PARTICLE CHARGING DEVICE FOR USE IN AN ELECTRIC DUST COLLECTING APPARATUS

The present invention relates to an electric dust collecting apparatus, and more particularly, to a two stage type of electric dust collecting apparatus consisting of a charging section and a dust collecting section, and the invention provides a charging device acting effectively on dust having a high electric resistance which has heen heretofore difficult to realise.

Among the conventional dust collectors, a so-called two-stage type of electric dust collector is known, which com¬ prises a charging section for mainly causing the dust to be charged and a dust collecting section for mainly collecting the charged dust.

In the above-mentioned type of charging section in the prior art, an electrode arrangement in which a group of discharge electrodes consisting of wires or barbed conductors are insula- tively disposed on a middle plane in a space between adjacent ones of a group of control electrode» consisting of panel plates arranged parallel to each other at an equal distance, has been commonly employed. However, the particle charging device having such an electrode arrangement could not obviate the basic tech- nical difficulties that firstly, insufficiently charged particles are produced owing to unevenness of ion flow in said space, and secondly, when the electric resistance of dust is extremely high and exceeds 10 (Î2>cm), the dust loses its electric charge owing to inverse ionization caused by an accumulated dust layer on the control electrodes, whereby the charging effect was greatly degraded and the dust collecting efficiency was limited in practice. In particular, with regard to the aforementioned second shortcoming, it is caused, as described above, by the fact that the electric resistance of the dust layer deposited and 5s accumulated on the control electrodes may rise to such extent that the electric field exceeds a hreak-dovm intensity, an elec¬ trical "break-down occurs within the dust layer producing inverse ionization points on the dust layer and from these points are fed ions of opposite polarity to the ions fed from the discharge electrodes, and said ions of opposite polarity will neutralize the particle charge; also the shortcoming occurs that particles which have lost their charge are conveyed Toy the gas and enter the dust collecting section. in view of the aforementioned shortcomings in the prior art, experiments were tried employing cylindrical rod-shaped electrodes as control electrodes, but even in such a case, satisfactory results could not always be obtained as a charging device for an exhaust gas containing dust having a high electric resistance. This was because when a dust layer was formed on the surface of the rod, inverse ionization still occurred.

It is an object of the present invention to provide dust collecting apparatus which is particularly efficient in use.

According to the invention there is provided electric dust collecting apparatus including: a body through which a flow of dust-containing gas is directed in use by way of an upstream charging section followed by a downstream dust collecting section; a charging device comprising control electrodes and at least one corona discharge electrode for establishing an ion generating zone in the charging section, co-acting electrodes for establishing electric fields in said section between the control electrodes and the co-acting electrodes, a pulse generating power supply operatively connected between said at least one corona discharge electrode and the control electrodes to apply a pulse-shaped 1.016082 voltage therebetween, and a B.C. power supply operatively con¬ nected between the control electrodes and the co-acting electrodes for establishing uneven D.C. electric fields therebetween; and collecting means comprising field-forming electrodes and collector electrodes for establishing an electric field in the collecting section, and a power supply operatively connected between the field-forming and the collector electrodes to provide an electric force for intercepting charged particles of dust passing from the charging section independently of the operation of the charging means.

Preferred embodiments of the invention are now more particularly described with reference to the accompanying drawings, wherein:

Pig. 1 is a longitudinal cross-section view of an electric dust collecting apparatus incorporating the present invention.

Fig. 2 is an enlarged cross-section view taken along line II-II in Pig. 1, Fig. 3 is an enlarged cross-section view of another embodiment of the present invention showing the portion corres¬ ponding to that showing in Fig. 2, Fig. 4 is a longitudinal cross-section view showing a part of still another embodiment of the present invention, and Fig. 5 is an enlarged cross-section view taken along line V-V in Fig. 4.

in the drawings, reference numeral 1 designates front co-acting electrodes disposed operatively upstream in a dust containing gas flowing through a charging section of a main body of an electric dust collector for establishing electric z fields a., reference numerals 2 and 4 designate first and second control electrodes positioned downstream of said electrodes 1 in said charging section and disposed respectively Tsefore and behind corona discharge electrodes 3 so as to sandwich said electrodes 3 therebetween for establishing an intermittent ion generating zone b, and the electrode arrangement is constructed in such manner that the first control electrodes 2 and the front co-acting electrodes 1 are disposed in a zig-zag form, and that the second control electrodes 4 and rear co-acting electrodes provided furthest downstream in the charging section are disposed in a zig-zag form. Reference numeral 6 designates a D.C. power supply for establishing electric fields, whose positive pole is connected to the co-acting electrodes 1 and 5, and whose negative pole is connected to the control electrodes 2 and 4 and also grounded. The corona discharge electrodes 3 are connected to a pulse generator 9 whereby a pulse-shaped voltage may be applied between said electrodes 3 and the grounded control electrodes 2 and 4.

In the particle charging device constructed as described above, uneven D.C. electric fields ja are formed between the re¬ spective front and rear co-acting electrodes 1 and 5 and the respective control electrodes 2 and 4 by applying pulse-shaped voltages between the corona discharge electrodes 3 and the control electrodes 2 and 4r the gas between these electrodes is ionized, the thus generated negative ions are introduced into the uneven electric fields established between the co-acting electrodes 1, and the respective control electrodes .2, 4.

The negative ions pass along the paths generally indi¬ cated by broken lines in Fig. 2 in a counter-flow from electrodes _ 4 - 2 to electrodes 1 in the front stage in a direction upstream and diagonally counter to the flow of gas from left to right as viewed in Fig. 2; and in a concurrent flow from the electrodes 4 to the co-acting electrodes 5 in the rear stage in a direction downstream and diagonally concurrent with said flow of gas; and thereby the dust-containing gas and the negative ions are brought in contact with each other in both counter- and concurrent flows, resulting in charging of the dust particles.

The charged particles of dust which have passed through the charging section are carried by the flow of gas into a dust collecting section of body 10 having collecting means including field forming electrodes 13 and collector electrodes 14 provided in the latter section of the body, where said particles are collected and removed from the gas flow by interception due to an electric force acting across the collecting section which is pro¬ vided by a separate power supply 15 connected between electrodes 13 and 14, and the induced adsorption, to be gathered on the col¬ lector electrodes 14 and the flowing gas is discharged from the collecting section to the next stage of a treatment process or to the atmosphere as a clean gas. The collecting means operates inde¬ pendently of the charging device.

While a device of the type in which the dust containing gas and the negative ions make contact in both counter and con¬ current flows has been explained in connection with the above- described embodiment, the present invention is not limited to this arrangement, but may be eiribodied in apparatus having a charging device of single flow-contact type employing either counter or concurrent flows, so long as the intermittent ion generating zone b and the electric fields a are established. in particular, if P't&.vV-, the present invention is included in a counterflow type of device having an arrangement in which the co-acting electrodes are disposed in the front stage (upstream) and the intermittent ion generating zone b is disposed in the rear stage (downstream), it is desirable to arrange the corona discharge electrodes 3 and the control electrodes 2 and 4 in the latter zone so as to align in a plane at right angle to the direction of the gas flow.

Since the apparatus according to the present invention comprises an ion generating zone b including corona discharge electrodes 3 and control electrodes 2 and 4 for intermittently generating ions between said electrodes 3 and said electrodes 2 and 4, and co-acting electrodes 1 and 5 for establishing uneven electric fields a between said control electrodes 2 and 4 forming said ion generating zone b and said co-acting electrodes 1 and and also for transferring the ions generated in said ion gen¬ erating zone b, a high electric potential is not generated on the dust layer having a high resistance deposited on the electrode surface, in contrast to certain electric dust collectors in the prior art in which a corona discharge current is made to flow continuously, and thus the faults caused by the inverse ionization phenomena can be obviated, whereby dust can be easily charged, and even dust collection from an exhaust gas where the electric resistance of dust is high and so the dust collection are here¬ tofore considered difficult to realize, can be readily practiced.

In addition, in Pig. 2, reference numeral 7 designates resistors, reference numeral 8 designates capacitors, and numeral 12 desig¬ nates a power supply for the pulse generator.

In the above embodiment the co-acting electrodes are rod-shaped but the present invention is not limited to such a >!Al 1016.08 configuration; for example parallel plane plates could be dis¬ posed along the flow of gas in the charging section with a similar effect and advantage. Such a construction is illustrated in Fig. 3.

In Fig. 3, reference characters a and b and reference numerals 2, 3., 4, 6, 13, 14 and 15, respectively, designate those parts which correspond to the parts bearing the same reference characters and numerals in Figs. 1 and 2, reference numeral 16 designates a pulse generator, numeral 17 designates a power supply for the control electrodes, and numeral 18 designates transfer electrodes in the form of parallel plane plates disposed along the flow of gas.

According to this modified embodiment, the positive pole of the D.C. power supply 6 for establishing electric fields is connected to the co-acting electrodes 18 in the form of parallel plane plates, and its negative pole is grounded. In addition, there is provided another and variable D.C. power supply 17, whose negative pole is connected to the control electrodes 2 and 4 and whose positive pole is grounded to apply a selected voltage to the electrodes 2 and 4 relative to the grounded potential, whereby a controlled electro-static shielding effect is provided and the corona discharge starting voltage of the electrodes 3 can be selected.

Another modified embodiment of the present invention is illustrated in Figs. 4 and 5. In these figures those parts bearing similar reference characters and numerals to those given in Figs.

1 and 2, correspond to the similarly referenced parts in Figs. 1 and 2, and have the same function as the latter. The only dif¬ ference between this modified embodiment and the first embodiment in Figs. 1 and 2 is that the particle charging device is arranged in two stages in the charging section. The particle charging device could toe provided in three or more stages if desired.

lOieiD&s PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS! 1. A particle charging device for use in an electric dust collecting apparatus of the type such that dust particles in a dust containing gas are charged in a charging section provided upstream in a dust collector body and thereafter they are collected toy a dust collecting section provided downstream., comprising:

A) control electrodes and at least one corona discharge electrode for establishing an ion generating zone in the charging section, co-acting electrodes for establishing electric field in said section between the control electrodes and the co-acting electrodes, B) a pulse generating power supply operatively connected between said at least one corona discharge electrode and the control electrodes to apply a pulse-shaped voltage therebetween, and C) a D.C. power supply operatively connected between the control electrodes and the co-acting electrodes for establishing uneven D.C. electric fields therebetween.

2. A particle charging device for use in an electric dust collecting apparatus as claimed in Claim 1, characterized in that said co-acting electrodes are disposed upstream of said ion generating zone.

3. a particle charging device for use in an electric dust collecting apparatus as claimed in Claim 1, characterized in that said co-acting electrodes are disposed downstream of said ion generating zone.

m