Abstract:
An acoustic system having a plurality of speakers applying acoustic energy as a series of acoustic waves to various target sites on the exterior of the reactor to vibrate and deflect the interior surfaces of the reactor structure such that the slag is dislodged from the internal surfaces of the reactor structure. Each speaker generates acoustic waves having a waveform corresponding to the resonant frequency of the ash crystallized on the reactor structures. The acoustic waves induce vibrations and/or deflections in the portion of the reactor wall to which the slag is engaged as well as the slag itself breaking the interstitial bonds of the slag deposit and bonding holding the slag to the wall. The separated or disintegrated slag can then be gravimetrically fall to the bottom of the reactor for removal from the reactor.

Description:
RELATED FOREIGN APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 61/569,476 entitled SONIQ CLEANING APPROACH AND SUGGESTED DEVELOPMENT AREAS filed Dec. 12, 2011, which is incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to an ultrasonic cleaning system and related method of using for removing slag and other industrial buildup from the interior surfaces of reactors. 
       BACKGROUND OF THE INVENTION 
       [0003]    In coal power plants, coal is combusted in large reactors to vaporize a water stream that is then used to operate a steam turbine and generate electricity. The combustion of the coal generates large quantities of ash particulates. “Bottom ash” or “coal ash” typically comprises larger ash particulates or molten ash that gravimetrically falls to the bottom of the reactor. The bottom ash is removed by accessing the bottom of the reactor and removing the ash collected at the bottom of the reactor as either dry or molten ash. As depicted in  FIG. 1 , “Fly ash” typically comprises smaller dry particulates ranging in size from 0.5 μm to 100 μm that are carried on the vapor currents within the reactor and before being captured by filters at the reactor chimney. A portion of the fly ash can crystallize on the walls and other internal surfaces of the reactor forming slag deposits that must be removed periodically for the reactor to operate efficiently. 
         [0004]    Fly ash typically comprises substantial amounts of amorphous and crystalline silicon dioxide (SiO 2 ), calcium oxide (CaO), aluminum oxide (Al 2 O 3 ) and iron oxide (Fe 2 O 3 ). The oxide components produce a hard, crystalline material that adheres to the internal surfaces of the reactor and can be difficult to separate from the reactor wall or internal structures without substantial mechanical effort. Depending on the amount of silicon oxide present, the slag can comprise a rounded, smooth texture or a sharp, pointed texture which can injure workers removing the slag. The slag can also include a plurality of toxic constituents including one or more of the following elements or substances in quantities from trace amounts to several weight percent: arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with dioxins and PAH compounds. Accordingly, in order to minimize worker exposure to the toxic materials, only certain techniques that can be used to separate the slag from the reactor structure. 
         [0005]    A conventional approach to cleaning reactors is to have workers enter the reactor and manually remove the slag with hand tools. The inherent challenge is that the reactors can be very large and are often several stories in height making manual removal of the slag tedious and time consuming. Projectile weapons, such as shotguns firing soft lead shot, are fired at the slag from inside the reactor chamber dislodge the slag from the surfaces of the reactor structure. Aside from the inherent danger of firing a projectile weapon within an enclosed space, the typically large amount of slag that must be removed requires a substantial number of shots to remove the slag creating a large quantity of shot that must also be removed. Similarly, liquid cleaners can be applied to dissolve or loosen the slag from the reactor surfaces. The dissolved slag or the liquid cleaner itself can be highly toxic to the users particularly if a portion of the slag or liquid cleaner vaporizes within the reactor. All of the approaches require shutdown of the reactor and require workers to enter the potentially toxic environment within the reactor to manually remove the slag. 
         [0006]    The inherent drawback of manual cleaning techniques and as well as risk of toxic exposure to workers cleaning the reactor demonstrates a need for an improved cleaning technique that can separate the slag from the reactor structure efficiently and cleanly. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is generally directed to an acoustic system having a plurality of speakers applying acoustic energy as a series of acoustic waves to various target sites on the exterior of the reactor to vibrate and deflect surfaces of the reactor structure such that the slag is dislodged from the internal surfaces of the reactor structure. Each speaker comprises a driver for generating acoustic waves having a waveform corresponding to the resonant frequency of the ash crystallized on the reactor structures. The acoustic waves induce vibrations and/or deflections in the portion of the reactor wall to which the slag is engaged as well as the slag itself breaking the interstitial bonds of the slag deposit and bonding holding the slag to the wall. In one aspect, the internal structure of the reactor proximate to the portion of the wall impacted by the acoustic waves can operate as a waveguide transmitting the acoustic energy from the acoustic waves deeper into the internal surfaces of the reactor structure. The separated or disintegrated slag can then gravimetrically fall to the bottom of the reactor for removal from the reactor. 
         [0008]    In general, the variables relevant to the removal of slag are: slag location in the boiler; number and spacing of speakers; volume of application (amplitude=sound pressure): duration of sound application during an acoustic pass; acoustic frequency of interest; acoustic wave shape; frequency of acoustic application; wave combinations and permutations; and sweep amplitude and duration. 
         [0009]    In one aspect, the speakers can be oriented to direct the acoustic waves at portions of the reactor wall unsupported by the reactor support structure or mounting elements. The unsupported portion of the reactor wall allows for inducement of the maximum possible deflection and oscillation from the acoustic waves. In one aspect, the centroid of the acoustic waves can be targeted at a point on the reactor exterior equidistant between the underlying reactor support structures along a linear axis, wherein the linear axis is a horizontal axis or a vertical axis. In one aspect, the spherical acoustic waves are oriented such that the centroid of each wave is normal to the reactor surface. 
         [0010]    In one aspect, the operation of the speakers can be cycled between active cycles in which the acoustic energy is applied to the reactor and rest cycles in which little or no acoustic energy is applied to the reactor. The amplitude and/or frequency of the acoustic waves applied during each active cycle can be modulated to correspond to changing resonant frequency of the slag as portions of the amount of slag attached to the reactor structure lessons. Alternatively, the acoustic waves can be modulated according to the chemical makeup of the slag to be removed. In one aspect, the exterior surface of the reactor structure can be struck during the rest cycle proximate to the slag deposits to induce an acoustic response for measuring the resonant frequency of the slag still adhered to the reactor structure. In certain aspects, the amplitudes of the acoustic waves must range across a substantial range to provide the necessary resonant frequencies. 
         [0011]    In one aspect, the acoustic waves can be initially introduced at a low frequency before the acoustic waves before the amplitude and/or the frequency the acoustic waves are varied through a predetermined spectrum. The varied waveforms can correspond to the resonant frequencies of a range of particulate sizes and compositions thereby disrupting the bonding of a plurality of particles. With mounted acoustic systems the programmed sweep of waveforms can be tailored for particular operating conditions and chemical compositions of the slag. 
         [0012]    A method of removing slag from an internal surface of a reactor, according to an embodiment of the present invention, comprises identifying a target point on an exterior surface of the reactor, wherein the target point is equidistant from at least two support structures along at least one linear axis. The method further comprises positioning a speaker a predetermined distance from the reactor, wherein the speaker comprises a driver for generating acoustic waves and a cone for directing the acoustic waves toward the target point. The method also comprises actuating the driver to generate acoustic waves that impact the target point of the reactor inducing oscillation and deflection of the exterior surface of the reactor. In one aspect, the speakers are oriented such that the acoustic waves have a centroid normal to the exterior surface of the reactor. The method further comprises examining the displacement of the reactor wall in response to the acoustic waves. In one aspect, the method can also comprise altering at least one waveform factor of the acoustic waves, wherein the waveform factor can be selected from the amplitude of the acoustic waves, the frequency of the acoustic waves and combinations thereof. In this configuration, the method can further comprise applying second acoustic waves from the speaker to the target point. 
         [0013]    A method of removing slag from an internal surface of a reactor, according to an embodiment of the present invention, comprises locating an exterior surface corresponding to the interior surface to which the slag is adhered. The method also comprises striking the located exterior surface to induce an acoustic response from the slag adhered to the interior surface. The method further comprises evaluating the acoustic response to determine a resonant frequency corresponding to the slag adhered to the interior surface. The method further comprises selecting a wave frequency and an amplitude for generating acoustic waves corresponding to the identified resonant frequency. The method also comprises positioning at least one speaker proximate to the located exterior surface. The method further comprises operating the speakers to apply acoustic waves having the selected waves frequency and amplitude to induce a response in the reactor at the resonant frequency, wherein the response at the resonant frequency disintegrates or separates the slag from the interior surface. 
         [0014]    In one aspect, the method can further comprise striking the reactor a second time to generate a second acoustic response. In this configuration, the second acoustic response can be evaluated to ascertain whether the wave frequency and amplitude must be altered to produce at least one second acoustic wave corresponding to the new resonant frequency. The process can be repeated as a portion of the slag gradually shed from the interior surface of the reactor. 
         [0015]    An acoustic system for generating acoustic waves for removing slag from a reactor, according to an embodiment of the present invention, can comprise a driver assembly and a cone assembly. Each cone comprises a first end and a second end, wherein the cone comprises a generally frustoconical shape in which the first end has a smaller diameter than the second end and is positioned against the driver assembly. The cone defines a central axis intersecting the center of the first and second ends. The driver assembly comprises a speaker coil and a permanent magnet, wherein the speaker coil is operably affixed to the first end of the cone. In operation, an alternating current is passed through the speaker coil to oscillate the speaker coil and cone along the central axis to generate acoustic waves centered on the central axis, wherein the central axis can be aligned with a target point on the exterior of the reactor. 
         [0016]    In one aspect, the speakers can be positioned such that the second end of the cone is a predetermined distance from the reactor exterior. The distance creates a heat dissipation zone reducing the heat transferred from the reactor to the speakers. It was found that the heat transfer from the reactor to the speakers can reduce the longevity of the speaker. The distance allows the speakers to be mounted in situ to provide regular acoustic treatments to the reactor to maintain efficient operation of the reactor without substantial down time for repositioning and targeting of the reactor. The mounted speakers can be permanently oriented at problem spots of the reactor where slag build up is likely or particularly heavy. In one aspect, the acoustic energy can be applied to the reactor during normal operation of the reactor to prevent the fly ash particulates from settling on the interior surface of the reactor. In this configuration, the constant acoustic energy limits the buildup of slag deposits and prevents large slag deposits from forming on the interior surfaces. 
         [0017]    A speaker, according to an embodiment of the present invention, comprises a driver assembly and a cone assembly. The driver assembly can comprise a speaker coil and a permanent magnet contained within a driver housing, wherein supplying an alternating current to the speaker coil causes the coil to oscillate along a central linear axis. The cone assembly comprises a cone flexibly mounted to a speaker housing, wherein the cone oscillates relative to the speaker housing along the central linear axis as the speaker coil is oscillated. The cone comprises a first end and a second end, wherein the cone comprises a frustoconical shape in which the first end has a smaller diameter than the second end. 
         [0018]    In one aspect, the driver housing can define at least one hole in the rear face of the driver housing. The oscillation of the speaker coil oscillates air into and out of the holes in the driver housing. Additional air is drawn perpendicular to a plane defined by the holes to create a synthetic jet oriented perpendicular to the plane of the hole that expels air rearward from the driver housing cooling the driver. The air flow cools the driver assembly increasing the longevity of the driver assembly. 
         [0019]    In one aspect, the driver assembly can further comprise a safety circuit linked to the speaker coil to monitor the draw of the speaker coil. It was found that the temperature in the driver assembly increases due to friction from the oscillation of the speaker coil and cone, which in turn increases the resistance of the speaker coil requiring additional power drawn to continue operation of the speaker. The ongoing cycle of additional power draw and increased resistance can result in thermal runway resulting in permanent damage to the speaker. The safety circuit comprises a plurality of rectifiers arranged in parallel and set at graduated power draw threshold levels, wherein each of the rectifiers closes as the power draw of the speaker coil exceeds the threshold level corresponding to the rectifier until the power coil is completely shut off. As the speaker cools and the power draw drops, the rectifiers reopen to allow the speaker to safely resume operation. 
         [0020]    A method of removing slag from an internal surface of a reactor, according to an embodiment of the present invention, comprises locating an exterior surface corresponding to the interior surface to which the slag/ash buildup occurs. The method also comprises analyzing the position of the buildup relative to the structure for placement of speakers. The speakers are positioned so that the sound/acoustic waves from the speakers impinges normal to the structure. The amp output is adjusted to eliminate clipping. The system resonance of the structure is then determined. The acoustic waveform is selected based on striking the located exterior surface to induce an acoustic response from the slag adhered to the interior surface. The method further comprises evaluating the acoustic response to determine a resonant frequency corresponding to the slag adhered to the interior surface. The method further comprises selecting a wave frequency and an amplitude for generating acoustic waves corresponding to the identified resonant frequency. Next the operator sets the sweep at +/−25 hz. The method also comprises positioning at least one speaker proximate to the located exterior surface. The method further comprises operating the speakers to apply acoustic waves having the selected waves frequency and amplitude to induce a response in the reactor at the resonant frequency, wherein the response at the resonant frequency disintegrates or separates the slag from the interior surface. The system may be cycled on/off to induce ash removal. The speakers may be repositioned and the entire process repeated. The duration of the removal process can be approximately one hour per speaker location. 
         [0021]    The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the invention. The figures in the detailed description that follow more particularly exemplify these embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention can be completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0023]      FIG. 1  is a photograph of scanning electron microscope image of fly ash magnified 2000 times. 
           [0024]      FIG. 2  is a cross-sectional side view of a speaker according to an embodiment of the present invention. 
           [0025]      FIG. 3  is a representative side cross-sectional side view demonstrating formation of a synthetic jet from a rear face of a driver assembly according to an embodiment of the present invention. 
           [0026]      FIG. 4  is a schematic diagram of a safety circuit according to an embodiment of the present invention. 
           [0027]      FIG. 5  is a representative perspective view illustrating an arrangement of speakers according to an embodiment of the present invention. 
           [0028]      FIG. 6  is a representative plan view illustrating an arrangement of speakers according to an embodiment of the present invention. 
           [0029]      FIG. 7  is a schematic diagram illustrating a method of slag removal according to an embodiment of the present invention. 
           [0030]      FIG. 8  is a schematic diagram illustrating a method of slag removal according to an embodiment of the present invention. 
       
    
    
       [0031]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0032]    As depicted in  FIG. 2 , an acoustic system  20 , according to an embodiment of the present invention, comprises at least one speaker  22  having a driver assembly  24  and a cone assembly  25 . The driver assembly  24  further comprises a speaker coil  26 , a driver  28 , a permanent magnet  30  and a driver housing  32 . As depicted in  FIG. 2 , the speaker coil  26  is arranged in a cylindrical coil around the driver  28 , wherein the permanent magnet  30  comprises a cylindrical pipe shape encircling the cylindrical speaker coil  26 . Alternatively, the permanent magnet  28  can comprise a cylindrical shape extending into the center of the speaker coil  26 , wherein the driver  28  defines an inner cavity extending longitudinally through the speaker coil  26 . The driver housing  32  comprises a cup shape having an open front end  34  and a closed rear end  36 . The cone assembly  26  can comprise a cone  38  and a speaker housing  40 . The cone  38  comprises a frustoconical shape having a first end  42  and a second end  44 , wherein the first end  42  has a diameter less than the second end  44 . The speaker housing  40  defines a speaker opening  46 . The first end  42  is affixed to the driver  28  while the second end  44  of the cone  38  is flexibly affixed to the speaker housing  40  with a hinge  48  at the speaker opening  46 . 
         [0033]    In operation, an alternating current can be supplied to the speaker coil  26  causing the speaker coil  26  and the attached driver  28  to oscillate along a central axis a-a extending through the center of the first and second ends  42 ,  44  of the cone  38 . In one aspect, the driver housing  32  can comprise a divider  50  having an orifice  52  for receiving the driver  28 , wherein the orifice  52  comprises a bearing  54  for guiding the driver  28  along the central axis a-a. The oscillation of the driver  28  correspondingly oscillates the cone  38  along the central axis a-a to generate a series of acoustic waves centered on the central axis a-a. The speaker  22  can be oriented to direct the acoustic waves at a targeted site by aligning the central axis a-a with the target site. 
         [0034]    In one aspect, the speaker  22  can further comprise a resonance chamber positioned at the second end  44  of the cone  38 . The resonance chamber focuses the acoustic energy generated by the oscillating cone  38  and directs the acoustic energy along the central axis a-a. In one aspect, the resonance chamber can be shaped to act as a wave guide focusing the acoustic waves generated by the cone  38  delaying the expansion of the acoustic waves. 
         [0035]    As depicted in  FIG. 3 , the driver housing  32  can define at least one hole  56  in the closed rear end  36  of the driver housing  32 . The temperature in the driver region increases due to friction. When the temperature increases sufficiently, the resistance increases and a thermal runaway results. To combat this temperature issue, holes are drilled into the rear face of the structure housing the driver. In one aspect, the hole  56  can be between 0.120 to 0.125 inches in diameter. In this configuration, the oscillation of the driver  28  through the orifice  52  of the divider  50  causes oscillation of air through the hole  56  creating a synthetic jet of air away from the rear of the driver housing  32  to facilitate cooling of the driver assembly  24 . The speaker acts as a diaphragm during operation. Expelled air forms toroids  33  due to vortex shedding at the orifice. Replenishment air  35  comes from the surface which demonstrates an air exchange. 
         [0036]    As depicted in  FIG. 4 , the induction coil  26  can be operably linked to a safety circuit for cutting off power to the induction coil  26  if the speaker  22  overheats. Increased friction from the moving driver  28  and increased temperature will in turn increase the amount of power drawn of the induction coil  26  to operate driver assembly  24 . The safety circuit comprises a plurality of rectifiers  27  arranged in parallel and set at graduated power level thresholds. Each of the rectifiers  27  is adapted to disconnect as the power level exceeds the corresponding power level threshold until all of the rectifiers  27  are disconnected and the power to the induction coil  26  is cutoff and the speaker  22  is disabled. As the disabled speaker cools and the power draw lessens, the rectifiers  27  reconnect in sequence to resume safe operation of the speaker  22 . 
         [0037]    As depicted in  FIGS. 5-6 , in one embodiment of the present invention, the acoustic system  20  can comprise a plurality of speakers  22  arranged around the exterior of a reactor  29 . The reactor  29  generally comprises a plurality of reactor supports overlaid with a reactor wall  31  having an exterior surface and an interior surface. During combustion, the slag can form on the interior surfaces and crystallize adhering to the interior surface. Each speaker  22  can be oriented such that central axis a-a of each speaker  22  is oriented at point on the exterior surface of the reactor  29  proximate to a slag deposit on the interior surface. The speaker  22  can then be operated to transmit acoustic waves to the exterior surface of the reactor  29  to deflect and vibrate the reactor wall  31  to shake the slag deposit loose from the interior surface or disintegrate the slag deposit. In one aspect, the cone  38  can be shaped to form a spherical wave, wherein the speaker  22  is oriented such that the centroid of each acoustic wave normal to the exterior of the reactor wall  31 . 
         [0038]    As depicted in  FIG. 7 , a method of removing a slag deposit from an interior surface of the reactor wall, according to an embodiment of the present invention, comprises an evaluation step  210 , a speaker positioning step  220 , an acoustic energy step  230  and an examination step  240 . In one aspect, the method can further comprise an adjustment step  250 . 
         [0039]    In the evaluation step  210 , the reactor is evaluated to identify at least one target site on the exterior wall of the reactor wall. The target site corresponds to a portion of the exterior surface of the reactor wall proximate to an interior surface of the reactor wall to which the slag is adhered. In one aspect, the target site is selected to be equidistant from at least two adjacent support structures along a linear axis. Alternatively, the target site can be relatively free of fixtures and other reactor structures. In this configuration, the target site is at or proximate to the least supported point of that portion of the reactor wall. The linear axis can be a horizontal axis, a vertical axis or a transverse axis depending on the underlying support structure. 
         [0040]    In the placement step  220 , each speaker  20  is oriented such that the central axis a-a of each speaker  20  aligns with the target site. In one aspect, the speaker  20  is aligned with target site such that the centroid of the acoustic waves is normal to the exterior surface of the reactor wall. As depicted in  FIGS. 5-6 , a plurality of speakers  20  can be arranged in a ring around the reactor to provide acoustic energy continuously around the periphery of the reactor. 
         [0041]    In the acoustic energy step  230 , the driver assembly  24  of each speaker  22  is operated to apply a series of acoustic waves to the exterior surface of the reactor centered at the target site. In one aspect, the acoustic energy can be cycled between active cycles in which a plurality of acoustic waves is directed at the reactor and rest cycles in which the speaker  20  is disabled. In one aspect, the active cycles and alternated with rest cycles, wherein each active cycle is about double the duration of the intervening rest cycles. In another aspect, each active cycle can comprise about 2 minutes and each intervening rest cycle can comprise about 1 minute. In certain aspects, the acoustic energy step  230  can last between 1 to 2 hours. 
         [0042]    In the examination step  240 , the reactor is examined to determine the amount of slag removed from the interior surface of the reactor. The reactor can also be examined to evaluate the amount of deflection and vibration of the reactor wall induced by the acoustic energy supplied by the acoustic system  20 . 
         [0043]    In the adjustment step  250 , the additional acoustic energy can be supplied to the reactor to dislodge additional slag. The duration of the active cycles and the overall length of the acoustic energy step  230  can be varied to further remove addition slag from the reactor. 
         [0044]    It is envisioned that a white noise base at 10% of total amplitude may be incorporated to help control the heat of the speaker. 
         [0045]    As depicted in  FIG. 8 , a method of removing a slag deposit from an interior surface of the reactor wall, according to an embodiment of the present invention, comprises an evaluation step  310 , a positioning step  320 , a resonant frequency step  330 , a selection step  340  and an acoustic energy step  350 . In one aspect, the method further comprises a loop back cycle in which the resonant frequency step  330 , the selection step  340  and the acoustic energy steps  350  are repeated at least once. 
         [0046]    In the evaluation step  310 , the reactor is evaluated to identify at least one target site on the exterior surface of the reactor wall corresponding to a slag deposit on the interior surface of the reactor wall. In the position step  320 , the speakers  22  can be positioned to align the central axis a-a of each speaker aligned with one of the identified target sites. 
         [0047]    In the resonant frequency step  330 , the exterior surface of the reactor wall is struck to induce an acoustic response corresponding to the size and chemical makeup of the slag deposits adhered to the inner surface of the reactor wall. The acoustic response is evaluated to determine a resonant frequency corresponding to the slag deposit and the present condition of the slag deposits within the reactor. 
         [0048]    In the selection step  340 , a desired frequency and a desired amplitude is selected from a library of operating conditions at which the speaker  22  to form an acoustic wave capable of inducing resonance in the reactor at the determined resonant frequency. The frequency, amplitude, duration of the active and rest cycles, and the overall treatment duration can be selected to provide the desired acoustic waveform characteristics. 
         [0049]    In the acoustic energy step  350 , the speaker  22  can be operated to provide the acoustic energy to the reactor, wherein the speaker  22  provides a plurality of acoustic waves having the selected characteristics to induce resonance in the reactor to cause separation of the slag from the interior surfaces of the reactor. In one aspect, the resonant frequency step  330 , the selection step  340  and the acoustic energy steps  350  are repeated as the slag is separated from the interior surface of the reactor. In this operation, the loop back cycle allows for adjustment of the acoustic waves to accommodate the changing resonant frequency of the slag deposits as portions of the slag are separated from the interior surfaces of the reactor. 
         [0050]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and described in detail. It is understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.