Abstract:
Systems and processes for regenerating catalyst are provided herein that include a catalyst regeneration tower having a cooling zone that receives a catalyst cooling stream generated by a cooling gas loop. The systems and processes include a first thermocompressor that utilizes a first motive vapor and a second thermocompressor that utilizes a second motive vapor in order to provide the catalyst cooling stream to the regeneration tower. The second thermocompressor operates in parallel with the first thermocompressor. The first thermocompressor can utilize combustion air as the motive vapor. The second thermocompressor can utilize nitrogen as the motive vapor.

Description:
FIELD OF THE INVENTION 
       [0001]    The systems and processes disclosed herein relate to the regeneration of spent catalyst in the art of catalytic conversion of hydrocarbons to useful hydrocarbon products, and more particularly to thermocompressors utilized in a continuous catalyst regeneration (CCR) process. 
       DESCRIPTION OF RELATED ART 
       [0002]    The catalysts used in catalytic processes for the conversion of hydrocarbons tend to become deactivated for one or more reasons. In instances where the accumulation of coke deposits causes the deactivation, regenerating of the catalyst to remove coke deposits can restore the activity of the catalyst. Coke is normally removed from catalyst by contact of the coke-containing catalyst at high temperature with an oxygen-containing gas to combust and remove the coke in a regeneration process. These processes can be carried out in-situ, or the catalyst may be removed from a reactor in which the hydrocarbon conversion takes place and transported to a separate regeneration zone for coke removal. Various arrangements for continuously or semicontinuously removing catalyst particles from a reaction zone and for coke removal in a regeneration zone have been developed. 
         [0003]    Some continuous catalyst regeneration systems provide a thermocompressor to facilitate continued operation of the continuous catalyst regeneration processes during brief periods of operation under low coke conditions. One system utilizing a thermocompressor is described, for example, in PCT Application No. PCT/US2006/062647, the content of which is hereby incorporated by reference in its entirety. A thermocompressor can circulate air from the outlet of the air heater to mix with combustion air going to the cooling zone and provide a net amount of combustion air to the cooling zone. The thermocompressor can utilize combustion air as the motive air, and difficulties in maintaining operation of the system can occur because the net quantity of combustion air in low coke conditions may be insufficient to satisfy the minimum flow requirement for the air heater and/or for cooling the catalyst. 
       SUMMARY OF THE INVENTION 
       [0004]    The systems and processes disclosed herein relate to continuous catalyst regeneration, particularly to such systems and processes that utilize a plurality of thermocompressors to facilitate continuous catalyst regeneration under low coke conditions. 
         [0005]    In one aspect, a catalyst regeneration system system is provided that includes a catalyst regeneration tower, a first thermocompressor, a second thermocompressor in parallel with the first thermocompressor, and one or more valves. The catalyst regeneration tower includes a cooling zone that receives a catalyst cooling stream. The first thermocompressor utilizes a first motive vapor. The second thermocompressor utilizes nitrogen as a motive vapor. The one or more valves can selectively direct a cooled stream to at least one of the first thermocompressor or the second thermocompressor to produce the catalyst cooling stream. 
         [0006]    In a second aspect, a process for providing a catalyst cooling stream to a catalyst regeneration tower is provided that includes selectively providing a cooled stream to at least one of a first thermocompressor or a second thermocompressor, to produce a catalyst cooling stream. and The first thermocompressor utilizes a first motive vapor. The second thermocompressor utilizes a second motive vapor. The catalyst cooling stream can be provided to a catalyst cooling zone in a catalyst regeneration tower. 
         [0007]    In a third aspect, a process for regenerating catalyst is provided that includes removing a first gas stream from a regeneration tower, passing the first gas stream to an air heater to form a heated first gas stream, dividing the heated first gas stream to form a regeneration tower return stream and a cooling loop stream, cooling the cooling loop stream in a cooling zone cooler to form a cooled stream, selectively providing the cooled stream to at least one of a first thermocompressor or a second thermocompressor to produce a catalyst cooling stream, and providing the catalyst cooling stream to the regeneration tower. The first thermocompressor utilizes a first motive vapor. The second thermocompressor utilizes a second motive vapor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Specific examples have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification. 
           [0009]      FIG. 1  is a simplified flow diagram of a portion of a continuous catalyst regeneration process that includes a cooling gas loop. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a simplified flow diagram of a continuous catalyst regeneration (CCR) system indicated generally at  100 . As illustrated, spent catalyst  102  can be removed from a reactor and provided to a catalyst regeneration tower  104 . The catalyst regeneration tower  104  can have a plurality of regeneration zones or stages through which the spent catalyst passes when undergoing regeneration. As illustrated, regeneration tower  104  includes a combustion zone  106 , a halogenation zone  108 , a drying zone  110 , and a cooling zone  112 . Spent catalyst can enter the regeneration tower  104  through an inlet at the top of the regeneration tower  104 . Upon entering the regeneration tower  104 , the spent catalyst can undergo the regeneration process by entering combustion zone  106 , and then subsequently proceeding through the halogenation zone  108 , the drying zone  110 , and the cooling zone  112 . Regenerated catalyst  114  can be removed from the catalyst regeneration tower  104 , and can be returned to the reactor. 
         [0011]    As illustrated in  FIG. 1 , the continuous catalyst regeneration process  100  has a cooling gas loop  116 . Cooling gas loop  116  includes a first gas stream  118  that is removed from a cooling zone outlet  120  in the cooling zone  112  of the regeneration tower  104 . First gas stream  118  can contain air, and can have a temperature of from about 300° F. (149° C.) to about 1000° F. (538° C.). First gas stream  118  can be passed through a conduit to an air heater  122 . Air heater  122  heats the first gas stream  118 , for example to a temperature of about 1050° F. (566° C.), to form a heated first gas stream  124 . The heated first gas stream  124  exits the air heater  122 , and can be divided into at least two gas streams, including a regeneration tower return stream  126  and a cooling loop stream  128 . The regeneration tower return stream  126  can be passed through a conduit back to the regeneration tower  104 , and can be provided to the drying zone  110 . After it enters the drying zone, the gas in the regeneration tower return stream  126  can rise within the regeneration tower  104 , and can be utilized in the combustion zone  106 . 
         [0012]    The cooling loop stream  128  can be passed through a conduit to a cooling zone cooler  130 . Cooling zone cooler  130  can be a heat exchanger, and is preferably an indirect heat exchanger such as, for example, a double pipe heat exchanger, or a shell and tube type heat exchanger. When the cooling zone cooler  130  is a shell and tube exchanger, the cooling loop stream  128  can be passed through the tube side of the cooling zone cooler  130  to form cooled stream  132 . 
         [0013]    The cooling zone cooler  130  can be cooled with any suitable medium, such as air or water. For example, as illustrated in  FIG. 1 , a cooler blower  134  can receive atmospheric air, or ambient air from the outdoors, and can provide an atmospheric air stream  136  to the cooling zone cooler  130  to act as a cooling fluid for cooling loop stream  128 . When cooling zone cooler is a shell and tube type heat exchanger, for example, atmospheric air stream  136  can be provided to the shell side of the cooling zone cooler  130 . 
         [0014]    As shown in  FIG. 1 , cooling gas loop  116  can include one or more thermocompressors, such as a first thermocompressor  138  and a second thermocompressor  140 . Generally, the thermocompressors  138  and  140  can utilize the kinetic energy of a primary fluid, such as the first and second motive vapors described below, to pump a secondary fluid, such as cooled stream  132 . The first thermocompressor can utilize a first motive vapor, and the second thermocompressor can utilize a second motive vapor. The second motive vapor can preferably have a composition that is different from the composition of the first motive vapor. For example, as illustrated in  FIG. 1 , first thermocompressor  138  can utilize combustion air as the first motive vapor, and second thermocompressor  140  can utilize nitrogen as the second motive vapor. 
         [0015]    First thermocompressor  138  and second thermocompressor  140  are preferably configured to operate in parallel. The cooled stream  132  can be selectively directed, and can be provided to at least one of the first thermocompressor or the second thermocompressor to produce a catalyst cooling stream  148 . The cooled stream  132  can form at least part of the catalyst cooling stream  148 . Catalyst cooling stream  148  can also include the motive vapor of any thermocompressor to which the cooled stream  132  is provided. Catalyst cooling stream  148  can thus include the first motive vapor, the second motive vapor, or both the first and second motive vapors. Catalyst cooling stream  148  can be passed through a conduit to an inlet  150  of the regeneration tower  104 , and can be provided to the cooling zone  112  of the catalyst regeneration tower  104 . 
         [0016]    The cooled stream  132  can be provided to the first thermocompressor  138 , to the second thermocompressor  140 , or can be divided and provided to both the first thermocompressor  138  and the second thermocompressor  140 . One or more valves, such as illustrated valve  154 , can be utilized to selectively direct the cooled stream  132 . The one or more valves can be operated by one or more switches, such as, for example, a software switch. The cooled stream  132  can be selectively directed based upon operating conditions, including, but not limited to, catalyst coke level, instrument header pressure, and other operating conditions. 
         [0017]    In some instances, it may be desirable to operate the first thermocompressor  138  during a first set of operating conditions, and to operate the second thermocompressor  140  during a second set of operating conditions. For example, the cooling gas loop  116  can utilize first thermocompressor  138  under normal operating conditions, or for short term operations under low coke conditions, and can utilize second thermocompressor  140  for operation during periods of continuous low coke conditions. 
         [0018]    With respect to the utilization of the first thermocompressor  138 , the first motive vapor  142  can be supplied to the first thermocompressor  138  through dryer  144 . As shown in  FIG. 1 , dryer  144  can receive a gas stream  146 , and can supply motive vapor  142  through a conduit to the first thermocompressor  138 . The gas stream  146  can be air, and can include oxygen and nitrogen. The flow rate or amount of the first motive vapor  142  can be controlled based upon the amount of oxygen required by the combustion zone  106 . The flow rate for the first motive vapor  142  can be based on a reduced combustion air rate, such as, for example, about 25% of the design combustion air, and a reduced instrument air header pressure, such as, for example, a pressure that is about 10 psi lower than the pressure available under normal operating conditions. 
         [0019]    To facilitate the operation of the first thermocompressor  138  under certain conditions, such as, for example, longer term low coke or very low coke operation conditions, a nitrogen stream  152  can be provided and combined with the first motive vapor  142  to add motive flow for the first thermocompressor  138 . The nitrogen stream  152  can provide added motive gas flow and gas pressure to help satisfy the process requirements, the nitrogen results in reduced oxygen concentration in the chlorination zone of the regeneration tower. Over extended periods of time, however, the lower oxygen concentration in the chlorination zone of the regeneration tower may adversely impact the quality of the catalyst regeneration. 
         [0020]    With respect to utilization of the second thermocompressor  140 , nitrogen stream  152  can be received by the second thermocompressor  140 , and can act as the second motive vapor for the second thermocompressor  140 . Nitrogen stream  152  can consist substantially completely of nitrogen. The nitrogen stream  152  can be provided to the second thermocompressor  140  at a higher pressure than the combustion air utilized as the motive vapor for first thermocompressor  138 . The second thermocompressor  140  can thus operate at a higher ratio of load gas to motive gas than the first thermocompressor  138 . The higher ratio can provide additional load gas flow to maintain long term low coke operation while maintaining an appropriate oxygen concentration in the halogenation zone  108  of the regeneration tower  104 . In some examples, the pressure of nitrogen stream  152  can be from about 30 psi to about 300 psi higher than the pressure of the combustion air utilized as the motive vapor for the first thermocompressor  138 . The flow rate of nitrogen stream  152  can preferably be controlled to maintain the oxygen content in the halogenation zone  108  at a level of above about 10%, and preferably at a level of above about 18%. 
         [0021]    From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.