Abstract:
The present disclosure provides a system and method for responding to an unintended increase in pressure within a high pressure processing system. The system and method of the present disclosure provides a pressure relief system that releases pressure reliably even if the material under pressure is of mixed phase. In addition, the system and method for releasing pressure avoids the need for complex subsystems to contain and process materials that escape the system during the pressure release process.

Description:
TECHNICAL FIELD 
     The present disclosure provides a system and method for protecting refining equipment from pressure build-up. 
     BACKGROUND 
     Hydrocracking is a major source of jet fuel, diesel, naphtha, and liquefied petroleum gas. Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial pressure of hydrogen gas. The process is operated at high temperatures (e.g., 600 to 900 degrees Fahrenheit) and high pressures (e.g., 1000-3500 pounds per square inch). The process involves flowing materials through a number of structures (e.g., flow control valves, pipes, etc.) any one of which can become clogged, jammed, or otherwise cause a constriction in flow that results in undesirable elevation of pressure within the system. To prevent the elevated pressure from damaging components in the system, pressure relief systems and methods have been developed. The present disclosure provides an improved pressure relief system and method that is useful in high pressure systems and processes, including refining systems and processes. 
     SUMMARY 
     The present disclosure provides a system and method for responding to an unintended increase in pressure within a high pressure processing system. In one embodiment system and method of the present disclosure provides a pressure relief system that releases pressure reliably even if the material under pressure is of mixed phase. In another embodiment, the system and method for releasing pressure avoids the need for complex subsystems to contain and process materials that may escape the system during the pressure release process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic showing a hydrocracking process with a conventional pressure relief system; and 
         FIG. 2  is a schematic showing a hydrocracking process with a pressure relief system according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  a reactor system having a conventional pressure relief valve based system for addressing unexpected increases in pressure in a high pressure, high temperature process is shown. The example high pressure, high temperature system is a hydrocracking process. In the hydrocracking process the material being processed is a mixture of gas, liquid, and solids comprising primarily a catalyst. The mixture is referred to herein as a slurry. As a mixed phase flow, the slurry is particularly susceptible to jams and buildups that constrict flow thereby resulting in unintended upstream pressure increases. 
     In the depicted conventional system, the first two reactors  10  and  12  and first two interstage separators  14  and  16  have conventional pressure relief devices  18  and  20  arranged to protect the interstage separators and upstream equipment (e.g., piping and instruments). In the event of a valve jam or other flow constriction or blockage (e.g., blockage at valve  21  or  22 ), pressures upstream of the valve will rapidly increase. Once the pressure reaches a threshold level, the pressure relief devices  18  and  20  are actuated and allow flow through lines  24  and  26  into line  32 . Line  32  directs the flow to a downstream flare header system (not shown). The entire downstream flare header system needs to be designed to handle the high temperature (600° F.-850° F.) mixed phased hazardous material as it exits the system (e.g., the stack height and burner design needs to accommodate the high temperature vapor being discharged via line  32 ) In the high pressure mixed phase processing system, the conventional system requires complex downstream subsystems for containing and handling the material exiting the relief valve. 
     Referring to  FIG. 2 , one embodiment of the systems and methods applying the principles of the present disclosure is shown.  FIG. 2  illustrates a hydrocracking process with an improved pressure relief system. The process relieves pressures that result from a flow constriction condition while avoiding the need for complex downstream subsystems for containing and handling high pressure hot mixed phased substances. In one aspect of the invention, the process includes providing a plurality of high pressure reactors  40 ,  42 ,  44  arranged in series for processing a slurry; providing separators  46 ,  48  connected between high pressure reactors  40 ,  42 ,  44  configured to separate vapors from the slurry; and providing a relief system wherein a rupture disk  52 ,  54  is designed to actuate or rupture in response to a flow constraint condition, which allows fluid to flow from the separators  46 ,  48  to a downstream high pressure system thereby relieving undesirable upstream pressure. 
     In the embodiment depicted in  FIG. 2 , the process further comprises a last downstream separator  50  positioned downstream of the downstream a last high pressure reactor  44  of the plurality of high pressure reactors  40 ,  42 ,  44 . The last downstream separator  50  is in fluid communication with a downstream fluid path  53  that is free of flow valves and is substantially free of slurry or conveys very low amounts of slurry. Given that the downstream fluid path  53  is free of flow valves and slurry, it is unlikely that the flow in path  53  will be constricted or blocked. In the depicted embodiment the pressure in the downstream fluid path  53  is less than the pressure in any one of the plurality of high pressure reactors  40 ,  42 ,  44 , and is substantially equal to the pressure in the downstream most separator  50 . In the depicted embodiment the pressure in the downstream fluid path  53  is slightly less than the pressure in the downstream most separator  50  due to friction pressure loss in the system (e.g., within 15 pounds per square inch, within 10 pounds per square inch, etc.). 
     In the depicted embodiment, the pressure in the plurality of high pressure reactors  40 ,  42 ,  44  decreases in a downstream direction. For example, the pressure in reactor  40  might be 2500 pounds per square inch, the pressure in reactor  42  might be 2450 pounds per square inch, and the pressure in reactor  44  might be 2400 pounds per square inch. Likewise, the pressure in the separators  46 ,  48  between the high pressure reactors  40 ,  42  also decreases in a downstream direction. 
     In the depicted embodiment the high pressure reactors  40 ,  42 ,  44  convert a portion of the unconverted oil to lower boiling point hydrocarbons, thereby creating a mixture of unconverted oil, hydrogen, converted oil and slurry catalyst. In the various embodiments of the invention the high pressure reactors include reactors such as a hydro-conversion slurry reactor, a circulating slurry bed reactor, an ebullating bed reactor, a coal to liquid reactor and a trickle flow fixed bed reactor. It should be appreciated that the foregoing list of high-pressure reactors is nonexclusive and that many alternative high pressure reactors are possible. In the depicted embodiment the separators  46 ,  48  are configured to separate lighter oil and hydrogen into vapor while permitting heavier converted and unconverted oil and slurry catalyst to flow downstream into a high pressure reactor of the plurality of high pressure reactors  40 ,  42 ,  44 . 
     In the depicted embodiment, when the system is operating normally (i.e., no flow constriction or blockage that causes unexpected pressure increases), the slurry exiting the separators  46 ,  48  is mixed with additional hydrogen via hydrogen lines  58 ,  59  before entering the downstream high pressure reactor  42 ,  44 . In addition, the vapor from the separator is routed downstream through flow valves  62 ,  64  under differential pressure control. 
     In the depicted embodiment a method of protecting any high pressure reactor system is provided. The method generally includes providing a rupture disk  52  within a high pressure chamber  66  that is in fluid communication with a processing chamber  46  configured to operate at pressure in excess of 1000 pounds per square inch (e.g., pressure between 1000-3500 pounds per square inch). The pressure in the high pressure chamber on a first side of the rupture disk  52  can be different than the pressure in the high pressure chamber on a second side of the rupture disk. For example, the pressure on a first side of the rupture disk  52  and in the processing chamber  46  might be at 2450 pounds per square inch, and on a second side of the rupture disk  52  the pressure might be at 2400 pounds per square inch. The rupture disk  52  can be configured to automatically rupture when the pressure difference between the first side and second side of the high pressure chamber is between 100-400 pounds per square inch. For example, in the example above the rupture disk may be configured to automatically rupture at 200 pounds per square inch. In other words, if the pressure on the second side is 2400 pounds per square inch, the rupture disk would automatically rupture when the pressure in the processing chamber is greater than or equal to 2600 pounds per square inch. When the rupture disk ruptures, flow is directed from the processing chamber  46  through the high pressure chamber  66  to a downstream high pressure system that has a pressure of at least 500 pounds per square inch (e.g., 2000 pounds per square inch, 1500 pounds per square inch, 1000 pounds per square inch, etc.). For example, a downstream pressure in the above example system might be 1500 pounds per square inch. 
     Still referring to  FIG. 2 , the configuration of a reactor system according to the present disclosure is further described. In the depicted embodiment the system includes a separator  46  constructed to operate at pressure in excess of 1000 pounds per square inch and temperature greater than 600 degrees Fahrenheit. The separator  46  includes at least one inlet (e.g., inlet  60 ) and at least two outlets (e.g., three outlets  70 ,  72 ,  74 ). At least one of the outlets is a vapor outlet (e.g.,  70 ). The system includes a pressure vessel  66  including an inlet  76 , an outlet  78 , and a rupture disk  52  that is configured to block flow entering the pressure vessel  66  from the inlet  76  from exiting the pressure vessel through the outlet  78 . The system includes a fluid path  80  between the vapor outlet  74  of the separator  46  and the rupture disk  52  in the pressure vessel  66 . The fluid path is open to the separator  46 . The system further includes a flow control valve  62 ,  84  positioned in a fluid path downstream from one of the at least two outlets  70 ,  72 ,  74  of the separator  46 . 
     As discussed above, the separator  46  is configured to separate lighter oil and hydrogen into vapor while permitting heavier converted and unconverted oil and slurry catalyst to flow through the flow control valve  84  positioned in a fluid path downstream from the outlet  72  of the separator  46 . In the depicted embodiment the system also includes a reactor  40  positioned upstream of the separator  46  such that fluid from the reactor flows into the inlet  60  of the separator  46 . As discussed above, the reactor in the depicted embodiment could be, for example, a hydro-conversion slurry reactor, ebullating bed reactor, coal to liquid reactor, or trickle flow fixed bed reactor. 
     In the depicted embodiment the system includes a second reactor  42  positioned downstream of the flow control valve  84 , and a second separator  48  in fluid communication with the second reactor  42 . In the depicted embodiment the second separator  48  is in fluid communication with a second pressure vessel  68 , which includes an inlet  86 , an outlet  88 , and a rupture disk  54 . The rupture disk  54  is configured to block flow entering the pressure vessel  68  from the inlet  86  from exiting the pressure vessel  68  through the outlet  88  unless the rupture disk  54  is ruptured. In the depicted embodiment, hot hydrogen is directed to either side of the rupture disk to keep the disk warm to ensure reliable operations. 
     In the depicted embodiment the system further includes a third reactor  44  positioned downstream of the second separator  48  and a third separator  50  in fluid communication with the third reactor  44 . In the depicted embodiment the third separator  50  is also in fluid communication with the outlet  78  of the first pressure vessel  66  and the outlet  88  of the second pressure vessel  68 . The third separator  50  is similar to the first separator  46  and second separator  48  in that it is also configured to separate out the vapors from the flow. The vapor that exits the third separator  50  is directed to downstream processing equipment that includes such components as a heat exchanger (i.e., cooler)  90 , in-line hydrotreater reactor  93 , and low temperature separator  92  without downstream flow control valves. The non-vapor materials (e.g., unconverted oil and slurry) are directed back via path  94  to the first reactor  40  or to other refining processes selected from the group consisting of: atmospheric distillation, vacuum distillation, delayed coking and combinations thereof. 
     It should be appreciated that the term fluid or flow is used herein to refer to any substance that can flow including, but not limited to, vapors, liquids, particles, and slurries. In addition, the term flow valves is used herein to refer to any valve that can control or block the flow of fluid including, but not limited to, block valves and level control valves. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.