Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Patent
1996-08-12
1998-06-16
Chiesa, Richard L.
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
96 98, B03C 360
Patent
active
057663181
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a precipitator for a two-stage electrostatic filter.
WO 93/16807 discloses a two-stage electrostatic filter which comprises an ionizer and a capacitor or electrostatic precipitator (collector) positioned downstream of the ionizer. Advantageously, the electrode elements of the precipitator, which in the illustrated embodiment are flat plates but may have different shapes in other embodiments, are made of a material that may be designated as highly resistive or antistatic (so-called dissipative material). With such a material a substantial improvement can be achieved, because the voltage that can be produced between adjacent electrode elements is self-regulating and can reach higher values than in the customary electrostatic filters having electrode elements made of a material of low resistivity, such as aluminium, and having a galvanic connection to the voltage source.
In the embodiment disclosed in the above-mentioned publication, the plates preferably are charged by the ion current from the corona electrode of the ionizer, and the voltage between them is stabilized because the electrode elements have field-concentrating formations, which may take the shape of, for example, sharp edges or other pointed parts of the electrode elements.
SUMMARY OF THE INVENTION
The present invention advantageously can be embodied in two-stage electrostatic filters of the kind disclosed in the above-mentioned publication, but it is not limited to use in filters of that kind. For example, the charged particles by means of which the precipitation of dust on the electrode elements is brought about need not necessarily be produced in an ionizer of the type disclosed, but may be produced and carried to and through the precipitator in any suitable manner. Moreover, it is not necessary that the electrode elements be charged by the air ions produced in the ionizer. Instead, the required voltage between adjacent electrode elements may be maintained by a connection of the electrode elements to a high-voltage source, preferably a very highly resistive connection.
An object of the invention is to provide a high, and yet stable, voltage, i.e. a high threshold voltage, with narrow air gaps between adjacent electrode or plate elements of the precipitator, so that the precipitator may be used in applications in which the precipitator has to meet high stringent demands in respect of precipitation capability.
According to the invention, this object is attained by using a highly resistive, antistatic or almost antistatic (dissipative) material of, or coating on, the electrode elements of the precipitator and at the same time avoiding field concentrations, especially at those edges of the electrode elements which are at the upstream end of the electrode elements and, consequently, confront the stream of air that carries the charged particles to be precipitated on the electrode elements.
According to the invention, this can be accomplished by providing the electrode element edges in question with a screen made of a non-conducting, insulating material. This screen need not necessarily be applied to the edges, meaning that it need not be physically connected with the edges, but may be slightly spaced from them; it is sufficient that the screen is constructed and positioned such that it electrostatically screens the edges from the electric field.
The screening may be provided by making the electrode elements from an insulating material and coating them with a semiconducting or antistatic material such that their edges are left insulated (uncoated) so that only the electrode element surface inwardly (downstream) of the edges is semiconducting or antistatic.
The same effect may be achieved if the electrode elements are made from a semiconducting or antistatic material and the edges thereof are coated with an insulating, non-conducting material.
Advantageously, the first-mentioned way of providing the screening may be used in cases in which a cellulose material, such as paper or cardboard, is us
REFERENCES:
patent: 2958393 (1960-11-01), Lueder
patent: 4354861 (1982-10-01), Kalt
patent: 5466279 (1995-11-01), Hattori et al.
Loreth Andrzej
Torok Vilmos
Chiesa Richard L.
TL-Vent Aktiebolag
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