Abstract:
An apparatus and process are presented for drying a catalyst in a reactor-regenerator system. The process includes a continuous operating system with catalyst circulating between a reactor and regenerator, and the catalyst is dried before returning the catalyst to the reactor. The process uses air that is split between the drying stage and the combustion stage without adding equipment outside of the regenerator, minimizing energy, capital cost, and space requirements.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an apparatus and process in catalytic hydrocarbon processing. In particular, this invention relates to improving regenerators, and the process of regenerating catalyst. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are many processes that have been developed for converting hydrocarbon streams to more useful products. Many of these processes involve the use of catalysts, and many of the catalytic processes are continuously operated. The continuous operation of a catalytic process can involve a fluidized bed reactor, and a regenerator. The catalyst is used in the reactor, and is continuously drawn off as spent catalyst and passed to a regenerator. The regenerator regenerates the spent catalyst and recycles the catalyst back to the reactor. 
         [0003]    One common process, as an example, is fluid catalytic cracking The process is a conversion process to convert heavy hydrocarbons into lighter hydrocarbons. The reaction occurs through contact between the hydrocarbon stream of heavy hydrocarbons with catalyst particles. The particles eventually lose their activity, and need to be regenerated. The basic components of such a process includes a reactor, a catalyst stripper and a regenerator. The reaction takes place in the reactor, where the catalyst is eventually deactivated through the accumulation of coke on the catalyst particles. The catalyst is carried out of the reactor, where residual hydrocarbons are stripped from the catalyst, and the catalyst is passed to the regenerator, where the coke is burned off, and the catalyst is regenerated. 
         [0004]    However, some processes using this basic structure may require additional steps to maintain the long term viability of the continuous process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present invention is a regenerator design for a paraffin dehydrogenation reactor-regenerator system. The regenerator design includes a combustion chamber having a spent catalyst inlet, a combustion gas inlet, and an outlet. The regenerator further includes a drying chamber having an inlet in fluid communication with the combustion chamber outlet, where the catalyst and combustion flue gas separate and the catalyst settles to be contacted with a drying gas. The drying chamber includes a catalyst outlet and a drying gas inlet, wherein the catalyst outlet is in fluid communication with a stripping chamber catalyst inlet. The stripping chamber has a stripping gas inlet and a catalyst outlet in fluid communication with the reactor catalyst inlet. 
         [0006]    In another embodiment, the regenerator design comprises an efficient stacking of the stripping chamber, drying chamber and combustion chamber. The combustion chamber has a spent catalyst inlet and a combustion gas inlet. The regenerated catalyst and combustion chamber flue gas pass to a separation chamber where the catalyst is separated from the flue gas. The catalyst is passed to the drying chamber positioned below the combustion chamber. A drying gas is passed to the drying chamber to remove water from the catalyst, and the moist gas is passed to the combustion chamber where the gas is used in the combustion of coke on the catalyst. The drying chamber has a catalyst outlet where the catalyst is passed to a stripping chamber. The stripping chamber has a stripping gas inlet, and the stripping gas after contacting the catalyst can be passed to the drying chamber, or can be passed to the separation chamber where the stripping gas will be passed out with the flue gas. The stripping chamber has a catalyst outlet where the catalyst can be returned to the reactor. 
         [0007]    Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]      FIG. 1  is a first configuration for performing the catalyst drying; and 
           [0009]      FIG. 2  is a second configuration for performing the catalyst drying. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    Propylene is an important precursor to the plastic polypropylene. A process has been developed to produce on-purpose propylene from a propane rich feedstock. The process of the present invention involves the dehydrogenation of propane using a non-noble metal catalyst in a fluidized reactor-regenerator system. However, depending upon which catalyst type is chosen, sensitivity of the catalyst to water can be an issue, and the regeneration process produces some moisture that can be adsorbed onto the regenerated catalyst. The dehydrogenation process comprises passing a paraffinic hydrocarbon to a dehydrogenation reactor. In the reactor, a dehydrogenation catalyst is circulated between the reactor and a regenerator for a continuous process, wherein the catalyst undergoes deactivation while in the reactor during the dehydrogenation process, and is regenerated in a regenerator and returned to the reactor. In particular, the design of the present invention is aimed at the process of converting propane to propylene. In addition, the presence of oxygen and/or carbon monoxide affects the dehydrogenation process. The catalyst needs to have residual oxygen and/or carbon monoxide that is adsorbed on the catalyst during regeneration needs to be removed. Simple purging of the catalyst from the regenerator is often insufficient to remove enough of the residual water to return the catalyst to a state to achieve the desired performance. 
         [0011]    The present invention represents an integrated catalyst regeneration and drying approach which is an improvement over a non-integrated approach where an additional drying vessel would be employed requiring additional complexity, and operation equipment and plot space. This invention reduces capital cost by avoiding the addition of a non-integrated dedicated drying system which would require catalyst handling and gas/catalyst separation equipment. The regenerated catalyst is contacted with a dry gas such as air or nitrogen to remove more than 90% of the water adsorbed by the catalyst in the regenerator, and preferably more than 99.9% of the water. The extent of drying is determined by the level of activity needed in the regenerated catalyst. 
         [0012]    The present invention is intended to include any reactor design that incorporates a recirculation of the catalyst between a reactor and a regenerator, including a fluidized bed system, a fast fluidized bed system, a bubbling bed reactor system, or a counter-current flow system involving trays or packing 
         [0013]    One embodiment of the present invention is a process for drying regenerated catalyst in a continuous catalyst regeneration system. The process includes passing spent catalyst from a dehydrogenation reactor to a regenerator. The catalyst is regenerated through the combustion of coke deposits on the catalyst to return the catalyst to an active state. In a regenerator, the catalyst is subject to heating and an oxidizing gas. The combustion of the coke provides the heating of the catalyst. Additional fuel can be added to the regenerator to insure sufficient heating and combustion of the coke on the catalyst. The catalyst is carried out of the combustor style regenerator with the combustion gas effluent. The catalyst and combustion gas effluent are partially separated, and the regenerated catalyst settles in a dryer positioned at the outlet of the regenerator, forming a dense bed of catalyst in the dryer. Water is generated in the combustion process and adsorbed onto the catalyst. A drying gas is passed to the dryer and flows over the catalyst in a fluidized bed to remove adsorbed water. The fluidized bed can be a bubbling bed, or other fluidized bed wherein the catalyst is well mixed with the drying gas, and the catalyst flows through the bed as it is dried. 
         [0014]    In another embodiment, the process further includes passing the dried catalyst to a stripping unit thereby creating a stripped and dried catalyst that is passed to the reactor. A stripping gas is passed to the stripping unit to remove residual oxygen on the catalyst. The stripping gas can be any inert gas, such as nitrogen, or other inert gas, or a mixture of inert gases. 
         [0015]    In this embodiment, the process can be shown in the apparatus of  FIG. 1 . The apparatus is a regenerator  10  includes a combustion chamber  12 , having a catalyst inlet  14  for admitting spent catalyst, a combustion gas inlet  16 , and an outlet  18  for conveying catalyst and effluent gas. The apparatus  10  further includes a drying chamber  20 , having a drying gas inlet  22 , and a catalyst outlet  24 . The catalyst from the combustion chamber  12  disengages from the effluent gas as it enters the upper section of the regenerator  10  where the catalyst settles into the drying chamber  20 . Drying gas flows over the catalyst and displaces residual combustion gases, and water that has adsorbed onto the catalyst. The catalyst in the drying chamber  20  is in a fluidized bed and flows into a stripping chamber  30 . The stripping chamber  30  has a stripping gas inlet  32  and a catalyst outlet  34 , where the catalyst is passed to a reactor. The stripping gas can mix with the effluent gases from the combustion chamber  12  and from the drying chamber  20  to be passed out to the atmosphere or other venting means of disposing of the gas. 
         [0016]    The regenerator  10  can include gas distributors attached to the gas inlets for the different chambers. The gas distributors will facilitate mixing of the catalyst and gases in the respective chambers, and are positioned near the bottom of each respective chamber to minimize or eliminate any zones where the catalyst can collect and sit without passing through the regenerator  10 . 
         [0017]    The drying gas and combustion gas can be dried air, and can originate from a common source. The air for combustion in the regenerator is supplied by a main air blower, and can be sized to accommodate additional capacity for the dryer  20 . A portion of the air for the combustion gas can also be used to lift the catalyst into the combustion chamber  12 , entering through the spent catalyst inlet  14 . 
         [0018]    The drying chamber  20  can comprise a series of trays that can be stacked for distributing and flowing the catalyst across the trays and down the stack. This provides for good contact with drying gas flowing up through the tray stack and contacting the catalyst. The drying gas then mixes with the effluent gas from the combustion chamber  12  and is passed out of the regenerator  10 . In an alternate arrangement, the drying chamber  20  can comprise a packing material. The packing material will consist of large open packing objects that allows for the free flow of catalyst down through the packing material, while drying gas flows up through the packing material. 
         [0019]    In one embodiment, the drying chamber  20  comprises an annular region around the upper section of the combustion chamber  12 . The drying gas is passed through a distributor that distributes the gas around the annular region. The annular bed can be a fluidized bed, or a drying chamber with annular trays or packing 
         [0020]    In another embodiment, the invention comprises a process for drying regenerated catalyst in a continuous catalyst regeneration system. The process includes passing spent catalyst form a dehydrogenation reactor to a regenerator. The catalyst is regenerated in a combustion regeneration process to remove coke deposits on the catalyst, and generates a stream of regenerated catalyst and combustion gas effluent. The regenerated catalyst is separated from the combustion gas, and the regenerated catalyst is passed to a dryer. The dryer is positioned proximate to the combustion chamber gas inlet. The gas for drying the catalyst flows through the dryer, thus drying the catalyst, and passes to the combustion chamber wherein the gas is used to burn the coke off the catalyst. A dried catalyst stream passes to a stripper, and the dried catalyst is contacted with a stripping gas to remove residual oxygen on the catalyst. The stripping gas after flowing over the catalyst is passed to the drying chamber to contribute to the drying of the catalyst. The regenerated, dried and stripped catalyst is then passed to the reactor. 
         [0021]    This embodiment is illustrated in the apparatus shown in  FIG. 2 . The apparatus is a regenerator  110  that includes a combustion chamber  112  with a catalyst inlet  114 , a combustion gas inlet  116  and an outlet  118  for carrying catalyst and effluent gas. The apparatus includes a separation chamber  120  in fluid communication with the combustion chamber outlet  118 . The separation chamber  120  has a catalyst outlet  122  and an effluent gas outlet. The apparatus further includes a drying chamber  130  with a catalyst inlet  132  in fluid communication with the separation chamber catalyst outlet  122 , a catalyst outlet  134 , a drying gas inlet  136 , and a gas outlet  138  for the dryer effluent gas. The dryer gas outlet  138  is in fluid communication with the combustion chamber  112 , and the dryer gas can be used in the combustion process in the combustion chamber  112 . The apparatus further includes a stripping chamber  140  having a catalyst inlet  142  in fluid communication with the dryer catalyst outlet  134 , a catalyst outlet  144 , a stripper gas inlet  146 , and an effluent gas outlet in fluid communication with the dryer  130 . 
         [0022]    The gas inlets in the respective chambers can include gas distributors attached to the inlets for distribution of the gas in the respective chambers. The stripping gas which is passed to the dryer, can be passed to a distributor, or passed to the dryer gas inlet and mixed with the drying gas. The drying gas is air and after drying the catalyst is passed to the combustion chamber where it is used in the combustion process. The combustion gas can be passed either entirely through the dryer  130  before being passed to the combustion chamber  112 , or can be split with a portion passed through the drying chamber  130  and a portion passed directly to the combustion chamber  112 . In this embodiment, a single air source provides the air for combustion and drying, and where the drying air is used in the combustion process without the need for additional air. 
         [0023]    In this process, and regenerator design, the drying gas, stripping gas, and combustion chamber flue gases are combined and no additional conduits are required. 
         [0024]    While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.