Gas separation: apparatus – Electric field separation apparatus – With means to add charged solid or liquid particles to...
Reexamination Certificate
2002-10-29
2003-12-02
Chiesa, Richard L. (Department: 1724)
Gas separation: apparatus
Electric field separation apparatus
With means to add charged solid or liquid particles to...
C096S053000, C096S063000
Reexamination Certificate
active
06656253
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to air cleaning equipment and is particularly directed to an air cleaner of the type which sprays electrically charged liquid droplets into the “dirty” air stream. The invention is specifically disclosed as an air filter that charges semiconductive liquid droplets and sprays them into a chamber in which an air flow that contains entrained dust particles is introduced. The particles are charged to one polarity, the liquid droplets are charged to an opposite polarity, and thus the particles are attracted to the droplets. The droplets are accumulated on a collecting surface, then recirculated and used again to collect further dust particles.
BACKGROUND OF THE INVENTION
Indoor air includes many small particles which, when inhaled or otherwise contacted by human beings, have a pernicious effect. Dust alone comprises dead skin, dust mite feces, pet dander, and other microscopic (less than 10 microns in size) particles which elicit a human immune response. This is exemplified by dust mite feces, which comprise a wide array of serine and cysteine protease enzymes that cause respiratory irritation and are responsible for many allergy symptoms.
While filtration systems have been used to reduce the amount of small particles present in selected locations, many of the most commonly irritating materials still exist as particles within a range of about 0.1 micron to about 10 microns in size. Filters having pore openings small enough to be effective at removing particles in this size range are known to become easily occluded and generate high backpressure, thereby requiring high power air blowers. Moreover, the ability to maintain proper air conduction through such filters requires a significant amount of electrical energy, is expensive and cumbersome.
Other types of air purifying devices, such as ionic and electrostatic devices, utilize the charge on particles to attract them to a specified collecting surface which is charged at an opposite polarity. Such devices require the collecting surface to be cleaned constantly and have met with limited success in terms of efficiency.
It will be appreciated that small particles can collect in the home and be re-breathed by the occupants without the benefit of elaborate and high power consumption filtration systems found in the public domain. One vestige of prior art systems is their size and high electrical power demand, which affects the cost of operation and the aesthetics of a sizable filtration apparatus.
With regard to the patent literature, an electrostatic scrubber is disclosed in U.S. Pat. No. 4,095,962 (by Richards) which produces highly charged liquid droplets without a concurrent production of a corona by providing a nozzle configured such that the nozzle's tip forms a substantially uniform electric field over the surface of the liquid on the tip, and this field is large enough to pull off droplets from the tip but not so large so as to create a corona discharge. Selected gas, solid particulates, and liquid mists from gaseous effluents are removed by an electrostatic collector that attracts the highly charged droplets. The droplets are caused to drift, by means of an electric field, through the gaseous effluent to a collecting electrode, thereby absorbing selected gases and aerosol particles, and carrying them to the collecting electrode. The droplet size of the charged droplets is in the range of 30-800 microns radius. One of the recommended scrubbing liquids is ammonium hydroxide, which is used when the effluent gas is sulphur dioxide.
Another patent by Richards, U.S. Pat. No. 6,156,098, also discloses a charged droplet gas scrubber apparatus, which allows scrubbing of uncharged particulates by use of a monopole-dipole attractive force between the charged liquid droplets and the electric dipoles that are induced in the uncharged particulates. The droplet production and charging produces a set of “spreading liquid sheet electrodes” in which the droplets are emitted from the edges of the liquid sheets, and these liquid sheets are interspersed with electrically conductive induction electrodes. This configuration again prevents corona discharge while charging the liquid droplets. Once the droplets are charged, they induce an electric dipole moment in the particulate particles. The droplets are collected by an impingement separator, and the liquid is then collected in a sump and strained through a strainer. In Richards '098, the liquid preferably is a conductive liquid such as tap water, and the size of the droplets is in the range of 25-250 microns diameter. An optimum size of these droplets is stated as being 140 microns. In situations where water is the liquid, the system can be an open-loop system, and the water need not be recirculated. Other liquids could be used, but they must have a minimum conductivity of 50 microSiemens per centimeter (which is 5 Ohm
−1
-meter
−1
). Richards '098 does not use the electrical charge on the droplets to “clean” the dirt particles in the air. Instead, the Richards device is merely attempping to create water droplets from a stream of water, not necessarily to retain an electrical charge on those droplets.
The two Richards patents are not directed toward room or office air cleaning systems, but are specifically directed toward scrubbing effluent gases, such as those produced in a power plant. Furthermore, the Richards patents use a conductive liquid, and this liquid is not necessarily recirculated, particularly when water is used since it is substantially inexpensive. Another feature of the two Richards patents is that the water droplets are fairly large in size, and again are directed toward removing fairly large particles from effluent gases, at a substantially high temperature in most cases. Such large droplets are not going to be substantially effective in removing particulate matter that is relatively small in particle size.
Another patent in this field is U.S. Pat. No. 3,958,959, by Cohen, which discloses a method of removing particles and fluids from a gas stream using charged droplets having a size between 60-250 microns, in which the preferred size is between 80-120 microns. The droplets are generated by ejecting a stable jet of liquid, such as water, in which the liquid jet is broken into charged droplets by applying an electric potential between the jet and the collecting walls of the scrubber. As the droplets are sprayed between two grounded wall plates, dirty inlet air flows at an angle to the liquid droplet flow direction and, once charged, the droplets are attracted to the walls. Since the droplets are moving at an angle to the direction of movement of the gas stream, this increases the relative velocity between the droplets and the particles. After the droplets impact against the grounded wall plates, they flow to the bottom of the walls and are collected in troughs below the walls, and this liquid thus contains some of the particulates from the gas stream. The resulting slurry is recirculated and the particulate matter is removed by a media filter. In this invention, the “droplet drift time” is generally less than 25 milliseconds.
The droplets in Cohen may consist of water, and in some cases there may be chemical agents added to the water that will react with the gas components that are to be removed. An example of such a chemical agent is sodium hydroxide for removing sulphur dioxide. Examples of collecting efficiency are illustrated in
FIG. 12
, which shows curves representing the specific collecting area in square feet per cfm (cubic feet per minute) of air volume movement. The curves are generated for mean particle sizes in the range of 1-10 microns, and it is clear that the smaller the particle size, the less the overall collecting efficiency. None of the curves run down to the 0.3 micron particle size, and it is clear that a fairly large specific collecting area would be required to keep efficiencies above 80-90% (and this is only an extrapolation of these curves: nothing is said in the patent documen
Gartstein Vladimir
Gaw Chinto Benjamin
Willey Alan David
Chiesa Richard L.
Hersko Bart S.
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