Gas separation: processes – Electric or electrostatic field – Including baffling – deflection – or restriction of gas flow
Patent
1996-03-08
1998-11-17
Chiesa, Richard L.
Gas separation: processes
Electric or electrostatic field
Including baffling, deflection, or restriction of gas flow
96 68, 96 69, 96 97, 96 98, B03C 345
Patent
active
058370358
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to a method and an apparatus for electrostatically precipitating impurities.
2. Description Of The Prior Art
The precipitation of microimpurities from gas flows is of relatively great importance. Lately, a considerable increase in asthmatic diseases could be observed; these are due to impurities, such as carbon or smoke particles. It is possible to precipitate such microimpurities from air with the aid of so-called electrostatic filters. To this end, known filters are, for instance, provided with an ionizing electrode as an ionization source for giving the impurities a negative charge. Precipitation electrodes which are positvely charged are then provided in parallel with one another behind the ionizing electrode in the direction of flow. On account of the opposite charge between the charged impurities and the precipitation electrodes, the impurities, when traveling between the plate-like precipitation electrodes, are deflected to one of the plates to adhere thereto. After a corresponding filtering period has passed, the precipitation electrodes may be flushed or also disposed off. Such an electrostatic filter is, for instance, described in EP-A-265451.
Although such a known electrostatic filter achieves degrees of precipitation that are quite high, it is not suited for use in rooms. On the one hand, the distance covered by the ionized particles through the precipitation electrodes that are arranged in parallel with each other must be chosen such that it is relatively long in order to achieve a high degree of precipitation; on the other hand, a relatively strong electric field is required for achieving adequate precipitation. However, the strong electric field has also the effect that a high electric voltage has to be applied to the ionizing electrodes on the one hand and to the precipitation electrodes on the other hand, which is bound to effect the production of ozone in known electrostatic filters. The production of ozone, however, is especially undesired for the intended use of the electrostatic filters, namely in rooms inhabited by persons suffering from allergies, since ozone affects the respiratory system.
Generic apparatuses are, for instance, known from GB-A-1 267 777, GB-A-746 324 and US-A-2 142 128.
SUMMARY OF THE INVENTION
It is the object of the present invention to improve a method and an apparatus of the above-mentioned type in such a manner that the electrostatic filter is especially suited for use in rooms.
As far as the method is concerned, this object is achieved according to the invention in that the gas flow is guided through openings which are tapered on their edges toward the opening in the manner of cutting edges.
As far as the apparatus is concerned, this object is achieved in that the edges of the openings of the perforated plate are tapered toward their respective opening in the manner of cutting edges.
The gas flow is not guided in parallel with the precipitation electrodes, but in a direction transverse thereto. Large particles directly impinge on the front side (raw gas side) of the perforated plate because of their inertia and because of their electric charge. By contrast, small particles can be entrained along with the gas flow through the openings of the perforated plate and thus pass onto the back side (clean gas side) of the perforated plate. When the gas flow passes through the individual holes of the perforated plate, the charged impurities are exposed to a strong electrostatic field, since the edges of the holes naturally effect a strong curvature of the field lines and thus a high density of the field lines. In addition, the gas flow expands immediately after having passed through the holes, thereby slowing down its speed. This has the effect, together with the intensified electrostatic field, that small impurities are deflected out of the gas flow after having left the openings and are precipitated on the back side of the perforated plate. An advantage which is not to be underesti
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Braun Werner
Gebhart Joseph
Rzeznik Jerry
Scheuch Gerhard
Sommerer Knut
Chiesa Richard L.
Maxs AG
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