CN101535756A - System for fluidizing solid particles comprising a novel vessel outlet - Google Patents

Abstract

The present invention provides a system for fluidizing solid particles, comprising a fluidized bed vessel, a fluidized bed section, a disengagement section, a recycle line, and a tapered outlet. The present invention also provides a method of fluidizing solids by providing the above system, fluidizing a bed comprising solid particles, and withdrawing a recycle stream through a tapered outlet.

Description

System for fluidizing solid particles including novel vessel outlet

Cross References to Related Applications

This application claims priority to Serial No. 60/860,166, filed November 20, 2006, the disclosure of which is incorporated herein by reference.

technical field

The present invention relates generally to fluidized bed systems, and more particularly to gas phase fluidized bed systems with reduced solids entrainment in a recycle stream.

Background technique

Fluidization of solids involves "suspension" of a bed of solid particles in a gas stream ascending through the fluidized bed. Fluidized bed vessels are used in various processes such as olefin cracking and polymerization processes. One of the most economical and common methods of making polymers uses gas phase polymerization in fluidized bed reactors.

Generally, in gas-phase fluidized bed processes for the preparation of polymers from monomers, a gaseous stream comprising one or more monomers is passed continuously through a fluidized bed under reactive conditions in the presence of a catalyst. This gaseous stream is withdrawn from the fluidized bed and recycled back to the reactor. Simultaneously, polymer product is removed from the reactor, and new monomer is added to replace the already polymerized monomer. The recycle gas stream is heated in the reactor by the heat of polymerization. This heat is removed in another part of the cycle by a cooling system external to the reactor.

It is understood that the amount of polymer produced by a fluidized bed polymerization process is directly related to the amount of heat that can be extracted from the fluidized bed reaction zone, since the heat released by the reaction is directly proportional to the rate of polymer formation. In steady state operation of a reaction process, the rate of heat removal from the fluidized bed necessarily equals the rate of heat generation, so that the bed temperature remains constant. Typically, heat has been removed from the fluidized bed by cooling the gas recycle stream in a heat exchanger outside the reactor.

One requirement of the fluidized bed process is that the gaseous recycle flow is sufficient to maintain the reaction zone in a fluidized state. In a conventional fluidized bed polymerization process, the amount of circulating fluid used to remove the heat of polymerization is greater than that required to support the fluidized bed and to thoroughly mix the solids in the fluidized bed. Excessive velocity allows additional gas to flow to or through the fluidized bed, resulting in additional cooling capacity and enhanced mixing in the reactor bed. However, in order to prevent excessive entrainment of solids in the gas withdrawn from the fluidized bed, the velocity of the gaseous stream must be adjusted.

Conventional gas phase fluidized bed reactors used in polymerizing olefins and/or dienes comprise a fluidized dense phase bed and a freeboard above the dense phase surface (bed height). The dilute phase mainly includes gas and a small amount of particles (especially fine particles). The dense bed is usually, but not always, maintained in the columnar straight section of the reactor. The dilute phase section is located above the dense phase bed. The dilute phase section (or disengagement section) is usually larger in diameter, also known as the expansion section, and is used to reduce the gas velocity and thereby reduce the amount of fine particles carried out of the reactor and into other parts of the reaction system. The expansion section generally consists of a conical section and a hemispherical top cover of the reactor. The reactor outlet is located on top of the hemispherical top.

During operation of the reactor, the gas mixture exits the top of the fluidized bed vessel through an outlet located in the top cover of the fluidized bed vessel. The gas mixture is passed back to the inlet of the fluidized bed vessel via a recycle loop or recycle line. The recycle loop includes other equipment necessary to operate a fluidized bed process, such as recycle compressors or pumps and recycle coolers. As the gas mixture leaves the top of the fluidized bed vessel, fine particles present in the disengagement section, especially near the reactor outlet, can be entrained by the gas mixture and circulated through the circulation loop by the recirculation flow. The recycle stream exits the reactor outlet, passes through the equipment in the recycle loop and re-enters the reactor near the bottom of the fluidized bed vessel. After re-entering the fluidized bed vessel, the recycle gas or gas/liquid stream typically flows back to the fluidized bed through a gas distributor.

Entrained fine particles in the recycle loop can lodge in equipment in the recycle loop, such as recycle compressors or recycle coolers, causing various quality and operational problems. These fine particles promote undesired polymer growth and foul the surfaces of recycle lines, recycle coolers, compressors, reactor head undersides and distribution plates, leading to undesired reactor shutdowns for system cleaning. Adhered particles in a circulating system may continue to polymerize over time under different process conditions than in a fluidized bed, and the polymers so formed may have significantly different properties (e.g., molecular weight, density and molecular weight distribution). A portion of the particles is eventually released from the surface of the circulation system and transported back into the fluidized bed by the circulation fluid (circulation flow). These particles contaminate polymer products and adversely affect their properties, such as increasing gel levels in end products such as plastic containers and films. Additionally, fine particles can slowly clog recirculating coolers or distribution plates, causing various operational problems. Clogging of circulation equipment or distribution plates may cause periodic shutdown of the reactor to remove accumulated fines. If the reactor is shut down for cleaning, not only the working time is reduced but also the cleaning cost is increased.

Various systems have been attempted to prevent fine particles from exiting the top of the fluidized bed vessel. US 5,382,638 discusses the use of cyclones to separate fine particles from the recycle stream. US 4,588,790 describes a process in which the expansion section is the only means for separating fine particles from the gas mixture before it reaches the outlet of the fluidized bed vessel. Other approaches to address the problems posed by fines in the recycle loop include formulating the catalysts disclosed in US 4,383,095 to minimize the generation of fines in the process and poisoning the catalyst fines in the recycle loop as described in US 6,180,729 . Other background documents include US 3,089,824, JP 59 052524, DE 197 44 710 and FR 2 764 207.

However, there is a need to further reduce the amount of solid particles leaving the fluidized bed vessel. In particular, there is a need to reduce the amount of polymer and catalyst fines leaving the top of a gas phase fluidized bed polymerization reactor.

Contents of the invention

In one embodiment, the present invention provides a system for fluidizing solid particles that results in a reduced amount of solid particles exiting the top of a fluidized bed vessel. In another embodiment, the fluidized bed system comprises: a fluidized bed vessel; a fluidized bed section in the fluidized bed vessel; a disengagement section above the fluidized bed section, wherein the disengagement section including a cap; a circulation line in fluid communication with the disengagement section; and a tapered outlet including a first outlet end connected to the cap and a second outlet end connected to the circulation line.

In another embodiment, the first outlet cross-section of the first outlet port is at least about 1.2 times the second outlet cross-section of the second outlet port, and in another embodiment, the first outlet cross-section is the second In another embodiment, the first outlet cross-section is at least about 3.0 times the second outlet cross-section.

In another embodiment, the first outlet cross-section is at least about 0.15 times the largest cross-section of the disengagement section, and in another embodiment, the first outlet cross-section is at least about 0.25 times the largest cross-section of the disengagement section , in another embodiment, the first outlet cross-section is at least about 0.35 times the largest cross-section of the disengagement section.

In any of the embodiments described herein, the transition section of the tapered outlet is frusto-conical, while in another embodiment, the tapered outlet is parabolic-conical.

In a class of embodiments, the present invention also provides a method for fluidizing solids, comprising the steps of: providing a fluidized bed system, wherein the fluidized bed system includes a fluidized bed vessel, the fluidized bed vessel The fluidized bed section in the fluidized bed section, the disengagement section including the top cover above the fluidized bed section, the circulation line in fluid communication with the disengagement section, and the first outlet port connected to the top cover and connected to the a tapered outlet at the second outlet end of a recycle line; fluidizing a bed comprising a plurality of solid particles in said fluidized bed section; and withdrawing from said fluidized bed vessel through said tapered outlet loop flow. In this embodiment, the velocity of the recycle flow at the first outlet port is about 71% or less of the velocity of the recycle flow at the second outlet port.

In another embodiment of the method, the velocity of the recycle flow at the first outlet port is about 25% or less of the velocity of the recycle flow at the second outlet port. In another embodiment, the velocity of the recycle flow at the first outlet port is about 11% or less of the velocity of the recycle flow at the second outlet port.

In another embodiment, the velocity of the recycle flow at the first outlet port is about 20 times or less than the superficial velocity in the fluidized bed section. In another embodiment, the velocity of the recycle flow at the first outlet port is about 8 times or less than the superficial velocity in the fluidized bed section. In another embodiment, the velocity of the recycle flow at the first outlet port is about 3.5 times or less than the superficial velocity in the fluidized bed section.

In any of the embodiments described herein, the plurality of solid particles comprises polymeric solids, such as polyethylene or polypropylene polymers.

In another embodiment of the process, the polymer solids comprise polyethylene polymer, the pressure in the fluidized bed vessel is from about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and the velocity of the recycle stream at the first outlet port is about 2.4-20m/s. In one embodiment where the polymer solids comprise polyethylene polymer, the velocity of the recycle flow at the first outlet port is about 2.4-15 m/s. In another embodiment where the solids comprise polyethylene polymer, the recycle stream comprises about 2 wt% or less of said plurality of solid particles.

In any of the embodiments described herein, the term "cross-section" may refer to a diameter.

Other features and advantages of the present invention will be apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are exemplary only and that it will be possible for those skilled in the art, from the detailed description herein, to develop various methods within the spirit and scope of the invention. changes and improvements.

Description of drawings

Figure 1 is a schematic diagram of a gas-phase fluidized bed polymerization system including an outlet of the prior art;

Figure 2 is a schematic diagram of a gas-phase fluidized polymerization system with tapered outlets of the present invention;

Figures 3 and 4 show CFD simulation results for two values of superficial gas velocity (SGV).

Detailed ways

A system for the fluidization of solid particles in which the amount of solid particles exiting the top of a fluidized bed vessel is reduced is provided. The system can be used with any gas phase fluidized bed system. The system is particularly applicable to gas phase polymerization systems where fine particles of polymer and/or catalyst can be entrained (or entrained) by the recycle stream leaving the top of the gas phase polymerization reactor. In another class of embodiments, the system can reduce the entrainment of "popcorn" or sheet in addition to reducing entrained fines. In one class of embodiments, the invention is described with respect to a gas phase fluidized bed polymerization system, but this is merely an example and does not limit the scope of the invention, and those skilled in the art will recognize other applicable applications.

Referring to FIG. 1 , a typical gas phase fluidization system includes a fluidized bed vessel 10 having a fluidized bed section 12 and a disengagement section 14 (also referred to as a dilute phase section) including a head 13 . In one embodiment, the top cover 13 is a hemispherical top cover, and the disengagement section 14 further includes a conical section 11 .

Fluidized bed section 12 contains a bed of solid particles which, in certain embodiments, may increase in size during the polymerization process. The solid particles are fluidized by flowing upwardly through fluidized bed section 12 by a continuous stream of fluid components (referred to herein as the fluidizing fluid). A fluidized bed has the general appearance of a bubbling bed of solid polymer particles in which the upward flow of gas bubbles causes the solid particles to mix thoroughly.

To ensure complete fluidization, a flow of circulating fluid (here also referred to as fluidizing fluid, which can be a gas or a gas/liquid combination) enters the reactor below the fluidized bed section 12 . The circulating fluid is evenly distributed to the fluidized bed section 12 by means of the gas distribution plate 18 . The circulating fluid absorbs the heat of reaction generated by polymerization or other reactions as it passes through the bed.

The unreacted portion of the circulating fluid in the bed exits the top of fluidized bed section 12 into disengagement section 14 . As the circulating fluid passes through the disengagement section above fluidized bed section 12, most of the solid particles fall back into the bed. The recycle fluid leaving the top of the fluidized bed vessel 10 as a recycle stream through recycle line 16 is compressed in a compressor 20 and passed through a heat exchanger 22 where the heat of reaction, if present, is removed and the recycle The flow returns to the fluidized bed vessel 10. The temperature of the fluidized bed can be monitored using an internal temperature sensor 19 .

Referring now to FIG. 2, in this embodiment, the present invention provides a fluidized bed system for fluidizing solid particles comprising: a fluidized bed vessel 10; a fluidized bed in the fluidized bed vessel section 12; a disengagement section 14 comprising a top cover 13 above the fluidized bed section 12; a circulation line 16 in fluid communication with the disengagement section 14; The tapered outlet of the second outlet port 28 . In one class of embodiments, the disengagement zone 14 includes a conical section 11 and a hemispherical cap 13 . As used herein, a "tapered outlet" generally refers to any outlet that has a first outlet and a second outlet that are in fluid communication and wherein the cross-sections (eg, diameters) of the first and second outlets are different. In one type of implementation, regardless of the shape, the cross section of the first outlet is larger than the cross section of the second outlet. Its shape can be conical, parabolic and so on.

The fluidized bed vessel 10 can be designed according to the desired fluidized bed system. Referring to Figure 2, in this embodiment, the fluidized bed vessel 10 has a disengagement section 14 located above the fluidized bed section 12 to allow solids that may be entrained by the gas leaving the top of the fluidized bed to fall back into the bed. The disengaged section 14 of the fluidized bed vessel 10 may be a divergent section, a straight-sided section, or a combination thereof. Disengagement section 14 may have the same or larger cross-section (eg, diameter) as fluidized bed section 12 .

The tapered outlet 24 may be of any shape and constructed of a material suitable for the desired fluidization process. In one embodiment of the invention, the tapered outlet 24 also includes a frusto-conical transition section 30 . In another embodiment of the present invention, the tapered outlet 24 further includes a parabolic-conical transition section 30 .

Continuing to refer to FIG. 2 , in this embodiment, the first outlet cross-section (eg, diameter) of the first outlet port 26 is greater than the second outlet cross-section (eg, diameter) of the second outlet port 28 . In one embodiment, the second outlet cross-section is substantially equal to the cross-section of the circulation line 16 . Unless otherwise stated, references herein to cross-section refer to the internal cross-section (eg, inner diameter) of the subject member. With a larger first outlet cross-section (eg diameter), the gas velocity near the outlet of the fluidized bed vessel is reduced. Without being limited by theory, it is believed that the reduction in gas velocity near the vessel outlet results in fewer solids being carried out of the fluidized bed vessel 10 and circulated through the recycle line 16 . In one embodiment, the first outlet cross-section is at least about 1.2 times the second outlet cross-section, preferably the first outlet cross-section is at least about 2.0 times the second outlet cross-section, even more preferably the second outlet cross-section An outlet cross-section is at least about 3.0 times the second outlet cross-section.

In one class of embodiments, the ratio of the first outlet cross-section to the maximum diameter 32 of the disengagement section also affects the amount of entrained solid particles. As shown in FIG. 2 , the disengagement section maximum diameter 32 is the maximum internal cross-section of the fluidized bed vessel 10 above the fluidized bed section 12 . In one embodiment of the invention, the first outlet cross-section is at least about 0.15 times, preferably at least about 0.25 times, more preferably at least about 0.35 times the largest diameter 32 of the disengagement section.

In another type of embodiment, the present invention also provides a method for fluidizing solids, comprising the steps of: providing a fluidized bed system, wherein the fluidized bed system includes a fluidized bed container 10, a fluidized bed A fluidized bed section 12 in the vessel 10, a disengagement section 14 above the fluidized bed section 12 including a top cover 13, a circulation line 16 in fluid communication with the disengagement section 14, and a first outlet port 26 connected to the top cover 13 and the tapered outlet connected to the second outlet port 28 of the circulation line 16; fluidize the bed comprising a plurality of solid particles in the fluidized bed section 12; Remove the recirculating flow. In these embodiments, the velocity of the recycle flow at the first outlet port 26 is about 71% or less of the velocity of the recycle flow at the second outlet port 28, preferably about 25% or less, even more preferably about 11% or less. smaller.

In any of the embodiments described herein, the velocity of the recycle flow at first outlet port 26 is about 20 times or less, preferably about 8 times or less, more preferably about 3.5 times the superficial velocity in fluidized bed section 12. times or less. As used herein, superficial velocity is the volumetric flow rate of the fluidizing stream divided by the cross-sectional area of the fluidized bed section 12 . It is well known in the art that this method of calculating velocity ignores the volume occupied by fluidized solids.

The amount of solids carried from the fluidized bed vessel 10 into the recycle line 16 also depends on the type of solid being fluidized, the pressure or density of the fluidized flow, and the velocity at various locations in the fluidized bed vessel 10 . Entrainment of solids is of particular concern for polymerization systems where catalyst fines or polymer fines containing active catalyst may circulate through the system and accumulate in undesired locations. In certain embodiments, the present invention helps to minimize the entrainment of fine particles and is therefore particularly suitable for fluidized bed polymerization of alpha-olefins. Thus, in one embodiment, the plurality of solid particles comprises polymeric solids. The polymer solids can be polyethylene, polypropylene or any other polymer produced in a fluidized bed system.

In one class of embodiments, the invention is also particularly applicable to various polymerization processes, such as polyethylene and polypropylene processes. In one embodiment, the polymer solids comprise polyethylene polymer, the pressure in the fluidized bed vessel 10 is from about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and the velocity of the recycle flow at the first outlet port 26 is preferably about 2.4 to about 20 m/s, more preferably about 2.4 to about 15 m/s.

As noted above, the presence of solids in the recycle stream can cause various operational problems in fluidized bed systems. Therefore, it is desirable to minimize solids circulating in the recycle stream. In one class of embodiments, the recycle stream includes about 2% by weight or less of the plurality of solid particles.

Polymerization process

Embodiments of the invention described herein are applicable to any gas phase fluidized bed process. Gas phase polymerization processes are preferred (see, eg, US Patent Nos. 4,543,399, 4,588,790, 5,028,670, 5,317,036, 5,352,749, 5,405,922, 5,436,304, 5,453,471, 5,462,999, 5,616,661, and 5,668,228).

In one embodiment, the process of the present invention involves a process for the gas phase polymerization of one or more olefin monomers having 2-30 carbon atoms, preferably 2-12 carbon atoms, more preferably 2 -8 carbon atoms. The invention is particularly applicable to the polymerization of two or more of the following olefinic monomers: ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene ene, 1-decene.

Other monomers useful in the process of the present invention include ethylenically unsaturated monomers, dienes having 4-18 carbon atoms, conjugated or non-conjugated dienes, polyenes, vinyl monomers and cyclic olefins . Monomers that may also be used include norbornene, norbornadiene, isobutylene, isoprene, vinylbenzocyclobutane, styrene, alkyl substituted styrenes, ethylidene norbornene, bicyclo pentadiene and cyclopentene.

In one embodiment, a copolymer of ethylene is prepared wherein ethylene is mixed with one or more alpha-olefin monomers (having 3-15 carbon atoms, preferably 4-12 carbon atoms, more preferably 4-8 carbon atoms) are polymerized in a gas phase process.

The reactor pressure in the gas phase polymerization process can vary from about 100 psig (690 kPa) to about 600 psig (4138 kPa), preferably from about 200 psig (1379 kPa) to about 400 psig (2759 kPa), more preferably from about 250 psig (1724 kPa) to about 350 psig (2414 kPa) ).

The temperature of the fluidized bed in the gas phase polymerization process may be about 30-140°C, preferably about 60-115°C, more preferably about 70-110°C, most preferably about 70-95°C.

In one embodiment of the present invention, the superficial velocity may be 0.4-1.5 m/s, preferably 0.5-0.9 m/s.

Other gas phase processes to which the method of the present invention is applicable include serial or multistage polymerization processes. Additionally, other gas phase processes used in the present invention include U.S. Patent Nos. 5,627,242, 5,665,818 and 5,677,375 and European Patent Publications EP-A-0 794 200, EP-B1-0 649 992, EP-A-0802 202 and EP-B- Those described in 634 421.

In one embodiment, the invention relates to a polymerization process for polymerizing ethylene alone or propylene alone or with one or more other monomers comprising atoms of alkenes. Polymers can be prepared using the metallocene catalysts described in US Patent Nos. 5,296,434 and 5,278,264. However, the present invention is not limited to use with any one type of catalyst system. Accordingly, the present invention can employ metallocene catalysts, constrained geometry catalysts, Ziegler-Natta catalysts, chromium-based catalysts, iron-based catalysts, nickel-based catalysts, and dual catalyst systems comprising the use of at least one metallocene and at least one A metal compound of a group 15 atom (such as N).

simulation

Figures 3 and 4 show the results of computational fluid dynamics (CFD) simulations. CFD simulation is a well-known method of solving fluid dynamic equations (eg, Navier-Stokes equations) to calculate the gas flow field. In this paper, CFD is used to simulate the flow field at the top (expansion section) of the UNIPOL ^™ reactor. The results show the advantages of embodiments of the invention employing a tapered outlet design.

Figures 3 and 4 were obtained using a two-dimensional axisymmetric geometry at superficial gas velocities (SGV) of 2.4 ft/s and 2.8 ft/s, respectively. Each figure simulates four different outlet geometries, including: (1) a standard outlet design; (2) a tapered outlet with a diameter ratio of 2:1 and a half-cone angle of 30° (30° half-cone Make the height of the truncated cone equal to 0.866 times the diameter of the outlet pipe); (3) a tapered outlet with a diameter ratio of 3:1 and the same height as (2) (0.866 times the outlet diameter); (4) a diameter ratio of 4:1 and same height tapered outlet as (2).

Figures 3 and 4 show CFD simulation results at two superficial gas velocities (SGV) as described above. Specifically, FIGS. 3 and 4 show the relationship between the calculated centerline velocity and the height of the expansion section. It should be noted that the position with a height of 0.0 corresponds to the top of the cylindrical section of the reactor (this position is at the junction of the cylindrical section and the conical section, also known as the "neck" of the reactor). With the standard design (no tapered outlet), the top of the reactor is located 37.1 feet above the neck. To facilitate comparison of velocity profiles for different outlet designs, this location is marked as a reference point.

From Figures 3 and 4 it can be seen that the gas velocity in the diverging section is substantially constant over the altitude range of 0 to 30 feet. Above this height, it can be seen that the gas velocity increases rapidly as the flow field approaches the outlet. Figures 3 and 4 show that the effect of the tapered outlet is to retard the velocity increase, effectively moving the point of velocity increase (or transition point) towards a higher position. The 2:1 diameter ratio conical outlet moves the transition point approximately 1.2 feet higher compared to the standard outlet design. Tapered outlets with diameter ratios of 3:1 and 4:1 move the transition point about 2.5 feet higher.

The tapered reactor outlet effectively alters the gas flow compared to standard reactor designs. The tapered exit makes the transition to high velocity higher, which is expected to reduce particle entrainment for a given SGV.

It should be noted that for the 3:1 and 4:1 tapered outlet designs, the difference between the velocity curves is relatively small (for both SGVs). Therefore, an embodiment with an outlet diameter ratio of 3:1 can be used.

As shown by the CFD simulations, the effect of the tapered outlet is to elevate the location of the velocity surge near the divergent section. For outlets with a 3:1 diameter ratio, the position is raised about 2.5 feet.

Thus, raising this position increases the effective height of the flared section at relatively low cost. Without being limited by theory, it is believed that this elevated position can be advantageously applied in the process in at least two ways. All other variables being equal, embodiments of the present invention will increase the efficiency of the disengagement section (i.e., increase the effective "disengagement height"), thereby reducing entrainment of, for example, fine particles (e.g., catalyst and resin fines) from the fluidized bed. amount of particles). This in turn reduces problems caused by particle entrainment in the process, including but not limited to fouling of equipment in the recycle system (e.g. recycle gas compressors, coolers, distribution plates, etc.).

In addition, reactors with reduced dimensions (eg, reduced height and/or reduced diameter) of the divergent section can also be designed at lower cost using embodiments of the present invention. In other words, at an equal particle entrainment rate, the required expansion section size can be reduced, thereby reducing the capital cost of the reactor.

Unless otherwise stated, the phrase "consisting essentially of" does not exclude the presence of other steps, elements or materials (whether mentioned in the description or not), provided that these steps, elements and materials do not affect the basic and novel aspects of the invention properties, and the phrase does not exclude the usual impurities associated with the components and materials used.

For the sake of brevity, only certain numerical ranges are explicitly disclosed herein. However, a certain lower limit may be used in combination with other lower limits to describe a range not expressly stated, and likewise a certain lower limit may be used in combination with any upper limit to state a range not expressly stated. Additionally, ranges include every point or individual value between the two endpoints even if not expressly recited. Thus, each point or individual value by itself may be used as an upper or lower limit in combination with other points or individual values or other upper and lower limits to recite ranges not expressly recited.

All prior art documents are incorporated herein by reference to the extent their disclosure does not contradict the description of the present invention. Furthermore, all references (including test procedures, publications, patents, journal articles, etc.) cited herein are hereby incorporated by reference to the extent their disclosure does not contradict the description of the present invention.

Although the present invention has been described above with reference to embodiments and examples, those skilled in the art will understand that other embodiments can be devised based on the disclosure herein without departing from the scope and spirit of the invention.

Claims (10)

1. A system for fluidizing solid particles, said system comprising: (a) fluidized bed vessels; (b) a fluidized bed section in said fluidized bed vessel; (c) a disengagement section above the fluidized bed section, wherein the disengagement section includes a head; (d) a circulation line in fluid communication with said disengagement section; and (e) comprising a tapered outlet connected to the first outlet end of the cap and connected to the second outlet end of the circulation line. 2. The system of claim 1, wherein the first outlet cross-section (preferably diameter) of the first outlet port is at least about 1.2, 2.0 or 3.0 times the second outlet cross-section (preferably diameter) of the second outlet port . 3. The system of claim 1 or 2, the first outlet cross-section (preferably diameter) being at least about 0.15, 0.25 or 0.35 times the largest cross-section (preferably diameter) of the disengagement section. 4. The system of any one of claims 1-3, wherein the transition section of the tapered outlet is frusto-conical or parabolic-conical. 5. A method for solid fluidization, comprising the steps of: (a) providing a fluidized bed system, wherein the fluidized bed system comprises: (1) Fluidized bed container; (2) a fluidized bed section in the fluidized bed vessel; (3) a disengagement section above the fluidized bed section, wherein the disengagement section includes a top cover; (4) a circulation line in fluid communication with the disengagement section; and (5) comprising a tapered outlet connected to the first outlet end of the cap and connected to the second outlet end of the circulation line; (b) fluidizing a bed comprising a plurality of solid particles in said fluidized bed section; and (c) withdrawing a recycle stream from said fluidized bed vessel through said tapered outlet, Wherein, the velocity of the circulation flow at the first outlet port is less than 71%, 25% or 11% of the velocity of the circulation flow at the second outlet port. 6. The method of claim 5, wherein the velocity of the recycle flow at the first outlet port is less than 20 times, 8 times or 3.5 times the superficial velocity in the fluidized bed section. 7. A method as claimed in claim 5 or 6, wherein said plurality of solids comprises polymeric solids. 8. The method of claim 7, wherein the polymer solid comprises a polyethylene or polypropylene polymer. 9. The method of any one of claims 5-8, wherein the pressure in the fluidized bed vessel is from about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and the speed of the recycle flow at the first outlet port is about 2.4-20m/s or about 2.4-15m/s. 10. The method of any one of claims 5-9, wherein said recycle stream comprises less than 2 wt% of said plurality of solid particles.

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