[0001]    This application claims priority from U.S. Provisional Application S/N 61/185,682 filed Jun. 10, 2009, which is hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a fluid catalytic cracking process which takes advantage of a flue gas conversion plant including a Fischer-Tropsch process to reduce carbon dioxide emissions and increase the production of useful hydrocarbon products, such as diesel oil, jet fuel, and other products. 
         [0003]    A fluid catalytic cracking unit typically includes a reactor, a catalyst regenerator, which burns off carbon from the catalyst used in the reactor, a flue gas treatment plant which treats the flue gas from the catalyst regenerator, and a fractionator, which separates the products from the reactor. 
       SUMMARY 
       [0004]    The present invention discloses modifications to a fluid catalytic cracking unit in order to improve its hydrocarbon yield and to substantially reduce its carbon dioxide (CO 2 ) emissions. As explained in more detail below, this is accomplished by combining one or more of the following modifications to the process:
       Send the flue gases from the fluid catalyst cracking unit to a flue gas conversion plant which includes a Fischer-Tropsch process to convert H 2  and CO into hydrocarbon products such as diesel fuel.   Operate the catalyst regenerator for the catalyst cracking unit in partial burn to increase the production of CO and reduce the production of CO 2 . The increased CO production is advantageously used in the Fischer-Tropsch process to improve the hydrocarbon yield,   Recycle the CO 2  from the flue gas of the catalyst regenerator back into the catalyst bed of the regenerator to drive the net production of CO 2  to extinction so that no new CO 2  is produced in order to substantially reduce the level of CO 2  emissions from the fluid catalytic cracking unit and result in more CO production, which improves the yield of hydrocarbons in the Fischer-Tropsch process.   Inject into the catalyst regenerator any low value refinery fuel or other hydrocarbon or carbon source product (in addition to the coke present in the catalyst to be regenerated) in order to increase the amount of carbon available for the production of CO (which is then utilized in the Fischer-Tropsch process to increase the hydrocarbon yield. Particularly useful for this purpose is the injection into the regenerator of the low value slurry oil from the bottoms of the main fractionator(s) of the fluid catalytic cracking unit. This also helps establish heat-balance in the reactor.       
 
         [0009]    The heat balance is negatively affected with the combustion of carbon to CO (only 4,000 BTU/lb of carbon) instead of its combustion to CO 2  (14,000 BTU/lb of carbon) when operating in partial burn.
       The incorporation of these process to the fluid catalytic cracking unit may include the physical modification of the facility beyond the addition of the flue gas conversion plant with Fischer-Tropsch process. These modifications may include the addition of nozzles and distribution grids to the catalyst regenerator, the addition or modification of nozzles to the main fractionator(s), as well as resizing of components such as the regenerator and the gas plant, especially if the flue gas conversion plant does not include its own fractionator(s) and instead makes use of the main fractionator(s) of the fluid catalytic cracking unit.       
 
         [0011]    In one embodiment, the regenerator flue gas from the fluid catalytic cracking unit (which is primarily a mixture of CO, CO 2 , and N 2 ) is sent to a flue gas conversion plant (which preferably is adjacent to the fluid catalytic cracking unit) that uses the Fischer-Tropsch process to react any CO in the flue gas with H 2  to make hydrocarbons such as diesel oil, jet fuel, gasoline, etc. (e.g., 33H 2 +16CO═C 16 H 34 +16H 2 O). The Fischer-Tropsch products may then be routed to the main fractionator of the fluid catalytic cracking unit or to a separate fractionator. 
         [0012]    The hydrogen required for the Fischer-Tropsch reaction can be purchased (imported to the facility) or produced from natural gas or produced from the hydrocarbons in the off-gas from the fluid catalytic cracking unit in a hydrogen plant in the refinery (CH 4 +2H 2 O═4H 2 CO 2 ). The hydrogen can also be extracted from the off-gas from the fluid catalytic cracking unit. Alternatively, the required amount of hydrogen for the Fischer-Tropsch process could be produced if 67% of the total CO in the flue gas from the fluid catalytic cracking unit is routed to a CO shift reactor (or a Fischer-Tropsch reactor with shift catalyst). In this case no external H 2  is required. (H 2 O+CO═CO 2 +H 2 ). 
         [0013]    In some embodiments, slurry oil is injected into the regenerator, and the control system may be programmed to control the slurry oil injection at between 1% and 10% of fluid catalytic cracking unit feed (preferably %). 
         [0014]    CO 2  can be recycled with the air being injected into the catalyst regenerator of the fluid catalytic cracking unit to recycle the CO 2  to extinction and produce more CO. The control system may be programmed to measure and maintain the CO 2  recycle at the desired level between 10% and 300% of the air or oxygen rate (preferably 200%) to ensure the stoichiometric reaction 2C+O 2 +2CO 2 ═2CO+2CO 2  inside the catalyst regenerator. The controller maintains equilibrium while effectively recycling the CO 2  to extinction. The effective overall equation becomes 2C+O 2 ═2CO. 
         [0015]    This further reduces CO 2  emissions by eliminating the CO 2  produced from the regenerator. The overall reaction in the catalyst regenerator becomes 2C+O 2 ═2CO instead of C+O 2 ═CO 2  or 4C+3O 2 ═2CO+2CO 2 . 
         [0016]    To heat-balance the fluid catalytic cracking unit when no CO is burned to CO 2 , heat can be supplied from extra coke on the catalyst, derived from cracking heavier, higher carbon feeds, or by rerouting the fluid catalytic cracking unit fractionator bottoms (slurry oil) into the regenerator instead of routing it to heavy fuel oil storage. The slurry oil is about 90% carbon, making it an ideal source of carbon to produce CO in the regenerator and provide heat to heat-balance the fluid catalytic cracking unit. The CO is converted into hydrocarbon in the Fischer-Tropsch unit. The use of heavier feeds in the reactor and/or the recycle of slurry oil to the regenerator provide good ways to heat-balance the fluid catalytic cracking unit. 
         [0017]    The reduction in available heat caused by not burning the CO to CO 2  in the regenerator also can be compensated by burning any other low value refinery fuel or product in the catalyst regenerator of the fluid catalytic cracking unit—such as absorber off-gas from the fluid catalytic cracking unit gas plant, and even gasoline from the fluid catalytic cracking unit if the puce of gasoline is below diesel puce, most of which will provide CO for diesel production in the Fischer-Tropsch process. In addition, any hydrocarbon or carbon source, for example charcoal or coal or wood or biomass, can be burned to produce the heat balance, and the CO from combustion can go to the Fischer-Tropsch process to produce hydrocarbons such as diesel fuel. 
         [0018]    Another source of heat for the reactor of the fluid catalytic cracking unit can be the excess heat from the Fischer-Tropsch process. For example, the heat from the Fischer-Tropsch process can be converted into electricity, which can be used to heat up the regenerator using microwaves or radiant heating coils. Also, electricity from any source could be used to balance the fluid catalytic cracking unit heat requirements. 
         [0019]    Also, the heat from the Fischer-Tropsch process can be used to drive the compressor for the flue gas treatment for the fluid catalytic cracking unit, either by generating steam to directly drive the compressor or by generating steam to produce electricity to drive the compressor. 
         [0020]    As indicated above, one embodiment of the present invention injects slurry oil (or any other solid, liquid or gaseous source of carbon or hydrocarbon such as charcoal, coal, biomass, etc into the catalyst regenerator, converts it to CO in the generator, and converts this CO to hydrocarbon in the Fischer-Tropsch flue gas conversion plant. Residue cracking (catalytic cracking of heavy, high carbon feedstocks, vacuum bottoms, and atmospheric bottoms, as well as gas oil cracking) may be included in the process that is carried out in the fluid catalytic cracking unit. 
         [0021]    The fluid cracking catalyst preferably is a zeolite or non zeolite silica alumina catalyst. It preferably contains less than one part per million Pt or other oxidation promoters, oxidation catalysts or oxidation chemicals. It preferably has pore volumes of 0.3 to 0.8 cc/gram and a surface area of at least 50 m 2 /g. It preferably has at least 1 ppm Ni or similar reducing promoter and less than 5000 ppm of Ti. 
         [0022]    The carbon on regenerated catalyst (CRC) regenerator temperature and the flue gas composition are preferably continuously monitored and the relative flows of combustion gas, slurry oil, and CO 2  recycle streams adjusted to achieve maximum CO production at the lowest CO 2  recycle rate. 
         [0023]    The diesel oil and other hydrocarbon products from the Fischer-Tropsch flue gas conversion plant may be processed in the fluid catalytic cracking unit main fractionator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic of a standard prior art fluid catalytic cracking unit (FCCU); 
           [0025]      FIG. 2  is a schematic of a fluid catalytic cracking unit including one embodiment of the present invention; 
           [0026]      FIG. 3  is a schematic showing the inputs and outputs for the Flue gas conversion unit, which is Section  6  in  FIG. 2 ; 
           [0027]      FIG. 4  is a schematic showing an alternative embodiment of the Flue gas conversion unit of  FIG. 3 ; 
           [0028]      FIG. 5  is a schematic showing a second alternative embodiment of the Flue gas conversion unit of  FIG. 3 ; 
           [0029]      FIG. 6  is a schematic showing another alternative embodiment of the Flue gas conversion unit; 
           [0030]      FIG. 7  is a schematic showing some of the modifications which may be made to the catalyst regenerator; 
           [0031]      FIG. 8A  is an enlarged view of the slurry oil injection nozzle of  FIG. 7 ; 
           [0032]      FIG. 8B  is an end view of the nozzle of  FIG. 8A ; 
           [0033]      FIG. 9  is a table showing the fuel oil yield for the base case of a prior art fluid catalytic cracking unit; 
           [0034]      FIG. 10  is a table showing the fuel oil yield for a fluid catalytic cracking unit with two different embodiments of the present invention wherein the regenerator is operated in partial CO burn. In case  2   a  the CO 2  is not recycled, while in case  2 B the CO 2  is recycled to extinction (in both cases there is no slurry oil injected into the regenerator); 
           [0035]      FIG. 11  is a table showing the fuel oil yield for a fluid catalytic cracking unit with the same two embodiments of the present invention as in  FIG. 10 , except slurry oil is injected into the regenerator in both of these cases; 
           [0036]      FIG. 12  is a table showing the fuel oil yield for a fluid catalytic cracking unit with the same two embodiments of the present invention as in  FIG. 10 , except that a shift reactor is used to produce H 2 , in one instance there is no CO 2  recycle while in the second case there is CO 2  recycle to extinction; and 
           [0037]      FIG. 13  is a table showing the fuel oil yield for a fluid catalytic cracking unit with the same two embodiments of the present invention as in  FIG. 10 , except with a different fresh feedstock. 
       
    
    
     DETAILED DESCRIPTION 
     Description of the Prior Art Fluid Catalytic Cracking Process shown in FIG.  1   
       [0038]    A typical prior art fluid catalytic cracking unit  10 ′ has five valor sect ions shown  FIG. 1 :
       section  1  is the fluid bed reactor  12 ′   section  2  is the main fractionator(s)  14 ′   section  3  is the gas plant  16 ′   section  4  is the catalyst regenerator  18 ′ and   section  5  is the flue gas treatment plant  20 ′.       
 
         [0044]    The yields from this fluid catalytic cracking unit  10 ′ are shown in  FIG. 9 . These are actual yields. (The yields in the other tables are calculated, not actual,) 
         [0045]    Fluid cracking catalyst (FCC) it the fluid bed reactor  12 ′ (Section facilitates a reaction which converts the heavy hydrocarbon feed  22  (long-chain hydrocarbon molecules) into high value transportation fuels  24 ,  26  and liquid petroleum gases (LPG)  28 ,  30 . The feed  22  is atomized with steam  34  on its way into the reactor. In the reactor  12 ′, the atomized heavy hydrocarbon feed  22  is mixed with very hot, powdered catalyst, causing the heavy hydrocarbon feed  22  to vaporize and crack into smaller molecules. The cracked product vapors are then separated from the spent catalyst. The spent catalyst is stripped with steam  36  in the reactor stripper  48 ′ to remove entrained hydrocarbons and is sent to the regenerator  18 ′, and the cracked hydrocarbon vapors are sent to the main fractionator(s)  14 ′. 
         [0046]    Some of the feed  22  either is not converted or is only partially converted, resulting in low value slurry oil  32 , which comes out of the bottoms of the fractionator(s)  14 ′). Some of the feed  2 ′ is converted to low value coke, which is deposited on the spent catalyst. 
         [0047]    The reactor  12 ′ operates between 850° F. and 1100° F., at pressures of between 2 psig and 60 psig and with catalyst to oil ratios of between 2:1 and 30:1. The main fractionator  14  (Section  2 ) separates the diesel  26  and slurry oil  32  from the gas  38 . LPG  28 ,  20  and gasoline  24  by distillation. 
         [0048]    The feed atomizing steam  34  and catalyst stripping steam  36  are removed from the fractionator  14 ′ overhead receiver as condensed water  40 . The gas plant  16 ′ (Section  3 ) further separates the off-gas  38 , LPG  28 ,  30  and gasoline  24  by distillation and absorption. 
         [0049]    In the catalyst regenerator  18 ′ (Section  4 ), the coke is burned off the spent catalyst with a gas containing oxygen, usually air  42 . The flue gases  44  from the catalyst regenerator  18 ′ (Section  4 ) are a mixture of CO, CO 2 , SO 2 , N 2 , NO x  and catalyst fines. The catalyst regenerator  18 ′ operates at temperatures between 1100° F. and 1600° F. and similar pressures to the reactor  12 ′. In the flue gas treatment section  20 ′ (Section  5 ), CO in the flue gas  44 , if present, is converted to CO 2  in a waste heat boiler, and the SO 2  and catalyst fines are removed in a wet gas scrubber. The CO 2  and N 2  exit the fuel gas treatment section  20 ′ (Section  5 ) at the outlet  46 . 
         [0050]    Fluid cracking catalyst (FCC) circulates continuously from the reactor  12 ′ (Section  1 ) to the catalyst regenerator  18  (Section  4 ), flowing from the regenerator  18 ′ to the reactor  12 ′ along the path (X), and from the reactor  12 ′ to the regenerator  18 ′ along the path (Y). The catalyst provides four important functions: cracking; coke removal; removal of heat from the regenerator  18 ′ (Section  4 ); and supply of heat to the reactor  12 ′ (Section  1 ). 
       The Fluid Catalytic Cracking Unit Reactor (Section  1 ): 
       [0051]    Hot catalyst from the catalyst regenerator  18 ′ (Section  4 ), at the regenerator temperature (approximately 1400° F.) flows into the reactor  12 ′ (Section  1 ) along the path labeled (X). The hot catalyst provides the endothermic heat of reaction, heat of vaporization, and the heat to heat the oil to its cracking temperature. The catalyst circulation rate depends on the feed preheat temperature, regenerator temperature, and reactor temperature, and is usually a ratio of about 6:1 catalyst to oil. However, some designs operate as high as a 30:1 catalyst to oil ratio. The reactor temperature is controlled at approximately 1000° F. 
         [0052]    The feed  22  to the reactor  12 ′ (Section  1 ) is atomized with steam  34 . The reactor  12 ′ converts a heavy hydrocarbon feedstock  22 , with an API gravity of between 10° and 35° and a Conradson Carbon content of between 0% and 10%, into C 5 + gasoline  24 , diesel  26 , slurry oil  32 , absorber off-gas  38  (which may include H 2 , H 2 S, C 1  s, C 2 s,), C 3 s LPG  28 , C 4 s LPG  30 , and coke. Most of the coke is produced in the cracking reaction where it is deposited onto the surface of the catalyst. The coke contains traces of sulfur, and some coke results from a small quantity of hydrocarbons that are entrained and absorbed onto the catalyst as it leaves the reactor-stripper  48 ′ and enters the regenerator  18 ′. 
         [0053]    The vapor products may be separated from the spent catalyst in the reactor  12 ′ by many known separation devices such as cyclones. This ensures the correct oil/catalyst residence time and ensures that no catalyst goes over into the main fractionators  14 ′ (Section  2 ). 
         [0054]    The catalyst is stripped with steam  36  in the reactor stripper  48 ′ as it flows from the reactor  12 ′ (Section  1 ) to the regenerator  18 ′ (Section  4 ), and the stripped hydrocarbons and steam are returned to the reactor  14   
         [0055]    The atomizing steam  34 , stripping steam  36 , and reactor products leave the reactor  12 ′ as a vapor and flow into the fractionator  14 ′ (Section  2 ) for separation. 
       The Fluid Catalytic Cracking Unit Regenerator (Section  4 ): 
       [0056]    The catalyst flows from the reactor  12 ′ (Section  1 ) to the regenerator  18 ′ (Section  4 ) where the coke is burned off and the catalyst is reheated. A fluid catalytic cracking unit  10 ′ that is processing a gas oil with low Conradson carbon (&lt;0.05%) may only produce 5% coke. However, a fluid catalytic cracking unit  10 ′ processing a residue feedstock with up to 10% Conradson carbon may produce up to 12% coke. The coke includes about 6% hydrogen 94% carbon, and trace amounts of sulfur. It is burned off the catalyst with an oxygen bearing gas  42 , such as air. The regenerator temperature is approximately 1400° F., and in some residue feedstock processing units the temperature is controlled with steam coils and heat exchangers to remove any excess heat. 
       Flue Gas Treatment (Section  5 ) 
       [0057]    The flue gases  44  (which may include H 2 O, SO 2 , N 2 , CO and CO 2 ,) flow from the regenerator  18 ′ (Section  4 ) to the flue gas treatment plant  20 ′ (section  5 ) where any CO is burned to CO 2 , and the SO 2  and catalyst fines are removed. The flue gases  44  before treating can have a varied composition. They may contain 0% to 50% CO; 25% to 100% CO 2 ; 0% to 6% O 2 ; and 0%-80% N 2  depending on how the fluid catalytic cracking unit is operated, and whether air, or oxygen, or oxygen in air, or O 2  with other gases are used for combustion in the regenerator  18 ′. The flue gas treatment plant  20 ′ may include a waste heat boiler which converts CO to CO 2  and may have a NO treatment reactor. 
       The Fluid Catalyst 
       [0058]    The fluid catalyst provides the surface area, catalytic acidity and activity in the reactor  12 ′. As it leaves the reactor  12 ′, it removes the unwanted coke (a compound with about 6% hydrogen and 94% carbon) produced during the cracking reactions. In the catalyst regenerator  18 ′ (Section  4 ) the catalyst absorbs most of the heat released when the coke is burned off the catalyst with an oxygen rich gas  42  (usually air). The catalyst is usually made from alumina-silica micro-spheres with diameters of 2-200 microns and impregnated with zeolites (including HY, REY, USY, ZSM-5), additives, including bottom cracking additive (BCA) max diesel additive, metal traps, and oxidation additives and co-catalysts such as Pt. 
       Modified Plant Including Flue Gas Conversion Using Fisher-Tropsch Process 
       [0059]      FIG. 2  shows the fluid catalyst cracking unit  10  that has been modified to incorporate a flue gas conversion plant  50  (Section  6   t  within the facility. 
       The Flue Gas Conversion Plant (Section  6 ): 
       [0060]    The flue gas conversion plant  50  (Section  6 ) has within it a number of individual process units, including a Fischer-Tropsch process Plant (also referred to as an F-T plant), which produces useful hydrocarbons from the CO in the flue gas of the regenerator  18 . There are, depending on the specifics of the usage a number of arrangements that may be used. For example, the Fischer-Tropsch reactor itself can be slurry-type or tubular fixed-bed or fluidized bed. The Fischer-Tropsch catalyst might be cobalt-hosed or iron-based or some other, newer, alternative. 
         [0061]    In general the flue gas conversion plant  50  may include the following elements (See  FIG. 6 ):
       Shift reactor in order to fix the ratio of H 2 /CO slightly above 2.   The Fischer-Tropsch reactor(s). Depending on the size and design of facility, this might be one or more reactors. Significant amounts of medium pressure steam (approx. up to 200° C.) are generated in these reactors. This steam can be used in heating other process streams and units, as necessary, and can be used to generate electricity for internal use or export.   Separation equipment for the removal of CO 2  as well as any remaining H 2 /CO, and separation of light hydrocarbon gases from naphtha, diesel/jet, and lubes/waxes.   Reactors and associated facilities for hydrotreating naphtha and diesel/jet fuel and hydrocracking lubes and waxes to lighter hydrocarbons.   Separation equipment for the separation of the various hydrocarbons from one another. (In this case, this might be replaced with the fluid catalytic cracking unit main fractionators  14 .)       
 
         [0067]    The schematic of  FIG. 2  involves several modifications to the standard, prior art fluid catalytic cracking unit  10 ′ of  FIG. 1 , which may include the modification of the fluid catalytic cracking unit main fractionator  14 ′, regenerator  18 ′, and gas plant  16 ′, as explained in more detail below. It also includes the addition of a flue gas conversion plant  50  (Section  6 ). The flue gas conversion plant  50  may have a CO shift reactor (See  FIG. 5 ), or there may not be a CO shift reactor (See  FIG. 3 ). It may include a hydrogen plant (See  FIG. 4 ), or it may use imported hydrogen. 
         [0068]    The fluid catalyst cracking unit  10  includes the full integration of the Flue gas conversion plant  50  (and associated equipment such as mild hydrocracker and additional hydrotreating facilities, shift reactor and hydrogen plant) with the fluid catalytic cracking unit regenerator  18 , fractionator  14  and gas plant  16 . Depending on the output from the Fischer-Tropsch flue gas conversion plant  5 , modifications to the main fractionator  14 ′ and the gas plant  16 ′ may not be necessary. For instance, if the Fischer-Tropsch flue gas conversion plant  50  includes its own fractionator(s), then modifications to the main fractionator  14 ′ and the gas plant  16 ′ may not be made. 
       New Equipment 
       [0069]    In order to modify the fluid catalyst cracking unit  10 ′ shown in  FIG. 1  to make the fluid catalyst cracking unit  10  shown in  FIG. 2 , a new fluid catalytic cracking unit flue gas conversion plant  50  (Section  6 ) is added to the fluid catalytic cracking unit. The main process unit in the flue gas conversion section  50  is a Fischer-Tropsch (FT) plant. 
         [0070]      FIG. 3  shows an example of a flue gas conversion plant  50  (Section  6  of  FIG. 2 ), without shift reactor, wherein H 2  is imported from outside the fluid catalytic cracking unit complex. In that case, only the Fischer-Tropsch process is needed to convert the CO to hydrocarbons such as diesel oil in the flue gas conversion plant  50  (Section  6 ). 
         [0071]      FIG. 4  shows an example of a flue gas conversion plant  50  (Section  6  of  FIG. 2 ), wherein H 2  is generated in a hydrogen plant that is incorporated into the fluid catalytic cracking unit complex, using either natural gas or absorber off-gas  38  from the fluid catalytic cracking unit gas plant. 
         [0072]      FIG. 5  shows an example of a flue gas conversion plant  50  (Section  6  of  FIG. 2 ), in which sufficient H 2  for the Fischer-Tropsch plant can be made on site in a shift reactor or modified Fischer-Tropsch Water is added to the shift reactor to facilitate the shift reaction. This amount of water will react exactly with the remaining flue gas CO in the Fischer-Tropsch plant to make hydrocarbons, including diesel fuel. 
         [0073]    In converting a prior art plant  10 ′ to the plant  10  shown in  FIG. 2  (assuming the flue gas conversion plant  50  does not have its own fractionator), a new nozzle may be added either in the reactor vapor overhead line  52  or into the main fractionation tower itself  54 . This allows the product from the flue gas conversion plant  50  (Section  6 ) to be introduced and processed in the fractionators (Section  2 ). 
         [0074]    The catalyst regenerator  18  also may be modified to improve the conversion of CO 2  to CO as shown in  FIGS. 2 and 7 , adding a spray nozzle and/or an additional combustion air grid. The slurry oil  32  from the main fractionators is injected into the lower section of the regenerator  18  (Section  4 ) preferably about three feet above the combustion air grid  56 , at a point in the regenerator where the carbon on the catalyst is lowest and the O 2  concentration is the highest. A secondary oxygen source  42 * is injected along with the slurry oil  32  to provide atomization and controlled stoichiometric combustion of the slurry oil  32  to CO and H 2 O. Part of the recycled CO 2  also can be injected along with the slurry oil  32  to facilitate a direct C+CO 2 =2CO reaction. The CO 2  recycle also can be injected through the combustion air grid  56  along with the oxygen rich combustion gas  42 . The addition of a nozzle  58  (See  FIGS. 7 ,  8 A, and  8 B) or nozzles  58  and a distribution grid  60  inside the regenerator, preferably between 2 feet and 20 feet, and more preferably approximately 6 feet, above the primary combustion air grid  56 , allows the recycle of CO 2  into the high carbon zone of the regenerator  18  away from the oxygen rich combustion air inlet  42  to maximize the reaction C+CO 2 +2CO. 
         [0075]    Nozzles  58 , described in more detail below, may be added to allow the injection of any hydrocarbon, crude oil, oil sand, tar sand, synthetic oil from coal, tar sands or oil sands, or bio-mass, natural gas, absorber fluid catalytic cracking unit gas plant off-gas  38  or fluid catalytic cracking unit fractionator bottoms (also referred to as slurry oil  32 ), without contacting water or water vapor, for the purpose of heat balancing the fluid catalytic cracking unit  10  when recycling CO 2 . 
         [0076]    In a two stage regenerator or a regenerator with two separate vessels, the slurry oil can be injected into both catalyst beds but preferentially is injected into the low CRC area in the full CO burn vessel. Similarly the CO 2  can be injected into both vessels, but preferentially into the high CRC area in the partial burn vessel. 
         [0077]    As can be appreciated from  FIG. 7 , the CO 2  recycle can be injected into the regenerator  18  through the combustion air grid  56  with the air or oxygen rich combustion gas, with the slurry oil  32  via the nozzle  58 , with the secondary oxygen source  42 * at the nozzle  58 , and/or through its own CO 2  recycle grid  60 . Referring briefly to  FIGS. 7 ,  8 A, and  8 B, the nozzle  58  includes a slurry oil delivery pipe  62  inside a slightly large “sleeve” pipe  64  in an arrangement similar to that of a single tube, shell and tube heat exchanger. The slurry oil travels in the “tube side”  62 , while air or recycled CO 2    42 * for a mixture of these) travels along the “shell side”  64 . This sleeve arrangement provides an insulating effect on the pipe  62  to keep it relatively cool against the heat of the regenerator  18 , to prevent unwanted coking of the slurry oil in the pipe  62 . 
         [0078]    The pipe  62  terminates inside the sleeve  64  at a perforated plate  66  which allows the air/recycled CO 2    42 * to flow around and along the pipe  62  to continually cool it, and then diffuse into the slurry oil  32  in an atomizing chamber  68 . Finally, the mixture of the slurry oil  32  and the air/recycled CO 2    42 * are sprayed out into the regenerator  18  through a horizontally oriented slotted opening  70  to ensure that the slurry oil is sprayed substantially horizontally, way from the refractory-lined walls of the regenerator  18  and not directed toward the distributor grids  60 ,  56 . 
         [0079]    The nozzle  58  includes a flange  72  for mounting to the regenerator wall. The nozzle  58  projects into the regenerator at least far enough to ensure that it clears the refractory material lining the wall of the regenerator  18 . 
       New Fluid Catalytic Cracking Unit Operation 
       [0080]    The fluid catalytic cracking unit  10  operates in partial CO burn. This means that the CRC is controlled between 0.1% and 1.2% in the fluid catalytic cracking unit regenerator  18  (Several methods are known in the industry for determining and controlling the CRC in the regenerator. For instance, the catalyst may be sampled hourly and the level of CRC can then be visually established, or the temperature in the regenerator can be monitored to empirically determine and control the CRC level). The treated flue gases  46  from the flue gas treatment  20  (Section  5 ) are routed to the new flue gas conversion plant  50  (Section  6 ) where the CO is converted to diesel fuel. The process is enhanced if the excess CO 2  from the flue gas conversion plant  50  (section  6 ) is recycled to the catalyst bed of the fluid catalytic cracking unit regenerator  18  to boost CO production, and ultimately convert all coke to CO instead of CO 2 . The CO 2  recycle, CRC, and combustion air flow are carefully controlled to establish the following reaction 2C+O 2 +2CO 2 ═2CO+2O 2 . By carefully controlling operating variables, the net reaction is 2C+O 2 ═2CO, and results in all of the carbon being converted into CO with no net production of CO 2 . The CO and CO 2  are in equilibrium at a ratio of about 1:1. This ratio stays constant as the CO 2  is recycled, as it is defined by thermodynamic conditions. Therefore, as the CO 2  is recycled, more Carbon is converted to CO. Ultimately, there is no net CO 2 , only CO 2  recycle. All the carbon on the catalyst is converted to CO. 
         [0081]    The heat released in the regenerator  18  in this operation is less than that typically required to balance the requirements of the fluid catalytic cracking unit reactor  12  (an exception may occur when processing high residue feedstocks, particularly if oxygen is injected into the regenerator to burn off the coke, as explained in more detail later). Therefore, additional fuel is injected into the catalyst regenerator  18 . This can come from any carbon or hydrocarbon source (in addition to the coke present in the catalyst to be regenerated), and will also be converted to CO (and eventually into diesel fuel in the flue gas conversion plant  50 ). A readily available source of additional fuel is the slurry oil  32  from the bottoms of the main fractionators, as it has a low value and a high carbon content, although absorber off-gas  38  from the fluid catalytic cracking unit gas plant could be used instead or in addition to the slurry oil to add heat or an entirely different source of carbon could be used. Heat balances are shown in  FIG. 12 , 
       The Flue Gas Conversion Plant  50 , FIG. 2 Section  6 , FIG. 3, and FIG. 4 
       [0082]    The flue gas conversion plant  50  (Section  6 ) converts the CO from the flue gas of the catalyst regenerator  18 , water, and external H 2  if needed by the Fischer-Tropsch (FT) plant to hydrocarbons. In the example of yields shown in  FIG. 12  the hydrocarbon product from the Fischer-Tropsch process is middle distillate or diesel fuel, which is then processed in the main fractionator  14  of the fluid catalytic cracking unit. The CO for the Fischer-Tropsch process comes from the flue gas of the catalyst regenerator  18 . 
         [0083]    The hydrogen may come from a variety of sources. For example, it can be imported as shown in  FIG. 3 . Alternatively, H 2  may be produced by an electrolytic process. Hydrogen also can be extracted from the fluid catalytic cracking unit absorber off-gas  38  by membrane separation or pressure swing absorption. This configuration also is shown in  FIG. 3 . 
         [0084]    Alternatively, as shown in  FIG. 4 , the H 2  can be generated from an onsite H 2  plant using natural gas or preferably fluid catalytic cracking unit off-gas  38  as a feed. (The H 2  also could be supplemented from are external source and/or from H 2  in the fluid catalytic cracking unit absorber off-gas  38 .) 
         [0085]    Alternatively, as shown in  FIG. 5 , the H 2  can also be produced in a shift reaction within the Fischer-Tropsch plant or in a separate shift unit ahead of the Fischer-Tropsch plant. In that case, the H 2  plant reaction is CH 4 +2H 2 O═4H 2 +CO 2 . (The H 2  also could be supplemented from an external source and/or from H 2  in the fluid catalytic cracking unit absorber off-gas  38 ). Other methods for the manufacture of H 2  include, but are not limited to, partial oxidation of hydrocarbons (e.g., 2CH 4 O 2 +2CO+4H 2 ). 
         [0086]    The CO 2  from either the hydrogen plant ( FIG. 4 ) or the shift reactor ( FIG. 5 ) is vented to atmosphere or, alternatively, can be recycled to the catalyst regenerator  18 . The shift reaction is H 2 O+CO═CO 2 +H 2 . The shift reactor consumes 67% of the CO from the treated flue gases  46  but still results in significant diesel fuel production in the Fischer-Tropsch plant. Heat (See dotted line in  FIG. 2 ) from the flue gas conversion plant  50  (Section  6 ) is recycled from the flue gas conversion plant  50  in the form of hot CO 2  that is recycled to the catalyst regenerator  18  to heat-balance the catalyst regenerator  18  (Section  4 ). 
         [0087]    The calculated yields from the modified fluid catalytic cracking unit with the Fischer-Tropsch flue gas conversion plant  50  (Section  6 ) are shown in  FIGS. 10 and 11 . The improved process results in increased diesel fuel yields, reduced slurry oil yields, and lower CO 2  emissions. 
         [0088]      FIG. 9  shows the base gas oil yields from the base fluid catalytic cracking unit  10 ′ without the Fischer-Tropsch flue gas conversion. In this case, it can be seen that a feed of 36,930 barrels per day yields 6,377 barrels per day of diesel fuel. This partial CO burn operation is in heat balance. 
         [0089]      FIG. 10  shows the yields in two different cases in which the fluid catalytic cracking unit  10  is coupled with the Fischer-Tropsch flue gas conversion plant  50  without shift in accordance with  FIGS. 2 and 4 , with the flue gases  46  being fed to the flue gas conversion plant  50  (Section  6 ) but without the slurry oil  32  being injected into the regenerator  18  (Section  4 ). Column  2   a  is for the case in which the CO 2  is not recycled, and column  2   b  is for the case in which the CO 2  is recycled to extinction. 
         [0090]    There is a substantial improvement in yield over the base case of  FIG. 9 , especially when the CO 2  is recycled to extinction and 100% of the regenerator CO 2  emissions are eliminated. Without recycling the CO 2  to extinction, the same feed yields 7,078 barrels per day of diesel fuel, and with recycling the CO 2  to extinction, it yields 7,773 barrels per day of diesel fuel as compared with 6,377 barrels per day in the base unit. No external heat is required to heat balance the coupled partial burn case  2   a . However, the recycled CO 2  case requires 98 million BTU/hr to heat balance. This heat (see dotted line in  FIG. 2 ) can be provided by the flue gas conversion plant  50  (Section  6 ) or, alternatively, from other sources. 
         [0091]      FIG. 11  shows yields for the same process as shown in  FIG. 10 , except with the slurry oil  32  being injected into the regenerator  18  (Section  4 ). In this case, the CO comes from the flue gases  46 , from the carbon deposited on the catalyst in the fluid catalytic cracking unit reactor  12  (Section  1 ), and from the carbon in the slurry oil  32  injected into the regenerator  18  (Section  4 ). The heat from burning the slurry oil  32  in the regenerator  18  once again heat-balances the operation. In this case, the same feed produces 8,637 barrels per day of diesel fuel without CO 2  recycle and 9,332 barrels per day of diesel fuel with CO 2  recycle, as compared with 6,377 barrels per day in the base case. 
         [0092]      FIG. 12  shows the case in which the shift reaction is used as shown in  FIG. 5 , and the flue gases  46  go to the flue gas conversion plant  50  (Section  6 ), but the slurry oil  32  does not go to the regenerator  18  (Section  4 ). In this case, part of the CO is converted to H 2  in the shift reactor. Carbon on the catalyst from the residue feedstock supplies the heat to once again heat-balance the operation. In this case, the same feed produces 6,638 barrels per day of diesel fuel without CO 2  recycle and 6,898 barrels per day of diesel fuel with CO 2  recycle. 
         [0093]      FIG. 13  shows a different fresh feed, using the arrangement of  FIGS. 2 and 4 , with the slurry oil  32  not being fed to the regenerator  18  (Section  4 ) and with the flue gases  46  being fed to the flue gas conversion plant  50  (Section  6 ), both with and without CO 2  recycle. 
         [0094]    It is interesting to note that the application of the processes disclosed in this specification also allows for the operation of fluid catalytic cracking units under some unique and particularly interesting condition. Already discussed above are the capabilities to operate:
       under partial burn in the regenerator  18  to increase the production of CO, which is advantageously used in the Fischer-Tropsch process to improve the yield of fuel oils from the fluid catalytic cracking unit  10 .   under CO 2  recycle to drive net production of CO 2  to extinction. This results in a substantial reduction, if not a complete elimination, of CO 2  emissions from the fluid catalytic cracking unit  10 .   under CO 2  recycle to increase production of CO in the regenerator  18 , which is advantageously used in the Fischer-Tropsch process to improve the yield of fuel oils from the fluid catalytic cracking unit  10 .   with injection of low value refinery fuel or other hydrocarbon or carbon source product in addition to the coke present in the catalyst to be regenerated (preferably low value slurry oil from the bottoms of the main fractionator) in order to increase the amount of carbon available for the production of CO (which is then utilized in the Fischer-Tropsch process to increase the yield of fuel oils in the fluid catalytic cracking unit).   with utilization of absorber Off-Gas from the gas plant  16  to obtain hydrogen for use in the Fischer-Tropsch process.       
 
         [0100]    Also, air can be injected into the regenerator  18  to help burn the coke. A better choice is to inject oxygen into the regenerator  18 , but if the coke is being burned to CO2, the amount of heat generated in the regenerator  18 , when injecting oxygen, may be too great. This is especially true when operating with high residue feedstocks (such as feedstock with up to 10% Conradson carbon which may produce up to 12% coke). The amount of heat generated can be so high that it risks melting the regenerator  18 , even when using steam coils to remove the excess heat. Even when high residue feedstocks are not involved, it may be necessary to dilute the air or oxygen with nitrogen to prevent this high heat load in the regenerator  18 . 
         [0101]    However, if the CO 2  is recycled so that there is no net production of CO 2 , then all the coke is burned to CO which has a considerably lower heat output (the thermodynamic equilibrium is normally a 1:1 ratio of CO:CO 2 . If the CO 2  is recycled, then the coke in the catalyst in the regenerator  18  will burn to CO in order to maintain that thermodynamic equilibrium). This substantially reduces the heat load as the heat released when burning the carbon to CO is one third of the heat released when burning the carbon to CO 2 . 
         [0102]    The fluid catalytic cracking unit can then operate using these high residue feedstocks with oxygen injection diluted with the CO 2  recycle, eliminating the need to dilute the oxygen with nitrogen. The reason is two-fold: 
         [0103]    1—The heat load is considerably lower when where burning the carbon to CO instead of when burning it CO 2 . 
         [0104]    2—The CO 2  recycle dilutes the oxygen without the need for nitrogen. 
         [0105]    This provides a distinct advantage in that there is no longer a need to contend with nitrogen coming off as part of the flue gases of the regenerator  18 . The separation is much simpler if there are only CO and CO 2  coming off of the regenerator  18  (because the recycled CO 2  is acting as the diluent for the oxygen) instead of CO, CO 2 , and nitrogen (with the nitrogen acting as the diluent). If the nitrogen is not separated out of the flue gas stream before it is sent to the flue gas conversion plant  50 , then this large volume of nitrogen must be pressurized from the operating pressure in the regenerator (up to 60 PSIG) to that of the Fischer-Tropsch process (about 300 PSIG), and this could be very expensive. 
         [0106]    It will be obvious to those skilled in the art that modifications may be made to the embodiments described above without departing from the scope of the present invention.
A method is provided to reduce carbon dioxide emissions and increase the output of more valuable hydrocarbon products in a fluid catalytic cracking unit.