Electrostatic precipitator with precipitator electrodes

The invention relates to an electrostatic precipitator with collecting electrodes which are arranged in rows adjacent to each other and in respective pairs at equal distances from a respective discharge electrode with which they cooperate. Spring elements are provided between the collecting electrodes and influence the stiffness and oscillating properties of the array of the collecting electrodes.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The invention relates to an electrostatic precipitator with a number of 
collecting electrodes which are arranged in rows adjacent to each other 
and in respective pairs at equal distances from a respective discharge 
electrode (for instance wire) with which they are opposite. 
(2) The prior art 
Electrostatic precipitators are commonly used to precipitate dust from 
waste gas or expelled air from a dust producing plant such as mixing and 
grinding plant, sintering plant, power station etc. In order to be able to 
fulfil the requirements of anti-air pollution legislation, which have been 
made more and more stringent in the last two decades, it has become 
necessary to construct substantially larger electrostatic precipitators 
with collecting or precipitator electrodes each having a length of up to 
14 meters. This length gives rise to various problems. 
On the one hand, long precipitator electrodes must have sufficient 
mechanical strength and resistance to twisting; they are therefore usually 
provided with longitudinal corrugations and are crimped at their edges. 
They are mounted in a suspended array in the precipitator, being arranged 
in rows and connected at their upper and lower ends such as, for example, 
by a yoke or retainer made of two pieces of flat iron. 
On the other hand, it is necessary to assure that the sheet metal 
precipitator electrodes can oscillate at their resonance frequency so that 
they can be rid of adhering dust by being subjected to rapping. The 
thickness of the sheet metal therefore should not exceed approximately 2.5 
mm in order to ensure a sufficiently large amplitude of oscillation 
following an impact of a hammer weight which is appropriate for performing 
the dust-dislodging operation. 
In previously proposed electrostatic precipitators, the precipitator 
electrodes have a relatively low mechanical strength: they have a 
substantial length and a low sheet metal thickness. In consequence, low 
frequency transverse and twisting oscillations occur in the precipitator 
electrodes, which are caused by the gas current flowing through the 
arrangement and can reach resonance levels. (In this respect, however, the 
resonance occurs at a very much lower frequency than the above mentioned 
resonance due to rapping). The consequence of this is that, owing to the 
reduction in the distances between the discharge electrodes and the 
precipitator electrodes, the amount of sparking increases and, as a 
result, the operational voltage is automatically reduced, which brings 
about a reduction in the precipitation output. 
Attempts have already been made to provide a yoke-like retainer-like 
stiffening member halfway along the length of long precipitator electrodes 
in order to avoid the low frequency transverse and torsional oscillations. 
Furthermore, attempts have been made to arrange screw means and holding 
iron elements halfway along the length or to provide holding guide cords. 
The disadvantage of these known solutions is that they, on the one hand 
promote local sparking that results in reduction in the operating voltage 
while, on the other hand substantial frictional wear occurs in contact 
zones under the action of the solid particles to be precipitated and the 
movement of the precipitator electrodes following the rapping. As a 
result, the discharge electrodes are damaged at certain regions by spark 
erosion and, furthermore, the thin precipitator electrodes are abraded and 
fractured. The frictional wear of the precipitator electrodes is 
furthermore augmented by spark erosion when the potentials are different. 
The efficiency and service life of the electrostatic precipitator are 
reduced as a result. 
OBJECTS AND SUMMARY OF THE INVENTION 
One object of the present invention is to avoid these disadvantages and 
provide an electrostatic precipitator of the initially mentioned type, 
whose precipitator electrodes have sufficient mechanical strength and are 
not damaged by abrasion. 
In order to achieve this and other objects in accordance with the invention 
spring elements are provided between any two precipitator electrodes 
arranged adjacent to each other. The stiffness and oscillating properties 
of the array of long precipitator electrodes is influenced by these spring 
elements, due to their mechanical properties. 
In accordance with a preferred form of the invention, the spring elements 
are made of spring strips in the form of flat steel so that the forces to 
which the gas current subjects the precipitator electrodes are 
counteracted (in addition to the damping force of the precipitator 
electrodes which alone is not sufficient owing to low degree of mechanical 
stiffness) by a sufficient damping force applied by the spring strips and 
no resonnance oscillations in the low frequency range, that is undesired 
so-called fluttering movements, can occur. 
The attachment of the spring strips to the precipitator electrodes is by 
means of a force-fit connection preferably using a known expedient such as 
a screw, spot weld, rivet, clip or plug-in connection. 
An advantage of the construction and attachment of the spring strips 
between adjacent precipitator electrodes is that the spring strips only 
apply forces opposing twisting of the precipitator electrode out of its 
central position; in this manner the inherent oscillations, which are 
excited by rapping the precipitator electrodes, are not impeded or 
suppressed. 
When the precipitator electrodes are rapped at their lower ends a 
small-scale pendular movement of the electrodes may occur in the direction 
of the row. Consequently, small vertical shift takes place between two 
points at the edges of adjacent precipitator electrodes. The extent of 
this vertical shift, primarily depends on the oscillating amplitude and 
the width of the electrode. Where this pendular movement can occur, in 
order to compensate for this extremely small vertical displacement of the 
two connection points of the spring strips, the latter are so constructed 
as to provide a suitable possibility of compensation, in the longitudinal 
direction, this may include an S or corrugated construction of the spring 
strip. 
Such spring strips arranged with force-fit joints between the precipitator 
electrodes offer the advantage of ensuring that mutual hindrance of the 
precipitator electrodes cannot occur with respect to their movement in the 
row direction upon rapping the same. 
The force fit connection between the spring strips and the precipitator 
electrodes also guarantees a good electrical connection and therefore 
potential equalization between the precipitator electrodes. 
The spring strips can be advantageously arranged at any desired level or 
height of the precipitator electrodes; any desired number of spring strips 
can be distributed along the length of the precipitator electrodes. In 
this manner thinner material can be used for the precipitator electrodes 
and the material can be more economically used. 
The invention will now be described with reference to some embodiments 
shown by way of example only.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1, reference numeral 1 denotes precipitator electrodes, whose 
grooved shape and crimped edges for mechanical stiffening will be readily 
apparent. These precipitator electrodes 1 are equally spaced from a 
discharge electrode or wire 6 (FIG. 7) in a paired fashion in long 
opposite rows. All precipitator electrodes 1 are at the same potential. 
The electrodes 1 and 6 are mounted, in a conventional manner, in a housing 
13 which is indicated in FIGS. 1 and 7 merely in phantom lines. They 
constitute, together with electric circuitry of conventional design which 
is diagrammatically indicated at 14, a precipitator 15. In order to ensure 
that the high voltage between the discharge electrodes 6 and the 
precipitator electrodes 1 can be as large as possible, low frequency 
twisting and transverse oscillations must be avoided in the sheet metal of 
the precipitator or collecting electrodes 1, which has a maximum thickness 
of 2.5 mm. Such oscillations would briefly reduce the clearance between 
the electrodes 1 and 6 and accordingly reduce the voltage at which 
sparking would occur. On the other hand, oscillations in the resonance 
range of precipitator electrodes 1 following rapping are not to be damped. 
This is ensured by the use of spring 2, 4, 5, 10, 11 or 12, which are so 
designed and arranged that they have a pronounced resiliency only in one 
specific direction and are mechanically stiffer and more resistant to 
torsion in the other directions. In accordance with one embodiment, spring 
strips 2, 4 and 5 have been found suitable. They are illustrated in detail 
in FIGS. 3a, 4a and 5a. The straight part of the spring strips when 
necessary, can be provided with suitable compensation means, such as a 
corrugated or S-construction as shown in the strip springs 10, 12, 11 of 
FIGS. 3b, 4b and 5b, for the purpose of compensation or equalization of 
vertical displacements of the attachment points owing to pendular 
movements of the precipitator electrodes 1. 
The precipitator electrodes 1, only fragments of which are shown in FIG. 2, 
generally have a length of up to 14 m and thus are capable of oscillating 
at a low frequency on excitation by the gas flow, in dependence on the 
dimensions. 
In order to prevent or suppress these low frequency oscillations, as shown 
in FIG. 2, adjacent precipitator electrodes 1 are connected by the strip 
springs 2, 4 and 5 rigidly connected to their crimped edges. 
FIG. 2 shows an embodiment in which all spring strips 2, 4 and 5 are used 
simultaneously, for illustrative purposes. In each specific application, 
only one type of spring strip 2, 4, 5, 10, 11, or 12 is employed, for 
example the spring strip 2 which is slightly angled twice, having a screw 
connection 3, a rivet connection or a spot weld connection, or the spring 
strip 5 with its tongs-like configuration and clip connection 9, these 
forms being particularly suitable for employment in pre-existing 
electrostatic precipitators. In a similar manner it is also possible to 
use the corrugated or S-shaped spring strips 10, 11 and 12 (FIGS. 3b-5b). 
For the construction of a new electrostatic precipitator unit 15 the spring 
strip 5 or 11 respectively with a plug connector 5a or 11a is particularly 
suitable. The precipitator electrodes 1 are provided during manufacture at 
regular spacings at their crimped edges with female pockets 9 (FIG. 2) by 
slotting and pressing. On assembly, the spring strips 4 and 10 (FIGS. 3a, 
3b) are then inserted into the female pockets 9, the desired number 
thereof being distributed over the length of the precipitator electrodes 
1. 
For stabilization of the first and the last precipitator electrode 1 of 
each row at a desired height auxiliary supports 8 are provided as shown in 
FIG. 6. They extend past the rows and are provided with female pockets 9. 
The first and the last precipitator electrode 1 of a row can be attached 
to the auxiliary support 8 by means of a spring strip 4 or 10 respectively 
inserted into the respective pockets 9. In lieu of the spring strips 4 
shown by way of example, those of the embodiment 2 and 5 can be used with 
a simultaneous adoption of a suitable construction of the auxiliary 
support 8. 
The flexible spring strips 2, 4, 5, 10, 11 and 12 which can only be bent in 
one direction without encountering a large counterforce, suppress, owing 
to their geometrically given stiffness in other directions, on the one 
hand, transverse and twisting oscillations of the precipitator electrodes 
1 and, on the other hand, in the event of a suitable construction of the 
spring elements 10, 11 and 12 in accordance with FIGS. 3a-5a there is no 
mutual hindrance of the precipitator electrodes 1 on movement in the 
direction of the row when the electrodes 1 are rapped. 
The spring strips 2, 4, 5, 10, 11 and 12 provided at the upper and lower 
ends of the precipitator electrodes 1 can also replace positive guide 
means previously necessary for preventing torsion movements. 
Spring strips 7 (FIG. 7) can in some cases also be provided as transverse 
support means between two mutually opposite precipitator electrodes 1 so 
that the latter are spaced apart from the discharge electrode 6, the 
resistance to deformation and twisting is increased and the movement of 
the precipitator electrodes 1 in the direction of the row upon rapping is 
not impeded. 
The connection of adjacent or oppositely placed precipitator electrodes 1 
with spring 2, 4, 5, 7, 10, 11, or 12 strips accordingly increases the 
mechanical stiffness and damping properties at low frequency without 
impeding the necessary impact-dislodging operation. Furthermore 
equalization of potential is ensured. Wear of the spring strips 2, 4, 5, 
10, 11 and 12 by solid particles and by the effect of an electric field 
and the production of local sparking are avoided, because they do not have 
any projecting edges and corners and are arranged in the flow shadows of, 
that is, they are shielded by, the crimped edges of the precipitator 
electrodes 1. Owing to the force-fit joint between the precipitator 
electrodes 1 and the spring strips 2 or 12 no frictional wear can occur. 
Furthermore, it is possible to use a thinner material for the precipitator 
electrodes. 
The invention is not limited to the embodiments shown and instead can be 
used with other embodiments of spring elements.