Abstract:
An FCC process and apparatus may include injecting hydrocarbon feedstock at different radial positions inside a riser. Multiple distributors may be used to position the openings for injecting feedstock at multiple radial positions. In addition, the openings may be away from riser peripheral wall and at different elevations along the riser wall or extending up from the riser bottom. The different opening positions introduce the feedstock across a larger area of the cross-section of the riser, which may improve the feedstock dispersion and mixing with catalyst. Improved mixing may increase conversion of the feedstock. Larger FCC units generally have greater riser diameters that may cause problems for feedstock dispersion and decrease the ability for the feedstock to mix with catalyst. Injecting the feedstock at multiple radial positions may improve feedstock dispersion in larger FCC units and increase mixing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to a process for catalytic cracking of hydrocarbons. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    Fluid catalytic cracking (FCC) is a catalytic conversion process for cracking heavy hydrocarbons into lighter hydrocarbons by bringing the heavy hydrocarbons into contact with a catalyst composed of finely divided particulate material in a fluidized reaction zone. Most FCC units use zeolite-containing catalyst having high activity and selectivity. As the cracking reaction proceeds, substantial amounts of highly carbonaceous material, referred to as coke, are deposited on the catalyst, forming spent catalyst. High temperature regeneration burns the coke from the spent catalyst. The regenerated catalyst may be cooled before being returned to the reaction zone. Spent catalyst is continually removed from the reaction zone and replaced by essentially coke-free catalyst from the regeneration zone. 
         [0003]    The basic components of the FCC process include a riser, a reactor vessel, a catalyst stripper, and a regenerator. In the riser, a feed distributor inputs the hydrocarbon feed which contacts the catalyst and is cracked into a product stream containing lighter hydrocarbons. Catalyst and hydrocarbon feed are transported upwardly in the riser by the expansion of the gases that result from the vaporization of the hydrocarbons, and other fluidizing mediums, upon contact with the hot catalyst. Steam or an inert gas may be used to accelerate catalyst in a first section of the riser prior to or during introduction of the feed. Coke accumulates on the catalyst particles as a result of the cracking reaction and the catalyst is then referred to as “spent catalyst.” The reactor vessel disengages spent catalyst from product vapors. The catalyst stripper removes absorbed hydrocarbon from the surface of the catalyst. The regenerator removes the coke from the catalyst and recycles the regenerated catalyst into the riser. 
         [0004]    A problem encountered during the FCC process is distributing the feed in the riser so that it can adequately mix with the catalyst. Adequate mixing is usually necessary for efficient conversion of the feed. Larger riser diameters may exacerbate this problem because of the difficulty in distributing the feedstock to the center of the riser. 
       SUMMARY OF THE INVENTION 
       [0005]    An FCC process and apparatus may include injecting hydrocarbon feedstock at different radial positions inside a riser. Multiple distributors may be used to position the openings for injecting feedstock at multiple radial positions. The different opening positions introduce the feedstock across a larger cross-section area of the riser, which may improve the feedstock dispersion and mixing with catalyst. Improved mixing may increase the efficiency of the FCC process and the conversion of the feedstock. Larger FCC units generally have greater riser diameters which may cause problems for feedstock dispersion, resulting in a decrease in the feedstock mixing with catalyst. Injecting the feedstock at multiple radial positions may improve dispersion and may increase the feedstock mixing with catalyst. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cross section taken along segment  1 - 1  in  FIG. 2 . 
           [0007]      FIG. 2  is an elevational diagram showing an FCC unit. 
           [0008]      FIG. 3  is a cross section showing an embodiment with different radial positions between two sets of distributors. 
           [0009]      FIG. 4  is an elevational diagram showing a feed distributor. 
           [0010]      FIG. 5  is a cross section showing a riser. 
           [0011]      FIG. 6  is an elevational diagram showing a distributor tip and a shaping vane. 
           [0012]      FIG. 7  is an elevational diagram showing two distributors attached to the wall of a riser with one extending to the approximately the middle of the riser and bending to extend upward. 
           [0013]      FIG. 8  is an elevational diagram showing a distributor attached to the wall of the riser and a distributor in a central position extending up from the bottom of a riser. 
           [0014]      FIG. 9  is a cross section taken along segment  9 - 9  in  FIG. 8 . 
           [0015]      FIG. 10  is an elevational diagram showing two distributors attached to the wall of the riser and a distributor in central position extending up from the bottom of a riser. 
           [0016]      FIG. 11  is a cross section taken along segment  11 - 11  in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    This invention relates generally to an improved FCC process and apparatus. Specifically, this invention may relate to an improved feedstock distributor arrangement and may be useful for FCC operation to improve feedstock conversion through greater feed dispersal, especially in larger FCC Units. The process and apparatus could be scaled up or down, as would be apparent to one skilled in the art. The process and apparatus aspects of this invention may be used in the design of new FCC units or to modify the operation of existing FCC units. 
         [0018]    Shown in  FIG. 1  is one embodiment of an arrangement of feed distributors  12  illustrating the different radial positions for injecting feedstock into the riser  20 . 
         [0019]    As shown in  FIG. 2 , an FCC unit  10  may be used in the FCC process. Feedstock may be injected by distributors  12  into the riser  20  where it contacts catalyst and fluidizing mediums. Fluidizing mediums may include inert gas or steam. In general, feedstock may be cracked in the riser  20  in the presence of catalyst to form a cracked stream. Distributors  12  may be at different radial positions to improve feedstock distribution in the riser  20  and mixing with catalyst. Multiple distributors  12 , as shown in  FIG. 3 , may be utilized at different radial positions, preferably at least two per radial position and spaced generally evenly. Distributors  12  of differing capacities may distribute different quantities of feedstock to different areas within the riser to optimize coverage across the riser  20 . The differing capacities may range from about 30% to 200% of the average distributor  12  capacity, preferable about 60% to about 150%. 
         [0020]    In one embodiment, as shown in  FIG. 4 , feedstock is injected through one or more orifices, or openings,  14  usually near or on the tip  16 . Preferably, a plurality of openings  14  are on the end of the tip  16 , arranged in a circular or oval pattern. In addition, multiple circular or oval patterns of openings  14  may be used on one tip  16 . At least one distributor  12  may position one of its openings  14  at a different radial position in the riser  20  than another. Referring to  FIG. 1 , the space S between the opening  14  and the closest portion of the wall  22  may be a distance equal to between about 5% and about 45% of the diameter D of the riser  20 , preferably between about 15% and about 35%. 
         [0021]      FIG. 4  shows a detail of a distributor  12 . In one embodiment, a riser may have a nozzle  24  which engages a distributor barrel  30  by a barrel body flange  32 . The distributor barrel  30  receives steam from a steam inlet pipe  34  and oil through an oil inlet pipe  36 , secured to the oil inlet flange  38  by bolts. Oil may pass through the internal oil pipe  40  and over vanes  42 , causing the oil to swirl before combining with the steam and exiting through the opening  14  in the tip  16 . 
         [0022]    Openings  14  may be positioned at different elevations along the riser  20 , as shown in  FIG. 5 , where the difference in elevation H, or height, between the openings of the distributors is depicted. The difference in elevation H may be a distance equal to between about 15% and 125% of said diameter D. Multiple distributors  12  may be utilized at each of the different elevation H levels in combination with, different radial positions. 
         [0023]    As shown in  FIG. 5 , and in detail in  FIG. 6 , a shaping vane  44  may be used to direct the flow of materials around the portion of the distributor  12  extending into the inside the riser  20 . Shaping vane  44  may be attached to the distributor  12  and to the wall  22  or only to the distributor  12  or wall  22 . A refractory coating may cover the surface of the shaping vane  44  or distributor  12 , or both, to protect against erosion. 
         [0024]    Distributor tip  16 , as shown in  FIG. 5 , may be positioned at angles α or β upward from horizontal. Feedstock may then be injected at an angle upward with the current of the catalyst and fluidizing medium. Angles α and β may differ to optimize coverage. Preferably, these angles α and β are each between about, 15 and about 60 degrees upward from horizon, and more preferably between about 20 and about 40 degrees. Fluidizing medium may be introduced into riser  20 , preferably near the bottom, through a steam distributor  46 . 
         [0025]    As shown in  FIG. 2 , the injected feed mixes with a fluidized bed of catalyst and moves up the riser  20  and enters the reactor  50 . In the reactor  50 , the blended catalyst and reacted feed vapors are then discharged from the top of the riser  20  through the riser outlet  52  and separated into a cracked product vapor stream and a collection of catalyst particles covered with substantial quantities of coke and generally referred to as “coked catalyst.” Various arrangements of separators to remove coked catalyst from the product stream quickly may be utilized. In particular, a swirl arm arrangement  54 , provided at the end of the riser  20 , may further enhance initial catalyst and cracked hydrocarbon separation by imparting a tangential velocity to the exiting catalyst and cracked product vapor stream mixture. The swirl arm arrangement  54  is located in an upper portion of a separation chamber  56 , and a stripping zone  58  is situated in the lower portion of the separation chamber  56 . Catalyst separated by the swirl arm arrangement  54  drops down into the stripping zone  58 . 
         [0026]    The cracked product vapor stream comprising cracked hydrocarbons including gasoline and light olefins and some catalyst may exit the separation chamber  56  via a gas conduit  60  in communication with cyclones  62 . The cyclones  62  may remove remaining catalyst particles from the product vapor stream to reduce particle concentrations to very low levels. The product vapor stream may exit the top of the reactor  50  through a product outlet  64 . Catalyst separated by the cyclones  62  returns to the reactor  50  through diplegs into a dense bed  66  where catalyst will pass through chamber openings  68  and enter the stripping zone  58 . The stripping zone  58  removes adsorbed hydrocarbons from the surface of the catalyst by counter-current contact with steam over the optional baffles  70 . Steam may enter the stripping zone  58  through a line  72 . A coked catalyst conduit  74  transfers coked catalyst to a regenerator  80 . 
         [0027]    As shown in  FIG. 2 , the regenerator  80  receives the coked catalyst and typically combusts the coke from the surface of the catalyst articles by contact with an oxygen-containing gas. The oxygen-containing gas enters the bottom of the regenerator  80  via a regenerator distributor  82 . Flue gas consisting primarily of N 2 , H 2 O, O 2 , CO 2  and perhaps containing CO, SO 2 , SO 3 , and NO passes upwardly from the regenerator  80 . A primary separator, such as a tee disengager  84 , initially separates catalyst from flue gas. Regenerator cyclones  86 , or other means, remove entrained catalyst particles from the rising flue gas before the flue gas exits the vessel through an outlet  88 . Combustion of coke from the catalyst particles raises the temperatures of the catalyst. The catalyst may pass, regulated by a control valve, through a regenerator standpipe  90  which attaches to the bottom portion of riser  20 . 
         [0028]    In the FCC process a fluidizing gas such as steam may be passed into the riser  20  to contact and lift the catalyst in the in the riser  20  to the feed point. Regenerated catalyst from the regenerator standpipe  90  will usually have a temperature in a range from about 649° and about 760° C. (1200° to 1400° F.). The dry air rate to the regenerator may be between about 3.6 and about 6.3 kg/kg coke (8 and 14 lbs/lb coke). The hydrogen in coke may be between about 4 and about 8 wt-%, and the sulfur in coke may be between about 0.6 and about 3.0 wt-%. Catalyst coolers on the regenerator may be used. Additionally, the regenerator may be operated under partial CO combustion conditions. Moreover, water or light cycle oil may be added to the bottom of the riser to maintain the appropriate temperature range in FCC unit. Conversion is defined by conversion to gasoline and lighter products with 90 vol-% of the gasoline product boiling at or below 193° C. (380° F.) using ASTM D-86. The conversion may be between about 55 and about 90 vol-% as produced. The zeolitic molecular sieves used in typical FCC gasoline mode operation have a large average pore size and are suitable for the present invention. Molecular sieves with a large pore size have pores with openings of greater than 0.7 nm in effective diameter defined by greater than 10 and typically 12 membered rings. Pore Size Indices of large pores are above about 31. Suitable large pore molecular sieves include synthetic zeolites such as X-type and Y-type zeolites, mordenite and faujasite. Y-type zeolites with low rare earth content are preferred. Low rare earth content denotes less than or equal to about 1.0 wt-% rare earth oxide on the zeolitic portion of the catalyst. Catalyst additives may be added to the catalyst composition during operation. 
         [0029]    In one embodiment, the fluidized catalyst is accelerated in the lower riser  20  to reach the distributor  12 . Catalyst velocity may be between about 9 and about 30 centimeters per second (0.3 and 1 feet per second), preferably between about 1.5 and about 6.1 meters per second (5 and 20 feet per second). Steam or other inert gas may be employed as a diluent through a steam distributor  46 . Only the steam distributor  46  is shown in the FIGURES. However, other steam distributors may be provided along the riser  20  and elsewhere in the FCC unit  10 . 
         [0030]    The riser  20  may operate with catalyst to oil ratio of between about 4 and about 12, preferably at about 8. Steam to the riser  20  may be between about 3 and about 15 wt-% feed, preferably between about 4 and about 12 wt-%. Before contacting the catalyst, the raw oil feed may have a temperature in a range of from about 149° to about 427° C. (300 to 800° F.), preferably between about 204′ and about 288° C. (400° and 550° F.). 
         [0031]    The reactor  80  temperature may operate at a range of between about 427° and 649° C. (800° and 1200° F.), preferably between about 482° and about 593° C. (900° and 1100° F.). The pressure in the reactor  80  may be between about 103 and about 241 kPa (gauge) (15 and 35 PSIG), preferably at about 138 kPa (gauge) (20 PSIG). 
         [0032]    The feed pressure drop across the feed distributor  12  may be between about 69 and about 690 kPa (gauge) (10 and 100 PSIG), preferably between about 205 and about 415 kPa (gauge) (30 and 60 PSIG). The steam on feed of the distributor may be between about 0.5 and about 7 wt-%, and preferably between about 1 and 6 wt-%. 
         [0033]      FIGS. 7 through 9  illustrate several additional embodiments of the invention. Elements in  FIGS. 7 through 9  which correspond to elements in  FIGS. 1-6  but with different configurations will be designated with the same reference numeral but appended with the prime symbol (′). In an embodiment, as shown in  FIG. 7 , a distributor  12 ′ is attached to the wall  22  and extends into the riser  20  toward the center and then bends to extend upward. The openings  14  are preferably positioned near the centerline of the riser and inject feedstock upward into approximately the center of the riser  20 . In one embodiment, a difference in elevation H′ between a bent distributor  12 ′ and another distributor  12  attached to the wall  22  would be a distance equal to between about 15% and about 150% of the diameter D′ of the riser  20 , preferably between about 50% and about 125%. Using more than one distributor  12  and  12 ′ is contemplated in this embodiment. 
         [0034]      FIGS. 8 and 9  depict a centrally located feed distributor  100  in addition to a feed distributor  12  attached to the wall  22 . The center distributor  100  has a different radial position than distributor  12 . More than one center distributor  100  may be used. Feed distributor  100  may have a cylindrical configuration and a diameter which increases from its bottom to its top. In one embodiment, a difference in elevation H′ between the center distributor  100  and another distributor  12  attached to the wall  22  would be a distance equal to between about 0% and about 200% of the diameter D′ of the riser  20 , preferably between about 25% and about 125%. As shown if  FIGS. 10 and 11 , a distributor  12  attached to the wall  22  may be positioned at the same elevation as the top of the center distributor  100 . Furthermore, two distributors  12  attached to the wall  22  may be positioned at different elevations and radial positions in addition to the center distributor  100 . 
         [0035]    Feed is introduced from the distributor  100  positioned near the center of the riser  20 ′, extending upwardly from the bottom of the riser  20 ′. The distributor  110  is positioned to introduce the feed into approximately the center between the side walls of the riser  20 ′ and at an elevated position above the input of steam from a steam distributor  46 ′ and regenerator standpipe  90 . In one embodiment, a distributor flange  102  may attach to the base  104  of the riser  20 ′ by bolts. A distributor barrel  106  receives steam from a steam inlet pipe  108 . An oil inlet pipe  110  delivers feedstock to an internal oil pipe  112 . An oil inlet barrel flange  114  secures the oil inlet pipe  110  to the distributor barrel  106  by bolts. Vanes  116  in the internal oil pipe  112  cause the oil to swirl in, the oil pipe before exiting. The internal oil pipe  112  distributes the swirling oil to the distributor barrel  106  where it mixes with steam, which passes around a pressure disc  118 , and the mixture is injected from orifices, or openings,  120  in the distributor tip  122 . 
         [0036]    As shown in  FIG. 9 , the openings  120  may be a series of holes, preferably arranged in a circle around a cap  124 , on the top of the tip  122 . The space S′ for a center distributor  100  between the opening  120  and the closest portion of the wall  22  may be a distance equal to between about 15% and about 50% of the diameter D′ of the riser  20 , preferably between about 35% and about 50%. A bracket attach the distributor  100  to the wall  22 ′ for stabilization, preferably attaching to the distributor  100  near its tip  122 . It is contemplated that the hole pattern in the tip  122  can take other types, of patterns such as concentric circles or other shapes and that a plurality of distributors  100  may be positioned in the riser  20 ′ to ensure adequate proportionation of the feed. The distributors  12  are available from Bete Fogg Nozzles, Inc. 
         [0037]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.