Tube handling method and apparatus
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. 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
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 INVENTIONThis 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.
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
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
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
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
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
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.
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.
Claims
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 works.
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.
Type: Application
Filed: Oct 29, 2007
Publication Date: Apr 30, 2009
Inventor: Alfredo R. Sanchez (Corpus Christi, TX)
Application Number: 11/978,297
International Classification: C10G 9/20 (20060101);