Electrostatic Precipitator Using Induction Charging

A. Katatani1, H. Hosono2, H. Murata2, H. Yahata2, and A. Mizuno3

1Panasonic Environmental Systems & Engineering Co., Ltd., Japan2Panasonic Ecology Systems Co., Ltd., Japan

3Department of Environmental and Life Sciences, Toyohashi University of Technology, Japan

Abstract—The authors have had an idea that the power consumption in electrostatic precipitators, ESPs, might be decreaseddrastically if particles are touching to a conductive electrode in electric field, and are charged by induction charging. One reason is thefact that, in a corona discharge, most of the energy of accelerated electrons near the discharge electrode is wasted by bombardmentto neutral molecules without ionization. To verify this idea, the authors have carried out an experiment using two-stage-electrodessets. The first set of electrodes is made of the flocking electrode covered with ACF (Activated carbon fiber). DC high voltage wasapplied to the electrodes set. The voltage value was adjusted to be below the corona starting voltage. The second set of electrodesmade of flat plates works as a collector of charged particles. This is designated as “a two-stage ESP with induction charging”.Varying the gas velocity inside the ESP, the collection efficiency of room-particles was measured. The result showed that the ESPwas able to collect particles without corona discharge. This study implies the possibility of ESPs which can minimize the electricalpower consumption.

Keywords—Electrostatic precipitator, electrostatic flocking, re-entrainment, induction charging

I. INTRODUCTION

Electrostatic precipitators (ESPs) have been widely adoptedfor purifying exhaust from motor-vehicle-tunnels or others[1]–[7]. Trend of the development of these ESPs has beento reduce the size by increasing the wind velocity. As a result,power consumption has been increasing recently, as shown in[8], [9].

There are studies on charge and sedimentation of fineparticles. Some reports have shown that particles in diesel-exhaust are charged either positively or negatively [10]–[14].Several studies have indicated that, in many cases, suspendedparticles in air have charge [15]–[20]. For sedimentation of fineparticles inside ESPs, gradient force in non-uniform electric-field plays an important role [21]–[23].

To improve collection efficiency of ESPs, there is a study touse the electrodes with nylon-piles (prepared by electrostaticflocking) that generate strong gradient-force at the tip ofpiles [24]. Furthermore, there are studies reporting on thephenomenon of re-entrainment which is inevitable to ESPs[25], [26]. The re-entrained particles are electrically chargedby induction charging [15], [27]–[30].

Taking these reports into account, the authors have the ideathat the power consumption of ESPs can be decreased drasti-cally if induction charging is used. The purpose of this studyis to clarify the process in which temporarily attached particlesonto the electrostatic-flocking electrodes are re-entrained withinduction charge, and are collected by the electric field.

Through the experimental observation, the new-concept ofESP using induction charging is discussed.

Corresponding author: Atsushi Katatanie-mail address: katatani.atsushi@jp.panasonic.com

Presented at the 3rd ISNPEDADM 2015 (New electrical technologies forenvironment), in October 2015

II. METHODOLOGY

The experimental ESP is composed of the charger in the firststage and the collector in the second stage. To prepare the elec-trode with fibers, electrostatic-flocking is used. The electrode-plates (flocked-plates, hereafter) are used as the charger. Howto make this flocked-plate is described as follows.

The electro-conductive glue (Three-Bond 3303G), which ismainly made from silver-paste and silicon-resin, is applied oneach one side of stainless-steel-plate (SUS304, 36×40 mm,0.4t) as base-plates for electrostatic flocking. Activated carbonfiber (ACF, production code CO6343 made by TORAY) is cutinto the length from approx. 0.1 to 3 mm by using scissorsto make ACF piles. The ACF piles are thrown in a device forelectrostatic flocking, to which dc voltage is applied. Then,some ACF piles contact to the adhesive glue on the surfaceby the effect of circulation-wind in the device, and are finallyfixed to form the flocked-plates.

A part of the craft-process of the flocked-plates is shown inFig. 1.

The layout/electric-circuit of the flocked-plates in thecharger is shown in Fig. 2, where twenty-four flocked-platesare arranged parallel with the gap of 10 mm. Two plates atthe end points are not flocked at all. In addition, the surfacesof twelve flocked-plates at leeward are facing to the oppositedirection of the flocked surfaces at windward.

The applied voltage to the charger was determined accord-ing to the concept to use induction charging that does not wantcorona-discharge from flocked-plates but does need the electricfield strength as strong as possible. Thus, taking into accountthe V-I characteristics in Fig. 3, the voltage of -2.4 kV whichrealizes the maximum electric field strength without formingcorona-discharge, was determined.

The collector consisted of parallel electrodes, and wasplaced downstream of the charger. The shape of all theelectrode-plates in the collector is 94×280 mm (0.4t). Seven

Katatani et al. 135

Fig. 1. Crafting-process of flocked-plates.

Fig. 2. Layout of electrode-plates with electrostatic flocking in the charger.

Fig. 3. V-I characteristic of the charger.

grounded-plates and six energized plates are alternately ar-ranged with 10 mm gap. The applied voltage to the energized-plates is -9 kV, which does not generate corona-discharge.

The schematic diagram of test equipment and the spec-ification of test equipment are shown in Fig. 4 and TableI, respectively. The particles to be collected in this studywere those suspended in the air of the laboratory room. Bymeasuring the wind velocity with the wind velocity meter #12

Fig. 4. Schematic diagram of test equipment.

TABLE ISPECIFICATIONS OF TEST EQUIPMENT

Items Details

Duct (#1, 2, 4, 6, 7) W 121, H 140, L 200 mm (Inside)

Charger duct (#3) Duct; W 121, H 32, L 180 mm (Inside) withslots for fixing electrode-plates

Collector duct (#5) Duct; W 121, H 90, L 300 mm (Inside) withslots for fixing electrode-plates

Fan (#8) MU1238A-11B (Oriental Motor), Quantity; 2(tandem coupled), With a variable frequencycontroller

High voltage powersupply (#9)

MODEL-600F (Pulse Electric), Max. output;DC -15 kV, 30 mA, Stability 0.005%

High voltage powersupply (#10)

APH-10K5N (Maxelec Co.,Ltd.), Max outputvoltage; DC -10 kV, Max current; 30 mA, Rip-ple; 0.02%

Particle counter (#11) KC-01E (RION), Light scattering, Range; 0.3,0.5, 1, 2, 5 over µm, Sampling volume for in-dividual measurement; sample-mode of 283 mL(per 34 s)

Wind velocity meter(#12)

Climomaster MODEL6531 (Kanomax), Mode;1 s measuring & 10 times ave.

Voltage meter &Probe (#13)

Digital multi meter type73303 (Yokogawa), Ra-tio; 1/1000 (FLUKE)

Current meter (#14) Type 201133 (Yokogawa), Range; 0.1, 0.3, 1,3 mA

at the inlet of the inlet duct, the wind velocity in the chargerduct #3 was adjusted with a fan-speed-controller in order toobtain four levels of wind velocity of 2, 5, 8 and 11 m/s. Theconcentration (count-concentration of particle diameter 0.3 µmover) of particles in the room-air was measured by the particlecounter of #11, whose two sampling tubes at the inlet-ductand the outlet-duct were alternately switched, to calculate thecollection efficiency.

The collection efficiency was measured for the three casesof different applied voltages. Each case includes the efficiencywith four levels of the wind velocity.

III. DISCUSSION

A. Case 1: charger -2.4 kV, collector 0 kV

The purpose of Case 1 is to evaluate the collection efficiencyof the charger only. The measured result is shown in Fig. 5

136 International Journal of Plasma Environmental Science & Technology, Vol.10, No.2, DECEMBER 2016

Fig. 5. Collection efficiency of Case 1 (charger; -2.4 kV, collector; 0 kV).

Fig. 6. Collection efficiency of Case 2 (charger; 0 kV, collector; -9 kV).

which indicates the collection efficiency of all the particle-diameters of 0.3 µm over. As the dispersion of three-times-measurement is within ±1% to the average indicated in solidline, there is repeatability. The collection efficiency was lessthan several percent.

B. Case 2: charger 0 kV, collector -9 kV

The purpose of Case 2 is to evaluate the collection efficiencyof the collector only. The measured result is shown in Fig. 6.As the dispersion of three-times-measurement is also within±1% to the average in solid line, there is repeatability. Thecollection efficiency was less than several percent. At the pointof wind velocity 2 m/s, the collection efficiency is almost 25%,which means the extremely-greater value compared to otherlevels of wind velocity. The one of reasons is that the strongerelectric field exists due to forming non-uniform electric fieldaround the vicinity-space of the edges of electrode plates.When the velocity reaches to 5 m/s, the collection efficiencydecreases to almost 7% “with diving”. The one of reasons isthat re-entrainment of collected particles increases due to thefaster wind velocity.

C. Case 3: charger -2.4 kV, collector -9 kV

The purpose of Case 3 is to evaluate the collection effi-ciency of both the charger and the collector, which means the

Fig. 7. Collection efficiency of Case 3 (charger; -2.4 kV, collector; -9 kV).

measurement with electric fields existing in both parts. Thatis; this is the evaluation for the two-stage-ESP.

The measured result is shown in Fig. 7. As the dispersionof three-times-measurement is also within ±1% to the averagein solid line, there is repeatability, too. At the point of windvelocity 2 m/s, the collection efficiency is about 40%, whichmeans the much-greater value compared to other velocitylevels. This tendency is similar to Case 2 of using the collectoronly. Therefore, this is the characteristic strongly affected bythe collector.

The three cases (Case 1 of “voltage to the charger only”,Case 2 of “voltage to the collector only” and Case 3 of“voltage to both”) should be synthetically discussed as follows.

Let X% as the collection efficiency of “charger only” undercertain wind-velocity condition and under certain particle-diameter. Let Y% as the collection of “collector only” underthe same conditions of velocity and diameter.

At this moment, the combined collection efficiency ofoperating both charger and collector simultaneously can becalculated using (1), although it should be under the conditionthat both parts do not interfere in each other.

Z =

(1−

(1− X

100

)(1− Y

100

))× 100% (1)

According to the above mentioned idea, the synthesizedcollection efficiency obtained from calculating the two cases ofcollection efficiency in operating “charger only” and “collectoronly” is shown as the broken line in Fig. 8. The solid line inthe figure indicates the result from the actual measurement,which has already shown, for the comparison.

Here, the following fact can be noticed. That is; althoughthe calculation (the broken line) resembles the measurement(the solid line) in the velocity characteristics of collectionefficiency, the measured characteristic is higher than the cal-culated one in all points. This means that the charger and thecollector are not independent of each other in case of applyingvoltage to both parts. That is; the particles which have con-tacted the charger or been collected at the charger temporarilydo re-entrain with being electrically charged by inductioncharging, then, the charged particles are collected in the secondstage collector with strong electric field. This might be thereason of the higher characteristic of measurement. The ref-erence [31] reports the aspects of particle-sediment/collection

Katatani et al. 137

Fig. 8. Comparison of collection efficiency between measurement andcalculation (charger: -2.4 kV, collector: -9 kV).

Fig. 9. The observation before/after using ACF.

by using one-stage-ESP without corona discharge-parts. Thereport includes that the re-entrained particles with inductioncharging can be re-collected in strong electric field even ifcorona discharge does not exist, which is similar to the resultof this study.

In order to confirm how much or less there is “particle-attaching” to the surfaces of ACF on flocked-plates in caseof using flocked-plates in ESPs, the observation with a SEM(scanning electron microscope, Hitachi S-3600N, gold evap-oration, acceleration voltage 10 kV, magnification 3000) wasdone. The observation results are shown in Fig. 9. The aspectof an ACF surface on an unused flocked-plate is shown in Fig.9(a). On the other hand, Fig. 9(b) displays the aspect of anACF surface under the condition for the ESP to be operatedfor approx. 10 h in the room atmosphere with applying -2.4 kVto the charger.

Comparing (a) with (b), no particle-attaching of room dust

can be seen on (a). On the other hand, small dust of “1 µmunder” on the ACF surface is found on (b). Although it seemsthat the ACF diameters of (a) and (b) slightly differ from eachother, both diameters are within the ACF product-specificationof diameter from 5 to 10 µm.

Any other differences on both figures cannot be found.

IV. CONCLUSION

Using the charger composed of metal plates to beelectrostatic-flocked with activated carbon fiber, a dc voltagewhich does not make them generate corona-discharge was ap-plied to the charger. In addition, the collector to be composedof parallel flat-plates was installed at the position after thecharger to form a two-stage-ESP. Making room-particles inthe atmosphere pass through the ESP, the collection efficiencywas measured by using a particle-counter. As a result, thefollowing points were found.

1) Under the condition of wind velocity 2 m/s, the collec-tion efficiency on all particle-sizes of “diameter 0.3 µmover” was measured as approx. 40% (No generation ofcorona discharge).

2) The above-mentioned collection efficiency was greaterthan the synthesized efficiency calculated by using themeasured efficiency of both “charger only” and “collec-tor only”.

3) The reason is as follows. That is; re-entrained particlesfrom flocked-plates in the charger might be electricallycharged by induction charging, even in case of usingchargers without generating corona-discharge. And theparticles, which obtain electric charge by inductioncharging, can be collected at the leeward collector withstrong electric field. These effects might have an in-fluence on the higher measured efficiency compared tocalculated efficiency.

4) Small room-dust of “1 µm under” on the surface of theactivated carbon fiber in flocked-plates was found.

REFERENCES

[1] N. Sugita, “Electrostatic precipitator: Collection efficiency in 2-stageelectrostatic precipitator (in Japanese),” Journal of the Institute ofElectrostatics Japan, vol. 31, pp. 154–159, 2007.

[2] R. Brandt and I. Riess, “Possibilities and limitations of tunnel-air filtra-tion and portal-flow extractions,” in the 13th International Symposium onAerodynamics and Ventilation of Vehicle Tunnels (conducted by BritishHydrodynamics Research Group), vol. 1, New Brunswick, NJ, August2009, pp. 37–50.

[3] PIARC Technical Committee C3.3 Road Tunnel Operations, “A guideto optimizing the air quality impact upon the environment,” the WorldRoad Association (PIARC), 2008.

[4] V. Ferro, H. Aigner, and C. Barbetta, “Air filtration system in an urbantunnel,” in the 12th International Symposium on Aerodynamics andVentilation of Vehicle Tunnels (conducted by British HydrodynamicsResearch Group), vol. 2, Portoroz, Slovenia, 2006, pp. 547–559.

[5] T. Baba, H. Ohashi, F. Nakamichi, and N. Akashi, “A new longitudinalventilation system using electrostatic precipitator for long vehiculartraffic tunnel,” in the 3rd International Symposium on Aerodynamicsand Ventilation of Vehicle Tunnels (conducted by British HydrodynamicsResearch Group), Sheffield, UK, 1979, pp. 201–226.

[6] T. Baba and K. Okano, “Ventilation system of tsuruga tunnel,” in the4th International Symposium on Aerodynamics and Ventilation of VehicleTunnels (conducted by British Hydrodynamics Research Group), York,UK, 1982, pp. 367–382.

138 International Journal of Plasma Environmental Science & Technology, Vol.10, No.2, DECEMBER 2016

[7] T. Baba, H. Ohashi, F. Nakamichi, E. Inami, and I. Akita, “Recenttrends in ventilation systems of long vehicle tunnels in japan,” in the5th International Symposium on Aerodynamics and Ventilation of VehicleTunnels (conducted by British Hydrodynamics Research Group), Lille,France, 1985, pp. 371–388.

[8] A. Zukeran and K. Yasumoto, “Electrostatic precipitator on fuji elec-tric systems: Collecting nano-pariticles and suppression of particle re-entrainment (in Japanese),” Journal of the Institute of ElectrostaticsJapan, vol. 32, pp. 192–197, 2008.

[9] A. Katatani, H. Hosono, H. Murata, and A. Mizuno, “Reduction of ozonegeneration in an electrostatic precipitator (in Japanese),” Journal of theInstitute of Electrostatics Japan, vol. 32, pp. 222–227, 2008.

[10] B. L. Wesborg, J. B. Howard, and G. C. Williams, “Physical mechanismsin carbon formations in flames,” in Proceeding of the 14th Symposiumon Combustion, Pennsylvania, PA, August 1973, pp. 929–940.

[11] D. B. Kittelson, J. Reinertsen, and J. Michalski, “Further studies ofelectrostatic collection and agglomeration of diesel particles,” SAETechnical Papers, p. 910329, 1991.

[12] M. M. Maricq, “On the electrical charge of motor vehicle exhaustparticles,” Journal of Aerosol Science, vol. 37, pp. 858–874, 2006.

[13] J. B. Gajewski and K. Gatner, “Interpretation of the results of researchon tribocharging in a rotating shaft-oil-lip seal system,” Journal ofElectrostatics, vol. 67, pp. 365–371, 2009.

[14] E. dela Cruz, J. S. Chang, A. A. Berezin, D. Ewing, J. S. Cotton, andM. Bardeleben, “Electrical effect of soot depositions in a co-axial wirepipe flow,” Journal of Electrostatics, vol. 67, pp. 128–132, 2009.

[15] H. J. White, Industrial Electrostatic precipitation. Addison-WesleyPublishing Company, 1963, pp. 331–342.

[16] The Institute of Electrostatics Japan, Handbook of Electrostatics (inJapanese). Ohm-Sha, 1981.

[17] S. Sakata, “Development of anti-electrostatic air ionizer with a low levelof electromagnetic noise and particle generation (in Japanese),” Journalof Japan Association of Aerosol Science and Technology, vol. 17, pp.105–114, 2002.

[18] T. Yoshida, “IX-4 precipitation by filtration (in Japanese),” Journal ofChemical Engineering, vol. 26, pp. 1218–1225, 1962.

[19] Y. Fujitani and S. Hirano, “Health effects of nanoparticles and nanoma-terials (II) methods for measurement of nanoparticles and their presencein the air (in Japanese),” Japanese Journal of Hygiene, vol. 63, pp. 663–669, 2008.

[20] A. Harano, “Single microparticle measurement using an electrodynamicbalance (in Japanese),” Journal of Japan Association of Aerosol Scienceand Technology, vol. 27, pp. 357–364, 2012.

[21] S. Fukuda, “Methods of electrostatic precipitators and the application(in Japanese),” Journal of the Institute of Electrical Engineers of Japan,pp. 1–41, 1930.

[22] The Institute of Electrostatics Japan, Handbook of Electrostatics (inJapanese), new ed. Ohm-Sha, 1998.

[23] S. Masuda, “Electrical properties of dust (I) (in Japanese),” Journal ofthe Society of Powder Technology, Japan, vol. 5, pp. 1238–1245, 1968.

[24] B.-J. Sung, A. Aly, S.-H. Lee, K. Takashima, S. Katsura, and A. Mizuno,“Fine particles collection using an electrostatic precipitator equippedwith electrostatic flocking electrodes as collecting plates,” Journal ofthe Institute of Electrostatics Japan, vol. 30, pp. 89–94, 2006.

[25] K. Yasumoto, A. Zukeran, Y. Takagi, and Y. Ehara, “Suppressions ofparticle re-entrainment from electrostatic precipitator with ac electricfield and particle deposition onto downstream walls (in Japanese),”Journal of the Society of Powder Technology Japan, vol. 43, pp. 198–204, 2006.

[26] H. Kawakami, A. Zukeran, K. Yasumoto, M. Kuboshima, Y. Ehara,and T. Yamamoto, “Diesel exhaust particle reduction using electrostaticprecipitator,” International Journal of Plasma Environmental Scienceand Technology, vol. 5, pp. 179–184, 2011.

[27] S. Masuda, “Electrical properties of dust (II) (in Japanese),” Journal ofthe Society of Powder Technology, Japan, vol. 6, pp. 121–129, 1969.

[28] T. Yamamoto, T. Mimura, T. Sakurai, Y. Ehara, A. Zukeran, andH. Kawakami, “Novel EHD-assisted ESP for collection of low resistivediesel particles,” International Journal of Plasma Environmental Scienceand Technology, vol. 5, pp. 151–156, 2011.

[29] H. Kawakami, A. Zukeran, K. Yasumoto, T. Inui, Y. Ehara, andT. Yamamoto, “Diesel PM collection for marine emissions using doublecylinder type electrostatic precipitator,” International Journal of PlasmaEnvironmental Science and Technology, vol. 5, pp. 174–178, 2011.

[30] S. Masuda and J. D. Moon, “Contamination of discharge electrodes in aprecipitator collecting carbon soot (in Japanese),” Journal of the Instituteof Electrostatics Japan, vol. 6, pp. 320–326, 1982.

[31] A. Katatani, H. Hosono, H. Murata, H. Yahata, and A. Mizuno,“Electrostatic precipitator without using corona discharge—state ofcollected particles on pole-plates—,” International Journal of PlasmaEnvironmental Science and Technology, vol. 10, pp. 35–40, 2016.

Katatani et al. 139