Method and apparatus for removing contaminants from gas streams

A method and apparatus 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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment, an apparatus for removing contaminants from gas streams generally identified by reference numeral10, will now be described with reference toFIGS. 1 through 4.

Structure and Relationship of Parts:

Referring toFIG. 1, apparatus10includes an ionization assembly12. Referring toFIG. 3, ionization assembly12has a first body14with a first set of conductive members16and a second body18with a second set conductive members20. First body14and second body18pass through openings22in and are supported by an insulated support24in parallel spaced relation with first set of conductive members16intermeshed with second set of conductive members20.

A tuner26is provided for selectively tuning ionization assembly12. Referring toFIG. 1, this produces an electric field with the characteristic ionizing energy value required to selectively ionize a selected contaminant28with minimal effect on other contaminants30in a gas stream32.

A collector assembly, generally indicated by reference numeral34, is provided for capturing selected contaminant28after ionization. Collector assembly34includes a charged metal substrate36, such as a plate or mesh grid. Charged metal substrate36is charged with an electric charge having a different polarity to that of selected contaminant28after ionization. This causes selected contaminant28to be attracted to collector assembly34. Charged metal substrate36is cooled below a characteristic liquifying temperature for selected contaminant28, thereby liquifying selected contaminant28. Charged metal substrate36is positioned at an angle, with a collection vessel38positioned beneath charged metal substrate36, such that after liquefaction, selected contaminant28flows down charged metal substrate36into collection vessel38. In the illustrated embodiment, metal substrate36is illustrated as being a plate, however, it will be appreciated that metal substrate36can be in other forms such as mesh and still operate.

A magnetic field generator40is provided for applying a magnetic field42to deflect selected contaminant28to collector assembly34. Magnetic field42is applied at an angle to the motion of selected contaminant28to deflect selected contaminant28along an arcuate path44to collector assembly34which can be predetermined based upon known data regarding mass and average drift velocity of selected contaminant28.

Referring toFIG. 2, a drive motor46with a reciprocating shaft47is provided as means to effect relative movement of first body14and second body18toward and away from each other as indicated by arrows48. When drive motor46is activated, reciprocating shaft47extends to move first body14and second body18away from each other and then reciprocating shaft47retracts to move first body14and second body18toward each other. This serves to clean first set of conductive members16and second set of conductive members20, as will hereinafter be further described. Referring toFIGS. 3 and 4, first set of conductive members16and second set of conductive members20include blades50and rods52. Referring toFIG. 4, blades50and rods52extend through openings22in insulating support24. In the illustrated embodiment, openings22are illustrated as being slots54and round apertures56so as to accommodate blades50and rods52. As first body14and second body18are moved toward and away from each other, blades50and rods52of first set of conductive members16and second set of conductive members20move through slots54and round apertures56of insulating support24. As blades50and rods52move back and forth through slots54and round apertures56, respectively, they rub against insulating support24. This rubbing action serves to clean first set of conductive members16and second set of conductive members20.

Referring toFIGS. 1 and 3, the preferred method for removing contaminants from gas streams32using apparatus10will now be described. Sulphur compounds will be used as an example of a contaminant28which can be removed using the teachings of the present method.

A first step involves selecting a contaminant28to be removed from gas stream32. In the illustrated embodiment, gas stream32is passing up through an exhaust chimney58. In this example we are selecting sulphur compounds. Various industries, such as pulp and paper, have gaseous emissions which include sulphur compounds. These sulphur compounds result, even when less than one percent of the emissions, in unpleasant odours. Beyond the presence of unpleasant odours, some persons experience allergic reactions when sulphur compounds are present in emissions. A characteristic ionizing energy value required to selectively ionize a given sulphur compound with minimal effect on other contaminants30in gas stream32is then determined. The research and experiments of Franck-Hertz serve as a basis for determining this characteristic ionizing energy value. It is preferred that the minimum resonance voltage be applied for best results, as such minimum resonance voltages can be more readily “tuned” to ionize the sulphur compounds without effecting other contaminants.

Electric field42with the characteristic ionizing energy value is applied to gas stream32and selectively ionizes selected contaminant28. Selected contaminant28is captured after ionization by applying magnetic field42at an angle to the motion of selected contaminant28to deflect selected contaminant28along arcuate path44. Arcuate path44can be predetermined based upon known data regarding mass and average drift velocity of selected contaminant28to collector assembly34. The motion of the ionized molecules which comprise selected contaminant28can be controlled by applying uniform magnetic field42. Magnetic field42can be supplied using a set of permanent magnets or a set of electromagnetic coils. For example, if magnetic field42is applied at a 90 degree angle with respect to the direction of the motion, it will deflect selected contaminant28by a force, Fmag, which makes 90 degree angle to both magnetic field42and velocity. This forces the ionized molecule to move on arcuate path44. The radius of arcuate path44can be calculated as follows:

where: n=1 for singly charged ion, e is the charge per one

electron, v is the velocity and B is the magnetic field.

Now Fmag=Fcentripetal

So by knowing the mass per each molecule “m” and the average drift velocity and magnetic field42, it can be predetermined where the selected contaminant will land and be collected.

Charged metal substrate36is cooled below a characteristic liquifying temperature for selected contaminant28, thereby liquifying selected contaminant28. By having charged metal substrate36positioned at an angle, after liquefaction, selected contaminant28flows down charged metal substrate36into collection vessel38positioned beneath charged metal substrate36.

Referring toFIGS. 2 and 3first body14and second body18can be moved toward and away from each other by activating drive motor46. As first body14and second body18are moved toward and away from each other first set of conductive members16and second set of conductive members20are pulled back and forth in openings22of insulated support and rub against insulated support24. This serves to clean first set of conductive members16and second set of conductive members20. With periodic cleaning, first conductive members16and second conductive20members maintain longer operational intervals between servicing, without short circuiting or sparking due to dust accumulations.