Abstract:
One exemplary embodiment can be a process for transferring catalyst in a fluid catalytic cracking apparatus. The process can include passing the catalyst through a conveyor wherein the conveyor contains a screw for transporting the catalyst.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention generally relates to a process for transferring catalyst, and an apparatus relating thereto. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Current catalyst withdrawal systems for fluid catalytic cracking apparatuses can have catalyst erosion issues resulting in shortened operations. Erosion can occur at the piping assembly near an air injection, at valves, and with internal components. Also the inclusion of finned piping can create difficulties in finding suitable piping at acceptable cost. Additionally, the withdrawal of catalyst in current systems may also have plugging issues. Furthermore, conventional withdrawal systems may not sufficiently cool the withdrawn catalyst from the hot regenerator to a cold equilibrium catalyst hopper. What is more, it would be desirable to recover heat from the withdrawn catalyst to be utilized in plant utilities. 
         [0003]    A current fluid catalyst cracking shell and tube cooler with a slide valve can be very expensive and create reliability concerns during normal operation with erosion and plugging. Preferably, an alternative can be provided that alleviates the erosion and plugging issues, as well as allow recovery of heat. 
       SUMMARY OF THE INVENTION 
       [0004]    One exemplary embodiment can be a process for transferring catalyst in a fluid catalytic cracking apparatus. The process can include passing the catalyst through a conveyor. The conveyor may contain a screw for transporting the catalyst. 
         [0005]    Another exemplary embodiment may be a fluid catalytic cracking apparatus. The apparatus can include a riser-reactor including a riser terminating in a reaction vessel, a regeneration vessel communicating with the riser-reactor for receiving spent catalyst from the riser-reactor and for sending regenerated catalyst to the riser-reactor, and a conveyor positioned in the line for facilitating transfer of the catalyst. Often, the regeneration vessel includes a line for transferring catalyst within the regeneration vessel and the conveyor contains a shaft coupled to a thread. 
         [0006]    A further exemplary embodiment can be a process for transferring catalyst in a fluid catalytic cracking apparatus. The process may include passing the catalyst through a conveyor. The conveyor may contain a screw for transporting the catalyst communicating with different portions of a shell of a regeneration vessel and passing the catalyst through another conveyor. This another conveyor may also contain a screw for transporting catalyst for disposal. 
         [0007]    The catalyst withdrawal cooling screw assembly can allow the refiner to remove the catalyst daily without having air injection at the assembly, thus generally minimizing erosion. The cooling screw assembly can also be easily available as such designs are often used in cooling dense phase solid transfer in other industrial applications. Using a variable speed motor cooling screw conveyor may move the hot catalyst while the heat transfer can occur between the hot catalyst to the jacket and shaft while cooling water may remove heat from the screw conveyor. Because the heat transfer is done via dense phase conveying, finned piping is not required and erosion is less severe as with a rapid, dilute phase system. 
         [0008]    A fluid catalytic cracking cooling screw conveyor may provide a lower cost, an easy to operate alternative to cooling the catalyst and provide a heated water supply to a flue gas steam generator for steam generation. The cooling screw conveyor does not have many internal parts other than the screw to operate at low rotations per minute to minimize erosion and move the hot catalyst along the shaft from the regeneration vessel. 
         [0009]    The cooling medium, such as water, may circulate along the jacket and or along the shaft picking up heat from the hot catalyst while cooling the catalyst down as required from the heat balance of the apparatus. The cooled catalyst can return to the regeneration vessel. The hot water may be sent to various locations as required within the refinery. In the fluid catalytic cracking apparatus, this hot water can be routed to the economizer of the flue gas steam generator, the desuperheater, and/or the main column bottom steam generator for steam generation. 
       DEFINITIONS 
       [0010]    As used herein, the term “stream” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances, such as gases, e.g., hydrogen, or impurities, such as heavy metals, and sulfur and nitrogen compounds. The stream can also include aromatic and non-aromatic hydrocarbons. Furthermore, a superscript “+” or “−” may be used with an abbreviated one or more hydrocarbons notation, e.g., C 3+ or C 3− , which is inclusive of the abbreviated one or more hydrocarbons. As an example, the abbreviation “C 3+ ” means one or more hydrocarbon molecules of three carbon atoms and/or more. A “stream” may also be or include substances, e.g., fluids or substances behaving as fluids, other than hydrocarbons, such as air or catalyst. 
         [0011]    As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. 
         [0012]    As used herein, the term “coupled” can mean two items, directly or indirectly, joined, fastened, associated, connected, or formed integrally together either by chemical or mechanical means, by processes including stamping, molding, or welding. What is more, two items can be coupled by the use of a third component such as a mechanical fastener, e.g., a screw, a nail, a staple, or a rivet; an adhesive; or a solder. 
         [0013]    As used herein, the term “hour” may be abbreviated “hr”, the term “kilogram” may be abbreviated “kg”, the term “kilopascal” may be abbreviated “KPa”, and the terms “degrees Celsius” may be abbreviated “° C.”. 
         [0014]    As depicted, process flow lines in the figures can be referred to interchangeably as, e.g., lines, pipes, feeds, products, or streams. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic, cross-sectional view of an exemplary fluid catalytic cracking apparatus. 
           [0016]      FIG. 2  is a schematic, cross-sectional view of an exemplary first conveyor. 
           [0017]      FIG. 3  is a schematic, cross-sectional view of an exemplary second conveyor. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 1 , a fluid catalytic cracking apparatus  10  can include a riser-reactor  100  and a regeneration vessel  200 . The riser-reactor  100  can include a riser  120  that terminates inside a reaction vessel  160 . The riser  120  can terminate in one or more disengaging arms  124  that may separate the hydrocarbons from the catalyst. The reaction vessel  160  can also contain one or more cyclone separators  180  that can communicate one or more hydrocarbons to an outlet  184 . One or more dip legs  128  can provide spent catalyst from the one or more cyclone separators  180  to a stripping zone  140 . Any suitable catalyst may be utilized, including a mixture of a plurality of catalysts including an MFI zeolite and a Y-zeolite. Exemplary catalyst mixtures are disclosed in, e.g., U.S. Pat. No. 7,312,370 B2. Exemplary reaction vessels and regeneration vessels are disclosed in, e.g., U.S. Pat. No. 7,261,807 B2; U.S. Pat. No. 7,312,370 B2; and US 2008/0035527 A1. 
         [0019]    The regeneration vessel  200  can include a direct fired air heater  204 , a shell  210 , air grids  230 , one or more cyclone separators  260 , and a plenum  268 . The regeneration vessel  200  may include the one or more cyclone separators  260  having one or more dip legs  264 . The one or more separators  260  can communicate flue gases to the plenum  268 , in turn communicating the flue gases to an outlet  270 . The one or more dip legs  264  can communicate catalyst to the base of the regeneration vessel  200 . 
         [0020]    In operation, a hydrocarbon feed  110 , that may include at least one of a gas oil, a vacuum gas oil, an atmospheric gas oil, a coke oil, a gas oil, a hydrotreated gas oil, a hydrocracker unconverted oil, and an atmospheric residue, can be provided to the riser  120  and fluidized with a gas  114 . The hydrocarbon feed  110  can also be contacted with the catalyst provided via a transfer conduit  290 , which can be a second transfer conduit  290 , to the base of the riser  120 . Generally, the regenerated catalyst and feed mixture can be at a temperature of about 500-about 650° C., and a pressure of about 110-about 450 KPa. The catalyst and feed can rise within the riser  120  and separate at the reaction vessel  160  using any suitable device. The catalyst can fall toward the base of the reaction vessel  160  while product gases can rise and be separated from the catalyst. The product gases can enter the outlet  184  and exit as a product stream  190 . The hydrocarbon products can be further processed, such as in downstream fractionation zones. An exemplary fractionation zone is disclosed in, e.g., U.S. Pat. No. 3,470,084. 
         [0021]    The separated catalyst can pass from the dip legs  128  and fall to the stripping zone  140 . A stripping steam  148  can be provided to the stripping zone  140  to strip hydrocarbons. The catalyst can pass through a transfer conduit  280 , such as a first transfer conduit  280 , to the regeneration vessel  200 . 
         [0022]    The regeneration vessel  200  can receive spent catalyst through the first transfer conduit  280 . A gas, as discussed in further detail hereinafter, can be provided in a line  394  to the direct fired heater  204 . The gas, typically air, can pass to the line  304  to the air grids  230  and mix with the spent catalyst from the first transfer conduit  280 . The catalyst may be regenerated and fall to the base of the regeneration vessel  200 . Furthermore, the one or more cyclone separators  260  can receive a mixture of flue gas and entrained catalyst. Catalyst can be separated in the one or more cyclone separators  260  and pass through the dip legs  264  and also fall to the base of the regeneration vessel  200 . From the base, the regenerated catalyst along with any make-up catalyst can pass through the second transfer conduit  290  to the riser  120 . Separated flue gases rise from the one or more cyclone separators  260  to the plenum  268  and exit via the outlet  270 . Generally, the direct fired heater  204  can combust any suitable fuel  384 , such as an auxiliary fuel, including a fuel gas. Often, the direct fired heater is used during initialization of the fluid catalytic cracking apparatus  100 , but is not activated during steady-state operations. The regeneration vessel  200  can operate at any suitable temperature, such as above about 650° C. or other suitable conditions for removing coke accumulated on the catalyst particles. 
         [0023]    Catalyst can be recirculated within the regeneration vessel  200  by passing through a conduit  320  and to a first conveyor  400 , as further described herein. Catalyst cooled by the first conveyor  400  may pass through a line  324  and into a line  398  returning the catalyst to the regeneration vessel  200 . Catalyst in the line  398  can be fluidized by air in the line  382 , and another part of the air provided to the line  394 . 
         [0024]    Catalyst may also be removed from the regeneration vessel  200  via a line  490  and passed to a second conveyor  500 , as hereinafter described. Cooled catalyst may be withdrawn via a line  494 . 
         [0025]    Referring to  FIG. 2 , the first conveyor  400  can include a jacket  410 , typically a water jacket, a screw  420 , and a variable speed motor  430 . Catalyst withdrawn from the regeneration vessel  200  via the conduit  320  can enter the conveyor  400  and be moved via the screw  420 . Usually, the catalyst exits the line  324 . The screw  420  can include a shaft  424  forming a void  426  therein and have one or more helical threads or blades  428  coupled to the shaft  424 . The one or more helical threads  428  can optionally be hollow as well. The variable speed motor  430  can be coupled to the screw  420  for rotating the screw  420 . The jacket  410  can form spaced apart walls forming an annular structure, i.e., a pair of spaced apart cylinders, for receiving a heat exchange medium therein. 
         [0026]    A line  402  can provide the heat exchange medium, such as cooling water, to cool the catalyst. A valve  412  can regulate the water passing in the water line  402 . The water line  402  can be split into lines  404 ,  406 , and  408  to provide water to the jacket  410  and the void  426 . In some cases, the one or more helical threads  428  may also receive a heat exchange medium. Heat can be transferred from the catalyst to the water and withdrawn via lines  432 ,  434 , and  436  and be combined into a line  440 . Generally, the cooling water receives heat from the hot catalyst along the shaft  424  and/or the jacket  410  of the conveyor  400 . The cooling water flow can be either counter or co-current flow with the hot catalyst pending the design requirement. 
         [0027]    The heated water can be provided to utility services for generating electricity or other utilities. As an example, the heated water can be routed to the economizer of the flue gas steam generator, the desuperheater, and/or the main column bottom steam generator for steam generation. 
         [0028]    The variable speed motor  430  can control the speed of the catalyst passing through the jacket  410 . Generally, the variable speed motor  430  is operated at a slower speed to prevent fluidization and controls the rate of catalyst circulation in the regeneration vessel  200 . Usually, the first conveyor  400  cools the catalyst from at least about 700° C. to no more than about 600° C. and transports about 130,000-about 450,000 kg/hr. An exemplary conveyor is disclosed in, e.g., US 2008/0295356 A1. 
         [0029]    Referring to  FIG. 3 , the second conveyor  500  can include a jacket  510 , typically a water jacket, a screw  520 , and a variable speed motor  530 , and have substantially the same components and operate similarly as the first conveyor  400 . As an example, the screw  520  can include a shaft  524  forming a void  526  and one or more helical threads or blades  528  coupled to the shaft  524 . The one or more helical threads  528  optionally can be hollow to receive a heat exchange medium. The variable speed motor  500  can be coupled to the screw  520  to rotate the screw  520 . The jacket  510  can form spaced apart walls forming an annular structure, i.e., a pair of spaced apart cylinders, for receiving a heat exchange medium therein. One difference is that the throughput through the second conveyor  500  can be quite less than the throughput through the first conveyor  400 . Generally, the second conveyor  500  can cool the catalyst from at least about 700° C. to no more than about 100° C., and transports about 15-about 200 kg/hr. 
         [0030]    Catalyst withdrawn from the regeneration vessel  200  can be provided by the line  490  to the second conveyor  500 . The catalyst can be transported from the second conveyor  500  via the line  494  to any suitable destination, such as storage, e.g., an equilibrium catalyst hopper, prior to disposal. A line  560  optionally regulated by a valve  562  can provide a fluidizing medium, such as air, to the line  494  to fluidize the catalyst. A line  502  can provide a heat exchange medium, such as water optionally regulated by a valve  512 . The line  502  can be split into lines  504 ,  506 , and  508  to provide water to the jacket  510  and the void  526  of the shaft  524 . At least a portion of the heat from the catalyst can be transferred to the water, which in turn can pass through lines  532 ,  534 , and  536  to be combined into a line  540  and be used in any suitable utility, such as steam, preferably high pressure, generation. 
         [0031]    Although the regeneration vessel  200  is disclosed as being a single stage, it should be understood that first and/or second conveyors may be utilized with any suitable regeneration vessel  200 , such as a high efficiency regeneration vessel, a two stage regeneration vessel, or a bubbling bed regeneration vessel. An exemplary two stage regeneration vessel is disclosed in, e.g., U.S. application Ser. No. 13/425,657 filed 21 Mar. 2012. In such an instance, the first conveyor  400  can transfer catalyst from the second stage to the first stage. The cool catalyst may travel along the screw and return to the regeneration vessel along the standpipe for high efficiency or two stage regeneration vessels. For a bubbling bed regeneration vessel, a cool catalyst lift riser may be required to return the catalyst back to the bed. 
         [0032]    Although two conveyors  400  and  500  are depicted, it should be understood that any suitable number of conveyors may be utilized. Particularly, multiple conveyors  400  can be used in parallel to correspond to the higher catalyst throughput. 
         [0033]    The embodiments provided herein allow hot catalyst withdrawal through a conveyor via a dense phase removal instead of the dilute phase using, e.g., finned piping. The catalyst can be withdrawn at a controlled rate using a variable speed controller at a low revolution per minute setting. The internal screw can operate at low speed while moving hot catalyst with the rotating blade coupled to the shaft. Usually, the only air injection utilized is air transferring the cooled catalyst after the cooling screw conveyor to the equilibrium catalyst hopper. The low overall revolutions per minute can minimize erosion. Heat transfer from the hot catalyst to the cooling water may occur along the shaft, jacket, and optionally helical threads of the conveyor. Hot water from the outlet of the conveyors can be sent to the appropriate utilities to generate, e.g., high pressure steam. 
         [0034]    Typically, the variable speed motor allows the screw to control the catalyst circulation rate as required for operation without using a conventional slide valve. The catalyst cooler circulation rate can be stopped completely, if required, by shutting down the variable speed motor. 
         [0035]    Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
         [0036]    In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
         [0037]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.