Electric precipitator and electric precipitation electrode...

Details Electric precipitator and electric precipitation electrode... Electric precipitator and electric precipitation electrode...

1999-10-01

2002-01-08

Chiesa, Richard L. (Department: 1724)

Gas separation: apparatus

Electric field separation apparatus

With control means responsive to sensed condition

C096S030000, C096S033000, C096S034000, C096S080000

Reexamination Certificate

active

06336961

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an electric dust precipitator and, more particularly, to an improvement of an electric dust precipitator comprising a hammering assembly that applies mechanical impact to collecting electrodes or precipitation electrodes to shake off the collected dust on the surface thereof, as well as an improvement of the collecting electrodes therein.
BACKGROUND ART
Referring to
FIGS. 1 and 2
, a conventional hammering assembly for an electric dust precipitator is described for its configuration and electrical connections with collecting electrodes and discharge electrodes. In a charging division housing in the electric dust precipitator, grounded collecting electrodes
11
through
15
(
15
is omitted in
FIG. 1
) are placed. Each of the collecting electrodes
11
through
15
is provided with a hammering assembly comprising a hammer
20
and a struck seat
24
which is provided at a lower portion of the corresponding collecting electrode. The hammers
20
are pivotally mounted on a common shaft
21
with fork ends
22
and pins
23
. Rotation force is transmitted from a motor (not shown) to the shaft
21
via a reduction gear mechanism, which causes the shaft
21
to rotate at a low speed in the direction depicted by an arrow in the figure. Rotation of the shaft
21
lifts the hammer
20
to the uppermost point of its movement. The hammer
20
then swings because of the gravity and strikes the struck seat
24
. The vibration generated by the hammer strike is transmitted to the collecting electrode and the collected dust is shaken off from the collective electrode surface.
Since the hammers
20
are attached to the shaft
21
at a different angle with respect to each other, the hammer
20
strikes the corresponding struck seat
24
from one to another. This is for preventing the collected dust from re-scattering simultaneously at two or more collecting electrodes after having been shaken off by the hammers. In other words, the collected dust is re-scattered in turn to make re-scattered puff (a cloud of visible smoke) inconspicuous that is escaped through a chimney into the air.
On the other hand, a plurality of discharge electrodes are placed between the adjacent collecting electrodes. In
FIG. 2
, four discharge electrodes A
1
through A
4
are placed between the collecting electrodes
11
and
12
. Likewise, four discharge electrodes B
1
through B
4
are placed between the collecting electrodes
12
and
13
, four discharge electrodes C
1
through C
4
are placed between the collecting electrodes
13
and
14
, and four discharge electrodes D
1
through D
4
are placed between the collecting electrodes
14
and
15
. All discharge electrodes are connected to a common power supply unit
30
. The power supply unit
30
comprises a transformer
31
, a rectifier bridge circuit
32
connected to a secondary output of the transformer
31
, and a spark detection voltage divider
33
. A primary input of the transformer
31
is connected to an alternative current power supply AC through two controlling thyristors
35
. A control unit
36
controls a conduction angle of the thyristor
35
, which in turn controls the voltage across the secondary output of the transformer
31
. More specifically, the control unit
36
monitors the voltage across the spark detection voltage divider
33
to determine the presence or absence of spark between the discharge electrode and the collecting electrode and controls the voltage across (or the current flowing through) the secondary output to have a proper value.
Though only five collecting electrodes and sixteen discharge electrodes are illustrated in
FIGS. 1 and 2
, an actual electric dust precipitator has several tens of collecting electrodes aligned transversally with respect to a gas flow and several hundreds of discharge electrodes.
As described above in conjunction with
FIG. 1
, the collected dust is shaken off from the surface of the collecting electrodes upon their vibration generated by the hammers. Although the dust is then fallen down as a mass into a lower hopper, a part of the falling dust is carried by the gas flow. This phenomenon is referred to as “re-scattering” by hammering and has been an obstacle to improved dust collecting capacity of the electric dust precipitator. In addition, hammering may not shake the collected dust completely off the surface of the collecting electrodes. The collected dust remained on the surface may re-scatter without being hammered off. Furthermore, accumulation of the collected dust on the electrode surface, if happened, may be a cause of back discharge and spark. Such a hammering technique is thus desired that can shake off the collected dust as much as possible without causing re-scattering thereof.
Conventional hammering has been made while applying the voltage to the discharge electrodes of the electric dust precipitator. For more complete shaking off of the collected dust, the hammering may be made by means of hammering with reduced voltage than usual or a power off rapping that the hammer strikes the collecting electrode with the power supply completely turned off. Since the hammering with the reduced voltage and the power off rapping require to reduce or eliminate the voltage, it may deteriorates the dust collecting function of the electric dust precipitator or even prevents the precipitator from displaying its function.
In the hammering assembly, slow rotation of the shaft
21
lifts the hammers
20
one by one to their respective uppermost point and the hammers
20
swing due to the gravity from the upper limit of their movement to the struck seat
24
. It takes several minutes for the shaft
21
to rotate once, so that the hammering with the reduced voltage or the power off rapping continues for at least several minutes and that the dust collecting capacity may be deteriorated during this length of time. The power off rapping is seldom used due to this problem. The power off rapping is used only under limited conditions. The limited conditions are the case that the dust collecting capacity has sufficient margins during operation of a plant including the electric dust precipitator at a significantly lower load than in the normal operating status. In other words, the power off rapping may be used if necessary only when sufficient dust collecting capacity can certainly be achieved even after down-time of one of the charging division housings in the electric dust precipitator.
The present inventor has found that the hammering based on the conventional hammering technique with the application of the voltage can shake off the dust only incompletely with a disadvantageously and relatively large amount of re-scattering dust. The present inventor has developed an apparatus to monitor motion of dust particles in the air separated by the hammering from the collecting electrodes of the electric dust precipitator and has examined behavior of the separated dust particles.
This is described more in detail below with reference to FIG.
3
. According to the results of the observation, the collected dust can hardly be shaken off by the hammering without being accumulated to a significant thickness on the collecting electrodes
11
and
12
at a position opposed to a corona generating region Cg (R
1
region in FIG.
3
). On the other hand, the collected dust is shaken off from the surface of the collecting electrodes
11
and
12
at a remaining position away from the R
1
region and not being opposed to the corona generating region Cg. Instead, the collected dust scatters in the air (R
2
region in FIG.
3
). In this way, it has been found that the shaking off is incomplete at and around the R
1
region while the re-scatter by the hammering occurs at and around the R
2
region.
A reason for this difference between the R
1
and the R
2
regions would be as follows. A large amount of negative ions generated around the discharge electrode A collides against the surface of the collected dust at the R
1
region, producing negative charges on the dust. The collecting electrod

Affiliated with

Also associated with

Rating

Electric precipitator and electric precipitation electrode... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electric precipitator and electric precipitation electrode..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric precipitator and electric precipitation electrode... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2817828