TITLE OF THE INVENTION
MOVING ELECTRODE-TYPE ELECTRIC DUST COLLECTION APPARATUS
BACKGROUND
(a) Field of the Invention
The present invention relates to a moving electrode-type
electric dust collection apparatus for charging dust in exhaust
gas by corona discharge generated by discharge electrodes and
capturing the dust with collecting-electrode plates.
(b) Description of the Related Art
In the past, there is an electric dust collection
apparatus for charging dust in exhaust gas by corona discharge
generated by discharge electrodes applied with a high voltage
and capturing and removing the dust with collecting-electrode
plates. In the electric dust collection apparatus, there are
a fixed electrode-type electric dust collection apparatus using
impactive force generated by a hammer device to scrape off dust
captured by collecting-electrode plates and a moving
electrode-type electric dust collection apparatus that moves
collecting-electrode plates and scrapes off the dust with a
rotating brush.
FIG. 6 is a figure illustrating a portion of a schematic
configuration of a moving electrode-type electric dust
collection apparatus. As shown in the figure the moving
electrode-type electric dust collection apparatus 10 includes
a casing 20 formed with a gas passageway for exhaust gas
discharged from a boiler and the like, collecting-electrode
plates 30 provided in the casing, discharge electrodes 40, and
a hopper 50 provided in a lower portion of the casing for
collecting captured dust.
Both end portions of each of the collecting-electrode
plates 30 formed in the gas passageway are connected by a pair
of endless chains 32, and the collecting-electrode plates 30
are rotated and moved by rotating the endless chains 32. The
rotationally moving collecting-electrode plates 30 are
provided with discharge electrodes 40 with a predetermined
interval therebetween. When a high voltage is applied to the
discharge electrodes 40, corona discharge is generated from the
discharge electrodes 40. With the corona discharge, dust in
the exhaust gas is charged, so that the dust is captured by the
collecting-electrode plates 30. The collecting-electrode
plates 30 are attached with brush means 34, and the brush rotates
along with the rotational movement of the collecting-electrode
plates 30, so as to scrape off the dust captured by the
collecting-electrode plates 30. This kind of moving
electrode-type electric dust collection apparatus is disclosed
in, for example, Japanese Patent Application Laid-Open No.
56-124457.
For example, as disclosed in the specification of Chinese
Utility Model Publication No. 101537390, a
collecting-electrode plate distance in a moving electrode-type
electric dust collection apparatus (the distance between the
collecting-electrode plates) is set in a range from 400 mm to
520 mm due to the specification of constituent members such as
sprockets (for example, the number of teeth) or due to ease of
manufacturing and installation work.
The distance between the collecting-electrode plates is
related to the size of area of collecting-electrode plate per
unit amount of the gas, and when the collecting-electrode plate
distance is increased, the size of area of dust collection per
unit amount of the gas is decreased, and therefore, it is
necessary to increase the entire size of the apparatus. On the
other hand, when the collecting-electrode plate distance is
reduced, inverse ionization phenomenon may occur in a dust layer
at a portion where the density of discharge current is high,
and in this case, the dust collection performance may be
significantly reduced.
Accordingly, the present invention has discovered an
optimum collecting-electrode plate distance that is not
clarified in the above conventional art, and it is an object
of the present invention to provide a small moving
electrode-type electric dust collection apparatus having a high
dust collection rate.
SUMMARY
In order to solve the above problem, a moving
electrode-type electric dust collection apparatus according to
the present invention is configured such that a plurality of
collecting-electrode plates are hung from an endless chain in
a gas passageway in a casing and are rotationally moved, the
moving electrode-type electric dust collection apparatus
including a brush for removing dust captured by the
collecting-electrode plate, wherein the dust in the exhaust gas
is captured by the collecting-electrode plates using corona
discharge generated between a plurality of discharge electrodes
provided between the collecting-electrode plates, and a
distance b between adjacent collecting-electrode plates is set
at 220 mm to 380 mm.
According to the above configuration, preferable
electric field distribution in a dust collection space and a
preferable current density is achieved, and inverse ionization
phenomenon is suppressed in dust layers captured by the
collecting-electrode plates, so that the dust collection rate
of the dust collection apparatus can be increased.
In this case, the distance b between the adjacent
collecting-electrode plates is preferably 300 mm. According
to the above configuration, the dust collection rate of the dust
collection apparatus can be increased to the maximum.
In this case, a dimension ratio a/b between a distance
a between discharge wires of the discharge electrodes and the
distance b between the collecting-electrode plates is
preferably set at a value more than 0.4 but less than 1.8.
According to the above configuration, the inverse
ionization phenomenon is suppressed in dust layers captured by
the collecting-electrode plates. Therefore, the dust
collection rate of the dust collection apparatus can be
increased.
According to the moving electrode-type electric dust
collection apparatus of the present invention having the above
configuration, the inverse ionization phenomenon can be
suppressed in dust layers captured by the collecting-electrode
plates, and the collection rate of dust in exhaust gas can be
increased.
As compared with the conventional apparatus, the distance
between the collecting-electrode plates can be reduced, so that
the dust collection area size per unit amount of the gas is
increased, whereby the footprint of the entire apparatus can
be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially enlarged view illustrating
collecting-electrode plates and discharge electrodes in a
moving electrode-type electric dust collection apparatus
according to an embodiment;
FIG. 2 is a graph illustrating a relationship between a
dust collection rate and a distance b between the
collecting-electrode plates when a distance a between discharge
wires is 200 (mm);
FIG. 3 is a graph illustrating a distribution (relative
value) of an electric field strength near the
collecting-electrode plate when the distance a between the
discharge wires is 200 (mm);
FIG. 4 is a graph illustrating a distribution (relative
value) of a current density at the collecting-electrode plate
when the distance a between the discharge wires is 200 (mm);
and
FIG. 5 is a graph illustrating a relationship between a
dust collection rate of the dust collection apparatus and a
dimension ratio a/b between the distance a between the discharge
wires and the distance b between the collecting-electrode
plates; and
FIG. 6 is a figure schematically illustrating a moving
electrode-type electric dust collection apparatus.
DETAILED DESCRIPTION OF EMBODIMENTS
An embodiment of a moving electrode-type electric dust
collection apparatus according to the present invention will
be hereinafter described in detail with reference to attached
drawings. The moving electrode-type electric dust collection
apparatus according to the present embodiment has basically the
same configuration as the electric dust collection apparatus
described in the related art. Fig. 1 is a partially enlarged
view illustrating collecting-electrode plates and discharge
electrodes in a moving electrode-type electric dust collection
apparatus according to an embodiment. In the present
embodiment, collecting-electrode plates 30 in a gas passageway
are arranged in series with a regular distance b. Further,
discharge electrodes 40 are arranged with a regular interval
at a position between the collecting-electrode plates 30 (a
central position between the collecting-electrodes 30). In
the discharge electrodes 40, discharge wires 42 are arranged
with a regular interval a.
Fig. 2 is a graph illustrating relationship between a dust
collection rate and the distance b between the
collecting-electrode 30. In Fig. 2, the horizontal axis
represents the interval b (mm) between the collecting-electrode
plates 30, and the vertical axis represents a dust collection
rate (%) of the moving electrode-type electric dust collection
apparatus 10. The dust collection condition of the moving
electrode-type electric dust collection apparatus 10 is as
follows. An average electric field strength is 3 kV/cm. A
loading duration is 7 seconds. The discharge wire is 4 nun square
wire. A gas temperature is 150 degrees Celsius. A dust
concentration is 6 g/m3N. A dust average particle diameter is
23 [ua. It should be noted that the distance a between the
discharge wires 42 is 200 mm.
As shown in the figure, when the distance b between the
collecting-electrode plates 30 is less than 220 mm or more than
380 mm, the dust collection rate is less than 99%. On the other
hand, when the distance b between the collecting-electrode
plates 30 is more than 220 mm and less than 380 mm, the dust
collection rate attains a high value, i.e., at least 99%. In
this case, the dust collection rate of at least 99% is not a
value defined based on legal regulation, but a high-performance
moving electrode-type electric dust collection apparatus is
usually expected to have this level of value. In the range from
more than 220 mm to less than 380 mm of the distance b between
the collecting-electrode plates 30, the dust collection rate
attains the highest value (maximum value) when the distance b
between the collecting-electrode plates 30 is 300 mm.
FIG. 3 is a graph illustrating a distribution (relative
value) of an electric field strength near the
collecting-electrode plate 30 when the distance a between the
discharge wires 42 is 200 (mm) . More specifically, FIG. 3 is
a graph illustrating electric field strengths near the
collecting-electrode plate 30 when the distance a between the
discharge wires 42 is 200 (mm) , and the distance b between the
collecting-electrode plates 30 is 200. 300, and 400 (mm). In
the graph, the vertical axis represents an electric field
strength E (-)» and the horizontal axis represents a position
in gas flow direction on the collecting-electrode. A broken
line indicates the position of the discharge wire 42. The
average electric field strength Eave, obtained by dividing the
applied voltage by the distance between both electrodes, is 3
kV/cm. In all of the cases where the distance b is 200, 300,
and 400 (mm), the electric field strength becomes the highest
at the position of the discharge wire 42. Further, as the
distance b between the collecting-electrode plates 30 increases
(widens), the electric field strength near the
collecting-electrode plate 30 increases, which makes the
distribution more flat.
FIG. 4 is a graph illustrating a distribution (relative
value) of a current density at the collecting-electrode plate
30 when the distance a between the discharge wires is 200 (mm) .
More specifically, likewise, FIG. 4 is a graph illustrating
current densities near the collecting-electrode plate 30 when
the distance a between the discharge wires 42 is 200 (mm) , and
the distance b between the collecting-electrode plates 30 is
200, 300, and 400 (mm). In the graph, the vertical axis
represents a current density I (-), and the horizontal axis
represents a position in gas flow direction on the
collecting-electrode. A broken line indicates the position of
the discharge wire 42. At this occasion, the average current
density obtained by dividing all the discharge currents by the
entire collecting-electrode area size, is 0.3 mA/m2. In all
of the cases where the distance b is 200, 300, and 400 (mm),
the current density becomes the highest at the position of the
discharge wire 42. The smaller (the narrower) the distance b
between the collecting-electrode plates 30 is, the higher the
current density is at the position of the discharge wire 42 on
the collecting-electrode plate 30. The larger (the wider) the
distance b of the collecting-electrode plates 30 is, the more
flat the distribution is.
The mechanism for capturing dust is as follows. A
synergistic action of the electric field strength (which moves
the charged dust to the collecting-electrodes by Coulomb force)
and the current distribution (which charges the dust) is exerted
on the dust, but the current density affects the potential of
the dust layer attached to the collecting-electrode. When the
current density increases, and the electric field strength of
the dust layer exceeds the dielectric breakdown strength of the
exhaust gas, inverse ionization phenomenon is generated, and
the dust collection rate decreases.
In other words, a performance curve In a shape of a
mountain as shown in FIG. 2 is considered to be obtained since
the following changes occur at the same time. As the distance
b between the collecting-electrode plates 30 increases, the
electric field strength near the collecting-electrode plate 30
increases. On the other hand, the distance b between the
collecting-electrode plates 30 increases, the current density
decreases on the contrary. Further, when the current density
becomes more than a certain value (a value at which inverse
ionization phenomenon is caused), the dust collection
performance is reduced.
Further, the inverse ionization phenomenon is affected
by the thickness of the dust layer and the electric resistivity
of the dust, but the present application has clarified the
optimum design conditions under the ordinary operation
condition of the moving electrode-type electric dust collection
apparatus (the moving speed of the collecting-electrode and the
electric resistivity of the dust in question).
As described above, in the moving electrode-type electric
dust collection apparatus 10 according to the present invention,
the plurality of collecting-electrode plates 30 are hung from
the endless chains in the gas passageway in the casing and are
rotationally moved. The moving electrode-type electric dust
collection apparatus 10 has a brush for removing the dust
captured by the collecting-electrode plates 30. In the moving
electrode-type electric dust collection apparatus 10, the dust
in the exhaust gas is captured by the collecting-electrode
plates 30 using the corona discharge generated between the
plurality of discharge electrodes 40 provided between the
collecting-electrode plates 30, and the distance b between
adjacent collecting-electrode plates 30 is set at 220 mm to 380
mm. More preferably, the distance b between adjacent
collecting-electrode plates 30 is set at 300 mm.
FIG. 5 shows a relationship, examined over a wide range,
between a dust collection rate of the moving electrode-type
electric dust collection apparatus 10 and a dimension ratio a/b
between the distance a between the discharge wires 42 and the
distance b between the collecting-electrode plates 30. In the
figure, the horizontal axis represents the dimension ratio a/b,
and the vertical axis represents the dust collection rate (%)
of the moving electrode-type electric dust collection apparatus
10. As shown in the figure, when the dimension ratio a/b is
more than 0.4 and less than 1.8, the dust collection rate of
99% or more can be obtained. In the range where the dimension
ratio a/b is more than 0.4 and less than 1.8, the dust collection
rate attains the highest value (maximum value) of 99.5% when
the dimension ratio a/b is 0.8.
This is because the dust collection rate is affected by
the electric field strength and the current density, described
in the description about the mechanism for capturing the dust,
due to a combination of the interval of the discharge wires 42
and the interval of the collecting-electrode plates 30. This
clarifies the optimum design condition.
As described above, in the moving electrode-type electric
dust collection apparatus 10 according to the present invention,
the dimension ratio a/b between the distance a between the
discharge wires 42 of the discharge electrodes 40 and the
distance b between the collecting-electrode plates 30 is set
at a value more than 0.4 but less than 1.8.
According to the moving electrode-type electric dust
collection apparatus 10 of the present invention, the optimum
collecting-electrode interval is discovered, and the dust
collection rate is increased, so that the size of the entire
apparatus can be reduced. Further, by reducing the distance
between the collecting-electrode plates 30, the dust collection
area size per unit amount of the gas is increased, so that the
footprint of the entire apparatus can be reduced.
WE CLAIM:
1. A moving electrode-type electric dust collection
apparatus,
wherein a plurality of collecting-electrode plates are
hung from an endless chain in a gas passageway in a casing and
are rotationally moved,
the moving electrode-type electric dust collection
apparatus comprises a brush for removing dust captured by the
collecting-electrode plate,
the dust in the exhaust gas is captured by the
collecting-electrode plates using corona discharge generated
between a plurality of discharge electrodes provided between
the collecting-electrode plates, and
a distance b between adjacent collecting-electrode
plates is set at 220 mm to 380 mm.
2. The moving electrode-type electric dust collection
apparatus according to claim 1, wherein the distance b between
the adjacent collecting-electrode plates is 300 mm.
3. The moving electrode-type electric dust collection
apparatus according to claim 1, wherein a dimension ratio a/b
between a distance a between discharge wires of the discharge
electrodes and the distance b between the collecting-electrode
plates is set at a value more than 0.4 but less than 1.8.
4. The moving electrode-type electric dust collection
apparatus according to claim 2, wherein a dimension ratio a/b
between a distance a between discharge wires of the discharge
electrodes and the distance b between the collecting-electrode
plates is set at a value more than 0.4 but less than 1.8.

A small moving electrode-type electric dust collection
apparatus having a high dust collection rate of dust in exhaust
gas is provided. In a moving electrode-type electric dust
collection apparatus according to the present invention, a
plurality of collecting-electrode plates are hung from an
endless chain in a gas passageway in a casing and are
rotationally moved, the moving electrode-type electric dust
collection apparatus including a brush for removing dust
captured by the collecting-electrode plate, wherein the dust
in the exhaust gas is captured by the collecting-electrode
plates using corona discharge generated between a plurality of
discharge electrodes provided between the
collecting-electrode plates, and a distance b between adjacent
collecting-electrode plates is set at 220 mm to 380 mm.