AN IMPROVEMENT IN GAS-OPERATED PRESSURE OSCILLATION GENERATORS OF THE DIAPHRAGM VALVE TYPE

Abstract: The invention relates to gas-operated pressure oscillation generators of the diaphragm valve type, particularly pneumatically operated sound emitters used in cleaning inside spaces of furnaces, heat exchangers and similar apparatus, through which gas is flown such as hot flue gases or exhaust gases from chemical processes tending to form a dust deposit on the surfaces in the space. In such cleaning operations gas-carried pressure oscillations of sound or infrasound frequency are used for physically actuating the dust of the deposit. In such applications it is necessary to cool the interior of the pressure oscillation generator and to blow away dust particles in order not to jeopardize or impair the operation of the generator. According to the invention, a scavenging gas at substantially lower pressure than that of the operating gas is supplied to the interior of the pressure oscillation generator through one or more scavenging gas openings (16) in the seat (7) of the diaphragm valve, said openings being arranged adjacent the surface (10) of the seat engaged by the diaphragm (11).

Description: AN I MPROVEMENT IN GAS-OPERATED PRESSURE OSC I LLATION GENERATORS OF THE D IAPHRAGM VALVE TYPE The present invention relates to gas-operated pressure oscillation generators of the diaphragm valve type. More particularly, the invention relates to a gas- -operated pressure oscillation generator comprising a housing, a wall portion in said housing to define there¬ in an outlet passage and an inlet compartment surround¬ ing said outlet passage, an annular seat provided on the wall portion between the outlet passage and the inlet compartment, a diaphragm, and a cover mounted to the housing and engaging the diaphragm at the periphery thereof to bias the diaphragm against the seat, said dia-phrag forming together with the seat a valve controlling the connection between the inlet compart¬ ment and the outlet passage. In some industrial applications of pressure oscillation generators of this type, cooling and/or blowing away of dust particles from the interior of the pressure oscillation generator is necessary in order not to jeopardize or impair the operation of the generator. For example, this is the case in so-called sonic cleaning of interior spaces in furnaces, heat exchangers and similar apparatus through which gas is flown such as hot flue gases or exhaust gases from chemical processes tending to form a dust deposit on the surfaces in the space. In sonic cleaning, gas- -carried pressure oscillations of sound or infrasound frequency are utilized to actuate physically the dust of the deposit, said pressure oscillations being gener¬ ated by means of pressure oscillation generators of the diaphragm valve type, which are mounted in an outer wall of the space to be cleaned. In a common application, -BUREACT the pressure oscillation generators comprise diaphragm valve-type sound emitters which are mounted to the outside of one or more outer walls of the space, the resonance horns of the sound emitters projecting into the space. In that case it is important to prevent the interior surfaςes of the sound emitter from being covered by dust because the sound generation will be adversely affected thereby, and also to prevent the inner parts of the sound emitter, particularly the diaphragm which usually consists of titanium or stain¬ less steel, from being heated to such temperatures at which the strength properties of the diaphragm as well as the ability of resisting corrosion are reduced too much. In applications known so far, the necessary cooling and blowing away of dust particles from the interior surfaces of the pressure oscillation generator are provided by using the operating gas of the pressure oscillation generator as scavenging gas, the gas being supplied continuously to the interior of the pressure oscillation generator through a small restriction bore which opens in the seat of the diaphragm valve at the outlet side thereof. This method provides several dis¬ advantages. The pressure of the operating gas is relatively high and therefore the production of such gas is relatively expensive and, moreover, an undesired cooling of the gas is obtained when the gas is passing through the restriction bore, the dimensions of which are minimized in order to limit the amount of scavenging gas. Due to such cooling, humidity may condense in the operating gas passing through the restricting bore, and in the gas such as flue gas wherein the pressure oscillations are to be effective. The primary object of the present invention is to provide an improvement in pressure oscillation generators of the kind referred to, which eliminates said dis¬ advantages of prior art embodiments of such generators. A further object is to provide a gas-operated pressure oscillation generator of the type referred to wherein scavenging gas the pressure of which is sub¬ stantially lower than that of. the operating gas, is continuously supplied to the interior of the housing for cooling interior portions of the housing and for blowing away dust particles from the interior of the housing. Thus, the scavenging gas can be produced at a substantially lower cost and an undesired cooling at the expansion of the scavenging gas is avoided. Another object of the invention is to provide a method in operating pressure oscillation generators of the type referred to above. — Additional objects and advantages of the invention in part will be set forth in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended cl aims. To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the improvement in the pressure oscillation generator of the type referred to above is characterized by a scavenging gas compartment provided between the inlet compartment and the outlet passage, which communicates with at least one scavenging gas opening in the seat, which opens in the seat at the outlet side thereof adjacent the surface of the seat engaged by the diaphragm, said scavenging gas compartment being connected to a scavenging gas source for the supply of scavenging gas of a pressure which is substantially Oλ.PI lower than the pressure of the operating gas. The invention also provides a method in operating pressure oscillation generators of the type referred to above, wherein scavenging gas at a pressure which is substantially lower than the operating pressure of the generator is supplied to the outlet passage at the outlet side of the seat adjacent the surface thereof, engaged by the diaphragm, independently of the supply of operating gas. The accompanying drawing which is incorporated in and constitutes a part of this specification, illustrate an embodiment of the invention and, together with the description, serves to explain the principles of the i nventi on. In the drawing, the single figure is a longitudinal cross-sectional view of a sound emitter of the diaphragm valve type for sonic cleaning of a furnace, a heat exchanger or a similar apparatus. The sound emitter is mounted to the outside of a wall of the space to be cleaned, the resonance horn of the sound emitter pro¬ jecting into said space. Referring to the drawing, the sound emitter dis¬ closed therein is generally designated 1 and comprises a housing 2 the interior of which is divided by means of an inner wall portion 3 into an annular inlet compart¬ ment 4 for the supply of operating gas, usually pressurized air, and an outlet passage 5 through which pressure oscillations of sound frequency are emitted through a resonance horn 6 which is shown fragmentari ly only in the drawing. The inner wall portion 3 of the housing 2 is provided with a seat 7 comprising a ring 9 attached to the bottom of the housing 2 by means of screws 8, said ring forming a sealing surface 10 engaged by a diaphragm 11. Furthermore, the ring 9 is constructed to define together with adjacent parts of the inner wall portion 3 of the housing an annular scavenging gas compartment ' 12 which is connected by a passage 13 in the bottom of the housing 2, a tube connector 14 and a tube conduit 15 to a source of pressurized air such as a fan not shown in the drawing for supplying scavenging gas at low pressure to the scavenging gas compartment 12. The pressure of the scavenging gas may be of the order of 2 to 3 kPa. The inner edge of the ring 9 and an adjacent edge of the inner wall portion 3 of the housing define an annular slot-like scavenging gas opening 16 adjacent the sealing surface 10 of the ring, engaged by the diaphragm 11. The diaphragm 11 is resiliently biased against the sealing surface 10 by means of a cover 17 closing the housing 2, which is attached by screws 18 to the housing 2 and engages the diaphragm 11 at the periphery thereof. The cover 17 and the diaphragm 11 define a so-called back pressure compartment 19 which communicates with the inlet compart¬ ment 4 through an opening in the diaphragm or through a restricting passage. The back pressure compartment 19 also communicates with the surrounding atmosphere through a tube conduit 20 and a solenoid valve 21. The inlet compartment 4 is connected to a source of pressurized gas, usually an air compressor or other source of pressurized air, not shown in the drawing, through a passage 22 in the housing 2 and a tube conduit 23. The operating pressure of the sound emitter usually is of the order of 0.35 to 0.45 MPa. As long as the solenoid valve 21 is closed and the connection of the back pressure compartment 19 to the surroundings accordingly is interrupted, the pressure in the back pressure compartment is the same as the pressure in the inlet compartment 4, which means that the diaphragm is locked sealingly engaging the seat 7. In the embodiment shown in the drawing, the housing 2 is connected by a flange 24 and screws 25, 26 to the resonance horn 6 as well as a connection metal sheet 27 at which the sound emitter is mounted by means of screw connections 28, 29 to a wall 30 of the space to be cleaned from soot or dust by sonic clean- ... ing, e.g. the furnace of a boiler, a heat exchanger or a similar apparatus. Usually, sonic cleaning is not performed as a continuous operation. The sound emitters used for sonic cleaning are operated at predetermined intervals only. However, the scavenging gas is supplied con¬ tinuously independently of the sound emitter being in an inoperative condition or emitting sound oscillations into the space to be sonically cleaned. During the period when the ' sound emitter is locked scavenging gas accordingly is supplied to the scavenging gas compart¬ ment 12 in the housing 2 through the conduit 15, the connector 14, and the passage 13. The scavenging gas flows from the opening 16 of the compartment 12 into the outlet passage and then primarily provides cooling of the diaphragm and the inner surfaces of the sound emitter to prevent the diaphragm from being heated to an adversely high temperature. At the same time, the diaphragm and adjacent surfaces are blown free from dust particles in order to avoid ah undesired dust coating which could adversely affect the sound genera¬ tion. Since the scavenging gas is supplied continuously at the diaphragm into the outlet passage the risk of corrosive hot gases formed in the space to be cleaned, penetrating into the interior of the sound emitter and adversely affecting the inner parts thereof, is elim¬ inated or reduced. Due to the fact that the arrangement according to the invention makes pos.sible to use a scavenging gas at a low pressure it is also avoided that the scavenging gas by expansion when passing through the opening 16 is cooled to such an extent that a risk of condensation will arise as in prior art constructions wherein the operating gas is used as scavenging gas. Moreover, the invention provides the advantage that the operating costs are reduced because the gas which has to be supplied continuously, viz. the scavenging gas, can be produced by substantially simpler means and at a lower cost than in prior art constructions wherein the operating gas is used also as scavenging gas. In some cases it may even be possible to use the surrounding air as scavenging gas, provided, however, that the space to be cleaned is at a subatmospheric pressure. When sonic cleaning is to be performed the solenoid valve 21 is energized, the back pressure in the back pressure compartment 19 being relieved thereby and the diaphragm being brought to oscillate in rela¬ tion to the seat 7 for the emission of gas-carried pressure waves from the sound emitter at a frequency which is determined by the resonance horn 6. Scavenging gas at low pressure is also supplied to the scavenging gas compartment during the cleaning operation, but according to the invention the low pressure air is . supplied so close to the opening between the seat and the diaphragm that at the short air blasts passing therethrough no operating air escapes through the scavenging gas opening in a direction opposite to the normal scavenging direction, which should involve a loss of acoustic power and, if it comes to the worst, disturbance of the sound generating process. Due to the fact that the ery short air blasts allowed to pass when the diaphragm rises momentarily from the seat, are directional and have a high flow velocity such air will pass the scavenging gas opening without escaping therethrough. On the contrary, by a proper construction an ejector action may be obtained, which means prin- O ΓI cipally that each air blast increases the amount of air thereof by taking an additional amount of air from the scavenging gas compartment. At the same time the instant pressure of the air blast " will be slightly decreased. From an acoustic point of view this means that each, air blast will be richer and will provide a sound wave having a stronger fundamental tone than in case of no scavenging air opening. The invention which has been described above with reference to a concrete illustrative embodiment, is not, of course, limited to this embodiment since the invention can be modified in several ways within the scope of the following claims. Thus, it is not necessary that the scavenging gas opening is formed as a continuous annular slot. Alternatively, said opening can comprise several bores in the seat, communicating with the scavenging gas compartment. Furthermore, the invention is not limited to pressure oscillation generators which generate pressure oscillations in the audible range; it can also be applied to pressure oscillation generators of the diaphragm valve type for generating low frequency pressure oscillations in the frequency range from 1 to 20 cps, e.g. diaphragm valve pulsators which are used for cleaning filters or as means for generating oscillations in infrasound transmitters.

Claims: CLAIMS 1. An improvement in a gas-operated pressure oscillation generator of the diaphragm valve type comprising a housing (2), a wall portion (3) in said housing to de.fine therein an outlet passage (5) and an inlet compartment (4) surrounding said, outlet passage, an annular seat (7) provided on the wall portion between the outlet passage and the inlet compartment, a diaphragm (11), and a cover (17) mounted to the housing and engaging the diaphragm at the periphery thereof to bias the diaphragm against the seat, said diaphragm forming together w th the seat a valve controlling the connection between the " inlet compartment and the outlet passage, " c h a r a c t e r i z e d by a scavenging gas compart- mejit (12) provided between the inlet compartment (4) and the outlet passage (5) which communicates with at least one scavenging gas opening (16) in the seat (7) which opens in the seat at the outlet side thereof adjacent the surface (10) of the seat engaged by the diaphragm (11), said scavenging gas compartment being connected to a scavenging gas source for the supply of scavenging gas of a pressure which is substantially lower than the pressure of the operating gas. 2. The improvement according to claim 1 , c h a r a c t e r i z e d in that the scavenging gas opening (16) forms a slot extending along the surface_ (10) of the seat (7) engaged by the diaphragm (11). 3. The improvement according to claim 2, c h a r a c t e r i z e d in that the seat (7) forming the surface (10) engaged by the diaphragm (11) comprises a seat ring (9) attached to the housing (2) and joining said wall portion (3), said seat ring forming together with adjacent parts of said wall portion (3) the scav- enging gas compartment (12) as well as the scavenging gas slot (16). 4. The improvement according to claim 1, c h a r a c t e r i z e d in that the scavenging gas opening (16) comprises several bores mutually spaced in the seat (7) adjacent the surface (10) of the seat engaged by the diaphragm (11), each of said bores communicating with the scavenging gas compartment (12). 5. The improvement according to any of claims 1, 2, and 4, c h a r a c t e i z e d in that the scavenging gas compartment (12) communicates with the surrounding atmosphere. 6. A method in operating pressure oscillation generators comprising a housing, a wall portion in said housing to define therein an outlet passage and an inlet compartment surrounding said outlet passage, an annular seat provided on the wall portion between the outlet passage and the inlet compartment, a diaphragm, and a cover mounted to the housing and engaging the - diaphragm at the periphery thereof to bias the dia¬ phragm against the seat, said diaphragm forming together with the seat a valve controlling the connection between the inlet compartment and the outlet passage, c h a r a c t e r i z e d in that scavenging gas at a pressure which is substantially lower than the operating pressure of the generator is supplied to the outlet passage at the outlet side of the seat adjacent the surface thereof, engaged by the diaphragm, indepen¬ dently of the supply of operating gas. 7. The method according to claim 6, c h a r a c ¬ t e r i z e d in that the scavenging gas is supplied at atmospheric pressure. OM

Inventors: ABRAHAMSSON P, HOLM B, NILSSON C
Applicants: ABRAHAMSSON P, HOLM B, KOCKUMATION AB, NILSSON C
Application year: 1980
Main classification: B06B1
IPC codes: B08B5, G10K9