Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Patent
1997-08-07
2000-07-18
Chiesa, Richard L.
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
96 79, 96 88, 96 96, 96 98, B03C 308, B03C 312, B03C 364
Patent
active
060901896
DESCRIPTION:
BRIEF SUMMARY
This application is a National Stage Application of International Application No. PCT/SE96/00151 filed on Feb. 8, 1996.
FIELD OF THE INVENTION
The present invention relates to an electrostatic filter for the separation of particles out of a flowing gaseous medium and a supply air terminal comprising such a filter. The filter comprises a particle charging unit arranged upstream comprising at least one corona wire for the charging of the particles and a particle collector unit arranged downstream relative to this. Such filters are known in the prior art.
BACKGROUND OF THE INVENTION
Normal air cleaners comprise a filter with an ionizing sector in which the particles comprised in the air flowing through the air cleaner are ionized. i.e. receive an electrical charge. The particles then pass a particle collector unit where the charged particles interact with an electrical field produced by plates charged with an opposite electrical charge. In this manner the particles are driven towards the plates and collide with the plates and are collected.
Swedish Patent DE-B-401 327 relates to an electrostatic filter which comprises wireshaped conductors, so called corona wires, and plates with different electrical potentials. There are particles in the medium flowing through the filter which are charged and attracted and struck onto the plates which have the reverse polarity relative to the particles charged during the passage between the corona wires. An insulating plate is arranged between each plate in order to prevent spark-over between the electrically charged plates, caused amongst others by the build-up of a layer of the particles attracted to the plates. The biggest disadvantage with such a filter is that one must use many plates, both charged and insulating, in order to achieve a suitable total filter area.
Another significant disadvantage is that after a relatively short period of time the filter loses a considerable amount of efficiency and particle collecting capacity. By reason of this the filter must be cleaned at relatively short time intervals which often is a laborious and time-consuming job.
Another disadvantage which appears with the above type of filter with electrically charged plates is that when the particles move in the field between the plates a number of the particles already become discharged at a distance from the plates through spark-over and the particles then may possibly not stick onto the plates but instead follow the air flow through the filter arrangement and out into the surroundings again.
Another type of filter device is shown in SE,A,7114330-9 (372 180). In this a device for the separation of particles out of a gas flow is described in which a number of high voltage electrodes and collector elements for the charged particles are alternatively arranged one after the other in the direction of the gas flow. The collecting elements consist of a network of paper, possibly metallized, which is earthed. The paper in the network has a weak conductivity.
It has now become apparent that the paper used for this purpose has a large disadvantage in that it is hygroscopic because in the case that the paper absorbs moisture it changes its characteristics with respect to its conductivity.
From JP-61-164664(A) a filter is known comprising corona electrodes and opposing electrodes which are electrically conducting and connected to the opposing pole (earth) of a voltage source with respect to the connection of the corona wires. Between these "opposingly charged" electrodes "acceleration electrodes" made of electrically insulating material are arranged. The distance between the corona electrode and the "opposingly charged" (earthed) electrodes is shorter than the corresponding distance between the corona electrode and the acceleration electrodes made of the electrically insulating material.
In this field it is also known to use sheet aluminum in the particle collection plates. This has, however, the disadvantage that during use it oxidizes. This means that the surface of the plates becomes more and
REFERENCES:
patent: 2181767 (1939-11-01), Penney
patent: 2873000 (1959-02-01), Elam
patent: 2875845 (1959-03-01), Penney
patent: 3487610 (1970-01-01), Brown et al.
patent: 3918939 (1975-11-01), Hardt
patent: 4072477 (1978-02-01), Hanson et al.
patent: 4652281 (1987-03-01), Masuda et al.
patent: 4861356 (1989-08-01), Penney
Fuji, Japanese Patent Abstracts, Document No. 53-69980, Jun. 21, 1978.
Hornquist Ulf
Wikstrom Goran
Chiesa Richard L.
Purocell S.A.
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