Patent Description:
The field of the subject matter relates to catalyst regeneration in fluidized catalytic cracking units, and more particularly relates to a partial burn regenerator.

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 regeneration 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 or full burn produces a catalyst having less than <NUM> and preferably less than <NUM> 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 of coke. Partial regeneration occurs when complete regeneration does not occur. Partial regeneration occurs when regeneration produces a catalyst having at least <NUM> and preferably at least <NUM> and typically at least <NUM> wt% coke.

In the regenerator, the coke is burned from the catalyst with oxygen containing gas, usually air. Flue gas formed by burning the coke in the regenerator is treated for removal of particulates and conversion of carbon monoxide, after which the flue gas may be normally discharged into the atmosphere. 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. The regenerator includes a dilute phase and a dense phase fluidized catalyst bed disposed in respective upper and lower regions of the vessel.

There are several types of catalyst regenerators in use today. A 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 an upper, first chamber and is partially regenerated with air. The partially regenerated catalyst is transported to a dense bed in a lower, second chamber and completely regenerated with air. The completely regenerated catalyst is withdrawn from the second chamber.

A combustor-style regenerator or high efficiency regenerator as disclosed in <CIT> has a lower chamber called a combustor that burns nearly all the coke to CO<NUM> with little or no CO promoter and with low excess oxygen, typically. A portion of the hot regenerated catalyst from the upper regenerator is recirculated to the lower combustor to heat the incoming spent catalyst and to control the combustor catalyst density and temperature for optimum coke combustion rate. As the catalyst and flue gas mixture enters an upper, narrower section of the combustor, the upward velocity is further increased and the two-phase mixture exits through a disengager into an upper chamber. The upper chamber separates the catalyst from the flue gas in the disengager and cyclones and returns the catalyst to a dense catalyst bed which supplies hot regenerated catalyst to both the riser reactor and the lower combustor chamber.

Afterbum is a phenomenon that occurs when hot flue gas that has been separated from regenerated catalyst contains carbon monoxide that combusts to carbon dioxide in a dilute phase of catalyst. Insufficient catalyst is present in the dilute phase to serve as a heat sink to absorb the heat thus subjecting surrounding equipment to higher temperatures that can be over metallurgical limits and perhaps creating an atmosphere conducive to the generation of nitrous oxides that are undesirable for the environment. Incomplete combustion to carbon dioxide can result from insufficient oxygen in the combustion gas, poor fluidization or aeration of the coked catalyst in the regenerator vessel or poor distribution of coked catalyst into the regenerator vessel.

Conventionally, in a partial combustion operation, it is difficult to burn all of the carbon off the catalyst and the residual carbon can have a negative effect on catalyst activity. It is considered to be partial burn in the regenerator when either the oxygen or carbon monoxide content or both of them are present in the flue gas in a concentration of less than <NUM>% and typically no greater than <NUM> ppm respectively at the outlet of the regenerator vessel. To avoid after burn, many refiners add carbon monoxide promoter (CO promoter) metal such as costly platinum 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 maintain NOx at low levels. While low excess oxygen reduces NOx, the simultaneous use of CO promoter often needed for after burn control can more than offset the NOx advantage of low excess oxygen. The CO promoter decreases CO emissions but increases NOx 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 NOx by up to <NUM>-fold from the <NUM>-<NUM> ppm possible when no platinum CO promoter is used and excess O<NUM> is controlled to below <NUM> vol%.

Therefore, there is a need for improved methods for preventing after burn and generation of nitrous oxides while operating a high efficiency regenerator in a partial burn mode. There is a need for a process and an apparatus to ensure thorough mixing of catalyst and combustion gas in a regenerator that can promote more uniform temperatures and catalyst activity fostering more efficient combustion of coke from catalyst.

An aspect of the invention is a process according to claim <NUM> for combusting coke from catalyst comprising contacting hydrocarbon feed with catalyst to produce cracked products and coked catalyst. The cracked products are separated from the coked catalyst. The coked catalyst is delivered to a lower chamber of a regeneration vessel. The coked catalyst is contacted with oxygen to combust coke from the coked catalyst. The catalyst and flue gas are transported from the lower to an upper chamber of the regeneration vessel through a dense catalyst bed in the upper chamber. The coked catalyst is contacted with oxygen to combust coke from the coked catalyst in the dense catalyst bed of the upper chamber. The flue gas is separated from the regenerated catalyst in the upper chamber. The regenerated catalyst is discharged from the upper chamber and the flue gas is discharged from the upper chamber of the regeneration vessel.

Another aspect of the invention is a catalyst regenerator vessel according to claim <NUM> for combusting coke from catalyst comprising a lower chamber having a catalyst inlet for feeding spent catalyst to the lower chamber and a gas distributor for distributing combustion gas to the lower chamber. An upper chamber having a catalyst distributor having an inlet in the lower chamber and an outlet in the upper chamber for distributing catalyst from the lower chamber to the upper chamber and the top of the outlet of the catalyst distributor being disposed in a lower third of the upper chamber. Cyclone separators in the regenerator vessel are for separating flue gas from the catalyst. A flue gas outlet is for discharging flue gas from the regenerator vessel and a regenerated catalyst outlet for discharging the regenerated catalyst from the regenerator vessel.

The present subject matter provides an improved method and apparatus for preventing after burn and generation of nitrous oxides while operating high efficiency regenerator in a partial burn mode. The present subject matter provides for conversion of a high efficiency regenerator from full burn to partial burn by raising the catalyst level in the upper chamber of the regenerator vessel. The coked catalyst and flue gas from the lower chamber are discharged into the dense catalyst bed in the upper chamber. Partial burn may be effected in the upper chamber. These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings and appended claims.

Although other uses are contemplated, the process and apparatus of the present invention may be embodied in an FCC unit. <FIG> shows an FCC unit that includes a reactor section <NUM> and a regenerator vessel <NUM>. A regenerated catalyst conduit <NUM> transfers regenerated catalyst from the regenerator vessel <NUM> at a rate regulated by a control valve <NUM> to a riser <NUM> of the reactor section <NUM>. A fluidization medium such as steam from a nozzle <NUM> transports regenerated catalyst upwardly through the riser <NUM> at a relatively high density until a plurality of feed distributor nozzles <NUM> 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 <NUM> to <NUM> (<NUM> to <NUM>°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 <NUM> to a top at which a plurality of disengaging arms <NUM> tangentially and horizontally discharge the mixture of gas and catalyst from a top of the riser <NUM> through ports <NUM> into a disengaging vessel <NUM> that effects separation of gases from the catalyst. A transport conduit <NUM> carries the hydrocarbon vapors, including stripped hydrocarbons, stripping media and entrained catalyst to one or more cyclones <NUM> in a reactor vessel <NUM> which separates coked catalyst from the hydrocarbon vapor stream. The reactor vessel <NUM> may at least partially contain the disengaging vessel <NUM>, and the disengaging vessel <NUM> is considered part of the reactor vessel <NUM>. A collection chamber <NUM> in the reactor vessel <NUM> gathers the separated hydrocarbon vapor streams from the cyclones <NUM> for passage to an outlet nozzle <NUM> and eventually into a fractionation recovery zone (not shown). Diplegs <NUM> discharge catalyst from the cyclones <NUM> into a lower portion of the reactor vessel <NUM>, and the catalyst and adsorbed or entrained hydrocarbons pass into a stripping section <NUM> of the reactor vessel <NUM> across ports <NUM> defined in a wall of the disengaging vessel <NUM>. Catalyst separated in the disengaging vessel <NUM> passes directly into the stripping section <NUM>. The stripping section <NUM> contains baffles <NUM>, <NUM> or other equipment to promote mixing between a stripping gas and the catalyst. The stripping gas enters a lower portion of the stripping section <NUM> through a conduit to one or more distributors <NUM>. The stripped, coked catalyst leaves the stripping section <NUM> of the reactor vessel <NUM> through a reactor catalyst conduit <NUM> and passes to the regenerator vessel <NUM> at a rate regulated by a control valve <NUM>. The coked catalyst from the reactor vessel <NUM> usually contains carbon in an amount of from <NUM> to <NUM> wt%, which is present in the form of coke. Although coke is primarily composed of carbon, it may contain from <NUM> to <NUM> wt% hydrogen as well as sulfur and other materials.

The regenerator vessel <NUM> for combusting coke from catalyst comprises a lower chamber <NUM> and an upper chamber <NUM>. The lower chamber has a catalyst inlet <NUM> for feeding coked catalyst to the lower chamber and a gas distributor <NUM>. The gas distributor <NUM> distributes the combustion gas comprising oxygen from combustion line <NUM> to the lower chamber <NUM>.

The catalyst inlet <NUM> delivers coked catalyst to the lower chamber <NUM> of the regenerator vessel <NUM>. Oxygen-containing combustion gas, typically air, from combustion gas line <NUM> is delivered by the distributor <NUM> to the lower chamber <NUM> of the regenerator vessel <NUM>. The combustion gas contacts coked catalyst in the lower chamber <NUM> and lifts the catalyst under fast fluidized flow conditions which form in a dilute phase <NUM> above a dense phase catalyst bed <NUM>. In an embodiment, flow conditions in the lower chamber <NUM> will include a superficial gas velocity of <NUM> to <NUM>/s (<NUM> to <NUM> ft/s) and a catalyst density of from <NUM>/m<NUM> (<NUM> lb/ft<NUM>) to <NUM>/m<NUM> ( <NUM> lb/ft<NUM>) in the dilute phase <NUM> and from <NUM>/m3 (<NUM> lb/ft3) to <NUM>/m<NUM> (<NUM> lb/ft3) in the dense phase catalyst bed <NUM>. The oxygen in the combustion gas contacts the coked catalyst and combusts carbonaceous deposits from the catalyst. Oxygen is added in proportion to combust coke from the coked catalyst in a partial burn mode to generate flue gas and partially regenerated catalyst.

The mixture of partially regenerated catalyst and flue gas flow through a frustoconical transition section <NUM> to the transport, riser section <NUM> of the lower chamber <NUM>. The riser section defines a tube that extends upwardly from the lower chamber <NUM>. A catalyst distributor <NUM> is connected to the riser section <NUM>. The mixture of partially regenerated catalyst and gas accelerates to a higher superficial gas velocity due to the reduced cross-sectional area of the riser section <NUM> relative to the cross-sectional area of the lower chamber <NUM> below the transition section <NUM>.

The partially regenerated catalyst and flue gas from the lower chamber <NUM> are transported to the upper chamber <NUM> of the regeneration vessel <NUM> through the regenerator riser section <NUM> to the catalyst distributor <NUM> with an inlet <NUM>. The distributor <NUM> that has the inlet <NUM> that comprises an outlet for the lower chamber <NUM>, and the distributor <NUM> has an outlet <NUM> that comprises an inlet to the upper chamber <NUM> for distributing partially regenerated catalyst and flue gas from the lower chamber <NUM> into the upper chamber <NUM>. To maintain partial burn conditions in the lower chamber <NUM>, the carbon monoxide concentration in the flue gas will be maintained at least <NUM> ppm and preferably at least <NUM> mole% and the CO<NUM> to CO mole ratio will be no more than <NUM> and preferably no more than <NUM> and at least <NUM> and preferably at least <NUM> at the inlet <NUM> to the upper chamber <NUM> and the outlet <NUM> from the lower chamber <NUM> of the regenerator vessel <NUM>. The oxygen concentration in the flue gas exiting the outlet <NUM> of the lower chamber is less than <NUM> mole% and preferably no greater than <NUM> ppm to achiever partial burn conditions in the lower chamber <NUM>.

The partially regenerated catalyst and the flue gas entering the upper chamber <NUM> from the lower chamber have a large concentration of carbon monoxide due to the partial burn operation in the lower chamber <NUM>. To avoid the after burn phenomenon in the upper chamber <NUM>, the flue gas and partially regenerated catalyst are discharged into a dense catalyst bed <NUM>. Oxygen is added to the upper chamber <NUM> into the dense catalyst bed <NUM> from a combustion gas distributor <NUM>. The oxygen oxidizes the carbon monoxide to carbon dioxide to generate heat, but sufficient catalyst is present in the dense catalyst bed <NUM> to absorb the heat of combustion, thus protecting the equipment from heat damage.

The catalyst distributor <NUM> preferably comprises at least one and preferably a plurality of nozzles <NUM> that provide outlets <NUM> communicating with the header <NUM> for discharging partially regenerated catalyst into the upper chamber <NUM> of the regenerator vessel <NUM>. The top of the outlet of the catalyst distributor <NUM> is disposed in a lower third of the upper chamber <NUM>, so the catalyst distributor <NUM> will be submerged in the catalyst bed <NUM>. <FIG> shows the total height from lower end of the upper chamber <NUM> to the upper end of the upper chamber as H and the position of the catalyst distributor <NUM> in a lower third of the upper chamber <NUM> as h which is no greater than H divided by <NUM> (H/<NUM>). Specifically, the top of the highest outlet <NUM> has a height h that is no greater than H/<NUM>. In <FIG>, all of the outlets <NUM> have the same height. The partially regenerated catalyst is transported from the regenerator riser <NUM> through the distributor <NUM> into a dense catalyst bed <NUM> in the upper chamber <NUM>. In operation, the catalyst distributor <NUM> is submerged in the catalyst bed <NUM> below a top surface <NUM> thereof. Additionally, the catalyst distributor <NUM> radially discharges partially regenerated catalyst into the dense catalyst bed <NUM> from under the top surface <NUM> of the dense catalyst bed <NUM>. The partially regenerated catalyst may discharge horizontally from the distributor. The flue gas in the regenerator riser <NUM> exiting from the lower chamber <NUM> assists in the discharge of the partially regenerated catalyst into the bed <NUM> from the catalyst distributor <NUM> and may also provide leftover oxygen for combustion requirements in the upper chamber <NUM>.

Oxygen containing combustion gas, perhaps air, is delivered to the combustion gas distributor <NUM> in the upper chamber <NUM> for distribution through outlets <NUM> to the upper chamber <NUM> of the regenerator vessel <NUM>. The oxygen in the combustion gas distributed to the upper chamber <NUM> burns remaining coke from partially regenerated catalyst in the dense phase catalyst bed <NUM> before ascending through the top surface <NUM> of the bed <NUM> into the dilute phase <NUM>. The top of the outlet of the combustion gas distributor <NUM> is disposed in a lower third of the upper chamber <NUM>, so the combustion gas distributor <NUM> will be submerged in the catalyst bed <NUM>. <FIG> shows the position of the combustion gas distributor <NUM> in a lower third of the upper chamber <NUM> below h which is no greater than H divided by <NUM> (H/<NUM>). Specifically, the top of the highest outlet <NUM> has a height h that is no greater than H/<NUM>.

Catalyst may get entrained with flue gas ascending in the dilute phase <NUM> in the upper chamber <NUM> of the regenerator vessel <NUM>. The catalyst entrained in the flue gas will therefore enter cyclone separators <NUM>, <NUM> which centripetally separate flue gas from heavier catalyst particles. The flue gas is separated from the regenerated catalyst in the upper chamber <NUM>. Catalyst particles will fall down diplegs <NUM>, <NUM> and enter dense phase catalyst bed <NUM> again. The diplegs may be submerged in the catalyst bed <NUM> below the top surface <NUM>. Completely regenerated catalyst from the dense catalyst bed <NUM> is discharged from the upper chamber <NUM> and transferred to the regenerated catalyst conduit <NUM>. Completely regenerated catalyst regulated by control valve <NUM> descends the reactor catalyst conduit <NUM> from the upper chamber <NUM> back to the reactor section <NUM> and enters the riser <NUM> where it again contacts feed as the FCC process continues.

In an embodiment, to accelerate combustion of the coke in the lower chamber <NUM>, hot fully regenerated catalyst from a dense catalyst bed <NUM> in the upper chamber <NUM> may be recirculated into the lower chamber <NUM> via an external recycle catalyst conduit <NUM> regulated by a control valve <NUM>. Hot fully regenerated catalyst enters an inlet of recycle catalyst conduit <NUM> which is connected to and in downstream communication with the upper chamber <NUM>. Recirculation of regenerated catalyst, by mixing hot catalyst from the dense catalyst bed <NUM> with relatively cool, coked catalyst from the reactor catalyst conduit <NUM> entering the lower chamber <NUM>, raises the overall temperature of the catalyst and gas mixture in the lower chamber <NUM>.

The regenerator vessel <NUM> is operated under partial burn conditions in the lower chamber <NUM> and the upper chamber <NUM>. No more than <NUM>-<NUM> wt% of the total gas requirements within the process enters the dense catalyst bed <NUM> in the upper chamber <NUM> with the remainder <NUM>-<NUM> wt% being added to the lower chamber <NUM>. In this embodiment, combustion gas may be added to the upper chamber <NUM> for both combustion and fluidization purposes. If air is the combustion gas, typically <NUM> to <NUM> (lbs) of air are required per kilogram (pound) of coke fed on catalyst to the regenerator vessel for partial burn. The regenerator vessel <NUM> typically has a temperature of <NUM> to <NUM> (<NUM> to <NUM>°F) in the lower chamber <NUM> and <NUM> to <NUM> (<NUM> to1400°F) in the upper chamber <NUM>. Pressure may be between <NUM> and <NUM> kPa (gauge) (<NUM> to <NUM> psig) in both chambers.

The superficial velocity of the combustion gas in the upper chamber <NUM> is typically between <NUM>/s (<NUM> ft/s) and <NUM>/s (<NUM> ft/s) and the density of the dense bed <NUM> is typically between <NUM>/m3 (<NUM> lb/ft3) and <NUM>/m<NUM> (<NUM> lb/ft3) and the density of the dilute phase <NUM> is typically between <NUM>/m<NUM> (<NUM> lb/ft3) and <NUM>/m<NUM> (<NUM> lb/ft3) depending on the characteristics of the catalyst.

Flue gas with a lighter loading of catalyst will ascend from the cyclone separators <NUM>, <NUM> through ducts into plenum <NUM> and discharge from the upper chamber <NUM> through a flue gas outlet <NUM>. The carbon monoxide content in the flue gas is maintained at least <NUM> ppm and preferably at least <NUM> mole% at the flue gas outlet <NUM> of the upper chamber <NUM> of the regenerator vessel and the CO<NUM> to CO mole ratio in the flue gas outlet <NUM> will be at least <NUM> and preferably at least <NUM> and no more than <NUM> and preferably no more than <NUM> to achieve partial burn combustion of coke. The oxygen concentration in the flue gas exiting the outlet <NUM> of the upper chamber <NUM> is less than <NUM> mole% and preferably no greater than <NUM> ppm to achiever partial burn conditions in the upper chamber. Although partial burn conditions will be maintained in the upper chamber <NUM>, the partially regenerated catalyst from the lower chamber <NUM> will encounter sufficient oxygen to be completely regenerated in the upper chamber <NUM>.

A plan view of the catalyst distributor <NUM> taken at segment <NUM>-<NUM> of <FIG> omitting the dip legs <NUM>, <NUM> is shown in <FIG>. The catalyst distributor may comprise a header <NUM> or a plurality of headers <NUM>. Four headers are exemplarily shown in <FIG>. The flue gas with partially regenerated catalyst from lower chamber <NUM> is transported to the distributor <NUM> in the upper chamber <NUM> through a plurality of headers <NUM>. Each header <NUM> defines a longitudinal axis L and an angular nozzle 68a in downstream communication with the header <NUM> that discharges the catalyst at an acute angle to the longitudinal axis. The catalyst is discharged from the distributor <NUM> through nozzles <NUM> with a bottom disposed in the lower quarter of the header <NUM>. The angular nozzle 68a defines an acute angle α with the longitudinal axis L of the header <NUM>. In other words, a longitudinal axis a defined by the angular nozzle 68a defines an acute angle α with the longitudinal axis L. The angular nozzle is in communication with the header <NUM>. There may be two angular nozzles defining two different angles with the longitudinal axis. The angular nozzle 68a discharges catalyst into the upper chamber <NUM> of the regenerator vessel <NUM> at an acute angle α to the longitudinal axis L. The bottom of the nozzle 68a is disposed in the bottom quarter of the header <NUM>. In an embodiment, pluralities of nozzles 68a-d in downstream communication with and connected to the header <NUM> each have an axis that defines an acute angle with longitudinal axis L. The nozzles 68b-d define acute angles β, γ and δ with the longitudinal axis L of the header <NUM>, respectively. In other words, longitudinal axes a-d defined by the nozzles 68a-d define acute angles with the longitudinal axis L, respectively. The plurality of nozzles 68a-d discharge partially regenerated catalyst into the regenerator vessel <NUM> at acute angles to the longitudinal axis L. A proximate nozzle 68e may be perpendicular to the longitudinal axis L. Similarly, a proximate nozzle 68f may be perpendicular to the longitudinal axis L. In other words, longitudinal axes e and f defined by the nozzles 68e and f each define right angles ε, ζ with the longitudinal axis L. Nozzles 68a, b and f are one side of the header <NUM> and nozzles c, d and e are on the opposite side of the header <NUM>. 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 <NUM> 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 <NUM> on the outer end <NUM> of the header <NUM> that defines a longitudinal axis g that is aligned with the longitudinal axis L.

In an embodiment, the smallest angles the nozzles 68a-g define with the longitudinal axis L successively decrease as the nozzles are positioned further away from the inlet <NUM> and closer to the outer end <NUM>. 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 cross section of the bed to which the header <NUM> is dedicated in the upper chamber <NUM> of the regenerator vessel <NUM>. Additionally, in an embodiment, the length of the nozzles 68a-f on both sides of the header <NUM> successively increase as the nozzles are positioned further away from the inlet <NUM> and closer to the outer end <NUM>. The catalyst distributor <NUM> may comprise four headers <NUM> with each header disposed in one quadrant of the cross section of the upper chamber of the regenerator vessel <NUM>. Moreover, the longitudinal axis L may intersect a sectional center C of the regenerator vessel <NUM>. The aligned distal nozzles <NUM> are also shown in <FIG>. Distal nozzles <NUM> also each have an axis g which is horizontally aligned with axis L.

<FIG> provides an enlarged, partial elevational view of the catalyst distributor <NUM> with the headers <NUM> defining a height T. A bottom 72a of the nozzle 68a is disposed in the bottom quarter of the height T of the header <NUM>. In an embodiment, the bottom 72a is defined as the lowest point of the inner circumference of the nozzle 68a. The positioning of the nozzle 68a with respect to the header <NUM> assures no catalyst stagnates in the header <NUM>. The nozzle 68a also has a height t. In an embodiment, over <NUM>% of the height t of the nozzle 68a is disposed below <NUM>% of a height T of the header <NUM>. <FIG> also illustrates that longitudinal axis a defined by the nozzle 68a is horizontal in an embodiment. In an embodiment, the longitudinal axis L of the header <NUM> is also horizontal. In a further embodiment, bottoms 72a-f of all the nozzles 68a-f are disposed in the bottom quarter of the height T of the header <NUM>. In an embodiment, the bottoms 72a-f is defined as the lowest point of the inner circumference of the nozzle 68a-f. In an embodiment, all the nozzles 68a-f have heights t and over <NUM>% of a height t of the nozzles 68a-f are disposed below <NUM>% of a height T of the header <NUM>. In an additional embodiment, the longitudinal axes defined by all the nozzles 68a-f are horizontal. The aligned distal nozzles <NUM> are also shown in <FIG>. Distal nozzles <NUM> also each have an axis g which is horizontal and parallel with axis L. The horizontal nozzles 68a-g discharge catalyst horizontally from header <NUM>.

The catalyst distributor <NUM>, will typically be made of stainless steel such as <NUM> 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.

While the subject matter has been described with what are presently considered the preferred embodiments, it is to be understood that the subject matter 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.

While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

Claim 1:
A process for combusting coke from catalyst comprising:
a. contacting hydrocarbon feed with catalyst to produce cracked products and coked catalyst;
b. separating said cracked products from said coked catalyst;
c. delivering coked catalyst to a lower chamber (<NUM>) of a regeneration vessel (<NUM>);
d. contacting coked catalyst with oxygen to combust coke from the coked catalyst in a partial burn mode;
e. transporting catalyst and flue gas from the lower chamber (<NUM>) to an upper chamber (<NUM>) of the regeneration vessel (<NUM>) through a catalyst distributor (<NUM>) into a dense catalyst bed (<NUM>) in the upper chamber (<NUM>), wherein the top of the outlet of the catalyst distributor (<NUM>) is disposed in a lower third of the upper chamber (<NUM>) so that the catalyst distributor (<NUM>) is submerged in the dense catalyst bed (<NUM>), below a top surface (<NUM>) of the dense catalyst bed (<NUM>), and wherein the catalyst distributor (<NUM>) radially discharges partially regenerated catalyst into the dense catalyst bed (<NUM>) from under the top surface (<NUM>) of the dense catalyst bed (<NUM>);
f. contacting coked catalyst with oxygen to combust coke from the coked catalyst in the dense catalyst bed (<NUM>) of the upper chamber (<NUM>), wherein combustion gas containing the oxygen is delivered to a combustion gas distributor (<NUM>) in the upper chamber (<NUM>) and distributed through outlets (<NUM>) to the upper chamber (<NUM>) of the regenerator vessel (<NUM>), and wherein the top of the outlet of the combustion gas distributor (<NUM>) is disposed in a lower third of the upper chamber (<NUM>), and wherein the combustion gas distributor (<NUM>) is submerged in the dense catalyst bed (<NUM>);
g. separating flue gas from regenerated catalyst in the upper chamber (<NUM>);
h. discharging regenerated catalyst from said upper chamber (<NUM>); and
i. discharging flue gas from said upper chamber (<NUM>).