Method and apparatus for stripping NOx, oxygen, CO and CO2 from FCC regenerated catalyst to improve safety and reliability of product recovery section

Abstract

The present invention provides a process for cracking hydrocarbons comprising contacting a hydrocarbon feedstock with a conditioned cracking catalyst in a riser reactor to recover an effluent. The effluent is separated to recover a cracked hydrocarbon stream and spent catalyst. The spent catalyst is contacted with steam, residual hydrocarbons are stripped from the spent catalyst, and the stripped catalyst is fed to a catalyst regenerator and regenerated via combustion of coke contained in the spent catalyst to form a regenerated catalyst and combustion products. The regenerated catalyst comprising entrained combustion products (e.g., NOx, SOx, and COx) including nitrogen from the regenerator is fed to a catalyst riser hopper. The regenerated catalyst comprising entrained combustion products is conditioned in the catalyst riser hopper by contacting the regenerated catalyst with steam to recover conditioned catalyst and a steam stream comprising steam and the combustion products. The conditioned catalyst depleting combustion products is then fed to the riser reactor.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to methods and systems for reducing flue gas components, such as nitrogen oxides, sulfur oxides, oxygen, carbon monoxide, and carbon dioxide, including nitrogen, from FCC regenerated catalyst flowing from a catalyst regenerator to a riser reactor. BACKGROUND

[0002] In recent years, the changing dynamics of the market have prompted refineries to explore new opportunities from the petrochemical production of crude oil, shifting their focus away from fuel production as fuel demand wanes. Among the key base feedstocks for the petrochemical industry, ethylene and propylene have significant importance. Due to the waning demand for fuels and the increasing demand for petrochemicals, refineries are forced to seek options to maximize petrochemicals from processing various crudes. Ethylene and propylene are expected to be in high demand as they are the main feedstocks for the petrochemical / polymer industry.

[0003] It has been proposed to directly process crude oil or select boiling range fractions therefrom, such as in a fluid catalytic cracking unit, without significant upstream processing. Unfortunately, limiting upstream processing can result in higher concentrations of various impurities, such as sulfur and nitrogen, which are introduced into the fluid catalytic cracking unit and associated downstream equipment. SUMMARY

[0004] In one aspect, embodiments disclosed herein relate to methods and apparatus for reducing flue gas components, such as sulfur oxides, carbon oxides, nitrogen oxides, and oxygen, within a fluid catalytic cracking (FCC) unit. The reduction of these flue gas components provides for safe and reliable operation of the downstream product recovery section. Specifically, NOx causes gum formation, which can be a safety hazard to the cold box section. This is achieved by adding internal members in the conventional regenerated catalyst standpipe hopper (RCSP hopper), which will enable effective stripping of these harmful components of the flue gas to the FCC reactor and product recovery section. The preferred stripping medium can be steam or other industrial inert gases, such as nitrogen, as compared to conventional puffed media (plant air or blower air).

[0005] In another aspect, embodiments disclosed herein relate to the reduction of the size of the oxygen converter and catalyst due to the reduction of flue gas components. This will also reduce the loss of ethylene product across the oxygen converter.

[0006] In another aspect, embodiments disclosed herein relate to the reduction of other flue gas components, such as sulfur oxides, carbon monoxide, carbon dioxide, etc.; which are the combustion products of feed impurities, falling into the FCC regenerator in the same claimed solution. This will help to reduce the size of the downstream product recovery section, and will also reduce utility consumption.

[0007] Accordingly, embodiments herein relate to a method for cracking hydrocarbons. The method includes contacting a hydrocarbon feed with a conditioned cracking catalyst in a riser reactor to recover a riser effluent comprising spent catalyst and cracked hydrocarbons. The riser effluent is separated to recover a cracked hydrocarbon stream and spent catalyst. The spent catalyst is then contacted with steam in a stripping column to strip residual hydrocarbons from the spent catalyst, and the spent catalyst is fed from the stripping column to a catalyst regenerator, where the spent catalyst is regenerated via combustion of coke contained in the spent catalyst to form regenerated catalyst and combustion products. The regenerated catalyst containing entrained combustion products from the catalyst regenerator is then fed to a catalyst standpipe hopper. The entrained combustion products include, for example, nitrogen oxides, sulfur oxides, and carbon oxides. In the catalyst standpipe hopper, the regenerated catalyst containing entrained combustion products is conditioned by contacting the regenerated catalyst containing entrained combustion products with steam to recover conditioned catalyst and a steam stream containing steam and combustion products. The conditioned catalyst is then fed to the riser reactor. The steam stream is fed to the catalyst regenerator, and the method further recovers the combustion products and the steam stream as flue gas from the catalyst regenerator.

[0008] In some embodiments, the catalyst standpipe hopper includes internal components configured to facilitate countercurrent contact of the regenerated catalyst containing entrained combustion products with steam.

[0009] In various embodiments, the stripping column includes internal components configured to facilitate countercurrent contact of the spent catalyst with steam.

[0010] The method of embodiments herein can further include catalyst fluffing. Accordingly, the feeding of the conditioned catalyst to the riser reactor can include feeding the catalyst from the regenerated catalyst standpipe hopper to the riser reactor via a regenerated catalyst standpipe, and the method further includes fluffing the catalyst within the regenerated catalyst standpipe with air. In other embodiments, the method further includes fluffing the catalyst within the spent catalyst standpipe with steam.

[0011] Embodiments herein also relate to a system for cracking hydrocarbons. The system includes a riser reactor for contacting a hydrocarbon feedstock with a conditioned cracking catalyst to recover a riser effluent comprising spent catalyst and cracked hydrocarbons. The system further includes a separation system for separating the riser effluent to recover a cracked hydrocarbon stream and spent catalyst, and a stripping column for contacting the spent catalyst with steam to strip residual hydrocarbons from the spent catalyst to produce a stripped catalyst. Additionally, the system includes a catalyst regenerator for regenerating the stripped catalyst via combustion of coke contained in the stripped catalyst to form a regenerated catalyst and a combustion product. A flow line is provided for feeding the regenerated catalyst comprising entrained combustion product from the catalyst regenerator to a catalyst standpipe hopper. A conditioning system within the catalyst standpipe hopper is provided for contacting the regenerated catalyst comprising entrained combustion product with steam to recover a conditioned catalyst and a steam stream comprising steam and combustion product. Additionally, a conditioned catalyst standpipe is provided for feeding the conditioned catalyst to the riser reactor, the system further including a flow line for feeding the steam stream to the catalyst regenerator, and a flow line for collectively recovering the combustion product and the steam stream as a flue gas from the catalyst regenerator.

[0012] Other aspects and advantages will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0013] The figure illustrates a block flow diagram of a fluid catalytic cracking (FCC) unit incorporating the claimed process scheme and arrangement in accordance with one or more embodiments disclosed herein. DETAILED DESCRIPTION

[0014] Embodiments herein relate to a processing scheme to reduce flue gas components (such as nitrogen oxides, sulfur oxides, oxygen, carbon monoxide, and carbon dioxide, including nitrogen) in an FCC system. More specifically, embodiments herein relate to a processing scheme to reduce flue gas components (such as nitrogen oxides, sulfur oxides, oxygen, carbon monoxide, and carbon dioxide, including nitrogen) present in FCC regenerated catalyst flowing from a regenerator to a riser reactor.

[0015] Reduction of these undesirable flue gas components is desirable for resulting enhanced performance, increased safety, and reliable operation of downstream product recovery sections. Specifically, NOx causes gum formation, which can be a safety hazard in the cold box section of an olefin recovery unit. According to embodiments herein, the addition of internal members in the regenerated catalyst standpipe hopper (RCSP hopper) enables efficient stripping of these harmful impurities and limits their introduction into the FCC reactor and product recovery section. The stripping medium can be steam or other industrial inert gas such as nitrogen.

[0016] The purpose is to strip the flue gas components entrained with catalyst from the regenerator to the RCSP hopper. The sparging / stripping steam is used in a counter-current mode with the catalyst, where the contacting can be with or without internal components such as MODGRID internals. MODGRID internals, available from Lummus Technology LLC, can improve the efficiency of the sparging / stripping. While the unique arrangement of the MODGRID trays increases the cross-sectional area for the sparging / stripping operation, other internals can also be used. The steam displaces the flue gas components, thereby reducing the flue gas components.

[0017] Referring now to the drawings, a simplified process flow diagram for a system for cracking hydrocarbons and producing light olefins according to embodiments disclosed herein is illustrated. For example, the system includes a riser reactor 3 for cracking various hydrocarbon feeds, including heavy hydrocarbon feeds processed directly.

[0018] The hydrocarbon feedstock is injected through one or more feed injectors 2 located near the bottom of the riser reactor 3. The hydrocarbon feedstock contacts the hot regenerated catalyst introduced through the J-bend 1. The catalyst fed to the first reactor 3 can be a single type of catalyst or a mixture of catalysts. For example, a mixture of catalysts that can be used can include a first catalyst selective for cracking heavier hydrocarbons, such as a Y-type zeolite-based catalyst, and a second catalyst selective for cracking C4 and naphtha range hydrocarbons to produce light olefins, such as ZSM-5 or ZSM-11. Other various catalysts for cracking hydrocarbons can also be used, either alone or in mixtures.

[0019] In addition to the lift steam, a feed stream such as C4 olefins and naphtha or similar external stream can also be injected through the gas distributors la located at the Y-section into the J-bend 1 as a lift medium for enabling the smooth transfer of the regenerated catalyst from the J-bend 1 to the riser reactor 3. The J-bend 1 can also act as a dense bed reactor for cracking the C4 olefins and naphtha stream into light olefins under conditions favorable for such reactions, such as 0.5 to 50 h -1 -1 of WHSV, a temperature of 640 °C to 750 °C, and a residence time of 2 to 10 seconds.

[0020] The vaporization of the feed and / or the heating of the feed to the desired reactor temperature, such as in the range of 500 °C to about 700 °C, and the heat required for the endothermic (heat of reaction) can be provided by the hot regenerated catalyst from the regenerator 17. The pressure in the riser reactor 3 is typically in the range of about 1 bar gauge to about 5 bar gauge.

[0021] After the main portion of the cracking reaction is complete, the mixture of product, unconverted feed vapor, and spent catalyst flows into a two-stage cyclone system housed in cyclone containment vessel 8. The two-stage cyclone system includes a primary cyclone 4 for separating spent catalyst from vapor. Spent catalyst is discharged through a primary cyclone immersion leg 5 into a stripper 9. Fine catalyst particles entrained with the separated vapor from primary cyclone 4 are separated in a secondary cyclone 6. The collected spent catalyst is discharged through an immersion leg 7 into the stripper 9. Vapor from secondary cyclone 6 is discharged through a secondary cyclone outlet 12b that can be connected to a plenum 11 and then sent to a main fractionator / gas processing plant (not shown) for recovery of products including desired olefins. If desired, the product vapor is further cooled by the introduction of steam or another suitable fluid as a quench medium through a distributor line 12a.

[0022] Spent catalyst recovered via immersion legs 5, 7 is stripped in a stripper bed 9 to remove interstitial vapor (hydrocarbon vapor trapped between catalyst particles) by countercurrent contact with steam introduced through a steam distributor 10 to the bottom of the stripper 9. Embodiments herein further provide for the use of internal members 30, such as MODGRID internals available from Lummus Technology LLC, to enhance the contact of steam 10 and spent catalyst within the stripper 9. Spent catalyst is then transferred to a regenerator 17 via a spent catalyst standpipe 13a and a lift line 15. A spent catalyst slide valve 13b located on the spent catalyst standpipe 13a is used to control the flow of catalyst from the stripper 9 to the regenerator 17. A small portion of combustion air or nitrogen can be introduced through a distributor 14 to aid in the smooth transfer of spent catalyst. Additionally, to maintain the flowability of the stripped catalyst and avoid bridging within the spent catalyst standpipe 13a, steam 32 can be introduced upstream of the slide valve 13b to "fluff" the catalyst.

[0023] Coked or spent catalyst is discharged through a spent catalyst distributor 16 in the center of the dense regenerator bed 24. Combustion air is introduced by an air distributor 18 located at the bottom of the regenerator bed 24. The coke deposited on the catalyst is then burned off in the regenerator 17 via reaction with the combustion air. For example, the regenerator 17 can operate at a temperature in the range of about 640 °C to about 750 °C and at a pressure in the range of about 1 bar gauge to about 5 bar gauge. Catalyst fines entrained with the flue gas are collected in a first stage cyclone 19 and a second stage cyclone 21 and discharged through respective immersion legs 20, 22 into the regenerator catalyst bed. Flue gas recovered from the outlet of the second stage cyclone 21 is directed to a flue gas line 50 via a regenerator plenum 23 for downstream waste heat recovery and / or energy recovery.

[0024] Regenerated catalyst is fed to the riser reactor 3 via a regenerated catalyst standpipe 27, which is in flow communication with the J-bend 1. Catalyst flow from the regenerator 17 to the riser reactor 3 can be regulated by a slide valve 28 located on the regenerated catalyst standpipe 27. The opening of the slide valve 28 is adjusted to control the catalyst flow to maintain the desired overhead temperature in the riser reactor 3. To maintain the flowability of the regenerated catalyst and avoid bridging within the regenerated catalyst standpipe 27, a small stream of air 31 can be introduced upstream of the slide valve 28 to "fluff" the catalyst.

[0025] Regenerated catalyst is discharged from the regenerator 17 to a regenerated catalyst (RCSP) hopper 26 via a discharge line 25, which is in flow communication with the regenerator 17 and the regenerated catalyst standpipe 27. The catalyst bed in the RCSP hopper 26 floats with the regenerator 17 bed level. The regenerated catalyst is then transferred from the RCSP hopper 26 to the reactor 3 via the regenerated catalyst standpipe 27, which is in flow communication with the J-bend 1. Catalyst flow from the regenerator 17 to the riser reactor 3 can be regulated by a RCSP slide valve 28 located on the regenerated catalyst standpipe 27. A pressure equalization line 29 can also be provided.

[0026] Combustion of coke and other deposits on the spent catalyst within the regenerator can produce a variety of oxygen-containing combustion products, such as nitrogen oxides, sulfur oxides, carbon monoxide, and carbon dioxide. Unconsumed oxygen in the combustion air can also be present in the combustion products. These combustion products are entrained with the catalyst via the discharge line 25 and, therefore, are contained with and within the catalyst in the regenerated catalyst standpipe hopper.

[0027] In embodiments herein, the regenerated catalyst is conditioned to remove combustion products from the regenerated catalyst within the regenerated catalyst standpipe hopper to minimize the introduction of oxygen, nitrogen oxides, sulfur oxides, nitrogen, carbon monoxide, and carbon dioxide into the riser reactor 3, the spent catalyst disengager 8, and the associated downstream separation systems that receive reaction product vapors via outlet 12b. The regenerated catalyst flowing via the discharge line 25 is conditioned in the RCSP hopper 26 to remove combustion product vapors that are entrained with the regenerated catalyst particles. Conditioning is performed by counter-current contact with steam 36 or a mixture of steam and air, which is introduced to the bottom of the RCSP hopper 26 by a steam distributor. Embodiments herein further provide for the use of internal members 34, such as MODGRID internal members available from Lummus Technology LLC, to enhance the contact of the steam 36 and the regenerated catalyst within the RCSP hopper 26. The regenerated catalyst is then transferred to the riser reactor 3 via the regenerated catalyst standpipe 27 and the J-bend 1.

[0028] As described above with reference to the figures, a fresh hydrocarbon feed is heated and injected into a riser reactor. The hydrocarbon feed contacts hot regenerated catalyst and cracks into lighter molecules. The cracked feed hydrocarbon vapors and catalyst exit the riser reactor and enter a set of cyclones where the catalyst and hydrocarbon vapors are separated. The recovered hydrocarbon vapors are transported to a main fractionator for product separation. The catalyst that flows from the bottom of the cyclones enters a stripper where absorbed hydrocarbon vapors are stripped from the catalyst. The stripped catalyst is transported to a regenerator. Combustion air is used to burn off the coke (deposits) on the spent catalyst. Flue gas and catalyst enter cyclones in the regenerator. Most of the flue gas is separated from the catalyst in the regenerator cyclones. The flue gas can be fed to a flue gas system to recover heat, clean up, and release to the atmosphere.

[0029] The regenerated catalyst is then transported to a regenerated catalyst standpipe (RSCP) hopper. Due to the small amount of flue gas entrained with the catalyst, the carryover gas from the RSCP hopper is essentially flue gas with combustion products including nitrogen oxides (NOx), excess oxygen (O2), including nitrogen and other flue gas components. The NOx, O2, etc. can cause unsafe operation in cold conditions. Therefore, to have safe and reliable operation, it is desirable to reduce / minimize the concentration of NOx, oxygen, etc.

[0030] Embodiments herein include a steam feed line to provide steam to the RSCP hopper to condition the regenerated catalyst and minimize the amount of nitrogen oxides and other combustion products that flow with the regenerated catalyst to the riser reactor and downstream systems. Internal members can be used in the RSCP hopper to enhance the contact of the conditioning steam and the regenerated catalyst. For example, the internal members can be MODGRID internal members available from Lummus Technology LLC. The flow rate of the steam and the height of the internal members will be determined on a case-by-case basis depending on the feed capacity and quality. By providing the internal members, the flue gas components will be effectively stripped from the catalyst with the help of the steam. This will reduce the unwanted combustion products from the RSCP hopper to the riser reactor and other downstream systems.

[0031] Embodiments herein can increase steam usage. In addition to this, embodiments herein can effectively reduce unwanted components in the riser reactor effluent and FCC off-gas. Initial testing of embodiments herein show a reduction in total nitrogen from about 18 mol% (in the range of 15.78 mol% to 19.12 mol%) to about 12 mol% (in the range of 11.24 mol% to 13.57 mol%). Note that nitrogen is one of the components that comes with the regenerated catalyst from the regenerator to the riser reactor and reactor steam; other combustion products should similarly be reduced.

[0032] In addition to using the internal components in the regenerative catalyst standpipe hopper, MODGRID stripper column internals and other internals can be used to strip hydrocarbon vapors from spent catalyst in the catalyst stripper column. Vapor is used as the stripping medium in spent catalyst stripper column applications. MODGRID or other internals can be utilized with MP vapor as the stripping gas medium.

[0033] As nitrogen is reduced with the help of the embodiments herein, other components of the flue gas, such as nitrogen oxides, oxygen, sulfur oxides, and carbon oxides, will be reduced in similar proportions in the FCC reactor vapor and subsequently in the hydrocarbon products. As a result, safe and reliable operation of the downstream recovery section, including any cold boxes operating at very low temperatures for the separation and recovery of methane, can be obtained.

[0034] Effective stripping of the combustion products within the catalyst standpipe hopper can also reduce the oxygen converter equipment size and thus the amount of catalyst. Additionally, ethylene loss through the oxygen converter can be reduced. Additionally, reducing undesirable combustion products in the product recovery section can improve the recovery section efficiency.

[0035] Furthermore, as the industry is developing and developing processing schemes to produce chemicals from crude oil, the embodiments herein thus provide for addressing any of these additional impurities that can be generated. With the present processing scheme, the feed treatment or separate product recovery section does not require a separate process. Also, additives to remove these impurities can not be necessary.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these systems, devices, methods, processes, and compositions belong.

[0037] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0038] As used herein and in the appended claims, the words "comprise," "have," and "include" and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not preclude the addition of more elements or steps.

[0039] "Optionally" means that the subsequently described event or circumstance can or can not occur. The description includes instances where the event or circumstance occurs and instances where it does not.

[0040] When the word "about" or "approximately" is used, the term can mean an amount that is within ± 10%, within ± 5%, within ± 2%, within ± 1%, within ± 0.5%, within ± 0.1%, or within ± 0.01% of the stated value.

[0041] Ranges can be expressed as from about one particular value to about another; however, another embodiment is from the one particular value to the other particular value, all particular values and ad combinations thereof unless otherwise indicated.

[0042] Although the present disclosure contains many embodiments, individuals having ordinary skill in the art will recognize that other embodiments can be practiced under apparent conditions which are within the scope of the present disclosure. Accordingly, all matter contained in the above description should be interpreted as illustrative and not in a limiting sense.

Claims

1. A method for cracking hydrocarbons, the method comprising: In a riser reactor, the hydrocarbon feed is contacted with a regulated cracking catalyst to recover the riser effluent containing spent catalyst and cracked hydrocarbons. The riser effluent is separated to recover cracked hydrocarbon stream and spent catalyst; The spent catalyst is contacted with steam in a stripping tower to strip residual hydrocarbons from the spent catalyst, forming a stripped catalyst. The stripped catalyst is fed into the catalyst regenerator; The stripped catalyst is regenerated in the catalyst regenerator by combustion of coke contained in the stripped catalyst to form a regenerated catalyst containing entrained combustion products. The regenerated catalyst, containing entrained combustion products, is fed from the catalyst regenerator into the regenerated catalyst riser hopper, wherein the entrained combustion products include nitrogen oxides, sulfur oxides, and carbon oxides including nitrogen. The regenerated catalyst in the riser hopper is regulated, wherein the regulation includes contacting the regenerated catalyst containing entrained combustion products with steam to recover the regulated catalyst and a steam stream containing steam and combustion products. The adjusted catalyst is fed into the riser reactor; The steam stream is fed into the catalyst regenerator; as well as The combustion products and the steam stream are recovered as flue gas from the catalyst regenerator.

2. The method of claim 1, wherein the regenerated catalyst riser hopper comprises an internal component configured to facilitate countercurrent contact between the regenerated catalyst, which contains entrained combustion products including nitrogen, and the steam or other industrial inert gas.

3. The method of claim 2, wherein the regenerated catalyst riser hopper comprises MODGRID internal components available from Lumes Technologies LLC.

4. The method according to any one of the preceding claims, wherein the stripping tower includes internal components configured to facilitate countercurrent contact between the spent catalyst and the steam.

5. The method according to any one of the preceding claims, wherein the feeding of the regulated catalyst into the riser reactor comprises feeding the regulated catalyst from the regenerated catalyst riser hopper into the riser reactor via the regenerated catalyst riser, the method further comprising agitating the regulated catalyst within the regenerated catalyst riser with air or steam.

6. The method according to any one of the preceding claims, wherein the feeding of the stripped catalyst from the stripping tower to the catalyst regenerator comprises feeding the stripped catalyst from the stripping tower to the catalyst regenerator via a waste catalyst riser, the method further comprising using steam to fluff the stripped catalyst within the waste catalyst riser.

7. A system for cracking hydrocarbons, the system comprising: Riser reactor, which is used to contact hydrocarbon feed with regulated cracking catalyst to recover riser effluent containing spent catalyst and cracked hydrocarbons; A separation system for separating the riser effluent to recover cracked hydrocarbon streams and spent catalyst; A stripping tower is used to contact the spent catalyst with steam to strip residual hydrocarbons from the spent catalyst, producing a stripped catalyst. A catalyst regenerator for regenerating the stripped catalyst by combustion of coke contained in the stripped catalyst to form a regenerated catalyst and combustion products; A feed line for feeding a regenerated catalyst containing entrained combustion products from the catalyst regenerator to a regenerated catalyst riser hopper, wherein the entrained combustion products include nitrogen oxides, sulfur oxides and carbon oxides including nitrogen. The regulating system within the riser hopper of the regenerated catalyst is used to contact the regenerated catalyst containing entrained combustion products with steam to recover the regulated catalyst and the steam stream containing steam and combustion products. A regulated catalyst riser for feeding the regulated catalyst into the riser reactor; A feed line for feeding the steam stream into the catalyst regenerator; as well as A feed line for recovering the combustion products and the steam stream as flue gas from the catalyst regenerator.

8. The system of claim 7, wherein the regulating system in the regenerated catalyst riser hopper includes internal components configured to facilitate countercurrent contact between the regenerated catalyst containing entrained combustion products and the steam or other industrial inert gas.

9. The system according to any one of claims 7 to 8, wherein the stripping tower includes internal components configured to facilitate countercurrent contact between the spent catalyst and the steam.

10. The system according to any one of claims 7 to 9, further comprising a waste catalyst riser for feeding stripped catalyst from the stripping tower to the catalyst regenerator, and further comprising a flow line for introducing steam into the waste catalyst riser.

11. The system according to any one of claims 7 to 10, further comprising a flow line for introducing air into the regulated catalyst riser.

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