Patent Publication Number: US-8984714-B2

Title: Method and systems for acoustic cleaning

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention relates generally to acoustic generators, and more specifically, to a method and system for generating high intensity narrow frequency band tone noise in the audible frequency range. 
     During operation, at least some known components of industrial processes experience deposits forming on surfaces within the component. Such deposits forming in for example, utility boilers or other industrial process components tend to adversely affect the operation of the components. Buildup on a surface of these components can cause heat transfer inefficiencies, pressure drops, excessive destructive cleaning, and excessive outage time. Removing these deposits while the process remains online facilitates an efficiency and an availability of the process. 
     At least some known methods of online deposit removal include shock cleaning systems, steam/air sootblowing, and acoustic horns. However, shock cleaning systems create intense sound waves through the combustion of fuel and oxidizer, which have operation costs associated with them. Steam soot blowing is expansive and erosive to surfaces being cleaned. Acoustic horns require a supply of compressed air to actuate a vibrating diaphragm plate and are known to have pressure intensity limits and wide frequency spectrum bands including frequencies that don&#39;t contribute to cleaning. The above technologies use moving parts that wear over time and must be replaced to maintain effectiveness. Such maintenance is time-consuming and disruptive to normal operations of the process. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a tone generator assembly includes a resonance chamber including a body having a resonance chamber opening and a resonance chamber cavity in flow communication with the resonance chamber opening. The tone generator assembly further includes a nozzle having an inlet opening configured to receive a flow of relatively high pressure fluid and an outlet opening coupled in flow communication to the inlet opening. The outlet opening is oriented in substantial axial alignment with the resonance chamber opening and spaced apart from the resonance chamber opening by a gap. The dimensions of the resonance chamber and nozzle are selected to facilitate emitting a tone having a frequency less than two kilohertz and tuned to a frequency determined to provide cleaning vibratory energy 
     In another embodiment, a method of generating a tone includes generating a jet of fluid, directing the jet of fluid into a closed end cavity, alternately forming compressive waves and expansion waves in the cavity at a rate of less than two kilohertz using the jet of fluid, generating a tone using the compressive waves and the expansion waves, and emitting the tone towards a surface to be cleaned. 
     In yet another embodiment, an acoustic cleaning system includes a nozzle configured to generate an underexpanded jet of fluid and a resonance chamber configured to receive at least a portion of the jet of fluid wherein the resonance chamber includes a selectively variable length in a direction of flow of the jet of fluid. The acoustic cleaning system also includes a housing surrounding the nozzle and the resonance chamber wherein the housing includes an opening sized to emit a tone having a frequency less than one kilohertz. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1-3  show exemplary embodiments of the method and system described herein. 
       The foregoing and other features and aspects of the invention will be best understood with reference to the following description of certain exemplary embodiments of the invention, when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram of an acoustic cleaning tone generator assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a schematic diagram of the tone generator assembly shown in  FIG. 1  in accordance with another embodiment of the present invention; and 
         FIG. 3  is a flow diagram of a method of generating a tone in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to generating acoustic tones for cleaning components in industrial, commercial, and residential applications. 
     Embodiments of the present invention describe a specifically designed device configure to utilize the interaction of a high pressure jet of air and a closed-ended tube that forms a cavity, to create a high intensity, narrow frequency band tone noise. This device is designed to emit tones as sound waves in the audible frequency range. These sound waves are then used to clean surfaces in processes where debris/ash/dirt builds up causing inefficiencies in the processes. The sound waves vibrate the deposits or build up and the deposits fall from the surfaces. This is a non-destructive inexpensive cleaning technology. Instead of vibrating a diaphragm to generate noise, embodiments of the present invention operate more similarly to a whistle. By directing the jet of air into the close ended tube, compression waves are created that reflect off the back of the closed-end towards an opening of the close ended tube. The tube relieves itself of high pressure by purging fluid. The resulting expansion wave travels back to the closed-end, which reflects back to the opening as an expansion wave, letting fluid into the tube. This movement of fluid results in a high intensity tuned tone, which is utilized as the sonic driver for cleaning purposes. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
       FIG. 1  is a schematic diagram of an acoustic cleaning tone generator assembly  100  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, tone generator assembly  100  includes a resonance chamber  102 , a nozzle  104 , and a housing  106  surrounding resonance chamber  102  and nozzle  104 . Resonance chamber  102  includes a body  108  having a resonance chamber inlet opening  110 . A resonance chamber cavity  112  is in flow communication with resonance chamber opening  110 . 
     Nozzle  104  includes an inlet opening  114  configured to receive a flow of relatively high pressure fluid  116  (e.g., compressed air) at about 50 psi-300 psi, and more preferably about 100 psi. An outlet opening  118  is coupled in flow communication to inlet opening  114  through a bore  119  therethrough that is convergent in a direction of fluid flow from inlet opening  114  to outlet opening  118 . Outlet opening  118  is oriented in substantial axial alignment with resonance chamber opening  110  and spaced apart from resonance chamber opening  110  by a gap  120 . Gap  120  is adjustable in an axial direction by adjusting an axial position of nozzle  104  and/or body  108 . 
     Housing  106  includes an annular body  122  including a cavity  124  surrounding resonance chamber  102  and nozzle  104 . Housing  106  includes a first opening  126  configured to receive the flow of relatively high pressure fluid  116  and a second opening  128  having a diameter  130  sized to facilitate emitting a tone having a frequency less than two kilohertz from tone generator assembly  100 . Relatively lower frequency tones facilitate cleaning of industrial process components while the process is online, and provide tunability, higher dB output. Tones having a frequency greater than two kilohertz have been found to have only limited cleaning ability as compared to tones having a frequency less than two kilohertz, for example, less than 400 Hertz. 
     In another embodiment, bore  119  has a convergent/divergent cross-section and may include a centerbody to streamline flow through bore  119  or to facilitate matching a velocity through bore  119  to requirements for a particular application. 
     Resonance chamber opening  110  includes a diameter  132  sized to facilitate generating a tone having a frequency less than two kilohertz. In various embodiments, diameter  132  is sized to receive an entire flow from a jet  142  emitted from nozzle  104 . In one embodiment, cavity  112  is a closed-ended cavity having a smooth wall surface  143 . In another embodiment, resonance chamber  102  includes a bore  133  therethrough rather than the smooth-walled cavity  112 . Bore  133  includes a threaded surface  134  that matingly engages threads on a plug  136 . An axial position of plug  136  is adjustable to vary a length  138  of cavity  112 . Varying length  138  by adjusting the axial position of plug  136  in bore  133  permits adjusting a pitch and/or efficiency of resonance chamber  102 . Varying of diameter  132  would also have a similar effect on the pitch and/or efficiency of resonance chamber  102 . 
     Outlet opening  118  includes a diameter  140  sized to facilitate generating underexpanded jet  142  of fluid. As used herein, underexpanded jet refers to flow through a converging nozzle where the flow velocity at the nozzle exit plane is almost sonic and is supersonic downstream of it. Underexpanded jet  142  is directed axially towards resonance chamber opening  110 . Several dimensions of tone generator assembly  100  impact the pitch/efficiency of tone generator assembly  100 . These dimensions include but are not limited to resonance cavity length  138 , resonance cavity diameter  132 , gap  120 , diameter  140 , and a volume of cavity  124 . In addition a pressure of flow of relatively high pressure fluid  116  may also have an influence on the pitch/efficiency of tone generator assembly  100 . In one embodiment, resonance cavity length  138  is approximately two times resonance cavity diameter  132 . 
     Adjustment of the above dimensions and parameters permits a user to adjust the pitch or tone of tone generator assembly  100  and to adjust an intensity of the tone as well as an efficiency of tone generator assembly  100 . For example, increasing a pressure of flow of relatively high pressure fluid  116  permits a greater intensity of the tone, however to maintain a predetermined pitch for the application others of the adjustable dimensions may also need to be adjusted. For example, diameter  140  may be increased to accommodate receiving a more powerful jet  142 . The axial position of resonance chamber  102  may also be adjusted to maintain the efficiency of tone generator assembly  100  in generating the tone. Changes in other dimensions which affect the generated tone and/or efficiency of tone generator assembly  100  may need to be adjusted to compensate for the interdependence of the dimensions on tone and/or efficiency. In addition to emitting a tone having a frequency of less than two kilohertz, the dimensions of tone generator assembly  100  may be adjusted to emit a tone having a frequency between ten and one thousand Hertz and even to emit tone having a frequency between fifty and four hundred Hertz for specific applications, such as, but not limited to, cleaning components in a particulate laden gas stream. 
       FIG. 2  is a schematic diagram of tone generator assembly  100  (shown in  FIG. 1 ) in accordance with another embodiment of the present invention. In the alternative embodiment, tone generator assembly  100  includes a bell  200  coupled in acoustic communication with tone generator assembly  100 . Bell  200  includes a throat  202  coupled to housing  106 , a mouth  204 , and an acoustic horn  206  having a predetermined shape extending therebetween. In various embodiments, the predetermined shape may be but is not limited to a cone, an exponential, or a tractrix. 
     Bell  200  is used to increase the overall efficiency of tone generator assembly  100 . Horn  206  is a passive component and does not amplify the sound from tone generator assembly  100  as such, but rather improves the coupling efficiency between tone generator assembly  100  and free air surrounding horn  206 . Horn  206  provides acoustics impedance matching between tone generator assembly  100  and ambient air of low density external to mouth  204 . The result is a greater acoustic output from a given tone generator assembly  100 . Acoustic horn  206  converts large pressure variations with a small displacement in throat  202  into a low pressure variation with a large displacement in mouth  204  and vice versa using a gradual increase of the cross sectional area of horn  206 . The small cross-sectional area of throat  202  restricts the passage of air thus presenting a high impedance to tone generator assembly  100 . This allows the tone generator assembly  100  to develop a high pressure for a given displacement. Therefore the sound waves at throat  202  are of high pressure and low displacement. The tapered shape of horn  206  allows the sound waves to gradually decompress and increase in displacement until they reach mouth  204  where they are of a low pressure but large displacement. 
       FIG. 3  is a flow diagram of a method  300  of generating a tone in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, method  300  includes generating  302  a jet of fluid, directing  304  the jet of fluid into a closed end cavity, alternately forming  306  compressive waves and expansion waves in the cavity at a rate of less than two kilohertz using the jet of fluid, generating  308  a tone using the compressive waves and the expansion waves, and emitting  310  the tone towards a surface to be cleaned. 
     The device used to generate the tone includes an underexpanded jet directed into a close-ended cylindrical tube or resonance chamber of approximately equal diameter. When the cylindrical tube of the resonance chamber is placed within a compression region of the underexpanded jet, the tube begins to draw fluid in and compression waves are created at the tube entrance (the beginning of compression phase and the overall cycle) that traverse towards the closed end of the tube. The compression waves are reflected by the end wall opposite the tube entrance as compression waves, which move back toward the entrance of the tube. When these waves reach the open end, they are reflected back into the tube as expansion waves (the end of compression phase and the beginning of expansion phase). At this time, the pressure within the tube has risen above the local jet pressure. The tube, therefore, starts relieving itself of the high pressure by ejecting some of the fluid accumulated within the tube. The expansion waves traveling through the tube are reflected on the back wall as expansion waves. Once these waves reach the open end of the tube, they are reflected as compression waves (the end of the expansion phase and the cycle). Once again, the pressure in the tube is sufficiently low to allow the flow of fluid into the tube. Thus, the expansion phase and the overall cycle are complete and the compression phase of the cycle begins again. This results in the pure tone and high decibel output that is being utilized for cleaning purposes. 
     Because tone generator assembly  100  described in various embodiments of the present invention uses only compressed air as the operating medium, any existing acoustic cleaning system can be upgraded using tone generator assembly  100  without significant addition of infrastructure or piping. In addition, tone generator assembly  100  permits cleaning of the industrial process components while the process is online, and provide tunability, higher dB output, and a more pure tone than known acoustic cleaners. 
     The above-described embodiments of a method and system of a jet-cylinder interaction for production of an acoustic tone capable of efficient acoustic cleaning provide a cost-effective and reliable means for providing a more aggressive cleaning action and superior cleaning system. More specifically, the methods and system described herein facilitate operation of a tone generator assembly capable of operating at a frequency range of approximately less than 400 Hertz used for cleaning. In addition, the above-described methods and system facilitate a longer cleaner life because the cleaner has no moving parts, a higher dB output, and a purer tone. As a result, the method and system described herein facilitate generating a tone for cleaning components in industrial processes in a cost-effective and reliable manner. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or system and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.