Patent Publication Number: US-11644255-B2

Title: Heat recovery steam generator cleaning system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation of U.S. application Ser. No. 17/204,423, filed on Mar. 17, 2021, which is a Continuation of U.S. application Ser. No. 16/249,120, filed on Jan. 16, 2019, now U.S. Pat. No. 10,962,311 granted on Mar. 30, 2021. The contents of each are herein incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to a heat recovery steam generator (HRSG) cleaning system and method. More specifically, the present disclosure relates to cleaning systems and methods for cleaning the HRSG finned-tubing using explosives and pressurized air. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     The HRSG finned-tubing become fouled over time, during use. The fouling can significantly reduce the efficiency and power output of an HRSG because the fouling reduces the amount and rate of heat exchange with the exhaust gas flowing across the finned-tubing. The fouling is caused by multiple factors, including certain salt deposits, sulfur compounds, and corrosion due to humidity and other factors. 
     It is known to use explosives, including detonation cord (detcord), in various configurations, to clean smooth-sided, non-finned tubes in coal-fired boilers. For example, U.S. Pat. No. 5,056,587, entitled Method for Deslagging a Boiler, teaches various arrangements of detcord attached directly to boiler tubes, including exploding a series of detcord lengths in sequence. U.S. Pat. No. 5,211,135, entitled Apparatus and Method of Deslagging a Boiler with an Explosive Blastwave and Kinetic Energy, teaches spacing a plurality of detcord clusters formed into three-dimensional geometries between tubing panels in a sequence. 
     It is also known to use sudden gas combustion to create a pressure wave to vibrate tubes, including HRSG finned-tubing, and dislodge fouling from the tubing. One such system is the PressureWave Plus™ developed by BANG&amp;CLEAN® GmbH and marketed by General Electric Company. As stated in a 2017 General Electric brochure for PressureWave Plus™, “[p]ressure waves generated by the combustion of gas typically propagate at much lower speeds than pressure waves generated by explosives”. Thus, prior to the present disclosure, those skilled in the art used gas combustion or other means and avoided using explosives to clean the HRSG finned-tubing due to the mistaken belief that explosives would damage the relatively thin fins surrounding the tubing. 
     Further, it is known to use pressurized air to at least partially clean smooth-sided boiler tubes. These devices are commonly known as soot blowers and generally have handheld hoses that users direct to banks of tubes as they walk across and up and down scaffolding. The scaffolding is erected and disassembled specifically for cleaning the tubes. This process is not efficient because of the significant down time required for erecting the scaffolding, cleaning the tubes, and the disassembly of the scaffolding. 
     Thus there is a need for an efficient HRSG finned-tubing cleaning system and method that improves on the previously known systems and methods. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a prior art elevation of a bank of HRSG finned-tubing; 
         FIG.  2    is a top view of  FIG.  1    taken along line  2 - 2 ; 
         FIG.  3    is a detail of a portion of  FIG.  1   ; 
         FIG.  4    is a top view of an HRSG facility, including an example cleaning system; 
         FIG.  5    is an elevation of a portion of  FIG.  4    along line  5 - 5 ; 
         FIG.  6    is an elevation of a portion of  FIG.  4    along line  6 - 6 ; 
         FIG.  7    is an elevation of an example explosive subsystem; 
         FIG.  8    is an elevation of an example pressurized air subsystem; 
         FIG.  9    is a partial perspective of  FIG.  8   ; 
         FIG.  10    is a detail of an example pressurized air blower assembly; and 
         FIG.  11    is a detail of a portion of an example automatic control. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     The applicants have unexpectedly discovered that the combined use of explosive detcord and pressurized air provides an efficient cleaning system and method for HRSG finned-tubing that allows for cleaning larger areas, quicker, more efficiently, and more thoroughly compared to prior art systems and methods. Typically, HRSG finned tubes  10  are constructed in a bank  12 , as shown in  FIG.  1   , with multiple banks  12  placed in an HRSG (see  FIG.  4   ). A single tube bank  12  may consist of multiple tubes  10  and be 24 feet wide by 60 feet tall by 7 rows of tubes  10 , as shown in  FIG.  2   . The rows of tubes  10  are typically tightly arranged such that each tube  10  generally contacts each adjacent tube  10 , as shown.  FIG.  3    is a partial detail  14  of  FIG.  1   , showing the general arrangement of fins  16 . 
     Prior to the present disclosure it was believed and feared that using explosives, including detcord, would damage the HRSG tubes because the fins  16  would be bent, damaged, and the efficiency of the heat transfer negatively impacted. The present disclosure unexpectedly shows that properly arranged and exploded explosive subassembly  20  in combination with a pressurized air subassembly  22  will clean HRSG finned-tubing more efficiently and more thoroughly than prior art systems. 
       FIG.  4    shows a top view inside an HRSG facility  24  that contains a plurality of tube banks  12  with an example explosive subassembly  20  and an example pressurized air subassembly  24  positioned between and adjacent banks  12  of HRSG finned-tubing. Each ‘x’  26  denotes a possible position for suspending the subassemblies  20 ,  22  to clean the banks  12 . The subassemblies may be partially assembled outside the facility  24 , where there is more room and assembly is more convenient. The assembled or partially assembled subassemblies may then be moved inside facility  24  through any available door  28 . 
       FIG.  5    is a partial elevation taken along line  5 - 5  of  FIG.  4   , showing an end view of the example explosive subsystem  20 . Referring to  FIGS.  4  and  5   , the explosive subsystem  20  may include a pair of elongated rods  30 , a plurality of detcords  32 , of essentially equal length and with an explosive grain loading of 18-50 grains per foot, and a detonation delay assembly  34 . Opposite ends of each detcord  32  are attached to each of the elongated rods  30 , in a generally uniformly spaced manner, forming a plurality of essentially parallel straight lengths of detcord  32  (best shown in  FIG.  7   ) when at least one of the rods  30  is suspended adjacent a bank  12  of HRSG finned-tubing, as shown. The detcords  32  may be attached to rods  30  by any acceptable manner, such as tape, fasteners, ties, etc. The detonation delay assembly  34  is connected to each length of detcord  32  such that each detcord  32  explodes in sequence with a predetermined delay between each explosion. 
     Blast waves from the detcords  32  cause dislodgement of rust scale and other fouling on the fins  16 . The fins  16  are durable, but also delicate at the same time. Replacing damaged tubes  10  is expensive and results in costly down time for the HRSG facility. A delay between each detcord explosion allows the pressure wave of each explosion to dissipate adequately before the next explosion, thus aiding in preventing damage to the fins by excessive blast wave pressure. The delay between explosions depends on the grain load of each detcord  32 , the spacing between detcords  32  (typically 12 inches), and the spacing between the detcord  32  and the banks  12  (typically 12 inches). The detonation delays are typically 5-25 milliseconds. 
       FIG.  5    also shows a balcony or scaffold  36  (not shown in  FIG.  4    for clarity), that is typically a part of facility  24 , and from which a pair of ropes  38  are suspended. Ropes  38  may be attached to one of the rods  30  to suspend and straighten each detcord  32 .  FIG.  7    shows a partial elevation of explosive subsystem  20  suspended by a rod  30 . Bank  12  is not shown in  FIG.  7    for clarity of showing the details of explosive subsystem  20 . It has been found that placing detcords  32  approximately 12 inches from a bank  12  provides safe and effective dislodgement of fouling from fins  16  without damaging fins  16 . 
       FIG.  6    is a partial elevation taken along line  6 - 6  of  FIG.  4   , showing an end view of pressurized air subsystem  22 . Referring to  FIGS.  4 ,  6 , and  8   , the pressurized air subsystem  22  may include an elongated beam  40 , a transport assembly  42  operably coupled to the elongated beam  40  for reciprocal movement (as shown by arrow  44  in  FIG.  8   ) along a portion of a length of the beam  40 , a pressurized air blower assembly  46  operably coupled to the transport assembly  42 , and a suspension assembly  48  suspends the elongated beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  adjacent the bank  12  of HRSG finned-tubing after the detcords  32  have been exploded.  FIG.  6    also shows the balcony or scaffold  36  that is typically a part of facility  24 , upon which suspension assembly  48  is mounted. Suspension assembly  48  may further include a pair of tripods  50  (only one tripod shown) supporting winches  52  having cables  54  from which suspension assembly  22  is suspended. The pair a winches  52  (only one shown) may be mounted above the bank  12  of HRSG finned-tubing and each winch  52  is connected to opposing ends of the elongated beam  40 . The transport assembly  42  moves the pressurized air blower assembly  46  along a portion of the beam at least once as the pressurized air blower assembly  46  directs pressurized air towards the bank  12  of HRSG finned-tubing. The suspension assembly  48  moves the suspended elongated beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  up or down (as indicated by arrow  56  of  FIG.  8   ) after the transport assembly  42  and pressurized air blower assembly  46  have moved along the portion of the beam length at least once, so that a next portion of the bank  12  of HRSG finned-tubing may be cleaned by pressurized air. 
     For a typical HRSG facility the rods  30  are at least 24 feet long, each of the detcords  32  are more than 60 feet long, the spacing between each detcord  32  is approximately 12 inches, the spacing between the detcords  32  and the bank  12  of HRSG finned-tubing is approximately 12 inches, the predetermined delay between each explosion is between 5-25 milliseconds, and the elongated beam  40  is at least 24 feet long. The beam  40  may be an aluminum four inch box beam or other beam of similar size and strength to support the transport assembly  42  and the pressurized air blower assembly  46 . 
     The transport assembly  42 , best seen in  FIG.  9   , may include a drive motor  60  connected to a set of drive wheels  62  for moving the transport assembly  42  back and forth along the elongated beam  40 . The transport assembly  42  may move along the elongated beam  40  at a rate of 1-12 inches per minute. The transport assembly  42  may further include a bracket  64  that may be conveniently attached to motor  60  with a pair of fast clamps  66  (only one clamp shown). Bracket  64  acts as a guide for wheels  62  and provides structure for operably coupling to the pressurized air blower assembly  46 . In the example shown motor  60  is a pneumatic motor powered by compressed air (source not shown) delivered via drive hoses  61 ,  63  connected to controller  100  (described in detail below). During operation, compressed air from drive hose  61  causes the motor  60  to rotate is a first direction to drive wheels  62  in a first direction across beam  40 . When transport assembly contacts a limit switch  102  or  104 , controller  100  (discussed below with respect to  FIG.  11   ) closes off the compressed air to drive hose  61  and supplies compressed air to drive hose  63  to cause a reversal of motor  60  and drive wheels  62  across beam  40  in an opposite direction. It is noted that motor  60  and the associated controls may be any type of suitable motor and controls, such as electrical, hydraulic, etc. 
     Referring to  FIGS.  8 - 10   , the pressurized air blower assembly  46  may include an inlet  68  for receiving pressurized air, and at least one outlet nozzle  70  for directing the pressurized air towards the bank  12  of HRSG finned-tubing. The pressurized air blower assembly  46  may deliver a volume of air between 250-1600 cubic-feet per minute. A pressure produced at the at least one outlet nozzle  70  may be 100-600 pounds per square-inch. The pressurized air blower assembly  46  may further include a motor  72  for oscillating the at least one outlet nozzle  70  during use. The at least one outlet nozzle  70  may be positioned approximately 4 inches from the bank  12  of HRSG finned-tubing. The motor  72  of the present example may be pneumatic and may be powered by pressurized air via hose  65 . Of course, motor  72  may be any type of suitable motor, such as electric, hydraulic, etc. The motor  72  causes the pipe  67  to rotate back and forth, as indicated by arrow  69 . 
     The pressurized air blower assembly  46  may further include at least a second outlet nozzle  74  for directing the pressurized air in an opposite direction from the at least one nozzle  70  and towards another bank  12  of HRSG finned-tubing. Still further, the pressurized air blower assembly  46  may include a third outlet nozzle  76  adjacent the at least one outlet nozzle  70  and a fourth outlet nozzle  78  adjacent the second outlet nozzle  74 . 
     Pressurized air flows into assembly  46 , as indicated by arrow  78 . Assembly  46  in operation is fully enclosed and relatively airtight such that the pressurized air from inlet  68  is forced into intake  80 , as indicated by arrows  82 , and through pipe  67  and nozzles  70 ,  74 ,  76 ,  78 . As assembly  46  moves, motor  72  causes pipe  67  to rotate in a first direction via cooperation between gear plates  84 ,  86 . Stop post  88 , attached to pipe  67 , contacting a poppet valve  90 ,  91  (e.g. available from Parker Hannifin Corporation) causes 3-way, 2-position valve  92  to switch the supply of compressed air to motor  72  causing the rotation of the motor  72  and pipe  67  to reverse. The pressurized air blower assembly  46  operates by receiving pressurized air through inlet  68  that is connected to an air compressor (not shown for convenience), such as a 1300H Sullair® air compressor. 
     Preferably, the transport assembly  42  moves the pressurized air blower assembly  46  along the portion of the beam  40  length twice before the suspension assembly  48  moves the suspended elongated beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  up or down. The suspension assembly  48  may move the suspended elongated beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  up or down 1-3 inches. 
     Referring to  FIG.  10    the pressurized air blower assembly  46  operates by receiving pressurized air through inlet  68  that is connected to an air compressor (not shown for convenience), such as a 1300H Sullair® air compressor. 
     An example cleaning system may further include an automatic control  100  (see  FIG.  11   ) having a first limit switch  102  (shown in  FIG.  8   ) connected to the elongated beam  40  for causing the transport assembly  42  to reverse direction once the transport assembly  42  contacts the first limit switch  102  and a second limit switch  104  connected to the elongated beam  40  for causing the suspension assembly  48  to move the suspended elongated beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  and causing the transport assembly  42  to again reverse direction once the transport assembly  42  contacts the second limit switch  104 . The automatic control  100  may further include a manual control for over-riding the automatic control  100 . 
     The example cleaning system described above may be used in a method of cleaning HRSGs. The method may include suspending at least one elongated rod  30  adjacent a bank  12  of HRSG finned-tubing such that a plurality of generally uniformly spaced detcords  32 , attached to the rod  30 , form essentially parallel straight lengths of detcords  32 , each detcord  32  having an explosive grain loading of 18-50 grains per foot. 
     Next, exploding each detcord  32  in a sequence where a detonation delay assembly  34  attached to each of the plurality of detcords  32  creates a predetermined delay between each detcord explosion. Then, after the detcords  32  are exploded, suspending an elongated beam  40 , having a transport assembly  42  and a pressurized air blower assembly  46  operably coupled to the elongated beam  40 , adjacent the bank  12  of HRSG finned-tubing. Next, moving the pressurized air blower assembly  46 , with the transport assembly  42 , along a portion of the beam  40  as the pressurized air blower assembly  46  directs pressurized air towards the bank  12  of HRSG finned-tubing. 
     Next, moving the beam  40 , the transport assembly  42 , and the pressurized air blower assembly  46  up or down, after the pressurized air assembly  46  has moved along the portion of the beam  40 , so that a next portion of the bank  12  of HRSG finned-tubing may be cleaned by pressurized air. 
     The winches  52  may each be 1000 pound pneumatic winches (with a line speed of 43 feet per minute at 90 pounds per square inch of air pressure) and the winch cables  54  may be attached to the beam  40  via any acceptable fasteners, such as eye-bolts attached to each end of the beam  40 . The distance the suspension assembly  48  moves the beam  40  may depend on the amount of fouling to be dislodged from the fins  16 , the air pressure generated, and the dispersion pattern created by outlet nozzles  70 ,  74 - 78 . Likewise, the rate at which the transport assembly  42  moves along beam  40  may depend on the condition of fins  16 , the air pressure generated, and the dispersion pattern of the outlet nozzles. 
     The pressurized air blower assembly  46  may include a motor  72  oscillating the outlet nozzles. The motor  72  may create about 55 foot-pounds of torque. 
     The pressurized air subsystem  22  may be run automatically as described above or manually. The automatic control  100 , shown in  FIG.  11   , may be connected to the pressurized air subsystem  22 . The control  100  may be connected to a source of pressurized air, (not shown for convenience) via hoses  106 ,  108  to a housing  101 . Manual control of the direction of travel for the transport assembly  42 , allows a user to override the automatic control via buttons  110 ,  112  on solenoid valve  114  (e.g. a 5-port, 4-way, 3-position double solenoid available from NITRA®). 
     Solenoid valve  114  controls the direction of travel of transport assembly  42  by switching the compressed air supply between lines  116 ,  118  that are connected to hoses  61  and  63 , as shown. Solenoid  114  is controlled by the timer  120  and inputs from limit switches  102 ,  104  that are received via cables  122 ,  124 . The inputs from limit switches cause the latching relay  126  to send signals causing solenoid  114  to switch the air supply from one of lines  116 ,  118  to the other line, thus reversing the travel direction. Control  100  receives electrical power via power cable  128  and a 12-volt power inverter  130 . The timer  120  may control the time of travel for travel assembly  42  and/or a duration that the travel assembly pauses before moving again after beam  40  is raised/lowered. 
     The motor  72  rotation direction and speed of oscillation is controlled by the combination of regulator  132  and the on/off switch valve  134 . Pressurized air is received through line  136  and delivered to hose  65  via line  138 . 
     The winches  52  (shown in  FIG.  6   ) are controlled by solenoid valve  140 , which may be the same type valve as solenoid  114 . Compressed air is received by solenoid  140  from hose  108  and switches the compressed air between lines  142 ,  144 , causing the winches to rotate in a desired direction to raise or lower pressurized air subassembly  22 . Hoses  146 ,  148  (not shown in other figures) are connected to winches  52 . Timer  150  may control the time between when the winches  52  are activated to raise/lower the subassembly  22  and an amount of time the winches are activated. A manual override of the winch movement may be achieved via buttons  152 ,  154 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.