Patent Description:
Numerous hydrocarbon conversion processes are widely used to alter the structure or properties of hydrocarbon streams. Such processes include isomerization from straight chain paraffinic or olefinic hydrocarbons to more highly branched hydrocarbons, dehydrogenation for producing olefinic or aromatic compounds, reforming to produce aromatics and motor fuels, alkylation to produce commodity chemicals and motor fuels, transalkylation, and others. Many such processes use catalysts to promote hydrocarbon conversion reactions. A particular example of a hydrocarbon conversion process employing a catalyst is a fluidized catalytic cracking (FCC) process.

FCC systems typically include a regeneration zone, many of which maintain a dense fluidized bed of catalyst particles through which an oxygen-containing regeneration gas, such as air, passes to combust coke. The coke forms as a byproduct of the cracking operation.

A common regeneration zone operation introduces the regenerator gas, e.g., air, into the bottom of the regenerator through a bottom closure of a regenerator vessel. An air distributor divides the introduced air and injects it into the catalyst bed at a multiplicity of points to obtain good air distribution. A particular example regeneration zone using an air distributor is a combustor style single stage regenerator (combustor style regenerator). This regenerator is particularly useful to achieve a low carbon level on regenerated catalyst that is uniform through the regenerated catalyst.

An example combustor style regenerator includes a lower combustor, an internal combustor riser, and an upper regenerator embodied in a disengaging vessel having cyclones. The combustor includes a metal vessel, e.g., carbon steel, having a bottom head at a base. The bottom head is insulated with a refractory lining material. To provide air for combustion, an air distributor is provided within the vessel above the bottom head, particularly at or near a lower tangent line of the vessel. A typical air distributor includes a hub that is in fluid communication with a plurality of nozzles disposed along an air grid, such as a pipe grid, mounted within the vessel. The nozzles are directed from the air grid into the vessel.

In an example combustion operation, air enters the combustor via a conduit centrally located in the bottom of the vessel that is in fluid communication with an air grid. The air grid divides the input air from the conduit to the plurality of nozzles, through which the air is injected into the interior of the vessel. Spent catalyst is introduced into the vessel near the base, for example via a spent catalyst standpipe leading to the vessel. At the bottom of the combustor the spent catalyst (e.g., from a reaction zone) mixes with the air and with (hot) recirculating catalyst from the upper regenerator, fluidizing the spent catalyst. The air is used to burn the coke off the fluidized spent catalyst as the fluidized spent catalyst moves up the combustor and the internal combustor riser.

During combustion, the region of the vessel above the bottom head and below the air grid becomes filled with unfluidized catalyst because the nozzle penetration may not be adequate to fluidize this region. This region can have a significant volume. For example, a distance of the vessel below the air grid and connected nozzles could be as much as two meters in larger size vessels. Unfluidized catalyst accumulates near the bottom head, and this accumulated catalyst acts as an insulator in addition to the refractory lining on the bottom head. This leads to very low skin temperatures of the vessel on the bottom head below the sulphuric acid dew point which could lead to corrosion of the vessel. Some examples of systems and methods for regenerating a spent catalyst are known from <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

Therefore, there remains a need for effective and efficient processes for fluidizing spent catalyst.

The present invention is directed to providing effective and efficient processes for fluidizing a catalyst.

Accordingly, one aspect of the present invention provides a method for fluidizing a spent catalyst in a regenerator during a combustion process. The regenerator includes a vessel and an air distributor. The air distributor includes an air grid and a plurality of first nozzles extending from the air grid. The spent catalyst is introduced into the vessel. Air is provided to the vessel via the plurality of first nozzles at a base combustion air rate.

Additional air is provided to the vessels via a plurality of second nozzles of a fluffing air distributor at a fluffing air rate that is between <NUM> wt% and <NUM> wt% of the base combustion air rate to fluidize the spent catalyst. The plurality of second nozzles have outlets that are disposed below the air grid and above a bottom head of the vessel.

The outlets of the plurality of second nozzles are disposed on at least two levels, each of the two levels being disposed at a different height distance from the air grid.

Another aspect of the present invention provides an apparatus for regenerating a spent catalyst. The apparatus comprises a vessel for receiving the spent catalyst through a catalyst inlet and an air distributor disposed in the vessel, the air distributor comprising an air grid below the catalyst inlet and a plurality of first nozzles extending from the air grid into the vessel; an air source coupled to the air distributor; and a fluffing air distributor disposed in the vessel for fluidizing the spent catalyst. The fluffing air distributor comprises a plurality of second nozzles having outlets disposed below the air grid and above a bottom head of the vessel. The plurality of second nozzles are disposed on at least two levels, each of the two levels being disposed at a different height distance from the air grid.

Additional objects, embodiments, and details of the invention are set forth in the following detailed description of the invention.

<FIG> shows an example single stage combustor style regenerator (combustor style regenerator) <NUM> for use in a catalyst regeneration zone. However, it will be appreciated that examples used herein can be used in various regenerators. The combustor style regenerator <NUM> generally includes a lower combustor <NUM>, an internal combustor riser <NUM> in communication with the lower combustor, and an upper regenerator <NUM> in communication with the internal combustor riser. The upper regenerator <NUM> may include, for example, a disengaging vessel <NUM> having cyclones (not shown) disposed therein. The combustor riser <NUM> terminates in a disengager <NUM>, e.g., a "tee" disengager, for separating combustion gases and catalyst from the combustor riser. A vent <NUM> is disposed at the top of the combustor style regenerator <NUM> for venting flue gas. A catalyst recirculation standpipe <NUM> and a regenerated catalyst standpipe <NUM> are coupled to the upper regenerator <NUM> for exiting regenerated catalyst. A catalyst cooler (not shown) can also be coupled to the upper regenerator <NUM> for cooling regenerated catalyst, though the catalyst cooler may be omitted in some embodiments.

The lower combustor <NUM> includes a generally cylindrical vessel <NUM> having inner walls within which spent catalyst is mixed with air to combust coke from the spent catalyst. The vessel <NUM> includes a combustor cone <NUM>, a bottom head <NUM>, and a centrally disposed conduit <NUM>, e.g., with an outlet in the vessel, for introduction of an oxygen-containing regeneration gas such as air. The vessel <NUM> is mounted on a vessel support skirt <NUM> for support. As air is a preferred regeneration gas, description of illustrative methods herein will refer to air. The conduit <NUM> is coupled to an air supply <NUM>, e.g., a controlled air blower, for passing high pressure air to an air distributor <NUM> for introduction into the vessel <NUM>. The air distributor <NUM> is preferably a pipe distributor, and includes a hub <NUM> in fluid communication with the conduit <NUM>, and an air grid <NUM> having a generally symmetrically arranged plurality of header arms <NUM> (best viewed in <FIG>), each having a plurality of generally symmetrically arranged pipes <NUM> coupled thereto. The header arms <NUM> and the pipes <NUM> are in fluid communication with the hub <NUM> for distributing air from the hub. The header arms <NUM> and pipes <NUM> each have bores <NUM> (see <FIG>) formed on lower and/or upper surfaces. In another example, only the pipes <NUM> include the bores <NUM>. Jets, such as nozzles <NUM>, protrude from the bores <NUM>. In the lower combustor <NUM>, each of the nozzles <NUM> protrude from the direction of flow through the pipes <NUM>. It is not required that the nozzles <NUM> all protrude at the same angle.

Preferably, the air grid <NUM> is disposed at or near a lower tangent line <NUM> of the vessel <NUM>. Elbows <NUM> are disposed between the hub <NUM> and the air grid <NUM> for support. The header arms <NUM> and pipes <NUM>, the elbows <NUM>, and/or the hub <NUM> can be lined, for example with abrasion resistant lining. An interior of the bottom head <NUM> may also be lined with refractory lining. Example refractor lining includes, but is not limited to, Light-weight Insulation Refractory, Mid-weight Refractory Lining, or High Density Refractory Lining.

As shown in <FIG>, spent catalyst standpipes <NUM> are coupled to the vessel <NUM>, preferably disposed near and above the lower tangent line, for introducing spent catalyst, e.g., from a reaction zone, and providing a catalyst inlet <NUM>. Another catalyst inlet <NUM> is provided by the catalyst recirculation standpipe <NUM>. The introduced spent catalyst is fluidized by air distributed by the air grid and exiting through the nozzles <NUM>.

To fluidize spent catalyst in a region below the air grid <NUM>, a fluffing air distributor <NUM> is provided below the air grid (i.e., below the header arms <NUM> and pipes <NUM>), disposed between the air grid and the bottom head <NUM>. Providing additional fluffing air enhances catalyst movement and heat transfer.

<FIG> show an example arrangement for the fluffing air distributor <NUM>, which arrangement is referred to herein as a wreath arrangement. The fluffing air distributor <NUM>, which is generally symmetrical, includes a radially inner ring (inner ring) <NUM> and a radially outer ring (outer ring) <NUM> of piping. Rings may be continuous (e.g., made of a single pipe forming a circle or part of a circle) or discontinuous (e.g., made from plural pipes each forming arced portions of a circle). The inner ring <NUM> and the outer ring <NUM> are preferably made from stainless steel, though other materials can be used. Air passages <NUM> coupled to and in fluid communication with the inner ring <NUM> and the outer ring <NUM> are provided to supply air to the inner ring <NUM> and the outer ring <NUM> from any of various sources, examples of which are described below. As best viewed in <FIG>, the outer ring <NUM> defines a plane that is disposed above a plane defined by the inner ring <NUM>, providing rings at different levels or heights.

A plurality of headers or arms <NUM> (e.g., pipe) are arranged circumferentially about the inner ring <NUM> and coupled to the inner ring using, for example, piping "tees" or welded connections, or other suitable connections. The arms <NUM> project outwardly from the inner ring, providing branches for the fluffing air distributor <NUM>.

The inner ring <NUM> and the outer ring <NUM> each include one or more air conduits <NUM> in fluid communication with the air passages <NUM> for distributing air to the inner ring and outer ring. Further, each of the inner ring <NUM>, the outer ring <NUM>, and the arms <NUM> have bores <NUM> formed on bottom and/or top surfaces. In the example fluffing air distributor <NUM>, the inner ring <NUM> includes twenty-four (inner) bores <NUM>, the arms <NUM> collectively include twenty-four (middle) bores, and the outer ring <NUM> includes <NUM> (outer) bores, or eighty total bores. Bores may be of various sizes (e.g., diameters).

Jets, such as nozzles <NUM>, extend into and from each of the bores <NUM>. Example nozzles <NUM> include nozzles having a diameter between <NUM> (<NUM>") and <NUM> (<NUM>").

The outlets of the nozzles <NUM> of the fluffing air distributor <NUM> are disposed below the air grid <NUM>, and below the outlets of the nozzles <NUM> of the air distributor <NUM>. For clarity, the nozzles <NUM> of the air distributor <NUM> may be referred to as first nozzles, and the nozzles <NUM> of the fluffing air distributor <NUM> may be referred to as second nozzles, though the nozzles may or may not be configured similarly. Both the inner ring <NUM> and the outer ring <NUM> are disposed below the header arms <NUM> and pipes <NUM> from which the (first) nozzles <NUM> extend, and below the lower tangent line <NUM>, so that outlets of the (second) nozzles <NUM> extending from the inner ring <NUM> and the outer ring <NUM> are disposed below the lower tangent line.

For example, outlets of the (second) nozzles <NUM> extending from the inner ring <NUM> and the arms <NUM> can be disposed at a level below the lower tangent line <NUM> by a height distance (that is, distance from top to bottom for the regenerator <NUM> in the orientation shown in <FIG> and <FIG>) that is between <NUM>% and <NUM>% of the height distance between the lower tangent line and the bottom of the vessel <NUM>. Similarly, outlets of the (second) nozzles <NUM> extending from the inner ring <NUM> (or from any arms extending from the outer ring, though none are provided in the fluffing air distributor <NUM>) can be disposed at a level below the lower tangent line <NUM> by a height distance that is between <NUM>% and <NUM>% of the height distance between the lower tangent line and the bottom of the vessel <NUM>. If only a single nozzle height is provided for the fluffing air distributor <NUM>, outlets of the nozzles <NUM> preferably are disposed at a level below the lower tangent line <NUM> at a height distance that is between <NUM>% and <NUM>% of the height distance between the lower tangent line and the bottom of the vessel <NUM>.

It will be appreciated that the wreath arrangement in the fluffing air distributor <NUM> of <FIG> is merely an example arrangement, and other arrangements are possible. In another example fluffing air distributor (not shown), more than three or more rings, e.g., between three and ten rings, are provided. Multiple rings can be disposed at the same heights or at different heights, so that nozzles are positioned at the same height or at different heights. In some embodiments, multiple rings and associated nozzles <NUM> are disposed at different respective radii and heights between the air grid <NUM> and the bottom of the vessel <NUM>. Non-circular shaped pipes and branches can be used in place of the additional rings, and the nozzles <NUM> can be disposed at various planar locations and levels. The nozzles <NUM> may be distributed evenly (e.g., in plan view) or unevenly on the fluffing air distributor <NUM>, though it is preferred to distributor the nozzles more evenly to provide more even catalyst fluidization. It is also contemplated to plug one or more selected nozzles <NUM> to configure fluidization. The quantity, arrangement, and size of the nozzles <NUM> in the fluffing air distributor <NUM> can be selected and provided in any combination, though certain combinations may be more desirable to achieve a particular fluidization of stagnant catalyst.

For instance, <FIG> show another example fluffing air distributor <NUM>. The fluffing air distributor <NUM> is generally similar to the fluffing air distributor <NUM>, but includes fewer arms <NUM> disposed about the inner ring <NUM>. Also, the fluffing air distributor <NUM> includes a greater number of bores <NUM> and associated nozzles <NUM> distributed along the inner ring <NUM>, the outer ring <NUM>, and the arms <NUM>.

Air for the fluffing air distributor <NUM>, <NUM>, e.g., via the air passages <NUM>, can be provided from various air sources, including by providing a dedicated connection to a separate air source, by providing a connection from an existing air source to divert air, or a combination of these. For example, air to the fluffing air distributor <NUM> can be provided by diverting a portion of the air feeding to the air supply <NUM> that is coupled to the air distributor <NUM>, providing a common air source embodied in an air blower. This air introduction can be controlled using suitable controls such as a flow indicating controller <NUM> that operates a valve <NUM>.

Alternatively or additionally, as shown in <FIG>, air to the fluffing air distributor <NUM>, <NUM> can be provided by diverting a portion of the air feeding to a separate air source <NUM>, e.g., a separate blower used for providing lance air to the catalyst cooler (not shown), a separate blower providing fluffing air to the upper regenerator <NUM>, auxiliary blowers or compressors, utility (plant) air, or other sources. Air from such additional air sources <NUM> can be controlled using suitable controls, such as but not limited to valves operated by flow indicating controllers. Injecting air into the fluffing air distributor <NUM>, <NUM> will not significantly affect energy usage if the air is provided from one of the existing air sources (e.g., air blowers/compressors) in the combustor style regenerator <NUM>. Further, this air will contribute towards coke combustion, and no increase in NOx will occur in this location.

The fluffing air rate provided by the fluffing air distributor <NUM>, <NUM> can be selected and configured based on the number of the nozzles <NUM>, the size(s) of the nozzles <NUM>, and/or the air pressure provided for the fluffing air distributor <NUM> from its source(s). For example, for smaller (or larger) diameter nozzles <NUM>, larger (or smaller) numbers of nozzles or increased (or decreased) pressure may be employed for a particular fluffing air rate.

An example fluffing air rate for the fluffing air distributor <NUM>, <NUM> can be expressed as a proportion, e.g., a percentage, of a base combustion air rate, that is, an air rate for the air distributor <NUM> for the combustion where the fluffing air distributor <NUM>, <NUM> is not used. Example fluffing air rates for the fluffing air distributor <NUM>, <NUM> range from <NUM> wt% to <NUM> wt% of the base combustion air rate, and preferably from <NUM> wt% to <NUM> wt% of the base combustion air rate.

Increased fluffing air rates can require additional air to be made available to the fluffing air distributor <NUM>, <NUM>. It is thus desirable to reduce the fluffing air rate where possible while still fluidizing the stagnant catalyst. It has been found that arrangements of the fluffing air distributor <NUM>, <NUM> that provide the nozzles <NUM> at multiple heights, such as by providing the inner ring <NUM> and the outer ring <NUM> at separate respective heights, can increase fluidization of the stagnant catalyst while limiting the required fluffing air rate for fluidization.

In an example combustion operation, air enters the regenerator <NUM> via the conduit <NUM> that is in fluid communication with the air distributor <NUM>. The air distributor <NUM> divides the input air from the conduit to the plurality of nozzles <NUM>, and the air is injected into the interior of the vessel. Spent catalyst (e.g., from a reaction zone (not shown)) is introduced into the vessel <NUM> via the spent catalyst standpipe <NUM> leading to the vessel. At the bottom of the combustor <NUM>, the spent catalyst mixes with the air and (hot) recirculating catalyst from the catalyst recirculation standpipe <NUM> connected to the (upper) regenerator <NUM>, fluidizing the spent catalyst. The air is used to burn the coke off the fluidized spent catalyst as the fluidized spent catalyst moves up the combustor <NUM> and the internal combustor riser <NUM>.

As coke is being combusted from the spent catalyst, air (or other regeneration gas) is provided from an air source to a lower region of the vessel <NUM> below the air grid <NUM> (i.e., below the header arm <NUM> and the pipes <NUM>) via the fluffing air distributor <NUM>, <NUM>. Providing this air can include introducing the air from an additional air source or sources <NUM>, or by diverting air from existing air sources by connecting the fluffing air distributor to the existing air source(s). The provided air is distributed by the fluffing air distributor to the plurality of nozzles <NUM>. To reduce the fluffing air rate, the air is directed to nozzles disposed along two rings, having respective levels and radii.

With example methods using the example fluffing air distributor <NUM>, <NUM>, the stagnant catalyst bed below the air distributor <NUM> can become active, and thus can be reduced. The fluffing air distributor <NUM>, <NUM> promotes stagnant catalyst circulation to increase the interaction of hot and cold solid catalyst, thus improving internal heat transfer. Enhanced heat transfer between the catalyst particles and the air (gas phase) occurs, resulting in a significant increase in the catalyst bed temperature, and promoting an increase of the vessel <NUM> temperature.

For example, by providing air to the fluffing air distributor <NUM>, <NUM> as described above, the gravity-induced flow of the catalyst down the inner wall of the vessel <NUM> creates a low intensity circulation in the lower region of the vessel below the (upper) air distributor <NUM>, particularly below the air grid <NUM> and near the bottom head <NUM>. The temperature of the region is equalized (or more equalized) with the remainder of the combustor <NUM> due to the enhanced mixing of the catalyst. Particularly, the hot catalyst interacts with colder catalyst below the air grid <NUM>, created by the effect of gas bubbles conveying cold catalyst in its wake above the air distributor <NUM>, and hot catalyst backfilling the region below the air distributor. This in turn can increase the temperature at the bottom head <NUM>, e.g., at the surface of the refractory, increasing the skin temperature of the vessel <NUM>.

As another benefit, fluidizing the stagnant catalyst below the air grid <NUM> using the fluffing air distributor can make it easier to unload the stagnant catalyst in the bottom head <NUM> during shutdowns/turnarounds, which can be time consuming.

It should be appreciated and understood by those of ordinary skill in the art that various other components such as valves, pumps, filters, coolers, etc. were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understating the embodiments of the present invention.

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.

A first embodiment of the invention is a method for fluidizing a spent catalyst in a regenerator during a combustion process, as defined in the appended claim <NUM>.

A second embodiment of the invention is an apparatus for regenerating a spent catalyst, the apparatus being defined in the appended claim <NUM>.

Claim 1:
A method for fluidizing a spent catalyst in a regenerator (<NUM>) during a combustion process, the regenerator including a vessel (<NUM>) and an air distributor (<NUM>), the air distributor including an air grid (<NUM>) disposed at a bottom of the vessel and a plurality of first nozzles (<NUM>) extending from the air grid, the method comprising:
introducing the spent catalyst into the vessel;
providing air to the vessel via the plurality of first nozzles at a base combustion air rate; and
providing additional air to the vessel via a plurality of second nozzles (<NUM>) of a fluffing air distributor (<NUM>, <NUM>) at a fluffing air rate that is between <NUM> wt% and <NUM> wt% of the base combustion air rate to fluidize the spent catalyst, the plurality of second nozzles having outlets that are disposed below the air grid and above a bottom head (<NUM>) of the vessel,
wherein the outlets of the plurality of second nozzles (<NUM>) are disposed on at least two levels, each of the two levels being disposed at a different height distance from the air grid; and
wherein said plurality of second nozzles are arranged in a plurality of rings (<NUM>, <NUM>), wherein the plurality of rings (<NUM>, <NUM>) includes a radially inner ring (<NUM>) and a radially outer ring (<NUM>) of piping, and wherein the outer ring (<NUM>) defines a plane that is disposed above a plane defined by the inner ring (<NUM>);
wherein a plurality of arms (<NUM>) are arranged circumferentially about the inner ring (<NUM>) and coupled to the inner ring (<NUM>), and wherein the arms (<NUM>) project outwardly from the inner ring (<NUM>), providing branches for the fluffing air distributor (<NUM>);
each of the inner ring (<NUM>), the outer ring (<NUM>), and the arms (<NUM>) have bores (<NUM>) formed on bottom and/or top surfaces.