameters Particle diameter (mm) Approximate number of elemntary units of charge
O S N
S 0
N , =
N s 16320
N oO
N & When an ion collides with a particle, it sticks, and the particle acquires its charge. Particles mixed with unipolar ions become charged by random collisions between the ions and the particles. The process is called diffusion charging. Diffusion charging is more efficient than field charging when charging of ultrafine particles is considered. We have found that in order for the diffusion charging to be efficient, the number of ions produced by the charging unit, N [1/s] must be at least 10 000 times, more preferably at least 100 000 times and most preferably at least 1 000 000 times the number of particles entering the diffusion chamber M [1/s]. Producing ions at such rate is an essential feature of the present invention. Free ions which have not been acquired by particles, further flow into a mechanical filter placed downstream the diffusion chamber. It has surprisingly been found that such filter loading by unipolar ions tends to improve the capture of charged particles by the filter. Without sticking to any particular theory, we assume that when the filter is essentially electrically non-conducting, ions are attached on the filter surface as well as inside the filter. Unipolar ions tend to repeal each other and on and in the filter, small, local electrical fields are formed which improve capturing charged particles by the filter.
Some ions may propagate through the filter and enter air outside the space where particles are removed from the particle-ladden air. The effect of ions in air to human health is not well understood. Some studies claim that negative ions in the air have positive effects and positive ions in the air have negative effects to the human health. Easier is to understand that free ions in the air attach to the particulate matter in the air and charge it, and such charged particles are then collected to surfaces, like room walls and ceiling, etc. Whilst such particle removal may have a positive effect on the human health, they effectively increase surface soiling by N particulate matter, which is a largely undesired effect. The method of electrical enhancement 5 presented in the current invention, comprises a method for removing the free ions from the air = flow by using an ion trap. Such ion trap is placed downstream the filter in the flow of the - 25 particle-ladden air. The method may also comprise purification of the air by an activated carbon S filter and such activated carbon filter may be placed either downstream or upstream the ion = trap. Activated carbon filter effectively removes any ozone (Os) generated in the ion-producing Q charger. & The ion trap may be based on collecting free ions with the help of an electrical field. In such method an electrical field is produced, either by one pair or several pairs of electrodes which are placed essentially perpendicular to the air flow. The electrodes are placed to different electrical potentials and an electrical field is formed between them. Electrical field forces the free ions to be collected on the electrodes and further zeroed. The ion trap may be switched to be either on or off, depending on the user’s wish.
The present invention thus descibes a method for electrically enhancing air purification. The method uses a ion generator to produce essentially unipolar ions to a space through which particle-ladden air stream flows. Unipolar ions are attached at least to the particles passing through the space, and to the fibers of an electrically essentially non-conducting filter placed downstream of the space. Some unipolar ions will pass through the filter. Number of ions generated in the ion generator, N is at least 10000 times the number of particles M passing through the space at time t. Characteristic for the present invention is that unipolar ions are produced by a corona charger having corona voltage of 10 kV or smaller, preferably maximum 8,5kV, which is considered to be a safe high voltage level in some countries, especially concerning production of ozone (03) by a corona charger. When designing an apparatus based on the method of the present invention, the ion current generated by the charger may essentially be calculated by following equations: Mv (1) V,=4/3xmx(d,/2)' (2) N 20 I =MxexC (3)
N © where N M is particle flow through the space [1/5]; E H is mass flow of particles passing through the space [g/s]; N p = is particle density [g/cm?]; V, is volume of a single particle [cm]; N d, isthe average diameter of the particles passing through the space [cm]; I. isthe ion current (corona current) generated by the charger (111) [A]; and C is the multiplication coefficient with minimum value of ten thousand (10000).
At the design, the calculated ion current may be compared with the current carried by the charged particles, which may be calculated from Equation (4). I.=M=xexN, (4) where N, is the average number of elementary charges on particle (see Table |).
For accurate results, one should know the particle size distribution in the particle-ladden air. In reality this is seldom the case. A reasonable accuracy can be achieved by assuming all particles to be born in combustion engine with average diameter of 100 nm. Such particles may carry four elementary carges per particle.
Mass flow rate, uu, of particles may be calculated from the flow of particle-ladden air, V [m*/h] with particle concentration Cpy [ug/m?] by Equation (5). = 19 (5) 3600 s Example of designing the ion current I. We assume the average particle concentration to be 100 ug/m?, which may be a typical case in highly polluted areas in Asia and Europe and assume the average particle diameter to be 100 nm, which gives us the following ion currents for different flows of particle-ladden air in the present invention. lon currents are compared with electrical currents carried by particles in the particle-ladden air. Table II lon current for apparatus design for different air streams of particle-ladden air with
O O average particle concentration of 100 ug/m* and 100 nm average particle size and particle O 20 density of 2 g/cm?, and multiplication coefficient of 100 000. Reguired power is calculated for O 8,5 kV high-voltage module. = a Air flow (m3/h) lon current (HA) Current carried by Power (W) N particles (LA) S | ow | 8 | oo | 06 |
S 3
N ww | aw | 4 | osa | om | om |e om | sm | cm | s | 130 | oe» | sa | 5 Brief description of the figures In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which Figure 1 shows a schematic view of mechanics of the apparatus in one embodiment of the present invention; Figure 2 shows a schematic view of electronics of the apparatus in one embodiment of the present invention; N Figure 3 shows a typical relation between the high voltage applied to a corona charger and the
O N . .
& 10 lon current generated by it; & I Figure 4 shows a schematic view of a charger used in one embodiment of the present invention; Ao - and
N
NN ~ S Figure 5 shows a schematic view of an ion trap based on removing free ions with the help of an
O N electrical field used in another embodiment of the present invention.
Detailed description of the invention Figure 1 shows a schematic view of mechanics of the apparatus 101 for air purification in one embodiment of the present invention.
The apparatus 101 for electrically enhanced air purification comprises a frame 103 with an intake 105 for particle-ladden air, with the particle mass flow rate 4, which mass flow rate gis related to the particle concentration Cem in the space where the intake 105 of apparatus 101 is.
The apparatus 101 further comprises an outlet 107 for air purified in the apparatus 101. A fan 109 passes air from intake 105 to outlet 107. In Figure 1, a charger 111 for generating unipolar ions to the air flow passing through the apparatus 101 is placed downstream (concerning the air flow generated by the fan 109) the fan 109, but it may also be placed upstream the fan 109. Charger 111 generates unipolar ions for diffusion charging of particles in the particle-ladden air entering the diffusion chamber 113, placed downstream the charger 111. In diffusion chamber 113 ions produced by charger 111 and particles in the air, having mass flow rate u, are effectively mixed together.
Downstream of the diffusion chamber 113, an electrically essentially non-conducting filter 115 and optionally an activated carbon filter 117, are placed.
Apparatus 101 also comprises functional means 125 for controlling ion current escaping from the charger 111 and functional means 123 for controlling rotation speed of the fan 109. The apparatus 101 also comprises functional means 129 for main control of the apparatus 101. Downstream the essentially non-conducting filter 115, the apparatus 101 comprises an ion trap 119 for removing free ions passing through the filter 115. The optional activated carbon filter 117 may be placed upstream or downstream the ion trap 119. At the outlet 107 of apparatus o 101 the mass flow rate of particles, u, is essentially zero, or at least 70% smaller than mass flow O rate gy at the intake 105 of apparatus 101. 2 0 In one embodiment of the current invention, the ion trap 119, placed downstream of the filter E 25 115, comprises means 127 with or connected to an electrical current sensor 131 for measuring N the current carried by free ions entering the ion trap 119. 3 S It is obvious that the functional means 123, 125 and 129 may also situate in one physical device.
In Figure 1 they are drawn separately to clarify the different functions reguired the apparatus 101 according to the present invention.
In another embodiment of the present invention the means 125 for controlling ion current escaping from the charger 111 comprises means for setting output voltage of a high voltage module 133. The ion current escaping from a corona charger 111, driven by the high voltage module 133, is highly unlinear as can be seen from Figure 3. The figure can be used to develop a general equation (6) for designing the required high voltage of the corona charger 111 when the ion current is known. log(L)=C, Hv*(Vuv Viper) (6) where both ion current I. and Vv, the high voltage of the high voltage module, is given in arbitary units [a.u.] and where Czv is the correlation coefficient between the logarithm (10- base) of the ion current I. and the high voltage Vuvand Vg. is the offset voltage below which the ion current is essentially zero. In another embodiment of the present invention, the maximum volumetric flow through apparatus 101 is 1500 mYh and the maximum corona voltage Vuvis 8.5 kV. The functional means 123 for controlling the rotation speed of the fan 109 set the fan speed (i.e. volumetric flow of air generated by the fan 109) to 1500, 1200, 900, 600 or 300 m>/h. Particle concentration Cpy at the intake 105 of apparatus 101 is 100 mg/m3. Using Table | one gets the required ion currents Ic and from that one can calculate the set values of the high voltage, Viv., taking into account that the maximum high voltage is 8.5kV. The results are shown in Table III Table III Set values for the high voltage Vuvof the high voltage module 133 in one embodiment o of the present invention
N & & Fan speed [m3/h] Corona current I. [uA] High voltage Vic [kV] :
LO “© eo TA
I E was
N O
N The control voltage for the fan 109 for generating different volumetric flows is usually linear, so converting the control voltage (with maximum of e.g. 15 VDC) to the control voltage of the high voltage module 133 requires typically an inverting amplifier comprising offset with another inverting amplifier with gain -1. For simplicity reason both functions are integrated to a single functional amplifier 201 in Figure 2.
Figure 2 shows a schematic view of electronics of the apparatus 101 in one embodiment of the present invention. The apparatus 101 comprises a functional amplifier 201. The input of the functional amplifier 201 is connected to the control signal of the fan 109 provided from the terminal 223 of the functional means 123 for controlling the rotation speed of the fan 109. The output of the functional amplifier 201 is connected to the control input of the high voltage module 133 and the output of the high voltage module 133 is connected to the charger 111.
Apparatus 101 may also work in an automatic mode, where the concentration of particles of the space to be purified determines the speed of fan 109 and thus also the control voltage of the high voltage module 133. Apparatus 101 comprises a functional hysteresis amplifier 203 with input 1 connected to one pin in terminal 229 of functional means 129 for controlling the apparatus 101 and input 2 is connected to a particle sensor 205. Appatarus 101 also comprises another functional hysteresis amplifier 207 with input 2 connected to another pin in terminal 229 of functional means 129 for controlling the apparatus 101 and input 1 connected to a particle sensor 205, and outputs of the functional hysteris amplifier 203 and functional hysteris amplifier 207 are connected to different pins in terminal 229 of the functional means 129 of controlling the apparatus 101.
The functional amplifiers 203 and 207 described above tell the functional means for controlling the fan speed 123, if the fan speed setting needs to be increased, kept as it is, or decreased.
N The functional amplifiers described may be realized by using analog or digital technigues or 5 such functions may be realized by software. The functional means for control, 123, 125, 129 and 0 127 may be realized separately or they may be separate functions in a single controller.
I 25 Controllers for both purposes comprise embedded controllers, card computers, computers, a programmable logics and similar devices.
= S In one embodiment of the present invention the charger 111 is a corona charger, the schematic O view of which is shown in Figure 4. Charger 111 comprises frame 405 through which air flow generated by fan 109 is blown. Two opposite ends of the frame 405 have an electrical insulation piece 403, to which piece 403 a high-voltage rail 407 is attached. Corona needles 409 are attached to the rail 407, so that they are in electrical contact with it. The hgh voltage rail 407 and the frame 405 are not in electrical contact with each other. In the embodiment of Figure 4, air is blown through the charger 111 from two slots, both having an area of A/2 and thus the total area for air flow is A. Air blows through it with speed var lons escaping from the tips of the corona needles 409 move towards the counter electrode, which in the case of Figure 4 is the wall of frame 405, with speed Vion. Speed Vion depends on the distance from the tips of needles 409 to the wall of frame 405 (the high-voltage rail 407 and frame 405 are connected to different potentials of high-voltage source 133), and on the electrical potential which the high-voltage generator 133 produces to the high-voltage rail and further to corona needles 408. ZxV nuv Vv, ————— 7 ion d ( ) where Z is the electrical mobility of the ion [m?/Vs] Vuv is the value of high voltage [V] d is the distance from the corona tip to the nearest wall of the frame [m] The reguired area size A can be designed when we know the width w of the wall of frame 405 which works as the counter electrode for corona needles 409. lons escaping from corona tips 409 must fly with the air flow having speed var so that the electrical mobility Z does not get them to hit wall of frame 405. Taking the boundary conditions into account, one gets the value
O N 20 for the air flow area A.
N O , © As CV (8) N Zx*V yy FW = > And taking into account the length of the corona tip, x, one can calculate the maximum length
N ™~ Imax Of a rectangular gap having area A/2.
S
O A N I =— 9 max d+x ( )
The equations show that the air flow area A and thus the maximum gap length 1,1ax need to be calculated for the minimum volumetric flow through the apparatus 101. For the boundary conditions of Table III we can thus calculate the maximum gap length to be about 300 mm when the distance d is 25 mm and the length of the corona needle is 5 mm. Mobility of a negative ion is 1.6*10* m?/Vs. In another embodiment of the present invention, the ion trap 119 is based on collection of ions with the help of an electrical field. Schematic view of such construction is shown in Figure 5. lon trap 119 comprises a frame 503, two opposite ends of the frame 503 being electrical insulators 505. The structure comprises multiple plates and their adjacent plates 507, 509 which are connected to different potentials of a direct-current voltage source 501. Switch 511, operated by means 513, can be switched to provide an electrical potential difference or eguivalent potentials to the plates 507, 509 and thus ions entering the ion trap 119 are either captured or let pass. The required voltage Vso; to be generated by voltage source 501 can be calculated when we know the maximum volumetric flow through the ion trap 119, length I; of the ion trap 119 in the direction of the air flow, the area of air flow through the ion trap 119 and distance d,.p between the plates 507 and 509. vote dat di 119) Axl *Z with the values of Table III, the minimum voltage between the plates 507 and 509 in ion trap 119 is less than 35 VDC when I; is 10 mm, distance d,., is 50 mm and air escape area A; of the S ion trap 119 is 200 cm”. 2 It is apparent to a person skilled in the art that as technology advances, the basic idea of the a invention can be implemented in various ways. The invention and its embodiments are E therefore not restricted to the above examples, but they may vary within the scope of the N 25 claims.
S S

Claims (9)

Claims
1. Apparatus (101) for electrically enhanced air purification, the apparatus (101) comprising a. aframe (103) with intake (105) and outlet (107); b. a fan (109) for passing air from intake (105) to outlet (107); c. acharger (111), placed downstream or upstream the fan (109), for diffusion charging of particles, by unipolar ions generated by charger (111) to the air flow passing through the apparatus (101), the air flow being generated by the fan (109); d. downstream the charger a diffusion chamber (113); e. downstream the diffusion charger (111), an electrically essentially non-conducting filter (115); f. functional means (125) for controlling ion current escaping from the charger (111); and g. functional means (123) for controlling rotation speed of the fan (109), characterized in that h. the apparatus (101) comprises downstream the essentially non-conducting filter (115), an ion trap (119) for removing free ions passing through the filter (115).
2. Apparatus (101) as in claim 1, characterized in that the means (125) for controlling ion current escaping from the charger (111) comprises means for setting output voltage of a high voltage module (133). = 20
3. Apparatus (101) as in any of the previous claims, characterized in that the ion trap (119)
O N placed downstream of the filter (115), comprises means (127, 131) for measuring the current
O Tv carried by free ions entering the ion trap (119).
S I
4. Apparatus (101) as in any of the previous claims, characterized in that the apparatus jami 5 (101) comprises a functional amplifier (201), the input of the functional amplifier (201) being
NN S 25 connected to the control signal of the fan (109) provided from the terminal (223) of the O functional means (123) for controlling rotation speed of the fan (109), and the output of the functional amplifier (201) being connected to the control input of the high voltage module (133), the output of the high voltage module (133) being connected to the charger (111).
5. Apparatus (101) as in any of the previous claims, characterized in that the apparatus (101) comprises a functional hysteresis amplifier (203) with input 1 connected to one pin in terminal (229) of functional means (129) for controlling the apparatus (101) and input 2 connected to a particle sensor (205) and another functional hysteresis amplifier (207) with input 2 connected to another pin in terminal (229) of functional means (129) for controlling the apparatus (101) and input 1 connected to a particle sensor (205), and outputs of the functional hysteresis amplifier (203) and functional hysteresis amplifier (207) being connected to different pins in terminal (229) of the functional means (129) of controlling the apparatus (101).
6. Method for electrically enhancing air purification, characterized in that the method uses a ion generator to produce essentially unipolar ions to a space through which particle-laden air stream flows, which unipolar ions are attached at least to the particles passing through the space, and to the fibres of an electrically essentially non-conducting filter placed downstream of the space, with some unipolar ions passing through the filter and optionally collected by an ion trap. the number of generated ions N being at least 10000 times the number of particles M passing through the space at time t.
7. Method for electrically enhancing air purification as in claim 6, characterized in that the unipolar ions are produced by a corona charger having corona voltage of 10 kV or smaller.
8. Method for electrically enhancing air purification as in any of the claims 6-7, characterized in that the ion current generated by the charger (111) is essentially calculated by equations: i=, pvp! = W = Ya + n « (dy/2)"; & | O [.=Mxecx*C; 5 where z 25 M is particle flow through the space [1/s]; N H is mass flow of particles passing through the space [g/s]; S p is particle density [g/cm]; N v, is volume of a single particle [cm?]; dp is the average diameter of the particles passing through the space [cm]; I. istheion current (corona current) generated by the charger (111) [A]; and
C is the multiplication coefficient with minimum value of ten thousand (10000).
9. Method as in any of the claims 6-8, characterized in that the unipolar ions passing through the essentially electrically non-conducting filter and optionally an activated carbon filter are captured with an ion trap which is placed downstream the essentially electrically non-conducting filter and downstream or upstream the optional activated carbon filter.
N
O
N
O
N oO
I Ao 2
N
NN
N
O
N
O
N
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