Patent Application
20140183281
The present disclosure relates to a device for mixing and distributing a fluid uniformly over the cross-section of an adsorbent bed. The device resides between two adsorbent beds where the effluent from an upper bed is collected and mixed with a feed fluid and redistributed over the top of the lower bed.
The chemical and petroleum process industries use many types of vessels in processing and/or purifying chemicals. The processing and/or purifying often involves mixing fluids and passing a mixture of the fluids over an adsorption bed, a reactor bed, or passing the fluids over trays in a distillation column. One particular type of vessel is a multi-bed reactor, with co-current flow of a process fluid and a feed fluid. The multi-bed reactor includes a series of solid particulate beds of catalyst particles that catalyze a reaction involving a process fluid flowing over the beds. The efficiency and life of the catalyst bed are influenced by the distribution of fluid flowing over the bed. The feed fluid can be added as a reactant, or as a quench fluid, for a process stream that flows over a catalyst bed. Redistribution and mixing is important for maximizing the life of the catalyst bed, and maximum utilization of the catalyst by preventing dead zones, or zones in the catalyst bed having low flow.
Other types of vessels include counter-current flow reactors, separation vessels having co-current flow, or countercurrent flow. Many of these processes are affected by the manner in which a fluid to be reacted, separated, or otherwise processed, is distributed in the vessel.
One important type of process is the adsorption separation process. The adsorption separation process has been developed through simulated moving bed (SMB) technology, where the adsorption separation process can be operated on a continuous basis. The simulation of a moving adsorbent bed is described in U.S. Pat. No. 2,985,589 (Broughton et al.). In accomplishing this simulation, it is necessary to connect a feed stream to a series of beds in sequence, first to bed no. 1, then to bed no. 2, and so forth for numerous beds, the number of beds often being between 12 and 24. These beds may be considered to be portions of a single large bed whose movement is simulated. Each time the feed stream destination is changed, it is also necessary to change the destinations (or origins) of at least three other streams, which may be streams entering the beds, such as the feed stream, or leaving the beds. The moving bed simulation may be simply described as dividing the bed into series of fixed beds and moving the points of introducing and withdrawing liquid streams past the series of fixed beds instead of moving the beds past the introduction and withdrawal points.
There are many different process requirements in moving bed simulation processes, resulting in different flow schemes. For example, in addition to the four basic streams described in Broughton (U.S. Pat. No. 2,985,589), it may be desirable to utilize one or more streams to purge, or flush, a pipeline or pipelines. A flush stream is used to prevent undesirable mixing of components. The flush substance is chosen to be one which is not undesirable for mixing with either main stream, that being purged or that which enters the pipeline after flushing is completed. U.S. Pat. No. 3,201,491 (Stine et al.) may be consulted for information on flushing lines as applied to the process of Broughton (U.S. Pat. No. 2,985,589). In addition, the efficiency of the process has many factors, including the redistribution of fluid from one bed to the next, and the mixing and redistribution of a process fluid with one of the feed streams between two beds.
Improvements in the fluid distribution means of such adsorption separation systems can improve efficiency and increase the life of the adsorbents in the adsorption separation system. Accordingly, it would be an advance in the state of the art to provide a fluid distribution system that is capable of mixing and distributing a fluid uniformly over the cross-section of an adsorbent bed. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.
The present disclosure provides embodiments of a fluid distribution apparatus. In one embodiment, an exemplary fluid distribution apparatus includes a distributor pipe configured to carry a fluid and a continuously tapered, ring-shaped collar distributor connected to the distributor pipe. The collar distributor includes a first portion and a second portion, the first portion having a continuous height along its circumference, the continuous height being at least as high as a diameter of the distributor pipe, the second portion extending from either end of the first portion and having a height that continuously tapers along its circumference from a height that is equivalent to the height of the first portion to a second height that is smaller than the height of the first portion. The distributor pipe connects to the collar distributor at the first portion. The apparatus further includes a plurality of inlet nozzles connected to the collar distributor. The second height is at least as great as a diameter of one the plurality of inlet nozzles.
In another embodiment, an exemplary fluid distribution apparatus includes a distributor pipe configured to carry a fluid and a ring-shaped collar distributor connected to the distributor pipe. The collar distributor includes a first portion and a second portion, the first portion having a continuous height along its circumference, the continuous height being at least as high as a diameter of the distributor pipe, the second portion extending from either end of the first portion and having a height that is reduced along its circumference from a height that is equivalent to the height of the first portion to a second height that is smaller than the height of the first portion. The distributor pipe connects to the collar distributor at the first portion. The apparatus further includes a plurality of inlet nozzles connected to the collar distributor. The second height is at least as great as a diameter of one the plurality of inlet nozzles. Each of the plurality of inlet nozzles includes a reducer portion that is proximate to a connection point between the collar distributor and each such inlet nozzle.
In yet another embodiment, an exemplary fluid distribution apparatus includes a distributor pipe configured to carry a fluid and a continuously tapered, ring-shaped collar distributor connected to the distributor pipe. The collar distributor includes a first portion and a second portion, the first portion having a continuous height along its circumference, the continuous height being at least as high as a diameter of the distributor pipe, the second portion extending from either end of the first portion, the second portion including an inlet section and an outlet section, the inlet section including a concave up or upward sloping shape and the outlet section including a concave down or downward sloping shape. The second portion has a height that is reduced along its circumference from a height that is equivalent to the height of the first portion to a second height that is smaller than the height of the first portion. The distributor pipe connects to the collar distributor at the first portion. The apparatus further includes a plurality of inlet nozzles connected to the collar distributor. The second height is at least as great as a diameter of one the plurality of inlet nozzles.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The collar distributor and its associated assemblies will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Furthermore, as used herein, numerical ordinals such as “first,” “second,” “third,” etc., such as first, second, and third components, simply denote different singles of a plurality unless specifically defined by language in the appended claims. All of the embodiments and implementations of the collar distributors described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention, which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.
A wide variety of processes use co-current flow reactors, or reactors where there is a single phase fluid that flows over a solid bed of particulate materials, to provide for contact between the fluid and a solid. In an adsorption separation system, the solid usually includes an adsorbent material which preferentially adsorbs one or more components in a mixture. The adsorbed material is then removed from the adsorbent by passing a desorbent over the solid bed, and the desorbed component or components are collected. The fluid can be a liquid, vapor, or mixture of liquid and vapor.
Co-current adsorbers with fixed beds are constructed such that the reactor allows for the fluid to flow over the adsorbent bed. When the fluid is a liquid, the fluid is usually directed to flow downward through the adsorber. There are many aspects for providing good contact between the fluid and the solid. Multi-bed adsorbers are also frequently used where the adsorbent beds are stacked one over the other within an adsorbent vessel. Typically, they are stacked with some space between the beds.
With multi-bed adsorbers, the spaces between beds are convenient mixing zones. In addition to remixing fluids passing from one bed to the next, the spaces between beds are often used to add additional fluids, or to draw off fluids. This is particularly true for a simulated moving bed system, where the system has two feed streams and two draw-off streams. The feed streams are the process stream containing components to be separated and a desorbent stream, and the two draw-off streams are the extract stream containing the components that were preferentially adsorbed and a raffinate stream containing the components that were not preferentially adsorbed.
Apparatus for the distribution of a fluid in a vessel previously known in the art include a distribution means with a toroidal, or ring, shaped device with a rectangular cross-section, or box shape. This “distributor box” is connected to a feed pipe with a solid splash plate at the bottom of the box and outlet holes on the sides of the box. A feed stream enters the box through an inlet feed pipe and flows out through the holes on the sides of the box. The feed pipe may be connected to a distributor collar, the distributor collar being configured to deliver the fluid to a plurality of feed pipes. The distributor collar, in turn, is connected to a single distributor pipe that supplies the fluid to the distributor collar. The distributor box is in a mixing zone between adsorbent beds. The process stream enters the mixing zone wherein a baffle directs the process stream toward the distributor box and the process stream and mixes with the feed stream.
The distributor box has a series of holes above the baffle, and a series of holes below the baffle. The process stream impinges on the distributor box as it passes from above the baffle to below the baffle, and mixes with the feed exiting the holes above the baffle in a counter-current flow mixing and mixes with the feed exiting the holes below the baffle in a co-current flow mixing. The resulting mixture is then redistributed on the screen below the baffle. The splash plate is designed to prevent any jet flow introduced from the gap between the baffle and the distributor box, which reduces the risk of localized fluidization of a particulate bed that can cause fine particle generation.
A design previously known in the art, as outlined above, is described in connection with
The splash plate 42 can include apertures for allowing some of the mixture to pass through to the adsorbent bed below the lower screen 40. The percent open area of the splash plate 42 from the apertures is less than the percent open area of the lower screen 40. The apertures in the splash plate 42 are sized smaller than the apertures in the lower screen 40. The smaller open area, or smaller apertures, facilitates the distribution of the fluid mixture across the lower screen 40 for a more uniform passage through to the bed below the lower screen 40, while permitting a portion of the fluid mixture to pass through the splash plate 42. The apertures in the lower screen 40 and the splash plate 40 are sized to be sufficiently small to prevent the passage of adsorbent particles from below the apparatus.
The previously known design for the distributor box 20 is a toroidal shape, as noted above and as illustrated in
The apparatus can, optionally, further include a flow distributor plate 50 as best seen with reference to
The flow of the process fluid passes through the upper screen 10 and a first portion passes through the central part of the screen 10 that is located within the inner edge of the distributor box 20, and a second portion passes through the screen that is located between the outer edge of the distributor box 20 and the outer edge of the screen 10. The first portion and second portion are in substantially equal amounts to provide a balanced flow across the gaps 34 between the distributor box 20 and the baffles 30. This leads to the center of the distributor box 20 cross-section being positions at approximately 0.707 times radius of the upper screen 10.
The apparatus includes a plurality of inlets 12 for a more even distribution of the feed stream. Each of the plurality of inlets 12 is connected to a ring-shaped distributor collar 60. The distributor collar 60 receives a fluid flow from a single distributor pipe (not shown). The distributor collar 60 distributes the fluid flow from the distributor pipe to each of the inlets 12. The distributor collar is disposed around a centerpipe 70 of the vessel 100.
The upper screen 10 includes a region over the distributor box 20 where there is little or no flow across the screen 10 due to the distributor box 20 blocking that region. The upper screen can include a solid piece of material in that location, or a portion of the distributor box 20 can protrude above the screen 10. The upper portion of the distributor box 20 can be shaped to facilitate flow around the distributor box 20, such as a triangular shape for fluid to direct the process stream around the distributor box 20.
The apparatus includes the upper screen 10, which is fitted around the distributor box 20, baffles 30 which are positioned beneath the outlet ports 22 of the distributor box 20. The gap 32 can be sized to maintain a maximum flow of the mixture of the process stream and feed stream through the gap 32. The distributor box 20 can be designed to have a substantial aspect ratio of width to height, in order to maintain the outlet ports 22 positioned above the baffles 30 and to enable control in the sizing of the gap 32. The aspect ratio also can be used to maintain the flow conditions for the feed stream, while minimizing the overall height of the apparatus, or the upper screen 10, the distributor box 20, the baffles 30, and the lower screen 40.
Two known distributor box 20 designs will now be described briefly with regard to
In
For an apparatus including the distributor box design of either
Greater detail regarding the design of a previously known collar distributor 60 is presented with regard to
In some vessel designs, a significant pressure drop within the chamber has been observed, limiting their operation. The possible cause of this pressure build up is that high fluid velocities within the chamber cause adsorbent movement and corresponding attrition, which leads to accumulation of fine particles that collect on the grids. Local high velocities are typically observed on the top of the adsorbent bed, around the splash plate, and under the side lower screen. Grids are designed to account for these high local velocities, however, it is assumed that there is equal flow to each of the typical 28 baffle sections.
Previous computational fluid dynamics (CFD) experimentation in some designs has shown that some collar distributors have a maldistribution to the typical 14 nozzles (1 nozzle feeds 2 grid sections) up to 20% higher than the designed flow. These high flows will increase the surface velocity and promote movement of the adsorbent on the bed surface. The cause of flow maldistribution to the nozzles is the collar distributor's “stepped” configuration, as described above with regard to
The stepped collar distributor design was tested using theoretical modeling of the flows using computational fluid dynamics. A computational simulation of the process is shown in
Embodiments of the present disclosure are directed to an improved collar distributor that does not suffer the recirculation and back-mixing encountered in other designs. In the presently described embodiments, certain design modifications to the collar distributor ring and the inlet nozzle shown in
The continuously tapered collar distributor design 160 of the present disclosure is shown, in an exemplary embodiment, in
In a further aspect of the present disclosure, it is desirable to minimize the pressure drop in the vessel to reduce loads on the rotary valve. In order to decrease the distributor collar 160 pressure drop, in one embodiment, the distributor pipe 65 and the inlet nozzles 12 are modified from straight pipe configurations to pipes with reducers as shown in
Embodiments of the present disclosure result in a substantially reduced flow deviation. With regard to
In addition, embodiments of the present disclosure show improvement in the RTD. With regard to
Another embodiment of the present disclosure is depicted with regard to
To more closely match the flow distribution, variations of this design may be provided. The flow distribution may be determined by experimentation or computational modeling. In an embodiment, the concave up inlet section 262 can be designed so as to be straight, thereby increasing the cross-sectional area (CSA) for the flow. In an embodiment, the concave down outlet section 263 can be a relatively flat section, thereby decreasing the CSA. In an embodiment, the transition zone (the region adjoining sections 262 and 263), in the case of the contoured section, passing through the point of inflection, can be a relatively steep straight section, thereby reducing the CSA. In an exemplary design, the CSA within the Collar is provided so as to match the loss of flow through the outlet.
The design depicted in
Accordingly, embodiments of an improved collar distributor for use in distributing a fluid have been described. It will be appreciated that the described embodiments of the collar distributor change the design of the collar ring from a stepped configuration to a continuously tapered configuration. This design change results in improved fluid flow distribution to the inlet nozzles, therefore reducing the fluid velocity over the adsorbent bed and preventing particle collisions and attrition. The design change further results in an improved RTD and a reduced liquid dispersion, which is expected to improve the vessel performance. It will further be appreciated that the described embodiments of the collar distributor change the design of the inlet nozzles and the distributor pipe from straight pipes to pipes with reducers proximate the collar ring to further decrease the pressure drop, which is expected to minimize the pressure loads on the rotary valve.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the processes without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of this disclosure.
