Note: Descriptions are shown in the official language in which they were submitted.
The present invention rela~es to an apparatus for
removing solid or llquid particles Erom a gas stream, wherein
the gas stream flows through a separating space bounded by two
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electrodes arrar,ged opposite to each other, and wherein an
electric field is generated between the electrodes with such an
intensity that substantially no ionisation occurs in the gas
stream.
~ An apparatus of this kind is indicated, in practice,
.~ as a dipole separator. Due to the use of a relatively low field
intensity in the separating space, there is no, or substantially
no ionisation in the gas stream, so that the separation is mainly
based on the phenomenon that dipole charges are generated in -the
particles to be removed. In order to a-ttain this effect, the
field intensity in the separating space must be lower than a
.1 critical value which may amount to 10-20 kV/cm when the gas
stream is an air stream. The theory of dipole separation has
been explained in an article by Dr. Gunter Zebel, entitled:
"Ueber die Aggregatbildung zwischen kugelformigen Aerosolteilchen,,"~ .
mit parallel ausgerichteten Dipolmomenten" in the German
; 20 periodical "Staub", Vol. 23, Nr. 5, May 1963, pages 263-268.
A suitable construction for a dipole separator is disclosed in
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U.S. Patent application No. ~47,775 which has subsequently
issued July 20, 1976 to Van Dieperbrock as U.S. Patent No~
3,970,437.
West German Patent Application 594,681 ln-~e name of Prof. Dr.-
Ing. Paul Denzel, published on April 29, 1971, discloses an
apparatus for removing sulfur dioxide fro~ smoke gases by means
of an electric field generated between two electrodes, wherein
the electrodes are provided with metallic points. West-German
30 Patent Application 2,000,768 in the name of Karl Simon, published
on July 2, 1971, discloses an apparatus for separating kitchen
odours from an air stream, by means of an electric field
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generated between two electrodes, wherein one of the electrodes
is made of a hygroscopic material, such as paper or cardboard,
impregnated with a conductive liquid.
Conventional dipole separators have the disadvantage
that the separating efficiency is rather low.
The invention improves the efficiency of a dipole
, separator in such a sense that a larger percentage of the
particles suspended in the gas stream is removed.
According to the present invention there is provided
apparatus for removing particles from a gas stream, comprising
two oppositely arranged electrodes defining a separating space
between them, means for leading the gas stream through said
separatiny space, means for generating an electric field between
~ the said electrodes having a relatively low intensity so that
`~1 substantially no ionisation occurs in the gas stream, and a
-`j coating on at least one of the said electrodes, consisting ofa fibrous material with a limited electric conductivity, having
a large number of outwardly projecting thin fibres.
~ The apparatus according to the present invention
`~ 20 thus has at least one of the electrodes provided with a coating
consisting of a fibrous material with a limited electric
conductivity, having a large number of outwardly extending
thin fibres.
` If the electrodes are constructed, in known manner,
`;~ as coaxial cylinders, it is generally sufficient for the
required effect to provide the coating exclusively on the
inner electrode.
In many cases, the effect of the invention is readily
; obtained to a sufficient extent when the coating only extends~ ~ -
through a portion of the length of the separating space~ the
-~ said portion being situated on the inlet side of the gas stream.
~ The expression "limited electric conductivity", as
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used herein means that the fihrous material used for the eoatinc~
is neither a good conduetor, nor an insulator. The use of a
hic~hl~ eonduetive coating only leads to a reduction of the dis-
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tanee between the eleetrodes, which has little or no influenee
on the efficiency. If the coating consists of an insulating
material, the field is exclusively determined by the electrodes,
I so that the desired effect is not obtained either.
¦ A coating material naturally satisfying the required
eonditions is asbestos. Asbestos is a fibrous material having
j 10 a large number of outwardly projecting thin fibres, and it is
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. somewhat, but not too strongly conductive. If the electrodes
are cylindrieal, it is preferred to use a ribbon woven from
asbestos fibres, which is wound on the inner electrode.
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Another coating material that may be successfully
used is a glass fabric of which the fibres ha~e been rendered sliyhtly
conductive by the application of a conductive sizing substance.
Furthermore, good results are obtained with a
coating materi~l consisting of fine metallic fibres embedded in a
carrier made of a synthetic material; the met llic fibres are preferably
made of stainless steel. A material o~ this kind is commercially avail-
able under the trade mark "Needlona".
Finally, good results may also be obtained with a
coating consis1;ing o~ a textile fabric of which the fibres have been
provided with a conductive layer by vacuum deposition. Although the effec~
of the coating cannot be conclusi~ely explained, it may be presumed that
an impact ionisation occurs at the beginnine f the operation of the
apparatus due to the activity of the flne ou~wardly directed fibres~ and
that this impact ionisation leads to B spray discharge.
When the operation of the apparatus is observed by
means of a ~indow, it may be seen that a dust layer is formed on the
fibres at the beginning of the separation. It may be presumed that this
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dust layer forms a good base for the attachment o~ ~urther dust particles,
and that the increased efficiency is due to this impro~ed attachment.
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Brief description Or the drawnn~ ~
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The drawl~g sho~s ~chemAtic~1ly a preferred embodi-
ment of the apparatus according to the invention.
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Detailed Description.
The apparatus shown in the drawing comprises a
separating space 1 bo~mded by two coaxial cylindrical electrodes,
namely an outer electrode 2 and an inner-electrode 3. The gas stream to
be puri~ied is supplied to the separating space 1 through an inclined
inlet ~9 and leaves this space through an outlet 5 likewise placed i~
an inclined position. At the bottom, the separating space communicates
with a funnel 6 for catching the separated particles, which is closed
of~ by means oi an outlet member 7 to be opened from time to time to
remove the separated dust.
According to the invention, the inner electrode 3
is provided9 on the side facing the outer electrode 29 wnth a coating 8
consisting o~ 2 hairy ~ibrous m~teria] ha~ing a l;mited electric conduc-
tivity and a laree numer of outwardly pro3ecting thin fibres. In the
embodiment as showm~ the coating 8 extends through the entire leneth o~
the separating space 1. Experiments have sho~m~ however, that the same
result may be obtained in many cases by means of a coating extending
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only throu~h a portion of the length of the separating spa~e, the said
portion being situated on the inlet side of the gas stream, i.e. at the
bottom in the drawing.
During experiments, a highly increased separating
e~iciency was observed with r~a~erialsof the above mentioned kind, n~me-
ly asbestos~ glass fibres with a conductive layer, metallic ~ibres em-
b edded in a carrier, and textile ~abrics rendered conductive by vacuum
deposit;on. In certain cases, the efficiency increased by the use of the
~oating from about 80% to about 95%.
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The manner in which the electrodes are supported and
fed are not shown in the drawing. The conventional means may be
used for these purposes.
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