Abstract:
An apparatus and method for both removing and installing an elongate member at an elevated location on a piece of equipment. The apparatus includes a cantilivered elongate bed having a lattice work support system that carries a motor driven cable draw works, a portion of the lattice work being removable. One method involves using the apparatus to remove a tube from a pyrolysis furnace. Another method involves using the apparatus to install a tube in a pyrolysis furnace.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to the insertion and/or extraction of a length of tube (pipe) into/from its resting place in a holding apparatus. More particularly this invention relates to the removal of a length of heat exchange tube from a furnace and the insertion of a replacement tube in place of the removed tube. 
         [0003]    2. Description of the Prior Art 
         [0004]    Although for sake of brevity and clarity this invention will be described in relation to a conventional thermal cracking furnace, this invention is applicable to other apparatus that holds one or more lengths of piping (conduit) at an elevated location above the earth&#39;s surface, and, with respect to which apparatus, it is necessary from time to time to remove and replace a length of that piping. 
         [0005]    Thermal cracking of hydrocarbons is a petrochemical process that is widely used to produce olefins such as ethylene, propylene, butenes, butadiene, and aromatics such as benzene, toluene, and xylenes. 
         [0006]    An olefin production plant is generally composed of a cracking unit and a hydrocarbons unit. 
         [0007]    In the cracking unit a hydrocarbonaceous feedstock such as ethane, naphtha, gas oil, or other fractions of whole crude oil is mixed with steam which serves as a diluent to keep the hydrocarbon molecules separated. This mixture, after preheating, is subjected to hydrocarbon thermal cracking using elevated temperatures (1,450 to 1,550 degrees Fahrenheit or F.) in a pyrolysis furnace (steam cracker or cracker). This thermal cracking process is carried out without the aid of any catalyst. 
         [0008]    The cracked product effluent of the pyrolysis furnace (furnace) contains hot, gaseous hydrocarbons of great variety (from 1 to 35 carbon atoms per molecule, or C1 to C35 inclusive, both saturated and unsaturated). This product contains aliphatics (alkanes and alkenes), alicyclics (cyclanes, cyclenes, and cyclodienes), aromatics, and molecular hydrogen (hydrogen). 
         [0009]    This furnace product is then subjected to further processing in the cracking unit to produce, as products of the olefin plant, various, separate and individual product streams such as hydrogen, ethylene, propylene, fuel oil, and pyrolysis gasoline. After the separation of these individual streams, the remaining cracked product contains essentially C4 hydrocarbons and heavier. This remainder is fed to a debutanizer wherein a crude C4 stream is separated as overhead while a C5 and heavier stream is removed as a bottoms product. 
         [0010]    The C4 stream can contain varying amounts of n-butane, isobutane, 1-butene, 2-butenes (both cis and trans isomers), isobutylene, acetylenes, and diolefins such as butadiene (both cis and trans isomers). 
         [0011]    The C5 stream can contain pentanes, pentenes, hexanes, hexenes, and aromatics such as benzene, toluene, and xylenes. 
         [0012]    The C4 and C5 streams are further processed in the hydrocarbons unit for the separation of other individual product streams such as butenes, butadiene, benzene, toluene, and the like. 
         [0013]    The heart of the cracking plant process is the pyrolysis furnace (furnace). Such furnaces are well known, and are composed of a lower, upstanding radiant heating (cracking) section surmounted by an upper, upstanding convection (preheating) heating section. These two sections are connected in a fluid communication manner by way of an offset (cross-over) section that conveys hot combustion gases (flue gas) from the interior of the radiant section up through the cross-over into the interior of the convection section without exposing the interior of the convection section to radiant heating. These furnaces are hundreds of feet in height, so the convection section is elevated a substantial distance, e.g., 100 feet or more, above the surface of the earth. 
         [0014]    The radiant section and convection section each contains a sinusoidal series of spaced apart, straight, elongate tube lengths. The elongate tube lengths are oriented essentially vertically in the radiant section, and essentially horizontally in the convection section. The elongate tubes were initially individual tubes that were joined to one another at their opposing ends with 180 degree U-tube fittings known as “bends,” see  FIG. 5 . Thus, for example, in the radiant section, a U-tube bend connects two side-by-side (adjacent) individual pieces of elongate tubes at their upper adjacent ends thereby to establish fluid communication from inside one tube to inside the adjacent tube. At the opposing lower ends of these two tubes, additional U-bends connect each tube to the lower end of an adjacent tube. By use of the U-bends, a plurality of straight, elongate tubes are connected to one another to form a sinusoidal assemblage of straight tubes connected by U-bends. This way, feed material introduced into a first end of the radiant tube assembly follows a unitary sinusoidal path through the interior of the assembly (all the tubes and connecting bends) until it reaches the far end of the assembly, at which time it exits the assembly as the cracked product effluent aforesaid. 
         [0015]    Although, in the case of a cracking furnace, the elongate tubes in the radiant section assembly are normally carried inside the furnace in an essentially vertical orientation, while the elongate tubes in the convection section assembly are carried in an essentially horizontal orientation, this invention is useful in removing and inserting not only horizontal tube lengths, but also vertical tube lengths that have first been moved to a horizontal orientation. This invention is particularly useful in removing and inserting convection section tubes that are already disposed in the furnace in an essentially horizontal orientation. 
         [0016]    The cracking feed passing through the interior of the sinusoidal radiant tubing assembly is indirectly heated by way of burners fired inside the radiant section of the furnace, but outside the radiant tubing assembly. The radiant tubing assembly is exposed to the flames from these burners, and is thereby heated to the desired cracking temperature for the particular cracking feed that is passing through the inside of this tubing assembly. 
         [0017]    Hot combustion gas passes from inside the radiant section, through the cross-over, and into the interior of the convection section wherein it indirectly preheats the cracking feed passing through the interior of the convection section tubing assembly. 
         [0018]    From time to time an individual length of elongate tube in the convection section assembly becomes plugged, corroded, or otherwise degraded to the point where it is necessary to replace that length of tube even though the horizontal elongate tubes adjacent (over and/or under) to the worn tube do not require replacement. When this occurs, the U-bends at either end of the worn length of tube must be removed, the worn length extracted from inside the furnace, a new tube length inserted into the furnace in place of the worn length, and the U-bends re-attached to the new length and its adjacent (over and under) lengths of tubing. This procedure has to be accomplished hundreds of feet in the air. 
         [0019]    The convection tubes are supported by a pair of cradles that are spaced apart along the length of the tube. These cradles are fixed to the furnace itself so that an individual piece of tubing, once freed of the U-bends that were fixed to its opposing ends, can be slipped out of its cradle, and a new piece of tubing inserted into that same cradle. Since an individual length of tubing can be essentially a carbon steel pipe 30 feet in length, the trick is to deftly and safely remove and replace such a long, heavy object from a location high up in the air. 
         [0020]    This invention provides an admirable solution for this problematic mid-air procedure. 
       SUMMARY OF THE INVENTION 
       [0021]    This invention provides apparatus whereby the length of worn tubing is pulled from its cradle on to a suspended platform that carries a lattice work support holding a reversible cable drawing mechanism, a part of the lattice work support being removable to allow the apparatus to be deployed around existing equipment that would otherwise prevent the apparatus from being used in the intended manner. 
         [0022]    This invention also provides methods for extracting and inserting a tube length using the aforesaid apparatus while suspended high above the earth&#39;s surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a plan view of one embodiment of apparatus within this invention. 
           [0024]      FIG. 2  shows a side view of the apparatus of  FIG. 1 . 
           [0025]      FIG. 3  shows an end view of the apparatus of  FIG. 1 . 
           [0026]      FIG. 4  shows an end view of the apparatus of  FIG. 1  with a portion of its lattice work support removed to avoid interfering equipment. 
           [0027]      FIG. 5  shows a side view of the apparatus of  FIG. 1  when used, pursuant to the method of this invention, to extract a worn tube length from its holding cradles. 
           [0028]      FIG. 6  shows a side view of the apparatus of  FIG. 1  when used, pursuant to the method of this invention, to insert a tube length into its holding cradles. 
           [0029]      FIG. 7  shows a plan view of the apparatus of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]      FIG. 1  shows platform assembly  1  having an elongate, open bed  2  whose upper surface is shown in this Figure. This bed  2  can be, for example, a wide-flange I-beam having a 24 inch web width and 7 inch deep sides (sides  3  and  4  of this Figure) on the opposing longitudinal sides of the web. In the case of a furnace tube extraction platform, bed  2 , the web of the I-beam, can be 24 inches wide and 40 feet long in order to accommodate furnace tubes having a longitudinal length of at least 30 feet. The upstanding, opposing sides  3  and  4  of bed  2 , i.e., the 7 inch deep sides of the I-beam, have their upper surfaces showing in this Figure. 
         [0031]    Platform  1  has opposing ends  9  and  10  at which are carried, in apertures  5  and  6 , rotating sheaves  7  and  8  so that a cable (rope, steel, or otherwise) can be passed through apertures  5  and  6  from below the lower surface of bed  2  (see  FIG. 2 ) to its upper surface that is shown in this Figure. 
         [0032]    Platform  1  also carries spaced apart, transverse members  16  and  17  that extend beyond both sides of bed  2  and terminate in platform lifting lugs  14 . Lugs  14  are used to lift the entire assembly into the air by way of cables attached to each such lug (see  FIG. 2 ) and to the lifting cable of a conventional crane. 
         [0033]    Platform  1  carries an extension member  11  on the under side  23  of bed  2 . Normally end  10  of platform  1  will be moved into abutment with the outside of the furnace (not shown, see  FIG. 5 ) from which a tube is to be extracted. However, if existing equipment outside the furnace prevents the movement of end  10  into physical contact with the outside wall of the furnace, extension  11  and its end  12  can be moved longitudinally away from end  10  until far end  12  contacts the outside wall of the furnace. Normally extension  11  is carried entirely under bed  2  against stop  15 , and is pinned in place in a conventional manner.  FIG. 2  shows member  11  partly extended for explanation purposes only. A series of apertures (not shown) can be employed in member  11  to provide flexibility in the length of extension to be employed. Once the desired length is determined for extension  11 , these apertures can be used to pin or otherwise fix member  11  in its extended configuration. 
         [0034]    Upstanding sides  3  and  4  carry front and back guide lugs  13  to which can be attached cables for guiding platform  1  from the earth&#39;s surface. This way end  10  can be gently and precisely guided into contact with the outer furnace wall by personnel standing on the earth&#39;s surface. 
         [0035]    Platform  1  also carries an operating mechanism for controlling the draw works shown in  FIG. 2 . This mechanism is represented by elements  32 ,  33 ,  35 , and  36  which will be described in greater detail hereinafter. The operator can stand on scaffolding adjacent the suspended platform  1  after it has been moved into place against the furnace. The operator will stand within arms reach of element  33 . 
         [0036]      FIG. 2  shows that bed  2  of platform  1  has a lower surface  23  opposing its upper surface. Apertures  5  and  6 , and sheaves  7  and  8  extend through this bed. Sheaves  7  and  8  are shown in exaggerated form for sake of clarity. In actuality, sheaves  7  and  8  would not extend as far above bed  2  and below surface  23  as shown in the Figure. 
         [0037]      FIG. 2  shows lifting lugs  14  to have apertures  20  extending there through for the attachment of lifting cables  21  to the main cable of the crane that is to lift platform  1  up and into contact with the outer wall of the furnace (not shown, see  FIG. 5 ). 
         [0038]    Side  4  carries a lattice work support system composed of floor  25 ; upstanding members  24 ,  37 ,  38 , and  39 ; and re-enforcing cross-members  18 ,  19 ,  46 , and  47 . This leaves an open central space in which is carried, on floor  25 , a conventional cable draw works composed of motor  26  which is operably connected to a cable wind drum  27 . Bed  2  is substantially longer than the lattice work support system so that the length of bed  2  at its end  10  extends well beyond the end  39  of the lattice work support system. This way the cantilevered part of bed  2  having an end at  10  can extend over interfering equipment that is adjacent to the outer wall of the furnace. Bed  2  can be re-enforced as desired to allow the cantilevering of bed  2  a substantial distance beyond the ends of this lattice work support system. 
         [0039]    Motor  26  can be any means for rotating drum  27  in either a clockwise or counterclockwise manner, as desired. Thus, motor  26  could be an internal combustion engine, an electric motor, or a fluid (air, hydraulic, etc.) driven motor. For sake of this description motor  26  will be a pneumatic driven device since plant compressed air is normally available at the furnace. 
         [0040]    Compressed air  34  is passed from the plant into hose  31  which is connected to an emergency cut off switch  30  that is within arms length of the operator. Hose  29  connects this air supply to motor  26  through standard connection chuck  28 . Mechanical linkage  32  extends from handle  33  adjacent the operator to a conventional control mechanism (not shown) on motor  26 . By movement of linkage  32  either forward or backward, as desired, the operator can engage motor  26  with drum  27  to cause that drum to rotate in the desired direction and roll cable (not shown, see  FIGS. 5 and 6 ) onto the drum. Reverse movement of linkage  32  disengages motor  26  from drum  27  causing the drum to stop its rotation. The linkage to the motor can vary widely, and can be electrical or fluid driven rather than mechanical, if desired. The linkage shown in  FIG. 2  is a rod assembly  32  that can be moved forward or backward along side  4  toward or away from motor  26  to activate or de-activate that motor. Linkage  32  is held along side  4  by way of a plurality of eye members  36  fixed to side  4 . A hinge  35  is provided so handle  33  can be moved by the operator away from side  4 . 
         [0041]      FIG. 3  shows an end view of platform  1  looking towards end  10  thereof, i.e., the end the furnace wall would see. In this Figure and the remaining Figures, certain elements shown in  FIGS. 1 and 2  are not shown only for the sake of clarity, and the elements not shown are to be considered to be part of the apparatus shown in  FIGS. 3 through 7 . 
         [0042]      FIG. 3  shows drum  27  carrying cable  40  rolled thereon. Cable  40  is used to remove or insert a tube length relative to the furnace. Drum  40  is conventionally supported in a rotatable manner by members  42  and  43 , and is linked by way of drive chain  45  to drive shaft  44  of motor  26  as is well known in the art. Other forms of draw works arrangements are well known in the art and are within the scope of this invention. 
         [0043]      FIG. 3  further shows the construction of the supporting lattice work of  FIG. 2 . Upstanding members  50  and  51  of this lattice work support are fixed (welded, bolted, riveted, etc.) to member  17 , sides  3  and  4  of web  2 , and floor  25 . Members  52  and  53  are fixed to member  17 , and carry flanges  54  and  56 , respectively. Upstanding members  58  and  59  are fixed to floor extension members  60  and  61 , and are re-enforced by cross-members  66  and  67 . Members  58  and  59  carry, respectively, bolt flanges  55  and  57  that mate with bolt flanges  54  and  56 . Members  60  and  61  carry, respectively, bolt flanges  62  and  65  that mate with bolt flanges  63  and  64 . Flanges  63  and  64  are carried by extensions  68  and  69  of floor  25 . By this arrangement, the lower, elongate, corner sub-assemblies represented, in brief, by elements  58  and  60  on the one hand, and by elements  59  and  61  on the other hand, and extending for the entire length of the lattice work support assembly from member  38  to member  39  (see  FIG. 2 ) are removably attached to the overall lattice work support system shown in  FIGS. 2 and 3 . 
         [0044]      FIG. 4  shows the apparatus of  FIG. 3  wherein the sub-assembly represented by elements  58  and  60  has been removed in its entirety to allow platform  1  to be moved alongside of interfering elongate pipe  70 . This way platform  1  can be moved into physical contact with the furnace (not shown, see  FIG. 5 ) with out having to remove pipe  70 . This Figure also shows the sub-assembly represented by elements  59  and  61  while in the process of being removed from the lattice work support, as shown by arrow  48 , to allow that side of platform  1  also to avoid another piece of interfering equipment (not shown). 
         [0045]    In operation, the U-bends on either end of a worn length of pipe to be removed from the furnace are themselves separated from that length of worn pipe and the pipes adjacent (over and under) to the worn pipe. A section of the outer wall of the furnace adjacent the worn pipe is removed to form an opening in the furnace wall. Platform  1  is then raised by a crane into place along side and in abutment with the furnace just below this opening, and in longitudinal alignment with the worn pipe to be removed. Cable  40  is passed from drum  27  under bottom surface  23 , around sheave  7 , over web  2 , and fixed to the nearest end of the worn pipe. The operator then activates motor  26  to re-wind cable  40  onto drum  27  thereby extracting the worn pipe from its cradles and on to the upper surface of bed  2 . Thereafter, platform  1  is lowered to the earth&#39;s surface for disposal of the worn length of pipe. The process is then reversed in that a new length of pipe is disposed on the upper surface of bed  2 , and platform  1  raised back to where the worn pipe was earlier removed. This time, cable  40  is passed around sheave  8  and attached to the end of the new pipe that is furthest from the furnace. The operator then activates motor  26  to re-wind cable  40  onto drum  27  thereby pulling the new pipe into the cradles from which the worn pipe was removed. Thereafter the U-bends that were earlier removed are re-attached to the new pipe and its adjacent pipe lengths. 
         [0046]      FIG. 5  shows platform  1  when that platform is in place against the outer wall  74  of the furnace, and in the process of removing a worn pipe length  76  from the interior of the furnace. Downwardly extending U-bend  71  was earlier removed from pipe  76  and from its adjacent lower pipe  72  that is supported by its own cradles, e.g., cradle  73 . An upwardly extending U-bend (not shown) similar to bend  71  was also earlier removed from end  84  of pipe  76  and from its adjacent upper pipe (not shown). This leaves pipe  76  resting in an unattached manner in its support cradles  75  and  77 . Cable  40  has been passed under bottom  23  through aperture  5 , around sheave  7 , and along the upper surface of bed  2  to end  74  of pipe  76 . An aperture  78  is formed through pipe  76  and a clevis  79  fixed therein. Cable  40  is looped at  80  through clevis  79  and fixed to itself by a cable clamp  81 . By movement of linkage  32 , the operator activates motor  26  to turn drum  27  clockwise and re-wind cable  40  onto drum  27  thereby pulling tube  76  out of cradles  75  and  77 , as shown by arrow  82 , and on to surface  2 . Thereafter platform  1  is lowered to the earth&#39;s surface for removal of pipe  76  there from. 
         [0047]      FIG. 6  shows platform  1  when in the process of installing a new length of pipe  85  in the cradles  75  and  76  that were vacated by the method shown in  FIG. 5 . In the installation method, cable  40  is passed below bottom  23  through aperture  6 , around sheave  8 , and over the upper surface of bed  2  to the far end of new pipe  85  where it is fixed to a strap  86  that is wrapped around the outer periphery of pipe  85 . By movement of linkage  32 , the operator activates motor  26  to turn drum  27  clockwise and re-wind cable  40  onto drum  27  thereby pulling pipe  85  off of bed  2  and through the vacated apertures  88  and  89  in cradles  75  and  76 , respectively, as shown by arrow  87 . Thereafter the U-bends that were earlier removed from worn pipe  76  are attached to new pipe  85  and its adjacent upper and lower pipes in sinusoidal form. 
         [0048]      FIG. 7  shows a top view of platform  1  when in use as shown in  FIG. 6 . This Figure better shows that strap  86  is wrapped at least twice around the outer periphery of pipe  85 . Cable  40  is looped around one of the strap wraps  86  and then clamped to itself by a cable clamp  89 . This way, when cable  40  is drawn downwardly around sheave  8  by operation of motor  26 , pipe  85  is pulled toward cradle  75  as shown by arrow  87 . 
         [0049]    Thus, it can be seen that the apparatus of this invention with its cantilevered bed  2 , removable sub-assemblies, and extension  11  provides unparalleled flexibility for maneuvering platform  1  around, over and under various and sundry equipment that is invariably located along the height and breadth of a furnace.