Patent application title: Tube handling method and apparatus
Alfredo R. Sanchez (Corpus Christi, TX, US)
IPC8 Class: AC10G920FI
Class name: Chemical conversion of hydrocarbons cracking with heating in tubular confined stream
Publication date: 2009-04-30
Patent application number: 20090107888
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.
1. Apparatus for longitudinally moving an elongate member, said apparatus
comprising an elongate bed having an open top and an open bottom and
opposing ends, said bed having upstanding sides, said bed carrying
sheaves at its opposing ends, said bed carrying a lattice work support
system attached to said sides and adjacent to said open bottom, said
lattice work support system being substantially shorter longitudinally
than said bed, said lattice work support system carrying a motor powered
cable draw works, said lattice work support system having lower elongate
corner sub-assemblies that are removable from the remaining portion of
said lattice work support system that carries said motor and cable draw
2. The apparatus of claim 1 wherein said bed carries lifting lugs for elevating said bed, and cable eye members for remotely guiding said bed.
3. The apparatus of claim 1 wherein said bed carries at least one telescoping extension member adjacent at least one of its ends.
4. The apparatus of claim 1 wherein said motor is one of internal combustion, electric, and fluid driven.
5. A method for removing an essentially horizontally disposed, elongate tube from an elevated location on a furnace, said tube having opposing ends and being slidably carried in a cradle in said furnace with fittings fixed to said opposing ends, said method comprising removing said fittings from said opposing ends of said tube, raising the apparatus of claim 1 to the location of one of said opposing ends of said tube, abutting the apparatus of claim 1 to said furnace, passing cable from said draw works under said bed over said sheave that is furthest removed from said furnace and up to the end of said tube that is closest to said apparatus, fixing said cable to said tube, and pulling said tube from said cradle on to said apparatus by operation of said motor to re-wind said cable on to said draw works.
6. A method for inserting an essentially horizontally disposed, elongate tube into a furnace at an elevated location on said furnace, said tube having opposing ends, said furnace carrying a cradle for slidably receiving and holding said tube, said method comprising disposing said tube on the apparatus of claim 1 and raising said apparatus to the location of said furnace cradle, abutting one of said opposing ends of said bed to said furnace, passing cable from said draw works under said bed over said sheave that is nearest to said furnace and up to the end of said tube that is furthest from said furnace, fixing said cable to said tube, and pulling said tube from said apparatus into said furnace by operation of said motor to re-wind said cable on to said draw works.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Prior Art
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's surface, and, with respect to which apparatus, it is necessary from time to time to remove and replace a length of that piping.
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.
An olefin production plant is generally composed of a cracking unit and a hydrocarbons unit.
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.
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).
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.
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).
The C5 stream can contain pentanes, pentenes, hexanes, hexenes, and aromatics such as benzene, toluene, and xylenes.
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.
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.
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.
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.
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.
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.
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.
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.
This invention provides an admirable solution for this problematic mid-air procedure.
SUMMARY OF THE INVENTION
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.
This invention also provides methods for extracting and inserting a tube length using the aforesaid apparatus while suspended high above the earth's surface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a plan view of one embodiment of apparatus within this invention.
FIG. 2 shows a side view of the apparatus of FIG. 1.
FIG. 3 shows an end view of the apparatus of FIG. 1.
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.
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.
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.
FIG. 7 shows a plan view of the apparatus of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
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.
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.
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.
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.
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'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's surface.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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).
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'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.
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's surface for removal of pipe 76 there from.
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.
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.
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.