U.S. patent application number 12/868034 was filed with the patent office on 2011-03-03 for exhaust gas treatment apparatus.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Takashi Egami, Atsuo Kondo, Takeshi Sakuma, Masahiro Tokuda.
Application Number | 20110047976 12/868034 |
Document ID | / |
Family ID | 43085836 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110047976 |
Kind Code |
A1 |
Tokuda; Masahiro ; et
al. |
March 3, 2011 |
EXHAUST GAS TREATMENT APPARATUS
Abstract
An exhaust gas treatment apparatus 1a of the present invention
includes: a tubular body 10, a discharge electrode 12 disposed
inside the tubular body 10, and a stick-shaped dust collection
electrode 14. The number of the particulates 22 suspended in the
exhaust gas 20 is decreased by charging the particulate matter 22
contained in the exhaust gas passing through the tubular body 10 by
corona discharge 24 caused by the discharge electrode 12,
collecting the charged particulate matter 22a on the inner wall
face 10a of the tubular body 10 by the electric field 26 generated
by the dust collection electrode 14 to agglomerate the particulate
matter 22a, and allowing the agglomerated particulate matter 22b to
scatter again.
Inventors: |
Tokuda; Masahiro;
(Nagoya-City, JP) ; Sakuma; Takeshi; (Nagoya-City,
JP) ; Egami; Takashi; (Tokoname-City, JP) ;
Kondo; Atsuo; (Okazaki-City, JP) |
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
43085836 |
Appl. No.: |
12/868034 |
Filed: |
August 25, 2010 |
Current U.S.
Class: |
60/275 |
Current CPC
Class: |
F01N 3/0275 20130101;
B03C 2201/12 20130101; F01N 3/0892 20130101; B03C 3/12 20130101;
B03C 3/49 20130101; F01N 2240/28 20130101; B03C 2201/10 20130101;
B03C 3/0175 20130101; F01N 3/01 20130101; Y02T 10/20 20130101; B03C
3/06 20130101; B03C 2201/30 20130101; Y02T 10/12 20130101; B03C
3/41 20130101 |
Class at
Publication: |
60/275 |
International
Class: |
F01N 3/08 20060101
F01N003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2009 |
JP |
2009-199401 |
Claims
1. An exhaust gas treatment apparatus comprising: a tubular body
functioning as a flow passage where exhaust gas passes, a discharge
electrode disposed in an central portion in a cross section
perpendicular to a flow direction of the flow passage inside the
tubular body and causing corona discharge in the vicinity thereof
by applying a voltage, and a stick-shaped dust collection electrode
disposed over the range of a length of at least twice the inner
diameter of the tubular body along the central axial direction of
the flow passage on the downstream side of the discharge electrode
in the flow passage and generating an electric field from the
central axis of the flow passage to an inner wall face of the
tubular body; wherein the number of particulates suspended in the
exhaust gas is decreased by charging the particulate matter
contained in the exhaust gas passing through the tubular body by
corona discharge caused by the discharge electrode, collecting the
charged particulate matter on the inner wall face of the tubular
body by the electric field generated by the dust collection
electrode to agglomerate the plural particulates, and allowing the
agglomerated particulates to scatter again.
2. The exhaust gas treatment apparatus according to claim 1,
wherein the length in the central axial direction of the flow
passage of the dust collection electrode is within the range of
twice to five times the inner diameter of the tubular body.
3. The exhaust gas treatment apparatus according to claim 1,
wherein the discharge electrode has a disc-like electrode support
disposed perpendicularly to the flow direction of the flow passage
and a needle-like discharger disposed perpendicularly to the
electrode support.
4. The exhaust gas treatment apparatus according to claim 2,
wherein the discharge electrode has a disc-like electrode support
disposed perpendicularly to the flow direction of the flow passage
and a needle-like discharger disposed perpendicularly to the
electrode support.
5. The exhaust gas treatment apparatus according to claim 1,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to one of the discharge electrode and the dust collection
electrode to apply a voltage on each of the electrodes.
6. The exhaust gas treatment apparatus according to claim 2,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to one of the discharge electrode and the dust collection
electrode to apply a voltage on each of the electrodes.
7. The exhaust gas treatment apparatus according to claim 3,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to one of the discharge electrode and the dust collection
electrode to apply a voltage on each of the electrodes.
8. The exhaust gas treatment apparatus according to claim 4,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to one of the discharge electrode and the dust collection
electrode to apply a voltage on each of the electrodes.
9. The exhaust gas treatment apparatus according to claim 1,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
10. The exhaust gas treatment apparatus according to claim 2,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
11. The exhaust gas treatment apparatus according to claim 3,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
12. The exhaust gas treatment apparatus according to claim 4,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
13. The exhaust gas treatment apparatus according to claim 5,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
14. The exhaust gas treatment apparatus according to claim 6,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
15. The exhaust gas treatment apparatus according to claim 7,
wherein the discharge electrode and the dust collection electrode
are disposed in an electrically connected state, and a voltage is
applied to each of the electrodes independently.
16. The exhaust gas treatment apparatus according to claim 1,
wherein the dust collection electrode is formed so that a diameter
in a cross section perpendicular to the flow direction of the flow
passage is 0.1 to 0.5 times the inner diameter of the tubular
body.
17. The exhaust gas treatment apparatus according to claim 1, which
is further provided with a second discharge electrode disposed in
the central portion in a cross section perpendicular to the flow
direction of the flow passage on the downstream side of the tip on
the flow passage upstream side of the dust collection electrode and
causing corona discharge in the vicinity thereof by applying a
voltage.
18. The exhaust gas treatment apparatus according to claim 1,
wherein at least one of the discharge electrode and the dust
collection electrode is supported in the central portion of the
fluid passage by a porcelain bushing passing through the wall face
of the tubular body and being extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
19. The exhaust gas treatment apparatus according to claim 18,
wherein the porcelain bushing has groove-shaped unevenness formed
on the surface thereof.
20. The exhaust gas treatment apparatus according to claim 1, which
is disposed in an exhaust system of a vehicle provided with a
gasoline engine as a drive mechanism.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to an exhaust gas treatment
apparatus. More specifically, the present invention relates to
exhaust gas treatment apparatus capable of decreasing the number of
the particulates present in exhaust gas by agglomerating the
particulate matter contained in the exhaust gas.
[0002] There is increased need to remove particulate matter and
harmful substances in exhaust gas discharged from internal
combustion engines such as automobile engines, construction machine
engines; industrial machine stationary engines and other combustion
burning appliances; and the like in consideration of influence on
the environment. In particular, in recent years, the regulations
regarding the removal of the particulate matter (hereinbelow
sometimes referred to as "PM") contained in exhaust gas have had a
tendency to be strengthened on a global basis.
[0003] As an exhaust gas treatment apparatus for treating exhaust
gas containing PM as described above, there is disclosed, for
example, an apparatus where PM is electrically collected by
adsorbing PM onto a positively electrified body with negatively
electrifying the PM by the electrified body after the PM is
agglomerated by allowing the PM to collide against a collision
guide member provided inside the flow passage where exhaust gas
passes (see, e.g., JP-A-2001-41024). The PM passed through the
positively electrified body is collected in the filter downstream
and incinerated and removed by applying current to the positively
electrified body to allow it to function as a heater.
[0004] Such an exhaust gas treatment apparatus has a defect of
increase in pressure loss because of complex flow passage
constitution, and manufacturing of the apparatus is not easy. In
addition, since sufficient agglomeration effect cannot be obtained,
the particulate matter passes through the apparatus and is released
without being agglomerated.
[0005] From such problems, there is disclosed an exhaust gas
treatment apparatus provided with an agglomerator which electrifies
particulate matter in exhaust gas by charge by corona discharge and
agglomerates the particulate matter in an electrode collecting the
charge by disposing two kinds of electrodes of charge emission and
charge collection communicating the charge by corona discharge due
to the application of a high voltage between them as an
agglomerator for agglomerating particulate matter (PM) in exhaust
gas in an exhaust gas passage which is formed by an exhaust pipe of
an internal combustion engine and where exhaust gas circulates in
the axial direction of the exhaust pipe in such a manner that a
charge communication portion of the first electrode is located in
almost the central portion in the diametral direction of the
exhaust gas passage (see, e.g., JP-A-2005-320955).
[0006] In addition, as an agglomerator for exhaust gas treatment
apparatus used for an exhaust gas treatment apparatus as described
above and agglomerating the exhaust gas PM charged by corona
discharge by an agglomeration portion, there is disclosed an
agglomerator for an exhaust gas treatment apparatus provided with
the first conductive body disposed on the downstream side of the
exhaust gas stream of the electrified portion in the agglomeration
portion with applying a voltage to the first conductive body to
have a positive electric potential (see, e.g.,
JP-A-2005-324094).
[0007] Further, there is disclosed an exhaust gas purification
apparatus provided with a PM agglomeration means generating
particulate matter (agglomerated PM) having a large particle
diameter by agglomerating the particulate matter contained in
exhaust gas of an engine and PM trapping means disposed downstream
of the exhaust gas flow direction of the PM agglomeration means and
trapping the agglomerated PM agglomerated by the PM agglomeration
means (see, e.g., JP-A-2006-29267).
[0008] However, in an exhaust gas treatment apparatus described in
the JP-A-2005-320955, since the electrode for discharge and one of
a pair of electrodes for generating an electric field for
collecting particulate matter are constituted of the same
electrode, in the case that the other electrode in the pair of
electrodes for generating an electric field is disposed on the
downstream side of the flow passage, charged particulate matter is
accelerated by the electric field and passes through without being
trapped by the other electrode. Therefore, in the case of such a
constitution, there is a problem that the effect in agglomerating
the particulate matter is small to be almost impossible to
agglomerate the particulate matter practically.
[0009] In addition, in the exhaust gas treatment apparatus
described in the JP-A-2005-320955, there is a description of
utilizing the other electrode in the pair of electrodes for
generating an electric field as an inner wall face of the flow
passage. In such a case, the range where an electric field having
strength sufficient for trapping particulate matter is generated is
extremely narrow, and the particulate matter always moving toward
the downstream side on stream of exhaust gas easily passes through
the range of the electric field. Therefore, even in such a case,
there is a problem that the effect in agglomerating the particulate
matter is small to be almost impossible to agglomerate the
particulate matter practically. In particular, in a case that the
exhaust gas flow rate is high or that the number of the
particulates contained in exhaust gas is small, it is very
difficult to trap the particulate matter on the inner wall face of
the flow passage.
[0010] In addition, in the agglomerator for an exhaust gas
treatment apparatus described in the JP-A-2005-324094, a high
voltage is applied to the first conductive body constituting the
agglomeration portion to draw the electrified particulate matter.
It can shorten the moving distance of the electrified particulate
matter and has high agglomeration effect in comparison with the
exhaust gas treatment apparatus disposed in the JP-A-2005-320955.
However, there is a problem that constitution of the electrode (the
electrified portion and the agglomeration portion) is extremely
complex to make it difficult to use it for an automobile or the
like where large vibrations and the like are applied.
[0011] In addition, a PM agglomeration means used for the exhaust
gas purification apparatus described in the JP-A-2006-29267
accelerates the particulate matter in the exhaust gas flow
direction like the exhaust gas treatment apparatus described in the
JP-A-2005-320955. Therefore, there is a problem that the effect in
agglomerating the particulate matter is small to be almost
impossible to agglomerate the particulate matter practically.
[0012] Further, the exhaust gas treatment apparatuses described in
the aforementioned JP-A-2005-320955, JP-A-2005-324094, and
JP-A-2006-29267 have been developed in order to treat exhaust gas
containing a relatively large amount of particulate matter of a
diesel engine or the like. In the case of using them for a gasoline
engine or the like having a small number of the particulates in
exhaust gas in comparison with a diesel engine or the like, the
number of the particulates to be agglomerated is small, and the
particle diameters of the particulates are small. Therefore, the
effect in agglomerating the particulate matter is further
reduced.
[0013] In particular, a new standard by EURO 6 is supposed to be
applied as an exhaust gas regulation from 2012, and there is
desired the development of an exhaust gas treatment apparatus
capable of corresponding with a vehicle provided with a gasoline
engine as a driving mechanism. In particular, since a gasoline
engine has a low torque, if a filter increasing pressure loss of
exhaust gas is disposed in an exhaust system, knocking is easily
caused to cause an engine trouble or the like. Therefore, there is
desired the development of an exhaust gas treatment apparatus
provided with a mechanism which hardly charge a burden on an engine
or the like.
[0014] In addition, when a filter is disposed in an exhaust system
of a gasoline engine to run over a long distance, deposition of ash
derived from component s contained in a gasoline of a fuel becomes
a serious problem. Since ash does not disappear even when
high-temperature regeneration (burning) is performed in a filter
unlike the PM, clogging is caused in the filter as a result to
cause the increase in pressure loss.
SUMMARY OF THE INVENTION
[0015] The present invention has been made in order to solve the
aforementioned problems of prior art and aims to provide an exhaust
gas treatment apparatus capable of decreasing the number of the
particulates contained in exhaust gas by agglomerating the
particulate matter contained in the exhaust gas.
[0016] As a result of earnest studies by the present inventors in
order to solve the aforementioned problems of prior art, they found
out that the problems can be solved by decreasing the number of
particulates present in the exhaust gas by charging the particulate
matter contained in the exhaust gas by discharge, collecting the
charged particulate matter on the inner wall face of a flow passage
by the electric field generated over the range of the predetermined
length from the central portion of the flow passage where exhaust
gas passes toward the inner wall face, and allowing the
agglomerated particulate matter to scatter again; which led to the
completion of the present invention. More specifically, according
to the present invention, the following exhaust gas treatment
apparatuses are provided.
[0017] [1] An exhaust gas treatment apparatus comprising: a tubular
body functioning as a flow passage where exhaust gas passes, a
discharge electrode disposed in an central portion in a cross
section perpendicular to a flow direction of the flow passage
inside the tubular body and causing corona discharge in the
vicinity thereof by applying a voltage, and a stick-shaped dust
collection electrode disposed over the range of a length of at
least twice the inner diameter of the tubular body along the
central axial direction of the flow passage on the downstream side
of the discharge electrode in the flow passage and generating an
electric field from the central axis of the flow passage to an
inner wall face of the tubular body; wherein the number of the
particulates suspended in the exhaust gas is decreased by charging
the particulate matter contained in the exhaust gas passing through
the tubular body by corona discharge caused by the discharge
electrode, collecting the charged particulate matter on the inner
wall face of the tubular body by the electric field generated by
the dust collection electrode to agglomerate the plural
particulates, and allowing the agglomerated particulates to scatter
again.
[0018] [2] The exhaust gas treatment apparatus according to [1],
wherein the length in the central axial direction of the flow
passage of the dust collection electrode is within the range of
twice to five times the inner diameter of the tubular body.
[0019] [3] The exhaust gas treatment apparatus according to [1] or
[2], wherein the discharge electrode has a disc-like electrode
support disposed perpendicularly to the flow direction of the flow
passage and a needle-like discharger disposed perpendicularly to
the electrode support.
[0020] [4] The exhaust gas treatment apparatus according to any one
of [1] to [3], wherein the discharge electrode and the dust
collection electrode are disposed in an electrically connected
state, and a voltage is applied to one of the discharge electrode
and the dust collection electrode to apply a voltage on each of the
electrodes.
[0021] [5] The exhaust gas treatment apparatus according to any one
of [1] to [3], wherein the discharge electrode and the dust
collection electrode are disposed in an electrically connected
state, and a voltage is applied to each of the electrodes
independently.
[0022] [6] The exhaust gas treatment apparatus according to any one
of [1] to [5], wherein the dust collection electrode is formed so
that a diameter in a cross section perpendicular to the flow
direction of the flow passage is 0.1 to 0.5 times the inner
diameter of the tubular body.
[0023] [7] The exhaust gas treatment apparatus according to any one
of [1] to [6], which is further provided with a second discharge
electrode disposed in the central portion in a cross section
perpendicular to the flow direction of the flow passage on the
downstream side of the tip on the flow passage upstream side of the
dust collection electrode and causing corona discharge in the
vicinity thereof by applying a voltage.
[0024] [8] The exhaust gas treatment apparatus according to any one
of [1] to [7], wherein at least one of the discharge electrode and
the dust collection electrode is supported in the central portion
of the fluid passage by a porcelain bushing passing through the
wall face of the tubular body and being extended up to the central
portion in a cross section perpendicular to the flow direction of
the flow passage.
[0025] [9] The exhaust gas treatment apparatus according to [8],
wherein the porcelain bushing has a groove-shaped unevenness formed
on the surface thereof.
[0026] [10] The exhaust gas treatment apparatus according to any
one of [1] to [9], which is disposed in an exhaust system of a
vehicle provided with a gasoline engine as a drive mechanism.
[0027] An exhaust gas treatment apparatus of the present invention
can decrease the number of the particulates present in exhaust gas
by agglomerating the particulate matter contained in exhaust gas.
In particular, since an exhaust gas treatment apparatus of the
present invention can decrease the number of the particulates even
without disposing a filter or the like causing increase in pressure
loss of the exhaust system, it can suitably be used as an exhaust
gas treatment apparatus for treating exhaust gas discharged from a
gasoline engine or the like where a harmful influence is caused by
disposing a filter or the like causing increase in pressure
loss.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a side view schematically showing an embodiment of
an exhaust gas treatment apparatus of the present invention.
[0029] FIG. 2 is a plan view from the upstream side of the exhaust
gas treatment apparatus shown in FIG. 1.
[0030] FIG. 3 is a cross-sectional view showing the A-A' cross
section of the exhaust gas treatment apparatus shown in FIG. 2.
[0031] FIG. 4 is an explanatory view schematically explaining the
process of treating exhaust gas by one embodiment of an exhaust gas
treatment apparatus of the present invention.
[0032] FIG. 5 is a front view schematically showing an example of a
discharge electrode used for an exhaust gas treatment apparatus of
the present invention.
[0033] FIG. 6 is a side view of the discharge electrode shown in
FIG. 5.
[0034] FIG. 7 is a cross-sectional view showing another embodiment
of an exhaust gas treatment apparatus of the present invention.
[0035] FIG. 8 is an explanatory view schematically explaining the
process of treating exhaust gas by another embodiment of an exhaust
gas treatment apparatus of the present invention.
[0036] FIG. 9 is a side view schematically showing an example of a
porcelain bushing used for an exhaust gas treatment apparatus of
the present invention.
[0037] FIG. 10 is a top view of the porcelain bushing shown in FIG.
9.
[0038] FIG. 11 is a side view schematically showing another example
of a porcelain bushing used for an exhaust gas treatment apparatus
of the present invention.
[0039] FIG. 12 is a top view of the porcelain bushing shown in FIG.
11.
[0040] FIG. 13 is a cross-sectional view showing still another
embodiment of an exhaust gas treatment apparatus of the present
invention.
[0041] FIG. 14 is an explanatory view schematically explaining the
process of treating exhaust gas by another embodiment of an exhaust
gas treatment apparatus of the present invention.
[0042] FIG. 15A is a graph showing the change of the number of the
particulates on the outlet side of the exhaust gas treatment
apparatus of Example 1.
[0043] FIG. 15B is a graph showing the change of the number of the
particulates on the outlet side of the exhaust gas treatment
apparatus of Example 1.
[0044] FIG. 15C is a graph showing the change of the number of the
particulates on the outlet side of the exhaust gas treatment
apparatus of Example 1.
[0045] FIG. 15D is a graph showing the change of the number of the
particulates on the outlet side of the exhaust gas treatment
apparatus of Example 1.
[0046] FIG. 16 is a graph showing an enlarged portion showing the
number of the particulates of 0.07 to 6.27 .mu.m in a graph shown
in FIG. 15.
[0047] FIG. 17A is a graph showing the measurement results for 10
seconds of each particle diameter in measurement of the number of
the particulates.
[0048] FIG. 17B is a graph showing enlarged results of the
measurement of the number of the particulates having a particle
diameter of 0.20 to 6.27 .mu.m in FIG. 17A.
[0049] FIG. 17C is a graph showing an enlarged results of the
measurement of the number of the particulates having a particle
diameter of 1.23 to 6.27 .mu.m in FIG. 17A.
[0050] FIG. 18A is a graph showing the change ratio (%) of the
number of the particulates having a particle diameter of 0.01 to
0.70 .mu.m.
[0051] FIG. 18B is a graph showing the change ratio (%) of the
number of the particulates having a particle diameter of 1.23 to
3.06 .mu.m.
REFERENCE NUMERALS
[0052] 1a, 1b, 1c: exhaust gas treatment apparatus, 10: tubular
body, 10a: inner wall face, 12: discharge electrode, 12a: electrode
support, 12b: discharger (needle-like discharger), 14: dust
collection electrode, 16: porcelain bushing, 18, 19: voltage
introduction portion, 20: exhaust gas, 22: particulate matter, 22a:
particulate matter (charged particulate matter), 22b: particulate
matter (agglomerated particulate matter), 24: corona discharge, 26:
electric field, 32: second discharge electrode, 34: unevenness
DETAILED DESCRIPTION OF THE INVENTION
[0053] Embodiments for carrying out the present invention will be
described with referring to drawings. However, the present
invention is by no means limited to these embodiments, and,
needless to say, various changes, modifications, and improvement
may be made on the basis of knowledge of a person of ordinary skill
in the art as long as they do not deviate from the scope of the
present invention.
[0054] [1] Exhaust Gas Treatment Apparatus:
[0055] FIG. 1 is a side view schematically showing an embodiment of
an exhaust gas treatment apparatus of the present invention, FIG. 2
is a plan view from the upstream side of the exhaust gas treatment
apparatus shown in FIG. 1, FIG. 3 is a cross-sectional view showing
the A-A' cross section of the exhaust gas treatment apparatus shown
in FIG. 2, and FIG. 4 is an explanatory view schematically
explaining the process of treating exhaust gas by one embodiment of
an exhaust gas treatment apparatus of the present invention.
Incidentally, FIG. 4 is a cross-sectional view showing an enlarged
portion of a cross-sectional view shown in FIG. 3.
[0056] As shown in FIGS. 1 to 4, the exhaust gas treatment
apparatus 1a of the present embodiment is provided with a tubular
body 10 functioning as a flow passage where exhaust gas 20 passes,
a discharge electrode 12 disposed in an central portion in a cross
section perpendicular to a flow direction of the flow passage
inside the tubular body 10 and causing corona discharge 24 in the
vicinity thereof by applying a voltage (specifically, high
voltage), and a stick-shaped dust collection electrode 14 disposed
over the range of a length of at least twice the inner diameter of
the tubular body 10 along the central axial direction of the flow
passage on the downstream side of the discharge electrode 12 in the
flow passage and generating an electric field from the central axis
of the flow passage to the inner wall face 10a of the tubular body
10.
[0057] The exhaust gas treatment apparatus 1a of the present
embodiment charges the particulate matter 22 contained in exhaust
gas 20 passing through the tubular body 10 by corona discharge 24
caused by the aforementioned discharge electrode 12, collects the
charged particulate matter 22a on the inner wall face 10a of the
tubular body 10 by the electric field 26 generated by the dust
collection electrode 14 to agglomerate plural particulates 22a, and
allows the agglomerated particulates 22b to scatter again, thereby
decreasing the number of the particulates 22 suspended in the
exhaust gas 20.
[0058] Incidentally, the electric field 26 generated by the dust
collection electrode 14 is radially generated in a cross section of
the flow passage over the entire region in the flow direction of
the range of the length of the dust collection electrode 14
disposed therein. The arrows with dotted lines shown by the number
26 in FIG. 4 show the direction of the electric field 26 generated
by the dust collection electrode 14.
[0059] The particulate matter 22a drawn to the inner wall face 10a
of the tubular body 10 by the electric field 26 communicates charge
by being brought into contact with the tubular body 10 and trapped
(i.e., dust collection) on the inner wall face 10a of the tubular
body 10. In such a manner, the charged particulate matter 22a is
drawn to the inner wall face 10a of the tubular body 10 in
sequence. The trapped plural particulates are agglomerated by the
Coulomb's force to form an aggregate of the plural particulates
22b. Then, the particulates 22b bloated by agglomeration up to a
certain size has increased mass and is unable to stay (i.e. to keep
being trapped) on the inner wall face 10a of the tubular body 10 to
be discharged toward the downstream side on stream of the exhaust
gas 20. Thus, the apparent number of the particulates 22 present in
the exhaust gas 20 is decreased.
[0060] Thus, the exhaust gas treatment apparatus of the present
embodiment traps the particulate matter contained in the exhaust
gas on the inner wall face of the tubular body by charging the
particulate matter to agglomerate plural particulates to be
bloated, followed by allowing the particulate matter to scatter
again, thereby decreasing the number (apparent number) of the
particulate matter in the exhaust gas. In particular, the exhaust
gas treatment apparatus of the present embodiment can decrease the
number of the particulates even without disposing a filter or the
like causing rise in pressure loss of the exhaust system and can
agglomerate the particulate matter in a good condition even in the
case that the number of the particulates of the exhaust gas is
small. For example, not only as the apparatus for treating exhaust
gas containing particulate matter in a relatively large amount such
as a diesel engine, but also as the apparatus for treating exhaust
gas discharged from a gasoline engine, it can suitably be used.
Incidentally, the aforementioned "apparent number" means the number
of the particles bloated by agglomerating plural particulates when
each of the bloated particles is counted as one.
[0061] Incidentally, conventionally, there has been proposed an
exhaust gas treatment apparatus (see, e.g., the aforementioned
JP-A-2005-320955) where plural particulates are agglomerated. In
such an exhaust gas treatment apparatus, since the electrode for
discharge and one of a pair of electrodes for generating an
electric field for collecting particulate matter are constituted of
the same electrode, in the case that the other electrode in the
pair of electrodes for generating an electric field is disposed on
the downstream side of the flow passage, charged particulate matter
is accelerated by the electric field and passes through without
being trapped by the other electrode. Therefore, it is almost
impossible to agglomerate the particulate matter practically.
[0062] In addition, in such a conventional exhaust gas treatment
apparatus, there has been proposed the usage of the other electrode
in the pair of electrodes for generating an electric field as the
inner wall face of the flow passage. However, the range where an
electric field having strength sufficient for trapping particulate
matter is generated is extremely narrow, and the particulate matter
always moving toward the downstream side on stream of exhaust gas
easily passes through the range of the electric field. Therefore,
it is almost impossible to agglomerate the particulate matter
practically. In particular, in a case that the exhaust gas flow
rate is high or that the number of particulates contained in
exhaust gas is small, it is very difficult to agglomerate the
particulate matter.
[0063] As shown in FIGS. 1 to 4, in the exhaust gas treatment
apparatus of the present embodiment, a stick-shaped dust collection
electrode 14 generating an electric field from the central axis of
the flow passage to the inner wall face 10a of the tubular body 10
is disposed along the central axial direction of the flow passage
on the downstream side of the discharge electrode 12 to be able to
trap the particulate matter 22a charged by corona discharge caused
by the discharge electrode 12 on the inner wall face 10a of the
tubular body 10 in a good condition. In particular, by controlling
the length to be at least twice the inner diameter of the tubular
body 10, there can be secured a distance capable of sufficiently
drawing even the particulate matter 20 (more specifically, charged
particulate matter 22a) moving in the vicinity of the central axis
of the flow passage up to the inner wall face 10a of the tubular
body 10. In addition, since the particulate matter 22a is trapped
on the inner wall face 10a of the tubular body 10, the pressure
loss of the exhaust system can be reduced.
[0064] Incidentally, in the case that the length of the dust
collection electrode 14 is below twice the inner diameter of the
tubular body 10, the length range where the electric field 26
generated in the flow direction of the exhaust gas 20 (i.e., range
were the electric field 26 effective for drawing the particulate
matter 22a is generated) is narrow, and effect in agglomerating the
particulate matter 22a cannot be obtained sufficiently. That is, a
large number of particulates among the particulate matter 22a
moving toward downstream side pass the aforementioned range where
the effective electric field 26 is generated before the
particulates are drawn up to the inner wall face 10a of the tubular
body 10 and discharged toward the downstream side without being
agglomerated.
[0065] Incidentally, regarding the length of the dust collection
electrode, it is preferably 2 to 5 times, more preferably 3 to 4
times, the inner diameter of the tubular body. Such a constitution
enables to agglomerate particulate matter in a good condition and
to inhibit growing in size of the apparatus. For example, when the
length of the dust collection electrode 14 is above five times the
inner diameter of the tubular body, the dust collection electrode
becomes too long, and the size of the apparatus becomes large,
which makes installation in an exhaust system of an automobile or
the like difficult. In addition, when the length is above five
times the inner diameter, there are increased the cases where the
particles scattered by scattering again are trapped again on the
inner wall of the tubular body. Even in such a case, the effect in
decreasing the substantive number of particles cannot be
expected.
[0066] Incidentally, when the length of the dust collection
electrode is at most five times the inner diameter of the tubular
body, though it depends on the number of a very large number of
particles in the charged particulates, for example, the number of
particulates in exhaust gas and the flow rate of exhaust gas, in a
general vehicle provided with a gasoline engine as a drive
mechanism, about 90% reduction (in terms of the number) is possible
by once trapping particles in the exhaust gas and agglomerating the
particulate matter.
[0067] Incidentally, as a method for confirming the decrease in the
number of the particulates in exhaust gas by the exhaust gas
treatment apparatus of the present embodiment, a particle counter
is disposed on the downstream side of the dust collection electrode
of the exhaust gas treatment apparatus to measure the number of the
particulates in the exhaust gas. An example of the aforementioned
particle counter is the Electrical Low Pressure Impactor
(hereinbelow sometimes referred to as "ELPI") produced by Dekati
Ltd. According to such ELPI, measurement (sampling) of the number
of particulates having a particle diameter of 0.007 to 10 .mu.m in
the particulate matter is possible. Incidentally, upon measurement,
the particulates are classified by the following particle
diameters: 0.007 to 0.014, 0.014 to 0.0396, 0.0396 to 0.0718,
0.0718 to 0.119, 0.119 to 0.200, 0.200 to 0.315, 0.315 to 0.482,
0.482 to 0.760, 0.760 to 1.23, 1.23 to 1.95, 1.95 to 3.08, 3.08 to
6.27 (unit of .mu.m).
[0068] As a more specific measurement method, in the first place, a
particle counter is disposed on the downstream side of the dust
collection electrode of the exhaust gas treatment apparatus, and
the number of the particulates in the exhaust gas is measured
(sampled) in each of the case of applying a voltage in each of the
electrodes (upon applying a voltage) and the case of applying no
voltage (upon applying no voltage). Next, from the sum of the
measurement data by each particle diameter range, the total number
(total discharge number) of the particulates discharged from the
downstream side is calculated out. Next, from the data of the total
discharge number at each of the time of applying a voltage and the
time of applying no voltage, the ratio of the number of the
particulates reduced by the exhaust gas treatment apparatus of the
present embodiment can be obtained.
[0069] In the case of treating exhaust gas by the use of an exhaust
gas treatment apparatus of the present embodiment, there is no
particular limitation on the flow rate of the exhaust gas to be
treated, and the number of the particulates can be decreased in a
good condition with an exhaust gas flow rate of, for example, 200
m/second or less. Incidentally, since the exhaust gas flow rate
upon running of a general vehicle provided with a gasoline engine
as a drive mechanism is 150 m/second (in the case of 2L engine,
6000 revolutions, and exhaust gas temperature of about 600.degree.
C.), even in such a vehicle, the treatment of exhaust gas can be
performed in a good condition by the use of the exhaust gas
treatment apparatus of the present embodiment.
[0070] Hereinbelow, the exhaust gas treatment apparatus of the
present embodiment will be described in more detail by each of the
constituents.
[0071] [1-1] Tubular Body:
[0072] The tubular body is connected to an exhaust system where
exhaust gas being discharged from an internal combustion engine or
the like and containing particulate matter passes to function as a
flow passage where exhaust gas passes. Such a tubular body may be
connected independently to the exhaust pipe for discharging exhaust
gas from the internal engine, or a part of the exhaust pipe
provided on the internal combustion engine may be used as the
tubular body in the exhaust gas treatment apparatus of the present
embodiment.
[0073] In the exhaust gas treatment apparatus of the present
embodiment, a discharge electrode and a dust collection electrode
are disposed inside the tubular body, and inside of the tubular
body is conducted a treatment where (1) the particulate matter is
charged by corona discharge, (2) the charged particulate matter is
trapped on the inner wall face of the tubular body by an electric
field, (3) plural trapped particulates are agglomerated, and (4)
the agglomerated particulates are scattered again.
[0074] Such a tubular body is used as not only a flow passage where
exhaust gas passes, but also the opposed electrode to generate an
electric field between the electrode and the dust collection
electrode. Therefore, the tubular body is preferably constituted of
a conductive material. Further, such a tubular body can be used
also as the opposed electrode of the discharge electrode.
Incidentally, when the tubular body is used as the opposed
electrode of the dust collection electrode or the like, the tubular
body is preferably grounded.
[0075] As the tubular body, there can suitably be used a body made
of a conductive material such as stainless and iron used for an
exhaust pipe of an automobile.
[0076] There is no particular limitation on the length of the
tubular body as long as the tubular body has a length where the
discharge electrode and the dust collection electrode having a
predetermined length are disposed and where the exhaust gas
treatment from the charge of the particulate matter to the
re-scattering of the aforementioned (1) to (4) can be performed in
the tubular body.
[0077] In addition, the tubular body preferably has a cylindrical
shape having a straight central axis. Such a constitution can
effectively inhibit rise in pressure loss due to the disposition of
the exhaust gas treatment apparatus in the exhaust system.
[0078] [1-2] Discharge Electrode:
[0079] The discharge electrode is an electrode for generating
corona discharge which charges the particulate matter in exhaust
gas and disposed in the central portion in across section
perpendicular to the flow direction of the flow passage inside the
tubular body. Incidentally, in the exhaust. gas treatment apparatus
1a shown in FIGS. 1 to 4, as the opposed electrode of the
discharged electrode 12, the tubular body 10 (more specifically,
the inner wall face 10a of the tubular body 10) is used.
[0080] The discharge electrode is preferably constituted to be able
to generate corona discharge in a region up to the inner wall face
of the flow passage formed by the tubular body including the
vicinity of the discharge electrode in such a manner that more
particulate matter, preferably all the particular matter in the
exhaust gas passing through the tubular body passes through the
space where the corona discharge is generated.
[0081] In the exhaust gas treatment apparatus 1a shown in FIGS. 1
to 4, the discharge electrode 12 is supported in the central
portion of the flow passage by the porcelain bushing 16 passing
through the wall face of the tubular body 10 and extended to the
central portion in a cross section perpendicular to the flow
direction of the flow passage by means of the dust collection
electrode 14. Inside the porcelain bushing 16 is disposed a voltage
introduction portion 18 including a wire for applying a voltage
(high voltage) to the discharge electrode 12, and the voltage
introduction portion 18 and the discharge electrode 12 are
electrically connected with each other in a state that electrical
insulation between the voltage introduction portion 18 and the
tubular body 10 is secured.
[0082] There is no particular limitation on the shape of the
discharge electrode as long as the discharge electrode has the tip
portion formed at a sharp angle and corona discharge generated
therein (more specifically, in the tip portion formed at a sharp
angle) by application of the high voltage between the discharge
electrode and the inner wall face of the tubular body. In the
exhaust gas treatment apparatus 1a shown in FIGS. 1 to 4, FIGS. 5
and 6 show an example of the case where the discharge electrode 12
has a disk-like electrode support 12a disposed perpendicularly to
the flow direction of the flow passage and a needle-like discharger
12b disposed perpendicularly to the electrode support 12a (i.e., in
parallel with the flow direction). By such a constitution, an
electric field concentrates in the tip portion of the needle-like
discharger 12b to cause corona discharge in a good condition. In
addition, by the needle-like discharger 12b , even if the tip
portion is worn away in some degree, corona discharge can be caused
by concentrating the electric field. Incidentally, "needle-like
discharger" means a discharger having a thin stick shape as the
entire shape besides a discharger having a sharp pointed tip
portion. Incidentally, in a discharge electrode 12 having such a
shape, the central portion of the electrode support 12a functions
as a portion where a voltage from the voltage introduction portion
18 (see FIG. 1) is introduced. More specifically, in FIG. 3, the
dust collection electrode 14 is connected with the central portion
of the electrode support 12a, and the electrode support 12a is
electrically connected with the voltage introduction portion 18 by
means of the dust collection electrode 14.
[0083] Here, FIG. 5 is a front view schematically showing an
example of the discharge electrode used for an exhaust gas
treatment apparatus of the present invention. FIG. 6 is a side view
of the discharge electrode shown in FIG. 5.
[0084] Incidentally, in FIGS. 5 and 6, 12 dischargers 12b are
disposed at regular intervals on the outside on each of the faces
of the electrode support 12a, and four dischargers 12b are further
disposed inside the positions of the 12 dischargers 12b. In
addition, the four discharger 12b disposed inside are longer than
the 12 discharger 12b disposed outside. Such a constitution can
cause corona discharge over a wider range inside the tubular body
to be able to charge the particulate matter in exhaust gas in a
good condition. In addition, assemblage and manufacturing of the
members are easy, and, since most of the particulate matter in
exhaust gas can be passed through in the vicinity of the discharge
portion, much particulate matter can be charged in a good
condition.
[0085] Incidentally, the shape of the discharge electrode is not
limited to the aforementioned shape where needle-like dischargers
are disposed on the electrode support, and, for example, a
plurality of plate-like bodies each having at least one sharp blade
edge-like side may be disposed on the electrode support. In the
case of such a discharge electrode, the electric field concentrates
on the blade edge of each plate-like body to cause corona
discharge.
[0086] Regarding the material constituting the discharge electrode,
there can suitably be used the same material as that constituting
an electrode having conventionally been used for an exhaust gas
treatment apparatus performing agglomeration by charging the
particulate matter in exhaust gas. Examples of the material include
stainless steel, iron, nickel, kovar, platinum, copper, gold,
molybdenum, and tungsten.
[0087] In addition, the discharge electrode used for the exhaust
gas treatment apparatus of the present embodiment preferably has a
shape where more sharp portions are formed in a discharger portion
so that the electric field may concentrate. In addition, it is
preferable that dischargers are radially disposed from the center
of the cross section of the tubular body and that it has a shape
causing no decrease in pressure. In addition, as the discharger 12b
shown in FIGS. 5 and 6, it is preferably constituted so that many
practical discharge positions are present.
[0088] [1-3] Dust Collection Electrode:
[0089] The dust collection electrode is an electrode for generating
an electric field for trapping the particulate matter charged by
corona discharge on the inner face of the tubular body and disposed
over the length of twice or more than the inner diameter of the
tubular body along the central axial direction of the flow passage
on the downstream side of the discharge electrode in the flow
passage. The opposed electrode disposed so as to face the dust
collection electrode is constituted of the tubular body. By
applying a voltage on the dust collection electrode, an electric
field is generated from the dust collection electrode toward the
inner wall face of the tubular body, and the charged particulate
matter is trapped on the inner wall face of the tubular body.
[0090] Incidentally, in the exhaust gas treatment apparatus 1a of
the present embodiment shown in FIGS. 1 to 4, the discharge
electrode 12 and the dust collection electrode 14 are disposed in
the state that they are electrically connected with each other,
and, by applying a voltage on one of the discharge electrode 12 and
the dust collection electrode 14, the voltage is applied on each of
the electrodes (i.e., the discharge electrodes 12 and the dust
correction electrode 14). In FIGS. 1 to 4, the voltage introduction
portion 18 is electrically connected to the stick-like dust
collection electrode 14, and the end portion on the upstream side
of the stick-like dust collection electrode 14 is electrically
connected to the disc-like electrode support 12a constituting the
discharge electrode 12 (see FIG. 5).
[0091] Thus, in the case that the dust collection electrode 14 and
the discharge electrode 12 are electrically connected with each
other, since the voltage introduction portion 18 for applying a
voltage (high voltage) is used in common, the constitution of the
portion for introducing a voltage to each of the electrodes can be
simplified. In addition, by supporting one of the dust collection
electrode 14 and the discharge electrode 12, both the electrodes
can be fixed in predetermined positions.
[0092] Incidentally, for example, as the exhaust gas treatment
apparatus 1b shown in FIGS. 7 and 8, the dust collection electrode
14 and the discharge electrode 12 may be disposed in the state that
they are electrically insulated to independently apply a voltage on
each of the electrodes (the dust collection electrode 14 and the
discharge electrode 12).
[0093] Here, FIG. 7 is a cross-sectional view showing another
embodiment of an exhaust gas treatment apparatus of the present
invention, and FIG. 8 is an explanatory view schematically
explaining the process of treating exhaust gas by another
embodiment of an exhaust gas treatment apparatus of the present
invention. Incidentally, FIG. 7 is a cross-sectional view showing a
cross section similar to that of the exhaust gas treatment
apparatus shown in FIG. 3, and FIG. 8 is a cross-sectional view
where a part of the cross-sectional view shown in FIG. 7 is
enlarged. In addition, in FIGS. 7 and 8, regarding the elements
constituted in the same manner as those of the exhaust gas
treatment apparatus 1a shown in FIGS. 3 and 4, the same numerals
are applied thereto to omit the explanations.
[0094] In FIGS. 7 and 8, the discharge electrode 12 is supported in
the central portion of the flow passage by the porcelain bushing
16a passing through the wall face of the tubular body 10 and
extended up to the central portion in a cross section perpendicular
to the flow direction of the flow passage and electrically
connected with the voltage introduction portion 18 (voltage
introduction portion for the discharge electrode). In addition, the
dust collection electrode 14 also is supported in the central
portion of the flow passage by the two porcelain bushings 16b each
passing through the wall face of the tubular body 10 and extended
up to the central portion in a cross section perpendicular to the
flow direction of the flow passage and electrically connected with
the voltage introduction portion 19 (voltage introduction portion
for the dust collection electrode).
[0095] In the exhaust gas treatment apparatus 1b constituted in
such a manner, since a voltage can be applied independently on each
of the discharge electrode 12 and the dust collection electrode 14,
it is possible that, for example, a voltage capable of causing
corona discharge 24 suitable for charging the particulate matter 22
is applied on the discharge electrode 12, while a voltage capable
of generating an electric field 26 suitable for trapping the
charged particulate matter 22a on the inner wall face 10a of the
tubular body 10 is applied on the dust collection electrode 14
independently.
[0096] The dust collection electrode preferably has a stick-like
shape where a diameter in a cross section perpendicular to the flow
direction of the flow passage is 0.1 to 0.5 times the inner
diameter of the tubular body. Such a constitution enables to
increase the strength of the electric field generated inside the
tubular body 10. For example, when the diameter of the dust
collection electrode is below 0.1 times the inner diameter of
tubular body, the dust collection electrode is too thin, and it is
sometimes impossible to draw the charged particulate matter
sufficiently to the inner wall face of the tubular body. On the
other hand, when the diameter of the dust collection electrode is
above 0.5 times the inner diameter of the tubular body, the size of
the dust collection electrode occupying the flow passage is too
large, and the pressure loss may be increased. Incidentally, the
diameter of the dust collection electrode is further preferably 0.3
to 0.5 times the inner diameter of the tubular body.
[0097] The material constituting the dust collection electrode is a
conductive material, for example, stainless steel, iron, nickel,
kovar, platinum, copper, gold, molybdenum, and tungsten.
[0098] In addition, the dust collection electrode used for the
exhaust gas treatment apparatus of the present embodiment
preferably has a shape where a high electric field can be generated
in the tubular body without causing local corona discharge or the
like even when a high voltage is applied thereon by reducing
protruding portions of the surface as much as possible by, for
example, chamfering the uneven portions of the surface. In
addition, for lightening the electrode members, it may have the
hollow in the inside thereof.
[0099] [1-4] Porcelain Bushing:
[0100] As described above, in the exhaust gas treatment apparatus
of the present embodiment, it is preferable that at least one of
the discharge electrode and the dust collection electrode is
supported in the central portion of the flow passage by a porcelain
bushing passing through the wall face of the tubular body, being
extended up to the central portion in a cross section perpendicular
to the flow direction of the flow passage, and having electrical
insulation. Such a constitution can cause corona discharge in a
good condition by the discharge electrode and can generate an
electric field for trapping the particulate matter in a good
condition by the dust collection electrode.
[0101] Examples of the material for the porcelain bushing include
alumina, cordierite, mullite, and glass, and alumina or the like
excellent in insulation, thermal resistance, thermal shock
resistance, corrosion resistance, mechanical strength, and the
like, can be used more suitably.
[0102] Such a porcelain bushing preferably has a constitution where
a creeping discharge is not caused on the surface of the porcelain
bushing upon applying a voltage on each of the electrodes. For
example, as shown in FIGS. 9 and 10, as a porcelain bushing 16 used
for the exhaust gas treatment apparatus of the present embodiment,
one having a groove-like unevenness 34 formed on the surface
thereof can suitably be used. Here, FIG. 9 is a side view
schematically showing an example of a porcelain bushing used for an
exhaust gas treatment apparatus of the present invention, and FIG.
10 is a top view of the porcelain bushing shown in FIG. 9.
[0103] In addition, when particulate matter such as soot adheres to
the porcelain bushing, insulation breakdown may be caused between
the tubular body and the discharge electrode or the dust collection
electrode by the particulate matter adhering to the porcelain
bushing to hinder the generation of the electric field for corona
discharge or the dust collection. Therefore, for example, it may
have a constitution having a heater disposed inside the porcelain
bushing so that particulate matter adheres to the surface of the
porcelain bushing can be combusted and removed by heating the
heater.
[0104] In addition, it may have a constitution where a catalyst is
applied on the surface of the porcelain bushing exposed inside the
tubular body to be able to combust and remove adhering particulate
matter by the heat of exhaust gas from an engine or the like when
particulate matter adheres to the surface of the porcelain bushing.
For example, as such a catalyst, an oxidation catalyst used for
purification of exhaust gas discharged from an internal combustion
engine or the like can suitably be used. Suitable examples of the
oxidation catalyst include a conventionally known oxidation
catalyst containing platinum (Pt), rhodium (Rh), palladium (Pd), or
the like.
[0105] In addition, as shown in FIGS. 11 and 12, it may have a
shape where the side portion exposed inside the tubular body of the
porcelain bushing 16 protrudes toward the upstream side of the flow
passage. A porcelain bushing 16 thus constituted hardly hinders the
flow of exhaust gas to reduce resistance of exhaust gas against the
porcelain bushing 16, and the particulate matter hardly adheres to
the surface of the porcelain bushing 16. Here, FIG. 11 is a side
view schematically showing another example of a porcelain bushing
used for an exhaust gas treatment apparatus of the present
invention, and FIG. 12 is a top view of the porcelain bushing shown
in FIG. 11.
[0106] [1-5] Second Discharge Electrode:
[0107] In addition, as shown in FIGS. 13 and 14, an exhaust gas
treatment apparatus may further be provided with the second
discharge electrode 32 disposed in the central portion in across
section perpendicular to the flow direction of the flow passage on
the downstream side of the tip portion on the flow passage upstream
side of the dust collection electrode 14 and causing corona
discharge in the periphery thereof by applying a voltage.
[0108] Here, FIG. 13 is a cross-sectional view showing still
another embodiment of an exhaust gas treatment apparatus of the
present invention, and FIG. 14 is an explanatory view schematically
explaining the process of treating exhaust gas by another
embodiment of an exhaust gas treatment apparatus of the present
invention. Incidentally, FIG. 13 is a cross-sectional view showing
the same cross section as that of the exhaust gas treatment
apparatus shown in FIG. 3, and FIG. 14 is a cross-sectional view
where a part of the cross-sectional view shown in FIG. 13 is
enlarged. In addition, in FIGS. 13 and 14, regarding the elements
constituted in the same manner as those of the exhaust gas
treatment apparatus 1a shown in FIGS. 3 and 4, the same numerals
are applied thereto to omit the explanations.
[0109] Thus, by providing the second discharge electrode 32 on the
downstream side of the tip on the flow passage upstream side of the
dust collection electrode 14, particles which could not be charged
by the first discharge electrode can be charged sufficiently to
improve the particle trapping performance.
[0110] In FIGS. 13 and 14, the second discharge electrode 32 is
disposed in the end portion on the flow passage downstream side of
the dust collection electrode 14, and a voltage is applied on the
second discharge electrode 32 by means of the dust collection
electrode 14. Incidentally, the second discharge electrode 32 used
for the exhaust gas treatment apparatus 1c is constituted in the
same manner as the discharge electrode 12 disposed in the end
portion on the upstream side of the dust collection electrode 14.
That is, for example, as the discharge element 12 shown in FIGS. 5
and 6, the second discharge electrode 32 is constituted by a
disc-like electrode support disposed perpendicularly to the flow
direction of the flow passage and a plurality of needle-like
discharger disposed perpendicularly to the electrode support (i.e.,
in parallel with the flow direction).
[0111] In addition, in the case that the second discharge electrode
is disposed inside the tubular body, it may be constituted so that
the second discharge electrode is disposed on the flow passage
downstream side of the dust collection electrode in the state that
the second discharge electrode and the dust collection electrode
are electrically insulated from each other to be able to apply a
voltage to the second discharge electrode independently though the
illustration is omitted.
[0112] [1-6] Voltage Introduction Portion:
[0113] The voltage introduction portion is a member including a
wire or the like for applying a voltage to the discharge electrode
and the dust collection electrode and connected to a power source
(not illustrated) for causing corona discharge and generating an
electric field for trapping the charged particulate matter.
Incidentally, in the exhaust gas treatment apparatus la of the
present embodiment shown in FIGS. 1 to 4, it passes through the
porcelain bushing 16 passing through the wall face of the tubular
body 10 from the outside of the tubular body 10 and extended up to
the central portion in a cross section perpendicular to the flow
direction of the flow passage to be electrically connected to the
electrode (dust collection electrode 14 in FIG. 3) disposed inside
the tubular body 10.
[0114] [1-7] Power Source:
[0115] The powder source is for applying a voltage to the discharge
electrode or the dust collection electrode, and, for example, a
direct current power source (DC power source), a pulse power
source, or the like may suitably be used. In particular, in the
exhaust gas treatment apparatus of the present embodiment, a direct
current power source (DC power source) is preferable. Incidentally,
the same power source may be used for the discharge electrode and
the dust collection electrode, and different power sources may be
used in the case that the discharge electrode and the dust
collection electrode are disposed in an electrically insulated
state. Incidentally, in the case of using different power sources,
the power sources may be constituted in the same manner. However,
it is preferable that the power source connected to the dust
collection electrode can apply a higher voltage.
[0116] Specific values of the voltage applied on the discharge
electrode and the dust collection electrode and the electric power
can suitably be determined so that suitable discharge and electric
field can be generated depending on the size of the tubular body
functioning as the flow passage; the flow amount and flow rate of
the exhaust gas passing through the flow passage; the amount, size,
number of the particulates contained in the exhaust gas; and the
like.
[0117] For example, though it is not particularly limited, in the
case that the discharge electrode and the dust collection electrode
are electrically connected with each other and that the exhaust gas
treatment apparatus of the present embodiment is used for treating
exhaust gas discharged from a gasoline engine, the voltage is
preferably 6 to 10 kV, more preferably 8 to 9 kV. In addition, the
electric power is preferably 2 to 30 W, more preferably 4 to 15 W.
Such a constitution enables to perform the treatment of exhaust gas
discharged from a gasoline engine in a good condition.
[0118] In addition, in the case that a power source is
independently connected to each of the discharge electrode and the
dust collection electrode, the voltage for the discharge electrode
is preferably 6 to 10 kV, more preferably 8 to 9 kV, and the
voltage for the dust collection electrode is preferably 10 to 18
kV, more preferably 13 to 15 kV. In addition, the power source of
the discharge electrode is preferably 2 to 8 W, more preferably 4
to 6 W, and the power source of the dust collection electrode is
preferably 10 to 40 W, more preferably 16 to 30 W.
EXAMPLE
[0119] Hereinbelow, the present invention will be described more
specifically by Examples. However, the present invention is by no
means limited to these Examples.
Example 1
[0120] There was manufactured an exhaust gas treatment apparatus 1a
as shown in FIGS. 1 to 3. The tubular body 10 had a circular
cylindrical shape having a length of 300 mm in the exhaust gas flow
direction, an outer diameter of 60.5 mm, and an inner diameter of
53.5 mm, and the material of the tubular body was stainless
steel.
[0121] An alumina porcelain bushing 16 was disposed in the position
of 30 mm from the end face on the upstream side of the flow
direction of the tubular body 10 so that it passed through the
tubular body 10, and a voltage introduction portion 18 was disposed
inside the porcelain bushing 16. A stick-shaped dust collection
electrode 14 where discharge electrode 12 was disposed in the end
portion of the upstream side was connected to the voltage
introduction portion 18 to fix the discharge electrode 12 and the
dust collection electrode 14 inside the tubular body 10.
[0122] As shown in FIGS. 5 and 6, the discharge electrode 12 was
constituted by the disc-like electrode support 12 and the 16
dischargers 12b (12 dischargers at an angle of 30.degree. outside,
and 4 dischargers at an angle of 90.degree. inside) disposed on the
disc-like electric support 12a.
[0123] The disc-like electrode support had a shape where 1/4
circles having a radius of 7 mm was gouged out of the ring-shaped
support having the outer periphery of 20 mm so that a cross-shaped
support having a width of 3 mm remains in the central portion. In
addition, through-holes each having a diameter of 1.5 mm were
formed in portions where the dischargers were to be disposed, and
the dischargers were disposed in the through-holes. Incidentally,
the electrode support was formed of stainless steel.
[0124] Each of the dischargers had a diameter of 1.5 mm with a
sharp needle-like tip end and was formed of stainless steel. Each
of the 12 dischargers disposed on the outside had a length of
protruding by 10 mm from the surface of the electrode support, and
each of the 4 dischargers disposed on the inside had a length of
protruding by 20 mm from the surface of the electrode support.
[0125] The dust collection electrode was a stick-like electrode
having a length of 150 mm and a diameter of 20 mm of a cross
section perpendicular to the longitudinal direction. The length of
the dust collection electrode was 2.8 times the inner diameter of
the tubular body.
[0126] The thus constituted exhaust gas treatment apparatus of
Example 1 was attached to a soot generator generating particulate
matter by a burner with light oil being used as the fuel, and test
exhaust gas (hereinbelow referred to as "exhaust gas" simply) at
about 195.degree. C. was introduced at a flow rate of 1.5
m.sup.3/min. In such a state, as shown in Table 1, a direct current
voltage of 8 kV with an electric power of 16 W was applied on the
discharge electrode and the dust collection electrode of the
exhaust gas treatment apparatus of Example 1 to treat the exhaust
gas. The mass (g/hour) of the particulate matter on the inlet side
of the exhaust gas treatment apparatus during treating the exhaust
gas, the number (.times.10.sup.7 particulates/sec.), the mass
(g/hour), and the average particle diameter (.mu.m) of the
particulates on the outlet side were measured. The measurement
results are shown in Table 2.
[0127] (Measurement of the Number of Particulates)
[0128] A particle counter (Electrical Low Pressure Impactor (ELPI)
produced by Dekati Ltd.) was equipped on the downstream side of the
discharge electrode and the dust collection electrode to measure
the number of the discharged particulates by each particle diameter
range on the downstream side of each electrode in the case that a
voltage was applied on each electrode (upon applying a voltage) and
in the case that no voltage was applied (upon applying no voltage).
Then, from the sum of the measurement data for each particle
diameter range, the total number (total discharge number) of the
particulate matter discharged from the downstream side was
calculated out. Incidentally, in the measurement, particles having
the diameter of 0.007 to 10 .mu.m were measured and classified into
the particulate diameter regions of 0.007 to 0.014, 0.014 to
0.0396, 0.0396 to 0.0718, 0.0718 to 0.119, 0.119 to 0.200, 0.200 to
0.315, 0.315 to 0.482, 0.0482 to 0.760, 0.760 to 1.23, 1.23 to
1.95, 1.95 to 3.08, 3.08 to 6.27 (unit of .mu.m). Incidentally, for
example, in the case of the particle diameter of "0.07 to 0.014",
particles having a particle diameter of 0.007 .mu.m or more and
below 0.014 .mu.m are included.
[0129] (Measurement of Ratio of Reduced Particulate Matter)
[0130] From the data of the total discharge number (.times.10.sup.7
particulates/sec.) upon each of the application of a voltage and
the application of no voltage obtained by the aforementioned
measurement of the number of particulates, the ratio of the reduced
number of the discharged particle by the use of the exhaust gas
treatment apparatus was calculated by the following formula
(1).
(Total number upon applying no voltage-total number upon applying a
voltage)/total number upon applying no voltage.times.100 (1)
[0131] (Measurement of Mass of Particulate Matter)
[0132] A bypass line from the exhaust gas flow passage was provided
on each of the upstream side and the downstream side of the
position where the exhaust gas treatment apparatus was disposed,
and a paper filter for sampling the particulate matter in the
exhaust gas passing through the bypass lines was disposed in each
of the bypass lines. The sampling time of the particulate matter by
the paper filter was three minutes, and the change in the paper
filter mass by the sampling was calculated from the paper filter
mass before sampling weighed in advance. By the mass change in the
mass of each of the paper filters disposed on the upstream side and
the downstream side, the mass (g/hour) of the particulate matter on
each of the inlet side and the outlet side of the exhaust gas
treatment apparatus was calculated.
[0133] (Average Particle Diameter of Particulate Matter)
[0134] From the measurement data by particle diameter obtained by
the aforementioned measurement of the number of particulates, the
average particle diameter of the particulates contained in exhaust
gas was calculated by the following formula (2).
Average particle diameter=[.SIGMA.{(average particle diameter in
each sampling range).times.(number of particulates sampled in each
sampling range)]/total discharge number (2)
[0135] Here, FIGS. 15A to 15D are graphs each showing the change in
the number of particulates (discharge number) on the outlet side of
the exhaust gas treatment apparatus of Example 1. FIG. 15A shows
the measurement results of the particulates each having a particle
diameter of 0.007 to 0.014 .mu.m, FIG. 15B shows the measurement
results of the particulates each having a particle diameter of
0.014 to 0.07 .mu.m and the particles each having a particle
diameter of 0.07 to 6.27 .mu.m, and FIG. 15C shows a measurement
result of all particulates (total number). In addition, FIG. 5D is
a graph where the measurement results of the FIGS. 15A to 15C are
shown together. In FIGS. 15A to 15D, the axis of abscissa shows
time (second), and the axis of ordinate shows the number
(particles/sec.) of the particulates. Incidentally, the treatment
of exhaust gas (application of a voltage) is disclosed from 480
sec. from the start of the measurement, and the application of the
voltage was once stopped at 2500 sec. In addition, FIG. 16 is a
graph where the portion showing the number of particulates of 0.07
to 6.27 .mu.m of FIG. 15B is enlarged.
[0136] In addition, FIG. 17A is a graph showing the measurement
results for 10 seconds of each particle diameter in the measurement
of the number of the particulates, where the axis of abscissa shows
the particle diameter (.mu.m), while the axis of ordinate shows the
number of particulates. In addition, FIG. 17B is a graph showing
enlarged results of the measurement of the number of the
particulates having a particle diameter of 0.20 to 6.27 .mu.m in
FIG. 17A. FIG. 17B is a graph showing enlarged results of the
measurement of the number of the particulates having a particle
diameter of 1.23 to 6.27 .mu.m.
[0137] Incidentally, in the aforementioned measurement of the
number of particulates, in the four states of before the voltage
was applied, right after the application of voltage was started
(specifically, after 5 seconds), after 7 minutes from the start of
the application of the voltage, and after the application of the
voltage was stopped, the number of the particulate for 10 seconds
of each particle diameter was obtained, and the ratio of the number
of the particulates in each of the states was calculated out as the
change ratio of the number of the particulates. Here, FIG. 18A is a
graph showing the change ratio (%) of the number of the
particulates having a particle diameter of 0.01 to 0.70 .mu.m, and
18B is a graph showing the change ratio (%) of the number of the
particulates having a particle diameter of 1.23 to 3.06 .mu.m.
Incidentally, in FIGS. 18A and 18B, the axis of abscissa shows each
particle diameter (.mu.m), and the axis of ordinate shows the
change ratio (%) of the number of particulates.
TABLE-US-00001 TABLE 1 Distance between Rate of length of discharge
Inner Length of dust Diameter of dust dust collection electrode and
Dust collection diameter of collection collection electrode dust
collection Discharge electrode electrode tubular body electrode
electrode to diameter electrode Voltage Electric Voltage Electric
(mm) (mm) (mm) of tubular body (mm) (kV) Power (W) (kV) Power (W)
Example 1 53.5 150 20 2.8 0 8 16 Same as left Example 2 53.5 112 20
2.1 0 8 16 Same as left Example 3 53.5 267.5 20 5 0 8 16 Same as
left Example 4 53.5 321 20 6 0 8 16 Same as left Example 5 53.5 535
20 10 0 8 16 Same as left Example 6 53.5 150 20 2.8 50 8 5 8 11
Example 7 53.5 112 20 2.1 50 8 5 8 11 Example 8 53.5 267.5 20 5 50
8 5 8 11 Example 9 53.5 321 20 6 50 8 5 8 11 Example 10 53.5 535 20
10 50 8 5 8 11 Comp. Ex. 1 53.5 None None -- -- 8 5 -- -- Comp. Ex.
2 53.5 96.3 20 1.8 0 8 16 Same as left Comp. Ex. 3 53.5 26.8 20 0.5
0 8 16 Same as left Comp. Ex. 4 53.5 96.3 20 1.8 50 8 5 8 11 Comp.
Ex. 5 53.5 26.8 20 0.5 50 8 5 8 11
TABLE-US-00002 TABLE 2 Particulate Ratio of Condition of matter on
Particulate matter on outlet side reduced exhaust gas inlet side
Average number of Flow rate Temperature Mass Mass Number particle
particulate (m/sec.) (.degree. C.) (g/hour) (g/hour)
(.times.10.sup.7/sec.) diameter (.mu.m) (%) Example 1 12 195 1.07
0.37 5.1 0.038 74 Example 2 12 195 1.08 0.38 5.3 0.038 73 Example 3
12 194 1.06 0.36 4.8 0.038 77 Example 4 12 198 1.05 0.36 4.6 0.038
78 Example 5 12 196 1.04 0.35 4.2 0.038 79 Example 6 12 195 1.08
0.36 4.8 0.039 77 Example 7 12 195 1.09 0.37 5.3 0.038 75 Example 8
12 195 1.05 0.31 2.4 0.039 90 Example 9 12 195 1.07 0.3 2.3 0.038
91 Example 10 12 194 1.06 0.3 2.3 0.038 91 Comp. Ex. 1 12 196 1.08
0.39 6.03 0.038 60 Comp. Ex. 2 12 194 1.08 0.37 5.5 0.038 71 Comp.
Ex. 3 12 196 1.06 0.37 5.6 0.037 65 Comp. Ex. 4 12 198 1.06 0.37
5.22 0.038 65 Comp. Ex. 5 12 196 1.08 0.38 5.35 0.038 64
Examples 2 to 5
[0138] Each of the exhaust gas treatment apparatuses constituted as
in Example 1 was manufactured except that the length of the dust
collection electrode was changed as shown in Table 1 to treat
exhaust gas in the same manner as in Example 1. The measurement
results of the mass (g/hour) of particulate matter on the inlet
side of the exhaust gas treatment apparatus during the exhaust gas
treatment and the number (.times.10.sup.7 particulates/sec.), mass
(g/hour), and average particle diameter (.mu.m) of particulates on
the outlet side during the exhaust gas treatment are shown in Table
2.
Example 6
[0139] As shown in FIG. 7, there was manufactured an exhaust gas
treatment apparatus constituted as in Example 1 except that the
discharge electrode 12 and the dust collection electrode 14 were
disposed with a space of 50 mm and that the voltage introduction
portions 18 and 19 were electrically connected with the discharge
electrode 12 and the dust collection electrode 14, respectively, to
treat exhaust gas in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
Examples 7 to 10
[0140] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 6 except that the length of
the dust collection electrode was changed as shown in Table 1, and
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
Comparative Example 1
[0141] A discharge electrode constituted in the same manner as the
tubular body used in Example 1 was disposed inside the tubular body
which was the same as that used in Example 1 to manufacture an
exhaust gas treatment apparatus. That is, in an exhaust gas
treatment apparatus of Comparative Example 1, a stick-like dust
collection electrode was not disposed. Incidentally, a voltage
introduction portion was electrically connected with the discharge
electrode. By the use of such an exhaust gas treatment apparatus,
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
Comparative Examples 2 and 3
[0142] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 1 except that the length of
the dust collection electrode was changed as shown in Table 1, and
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
Comparative Examples 4 and 5
[0143] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 6 except that the length of
the dust collection electrode was changed as shown in Table 1, and
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
TABLE-US-00003 TABLE 3 Distance between Rate of length of discharge
Inner Length of dust Diameter of dust dust collection electrode and
Dust collection diameter of collection collection electrode dust
collection Discharge electrode electrode tubular body electrode
electrode to diameter electrode Voltage Electric Voltage Electric
(mm) (mm) (mm) of tubular body (mm) (kV) Power (W) (kV) Power (W)
Example 11 53.5 150 20 2.8 20 8 5 8 11 Example 12 53.5 150 20 2.8
80 8 5 8 11 Example 13 53.5 150 5 2.8 0 8 16 Same as left Example
14 53.5 150 10 2.8 0 8 16 Same as left Example 15 53.5 150 5 2.8 50
8 5 8 11 Example 16 53.5 150 10 2.8 50 8 5 8 11 Example 17 53.5 150
20 2.8 0 9 18 Same as left Example 18 53.5 150 20 2.8 0 7 14 Same
as left Example 19 53.5 150 20 2.8 0 14 27 Same as left Example 20
53.5 150 20 2.8 0 15 29 Same as left Example 21 53.5 150 20 2.8 0
13 25 Same as left Example 22 53.5 150 20 2.8 50 9 5.5 9 13 Example
23 53.5 150 20 2.8 50 7 4.8 7 10 Example 24 53.5 150 20 2.8 50 8 5
14 20 Example 25 53.5 150 20 2.8 50 9 5.5 15 22 Example 26 53.5 150
20 2.8 50 7 4.8 13 19 Example 27 53.5 150 20 2.8 0 8 16 Same as
left Example 28 53.5 150 20 2.8 0 8 16 Same as left Example 29 53.5
150 20 2.8 0 8 16 Same as left Example 30 53.5 150 20 2.8 0 8 16
Same as left
TABLE-US-00004 TABLE 4 Particulate Ratio of Condition of matter on
Particulate matter on outlet side reduced exhaust gas inlet side
Average number of Flow rate Temperature Mass Mass Number particle
particulate (m/sec.) (.degree. C.) (g/hour) (g/hour)
(.times.10.sup.7/sec.) diameter (.mu.m) (%) Example 11 12 195 1.07
0.36 4.7 0.039 78 Example 12 12 196 1.06 0.39 5 0.038 73 Example 13
12 195 1.05 0.41 7 0.038 64 Example 14 12 197 1.05 0.4 6.1 0.038 68
Example 15 12 196 1.06 0.4 6.8 0.038 66 Example 16 12 193 1.07 0.4
5.8 0.038 71 Example 17 12 195 1.05 0.37 5 0.038 74 Example 18 12
195 1.06 0.38 5.1 0.038 74 Example 19 12 195 1.06 0.35 5 0.04 76
Example 20 12 196 1.08 0.35 4.9 0.04 77 Example 21 12 196 1.05 0.35
5 0.04 76 Example 22 12 194 1.05 0.36 4.7 0.039 78 Example 23 12
194 1.05 0.39 5 0.039 76 Example 24 12 195 1.09 0.35 4.2 0.04 79
Example 25 12 194 1.08 0.34 4 0.04 82 Example 26 12 196 1.09 0.39
4.5 0.039 77 Example 27 50 195 1.07 0.37 5.1 0.038 72 Example 28
100 195 1.07 0.37 5.1 0.038 70 Example 29 150 195 1.07 0.37 5.1
0.038 66 Example 30 200 195 1.07 0.37 5.1 0.038 60
Example 11 and 12
[0144] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 6 except that the space
between the discharge electrode and the dust collection electrode
was changed as shown in Table 3, and exhaust gas was treated in the
same manner as in Example 1. The measurement results of the mass
(g/hour) of particulate matter on the inlet side of the exhaust gas
treatment apparatus during the exhaust gas treatment and the number
(.times.10.sup.7 particulates/sec.), mass (g/hour), and average
particle diameter (.mu.m) of particulates on the outlet side during
the exhaust gas treatment are shown in Table 4.
Example 13 and 14
[0145] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 1 except that the diameter of
the dust collection electrode was changed as shown in Table 3, and
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 4.
Example 15 and 16
[0146] There was manufactured each of the exhaust gas treatment
apparatuses constituted as in Example 6 except that the diameter of
the dust collection electrode was changed as shown in Table 3, and
exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus during the
exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 4.
Example 17 to 21
[0147] There was manufactured each of the exhaust gas treatment
apparatus constituted as in Example 1, and exhaust gas was treated
in the same manner as in Example 1 except that the voltage (kV)
applied to the discharge electrode and the dust collection
electrode and the electric power (W) were changed as shown in Table
3. The measurement results of the mass (g/hour) of particulate
matter on the inlet side of the exhaust gas treatment apparatus
during the exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 4.
Example 22 to 26
[0148] There was manufactured each of the exhaust gas treatment
apparatus constituted as in Example 6, and exhaust gas was treated
in the same manner as in Example 1 except that the voltage (kV)
applied to the discharge electrode and the dust collection
electrode and the electric power (W) were changed as shown in Table
3. The measurement results of the mass (g/hour) of particulate
matter on the inlet side of the exhaust gas treatment apparatus
during the exhaust gas treatment and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 4.
Examples 27 to 30
[0149] There was manufactured each of the exhaust gas treatment
apparatus constituted as in Example 1, and exhaust gas was treated
in the same manner as in Example 1 except that the flow rate
(m/sec.) of exhaust gas passed through the apparatus was changed as
shown in Table 4. The measurement results of the mass (g/hour) of
particulate matter on the inlet side of the exhaust gas treatment
apparatus during the exhaust gas treatment and the number
(.times.10.sup.7 particulates/sec.), mass (g/hour), and average
particle diameter (.mu.m) of particulates on the outlet side during
the exhaust gas treatment are shown in Table 4.
[0150] (Discussion)
[0151] As shown in Tables 2 and 4, it was found out that, in the
exhaust gas treatment apparatuses of Examples 1 to 26, particulate
matter could be reduced at an extremely high ratio. In addition,
even in Examples 27 to 30, where the flow rate (m/sec.) of exhaust
gas was high, particulate matter could be reduced at a high
ratio.
[0152] In addition, as shown in FIG. 16, it is understood that the
number of particulates having relatively larger particle diameters
of 0.07 to 6.27 .mu.m increases with the passage of discharge time.
This is because the particulates were bloated due to agglomeration
and re-scattering of particulates. Incidentally, in Tables 2 and 4,
the masses of the particulate matter on the inlet side were reduced
compared with that on the outlet side. This is because the
agglomerated particulates trapped on the inner wall face of the
tubular body stayed in the state without being scattered again.
Incidentally, the reduced mass can be confirmed by measurement of
the total mass change of the tubular body before and after the
measurement.
[0153] In addition, as shown in FIGS. 17A to 17C, by applying a
voltage on an electrode, for example, the number of particulates
having relatively small particle diameters of 0.01 to 0.20 .mu.m
was reduced (see FIG. 17B), while the number of particulates having
relatively large particle diameters of 1.23 .mu.m or more was
increased (see FIG. 17C).
[0154] In FIGS. 18A and 18B, it is understood that the change ratio
of the number of the particulates having relatively small particle
diameters shows a minus value (i.e., by applying a voltage, the
number is reduced), while the change ratio of the number of the
particulates having relatively large particle diameters (e.g.,
particulates having a particle diameter of 1.23 .mu.m or more)
shows a plus value (i.e., by applying a voltage, the number is
increased).
[0155] On the other hand, regarding Comparative Example 1, where no
dust collection electrode is disposed, and Comparative Examples 2
to 5, the reduction ratio of the number of the particulate was low
in comparison with that of the exhaust gas treatment apparatus of
Example 1.
[0156] In addition, from the results of Examples 1 to 10, it is
understood that, as the length of the dust collection electrode
becomes long, the reduction ratio of the particulate matter becomes
high, and, in comparison with the unitary type exhaust gas
treatment apparatuses (Examples 1 to 5), where the discharge
electrode and the dust collection electrode are unitary formed, the
separation type exhaust gas treatment apparatuses (Examples 6 to
10), where the discharge electrode and the dust collection
electrode are separated, had high reduction ratio of the
particulate matter. Incidentally, in a separation type exhaust gas
treatment apparatus, as the distance between the discharge
electrode and the dust collection electrode becomes short, the
reduction ratio of the number becomes high.
[0157] In addition, from the comparison of Examples 1 and 6 with
Examples 13 to 16, it is understood that, as the diameter of the
dust collection electrode becomes large, the reduction ratio of the
particulate matter becomes high. Further, in a separation type
exhaust gas treatment apparatus, as the applied voltage of the dust
collection electrode is increased, the reduction ratio of the
number becomes high.
INDUSTRIAL APPLICABILITY
[0158] An exhaust gas treatment apparatus of the present invention
can be used as an exhaust gas treatment apparatus decreasing the
number of the particulates present in exhaust gas by agglomerating
and bloating the particulate matter in the exhaust gas discharged
from internal combustion engines such as automobile engines,
construction machine engines; industrial machine stationary engine
and other combustion burning appliances.
* * * * *