Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION:
Method And Apparatus For Removing Contaminants From Gas Streams
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
United States Patents 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.
2 5 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
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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.
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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
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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.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to in any way limit the
scope of the invention to
the particular embodiment or embodiments shown, wherein:
FIGURE 1 is a side elevation view, in section, of an apparatus for removing
contaminants from gas streams constructed in accordance with the teachings of
the present
invention.
FIGURE 2 is a side elevation view of an ionization assembly from the apparatus
for
removing contaminants from gas streams illustrated in FIGURE 1.
FIGURE 3 is a top plan view, in section, of the ionization assembly
illustrated in
FIGURE 2.
FIGURE 4 is a detailed perspective view of the internal structure of the
ionization
assembly illustrated in FIGURE 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment, an apparatus for removing contaminants from gas
streams
generally identified by reference numeral 10, will now be described with
reference to FIGURES
1 through 4.
Structure and Relationship of Parts:
Referring to FIGURE 1, apparatus 10 includes an ionization assembly 12.
Referring to
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FIGURE 3, ionization assembly 12 has a first body 14 with a first set of
conductive members 16
and a second body 18 with a second set conductive members 20. First body 14
and second body
18 pass through openings 22 in and are supported by an insulated support 24 in
parallel spaced
relation with first set of conductive members 16 intermeshed with second set
of conductive
5 members 20.
A tuner 26 is provided for selectively tuning ionization assembly 12.
Referring to
FIGURE 1, this produces an electric field with the characteristic ionizing
energy value required
to selectively ionize a selected contaminant 28 with minimal effect on other
contaminants 30 in a
gas stream 32.
A collector assembly, generally indicated by reference numeral 34, is provided
for
capturing selected contaminant 28 after ionization. Collector assembly 34
includes a charged
metal substrate 36, such as a plate or mesh grid. Charged metal substrate 36
is charged with an
electric charge having a different polarity to that of selected contaminant 28
after ionization. This
causes selected contaminant 28 to be attracted to collector assembly 34.
Charged metal substrate
36 is cooled below a characteristic liquifying temperature for selected
contaminant 28, thereby
liquifying selected contaminant 28. Charged metal substrate 36 is positioned
at an angle, with a
collection vessel 38 positioned beneath charged metal substrate 36, such that
after liquefaction,
selected contaminant 28 flows down charged metal substrate 36 into collection
vessel 38. In the
illustrated embodiment, metal substrate 36 is illustrated as being a plate,
however, it will be
appreciated that metal substrate 36 can be in other forms such as mesh and
still operate.
A magnetic field generator 40 is provided for applying a magnetic field 42 to
deflect
selected contaminant 28 to collector assembly 34. Magnetic field 42 is applied
at an angle to the
motion of selected contaminant 28 to deflect selected contaminant 28 along an
arcuate path 44 to
collector assembly 34 which can be predetermined based upon known data
regarding mass and
average drift velocity of selected contaminant 28.
Referring to FIGURE 2, a drive motor 46 with a reciprocating shaft 47 is
provided as
means to effect relative movement of first body 14 and second body 18 toward
and away from
each other as indicated by arrows 48. When drive motor 46 is activated,
reciprocating shaft 47
extends to move first body 14 and second body 18 away from each other and then
reciprocating
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shaft 47 retracts to move first body 14 and second body 18 toward each other.
This serves to
clean first set of conductive members 16 and second set of conductive members
20, as will
hereinafter be further described. Referring to FIGURES 3 and 4, first set of
conductive members
16 and second set of conductive members 20 include blades 50 and rods 52.
Referring to
FIGURE 4, blades 50 and rods 52 extend through openings 22 in insulating
support 24. In the
illustrated embodiment, openings 22 are illustrated as being slots 54 and
round apertures 56 so as
to accommodate blades 50 and rods 52. As first body 14 and second body 18 are
moved toward
and away from each other, blades 50 and rods 52 of first set of conductive
members 16 and
second set of conductive members 20 move through slots 54 and round apertures
56 of insulating
support 24. As blades 50 and rods 52 move back and forth through slots 54 and
round apertures
56, respectively, they rub against insulating support 24. This rubbing action
serves to clean first
set of conductive members 16 and second set of conductive members 20.
Operation:
Referring to FIGURES 1 and 3, the preferred method for removing contaminants
from
gas streams 32 using apparatus 10 will now be described. Sulphur compounds
will be used as an
example of a contaminant 28 which can be removed using the teachings of the
present method.
A first step involves selecting a contaminant 28 to be removed from gas stream
32. In the
illustrated embodiment, gas stream 32 is passing up through an exhaust chimney
58. 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 contaminants 30 in gas stream 32
is 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
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ionize the sulphur compounds without effecting other contaminants.
The electric field with the characteristic ionizing energy value is applied to
gas stream 32
and selectively ionizes selected contaminant 28. Selected contaminant 28 is
captured after
ionization by applying magnetic field 42 at an angle to the motion of selected
contaminant 28 to
deflect selected contaminant 28 along arcuate path 44. Arcuate path 44 can be
predetermined
based upon known data regarding mass and average drift velocity of selected
contaminant 28 to
collector assembly 34. The motion of the ionized molecules which comprise
selected
contaminant 28 can be controlled by applying uniform magnetic field 42.
Magnetic field 42 can
be supplied using a set of permanent magnets or a set of electromagnetic
coils. For example, if
magnetic field 42 is applied at a 90 degree angle with respect to the
direction of the motion, it will
deflect selected contaminant 28 by a force, F,,,ag, which makes 90 degree
angle to both magnetic
field 42 and velocity. This forces the ionized molecule to move on arcuate
path 44. The radius
of arcuate path 44 can be calculated as follows:
Finag q vx B=nevB
where: n=1 for singly charged ion, e is the charge per one electron, v is the
velocity
and B is the magnetic field.
Fcentripetal=[m v z]/R
Now Finag Fcentripetal
Therefore, R=[m v 2]/evB=[mv]/eB
So by knowing the mass per each molecule "m" and the average drift velocity
and
magnetic field 42, it can be predetermined where the selected contaminant will
land and be
collected.
Charged metal substrate 36 is cooled below a characteristic liquifying
temperature for
selected contaminant 28, thereby liquifying selected contaminant 28. By having
charged metal
substrate 36 positioned at an angle, after liquefaction, selected contaminant
28 flows down
charged metal substrate 36 into collection vessel 38 positioned beneath
charged metal substrate
36.
Referring to FIGURES 2 and 3 first body 14 and second body 18 can be moved
toward
and away from each other by activating drive motor 46. As first body 14 and
second body 18 are
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moved toward and away from each other first set of conductive members 16 and
second set of
conductive members 20 are pulled back and forth in openings 22 of insulated
support and rub
against insulated support 24. This serves to clean first set of conductive
members 16 and second
set of conductive members 20. With periodic cleaning, first conductive members
16 and second
conductive 20 members maintain longer operational intervals between servicing,
without short
circuiting or sparking due to dust accumulations.
In this patent document, the word "comprising" is used in its non-limiting
sense to mean
that items following the word are included, but items not specifically
mentioned are not excluded.
A reference to an element by the indefinite article "a" does not exclude the
possibility that more
than one of the element is present, unless the context clearly requires that
there be one and only
one of the elements.
It will be apparent to one skilled in the art that modifications may be made
to the
illustrated embodiment without departing from the spirit and scope of the
invention as hereinafter
defined in the Claims.
