GB2112305A

GB2112305A - An emission electrode system for electro-filters

Info

Publication number: GB2112305A
Application number: GB08232173A
Authority: GB
Inventors: Seppo Henrik Loytty; Eero Ilmari Piirainen; Martti Sakari Raisa
Original assignee: Kemira Oyj
Current assignee: Kemira Oyj
Priority date: 1981-11-16
Filing date: 1982-11-11
Publication date: 1983-07-20
Also published as: GB2112305B; DE3241629A1; SE439594B; FI813628L; FR2516405A1; SE8206477D0; FR2516405B3; FI67183B; FI67183C; SE8206477L

Abstract

An emission electrode system for electro-filters, a system which has a rectangular frame having parallel emission electrodes (6) strung between its upper (1) and lower parts and/or transverse stiffeners (4). The frame is made from tubing having a rectangular, oval, or other cross section, the height (h) of the tubing cross-section being greater than its width (l), in order to stiffen the emission electrode system in the longitudinal direction, without increasing its thickness. Furthermore, at one end of the emission electrode (6) there is fitted a spring member (10) and a tightening member (11) for keeping the emission electrode taut in spite of the different thermal longitudinal expansion of the emission electrode and the frame. <IMAGE>

Description

SPECIFICATION An emission electrode system for electro-filters The present invention relates to an emission electrode system for electro-filters and in particular to an emission electrode system which has a substantially rectangular frame with possible transverse and longitudinal stiffeners and several parallel, usually wire-like, emission electrodes strung between the transverse stiffeners and/or the upper and lower parts of the frame.

Such emission electrode systems are used in electro-filters for separating dust from a dustbearing gas, in which case several emission electrode systems are fitted, as seen in the gas flow direction, adjacently in the vertical position, in addition to which there is, between each two adjacent emission electrode systems, a precipitation electrode system. For the separation efficiency of the electro-filter it is preferable that the emission electrodes and the adjacent precipitation electrodes are as close to each other as possible, but not so close that the electrode systems touch each other. For this reason the aim is to make the frame of the electrode system as narrow as possible.

For removing the dust adhering to the emission electrodes the electro-filter has striking devices by means of which the emission electrode system is struck in order to remove any dust possibly adhering to the emission electrodes. The striking effect is more efficient the tauter the emission electrodes are. For this reason the emission electrodes are strung as taut as possible between the transverse stiffeners of the frame and/or the upper and the lower parts of the frame. This requires, however, that the upper and the lower parts of the frame are structurally as sturdy as possible, i.e. massive. Tubing has been used as the frame material. If in this case it is desired to increase the tautness of the emission electrodes, the diameter and wall thickness of the upper and the lower tubes of the frame have to be increased respectively.However, this also increases the width of the frame, in which case the emission electrodes can no longer be fitted so close to the precipitation electrodes as would be desirable in terms of the efficiency of the electro-filter.

The temperature inside the electro-filter may vary very greatly. It is at its lowest when inside maintenance, repairs or cleaning is being carried out in the electro-filter, and at its highest it may be several hundred degrees Celsius. If the frame and the emission electrode wires are of different materials, they also have different thermal elongation coefficients. Emission electrode wires are usually of a material which has a greater thermal elongation coefficient than has the frame material. For this reason, the emission electrode wires tend to slacken at the high temperatures prevailing in an electro-filter, in which case their cleaning by means of striking devices becomes difficult or totally impossible.

Owing to the greater thermal elongation coefficient of the emission electrode wires it would be even more important to have them strung so tautly in the frame that even upon elongation they would be taut enough for cleaning by means of a striking device. However, this is not possible without increasing the thickness of the frame structure so much that the adjacent emission and precipitation electrode systems are too far apart.

It is prior known to suspend weights at the lower end of emission electrode wires in order to maintain them taut regardless of longitudinal expansion. However, by means of reasonably large weights it is not possible to get the wires sufficiently taut in this manner. Furthermore, such weights tend to become detached and cause clogging, as well as to increase the weight of the filter. Because of the weights, the upper part of the frame must also be made so sturdy that, again, the precipitation and emission electrode systems cannot be fitted sufficiently close to each other.

The object of the present invention is to eliminate the above-mentioned disadvantages and to provide an emission electrode system for electro-filters, an emission electrode system in which the thickness of the frame is very small but the structure is still so sturdy that the emission electrodes can be strung sufficiently taut for cleaning, and in which any change in tautness due to a different thermal elongation coefficient of the emission electrode wires can be leveled out without substantially increasing the weight of the emission electrode system.

The main characteristics of the invention are given in accompanying Claim 1.

The present invention is thus based on the idea that, by an increase in the height of the cross section of the upper and the lower parts of the frame, these parts can be stiffened in the vertical direction without their width simultaneously increasing. Owing to this, the emission electrode wires can be strung tauter than previously without increasing the thickness of the frame. The frame material used is thus, instead of the previous type of tubing, tubing having an oval cross section which has height greater than its width.

Alternatively, upper and lower parts having a rectangular cross section can be used. Also other cross sectional shapes in which the height is greater than the width are possible.

In order to maintain the tautness of the emission electrode wires approximately unchanged regardless of the temperature prevailing in the electro-filter and of the different longitudinal expansion of the emission electrode wires, a spring member and a tightening member for tensing the spring member at a temperature lower than the operating temperature can be fitted at one end of the emission electrode wires in order to keep the emission electrode wires taut in spite of their longitudinal expansion. The opposite end of an emission electrode wire is preferably attached by welding to a possible transverse stiffener or, if there is no such stiffener, to the opposite lower or upper part.

The invention is described below in greater detail with reference to the accompanying drawing, in which: Figure 1 is a perspective representation of an emission electrode system according to the invention, and Figure 2 is a perspective representation of the emission electrode system of Figure 1 on an enlarged scale.

In Figure 1, the frame of the emission electrode system is indicated by numerals 1, 2 and 3.

Numeral 1 indicates the upper part of the frame, 2 its lower part, and 3 its two side parts. The frame 1, 2 and 3 has, in addition, been stiffened by means of a transverse stiffener 4 and two longitudinal stiffeners 5. The emission electrode wires, which are indicated by 6, have been strung in parallel to the side parts 3 between the longitudinal stiffener 4 and the upper 1 and respectively lower part 2.

Electro-filters are usually very large in size, and in such a case the height of the emission electrode system may also be very great, for example 10 meters. Even a small difference in thermal elongation between the side parts 3 and the emission electrode wires 6 may in such a case cause the emission electrode wires 6 to slacken when the temperature increases, if the thermal elongation coefficient of the material of the emission electrode wires is greater than that of the side parts 3 of the frame, or to be strung so taut that they may break, if the thermal elongation coefficient of the material of the emission electrode wires is smaller than that of the side parts 3 of the frame.In the former case the dust possibly adhering to the emission electrode wires cannot be detached from them by means of striking devices which strike the emission electrode system, and in the latter case the electrode wires may break, or the frame and especially its upper 1 and lower 2 parts can become twisted.

As can be seen in greater detail in Figure 2, this can be prevented in part by using, in the frame structure, tubes having a rectangular cross section, the height h of the tubes being greater than their width I. In this case the transverse 4 and longitudinal 5 stiffeners are preferably of the same pipe profile. The stiffness of such a frame in the vertical direction is considerabiy greater than that of a frame made from symmetrical tubing, and, consequently, the emission electrode wires 6 can be strung much tauter than previously, without increasing the thickness of the frame 1, 2 and 3, and 4 and 5.

On the other hand, the slackening or tightening, due to the different thermal elongation coefficients of the emission electrode wires 6 and the frame 1, 2 and 3, as a result of variations in the temperature of the electro-filter can be eliminated, or at least minimized, by attaching at least one end of the emission electrode 6 via a spring member 10 to the upper part 1 of the frame or respectively to the lower part 2, as seen in greater detail in Figure 2. Each end of the emission electrode wire is preferably fitted through a constricted opening in the transverse stiffener 4 and in the upper part 1 or respectively the lower part 2, one end 8 of the emission electrode wire 6 having been bent against the transverse stiffener 4 and attached to it by welding.On the other hand, the opposite end 7 of the emission electrode wire is provided with threading to which a nut 11 and a locking nut 12 can be fastened and tightened in such a manner that the spiral spring 1 0 between the nut 11 and the upper part 1 or respectively the lower part 2, passed through the end 7 of the emission electrode wire 6, compresses to tighten the emission electrode wire 6. The spiral spring 10 is compressed completely by means of the nut 11 when the thermal elongation coefficient of the emission electrode wire 6 is greater than that of the side parts 3 of the frame. When the temperature then rises during the operation of the electro-filter, the emission electrode wire 6 lengthens in relation to the frame, at which time that end of the emission electrode wire 6 which is provided with nuts 11 and 12 is pushed further out from the upper part 1 or respectively the lower part 2. In this case, however, the emission electrode wire cannot slacken but the spiral spring 10 continues to keep it taut.

Claims

1. An emission electrode system for electrofilters, such system comprising a substantially rectangular frame having possible transverse and longitudinal stiffeners, as well as several parallel emission electrodes strung between the transverse stiffeners and/or the upper and the lower parts of the frame, wherein the height of the cross-sectional diameter of at least the upper and the lower parts of the frame in a direction parallel to the longitudinal stiffeners is greater than the cross-sectional dimension of the same parts in a direction perpendicular to the plane of the rectangle, in order to stiffen these parts in the said direction parallel to the longitudinal stiffeners.

2. An emission electrode system according to Claim 1, wherein at least the upper and the lower parts of the frame have rectangular cross sections

3. An emission electrode system according to Claim 1 or 2, including a spring and tightening member fitted at least at one end of each emission electrode in order to tighten it at a temperature lower than the operating temperature of the electro-filter in order to keep the emission electrode taut in spite of its longitudinal expansion.

4. An emission electrode system according to Claim 3, wherein one end of the emission electrodes is equipped with threading and fitted through a constricted opening in the upper or the lower part of the frame, the tightening member is a nut mounted on this threaded end; and the spring member is a compressible helical spring passed between the nut and the upper or the said lower part of the frame.

5. An emission electrode system according to Claim 3 or 4, wherein the opposite end of the emission electrode has also been fitted through a constricted opening in the transverse stiffener or in the opposite lower or upper part of the frame, and has been bent along it.

6. An emission electrode system according to Claim 5, wherein said bent opposite end of the emission electrode has been welded to the, transverse stiffener.

7. An emission electrode system for electrodefiiters, such system being substantially as hereinbefore described with reference to the accompanying drawings.