System and process for residence time control in a downer reactor

Abstract

The downer reactor assembly includes an outer separator vessel, at least one downer reactor extending vertically from an upper end to a lower end within the outer separator vessel, and a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor. A process for cracking a hydrocarbon feedstock includes providing a catalyst feed to the at least one downer reactor assembly. The catalyst feed is discharged below the mushroom-shaped distributor cap at the lower end of the at least one downer reactor. The process includes separating hydrocarbon vapors from the catalyst feed under gravity and distributing the upwardly flowing hydrocarbon vapors separated from the catalyst feed through nozzle holes in the mushroom-shaped distributor cap.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Patent Application No. 63 / 374,239, filed August 31, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] FIELD OF THE INVENTION The present disclosure relates to downer reactors, and more particularly to downer reactors that terminate in a vertical primary separator. [Background technology]

[0003] A conventional downer reactor terminates in a vertical primary separator, which separates most of the catalyst from the vapor. The vapor with entrained catalyst exiting the separator is further separated in a close-coupled cyclone system before entering the main fractionator. The separated catalyst falls through each dipleg into the reactor / stripper. Vapor residence time in the downer ranges from 0.5 to 1 second. Because downflow systems are stacked units, the height of the downer affects the overall height of the system and, therefore, the required capacity and capital expenditure (CAPEX). The downer height-to-diameter ratio is adjusted to minimize the overall height while simultaneously reducing scale-up risks related to the downer diameter and its effect on catalyst-feed contact.

[0004] In a conventional dual-downer system, light and paraffinic hydrocarbon feedstocks with boiling points below 660°F are processed in a light feed (LF) downer and respective reactor, while highly decomposable feedstocks with boiling points above 660°F are processed in a heavy feed (HF) downer and reactor. The processing objective is typically to maximize the total amount of olefins produced. The paraffinic LF requires very severe operating conditions in terms of longer residence time, higher temperature, and higher catalyst-to-oil ratio. The catalyst temperature and catalyst-to-oil ratio are set by the regenerator temperature. The vapor residence time depends on the diameter and height of the downer. As mentioned above, typical vapor residence times in downer systems are 0.5 to 1 second. Increasing the residence time beyond 1 second requires either a diameter increase at a constant downer height or a height increase at a constant downer diameter. Both options involve capital cost and performance tradeoffs.

[0005] Conventional techniques have been considered satisfactory for their intended purposes. However, there is a continuing need for improved downer reactors. The present disclosure provides a solution to this need. Summary of the Invention

[0006] The downer reactor assembly includes an outer separation vessel, at least one downer reactor extending vertically from an upper end to a lower end within the outer separation vessel, and a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor.

[0007] One or more embodiments include the assembly of any preceding paragraph, wherein the at least one downer reactor can include two downer reactors.

[0008] One or more embodiments include the assembly of any preceding paragraph, wherein a mushroom-shaped distributor end cap can be positioned at the lower end of each of the two downer reactors.

[0009] One or more embodiments can include the assembly of any preceding paragraph, wherein the mushroom-shaped distributor end cap includes a convex surface facing the top end of the at least one downer reactor.

[0010] One or more embodiments can include the assembly of any preceding paragraph, wherein the at least one downer reactor includes an inlet adjacent an upper end.

[0011] One or more embodiments include the assembly of any preceding paragraph, wherein the lower end of the at least one downer reactor can be configured and adapted to be immersed in the catalyst bed.

[0012] One or more embodiments include the assembly of any preceding paragraph, wherein the mushroom-shaped distributor end cap can be configured and adapted to be immersed in the catalyst bed.

[0013] One or more embodiments include the assembly of any preceding paragraph, wherein the assembly can include a close-coupled cyclone system above a lower end of the at least one downer reactor. One or more embodiments include the assembly of any preceding paragraph, wherein the vapor residence time in the at least one downer reactor is in the range of 0.5 to 1 second.

[0014] According to another embodiment, a process for cracking a hydrocarbon feedstock includes providing a catalyst feed to at least one downer reactor assembly, discharging the catalyst feed at a lower end of the at least one downer reactor below a mushroom-shaped distributor cap, separating hydrocarbon vapors from the catalyst feed under gravity, and distributing the upwardly flowing hydrocarbon vapors separated from the catalyst feed through nozzle holes in the mushroom-shaped distributor cap.

[0015] One or more embodiments include the process of any preceding paragraph, wherein the mushroom-shaped distributor can include a convex surface facing the top end of the at least one downer reactor.

[0016] One or more embodiments include the process of any preceding paragraph, wherein discharging the catalyst feed at the lower end of the at least one downer reactor can include discharging at least a catalyst portion of the catalyst feed into a catalyst bed.

[0017] One or more embodiments include the process of any preceding paragraph, which can include providing additional residence time for the upwardly flowing vapors after discharge from the lower end of the at least one downer reactor to promote additional conversion of unreacted portions of the hydrocarbon portion of the catalyst feed.

[0018] One or more embodiments include the process of any preceding paragraph, wherein the mushroom-shaped distributor end cap can be configured and adapted to be immersed in the catalyst bed.

[0019] One or more embodiments include the process of any preceding paragraph, wherein the process can include discharging the upwardly flowing vapor into a close-coupled cyclone system.

[0020] These and other features of the systems and methods of the present disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. [Brief explanation of the drawings]

[0021] Preferred embodiments of the present disclosure are described in detail herein below with reference to specific figures so that those skilled in the art to which the present disclosure pertains will readily understand how to make and use the devices and methods of the present disclosure without undue experimentation. [Figure 1] FIG. 1 is a schematic plan view of a reactor and separation vessel having a downer reactor assembly according to an embodiment of the present disclosure, showing a mushroom-shaped distributor end cap. [Figure 2] FIG. 1 is a schematic perspective view of a mushroom-shaped distributor end cap of a downer reactor assembly according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] Reference is now made to the drawings, in which like reference numerals identify like structural features or aspects of the present disclosure. For purposes of explanation and illustration, and not limitation, a schematic diagram of an exemplary embodiment of a downer reactor assembly according to the present disclosure is shown in FIG. 1, which is generally designated by the reference numeral 100. Another embodiment of a downer reactor assembly according to the present disclosure, or aspects thereof, is shown in FIG. 2 and described throughout this specification. The systems and methods described herein can be used to maximize the total amount of olefins produced by increasing the vapor residence time without increasing either the downer diameter or height.

[0023] 1, the dual downer reactor assembly 100 includes at least one reactor 102 having an outer separation vessel 104. The downer reactor assembly 100 includes a reactor, for example, two downer reactors 106, terminating in the reactor 102. The reactor 102 can be a light feed (LF) reactor and / or a heavy feed (HF) reactor. The downer reactor assembly 100 can process light and paraffinic hydrocarbon feedstocks in combination with a catalyst in an LF downer, for example, the first of the two downer reactors 106, while heavier, more crackable hydrocarbon feedstocks are processed in combination with a catalyst in an HF downer, for example, the second of the two downer reactors 106. In assembly 100, instead of a separator at the bottom of downer reactor 106, downer reactor 106 discharges below a mushroom distributor end cap 108 located within separator vessel 104, where the catalyst separates under gravity and vapors are distributed through nozzles 112 of mushroom distributor 108 into the catalyst bed 110 above. The residence time in a given downer reactor 106 is approximately 1 second. If needed, additional residence times on the order of minutes are achieved in the fluidized bed 110 described below.

[0024] As shown in Figures 1 and 2, a mushroom-shaped distributor end cap 108 is positioned above the lower end 120 of each of the two downer reactors 106. The mushroom-shaped distributor end cap 108 includes a convex surface 116 facing the upper end 118 of the downer reactor 106. The downer reactors 106 each include an inlet 114 adjacent the upper end 118. The catalyst entering the inlet 114 is indicated diagrammatically by a downward-pointing arrow. The lower end 120 of each downer reactor 106 is configured and adapted to be immersed in the catalyst bed 110. The mushroom-shaped distributor end cap 108 is also configured and adapted to be immersed in the catalyst bed 110. The assembly 100 includes a close-coupled cyclone system 124 above the lower ends 120 of the downer reactors 106, closer to the upper ends 118 than the lower ends 120. The vapor residence time in the downer reactor 106 ranges from 0.5 to 1 second. Additional residence times in the order of minutes are achieved in the fluidized catalyst bed 110 below the downer reactor 106. If necessary, the height A of the catalyst bed level 122 above the mushroom-shaped distributor is varied to achieve the residence time required for further conversion of the unreacted feed exiting the downer reactor 106. The vapor, along with stripping vapor, passes through a cyclone system before entering the main fractionator.

[0025] The process for cracking a hydrocarbon feedstock includes providing a catalyst feed to a downer reactor assembly, e.g., downer reactor assembly 100, as shown schematically by the arrow pointing to the inlet 114 of the downer reactor 106. The catalyst feed is combined with a hydrocarbon feedstock (LF or HF) to crack the hydrocarbon feedstock (which may be in the form of hydrocarbon vapors). The process includes discharging the catalyst feed at a lower end, e.g., lower end 120, of the downer reactor below a mushroom-shaped distributor cap, e.g., mushroom-shaped distributor cap 108. It is contemplated that at least a portion of the hydrocarbon feedstock (e.g., in the form of hydrocarbon vapors) is also discharged at lower end 120. The process includes separating the catalyst feed from the hydrocarbon feed under gravity and distributing the upwardly flowing vapors (e.g., hydrocarbon vapors) separated from the catalyst feed through nozzle holes, e.g., nozzle holes 112, of the mushroom-shaped distributor cap. Discharging the catalyst feed at the lower end of the downer reactor includes discharging the catalyst feed into a catalyst bed, e.g., catalyst bed 110. The process includes providing additional residence time for the upwardly flowing vapor (e.g., hydrocarbon vapor) after discharge to promote additional conversion of unreacted hydrocarbon portions of the catalyst feed discharged from the lower end of the at least one downer reactor. The mushroom-shaped distributor end cap is configured and adapted to be immersed in the catalyst bed. In some embodiments, the process includes discharging the upwardly flowing vapor into a two-stage cyclone system, e.g., close-coupled cyclone system 124.

[0026] Embodiments of the present disclosure provide increased feed conversion in downer processing of light hydrocarbon feedstocks. The reactor system 100 incorporates dense bed cracking with the ability to control dense bed gas residence time and hydrocarbon partial pressure. Embodiments of the present disclosure provide a downer reactor with improved selectivity to propylene without increasing CAPEX and operational expense (OPEX). Embodiments of the present disclosure provide increased catalyst utilization to offset partial catalyst bypass in the downer.

[0027] The methods and systems of the present disclosure, as described above and shown in the drawings, provide a downer reactor assembly system and method having superior properties, including increased controllability and improved selectivity to propylene, without increasing CAPEX and OPEX costs. The systems and methods of the present invention may be applied to HS-FCC technology or the like. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily understand that changes and / or modifications may be made therein without departing from the scope of the subject disclosure.

Claims

1. 1. A downer reactor assembly comprising: an outer separation container; at least one downer reactor extending vertically from an upper end to a lower end within the outer separation vessel; a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor.

2. 2. The assembly of claim 1, wherein the at least one downer reactor comprises two downer reactors, and the mushroom-shaped distributor end cap is positioned at the lower end of each of the two downer reactors.

3. 10. The assembly of claim 1, wherein the mushroom-shaped distributor end cap includes a convex surface facing the upper end of the at least one downer reactor.

4. The assembly of claim 1 , wherein the at least one downer reactor includes an inlet adjacent the upper end.

5. The assembly of claim 1 , wherein the lower end of the at least one downer reactor is configured and adapted to be immersed in a catalyst bed.

6. The assembly of claim 1 , wherein the mushroom-shaped distributor end cap is configured and adapted to be immersed in a catalyst bed.

7. The assembly of claim 1 further comprising a close-coupled cyclone system above the lower end of the at least one downer reactor.

8. 10. The assembly of claim 1, wherein the vapor residence time in the at least one downer reactor is in the range of 0.5 to 1 second.

9. 1. A process for cracking a hydrocarbon feedstock, comprising: providing a catalyst feed to at least one downer reactor assembly; Discharging the catalyst feed below a mushroom-shaped distributor cap at the lower end of the at least one downer reactor; separating hydrocarbon vapors from said catalyst feed under gravity; and distributing the upwardly flowing hydrocarbon vapors separated from the catalyst feed through nozzle holes in the mushroom-shaped distributor cap.

10. 10. The process of claim 9, wherein the mushroom-shaped distributor comprises a convex surface facing the top end of the at least one downer reactor.

11. 10. The process of claim 9, wherein discharging the catalyst feed at the lower end of the at least one downer reactor comprises discharging at least a catalyst portion of the catalyst feed into a catalyst bed.

12. 10. The process of claim 9, wherein additional residence time is provided to the upwardly flowing vapor after discharge to promote additional conversion of unreacted portions of the hydrocarbon portion of the catalyst feed discharged from the lower end of the at least one downer reactor.

13. 10. The process of claim 9, wherein the mushroom-shaped distributor end cap is configured and adapted to be immersed in a catalyst bed.

14. 10. The process of claim 9, further comprising discharging the upwardly flowing vapor to a two-stage cyclone system.

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