GB2207543A

GB2207543A - Sound generating system

Info

Publication number: GB2207543A
Application number: GB08816674A
Authority: GB
Inventors: Rolf Robert Jerlin
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-07-22
Filing date: 1988-07-13
Publication date: 1989-02-01
Anticipated expiration: 2008-07-13
Also published as: GB8717312D0; EP0300696A3; EP0300696A2; GB8816674D0; GB2207543B

Description

1 2207-043 Sound Generating -"tem The present invention is concerned with

the generating of sound, especially of low-frequency sound, and the use of that sound:In a resonator for, among other possible purposes, keeping clean boilers, econcnUsers and other units in vkdch dust and/or soot may otherwise be deposited.

Sound at relatively low frequencies, for example of the order of 20 Hz or =h lower, has proved to be very successful:in preventing or discouraging the build-up of deposits of dust and/or soot in, for example, the boilers of ships. In a typical installation for this purpose, a rotating member located in a line conveying air (or gas) under pressure interrupts the air flow at regular intervals and thereby generates impulses of low-frequency sound, which are passed to a resonator wtich is in cammunication with the boiler or the like to be kept clean. The resonator is typically a tube of which the length is of the order of one quarter of the wavelength of the sound it receives fram the sound generator.

A cleaning system of the foregoing type is operated at frequent intervals, say every ten or twenty minutes or so, and it is therefore usual to keep the sound generator and the resonator, and therefore the boiler itself, in penmnent caL,Ltoxiicaticn, both while sound is being generated and throughout the time in between cleaning operations. Cule the sound gemerator is cperating there is a positive flow of air through the system but in the intervening intervals hot air and also dust may pass back frcin the boiler to the sound generator, with the risk of damging or blocking the latter. To counteract this effect, it has been proposed to keep.the sound generator operating continuously at a reduced air flow rate. Homver it is then necessary to keep the bearings of the rotary manber cool by, for example, diverting a part of the reduced air flow towards the bearings. This approach to the problem may necessitate designing rotary sound generators which are unduly expensive and of course there is the further disadvantage that running the sound generator continuously gives rise to continuous wear of the moving parts.

It is an objeat of the present invention to provide a sound generating system, suitable among other purposes for redwing or preventing deposition in boilers and the like, wherein same at least of the disadvantages of prior such systems are red or eliminated.

The sound generating system according to the present invention rises a sound generator, preferably a rotary generator of sound, which functions by interrupting at predetermined frequent intervals a supply of air or gas under pressure, at least one resonance tube connected to receive sound pulses produced by said sound generator, and, disposed in the connecting line between the sound generator and the or each resonance tube,, a valve having a straight-through flow passage therein which can be closed by rotation of a rotary valve 5 marber.

The sound generator may be any such generator,, preferably a rotary generator, which functions by interrupting the air flow therethrough. In such rotary generators one or more apertures in a fixed m may be designed to move into and lo out of register with one or more apertures in the rotary nx as the latter xer rotates. The frequency of the sound generated is a function of the relative nmters of fixed and rotary apertures and of the frequency of rotation of the rotary mmiber. The positions of the apertures in the relatively movable nmbers may be such that the air flow is interrupted by a rotating disc as it flows axially through the device or by a rotating cylindrical m as the air flaws radially through the latter. A less preferred sound generator is one in which a raffial air flow is interrupted by relative axial movement of fixed and movable coaxial cylindrical mm-hears.

The resonance tube is a tube suspended so as to be able to vibrate with a ndni= of restriction. To a first, closed end of the tube the relatively low-intensity sound pulses frem the sound generator are supplied and the other end of the tube is open and is located within, or in direct conTnunication with, the space in which de-?:)sition is to be discouraged. Thus, for exarrple, the tube rray hang free within a boiler or my be linked with an econumiser via a bellows.

The valve is disposed between the sound generator and the resonance tube and, when closed, completely cuts off any flow of air or gas frcrn the sound generator and also prevents any backflow of exhaust or other hot gases from the boiler or the like to the sound generator. It is a feature of the invention that the valve should be of the type Yterein the flow through the valve is via a straight- through flow passage therein and that the passage should be closable, by rotation of a rotary valve niarther. Suitable valves ting these criteria are butterfly valves and ball valves, of which the fonrer are particularly preferred.

Because the rotary valve very effectively prevents hot gases penetrating back to the sound generator, it is not necessary.

to keep the latter operating continuously nor to provide it with a continuous air flow to cool its bearings. However, in order to protect the rotary valve itself from harm attributable to the hot gases, it is preferred to provide a continuous low-volume flow of air to the downstreant side of the rotary valve, that is to that side of the valve which is nearer to the resonance tube.

The type of valve specified in general terms above has the particular advantage that, when the sound generator is in operation and producing sound inpulses, the valve allows the pulsed air to pass through without restriction'or otherwise distorting the impulses and thus reducing the efficiency of the generated sound.

1 An important advantage of the sound generating system according to the present invntim is that, for what is believed to be the first time in the use of such systems for preventing deposition, it becames possible to operate two or more resonance tubes frctn a single sound generator. Thus the invention includes a system wherein two or more resonance tubes are connected to receive sound pulses produced by a single generator, a valve of the above-defined type being Included in each of the connecting lines fram the sound generator to one of the resonance tubes.

lo rihis is a major aspect of the invention since sound generating system of the kwm type are relatively expensive and it has hitherto been necessary to provide a cmplete system for each boiler. Using the sound generating system according to the present invention, while the cost of the system for a first boiler may be =parable to the cost of prior systems, the cost for second and subsequent boilers may be as little as one third of the cost for the first boiler.

The present system may be used for more than two boilers. Two factors determine the maximum number of boiles to which the 2 0 system may be applied. Firstly, it is rtant that the sound generator should not be too distant frctn any boiler since otherwise any loss of sound intensity between the sound generator and the respective resonance tube may be excessive. It is preferred that the distance apart of the sound generator and any associated resonance tube should not exceed about eight metres. Secondly, since it may be desired to obtain a ompressed air supply to the sound generator from a source such as a ship's compressor and it may fore be necessary to build up the pressure of the supply between cleaning operatims, the total desired lapsed time between successive operations of any one resonance tube way limit the nurber of cleaning operaticns which can take place. Nonetheless, within the---two - foregoing constraints, it has proved possible to envisage as many as seven econcmisers being cleaned at 20-minute intervals with a single sound generating system according to the inventicn.

The invention will now be further described, by way of lo example, with reference to the ac=rpanying drawings, wherein:- Fig. 1 represents schematically one preferred entodiiTmt of the sound generating system according to the present invention, as applied to the cleaning.,.of three eocnamiser units; and Fig. 2 is an axial secimal view U a sound generator suitabii for use in the system of Fig. 1.

Referring firstly to Fig. 2, the illustrated sound generator ccinprises a generally cylindrical housing 3 closed by an end plate 4. Suppbrted on bearings 5, 5 and within the housing 3 is a shaft 6 to which is secured a generally cylindrical rotor 7. The rotor 7 is open at one end 8 and has in its cylindrical side wall a circular aperture 9. An air inlet 10 is provided in the cylindrical wall of the housing 3 and an air outlet 11, also in the cylindrical wall of the housing 3, is disposed with its axis in a plane at right angles to that of the axis of the inlet 10.

1 MW r 7 is aligned, with the air outlet 11 such that, in each rotation of the rotor 7,, the aperture 9 coincides once with the air outlet 11. Thus air introduced at the air inlet 10 Is expelled at the air outlet 11 in pulses at a frequency directly corresponding to the frequency of rotatim of the rotor 7.

2-me- shaft 6 is driven by a belt drive (not sham) applied to a. pulley 12 and driven by an electric motor (also not shown). If the rotor is rotated at,, say,, 1200 revolutions per minute, pulses are delivered from the air outlet 11 at a frequency of 1200 per minute, %tdch corresponds to a sound at 20 Hz frequency.

Referring now to Fig. 1 of the drawings, the sound generator is designated by the reference numeral 13. Air from the- ship's compressor is Introduced via a supply line 14, at a pressure of the.order of 7 - 8 bar.to an air receiver 15. A master valve 16 controls the flaw of air into the sound per. Fr= the sound producer 13, sound pulses generated t=ein are conveyed by air supply line 17 to resonance tubes 18j, 19 and 20 respectively. Butterfly valves 21, 22 and 23 are interposed in the lines to the respective resonance tubes. The respective remnance tubes are linked by bellows 24, 25 and 26 to economisers 27, 28 and 29. An air cool ing line 30 bypasses master valve 16 and butterfly valves 21, 22 and 23 and provides a continuous low-volume supply of air to the resonance tubes. Since the internal dLmreter of the a= cooling line 30 niay be as little as, say, 3 mm, the continuous air consumpticn is at a very low level.

The operation of the sound producing system, and in particular of the various valves and of the sound producer 13 itself, may be controlled tl cal ly by a control box. The following is a typical operational cycle of the system:- A. Butterfly valve 21 is opened.

B. The sound generator 13 is started up.

C. %m the sound producer 13 has achieved the desired operating speed, for example 20 Hz, master valve 16 is opened.

D. After a short operating spell. typically within the range from 5 secands, the master valve 16 is closed and the sound producer 13 is stopped.

E. After an interval which,,nlay be as little as perhaps two minutes but may, in the illustrated enbodiment, amount to approximately one third of the value of the desired interval of cleaning of each ecorúcdser, the butterfly valve 22 is opened, the sound producer 13 is again started up and the abave sequence is repeated for resonance tube 19.

F. The procedure is further repeated for resonance tube 20 whereafter, after the lapse of the desired interval, the whole cycle is repeated.

The illustrated entodiment has been described specifically as applied to three e'ca.icmisers but it may, as already described, l X i be applied to a larger n of econcmisers subject to the limitatims set forth above. Haever,, the sound producing system according to the present invention is envisaged as having application in other situations where infrasonic air is required, for example for airing clothes on a ccnxmrcial scale or for encouraging the flow of pulverulent products such as dried cment in hoppers and/or delivery pipes.

- CLADE 1.. A sound generating system which c=rprises a sound generator which functions by interrupting at predetexmined frequent i-ntervals a supply of air or gas under pressure, at least one re-qaMCe tube connected to-receive sound pulses produced by said sound generator# and, dispc)sed in the connecting line between the sound generator and the or each resonanceI tube, a valve having a straight-through flow passage therein which can be closed by rotation of a rotary valve nr.

2. A sound generating system as claimed in claim 1, rein the sound generator is a rotary sound generatQr.

3. A sound generating system as claimed in claim 2, rein said rotary sound generator comprises a rotary disc Yiich interrupts an axial air flow therethrough.

4. A sound generating system as claimed in claim 2, wherein said rotary sound generator cmprises a rotary cylindrical nwiber which interrupts a radial air flow therethrough.

5. A sound generating system as claimed in any of the preceding claim, wherein the valve is a butterfly valve. or a ball valve.

6. A sound generating system as claimed in any of the preceding claim, wherein a continuous low-volume flow of air is provided to that side of the valve wtdch is nearer to the resonance tube.

3 1 X k 7. A sound generating system as claIned in any of the preceding claims, cising two or more said resonance tubes connected to receive sound pulses produced by a single said sound generator, a said valve being included in each of the connecting lines from the sound generator to one of the resonance tubes.

8. A sound generating system as claimed in claim 7J, ein the operation of said valves and of said sound generator is controUed autcmatically by a control box.

9. A sound generating system as clained in any of the preceding claims, wherein the distance apart of the sound generator and the or each resonance tube is not greater than about eight netres.

10. A sound generating system substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 and/or Fig. 2 of the accarpanying drawings.

Published 1988 at The Patent Office, State House, 66.71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.