MXPA01005743A - Method and apparatus for contacting of gases and solids in fluidized beds - Google Patents

Abstract

A gas-solid fluidized bed is formed within a contacting element (10) having pairs of planar portions (14) arranged in intersecting planes, each planar portion (14) being formed by one or more webs (16) and one or more open slots (18) adjacent each web, the webs (16) and slots (18) being arranged such that a web in one of the planar portions (14) intersects a slot (18) in the paired planar portion. The fluidized bed can be catalyst particles fluidized by a gas stream, such as in a catalyst stripper and/or regenerator in an FCC system.

Description

METHOD AND APPARATUS FOR CONTACT BETWEEN GASES AND SOLIDS WITHIN FLUIDIZED BEDS Background of the Invention This invention relates generally to fluidized beds in which solids and fluids flow in a countercurrent relationship and more particularly, to the use of internal structures to facilitate contact between solids and fluids within the fluidized bed. Fluidized beds are often used in petroleum, chemical, combustion and other processes to promote vigorous mixing and intimate contact between fluid streams and solid particles within a container. This intimate contact can be used to obtain an efficient heat transfer, mass transfer and / or chemical reaction between the fluid streams, the solid particles and / or the fluids coated on, or entrained with the solid particles. Fluidized beds are typically generated by passing the fluid stream, typically a vapor current, upwards Ref: 129724 and through a bed of small solid particles, at a flow rate sufficient to suspend the particles and cause a turbulent mixing of the solid particles. The lower limit of the fluidized bed is formed at or just below the level of the fluid intake. The upper limit varies in relation to the velocity of the fluid stream and is formed at the level where the fluid is separated from the particles. The flow velocity of the fluid is maintained above which, it causes the suspension of the solid particles and below which, causes the particles to be transported outside the container or above the level of the desired upper limit. In some types of fluidized beds, the solid particles remain suspended in the fluidized bed and there is no net downward flow of the solid particles. In other types of fluidized beds, the solid particles are continuously added from above and removed from the bottom of the fluidized bed, such that there is a downward flow resulting from solid particles, in countercurrent to the fluid flowing upwardly. In both types of fluidized beds, it is generally desirable to reduce the channeling of the fluid through the solid particles and the formation of stagnant zones of fluid or solid particles within the fluidized bed. It may also be desirable, particularly in the case of countercurrent fluidized beds, to reduce the recirculation and back-mixing of the solid particles and the fluid within the fluidized bed, caused by the negative effect the backmixing may have on the efficiency of the process in particular, that is occurring within the fluidized bed. An example of a fluidized bed that involves the countercurrent flow of fluid streams and solid particles, is found in certain types of depleting and regenerators used in fluid catalytic decay systems or FCC. In such FCC systems, hydrocarbons with intermediate and high boiling points are atomized and contacted at high temperature with fluidized catalyst particles within a reactor in which the hydrocarbons are disintegrated to produce reaction products of a lower boiling point, such as gasoline. The reaction products and catalyst particles are then separated, such as within a centrifuge, and each proceeds separately for further processing. The catalyst particles are typically removed from the reactor in a continuous manner and are subjected to further processing, first within a stripping catalyst to remove the volatile hydrocarbons and then into a regenerator to remove the non-volatile carbonaceous material, called coke, which is deposited on the catalyst particles during the reaction process and reduces the effectiveness of the catalyst. In the exhausting catalyst, adsorbed and interstitial volatile hydrocarbons, entrained, are removed from the catalyst within a fluidized bed by means of contacting the catalyst concurrently with a stream of influent gas, such as water vapor, within a process referred to as "depletion". The removal of these residual hydrocarbons from the catalyst is desirable since the hydrocarbons can be recovered and returned to the process as a reaction product, instead of being transported together with the catalyst particles to the regenerator, where they could be combusted, causing with this an increase in the demand of the air for the regenerator. The combustion of residual hydrocarbons within the regenerator can also contribute to catalyst degradation by exposing the catalyst to elevated temperatures. The catalyst particles leave the depleting and then are directed to a regenerator where the deposits of coke and any other residual hydrocarbon are burned by passing the catalyst particles through a fluidized bed in countercurrent to an oxidation gas, typically air, within a process referred to as regeneration. The regenerated catalyst particles are then returned to the reactor for further catalytic disintegration of the hydrocarbons. In these fluidized beds found in the FCC depleting and regenerating, it may be desirable for all catalyst particles and fluid streams to pass through the fluidized beds in a fully countercurrent manner, without channeling or backmixing, and with all catalyst particles. and gas streams passing through the fluidized beds within the defined time intervals, a condition known as piston flow, in order to obtain better and more predictable efficiencies in the processes. It has been reported that devices such as random packages, which have been used to address the condition of piston flow in gas and liquid systems flowing in countercurrent, do not necessarily work well in solid and gas particle systems, since the particles solid ones can be housed in non-aerated stagnant areas within the package. It has also been reported through trial and error, that some grid-type gaskets, such as V-shaped, or disk-and-ring, have proven to be relatively effective in retarding the top-to-bottom mixing ratio of bed solids. well fluidized. However, these grid-type gaskets can reduce the amount of fluids and solids that can pass through the fluidized bed, since gaskets force fluids and solids to flow through contracted flow paths. In addition to reducing flowability, packaging often has poor "reverse" behavior, since they offer only acceptable processing efficiency within a limited range of flow rates. Additionally, these gaskets can allow large gas bubbles to form inside the fluidized bed with several undesired consequences, including reducing the contact efficiency between the steam and the solids, increasing the back-mixing of solids by means of the upward displacement of particles. solids caused by the gas bubbles and increase the entrainment of solids within the dilution phase above the fluidized bed, as a result of which the large gas bubbles burst upwards, through the fluidized bed. As a result, the need has evolved for a packing-type element that restricts a smaller part of the cross-sectional flow area of the fluidized bed, which performs well over a wider range of gas flow ratios and that reduces the formation of large gas bubbles within the fluidized bed. Static mixing elements consisting of rigid shapes, are conventionally used for purposes such as obtaining thorough mixing, mass transfers, heat transfers or chemical reactions, in streams of tributaries flowing concurrently through a pipe, a vessel or any other conduit. These elements can take many forms, although typically they use stationary deflectors that divide, cut and then recombine fluid currents or fluids and solids, until a generally homogeneous current exists. Static mixers are typically of a special design for specific use applications, such as those involving, either, a concurrent flow of liquid-liquid, solid-liquid or solid-gas, since a good behavior in a type of application, does not necessarily mean that the static mixer will behave well or even acceptable in other applications. It has been suggested that a type of static mixing element, commonly known as an SMV element, can be used in liquid-solid bed fluid to obtain higher concentrations of solids under certain liquid flow conditions. The SMV element comprises a group of corrugated sheets that are positioned in such a way that the corrugations of adjacent sheets are in contact and extended at an angle to one another, thereby forming flow paths of liquids and solids along ridges and corrugation valleys. . The effect of the SMV element on the backmixing of solids and the convenience of the element for use in gas-solid fluidized beds, instead of liquid-solid, has not been reported. It has also been suggested in U.S. Patent No. 5,716,585, that corrugated packaging sheets, such as modified SMV elements, can be used to facilitate the depletion of solids in gas-solidified fluidized beds. In this patent, the use of corrugated packaging sheets within exhaustion units is specifically described for use in spent FCC catalysts. However, the impermeable nature of the corrugated sheets blocks the passage of gases and solids through the sheets, and may serve as an impediment to the desired exchange between the depleting gas and the hydrocarbons associated with the catalyst particles. Another type of static mixing element is described in U.S. Patent No. 4,220,416 assigned to Bra uner et al. The element described in this patent comprises pairs of flat portions configured in a separate relationship in the perpendicular planes and joined together along a connecting column, with a plurality of flat portions in pairs, being typically placed from one end to the other, inside a pipe or any other conduit. Each planar portion comprises at least one mesh, and typically two or more meshes that are spaced apart to provide open slots through which substances can flow to mix. Although they are also used for other applications, these types of elements have proven to be particularly useful in mixing polymer composites that flow in a concurrent laminar flow. To date, there have been no reports suggesting the applicability of these elements for use in fluidized beds.

Brief Compendium of the Invention It is an object of this invention to provide a fluidized bed with a contact element that reduces the back-mixing of solids and gases within the fluidized bed, so that a higher degree of piston flow and higher processing efficiency can be obtained in comparison to many types of conventional elements. It is also an object of this invention to provide a vapor-solid fluidized bed with a contact element that reduces the size of the gas bubbles formed within the fluidized bed, such that more gas surface area is available to make contact with. solids within the fluidized bed, with resulting increases in processing efficiency. J It is another object of this invention to provide a vapor-solid fluidized bed with a contact element that provides a more homogeneous distribution of smaller gas bubbles, of more uniform sizes, than those resulting from the use of many types of conventional elements. , such as disc and ring elements, so that greater processing efficiency and reduced vapor carryover of solid particles can be obtained. It is still another object of this invention to provide a fluidized bed with a contact element that allows a high processing efficiency to be obtained, while restricting a much smaller portion of the cross-sectional area of the fluidized bed, compared to many. conventional types of elements, such as disk and loop elements, in such a way that a fluid and a higher solids flow capacity can be maintained for the fluidized bed. It is a further object of this invention to provide a fluidized bed with a contact element that allows a high capacity and processing efficiency over a wide range of surface gas velocities, such that the contact element can be used in Applications that have a wide variety of gas speeds. To accomplish these and other related objectives of the invention, a contact device, such as the general type described in US Pat. No. 4,220,416, which is incorporated herein in its entirety for reference, is placed in a fluidized bed gas-solid inside a container. The contact device comprises one or more bypass portions in pairs, each bypass portion being typically, but not necessarily, planar and comprising a plurality of separate meshes extending at an acute angle along all or a portion of the cross section of the fluidized bed. The offset portions in pairs are linked together and form an angle that is typically 60 or 90 degrees, although other angles could be used if desired. Open slots formed between the meshes within each bypass portion allow the flow of gas and solids therethrough. It has been unexpectedly discovered that the use of this type of mixing device within fluidized gas-solid beds, provides greater flow capacity and overall efficiency, compared to corrugated sheets and disc and ring trays.

Brief Description of the Drawings In the accompanying drawings, which are part of the specification and should be read in conjunction with it and in which similar reference numerals are used to indicate similar parts in the different views: Fig. 1 is a schematic view of a column showing a fluidized bed containing a contact element in accordance with the present invention; Fig. 2 is a schematic view of an FCC system employing the contact element of the present invention; and Fig. 3 is a graph comparing the total depletion efficiencies of the contact element of the present invention with another contact element.

Detailed description of the invention Referring now in greater detail to the drawings, and initially to FIG. 1, a contact element used in the present invention is designated generally by the numeral 10 and is shown in a certain schematic way placed inside a cylindrical container or column 12. Column 12 is a container having a square, rectangular or other cross section and is constructed of appropriate materials compatible with processing occurring within an open, inside region within an outer shell of the column. Column 12 can be used for various types of fluidized bed processing of gases and solids, such as processes involving heat exchange, mass transfer and / or chemical reaction. For example, column 12 can be used to deplete hydrocarbons from spent catalysts or to regenerate spent catalysts by burning coke from the spent catalyst within fluid catalytic decay (FCC) processes. As other examples, column 12 can be used to effect the exchange of heat between gases and hot catalysts in FCC processes and other processes, to purify pollutants from combustion gases, to burn coal or other fuel in generation processes. electrical energy, to cause the drying of solid particles and to cause the incorporation, the coating or the agglomeration of solid particles. It is not intended that these examples limit the scope of the invention, but are established to illustrate the particular embodiments of the invention. The contact element 10 comprises a plurality of bypass portions in pairs 14, each bypass portion 14 comprising at least one, and usually a plurality, of separate meshes 16 extending at an acute angle along the whole, or a portion of the cross section of the fluidized bed. Open grooves 18 are formed between or adjacent the meshes 16 within each diverting portion 14, to allow the flow of gases and solids therethrough. The meshes 16 themselves may be perforated to allow fluid to flow through the meshes. The deviation portions in pairs 14 extend in intercepted planes and are joined together, either at one end or at an intermediate portion along their length. The meshes 16 within each deviation portion 14 are aligned to intersect the grooves 18 formed in the deviation portion in pairs 14. The angle formed by the intersecting deviation portions 14 is typically 60 or 90 degrees, although they may be used. other angles if desired. The meshes 16 that are inside each deviation portion 14, will typically lie in the same plane, although they may extend in different planes if desired. Instead of being essentially flat, the meshes 16 can also be constructed in curved form or any other desired shape.

Several bypass portions in pairs 14 are joined together in an aligned, interconnected and intersected manner to form each contact element 10. A number of contact elements 10 can then be placed from one end to the other in a separate or contacting relationship. with column 12. Adjacent elements can be placed in alignment or they can be rotated at an angle to each other, such as 45 °, 90 ° or any other desired angle. The angle formed by the plane of each diverting portion 14 and a longitudinal axis of the column 12, varies depending on the intersecting angle selected for the bypass portions in pairs. For example, when an intersection angle of 90 ° is used, the diverting portions 14 extend at angles of 45 and 135 degrees with respect to the axis of the column. When an intersection angle of 60 degrees is selected, the diverting portions 14 extend to 60 and 120 degrees with respect to the axis of the column. The contact elements 10 can each have such a size to completely fill the cross section of the column 12, or a number of smaller elements 10 can be placed in a side-to-side relationship to fill the cross section of the column. When placed in a side-to-side relationship, the elements 10 can be oriented in the same or in different directions and can be placed within a plurality of rows displaced from each other. According to the present invention, a fluidized bed 20 is formed in the portion of the column 12, in which the contact element is placed, or a plurality of contact elements 10. The fluidized bed 20 is formed by solids, in particular represented schematically by the arrows 22 and a fluidized gas q? e flowing upwards, represented by the arrows 24. The solids 22 are of a previously selected shape, size and composition of the particle and the gas 24 of a composition and speed previously selected Preferably, the solids 22 will be added from the top and withdrawn from the bottom of the fluidized bed 20 in a continuous manner, such that the solids 22 and the gas 24 travel in countercurrent through the fluidized bed. Alternatively, the solids 22 remain in the fluidized bed 20 until the processing has been completed and are then drained from the fluidized bed. The gas 24, after traveling up through the fluidized bed 20, enters a dilution phase above the fluidized bed and can be passed through a separator, such as a centrifuge (not shown) to remove any solid particles. dragged, before it is transported to a final or intermediate destination. The solids 22, after being removed from the fluidized bed 20, can also be transported to a final or intermediate destination. The contact element 10 can be placed in a desired vertical location within the fluidized bed 20. In some applications, it may also be desirable to place the element 10, or a plurality of elements 10, near the upper and lower limits of the fluidized bed. , while in other applications it may be desirable to place the elements at a previously selected distance from the boundaries. Even in additional applications, the elements 10 may extend above, or even below, the fluidized bed 20. The type of processing that occurs within the fluidized bed 20 may include heat transfer, mass transfer, combustion and / or reaction chemistry. For example, the fluidized bed 20 can be used to deplete hydrocarbons from spent catalysts or burnt coke deposits on spent catalysts in FCC systems. An FCC system employing contact element 10 is illustrated in Fig. 2, in which volatile hydrocarbons are exhausted from depleted solid catalyst particles (represented schematically by arrow 28) in a strenuous column 26, before that the catalyst particles are transported to a regenerator 30, where the coke deposits are burned to regenerate the catalyst particles. The exhaust column 26 has a central lifting tube 32 which supplies depleted catalyst particles in a transport gas stream within the open internal region of the column 26. The catalyst particles then flow downwards, under the influence of gravity inside and Through the contact element 10. Steam or any other exhaust gas is fed through the flow line 34 to the column 26 at a location below the contact element and flows upward to cause the fluidization of the catalyst particles in the contact element 10 and resulting in the depletion of volatile hydrocarbons associated with the catalyst particles. Since the catalyst particles are fluidized during this contact with the gas stream, a high degree of piston flow and higher processing efficiency can be obtained., compared to conventional depletion processes.

The overhead gas stream containing the depleted volatile hydrocarbons can be routed from the stripping 26 to the FCC reactor (not shown) or to any other desired location through the flow line 35. The depleted cata particles are transferred. by means of another flow line 36 from the stubborn 26 to the regenerator 30, where they flow downward through another contact element 10. Air or any other oxidation gas is fed through the flow line 38 towards a burner 40 placed in a lower portion of the regenerator, to a location below the contact element 10. The coke deposits on the cata particles are burned as long as the cata particles are fluidized within the contact element 10, with the resulting regeneration of the cata particles. The cata particles can then be returned through the flow line 42, to the exhaust 26, or they can be routed to the FCC reactor (not shown). The combustion gas above is routed through the flow line 44 to a scrubber (not shown) or is processed in another way. Centrifugal separators 46 are used, both in the regenerator 30, and in the exhaust 26 to remove cata particles entrained from the upper gas streams. The contact element 10 can also be used as an exchanger, by forming the meshes 16 as a double wall, in such a way that the heat exchange medium is able to flow inside the meshes 16 for the exchange of heat with a surrounding medium. As an example of this type of use, the ends of the meshes 16 can extend through the column 12 and be connected to a manifold-head that distributes a fluid towards the meshes 16, for which they circulate through them. Another means, such as an affluent or static solid, or any other fluid, surrounds the meshes 16 and undergoes an exchange of heat with the secreted fluid circulating within the meshes 16. It has been discovered that the contact element 10 provides a good unpredictable behavior in gas-solid fluidised beds. In a series of comparative tests involving the use of air to exhaust helium from an FCC balance cata, the contact element 10 demonstrated a higher flow capacity up to 20%, compared to the disc and ring trays, and a higher total depletion efficiency in comparison, both to the disc and ring trays, and to the corrugated packing elements of the SMV type. The reasons why the contact element 10 has an unexpectedly good behavior in gas-solid fluidized beds are not fully understood, but it is believed that it results in part because the intersecting meshes 16 provide catch points that block the upward displacement. and the recirculation of solids 22. By reducing this recirculation or backmixing, the solids 22 are able to advance downwardly through the fluidized bed 20, in a uniform manner, approaching the piston flow. The numerous intersecting meshes 16 also reduce the size of the gas bubbles that may be formed in the fluidized bed 20 and contribute to a more even distribution of the small gas bubbles. These small gas bubbles provide a larger surface area for gas contact with solids 22 and so on, resulting in efficiency increases. Additionally, small gas bubbles are less likely to cause upward displacement of solids and these reduce the amount of solids that are entrained along with the gas and that must be separated from it, which is in a dilution phase by above the fluidized bed 20. The uniform distribution of gas and solids also reduces the formation of stagnation zones that could reduce operating efficiencies. Notably, the increased efficiencies that can be obtained with the contact element 10 are obtained over a wide range of surface gas velocities and can be obtained without reducing the flow capacity of gases and solids to an undesired level. The following example is constituted to illustrate the invention and should not be interpreted in a limiting sense.

Example 1 A series of different packing elements were tested to determine depletion efficiencies using air to deplete helium from an FCC equilibration catalyst within a dynamic cold flow column. Two embodiments of contact elements of the present invention were tested having deflecting portions 14 configured at an angle of 60 ° with respect to the vertical axis of the column. In the first embodiment, the diamond pattern formed by the deviation portions at intersection 14 had dimensions of 19 cm (7.5 inches) high by 11 cm (4.33 inches) wide. The corresponding dimensions of the second modality were 12.7 cm (5 inches) high by 7.35 cm (2.88 inches) wide. The contact elements were tested against the corrugated sheets that have a height in their fold of 6.35 cm (2.5 inches) with a corrugation angle of 60 ° and a baffle plate and disc type baffles. The results of the tests were then analyzed using a stepwise efficiency model in which a disk tray was equal to one stage. The results analyzed are described in Fig. 3 and it can be seen that the contact elements 10 behaved significantly, and even remarkably better than, both the corrugated sheets, and the disc and rim trays through the full range of speeds of gas flow. The contact elements 10 also demonstrated excellent behavior in the opposite direction. It is noted that, with regard to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (15)

2. Having described the invention as above, the content of the following is claimed as property. A gas-solid fluidized bed characterized in that it comprises: a container having a shell and an internal region open inside the shell; a contact device positioned within the open internal region and comprising pairs of flat portions configured in intersecting planes, each flat portion comprising one or more meshes and one or more open slots adjacent to each mesh, the meshes and the slots being configured of such that a mesh that is within one of the flat portions intersects a slot within the flattened portion; solid particles within the contact device; and at least one gas stream flowing in a first direction through the contact device and causing fluidization of the solid particles within the contact device. 2. The gas-solid fluidized bed according to claim 1, characterized in that it includes gas stream flow conduits in communication with the container, to direct the gas stream within the internal region open for flow through the container. contact device and withdrawing the gas stream from the container, after the flow passing through the contact device.
3. 3. The gas-solid fluidized bed according to claim 2, characterized in that it includes solid particle flow conduits in communication with the container to direct the solid particles towards the contact device and remove the solid particles from the container after having passed to the container. through the contact device.
4. 4. The gas-solid fluidized bed according to claim 2, characterized in that the gas flow conduits and the solid particle flow conduits are configured to provide a countercurrent flow of the solid particles and the gas stream.
5. 5. The gas-solid fluidized bed according to claim 2, characterized in that the solid particles comprise catalyst particles.
6. 6. The gas-solid fluidized bed according to claim 5, characterized in that it is selected from the group consisting of a FCC catalyst scavenger and a FCC catalyst regenerator.
7. 7. A process for fluidizing solid particles within a container having a shell and a contact device positioned within an open internal region within the shell, characterized in that the contact device comprises pairs of flat portions configured in intersecting planes, each flat portion comprising one or more meshes and one or more open slots adjacent to each mesh, the meshes and the slots being configured in such a way that a mesh that is within one of the flat portions intersects a slot within the flat portion , the process comprising the steps of providing a quantity of solid particles within the contact device; and flowing at least one gas stream through the contact device and causing fluidization of the solid particles within the contact device.
8. 8. The process according to claim 7, characterized in that it includes directing the solid particles through the contact device, in a direction countercurrent to a flow direction of the gas stream.
9. 9. The process according to claim 8, characterized in that it includes providing additional quantities of solid particles within the contact device, while removing at least sof the fluidized solid particles from the contact device, while the gas stream is flowing to the contact device. through the contact device.
10. 10. The process according to claim 7, characterized in that it includes retaining the amount of solid particles within the contact device, while the gas stream is flowing through the contact device.
11. 11. The process according to claim 7, characterized in that the solid particles are catalyst particles associated with volatile hydrocarbons, and wherein during the step of flowing the gas stream through the contact device, at least some of the volatile hydrocarbons they are exhausted from the catalyst particles, by means of the gas stream, during fluidization.
12. 12. The process according to claim 11, characterized in that the gas stream comprises water vapor.
13. 13. The process according to claim 7, characterized in that the solid particles are catalyst particles containing coke deposits, including the step of burning the coke deposits to cause the regeneration of the catalyst particles during the step of flowing the gas stream through the contact device.
14. 14. The process according to claim 7, characterized in that during the fluidization of the solid particles that are inside the contact device, the meshes of the contact device prevent the flow of the solid particles in a flow direction of the gas stream.
15. 15. The process according to claim 7, characterized in that the processing, which is selected from the group consisting of one or more of the mass transfer, heat exchange and chemical reaction, occurs during the fluidization of the solid particles. .