Systems and methods for residence time control in downer reactors

Abstract

A downer reactor assembly includes an outer settler vessel, at least one downer reactor extending vertically within the outer settler vessel from a top end to a lower end, and a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor. A method for cracking a hydrocarbon feedstock includes providing a catalyst feed to at least one downer reactor assembly. The catalyst feed is discharged at a lower end of the at least one downer reactor below the mushroom-shaped distributor cover. The method 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 cover.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 374,239, filed on August 31, 2022, the disclosure of which is incorporated herein by reference in its entirety. Background Art 1. Technical Field

[0004] The present disclosure relates to downer reactors, and more particularly to downer reactors terminating in a vertical primary separator.

[0005] 2. Description of related technologies

[0006] The conventional downflow reactor terminates in a vertical primary separator that separates the bulk catalyst from the vapor. The vapor leaving the separator with the entrained catalyst is further separated in a closely coupled cyclone system before entering the main fractionator. The separated catalyst falls into the reactor / stripper through the corresponding dipleg. The vapor residence time in the downflow bed is 0.5 to 1 second. Since the downflow system is a stacked unit, the height of the downflow bed affects the total height of the system, and therefore affects the required capacity and capital expenditure (CAPEX). The ratio of the downflow bed height to the diameter is adjusted to minimize the total height while reducing the risk of expansion in terms of the downflow bed diameter and its impact on the catalyst-feed contact.

[0007] In a conventional dual downer system, light and paraffinic feedstocks with boiling points below 660°F are processed in the light feed (LF) downer and corresponding reactor, while more crackable feedstocks with boiling points above 660°F are processed in the heavy feed (HF) downer and reactor. The processing goal is usually to maximize the total olefins produced. LF is a paraffin and requires more severe operating conditions, including longer residence times, higher temperatures, and higher catalyst to oil ratios. 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, the typical vapor residence time for a downer system is 0.5 seconds to 1 second. Increasing the residence time beyond 1 second will require increasing the diameter with a constant downer height, or increasing the height with a constant downer diameter. Both options have trade-offs in capital cost and performance.

[0008] Conventional technology has been considered to meet its intended purpose. However, there is always a need to improve downer reactors. The present disclosure provides a solution to this need. Summary of the invention

[0009] A downer reactor assembly includes an external settler vessel, at least one downer reactor vertically extending from a top end to a lower end in the external settler vessel, and a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor.

[0010] One or more embodiments include the assembly of any preceding paragraph, and wherein the at least one downer reactor may include two downer reactors.

[0011] One or more embodiments include the assembly of any preceding paragraph, and wherein the mushroom-shaped distributor end cap may be positioned at the lower end of each of the two downer reactors.

[0012] One or more embodiments include the assembly of any of the preceding paragraphs, and wherein the mushroom-shaped distributor end cap may include a convex surface facing a top end of the at least one downer reactor.

[0013] One or more embodiments include the assembly of any preceding paragraph, and wherein the at least one downer reactor may include an inlet proximate the top end.

[0014] One or more embodiments include the assembly of any preceding paragraph, and wherein the lower end of the at least one downer reactor can be constructed and adapted to be submerged in the catalyst bed.

[0015] One or more embodiments include the assembly of any of the preceding paragraphs, and wherein the mushroom-shaped distributor end cap can be constructed and adapted to be immersed in the catalyst bed.

[0016] One or more embodiments include the assembly of any preceding paragraph, and wherein the assembly may include a close-coupled cyclone separator system above the lower end of the at least one downer reactor. One or more embodiments include the assembly of any preceding paragraph, and wherein the vapor residence time in the at least one downer reactor is 0.5 seconds to 1 second.

[0017] According to another aspect, a method for cracking a hydrocarbon feedstock includes providing a catalyst feed to at least one downer reactor assembly. The catalyst feed is discharged at a lower end of the at least one downer reactor assembly below a mushroom-shaped distributor cap. The method includes separating hydrocarbon vapor from the catalyst feed under gravity and distributing the upwardly flowing hydrocarbon vapor separated from the catalyst feed through nozzle holes in the mushroom-shaped distributor cap.

[0018] One or more embodiments include the method of any preceding paragraph, and wherein the mushroom-shaped distributor may include a convex surface facing a top end of the at least one downer reactor.

[0019] One or more embodiments include the method of any preceding paragraph, and wherein discharging the catalyst feed at the lower end of the at least one downer reactor can include discharging at least the catalyst portion of the catalyst feed into a catalyst bed.

[0020] One or more embodiments include the method of any of the preceding paragraphs, and wherein the method may include providing additional residence time for the upwardly flowing vapor after discharge to promote additional conversion of an unreacted portion of the hydrocarbon portion of the catalyst feed discharged from the lower end of the at least one downer reactor.

[0021] One or more embodiments include the method of any preceding paragraph, and wherein the mushroom-shaped distributor end cap can be constructed and adapted to be immersed in the catalyst bed.

[0022] One or more embodiments include the method of any preceding paragraph, and wherein the method can include discharging the upwardly flowing vapor to a close-coupled cyclone separator system.

[0023] These and other features of the systems and methods of the subject 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 accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Therefore, those skilled in the art to which the subject disclosure belongs will readily understand how to make and use the devices and methods disclosed herein without undue experimentation, and preferred embodiments of the present invention will be described in detail below with reference to certain drawings, in which:

[0025] Figure 1 is a schematic plan view of a reactor and settler vessel having a downer reactor assembly according to an embodiment of the present disclosure, showing a mushroom-shaped distributor end cap; and

[0026] Figure 2 is a schematic perspective view of a mushroom-shaped distributor end cap of a downcomer reactor assembly according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0027] Reference will now be made to the drawings, wherein like reference numerals identify similar structural features or aspects of the subject disclosure. Figure 1 A schematic diagram of an exemplary embodiment of a downer reactor assembly according to the present disclosure is shown in FIG. 1 and is generally indicated by reference numeral 100. Other embodiments of downer reactor assemblies according to the present disclosure or aspects thereof are shown in FIG. Figure 2 The systems and methods described herein can be used to maximize total olefins produced by increasing vapor residence time without increasing downer diameter or height.

[0028] like Figure 1 As shown, the dual downer reactor assembly 100 includes at least one reactor 102 having an external settler vessel 104. The downer reactor assembly 100 includes two downer reactors 106 terminating in a reactor (e.g., reactor 102). The reactor 102 may be a light feed (LF) reactor and / or a heavy feed (HF) reactor. The downer reactor assembly 100 may process light and paraffinic feedstocks in combination with a catalyst in the LF downer (e.g., the first downer reactor of the two downer reactors 106), and process heavier and more crackable hydrocarbon feedstocks in combination with a catalyst in the HF downer (e.g., the second downer reactor of the two downer reactors 106). In assembly 100, instead of a separator at the bottom of downer reactor 106, downer reactor 106 is discharged below a mushroom-shaped distributor end cap 108 located in settler vessel 104, where the catalyst separates under gravity and the vapor is distributed to the catalyst bed 110 above the mushroom-shaped distributor through nozzles 112 in the mushroom-shaped distributor 108. The residence time in a given downer reactor 106 is about one second. If desired, additional residence times of about several minutes are achieved in the fluidized bed 110 described below.

[0029] like Figure 1 to Figure 2 As shown, 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 top end 118 of the downer reactor 106. The downer reactors 106 each include an inlet 114 near the top end 118. The catalyst entering the inlet 114 is schematically shown by the arrow pointing downward. The lower end 120 of each downer reactor 106 is constructed and adapted to be immersed in the catalyst bed 110. The mushroom-shaped distributor end cap 108 is also constructed and adapted to be immersed in the catalyst bed 110. The assembly 100 includes a closely coupled cyclone separator system 124 above the lower end 120 of the downer reactor 106 closer to the top end 118 than the lower end 120. The vapor residence time in the downer reactor 106 is 0.5 seconds to 1 second. An additional residence time of about several minutes is achieved in the fluidized catalyst bed 110 below the downer reactor 106. If necessary, the height A of the catalyst bed 122 above the mushroom distributor is varied to achieve the residence time required for additional conversion of the unreacted feed leaving the downer reactor 106. The vapor flows through a cyclone system along with the stripping steam and then enters the main fractionator.

[0030] A method for cracking a hydrocarbon feedstock includes providing a catalyst feed to a downcomer reactor assembly (e.g., downcomer reactor assembly 100), as schematically shown by an arrow pointing to an inlet 114 of downcomer 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 vapor). The method includes discharging the catalyst feed at a lower end (e.g., lower end 120) of the downcomer reactor below a mushroom-shaped distributor cover (e.g., mushroom-shaped distributor cover 108). At the lower end 120, it is contemplated that at least a portion of the hydrocarbon feedstock (e.g., in the form of hydrocarbon vapor) is also discharged. The method includes separating the catalyst feed from the hydrocarbon feed under gravity, and distributing the upwardly flowing vapor (e.g., hydrocarbon vapor) separated from the catalyst feed through a nozzle hole (e.g., nozzle hole 112) in the mushroom-shaped distributor cover. Discharging the catalyst feed at the lower end of the downcomer reactor includes discharging the catalyst feed into a catalyst bed (e.g., catalyst bed 110). The method includes providing additional residence time for the upwardly flowing vapor (e.g., hydrocarbon vapor) after discharge to promote additional conversion of the unreacted portion of the hydrocarbon portion of the catalyst feed discharged from the lower end of at least one downer reactor. The mushroom-shaped distributor end cap is constructed and adapted to be immersed in the catalyst bed. In some embodiments, the method includes discharging the upwardly flowing vapor to a two-stage cyclone separator system, such as a closely coupled cyclone separator system 124.

[0031] Embodiments of the present disclosure provide improved feed conversion in downer processing of light hydrocarbon feedstocks. Reactor system 100 combines dense bed cracking with the ability to control dense bed gas residence time and hydrocarbon partial pressure. Embodiments of the present disclosure provide downer reactors with improved selectivity to propylene without increasing CAPEX and operating expenses (OPEX). Embodiments of the present disclosure provide increased catalyst utilization, offsetting partial catalyst bypass in the downer.

[0032] The method and system of the present disclosure as described above and shown in the accompanying drawings provide a system and method of a downer reactor assembly having excellent performance without increasing CAPEX and OPEX costs, including improved controllability, improved selectivity to propylene. The system and method of the present invention can be applied to HS-FCC technology, etc. Although the apparatus and method of the present disclosure have been shown and described with reference to preferred embodiments, it will be readily understood by those skilled in the art that changes and / or modifications may be made thereto without departing from the scope of the present disclosure.

Claims

1. A downer reactor assembly, comprising: External settler vessel; at least one downer reactor, the at least one downer reactor vertically extending from a top end to a lower end in the external settler vessel; and A mushroom-shaped distributor end cap is positioned at the lower end of the at least one downer reactor.

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

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

4. The assembly of claim 1, wherein said at least one downer reactor comprises an inlet proximate said top end.

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

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

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

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

9. A method for cracking a hydrocarbon feedstock, the method comprising: providing a catalyst feed to at least one downer reactor assembly; Discharging the catalyst feed at the lower end of at least one downer reactor below a mushroom-shaped distributor cover; separating hydrocarbon vapor from the catalyst feed under the action of gravity; as well as Upwardly flowing hydrocarbon vapor separated from the catalyst feed is distributed through nozzle holes in the mushroom-shaped distributor cap.

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

11. The method 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. The process of claim 9 providing additional residence time for the upwardly flowing vapor after discharge to promote additional conversion of an unreacted portion of the hydrocarbon portion of the catalyst feed discharged from the lower end of the at least one downer reactor.

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

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

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