WO2008063463A1

WO2008063463A1 - System for fluidizing solid particles including novel outlet for vessel

Info

Publication number: WO2008063463A1
Application number: PCT/US2007/023750
Authority: WO
Inventors: Robert O. Hagerty; Mark B. Davis; Marc L. Dechellis; David F. Hussein
Original assignee: Univation Technologies, Llc
Priority date: 2006-11-20
Filing date: 2007-11-13
Publication date: 2008-05-29
Also published as: CN101535756A; BRPI0719119A2; EP2084478A1; CN101535756B

Abstract

A system for fluidizing solid particles is provided, wherein the fluidized bed system includes a fluidized bed vessel, a fluidized bed section, a disengagement section, a recycle line, and a tapered outlet. Also provided is a method of fluidizing solids by providing a system as described above, fluidizing a bed comprising solid particles, and removing a recycle stream through the tapered outlet.

Description

SYSTEM FOR FLUIDIZING SOLID PARTICLES INCLUDING NOVEL

OUTLET FOR VESSEL

CROSS REFERENCE TO RELATED APPLICATIONS

100011 This application claims the benefit of Serial No. 60/860,166, filed November 20, 2006, the disclosure of which is incorporated by reference.

FIELD OF THE INVENTION

10002] This disclosure relates generally to fluidized bed systems, and particularly to gas phase fluidized bed systems with reduced solids entrainment in the recycle stream.

BACKGROUND OF THE INVENTION

[0003| The fluidization of solids involves the "suspension" of a bed of solid particles in a gas stream passing upwards through the fluidization bed. Fluidized bed vessels are utilized in a variety of processes, for example olefins cracking and polymerization processes. One of the most economic and commonly used methods to manufacture polymers is gas phase polymerization using a fluidized bed reactor.

[0004] Generally in a gas-phase fluidized bed process for producing polymers from monomers, a gaseous stream containing one or more monomers is continuously passed 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 This gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and new monomer is added to replace the polymerized monomer.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.

|0005) It is understood that the amount of polymer produced in a fluidized bed polymerization process is directly related to the amount of heat that can be withdrawn from the fluidized bed reaction zone since the exothermic heat generated by the reaction is directly proportional to the rate of polymer production. In steady state operation of the reaction process, the rate of heat removal from the fluidized bed must equal the rate of rate of heat generation, such that the bed temperature remains constant. Conventionally, heat has been removed from the fluidized bed by cooling the gas recycle stream in a heat exchanger external to the reactor.

|0006l A requirement of a fluidized bed process is that the velocity of the gaseous cycle stream be sufficient to maintain the reaction zone in a fluidized state. In a conventional fluidized bed polymerization process, the amount of fluid circulated to remove the heat of polymerization is greater than the amount of fluid required for support of the fluidized bed and for adequate mixing of the solids in the fluidized bed. The excess velocity provides additional gas flow to (and through) the fluid bed for additional cooling capacity and more intensive mixing of the reactor bed. However, to prevent excessive entrainment of solids in a gaseous stream withdrawn from the fluidized bed, the velocity of the gaseous stream must be regulated.

[0007] A conventional gas phase fluidized bed reactor used in polymerizing olefins and/or diolefins contains a fluidized dense-phase bed and a freeboard above the dense-phase surface (bed level). The freeboard contains mainly gas and a small amount of particles, especially the fine particles (fines). The dense-phase bed is usually but not always maintained in a cylindrical straight section of the reactor. The freeboard section is above the dense-phase bed. The freeboard section (or disengagement section) often has a larger diameter, the so called expanded section, to reduce the gas velocity for the purpose of reducing the amount of fines carried out of the reactor to other parts of the reaction system. The expanded section typically consists of a tapered conical section and a hemispherical top head of the reactor. A reactor outlet is located at the top of the hemispherical top head. [0008] During reactor operation, a gas mixture is removed out of the top of the fluidized bed vessel through an outlet located in the top head of the fluidized bed vessel. The gas mixture is circulated back to the inlet of the fluidized bed vessel through a recycle loop or recycle line. The recycle loop includes other equipment essential to the operation of the fluidized bed process, such as recycle compressors or pumps, and recycle coolers. When the gas mixture exits the top of the fluidized bed vessel, fines present in the disengagement section, particularly fines near the reactor outlet, may be entrained with the gas mixture and circulated through the recycle loop with the recycle stream. The recycle stream exits the reactor outlet, passes through any equipment in the recycle loop, and re-enters the reactor near the bottom of the fluidized bed vessel. After reentering the fluidized bed vessel, the recycle gas or gas/liquid stream typically passes through a gas distributor plate and back into the fluidized bed.

[0009] Entrained fines in the recycle loop can become lodged in the equipment in the recycle loop, such as the recycle compressor or recycle cooler, causing various quality and operating problems. Such fines promote undesirable polymer growth and fouling of surfaces in the cycle piping, cycle cooler, compressor, lower reactor head, and distributor plate resulting in undesirable reactor shutdowns for system cleaning. Adhered particles in the recycle system may continue to polymerize over time under process conditions different from the fluidized bed, forming polymer of significantly different properties, such as molecular weight, density, and molecular weight distribution, from that of the fluidized bed. Some particles are eventually released from the recycle system surfaces and are conveyed by the recycle fluid (recycle flow) back into the fluidized bed. Such particles contaminate and adversely affect properties of the polymer product, such as by increasing the gel level in end-use products such as plastic containers and films. In addition, the fines may cause the recycle cooler or distributor plate to slowly plug causing various operating problems. The pluggage of the recycle equipment or distributor plate may result in periodic reactor shutdowns to remove the accumulated fines. When a reactor is down for cleaning, operation time is lost, in addition to the cost of the cleaning itself. [0010) Various systems have been used to try and prevent fines from exiting the top of the fluidized bed vessel. U.S. Patent No. 5,382,638 discusses the use of cyclones to try and disengage the fines from the recycle stream. U.S. Patent No. 4,588,790 shows a process wherein an expanded section is the only device used to disengage fines from the gas mixture before the gas mixture reaches the outlet of the fluidized bed vessel. Other methods of addressing the problems with fines in the recycle loop include formulating the catalyst as disclosed in U.S. Patent No. 4,383,095 to minimize fines produced in the process, and poisoning the catalyst fines in the recycle loop as disclosed in U.S. Patent No. 6,180,729. Other background references include U.S. Patent No. 3,089,824, JP 59 052524, DE 197 44 710, and FR 2 764 207.

(0011 ] However, there exists a need to further reduce the amount of solid particles that exit a fluidized bed vessel. In particular, there exists a need to reduce the amount of polymer and catalyst fines that exit the top of a gas phase fluidized bed polymerization reactor.

SUMMARY OF THE INVENTION

|0012] In an embodiment, the invention provides a system for fluidizing solid particles with a reduced amount of solid particulates exiting the top of the 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 comprises a top head; a recycle line in fluid communication with the disengagement section; and a tapered outlet comprising a first outlet end connected to the top head and a second outlet end connected to the recycle line.

10013] In yet another embodiment, a first outlet cross section of the first outlet end is at least about 1.2 times a second outlet cross section of the second outlet end, while in another embodiment the first outlet cross section is at least about 2.0 times the second outlet cross section, and in yet another embodiment the first outlet cross section is at least about 3.0 times the second outlet cross section.

|00l4) In still another embodiment, the first outlet cross section is at least about 0.15 times a disengagement section maximum cross section, while in another embodiment the first outlet cross section is at least about 0.25 times a disengagement section maximum cross section, and in yet another embodiment, the first outlet cross section is at least about 0.35 times a disengagement section maximum cross section.

|00l5) In any of the embodiments described herein, a transition section of the tapered outlet is a conical frustum shape, while in another embodiment the tapered outlet is a parabolic cone shape.

[0016] In a class of embodiments, the invention also provides a method of fluidizing solids comprising the steps of: providing a fluidized bed system, wherein 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 comprises a top head, a recycle line in fluid communication with the disengagement section, and a tapered outlet comprising a first outlet end connected to the top head and a second outlet end connected to the recycle line; fluidizing a bed comprising a plurality of solid particles in the fluidized bed section; and removing a recycle stream from the fluidized bed vessel through the tapered outlet. In this embodiment, a velocity of the recycle stream at the first outlet end is about 71% or less of the velocity of the recycle stream at the second outlet end.

|0017) In another embodiment of the method, the velocity of the recycle stream at the first outlet end is about 25% or less of the velocity of the recycle stream at the second outlet end. In yet another embodiment, the velocity of the recycle stream at the first outlet end is about 11 % or less of the velocity of the recycle stream at the second outlet end. |00l8] In still another embodiment, the velocity of the recycle stream at the first outlet end is about 20 times or less a superficial velocity in the fluidized bed section. In yet still another embodiment, the velocity of the recycle stream at the first outlet end is about 8 times or less a superficial velocity in the fluidized bed section. In yet still another embodiment, the velocity of the recycle stream at the first outlet end is about 3.5 times or less a superficial velocity in the fluidized bed section.

|00191 In any of the embodiments described herein, the plurality of solids comprises a polymer solid, for example, polyethylene or polypropylene polymers.

[0020| In yet another embodiment of the method, the polymer solid comprises polyethylene polymer, a pressure in the fluidized bed vessel is about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and a velocity of the recycle stream at the first outlet end is about 2.4 to about 20 meters/sec. In one embodiment wherein the polymer solid comprises polyethylene polymer, the velocity of the recycle stream at the first outlet end is about 2.4 to about 15 meters/sec. In a further embodiment wherein the solid comprises polyethylene polymer, the recycle stream comprises about 2 wt% or less of the plurality of solid particles.

|002i] In any of the embodiments described herein, the cross section may be a diameter.

|0022] Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF SUMMARY OF THE DRAWINGS

|0023] Figure 1 is schematic drawing of a gas phase fluidized bed polymerization system including an outlet of the prior art.

|0024] Figure 2 is a schematic drawing of a portion of a gas phase fluidization system with a inventive, tapered outlet.

[0025] Figures 3 and 4 show the results of the CFD simulations for two values of superficial gas velocity (SGV).

DETAILED DESCRIPTION OF THE INVENTION

|0026] A system for fluidizing solid particles with a reduced amount of solid particulates exiting the top of the fluidized bed vessel is provided. The system is useful in any gas phase fluidized bed system. It is particularly useful in a gas phase polymerization system wherein polymer and/or catalyst fines may be carried out (or entrained) with the recycle stream exiting the top of the gas phase fluidized bed reactor. In another class of embodiments, in addition to reducing fine particle carryover, the system may reduce "popcorn" or sheet carryover. In a class of embodiments, the invention is described in reference to a gas phase fluidized bed polymerization system; however, this is only intended to provide an example and should not limit the invention as a skilled artisan will recognize other useful applications.

[0027] Referring to Figure 1, a typical gas phase fluidization system comprises a fluidized bed vessel 10 with a fluidized bed section 12, and a disengagement section 14 (also known as a freeboard section) comprising a top head 13. In one embodiment, the top head 13 is a hemispherical top head, and the disengagement section 14 further comprises a conical section 1 1.

|0028] The fluidized bed section 12 contains a bed of solid particles, which in some embodiments may be growing in size during the polymerization process. The solid particles are fluidized by the continuous flow of fluid components, referred to herein as a fluidizing fluid, flowing up through the fluidized bed section 12. The fluidized bed has the general appearance of a bubbling bed of solid polymer particles, wherein the upward flow of gas bubbles provides significant mixing of the solid particles.

[0029| To ensure complete fluidization, a flow of cycle fluid (also referred to herein as a fluidizing fluid), which may be a gas or a gas/liquid combination, enters the reactor at point below the fluidized bed section 12. There may be a gas distributor plate 18 to aid in the distribution of the cycle fluid evenly to the fluidized bed section 12. In passing through the bed, the cycle fluid absorbs the heat of reaction generated by a polymerization or other reaction.

|0030] The portion of the cycle fluid that does not react in the bed exits the top of the fluidized bed section 12 and enters the disengagement section 14. As the cycle fluid passes through the disengagement section 14 above the fluidized bed section 12, most of the solid particles drop back into the bed. The cycle fluid exits the top of the fluidized bed vessel 10 as a recycle stream via the recycle line 16, is compressed in a compressor 20, and passed through a heat exchanger 22 wherein the heat of reaction, if any, is removed before the recycle stream is returned to the fluidized bed vessel 10. The temperature of the fluidized bed may be monitored by means of an internal temperature sensor 19.

|003l I Now referring to Figure 2, in this embodiment, the invention provides a fluidized bed system for fluidizing solid particles comprising a fluidized bed vessel 10; a fluidized bed section 12 in the fluidized bed vessel; a disengagement section 14 above the fluidized bed section 12 comprising a top head 13; a recycle line 16 in fluid communication with the disengagement section 14; and a tapered outlet 24 comprising a first outlet end 26 connected to the top head 13 and a second outlet end 28 connected to the recycle line 16. In a class of embodiments, the disengagement section 14 comprises a conical section 1 1 and a hemispherical top head 13. As used herein, "tapered outlet" generally refers to any outlet having a first outlet in fluid communication with a second outlet, wherein the cross sections, such as, for example, diameters, of the first outlet and the second outlet are different. In a class of embodiments, the cross section of the first outlet is greater than the cross section of the second outlet, regardless of shape. The shape may be conical, parabolic, etc.

[0032| The fluidized bed vessel 10 may be any design appropriate for the fiuidized bed system of interest. 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 the solids that may escape with the gas exiting the top of the fluidized bed to fall back into the bed. The disengagement section 14 of the fluidized bed vessel 10 may be an expanded section, a straight-sided section, or a combination thereof. The disengagement section 14 may be the same or larger cross section, such as, for example, diameter than the fluidized bed section 12.

100331 The tapered outlet 24 may be any shape and be constructed of any materials suitable for the fluidization process of interest. In one embodiment of the invention, the tapered outlet 24 further comprises a transition section 30 in the shape of a conical frustum. In another embodiment of the invention, the tapered outlet 24 further comprises a transition section 30 with a parabolic cone shape.

[0034) Continuing with reference to Figure 2, in this embodiment, a first outlet cross section, such as, for example, diameter, of the first outlet end 26 is larger than a second outlet cross section, such as, for example, diameter, of the second end 28. In an embodiment the second outlet cross section is substantially equal to the recycle line 16 cross section.- The cross sections referenced in this application are the inside cross sections, e.g., diameter, of the subject parts, unless otherwise noted. By using a larger first outlet cross section, e.g., diameter, the velocity of the gas in the vicinity of the fluidized bed vessel outlet is lower. Without being bound to theory it is believed that lowering the gas velocity in the vicinity of the vessel outlet results in fewer solid particles 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, and even more preferably the first outlet cross section is at least about 3.0 times the second outlet cross section.

|0035] In a class of embodiments, the ratio of the first outlet cross section to a disengagement section maximum diameter 32 also influences the amount of solid particle carryover. As can be seen in Figure 2, the disengagement section maximum diameter 32 is the largest inside 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 a disengagement section maximum diameter 32, preferably at least about 0.25 times the disengagement section maximum cross section 32, and more preferably at least about 0.35 times the disengagement section maximum cross section 32.

|0036] In another class of embodiments, the invention also provides for a method of fluidizing solids comprising the steps of: providing a fluidized bed system, wherein the fluidized bed system comprises a fluidized bed vessel 10, a fluidized bed section 12 in the fluidized bed vessel 10, a disengagement section 14 above the fluidized bed section 12, wherein the disengagement section 14 comprises a top head 13, a recycle line 16 in fluid communication with the disengagement section 14, and a tapered outlet 24 comprising a first outlet end 26 connected to the top head 13 and a second outlet end 28 connected to the recycle line 16; fluidizing a bed comprising a plurality of solid particles in the fluidized bed section 12; and removing a recycle stream from the fluidized bed vessel 10 through the tapered outlet 24. In these embodiments, a velocity of the recycle stream at the first outlet end 26 is about 71% or less of the velocity of the recycle stream at the second outlet end 28, preferably, about 25% or less of the velocity of the recycle stream at the second outlet end 28, and even more preferably, about 1 1% or less of the velocity of the recycle stream at the second outlet end 28.

|0037] In any of the embodiments described herein, a velocity of the recycle stream at the first outlet end 26 is about 20 times or less a superficial velocity in the fluidized bed section 12, preferably, about 8 times or less the superficial velocity of the fluidization stream in the fluidized bed section 12, and more preferably, about 3.5 or less times the superficial velocity of the fluidization stream in the fluidized bed section 12. The superficial velocity as used herein is the volumetric flow of the fluidization stream divided by the cross sectional area of the fluid bed section 12. It is generally understood in the art that this calculation of velocity ignores the volume occupied by the fluidized solids.

|0038| The amount of solids carried out of the fluidized bed vessel 10 to the recycle line 16 also depends on the type of solid being fluidized, pressure or density of the fluidizing stream, and velocity at various points in the fluidized bed vessel 10. Solids carryover is of particular concern for polymerization system wherein catalyst fines or polymer fines containing active catalyst may circulate through the system and lodge in undesirable locations. Because, in some embodiments, the invention helps minimize the amount of fines carryover, it is particularly useful for the fluidized bed polymerization of alpha olefins. Thus, in one embodiment, the plurality of solids comprises a polymer solid. The polymer solids may be polyethylene, polypropylene, or any other polymer produced in a fluidized bed system.

|0039] In a class of embodiments, the invention is also particularly useful in various polymerization processes, such as polyethylene and polypropylene processes. In one embodiment, the polymer solid comprises polyethylene polymer, a pressure in the fluidized bed vessel 10 is about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and a velocity of the recycle stream at the first outlet end 26 is preferably about 2.4 to about 20 meters/sec, and more preferably the velocity of the recycle stream at the first outlet end 26 is about 2.4 to about 15 meters/sec.

[0040] As discussed above, the presence of solids in the recycle stream can cause various operating problems in the fluidized bed system. Thus, it is desirable to minimize the solids circulated in the recycle stream. In a class of embodiments, the recycle stream comprises about 2 wt% or less of the plurality of solid particles.

Polymerization Processes |004l] Embodiments of the invention described herein are suitable for use in any gas phase fluid bed process. A gas phase polymerization process is preferred {see,or example, U.S. Pat. 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).

|0042] In one embodiment, the process of this invention is directed toward a gas phase polymerization process of one or more olefin monomers having from 2 to 30 carbon atoms, preferably 2 to 12 carbon atoms, and more preferably 2 to 8 carbon atoms. The invention is particularly well suited to the polymerization of two or more olefin monomers of ethylene, propylene, butene-1, pentene-1, 4- methyl-pentene-1, hexene-1, octene-1, and decene-1.

|0043| Other monomers useful in the process of the invention include ethylenically unsaturated monomers, diolefins having 4 to 18 carbon atoms, conjugated or nonconjugated dienes, polyenes, vinyl monomers and cyclic olefins. Useful monomers also include norbornene, norbornadiene, isobutylene, isoprene, vinylbenzocyclobutane, styrenes, alkyl substituted styrene, ethylidene norbornene, dicyclopentadiene and cyclopentene.

|0044] In one embodiment, a copolymer of ethylene is produced, wherein ethylene and one or more alpha-olefin comonomers having from 3 to 15 carbon atoms, preferably from 4 to 12 carbon atoms, and most preferably, from 4 to 8 carbon atoms, are polymerized in a gas phase process.

|0045] The reactor pressure in a gas phase polymerization process may vary from about 100 psig (690 kPa) to about 600 psig (4138 kPa), preferably in the range of from about 200 psig (1379 kPa) to about 400 psig (2759 kPa), more preferably in the range of from about 250 psig (1724 kPa) to about 350 psig (2414 kPa).

|0046] The temperature of the fluidized bed in a gas phase polymerization process may vary from about 30⁰C to about 14O⁰C, preferably from about 60⁰C to about 115°C, more preferably in the range of from about 7O⁰C to 110⁰C, and most preferably in the range of from about 75°C to about 95°C. |0047] The superficial velocity in one embodiment of the invention may vary from 0.4 to 1.5 meters/sec, preferably from 0.5 to 0.9 meters/sec.

[0048| Other gas phase processes contemplated by the process of the invention include series or multistage polymerization processes. Other gas phase processes contemplated by the invention include those described in U.S. Patent Nos. 5,627,242, 5,665,818 and 5,677,375, and European publications EP-A- 0 794 200 EP-Bl-O 649 992, EP-A- 0 802 202 and EP-B- 634 421.

|0049] In one embodiment, the invention is directed to a gas phase process for polymerizing ethylene or propylene alone or with one or more other monomers including olefins having from 2 to 12 carbon atoms. Polymers may be produced using the metallocene catalysts as described in U.S. Patent Nos. 5,296,434 and 5,278,264. However, the invention is not necessarily limited to the application of any one catalyst system type. Thus, the invention has application with metallocene catalysts, constrained geometry catalysts, Ziegler-Natta catalysts, chrome based catalysts, iron based catalysts, nickel based catalysts, as well as dual catalysts systems, including the application of at least one metallocene with at least one Group 15 atom (such as N) metal compound.

SIMULATIONS

[0050] Figures 3 and 4 are derived from Computational Fluid Dynamics (CFD) simulations. This is a well known method to solve equations (e.g., the Navier- Stokes equations) of fluid dynamics to produce calculations of gas flow fields. As used here, CFD is used to model the flow field in the top (expanded) section of a UNIPOL™ Reactor. The results show the advantages of embodiments of the invention employing a tapered outlet design.

|005l I They were generated using 2D, axisymmetric geometry and superficial gas velocity (SGV) and at 2.4 ft/s and 2.8 ft/s SGV. Each figures shows simulated four cases of different geometry including (1) a standard outlet design; (2) a tapered outlet with a 2:1 diameter ratio, and a 30 degree cone half-angle. (The 30 degree cone half-angle produced a height of the truncated cone (or "frustum") equal to 0.866 times the outlet pipe diameter); (3) a tapered outlet with a 3:1 diameter ratio and the same height as the 2: 1 case (0.866 times the outlet diameter); and (4) a tapered outlet with a 4:1 diameter ratio and the same height as the 2: 1 simulation.

|0052l The results of the CFD simulations are shown in Figures 3 & 4 for two values of superficial gas velocity (SGV) as described above. In particular, Figures 3 & 4 show calculated centerline velocities as a function of height in the expanded section. Note that the position of 0.0 height corresponds to the top of the reactor cylindrical section. (This position, at the junction of the cylindrical and conical sections, is also referred to as the "neck" of the reactor. In the case of the standard design (without the tapered outlet) the top of the reactor is at an elevation of 37.1 feet above the neck. This marks a convenient point of reference to compare the velocity profiles of the different outlet designs.

|0053] As can be seen by Figures 3 & 4, the gas velocity in the expanded section is approximately constant over the range of elevations between zero and 30 feet. Above this height, the gas velocity is seen to increase rapidly as the flow field approaches the outlet. Figures 3 & 4 show that the effect of the tapered outlet is to delay the increase in velocity, effectively moving the point of velocity increase (or point of transition) to higher elevations. Compared with the standard outlet design, the effect of the 2:1 cone is to move the point of transition approximately 1.2 ft. higher. The 3;1 and 4:1 tapered outlets move the point of transition approximately 2.5 feet higher.

|0054l Compared to the standard reactor design, the tapered reactor outlet is effective in altering the gas flow. The tapered outlet produces a higher point of transition to high velocity, which is expected to produce a reduction in particle carryover, at a given value of SGV.

|0055] Note that there is relatively little difference between the velocity curves for the 3:1 and 4:1 tapered outlet designs (at both values of SGV). Thus, the 3: 1 outlet diameter ratio represents a useful embodiment. |0056| As shown by the CFD simulations, the effect of the tapered outlet is to raise the height at which the sharp increase in velocity occurs near the top of the expanded section. In the case of the 3/1 diameter outlet, the height was raised by about 2.5 feet.

|0057] Thus, this increase raises the effective height of the expanded section at a relatively low cost. Without being bound to theory, it is believed that this increase could advantageously applied in industry in at least two ways. With all other variables equal, embodiments of the invention would improve the effectiveness of the disengagement section (i.e., it would add to the effective "disengagement height"), and thereby reduce, for example, the amount of entrainment of fine particles (e.g., catalyst and resin fines) from the fluidized bed. This would, in turn, reduce the problems associated with particle carryover in the process, including but not limited to fouling of the equipment in the recycle system, e.g., the cycle gas compressor, cooler, distributor plate, etc.

|0058] Additionally, one could utilize embodiments of the invention to design reactors with reduced size of the expanded section ( for example, reduced height and/or diameter) at lower cost. In other words, for equivalent rates of particle entrainment, the required size of the expanded section could be reduced to lower the investment cost of a reactor.

|0059] The phrases, unless otherwise specified, "consists essentially of and "consisting essentially of do not exclude the presence of other steps, elements, or materials, whether or not, specifically mentioned in this specification, as along as such steps, elements, or materials, do not affect the basic and novel characteristics of the invention, additionally, they do not exclude impurities normally associated with the elements and materials used.

|0060] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

|00611 All priority documents are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted and to the extent such disclosure is consistent with the description of the present invention. Further, all documents and references cited herein, including testing procedures, publications, patents, journal articles, etc. are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted and to the extent such disclosure is consistent with the description of the present invention.

[0062] While the invention has been described with respect to a number of embodiments and examples, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope and spirit of the invention as disclosed herein.

Claims

CLAIMSWhat is claimed is:

1. A system for fluidizing solid particles, wherein the fluidized bed system comprises:

(a) a fluidized bed vessel;

(b) a fluidized bed section in the fluidized bed vessel;

(c) a disengagement section above the fluidized bed section, wherein the disengagement section comprises a top head;

(d) a recycle line in fluid communication with the disengagement section; and

(e) a tapered outlet comprising a first outlet end connected to the top head and a second outlet end connected to the recycle line.

2. The system of claim 1, wherein a first outlet cross section, preferably, diameter, of the first outlet end is at least about 1.2, 2.0, or 3.0 times a second outlet cross section, preferably, diameter of the second outlet end.

3. The system of any of the preceding claims, wherein the first outlet cross section, preferably, diameter, is at least about 0.15, 0.25, or 0.35 times a disengagement section maximum cross section, preferably, diameter.

4. The system of any of the preceding claims, wherein a transition section of the tapered outlet is a conical frustum shape or a parabolic cone shape.

5. A method of fluidizing solids comprising the steps of:

(a) providing a fluidized bed system, wherein the fluidized bed system comprises:

(1) a fluidized bed vessel;

(2) a fluidized bed section in the fluidized bed vessel; (3) a disengagement section above the fluidized bed section, wherein the disengagement section comprises a top head;

(4) a recycle line in fluid communication with the disengagement section; and

(5) a tapered outlet comprising a first outlet end connected to the top head and a second outlet end connected to the recycle line;

(b) fluidizing a bed comprising a plurality of solid particles in the fluidized bed section; and

(c) removing a recycle stream from the fluidized bed vessel through the tapered outlet, wherein a velocity of the recycle stream at the first outlet end is less than about 71%, 25%, or 11% of the velocity of the recycle stream at the second outlet end.

6. The method of claim 5, wherein the velocity of the recycle stream at the first outlet end is less than 20 times a superficial velocity in the fluidized bed section, less than 8 times a superficial velocity in the fluidized bed section, or less than 3.5 times a superficial velocity in the fluidized bed section.

7. The method of any of the claims 5-6, wherein the plurality of solids comprises a polymer solid.

8. The method of claim 7, wherein the polymer solid comprises polyethylene, or polypropylene polymer.

9. The method of any of the claims 5-8, wherein a pressure in the fluidized bed vessel is about 250 psig (1724 kPa) to about 350 psig (2414 kPa), and the velocity of the recycle stream at the first outlet end is about 2.4 to about 20 meters/sec, or about 2.4 to about 15 meters/sec.

10. The method of any of the claims 5-9, wherein the recycle stream comprises less than 2 wt% of the plurality of solid particles.