Patent Publication Number: US-2005126512-A1

Title: Pressure probe

Description:
BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The invention relates to industrial equipment. More particularly, the invention relates to the detonative cleaning of industrial equipment.  
      (2) Description of the Related Art  
      Surface fouling is a major problem in industrial equipment. Such equipment includes furnaces (coal, oil, waste, etc.), boilers, gasifiers, reactors, heat exchangers, and the like. Typically the equipment involves a vessel containing internal heat transfer surfaces that are subjected to fouling by accumulating particulate such as soot, ash, minerals and other products and byproducts of combustion, more integrated buildup such as slag and/or fouling, and the like. Such particulate build-up may progressively interfere with plant operation, reducing efficiency and throughput and potentially causing damage. Cleaning of the equipment is therefore highly desirable and is attended by a number of relevant considerations. Often direct access to the fouled surfaces is difficult. Additionally, to maintain revenue it is desirable to minimize industrial equipment downtime and related costs associated with cleaning. A variety of technologies have been proposed. By way of example, various technologies have been proposed in U.S. Pat. Nos. 5,494,004 and 6,438,191 and U.S. patent application publication 2002/0112638. Additional technology is disclosed in Huque, Z. Experimental Investigation of Slag Removal Using Pulse Detonation Wave Technique, DOE/HBCU/OMI Annual Symposium, Miami, Fla., Mar. 16-18, 1999. Particular blast wave techniques are described by Hanjalić and Smajević in their publications: Hanjalić, K. and Smajević, I., Further Experience Using Detonation Waves for Cleaning Boiler Heating Surfaces, International Journal of Energy Research Vol. 17, 583-595 (1993) and Hanjalić, K. and Smajević, I., Detonation-Wave Technique for On-load Deposit Removal from Surfaces Exposed to Fouling: Parts I and II, Journal of Engineering for Gas Turbines and Power, Transactions of the ASME, Vol. 1, 116 223-236, January 1994. Such systems are also discussed in Yugoslav patent publications P 1756/88 and P 1728/88. Such systems are often identified as “soot blowers” after an exemplary application for the technology.  
      Nevertheless, there remain opportunities for further improvement in the field.  
     SUMMARY OF THE INVENTION  
      Accordingly, one aspect of the invention involves an apparatus for cleaning a surface within a vessel. A vessel wall separates a vessel exterior from a vessel interior and has a wall aperture. The apparatus includes an elongate conduit having an upstream first and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior. A pressure probe includes a body held in an operative position within the vessel so as to be exposed to the shockwave after the shockwave exits the conduit second end. The body has an exterior surface with a convergent nose portion. There is a first port in the body. A passageway extends between the first port and a pressure sensor. A support member holds the body in the operative position.  
      In various implementations, the probe may further include a cooling fluid circuit at least partially through the support member and body. The support member may include a cooling liquid-carrying conduit joining the body from above. The cooling liquid-carrying conduit may extend through the vessel wall. A source of fuel and oxidizer may be coupled to the conduit to deliver the fuel and oxidizer to the conduit. An initiator may be positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave.  
      Another aspect of the invention involves a pressure probe apparatus with a body having an exterior surface with a forwardly-convergent nose portion. A passageway extends between a first port in the body and a pressure sensor. A support member holds the body in an operative position. A cooling fluid circuit extends at least partially through the support member and body.  
      In various implementations, the cooling circuit may extend around a periphery of a conduit defining the passageway. The body may have an aft surface with a second port and the cooling circuit may extend through the second port. The first port may be on a flat. The aft surface may have a third port and the cooling circuit may bifurcate so as to extend through the second and third ports. The apparatus may be combined with a cooling liquid flow in the cooling circuit. The support may carry a signal communication line from the pressure sensor. The nose may extend for at least 50% of a body length. Along at least 50% of a nose length, the nose may essentially converge forwardly with a half angle between 5° and 15°. The cooling circuit may span, within the body, at least 50% of the body length. An exemplary body length is between 2 cm and 20 cm and an exemplary maximum transverse dimension is no more than 4 cm. The apparatus may be used in combination with a detonative cleaning apparatus.  
      Another aspect of the invention involves a method for cleaning a surface within a vessel. Fuel and oxidizer are introduced to a conduit. A reaction of the fuel and oxidizer is initiated so as to cause a shockwave to impinge upon the surface. A pressure probe is used within the vessel to measure a pressure magnitude of the shockwave.  
      In various implementations, the method may be performed in a repeated sequential way. The reaction may include a deflagration-to-detonation transition. A cooling fluid may be passed through the pressure probe. The pressure probe may be repositioned by acting upon a support portion of a probe support member outside of the vessel.  
      The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view of an industrial furnace associated with several soot blowers positioned to clean a level of the furnace.  
       FIG. 2  is a side view of one of the blowers of  FIG. 1 .  
       FIG. 3  is a partially cut-away side view of an upstream end of the blower of  FIG. 2 .  
       FIG. 4  is a longitudinal sectional view of a main combustor segment of the soot blower of  FIG. 2 .  
       FIG. 5  is an end view of the segment of  FIG. 4 .  
       FIG. 6  is a partial side view of a pressure probe assembly associated with the outlet end of a combustion conduit.  
       FIG. 7  is a partial longitudinal sectional view of a probe unit of the assembly of  FIG. 6 .  
       FIG. 8  is an aft end view of the probe unit of  FIG. 7 .  
       FIG. 9  is a view of a pressure probe mounting bracket. 
    
    
      Like reference numbers and designations in the various drawings indicate like elements.  
     DETAILED DESCRIPTION  
       FIG. 1  shows a furnace  20  having an exemplary three associated soot blowers  22 . In the illustrated embodiment, the furnace vessel is formed as a right parallelepiped and the soot blowers are all associated with a single common wall  24  of the vessel and are positioned at like height along the wall. Other configurations are possible (e.g., a single soot blower, one or more soot blowers on each of multiple levels, and the like).  
      Each soot blower  22  includes an elongate combustion conduit  26  extending from an upstream distal end  28  away from the furnace wall  24  to a downstream proximal end  30  closely associated with the wall  24 . Optionally, however, the end  30  may be well within the furnace. In operation of each soot blower, combustion of a fuel/oxidizer mixture within the conduit  26  is initiated proximate the upstream end (e.g., within an upstreammost 10% of a conduit length) to produce a detonation wave which is expelled from the downstream end as a shockwave along with associated combustion gases for cleaning surfaces within the interior volume of the furnace. Each soot blower may be associated with a fuel/oxidizer source  32 . Such source or one or more components thereof may be shared amongst the various soot blowers. An exemplary source includes a liquefied or compressed gaseous fuel cylinder  34  and an oxygen cylinder  36  in respective containment structures  38  and  40 . In the exemplary embodiment, the oxidizer is a first oxidizer such as essentially pure oxygen. A second oxidizer may be in the form of shop air delivered from a central air source  42 . In the exemplary embodiment, air is stored in an air accumulator  44 . Fuel, expanded from that in the cylinder  34  is generally stored in a fuel accumulator  46 . Each exemplary source  32  is coupled to the associated conduit  26  by appropriate plumbing below. Similarly, each soot blower includes a spark box  50  for initiating combustion of the fuel oxidizer mixture and which, along with the source  32 , is controlled by a control and monitoring system (not shown).  FIG. 1  further shows the wall  24  as including a number of ports for inspection and/or measurement. Exemplary ports include an optical monitoring port  54  and a temperature monitoring port  56  associated with each soot blower  22  for respectively receiving an infrared and/or visible light video camera and thermocouple probe for viewing the surfaces to be cleaned and monitoring internal temperatures. Other probes/monitoring/sampling may be utilized, including pressure monitoring, composition sampling, and the like.  
       FIG. 2  shows further details of an exemplary soot blower  22 . The exemplary detonation conduit  26  is formed with a main body portion formed by a series of doubly flanged conduit sections or segments  60  arrayed from upstream to downstream and a downstream nozzle conduit section or segment  62  having a downstream portion  64  extending through an aperture  66  in the wall and ending in the downstream end or outlet  30  exposed to the furnace interior  68 . The term nozzle is used broadly and does not require the presence of any aerodynamic contraction, expansion, or combination thereof. Exemplary conduit segment material is metallic (e.g., stainless steel). The outlet  30  may be located further within the furnace if appropriate support and cooling are provided.  FIG. 2  further shows furnace interior tube bundles  70 , the exterior surfaces of which are subject to fouling. In the exemplary embodiment, each of the conduit segments  60  is supported on an associated trolley  72 , the wheels of which engage a track system  74  along the facility floor  76 . The exemplary track system includes a pair of parallel rails engaging concave peripheral surfaces of the trolley wheels. The exemplary segments  60  are of similar length L 1  and are bolted end-to-end by associated arrays of bolts in the bolt holes of their respective flanges. Similarly, the downstream flange of the downstreammost of the segments  60  is bolted to the upstream flange of the nozzle  62 . In the exemplary embodiment, a reaction strap  80  (e.g., cotton or thermally/structurally robust synthetic) in series with one or more metal coil reaction springs  82  is coupled to this last mated flange pair and connects the combustion conduit to an environmental structure such as the furnace wall for resiliently absorbing reaction forces associated with discharging of the soot blower and ensuring correct placement of the combustion conduit for subsequent firings. Optionally, additional damping (not shown) may be provided. The reaction strap/spring combination may be formed as a single length or a loop. In the exemplary embodiment, this combined downstream section has an overall length L 2 .  
      Extending downstream from the upstream end  28  is a predetonator conduit section/segment  84  which also may be doubly flanged and has a length L 3 . The predetonator conduit segment  84  has a characteristic internal cross-sectional area (transverse to an axis/centerline  500  of the conduit) which is smaller than a characteristic internal cross-sectional area (e.g., mean, median, mode, or the like) of the downstream portion ( 60 ,  62 ) of the combustion conduit. In an exemplary embodiment involving circular sectioned conduit segments, the predetonator cross-sectional area is a characterized by a diameter of between 8 cm and 12 cm whereas the downstream portion is characterized by a diameter of between 20 cm and 40 cm. Accordingly, exemplary cross-sectional area ratios of the downstream portion to the predetonator segment are between 1:1 and 10:1, more narrowly, 2:1 and 10:1. An overall length L between ends  28  and  30  may be 1-15 m, more narrowly, 5-15 m. In the exemplary embodiment, a transition conduit segment  86  extends between the predetonator segment  84  and the upstreammost segment  60 . The segment  86  has upstream and downstream flanges sized to mate with the respective flanges of the segments  84  and  60  has an interior surface which provides a smooth transition between the internal cross-sections thereof. The exemplary segment  86  has a length L 4 . An exemplary half angle of divergence of the interior surface of segment  86  is ≦12°, more narrowly 5-10°.  
      A fuel/oxidizer charge may be introduced to the detonation conduit interior in a variety of ways. There may be one or more distinct fuel/oxidizer mixtures. Such mixture(s) may be premixed external to the detonation conduit, or may be mixed at or subsequent to introduction to the conduit.  FIG. 3  shows the segments  84  and  86  configured for distinct introduction of two distinct fuel/oxidizer combinations: a predetonator combination; and a main combination. In the exemplary embodiment, in an upstream portion of the segment  84 , a pair of predetonator fuel injection conduits  90  are coupled to ports  92  in the segment wall which define fuel injection ports. Similarly, a pair of predetonator oxidizer conduits  94  are coupled to oxidizer inlet ports  96 . In the exemplary embodiment, these ports are in the upstream half of the length of the segment  84 . In the exemplary embodiment, each of the fuel injection ports  92  is paired with an associated one of the oxidizer ports  96  at even axial position and at an angle (exemplary 90° shown, although other angles including 180° are possible) to provide opposed jet mixing of fuel and oxidizer. Discussed further below, a purge gas conduit  98  is similarly connected to a purge gas port  100  yet further upstream. An end plate  102  bolted to the upstream flange of the segment  84  seals the upstream end of the combustion conduit and passes through an igniter/initiator  106  (e.g., a spark plug) having an operative end  108  in the interior of the segment  84 .  
      In the exemplary embodiment, the main fuel and oxidizer are introduced to the segment  86 . In the illustrated embodiment, main fuel is carried by a number of main fuel conduits  112  and main oxidizer is carried by a number of main oxidizer conduits  110 , each of which has terminal portions concentrically surrounding an associated one of the fuel conduits  112  so as to mix the main fuel and oxidizer at an associated inlet  114 . In exemplary embodiments, the fuels are hydrocarbons. In particular exemplary embodiments, both fuels are the same, drawn from a single fuel source but mixed with distinct oxidizers: essentially pure oxygen for the predetonator mixture; and air for the main mixture. Exemplary fuels useful in such a situation are propane, MAPP gas, or mixtures thereof. Other fuels are possible, including ethylene and liquid fuels (e.g., diesel, kerosene, and jet aviation fuels). The oxidizers can include mixtures such as air/oxygen mixtures of appropriate ratios to achieve desired main and/or predetonator charge chemistries. Further, monopropellant fuels having molecularly combined fuel and oxidizer components may be options.  
      In operation, at the beginning of a use cycle, the combustion conduit is initially empty except for the presence of air (or other purge gas). The predetonator fuel and oxidizer are then introduced through the associated ports filling the segment  84  and extending partially into the segment  86  (e.g., to near the midpoint) and advantageously just beyond the main fuel/oxidizer ports. The predetonator fuel and oxidizer flows are then shut off. An exemplary volume filled the predetonator fuel and oxidizer is 1-40%, more narrowly 1-20% of the combustion conduit volume. The main fuel and oxidizer are then introduced, to substantially fill some fraction (e.g., 20-100%) of the remaining volume of the combustor conduit. The main fuel and oxidizer flows are then shut off. The prior introduction of predetonator fuel and oxidizer past the main fuel/oxidizer ports largely eliminates the risk of the formation of an air or other non-combustible slug between the predetonator and main charges. Such a slug could prevent migration of the combustion front between the two charges.  
      With the charges introduced, the spark box is triggered to provide a spark discharge of the initiator igniting the predetonator charge. The predetonator charge being selected for very fast combustion chemistry, the initial deflagration quickly transitions to a detonation within the segment  84  and producing a detonation wave. Once such a detonation wave occurs, it is effective to pass through the main charge which might, otherwise, have sufficiently slow chemistry to not detonate within the conduit of its own accord. The wave passes longitudinally downstream and emerges from the downstream end  30  as a shockwave within the furnace interior, impinging upon the surfaces to be cleaned and thermally and mechanically shocking to typically at least loosen the contamination. The wave will be followed by the expulsion of pressurized combustion products from the detonation conduit, the expelled products emerging as a jet from the downstream end  30  and further completing the cleaning process (e.g., removing the loosened material). After or overlapping such venting of combustion products, a purge gas (e.g., air from the same source providing the main oxidizer and/or nitrogen) is introduced through the purge port  100  to drive the final combustion products out and leave the detonation conduit filled with purge gas ready to repeat the cycle (either immediately or at a subsequent regular interval or at a subsequent irregular interval (which may be manually or automatically determined by the control and monitoring system)). Optionally, a baseline flow of the purge gas may be maintained between charge/discharge cycles so as to prevent gas and particulate from the furnace interior from infiltrating upstream and to assist in cooling of the detonation conduit.  
      In various implementations, internal surface enhancements may substantially increase internal surface area beyond that provided by the nominally cylindrical and frustoconical segment interior surfaces. The enhancement may be effective to assist in the deflagration-to-detonation transition or in the maintenance of the detonation wave.  FIG. 4  shows internal surface enhancements applied to the interior of one of the main segments  60 . The exemplary enhancement is nominally a Chin spiral, although other enhancements such as Shchelkin spirals and Smirnov cavities may be utilized. The spiral is formed by a helical member  120 . The exemplary member  120  is formed as a circular-sectioned metallic element (e.g., stainless steel wire) of approximately 8-20 mm in sectional diameter. Other sections may alternatively be used. The exemplary member  120  is held spaced-apart from the segment interior surface by a plurality of longitudinal elements  122 . The exemplary longitudinal elements are rods of similar section and material to the member  120  and welded thereto and to the interior surface of the associated segment  60 . Such enhancements may also be utilized to provide predetonation in lieu of or in addition to the foregoing techniques involving different charges and different combustor cross-sections.  
      The apparatus may be used in a wide variety of applications. By way of example, just within a typical coal-fired furnace, the apparatus may be applied to: the pendants or secondary superheaters, the convective pass (primary superheaters and the economizer bundles); air preheaters; selective catalyst removers (SCR) scrubbers; the baghouse or electrostatic precipitator; economizer hoppers; ash or other heat/accumulations whether on heat transfer surfaces or elsewhere, and the like. Similar possibilities exist within other applications including oil-fired furnaces, black liquor recovery boilers, biomass boilers, waste reclamation burners (trash burners), and the like.  
       FIG. 6  shows a pressure probe assembly  150  having a head or probe unit  152  positioned facing the outlet  30 . In the exemplary embodiment, the probe is positioned in the area swept by the internal cross-section of the combustion conduit outlet in the direction of the centerline  500  and is in relatively close facing proximity (e.g., within 3 m of the outlet, more preferably 0.1 m-2 m). The probe unit  152  is held at the distal end  154  of a support arm  156 . As discussed below, the support arm  156  functions not only to support and locate the probe unit but to carry signal and cooling fluid communication for the probe unit. In the exemplary embodiment, the arm  156  is supported by a mounting bracket  158  held relative to some environmental structure (e.g., the furnace wall, or, as illustrated, the combustion conduit such as via the flange joints between the nozzle segment  62  and the segment upstream thereof). The bracket  158  may rigidly locate the arm or may provide for angular and translational excursions of the arm. In the exemplary embodiment, proximate an upstream end  160  of the arm, the arm is provided with port fittings for signal and fluid lines  162  and  164 , respectively discussed in further detail below. An exemplary arm length is 2-6 m and diameter is 2-5 cm. For pressure monitoring in locations more remote from the nozzle and/or wall aperture, other arm constructions and mounting arrangements may be more appropriate.  
       FIG. 7  shows further details of the exemplary probe unit. The unit has a body which may be formed of a material suitable for withstanding expected thermal and mechanical shock stresses. An exemplary body has a main piece  170  which may be machined from a metal (e.g., nickel- or cobalt-based superalloy, stainless steel, or the like). The main piece extends along a nose portion  172  aft from a tip  174 . The nose portion has a generally frustoconical surface  176  of half angle θ. Exemplary θ is ≦30°, more narrowly 5°-15°. The nose portion conical, or near conical, shape helps minimize formation of static shocks and the low angle taper helps keep the passing shockwave essentially attached to the body. The nose portion extends aft to an aft portion  178  which has a generally cylindrical external surface  180  provided with a single flat facet  182 . The body aft portion has an aft rim  184  secured relative to an aft endplate  186 . The body aft portion has a pair of opposed apertures. A first aperture  188  in the facet  182  accommodates a first (outboard) end portion  190  of a conduit  192  extending inboard (i.e., into an interior space  194  of the probe body) to a second (inboard) end portion  196 ). A second aperture  198  is in the cylindrical surface  180  opposite the aperture  188  and accommodates a support conduit  200 . The support conduit  200  may be formed as the distal end portion  154  of the arm  156  or may be secured thereto. Centrally within the conduit  200 , a pressure transducer  202  is held within a mounting fixture  204 . The fixture  204  extends from an upstream end portion  206  to a downstream end portion  208 . The downstream end portion  208  is coupled to the tube inboard end portion  196  to combine to define a flowpath  210  from an inlet  212  at the tube first end  190  to the operative end (e.g., membrane) of the pressure transducer  202 . An exemplary length of the flowpath  210  is 0.5-5 cm. The fixture  204  may be supported entirely by its interaction with the tube or may be supported via webs (not shown—e.g., left between longitudinally-drilled holes) extending radially outward to the conduit  200 . Overall body size may balance minimizing interference with the shockwave (indicating a small body) with appropriate robustness and economy of manufacture (indicating a potentially larger body). Exemplary body lengths are 2-20 cm and exemplary maximum transverse dimensions (e.g., diameter along the aft portion) are less than 4 cm.  
      The signal communication line  162  (e.g., coaxial cable). The line  162  may be connected to a control/monitoring system (not shown). As the length of the flowpath  210  may affect measured pressure values relative to the inlet  212 , the control/monitoring subsystem may be programmed to correct for this (e.g., ID pressure magnitude attenuation and phase corrections).  
      An annular or interrupted annular space  216  between the fixture  204  and conduit  200  accommodates the downstream flow of fluid from the fluid line  164  along fluid flowpaths  218 . In the exemplary embodiment, the probe body interior  194  has a series of progressively smaller cross-section areas, one ahead of the other within the nose, to permit the pathway to pass therewithin to cool the nose. In the exemplary embodiment, the endplate  186  has a pair of apertures  220  ( FIG. 8 ) associated with fittings  222  coupled to a coolant return line  224  ( FIG. 6 ) which may be secured relative to the arm  156  such as via hose clamps  226 .  
       FIG. 9  shows further details of the mounting bracket  158 . The exemplary bracket includes a body piece  240  formed as a sector of an annular metallic plate having first and second faces and extending between first and second circumferential ends and inner and outer diameter perimeter portions  242  and  244 . Near the inner diameter perimeter portion  242  bolt holes  246  correspond to the pattern of bolt holes of the associated nozzle and downstreammost doubly flanged segment flanges so as to permit the plate to be secured to the flanges by a group of the flange bolts. The outer diameter perimeter portion  244  includes a recess with a base portion  248  complementary to a portion of the cross-section of the arm  156 . A remaining portion of the recess is dimensioned to accommodate a clamp body  250  having an inner surface  252  complementary to an opposite portion of the arm cross-section (e.g., to form an approximate circle with the surface  248 ). Knob-headed bolts  254  may secure the clamp body  250  to the bracket body  240  to permit a secure clamping of the arm between the two to precisely hold the arm in a given position. This permits precise positioning of the probe unit a given distance from the outlet end. Due to an offset of the probe from the clamped length of the arm, the rotational orientation of the arm may be used to position the probe transversely relative to the outlet.  
      In operation, the shockwave passes downstream over the nose, and along the body aft portion  178 . When the shockwave reaches the port  212 , its effects can pass along the path  210  to the pressure transducer that in turn provides an output signal indicative of the pressure magnitude of the shockwave. The probe assembly is initially positioned so that the probe unit is at a predetermined location relative to the combustion tube outlet. This may be performed while the outlet is disengaged from the furnace. Thereafter, the outlet may be inserted into the furnace, and the reaction strap or other restraints installed. The firing process may then be initiated.  
      One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the invention may be adapted for use with a variety of industrial equipment and with variety of soot blower technologies. Aspects of the existing equipment and technologies may influence aspects of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.