Patent Publication Number: US-2005125932-A1

Title: Detonative cleaning apparatus nozzle

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  
      One aspect of the invention involves an apparatus for directing gas from an upstream conduit through a vessel wall for cleaning surfaces within the vessel. A mounting flange couples the apparatus to the upstream conduit delivering the gas and has first and second faces, an inboard surface bounding a central aperture, an outboard perimeter, and an array of bolt holes extending between the first and second faces. A conduit extends downstream from the flange and has inner and outer walls along at least a portion of a length. A space between the inner and outer walls carries a cooling fluid. There is a cooling fluid inlet and a cooling fluid outlet.  
      In various implementations, the space may extend from an upstream end outside the vessel wall at least partially downstream within the wall. The cooling fluid outlet may be along the conduit and the cooling fluid inlet may be along the flange. The inner and outer walls may each have a downstream rim. The cooling fluid outlet may be between the inner and outer walls. The inner wall may essentially be formed by a first tubular piece extending from an upstream rim to a downstream rim and having interior and exterior surfaces. Along an upstream portion, the interior surface may provide the flange inboard surface. The apparatus may be combined with the vessel. The vessel may be a furnace having a furnace wall separating a furnace exterior from a furnace interior and having a wall aperture. The combination may include a detonative source of the gas. The flange may be upstream of an exterior surface of the furnace wall. The conduit may extend through the furnace wall to protrude downstream of an interior surface of the furnace wall.  
      Another aspect of the invention involves a soot blower nozzle. Means mount the nozzle to an upstream soot blower gas conduit. A surface guides gas from the soot blower gas conduit into the interior of the vessel. Means cool the nozzle.  
      Another aspect of the invention involves a method for operating an apparatus for cleaning interior surfaces within a vessel having a vessel wall. A combustion pulse is caused in a combustion conduit. Combustion gases are directed along the combustion conduit through the vessel wall to be ejected from an outlet of the combustion conduit. A cooling gas is passed along a portion of the combustion conduit exposed to heat from the vessel.  
      In various implementations, the passing may be essentially continuous between a number of the combustion pulses. The passing may include passing the cooling fluid along a path at least partially surrounding a portion of the combustion gas flowpath. The passing may include passing the cooling fluid along a path into the vessel interior.  
      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 side view of an alternate discharge end portion of a combustion tube assembly.  
       FIG. 7  is a view of an air curtain flange of the assembly of  FIG. 6 .  
       FIG. 8  is a downstream end view of the flange of  FIG. 7 .  
       FIG. 9  is a downstream end view of a thermal isolation flange assembly.  
       FIG. 10  is an exploded view of the assembly of  FIG. 9 .  
       FIG. 11  is a view of a nozzle assembly.  
       FIG. 12  is a downstream end view of a nozzle assembly of  FIG. 11 .  
       FIG. 13  is a longitudinal sectional view of the nozzle assembly of  FIG. 12 , taken along line  13 - 13 .  
       FIG. 14  is an enlarged view of a flange portion of the nozzle assembly of  FIG. 13 .  
       FIG. 15  is a partial longitudinal sectional view of a downstream end portion of the nozzle assembly of  FIG. 11 .  
       FIG. 16  is a partial longitudinal sectional view of an alternate air curtain flange. 
    
    
      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 liquified 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 . Alternative resilient recoil absorbing means may include non-metal or non-coil springs or rubber or other elastomeric elements advantageously at least partially elastically deformed in tension, compression, and/or shear, pneumatic recoil absorbers, and the like.  
      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.  
      Further steps may be taken to isolate the combustion conduit (or major portion thereof) from chemical contamination and thermal stresses.  
       FIG. 6  shows an outlet/discharge end assembly  140  extending to an outlet  30 ′. The outlet end assembly  140  may be used as a downstream nozzle/outlet conduit section in place of the section  62  of  FIG. 2 . Although identified as a nozzle, this does not require the presence of any particular convergence, divergence, or combination thereof in the nozzle. The exemplary assembly  140  provides means for thermally and chemically isolating upstream portions of the combustion conduit. From upstream to downstream, the assembly  140  includes a doubly flanged conduit segment  142  having upstream and downstream bolting flanges  144  and  146 . The body of the conduit segment  142  may have a number of instrumentation and/or sampling ports  148  which may be plugged to the extent not in use. The flange  144  has an upstream face for mounting to the downstream face of the downstream flange of the penultimate conduit segment. This junction may also serve for connection of the reaction strap or other means. The flange  146  has a downstream face for mating with the upstream face of an air curtain flange  150  which, as described below, provides chemical isolation for portions of the combustion conduit upstream thereof. The air curtain flange  150  has a downstream face for mating with the upstream face of a thermal isolation flange  152  which is cooled to isolate upstream portions of the combustion conduit from heating (thermal soakback) from the furnace. The thermal isolation flange  152  has a downstream face for mating with an upstream face of a flange  154  of a nozzle assembly  156  having a nozzle body  158  extending to the outlet  30 ′ and further cooled as described below. Nut and bolt combinations  160  extend through the bolt holes of the flanges  146 ,  150 ,  152  and  154  to structurally and sealingly secure the assembly components together.  
      The exemplary air curtain flange  150  ( FIGS. 7 and 8 ) includes the upstream and downstream faces, an exterior perimeter surface  170  and an interior surface  172  circumscribing the combustion gas flowpath. An array of bolt holes extend between the upstream and downstream faces. The interior surface  172  is at substantially even radius from the detonation conduit centerline as is the interior surface of the adjacent conduit segment  142 . An annular channel  174  is formed in one of the faces (e.g., the downstream face) and is in communication via a connecting passageway  176  with an exterior port  178  on the perimeter surface. An interior rim  180  (shown as a portion of the downstream face separated from the remainder by the channel) of the channel along the interior surface is segmented or castellated by a circumferential array of slots  182 . In the assembled condition, the mouth of the rim is closed by the adjacent face of its mating flange (e.g., the upstream face of the thermal isolation flange or the downstream face of downstream flange  146  of the conduit segment  142 ). Gas (e.g., air, N 2 , CO 2 , or other relatively inert gas) may be introduced to the channel  174  through the passageway and port (which may be provided with an appropriate connection fitting (not shown in  FIGS. 7 and 8 )). When so introduced, the gas fills the channel and flows inward into the combustion conduit interior through the slots. Exemplary air curtain flanges may be machined (e.g., directly or from a casting or forging) of appropriate metal (e.g., steel or nickel- or cobalt-based superalloy).  
       FIG. 16  shows an alternate thermal isolation flange  184  including a channel  185  and passageway  186 . The alternate flange  184  may be similarly constructed to the flange  150 . The exemplary alternate flange  184  differs in that its outlets are provided by full holes  188  in the inboard/interior surface rather than by recesses. Furthermore, those holes are angled so that the discharge outflow is off-radial (e.g., by an angle θ so as to have a downstream longitudinal component). The hole centerlines may, also, be oriented with a tangential component if a tangential flow component is desired. The downstream longitudinal flow component may further assist in preventing contaminant from passing upstream from the furnace. Exemplary values for θ are between 5° and 60°.  
      In operation, the gas flow may supplement or replace a baseline continuous purge gas flow. The proximity of the air curtain flange  150  to the outlet  30 ′ may provide improved resistance to the upstream reinfiltration of combustion gases discharged from the apparatus and infiltration of general furnace gases as well as particulate contamination. In addition to contamination from particulates generated within the furnace, the air curtain flow prevents accumulation of particulate reaction products from the combustion gases especially as such gases may cool and precipitate out particles or liquid condensate which may, in turn, accommodate particle formation or sludge formation. If operated in a baseline fashion, the continuous gas flow may also provide supplemental cooling of the conduit (especially downstream of the point of introduction).  
       FIGS. 9 and 10  show details of the exemplary thermal isolation flange  152 . The flange includes the upstream and downstream faces and an exterior perimeter surface  190 . It further includes an interior surface  192  encircling the combustion gas flowpath at substantially even radius as the interior surfaces of the adjacent components. An array of bolt holes extend between the upstream and downstream faces. A channel  194  formed on one of the faces (e.g., the downstream face) extends longitudinally inward therefrom. In the illustrated embodiment, the channel has two general portions: a deep base portion  196  which is less than a full annulus; and a mouth portion  198  which extends to the associated face and is a full annulus. The mouth portion is wider than the base portion extending both radially outward and radially inward therefrom to define a pair of annular shoulder surfaces  200  and  202 . In the exemplary embodiment, the channel is machined in two steps. The mouth portion may be machined and then the base portion may be machined below a base of the mouth portion, leaving a divider portion  204  of the flange between two ends of the base portion. Alternatively, the base portion may initially be formed as a full annulus and then a separate divider element inserted to turn the base channel into the partial annulus. A pair of passageways  206  and  208  connect the associated end portions of the channel base portion to associated exterior ports  210  and  212  (e.g., in the flange perimeter surface). The exterior ports may be equipped with appropriate fittings. In the exemplary embodiment, the mouth portion of the channel accommodates a full annulus sealing ring  214  which seats against the shoulder surfaces of the remaining body piece of the flange and may be welded in place to close the channel. Alternatively, in the absence of a mouth portion and sealing ring, the adjacent flange itself may close and seal the channel. In operation, a heat transfer fluid is introduced through one of the ports and withdrawn from the other after passing circumferentially through the channel. Exemplary heat transfer fluid may be liquid (e.g., aqueous (water or a water/glycol mixture) or oil-based) or gaseous (e.g., air or compressed/refrigerated C 0   2  or N 2 ) as may be appropriate for desired heat transfer. Similarly, the heat transfer flowpath (e.g., channel) geometry and the flow rate may be tailored to achieve a desired heat transfer. The heat transfer fluid can both assist in cooling of the nozzle and in isolating elevated nozzle temperatures from upstream components. Such a thermal isolation flange may be used elsewhere in the system and may be used in other soot blower and different applications where thermal isolation is required. Materials and manufacturing techniques similar to those of the air curtain flange may be used.  
       FIGS. 11-14  show further details of the nozzle assembly  156 .  FIG. 13  shows the nozzle assembly as including a main tube  220  having an interior surface  222  and an exterior surface  224  and extending from an upstream rim  226  to a downstream rim  230  essentially defining the outlet  30 ′. The interior surface may be at substantially even radius from the centerline as interior surfaces of other components described above. The flange  154  includes a main upstream piece  232  having upstream and downstream faces  234  and  236 , an interior surface  237 , and an exterior peripheral surface  238 . The main piece  232  is secured to an upstream portion of the main tube  220  with its interior surface contacting the exterior surface of the tube. Exemplary connection is by welding. An annular plenum  240  may be machined in the main flange piece  232  (e.g., as a rebate of an inboard portion of the downstream face). An outboard portion of the channel is closed by the second flange piece  242  having upstream and downstream faces  244  and  246 , an interior surface  248 , and an exterior periphery  250 . The upstream face  244  may abut the first piece downstream face  236  and be sealed thereto such as via an O-ring  252  residing at least partially in a channel in one or both of the pieces. The two pieces may be held together by the same bolts/nuts  160  or by separate bolts, welds, or the like. The interior surface  248  is spaced slightly apart from the tube exterior surface  224 . A sleeve  254  has interior and exterior surfaces  256  and  258  and extends from an upstream end/rim  260  to a downstream end/rim  262  ( FIG. 13 ). The interior surface  256  is similarly spaced apart from the tube exterior surface  224  and an upstream end portion is secured to the flange second piece (e.g., accommodated in an annular rebate and welded thereto). A metering ring  264  circumscribes the plenum  240  to separate radially inboard and outboard portions thereof and has a plurality of apertures therein. One or more feed passageways  270  (two shown) are in communication with the plenum  240 . The passageways  270  are in communication with ports (e.g., in the flange first piece)  272  carrying fittings  274 . A cooling fluid (e.g., a gas which may be similar to the air curtain gas) is introduced along a nozzle cooling flowpath downstream through the fittings, passageways, and into the outboard portion of the plenum  240 . The ring  264  and its apertures meter the flow from the outboard portion of the plenum  240  to the inboard portion and help circumferentially distribute the flow when there are a relatively small number of discrete feed ports. From the inboard/downstream portion of the plenum  240 , the flow proceeds downstream in generally annular space  276  between the sleeve  254  and tube  220 . In the exemplary embodiment, the cooling gas flow is discharged from a cooling gas outlet  278  between the sleeve downstream rim  262  and the adjacent portion of the tube exterior surface  224 . In the exemplary embodiment, the sleeve downstream rim is slightly recessed relative to the tube downstream rim so as to mitigate the influence of the detonation wave on the cooling gas flow and mitigate the effect of the wave on the potentially relatively thin and fragile sleeve.  
      Advantageously, means are provided for maintaining the circumferentially spaced-apart relationship between the tube  220  and sleeve  254 . Exemplary means include one or more spacer elements. The spacer elements may be associated with means for measuring temperature parameters of the nozzle body largely defined by the tube and sleeve downstream of the flange.  FIG. 11  shows an exemplary first spacer  280 . The exemplary first spacer is forked, having two tines  282  and  284  extending from upstream ends to a junction  286  from which a single leg  288  extends further downstream to a leg downstream end proximate the sleeve downstream end. The space between the tines may accommodate an additional thermocouple (not shown) adjacent the junction and with its wires running back upstream and passing through a thermocouple fitting port  290  in the main flange piece  232 .  FIG. 15  shows a second spacer  292  as an elongate, nominally rectangular, strip extending from an upstream end at the sleeve upstream end to a downstream end at the tube downstream end  230 . The exemplary spacer  292  has, at its downstream end, an aperture between its outboard and inboard surfaces an aligned similar blind aperture extends inward from the tube exterior surface. A thermocouple  294  is mounted within the blind aperture and has its body  296  extending outward, around the sleeve, and through a protective tube  298  (also  FIG. 11 ) secured to the exterior surface of the sleeve. The thermocouple  294  serves to measure temperatures at the tube downstream rim. Flange materials and mounting techniques may be similar to those of the air curtain and thermal isolation flanges. Tube, sleeve, and ring materials may be similar and may be made by a variety of known manufacturing techniques (e.g., rolling and welding of sheet stock or machining).  
      In operation, the control and monitoring system uses the first thermocouple  294  to principally monitor the temperature of the nozzle assembly portion exposed to the furnace interior. The aforementioned additional thermocouple may be monitored as a back-up in the event of a failure of the first thermocouple when it is not desirable to immediately initiate a shutdown for repair. The same or different critical temperatures may be utilized in determining shutdown based upon the outputs of the two thermocouples.  
      Returning to  FIG. 6 , the nozzle assembly may be provided with an interface plate  300  largely closing the portion of the furnace wall aperture outboard of the nozzle body. In operation, the plate  300  is normally positioned in close or contacting proximity to the furnace wall outer surface. The plate may have a number of apertures for accommodating various measuring, sampling, observation, and other equipment. These apertures may be provided with covers when not in use. A series of struts  302  connect the plate  300  to the flange  154  to hold the plate relative to the flange. The plate may have an aperture closely encircling the body  158 . The plate normally blocks the wall aperture to at least partially restrict flow of gases and particles from between the combustion tube and wall aperture (e.g., inflow with a negative pressure furnace). Upon discharge of the apparatus, the exemplary plate recoils with the combustion conduit and is returned along therewith to its original place by the action of the reaction strap/spring combination. The exemplary plate material is steel or nickel—or cobalt-based superalloy, optionally provided with an insulating layer (e.g., cementaceous material).  
      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. Other shapes of combustion conduit (e.g., non-straight sections to navigate external or internal obstacles) may be possible. Accordingly, other embodiments are within the scope of the following claims.