GB2047576A

GB2047576A - Electro-precipitation

Info

Publication number: GB2047576A
Application number: GB8008461A
Authority: GB
Original assignee: Lodge Cottrell Ltd
Current assignee: Lodge Cottrell Ltd
Priority date: 1979-04-12
Filing date: 1980-03-13
Publication date: 1980-12-03
Also published as: EP0026771A1; IT1140802B; AU5719780A; IT8021106A0; FR2453677A1; WO1980002118A1

Abstract

An electro-precipitator rapping apparatus comprises a plurality of rapping devices mounted on a shaft for rapping impact with rapping points of an electro-precipitator; and a drive mechanism (40) arranged to rotate the shaft to operate the rapping devices. The drive mechanism comprises a rotatable shaft (212) which is coupled to the rapping shaft and a pneumatic linear actuator (218) creating a reciprocating motion, which is converted into step wise discontinuous rotating motion of the shaft (212) via a crank member (230) and a ratchet mechanism (214).

Description

SPECIFICATION Improvements in or relating to electro-precipitation This invention is concerned with improvements in or relating to electro-precipitation.

An electro-precipitator for the precipitation of dust and the like from gases comprises discharge electrodes and earthed collector electrodes; the discharge electrodes are charged to a high potential to provide an electrical field for precipitation of the dust; in practice dust collects not only on the collector electrodes but also on the discharge electrodes. Dislodging of the dust from the electrodes at times presents a problem and rapping apparatus is usually provided to give periodic rapping blows to the electrodes to dislodge the dust.

It is an object of the present invention to provide an improved electro-precipitator rapping apparatus.

The invention provides an electro-precipitator rapping apparatus comprising a rapping device adapted for rapping impact with a rapping point of an electro-precipitator, and a drive mechanism comprising (a) a rotatable shaft through rotation of which in the operation of the apparatus the rapping energy is transmitted, (b) a motive device connectible to a source of energy to produce directly a reciprocating output motion, and (c) means for converting the reciprocating motion into rotating motion to rotate the shaft.

Examples of motive devices which produce directly a reciprocating output motion include pneumatic or hydraulic piston and cylinder devices and electrical linear actuators. Examples of means for converting a reciprocating motion into rotating motion include sprag clutches and ratchet mechanisms.

The invention also provides an electro-precipitator rapping apparatus comprising a rapping device adapted for rapping impact with a rapping point of an electro-precipitator, and a drive mechanism comprising (a) a rotatable shaft through rotation of which in the operation of the apparatus the rapping energy is transmitted, and (b) a fluid operable motive device connectible to a source of fluid to produce an output which causea rotation of the shaft.

The invention also comprehends an assembly of a plurality of rapping apparatus according to the invention; an electro-precipitator comprising rapping apparatus according to the invention; and a drive mechanism.

There now follows a description, to be read with reference to the accompanying drawings of embodiments of the invention. This description is given by way of example only and not by way of limitation of the invention.

In the accompanying drawings: Figure 1 shows a diagrammatic side view of an electro-precipitator embodying the invention; Figure 2 shows a diagrammatic plan view of collector electrodes and discharge electrodes of the electro-precipitator; Figure 3 shows in broken perspective parts of a discharge electrode rapping apparatus of the electro-precipitator; Figure 4 shows in broken perspective parts of a collector electrode rapping apparatus of the electro-precipitator; Figure 5 shows a side view of a drive mechanism; Figure 6 shows a sectional end view corresponding to Fig. 5; Figure 7 shows a side view of parts of a modified and preferred drive mechanism; Figure 8 is a section on the line VIII-VIII of Fig. 7; and Figure 9 shows a pneumatic circuit diagram.

The electro-precipitator embodying the invention is of the single stage type and comprises (Fig. 1) a casing 2, a plurality of spaced collector electrodes 1 2 (only one of which is shown in Fig. 1) supported in the casing 2, and a plurality of discharge electrodes 14 of known type also supported in the casing 2 and located in the spaces between the collector electrodes (see Fig. 2).

The arrangement of the collector electrodes 1 2 and discharge electrodes 14 is similar in many respects to those described in our U.K.

Patent Specification No. 1,235,738 to which reference may be made.

The precipitator comprises a gas inlet 3 and a gas outlet 5, through which dust-laden gas to be cleaned is passed in the direction of the arrows X. The casing has a roof 7 and an outlet opening 9 for precipitated dust. The precipitator also comprises means (not shown) for supplying high potential to the discharge electrodes 14.

In the operation of the electro-precipitator the collector electrodes 1 2 are earthed and the discharge electrodes 14 are charged to a high potential; as a result dust is precipitated from the gas and collects on the collector electrodes 12; quantities of dust also collect on the discharge electrodes 1 4.

The precipitator comprises rapping apparatus 1 6 adapted to dislodge collected dust from the collecting electrodes 1 2 and also comprises rapping apparatus 1 8 adapted to dislodge collected dust from the discharge electrodes 14.

The discharge electrodes 14 are arranged in generally planar rows parallel to the direction of gas flow, the rows alternating with the collecting electrodes 1 2. Each row of discharge electrodes 14 is secured to a horizontal angle member 20 (Figs. 1 and 3). The discharge electrodes 14 are supported from the roof 7 by supporting structures 22 (only two of which are shown). Each structure 22 comprises an elongated vertical tube 24 which is supported by an insulator assembly 26 mounted on the roof 7. The tube 22 extends downwardly through the roof 7 and a lower end portion of the tube 24 is secured to one of two beams 28 extending at right angles to the direction of gas flow. The members 20 are resiliently secured to the beams 28 by spring mountings 30.

The rows of discharge electrodes 14 are arranged in pairs (Fig. 3) and the two rows of each pair have a bridge anvil 32 secured to the angle members 20 thereof and extending between said members 20; each bridge anvil 32, in the operation of the apparatus, receives rapping blows to dislodge collected dust from the electrodes 14.

The discharge electrode rapping apparatus 1 8 comprises a horizontal shaft 34 located inside the casing 2. The shaft 34 is mounted for rotation in bearings 35 (only one of which is shown) each of which is mounted on a bracket assembly 37 which bridges the two beams 28. On the shaft 34 are mounted a plurality of rotary tumbling hammers 36 of the well-known type; there is a hammer 36 associated with each pair of rows of electrodes 14. In the operation of the apparatus the shaft 34 rotates and the hammers 36 impart rapping impact to the anvils 32. For the locus of a tumbling hammer reference may be made to our U.K. Patent Specification No.

1,151,841 (Fig. 2thereof).

The rapping apparatus 1 8 comprises a drive mechanism 40 adapted to operate the hammers 36 through rotation of the shaft 34. The drive mechanism 40 is mounted between the beams 28 on a member 41 which is secured to the beams 28.

Each collector electrode 1 2 (Figs. 1 and 4) is suspended from two horizontal beams 42 which themselves are supported on ledges 44 in the casing 2 and extend at right angles to the direction of gas flow. The collector electrode 1 2 comprises horizontal rectangular tubular support member 46 which is secured at each of its ends to the beams 42 by spring mounted U - brackets 48.

The collector electrodes 1 2 are arranged in pairs and each pair has a bridge anvil 50 extending between the support members 46; each bridge anvil 50, in the operation of the apparatus, receives rapping blows to dislodge collected dust from the collector electrodes 12.

The collector electrode rapping apparatus 1 6 (Fig. 4) comprises a horizontal shaft 52 located outside the casing 2 above the roof 7.

The shaft 52 is mounted for rotation in bearings 54 (only one of which is shown) each of which is mounted on an angled support structure 56 mounted on the roof 7. On the shaft 52 are secured a plurality of trip dogs 58 (only one of which is shown) each arranged to actuate a vertical drop rod hammer 60 of the well-known type there is a drop rod hammer 60 associated with each pair of collector electrodes 12. Each drop rod hammer 60 is slidably received in a vertical sleeve 62 which extends through the roof 7 and is secured to the appropriate bridge anvil 50; the drop rod hammer 60 is also slidably received in a ring 64 mounted on the support structure 56. An upper end portion of the hammer 60 comprises a disc 66 arranged to co-operate with the appropriate trip dog 58.In the operation of the apparatus the shaft 52 rotates end each trip dog 58 engages the appropriate disc 66 to raise the hammer 60 to an upper position, when continued rotation of the shaft 52 results in disengagement of the trip dog 58 and the hammer 60 falls to impart a rapping impact to the anvil 50; this cycle is repeated as the shaft 52 continues to rotate.

The rapping apparatus 1 6 comprises a drive mechanism essentially the same as the mechanism 40 but which is not shown in Fig. 4.

It will be realised that in the case of both discharge electrode rapping and collector electrode rapping, the anvils 32 or 50 are not all rapped simultaneously but rather in a preselected sequence determined by the relative orientation of the tumbler hammers 36 or the trip dogs 58 to each other; the relative orientation of the tumbler hammers 36 can be seen.in Fig. 3.

It will be realised that although tumbler hammers have been described in relation to discharge electrode rapping and drop rod hammers in relation to collector electrode rapping, either type of rapping hammer can be used with either discharge electrodes or collector electrodes; or again other types may be used e.g. spring assisted rapping hammers. The drive mechanism 40 will now be described and it will be realised this description applies equally to the drive mechanism for rapping apparatus 1 6 as for the rapping apparatus 1 8. Two versions of the drive mechanism 40 are described one with reference to Figs. 5 and 6 and the other with reference to Figs. 7 and 8. The one of Figs. 7 and 8 is preferred and is the version also shown in Figs. 1 and 3. However the version of Figs. 5 and 6 is described first.

The drive mechanism 40 shown in Figs. 5 and 6 comprises a drive shaft 70 arranged to directly rotate the shaft 34 or 52 at the same speed as the shaft 70 via a direct shaft coupling 72 and comprises a casing 76 in which the shaft 70 is mounted for rotation.

The drive mechanism 40 comprises a pneumatic linear actuator 78 comprising a cylinder 80 in which is mounted a piston (not shown) arranged to produce directly a linear reciprocating output motion of a piston rod 82 when the cylinder 80 is connected to a source of compressed air; it will be realised that the linear actuator 78 may alternatively be a hydraulic piston and cylinder device or electri cally powered. The cylinder 80 is pivoted to the casing 76 at 84.

The drive mechanism 40 also comprises means for converting the linear reciprocating motion into discontinuous rotating motion to rotate the coupled shafts 70 and 34 or 52.

The piston rod 82 is secured to a link member 86 which is pivotally connected at 88 to a crank member 90.

The crank member 90 extends from the link member 86 to a first motion shaft 92 to which it is secured by a stud 94. The first motion shaft is mounted for rotary reciprocation in the casing 76 axially of the drive shaft 70; a stub 93 of the shaft 92 is freely received in a corresponding axial cylindrical recess 95 in the shaft 70; a bearing washer 99 is provided between an end flange 104 of the shaft 70 and a shoulder 105 of the shaft 92. A uni-directional rotational drive device 96 of known type is mounted on the shaft 92 and this is a ratchet mechanism similar to a bicycle free-wheel; an inner ring 98 of the device 96 is fixed on the shaft 92 and an outer toothed ring 100 is locked to the shaft 70 by a locking pin 102 secured in the end flange 104 and extending between two adjacent teeth of the outer ring 100.

Another uni-directional rotational drive device 106 is mounted on the shaft 70 and is of the same type as the device 96; an inner ring 108 of the device 106 is fixed on the shaft 70 and an outer toothed ring 110 is locked to an upstanding limb 112 of the casing 76 by a locking bolt 114 which is secured in the limb 112.

In the operation of the apparatus, compressed air is supplied to the cylinder 78 resulting in linear reciprocating motion of the piston rod 82; this is converted into rotary reciprocating motion of the shaft 92 and of the inner ring 98 of the device 96 via the link member 86 and the crank member 90; it will be realised that this results in step wise discontinuous rotation of the outer ring 100 in one sense only. This step wise rotation is transmitted to the shaft 70 via the locking pin 102 which is secured in the flange 1 04.

The device 106 positively prevents reverse rotation of the shaft 70 in dwell periods of the ratchet cycle, which is important with rapping devices which impose a reverse thrust on the shaft 10, for example the drop rod hammers 60. The inner ring 108 rotates with the shaft 70 in the intended sense of rotation of the shaft, but the inner ring 108 is held against rotation in the reverse sense by engagement between the outer ring 110 and the inner ring 108, the ring 110 being prevented from rotation by the locking bolt 11 4. Rotation of the shaft 34 or 52 in a step wise discontinuous fashion is quite satisfactory for the periodic requirements of rapping.

It will be realised that the rapping energy is transmitted through the rotation of the shaft 70 with the frequency of rapping being dependent on the speed of rotation of the shaft 70.

The required rotational speed of the shaft 34 or 52 for rapping purposes is for example from 1 revolution per hour to 1 5 revolutions per hour and with the mechanism 40 it will be noted that this low speed is achieved without the need for complex reduction gearing as would be required e.g. with a conventional electric motor.

Also with the mechanism 40 the rapping energy is transmitted to the required locality without the need for complicated insulating arrangements through the casing 2; it is also advantageous from this viewpoint to have the mechanism 40 located within the casing 2, as is the case with the discharge electrode rapping apparatus 18, more particularly with discharge electrodes, which always operate at a high electrical potential from which it is necessary to insulate any exposed items.

Figs. 7 and 8 show the preferred version of drive mechanism in which the means for converting the linear reciprocating motion into discontinuous rotating motion is simplified.

The modified mechanism comprises a casing 216 corresponding generally to the casing 76. The two shafts 70, 92 of the mechanism shown in Figs. 5 and 6 are replaced by a single shaft 212 which is rotatable in bearings 213 secured to the casing 216. The shaft 212 is driven via a ratchet mechanism 214, and the modified drive mechanism comprises a pneumatic linear actuator 218 generally corresponding to the actuator 78. The linear actuator 218 is located within the casing 216 and comprises a cylinder 220 and a piston rod 222. The cylinder 220 is pivoted at 224 to a bracket 225 mounted in the casing 216, and the piston rod 222 is pivoted at 228 to a bracket 227 of the crank member 230. The crank member 230 comprises two spaced arms 231 upper end portions of which are bolted to a spacing member 233; the bracket 227 is also bolted to the spacing member 233.A lower end portion of each arm 231 comprises a bearing 235 which is freely mounted on the shaft 212.

A ratchet wheel 232 of the ratchet mechanism 214 is fixed onto the shaft 212 for rotation therewith. The ratchet wheel 232 comprises two circular plates 237, which are spaced by tubular spacers 239 and secured together by bolts 241 extending through the spacers 239. A plurality of evenly spaced dogs 234 extend between the plates 237 peripherally of the wheel 232 and parallel to the shaft 212; each dog 234 comprises a steel tube 235 freely rotatable on a short shaft 243 extending between the plates 237.

A drive pawl 238 is pivoted to the crank member 230 between the plates 231 on a pivot 236 extending between and secured to the plates 231; the pawl 238 is urged by gravity about the pivot 236 towards an adjacent dog 234. A check pawl 240 is pivoted on the casing 216 as 244, and the check pawl 240 is also urged by gravity towards an adjacent dog 234.

In the operation of the modified mechanism on the return stroke of the piston rod 222 the drive pawl 238 engages the adjacent dog 234 and moves the ratchet wheel 232 and thus the shaft 212 in a clockwise (Fig. 7) direction; in this movement the check pawl 240 is cammed out of the path of the approaching dog 234 against the action of gravity by virtue of a camming surface 246 on the pawl 240. In the outward stroke of the piston rod 222 the check pawl 240 is in engagement with the dog 234 to prevent movement of the wheel 232 and the shaft 212 in an anticlockwise direction; the drive pawl 238 is cammed out of the path of the dog 234 which it is approaching, against the action of gravity by virtue of a camming surface 248.

It will be noted that the shaft 21 2 extends out of the casing 216 on both sides thereof and the shaft 34 as shown in Fig. 3 comprises two separate co-axial portions on either side of the casing 216, each portion of the shaft 34 being connected to the shaft 212 via a direct shaft coupling 250 (only one of which is shown).

In a modification, one or both of the pawls 238, 240 are spring urged.

In another modification, the apparatus is rearranged for anticlockwise rotation of the shaft 212 by reversing the pawls 238, 240, with a counterbalance for the pawl 240 so that it is still urged towards the appropriate adjacent dog 234; it will be realized that this reversibility is permitted by the clockwise/ anticlockwise rotational symmettry of the ratchet wheel 232.

The speed of rotation of the shaft 34 or 52 and thus the frequency of rapping are readily adjustable by the use of conventional valving arrangements, without any need for variable speed gearing.

Fig. 9 illustrates a plurality of drive mechanisms 40 connected in parallel by lines 304 which are connected by a single line 305 to a central compressor 300 and reservoir 302.

Each drive mechanism 40 has its own individual valved control assembly 306 and each mechanism 40 is incorporated in a different rapping apparatus which may be either for discharge electrode or collector electrode rapping. Thus it will be realized the speed of rapping can be locally varied by separately adjusting the control assemblies 306.

Claims

1. An electro-precipitator rapping apparatus comprising a rapping device adapted for rapping impact with a rapping point of an electro-precipitator, and a drive mechanism comprising (a) a rotatable shaft through rotation of which in the operation of the apparatus the rapping energy is transmitted, (b) a motive device connectible to a source of energy to produce directly a reciprocating output motion, and (c) means for converting the reciprocating motion into rotating motion to rotate the shaft.

2. An apparatus according to claim 1, wherein the means for converting the reciprocating motion into rotating motion comprises a ratchet mechanism.

3. An apparatus according to claim 2, wherein the ratchet mechanism comprises a check device to prevent reverse rotation of the shaft in dwell periods of the ratchet cycle.

4. An apparatus according to any one of claims 1, 2 and 3, wherein the motive device is fluid operable, being connectible to a source of fluid to produce directly the reciprocating output motion.

5. An electro-precipitator rapping apparatus comprising a rapping device adapted for rapping impact with a rapping point of an electro-precipitator, and a drive mechanism comprising (a) a rotatable shaft through rotation of which in the operation of the apparatus the rapping energy is transmitted, and (b) a fluid operable motive device connectible to a source of fluid to produce an output which causes rotation of the shaft.

6. An apparatus according to claim 4 or claim 5 wherein the motive device is a pneumatic piston and cylinder device.

7. An apparatus according to claim 4 or claim 5 wherein the motive device is a hydraulic piston and cylinder device.

8. An apparatus according to any one of claims 1 to 5, wherein the motive device is adapted to produce a linear reciprocating output motion.

9. An apparatus according to any one of the preceding claims wherein the rapping device is of the rotary tumbler hammer type.

10. An apparatus according to any one of claims 1 to 8 wherein the rapping device is of the drop rod hammer type.

11. An apparatus acording to any one of the preceding claims comprising a plurality of rapping devices each adapted for rapping impact with a different rapping point of the electro-precipitator, and a rotatable shaft on which the rapping devices are mounted and which is arranged to be rotated by the rotation of the shaft of the drive mechanism.

1 2. An apparatus according to claim 11 wherein the shaft on which the rapping devices are mounted is directly coupled to the shaft of the drive mechanism so that in the operation of the apparatus the shafts rotate at the same speed.

1 3. An apparatus according to any one of the preceding claims comprising means for controlling the motive device to adjust the speed of rotation of the shaft of the drive mechanism, the frequency of rapping being dependent on the speed of rotation of the shaft.

14. An electro-precipitator rapping apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to (a) Fig. 3 or Fig. 4 and (b) Figs. 5 and 6; or Figs. 7 and 8 of the accompanying drawings.

1 5. An assembly of a plurality of rapping apparatus according to any one of the preceding claims wherein the motive devices are connected together in parallel and are thus connectible by a single line to the source of energy.

16. An assembly of a plurality of rapping apparatus according to claim 1 3 wherein the motive devices are connected together in parallel and are thus connectible by a single line to the source of energy, each motive device having its own individual control means to adjust the speed of rotation of the shaft of the drive mechanism.

1 7. An electro-precipitator comprising a casing, a plurality of spaced collector electrodes supported in the casing, a plurality of discharge electrodes supported in the casing and located in the spaces between the collector electrodes, and rapping apparatus according to any one of claims 1 to 14.

1 8. An electro-precipitator according to claim 17, wherein the rapping apparatus is arranged to rap the discharge electrodes.

1 9. An electro-precipitator according to claim 17, wherein the rapping apparatus is arranged to rap the collector electrodes.

20. An electro-precipitator constructed, arranged and adapted to operate substantially as hereinbefore described with reference to (a) Figs. 1 to 4 and (b) Figs. 5 and 6; or Figs. 7 and 8 of the accompanying drawings.

21. A drive mechanism constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 5 and 6; or Figs. 7 and 8 of the accompanying drawings.