A catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing

Abstract

The application discloses a catalytic cracking riser reactor which strengthens mixing and inhibits gas-solid back mixing, and the reactor comprises a pre-lifting section, a raw oil feeding section, a first reaction section, a flow regulation mixing section and a second reaction section from bottom to top in sequence; the inner wall of the first reaction section is provided with downwardly inclined turbulence baffles for guiding the catalysts descending along the wall to the center of the pipe; the flow regulation mixing section is in a Venturi tube structure and comprises a contraction section, a throat and an expansion section; the center of the throat is provided with a secondary distribution cone with a tip pointing downward, which is fixed to the inner wall of the expansion section through a support rib plate. The catalyst wall back mixing is inhibited through the turbulence baffles, the catalyst clusters are broken through the high shearing force of the Venturi throat, and the radial uniform distribution of the gas-solid two-phase is realized through the secondary distribution cone, so that the residence time distribution is optimized, the thermal cracking degree is reduced, and the light oil yield is improved.

Description

Technical Field

[0001] This invention relates to the fields of petroleum refining and chemical technology, specifically to a catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing. Background Technology

[0002] Catalytic cracking is a core technology for the refining of heavy oil into lighter forms and the production of high-value-added gasoline, diesel, and low-carbon olefins. The riser reactor, as the core reaction equipment in a catalytic cracking unit, directly determines the gas-solid two-phase contact efficiency, reaction depth, and final product distribution through its internal hydrodynamic characteristics.

[0003] With the continuous development of heavy oil catalytic cracking technology, the quality of processed feedstocks is deteriorating, placing more stringent demands on the uniformity of gas-solid mixing within the riser. However, in traditional constant-diameter or simply variable-diameter riser reactors, the gas-solid two-phase fluid generally exhibits a severe "ring-core" flow pattern on a macroscopic scale, meaning that the gas-solid concentration is low in the central region and high in the sidewall region, while catalyst particles also undergo backmixing along the sidewalls. This has become a major industry challenge restricting the improvement of catalytic cracking process efficiency.

[0004] In the existing technology, the design of the riser has serious problems of catalyst backmixing and uneven radial distribution, resulting in low contact efficiency between oil and gas and catalyst, poor reaction selectivity, and consequently a sharp increase in dry gas and coke yields and a decrease in the yield of high-value-added light oil. Summary of the Invention

[0005] The purpose of this invention is to overcome or at least partially solve the above-mentioned problems by providing a catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing, wherein the reactor comprises, from bottom to top, a pre-lifting section, a feedstock section, a first reaction section, a rectifying and mixing section, and a second reaction section;

[0007] The inner wall of the first reaction section is provided with a downwardly inclined baffle to guide the catalyst that is attached to the wall and moving downward toward the center of the tube.

[0008] The rectifier mixing section is a Venturi tubular structure, including a contraction section, a throat, and an expansion section arranged sequentially from bottom to top;

[0009] The throat has a secondary distribution cone with its tip pointing downwards at its internal center, and the secondary distribution cone is fixed to the inner wall of the expansion section by a supporting rib.

[0010] Preferably, multiple sets of baffles in the first reaction section are staggered along the axial direction of the riser pipe, with adjacent sets of baffles staggered in the circumferential direction, and each set of baffles is composed of multiple inclined blades evenly distributed in a ring along the inner wall of the riser pipe.

[0011] Preferably, the inclined blade is inclined downwards, and the angle between its plane and the central axis of the riser tube is 30°~45°.

[0012] Preferably, the cross-sectional shape of the inclined blade is rectangular, semi-circular, or triangular.

[0013] Preferably, the contraction section in the rectifier mixing section is a straight contraction cone or a streamlined curved contraction tube.

[0014] Preferably, the flow cross-sectional area of ​​the throat is 30% to 60% of the flow cross-sectional area of ​​the first reaction section.

[0015] Preferably, the secondary distribution cone is a cone or a rotating body with a streamlined surface, and the maximum diameter of the secondary distribution cone is 0.2 to 0.4 times the inner diameter of the throat 7.

[0016] Preferably, the horizontal plane at the bottom of the secondary distribution cone where the maximum diameter is located is at the same horizontal level as the junction of the throat and the expansion section, or is lower than the junction.

[0017] Preferably, the supporting stiffeners are evenly distributed in the radial direction, and the cross-section of the supporting stiffeners 11 is streamlined or teardrop-shaped.

[0018] Preferably, the inclined blade is connected to the metal shell of the first reaction section via an anchoring base, and the upstream surface of the inclined blade is provided with a wear-resistant alloy layer.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The turbulence baffles in the first reaction section can forcibly strip away part of the catalyst that is attached to the wall and descends, fundamentally reducing the macroscopic backmixing path and improving the ring core flow pattern that is thin in the center and rich in the side walls.

[0021] The fluid accelerates at the throat annular gap, and the extremely strong gas-solid slip velocity and shear force instantly tear and break up the microscopic catalyst agglomerates, ensuring the uniform mixing of the catalyst and oil and gas.

[0022] The synergistic application of streamlined curve contraction section, downward-pointing secondary distribution cone and streamlined support rib plate significantly reduces the frontal wind resistance of the component, eliminates the wake dead zone, and avoids catalyst stagnation and coking.

[0023] The gas-solid two-phase system achieves uniform distribution across the entire cross-section within the expansion section, narrowing the residence time distribution of oil and gas, suppressing excessive thermal cracking side reactions, and improving the yield of high-value-added light oil. Attached Figure Description

[0024] Figure 1 This is a schematic front sectional view of the overall structure of the present invention;

[0025] Figure 2 for Figure 1 Schematic diagram of the top view of the first reaction section AA in the middle;

[0026] Figure 3 for Figure 1 Schematic diagram of the top view of the BB section of the intermediate rectification and mixing unit;

[0027] Figure 4 This is a cross-sectional view of the teardrop-shaped support rib of the present invention;

[0028] Figure 5 This is a graph comparing the beneficial effects of the embodiments of the present invention with those of the traditional empty tube structure; the left side shows a comparison of residence time distribution curves, and the right side shows a comparison of radial catalyst concentration distribution curves.

[0029] In the diagram: 1. Pre-lifting section; 2. Feedstock section; 3. First reaction section; 4. Rectifying and mixing section; 5. Second reaction section; 6. Contraction section; 7. Throat; 8. Expansion section; 9. Baffle; 10. Secondary distribution cone; 11. Support ribs. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings.

[0031] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this description, those skilled in the art can make creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

[0032] This invention provides a catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing, solving the technical problems in the prior art. The overall concept is as follows:

[0033] Example 1

[0034] Combination Figure 1 and Figure 2 As shown, this embodiment provides a catalytic cracking riser reactor that enhances mixing and suppresses gas-solid backmixing. Its main body is a vertical cylindrical structure. The five sections connected sequentially from bottom to top are: a pre-lifting section 1, a feedstock section 2, a first reaction section 3, a rectifying and mixing section 4, and a second reaction section 5.

[0035] Furthermore, in this embodiment, three sets of turbulence baffles 9 are arranged along the axial direction of the riser tube on the inner wall surface of the first reaction section 3. Each set of turbulence baffles 9 consists of multiple triangular inclined blades evenly distributed along the circumference of the tube wall, for example, 4, 4, and 8 blades from top to bottom. In particular, adjacent sets of turbulence baffles 9 are staggered by 22.5° in the circumferential direction to ensure that when viewed from above, the lower baffle is exactly below the gap of the upper baffle. The triangular inclined blades are inclined downwards, and the angle between their frontal surface and the central axis of the riser tube is set to 35° (within the preferred range of 30°~45°). The blades are welded to the metal shell of the riser tube through an anchoring base that penetrates the wear-resistant lining, and a wear-resistant alloy layer is deposited on the frontal surface.

[0036] Through the above design, while avoiding excessive total pressure drop, a portion of the catalyst adhering to the wall and descending can be forcibly stripped, fundamentally reducing the macroscopic backmixing path.

[0037] Optionally, the arrangement and number of turbulence baffles are not limited, and those skilled in the art can make adaptive adjustments based on the specific operating conditions and hydrodynamic characteristics of the riser reactor. Actual conditions include, but are not limited to: the reactor's geometric dimensions (such as pipe diameter and effective reaction section height), the designed processing capacity of the unit, process operating conditions (such as apparent gas-solid velocity, catalyst-to-oil ratio, and the system's maximum allowable pressure drop limit), and the physicochemical properties of the feedstock and the target reaction depth requirements. Any conventional equivalent substitutions or dimensional adjustments made to the number, arrangement layers, staggered angle, and cross-sectional shape of the aforementioned inclined blades using the wall-mounted catalyst forced stripping and guiding principle disclosed in this invention should be covered within the scope of protection of this invention.

[0038] Combination Figure 1 , Figure 3 and Figure 4 As shown, in this embodiment, the rectifier mixing section 4 is disposed above the first reaction section 3, and is composed of a streamlined contraction section 6, a throat 7, and an expansion section 8 connected smoothly in sequence. The flow cross-sectional area of ​​the throat 7 is reduced to 45% of the cross-sectional area of ​​the first reaction section 3 (within the preferred range of 30% to 60%).

[0039] A secondary distribution cone 10 is suspended at the center of the throat 7. The secondary distribution cone 10 is a streamlined cone with its tip pointing vertically downwards, and its bottom surface at its maximum diameter is flush with the boundary line between the throat 7 and the expansion section 8. The maximum diameter of the secondary distribution cone 10 is 0.3 times the inner diameter of the throat 7 (preferably within the range of 0.2 to 0.4 times).

[0040] To firmly support the secondary distribution cone 10, four supporting stiffeners 11 are evenly arranged within the expansion section 8. One end of each supporting stiffener 11 is connected to the secondary distribution cone 10, and the other end is fixed to the inner wall of the expansion section 8. To reduce resistance and wear at high air velocities, the cross-section of the supporting stiffener 11 adopts a teardrop-shaped streamlined structure, with its sharp end facing downwards to meet the incoming flow and its rounded end facing upwards.

[0041] Through the above design, the fluid accelerates at the throat annular gap, and the extremely strong gas-solid slip velocity and shear force instantly tear and break up the microscopic catalyst agglomerates. The synergistic application of the streamlined contraction section, the downward-pointing secondary distribution cone, and the teardrop-shaped support ribs significantly reduces the frontal wind resistance of the components, eliminates the wake dead zone, and avoids catalyst stagnation and coking. The gas-solid two-phase system achieves uniform distribution across the entire cross-section within the expansion section 8, narrowing the residence time distribution of oil and gas, suppressing excessive thermal cracking side reactions, and improving the yield of high-value-added light oil.

[0042] Optionally, the flow cross-sectional area of ​​the throat, the shape and installation position of the secondary distribution cone, and the number and cross-sectional structure of the supporting ribs in the rectifying and mixing section are not limited. Those skilled in the art can make adaptive adjustments according to the actual operating conditions and hydrodynamic requirements of the riser reactor. Actual conditions include, but are not limited to: the maximum allowable total pressure drop margin of the system, the apparent gas velocity of the fluid, the catalyst circulation rate, the atomization state of the feed oil, and the comprehensive design requirements for the equipment's resistance to erosion and wear and its mechanical strength. In addition, the axial position of the secondary distribution cone 10 can also be finely adjusted according to the flow field requirements (for example, making its tip slightly extend into the contraction section, or its bottom surface slightly protrude into the expansion section); for heavy-duty risers with large diameters or high catalyst flux, in order to resist the huge high-speed fluid impact force, the number of supporting ribs can be appropriately increased, and the aspect ratio of its streamlined droplet cross-section and the thickness of the wear-resistant layer on the flow-facing surface can be adjusted accordingly.

[0043] Any conventional equivalent substitutions or parameter fine-tunings made to the throat size ratio, the specific shape and spatial position of the distribution cone, and the arrangement structure of the supporting ribs, using the Venturi constriction shearing and radial divergence principle of the central inverted cone disclosed in this invention, in order to break up the micro-agglomerates of the catalyst and achieve uniform cross-sectional distribution, should be covered within the protection scope of this invention.

[0044] When the riser reactor of the present invention is put into operation, its hydrodynamic working process is as follows:

[0045] Phase 1: The highest-temperature regenerated catalyst from the regenerator first enters the pre-lifting section 1, where it accelerates upward under the carry of pre-lifting steam. Subsequently, the atomized feed oil is injected at high speed into the feed oil inlet section 2, where it comes into instantaneous contact with the high-temperature catalyst, vaporizes, and undergoes a preliminary cracking reaction, forming a high-speed upward gas-solid two-phase flow.

[0046] Stage Two: The gas-solid two-phase flow enters the first reaction section 3. During the upward movement, due to gravity and the sidewall effect, some catalyst particles tend to adhere to the wall and descend. At this time, the staggered downward-sloping baffles 9 play an interception and guiding role, forcibly stripping the catalyst adhering to the wall and guiding it to the high-speed airflow zone in the center of the tube. The staggered arrangement ensures that most of the catalyst around the tube wall can be effectively intercepted, which to some extent improves the "lean center, concentrated sidewall" ring-core flow pattern.

[0047] Stage 3: The gas-solid mixture enters the rectifying mixing section 4. Guided by the contraction section 6, the fluid converges and accelerates towards the center. Upon entering the throat 7, the flow cross-sectional area decreases sharply, and the slip velocity of the gas and solid phases increases dramatically. The high shear force environment instantly tears apart the liquid bridges and agglomerates between catalyst particles. Simultaneously, the downward-pointing secondary distribution cone 10 evenly distributes the high-speed fluid from the center to the surrounding annular gaps, further enhancing the radial diffusion kinetic energy.

[0048] Stage Four: Fluid flows out of throat 7 and into expansion section 8, increasing the flow area, reducing the flow velocity, and restoring static pressure. Under the divergent effect of the tail end of secondary distribution cone 10, the catalyst and oil / gas are diffused extremely uniformly across the entire cross-section. Subsequently, the highly uniform gas-solid mixture enters the second reaction section 5 to continue the deep cracking reaction.

[0049] The results of CFD three-dimensional numerical simulation confirm that, after adopting the structure of this embodiment:

[0050] Radial concentration distribution: The cross-sectional catalyst concentration distribution curves at the outlet of the first reaction section 3 and the outlet of the rectifier mixing section 4 tend to be significantly flatter, which reduces the high concentration peak near the wall in the traditional structure and reduces the cross-sectional non-uniformity coefficient.

[0051] Residence time distribution: Due to the reduction of dead zones and backmixing on the sidewalls, the peak width of the overall oil and gas residence time distribution curve is significantly narrowed, the tailing phenomenon is greatly reduced, and the flow field is close to the ideal plug flow state.

[0052] Pressure drop performance: Thanks to the streamlined aerodynamic design of the contraction section 6, secondary distribution cone 10 and supporting stiffener 11, although strong mixing disturbance is added, the additional pressure drop of the entire reactor is limited and is well within the economic operating range that the industrial main fan can withstand.

[0053] The above description of the embodiments is provided to facilitate understanding and use of the present invention by those skilled in the art. It is obvious to those skilled in the art that various modifications can be made to the embodiments, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing, the reactor comprising, from bottom to top, a pre-lifting section (1), a feedstock section (2), a first reaction section (3), a rectifying and mixing section (4), and a second reaction section (5), characterized in that: The inner wall of the first reaction section (3) is provided with a downwardly inclined baffle (9) to guide the catalyst that is attached to the wall and descends towards the center of the tube; The rectifier mixing section (4) is a Venturi tubular structure, including a contraction section (6), a throat (7) and an expansion section (8) arranged sequentially from bottom to top. The throat (7) has a secondary distribution cone (10) with its tip pointing downwards at its center. The secondary distribution cone (10) is fixed to the inner wall of the expansion section (8) by a supporting rib (11).

2. The catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 1, characterized in that: The first reaction section (3) has multiple sets of turbulence baffles (9) arranged alternately along the axial direction of the riser pipe. The adjacent sets of turbulence baffles (9) are staggered in the circumferential direction. Each set of turbulence baffles (9) consists of multiple inclined blades evenly distributed in a ring along the inner wall of the riser pipe.

3. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 2, characterized in that: The inclined blade is inclined downward, and the angle between its plane and the central axis of the riser tube is 30°~45°.

4. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 2, characterized in that: The cross-sectional shape of the inclined blade is rectangular, semi-circular, or triangular.

5. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 1, characterized in that: The contraction section (6) in the rectifier mixing section (4) is a straight contraction cone or a streamlined curved contraction tube.

6. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 1, characterized in that: The flow cross-sectional area of ​​the throat (7) is 30% to 60% of the flow cross-sectional area of ​​the first reaction section (3).

7. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 1, characterized in that: The secondary distribution cone (10) is a cone or a rotating body with a streamlined surface, and the maximum diameter of the secondary distribution cone (10) is 0.2 to 0.4 times the inner diameter of the throat (7).

8. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 7, characterized in that: The horizontal plane at the bottom of the secondary distribution cone (10) with the maximum diameter is at the same level as or below the junction of the throat (7) and the expansion section (8).

9. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 1, characterized in that: The supporting stiffeners (11) are evenly distributed in the radial direction, and the cross-section of the supporting stiffeners (11) is streamlined or teardrop-shaped.

10. A catalytic cracking riser reactor for enhanced mixing and suppression of gas-solid backmixing according to claim 2, characterized in that: The inclined blade is connected to the metal shell of the first reaction section (3) through the anchor base, and the frontal surface of the inclined blade is provided with a wear-resistant alloy layer.

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