Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Reexamination Certificate
2003-04-09
2004-10-19
Chiesa, Richard L. (Department: 1724)
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
C055SDIG005, C095S059000, C096S069000, C264S129000, C264SDIG004
Reexamination Certificate
active
06805732
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to the technical domain of devices for air processing, and more particularly to devices for submitting a fluid charged with aerosol particles (specific dusts or molecules, etc.) to the action of an electrostatic field with high variations of amplitude and orientation, with a view to carrying out a specific electromagnetic action on these particles. This electromagnetic action on the particles can have the aim of mechanical, physical or chemical consequences etc.
The device for generating the electrostatic field according to the invention is of the type constituted of a porous electrostatic module in dielectric material, arranged in sandwich between two porous conducting electrodes, put under different electric voltages, to induce a distribution of charges and an electric field inside the electrostatic module. The charged fluid is pushed through the porous sandwich, in particular using a ventilator. Such devices for electrostatic action on aerosol particles are at present used mainly for electrostatic filtering of particles transported by an air flux. But they use a non-organised electrostatic module in a three-dimensional network and the actual geometry of the cells is random. They implement an electrostatic field which is weakly amplified locally and with small variations of amplitude and orientation.
The electrostatic module of a generator according to the invention is constituted of a meshed network, whose meshes have an organised three-dimensional periodicity and whose mesh cells have a recessed structure, convex externally and concave internally and compact, with a particular repetitive geometry for achieving the required amplification effect and electrostatic field structure.
STATE OF PRIOR ART
The device for amplified electrostatic action according to the invention has much wider applications than those of the domain of filtration. Nonetheless, the closest prior art is essentially constituted of electrostatic filters for dusts. Consequently, the analysis of prior art given below is restricted to this technical field and more generally to the different techniques for filtering dusts.
For medical, sanitary and air purity reasons, it is advantageous to filter the small particles in the air and in particular industrial dusts, pollens, bacteria, viruses, fungi, algae and other fine dusts. Apart from systems operating using gravitation (settling of particles due to their weight) and cyclone systems operating through the effect of centrifugal forces (both of them used together in certain specific industrial applications, resulting in systems with large overall dimensions), the two most common methods for ensuring decontamination of dust particles in the air comprise:—one to block the air flow with the aid of a medium (mechanical filter);—and the other to deflect and capture the dusts using an electrostatic method (electro-filter).
According to the first method with a mechanical filter, the air passes through a porous filtering medium. A distinction can be made between: mechanical filters with surface filtration; and mechanical filters with in-depth filtration.
In the case of surface-effect mechanical filters, the medium is generally constituted of a sheet of woven metallic threads, a meshed material, a paper filter, a membrane etc. The medium has surface pores or holes. The size of the pores in the medium is chosen such that the air passes through whereas, because of their size, the “big particles” are captured and held on the fibres or material of the medium. Although, in practice, mechanical filters rarely have holes smaller than the size of the particles they have to capture, they act as if they had. The particles are captured progressively on the edges of the holes and tend to create a porous wall bridging the hole by agglutination. The collected particles cling together on the surface of the filtering medium and progressively constitute a “cake” of increasing thickness. Thus, with use, the “cake” of collected particles becomes the filter and the initial medium becomes the filter support.
In the case of mechanical filters with in-depth filtration, the particles do not only form a coherent surface cake, but the particles are caked to a certain depth in the vicinity of the surface of the medium. An example of such a filter is constituted by cigarette filters. The medium has a certain thickness and its fibres are not woven to form a surface, but are collected together in thickness according to more or less random directions. When the fluid meets a fibre placed approximately transversal, the flux is deflected around the fibre, but part of the particles, denser than the gas, have a tendency to be deflected less. They hit the fibre instead of following the gas. The separation of dusts is carried out by inertial impact on the fibres. The captured particles are then partly kept in place according to Van der Waals electrostatic forces.
In applications requiring high filtration efficiency, such as sterile rooms, a variant of the mechanical filter is used, applying folded filtering medium cartridges, called high efficiency filters (HEPA) or very high efficiency filters (ULPA).
The second method, with an electrostatic filter or electro-filter, is based on the fact that particles with a certain charge are attracted by a collector electrode of the opposite charge. This method has been used widely in industry since its invention by F. G. Cottrell in 1910. Preliminary means are used to give an electrostatic charge to the particles and, using an electrostatic field, these charged particles can be precipitated on a collecting wall or a collecting medium maintained at a voltage of the opposite sign. There exist two principal classes of electrostatic filter structures:—those with one stage,—and those with two stages. There also exist two variants of electrostatic precipitation means:—those with electrodes under voltage generated externally by electrical supply,—and those with electrostatic self-charging, charged by air friction.
Single stage electro-filters, or filters charged electrostatically, are produced according to the self-charging variant, according to which their filtering medium accumulates an electrostatic charge resulting from the passage of the air flux through the medium constituting them. In general they also use the fact that the particles are previously charged electrostatically from air friction. They are of low cost and of low efficiency.
Two stage electro-filters, also called electrostatic precipitators, are of higher complexity, cost and efficiency. They comprise a stage of electric charging of the particles by corona effect plus a precipitation stage. In the electric charging stage, the air passes through an ionisation zone constituted of one of several wires set at high voltage to generate an intense electrostatic field, within which the particles are electrically charged by ionisation. Then the air flux comprising the charged particles passes through a second collection stage. There are two types of two-stage electrostatic filters, depending on the structure of the collector stage for charged particles (—with plates,—or with a filtering medium).
According to the first type of electrostatic filter, with parallel plates but with electric field transversal to the flux (used in particular for treating industrial gaseous effluents), the collector is formed of an alternate parallel plurality of plates under high voltage and earthed plates, oriented parallel to the air flux. The charged particles are deflected perpendicularly to the flow path because of the transversal electric field, perpendicular to the plates and thus to the flow. As a result, the particles are precipitated onto the plates.
According to a second type of electrostatic filter, with filtering medium, the collector stage is constituted of one or several grids or porous electrodes (generally put under alternating voltages) and separated by plates of a filtering porous collector medium. The grid and the plates are located perpendicular to the air flow. The
Basset Frederic
Billiotte Jean-Marie
Nagolkin Alexandre Vladimirovitch
Volodina Elena Vladimirovna
Airinspace Ltd.
Chiesa Richard L.
LandOfFree
Electrostatic treatment of aerosols, devices and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrostatic treatment of aerosols, devices and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrostatic treatment of aerosols, devices and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3308736