U.S. patent application number 10/569841 was filed with the patent office on 2007-01-04 for exhaust gas processing method and exhaust gas processing system.
Invention is credited to Junichi Kasai, Akira Mizuno, Kenta Naito, Satoru Senbayashi.
Application Number | 20070000236 10/569841 |
Document ID | / |
Family ID | 34269383 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000236 |
Kind Code |
A1 |
Naito; Kenta ; et
al. |
January 4, 2007 |
Exhaust gas processing method and exhaust gas processing system
Abstract
An exhaust gas processing method and an exhaust gas processing
system for controlling the spatial density distribution of
particulate matter in exhaust gas by utilizing corona discharge in
exhaust gas containing floating particulate matter such as diesel
engine exhaust gas to form a relatively particulate matter-rich
area and a relatively particulate matter-lean area, and diving
exhaust gas particulates to the former and the latter. An exhaust
gas processing system (10) provided with a high-voltage electrode
(12) and a low-voltage electrode (11), wherein exhaust gas G is
allowed to flow between the facing high-voltage electrode (12) and
low-voltage electrode (11), and a high voltage is applied to
between the counter electrodes to generate corona discharge in the
exhaust gas G, whereby floating particulate matter (20) in the
exhaust gas G is charged, the spatial density distribution of the
floating particulate matter in the exhaust gas is controlled by an
electrostatic force between the counter electrodes, and the exhaust
gas G is divided into a high-concentration exhaust gas Gb in the
vicinity of the low-voltage electrode where a particulate matter
concentration is relatively high and a low-concentration exhaust
gas Ga in the vicinity of the high-voltage electrode where a
particulate matter concentration is relatively low.
Inventors: |
Naito; Kenta; (Kyoto,
JP) ; Senbayashi; Satoru; (Kyoto, JP) ; Kasai;
Junichi; (Kanagawa, JP) ; Mizuno; Akira;
(Aichi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
34269383 |
Appl. No.: |
10/569841 |
Filed: |
August 26, 2004 |
PCT Filed: |
August 26, 2004 |
PCT NO: |
PCT/JP04/12262 |
371 Date: |
February 28, 2006 |
Current U.S.
Class: |
60/275 |
Current CPC
Class: |
B03C 3/41 20130101; B03C
3/155 20130101; B03C 3/64 20130101; B03C 3/06 20130101; Y02T 10/20
20130101; B03C 2201/08 20130101; F01N 3/01 20130101; B03C 3/49
20130101; B03C 3/62 20130101; B03C 2201/30 20130101; F01N 3/021
20130101; Y02T 10/12 20130101; B03C 2201/04 20130101; B03C 2201/12
20130101 |
Class at
Publication: |
060/275 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2003 |
JP |
2003-306307 |
Claims
1. An exhaust gas processing method, comprising a high-voltage
electrode and a low-voltage electrode facing said high-voltage
electrode, wherein exhaust gas flows through between the counter
electrodes, a high voltage is applied between the counter
electrodes to generate corona discharge in the exhaust gas,
floating particulate matter in the exhaust gas non-uniformly
distributes near the low-voltage electrode by electrification and
coheres through the corona discharge, and the exhaust gas near the
low-voltage electrode is divided into high-concentration exhaust
gas in which the concentration of the floating particulate matter
is relatively high and low-concentration exhaust gas in which the
concentration of the floating particulate matter is relatively
low.
2. The exhaust gas processing method according to claim 1,
comprising purifying the high-concentration exhaust gas with a
filter.
3. An exhaust gas processing system having a high-voltage electrode
and a low-voltage electrode facing said high-voltage electrode,
comprising: an electrifying area in which exhaust gas flows through
between the counter electrodes, a high voltage is applied between
the counter electrodes to generate corona discharge in the exhaust
gas, and the floating particulate matter is electrified, a
condensing area for non-uniformly distributing the floating
particulate matter electrified by the electrifying area near the
low-voltage electrode, and a divide-flow area for dividing the
exhaust gas near the low-voltage electrode in which the
concentration of the floating particulate matter is relatively
high, into high-concentration exhaust gas in which the
concentration of the floating particulate matter is relatively high
and low-concentration exhaust gas in which the concentration of the
floating particulate matter is relatively low.
4. The exhaust gas processing system according to claim 3, wherein
the low-voltage electrode is formed into a cylindrical body, the
high-voltage electrode is provided in the longitudinal direction
along near the center of the low-voltage electrode of the
cylindrical body in the electrifying area in at least the upstream
side of the low-voltage electrode, and an inner cylinder for
dividing exhaust gas is provided inside the low-voltage electrode
in the divide-flow area in at least the downstream side of the
low-voltage electrode, so that the low-concentration exhaust gas
flows through the inside of the inner cylinder and the
high-concentration exhaust gas flows through the outside of the
inner cylinder.
5. The exhaust gas processing system according to claim 3, wherein
the low-voltage electrode is formed into a cylindrical body, the
high-voltage electrode is provided in the longitudinal direction
along near the center of the low-voltage electrode in the
cylindrical body in the electrifying area in at least the upstream
side of the low-voltage electrode, the low-voltage electrode is
formed to be gas-permeable in the condensing area in the downstream
side of the electrifying area, and an outer cylinder is provided
outside the low-voltage electrode in the condensing area and the
divide-flow area so that the exhaust gas flowing in from the
upstream side of the low-voltage electrode is divided into the
low-concentration exhaust gas flowing through the inside of the
low-voltage electrode and the high-concentration exhaust gas
flowing through the outside of the low-voltage electrode.
6. The exhaust gas processing system according to any one of claims
3 to 5, comprising a filter for purifying floating particulate
matter included in the high-concentration exhaust gas.
7. The exhaust gas processing system according to any one of claims
3 to 5, wherein the exhaust gas is exhaust gas of an internal
combustion engine.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an exhaust gas processing
method and system for collecting floating particulate matter in
exhaust gas using corona discharge.
DESCRIPTION OF RELATED ART
[0002] To remove floating particulate matter (particulate matter:
hereafter referred to as PM) included in the exhaust gas emitted by
diesel engines, a technique that collects the particulate matter
with a filter, referred to as a diesel particulate filter
(hereafter referred to as DPF), so as to decrease the quantity of
PM to be externally discharged is being developed.
[0003] On the other hand, in the case of the PM which causes air
contamination, ultra-fine particles with diameters of 2.5 .mu.m or
smaller (particularly, with diameters of tens of nanometers)
referred to as PM2.5 have recently become a problem on
antipollution measures. It is considered that ultra-fine particles
are also discharged from the direct-injection gasoline engine that
is frequently used as an automobile engine at present. Therefore,
establishment of a technique for removing the ultra-fine particles
is very necessary.
[0004] However, when collecting the ultra-fine particles using only
a DPF method, a filter with extremely fine meshes is necessary.
Therefore, it is very difficult to collect the ultra-fine particles
without a large pressure loss.
[0005] Therefore, as a method for collecting the ultra-fine
particles with a diameter of tens of nanometers without a large
pressure loss, a technique using an electric dust collection is
being considered. To use the electric dust collection technique, a
method and an apparatus for applying a high voltage to a
high-voltage discharge wire for a dust-collecting electrode formed
of a metal thin wire strained in a metal cylinder pipe and removing
floating particulate matter such as white smoke and mist-like
substance in like plant exhaust gas by electrostatically absorbing
them, are proposed, as shown for example in registered utility
model No. 3019526 and Japanese patent application Kokai publication
No. 1994-142551.
[0006] In the case of the electric dust collection method and
electric dust collector, floating particulate matter is electrified
by generating corona discharge in exhaust gas at a charged area.
Moreover, the particulate matter electrified at a dust-collecting
area is removed from the gas by using electrostatic force (Coulomb
force) and capturing the particulate matter in a dust-collecting
electrode that is a sheet electrode with a low voltage (generally,
ground potential).
[0007] Moreover, an apparatus for collecting the PM of an internal
combustion engine, disclosed in Japanese patent application Kokai
publication No. 1984-85415, is proposed. In the case of this
apparatus, an electric dust collector is provided in an exhaust gas
passage and an electric heater is provided to a dust-collecting
electrode. Furthermore, a collected amount of the PM attached to
the surface of the electric heater is detected in accordance with
the occurrence frequency of combustion discharge, and the electric
heater is operated for a predetermined period of time based on this
occurrence frequency to burn and remove the collected PM.
[0008] However, though the electric dust collector captures
electrified particulate matter by using electrostatic force and
using a vessel wall surface with a low voltage potential
(generally, ground potential) as a dust-collecting electrode, there
is a problem that a purifying performance is deteriorated in a
comparatively short time (for example, in several minutes). That
is, in the case of a configuration for collecting electrified
particles by simply using the vessel wall surface as a
dust-collecting electrode, the dust-collection area for the
quantity of gas (exhaust gas) becomes comparatively small.
Therefore, the quantity of particulate matter that can be collected
becomes small, and the purifying performance is deteriorated in a
comparatively short time due to deposition of particulate matter on
the dust-collecting electrode.
[0009] Moreover, in the case of collecting the PM in the exhaust
gas emitted by an internal combustion engine such as a diesel
engine, there is a problem that a re-entrainment easily occurs
because the PM has a comparatively low resistivity. To capture the
re-entrained PM, it is considered to increase the dust-collection
area and capture the re-entrained particles by providing a filter
in the downstream side of an electrifying area. However, to keep
the collection performance of the filter and prevent the pressure
loss from increasing, it is necessary to decrease the flow rate of
exhaust gas flowing into the filter to a certain extent (for
example, 3 m/s or less), and the opening area of the filter is
inevitably increased. Therefore, a problem occurs that the dust
collector cannot be downsized.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide an
exhaust gas processing method and an exhaust gas processing system
for controlling the spatial density distribution of floating
particulate matter in exhaust gas by utilizing corona discharge in
exhaust gas containing floating particulate matter such as diesel
engine exhaust gas to form a relatively particulate matter-rich
area and a relatively particulate matter-lean area, and dividing
exhaust gas particulate matter to the former and the latter.
[0011] An exhaust gas processing method of the present invention
for achieving the above object comprises a high-voltage electrode
and a low-voltage electrode facing said high-voltage electrode,
wherein exhaust gas flows through between the counter electrodes, a
high voltage is applied between the counter electrodes to generate
corona discharge in the exhaust gas, floating particulate matter in
the exhaust gas non-uniformly distributes near the low-voltage
electrode by electrification and coheres through the corona
discharge, and the exhaust gas near the low-voltage electrode is
divided into high-concentration exhaust gas in which the
concentration of the floating particulate matter is relatively high
and low-concentration exhaust gas in which the concentration of the
floating particulate matter is relatively low.
[0012] The relation between high voltage and low voltage in this
case is that a voltage with a larger absolute value of positive and
negative voltages is assumed as a high voltage and a voltage with a
smaller absolute value of the voltages is assumed as a low voltage.
Moreover, when one voltage is positive and the other is negative,
the high and low of voltages are determined in accordance with
magnitudes of the absolute values.
[0013] That is, in the case of an exhaust gas processing system
having a high-voltage electrode and a low-voltage electrode, corona
discharge is generated in exhaust gas by flowing exhaust gas G
between the facing high-voltage electrode and low-voltage electrode
and applying a high voltage between the counter electrodes.
Thereby, the floating particulate matter in the exhaust gas G is
electrified and the spatial density distribution of the floating
particulate matter in the exhaust gas is controlled with the
electrostatic force between the counter electrodes. Moreover, the
exhaust gas is divided into a high-concentration exhaust gas near
the low-voltage electrode in which the particulate matter
concentration is relatively high and a low-concentration exhaust
gas near the high-voltage electrode in which the particulate matter
concentration is relatively low.
[0014] Furthermore, the flow of the exhaust gas undergoing the
corona discharge treatment in a corona discharge area is divided by
a double-pipe structure or the like. When dividing the flow, the
particulate matter is non-uniformly distributed to one flow of the
exhaust gas to separate and condense them by attracting the
particulate matter electrified through the corona discharge
treatment to a dust-collecting electrode by an electrostatic
force.
[0015] According to this exhaust gas processing method, even a
particulate matter with comparatively small electric resistance
that abnormal re-entrainment in the case of electric dust
collection, like the PM in the exhaust gas emitted by diesel
engines, can be easily condensed.
[0016] Moreover, in the case of the exhaust gas processing method,
when purifying the high-concentration exhaust gas with a filter,
floating particulate matter can be easily collected even with a
wide-mesh filter because the cohesion and corpulence of the
floating particulate matter occurs, and only a small pressure loss
occurs. Furthermore, because the quantity of the high-concentration
exhaust gas is smaller than the quantity of the original exhaust
gas, it is possible to decrease the capacity of the filter.
Therefore, it is possible to downsize an exhaust gas processing
system.
[0017] An exhaust gas processing system of the present invention
for achieving the above object having a high-voltage electrode and
a low-voltage electrode facing said high-voltage electrode,
comprises an electrifying area in which exhaust gas flows through
between the counter electrodes, a high voltage is applied between
the counter electrodes to generate corona discharge in the exhaust
gas, and the floating particulate matter is electrified, a
condensing area for non-uniformly distributing the floating
particulate matter electrified by the electrifying area near the
low-voltage electrode, and a divide-flow area for dividing the
exhaust gas near the low-voltage electrode in which the
concentration of the floating particulate matter is relatively
high, into high-concentration exhaust gas in which the
concentration of the floating particulate matter is relatively high
and low-concentration exhaust gas in which the concentration of the
floating particulate matter is relatively low.
[0018] The boundary between the downstream side of the electrifying
area and the upstream side of the condensing area and the boundary
between the downstream side of the condensing area and the upstream
side of the divide-flow area are not always clear, and they are
frequently overlapped each other. However, the electrifying area,
the condensing area, and the divide-flow area are constituted from
the upstream side.
[0019] In the case of the exhaust gas processing system described
above, the low-voltage electrode is formed into a cylindrical body,
the high-voltage electrode is provided in the longitudinal
direction along near the center of the low-voltage electrode of the
cylindrical body in the electrifying area in at least the upstream
side of the low-voltage electrode, and an inner cylinder for
dividing exhaust gas is provided inside the low-voltage electrode
in the divide-flow area in at least the downstream side of the
low-voltage electrode, so that the low-concentration exhaust gas
flows through the inside of the inner cylinder and the
high-concentration exhaust gas flows through the outside of the
inner cylinder. Thereby, the diameter of an exhaust gas purifying
apparatus is decreased and the configuration of the apparatus is
simplified.
[0020] In the case of the exhaust gas processing system described
above, the low-voltage electrode is formed into a cylindrical body,
the high-voltage electrode is provided in the longitudinal
direction along near the center of the low-voltage electrode of the
cylindrical body in the electrifying area in at least the upstream
side of the low-voltage electrode, the low-voltage electrode is
formed to be gas-permeable in the condensing area in the downstream
side of the electrifying area, and an outer cylinder is provided
outside the low-voltage electrode in the condensing area and the
divide-flow area so that the exhaust gas flowing in from the
upstream side of the low-voltage electrode is divided into the
low-concentration exhaust gas flowing through the inside of the
low-voltage electrode and the high-concentration exhaust gas
flowing through the outside of the low-voltage electrode. This
configuration enables to easily secure a space in which a gas
treatment member such as a filter can be provided between the
dust-collecting electrode and the outer cylinder.
[0021] Moreover, in the case of the exhaust gas processing system
described above, it is possible to easily purify the floating
particulate matter in the exhaust gas by using a filter for
purifying floating particulate matter included in the
high-concentration exhaust gas. When providing this filter to the
condensing area and the divide-flow area, it is possible to
downsize the whole exhaust gas processing system. Moreover, it is
possible to provide a well-known DPF, separately from the
low-voltage electrode of the exhaust gas processing apparatus. In
this case, it is possible to use an existing DPF.
[0022] When purifying high-concentration exhaust gas with a filter,
it is possible to easily collect the floating particulate matter by
a wide-mesh filter because the cohesion and corpulence of the
floating particulate matter occurs, and only a small pressure loss
occurs. Moreover, because the quantity of the high-concentration
exhaust gas is smaller than the quantity of the original exhaust
gas, it is possible to decrease the capacity of the filter.
Therefore, it is possible to downsize the exhaust gas processing
system.
[0023] Moreover, if the low-concentration exhaust gas is purified
up to a degree at which the exhaust gas does not require further
processing, it is possible to configure the system so that the
low-concentration exhaust gas is directly discharged. Furthermore,
when the exhaust gas requires slight purification, it is possible
to eliminate the necessity of further exhaust gas processing of the
low-concentration exhaust gas by re-circulating the gas into
cylinders as EGR gas.
[0024] Furthermore, when the low-concentration exhaust gas requires
further exhaust gas processing and is purified with a filter, large
floating particulate matter is removed and moreover, the PM
quantity is extremely decreased. Therefore, it is possible to
collect the remaining ultra-fine particles with tens of nm sizes by
using a fine-mesh filter. Moreover, even if using a fine-mesh
filter, clogging hardly occurs. Therefore, it is possible to remove
the PM at a low pressure-loss for a long period of time. Moreover,
it is possible to decrease the capacity of a filter because the
quantity of low-concentration exhaust gas is smaller than the
quantity of the original exhaust gas.
[0025] That is, it is possible to efficiently purify the
high-concentration exhaust gas that includes the corpulence PM and
the low-concentration exhaust gas that does not include the
corpulence PM by a dust arrester or dust collector suitable for
each, such as a filter.
[0026] Then, an exhaust gas processing method and an exhaust gas
processing system of the present invention is particularly
effective when exhaust gas is the exhaust gas of an internal
combustion engine, particularly the exhaust gas emitted by diesel
engines because the PM included in this exhaust gas has a
comparatively low electric resistance and the PM collected by
electric dust collector easily re-entrains.
[0027] Moreover, the exhaust gas processing system can be used
independently or by combining a plurality of the systems in
accordance with the relation between the quantity of the exhaust
gas to be processed and the capacity of an exhaust gas processing
system. Furthermore, by combining the exhaust gas processing
systems at multistage, it is possible to further improve the degree
of dilution or condensation and PM purifying performance.
[0028] The target gas of an exhaust gas processing method and an
exhaust gas processing system of the present invention is not
limited to the exhaust gas emitted by diesel engines, and it
includes not only exhaust gas of an internal combustion engine for
other vehicle or fixed-type internal combustion engine but also
exhaust gas of a boiler, power generator, or combustion system such
as a co-generator. Moreover, the dust includes not only the dust
caused by combustion but also the dust caused by machining.
[0029] An exhaust gas processing method and an exhaust gas
processing system of the present invention have the following
advantages.
[0030] By applying a high voltage to a high-voltage electrode and
generating corona discharge in exhaust gas, it is possible to
electrify the floating particulate matter in the exhaust gas and
result in the cohesion and non-uniform distribution of the matter
on a low-voltage electrode or near the electrode. Moreover, the
exhaust gas is divided into high-concentration exhaust gas in which
the concentration of the floating particulate matter is high and
low-concentration exhaust gas in which the concentration of the
matter is low. Therefore, it is possible to easily condense even a
particulate matter with a comparatively low electric resistance
that re-entrains in the case of electric dust collection, like the
PM in the exhaust gas emitted by diesel engines.
[0031] Moreover, in the case of high-concentration exhaust gas, it
is possible to easily and efficiently collect the floating
particulate matter even by a wide-mesh filter, and only a small
pressure-loss occurs, because the cohesion and corpulence of the
matter occurs and condensed. Furthermore, it is possible to
decrease the capacity of a filter because the quantity of the
high-concentration exhaust gas is smaller than the quantity of the
original exhaust gas. Therefore, it is possible to downsize an
exhaust gas processing apparatus and exhaust gas processing
system.
[0032] Furthermore, large floating particulate matter is removed
from low-concentration exhaust gas, and the PM quantity is
extremely decreased. Therefore, it is possible to collect
ultra-fine particles by using a fine-mesh filter when purifying the
exhaust gas by the filter in order to raise the degree of
purification. Furthermore, it is possible to remove the PM at a low
pressure-loss for a long period of time because clogging hardly
occurs even when using a fine-mesh filter. Furthermore, it is
possible to decrease the capacity of the filter because the
quantity of the low-concentration exhaust gas is smaller than the
quantity of the original exhaust gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a block diagram of an exhaust gas processing
system of first embodiment of the present invention.
[0034] FIG. 2 (a) is a sectional view of the exhaust gas processing
system in FIG. 1, which is an illustration showing a cylindrical
low-voltage electrode and a single high-voltage electrode.
[0035] FIG. 2 (b) is a sectional view of the exhaust gas processing
system in FIG. 1, which is an illustration showing a rectangular
low-voltage electrode and a plurality of high-voltage
electrodes.
[0036] FIG. 3 is a block diagram of a separator of second
embodiment of the present invention.
[0037] FIG. 4 (a) is a sectional view of the exhaust gas processing
system in FIG. 3, which is an illustration showing a cylindrical
low-voltage electrode and a single high-voltage electrode.
[0038] FIG. 4 (b) is a sectional view of the exhaust gas processing
system in FIG. 3, which is an illustration showing a low-voltage
electrode having a slender sectional-form and a plurality of
high-voltage electrodes.
[0039] FIG. 5 is a block diagram of a separator of third embodiment
of the present invention.
[0040] FIG. 6 is a block diagram of a separator of fourth
embodiment of the present invention.
[0041] FIG. 7 (a) is a sectional view of the exhaust gas processing
system in FIG. 6, which is an illustration showing a cylindrical
low-voltage electrode and a single high-voltage electrode.
[0042] FIG. 7 (b) is a sectional view of the exhaust gas processing
system in FIG. 6, which is an illustration showing a low-voltage
electrode having a slender sectional-form and a plurality of
high-voltage electrodes.
[0043] FIG. 8 is a block diagram of a separator of fifth embodiment
of the present invention.
[0044] FIG. 9 is an illustration showing a cylindrical low-voltage
electrode and a plurality of high-voltage electrodes.
DETAILED DESCRIPTION OF THE INVENTION
[0045] An embodiment of the present invention is described below by
using an exhaust gas processing system for separating and
condensing the PM included in the exhaust gas emitted by diesel
engines as an example and referring to the accompanying drawings.
The target gas of the present invention is not limited to the
exhaust gas emitted by diesel engines, and it includes not only the
exhaust gas of an internal combustion engine for other vehicle or
fixed-type internal combustion engine but also the exhaust gas of a
boiler, power generator, or combustion system such as a
co-generator and the exhaust gas including dust caused by
machining.
[0046] FIGS. 1 and 2 show a configuration of an exhaust gas
processing system 10 of first embodiment of the present invention.
The exhaust gas processing system 10 is constituted including a
cylindrical low-voltage electrode 11, high-voltage electrode 12,
and inner cylinder 13.
[0047] The low-voltage electrode 11 is provided with facing the
high-voltage electrode 12 and has a dust-collection function for
collecting a floating particulate matter 20 electrified through
corona discharge generated by a high voltage applied between the
high-voltage electrode and the low-voltage electrode. Moreover, the
low-voltage electrode 11 forms the outer wall of the flow path of
exhaust gases G and Gb, which is formed of an electrical conductor
of a metal such as stainless steel. One end of the low-voltage
electrode 11 serves as an entrance 11a of the exhaust gas G and the
other end of it serves as an exit 11b of the high-concentration
exhaust gas Gb in which the floating particulate matter 20 is
condensed. Moreover, the low-voltage electrode 11 is electrically
grounded (earthed).
[0048] Furthermore, the high-voltage electrode 12 serves as a
discharge electrode (corona discharge electrode) for generating
corona discharge, which is provided in the longitudinal direction
on almost the center line of the low-voltage electrode 11, that is,
along an area near the center of the low-voltage electrode 11, at a
corona discharge area Z0 including at least an electrifying area Z1
in the upstream side of the entrance 11a of the low-voltage
electrode 11. To improve occurrence of discharge and effect of
electric force, and in consideration of mechanical strength and the
like, the high-voltage electrode 12 is constituted of a thin wire,
rod, or stranded wire having a circular, angular, or angular twist
cross section, or thin wire, rod, or stranded wire having an edge
structure like barbed wire or twist brush. For example, it is also
allowed to use a stainless wire, piano wire, or non-rust steel
wire, having a diameter of 0.2 to 2 mm. Moreover, as a material, it
is allowed to use a metal wire that is superior in corrosion
resistance such as tungsten, nickel, titanium, inconel or the like,
or a metal wire whose outer surface is coated with resin, glass,
ceramic or the like, depending on the application.
[0049] Moreover, the inner cylinder 13 is a cylindrical
exhaust-gas-dividing pipe, which is provided concentrically with
the inside of the low-voltage electrode 11, and is provided at a
divide-flow area Z3 in the downstream side of the low-voltage
electrode 11. The exhaust gas G is divided with the inner cylinder
13. The low-concentration exhaust gas Ga in which the floating
particulate matter 20 is diluted is flowed through the inside of
the inner cylinder 13 and the high-concentration exhaust gas Gb in
which the floating particulate matter 20 is condensed is flowed
through the outside of the inner cylinder 13. It is allowed that
the inner cylinder 13 is an electrical conductor or is not an
electrical conductor. Therefore, the inner cylinder 13 is formed of
a metal or other material in accordance with the type of the
exhaust gas G. In this case, the inner cylinder 13 is made of
stainless steel in response to the exhaust gas G emitted by diesel
engines.
[0050] The low-voltage electrode 11 and the inner cylinder 13 are
formed like a cylinder having a circular cross section as shown in
FIG. 2 (a) when the quantity of exhaust gas to be processed is
small and one high-voltage electrode 12 is provided in the center
of it. However, the low-voltage electrode 11 and the inner cylinder
13 are respectively formed like a cylinder having a rectangular
cross section and a plurality of high-voltage electrodes 12 are
also provided in parallel in the center of it, as shown in FIG. 2
(b) when the quantity of exhaust gas to be processed is large.
[0051] In the case of the exhaust gas processing system 10 having
the above structure, the exhaust gas G emitted by diesel engines is
supplied from the entrance 11a. Moreover, a negative high voltage
(e.g. -10 kV) is applied to the high-voltage electrode 12. By
applying the high voltage, corona discharge occurs around the
high-voltage electrode 12 and the circumferential area is filled
with ions. Therefore, the PM (floating particulate matter) 20 in
the exhaust gas G is electrified by adsorbing the ions.
[0052] The PM 20 electrified at the electrifying area Z1 in the
upstream side of the discharging area Z0 is collected by the
electrode surface 11s of the low-voltage electrode 11 (ground
potential in the case of this example) by an electrostatic force
(Coulomb force) at the condensing area Z2 in the downstream side of
the discharging area Z0. The PM 20 that includes ultra-fine
particles of tens-of-nm size is collected on the low-voltage
electrode surface 11s and the cohesion occurs to form the PM 20
with a larger size. Thereby, the corpulence of PM 20 occurs.
[0053] The PM 20 included in the exhaust gas G emitted by diesel
engines easily loses electric charges because it has a
comparatively low electric resistance. Therefore, the corpulence PM
20 loses electric charges and electrostatic force, removing from
the low-voltage electrode surface 11s due to the flow of the
exhaust gas G and re-entrains. This re-entrained PM 20 is
discharged from the exit 11b together with the exhaust gas Gb by
passing through the passage between the inner cylinder 13 and the
low-voltage electrode 11 because it moves to the downstream side
along the low-voltage electrode surface 11s.
[0054] Then, most PM 20 in the exhaust gas G is attracted to the
low-voltage electrode 11 by an electrostatic force, the
concentration of the PM 20 relatively rises (compared to the
exhaust gas at the entrance) around the high-voltage electrode 12,
and the PM 20 is condensed near the low-voltage electrode 11.
Therefore, the exhaust gas Gb discharged from the exit 11b becomes
high-concentration exhaust gas in which the concentration of the PM
20 relatively rises.
[0055] The exhaust gas Ga flowing through the central area of the
low-voltage electrode 11, that is, the circumferential area of the
high-voltage electrode 12, enters the inner cylinder 13 from the
entrance 13a, and is discharged from the exit 13b, passing through
the passage inside. The exhaust gas Ga becomes low-concentration
exhaust gas because most PM 20 in the exhaust gas G is attracted to
the low-voltage electrode 11 by an electrostatic force and the
concentration of PM 20 is diluted.
[0056] Therefore, according to the exhaust gas processing system
10, by providing a condensing area Z2 in the downstream side of the
electrifying area Z1 through corona discharge, the PM 20
electrified through the corona discharge is collected on the
low-vollage electrode surface 11s. It is possible to condense the
PM 20 near the low-voltage electrode 11 by using a phenomenon that
the collected, cohered, and enlarged PM 20 re-entrains from the
low-voltage electrode surface 11s. Moreover, by providing the
divide-flow area Z3 using the inner cylinder 13, it is possible to
separate the exhaust gas into the low-concentration exhaust gas Ga
in which the PM near the high-voltage electrode 12 is diluted and
the high-concentration exhaust gas Gb in which the PM 20 near the
low-voltage electrode 11 is condensed.
[0057] When forming the inner cylinder 13 by an electrical
conductor and equalizing its potential with that of the low-voltage
electrode 11, it is possible to obtain the enlarging effect of the
PM due to cohesion and re-entrainment of the PM 20 on the inner
surface and outer surface of the inner cylinder 13. Moreover,
though the high-voltage electrode 12 is provided in the upstream
side of the inner cylinder 13 in FIG. 1, it is also allowed to use
a configuration of extending the high-voltage electrode 12 up to
the inside of the inner cylinder 13 so as to obtain the enlarging
effect of the PM inside the inner cylinder 13 to the separated
low-concentration exhaust gas Ga. In fact, however, in the
downstream end 12b of the high-voltage electrode 12 and the front
end of the inner cylinder 13, it is necessary to relax an electric
field of the terminal area of the high-voltage electrode 12 to
stabilize the discharge, in consideration of dielectric breakdown,
by bringing an electrostatic field (electric flux) into a
preferable state.
[0058] FIGS. 3 and 4 show a configuration of an exhaust gas
processing system 10A of second embodiment of the present
invention. The exhaust gas processing system 10A is constituted
including cylindrical low-voltage electrode 11, high-voltage
electrode 12, and an outer cylinder 14.
[0059] The cylindrical low-voltage electrode 11 at condensing area
Z2 has a dust-collecting function for attracting tne floating
particulate matter 20 electrified through the corona discharge
generated when applying a high voltage to the high-voltage
electrode 12 and a function serving as a boundary for separating
some Gb of the exhaust gas G. Moreover, the electrode 11 functions
as a material for forming flow path walls of exhaust gases G, Ga,
and Gb at the divide-flow area Z3.
[0060] The low-voltage electrode 11 is formed of an electrical
conductor such as a metal, similarly to the case of the exhaust gas
processing system 10 of the first embodiment and electrically
grounded (earthed). However, the low-voltage electrode 11 is
constituted by forming a gas-permeable area 11p through which
exhaust gas Gb can pass at the condensing area Z2 slightly in the
downstream side of the upstream end 12a of the high-voltage
electrode 12. The gas-permeable area 11p is formed into a meshed
state or porous state by using a wire sheet, punching metal, foam
metal, and the like and has a dust collecting function and a
function for passing the exhaust gas Gb and the PM 20. Moreover,
the low-voltage electrode 11 is formed of a wall surface 11c, which
is not gas-permeable, at divide-flow area Z3 in the downstream side
of the gas-permeable area 11p.
[0061] Moreover, the high-voltage electrode 12 is formed of an
electrical conductor such as a metal similarly to the case of the
exhaust gas processing system 10 of the first embodiment.
Furthermore, the outer cylinder 14 serves as a cylindrical outer
wall provided to the outside of the low-voltage electrode 11 at
condensing area Z2 and divide-flow area Z3 and is formed of a metal
or other material.
[0062] The low-voltage electrode 11 and the outer cylinder 14 are
respectively formed like a cylinder having a circular cross section
as shown in FIG. 4 (a) when the quantity of exhaust gas processed
is small, and one high-voltage electrode 12 is provided in the
center of it. However, when the quantity of exhaust gas processed
is large, the low-voltage electrode 11 and the outer cylinder 14
are respectively formed like a cylinder having a slender cross
section as shown in FIG. 4 (b) and a plurality of high-voltage
electrodes 12 are provided in the center of it in parallel.
[0063] In the case of the exhaust gas processing system 10A having
the above structure, the exhaust gas G emitted by diesel engines is
supplied from the entrance 11a and a high voltage is applied to the
high-voltage electrode 12. By applying the high voltage, corona
discharge is generated around the high-voltage electrode 12 and its
circumferential area is filled with ions. Therefore, the PM
(floating particulate matter) 20 in the exhaust gas G attracts the
ions and is electrified.
[0064] The PM 20 electrified in the electrifying area Z1 in the
upstream side of the discharging area Z0 is attracted to the
gas-permeable area 11p of the low-voltage electrode 11 by an
electrostatic force (Coulomb force) at the condensing area Z2 in
the downstream side of the discharging area Z0. The attracted PM 20
attaches to the gas-permeable area 11p or passes through the gap or
hole of the mesh of the gas-permeable area 11p in accordance with
inertia force. Even if getting away from the corona discharge field
formed near the high-voltage electrode 12, the electrified PM 20 is
drifted toward the low-voltage electrode 11 by an electrostatic
force.
[0065] The cohesion of the PM 20 that includes ultra-fine particles
of tens-of-nm size once attached to the gas-permeable area 11p
occurs, and the larger-size PM 20 is formed and enlarged. Moreover,
the PM included in the exhaust gas emitted by diesel engines has a
comparatively low electric resistance and easily loses electric
charges. Therefore, the corpulence PM 20 removes from the
gas-permeable area 11p of the low-voltage electrode 11 and
re-entrains in accordance with the flow of the exhaust gas Gb and
moves to the downstream side because it loses electric charges and
electrostatic force. Then, the high-concentration exhaust gas Gb
that includes the PM 20 passes between the outer cylinder 14 and
the low-voltage electrode 11 and is discharged from the exit
14b.
[0066] However, the low-concentration exhaust gas Ga flowing
through the central area of the low-voltage electrode 11, that is,
the circumferential area of the high-voltage electrode 12, passes
through the inside of the low-voltage electrode 11 and is
discharged from the exit 11b.
[0067] In the case of the exhaust gas Ga at the side of the central
area, the quantity of the PM 20 decreases and it becomes
low-concentration exhaust gas in which the PM 20 is diluted. On the
other hand, in the case of the exhaust gas Gb at the outside of the
low-voltage electrode 11, the quantity of the PM 20 increases and
it becomes high-concentration exhaust gas in which the PM 20 is
condensed.
[0068] In FIG. 3, the high-voltage electrode 12 is extended to the
upstream side of the gas-permeable area 11p, the electrifying area
Z1 is provided to the upstream side, and the PM 20 collected by the
low-voltage electrode 11 is enlarged at this area and re-entrained.
To simplify the structure, it is also allowed to provide the
upstream end 12a of the high-voltage electrode 12 to the same area
as the upstream end of the gas-permeable area 11p.
[0069] Moreover, in FIG. 3, the downstream end 12b of the
high-voltage electrode 12 is constituted so as to extend up to the
inside of divide-flow area Z3 of the low-voltage electrode 11.
Thereby, after separating the low-concentration exhaust gas Ga,
corona discharge field is further maintained. The cohesion of the
PM remaining in the low-concentration exhaust gas Ga occurs at this
area to perform preprocessing for the PM secondary processing. To
simplify the configuration, it is also allowed to provide the
downstream end 12b of the high-voltage electrode 12 to the upstream
side of the divide-flow area Z3.
[0070] It is allowed to use any cylinder as the outer cylinder 14
as long as it has a function for forming a passage of the
high-concentration exhaust gas Gb. The outer cylinder 14 is formed
of an electrical conductor to hold its potential at the same
potential (ground) as the low-voltage electrode 11. According to
this configuration, the PM 20 easily separates and re-entrains
because it easily loses electric charges, when the PM 20 that
directly passes through the gas-permeable area 11p in accordance
with inertia force, coheres in the inner wall surface of the outer
cylinder 14.
[0071] According to the exhaust gas processing system 10A, the PM
20 electrified through corona discharge can be condensed by
providing the PM condensing area Z2 in the downstream side of the
electrifying area Z1 through corona discharge. That is, it is
possible to condense the PM 20 at the outside of the gas-permeable
area 11p of the low-voltage electrode 11 by using the following two
phenomena. One phenomenon is a phenomenon in which the electrified
PM 20 attaches to the gas-permeable area 11p serving as the
electrode surface of the gas-permeable area Z2 and the cohesion and
corpulence occurs at this area, and re-entrains from the
gas-permeable area 11p. The other phenomenon is a phenomenon in
which the PM 20 passes through the gas-permeable area 11p in
accordance with inertia force of gas flow.
[0072] Moreover, at the divide-flow area Z3, the exhaust gas Ga
near the high-voltage electrode 12 is supplied to the inside of the
low-voltage electrode 11 to supply the exhaust gas Gb passing
through the gas-permeable area 11p to the outside of the
low-voltage electrode 11. Thereby, it is possible to separate the
low-concentration exhaust gas Ga in which the PM 20 is diluted from
the high-concentration exhaust gas Gb in which the PM 20 is
condensed.
[0073] FIG. 5 shows a configuration of an exhaust gas processing
system 10B of third embodiment of the present invention. The
exhaust gas processing system 10B is constituted by providing an
attractive electrode 15 serving as a third electrode, in order to
form an electrostatic field for attracting the electrified PM 20
from the gas-permeable area 11p of the low-voltage electrode 11, in
addition to the configuration of the exhaust gas processing system
10A of the second embodiment.
[0074] When providing the attractive electrode 15, the attractive
electrode 15 is electrically grounded and a proper intermediate
potential between the high-voltage electrode 12 and the attractive
electrode 15 is applied to the low-voltage electrode 11.
[0075] Moreover, though the attractive electrode 15 is provided
between the low-voltage electrode 11 and outer cylinder 14 in FIG.
5, it is also allowed to use the function of the attractive
electrode 15 by forming the outer cylinder 14 by an electrical
conductor and electrically grounding.
[0076] According to the exhaust gas processing system 10B having
the above structure, it is possible to more strongly attract the
re-entraining PM 20 at the gas-permeable area 11p of the
low-voltage electrode 11 or the electrified PM 20 passing through
the gas-permeable area 11p to the outside of the gas-permeable area
11p of the low-voltage electrode 11 by electric field formed by the
attractive electrode 15. Therefore, it is possible to prevent the
re-entrained PM 20 or the electrified PM 20 from entering inside
the low-voltage electrode 11. Therefore, it is possible to more
efficiently separate and condense the PM 20.
[0077] FIGS. 6 and 7 show a configuration of an exhaust gas
processing system 10C of fourth embodiment of the present
invention. The exhaust gas processing system 10C is constituted so
as to remove PM 20 from the high-concentration exhaust gas Gb in
which the PM 20 is condensed, by additionally providing a filter 16
to the configuration of the particulate matter separator 10A or 10B
of the second or third embodiment. Symbol 17 denotes an insulator
for electrically insulating the high-voltage electrode 12.
[0078] Moreover, the outer cylinder 14 at the outside of the
low-voltage electrode 11 compartmentalizes an area for providing
the filter 16 and an area for passing the low-concentration exhaust
gas Ga by providing a partition wall 14a in the downstream side of
the gas-permeable area 11p of the low-voltage electrode 11.
Furthermore, a first discharge port 14b for discharging filtered
exhaust gas Gb' is formed in the upstream side of the partition
wall 14a and a second discharge port 14c for discharging the
low-concentration exhaust gas Ga is formed in the downstream side
of the partition wall 14a.
[0079] Furthermore, a second gas-permeable area 11d that can be
ventilated is further provided in the downstream side of the wall
surface 11c that cannot be ventilated in the downstream side of the
gas-permeable area 11p of the low-voltage electrode 11, so that the
low-concentration exhaust gas Ga passing through the wall surface
11c passes through the second gas-permeable area 11d and can be
discharged from the second discharge port 14c.
[0080] The filter 16 provided in a space in the upstream side of
the partition wall 14a of the low-voltage electrode 11 and the
outer cylinder 14 is a filter for purifying the high-concentration
exhaust gas Gb passing through the gas-permeable area 11p of the
low-voltage electrode 11. The filter 16 can be formed by using a
well-know,n filter such as a punching metal, sintered wire sheet,
sintered filter, metallic fiber filter, ceramic filter whose pore
diameter is larger than that of a DPF, metallic honeycomb, ceramic
honeycomb, glass wool, or a filter obtained by carrying an
oxidation catalyst to these base materials.
[0081] Moreover, in the case of this filter 16, it is possible to
easily collect the PM 20 even by a wide-mesh filter because it is
enlarged in the high-concentration exhaust gas Gb. Therefore, it is
possible to decrease a pressure loss. The configuration in FIG. 6
is constituted by forming a punching metal with a pore diameter of
1 mm (pitch of 2 mm) into three layers.
[0082] Moreover, in the case of the PM 20 collected by the filter
16, the PM collection surface is reproduced to keep the PM
collection performance for a long time, by a method for providing a
fourth PM burning electrode near a PM collection surface, by a
method for applying an oxidation catalyst on the PM collection
surface, or by a method for providing a heater near the PM
collection surface.
[0083] When burning and removing PM by using the fourth PM burning
electrode, the following constitution is used. The pitch of
multi-layer arrangement of a punching metal is increased. Moreover,
a wire sheet (not illustrated) electrically insulated from the pipe
of the low-voltage electrode 11 or the like is provided by keeping
an interval of 1 to 2 mm from the PM collection surface of the
punching metal as the fourth PM burning electrode. Discharge is
generated between the wire sheet and the PM collection surface by
supplying a voltage to the wire sheet from the outside. Thereby,
the PM collected in the filter 16 is burned and removed.
[0084] Moreover, when applying an oxidation catalyst, an oxidation
catalyst of titanium oxide, platinum, or the like is applied to the
PM collection surface of the filter 16, or a catalyst carrier
having a wall thickness of 3 mm or smaller is provided to the PM
collection surface. PM combustion start temperature is lowered as a
result of effects of these oxidation catalysts. It is allowed to
use a metal or insulating material for the catalyst carrier.
Moreover, a bulky or porous body can be used as the shape of the
catalyst carrier.
[0085] Furthermore, when using a heater, a heater constituted of a
Nichrome wire is provided to the PM collection surface of the
filter 16, and the heater is regularly heated to burn and remove
the PM.
[0086] When the quantity of exhaust gas to be processed is small,
the low-voltage electrode 11, the outer cylinder 14, and the filter
16 are respectively formed like a cylinder with a circular cross
section as shown in FIG. 7 (a), and one high-voltage electrode 12
is also provided in the center of it. However, when the quantity of
exhaust gas to be processed is large, the low-voltage electrode 11,
the outer cylinder 14, and the filter 16 are respectively formed
into a cylinder with a slender cross section as shown in FIG. 7
(b), and a plurality of high-voltage electrodes 12 are provided in
the center of it in parallel.
[0087] According to the exhaust gas processing system 10C having
the above configuration, by providing the filter 16, it is possible
to efficiently purify the high-concentration exhaust gas Gb in
which the PM 20 is enlarged and condensed. Therefore, it is
possible to make the exhaust gas Gb' discharged from the first
discharge port 14b clean gas.
[0088] It is not always necessary to pass the low-concentration
exhaust gas Ga through a PM collection filter because the PM 20 is
diluted. However, even when providing a filter for the
low-concentration exhaust gas Ga, the quantity of the exhaust gas
is greatly decreased compared to the quantity of the original
exhaust gas G and moreover, the large PM is removed. Therefore, it
is possible to use a fine-mesh filter. Moreover, even if using the
fine-mesh filter, the pressure loss is small because the progress
of clogging is slow.
[0089] When re-circulating the low-concentration exhaust gas Ga in
a cylinder as exhaust gas for EGR, the low-concentration exhaust
gas Ga is not directly discharged to the outside air and it is
unnecessary to provide a filter.
[0090] FIG. 8 shows an exhaust gas processing system 10D of fifth
embodiment of the present invention. The exhaust gas processing
system 10D is constituted so as to join the exhaust gas Gb' passing
through the filter 16 with the low-concentration exhaust gas Ga and
then discharge the merged gas as exhaust gas Gc.
[0091] Thereby, flows of the exhaust gases G, Ga, and Gb are
smoothed. Moreover, the unevenness of the apparatus like the first
discharge area 14b of the exhaust gas Gb shown in FIG. 6 is
eliminated to realize space saving so that pipe arrangement can be
easily made.
[0092] In the case of the configuration of the exhaust gas
processing system 10D of the fifth embodiment, the area of the wall
surface 11c that is not gas-permeable in the downstream side of the
gas-permeable area 11p of the low-voltage electrode 11 is not
always necessary. In this case, the area of the partition wall 14a
corresponds to the divide-flow area Z3.
[0093] Moreover, the configuration in FIGS. 6 to 8 houses the
filter 16 in the outer cylinder 14 to downsize the apparatus. Even
when providing a filter separately from the exhaust gas processing
system 10, 10A, or 10B, it is easy to collect the PM even by a
wide-mesh filter and it is possible to decrease the pressure loss
because the PM in the high-concentration exhaust gas Gb is
enlarged.
[0094] In the case of the exhaust gas processing systems 10 and 10A
to 10D of the above embodiments, the low-voltage electrode 11 is
described as a cylinder as shown in FIGS. 2 (a), 4 (a), and 7 (a).
However, the present invention is not restricted to this
configuration, and a polygonal housing such as a quadrangle other
than a cylinder is also allowed. Moreover, when the quantity of
exhaust gas is large, the cross section of the low-voltage
electrode 11 is formed into a rectangle and a plurality of
high-voltage electrodes 12 are arranged in parallel along the
longitudinal direction (direction vertical to rectangular cross
section) near the center of the electrodes 11 as shown in FIGS. 2
(b), 4 (b), and 7 (b). Furthermore, when the quantity of exhaust
gas is large, it is also possible to arrange a plurality of
high-voltage electrodes 12 in parallel and spread a corona
discharge area as shown in FIG. 9. Furthermore, when the quantity
of exhaust gas is large, it is possible to correspond to it by
arranging exhaust gas processing systems of the embodiments in
parallel. When further raising the condensation degree of
high-concentration exhaust gas and the purifying efficiency of
low-concentration exhaust gas, it is possible to correspond to it
by arranging the systems at multistage.
Embodiment 1
[0095] In the case of the exhaust gas processing system 10 of the
first embodiment shown in FIGS. 1 and 2 (a), the high-voltage
electrode 12 is formed of a stainless wire with a diameter of 0.2
mm .phi., the low-voltage electrode 11 is formed by a stainless
cylinder with an inside diameter of 38 mm .phi., and the inner
cylinder 13 is formed of a stainless cylinder with an inside
diameter of 15 mm .phi.. The ratio between the inside and outside
cross-sectional area of a cylinder becomes 5:3.
[0096] The exhaust gas processing system 10 is directly connected
to the exhaust gas pipe area of a small diesel power generator
(maximum output of 5 kW) to perform an experiment under an
operation condition at 2.4 kW (48%) load. A voltage of -10 kV and a
current of 0.4 mA are supplied to a high-voltage electrode by using
a negative electrode direct high voltage power supply. The
temperature of the exhaust gas processing system 10 is set to
100-200.degree. C., flow rate of exhaust gas is set to approx. 200
L/min (in terms of ordinary temperature), and retention time at a
discharge area (length of 120 mm) is set to approx. 0.1 s.
[0097] At the above experiment, the PM in each exhaust gas is
collected by a quartz filter capable of collecting particulate
matter of 0.6 .mu.m, 50 L is sampled, and then the surface of the
filter is observed by a low vacuum electronic scanning microscope
to observe the distribution of particle diameters.
[0098] As a result, a clear difference between the cases of
presence of discharge and absence of discharge is observed on the
filter inside a double tube through which low-concentration exhaust
gas passes. It is found that particulate matter with a
several-.mu.m size is hardly observed and diluted in the case of
presence of discharge even through the microscope observation.
Moreover, as a result of observing the PM included in
high-concentration exhaust gas by a microscope, particulate matter
of tens of microns to several hundred microns are present.
Therefore, it is found that particle diameter of the PM becomes
larger than particle diameter (several microns) of the PM in
exhaust gas before processed, and there is an extreme enlarging
effect.
[0099] That is, as a result of the experiment, it is possible to
confirm that the PM emitted by diesel engines is collected in a gas
discharge line near a low-voltage electrode and can be almost
completely separated from a gas discharge line near a high-voltage
electrode, without increasing the exhaust gas pressure. Moreover,
it is possible to confirm that particulate matter of several
microns can be enlarged to larger particulate matter by applying a
high voltage.
Embodiment 2
[0100] In the case of the exhaust gas processing system 10C of the
fourth embodiment shown in FIGS. 6 and 7 (a), the high-voltage
electrode 12 is formed of a stainless wire with a diameter of 0.6
mm .phi., the low-voltage electrode 11 is formed of a stainless
cylinder with an inside diameter of 58 mm .phi., and the outer
cylinder 14 is formed of a stainless cylinder with an outside
diameter of 220 mm .phi.. The filter 16 is provided to three layers
by punching metal with a pore diameter of 1 mm at 2-mm pitch.
[0101] The exhaust gas processing system 10C is directly connected
to the exhaust gas pipe area of a 2-ton truck to perform an
experiment under conditions of an engine speed of 550 rpm, exhaust
gas temperature of approx. 70.degree. C., and exhaust gas quantity
of approx. 1,400 L/min. A voltage of -18 kV is applied to a
high-voltage electrode by using a negative electrode direct high
voltage power supply. The retention time at the electrifying area
(length of 300 mm) is approx. 30 ms and the retention time at a
condensing area (length of 550 mm) is approx. 55 ms.
[0102] In the above experiment, the PM in exhaust gas is collected
by using a glass fiber filter paper having a 0.3 .mu.m .phi.
(particle with capturing rate of 99.9% or more and aspirating
exhaust gases Ga and Gb' by a constant-flow-rate pump.
[0103] As a result, a clear difference between the cases of
presence of discharge and absence of discharge is observed in
filter paper through which the exhaust gas Ga passes and in filter
paper through which the exhaust gas Gb' after passing through the
filter 16 passes. Moreover, by applying a voltage to a corona
discharge electrode, it is found that the PM can be extremely
decreased.
Embodiment 3
[0104] In the case of the exhaust gas processing system 10D of the
fifth embodiment shown in FIG. 8, an experiment is performed in the
same dimension and condition as the case of the embodiment 2 to
collect the PM in exhaust gas by using glass fiber filter paper
having a 0.3 .mu.m .phi. particle with capturing rate of 99.9% or
more and aspirating the re-merging exhaust gas Gc by a
constant-flow-rate pump.
[0105] As a result, a clear difference between the cases of
presence of discharge and absence of discharge is observed in the
filter paper through which the exhaust gas Gc passes. Thereby, it
is found that the PM is extremely decreased by applying a voltage
to a corona discharge electrode.
* * * * *