Gas separation: processes – With control responsive to sensed condition – Electric or electrostatic field
Reexamination Certificate
2003-02-14
2004-11-30
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
With control responsive to sensed condition
Electric or electrostatic field
C095S028000, C095S067000, C095S073000, C095S076000, C096S003000, C096S023000, C096S024000, C096S051000
Reexamination Certificate
active
06824587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for removing contaminants from gas streams and, in particular, fine particle sulphur compounds emissions from exhaust gases.
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 4,093,430 and 4,110,086 (collectively the Schwab et al references) disclose a method for removing contaminants from exhaust gas streams and, in particular, fine particle emissions. The Schwab et al reference teaches that exposing the exhaust gases to a high energy, extremely dense electrostatic field serves to charge contaminants in the exhaust gas stream, which can then be collected. Water was introduced into the exhaust gas stream as an added wet scrubbing medium to assist with collection of contaminants. The Schwab et al references reported collection efficiency of approximately 95% of 0.5 micron sized contaminants and 97.5% of 1.25 micron sized contaminants. At these efficiency levels the system consumed about 6 gpm/1000 acfm of water, 150 watts/1000 acfm charging unit power and experienced 6 inches of water pressure drop.
Although the teachings of the Schwab et al references demonstrate promising results in terms of the ability to capture a high percentage of fine particulate emissions, the energy costs in doing so are unacceptably high.
SUMMARY OF THE INVENTION
What is required is a more energy efficient method for removing contaminants from gas streams.
According to one aspect of the present invention there is provided a method for removing contaminants from gas streams. A first step involves selecting a contaminant to be removed from a gas stream and determining a characteristic ionizing energy value required to selectively ionize the selected contaminant with minimal effect on other contaminants in the gas stream. A second step involves applying the characteristic ionizing energy value to the gas stream and selectively ionizing the selected contaminant. A third step involves capturing the selected contaminant after ionization.
In contrast to the teaching of the Schwab et al references which attempted to capture over 95% of all particulate contaminants, the present method is to select a contaminant and to the extent possible with present technologies ionize only the selected contaminant with minimal effect on other contaminants. This technique is particularly effective with contaminants, such as sulphur compounds, which cause unpleasant smells in emissions but constitute only a very small percentage of total emissions. Where multiple contaminants are to be removed, the teachings of the present method can be performed sequentially in stages, removing one of the selected contaminants at each stage. As only a small fraction of the contaminants are effected, the cost of implementing this type of system is a fraction of the cost of implementing the teachings of the Schwab et al references.
According to another aspect of the present invention there is provided an apparatus for removing contaminants from gas streams which includes an ionization assembly and a tuner for selectively tuning the ionization assembly to produce an electric field having a characteristic ionizing energy value required to selectively ionize a selected contaminant with minimal effect on other contaminants in a gas stream. A collector is then provided for capturing the selected contaminant after ionization.
There are a variety of further enhancements which can be added to further enhance the beneficial results obtained through the use of both the described method and apparatus.
Even more beneficial results may be obtained when the selected contaminant is captured after ionization by applying a magnetic field which directs the selected contaminant to the collector.
Even more beneficial results may be obtained when the magnetic field is applied at an angle to the motion of the selected contaminant to deflect the selected contaminant along an arcuate path to the collector which can be predetermined based upon known data regarding mass and average drift velocity of the selected contaminant.
Even more beneficial results may be obtained when the collector is charged with an electric charge having a different polarity to that of the ionized selected contaminant, whereby the selected contaminant is attracted to the collector.
Even more beneficial results may be obtained when the collector includes a charged metal substrate cooled below a characteristic liquifying temperature for the selected contaminant, thereby liquifying the selected contaminant.
Even more beneficial results may be obtained when the charged metal substrate is positioned at an angle, with a collection vessel positioned beneath the charged metal substrate, such that after liquefaction the selected contaminant flows down the charged metal substrate into the collection vessel.
A preferred configuration for the ionization assembly includes a first body having a first set of conductive members and a second body having a second set conductive members. The first body and the second body are supported by and extending through openings in an insulated support in parallel spaced relation with the first set of conductive members intermeshed with the second set of conductive members.
Even more beneficial results may be obtained from the ionization assembly with means is provided to effect relative movement of the first body and the second body toward and away from each other. This serves to clean the first set of conductive members and the second set of conductive members by rubbing them against the insulated support. In the absence of periodic cleaning dust would start to accumulate. An accumulation of dust short circuits the ionization assembly so that it no longer functions and can lead to sparking.
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Fundamentals of Optics and Modern Physics, Hugh D. Young, McGraw-Hill Book Company, 1968, p. 157160.
Chiesa Richard L.
Davis & Bujold P.L.L.C.
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