Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~lZZ5~2
RAPPER ASSEMBLY FOR ELECTROSTATIC PRECIPITATORS
BACKGROUND OF THE INVENTION
Electrostatic precipitators which use a plurality
of electrodes to remove particulate matter must be cleaned
periodically during operation if -they are to function with
any reasonable efficiency. Otherwise, the electrodes will
become coated with the matter which has been removed from the
air or other gas circulating through the precipitator and
will no longer attract the particulate matter with any
reasonable degree of efficiency.
A common way to clean the electrodes is to provide
rappers which are connected with one or more electrodes.
While the precipitator is in operation, each rapper is
periodically operated to rap the electrode or electrodes
causing the particulate matter to drop off. Each rapper is
conventionally composed of a solenoid containing a core which
strikes an anvil when the solenoid is energized. The anvil is
connected with one or more electrodes which are vibrated when
the anvil is struck by the core.
~0 It is a common practice to seal the coil of each
solenoid with varnish except for electrical conductors,
usually wires, which must be accessible for connecting the
coils to a power source. The varnish protects the solenoid
coil from the moisture present during and after construction
of the precipitator.
A serious problem has been encountered in the use
of such electromagnetic rappers. In some ins-tances a current
is induced in the solenoid coil when the energizing current
is discontinued. As the flux deteriorates, the induced
electromagnetic force causes the current to flow out of the
coil. This induced voltage is problematic because it can
X
1122542
damage the switching device used to discontinue the current
supply to the rapper.
It has been found in practice that the contacts of
the switches deteriorate due to the arcing caused by the
voltage induced at the coil. Conse~uently, the contacts
have to be carefully maintained for reliable services.
The phenomenon discussed above has produced a some-
what similar problem when solid state devices have been sub-
stituted for the mechanical contacts. The problem is com-
pounded when solid state devices are used to control rectifiedalternating current for distribution to the solenoids because
it is impossible to directly interrupt rectified current flow
to the solenoids.
SUMMARY OF TH~ INVENTION
It is an object of the present invention to overcome
drawbacks in the prior art such as those discussed above.
Accordingly, an electrode rapper assembly for
electrostatic precipitators is provided with a cylindrical
cover, a coil within the cover and concentric therewith, and
an anvil which is rigidly connected with the cover. A ferro-
magnetic plunger is movably mounted within the coil and is
movable to strike the anvil. The coil is connected between
a first and a second junction. The electrode rapper assembly
also includes a series solid state rectifier diode and a
parallel solid state rectifier diode, a wire connecting one
end of the parallel solid state rectifier diode with the first
junction and another wire connecting the other end of the
parallel rectifier diode to the second junction so as to be
in parallel with the coil and permit current flow through
the parallel rectifier diode so that it passes from the second
-- 2 --
~Z~S42
junction through the parallel rectifier diode to the first
junction. Two conductors supply rectified A.C. current, one
of the conductors being connected to one of the junc-tions and
the other of the conduc-tors being connected to one end of the
series rectifier diode. A wire connects the other end of the
series rectifier diode with the other of the junctions so that
current passing through the series rectifier diode can pass only
from the first junction to the second junction while passing
through the coil whereby energizing current can flow through
the coil to generate a magnetic field and move the plunger
upward. Interruption of the energizing current will permit
the plunger to drop, the current induced in the coil upon the
interruption flowing through the second junction, the parallel
rectiier, the first junction and the coil until dissipated.
.
~i
~l~Z2~
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary view, partly in section,
showing a rapper assembly connected with electrodes in an
electrostatic precipitator;
FIG. 2 is a view, partly in section, of a rapper
assembly;
FIG. 3 is a view showing how the diodes and coil
of the rapper assembly are wired; and
FIG. 4 is a schematic view of the electrical cir-
cuit of the present rapper assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 a rapper assembly, indicated generally as10, is shown mounted above the roo 12 of an electrostatic
precipitator. The ra~per assembly 10 includes an outer cylin-
drical cover 14 having an anvil 18 at its upper end. The
rapper assembly 10 is mounted on top of a support rod 20 which
extends down from the rapper assembly 10 through a vertical
guide bearing 22 which is secured to the top of the roof 12.
The rod 20 extends downward through the top o a ceiling 24
to a horizontal end plate 26. The end plate 26 is secured to
several cross beams 28. From some of the cross beams extends
rod-like hangars 30 which support a number of flat electrodes
31 while electrodes in the form of wires 32 hang from alter-
nately spaced cross beams 28. The electrodes 31 and 32 are
energized in a conventional manner. Thus, if the rapper
assembly is energized so that its associated support rod 20
Z5~2
.
is vibrated, the support rod will vibrate one or more cross
beams 28 which will convey the impulse to an electrode ox
electrodes connected with that cross beam.
FIG. 2 shows in some detail a rapper assembly 10.
As pointed out above, rapper assemhly 10 has a outer cylin-
drical cover 14. The cylindrical cover 14 is closed at one
end by the anvil 18 which is welded about its periphery at 36
to the end o the cover 14.
The other end of the cover 1~ has a 1ange 38 which
is welded at 40 to provide a means to secure an end closure
42 to that end. Bolts 44 project through the 1ange 38 and
end closure 42 and have nuts 46 threaded on their ends to
secure the end closure 42 to the flange 38.
A solenoid coil 48 its snuggly within the cover 14
so that it is adjacent to the anvil 18. A ferro-magnetic
core or plunger 50 is positioned within the coil 48 so that
it can move axially. When the coil is energized, the ferro-
magnetic plunger is accelerated toward the anvil 18 to strike
it and bounce downward. The coil is then de-energized so
that the plunger drops against the end closure 42 and comes
to rest. Thus, the anvil 18 receives the impulse transmitted
by the moving plunger.
In order to provide for the flux necessary to raise
the plunger, the cover 14, anvil 18, end closure 42 as well
as the plunger 50 are of ferro-magnetic material so that the
flux lines extend through these members. A stainless steel
disc 52 is provided between the anvil 18 and the plunger 50
so that when the coil is de-energized, the magnetic field
will quickly decay and permit the plunger to drop.
The solenoid is energized by means of rectified
-- 5 --
~l2~542
alternating current flowing through conductors in the form of
lead wires 53 and 54. A parallel rectifier in the form of a
solid state diode 56 and a series rectifier in the form of a
solid state diode 58 are embedded in insulating material 60
adjacent to the lower end of the solenoid coil 48. The diodes
56 and 58 may also be located elsewhere, so long as they do not
interfere in the operation of the rapper.
The Plectrical circuit, shown best perhaps in
FIG. 4, includes the lead wires 53 and 54. The diode 58 is
connected to the lead wire 53 and to wire 62 which leads to
junction 64. A wire 66 connects the junction 64 to the diode
56 and a wire 68 connects the diode 56 to a junction 70 which
is connected to the solenoid 48 so that the solenoid is
connected between the junctions 64 and 70. The lead wire 54
is connected to the junction 70.
The solenoid coil 48 is energized by rectified
alternating current passing through lead wire 53, diode 58,
wire 62, junct~on 64, solenoid coil 48, junction 70 and lead
wire 54. The energizing current will not pass through wires
66 and 68 to by-pass the coil 48 because the diode 56 prevents
flow oE current in the direction of the energizing current.
Energization of the coil 48 raises the plunger 50 to collide
with the anvil 18. Interruption of the energizing current
through the lead wire 53 will cause collapse of the magnetic
field in the rapper assembly 10 and consequently, the plunger
50 will drop.
It is the interruption of current through the coil
48 that causes the induced current which has in the past
caused deterioration of the device used to discontinue the
energizing current. The induced current is dissipated to
avoid such deterioration. This is accomplished by use of the
present circuit in each assembly where the induced current
25~Z
cannot pass through the wires 53 and 54 to damage any
switches used to establish and interrupt continuity with the
power source. The induced current passes from coil 48 through the
junction 70, through the wire 68, the diode 56, the wire 66,
the junction 64 and back to the coil 48 until dissipated. None
of the induced current will leave the rapper assembly 10 but
will flow within the assembly until dissipated. Since no
induced current leaves the rapper assembly 10, any inter-
fering current in the system is avoided and therefore it
1~ is possible to immediately apply power to any other rapper
assembly in the electrostatic precipitator.
Another advantage of the present rapper assembly is
that if it is inadvertently connected improperly, it will not
be damaged when an attempt it made to operate it. If, by
accident the lead wires 53 and 54 were reversed when the
rapper was installed, the application of an energizing voltage
across the rapper assembly will not damage the diode 56 because
the diode 58 will prevent the flow of current in a direction
opposite to that in which the current would flow i the lead
wires 53 and 54 were properly connected.
The foregoing describes but one embodiment of the
present invention, other embodiments being possible withou-t
exceeding the scope thereof.
`' 6;
