Abstract:
A rotary joint for a decoking tool. The rotary joint includes a seal assembly that has one or more primary seals and one or more secondary seals. The secondary seals become operative upon the presence of a leak in the primary seals such that the rotary joint can continue to be used until a scheduled maintenance outage. A selective vent is used to route leaking fluid so that one or the other of the primary and secondary seals can be activated.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to device and method for decoking delayed petroleum coke vessels, and more particularly to a rotary joint used to drive a drill stem and cutting tools, as well as an improved-reliability seal assembly used in the rotary joint. This invention even more particularly relates to a way to reduce operational downtime of a decoking tool by providing enhanced sealing of the rotary joint. 
     In a delayed coker operation of a petroleum refinery, residual feedstocks are first heated in a furnace and then moved to a vessel where the feed is allowed to coke by operating at a temperature sufficient to drive off the remaining volatile materials. After such heating the residue remaining in the vessel is essentially solidified petroleum coke. These vessels are currently as large as 32 feet in diameter and 150 feet in height. 
     The solid petroleum coke must be removed from the vessel in a decoking operation in order to prepare the coke for further hydrocarbon processing. Decoking is accomplished using high pressure water jets used to bore and cut the coke. The tool first bores a pilot hole through the coke bed and subsequently cuts the coke to the vessel wall, draining it out of the vessel through the pilot hole. This is accomplished by a tool or tools with arrays of vertical and horizontal nozzles to provide suitable jets for boring and cutting the coke bed. The tool or tools are rotated and reciprocated vertically through the vessel to accomplish the boring and cutting process. 
     Such tools are attached to a hollow drill stem through which the high pressure cutting water is conveyed to the rotating and reciprocating tool nozzles. The top end of the drill stem is attached to a rotary joint, which is used to bridge a non-rotating water supply line with the rotating drill stem and tool. The rotary joint is hoisted up and down within a tower above the coke vessel to impart the reciprocating motion to the assembly. The water supply line is in the form of a flexible hose that conveys the high pressure cutting water to the non-rotating portion of the rotary joint. The flexible nature of the water supply line allows it to accommodate the reciprocating motion of the assembly. 
     One important component within the rotary joint is the seal between the non-rotating and rotating portion of the rotary joint&#39;s water passage ways. Most current rotary joints in this service use lip type seals or packing, either of which tend to fail very quickly once a small leak develops. Such difficulties with seal leakage are exacerbated by the nature of the water being used in the decoking operation, as during the boring and cutting operations, the water is recycled, containing a quantity of suspended coke fines and related particulate. Changing a seal in a rotary joint can be time consuming and laborious process. Since delays in emptying the coke from the vessel result in loss of throughput in the overall refining process and concomitant operational impact on the refinery, having to shut down the process to change failed seals is commercially disadvantageous. 
     What is desired is a seal for the rotary joint that is not prone to failure. What is further desired is a seal that is easy and inexpensive to operate. 
     SUMMARY OF THE INVENTION 
     These desires are met by the present invention, where an assembly includes one or more primary seals and one or more secondary seals spaced apart from the primary seals. The primary seals actively seal the rotary joint, and a space between the primary and secondary seals is vented to atmosphere during normal operation and allows a failure of the primary seal to be detected. The secondary seals remain inactive during normal rotary joint operation, but once leakage from the primary seal is detected, the vent can be closed, activating the secondary seal. The secondary seal then allows continued operation of the rotary joint until the next planned outage. Closure of the vent is a simple process which has little impact on the coke removal time and mitigates any commercial impact on the refinery due to seal failure and change out. 
     According to a first aspect of the invention, a rotary joint is disclosed. The rotary joint includes rotatable and non-rotatable flowpaths in fluid communication with one another, as well as a seal assembly disposed between the flowpaths. The seal assembly is made up of one or more primary seals and one or more secondary seals. The secondary seal is positioned relative to the primary seal so that a space is formed between them. Such a space, which may be thought of as a vent area, can be placed in selective venting communication with the ambient atmosphere. To achieve such selective venting, a valve or other means can be positioned as part of a flowpath between the space and the ambient atmosphere. Thus, for example, in a first operating condition, while there is little or no leakage past the primary seal, the secondary seal is exposed to ambient pressures on both sides, hence not activated. In a second operating condition (which may, for example, coincide with a measurable leakage flow past the primary seal), the space between the primary and secondary seals can be, by operation of the valve or other means, cut off from the ambient environment, thereby promoting a pressure differential across the secondary seal such that it becomes activated. 
     Optionally, the selective venting communication means is a valve. In one form, a tortuous channel is set up such that any jetting action caused by the leakage being vented to the atmosphere is converted to substantially nonjetting leakage stream. In this way, risk of direct exposure to a high pressure jet of leaked fluid is reduced or eliminated. This can be effected by having a discharge hole or related orifice be adjacent a cavity wall such that the jetting of the discharged leakage through the hole impinges on the wall, causing diffusion of the jet. Additional flow impediments, such as deflectors, can be used to further cause jet diffusion. The assembly may also include a locking mechanism such that once a valve or related selective venting communication means is placed in a particular open or closed position, that position cannot be inadvertently changed. In this way, operator error or vibration due to prolonged operation will not cause the selective venting communication means to change position. 
     In another option, the first operating condition corresponds to a fluid flow situation where no measurable leakage is taking place to the space between the primary and secondary seals, while a second operating condition corresponds to a fluid flow situation where measurable leakage is taking place past the primary seal and into the space. In the present context, the term “measurable” corresponds to levels sufficient to cause an operator (in manual configurations) or a sensor (in automated configurations) to justify changing vent settings. In a manual form, this may be a level that an operator (through experience or other criteria) knows is indicative of a problem operating condition. In an automated form, this may be a threshold level over which the sensor is designed to send an appropriate notification or control signal. In one form, the primary seal may be configured as a lip seal. In another option, the assembly may also include a leakage detection device. The device, which may be in the form of a sensor, can be configured to send a signal to a controller, computer or other device to apprize an operator or the system of a leakage level in the rotary joint. Leakage detection may also be done manually. 
     According to another aspect of the present invention, a decoking tool is disclosed. The tool includes a fluid supply conduit with one or more fluid dispensing nozzles fluidly connected to the fluid supply conduit. The tool also includes, between the fluid supply conduit and the fluid dispensing nozzles, a rotary joint made up of a rotatable flowpath, a non-rotatable flowpath and a seal assembly disposed between the rotatable and non-rotatable flowpaths. In this way, the rotary joint allows the fluid dispensing nozzles to rotate relative to the fluid supply conduit, where such rotary motion allows the fluid dispensing nozzle or nozzles to perform at least one of a boring and cutting operation on solidified coke, such as that found in a coke vessel or drum. Such rotary motion improves the ability of the fluid to cut or bore into the solidified coke. 
     The seal assembly is made up of seals to prevent leakage of high pressure fluid (such as water used in a decoking operation) between the rotatable and non-rotatable flowpaths. These seals include a primary seal and a secondary seal disposed relative to the primary seal such that in the event of leakage past the primary seal or seals that exceeds a threshold level, a selective venting device placed in fluid communication with the space between the primary and secondary seals can be adjusted to change the amount of venting between such space and the ambient atmosphere. As mentioned above, such fluid dispensing nozzle of the tool can be a single nozzle or a combination, such as a cutting nozzle and a boring nozzle, where the latter is used to form a path along the substantially longitudinal dimension of a coke vessel while the former is used to rotate about the longitudinal axis such that water emanating therefrom can form radial cuts into the solidified coke. The device to effect the selective venting communication between the space and the ambient atmosphere may be in the form of a valve (such as a bleed valve) such that in a first operating condition, a vent is left open to the atmosphere so that the secondary seal is not pressurized or otherwise activated, while in a second operating condition, the vent is closed so that the secondary seal is activated. This activation of the secondary seal accompanies the recirculation and containment of the fluid that has leaked past the primary seal so that the leakage past the primary seal continues to be contained. 
     Optionally, the selective venting communication may be manually or automatically adjustable. In the case of the former, it can be configured as an adjustable valve with a plug, stopcock or related flow control mechanism that allows an operator, upon attainment of a threshold leakage level past the primary seal or seals, to adjust the valve at a time that minimizes impact on the operation of the decoking tool. In the case of the latter, the tool may further include a leakage sensing device that can be used in conjunction with the valve (and related control equipment) to measure leakage levels. Such sensor may deliver the measured level to an output device, such as a gauge, readout screen, audible warning device or the like so that an operator or control mechanism (such as a microprocessor-controlled system) can make appropriate adjustments. Regardless of whether a sensor is included, the valve may further include a lock to keep the valve in one of an open position or a closed position so that the position cannot be inadvertently changed, such as by vibration, human error or the like. The lock may include safety wire or other device that both keeps the valve in a preferred position, as well as enable ease of adjustment by an operator. 
     According to another aspect of the invention, a method of operating a rotary joint for a decoking tool is disclosed. The method includes configuring a seal assembly in the rotary joint to comprise one or more primary seals and one or more secondary seals with a venting region (or space) disposed fluidly between them. In this way, when a leakage level that exceeds a predetermined threshold past the primary seal occurs, the secondary seal can be activated to substantially contain the leakage. The method further includes flowing a decoking fluid through the rotary joint, checking for leakage of the fluid around the primary seal or seals, and venting the region or space to the atmosphere until the leakage exceeds a predetermined threshold. Such a predetermined threshold could be based on an amount of leakage below which a user may determine is acceptable. 
     Optionally, the venting comprises operating a bleed valve. In this way, the venting is selective in that it can be turned on, off or set in between an on and off position. In addition, checking for leakage may include operating an automated leak detection device, such as a sensor signally coupled to a controller, leakage notification device (such as an audible or visual alarm) or both. The selectively venting may include shifting a sealing load from the primary seal to the secondary seal such that any leakage past the primary seal is picked up by the secondary seal. In the present context, a sealing load may be a force due to the presence of a fluid that presses against the seal. Adjustment of the bleed valve or other shifting such a sealing load is such that it can be accomplished without having to shut the tool down. For example, an operator may make an adjustment that can be effected without having to suspend operation of the decoking tool. In another option, the jetting action reduction can be effected by placing one or more deflectors in the leakage discharge path. In still another option (which may or may not be combined with the deflectors), the jetting action reduction occurs by placing the bleed valve at least partially in or adjacent the seal assembly such that upon discharge of the leakage from the valve, the leakage impinges upon a wall formed between the valve and seal assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is a view of a decoking system which can use the rotary joint seal assembly of the present invention; 
         FIG. 2  is a partial cutaway rotary joint showing placement of primary and secondary seals from the seal assembly; 
         FIG. 3A  is a detailed view of the seal assembly of  FIG. 2  with an open vent during normal rotary valve operation; 
         FIG. 3B  is a detailed view of the seal assembly of  FIG. 2  after a leak has developed in the primary seal; 
         FIG. 3C  is a detailed view of a closed vent leak path that may be set up to avoid the leakage shown in  FIG. 3B  being vented to the atmosphere; 
         FIG. 4A  is a view of a venting arrangement within the seal assembly; 
         FIG. 4B  is a detailed view of a valve used to effect venting to atmosphere; and 
         FIG. 5  is a view of how to reduce the intensity of high pressure leakage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1 , a decoking system  1  includes a pair of coke vessels  5 , a cutting and boring tool  10 , a drill stem  15 , a tower  20 , a flexible water supply hose  25  and a rotary joint  30 . The vessel  5  on the left shows a partial cutaway, where the vessel  5  is full of coke  7  that needs to be removed, while the vessel  5  on the right shows the cutting and boring tool  10  being lowered through the coke  7  during boring of a pilot hole  9 . The cutting and boring tool  10  is mounted at the lower end of the drill stem  15  such that both can move translationally (specifically, vertically) along the length of vessel  5 . The upper end of drill stem  15  is coupled to the rotary joint in such a way that the cutting and boring tool  10  and drill stem  15  can rotate about a longitudinal axis formed by both in response to water passing through the radially-oriented nozzles (not shown) of the cutting and boring tool  10 . The flexible water supply hose  25  is also coupled to the rotary joint  30  and is used to supply high pressure water to the cutting and boring tool  10 . While the cutting and boring tool  10  is mentioned as a single device, it will be appreciated by those skilled in the art that such functions may be separated, as a separate tool that provides cutting and a separate tool for cutting may be employed. The construction of the rotary joint  30  is such that it acts as the intermediary between the flexible, yet non-rotational water supply coming from the flexible water supply hose  25  and the rigid, yet rotational drill stem  15  and the cutting and boring tool  10 . Tower  20  acts as a hoist to lift and lower the cutting and boring tool  10 , drill stem  15 , flexible water supply hose  25  and rotary joint  30 . 
     Referring next to  FIG. 2 , details of the rotary joint  30  are shown. Inlet  310  and outlet  320  are disposed on opposing fluid sides of the rotary joint  30 , and are in fluid communication with one another through an elongate flowpath  315  that is situated along the generally longitudinal dimension of the rotary joint  30 . In this way, inlet  310  corresponds to the portion of the rotary joint  30  where the incoming water from the flexible water supply hose  25  is introduced to the rotary joint  30 , while the outlet  320  corresponds to the portion of the rotary joint  30  that leads to the drill stem  15 . Flow rates and pressures of water coming from the water supply hose  25  tend to be rather high, with flow rates of up to a couple of thousand gallons per minute, and pressures of between 3000 and 5000 pounds per square inch. The inlet  310  includes a generally U-shape, while the outlet  320  forms part of a generally linear shape. Flowpath  315  includes both a non-rotatable portion  315 A adjacent inlet  310  and a rotatable portion  315 B adjacent outlet  320 . A rotatable coupling  340  circumscribes flowpath  315  and acts as a transition of the rotary joint  30  from the non-rotatable portion  315 A to the rotatable portion  315 B. A series of bearings  342 A- 342 D (shown notionally as roller bearings) allow rotational movement of the coupling  340  while leaving a sleeve or other conduit making up the non-rotatable portion  315 A of flowpath  315  stationary so that it is rigidly affixed to the inlet  310  of the rotary joint  30 . 
     Seal assembly  360  is used to prevent leakage where the first and second portions  315 A,  315 B of flowpath  315  join. Referring next to  FIGS. 3A through 3C , details of seal assembly  360  with primary seal  364  and secondary seal  366  are shown. Each of the three figures depicts a different operating condition, including for an open vent leak path during normal operation ( FIG. 3A ), an open vent leak path during operation where leakage around the primary seal  364  occurs ( FIG. 3B ) and a closed vent leak path where the secondary seal  366  is activated ( FIG. 3C ). The non-rotatable portion  315 A is shown as the aforementioned sleeve or washpipe, while gland  362  rotates relative to the sleeve  315 A. The primary seal  364  is situated between the sleeve  315 A and the gland  362  such that during normal rotary joint  30  operation, the primary seal  364  is active. Secondary seal  366  is inactive during normal operation, insofar as it is exposed to atmospheric pressures on both sides. Specifically, its upper side is exposed to atmospheric pressure conditions through the space between the secondary seal  366  and the close-clearance bushing  365 , while the lower side is exposed to atmospheric pressure conditions through a vent passage  368  that is positioned between the primary and secondary seals  364 ,  366 , and is left open such that fluid communication between the space defined between the primary sand secondary seals  364 ,  366  and the ambient environment is maintained. This has the effect of keeping the pressure off the secondary seal  366  during normal operation, while allowing detection of leakage downstream of the primary seal  364 . 
     Referring next to  FIGS. 4A and 4B  in conjunction with  FIGS. 3A through 3C , one means for venting and blocking the space between the primary and secondary seals  364  and  366  is shown. A seal gland  362  acts as a housing that is disposed about the interface between the first and second portions  315 A,  315 B of flowpath  315 . The primary and secondary seals  364 ,  366  are situated in the region between the gland  362  and the washpipe of the non-rotatable portion  315 A of the flowpath  315 . The vent passage  368  of  FIGS. 3A through 3C  is fluidly coupled to a closure mechanism through a radial conduit  369 , which may be formed in the body of gland  362  through any well-known means, such as cross-drilling or the like. The closure mechanism may be made up of a bleed valve  370  the body of which is mounted in a generally vertical recess  362 A in the gland  362  such that a fluidly continuous path from the vent passage  368  through the conduit  369  and into the recess  362 A and valve  370  is formed. As shown with particularity in  FIG. 4A , an identifying plaque or related label  380  may be placed on the lower part of the gland  362  to provide indicia of the valve, including operating conditions, scheduled maintenance times or the like. 
     Leakage is detected either visually by an operator (such as by perceiving the presence of a high pressure fluid emanating from the area around the rotary joint), or automatically by a sensor  390  (shown in  FIG. 4B ) that can be connected to an alarm or related warning. During normal operation (such as that shown in  FIG. 3A ), valve  370  is opened such that vent passage  368 , conduit  369  and the space between the primary and secondary seals  364  and  366  is open to the ambient atmosphere. 
     As shown with particularity in  FIG. 4B , a plug  372  of the bleed valve  370  allows rotation of the valve  370  to expose the vent area adjacent the primary and secondary seals  364 ,  366  to the atmosphere through a bleed hole  374  formed in the bleed valve  370  body. By rotating the plug  372 , the relationship between the bleed hole  374  and an internal passage (not shown) can be altered so that the fluid path from the seal assembly  360  to the ambient environment can be selectively cut off. The size of the bleed hole  374  is limited so that, in the event of a primary seal  364  failure, the leakage will be visible and obvious, but not so great that the leakage will force shutdown of the rotary joint  30  and immediate replacement of the primary seal  364 . By proper control of the size of hole  374 , discharge of the high pressure fluid can be metered. A locking mechanism  377  may be attached to the plug  372  to prevent the letter from inadvertent rotation. Locking mechanism forms a fixed relationship with gland  362 , such as by screwing, welding, integral forming or other related fastening, and when used in conjunction with safety wire  378 , can keep the preferred orientation of valve  370 . Thus, once the valve  370  is placed in a particular open or closed position, that position remains. This prevents vibration or accidental contact from changing valve  370  position, thereby preserving the desired vent setting. By having the plug  372  readily accessible to an operator, adjustment of the valve  370  is simplified. 
     Sensor  390  can be fluidly coupled to any one of numerous locations along the leakage path in order to detect leakage therefrom. Once leakage of the primary seal  364  (such as that shown in  FIG. 3B ) is detected, the vent passage  368  can be blocked off by adjusting valve  370 , where once closed, cuts off access to the ambient environment, thereby preventing further leakage and making the secondary seal  366  fully active. In this way, the pressurized fluid that leaks past the now-failed primary seal  364  encounters the secondary seal  366 . With nowhere to go, the leaked fluid will build up pressure in the space between the two seals  364 ,  366  so that the secondary seal  366  is exposed to the high pressure fluid. The amount of leakage past the primary seal  364  deemed sufficient to justify adjusting valve  370  may vary depending on the operational needs of the decoking tool, and is known to one skilled in the art how much leakage is acceptable. The secondary seal  366  is of such integrity that it allows operation for a reasonable period of time until a planned outage of the vessel can be reached and the primary seal  364  changed out. As shown with particularity in  FIG. 4B , the sensed leakage may cause the sensor  390  to send a signal to a controller or alarm so that either automated or manual adjustment in the valve  370  setting may be initiated. 
     Referring next to  FIG. 5 , features used to reduce the direct flow of a high pressure jet of leaked fluid is shown. As can be seen, valve  370  is countersunk into gland  362  such that a chamber  376  is formed between the inner wall of gland  362  and the faceted outer surface of valve  370 . Since the leakage path from the seal assembly  360  terminates at bleed hole  374  formed in valve  370 , and the pressures associated with the leakage could be excessive, the placement of the bleed hole  374  within the chamber  376  acts to cause direct impingement of the leakage onto the inner wall of the gland  362 , thereby acting to diffuse the leakage jet. Further diffusion of the jet can occur through the use of surface-mounted deflectors  379 . In this way, a tortuous flowpath is set up, such that the high pressure jet can be diffused and redirected to a more safe pressure level. While the deflectors  379  are shown notionally as a pair of generally planar panels, it will be appreciated by those skilled in the art that other shapes, as well as adjustable features, are also contemplated. 
     Having described the present invention in detail and by reference to the embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention in the following claims.