Abstract:
A coke drum bottom head removal system and method for deheading the bottom head cover of a coke drum comprises a carriage that is positionable beneath the bottom head cover, and a cart mounted to the carriage. Several clamps vertically mounted to the cart are positionable in a closed position, in which the clamps apply a compressive force that maintains substantially fluid tight engagement between the bottom head cover and bottom head flange, and an opened position, in which the clamps allow a limited spacing between the bottom head cover and the bottom head flange. A plurality of supports mounted to the cart support the bottom head cover once the fasteners coupling the bottom head cover to the bottom head flange are removed and the clamps are in the opened position. The system can be remotely operated to enhance operator safety when the bottom head cover is removed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to the removal of head covers from coke drums, and more particularly to devices and methods for the safe removal of bottom head covers from coke drums.  
           [0003]    2. Description of the Related Art  
           [0004]    Coke drums are vertical pressure vessels used in the refining of crude oil for the coking of various heavy hydrocarbon materials. The coking process generally involves placing petroleum residues inside the coke drum and cracking them into light products and a solid coke residue. This is accomplished by exposing the residues to elevated temperatures (typically approximately 900° F.) and pressures (typically approximately 10 to 30 psig).  
           [0005]    Coke is a hard, coal-like substance which builds up inside the coke drum during the coking process. Once the coke drum is full of coke, the coke drum is “decoked” by introducing steam and water into the coke drum to quench the temperature to approximately 200° F. The quench water is then drained via piping to a storage tank. After draining the quench water, the top head and bottom head of the coke drum are removed (or “deheaded”) to provide access to the inside of the coke drum. The coke is then cut away using high pressure hydraulic drilling, permitting it to fall from the coke drum into a chute positioned at the bottom opening to direct the removed coke to a desired location.  
           [0006]    The loosening and removal of the bottom head entails risk to personnel in the vicinity of the bottom head during deheading. In this regard, the quench water, hydrocarbon material, and coke remaining inside the coke drum are still quite hot after the quench water is drained. Accordingly, when the residual quench water is drained through the loosened bottom head cover, the hot quench water and steam pose a risk to personnel in the area. In addition, the quench water, hydrocarbon material and loose coke resting on the bottom head cover are quite heavy. The weight of these materials can result in the failure of the equipment or other structures supporting the bottom head cover as it is removed, thereby posing an additional potential risk.  
           [0007]    Accordingly, a need has existed for a device and method for the removal of the bottom head cover of a coke drum that is relatively easy to use, reduces risks and maximizes the safety for the operator. The present invention satisfies these and other needs and provides further related advantages.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a coke drum bottom head removal system for removing a bottom head attached by fasteners to a bottom head flange of a coke drum. The system comprises a carriage that is positionable beneath the bottom head cover, and a cart mounted on the carriage that can be moved vertically between a raised position and a lowered position. The system also comprises a plurality of clamps and supports mounted on the cart. In accordance with the invention the system is operable from a remote location to reduce risks and maximize safety for the operator.  
           [0009]    In the preferred embodiment, the carriage is suspended by trolleys from a pair of overhead tracks positioned along opposite sides of the bottom head cover. The cart is preferably suspended from an upper portion of the carriage by a plurality of hoists. These hoists are operated to raise and lower the cart with respect to the carriage when the carriage is positioned beneath the bottom head cover.  
           [0010]    Each of the clamps mounted on the cart comprises an upper clamping surface, such as a fixed jaw, adapted for engagement with the bottom head flange. Each clamp also comprises a lower clamping surface, such as a movable ram, adapted for engagement with the bottom head cover. The clamps are actuated between a closed position, in which the clamping surfaces apply a compressive force that maintains a substantially tight fluid engagement between the bottom head flange and the bottom head cover upon removal of the fasteners, and an opened position, in which the clamping surfaces are moved apart to permit a limited spacing between the bottom head flange and the bottom head cover when the fasteners are removed.  
           [0011]    In use, the carriage is positioned beneath the bottom head cover, with the cart in the lowered position. A plurality of the fasteners connecting the bottom head cover to the bottom head flange are removed, exposing fastener holes. The cart is then moved to the raised position such that the supports are inserted into a plurality of the fastener holes. The clamps are then positioned for engagement with the bottom head cover and the bottom head flange and moved to the closed position.  
           [0012]    With the clamps in the closed position, the remaining fasteners are removed. The compressive force applied by the clamps maintains a substantially fluid tight engagement between the bottom head flange and the bottom head cover when the fasteners are removed. Since the fasteners are removed manually, the clamps ensure operator safety while the fasteners are being removed.  
           [0013]    Once the fasteners are removed, the operator, from a remote location, reduces the compressive force applied by the clamps, moving them to the opened position. This allows the bottom head cover to be lowered onto a support surface of each support. The lowering of the bottom head cover creates a space between the bottom head cover and the bottom head flange through which residual quench water drains.  
           [0014]    When the quench water and other materials in the coke drum have drained, the cart is moved to the lowered position. This disengages the supports from the fastener holes in the bottom head flange, with the bottom head cover remaining on the cart and supported by the supports. The carriage can then be moved to transport the bottom head cover away from the bottom head to permit further decoking of the coke drum.  
           [0015]    Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The accompanying drawings illustrate the invention. In such drawings:  
         [0017]    [0017]FIGS. 1A and 1B are schematic elevational views of a coke drum bottom head removal system embodying the novel features of the present invention.  
         [0018]    [0018]FIG. 2 is a schematic elevational view of certain features of the coke drum bottom head removal system, including a clamp, support, and hydraulic pump.  
         [0019]    [0019]FIG. 3 is a schematic top plan view of the coke drum bottom head removal system, showing the orientation of the clamps and supports in relation to a cart and bottom head cover of the coke drum.  
         [0020]    [0020]FIG. 4 is a schematic illustration of a control panel for use with the coke drum bottom head removal system.  
         [0021]    [0021]FIG. 5 is a schematic elevational view illustrating the bottom head of the coke drum with half its bolts removed and the cart in a lowered position below the bottom head.  
         [0022]    [0022]FIG. 6 is a schematic elevational view illustrating the cart in a raised position, and showing the supports engaged with aligned fastener holes in the bottom head cover and the bottom head flange.  
         [0023]    [0023]FIG. 7 is another schematic elevational view illustrating the bottom head cover and the bottom head flange being compressed together by the clamp.  
         [0024]    [0024]FIG. 8 is another schematic elevational view illustrating the system after the remaining fasteners have been removed from the bottom head cover and bottom head flange.  
         [0025]    [0025]FIG. 9 is another schematic elevational view illustrating the bottom head cover lowered from the bottom head flange and the resulting gap through which materials remaining in the coke drum pass.  
         [0026]    [0026]FIG. 10 is another schematic elevational view showing the clamp released from the bottom head cover to allow complete removal of the bottom head cover from the coke drum. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    As shown in the exemplary drawings, the present invention is embodied in a coke drum bottom head removal unit for removing the bottom head cover of a coke drum. Referring to FIGS. 1A and 1B, a preferred embodiment of the present invention comprises a carriage  10  suspended by a plurality of trolleys  12  coupled to a pair of parallel overhead tracks  20 A and  20 B positioned along opposite sides of a bottom head  30  of a coke drum  32 . The bottom head  30  comprises a bottom head cover  34  fastened to a bottom head flange  36  by a plurality of fasteners, such as bolts  38 , extending through bolt holes  39  positioned along the perimeter of both the bottom head cover  34  and the bottom head flange  36 .  
         [0028]    The carriage  10  has a cart  40 , a plurality of hoists  50 , a plurality of elongated supports  60 , a plurality of clamps  70 , and at least one hydraulic pump  80 . The hoists  50  are fastened to the carriage  10  and to the cart  40 , thereby suspending the cart  40  from the carriage  10 . The supports  60  are fixedly mounted vertically to the cart  40 , the clamps  70  are mounted via rotatable shafts  72  to the cart  40  in a vertical orientation, and the hydraulic pumps  80  are fixedly mounted to the cart  40 . The angular position of each clamp  70  about its rotatable shaft  72  is adjusted by a rotary actuator  73  coupled to each rotatable shaft  72 .  
         [0029]    In the flooring below the bottom head  30  is a chute  90  through which materials removed from the coke drum  32  can be directed to a desired location. The chute  90  is covered by a cover grate  91  when not in use. A control panel  100  (illustrated in FIG. 4) is coupled to one or more of the trolleys  12 , hoists  50 , clamps  70 , rotary actuators  73 , hydraulic pumps  80 , and chute  90 , and most preferably the control panel is coupled to all of these components. The control panel  100  enables the various components of the preferred embodiment of the present invention to be controlled remotely, thereby keeping personnel away from the bottom head  30  during the hazardous stages of the deheading process.  
         [0030]    The plurality of trolleys  12  enable the carriage  10  to be translated along the pair of parallel tracks  20 A,  20 B into position below the bottom head  30 . When not in use, the carriage  10  is translated away from the bottom head  30 , as illustrated in FIG. 1A. In the preferred embodiment, the pair of parallel tracks  20 A,  20 B extends between the bottom heads of two adjacent coke drums. In this way, the carriage  10  can be used to dehead both adjacent coke drums at different times.  
         [0031]    In the preferred embodiment, the plurality of trolleys  12  comprises four pneumatically-actuated trolleys  12 A- 12 D, with two trolleys  12 A,  12 B coupled to one track  20 A, and two trolleys  12 C,  12 D coupled to the other track  20 B. The parallel tracks  20 A,  20 B of the preferred embodiment are steel I-beams securely fastened overhead to a ceiling. The overhead tracks  20 A,  20 B and the trolleys  12 A- 12 D are able to support the combined weight of the carriage  10  and the bottom head cover  34 . The trolleys  12 A- 12 D are positioned substantially symmetrically to evenly bear the weight load of the carriage  10  and the bottom head cover  34 . In other embodiments, the plurality of trolleys  12  may comprise a number of trolleys  12  other than four. In addition, other embodiments may include trolleys  12  that are electrically-actuated or manually-actuated. Persons skilled in the art can recognize that other configurations of trolleys  12  and tracks  20  are compatible with the present invention.  
         [0032]    Electrical power and electronic control signals are supplied to the trolleys  12 , hoists  50 , rotatable shafts  72 , and hydraulic pumps  80  via an electrical cable  14 . Pressurized air to operate the trolleys  12 , hoists  50 , rotary actuators  73 , and hydraulic pumps  80  is provided via a supply air hose  16 , and a return air hose  17 . In the preferred embodiment, the air hoses  16  and  17  are fifty foot recoil nylon hoses, with a ¾″ inner diameter, which are available from Ingersoll-Rand as Item #134-508.  
         [0033]    The electrical cable  14  and the air hoses  16 ,  17  preferably are suspended from a hose trolley  18  which travels along one of the tracks  20 . In the preferred embodiment, the hose trolley  18  has approximately seven segments, and is available from Ingersoll-Rand as Item #7703. The electrical cable  14  and the air hose  16  are festooned from the hose trolley  18  so as to provide adequate slack across the whole range of travel of the carriage  10  between the coke drum  32  and a second coke drum (not shown). It will be appreciated that persons skilled in the art can select other configurations to provide the appropriate electrical, pneumatic and other power supplies to the various components of the present invention.  
         [0034]    The coke drum  32  is a vertically-oriented vessel supported by a platform and frame structure. Coke drums used in petroleum refineries are typically 80 to 100 feet tall and 18 to 30 feet in diameter, tapering down to approximately 4 to 7 feet in diameter in the region of the bottom head  30 . The bottom head cover  34  and bottom head flange  36  are typically 4 to 7 feet in diameter, fastened together by approximately 20 to 60 fasteners or bolts  38 . Between the bottom head cover  34  and the bottom head flange  36  is a seal  33  which helps prevent leakage of material from the inside of the coke drum  32 .  
         [0035]    The bottom head cover  34  includes a lateral pipe  35  used for feeding hydrocarbon material, steam, and water into the coke drum  32 . This lateral pipe  35  is also used to drain hydrocarbon materials and water from the coke drum  32  following the cooling of the temperature and prior to the deheading of the bottom head cover  34 . A pair of lateral pipe flanges  37  are fastened together by fasteners  31 , thereby connecting the lateral pipe  35  to additional piping structures.  
         [0036]    In the preferred embodiment, the cart  40  is suspended from the carriage  10  by four pneumatically-actuated hoists  50  fastened to an upper portion of the carriage  10 . The hoists  50  are able to support the combined weight of the cart  40  and the bottom head cover  34 . The hoists  50  are preferably positioned substantially symmetrically along the perimeter of the carriage  10  and the cart  40  to evenly bear the weight load of the cart  40  and the bottom head cover  34 . By adjusting the hoists  50 , the cart  40  can be placed in a raised position, a lowered position, and a plurality of intermediate positions in relation to the carriage  10 .  
         [0037]    In other embodiments, the plurality of hoists  50  comprises a number of hoists  50  other than four. In addition, other embodiments may include hoists  50  that are electrically-actuated or manually-actuated. Furthermore, in other embodiments, the cart  40  is not suspended from the carriage  10 , but is supported from below by a plurality of pneumatically-actuated jacks fastened to the carriage  10 . By adjusting these jacks, the cart  40  can be placed in the raised position, the lowered position, or the plurality of intermediate positions. Persons skilled in the art can recognize that other configurations of the cart  40  and its mounting to the carriage  10  are compatible with the present invention.  
         [0038]    [0038]FIG. 3 shows a preferred embodiment, in which four supports  60  are vertically mounted to the cart  40 . As further illustrated in FIG. 2, each support  60  has a narrow upper portion  62  and a shelf  64 . When positioned below the bottom head cover  34 , the supports  60  are positioned substantially symmetrically around the perimeter of the bottom head cover  34 . In addition, the upper portion  62  of each support  60  is aligned with a corresponding bolt hole  39  located along the perimeter of the bottom head cover  34  and the bottom head flange  36 .  
         [0039]    After removing the bolts  38 , the supports  60  are aligned with the bolt holes  39 . The cart  40  is then moved to the raised position relative to the carriage  10  to engage the upper portion  62  of each support  60  with the corresponding hole  39  of the bottom head cover  34 . When removed from the bottom head flange  36 , the bottom head cover  34  rests on the shelf  64  of each of the supports  60 . In other embodiments, the plurality of supports  60  comprises a number of supports  60  other than four. Persons skilled in the art can recognize that other configurations of supports  60  are compatible with the present invention.  
         [0040]    In the preferred embodiment, four clamps  70  are vertically mounted to the cart  40  via rotatable shafts  72  and rotary actuators  73 . Each clamp  70  is hydraulically-actuated, and has a first, upper clamping surface or jaw  74  and a second, lower clamping surface or ram  76 , as illustrated in FIG. 2. The rotatable shafts  72  are each rotatable by a rotary actuator  73  which is pneumatically-actuated, thereby rotating each clamp  70  to an engaged position or a disengaged position. In the preferred embodiment, pressurized air is provided to each rotary actuator  73  via a pair of ¼″ NPT pneumatic connections for supply and return. The rotary actuators  73  provide approximately 94° of rotation, and are available from Flo-Tork as Model # A-500. Pressurized hydraulic fluid is provided to each clamp  70  from at least one hydraulic pump  80  via, for example, a 0.38″ I.D. rubber wire-braided hydraulic supply hose. Persons skilled in the art can recognize that other configurations of pneumatic and hydraulic systems are compatible with the present invention.  
         [0041]    When the cart  40  is in the lowered position, the clamps are in the disengaged position to prevent the clamps  70  from hitting the bottom head cover  34  when the cart  40  is raised. Once the cart  40  is in the raised position, rotating a clamp  70  into the engaged position engages the jaw  74  of the clamp  70  with the bottom head flange  36 . As noted above in the disengaged position, the jaw  74  and the ram  76  of each clamp  70  are rotated away from the bottom head cover  34  and bottom head flange  36  to permit vertical movement of the cart  40  without interference.  
         [0042]    Alternatively, in other embodiments, the clamps  70  are vertically mounted to the cart  40  by non-rotatable shafts and translation actuators (not shown). These translation actuators translate the clamps  70  parallel to the upper surface of the bottom head flange  36  from the engaged position to the disengaged position. Furthermore, in other embodiments, the clamps  70  are vertically mounted to the cart  40  by shafts and actuators which provide both rotation and translation to position the clamps  70  in the engaged or disengaged positions.  
         [0043]    By hydraulically actuating a clamp  70 , its ram  76  is extended and any material between the ram  76  and the jaw  74  experiences a compressive force as it is squeezed between the ram  76  and the jaw  74 . By controlling the hydraulic pressure provided to the clamp  70 , the compressive force applied by the ram  76  and the jaw  74  of the clamp  70  can be adjusted from zero to  25  tons. In the preferred embodiment of the present invention, all the rams  76  are provided hydraulic pressure from a single hydraulic system to ensure equal compressive force at each clamp  70 . The sum of the compressive forces applied by the clamps  70  is more than sufficient to fully support the combined weight of the bottom head cover  34  and the contents of the coke drum  32  weighing on the bottom head cover  34 , thus providing a substantially fluid tight engagement preventing the leakage of quench water between the bottom head cover  34  and the bottom head flange  36 .  
         [0044]    As shown in FIG. 3, the clamps  70  preferably are positioned substantially symmetrically along the perimeter of the bottom head cover  34  to evenly bear the weight load of the bottom head cover  34  and the contents of the coke drum  32 . In other embodiments, the plurality of clamps  70  comprises a number of clamps  70  other than four. In addition, other embodiments may include rotatable shafts  72  that are electrically-actuated or manually-actuated. Persons skilled in the art can recognize that other configurations of clamps  70  are compatible with the present invention.  
         [0045]    The two hydraulic pumps  80  of the preferred embodiment are mounted on the cart  40 , and each is covered by a pump shroud  82 . In addition, each hydraulic pump has a 0-10,000 psi hydraulic pressure gauge  83 , which is available from Power Team, Item #9063. Each hydraulic pump  80  is preferably driven by air pressure instead of electricity and is connected to the same pneumatic system as the rotary actuators  73  of the clamps  70 . Driving the hydraulic pumps  80  pneumatically enables the reduction of the cost and complexity of the electrical system. Each hydraulic pump  80  comprises a solenoid valve  84  that is used to control the hydraulic pressure produced by the hydraulic pumps  80 . By providing more than one hydraulic pump  80 , the preferred embodiment of the present invention achieves faster pressurization of the rams  76 , and provides redundancy in the event of failure of one hydraulic pump  80 .  
         [0046]    The chute  90  in the flooring beneath the bottom head  30  provides a conduit through which materials removed from the coke drum  32  can be directed to a desired location. When not in use, the chute  90  is covered by a lightweight cover grate  91  that is removed before the chute  90  is used. Once the bottom head cover  34  is removed from the bottom head  30 , the carriage  10  is moved away from the bottom head  30 , and the cover grate  91  is removed from the chute  90 . A telescoping portion of the chute  90  is then raised to be in proximity to the bottom head  30 . In this way, the chute  90  is able to catch materials from the coke drum  32  and direct these materials to a desired location. To raise and lower the chute  90 , two air-operated hoists are used, the hoists being attached to opposite points on the chute  90  and controlled via buttons on the control panel  100 .  
         [0047]    The preferred embodiment of the present invention utilizes a control panel  100  as illustrated in FIG. 4. By pressing the appropriate buttons of the control panel  100 , an operator can control the various features of the system from a location remote from the bottom head  30 . In other embodiments, other configurations of control panels  100  can be used, including multiple control panels  100  to provide access to some or all of the functions in multiple locations. Control of the position of the trolleys  12  is provided by lighted buttons  101 A-D. By pressing button  101 A, the operator generates signals which correspond to the translation of trolleys  12 A and  12 B in one direction along track  20 A, and button  101 B corresponds to translation of trolleys  12 A and  12 B in the opposite direction along track  20 A.  
         [0048]    Similarly, buttons  101 C and  101 D on the control panel  100  correspond to the translation of trolleys  12 C and  12 D in two directions along the track  20 B. Buttons  102 A-D correspond to raising the four hoists  50  individually, and button  102 E corresponds to raising the four hoists  50  together. Buttons  103 A-D correspond to lowering the four hoists  50  individually, and button  103 E corresponds to lowering the four hoists  50  together. Buttons  104 A-B correspond to raising the chute  90  underneath the coke drum  32 , and buttons  105 A-B correspond to lowering the chute  90 . Buttons  104 C-D and buttons  105 C-D correspond to the same operations for the chute  90  underneath a second coke drum (not shown).  
         [0049]    Button  106 A on the control panel  100  corresponds to rotating the clamps  70  into the engaged position, and button  106 B corresponds to rotating the clamps  70  into the disengaged position. Button  107 A corresponds to closing the clamps  70  by moving the rams  76  toward the jaws  74 , and button  107 B corresponds to opening the clamps  70  by moving the rams  76  away from the jaws  74 . A power-on button  108  and a power-off button  109  are also provided in the preferred embodiment of the present invention. Persons skilled in the art can select other appropriate button styles and control configurations that are compatible with the present invention.  
         [0050]    In the preferred embodiment of the present invention, as illustrated in FIGS.  510 , the deheading of the coke drum  32  begins by cooling the coke drum  32  and its contents, and draining the quench water from the coke drum  32  through the lateral pipe  35 . After the coke drum  32  has been cooled and drained, the bottom head cover  34  is prepared for lowering by removing approximately one-half of the bolts  38  fastening the bottom head cover  34  to the bottom head flange  36 , leaving empty bolt holes  39 . In the preferred embodiment of the present invention, every other bolt  38  around the perimeter of bottom head cover  34  is removed, leaving a sufficient number of bolts  38  to keep the bottom head cover  34  from loosening and thereby leaking material from inside the coke drum  32 .  
         [0051]    The carriage  10  with the cart  40  in its lowered position is then translated along the tracks  20  into position below the bottom head  30 , as illustrated in FIG. 5. The hoists  50  are then actuated to lift the cart  40  into its raised position with the clamps  70  in their disengaged and fully opened position. In the raised position of the cart  40 , as illustrated in FIG. 6, the upper portion  62  of each support  60  engages an empty bolt hole  39  of at least the bottom head cover  34 , with the shelf  64  of each support  60  being spaced approximately one inch below the lower surface of the bottom head cover  34 .  
         [0052]    By operating the rotary actuators  73 , the clamps  70  are then rotated to the engaged position as illustrated in FIG. 6. In this position, the jaw  74  of each clamp  70  is engaged with the top surface of the bottom head flange  36  in proximity to an empty bolt hole  39 . Both the bottom head cover  34  and the bottom head flange  36  are thereby positioned between the jaw  74  and the ram  76  of each clamp  70 . By pressurizing the rams  76  of the clamps  70  by activating the hydraulic pumps  80 , the clamps  70  are closed onto the bottom head cover  34  and bottom head flange  36 , as illustrated in FIG. 7, thereby applying a compressive force pressing the bottom head cover  34  and the bottom head flange  36  tightly together in substantially fluid tight engagement. The hydraulic pumps  80  are operated until the hydraulic pressure reaches its maximum setting. At this maximum setting, the sum of the compressive forces of the clamps  70  is sufficient to support the combined weight of the bottom head cover  34  and the contents of the coke drum  32  weighing on the bottom head cover  34 . In addition, the compressive forces preferably are applied substantially symmetrically around the perimeter of the bottom head cover  34 , as illustrated in FIG. 3.  
         [0053]    With the bottom head cover  34  securely held onto the bottom head flange  36  by the clamps  70 , the remaining bolts  38  can safely be loosened and removed from the bolt holes  39  by personnel without the risk of leakage of material from inside the coke drum  32 , as illustrated in FIG. 8. In addition, the fasteners  31  holding the lateral pipe flanges  37  together are removed after a manual clamp (not shown) is placed over the lateral connection flanges  37  to maintain their closure. Once the bolts  38  are removed from the bottom head  30 , the personnel move to a remote location for the subsequent stage of the deheading procedure.  
         [0054]    The hydraulic pressure applied to the rams  76  of the clamps  70  is then reduced, thereby controllably relieving the compressive force applied to the bottom head cover  34  and bottom head flange  36 . When the compressive force is reduced below the combined weight of the bottom head cover  34  and the contents of the coke drum  32  weighing on the bottom head cover  34 , the rams  76  begin to retract and the bottom head cover  34  separates slightly from the bottom head flange  36 , as illustrated in FIG. 9. The resulting gap allows quench water and loose coke remaining in the coke drum  32  to flow out of the coke drum  32  while personnel are safely away from the bottom head  30 .  
         [0055]    The bottom head cover  34  is eventually lowered onto the support shelves  64  of the supports  60 , such that the weight of the bottom head cover  34  is supported by the supports  60  of the cart  40 , and not the bottom head flange  36  and the clamps  70 . With the personnel safely away from the bottom head  30 , the manual clamp holding the lateral pipe flanges  37  together is then released.  
         [0056]    Once the bottom head cover  34  is fully resting on the supports  60 , the rams  76  are fully retracted, as illustrated in FIG. 10, and the clamps  70  are moved away from the bottom head flange  36  to their disengaged position. This provides sufficient clearance for the cart  40  to be lowered away from the bottom head flange  36 , and then the carriage  10  can be translated away from the bottom head  30  so that the decoking operation may continue.  
         [0057]    This invention may be embodied in other specific forms without departing from the essential characteristics as described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner. The scope of the invention is indicated by the following claims rather than by the foregoing description. Any and all changes which come within the meaning and range of equivalency of the claims are to be considered within their scope.