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| United States Patent |
4,955,991 |
| Torok , et al. |
September 11, 1990 |
Arrangement for generating an electric corona discharge in air
Abstract
An arrangement for generating an electric corona discharge in air having a
corona electrode, a target electrode which is spaced from the corona electrode,
and a d.c. voltage source, the respective terminals of which are connected to
the corona electrode and the target electrode. The voltage of the voltage source
and the construction of the corona electrode are such as to generate a corona
discharge at the corona electrode. A conduit is provided for continuously
removing the air present in the immediate vicinity of the corona electrode and
dealing with the air thus removed in a manner to render innocuous
physiologically harmful substances or irritants present in the air and generated
by the corona discharge, such as primarily ozone and nitrogen oxides.
| Inventors: |
Torok; Vilmos (Lidingo, SE); Loreth;
Andrezej (Akersberga, SE) |
| Assignee: |
Astra-Vent AB (Stockholm, SE) |
| Appl. No.: |
252362 |
| Filed: |
September 26, 1988 |
| PCT Filed: |
April 13, 1987 |
| PCT NO: |
PCT/SE87/00183 |
| 371 Date: |
September 26, 1988 |
| 102(e) Date: |
September 26, 1988 |
| PCT PUB.NO.: |
WO87/06501 |
| PCT PUB. Date: |
November 5, 1987 |
Foreign Application Priority Data
| Current U.S. Class: |
96/50; 96/55; 96/97 |
| Intern'l Class: |
B03C 003/00 |
| Field of Search: |
55/2,129,138,130,150-152,120
361/230-232 |
References Cited [Referenced
By]
U.S. Patent Documents
| 2004352 |
Jun., 1935 |
Simon |
55/138. |
| 3184901 |
May., 1965 |
Main |
55/138. |
| 4339782 |
Jul., 1982 |
Yu et al. |
55/131. |
| 4435190 |
Mar., 1984 |
Taillet et al. |
361/230. |
Primary
Examiner: Nozick; Bernard
Attorney, Agent or Firm: Browdy and
Neimark
Claims
We claim:
1. An arrangement for generating an electric corona
discharge in an air flow path which is in communication with a human environment
and continuously removing harmful gases produced as a consequence of the corona
discharge from the air flow path comprising
a duct having an air flow
therethrough;
a corona electrode, and a target electrode spaced from
said corona electrode in said air flow of said duct;
a d.c. voltage
source having first and second terminals to which said corona electrode and said
target electrode, respectively, are connected, the voltage between said
terminals of said voltage source capable of creating a corona discharge at said
corona electrode;
piping means to continuously remove harmful gases
produced as consequence of said corona discharge, extending from inside said
duct and out said duct, and having a first pipe with an orifice at one end of
said first pipe;
said orifice of said first pipe located in the vicinity
of and opening in the direction of said corona electrode, and said pipe over the
remainder of its length being hermetically sealed relative to said air flow in
said duct;
a second pipe having an open end located axially opposite to
and spaced from said orifice of said first pipe;
air pumping means
connected to said second pipe for generating a jet of air out through said open
end of said second pipe closely past said corona electrode and into said orifice
of said first pipe.
2. The arrangement as claimed in claim 1 wherein
a purifying means for removing said harmful gases from a flow of air
through said first pipe is connected to an other end of said first pipe.
3. The arrangement as claimed in claim 1 wherein
said corona
electrode comprises a short needle element oriented substantially axially in
said air flow in said duct and said orifice is substantially circular.
Description
The present invention relates to an arrangement for generating an
electric corona discharge in air, comprising a corona electrode, a target
electrode located at a distance from the corona electrode, and a d.c. voltage
source, the two terminals of which are connected to the corona electrode and the
target electrode respectively, the voltage between the two terminals of the
voltage source and the construction of the corona electrode being such as to
generate a corona discharge at the corona electrode.
Corona discharge
arrangements of this kind are used to a significant extent in, e.g.,
electrofilters intended for air purification purposes, in which filters the air
ions generated through the corona discharge are utilized to charge electrically
the particulate contaminants and/or liquid droplets present in the air. The
electrically charged particles/droplets are attracted to and fasten on
collecting surfaces which have an opposite polarity to the charged particles or
droplets, thus being extracted from the air. The polarity obtained by the
particles or droplets is the same polarity as that obtained by the air ions, the
polarity of which ions is dependent, in turn, on the polarity of the corona
electrode. Electrofilters of this kind are known in many different structural
forms. Such corona discharge arrangements may also be used in air transportation
systems of the kind which utilize so-called electric ion-winds or corona-winds.
Such air transportation systems are found described in, for example, U.S. Pat.
No. 4,812,711.
One serious problem encountered with the use of corona
discharge generators in localities where people are to be found, such as in
domestic dwellings or places of work for instance, and also in ventilation
systems or air processing systems which are connected to such localities, is
that the corona discharge generates chemical compounds, primarily ozone and
nitrogen oxides, which if present in excessively high concentrations can be
experienced as irritative, and may also be harmful to the health. The generation
of these irritants in conjunction with a corona discharge occurs at a rate which
is contingent on the magnitude of the electric corona current, and is much
greater in the case of a negative corona discharge than in the case of a
positive corona discharge. Consequently, a positive corona discharge has been
used practically always when employing such systems and apparatus in human
environments However, the aforesaid irritants are still generated even when
employing a positive corona discharge, and the problem thus still remains
Consequently, it is necessary to limit the corona current in relation to the
quantity of air that passes the corona discharge arrangement per unit of time,
so that the proportion of irritants present in this quantity of air is
restricted to acceptable values. In particular the corona current must be
limited quite radically when the arrangement used is one in which the same air
passes by the corona discharge arrangement a number of times and therewith
results in a successive accumulation of irritants in the air. In the case of
electrofilters this necessary radical limitation of the corona current results
in a filter of low efficiency and also in filters of large dimensions, while in
the case of air transportation systems which operate with ion winds, it is
extremely difficult to transport air in quantities which are sufficiently large
from a practical point of view The use of pointed or needle-like corona
electrodes has been practically excluded by the necessity of working with a
positive discharge, despite the fact that such electrodes are beneficial both
from an electrotechnical and a mechanical aspect. This is because when using
needle-like or pointed corona electrodes and creating a positive corona
discharge, so-called streamers, i.e. long thread-like corona discharge channels,
readily form in the ambient air, these streamers resulting in an unstable corona
discharge and in an increase in the generation of irritants.
Consequently, the object of the present invention is to provide a corona
discharge arrangement of the kind described in the introduction with which the
problem created by the aforedescribed irritants produced in conjunction with the
corona discharge can be eliminated, or at least greatly reduced.
This
object is achieved in accordance with the invention by constructing the corona
discharge generating arrangement in accordance with the accompanying claims.
The invention is based on the discovery that it is possible to recover
the predominant part of the irritants generated in conjunction with a corona
discharge and to render these recovered irritants innocuous, by removing
continuously the air present in the immediate vicinity of the corona electrode
and dealing with the thus removed air in a manner which will render harmless the
irritants present in said air and generated by the corona discharge. This can be
effected, for example, by passing the air removed from the immediate vicinity of
the corona electrode to a location at which the irritants are no longer
offensive, e.g. to the outdoor atmosphere, or by cleansing said removed air of
the irritants present therein with the aid of suitable sorbents effective in
extracting the irritants from said air. It has been found that only relatively
small amounts of air need be removed from the immediate vicinity of the corona
electrode, since the irritants are formed in the so-called corona layer on the
electrically active part of the corona electrode. This removal can be effected
without appreciably disturbing the desired air flow past the corona electrode
and without needing to disturb in any way the desired generation of air ions and
the movement of these ions towards the target electrode.
The invention
will now be described in more detail with reference to the accompanying
drawings, which illustrate a number of exemplifying embodiments of an
arrangement according to the invention and in which
FIG. 1 illustrates
schematically a first embodiment of an arrangement according to the invention;
FIG. 2 illustrates schematically a second embodiment of an arrangement
according to the invention;
FIG. 2A is a schematic side view of the
upper portion of conduit 7 in duct 1 of FIG. 2;
FIG. 3 illustrates
schematically a third embodiment of an arrangement according to the invention;
and
FIG. 4 illustrates schematically a fourth embodiment of an
arrangement according to the invention.
FIG. 1 illustrates schematically
and in axial section an arrangement for transporting air with the aid of a
so-called electric ion-wind. The arrangement includes an air flow channel or
duct 1, in which a corona discharge arrangement is located. The corona discharge
arrangement comprises a pointed or needle-like corona electrode K which extends
axially within the duct 1, and a target electrode M in the form of a cylindrical
surface spaced axially from and located downstream of the corona electrode K.
The target electrode M and the corona electrode K are each connected to a
respective terminal of a d.c. voltage source 2, the voltage of which is such as
to generate a corona discharge at the corona electrode K. The air ions generated
by this corona discharge migrate to the target electrode at high speed,
colliding with and transferring kinetic energy to the surrounding air molecules
during their journey, so as to produce an air flow through the duct 1 in the
direction indicated by the arrow 3. The mechanism by which air is transported in
this way with the aid of an electric ion-wind is described in detail in the
aforementioned International Patent Application.
As mentioned in the
aforegoing, the generation of a corona discharge at the corona electrode results
in the production of chemical substances, primarily ozone and nitrogen oxides,
which may have an irritating effect, and even a harmful effect, on people
present. A particularly large quantity of such irritants is produced when the
corona electrode K is connected to the negative terminal of the voltage source
2, as in the embodiment illustrated in FIG. 1, such as to produce a negative
corona discharge. The quantity of irritants thus produced increases with
increasing values of the corona current. A high corona current is desirable,
however, in order to transport a large quantity of air through the duct 1. In
the FIG. 1 embodiment of the inventive arrangement, the predominant part of
these irritants generated at the corona electrode K is removed, by placing the
corona electrode within a narrow tube 4 which surrounds the corona electrode K
co-axially therewith and which presents in a direction towards the target
electrode M an open end which is located approximately on the same level as the
point of the corona electrode K. This tube 4 is connected.-d to a fan, air pump
or some corresponding device 5 effective in maintaining a flow of air through
the tube in the direction of arrow 6. The air located in the immediate vicinity
of the corona electrode is hereby removed continuously, and therewith also the
predominant proportion of those irritants that form as a result of the corona
discharge on the corona electrode. The irritant-containing air removed through
the tube, e.g. by suction, can be released to the outdoor atmosphere, where the
irritants will have no deleterious effect, or can be passed to a cleansing
purifying device in which the irritants are removed from the air with the aid of
some suitable absorbent material, such as active carbon for example, as shown in
FIGS. 1 and 4. For example, it has been found that in the case of a corona
current of 20 .mu.A from a point, the predominant part of the irritants
generated can be removed with a rate of air flow within the tube 4 of from 1 to
2 m/s. The tube 4 embracing the corona electrode K can therewith be given a
diameter of, for example, 5-10 mm. It has also been found that this continuous
removal by suction of the air located in the immediate vicinity of the corona
electrode K has no appreciable disturbing influence on the air flow 3 through
the duct 1. Neither is there any disturbing effect on the corona discharge, and
therewith on the generation of ions, or on the movement of the ions towards the
target electrode M, when the point of the needle-like electrode K is located
flush with the plane of the orifice or opening of the tube 4 in the illustrated
manner. At least that part of the tube 4 which is located nearest the corona
electrode K may also comprise an electrically conductive or semi-conductive
material and be connected to a potential close to the potential of the corona
electrode K, in the manner illustrated in FIG. 1. The tube 4 will, in this way,
function as an excitation electrode for the corona discharge, which takes up
solely a small part of the total corona current. This will eliminate the risk of
the tube 4 having a screening influence on the corona electrode K, which could
otherwise disturb the corona discharge.
Because the inventive
arrangement enables the predominant part of the irritants generated by the
corona discharge to be removed and rendered innocuous, an arrangement that is
constructed in accordance with the invention can be used without detriment in
peopled environments. In addition hereto, the arrangement also enables the use
of a negative corona discharge, thereby facilitating the use of a pointed or
needle-like corona electrode, which affords benefits in other connections. It
has been found that removal by suction of air located around the pointed corona
electrode K through the tube 4 also prevents the formation of so-called
streamers when the corona electrode is positive, and hence it would seem that
the invention enables the use of a pointed or needle-like corona electrode
together with a positive corona discharge. Furthermore, it is also possible to
use a larger corona current, which in turn results in a greater flow of air
through the duct 1 and improved electrical charging of the aerosols in the air,
thereby enabling these aerosols to be extracted more readily.
FIG. 2
illustrates schematically and in section a similar arrangement for transporting
air through an air flow channel or duct 1, in the direction of the arrow 3. The
duct 1 of this embodiment is of elongated rectangular cross-section and the
corona electrode K comprises a wire which extends perpendicular to the plane of
the drawing along the long centre axis in the rectangular cross-section of the
duct 1. The target electrode M of this embodiment comprises two surfaces which
extend parallel with the side walls of the duct 1 and also with the wire-like
corona electrode K. The suction means for removing continuously air located in
the immediate vicinity of the corona electrode K comprises in this case a
conduit 7 with a narrow elongated rectangular crosssection and an orifice which
faces the target electrode M and in which the wire-like corona electrode K is
located centrally, approximately flush with or slightly inwardly of the plane of
the orifice. As with the tube of the former embodiment, the conduit 7 is also
connected to a fan, pump or corresponding device 5 effective to maintain a flow
of air through the conduit 7, in the direction of the arrow 6. FIG. 2A is a
schematic side view of the duct 1, the suction conduit 7, and the corona wire K
located in the proximity of the conduit orifice.
FIG. 3 illustrates
schematically and in section an air transporting arrangement similar to that
illustrated in FIG. 1 and described in the aforegoing In this case, however, the
air present in the immediate vicinity of the corona electrode K is removed
continuously from the system with the aid of a conduit which is located
downstream of the corona electrode K with the tube orifice facing said
electrode. The conduit 8 is connected to a fan, air pump, or some equivalent
device 5 similar to the aforedescribed embodiments, so that air can be withdrawn
through the conduit 8 by suction. However, if the rate of air flow through the
duct 1 is sufficiently high and substantially laminar, the provision of a
separate fan, pump or like suction device may conceivably be dispensed with.
This is thought to apply particularly in the case of electrofilters with which a
relatively powerful air flow is generated in the duct 1 through the use of an
external fan or like device. It must be ensured in the arrangement according to
FIG. 3 that the air suction conduit 8 does not obstruct the view from the corona
electrode K to the target electrode M and therewith prevent the desired
migration of ions from the corona electrode K to the target electrode M.
The arrangement illustrated schematically and in section in FIG. 4 is in
principle the same as that illustrated in FIG. 3. With the arrangement of FIG.
4, however, the air located in the immediate vicinity of the corona electrode K
is removed still more effectively, by directing a relatively powerful and
concentrated jet of air along the corona electrode K with the aid of a nozzle 9
located upstream of the corona electrode and supplied from a fan, air pump or
corresponding device 10. The air jet passing the corona electrode in the manner
just described entrains the irritants generated in conjunction with the corona
discharge and is captured in and carried away by a conduit 11 located downstream
of the corona electrode K, the open inlet orifice of said conduit facing said
electrode. If desired, the conduit 11 can also be connected to a fan, air pump,
or some corresponding device which supports the desired air flow through the
conduit 11.
It will be seen from the aforegoing that an arrangement
constructed in accordance with the invention for removing continuously the air
present in the immediate vicinity of the corona electrode such as to enable the
irritant-containing air to be dealt with in a suitable manner, may be formed in
various ways depending upon the construction of the corona discharge arrangement
used. Although the invention has been described in the aforegoing with reference
to air transporting systems which operate with an ion-wind, it will be
understood that the invention, while affording the same advantages, can be used
also with corona discharge arrangements which are not intended to produce an
air-transporting ion-wind but are incorporated in, e.g., an electrofilter
through which air is transported with the aid of a fan or corresponding device
* * * * *
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