Gas separation: processes – Electric or electrostatic field – With addition of solid – gas – or vapor
Reexamination Certificate
2002-06-07
2004-08-10
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
Electric or electrostatic field
With addition of solid, gas, or vapor
C055SDIG003, C095S074000, C096S050000, C096S069000
Reexamination Certificate
active
06773488
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to filters and, more particularly, an electrostatic filter and a method thereof.
BACKGROUND OF THE INVENTION
There is an increasing need for effective particle filters. One existing type of particle filter uses a filtering material with a plurality of passages or pores through which the air or gas to be filtered is passed through. If particles in the gas or air are larger than the passages or pores in the filtering material, then the particles are trapped by the filtering material. These filters are rated according to the smallest size particles that they can effectively trap.
Unfortunately, the ability to trap smaller particles requires smaller pore sizes for the filtering material which requires more energy to move the air or gas through the filter. As a result, the energy costs for filtering can become quite large when it becomes necessary to trap small particles.
Another type of particle filter is an electrostatic filter which uses an electret. The electret is a single sheet of material that holds a persistent or quasi-permanent electric charge in the sheet of material. The electrostatic filter with the electret operates by coulombic attraction between the electret and a particle or particles.
Unfortunately, there are limits on the obtainable charge in an electret. For example, U.S. Pat. No. 5,057,710 to Nishiura et al., which is herein incorporated by reference in its entirety, teaches at col 4 lines 25-29 an electret with a charge density of up to 7×10
−10
coulombs per cm
2
which is equivalent to a charge level of 4.4×10
9
charges per cm
2
. In another example, U.S. Pat. No. 6,214,094 to Rousseau et al., which is herein incorporated by reference in its entirety, teaches at col. 22, lines 16-21, and FIGS. 13A and 13B an electret with a charge density of 2×10
−5
coulombs per m
2
which is equivalent to a charge level of 1.25×10
10
charges per cm
2
. As a result, some of the particles in gas or air that pass through the electrostatic filter are not trapped by the electrets because the obtainable charge levels are too low.
SUMMARY OF THE INVENTION
A filter system in accordance with one embodiment of the present invention includes a housing defining a passage between an inlet and an outlet and one or more structures located in the passage in the housing. Each of the structures comprises two or more layers of insulating materials with an imbedded fixed charge located at at least one of the interfaces between the two or more layers.
A filter system in accordance with another embodiment of the present invention includes a housing defining a passage between an inlet and an outlet and one or more structures located in the passage in the housing. At least one of the structures has an imbedded fixed charge at a charge level of at least 1×10
12
charges per cm
2
.
A method for filtering one or more particles from a fluid in accordance with another embodiment of the present invention includes moving the fluid past one or more structures. Each of the one or more structures comprises two or more layers of insulating materials with an imbedded fixed charge located at at least one of the interfaces between the two or more layers. The one or more particles are attracted to at least one of the one or more structures and are trapped against the at least one of the one or more structures.
A method for filtering one or more particles from a fluid in accordance with another embodiment of the present invention includes moving the fluid past one or more structures. Each of the one or more structures has an imbedded fixed charge at a charge level of at least 1×10
12
charges per cm
2
. The one or more particles are attracted to at least one of the one or more structures and are trapped against the at least one of the one or more structures.
The present invention provides an electrostatic filter with lower energy requirements then prior filters. Since the passages in the filter are not restricted to the smallest size particles desired to be captured, energy requirements for moving the fluid through the filter are low. This represents a significant savings in energy cost.
The present invention also provides more effective electrostatic filter. The present invention provides a significant improvement over electrets and other materials in stored charge density. As a result, the present invention is much more effective in attracting and filtering out particles from a fluid.
The present invention also provides a filter that is easier to clean and reuse then prior filters. This represents a further cost savings to the end user of the filter.
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Chiesa Richard L.
Nixon & Peabody LLP
Rochester Institute of Technology
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