Gas separation: apparatus – Electric field separation apparatus – Including gas flow distribution means
Patent
1996-04-19
1998-09-15
Chiesa, Richard L.
Gas separation: apparatus
Electric field separation apparatus
Including gas flow distribution means
96 96, 96 99, B03C 3155
Patent
active
058074252
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a filter device for removing particles from gas such as from air.
There is an ever increasing awareness of the need to remove undesirable particles, such as resulting from the smoking of tobacco, from the air in public places, such as offices and from domestic environments and it is an object of the present invention to provide an improved means for enabling such particle removal.
Simple mechanical filters are known but, unless they are of a particularly expensive type, such are not sufficiently efficient for the intended purpose and soon become clogged. In prior, known devices it is possible to remove and discard the contaminated filter media although the support frame which forms part of the filter device is also often contaminated--especially by tobacco smoke--and retains foul odours, such frame is not readily cleaned because all its components were permanently attached, usually by some form of hinge. Thus even after replacement of the filter media, foul odours of such prior devices are still apparent on the framing and are subsequently emitted.
It is also known that particles are removed by ionisers which produce negatively charged ions which combine with other airborne particles in the air and are then attracted to walls and other surfaces inside and outside of the device. Electro static precipitators are also known which include a duct containing charge applying means which uses a high voltage corona discharge which charges airborne particles and then downstream thereof with respect to the flow of air, a plurality of electrically conductive metal baffle plates, which may be oppositely charged attract the charged particles (e.g. of 0.30 micron) which adhere thereto and to the subsequent downstream walls. Such devices are not particularly efficient and require very high DC potential which is also particularly expensive to produce and also produces ozone which can be dangerous to health and some such devices are banned in USA and Canada.
Electro-static filters are also known wherein a fan passes air through a filter material and such mechanical frictional action causes the filter material to be electrostatically charged so as to draw particles to such although such devices have a limited efficiency. EP-A-0292036 discloses an electrostatic air filtration system having an electrically conductive screen sandwiched between first and second dielectric fibrous filter pads which in turn are sandwiched between outer electrically conductive screens so as to thereby apply electrostatic charges to particles in the air passing therepast.
I recently discovered that when a high voltage field is applied to a very low efficiency filter medium of dielectric material and providing such is non-tackified, such will increase the capability of the filter medium to arrest particles many times beyond its original efficiency ratings. I accordingly proposed a filter device comprising a filter medium for gas of dielectric material, a charge applying means of electrically conductive material connectable to a supply of high voltage power and juxtaposed said filter material such that when said electrically conductive material is subject to a high voltage a charge is applied to said dielectric material over its surface area, and an earth or ground means juxtaposed said filter medium on a side of said filter medium opposite to said charge applying means.
However, research and tests have shown that the feature of the ground means on a side of the filter medium opposite to the charge applying means and preferably at least the downstream side relative to the air flow, whilst initially increasing efficiency and minimising the discharge of particles which may become charged in the filter medium, does have a serious disadvantage when the filter has become laden with precipitate/deposits. It is found that the charge of the filter device drops as a consequence of current flowing through the laden filter medium to the ground means. This results in the efficiency of the filter device
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