Improved mixing device for downflow hydrogenation reactors

Abstract

To provide an improved vortex-type mixing device for a down-flow hydroprocessing reactor.SOLUTION: A mixing device for a multi-bed down-flow catalytic reactor comprises: a top plate 34; a base plate 32 extending parallel to the top plate; a plurality of inwardly directed vanes 36 contained in the interior region of the mixing device; and a mixing region. The mixing device does not include a weir ring extending from an inner surface of the base plate, or a bubble cap extending from an inner surface of the top plate. The device provides improved overall mixing efficiency of an existing mixing volume in the mixing of gas and liquid phases in two-phase systems while reducing the pressure drop in the device, compared with prior art devices. Typical hydroprocessing applications include hydrorefining, hydrofinishing, hydrocracking and hydrodewaxing.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] An improved vortex mixing device for a down-flow hydroprocessing reactor is disclosed. Such down-flow hydroprocessing reactors are used in the petroleum and chemical processing industries to carry out catalytic reactions of hydrocarbon-based feeds in the presence of hydrogen at high temperatures and pressures. Suitable hydroprocessing applications include hydrotreating, hydrofinishing, hydrocracking, and hydrodewaxing.

Background Art

[0002] In a fixed-bed hydroprocessing reactor, gaseous and liquid reactants (such as hydrogen and hydrocarbon-based feeds) flow downward through one or more beds of solid catalyst (see, for example, U.S. Patent No. 4,597,854 to Penick).

[0003] As the reactants flow downward through the catalyst bed of the reactor, the reactants contact and react with the catalyst material to produce the desired products. Gaseous reactants such as hydrogen are consumed and heat is generated by the catalytic reaction. Controlling the temperature of the feed as it moves downward through the reactor is important to ensure that the quality and quantity of the resulting products are maximized towards target products.

[0004] To suppress temperature increases and replenish hydrogen consumed by the reaction, a low-temperature, hydrogen-rich gas can be introduced between catalyst beds. To maintain the overall reactor performance, the temperature of the fluids within the reactor should be as uniform as possible, and the liquids and gases should be thoroughly mixed to maximize performance. Insufficient mixing of fluids between beds can limit reactor operation in various ways. If radial temperature differences cannot be eliminated by mixing between beds, these differences will persist or increase as the process fluid moves downwards through the reactor. The presence of hot spots in the beds can cause rapid deactivation of the catalyst in those areas, potentially shortening the total cycle length of the reactor. Product selectivity is typically poor at high temperatures. For example, high-temperature regions can result in substandard color, viscosity, and other product quality characteristics. Also, if the temperature exceeds a certain value (typically 800-850°F) at any location, the exothermic reaction can self-accelerate, leading to a runaway phenomenon that could damage the catalyst, vessel, or downstream equipment.

[0005] Due to these hazards, refiners operating with substandard reactor internal hardware must sacrifice yield and / or process capacity to avoid the detrimental effects of poor inter-bed fluid mixing. Non-uniform temperature distribution and hot spots in reactors can be minimized by mixing and balancing reactants between catalyst beds, correcting non-uniform temperature and flow distributions, and minimizing pressure drops. Inter-catalyst fluid mixing can be achieved by using disperser assemblies (distributor assemblies) and mixing chambers. In today's refinery economics, where hydrogenation units are commanded to operate at feed rates far exceeding their design, optimal inter-bed fluid mixing represents a valuable, low-cost bottleneck elimination.

[0006] Disperser assemblies can be used to collect, mix, and distribute fluids in the region between the beds of a multi-bed catalytic reactor. A disperser assembly typically includes a trough for collecting and mixing liquids and gases flowing from the catalyst bed above, and a mixing device or mixing chamber located in the center of the trough to receive liquids from the trough and further mix the liquids and gases.

[0007] Mixing devices are a crucial component of many disperser assemblies because they provide efficient and thorough mixing of fluids / gases, helping to avoid hot spots and unfavorable temperature distributions.

[0008] The mixing device has at least one inlet for receiving liquid from a trough and at least one outlet for directing the flow to a catalyst bed below. Mixing device designs vary and include, for example, baffle mixer designs such as ribbon blenders and disk-and-donut mixers, which facilitate mixing by changing the direction of fluid and gas.

[0009] Another type of mixer is the centrifugal or vortex design. In this type of mixer, the flow of liquid and gas flowing downward through the reactor is collected and introduced into a circular chamber, where it rotates several times before passing downward through a centrally located opening.

[0010] Where present, mixing devices are generally located in the inter-floor space between catalyst beds within the reactor. In many reactors, this inter-floor space is limited by the presence of support beams, piping, and other obstructions occupying the space. Due to these spatial constraints, custom hardware, such as mixing devices scaled to fit the available space, is required to perform efficient two-phase mixing in a limited volume. Furthermore, a lower-profile disperser assembly can increase the amount of catalyst loaded in the same reactor volume, thus improving the utilization of the reactor volume.

[0011] Various types of mixing devices are described in several patents. For example, see U.S. Patent Application Publication No. 2014 / 0231308. The present invention provides specific improvements to prior art vortex mixing devices, such as those described in U.S. Patent Nos. 9,079,141 and 8,017,095.

[0012] Because adequate inter-floor fluid mixing is crucial for good catalyst life, high yield, long cycle length, and overall reactor performance, improved mixing devices are needed. There is a continuing need for mixing devices that are compact in vertical dimensions, have low pressure loss, and can be retrofitted to existing reactors with limited inter-floor space. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] U.S. Patent No. 4,597,854 [Patent Document 2] U.S. Patent Application Publication No. 2014 / 0231308 [Patent Document 3] U.S. Patent No. 9,079,141 [Patent Document 4] U.S. Patent No. 8,017,095 [Overview of the project]

[0014] This invention relates to a vortex mixing device for a downflow hydrogenation reactor. This mixing device provides more effective mixing of fluids in the space between catalyst beds in a multi-bed reactor. Compared to other vortex mixing devices, this mixing device provides effective mixing of the existing mixing volume in the mixing of gas and liquid phases in a two-phase system while reducing pressure loss in the mixing device. Due to its relatively small size, this device is well-suited for retrofit applications and can be scaled up or down to match the design of new reactors to achieve efficient fluid mixing in the inter-bed space of a multi-bed reactor. Combined with further mixing and distribution components of a multi-bed downflow reactor, such as flow nozzles, this mixing device provides effective mixing of the liquid and gas phases, as well as mixing of the gas and liquid phases with each other.

[0015] This mixing device includes a top plate with an inner surface and a base plate extending parallel to the top plate. The base plate has an inner surface and a base plate opening. Both the top plate and the base plate have an outer perimeter that defines the outer edge of each plate. Multiple inward-facing vanes extend perpendicularly to the inner surfaces of the top plate and the base plate and are interposed between the inner surfaces of the top plate and the base plate, and the top plate and the base plate are separated such that an internal region for receiving the vanes and reactor fluid exists between the plates. The vanes are oriented inward from the outer perimeter of the top plate and the base plate towards the base plate opening and are spaced apart over a region extending from the base plate opening to the outer perimeter of the top plate and the base plate. This mixing device includes a mixing region that extends roughly from the base plate opening to the inlet region of the mixing device, which is located between adjacent vanes. In contrast to certain prior art devices, such as those described in U.S. Patent No. 9,079,141, the mixing device of the present invention does not include a weir ring extending from the inner surface of the base plate or a bubble cap extending from the inner surface of the top plate.

[0016] Furthermore, the present invention relates to a multi-bed downflow catalytic reactor having an upper and a lower catalyst bed housed within a reactor shell having an inner surface, and an inter-bed dispersion assembly interposed between the upper and lower catalyst beds, wherein the inter-bed dispersion assembly includes a mixing device according to the present invention.

[0017] Figures 1 to 7 show representative views of the mixing device according to the present invention. It should be understood that the scope of the present invention is not limited by these representative views, but is defined by the claims of the present application.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic view of an embodiment of the mixing device of the present invention disposed within a multi-bed catalytic reactor. [Figure 2] It is a cross-sectional view of the mixing device of the present invention. [Figure 3] It is a perspective view of half of the mixing device 26 of the present invention. [Figure 4] It is a top view of the mixing device. [Figure 4A] It is another top view of the mixing device of the present invention showing the holes of an optional additional top plate. [Figure 5] It is a top view showing the arrangement of the vanes curved inward of the present invention. [Figure 6] It is a perspective view of a collection plate showing the arrangement of the slotted risers according to the present invention. [Figure 7] It is a cross-sectional view of a part of the collection plate showing the details of the riser.

Modes for Carrying Out the Invention

[0019] The vortex mixing device of the present invention provides advantages over technically known vortex mixing devices. Such advantages include a reduction in the vertical dimension within the reactor (reduction of the reactor volume occupied by the in-bed distributor assembly), high throughput, enhanced mixing, reduced pressure loss, and an overall improvement in reactor performance. Specific embodiments and advantages will be apparent from the detailed description presented herein. However, it should be understood that the detailed description, drawings, and specific examples illustrate beneficial embodiments including some preferred embodiments, and are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0020] The present invention relates to a vortex mixing device for a multi-bed (multibed) hydrotreating reactor. A cross-sectional view of a portion of a multi-bed downflow reactor 10 is shown in FIG. 1. The reactor 10 includes a vessel shell 12 and upper and lower catalyst beds (14 and 16, respectively) containing packed catalyst extrudates. Each catalyst bed 14, 16 is supported on a grid screen assembly 18 (shown only for catalyst bed 14) composed of a support grid and optionally a space cross and a screen, all of which are technically well-known. The grid screen assembly is attached horizontally to the inner wall 22 of the reactor vessel and is attached to parallel support beams 20 that extend upward to the catalyst bed 14.

[0021] An in-bed dispersion assembly 24 is disposed vertically between the catalyst beds 14, 16. The in-bed dispersion assembly 24 includes the vortex mixing device 26 of the present invention. The mixing device 26 is attached below the catalyst bed 14 and is in fluid communication in a fluid-tight manner with a collection plate 28 configured to receive and mix the liquid and gas flowing down from the upper catalyst bed. A cooling gas inlet pipe 30 distributes a cooling gas (e.g., hydrogen) to the region above the mixing device 26.

[0022] Figure 2 is a cross-sectional view of the mixing device 26, Figure 3 is a perspective view of half of the mixing device 26, i.e., part 26a, and Figure 4 is a top view of the mixing device 26. Figure 4A shows another top view of the mixing device, showing holes 74 provided in the top plate and distributed across the top plate.

[0023] The mixing device includes a base plate 32 having an inner surface 32a and mounted to be fluid-sealed to a collection plate 28 (Figure 1), and a top plate 34 having a top plate inner surface 34a extending substantially horizontally to the base plate 32. The top plate may include holes 74 in the plate distributed across the top of the mixing device to allow gas entry, as shown in Figure 4A. The collection plate 28 collects the fluid that flows down from the catalyst bed above.

[0024] Multiple vanes 36, arranged alternately (in a staggered pattern), facing inward, or more specifically, curved inward, are fixedly mounted between the inner surface 32a of the base plate and the inner surface 34a of the top plate, extending perpendicularly between the inner surface 32a of the base plate and the inner surface 34a of the top plate. The vanes 36 preferably communicate fluidly with the inner surface 32a of the base plate and the inner surface 34a of the top plate. The number of vanes is typically 3 to 8, preferably 4 to 6. As shown in Figures 4 and 4A, the number of vanes may be 6, and the vanes are distributed over a region extending from the outer periphery of the base plate to the base plate opening 46. The vanes may be straight or curved, preferably curved inward (Figure 4).

[0025] As shown in Figure 4, each vane has an outer end 38 attached adjacent to the outer periphery of the top plate 34 and an inner end 40 located adjacent to the mixing region of the mixing device 26 (described later herein). The open spaces between the vanes 36 define a series of mixing device inlet regions 42, each inlet region 42 defined as a region demarcated by adjacent vanes 36 and their respective inner ends 38 and outer ends 40.

[0026] The collection plate 28 includes an opening 60 defined by its edge and a riser (upright portion) 62 located adjacent to the collection plate opening 60, the riser 62 extending away from the collection plate 28 into the mixing area. The riser 62 has an upper edge 64 and is located within the mixing area. The mixing region of a mixing device is defined as the region between the top plate and the base plate, excluding the region that defines the inlet region. The riser height is typically 25–75% of the distance between the top plate and the base plate. As shown in Figure 6, the collection plate opening and the riser may be circular, and the riser is referred to as the riser tube. The riser typically includes upper edge slots 58 that are spaced apart around the upper edge of the riser (Figures 2 and 7). Each collection plate opening 60 has a diameter 60a (Figure 2).

[0027] During operation, a hydrocarbon-based liquid feed falls from the catalyst bed 14 through the grid screen assembly 18 to the annular collection plate 28. The gas from the upper catalyst bed 14, mixed with a cooling gas (e.g., hydrogen gas) introduced via the cooling gas introduction pipe 30, fills the gap between the liquid collected on the collection plate 28 and the catalyst bed 14.

[0028] The liquid and gas enter the mixing device 26 through the mixing device inlet region 42, where the vanes 36 tangentially orient the liquid and gas so that they flow in an arcuate or circular flow pattern as they enter the mixing region of the mixing device 26. The liquid and gas flow over the riser tube upper end 64 into the riser tube 62. The gas and liquid are mixed to some extent and flow downward from the riser tube 62 into a tray, typically containing multiple perforations, descending tubes, or nozzles, and then into the catalyst bed 16 below. The inner surface of the riser 62 typically includes a perforated helical plate to further improve gas / liquid mixing as it flows downward within the riser 62.

[0029] The mixing device 26 described herein is intended for use in large hydrogenation reactors designed to process thousands or tens of thousands of barrels (1 barrel = 43 gallons; 164 L) of raw materials per day. Typically, the mixing device 26 may be several feet in diameter and may weigh several hundred pounds (lbs) when fabricated, depending on the material used to construct the device 26 (e.g., 1 / 4 inch to 1 / 2 inch steel plates).

[0030] The mixing device 26 of the present invention can be manufactured on-site by welding or otherwise attaching individual components to each other to achieve the manufacture of the final device 26. On-site manufacturing of the device 26 using this method may take several days, delaying the operation of the reactor unit. When the device 26 is used to update or improve the design of an existing reactor, it is desirable to reduce the amount of assembly performed inside the reactor vessel (due to safety concerns such as the possibility of ignition of residual hydrocarbon material remaining in the reactor).

[0031] To reduce the time required to manufacture a new reactor or to improve an existing one, parts of the mixing device 26 are preferably pre-assembled to form subassemblies, and these subassemblies are inserted into the reactor and assembled to form the final mixing device 26.

[0032] In one embodiment shown in Figures 2, 3, and 4, the mixing device 26 is formed from two mixing device subassemblies 26a and 26b, each representing half of the mixing device 26. Each subassembly 26a and 26b comprises one or more lift lugs 66 and 68. The lift lugs 66 and 68 are provided for attaching each subassembly 26a and 26b to a hoist, crane, or other device that can lower the subassemblies into the reactor and move them to a predetermined location.

[0033] Each subassembly 26a, 26b comprises a pair of flanges 70 and 72, respectively, which include multiple openings into which a combination of nuts / bolts (or such other suitable fastening devices) can be inserted to hold the subassemblies 26a, 26b immobile during operation, and the subassemblies 26a, 26b can be disassembled to allow access to the areas above and below the mixing device 26 during maintenance during operation. The mixing device 26 can be mounted to the collection plate by aligning the slots around the base plate 32 with the mounting points 76 on the collection plate.

[0034] The arrangement of the inwardly curved vanes 36 is shown in Figure 5. Circle R1, representing the outer diameter of the mixing device 26 as defined by process fluid calculations used by those skilled in the art, is shown together with circle R3, representing the inner diameter of the mixing device inlet region 42, also defined by process fluid calculations. Circle R2 is located at half the radial distance between R1 and R3.

[0035] The angle "A" in Figure 5 represents the angular offset between the outer end of one vane and the inner end of an adjacent vane, which results in a radial "overlap" between the inner end 40 of the vane and the larger diameter portion of the outer end 38 of an adjacent vane (see Figure 4). While not necessarily limited to a specific value, an appropriate value for angle A may be 15° in a 4-vane system, 10° in a 6-vane system, and 8° in an 8-vane system. The angle "B" represents the radial distance occupied by the vane 36 in the region between R1 and R3. A typical value for angle B is 360° / (number of vanes), but it is not limited to this. At angle "A", the inner surface of vane 36 intersects with R1. At an angle equal to the sum of angles "A" and "B" (A+B), the inner surface of vane 36 intersects with R3. At an angle equal to A+B / 2, the inner surface of vane 36 intersects with R2.

[0036] The distance "D" between adjacent vanes in the overlapping region (i.e., the distance R1-R3 in Figure 5) can be varied to define the inlet region 42 (Figures 4 and 5). In one aspect of the present invention, the distance "D" is greater than that of prior art vortex mixing devices, and in particular greater than that of the mixing device described in U.S. Patent No. 9,079,141. Preferably, "D" is at least about 5%, more preferably at least about 10%, greater than that of such prior art devices.

[0037] The above description of embodiments of the present invention is primarily illustrative, and it should be understood that numerous variations are available that still capture the essence of the invention. In determining the scope of the invention, refer to the appended claims.

Claims

1. Upper and lower catalyst beds housed within a reactor shell having an inner surface, A floor-to-floor distributed assembly inserted between the upper and lower catalyst floors. A multi-bed downflow type catalytic reactor having, The aforementioned inter-floor distributed assembly is A mixing device, a) A top plate having an inner surface and an outer surface, b) A base plate extending parallel to the top plate, having an inner surface, an outer periphery, and a base plate opening, wherein the top plate and the base plate are separated by a predetermined distance to define the internal region of the mixing device, c) A plurality of inward-facing vanes housed within the internal region of the mixing device, extending perpendicularly to the inner surface of the top plate and the inner surface of the base plate, and inserted between the inner surface of the top plate and the inner surface of the base plate, wherein the plurality of inward-facing vanes are directed inward from the outer periphery of the top plate and the base plate toward the base plate opening, and are spaced apart over a region extending from the base plate opening toward the outer periphery of the top plate and the base plate, d) Mixed region and A mixing device having a base plate and no weir ring extending from the inner surface of the base plate, nor a bubble cap extending from the inner surface of the top plate. It has, A multi-bed downflow catalytic reactor, wherein the mixing device is mounted above a collection plate and is in fluid-sealed contact with the collection plate, the collection plate having a collection plate opening and a riser extending from the collection plate adjacent to the collection plate opening, the riser extending through the base plate opening to the mixing region of the mixing device.

2. The reactor according to claim 1, wherein the base plate opening, the collection plate opening, and the riser are each circular, and the diameter of the base plate opening is greater than the diameter of the riser.

3. The reactor according to claim 1, wherein the vanes are straight or curved.

4. The reactor according to claim 3, wherein the vanes are curved inward.

5. The reactor according to claim 1, wherein each vane of the mixing device has an outer end adjacent to the outer periphery of the top plate and an inner end adjacent to the mixing region, and the mixing device further has a plurality of inlet regions defined as regions defined by adjacent vanes and the corresponding inner and outer ends of each vane.

6. The reactor according to claim 5, wherein the mixing region of the mixing device is defined as the region between the top plate and the base plate, excluding the region defining the inlet region.

7. The reactor according to claim 5, wherein the inner end of each vane overlaps radially with the outer end of an adjacent vane.

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