GB2261080A - Cleansing system for reducing soot deposition - Google Patents

Abstract

A cleansing system for reducing and/or preventing the deposition of soot and/or dust in boilers, economisers and other units includes a sound generator 4 which functions by interrupting a flow of pressure air or gas at regular intervals, a reservoir 1 for containing the air or gas under pressure and supplying the sound generator, at least two resonance tubes 8, 9, 10 to receive sound pulses from the generator, a master valve 6 between the reservoir 1 and the sound generator 4, individual valves 15, 16, 17 between the sound generator and each resonance tube, a sensor 20 responsive to pressure changes in the reservoir 1 to open and close the master valve 6 and an independently-operating timer 18 for each of the individual resonance tube valves. The system uses a single sound generator to clean a plurality of boilers/economisers 12, 13, 14. <IMAGE>

Description

Cleansing System for Reducing Soot Deposition The present invention is concerned with systems for reducing and/or preventing the deposition of soot and/or dust in boilers, econanisers and other units in which such deposition may occur.

It is known that the build-up of deposits of soot and/or dust in a boiler or econaniser may be greatly reduced by applying impulses of low-frequency sound to a resonator which is in communication with the boiler or econartiser. The sound, for example at frequencies of the order of 20 Hz or much lower, is typically generated in a generator which interrupts at correspondingly frequent intervals a flow of air under pressure. The resulting impulse of sound is applied to the resonator for a short period, typically just a few seconds, at regular intervals, say of the order of ten or twenty minutes.

In UK Patent Specification No. 2207543, I have disclosed such a system wherein a single sound generator may supply impulses to each in turn of two or more resonators. Previously each resonator had been supplied fran a separate sound generator, so the new system disclosed in that patent specification affords the opportunity of making significant capital savings when applied to two or more resonators.

However when it is desired, as is usual, to operate that system autanatically, then it has hitherto been necessary to provide a control box to operate the master valve, the sound generator and individual valves associated with the individual resonators, all in the desired sequence and at the chosen intervals of time. The control box may be a relatively expensive feature of the system and it would therefore be advantageous to replace the control box by scane other means of ensuring the desired operation of the various ccmpDnents, if that could be achieved without any loss in performance of the system overall.

It is therefore an object of the present invention to provide a system for reducing or preventing the deposition of soot, dust or the like by means of a sound generator which supplies pulses of sound to at least two resonators, wherein the operation of the resonators independently of each other is achieved without the use of a central control box.

The cleansing system according to the present invention comprises a sound generator which functions by interrupting at regular intervals a supply of air or gas under pressure, a reservoir for containing said air or gas and supplying it to said sound generator, at least two resonance tubes connected to receive sound pulses produced by said sound generator, a first valve disposed between and ccmmunicating with said reservoir and said sound generator, two or more second valves, each disposed between and communicating with said sound generator and one of said resonance tubes, a sensor adapted to open and close respectively said first valve in response to changes in pressure in said reservoir, and a timer associated with each of said second valves to operate each said second valve independently of the other said second valves.

By means of the present invention, it becomes possible to apply the desired sound impulses to each of the resonant tubes in a desired sequence, without requiring the provision of any central control system. The operation of the first valve (the "master valve") is effected by means of the pressure sensor and the independent operation of the second valves is effected by individual timers.

Sound generators which function by interrupting a supply of air or gas are well known and are described in GB2207543.

The form of sound generator particularly preferred for use in the cleansing system according to the present invention is a rotary generator in which one or more apertures in a rotary member move into and out of register with one or more apertures in a fixed member as the rotary member rotates.

The resonance tubes are tubes suspended so as to be able to vibrate with a minimum of restriction. To a first, closed end of each tube the relatively low-intensity sound pulses fran the sound generator are supplied and the other end of the tube is open and is located within, or in direct communication with, the space in which deposition is to be discouraged. Thus, for example, the tube may hang free within a boiler or may be linked with an econoniser via a bellows.

The pressure sensor associated with the reservoir is connected to operate the master valve in response to changes in pressure in the reservoir. Thus the sensor may produce a first signal when pressure in the reservoir reaches a predetermined upper value, which signal causes the valve to open, and produce a second signal when the reservoir pressure falls to a predetermined lower value, which second signal causes the master valve to close. Since opening of the valve causes the reservoir pressure to fall and closing of the valve allows the pressure to rise again, the valve will open and close at regular intervals.The length of those intervals may be varied by modifying the rate at which air or gas is supplied to the reservoir; good control of that interval length may be achieved by installing a suitable valve, for example a needle valve, in the line supplying the reservoir. Typically, the master valve will be open for only a small proportion of the time, compared with the interval between openings. For example, the valve may open for, say, 4 seconds every 4 minutes.

Preferably the pressure sensor also causes the sound generator to switch into and out of operation, at the same time as the master valve opens and closes respectively.

The second valves, that is the valves associated with the individual resonance tubes, are preferably of the type having a straight-through flow passage therein which can be closed by rotation of a rotary valve member. Suitable valves meeting these criteria are butterfly valves and ball valves, of which the former are preferred. Valves of this general type have the particular advantage that, when the sound generator is in operation and producing sound impulses, 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.

Each of the second valves has a timer associated with it and the timers are operable independently of each other.

Thus, by means of its associated timer, each of these valves opens for a predetermined time at predetermined intervals.

Ideally, the valves open in succession in a selected sequence in which at any time only one valve is open (except perhaps for a brief period of overlap), and at no time are all the valves closed. However it does not matter if such an ideal operation is not achieved. If by chance at any time all of the second valves were simultaneously in the closed position when the master valve opened, the sound generator would simply run briefly without effect on the resonators; no build-up of pressure downstream of the reservoir would occur.

The invention will now be further described with reference to the accompanying drawing, which illustrates schematically one preferred embodiment of the system according to the present invention.

The illustrated cleansing system comprises a pair of air reservoirs 1, 1, supplied with compressed air by a line 2 via a needle valve 3. Compressed air from the reservoirs is in turn fed to a rotary sound generator 4 via a line 5 in which is disposed a master valve 6. When the master valve 6 is open and the sound generator 4 is rotating, the air is transmitted in pulses of a predetermined frequency, by a line 7, towards one or more of three resonance tubes 8, 9 and 10, each of which is connected by bellows 11 to an economiser 12, 13 or 14. Interposed between each resonance tube and the line 7 is a butterfly valve 15, 16 or 17, which is opened and closed independently of the other butterflyo alves by a timer 18.

A pressure switch 19, supplied with electrical power by a unit 20, is set to send an electrical signal to the master valve 6 when the pressure in the air reservoirs 1, 1 moves above 8 bar or drops below 4 bar. At the same time a signal is sent to an electric motor 21 by means of which the sound generator 4 is driven. Thus, as the reservoir pressure rises above 8 bar, the valve 6 is opened and the sound generator is switched on. Loss of air via the valve and sound generator causes the pressure in the reservoir to fall and when it drops below 4 bar, the valve 6 is closed and the sound generator is switched off. The reservoir pressure builds up again at a rate controlled by the needle valve 3 and the cycle is repeated.Because the rate of flow of air out via the sound generator 4 greatly exceeds the inward flow through the needle valve 6, the pressure falls much more quickly than it rises, with the result that the period for which the sound generator operates each time is much less than the time intervals between its operating periods. For example, the sound generator may operate for, say, 4 seconds at a time, at intervals of the order of 5 minutes.

The timers 18 are independently set to operate in sequence. Thus, by way of example, in a period of 60 minutes, butterfly valve 15 may be open fran the beginning of the period until the 20th minute; valve 16 may be open fran the 18th to the 40th minute and valve 17 fran the 38th to the 60th minute. In other words, these valves are opened in succession for 20-minute periods with a 2-minute overlap. While each butterfly valve is open, the sound generator will send a 4-second sound impulse to the associated resonator four or five times.

As can be seen, the result is that the economisers 12 to 14 are each subjected to four or five short treatments per hour, from a single common sound generator, without requiring a costly central control box to regulate the operation. The frequency of treatment may be controlled by adjusting the needle valve 3. The system may readily be adapted to include more than three resonance tubes, needle valve 3 being adjusted to increase the number of treatments in a given period accordingly, if desired.

Claims (9)

CLAIMS.

1. A cleansing system for reducing the deposition of soot or dust, which comprises a sound generator which functions by interrupting at regular intervals a supply of air or gas under pressure, a reservoir for containing said air or gas and supplying it to said sound generator, at least two resonance tubes connected to receive sound pulses produced by said sound generator, a first valve disposed between and communicating with said reservoir and said sound generator, two or more second valves, each disposed between and communicating with said sound generator and one of said resonance tubes, a sensor adapted to open and close respectively said first valve in response to changes in pressure in said reservoir and a timer associated with each of said second valves to operate each said second valve independently of the other said second valves.

2. A cleansing system as claimed in Claim 1, wherein said rotary generator is one in which one or more apertures in a rotary member move into and out of register with one or more apertures in a fixed member as the rotary member rotates.

3. A cleansing system as claimed in either of Claims 1 and 2, wherein said sensor produces a first signal when pressure in the reservoir reaches a predetermined upper value and a second signal when said pressure falls to a predetermined lower value, which first and second signals cause the first valve to open and to close respectively.

4. A cleansing system as claimed in any of the preceding claims, having an adjustable valve in the line supplying air or gas to said reservoir.

5. A cleansing system as claimed in any of the preceding claims, wherein said sensor causes the sound generator to switch into and out of operation at the same time as the first valve opens and closes respectively.

6. A cleansing system as claimed in any of the preceding claims, wherein said second valves are of a type having a straight-through flow passage therein which can be closed by rotation of a rotary valve member.

7. A cleansing system as claimed in Claim 6, wherein said second valves are butterfly valves or ball valves.

8. A cleansing system as claimed in any of the preceding claims, wherein said timers are set to open said second valves in succession in a sequence wherein at any time essentially only one valve is open and at no time are all the valves closed.

9. A cleansing system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.