An electrostatic precipitator

Abstract: An electrostatic precipitator (80) including a cylindrical tube (81) the upper end of which is provided with a gas outlet (87) while the lower end is provided with a gas inlet (88). Mounted adjacent the upper end of the tube (81) is an ion source (95). Adjacent the lower end of the tube (81) is a diaphragm (92) which is vibrated by an ultrasonic transducer (93). A liquid is supported on the diaphragm (92) and caused to vibrate in order to produce a mist. An electric potential is established between the ion source (95) and the liquid so that carbon particles contained in the gas stream passing through the precipitator are trapped by liquid droplets which are then conveyed back to a reservoir for the liquid.

Description: The present invention relates to electrostatic precipitators. Described in US Patent 5,064,634 is a method and apparatus for producing an inhalable radionuclide. In particular there is described a carbon crucible heated to a temperature within the range of 1500°C to 2500°C. The carbon crucible under such a temperature produces carbon particles of the size about 10nm. Ordinary methods of incorporating these particles into solution by bubbling are unsatisfactory. A further problem associated with their collection is their radioactive nature. Any collection system needs to shield against operator exposure. AT-B-392741 discloses a precipitator in which a liquid is delivered to the top of the tube and allowed to fall vertically through the tube while a gas is caused to flow in a counter direction. The gas (air) passes an ion source, while the tube is oppositely charged. DE-A-3600137 delivers a liquid to the top of the tube, with the delivery nozzle being charged. The tube has an oppositely charged portion through which the liquid falls. According to the present invention there is provided an electrostatic precipitator comprising: a housing defining a generally upwardly extending duct through which a gas containing carbon particles can pass, said duct having a lower inlet for said gas and an upper outlet for said gas; an ion source projecting into said duct and located between said inlet and said outlet; a wall surrounding at least part of said duct between said inlet and said outlet; characterised in that said precipitator further includes: a generally horizontally oriented diaphragm extending across a lower extremity of said duct and to which a liquid is to be delivered; a vibrator operatively positioned with respect to said diaphragm to cause vibration thereof so that liquid on said diaphragm is caused to form a mist upon the vibration of said diaphragm; and means enabling the establishment of an electric potential between said ion source and said liquid, so that upon the application of said electric potential droplets and particles are attracted to said wall. A preferred form of the present invention will now be described by way of example with reference to the accompanying drawing which is a schematic sectioned side elevation of a precipitator. In the Figure there is schematically depicted an electronic precipitator 80. The precipitator 80 includes a generally cylindrical tube 81 closed at its upper end by an end cap 82. The lower end of the tube 81 is mounted in a base assembly 83 including an upper part 84, and a lower part 85. The tube 81, and upper part 84 cooperate to define a duct 86, with the cap 82 providing a gas outlet 87, and the upper part 84 providing a gas inlet 88. The gas inlet 88 terminates at the duct 86 with an opening 89. The opening 89 and passage 90 extending therefrom, extend substantially at a "tangent" to the cylindrical (or frusto-conical) wall 91, so that gas entering the duct 86 swirls about the longitudinal axis of the tube 81. The cap 82 is formed of a insulating material such as teflon as is the upper part 84. The lower part 85 can be formed of stainless steel. Sandwiched between the upper part 84 and lower part 85 is a diaphragm 92 which may be formed of Mylar™. Mounted in the lower part 85 is an ultrasonic transducer and gas assembly 93. The cap 82 is formed integral with a stem 101. An ion source in the form of a needle 94 extends through the cap 82 and stem 101 to exit at the lower end thereof. The ion source needle 94 has a lower extremity 95. Extending through the upper part 84 is a passage 95 through which there can extend or enter a needle 96 of a hypodermic syringe. The precipitator 80 has a hydrophobic section 97 and a hydrophilic section 98. In operation of the above described precipitator 80, the cavity 101 between the diaphragm 92 and transducer and gas assembly 93 is filled with water and a trace of a surfactant, for example glycerin. Initially, water would be delivered to the upper surface of the diaphragm 92 via a hypodermic syringe or other means. Thereafter, the ultrasonic transducer 93 would be activated to cause the diaphragm 92 to vibrate. Typically the transducer would be an ultrasonic crystal oscillating at approximately 1.7MHz. The water on the diaphragm 92 would be energised to form a dense stream of "mist" (small water droplets). The water delivered to the diaphragm 93 would want to be saline, or other ionic chemical, in order to provide the free ions necessary for the water or other ionic chemical to be conductive. An electric potential is applied between the extremity 95 (corona point) and the liquid delivered to the diaphragm 92. This can be done via the needle 96. The ultrasonic transducer in creating the above discussed mist, causes a "washing down" of the interior wall 99 of the tube 81 surrounding the section 98. The water also runs down the internal wall 100 of the upper part 84. The water on the diaphragm 92, and the wetted walls 99 and 100, form the electrostatic collection electrode. Particles in the gas which become charged are therefore attracted to the water droplets and wall, while the water droplets themselves becomes charged and are also attracted to the walls 99 and 100. In this regard it should be appreciated that an electric potential is applied to the needles 94 and 96, more particularly a positive 8kV charge is applied to the needle 95, at about 100 micro amp maximum current. The ultrasonic transducer is controlled to ensure that the mist does not rise to an extent that it will cause a short circuit to the extremity 95. The hypodermic syringe having the needle 96 is inserted in the upper part 84 to make electrical contact with the liquid on the upper part of the diaphragm 92, thereby making a return ground potential and also providing a means of introducing liquid to the interior of the precipitator 80. The needle 96 may also be used to remove liquid containing the carbon particles. In the above described precipitator 80, other liquids apart from water could be used. For example the liquid could be an oil based liquid.

Claims: An electrostatic precipitator (80) comprising: a housing (81) defining a generally upwardly extending duct (86) through which a gas containing carbon particles can pass, said duct (86) having a lower inlet (88) for said gas and an upper outlet (87) for said gas; an ion source (94) projecting into said duct (86) and located between said inlet (88) and said outlet (97); a wall (99) surrounding at least part of said duct (86) between said inlet (88) and said outlet (87); characterised in that said precipitator further includes: a generally horizontally oriented diaphragm (92) extending across a lower extremity of said duct (86) and to which a liquid is to be delivered; a vibrator (93) operatively positioned with respect to said diaphragm (92) to cause vibration thereof so that liquid on said diaphragm (92) is caused to form a mist upon the vibration of said diaphragm (92); and means enabling the establishment of an electric potential between said ion source (94) and said liquid, so that upon the application of said electric potential droplets and particles are attracted to said wall (81). The electrostatic precipitator (80) of claim 1, wherein said vibrator (93) is an ultrasonic transducer (93). The electrostatic precipitator (80) of claim 1 or 2, further including means (102) to deliver and withdraw the liquid from within said duct (86). The electrostatic precipitator (80) of claim 1, 2 or 3, wherein said wall (99) includes an upper hydrophobic portion and a lower hydrophilic portion. The electrostatic precipitator (80) of any one of claims 1 to 4, wherein said ion source (94) is a needle (94) projecting into said duct (86) and has a lower extremity (95) located at a position spaced above said diaphragm (92). The electrostatic precipitator (80) of claim 5, wherein the means (102) to deliver and withdraw the liquid from within said duct (86) is used to establish said electric potential. The electrostatic precipitator (80) of claim 6, wherein the means (102) to deliver and withdraw said liquid is a hypodermic syringe (96) with the means to establish the electric potential being positioned with respect to the syringe (96), so that the electric potential exists between the ion source (94) and the liquid ejected from the syringe (96). The electrostatic precipitator (80) of any one of claims 1 to 7, wherein the inlet (88) extends at least partially tangential with respect to said duct (86).

Inventors: BROWITT RODNEY, BROWITT, RODNEY
Applicants: ALLRAD NO 19 PTY LTD, ALLRAD NO 28 PTY LTD, ALLRAD NO 29 PTY LTD, ALLRAD NO. 19 PTY LTD, ALLRAD NO. 28 PTY LTD, ALLRAD NO. 29 PTY LTD
Application year: 1995
Main classification: B03C3
IPC codes: B03C3