Process for cracking to light olefins

Abstract

A process for catalytic production of olefins includes contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream. The first cracked product stream is separated in the main column. The overhead stream from the main column is separated into a second hydrocarbon stream. The second hydrocarbon stream is contacted with a second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream. A third hydrocarbon stream is obtained from the overhead stream and / or from the second cracked product stream. The third hydrocarbon stream is contacted with a third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream.

Description

[0001] Priority declaration

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 391,756, filed on July 24, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The field of the invention relates to the reaction of a feed with a fluid catalyst. In particular, the field of the invention relates to FCC processes for producing light olefins using multiple reactors. Background Art

[0004] Catalytic cracking can form a variety of products from larger hydrocarbons. Typically, a heavy hydrocarbon feed, such as vacuum gas oil, is provided to a catalytic cracking reactor, such as a fluid catalytic cracking (FCC) reactor. A variety of products can be produced from such systems, including gasoline products and / or light products, such as propylene and / or ethylene.

[0005] In such a system, a single reactor or a dual reactor may be used. Although the use of a dual reactor system may incur additional capital costs, one of the reactors may be operated to adjust the conditions that maximize the yield of products such as light olefins including propylene and / or ethylene.

[0006] It is generally advantageous to maximize the product yield in one of the reactors. In addition, it may be desirable to maximize the product yield of one reactor, which can be recycled back to another reactor to produce a desired product, such as propylene.

[0007] In addition, some dual reactor systems use a mixture of catalysts, such as a macroporous catalyst and a small pore catalyst. In some cases, the proportion of the small pore catalyst limits the production of the desired light olefins. Therefore, it is usually beneficial to separate the catalyst to control its reaction.

[0008] Therefore, it is desirable to provide a reactor system for catalytic cracking that can best optimize operating conditions to maximize propylene production. Summary of the invention

[0009] The method for catalytic production of olefins comprises contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream. The first cracked product stream is separated in a main tower. The overhead stream from the main tower is separated into a second hydrocarbon stream. The second hydrocarbon stream contacts the second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream. A third hydrocarbon stream is obtained from the overhead stream and / or from the second cracked product stream. The third hydrocarbon stream contacts the third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream.

[0010] Other details and embodiments of the invention will become apparent from the following detailed description of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are cross-sectional elevation views of the disclosed method and apparatus.

[0012] definition

[0013] The term "downstream communication" means that at least a portion of the fluid flowing to the body in the downstream communication can operatively flow from the object in fluid communication therewith.

[0014] The term "upstream communication" means that at least a portion of the fluid flowing out of the body in the upstream communication can be operatively flowed to the object in fluid communication therewith.

[0015] The term "direct communication" means that the fluid flows from the upstream component into the downstream component without passing through any other intervening container.

[0016] The term "indirect communication" means that the fluid flow from the upstream component enters the downstream component after passing through an intervening container.

[0017] The term "bypass" means that the object loses downstream communication with the bypassed body at least within the scope of the bypass.

[0018] As used herein, the term "predominantly" or "majority" means greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0019] The term "tower" means one or more distillation towers for separating one or more components with different volatilities. Unless otherwise specified, each tower includes a condenser on the top of the tower for condensing a portion of the overhead stream and refluxing it back to the top of the tower, and a reboiler at the bottom of the tower for vaporizing a portion of the bottom stream and sending it back to the bottom of the tower. The feed to the tower can be preheated. The top pressure is the pressure of the overhead vapor at the vapor outlet of the tower. The bottom temperature is the liquid bottom outlet temperature. The top line and the bottom line refer to the net line from any reflux or reboil to the tower downstream. The stripping tower can omit the reboiler at the bottom of the tower, but provide heating requirements and separation power for the liquefied inert medium (such as steam). The stripping tower is usually fed from the top tray and the main product is taken out from the bottom.

[0020] As used herein, the term "separator" means a vessel having an inlet and at least one overhead vapor outlet and one bottom liquid outlet, and may also have an outlet for an aqueous stream from a boot. A flash tank is a type of separator that may be connected downstream to a separator that may operate at a higher pressure.

[0021] As used herein, the term "boiling point temperature" means the atmospheric equivalent boiling point (AEBP) calculated from the observed boiling temperature and the distillation pressure, as calculated using the formula provided in ASTM D1160 Appendix A7, entitled "Practice for Converting Observed Vapor Temperatures to Atmospheric Equivalent Temperatures."

[0022] As used herein, the term "true boiling point" (TBP) means a test method for determining the boiling point of a substance in accordance with ASTM D-2892 for producing standardized masses of liquefied gases, distillate fractions, and residues for which analytical data are available, and for determining the yields of the above fractions by both mass and volume from which a plot of distillation temperature versus mass % is obtained in a column having a reflux ratio of 5:1 using fifteen theoretical plates.

[0023] As used herein, "bitumen" means a hydrocarbon material boiling above 524°C (975°F) AEBP as determined by any standard gas chromatography simulated distillation method such as ASTM D2887, D6352, or D7169 (all of which are used by the petroleum industry).

[0024] As used herein, the term "T5" or "T95" means the temperature at which 5 mass percent or 95 mass percent of a sample boils, respectively, using ASTM D-86 or TBP, as the case may be.

[0025] As used herein, the term "initial boiling point" (IBP) means the temperature at which a sample begins to boil using ASTM D-7169, ASTM D-86, or TBP, as appropriate.

[0026] As used herein, the term "endpoint" (EP) means the temperature at which a sample is brought to a complete boil using ASTM D-7169, ASTM D-86, or TBP, as appropriate.

[0027] As used herein, "vacuum gas oil" means a hydrocarbon material produced by vacuum fractionation of atmospheric residue, having an IBP of at least 232°C (450°F), a T5 between 288°C (550°F) and 392°C (700°F), usually not exceeding 343°C (650°F), a T95 between 510°C (950°F) and 570°C (1058°F), and / or an EP not exceeding 626°C (1158°F), as determined by any standard gas chromatography simulated distillation method such as ASTM D2887, D6352, or D7169 (all of which are used by the petroleum industry).

[0028] As used herein, "atmospheric residue" refers to a hydrocarbon material obtained from the bottom of an atmospheric crude distillation column, having an IBP of at least 232°C (450°F), a T5 between 288°C (550°F) and 392°C (700°F), usually not exceeding 343°C (650°F), and a T95 between 510°C (950°F) and 700°C (1292°F).

[0029] As used herein, "atmospheric residue" means a hydrocarbon material boiling at an IBP of at least 500°C (932°F). DETAILED DESCRIPTION

[0030] We have found that twice cracked naphtha or once or twice cracked C4 hydrocarbons can still produce more propylene by cracking. However, the cracking conditions of twice cracked naphtha or C4 hydrocarbons should be adjusted to maximize the propylene production. We propose to use a third riser to provide favorable reaction conditions to maximize the propylene yield.

[0031] Turning now to the drawings, in which like numerals represent like parts, the process and apparatus generally include an FCC unit section 6 and a product recovery section 8. The FCC unit section 6 includes a first FCC reactor 10, which includes a first reactor unit 12 and a catalyst regenerator 14. The process conditions in the first FCC reactor 10 may include a cracking reaction temperature at the reactor outlet of 400° C. to 600° C., preferably 538° C. to 593° C., and a catalyst regeneration temperature of 500° C. to 900° C. Cracking and regeneration are both carried out at an absolute pressure between 100 kPa (14 psia) and 650 kPa (94 psia), preferably between 140 kPa (20 psia) and 450 kPa (65 psia).

[0032] 1 shows a first FCC reactor vessel 12 in which a first hydrocarbon feedstock in line 15 through distributor 16 is contacted with a first fluid catalyst stream entering from regenerated catalyst standpipe 18 and recycle catalyst standpipe 19. The first hydrocarbon feedstock may comprise vacuum gas oil, atmospheric residue, deasphalted oil, vacuum residue, or any other stream processed in a conventional FCC unit.

[0033] The catalyst can be a single catalyst or a mixture of different catalysts. Typically, the catalyst includes two components or catalysts, i.e. a first component or catalyst and a second component or catalyst. Such catalyst mixtures are disclosed in, for example, U.S. Patent No. 7,312,370B2. Typically, the first component can include any known catalyst used in the FCC field, such as an active amorphous clay-type catalyst and / or a highly active crystalline molecular sieve. Zeolite can be used as a molecular sieve in the FCC process. Preferably, the first component includes a large pore zeolite (such as Y-type zeolite), an active alumina material, a binder material (including silica or alumina) and an inert filler (such as kaolin).

[0034] Typically, the zeolite molecular sieve suitable for the first component has a large average pore size. Typically, the molecular sieve with a large pore size has a hole, wherein the opening of the hole is greater than 0.7nm, and the effective diameter is defined by more than 10 and typically 12 component rings. The pore size index of the macropore may be above 31. Suitable large-pore zeolite components may include synthetic zeolites, such as X and Y zeolites, mordenite and faujasite. A portion of the first component (such as a zeolite) may have any suitable amount of rare earth metal or rare earth metal oxide.

[0035] The second component may include a mesoporous or relatively small pore zeolite catalyst, such as an MFI zeolite, for example at least one of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similar materials. Other suitable mesoporous or relatively small pore zeolites include ferrierite and erionite. Preferably, the second component is a mesoporous or relatively small pore zeolite dispersed on a matrix, the matrix including a binder material (such as silica or alumina) and an inert filler (such as kaolin). The second component may also include some other active materials, such as beta zeolite. These compositions may have a crystalline zeolite content of 10% to 50% by weight or more and a matrix material content of 50% to 90% by weight. Preferably, a component comprising 40% by weight of a crystalline zeolite material, and those components having a larger crystalline zeolite content may be used. Typically, mesoporous and relatively small pore zeolites are characterized by having an effective pore opening diameter less than or equal to 0.7nm, a ring of 10 yuan or less yuan and an aperture index less than 31.

[0036] The total catalyst mixture in the first FCC reactor 12 may include 1 wt % to 25 wt % of the second component, i.e., medium-pore to small-pore crystalline zeolite, preferably greater than or equal to 1.75 wt % of the second component. The first component may account for the remainder of the catalyst composition. In some preferred embodiments, the relative proportions of the first component and the second component in the mixture may remain essentially unchanged throughout the first FCC reactor 12. High concentrations of medium-pore or small-pore zeolites as the second component of the catalyst mixture may improve the selectivity to light olefins. In an exemplary embodiment, the second component may be a ZSM-5 zeolite, and the mixture may include 4 wt % to 10 wt % of the ZSM-5 zeolite, excluding any other components, such as a binder and / or filler.

[0037] Preferably, at least one of the first and / or second catalysts is an MFI zeolite having a silicon to aluminum ratio greater than 15, preferably greater than 75. In an exemplary embodiment, the silicon to aluminum ratio may be from 15:1 to 35:1.

[0038] This contact may occur in a narrow first riser 20 that extends upward to the bottom of a first reactor vessel 22. The contact of the first hydrocarbon feedstock with the first fluid catalyst stream is fluidized by a gas, such as steam, from a fluidizing distributor 24. In one embodiment, heat from the catalyst vaporizes the first hydrocarbon feedstock, which is then cracked in the presence of the first catalyst stream into a first cracked product stream of lighter molecular weight as both are transferred upward along the riser 20 into the reactor vessel 22, thereby providing a first mixture of catalyst and product gas.

[0039] The pressure in the first riser 20 can be 200 kPa (29 psia) to 450 kPa (65 psia), but can also be lower. The steam flow rate added to the first riser 20 is 3% to 7% by weight of the first hydrocarbon feedstock. Inevitable side reactions occur in the first riser 20, leaving coke deposits on the catalyst, thereby reducing the catalyst activity and producing a spent catalyst stream. The first cracked product stream in the first mixture of catalyst and product gas is then separated from the spent catalyst stream using a cyclone separator, which may include a single or two-stage cyclone separator 62 in the reactor vessel 22. The gaseous first cracked product stream leaves the reactor vessel 22 through the first product outlet 31 and enters the pipeline 32 for transportation to the downstream product recovery section 8.

[0040] The spent catalyst or coked catalyst requires regeneration for further use. The spent catalyst stream, after being separated from the first cracked product stream by the disengagement device 54 in the first disengagement chamber 56, falls into the stripping section 34 where steam is injected through the distributor 35 to remove any residual hydrocarbon vapors. After the stripping operation, the stripped coked catalyst is carried to the catalyst regenerator 14 through the spent catalyst riser 36. Another portion of the stripped coked catalyst can be recycled to the riser 20 through the recycle catalyst riser 19 without undergoing regeneration.

[0041] FIG. 1 shows a regenerator 14 referred to as a burner. However, other types of regenerators are also suitable. In the catalyst regenerator 14, a stream of an oxygen-containing gas (such as air) is introduced through an air distributor 38 to contact the coked catalyst. The coked catalyst is burned in a combustion chamber 80 to form coke to provide a regenerated catalyst and flue gas. The catalyst regeneration process adds a large amount of heat to the catalyst, thereby providing energy to offset the endothermic cracking reaction occurring in the first riser 20. The catalyst and air flow upward together in the combustion chamber 80 of the regenerator 14, and after regeneration, are discharged through the settler 40 for preliminary separation and enter the separation chamber 86. The regenerated catalyst and flue gas leaving the settler 40 are additionally recovered using the first stage cyclone separator 44 and the second stage cyclone separator 46 in the separation chamber 86 of the catalyst regenerator 14, respectively. The catalyst separated from the flue gas is distributed through the feed pipes in the cyclone separators 44, 46, and the relatively light flue gas in the catalyst leaves the cyclone separators 44, 46 in turn and leaves the regenerator vessel 14 through the flue gas outlet 47 in the flue gas line 48. The regenerated catalyst is carried back to the standpipe 20 through the regenerated catalyst standpipe 18. Due to the combustion of the coke, the flue gas vapor leaving the top of the catalyst regenerator 14 contains CO, CO2, N2 and H2O as well as small amounts of other substances.

[0042] The product recovery section 8 is in downstream communication with the product outlet 31. In the product recovery section 8, the first cracked product stream in the pipeline 32 is directed to the lower section of the FCC main fractionation tower 92. The main tower 92 is in downstream communication with the first product outlet 31. Several fractions of the FCC product can be separated and taken out from the main tower, including heavy slurry oil from the bottom in the pipeline 93, heavy cycle oil stream in the pipeline 94, light cycle oil in the pipeline 95 taken out from the outlet 95a, and heavy naphtha stream in the pipeline 96 taken out from the outlet 96a. Any one or all of the pipelines from the pipeline 93 to the pipeline 96 can be cooled and pumped back to the main tower 92 to cool the main tower usually at a higher position. Gasoline and gaseous light hydrocarbons are removed from the main tower 92 in the main tower top pipeline 97 and condensed before entering the main tower receiver 99. The main tower receiver 99 is in downstream communication with the product outlet 31, and the main tower 92 is in upstream communication with the main tower receiver 99. From main overhead line 97 a second hydrocarbon stream and possibly a third hydrocarbon stream are withdrawn.

[0043] The aqueous stream is removed from a storage tank in the main column receiver 99. In addition, a condensed light naphtha stream is removed in line 101, while an overhead stream is removed in line 102. The overhead stream in line 102 contains gaseous light hydrocarbons with a high olefin content. The streams in lines 101 and 102 may enter the vapor recovery section 120 of the product recovery section 8.

[0044] The steam recovery section 120 shown is an absorption-based system, but any steam recovery system can be used, including a cold box system. In order to fully separate the light gas components, the gaseous stream in line 102 is compressed in compressor 104. More than one compressor stage can be used, but two-stage compression is usually used. The compressed light hydrocarbon stream in line 106 is combined with the streams in lines 107, 108 and 422, cooled and delivered to a high-pressure receiver 110. The water-containing stream from receiver 110 can be sent to the main tower receiver 99. The gaseous hydrocarbon stream in line 112 is directed to a primary absorber 114, where it contacts the unstabilized gasoline from the main tower receiver 99 in line 101 to achieve separation between C3+ hydrocarbons and C2- hydrocarbons. Primary absorber 114 is connected to the main tower receiver 99 downstream. The liquid C3+ hydrocarbon stream in line 107 is returned to line 106 before cooling. The primary tail gas stream in line 116 from the primary absorber 114 may be directed to a secondary absorber 118, wherein a recycle stream of light cycle oil in line 121 branched from line 95 absorbs most of the remaining C5+ hydrocarbons and some C3-C4 hydrocarbons in the primary tail gas stream. The secondary absorber 118 is in downstream communication with the primary absorber 114. The light cycle oil enriched in C3+ hydrocarbons from the bottom of the secondary absorber in line 119 is circulated back to the main tower 92 via a pump in line 95. The top of the secondary absorber 118 contains dry gas that is primarily C2- hydrocarbons as well as hydrogen sulfide, ammonia, carbon oxides, and hydrogen, which is removed in the secondary tail gas stream in line 122.

[0045] The liquid from the high pressure receiver 110 in line 124 is sent to a stripper 126. Most of the C2- hydrocarbons are removed in the top of the stripper 126 and returned to the line 106 via the top line 108. The liquid bottoms stream from the stripper 126 is sent to the first debutanizer 130 in the bottoms line 128. The first debutanizer 130 provides an overhead stream in line 132, which comprises a C3-C4 hydrocarbon stream from the first debutanizer. The bottoms stream in line 134 may comprise a first debutanized naphtha stream.

[0046] In a first embodiment, a first recycle light cracked naphtha stream may be taken from the first debutanized naphtha stream in line 134 in line 137 via a control valve thereon, while the remainder of the first debutanized naphtha stream in line 141 may be passed through a control valve thereon for further processing into gasoline or other products. In this embodiment, it is contemplated that a naphtha splitter 136 may be located upstream of the product recovery section 8.

[0047] In an alternative embodiment, the first debutanized naphtha stream in line 134 can be fed to a naphtha splitter 136 in line 142 via a control valve thereon. In this alternative embodiment, the naphtha splitter is located downstream of the product recovery section 8, as shown, and the control valves on lines 137 and 141 are closed. The naphtha splitter separates the debutanized naphtha stream into a first separated light naphtha stream comprising C5-C7 hydrocarbons in an overhead line 138 and a heavy naphtha stream in a bottoms line 140. An alternative first recycle light cracked naphtha stream can be taken in line 139 via a control valve thereon, and the remainder of the first separated light naphtha stream in the overhead line 138 can be further processed into gasoline or other products.

[0048] The C3-C4 hydrocarbon stream obtained in the pipeline 132 can be separated into a C3 hydrocarbon stream in the tower top pipeline 146 and a C4 hydrocarbon stream in the tower bottom pipeline 148 in the C3-C4 separation tower 144. A first recycled C4 hydrocarbon stream can be obtained in the pipeline 149 through a control valve thereon, and the remaining C4 hydrocarbon stream in the pipeline 147 can be further processed into other products. The C3 hydrocarbon stream in the tower top pipeline 146 can be further processed for propylene recovery.

[0049] One or both of the first recycled light cracked naphtha stream comprising olefinic C5-C7 hydrocarbons taken from the first debutanizer naphtha stream in line 134 of the first debutanizer 130 connected downstream to the main tower 92 in line 137 or the alternative first recycled light cracked naphtha stream comprising olefinic C5-C7 hydrocarbons taken from the tower top line 138 of the naphtha splitter 136 connected downstream to the main tower 92 in line 139 and the first recycled C4 stream comprising olefinic C4 hydrocarbons taken from the tower bottom line 148 of the C3-C4 splitter also connected downstream to the main tower 92 in line 149 may be circulated to the second FCC reactor 202 as the second hydrocarbon stream in the second loading line 150. The second hydrocarbon stream may be preheated to a temperature of 221° C. (400° F.) to 704° C. (1300° F.) and charged to the second FCC reactor 202.

[0050] The accompanying drawings show a second FCC reactor 200, which includes a second reactor unit 202 and a catalyst heater 238. The second reactor unit 202 includes a second riser 212 in which a second hydrocarbon stream in line 150 charged through a distributor 213 or closer to the base of the second riser 212 contacts a second fluid catalyst stream in the second riser 212. The second hydrocarbon stream may contain at least 20 wt% olefins, suitably at least 60 wt% olefins, and preferably at least 70 wt% olefins. The second hydrocarbon stream may contain at least 1 wt% paraffins, suitably at least 15 wt% paraffins, and preferably at least 25 wt% paraffins. The second hydrocarbon stream may contain primary cracked C4 to C7 hydrocarbons.

[0051] The second riser 212 extends upward through the second reactor vessel 210 in the second FCC reactor 202. The second fluid catalyst stream can be fluidized with steam distributed from the distributor 218 at the bottom of the second riser 212. The second hydrocarbon stream contacts the second fluid catalyst stream in the second riser 212. The second fluid catalyst stream can be provided by a mixture of the first hot catalyst stream from the first hot catalyst tube 220 and the first recycle catalyst stream from the first recycle catalyst tube 222. The second hydrocarbon stream evaporates and converts or cracks into a second cracked product stream, which contains ethylene and propylene at a higher concentration than in the second hydrocarbon stream. Molar expansion causes the second hydrocarbon stream and the second cracked product stream to rise rapidly to the second riser 212, entraining the second fluid catalyst stream as a second mixture of catalyst and product gas.

[0052] The second fluid catalyst stream may comprise less than 20 wt%, preferably less than 5 wt%, of the first component and at least 20 wt% of the second component. In a preferred embodiment, the second fluid catalyst stream may comprise at least 20 wt% of ZSM-5 zeolite and less than 20 wt%, preferably less than 5 wt%, of Y-zeolite. In another preferred embodiment, the second fluid catalyst stream may comprise primarily the second component, and in another embodiment, may comprise only the second component, preferably ZSM-5 zeolite, as a catalyst.

[0053] In one aspect, the second fluid catalyst stream may contain 0.005 wt % to 1.2 wt % coke. The presence of such a concentration of coke can passivate the acid sites, thereby helping to prevent the generation of dry gas. Dry gas can be defined as H2, H2S, carbon oxides, and C1-C2 hydrocarbons. Dry gas represents a loss of valuable product yield and increases operating and equipment costs due to handling a larger gas flow rate. The presence of coke in the riser in an amount of 0.005 wt % to 1.2 wt % is sufficient to passivate the acid sites, which in turn limits the generation of dry gas.

[0054] The coke concentration in the second riser is increased by recycling the unregenerated catalyst to the riser and promoting the generation of coke in the riser. If the FCC reaction generates coke on the catalyst, recycling the first catalyst stream in the first recycle catalyst tube 222 to the second riser 212 will increase the coke in the riser because it bypasses regeneration. Increasing the recycle rate of the first recycle catalyst relative to the recycle rate of the first hot catalyst stream from the first hot catalyst tube 220 will increase the coke concentration in the second riser. Some types of catalysts, such as ZSM5, generate very little coke in the FCC reactor. If the coke generation in the second riser is insufficient, other methods can be used to increase the coke concentration in the second riser, which will be described below.

[0055] The process conditions in the second riser 212 will be more severe than in the first riser 20 because the second hydrocarbon stream is less susceptible to cracking than the first hydrocarbon stream because the former has been cracked in the first riser 20. The second riser 212 may be operated at one or more of the following conditions relative to the first riser 20: a higher outlet temperature, a lower hydrocarbon partial pressure, or a different catalyst density. The hydrocarbon partial pressure is reduced by reducing the total pressure in the second riser 212 independently of the pressure in the first FCC reactor 10 and possibly adjusting the steam rate to the second riser 212.

[0056] The conditions in the second riser 212 may include a cracking reaction temperature of 400° C. to 650° C., preferably 565° C. to 635° C. at the reactor outlet. Cracking is carried out at an absolute pressure between 100 kPa (14 psia) and 506 kPa (74 psia), preferably between 138 kPa (20 psia) and 310 kPa (45 psia). The steam flow rate added to the second riser 20 is 5% to 25% by weight of the second hydrocarbon stream. However, the steam flow rate in the second riser 212 may be as low as 2% to 25% by weight, or may be eliminated. Control valves on the first hot catalyst tube 220 and the first recycle catalyst tube 222 can be used to adjust the catalyst density in the second riser 212, thereby enabling control of the space velocity therein. In addition, increasing the flow rate of the first recycled catalyst flowing in the first recycled catalyst tube 222 to the second riser 212 can increase the catalyst density in the second riser without affecting the heat input to the second riser, which is supplied by the first hot catalyst flow in the first hot catalyst tube 220 fed to the second riser 212.

[0057] The second riser 212 terminates at a curved conduit 214 or a plurality of curved conduits at the upper end of the second disengaging chamber 211 located in the second reactor vessel 210. The curved conduit 214 can centrifugally discharge the second mixture of product gas and catalyst into the second disengaging chamber 211. By centrifugal discharge, the first mixture is discharged from the inside to the outside. The centrifugal discharge of gas and catalyst generates a spiral vortex inside the second disengaging chamber 211, thereby disengaging the second mixture of catalyst and product gas into a second cracked product stream and a first cold catalyst stream in the second disengaging chamber 211.

[0058] The first cold catalyst stream is collected in a dense catalyst bed 228. The second product gas stream passes upward through a second gas recovery conduit 226, is further separated from the catalyst in a cyclone separator 232, and is discharged from the second reactor vessel 210 through an outlet 230 in a product line 231.

[0059] The accompanying drawings show a third FCC reactor unit 302, in which a third hydrocarbon stream in a line 315 distributed by a distributor 313 or closer to the base of a third riser 312 contacts a third fluid catalyst stream in the third riser. In one embodiment, the third FCC reactor unit 302 is integrated with the second FCC reactor unit 202 in the second FCC reactor 200. However, the third FCC reactor unit 302 may be independent of the second FCC reactor unit 202, in its own FCC reactor. The third hydrocarbon stream may contain at least 20 wt% olefins, typically at least 30 wt% olefins, suitably at least 50 wt% olefins, and preferably at least 60 wt% olefins. The third hydrocarbon stream may contain at least 25 wt% paraffins, and preferably at least 35 wt% paraffins. The second hydrocarbon stream is generally more olefin-containing and / or more crackable than the third hydrocarbon stream. The third hydrocarbon stream may contain a twice-cracked light cracked naphtha stream and / or a twice-cracked C4 hydrocarbon stream and / or a once-cracked C4 hydrocarbon stream. The third hydrocarbon stream may be preheated to a temperature of 221° C. (400° F.) to 704° C. (1300° F.) and charged to the third FCC reactor 302 .

[0060] The third catalyst stream can be fluidized with steam distributed from the distributor 358 at the bottom of the third riser 312. The third catalyst stream may have the same catalyst composition as the second catalyst stream. The catalyst composition of the first catalyst stream is different from the catalyst composition of the second catalyst stream and the third catalyst stream. The third hydrocarbon stream contacts the third fluid catalyst stream in the third riser 312. The third fluid catalyst stream can be provided by a mixture of a second hot catalyst stream from the second hot catalyst tube 362 and a second recycled catalyst stream from the second recirculating catalyst tube 264. The third hydrocarbon feedstock is converted or cracked into a third cracked product stream, which contains hydrocarbons with a molecular weight less than the third hydrocarbon stream. Molar expansion causes the third hydrocarbon stream and the third cracked product stream to rise rapidly to the third year riser 312, entraining the third fluid catalyst stream as a third mixture of catalyst and product gas.

[0061] The process conditions in the third riser 312 may be more severe than the process conditions in the second riser 212 and the first riser 20. The third riser 312 may be operated at one or more of the following conditions relative to the second riser 212: a higher outlet temperature, a lower hydrocarbon partial pressure, and a different catalyst density than the second riser. The hydrocarbon partial pressure may be reduced by reducing the total pressure in the third riser 312 independently of the pressure in the first FCC reactor 10 and possibly adjusting the steam flow to the third riser 312.

[0062] The conditions in the third riser 312 may include a cracking reaction temperature of 400°C to 705°C, preferably 565°C to 675°C at the reactor outlet. Cracking is carried out at an absolute pressure between 100kPa (14psia) and 506kPa (74psia), preferably between 138kPa (20psia) and 310kPa (45psia). The steam added to the third riser 312 is 25% to 50% by weight of the third hydrocarbon flow. However, the steam flow in the third riser 312 can be as low as 2% to 50% by weight, and it can be eliminated. The control valves on the second hot catalyst tube 362 and the second recycle catalyst tube 264 can be used to adjust the catalyst density in the third riser 312, thereby enabling control of the space velocity therein. In addition, increasing the flow rate of the spent second recycle catalyst stream flowing to the third riser 312 in the second recycle catalyst tube 264 can increase the catalyst density in the third riser 312 without affecting the heat input to the third riser.

[0063] The coke concentration in the third riser 312 is increased by recycling unregenerated catalyst to the riser and promoting the generation of coke in the riser. If the FCC reaction generates coke on the catalyst, recycling the second recycle catalyst stream in the second circulating catalyst tube 264 to the third riser 312 will increase the coke in the riser because it bypasses regeneration. Increasing the recycle rate of the second recycle catalyst stream relative to the recycle rate of the second hot catalyst stream from the second hot catalyst tube 362 will increase the coke concentration in the third riser 312. Some types of catalysts, such as ZSM5, generate very little coke in the FCC reactor. If the coke generation in the third riser 312 is insufficient, other methods can be used to increase the coke concentration in the third riser, which will be described below.

[0064] The third riser 312 of the third FCC reactor 302 can be located outside the second reactor vessel 210, but share the second reactor vessel with the second riser 212 and the second FCC reactor 202. The third riser 312 includes a discharge opening 349 in a third disengagement chamber 360. The third disengagement chamber 360 includes the discharge opening 349 of the third riser 312. The third disengagement chamber 360 can be in the second reactor vessel 210. In one embodiment, the horizontal transfer line 348 of the third riser 312 terminates in the third disengagement chamber 360. The discharge opening 349 of the third riser 302 discharges the third mixture of catalyst and product gas tangentially into the third disengagement chamber 360. In other embodiments, the horizontal transfer line 348 can be replaced with an alternative connector, such as a T-connector or an elbow with a sharper or more obtuse angle. The tangential discharge of the third mixture of catalyst and product gas from the third riser 312 through the discharge opening 349 can generate a spiral vortex inside the third disengagement chamber 360. The separation of the third mixture of catalyst and product gas into a second cold catalyst stream and a third cracked product stream can be performed concentrically outwardly with the separation of the second mixture of catalyst and product gas into a second cracked product stream and the first cold catalyst stream. Importantly, the second mixture of catalyst and product gas is not mixed with the third mixture of catalyst and product gas until a majority of the catalyst is removed from the product gas to maximize selectivity to propylene.

[0065] In one embodiment, the second cold catalyst stream is collected with the first cold catalyst stream in the dense catalyst bed 228. In other embodiments, the third cracked product stream is passed upwardly with the second cracked product stream through the second gas recovery conduit 226, is further separated from the catalyst in the cyclone separator 232, and is discharged from the second reactor vessel 210 through the outlet 230 in the product pipeline 231 as the second product stream.

[0066] The mixed stream of disengaged cold catalyst from the dense catalyst bed 228 passes downwardly through the stripping section 284. A stripping fluid, typically steam, enters the lower portion of the stripping section 284 through a distributor 234. As the catalyst continues downwardly through the stripping section 284, it is countercurrently contacted by the stripping fluid through a series of stripping baffles, packings, or grids, displacing product gas from the catalyst.

[0067] The first stripping catalyst stream from stripping section 284 arrives at catalyst heater 238 through heater conduit 236. In one embodiment, catalyst heater 238 heats the catalyst by heat exchange with the regenerated catalyst from the regenerator. In a second embodiment, catalyst heater 238 contacts the first stripping catalyst stream with the oxygen supply gas from pipeline 219 to burn the coke from the catalyst. Flue gas is discharged in pipeline 242. The second embodiment is applicable to the case where the catalyst generates a large amount of coke in the FCC reaction. Catalyst heater 238 provides a first hot catalyst stream fed to the second riser 212 in the first hot catalyst tube 220, and provides a second hot catalyst stream fed to the third riser 312 in the second hot catalyst tube 362.

[0068] The second stream of stripped catalyst from the dense bed 228 is passed in the recycle conduit 240 to provide the first recycle catalyst stream in the first recycle catalyst tube 222 to the second riser 212 and the second recycle catalyst stream in the second recycle catalyst tube 264 to the third riser 312. In the first embodiment of the catalyst heater 238, the catalyst in the second FCC reactor 202 and the third FCC reactor 302 may not coke as much as in the first FCC reactor 12. Therefore, in the second FCC reactor 202 and the third FCC reactor 302, the coke burned is insufficient to balance the heat demand in the reactor. In order to supplement heat to the second FCC reactor 202 and the third FCC reactor 302, a portion of the hot regenerated catalyst can be delivered to the catalyst heater 238 in the regenerator heater riser 42. In the catalyst heater, a portion of the second fluid catalyst stream can be heat exchanged with a portion of the hot regenerated catalyst before contacting the second fluid catalyst stream with the second hydrocarbon stream. In addition, a portion of the third fluid catalyst stream may be heat exchanged with a portion of the hot regenerated catalyst prior to contacting the third fluid catalyst stream with the third hydrocarbon stream. In the catalyst heater 238 of the first embodiment, the hot regenerated catalyst may be on one side of the indirect heat exchanger, while the second fluid catalyst stream and the third fluid catalyst stream may be on the other side of the indirect heat exchanger. Catalyst from the second FCC reactor 202 and the third FCC reactor 302 may be delivered to the catalyst heater 238 via the heater conduit 236. The cooled regenerated catalyst may be returned from the catalyst heater 238 to the regenerator 14 in the cooled regenerated catalyst conduit 48.

[0069] It is contemplated that a heat exchange fluid may also be used in the first embodiment of the catalyst heater 238 to transfer heat from the regenerated catalyst to the second and third catalyst streams, rather than by direct heat exchange between the catalyst streams. In one embodiment, heat may be exchanged from the flue gas from the flue gas outlet 47 in a direct or indirect manner to heat the second and third catalyst streams. In another embodiment, the catalyst heater 238 may provide the required heat by fuel combustion. Before the second fluid catalyst stream contacts the second hydrocarbon stream, a portion of the second fluid catalyst stream is heated in the catalyst heater 238. Before the third fluid catalyst stream contacts the third hydrocarbon stream, a portion of the third fluid catalyst stream is heated in the catalyst heater 238. The flue gas flow generated from the catalyst heater 238 in the pipeline 242 may be appropriately directed to a flue gas treatment unit. In another embodiment, the fuel combustion in the catalyst heater 238 may be replaced by an electric coil powered by renewable electricity or fossil fuel-based electricity.

[0070] To generate more coke on the catalyst, the C4+ hydrocarbon stream can be fed to the catalyst heater 238 of the first embodiment through the first coking line 221, directly to the catalyst in the catalyst heater 238, or one or more of the following: to the first hot catalyst stream in the first hot catalyst tube 220 through the second coking line 223, to the second hot catalyst stream in the second hot catalyst tube 362 through the third coking line 225, to the recycle catalyst in the first recycle catalyst tube 222 through the fourth coking line 227, and to the recycle catalyst in the second recycle catalyst tube 264 through the fifth coking line 229. Injecting C4+ in the catalyst tubes will help optimize the coke level in the catalyst, which maximizes the propylene selectivity in the second and third risers. The C4+ hydrocarbon injection should be located downstream of the control valve in the catalyst tubes. The distribution of coke in the catalyst should be 0.005 wt % to 5 wt % coke on the catalyst, preferably 0.1 wt % to 2 wt % coke on the catalyst in the second riser 212, and 0.1 wt % to 1 wt % coke on the catalyst in the third riser 312. In one embodiment, the coke on the catalyst can be 0.005 wt % to 1.2 wt % coke on the catalyst in the second riser 212 and the third riser 312. If it is necessary to increase the heat of combustion to provide more heat input for the FCC reaction in the second reactor 202 and the third reactor 302, the hydrocarbon stream can also be fed to the catalyst heater 238 of the second embodiment in the first coking line 221.

[0071] Coked catalyst from stripping section 284 may be directly and periodically distributed to catalyst regenerator 14 in distribution conduit 250. The distributed catalyst may combine with the catalyst mixture in catalyst regenerator 14 and provide additional catalyst activity to the catalyst in FCC unit section 6.

[0072] The second product stream in line 231 from the second riser 212 and the third riser 312 can be sent to a wash column 392. In the wash column 392, the second product stream in line 231 is contacted with a wash stream. In one embodiment, the wash stream can be a fresh charge stream in line 394, which is contacted with the hot second product stream to achieve direct heat exchange. The direct heat exchange quenches the hot second product stream and absorbs catalyst fines from the second product stream. The quenched charge stream with catalyst fines is discharged from the bottom of the wash column 392 in line 15 and charged to the first FCC reactor 12 as the first hydrocarbon stream.

[0073] In another embodiment, the second product stream in line 231 can be used to preheat the second hydrocarbon stream 150 and / or the third hydrocarbon stream 315 by indirect heat exchange before being sent to the scrubber 392. In another embodiment, the second hydrocarbon stream 150 and / or the third hydrocarbon stream 315 can be preheated by the flue gas stream 48 from the flue gas outlet 47.

[0074] After several stages of cooling pump circulation, the quenched second product tower top stream is taken from the washing tower top pipeline 396 at the top of the washing tower 392 to further cool the second product stream in the pipeline 396 and send it to the product recovery section 90. The washing tower 392 is connected to the downstream of the second product outlet 231. In the product recovery section 90, the second product stream in the washing tower top pipeline 396 is guided to the washing tower receiver 399. The washing tower receiver 399 is connected to the downstream of the second product outlet 231.

[0075] The aqueous stream is removed from a storage tank in the scrubber receiver 399. In addition, a condensed light naphtha stream is removed in line 401, while an overhead gas stream is removed in a scrubber receiver overhead line 402. The overhead stream in line 402 contains gaseous light hydrocarbons that are high in olefins. The streams in lines 401 and 402 may enter the scrubber recovery section 420 of the product recovery section 90. In another embodiment, the scrubber 392 may be an integral part of the product recovery section 8 by utilizing a downstream depropanizer (not shown) therein and the first debutanizer 130 in the vapor recovery section 120.

[0076] The scrubber recovery section 420 shown is an absorption-based system, but any vapor recovery system can be used, including a cold box system. In order to fully separate the light gas components, the overhead stream in line 402 is compressed in compressor 404. More than one compressor stage can be used, but two-stage compression is typically used. The compressed light hydrocarbon stream in line 406 is delivered to a high pressure receiver 410. Aqueous streams can be taken from receivers 399 and 410. The high pressure liquid stream in line 412 from the bottom of receiver 410 is directed to a depropanizer 420 along with the light naphtha stream in line 401 from the bottom of the scrubber receiver 399 in line 414.

[0077] The depropanizer 420 separates the high pressure liquid stream in line 412 and the light naphtha stream in line 401 into a C3- hydrocarbon stream in line 422 and adds it to the compressed light hydrocarbon stream in line 106 for processing therein. The depropanizer bottoms stream in line 424 may be directed to a debutanizer flash tank 426. In the debutanizer flash tank 426, the depropanized bottoms stream is separated into a second C4 hydrocarbon stream in an overhead line 432 and a debutanizer naphtha stream in a bottoms line 434. The second C4 hydrocarbon stream may be recycled in line 432 to the second recycle stream in line 314 via a control valve thereon.

[0078] The debutanizer feed stream in line 434 is fed to a second debutanizer 440. The second debutanizer 440 separates the debutanizer feed stream into a C4 product stream in an overhead line 442 and a second light cracked naphtha stream in a bottom line 444. A second recycled light cracked naphtha stream may be taken in line 446 through a control valve thereon, while the remainder may be further processed into gasoline or other products. The second recycled light cracked naphtha stream in line 446 may be fed to the second recycle stream in the second recycle line 314.

[0079] One or both of the second recycled light cracked naphtha stream comprising olefinic C5-C7 hydrocarbons taken in line 446 from the second debutanizer 440 in downstream communication with the scrubber 392 and the second recycled C4 stream comprising olefinic C4 hydrocarbons taken in line 432 from the debutanizer flash tank 426 also in downstream communication with the scrubber 392 may be recycled to the third FCC reactor 302 as the third hydrocarbon stream in the third charging line 315. The third hydrocarbon stream may be preheated to a temperature of 204° C. (400° F.) to 704° C. (1300° F.) and charged to the third FCC reactor 302.

[0080] The second hydrocarbon stream and / or the third hydrocarbon stream may be supplemented with a C4 hydrocarbon stream, a C5 hydrocarbon stream or a light cracked naphtha stream from a refinery or a steam cracking unit.Such streams will typically contain greater than 20% by weight of olefins.

[0081] In another embodiment, part or all of the first C4 hydrocarbon stream in line 149 can be taken out in line 160 through a control valve thereon and fed to the second recycle line 314. The first C4 hydrocarbon stream fed to the second recycle line 314 can be taken out in the third feed line 315 as all or part of the third hydrocarbon stream as the third hydrocarbon stream.

[0082] The third FCC reactor 302 may be used to further crack the olefin feed to produce additional propylene by cracking the less susceptible feed in the third riser 312 at more severe conditions than in the second riser 212, and this uniquely facilitates propylene production of the third hydrocarbon stream.

[0083] Example

[0084] Example 1

[0085] The hydrocarbon feed was cracked in three separate risers having the compositions in the table. The C4 hydrocarbons from the effluent of the first riser were charged to the second riser, and thus the C4 hydrocarbons from the second riser were fed to the third riser. It was reported that only propylene was in the effluent of the third riser. The yields are provided in Table 1. The riser conditions were consistent with those taught in the specific embodiment.

[0086] Table 1

[0087] No. 1 lifting pipe No. 2 lifting pipe No. 3 lifting pipe Feed VGO, wt% 100.0％ --- --- C4 paraffins, weight % --- 21.9％ 39.8％ C4 olefins, weight % --- 78.1％ 60.2％ product Propylene, weight % 17.5％ 28.2％ 43.1％ Propane, weight % 1.6％ 2.0％ Not reported Butene, weight % 13.5％ 33.9％ Not reported Isobutane, weight % 2.8％ 15.7％ Not reported n-Butane, weight % 1.0％ 6.7％ Not reported Propylene, weight % of VGO 17.5％ 4.9％ 4.2％

[0088] By using three separate risers, more than 26 wt% propylene can be produced as a percentage of the feed.

[0089] Example 2

[0090] The hydrocarbon feed is cracked in two separate risers with the composition in the table. All C5-C7 hydrocarbons from the first riser effluent are fed to the second riser. In Example 1, the MFI type catalyst is fully regenerated in the second riser, so the catalyst contains less than 0.005 wt % coke. In Example 2, the coke contained in the catalyst in the second riser has a distribution of coke in the range of 0.005 wt % to 1.2 wt % on the MFI type catalyst. The total product yields of the first and second risers are provided in Table 2. The riser conditions are consistent with those taught in the specific embodiment.

[0091] Table 2

[0092]

[0093]

[0094] By recycling C5-C7 hydrocarbons from the first riser to the second riser, more light olefins such as ethylene, propylene and butenes are produced. On the ZSM-5 catalyst, 40% to 60% propylene selectivity is achieved. The partially coked catalyst increases the yield of propylene and butenes while reducing the production of dry gas and heavies.

[0095] Specific implementation plan

[0096] While the following is described in conjunction with specific embodiments, it should be understood that this description is intended to illustrate and not to limit the scope of the foregoing description and the appended claims.

[0097] The first embodiment of the present invention is a method for catalytically producing olefins, the method comprising contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream; separating the first cracked product stream in a main tower; separating the top stream from the main tower into a second hydrocarbon stream; contacting the second hydrocarbon stream with a second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream; and obtaining a third hydrocarbon stream from the top stream and / or from the second cracked product stream; and contacting the third hydrocarbon stream with a third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the second hydrocarbon stream contains more olefins and / or is more easily cracked than the third hydrocarbon stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the second hydrocarbon stream is a light cracked naphtha stream, and the embodiment further includes separating the top stream from the main tower into a first C4 hydrocarbon stream and obtaining the first C4 hydrocarbon stream as the third hydrocarbon stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, and further includes washing the second cracked product stream in a washing tower and obtaining the third hydrocarbon stream from the washing tower. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the second hydrocarbon stream is a first C4 hydrocarbon stream, and the third hydrocarbon stream is a second C4 hydrocarbon stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, and further includes compressing the top stream from the washing tower to provide a compressed top stream, and depropanizing the compressed top stream to provide a depropanized compressed top stream, and obtaining the third hydrocarbon stream from the depropanized compressed top stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, further comprising separating the depropanized compressed tower top stream into a second C4 stream and a second light cracked naphtha stream, and obtaining the third hydrocarbon stream from the second light cracked naphtha stream and / or from the second C4 stream. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the second fluid catalyst stream and the third fluid catalyst stream contain 0.005 wt. % to 1.2 wt. % coke. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the third riser is operated at a higher outlet temperature and / or a lower hydrocarbon partial pressure and / or a different catalyst density than the second riser.One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, further comprising regenerating a spent catalyst stream by burning coke from the spent catalyst to provide hot regenerated catalyst, and before contacting the second fluid catalyst stream with the second hydrocarbon stream, heat exchanging a portion of the second fluid catalyst stream with a portion of the hot regenerated catalyst. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, further comprising regenerating a spent catalyst stream by burning coke from the spent catalyst to provide hot regenerated catalyst, and before contacting the third fluid catalyst stream with the third hydrocarbon stream, heat exchanging a portion of the third fluid catalyst stream with a portion of the hot regenerated catalyst stream. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the third hydrocarbon stream has greater than 20 wt% olefins. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, further comprising recycling a C4+ stream to a catalyst tube that provides catalyst to the second riser and / or the third riser.

[0098] The second embodiment of the present invention is a method for catalytically producing olefins, the method comprising contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream; separating the first cracked product stream in a main tower; obtaining a second hydrocarbon stream from the main tower; contacting the second hydrocarbon stream with a second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream; and separating the second cracked product stream in a wash tower and obtaining a third hydrocarbon stream from the wash tower; and contacting the third hydrocarbon stream with a third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream. An embodiment of the present invention is one, any one or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, and further comprising compressing the top stream from the wash tower to provide a compressed top stream, and depropanizing the compressed top stream to provide a depropanized compressed top stream, and obtaining the third hydrocarbon stream from the depropanized compressed top stream. An embodiment of the invention is one, any or all of the second embodiment of this paragraph through prior embodiments of this paragraph wherein the third hydrocarbon stream has greater than 20 wt% olefins.

[0099] The third embodiment of the present invention is a method for catalytically producing olefins, the method comprising contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream; separating the first cracked product stream in a main tower; obtaining a second hydrocarbon stream from the top pipeline of the main tower system; contacting the second hydrocarbon stream with a second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream; and obtaining a third hydrocarbon stream from the first cracked product stream or the second cracked product stream; and contacting the third hydrocarbon stream with a third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream. One embodiment of the present invention is one, any or all of the third embodiments of this paragraph to the previous embodiments of this paragraph, wherein the second hydrocarbon stream contains more olefins and / or is more susceptible to cracking than the third hydrocarbon stream. One embodiment of the present invention is one, any or all of the third embodiments of this paragraph to the previous embodiments of this paragraph, wherein the third hydrocarbon stream has more than 20% by weight of olefins. An embodiment of the invention is one, any or all of the third embodiment of this paragraph through prior embodiments of this paragraph, further comprising operating the third riser at a higher severity than the second riser.

[0100] Although there is no further detailed description, it is believed that those skilled in the art can utilize the present invention to the greatest extent by using the foregoing description and can easily determine the essential characteristics of the present invention without departing from the spirit and scope of the present invention to make various changes and modifications of the present invention and adapt it to various usages and conditions. Therefore, the aforementioned preferred specific embodiments should be understood as merely illustrative and not to limit the rest of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0101] In the foregoing, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A method for catalytically producing olefins, the method comprising: contacting a first hydrocarbon stream and a first fluid catalyst stream in a first riser to produce a first cracked product stream and a spent catalyst stream; separating the first cracked product stream in a main column; separating an overhead stream from the main column into a second hydrocarbon stream; contacting the second hydrocarbon stream with a second fluid catalyst stream in a second riser to produce a second cracked product stream and a first cold catalyst stream; as well as obtaining a third hydrocarbon stream from the overhead stream and / or from the second cracked product stream; as well as The third hydrocarbon stream is contacted with a third fluid catalyst stream in a third riser to produce a third cracked product stream and a second cold catalyst stream.

2. The process according to claim 1, wherein the second hydrocarbon stream contains more olefins and / or is more susceptible to cracking than the third hydrocarbon stream.

3. The method of claim 1, wherein the second hydrocarbon stream is a light cracked naphtha stream, and the method further comprises separating the overhead stream from the main tower into a first C4 hydrocarbon stream and taking the first C4 hydrocarbon stream as the third hydrocarbon stream.

4. The method of claim 1, further comprising washing the second cracked product stream in a wash column and obtaining the third hydrocarbon stream from the wash column.

5. The process according to claim 4, wherein the second hydrocarbon stream is a first C4 hydrocarbon stream and the third hydrocarbon stream is a second C4 hydrocarbon stream.

6. The method of claim 1 , further comprising compressing an overhead stream from the scrubber to provide a compressed overhead stream, depropanizing the compressed overhead stream to provide a depropanized compressed overhead stream, and obtaining the third hydrocarbon stream from the depropanized compressed overhead stream.

7. The method according to claim 6, further comprising separating the depropanized compressed tower overhead stream into a second C4 stream and a second light cracked naphtha stream, and obtaining the third hydrocarbon stream from the second light cracked naphtha stream and / or from the second C4 stream.

8. The method of claim 1, wherein the second fluid catalyst stream and the third fluid catalyst stream have the same catalyst composition.

9. The process of claim 1, wherein the third riser operates at a higher outlet temperature and / or a lower hydrocarbon partial pressure and / or a different catalyst density than the second riser.

10. The method of claim 1 further comprises regenerating the spent catalyst stream by burning coke from the spent catalyst to provide hot regenerated catalyst, and heat exchanging a portion of the second fluid catalyst stream with a portion of the hot regenerated catalyst before contacting the second fluid catalyst stream with the second hydrocarbon stream.

Images