EP0978118A1

EP0978118A1 - Acoustic apparatus and method

Info

Publication number: EP0978118A1
Application number: EP98917421A
Authority: EP
Inventors: Howard T. British Nuclear Fuels Plc JENNINGS
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1997-04-26
Filing date: 1998-04-20
Publication date: 2000-02-09
Also published as: AU7065498A; WO1998049671A1; GB9708449D0; ZA983377B

Abstract

A method and apparatus for removing contamination or corrosion, as defined, in a chamber or pipe is described. The apparatus comprises a horn and transducer assembly; said horn having two ends, a first end of which is in contact with an external surface of the chamber or pipe; an acoustic transducer in contact with the other end of the horn; and means for energising the acoustic transducer, whereby in use acoustic energy from the transducer is guided through the horn to the surface of the chamber or pipe and thereby into the liquid contained therein.

Description

Acoustic Apparatus and Method

This invention relates generally to apparatus for introducing acoustic energy into a chamber or pipe. In many industries, such as the nuclear industry, it is a problem that as a consequence of use with hazardous substances, the internal surfaces of chambers or pipes, become contaminated with hazardous material. Generally, removal of this contamination requires that the contaminated section of the chamber or pipe is removed from its working environment by a fully protectively- suited worker before it is subjected to a decontamination process. Furthermore, the chemical decontamination methods often used can themselves produce considerable secondary waste.

In other methods which require breaching of the chamber or pipe, so-called "pigs" may be used which themselves become contaminated and thereby create further waste. Ultrasonic cleaning is one possible means for removing contamination from surfaces but problems are presented in trying to introduce ultrasound into pipes or other chambers of awkward dimensions and/or geometries.

An object of the present invention is to provide a method and means for removing contamination from the internal surfaces of a chamber or pipe which does not require removal of the chamber or pipe and does not generate significant secondary waste. A further object of the present invention is to provide a method and apparatus to assist or maintain the flow of solid/liquid systems, such as slurries for example, in pipe systems.

According to a first aspect of the present invention, there is provided a method of removing contamination or corrosion from the internal surfaces of a liquid-containing chamber or pipe, the method comprising providing apparatus including an acoustic transducer and a horn connected thereto for introducing acoustic energy into the chamber or pipe the horn being in direct contact with an outer surface of the chamber or pipe, whereby in use acoustic energy is introduced into the liquid in the chamber or pipe causing cavitation in the liquid to assist in removing the contamination or corrosion.

The chamber or pipe contains a liquid and the acoustic energy introduced into the chamber or pipe in use causes cavitation within the liquid which assists in removing the contamination or corrosion.

The liquid may contain a chemical reagent which may assist in removing the contamination or corrosion. The cavitation caused within the liquid in the chamber or pipe may increase the rate of any chemical reactions occurring which may otherwise proceed at a much slower rate.

According to a second aspect of the present invention, there is provided apparatus for introducing acoustic energy into a liquid-containing chamber or pipe, the apparatus comprising, a horn, one end of which is in contact with an external surface of the chamber or pipe, an acoustic transducer in contact with the other end of the horn, and means for energising the acoustic transducer, whereby in use acoustic energy from the transducer is guided through the horn to the surface of the chamber or pipe and thereby into the liquid contained therein. The apparatus according to the second aspect of the present invention may be used for removing contamination or corrosion from the internal surfaces of a chamber or pipe in the method according to the first aspect of the present invention. In this specification the terms "contamination" and "corrosion" also include the situation where, for example, a pipe is actually blocked. Thus, the method and apparatus of the present invention also encompasses the removal of blockages. Such blockages may result from the settling-out of solids in slurries where such are being transported in pipes for example. The method and apparatus of the present invention may be used to maintain continuity of flow of solid/liquid systems in pipes where the geometry thereof, for example, may tend to restrict or hamper the flow. The acoustic energy introduced into the liquid within the chamber or pipe by the apparatus according to the present invention may cause cavitation within the liquid which assists in removing contaminated matter from the internal surfaces of the chamber or pipe. Dislodging of matter from the internal surfaces of the chamber or pipe may occur as a result of the mechanical forces and raised temperatures and pressures associated with the implosion of the bubbles formed during cavitation.

The horn may be incorporated into a clamp arrangement which holds the smaller area of the horn against the pipe or chamber exterior under pressure.

The horn might be generally conical in shape with the smaller cross sectional area end being in contact with the external surface of the chamber or pipe. The precise shape and dimensions of the horn will be dependant on the pipe or chamber to be decontaminated and its design will be provided by those skilled in the art.

The horn provides a physical path from the transducer to the chamber or pipe and concentrates the power of the transducer by a factor depending on the horn design.

The horn may also include a ring at the workpiece end, the ring forming the horn end and closely surrounding a pipe for example. Such rings may be in the form of a split ring, the parts of which are bolted together around the pipe for example, one half of the ring being joined by bolting or welding, for example, to the end of the horn.

The acoustic transducer may be a piezoelectric transducer or preferably it may be a magnetostrictive transducer. Magnetostrictive transducers provide certain advantages over piezoelectric transducers such as greater robustness, greater power, longer lifetime and are safer to use due to the smaller operating voltages required as compared with piezoelectric transducers.

Due to the energy imparted to the horn/transducer assembly, the assembly may be cooled by suitable means such as gas or water pipes for example.

Preferably, the horn is arranged such that, for the particular wavelength of acoustic energy used, the peak energy of the acoustic wave occurs just inside the internal surface of the chamber or pipe, the cavitation thereby induced in the liquid in the region adjacent the internal surface being especially effective in removing contaminated matter from the internal surface.

Cavitation induced in the liquid in operation may assist in chemical reactions where a decontaminant chemical is used in the removal of contamination.

The frequency of the acoustic energy may be in the range 10 kHz to 20 kHz but in some circumstances it may be advantageous to use frequencies higher than 20 kHz, i.e. ultrasound, or frequencies lower than 10 kHz. In some circumstances it may be advantageous to use frequencies lower than 20 Hz, i.e. infrasound. In practical embodiments of the apparatus according to the present invention, there may be a plurality of horns and transducers.

For a pipe, the horns may be arranged in a radial array around the pipe or in a linear array along the pipe or chamber or both. The horns in a radial array may also be axially staggered to allow complete coverage of the pipe external area.

The apparatus may also include means to automatically move it along a pipe in incremental steps.

The apparatus may have means for allowing an individual horn to move relative to adjacent horns in, for example, a radial direction relative to a pipe axis in order to accommodate surface variations such as welds, for example, in the workpiece.

The invention will now be described in detail by way of example and with reference to the accompanying schematic diagrams in which:

Figure 1 shows, in one embodiment of the present invention, apparatus for introducing acoustic energy into a liquid-containing pipe;

Figure 2 shows a second embodiment of the present invention;

Figure 3 shows a third embodiment of the present invention;

Figure 4 shows another embodiment of the present invention;

Figure 5 shows a further embodiment of the present invention; Figure 6 shows a still further embodiment of the present invention: and

Figure 7 which shows a schematic cross section of part of a horn having a ring at the first end thereof.

Referring to Figure 1, a horn and transducer assembly 1 is shown comprising principally an acoustic horn 2 and an acoustic transducer 8. The acoustic horn 2, having two ends, has a tip 7 at one of its ends which in use contacts an external surface 4 of a pipe 3. The horn 2 may be generally conical in shape, having a smaller cross sectional area at one end than the other, with the tip 7 being located at the end having the smaller cross sectional area. The horn 2 may be composed of stainless steel. The tip 7 may be composed of the same material as the horn 2 or it may be composed of a dissimilar material. The tip 7 may, for example, be composed of titanium. The acoustic transducer 8 contacts the other end of the horn 2. The transducer 8 is a magnetostrictive transducer. Around the transducer 8 is wound a coil 9 through which is passed an alternating electrical current fed from an amplifier 10. The amplifier 10 uses a feedback loop to ensure that the electrical current supply to the coil 9 is controlled. The horn is held in intimate contact with the external surface 4 of the pipe 3 by means of a clamp 11 having an upper jaw 14 and a lower jaw 15. The upper jaw 14 of the clamp 11 is fixed to the horn 2 at a point 12 on the horn 2 which in use is located in a nodal region of the acoustic wave. The inner surface 13 of the lower jaw 15 contacts the external surface 4 of the pipe 3 on the opposite side of the pipe 3 to the side which the horn 2 contacts. The jaws 14,15 of the clamp 11 can be tightened (by means not shown) so that the horn 2 is held in contact with the external surface 4 of the pipe 3 under a pressure applied by the clamp 11 in the direction shown by arrow F. Contacting the end 7 of the horn 2 on the pipe 3 under a slight pressure increases the efficiency of acoustic energy transfer from the horn 2 to the pipe 3 in use.

In operation, the amplifier 10 supplies an alternating electrical current to the coil 9 wound round the acoustic transducer 8, whereby the transducer 8 is energised and generates acoustic energy. The horn 2 guides and concentrates the acoustic energy generated by the transducer 8 to the pipe 3 and thereby into the liquid 6 contained therein. The acoustic energy thus introduced into the liquid 6 causes cavitation within the liquid 6. The liquid 6 may be water or an aqueous solution of a chemical composition to assist in corrosion or contamination removal. Preferably, the horn is arranged such that, for the particular wavelength of acoustic energy used, the peak energy of the acoustic wave occurs just inside the internal surface 5 of the pipe 3, the cavitation induced in the liquid 6 in the region adjacent the internal surface 5 being particularly effective in removing corrosion or contaminated matter from the internal surface 5. The dislodging of matter, including the clearing of blockages, from the internal surface 5 of the pipe 3 occurs as a result of the mechanical forces and raised temperatures and pressures associated with the implosion of the bubbles formed during cavitation.

The liquid 6 may be in a flow through the pipe 3 so that any matter which is dislodged from the internal surface 5 of the pipe 3 into the liquid 6 may be collected at the end of the pipe. The flow of liquid 6 may be additionally re-fed back into the pipe 3 after passing through a filter to remove the contaminated matter.

A chemical reagent, such as citric acid or nitric acid, may be added to the liquid 6 to aid the dislodging of matter from the internal surface 5 of the pipe 3.

The frequency of the acoustic energy applied to the pipe or chamber by the apparatus described hereinabove may be in the range from very low frequencies to greater than 20 kHz, i.e. in the range from infrasound to ultrasound.

Preferably, the frequency of the acoustic energy applied to the pipe by the apparatus described hereinabove is in the region 10 to 20 kHz. Referring now to Figure 2, an apparatus is shown having a plurality of horn and transducer assemblies radially disposed about a pipe for introducing acoustic energy into the pipe and thereby into the liquid contained therein. A plurality of horns 22 (eight are shown as an example) are disposed about and are in contact with an external surface 24 of a pipe 23, each horn 22 being of a similar type as the horn 2 in the apparatus shown by Figure 1. Each horn 22 has a transducer 28 of a similar type as the transducer 8 and coil 9 in the apparatus shown by Figure 1. Each transducer 28 has a coil 29 through which an electrical current from an amplifier/control system (not shown) passes in use. Each horn 22 is linked at a nodal point 32 on the horn to a strap 30 which passes round the pipe 23. The strap 30 can be tightened (by means not shown) so that the horns 22 are held in contact with the external surface 24 of the pipe 23 under a positive pressure, thereby increasing the efficiency of the acoustic energy transfer from the horns 22 to the pipe 23 in use.

The apparatus of Figure 2 operates in a similar manner to the apparatus of Figure 1 but has the advantage that by having a plurality of horns disposed about the pipe, the acoustic energy introduced may be more evenly distributed around the pipe resulting in a more efficient and uniform removal of contamination from the internal surface of the pipe.

Referring now to Figure 3, which shows apparatus having a plurality (four are shown) of horn and transducer assemblies disposed longitudinally along a pipe 43 containing a liquid 46. Each individual assembly 42 may be linked to adjacent assemblies by means of a linkage (not shown) . Each assembly 42 may also be clamped to the pipe 43 by a clamp (not shown) in the manner of clamp 11 used in the apparatus shown in Figure 1. The apparatus of Figure 3 operates in a similar manner to the apparatus of Figure 1 but has the advantage that the acoustic energy is applied over a larger region of the pipe than would be possible with the single assembly arrangement of Figure 1.

A plurality of linear arrays as shown in Figure 3 may be assembled together in a radial array similar to that as shown in Figure 2.

Referring now to Figure 4, another form of the apparatus is shown, comprising means for moving a horn and transducer assembly, or a plurality of such assemblies, along a pipe. A plurality of horn and transducer assemblies accommodated on a strap unit 51 of the type shown in Figure 2 are radially disposed around a pipe 53. The strap unit 51 is connected to a first clamp 52 located around the circumference of the pipe 53. The clamp 52 is connected by a number of screw-like devices 57 to a second clamp 54. Integral with the screw-like devices 57 are a number of electric actuators 55, each actuator 55 being integral with one screw-like device 57. Each clamp 52,54 and the strap unit 51 have integral electric actuators (not shown) to tighten or loosen them around the pipe.

The horn and transducer assemblies accommodated on the strap 51 are operated in a similar manner to the apparatus of Figure 2 to introduce acoustic energy into the pipe 53. In operation of the means for moving the plurality of horn and transducer assemblies along the pipe 53, the clamp 54 is initially clamped tightly around the pipe 53 by means of its integral actuator (not shown) but the clamp 52 and the strap unit 51 are not tightly clamped around the pipe 53. Actuation of the electric actuators 55 turns the screw-like devices 57 so that the clamp 52 and hence the strap 51 are pulled toward the clamp 54. After moving the strap 51 the desired distance along the pipe 53, the electric actuators 55 are stopped and the actuators (not shown) on the clamp 52 and the strap 51 tighten the clamp 52 and the strap 51 so as to form an intimate coupling once more between the horns and the pipe surface. The clamp 54 is then loosened around the pipe 53 and the actuators 55 are actuated once more so as to turn the screw-like devices 57 in the opposite direction to that used in pulling clamp 52 towards clamp 54 thereby pushing clamp 54 forwards. Clamp 54 is then firmly tightened about the pipe 53 once more by its integral actuator. The apparatus may be moved along the length of the pipe by repetition of this process.

Yet further specific embodiments can be envisaged, in which pluralities of horn and transducer assemblies of the type shown in Figure 1 are disposed both radially around a pipe or chamber and longitudinally along the same pipe or chamber.

Still further specific embodiments can be envisaged in which the apparatus includes means for moving a horn and transducer assembly, or a plurality of such assemblies, circumferentially around a pipe.

The operation of the apparatus shown in Figures 1-4 may be further illustrated by way of the following Example. An apparatus of the type shown in Figure 1 was disposed about a water-containing pipe in the manner shown in Figure 1, the pipe having had a several μm thick film of copper plate electron beam deposited on its internal surface. The pipe diameter was 30 mm and the pipe wall thickness was 3 mm. The transducer of the apparatus was energised to provide about 800 at a frequency of about 20kHz so as to effect the introduction of acoustic energy into the pipe and into the liquid therein. The cavitation induced in the liquid by the introduction of the acoustic energy had the effect of WO 98/49671 -^■_ -^•_ PCT/GB98/01154

removing the copper plate film from the internal surface of the pipe very rapidly. The removal of the copper plate film from the internal surface was accompanied by a change in the water colour from clear to black. Referring now to Figure 5, an embodiment of the present invention is shown wherein a horn 60 has a plurality of piezoelectric crystal transducers 62 stacked in series. The piezoelectric crystals 62 are separated by metal plates 64. In use, the metal plates 64 are supplied with alternating electrical current such that adjacent metal plates carry oppositely charged electrical potential .

Referring now to Figure 6 , a plurality of horn and transducer assemblies 70, similar in type to the horn and transducer assemblies in Figure 5, are arranged longitudinally along a pipe 72. Each assembly 70 is individually movable in a direction normal to the surface of the pipe 72 in order to allow efficient coupling of the horns with the pipe, i.e. individual horns can move up and down to follow the contours of the pipe 72. As an example, one of the horn and transducer assemblies 70 is shown as displaced so as to accommodate a pipe weld 74.

Figure 7 shows a cross section through a horn and ring assembly 80 for transmitting acoustic waves of about 20kHz frequency to a pipe 82 carrying a slurry of particulate matter in a liquid 84. The assembly 80 comprises a horn 86 (shown in part only) and a ring 88 split into two halves 90, 92 about the pipe 82. The first half 90 is fixed to the end of the horn 86 by a bolt 94 passing through a recessed hole 96 in the half ring 90 into a threaded hole 98 in the horn. The second ring half 92 is clamped to the first half 90 tightly about the pipe 82 by bolts 100 passing through holes 102 in the halves. It has been found that adequate coupling of the acoustic energy into the pipe and contents is achieved even though the faces 104, 106 of the ring halves may not be in contact. Thus, the dimensional tolerances for the ring 88 may be greatly relaxed. The assembly of Figure 7 may be permanently located in desired positions, for example, to maintain continuity of slurry flow in difficult regions of pipework or to clear a blockage where, for example, solids have settled-out due to flow being interrupted for some reason.

Claims

1. A method of removing contamination or corrosion from the internal surfaces of a liquid-containing chamber or pipe, the method comprising providing apparatus including an acoustic transducer and a horn connected thereto for introducing acoustic energy into the chamber or pipe the horn being in direct contact with an outer surface of the chamber or pipe, whereby in use acoustic energy is introduced into the liquid in the chamber or pipe causing cavitation in the liquid to assist in removing the contamination or corrosion.

2. A method according to claim 1 wherein the peak energy of the acoustic waves occurs adjacent the inner surface of the chamber or pipe.

3. A method as in either claim 1 or 2 wherein the liquid is provided with a chemical reagent to assist in removing the contamination or corrosion.

4. A method according to any one preceding claim wherein the acoustic waves have a frequency of 10kHz to 20 kHz.

5. Apparatus for introducing acoustic energy into a liquid-containing chamber or pipe, the apparatus comprising a horn and transducer assembly; said horn having two ends, a first end of which, in use, is in contact with an external surface of the chamber or pipe; an acoustic transducer in contact with the other end of the horn; and means for energising the acoustic transducer, whereby in use acoustic energy from the transducer is guided through the horn to the surface of the chamber or pipe and thereby into the liquid contained therein.

6. Apparatus as in claim 5 wherein the horn is arranged such that the peak energy of the acoustic energy occurs inside the chamber or pipe near to the internal surface of the chamber or pipe.

7. Apparatus as in either claim 5 or 6 including clamping means for holding the first end of the horn in close contact with the chamber or pipe.

8. Apparatus as in claim 7 wherein the clamping means are fixed to the horn at a point located in a node of the acoustic energy in use.

9. Apparatus as in any one of claims 5 to 8 wherein the horn is generally conical in shape.

10. Apparatus as in any one of claims 5 to 9 wherein the horn includes a ring at its first end, said ring being around and in close contact with the chamber or pipe in use .

11. Apparatus as in any one of claims 5 to 10 wherein the acoustic transducer is a piezoelectric transducer.

12. Apparatus as in any one of claims 5 to 10 wherein the acoustic transducer is a magnetostrictive transducer.

13. Apparatus as in any one of claims 5 to 11 wherein the frequency of the acoustic energy is in the range from infrasound to greater than 20 kHz.

14. Apparatus as in claim 13 wherein the frequency of the acoustic energy is in the region between about 10kHz and about 20 kHz.

15. Apparatus comprising a plurality of the horn and transducer assemblies according to any one of claims 5 to 14 radially disposed about a chamber or pipe.

16. Apparatus comprising a plurality of the horn and transducer assemblies according to any one of claims 5 to 14 longitudinally disposed along a chamber or pipe.

17. Apparatus comprising a plurality of the horn and transducer assemblies according to any one of claims 5 to

14 disposed radially about and longitudinally along a chamber or pipe.

18. Apparatus as in either claim 15 or 17 wherein the assemblies are connected to a strap disposed about the chamber or pipe. lb

19. Apparatus as in any one of claims 5 to 18 including means for moving the horn and transducer assemblies along the chamber or pipe.

20. Apparatus as in any one of claims 5 to 19 including means for moving the horn and transducer assemblies around the chamber or pipe.

21. Apparatus as in any one of claims 15 to 20 wherein individual horn and transducer assemblies can move in a direction normal to the surface of the chamber or pipe.

22. Apparatus for introducing acoustic energy into a liquid-containing chamber or pipe substantially as hereinbefore described with reference to Figure 1 or Figure 2 or Figure 3 or Figure 4 or Figure 5 or Figure 6 of the accompanying drawings.

23. A method of removing contamination or corrosion from the internal surfaces of a chamber or pipe substantially as hereinbefore described with reference to Figure 1 or Figure 2 or Figure 3 or Figure 4 or Figure 5 or Figure 6 of the accompanying drawings.