Electrostatic precipitator

Abstract: A rapping mechanism for rapping or vibrating collecting electrodes (3) of each precipitator section or each electrode row of an electrostatic precipitator comprises a pair of impact beams (1,1') so arranged that the beams slide upon the upwards facing egdes of a support carrier pair (2,2') secured in the precipitator housing, an anvil (6) secured to the beam pair (1,1'), a drop hammer (7) rotating about a horizontal shaft, said hammer transmitting via the anvil (6) impact energy to the beam pair (1,1') between which the electrodes (3) are suspended, and whereby the electrodes (3) are rapped or vibrated through a horizontal movement of the beam pair (1,1') on the upwards facing edges of the carrier pair (2,2') without the impact energy being transmitted to the fixed construction of the precipitator housing, and a spring (12) secured in the precipitator housing construction at each end of a beam pair (1,1'), said spring imparting through a stop pin (13) a recoiling movement of the beam pair back to its starting position before the anvil (6) is again hit by the drop hammer (7).

Description: The invention relates to an electrostatic precipitator comprising a rapping mechanism for rapping or vibrating the electrodes, preferably the collecting electrodes, of the electrostatic precipitator which is adapted for the cleaning of smoke gases from industrial plants, power plants, etc. Such rapping is necessitated by the fact that, due to the way in which the precipitator operates, dust is deposited on the precipitator electrodes which must consequently be cleaned regularly of this dust during operation, said cleaning being effected by a transmission of impact energy to the electrodes thus exposing the latter to intensive vibration whereby the deposited dust is released. The impact energy required for rapping or vibrating the electrodes is usually produced by a number of hammers being lifted by a rotating shaft extending across the precipitator width from their vertically suspended position and subsequently being released so as to revert to their vertical position. For each hammer an impact rod or an impact beam is provided which is hit by the hammer when the latter reverts to its vertical position and from the impact rod/beam the supplied impact energy is then transmitted to a section of precipitator electrodes. The collecting electrodes usually comprise vertically suspended, narrow and substantially rectangular plates which, at their upper ends, are secured to a suspension device in a precipitator housing containing the electrodes. The latter may be arranged in mutually parallel rows or precipitator sections and the rapping is effected for the separate sections by means of drop hammers and impact rods for each section. Rapping mechanisms of this type are known, e.g. from Duda: "Cement Data Book", 3rd edition, pp 596-598 (Bauverlag GmbH - Wiesbaden und Berlin 1985), and from patent disclosures Nos. US-A-3,844,742 and EP-A-0,398,476. In the so-called European type electrostatic precipitators are generally used drop hammers and impact rods which are connected to the lower ends of the collecting electrodes, and thereby representing the disadvantage that the hammers and their carrier bridges occupy comparatively much space at the end of and below the precipitator sections which, in turn, presupposes an increased length and height of the precipitator housing containing the sections. In the so-called American type electrostatic precipitators the rapping of the electrodes is often effected from the top of the precipitator, the rapping mechanism then being mounted externally on top of the precipitator housing and the rapping being effected by means of small, vertically mounted impact rods which hit the electrode suspension device vertically. In this case each impact rod is provided with slide sealings around the passage through the precipitator housing roof. Certain types of "American" precipitators may alternatively be provided with a vertically acting rapping mechanism mounted inside the precipitator housing and which actuates the electrodes axially. In order to avoid absorption of the impact energy by the precipitator housing construction the so-called European type as well as the American type precipitators may have insulators and protectiving spring elements, discs or leaf springs mounted between the housing construction and the rapping mechanism. It is a disadvantage of the American-type precipitators that a fracture in the rapping mechanism, which also acts as suspension device for the electrodes, may cause the latter to fall from the relevant precipitator section with the ensuing risk of causing a short-circuit and power cuts with a resulting precipitator shutdown. In case of American-type precipitators having the rapping mechanism mounted on top of the precipitator housing roof, the volume occupied by the aggregate precipitator construction in the relevant plant is substantially increased. It is a further disadvantage of the above-mentioned hitherto known electrostatic precipitators that some of the impact energy which actuates the electrodes is immediately transmitted to the supporting construction of the precipitator construction thereby reducing the lifetime of the precipitator housing, irrespective of any optional damping of said energy by means of the inserted spring systems, and wherein energy which may usefully be used for electrode vibration is lost. DE-A-3539205 discloses a rapping mechanism for rapping or vibrating the electrodes of an electrostatic precipitator and wherein the electrodes at their upper ends, are secured to a suspension device, and wherein the rapping mechanism is constituted of drop hammers which are rotating in the vertical plane and about horizontal shafts, said drop hammers being through their rotation caused to act against horizontal impact rods or impact beams which, at the top and at the bottom of the precipitator, are connected to the electrodes, and which, when influenced by a hammer, transmit the supplied impact energy to a row or a section of precipitator electrodes, wherein at the upper part of the precipitator housing, horizontally arranged support carriers are provided, wherein at least one anvil forming an abutment for a rotating drop hammer is secured to the edges of the impact beam facing away from the electrodes, and wherein resilient elements are mounted in the fixed construction of the precipitator housing at the end of each impact beam, for moving the impact beams back to their starting position after a rapping or vibrating movement. This construction also shows the above mentioned disadvantages. It is therefore the object of the present invention to provide a rapping mechanism for electrodes, preferably collecting electrodes, in an electrostatic precipitator, and which remedies the above-mentioned disadvantages of the prior art technique. The object is achieved by means of an electrostatic precipitator of the type disclosed in the introductory part of claim 1 which is known from DE-A-3539205 and which is characterized by the features given in the characterizing part of that claim. The collecting electrodes being at their top only secured between and to an impact rod pair comprising two flat beams bolted together, and by their weight and only with their downwardly facing edges each resting on a support carrier of a pair of support carriers, but without being secured to said support carriers, and so that the impact beams may slide on the latter. The impact beams are hereby separated from the supporting construction of the precipitator whereby the impact energy imparted to the impact beams by the drop hammers is not transmitted to the supporting construction contrary to the hitherto known precipitator constructions, and so that fractures, if any, in the impact beams do not result in the collecting electrodes falling and causing short circuit in the electrostatic precipitator. Particular embodiments of the rapping mechanism are disclosed in claims 2-4. The invention will be explained in more detail in the following with reference to the drawings which are examples and non-limiting illustrations of embodiments of the invention, and wherein Figure 1 is a perspective view of a part of the upper portion of an electrostatic precipitator and showing three precipitator sections, Figures 2A, 2B and 2C are also perspective and partially exploded views of a suspension of a collecting electrode in a rapping mechanism according to the invention, Figure 3 is a perspective view of a rapping mechanism having a common anvil for two precipitator sections, and Figure 4 is a precipitator section with a rapping mechanism according to the invention and supplemented with a known rapping mechanism acting upon the lower part of the section. As shown in Figures 1 and 2A the rapping mechanism of a precipitator comprises two impact beams or carriers 1,1' which in their mounted position in the precipitator housing each rests upon a support carrier 2,2' at the top of a precipitor section, and wherein the support carriers constitute a part of the precipitator frame construction, an anvil 6 and a drop hammer 7 which, during use, is caused to rotate about a not shown horizontal axis above the precipitator sections. The support carriers 2,2' surround in pairs the upper end of the electrodes 3 of a precipitator section and rest at each end on angular support irons 8 which are secured to a not shown wall construction of the precipitator housing. The support carriers 2,2' are provided with assembly holes 5 wherein assembly bolts 5' may be inserted. When an electrode 3 is to be suspended its one end is moved upwards between two carriers 2,2' together forming a carrier pair and are secured temporarily to the latter by means of an assembly bolt 5' which is placed in the assembly hole 5 of the one carrier 2 and is then passed through a corresponding assembly hole 5'' in the electrode 3 and finally into an assembly hole 5 in the other carrier 2' of the carrier pair. Thus, with the upper end of the electrode extending upwards through the carrier pair 2,2', cf. Figure 2B, the beam pair 1,1' of the rapping mechanism is restingly placed upon the upwards facing edges of the carrier pair 2,2' and on each side of the electrode 3. By means of securing bolts 4' which are inserted into securing holes 4 in the beams 1,1' and 4'' in the electrode the latter is suspended in the beam pair 1,1', cf. Figure 2C, whereupon the assembly bolt 5' is removed from the electrode and the support carriers 2,2' so that the electrode is now suspended from the beam pair 1,1' only. With the anvils 6 secured, e.g. by welding, on the upwards facing edges of the beam pairs 1,1' so as to make the anvils form abutments for the drop hammers 7 the latter emit, by rotation about their rotational shaft, impact energy to the anvils 6 which energy actuates the beams 1,1' horizontally and thus vibrates the electrodes suspended in the beams. As it appears most clearly from Figure 1 the supplied impact energy will make the beams 1,1' slide to the right on the upwards facing edges of the carriers 2,2'. This movement of the beams 1,1' is caught by leaf springs 12 being secured to angular support irons 8, each of said beams 1,1' being at their ends provided with transversal bolts 13 which, by the movement, are caused to abut the leaf springs 12 which thus catch the movement of the beams 1,1' and recoil the latter to their starting position before the anvil 6 is again hit by the drop hammer 7, As will appear from Figure 3, an anvil may be of such length that it is secured to several (in the figure two) adjacent impact beam pairs 1,1' whereby the rapping of corresponding adjacent precipitator section electrodes is effected simultaneously. This construction is particularly suitable where a precipitator with only moderate rapping is required. In the embodiment shown in Figure 4 a rapping mechanism 1,6,7 according to the invention is combined with a rapping mechanism 10,11 of a known type and coupled to the lower ends of the electrodes 3. This construction is used in precipitators wherein a particularly high level of rapping is desired, presupposing, however, larger precipitator housing dimensions in order to make space for the lower rapping mechanism. The rapping level may be further increased through a convenient synchronization of the abutment of the drop hammers 7,11 against the anvil 6 and the rods 10, respectively. As will appear from the above the rapping mechanism according to the invention represents in particular the following advantages: The impact energy from the drop hammers is transmitted directly to the electrodes without actuating the precipitator housing construction proper As the impulse time for the individual rapping or vibrating is very short the friction between the impact beams (1,1'), and the support carriers (2,2') will have no significant influence The rapping mechanism may be integrated into existing electrostatic precipitator housings requiring only insignificant modifications of their constructions The noise level of the rapping mechanism is significantly lower than the noise level of corresponding known rapping mechanisms being mounted on the exterior of a precipitator housing, even in case of precipitators with no screening roofs or walls.

Claims: An electrostatic precipitator comprising a rapping mechanism for rapping or vibrating the electrodes, preferably the collecting electrodes (3), comprising vertically suspended, narrow and substantially rectangular plates, wherein the upper ends of the electrodes are secured to a suspension device (4,4',4''), and wherein the rapping mechanism is constituted of drop hammers (7) which are rotating in the vertical plane and about horizontal shafts, said drop hammers being through their rotation caused to act against horizontal impact rods or impact beams (1) which, at the top of the precipitator, are connected to the electrodes (3), and which, when influenced by a rotating drop hammer (7) through at least one anvil (6) secured to the edges of the impact beam (1) facing away from the electrodes which forms an abutment for the hammer (7), transmit the supplied impact energy to a row or a section of precipitator electrodes (3) and wherein resilient elements (12) are mounted in the fixed construction of the precipitator housing at the end of each impact beam (1), for moving the impact beam (1) back to its starting position after a rapping or vibrating movement, characterized in that, at the upper part of the precipitator housing, horizontally arranged support carriers (2,2') in pairs surround the upper ends of the electrodes (3) of a precipitator section, that, at their upper ends, the electrodes (3) are secured between and to beams (1,1') acting as impact beams and which are arranged horizontally and in pairs and movably in the horizontal plane of the relevant section each rests upon the upwards facing edges of support carriers (2,2'). An electrostatic precipitator according to claim 1, characterized in that one and the same anvil (9) is secured to more precipitator sections, the anvil (9) thus having a sufficient length perpendicularly to the width of the section to permit securing of the anvil (9) to the upper edges of several pairs of impact beams (1,1'). An electrostatic precipitator according to claims 1 and 2, characterized in that it further comprises impact rods or beams (10) known per se and secured to the lower ends of the electrodes of a precipitator section and forming an abutment for rotating drop hammers (11) at least with one of their ends. An electrostatic precipitator according to claims 1-3, characterized in that it comprises means to synchronize the hammer impacts at the top and at the bottom, respectively, of the electrodes (3), so that a given minor diffence in time occurs between the respective hammer abutments to the anvils (6,9) and to the lower impact rods (10).

Inventors: BOJSEN ERIK MOE, BOJSEN, ERIK MOE
Applicants: FLS MILJO AS, FLS MILJO A/S
Application year: 1993
Main classification: B03C3
IPC codes: B03C3