Abstract:
Disclosed is a catalyst distributor and process for spreading catalyst over a regenerator vessel. Nozzles disposed angular to a header of the distributor spread catalyst throughout a full cross section of the catalyst bed.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention is the distribution of catalyst in a catalyst regenerator vessel. 
     Fluid catalytic cracking (FCC) is a hydrocarbon conversion process accomplished by contacting hydrocarbons in a fluidized reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds substantial amounts of highly carbonaceous material referred to as coke is deposited on the catalyst. A high temperature regeneration operation within a regenerator zone combusts coke from the catalyst. Coke-containing catalyst, referred to herein as coked catalyst, is continually removed from the reaction zone and replaced by essentially coke-free catalyst from the regeneration zone. Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone. 
     A common objective of these configurations is maximizing product yield from the reactor while minimizing operating and equipment costs. Optimization of feedstock conversion ordinarily requires essentially complete removal of coke from the catalyst. This essentially complete removal of coke from catalyst is often referred to as complete regeneration. Complete regeneration produces a catalyst having less than 0.1 and preferably less than 0.05 wt-% coke. In order to obtain complete regeneration, the catalyst has to be in contact with oxygen for sufficient residence time to permit thorough combustion. 
     Conventional regenerators typically include a vessel having a coked catalyst inlet, a regenerated catalyst outlet and a combustion gas distributor for supplying air or other oxygen containing gas to the bed of catalyst that resides in the vessel. Cyclone separators remove catalyst entrained in the flue gas before the gas exits the regenerator vessel. 
     There are several types of catalyst regenerators in use today. The conventional bubbling bed regenerator typically has just one chamber in which air is bubbled through a dense catalyst bed. Coked catalyst is added and regenerated catalyst is withdrawn from the same dense catalyst bed. Relatively little catalyst is entrained in the combustion gas exiting the dense bed. Two-stage bubbling beds have two chambers. Coked catalyst is added to a dense bed in a first chamber and is partially regenerated with air. The partially regenerated catalyst is transported to a dense bed in a second chamber and completely regenerated with air. The completely regenerated catalyst is withdrawn from the second chamber. 
     Complete catalyst regeneration can be performed in a dilute phase fast fluidized combustion regenerator. Coked catalyst is added to a lower chamber and is transported upwardly by air under fast fluidized flow conditions while completely regenerating the catalyst. The regenerated catalyst is separated from the flue gas by a primary separator upon entering into an upper chamber from which regenerated catalyst and flue gas is removed. U.S. Pat. No. 4,197,189 and U.S. Pat. No. 4,336,160 teach a riser combustion zone in which fast fluidized flow conditions are maintained to effect complete combustion without the need for the additional combustion in the catalyst bed collected from the top of the riser. 
     Oxides of nitrogen (NO X ) are usually present in regenerator flue gases but should be minimized because of environmental concerns. Production of NO X  is undesirable because it reacts with volatile organic chemicals and sunlight to form ozone. Regulated NO X  emissions generally include nitric oxide (NO) and nitrogen dioxide (NO 2 ), but the FCC process can also produce N 2 O. In an FCC regenerator, NO X  is produced almost entirely by oxidation of nitrogen compounds originating in the FCC feedstock and accumulating in the coked catalyst. At FCC regenerator operating conditions, there is negligible NO X  production associated with oxidation of N 2  from the combustion air. Low excess air in the regenerator is often used by refiners to keep NO X  emissions low. 
     After burn is a phenomenon that occurs when hot flue gas that has been separated from regenerated catalyst contains carbon monoxide that combusts to carbon dioxide. The catalyst that serves as a heat sink no longer can absorb the heat thus subjecting surrounding equipment to higher temperatures and perhaps creating an atmosphere conducive to the generation of nitrous oxides. Incomplete combustion to carbon dioxide can result from poor fluidization or aeration of the coked catalyst in the regenerator vessel or poor distribution of coked catalyst into the regenerator vessel. 
     To avoid after burn, many refiners have carbon monoxide promoter (CO promoter) metal such as costly platinum added to the FCC catalyst to promote the complete combustion to carbon dioxide before separation of the flue gas from the catalyst at the low excess oxygen required to control NO X  at low levels. While low excess oxygen reduces NO X , the simultaneous use of CO promoter often needed for after burn control can more than offset the advantage of low excess oxygen. The CO promoter decreases CO emissions but increases NO X  emissions in the regenerator flue gas. 
     On the other hand, many refiners use high levels of CO promoter and high levels of excess oxygen to accelerate combustion and reduce afterburning in the regenerator, especially when operating at high throughputs. These practices may increase NO X  by up to 10-fold from the 10-30 ppm possible when no platinum CO promoter is used and excess O 2  is controlled below 0.5 vol-%. 
     Improved methods are sought for preventing after burn and generation of nitrous oxides. Thorough mixing of catalyst and combustion gas in a regenerator promotes more uniform temperatures and catalyst activity fostering more efficient combustion of coke from catalyst. 
     SUMMARY OF THE INVENTION 
     We have discovered an apparatus and process for distributing coked catalyst to a regenerator vessel that spreads catalyst out in the catalyst bed of the regenerator to equalize temperatures in the bed. The more uniform temperatures in the dense bed promote a more uniform exposure of coked catalyst to oxygen resulting in higher regeneration efficiency. The regeneration is also more predictable and thus controllable to complete combustion to carbon dioxide without the need for a CO promoter to prevent after burn. Without after burn and CO promoter, less nitrous oxide is generated in the flue gas. 
     The catalyst distributor comprises a header having a longitudinal axis and an angular nozzle in communication with the header. The nozzle defines an acute angle with the longitudinal axis and discharges catalyst angularly from the header into the regenerator vessel. In an embodiment, a bottom of the nozzle is disposed in a bottom quarter of the header. In an additional embodiment, the nozzle discharges the catalyst horizontally. In a further embodiment, the catalyst distributor is submerged in the catalyst bed 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, elevational view of an FCC unit incorporating the present invention. 
         FIG. 2  is a plan view of the regenerator vessel of  FIG. 1  showing the catalyst distributor of the present invention. 
         FIG. 3  is an enlarged partial side view of the catalyst distributor of the present invention. 
         FIG. 4  is a schematic, elevational view of an alternative FCC unit incorporating an additional embodiment of catalyst distributor of the present invention. 
         FIG. 5  is a schematic, elevational view of an alternative FCC unit incorporating a further embodiment of catalyst distributor of the present invention. 
         FIG. 6  is a radar plot of catalyst distribution provided by the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although other uses are contemplated, the process and apparatus of the present invention may be embodied in an FCC unit.  FIG. 1  shows an FCC unit that includes a reactor section  10  and a regenerator vessel  50 . A regenerated catalyst conduit  12  transfers regenerated catalyst from the regenerator vessel  50  at a rate regulated by a control valve  14  to a riser  20  of the reactor section  10 . A fluidization medium such as steam from a nozzle  16  transports regenerated catalyst upwardly through the riser  20  at a relatively high density until a plurality of feed injection nozzles  18  inject hydrocarbon feed across the flowing stream of catalyst particles. The catalyst contacts the hydrocarbon feed cracking it to produce smaller, cracked hydrocarbon products while depositing coke on the catalyst to produce coked catalyst. 
     A conventional FCC feedstock or higher boiling hydrocarbon feedstock are suitable feeds. The most common of such conventional feedstocks is a “vacuum gas oil” (VGO), which is typically a hydrocarbon material having a boiling range of from 343 to 552° C. (650 to 1025° F.) prepared by vacuum fractionation of atmospheric residue. Such a fraction is generally low in coke precursors and heavy metal contamination which can serve to contaminate catalyst. Heavy hydrocarbon feedstocks to which this invention may be applied include heavy bottoms from crude oil, heavy bitumen crude oil, shale oil, tar sand extract, deasphalted residue, products from coal liquefaction, atmospheric and vacuum reduced crudes. Heavy feedstocks for this invention also include mixtures of the above hydrocarbons and the foregoing list is not comprehensive. 
     The resulting mixture continues upwardly through the riser  20  to a top at which a plurality of disengaging arms  22  tangentially and horizontally discharge the mixture of gas and catalyst from a top of the riser  20  through ports  24  into a disengaging vessel  26  that effects separation of gases from the catalyst. A transport conduit  28  carries the hydrocarbon vapors, including stripped hydrocarbons, stripping media and entrained catalyst to one or more cyclones  30  in a reactor vessel  32  which separates coked catalyst from the hydrocarbon vapor stream. The reactor vessel  32  may at least partially contain the disengaging vessel  26  and the disengaging vessel  26  is considered part of the reactor vessel  32 . A collection chamber  34  in the reactor vessel  32  gathers the separated hydrocarbon vapor streams from the cyclones  30  for passage to an outlet nozzle  36  and eventually into a fractionation recovery zone (not shown). Diplegs  38  discharge catalyst from the cyclones  30  into a lower portion of the reactor vessel  32  that eventually passes the catalyst and adsorbed or entrained hydrocarbons into a stripping section  40  of the reactor vessel  32  across ports  42  defined in a wall of the disengaging vessel  26 . Catalyst separated in the disengaging vessel  26  passes directly into the stripping section  40 . The stripping section  40  contains baffles  43 ,  44  or other equipment to promote mixing between a stripping gas and the catalyst. The stripping gas enters a lower portion of the stripping section  40  through a conduit to one or more distributors  46 . The coked catalyst leaves the stripping section  40  of the reactor vessel  32  through a reactor catalyst conduit  48  and passes to the regenerator vessel  50  at a rate regulated by a control valve  52 . The coked catalyst from the reactor vessel  32  usually contains carbon in an amount of from 0.2 to 2 wt-%, which is present in the form of coke. Although coke is primarily composed of carbon, it may contain from 3 to 12 wt-% hydrogen as well as sulfur and other materials. 
     The regenerator vessel  50  may be a bubbling bed type of regenerator as shown in  FIG. 1 . However, other regenerator vessels and other flow conditions may be suitable for the present invention. The reactor catalyst conduit  48  with an inlet  48   a  in downstream communication with the reactor vessel  32  may feed coked catalyst to a regenerator riser  54  to which air or other oxygen-containing combustion gas may be added through an outlet of a combustion gas line  55  via riser gas line  55   a . It is also contemplated that other lift gases may be used to lift the coked catalyst up the regenerator riser  54 . In the embodiment of  FIG. 1 , the coked catalyst descends the reactor catalyst conduit  48  to a bight which communicates with the regenerator riser  54 . The coked catalyst bends around the bight as it is picked up by the lift gas from riser gas line  55   a  with an outlet in upstream communication with the regenerator riser  54 . The coked catalyst then travels up the regenerator riser  54  and enters the regenerator vessel  50  through a coked catalyst inlet  56 . Coked catalyst is delivered to a catalyst distributor  60  with an entrance  64  in downstream communication with the catalyst inlet  56  and the outlet from riser gas line  55   a  for distributing coked catalyst to the regenerator vessel  50 . The regenerator riser  54  may terminate at a top head  62 . The regenerator riser  54  is a portion of the reactor catalyst conduit  48  that is immediately upstream of the catalyst distributor  60  and is disposed below the catalyst distributor  60 . The entrance  64  to a header  66  which may comprise a longitudinal pipe may be disposed below the top head  62 . Additionally, the header  66  may be perpendicular to the regenerator riser  54 . The catalyst distributor  60  comprises at least one and preferably a plurality of nozzles  68  communicating with the header for discharging catalyst into the regenerator vessel  50 . The catalyst distributor  60  discharges coked catalyst in an embodiment from under a top surface of a dense catalyst bed  58 , and the catalyst distributor  60  is preferably submerged in the bed below the top surface. Additionally, the catalyst distributor  60  is disposed in an eccentric position in the regenerator vessel  50  and radially projects catalyst into the dense catalyst bed  58  therefrom across the entire cross-section of the dense bed. The combustion gas in the regenerator riser  54  assists in the projection of the catalyst into the bed from catalyst distributor  60  and also provides oxygen for combustion requirements. 
     Oxygen-containing combustion gas, typically air, from combustion gas line  55  is primarily delivered to the regenerator vessel  50  by a combustion gas distributor  80  below the catalyst distributor  60 . In an embodiment, combustion gas distributor  80  distributes most of the combustion gas to the regenerator vessel  50  and is fed by a distributor gas line  55   b  from combustion gas line  55  regulated by a control valve. Flutes  82  in the combustion gas distributor  80  are arranged to emit combustion gas equally to the entire cross section of the regenerator vessel  50 . The oxygen in the combustion gas contacts the coked catalyst and combusts carbonaceous deposits from the catalyst to regenerate the catalyst and generate flue gas. Catalyst may get entrained with flue gas ascending in the regenerator vessel  50 . The catalyst entrained in the flue gas will therefore enter cyclone separators  86 ,  88  which centripetally separate flue gas from heavier catalyst particles. Catalyst particles will fall down dip legs  87 ,  89  and enter dense catalyst bed  58  again. Cleaned flue gas will ascend from the cyclone separators  86 ,  88  through ducts into plenum  90  and discharge through flue gas outlet  92 . Regenerated catalyst will depart the dense catalyst bed  58  in the regenerator vessel  50  through a regenerated catalyst outlet  96 . Regenerated catalyst conduit  12  in downstream communication with the outlet  96  delivers regenerated catalyst back to the reactor riser  20  at a rate regulated by control valve  14 . 
     Combustion gas such as air may be used to lift coked catalyst up the regenerator riser  54  which may allow regeneration to occur within the regenerator riser. The combustion gas to the regenerator riser  54  may be 10-20 wt-% of combustion gas to the regenerator vessel  50 . If air is the combustion gas, typically 13-15 kg (lbs) of air is required per kilogram (pound) of coke fed on catalyst to the regenerator. The temperature of the regenerator vessel  50  is about 500 to 900° C. and usually about 600 to 750° C. Pressure in the regenerator vessel  50  is preferably 173 to 414 kPa (gauge) (25 to 60 psig). The superficial velocity of the combustion gas is typically less than 1.2 m/s (4.2 ft/s) and the density of the dense bed is typically greater than 320 kg/m 3  (20 lb/ft 3 ) depending on the characteristics of the catalyst. 
     A plan view of the catalyst distributor  60  is shown in  FIG. 2  above air distributor  80  and the flutes  82  thereof. The header  66  defines a longitudinal axis L and an angular nozzle  68   a  in downstream communication with the header  66 . The angular nozzle  68   a  defines an acute angle α with the longitudinal axis L of the header  66 . In other words, a longitudinal axis a defined by the angular nozzle  68   a  defines an acute angle α with the longitudinal axis L. The angular nozzle  68   a  discharges catalyst into the regenerator vessel  50  at an acute angle α to the longitudinal axis L. In an embodiment, a plurality of nozzles  68   a - d  in downstream communication with the header  66  each have an axis that defines an acute angle with longitudinal axis L. The nozzles  68   b - d  define acute angles β, γ and δ with the longitudinal axis L of the header  66 , respectively. In other words, longitudinal axes a-d defined by the nozzles  68   a - d  define acute angles with the longitudinal axis L. The plurality of nozzles  68   a - d  discharge catalyst into the regenerator vessel  50  at an acute angle to the longitudinal axis L. A proximate nozzle  68   e  is perpendicular to the longitudinal axis L. Similarly, a proximate nozzle  68   f  is perpendicular to the longitudinal axis L. In other words, longitudinal axes e and f defined by the nozzles  68   e  and  f  each define right angles ε, ζ with the longitudinal axis L. Nozzles  68   a, b  and  f  are one side of the header  66  and nozzles c, d and e are on the opposite side of the header  66 . Nozzles directly opposed to each other may have the same length and define the same angle with the longitudinal axis L. In an embodiment angular nozzles on the same side of the header  66  define angles α and β and γ and δ with longitudinal axis L that are each different. The catalyst distributor may include a distal nozzle  68   g  on the outer end  70  of the header  66  that defines a longitudinal axis g that is aligned with the longitudinal axis L. 
     In an embodiment, the smallest angles the nozzles  68   a - g  define with the longitudinal axis L successively decrease as the nozzles are positioned further away from the entrance  64  and closer to the outer end  70 . The nozzles discharge catalyst at angles to the longitudinal axis L at angles that successively decrease as the distance from the inlet end increases. This allows the nozzles to radially project catalyst in equal portions across the entire cross section of the bed from an eccentric position in the regenerator vessel  50 . Additionally, in an embodiment, the length of the nozzles  68   a - f  on both sides of the header  66  successively increase as the nozzles are positioned further away from the entrance  64  and closer to the outer end  70 . The catalyst distributor  60  is disposed in one quadrant of the cross section of the regenerator vessel  50  and the longitudinal axis L may intersect a sectional center C of the regenerator vessel  50 . The opposite position of outlet  96  relative to the distributor  60  is also seen in  FIG. 2  in which outlet  96  is disposed in a quadrant opposed to the quadrant containing the distributor  60 . 
       FIG. 3  provides an enlarged, partial elevational view of the catalyst distributor  60  with the header  66  defining a height H. A bottom  72   a  of the nozzle  68   a  is disposed in the bottom quarter of the height H of the header  66 . In an embodiment, the bottom  72   a  is defined as the lowest point of the inner circumference of the nozzle  68   a . The positioning of the nozzle  68   a  with respect to the header  66  assures no catalyst stagnates in the header  66 . The nozzle  68   a  also has a height h. In an embodiment, over 50% of the height h of the nozzle  68   a  is disposed below 50% of a height H of the header  66 .  FIG. 3  also illustrates that longitudinal axis a defined by the nozzle  68   a  is horizontal in an embodiment. In an embodiment, the longitudinal axis L of the header  66  is also horizontal. In a further embodiment, bottoms  72   a - f  of all the nozzles  68   a - f  are disposed in the bottom quarter of the height H of the header  66 , but only nozzles  68   a, b  and  f  are shown in  FIG. 3 . In an embodiment, the bottoms  72   a - f  are defined as the lowest point of the inner circumference of the nozzle  68   a - f . In an embodiment, all the nozzles  68   a - f  have heights h and over 50% of a height h of the nozzles  68   a - f  are disposed below 50% of a height H of the header  66 . In an additional embodiment, the longitudinal axes define by all the nozzles  68   a - f  are horizontal, although only  68   a, b  and  f  are shown in  FIG. 3 . Aligned distal nozzle  68   g  is also shown in  FIG. 3 . Distal nozzle  68   g  also has an axis g which is horizontal and aligned with axis L. The horizontal nozzles  68   a - g  discharge catalyst horizontally from header  66 . 
       FIG. 4  shows an embodiment in a regenerator vessel  50 ′ that is a combustor type of regenerator, which may use hybrid turbulent bed-fast fluidized conditions in a high-efficiency regenerator vessel  50 ′ for completely regenerating coked catalyst. Elements in  FIG. 4  with the same configuration as in  FIG. 1  will have the same reference numeral as in  FIG. 1 . Elements in  FIG. 4  which have a different configuration as the corresponding element in  FIG. 1  will have the same reference numeral but designated with a prime symbol (′). The configuration and operation of the reactor section  10  in  FIG. 4  is essentially the same as in  FIG. 1  and the foregoing description is incorporated by reference into the embodiment of  FIG. 4 . However, the reactor catalyst conduit  48 ′ communicates with a catalyst distributor  60 ′. An inlet  48   a  of the reactor catalyst conduit  48 ′ is in communication with the reactor vessel  32 . A predominant portion of the reactor catalyst conduit  48 ′ is disposed above the catalyst distributor  60 ′. A fluidizing gas which may be a combustion gas is provided by fluidizing gas line  55   a ′ to propel the coked catalyst through the catalyst distributor  60 ′. However, relatively less fluidizing gas from fluidizing gas line  55   a ′ is required than in the embodiment of  FIG. 1  because gravity assists in the transport of coked catalyst in reactor catalyst conduit  48 ′ since the portion of the reactor catalyst conduit  48 ′ immediately upstream the catalyst distributor  60 ′ is disposed above the catalyst distributor  60 ′. Coked catalyst regulated by control valve  52  descends the reactor catalyst conduit  48 ′ and enters a lower or first chamber  102  of the combustor regenerator vessel  50 ′ through catalyst inlet  56 ′. 
     The catalyst distributor  60 ′ with an entrance  64 ′ in downstream communication with the catalyst inlet  56 ′ and the outlet from fluidizing gas line  55   a ′ distributes coked catalyst to the lower chamber  102  of combustor regenerator vessel  50 ′. The entrance  64 ′ communicates with a header  66  which may define a longitudinal axis. Additionally, the header  66  may be angular to the immediately upstream portion of the reactor catalyst conduit  48 ′. The catalyst distributor  60 ′ comprises at least one and preferably a plurality of nozzles  68  communicating with the header  66  for discharging catalyst into the lower chamber  102  of the regenerator vessel  50 ′. The catalyst distributor  60 ′ discharges coked catalyst in an embodiment from under a top surface of a dense catalyst bed  58 ′, and the catalyst distributor  60 ′ is preferably submerged in the bed below the top surface. Additionally, the catalyst distributor  60 ′ is disposed in an eccentric position in the combustor regenerator vessel  50 ′ and radially projects catalyst into the dense catalyst bed  58 ′ therefrom across the entire cross-section of the dense bed. The fluidizing gas from the fluidizing gas line  55   a ′ assists in the projection of the catalyst into the bed from catalyst distributor  60 ′. If the fluidizing gas contains oxygen to provide oxygen for combustion requirements, fluidizing gas line  55   a ′ may be a branch from combustion gas line  55 ′. The header  66  and nozzles  68  of catalyst distributor  60 ′ are configured as described with respect to  FIGS. 1-3 . 
     A combustion gas distributor  80 ′ distributes gas from distributor gas line  55   b ′ to the lower chamber  102 . Combustion gas line  55 ′ may feed the distributor gas line  55   b ′. The combustion gas contacts coked catalyst entering from catalyst distributor  60 ′ and lifts the catalyst at a superficial velocity of combustion gas in the lower chamber  102  of at least 1.1 m/s (3.5 ft/s) under fast fluidized flow conditions. In an embodiment, flow conditions in the lower chamber  102  will include a catalyst density of from 48 to 320 kg/m 3  (3 to 20 lb/ft 3 ) and a superficial gas velocity of 1.1 to 2.2 m/s (3.5 to 7 ft/s). In an embodiment, to accelerate combustion of the coke in the lower chamber  102 , hot regenerated catalyst from a dense is catalyst bed  59  in an upper or second chamber  104  may be recirculated into the lower chamber  102  via an external recycle catalyst conduit  108  regulated by a control valve  106 . Hot regenerated catalyst enters an inlet of recycle catalyst conduit  108  which is in downstream communication with the upper chamber  104 . The outlet end of the recycle catalyst conduit may be in upstream communication with a catalyst distributor  110  in the lower chamber  102 . Although described differently herein, it is contemplated that recycle catalyst could be added to the lower chamber  102  without using a catalyst distributor  110 . It is also contemplated that recycle catalyst could be added to the lower chamber  102  using the catalyst distributor  110  but the coked catalyst in reactor catalyst conduit  48  be added without distributor  60 ′. The hot regenerated catalyst may enter the lower chamber  102  through the second catalyst distributor that may be disposed at a higher height than catalyst distributor  60 ′. The catalyst distributors  60 ′ and  110  are preferably disposed on opposite sides of the regenerator vessel  50 ′. Recirculation of regenerated catalyst, by mixing hot catalyst from the dense catalyst bed  59  with relatively cool coked catalyst from the reactor catalyst conduit  48 ′ entering the lower chamber  102 , raises the overall temperature of the catalyst and gas mixture in the lower chamber  102 . A predominant portion of the recycle catalyst conduit  108  and a portion of recycle catalyst conduit  108  immediately upstream of the distributor  110  is disposed above the catalyst distributor  110 . 
     The catalyst distributor  110  with an entrance  114  in downstream communication with a catalyst inlet  116  and an outlet from recycle gas line  55   c  distributes recycled regenerated catalyst to the lower chamber  102  of combustor regenerator vessel  50 ′. If the recycle gas contains oxygen it may be a branch from combustion gas line  55 . The entrance  114  communicates with a header  66  which may comprise a longitudinal axis. Additionally, the header  66  may be angular to the immediately upstream portion of the recycle catalyst conduit  108 . The catalyst distributor  110  comprises at least one and preferably a plurality of nozzles  68  communicating with the header  66  for discharging catalyst into the combustor regenerator vessel  50 ′. The catalyst distributor  110  discharges catalyst in an embodiment from under a top surface of a dense catalyst bed  58 ′, and the catalyst distributor  110  is preferably submerged in the bed below the top surface. Additionally, the catalyst distributor  110  is disposed in an eccentric position in the lower chamber  102  of the combustor regenerator vessel  50 ′ and radially projects catalyst into the dense catalyst bed  58 ′ therefrom preferably across the entire cross-section of the dense bed. The recycle gas from the catalyst distributor  110  assists in the projection of the catalyst into the bed from catalyst distributor  110  and may also provide oxygen for combustion requirements. The header  66  and nozzles  68  of the catalyst distributor  110  are configured as described with respect to  FIGS. 1-3 . 
     The mixture of catalyst and combustion gas in the lower chamber  102  ascend through a frustoconical transition section  116  to the transport, riser section  118  of the lower chamber  102 . The riser section defines a tube and extends upwardly from the lower chamber  102 . The mixture of catalyst and gas travels at a higher superficial gas velocity than in the lower chamber  102  due to the reduced cross-sectional area of the riser section  118  relative to the cross-sectional area of the lower chamber  102  below the transition section  116 . Hence, the superficial gas velocity will usually exceed about 2.2 n/s (7 ft/s). The riser section  118  will have a relatively lower catalyst density of less than about 80 kg/m 3  (5 lb/ft 3 ). 
     The mixture of catalyst particles and flue gas is discharged from an upper portion of the riser section  118  into the upper chamber  104 . Substantially completely regenerated catalyst may exit the top of the riser section  118 , but arrangements in which partially regenerated catalyst exits from the lower chamber  102  are also contemplated. Discharge is effected through a disengaging device  120  that separates a majority of the regenerated catalyst from the flue gas. Initial separation of catalyst upon exiting the riser section  118  minimizes the catalyst loading on cyclone separators  122 ,  124  or other downstream devices used for the essentially complete removal of catalyst particles from the flue gas, thereby reducing overall equipment costs. In an embodiment, catalyst and gas flowing up the riser section  118  impact a top elliptical cap  126  of the riser section  118  and reverse flow. The catalyst and gas then exit through downwardly directed openings in radial disengaging arms  128  of the disengaging device  120 . The sudden loss of momentum and downward flow reversal cause at least about 70 wt-% of the heavier catalyst to fall to the dense catalyst bed  59  and the lighter flue gas and a minor portion of the catalyst still entrained therein to ascend upwardly in the upper or second chamber  104 . Downwardly falling, disengaged catalyst collects in the dense catalyst bed  59 . Catalyst densities in the dense catalyst bed  59  are typically kept within a range of from about 640 to about 960 kg/m 3  (40 to 60 lb/ft 3 ). 
     A fluidizing gas line  55   d  delivers fluidizing gas to the dense catalyst bed  59  through a fluidizing distributor  131 . Fluidizing gas may be combustion gas, typically air, and may branch from combustion gas line  55 . In combustor regenerator vessel  50 ′, in which full combustion of coke is effected in the lower chamber  102 , approximately no more than 2 wt-% of the total gas requirements within the process enters the dense catalyst bed  59  through the fluidizing distributor  131  with the remainder being added to the lower chamber  102 . In this embodiment, gas is added to the upper chamber  104  not for combustion purposes, but only for fluidizing purposes, so the catalyst will fluidly exit through the catalyst conduits  108  and  12 . Combustion gas added via gas lines  55   a ′ and  55   c ′ will account for about 10-20 wt-% of the gas to the combustor regenerator vessel  50 ′. If air is the combustion gas, typically 13 to 15 kg (lbs) of air is required per kilogram (pound) of coke fed on catalyst to the regenerator. The combustor regenerator vessel  50 ′ typically has a temperature of about 594 to about 704° C. (1100 to 1300° F.) in the lower chamber  102  and about 649 to about 760° C. (1200 to 1400° F.) in the upper chamber  104 . Pressure may be between 173 and 414 kPa (gauge) (25 to 60 psig) in both chambers. 
     The combined flue and fluidizing gas and entrained particles of catalyst enter one or more separation means, such as the cyclone separators  122 ,  124 , which separates catalyst fines from the gas. Flue gas, relatively free of catalyst is withdrawn from the combustor regenerator vessel  50 ′ through an exit conduit  130  while recovered catalyst is returned to the dense catalyst bed  59  through respective diplegs  132 ,  134 . Catalyst from the dense catalyst bed  59  is transferred through the regenerated catalyst conduit  12  back to the reactor section  10  where it again contacts feed as the FCC process continues. 
       FIG. 5  shows an embodiment in a regenerator vessel  50 ″ that is a two-stage bubbling bed regenerator, which may be suitable in an FCC unit that processes heavier feed such as a resid unit. Elements in  FIG. 5  with the same configuration as in  FIG. 1  or  4  will have the same reference numeral as in  FIG. 1  or  4 . Elements in  FIG. 5  which have a different configuration as the corresponding element in  FIG. 1  or  4  will have the same reference numeral but designated with a double prime symbol (″). The configuration and operation of the reactor section  10  in  FIG. 5  is essentially the same as in  FIG. 1  and the foregoing description is incorporated by reference into the embodiment of  FIG. 5 . The reactor catalyst conduit  48 ″ with an inlet  48   a  in downstream communication with the reactor vessel  32  may feed coked catalyst to a regenerator riser  54 ″ at a rate regulated by control valve  52 . Lift gas pushes the catalyst up the regenerator riser. If air or other oxygen-containing combustion gas is used as the lift gas, it may be added from an outlet of a riser gas line  55   a ″ branching from a combustion gas line  55 ″. The reactor catalyst conduit  48 ″ has an outlet that communicates with a catalyst distributor  60 ″ in an upper chamber  104 ″ of the regenerator vessel  50 ″. The fluidizing gas which may be a combustion gas propels the coked catalyst through the catalyst distributor  60 ″. In the embodiment of  FIG. 5 , the coked catalyst descends the reactor catalyst conduit  48 ″ to a bight which communicates with the regenerator riser  54 ″. The coked catalyst bends around the bight as it is picked up by the lift gas from gas line  55   a ″ with an outlet in upstream communication with the regenerator riser  54 ″. The coked catalyst then travels up the regenerator riser  54 ″ and enters the upper chamber  104 ″ of the regenerator vessel  50 ″ through a coked catalyst inlet  56 ″. It is also contemplated that coked catalyst may first enter the lower chamber of a two-stage regenerator if a two-stage generator were ever designed so. The catalyst distributor  60 ″ with an entrance which may be in downstream communication with the catalyst inlet  56 ″ and the outlet from riser gas line  55   a ″ distributes coked catalyst to the upper chamber  104 ″ of the regenerator vessel  50 ″. In the embodiment of  FIG. 5 , the entrance to the catalyst distributor  60 ″ and the catalyst inlet to the regenerator vessel  50 ″ may be coterminous. The regenerator riser  54 ″ may terminate at a top head  62 . The regenerator riser  54 ″ is a portion of the reactor catalyst conduit  48 ″ that is immediately upstream of the catalyst distributor  60 ″ and is disposed below the catalyst distributor  60 ″. A header  66  may comprise a longitudinal pipe that may be disposed below the top head  62 . Additionally, the header  66  may be perpendicular to the regenerator riser  54 ″. The catalyst distributor  60 ″ comprises at least one and preferably a plurality of nozzles  68  communicating with the header for discharging catalyst into the upper chamber  104 ″ of the regenerator vessel  50 ″. The catalyst distributor  60 ″ discharges coked catalyst in an embodiment from under a top surface of a dense catalyst bed  58 ″, and the catalyst distributor  60 ″ is preferably submerged in the bed below the top surface. Additionally, the catalyst distributor  60 ″ is disposed in an eccentric position in the upper chamber  104 ″ of the regenerator vessel  50 ″ and radially projects catalyst into the dense catalyst bed  58 ″ therefrom across the entire cross-section of the dense bed. The lift gas in the regenerator riser  54  assists in the projection of the catalyst into the bed from catalyst distributor  60  and may also provide oxygen for combustion requirements. The header  66  and nozzles  68  of catalyst distributor  60 ″ are configured as described with respect to  FIGS. 1-3 . 
     Oxygen-containing combustion gas, typically air, from combustion gas line branches  55   d ″ and  55   e  of combustion gas line  55 ″ regulated by control valves are primarily distributed to the upper chamber  104 ″ of the regenerator vessel  50 ″ by combustion gas distributors  200  and  202 , respectively, below the catalyst distributor  60 ″. In an embodiment, combustion gas distributors  200 ,  202  distribute most of the combustion gas to the upper chamber. The oxygen in the combustion gas contacts the coked catalyst and combusts most of the carbonaceous deposits from the catalyst to regenerate the catalyst and generate flue gas. Catalyst may get entrained with flue gas ascending in the upper chamber  104 ″. The catalyst entrained in the flue gas will therefore enter cyclone separators  122 ″,  124 ″ which centripetally separate flue gas from heavier catalyst particles. Catalyst particles will fall down dip legs  132 ″,  134 ″ and enter dense catalyst bed  58 ″ again. The ends of the dip legs  132 ″,  134 ″ may be submerged in the dense catalyst bed  58 ″. Cleaned flue gas will ascend from the cyclone separators  122 ″,  124 ″ through ducts into plenum  90 ′ and discharge through flue gas outlet  130 . Partially regenerated catalyst will depart the dense catalyst bed  58 ″ through a transport catalyst conduit  108 ″ regulated by control valve  106  and enter lower chamber  102 ″. 
     Hot partially regenerated catalyst enters an inlet of recycle catalyst conduit  108  which is in downstream communication with the upper chamber  104 ″. The outlet end of the transport catalyst conduit  108 ″ may be in upstream communication with a catalyst distributor  110  in the lower chamber  102 ″. The hot partially regenerated catalyst enters the lower chamber  102 ″ through the second catalyst distributor  110 . A predominant and immediately upstream portion of the transport catalyst conduit  108 ″ is disposed above the catalyst distributor  110 . 
     The catalyst distributor  110  with an entrance  114  in downstream communication with a catalyst inlet  116  and an outlet from recycle gas line  55   c ′ distributes recycled regenerated catalyst to the lower chamber  102 ″ of the regenerator vessel  50 ″. The entrance  114  communicates with a header  66  which may comprise a longitudinal axis. Additionally, the header  66  may be angular to an immediate upstream portion of the transport catalyst conduit  108 ″. The catalyst distributor  110  comprises at least one and preferably a plurality of nozzles  68  communicating with the header  66  for discharging catalyst into the combustor lower chamber  102 ″ of the regenerator vessel  50 ″. The catalyst distributor  110  discharges coked catalyst in an embodiment from under a top surface of a dense catalyst bed  58 ′, and the catalyst distributor  110  is preferably submerged in the bed below the top surface. Additionally, the catalyst distributor  110  is disposed in an eccentric position in the regenerator vessel  50 ″ and radially projects catalyst into the dense catalyst bed  59 ″ therefrom across the entire cross-section of the dense bed. The gas from the recycle gas line  55   c ′ assists in the projection of the catalyst into the bed from catalyst distributor  110  and may also provide oxygen for combustion requirements. The header  66  and nozzles  68  of catalyst distributor  110  are configured as described with respect to  FIGS. 1-3 . Catalyst distributor  110  and catalyst distributor  60 ″ may be on opposite sides of the regenerator vessel  50 ″. 
     Combustion gas distributor  80 ′ fed by distributor gas line  55   b ′ branching from combustion gas line  55 ″ distributes most of the combustion gas to the lower chamber  102 ″. Flutes  82  in the combustion gas distributor  80  are arranged to emit combustion gas equally to the entire cross section of the lower chamber  102 ″ of the regenerator vessel  50 ″. The oxygen in the combustion gas contacts the coked catalyst and combusts most of the remaining carbonaceous deposits from the catalyst to regenerate the catalyst and generate flue gas. Catalyst may get entrained with flue gas and ascend in the lower chamber  102 ″ and exit through vents  204  into the upper chamber  104 ″. Partially regenerated catalyst entering the lower chamber  102 ″ is fully regenerated by any combustion gas from the catalyst distributor  110  and the combustion gas distributor  80 ′. 
     A regenerated catalyst outlet  96 ″ from the lower chamber  102 ″ of the regenerator vessel  50 ″ allows fully regenerated catalyst to depart through a regenerated catalyst conduit  12 ″. Regenerated catalyst conduit  12 ″ in downstream communication with said outlet  96 ″ delivers regenerated catalyst back to the reactor riser  20  at a rate regulated by control valve  14 . 
     Combustion gas such as air may be used to lift coked catalyst up the regenerator riser  54 ″ which may allow regeneration to occur within the regenerator riser. The combustion gas to the regenerator riser  54  may be 10-20 wt-% of combustion gas to the regenerator vessel  50 . If air is the combustion gas, typically 11-13 kg (lbs) of air is required per kilogram (pound) of coke fed on catalyst to the regenerator  50 ″ in the upper chamber  104 ″ and about 2-4 kg (lbs) of air is required per kilogram (pound) of coke fed on catalyst to the regenerator  50 ″ in the lower chamber  102 ″. Seventy-five weight percent of all to combustion gas requirements are fed to the upper chamber  104 ″. Twenty-five weight percent of all combustion gas requirements are fed to the lower chamber with about 6 to 10 wt-% entering the upper chamber  104 ″ from the lower chamber  102 ″ through vents  204 . The two-stage regenerator vessel  50 ″ typically has a temperature of about 594 to about 760° C. (1100 to 1400° F.) in both the lower chamber  102 ″ and the upper chamber  104 ″. In both chambers, the superficial velocity of the combustion gas is typically less than 1.2 m/s (4.2 ft/s) and the density of the dense bed is typically greater than 320 kg/m 3  ( 20  lb/ft 3 ) depending on the characteristics of the catalyst. Pressure may be between 173 and 414 kPa (gauge) (25 to 60 psig) in both chambers. 
     The embodiment of  FIG. 5  provides for the reactor section  10  to be disposed at a lower relative height while maintaining a similar downward angle for reactor catalyst conduit  48 ″ as in  FIGS. 1 and 4  despite that the outlet end of the reactor catalyst conduit  48 ″ is disposed at a higher elevation in the upper chamber  104 ″. 
     The catalyst distributor  60 ,  60 ′,  60 ″ and  110  will typically be supported by the end of the catalyst conduit with which it communicates. The catalyst distributor  60 ,  110  will typically be made of stainless steel such as 304 stainless steel, and coated with abrasion resistant lining both externally and internally. The regenerator may be equipped with one or more catalyst coolers to avoid excessively hot regenerator temperatures. 
     EXAMPLE 1 
     The catalyst distributor of the present invention was tested in a FCC regenerator by injecting radioactive sodium-24 liquid into various locations, which allowed monitoring of its progression through the catalyst bed of the regenerator. The sodium isotope was injected into the regenerator in an aqueous-soluble form. Once injected, the liquid component flashed due to the high process temperature, causing the radioactive sodium isotope to adhere to the catalyst. Detectors around the circumference of the regenerator vessel monitored catalyst distribution and flow characteristics in the solid phase. 
       FIG. 6  presents the distribution analysis of catalyst in the regenerator in the form of a radar plot. The catalyst distributor was disposed just counter-clockwise of the radial line at 240 degrees and its longitudinal axis was aimed toward a center of the vessel. A catalyst outlet was disposed between the center and the outer wall of the regenerator vessel on the radial line at about 40 degrees. Actual catalyst distribution data is indicated by the smaller diamonds. The ideal catalyst distribution profile is indicated by the larger squares for comparison. The scale percentages indicate relative flow of spent catalyst to the particular detector location. 
     The detector ring revealed responses similar to ideal distribution all around the circumference of the regenerator vessel. Consequently, the catalyst distributor of the present invention provides a good catalyst distribution relative to the ideal distribution profile for uniformly exposing catalyst to combustion gas. 
     EXAMPLE 2 
     We compared actual performance of an FCC regenerator before and after installation of the spent catalyst distributor of the present invention. Regenerator conditions were kept the same except less CO promoter was used in the catalyst after installation of the catalyst distributor. 
     We found that the greatest temperature differential across a diameter of the regenerator vessel diminished from about 38° C. (100° F.) to about 4° C. (40° F.) as a result of installing the catalyst distributor of the present invention. This indicates that less after burn is occurring due to the improved spent catalyst distribution in the regenerator. Similarly, we found nitrous oxide emissions in the flue gas decreased from about 80 wppm to about 35 wppm after installing the catalyst distributor of the present invention also due to the improved catalyst distribution.