Title of Invention	"A CYCLONE SEPARATOR FOR SEPARATING FINE SOLID PARTICULATES FROM A GAS STREAM"
Abstract	In accordance with the present invention there is provided a cyclone separator for use between an upper and a lower tube sheet, the cyclone comprising, a vertical cyclone body (106) having a closed bottom end and a top end fixed with respect to the upper tube sheet, the cyclone body having a feed gas inlet at its top end, the feed gas inlet extending above the upper tube sheet for receiving a particle-contaminated gas stream therefrom, the cyclone body having a sidewall of the cyclone body, the sidewall having a plurality of discharge openings located between the upper and the lower tube sheets for discharging particles and a minor amount of an underflow gas stream; one or more swirl vanes located proximate the gas inlet to induce centripetal acceleration of the particle-contaminated gas stream; a gas outlet tube defining a clean gas inlet end located centrally within the cyclone body for receiving a purified gas stream and having a clean gas outlet located below the lower tube sheet for discharging the purified gas stream, the gas outlet tube extending through the closed bottom end of the cyclone body and extending through the lower tube sheet characterized in that discharge openings are rectangular slots having lengths parallel to the axis of the cyclone body, the slots spaced uniformly about the circumference of the cyclone body and the discharge openings have a total open area from 0.05% to 0.5% of the surface area of the cyclone body.

Title of Invention

"A CYCLONE SEPARATOR FOR SEPARATING FINE SOLID PARTICULATES FROM A GAS STREAM"

Abstract

In accordance with the present invention there is provided a cyclone separator for use between an upper and a lower tube sheet, the cyclone comprising, a vertical cyclone body (106) having a closed bottom end and a top end fixed with respect to the upper tube sheet, the cyclone body having a feed gas inlet at its top end, the feed gas inlet extending above the upper tube sheet for receiving a particle-contaminated gas stream therefrom, the cyclone body having a sidewall of the cyclone body, the sidewall having a plurality of discharge openings located between the upper and the lower tube sheets for discharging particles and a minor amount of an underflow gas stream; one or more swirl vanes located proximate the gas inlet to induce centripetal acceleration of the particle-contaminated gas stream; a gas outlet tube defining a clean gas inlet end located centrally within the cyclone body for receiving a purified gas stream and having a clean gas outlet located below the lower tube sheet for discharging the purified gas stream, the gas outlet tube extending through the closed bottom end of the cyclone body and extending through the lower tube sheet characterized in that discharge openings are rectangular slots having lengths parallel to the axis of the cyclone body, the slots spaced uniformly about the circumference of the cyclone body and the discharge openings have a total open area from 0.05% to 0.5% of the surface area of the cyclone body.

Full Text	BACKGROUND OF THE INVENTION [0001] The present invention relates to a novel cyclone separator for removing fine solid participates from a gas stream. The cyclone is especially applicable in a third stage separator apparatus, often used to purify the catalyst fines-laden flue gas stream exiting a refinery fluid catalytic cracking (FCC) catalyst regenerator. [0002] The emission of particulates in industrial gas streams must be carefully controlled in light of federal, state, and local regulations designed to curtail pollution. In the area of oil refinery operations, a major concern regarding paniculate emissions lies in the flue gas exiting the catalyst regenerator section of fluid catalytic cracking (FCC) units. Current United States federal regulations limit paniculate levels to 1 kg of solids per 1000 kgs of coke burned in the catalyst regenerator, or the equivalent of a flue gas paniculate concentration of approximately 80-110 mg/Nm^. Corresponding European regulations currently vary considerably, from 80-500 mg/Nm^; however, this value is expected to decline potentially to 50 mg/Nm^. [0003] FCC technology, now more than 50 years old, has undergone continuous improvement and remains the predominant source of gasoline production in many refineries. This gasoline, as well as lighter products, is formed as the result of cracking heavier (i.e. higher molecular weight), less valuable hydrocarbon feed stocks such as gas oil. Although FCC is a large and complex process involving many factors, a general outline of the technology is presented here in the context of its relation to the present invention. [0004] In its most general form, the FCC process comprises a reactor that is closely coupled with a catalyst regenerator, followed by downstream hydrocarbon product separation. A major distinguishing feature of the process is the continuous fluidization and circulation of large amounts of catalyst having an average particle diameter of 50- 100 microns, equivalent in size and appearance to very fine sand. For every ton of cracked product made, approximately 5 tons of catalyst are needed, hence the considerable circulation requirements. Coupled with this need for a large inventory and recycle of a small particle diameter catalyst is the ongoing challenge to prevent this catalyst from exiting the reactor/regenerator system into effluent streams. « [0005] Overall, the use of cyclone separators internal to both the reactor and regenerator has provided over 99% separation efficiency of solid catalyst. Typically, the regenerator includes first and second (or primary and secondary) stage separators for the purpose of preventing catalyst contamination of the regenerator flue gas, which is - essentially the resulting combustion product of catalyst coke in air. While normal-sized catalyst particles are effectively removed in the internal regenerator cyclones, fines material (generally catalyst fragments smaller than 50 microns resulting from attrition and erosion in the harsh, abrasive reactor/regenerator environment) is substantially more difficult to separate. As a result, the FCC flue gas will usually contain a particulate concentration in the range of 200-1000 mg/Nm^. This solids level can present difficulties related to either the applicable legal emissions standards or the desire to recover power from the flue gas stream. In the latter case, the solids content in the FCC flue gas may be sufficient to damage turbine blades of an air blower to the regenerator if such a power recovery scheme is indeed selected. [0006] A further reduction in FCC flue gas fines loading is therefore often warranted, and may be obtained from a third stage separator (TSS) device containing a manifold of cyclones. Electrostatic precipitators. are known to be effective for this gas/solid separation but are far more costly than a TSS, which relies on the induction of centripetal acceleration to a particle-laden gas stream, forcing the higher-density solids to the outer edges of a spinning vortex. To be efficient, a cyclone separator for an FCC flue gas effluent will normally contain many, perhaps 100, small individual cylindrical cyclone bodies installed within a single vessel acting as a manifold. Tube sheets affixing the upper and lower ends of the cyclones act to distribute contaminated gas to the cyclone inlets and also to divide the region within the vessel into sections for collecting the separated gas and solid phases. [0007] In the area of cyclone design, significant emphasis has been placed on socalled "reverse flow" types where incoming gas is added around a gas outlet tube extending from the inlet side of a cylindrical cyclone body. Particle-rich gas can be withdrawn from openings in the sidewall of the cyclone body, while clean gas essentially reverses flow from its initial path toward the end of the cyclone body opposite the gas inlet, badk toward the gas outlet. The gas outlet is a tube normally concentric with, and located within the cyclone body. These types of cyclones are described in US 5,514,271 Bl and US 5,372,707 Bl, where the inventive subject matter is focused on the shape and distribution of the sidewall openings in order to minimize turbulent eddy formation that can re-entrain solids into the clean gas outlet. In US 5,643,537 Bl and parent US 5,538,696 B1, devices are contemplated for use with this fundamental cyclone design to further extend, or improve the uniformity of, the vortex flow pattern and thereby increase separation efficiency. [0008] Unfortunately, the requirement by itself for a gas stream to reverse direction and exit the cyclone body on the same side as the gas inlet imposes flow disturbances that are not easily overcome. Cyclones of the type described in US 5,690,709 Bl, termed "uniflow", eliminate the re-entrainment of solids associated with the reversal of gas direction. In this case, clean gas moves continually downward and exits the cyclone body below a lower tube sheet, which serves as the physical boundary between the separated particles and purified gas. This design, however, also promotes non-uniform flow patterns, which are here associated with the discharge of particles at essentially right angles to the particle-laden gas vortex, through the open bottom in the cylindrical cyclone body. Again, the basic operation of the cyclone in this case involves a change in direction of gas flow that should ideally be avoided. Furthermore, the open bottom design provides a relatively large surface area for exiting "dirty" gas to enter the bodies of adjacent cyclones in an overall arrangement of cyclones, such as in a TSS. This communication of gas among cyclones reduces separation efficiency. [0009] Aside from general considerations about cyclone design, such as the induction of centripetal acceleration and the maintenance of a uniform flow pattern, further improvements in efficiency associated with any particular cyclone configuration must be verified through actual testing. Indeed, some proposed designs that were believed in principle to mitigate uneven flow patterns and localized eddy formation actually performed quite poorly in laboratory experiments. Even sophisticated computational fluid dynamics computer software has been found in some cases to be a poor predictor of TSS separation efficiency. Therefore, through extensive trial and error, coupled with the overall objective of refining the cyclone internal flow pattern, a significant improvement in fine particle separation from gas streams has been achieved. SUMMARY OF THE INVENTION [0010] The present invention is an improved cyclone for the separation of solid particulates from a gas stream. Many of these cyclones can be combined in a vessel for use as a third stage separator in the treatment of solid-contaminated gas streams, and in particular flue gas from a refinery fluid catalytic cracking unit or other solidcontaminated gas streams. The cyclone provides a high separation efficiency because a particulate-laden gas vortex is established and travels through the device with minimal flow pattern disturbances. The feed gas and exiting clean gas move in the same direction throughout the separation, and the clean gas, representing the bulk of the feed gas on a volume basis, is removed from the central portion of the vortex using a gas outlet tube extending with the cyclone body. Furthermore, solid particles are forced through openings in the sidewall of the cyclone body to prevent backflow and gas communication among adjacent cyclones, rather than discharged axially. [0011] The use of a plate or other structure to close off the bottom of cyclone body means that particle-laden gas can exit only through openings on the cylinder wall. Thus, the pressure drop across the area through which the gas discharges is generally higher than that for open bottom designs. This increase in pressure drop and gas velocity induces a more forceful ejection of particulates through the cylinder sidewall, thereby preventing re-entry of solids into the cyclone body or any adjacent cyclones operating upon the same principal. In effect, the slots through which the ^article-contaminated gas exits act as a "check valve" to prevent backflow and particle re-entrainment into the cyclone body. [0012] The cyclone of the present invention is effective for separating even fine dust particles as small as 4-5 microns in diameter from the feed gas stream. These solid contaminants would otherwise render the contaminated gas non-compliant with environmental regulations or possibly prove detrimental to the proper functioning of power recovery turbines. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 is a simplified schematic view of an FCC unit of the prior art. [0014] FIG. 2 is a simplified schematic view of a third stage separator of the prior art. [0015] FIG. 3 is a cross sectional view "of the cyclone of the present invention. [0016] FIG. 4 is a sectional view of FIG. 3 taken along line AA. [0017] FIG. 5 shows the improved separation performance efficiency of the cyclone of the present invention, compared to those of the prior art. [0018] FIG. 6 shows the improvement associated with the present invention in terms of its d50 value, or measure of the particle diameter for which 50% removal would be obtained. DETAILED DESCRIPTION OF THE INVENTION [0019] The present invention applies to the purification of a broad range of solidcontaminated gas streams, and especially those containing dust particles in the 1-10 «m range. A number of commercial gas purification operations meet this description, including the treatment of effluent streams of solid catalyst fluidized bed processes, coal fired heaters, and power plants. Several well-known refinery operations rely on fluidized bed technology, such as a preferred embodiment of the process for converting methanol to light olefins, as described in US 6,137,022 Bl, using a solid zeolitic catalyst composition. Another area of particular interest lies in the purification of fluid catalytic cracking (FCC) effluent streams that contain entrained catalyst particles resulting from attrition, erosion, and/or abrasion under process conditions within the reactor. [0020] As mentioned, fluid catalytic cracking (FCC) is a well-known oil refinery operation relied upon in most cases for gasoline production. Process variables typically, include a cracking reaction temperature of 400-600°C and a catalyst regeneration temperature of 500-900°C. Both the cracking and regeneration occur at an absolute pressure below 5 atmospheres. FIG. 1 represents a typical FCC process unit of the prior art, where a heavy hydrocarbon feed or raw oil in line 12 is contacted with a newly regenerated catalyst entering from a regenerated catalyst standpipe 14. This contacting occurs along a narrow section extending from the bottom of the reactor 10, known as the reactor riser 16. Heat from the catalyst vaporizes the oil, and the oil is thereafter cracked in the presence of the catalyst as both are transferred up the reactor riser into the reactor 10 itself, operating at a pressure somewhat lower than that of the riser 16. The cracked light hydrocarbon products are thereafter separated from the catalyst using first stage 18 and second stage 20 internal reactor cyclones and exit the reactor 10 through line 22 to subsequent fractionation operations. At this point, some inevitable side reactions occurring in the reactor riser 16 have left detrimental coke deposits on the catalyst that lower its activity. The catalyst is therefore referred to as being spent (or at least partially spent) and requires regeneration for further use. Spent catalyst, after separation from the hydrocarbon product, falls into a stripping section 24 where steam is injected in line 26 to purge any residual hydrocarbon vapor. After the stripping operation, the spent catalyst is fed to the catalyst regenerator 30 using a spent catalyst standpipe 32. [0021] In the catalyst regenerator 30, a stream of air from line 34 is introduced through an air distributor 28 to contact the spent catalyst, burn coke deposited thereon, and provide regenerated catalyst. The catalyst regeneration process adds a substantial amount of heat to the catalyst, providing energy to offset the endothermic cracking reactions occurring in the reactor riser 16. Some fresh catalyst is added in line 36 to the base of the regenerator 30 to replenish catalyst exiting the reactor as fines material or entrained particles. Catalyst and air flow upward together along the combustor riser 38 located within the regenerator 30 and, after regeneration (i.e. coke burn), are initially separated by discharge through a "T" disengager 40, also within the regenerator 30. Finer separation of the regenerated catalyst and flue gas exiting the disengager 40 is achieved using first stage 44 and second stage 46 regenerator cyclone separators within the catalyst regenerator 30. Regenerated catalyst is recycled back to the cracking reactor 10 through the regenerated catalyst standpipe 14. As a result of the coke burning, the flue gas vapors exiting at the top of the regenerator in line 42 contain C02 and H,O, along with smaller amounts of other species. While the first stage 44 and second stage 46 regenerator cyclone separators can remove the vast majority of the regenerated catalyst from the flue gas in line 42, fine catalyst particles, resulting mostly from attrition, invariably contaminate this effluent stream. The fines-contaminated flue gas therefore typically contains 200-1000 mg/Nm^ of particulates, most of which are less than 50 microns in diameter. In view of this contamination level, and considering both environmental regulations as well as the option to recover power from the flue gas, the incentive to further purify the flue gas using a third stage separator (TSS) is significant. [0022] A typical TSS of the prior art, containing numerous individual cyclones, is shown in FIG. 2. The TSS vessel 50 is normally lined with refractory material 52 to reduce erosion of the metal surfaces by the entrained catalyst particles. The finescontaminated flue gas from the FCC regenerator enters the top of the TSS at its inlet 54 above an upper tube sheet 56 that retains the top ends 58 of each cylindrical cyclone body 62. The contaminated gas stream is then distributed among cyclone feed gas inlets 60 and contacted with one or more swirl vanes 64 proximate these inlets to induce centripetal acceleration of the particle-contaminated gas. The swirl vanes are structures within the cyclone body that have the characteristic of restricting the passageway through which incoming gas can flow, thereby accelerating the flowing gas stream. The swirl vanes also change the direction of the contaminated gas stream to provide a helical or spiral formation of gas flow through the length of the cyclone body. This spinning motion imparted to the gas sends the higher-density solid phase toward the wall of the cyclone body 62. [0023] The cyclone design shown in FIG. 2 represents the so-called " uniflow" apparatus where a bottom end 66 of the cyclone body 62 is open, allowing solid particles that have been thrown near the wall of this cylinder to fall into the space 68 between the upper and lower tube sheets. Clean gas, flowing along the centerline of the cyclone body, passes through an inlet 70 of a gas outlet tube 72 before reaching the bottom end 66 of the cyclone body 62. The clean gas is then discharged via the gas outlet tube 72 below a lower tube sheet 74. The combined clean gas stream, representing the bulk of the finescontaminated flue gas, then exits through a gas outlet 76 at the bottom of the TSS vessel 50. The separated particles and a minor amount (typically less than 10% of the finescontaminated flue gas) of underflow gas are removed through a separate paniculate and underflow gas outlet 78 at the bottom of the TSS 50. [0024] In FIG. 3, an individual cyclone separator 100 of the present invention, also affixed between an upper tube sheet 102 and a lower tube sheet 104, is shown. The cyclone 100 comprises an essentially vertical cyclone body 106 having a closed bottom end 108 with the cyclone body fixed at its top end 110 to the upper tube sheet 102. The closed bottom end 108 is preferably in the form of a horizontal plate. The cyclone body defines a feed gas inlet 112 at its top end 110 for receiving a particle-contaminated gas stream (e.g. a fines-contaminated flue gas stream) from above the upper tube sheet 102. Also, the cyclone body further defines a plurality of openings 114 for discharging gas. These openings 114 are between the upper, tube sheet 102 and the lower tube sheet 104, and are generally located in the lower portion of the cyclone body 106. Preferably, these openings 114 are proximate the bottom end 108 and extend upward from it. These openings allow for the discharge of particles along with a minor amount of an underflow gas, typically less than 10% of the particle-contaminated gas by volume, between the upper tube sheet 102 and the lower tube sheet 104. Closure of the bottom end 108 induces a high gas velocity and pressure drop through the discharge openings 114 by providing relatively little surface over which the exiting gas can escape. This leads to an overall improved separation. [0025] One or more swirl vanes 116 are located proximate the gas inlet at the top of the cyclone to induce centripetal acceleration of the particle-contaminated gas stream. A gas outlet tube 118 is located centrally within the cyclone body 106, extends through the closed bottom end 108, and further extends upward through the lower tube sheet 104. The top and bottom ends of this gas outlet tube 118 define, respectively, a clean gas inlet 120 for receiving a purified gas stream from within the cyclone body 106 and near its centerline, and a clean gas outlet 122 below the lower tube sheet 104 for discharging the purified gas stream. The clean gas inlet 120 is generally located above the discharge openings 114. The clean gas outlet 122 can be located anywhere below the bottom end 108. As mentioned, the cyclone body 106 is oriented generally vertically, so that separation of the solid phase is assisted by gravity. Preferably, the cyclone body is in the form of a vertical cylinder, however, other shapes are certainly possible, including, for example, a cone shape. [0026] As noted previously, the major advantage of this design is that it provides a very uniform vortex of swirling gas that is essentially undisturbed along its downward path through the cyclone body and gas outlet tube. A further advantage is related to the increased pressure drop accompanying the ejection of particulate-rich gas through the cylinder wall openings. These openings provide a relatively small surface area for gas to exit, compared to the larger bottom ring-shaped surface between the cyclone body and the gas outlet tube, used in the aforementioned uniflow cyclone designs. As a result, each opening provides a type of "check valve" through which backflow of discharged gas, a cause of reduced separation efficiency, is substantially eliminated. [0027] The uniformity in gas flow is maintained in part through the use of a plurality of openings on the cyclone cylinder body for discharge of particles and a small amount of underflow gas. The openings may be of virtually any shape and located anywhere on the cyclone cylinder body, although it is preferred that at least some of these openings are near the closed bottom end of the cyclone to prevent an accumulation of solid particles in this region. The openings may also be of varying shapes, for example, slots and holes, and located at various elevations on the cyclone body. Preferably, at least some of the openings are in the form of rectangular slots with their major dimension (length) substantially parallel to the axis of the cyclone body, as depicted in FIG. 3. These slots are normally spaced uniformly about the circumference of the cyclone body. Also, the vertical slot lengths usually range from 5% to 25% of the length of the cyclone body. In a preferred embodiment, the lower ends of the rectangular slots are adjacent to the closed bottom of the cyclone body. [0028] To further promote flow uniformity and thereby improve overall solid-gas separation efficiency, that the gas discharge openings are inclined from a radial direction. This allows gas to exit the cyclone body without a substantial change in its swirling, tangential flow direction, as established within the cyclone body. An example of this desired configuration is illustrated in FIG. 4, where the slots 114 also have edges 200 that are beveled (i.e. not normal to the line tangent to the circular cross section of the cyclone body 106 where the slots 114 are located). This beveling with respect to the curvature of the cyclone body 106 has the desired effect of allowing gas to exit the cyclone body 106 with a significant tangential velocity component and minimal change from the direction of gas flow within the cyclone body. Also, the leading edge along the principal length of each rectangular slot may be slightly raised from the general curvature of the cyclone body to divert the gas flow in the desired tangential direction. Alternatively or concurrently, the trailing edge of the slot may be sunk into the general curvature for a similar effect. [0029] Furthermore, it has been determined that good solid/gas separation efficiencies are obtained when the openings are located below the clean gas inlet, which is also represented in FIG. 3. The total open area through which spinning gas may be discharged is preferably from 0.05% to 5% of the surface area of the cyclone body. This parameter, of course, depends on several factors including solid contaminant concentration, average particle size, gas flow rate, and pressure. When multiple cyclones of the present invention are used in the design of a third stage separator (TSS) for an FCC refinery unit, the separator performance efficiency preferably includes a d50 particle size of below 5 microns. As understood in the art, the d50 value represents the diameter of a dust particle that is 50% removed in the underflow gas of the TSS. Accordingly, in a preferred embodiment, the purified gas stream has a concentration of particles of 5 microns or greater that is less than 50% of the concentration of particles of 5 microns or greater in the catalyst fines-contaminated flue gas stream. [0030] The performance benefit obtained using the cyclone of the present invention is further clarified in the following examples, which provide laboratory test data from experiments designed to simulate conditions found in FCC flue gas effluent streams. Although the following examples illustrate specific embodiments of the cyclone separator of the present invention, they are not intended to limit the overall scope of the invention as set forth in the claims. COMPARATIVE EXAMPLES 1-7 [0031] The previously mentioned "uniflow" type cyclone separators of the prior art were compared in performance to various cyclone separators according to the present invention. Separation of paniculate matter of 40 microns in diameter and smaller from a flowing gas stream was investigated. The cyclone separator in each test included a 280 mm i.d. cylindrical body with a 130 mm gas outlet tube concentric with the cylinder and extending from 250 mm above, to well below, the bottom of the cylinder. [0032] In the comparative tests, except for this gas outlet tube extension, the bottom of the cylinder was open, although a disk was mounted on the exterior of the gas outlet tube 130 mm below the cylinder bottom. Separated particulates, having been discharged at essentially right angles to the spinning feed gas flow, were collected, along with a minor amount of underflow gas, in a dust hopper surrounding the cylindrical cyclone body. Both this gas and the clean (overflow) gas exiting through the gas outlet tube were analyzed for solid contamination levels as well as the particle size distribution of these contaminants. Likewise, these analyses were performed on the feed gas. [0033] In each separate experiment, the feed gas inlet flow rate to the cyclone was maintained at 0.45-0.50 Nm^/sec. This gas contained 300-400 mg/Nm^ of solids with a median particle diameter of 10-20 microns. After exiting the swirl vanes near the gas inlet, the gas velocity gas was accelerated due to the flow restriction effected by these vanes. The gas discharged with the bulk of separated solids, called the underflow gas, represented either 1% or 3% by volume of the feed gas, depending on the specific test. After each test, the efficiency of solid paniculate removal was calculated as a weight percentage of the feed solids that were removed in the underflow gas. The percentage of solid particles in this stream of less than 10 microns in diameter was also determined, along with the calculated estimate of the particle diameter for which 50% removal would be achieved (the d50 value). [0034] Results for these comparative examples are summarized in Table 1. (Table Removed) EXAMPLES 8-12 [0035] The cyclone separator of the present invention was tested, by including in the cyclone design a horizontal base that was used to close the bottom of the cylinder body. In accordance with the description of the present invention, the solid particulates were in this case discharged from the spinning feed gas through openings in the cyclone cylinder sidewall. This was achieved by forming two rectangular slots of 90 mm in length and 10 mm in width. The length was parallel to the axis of the cylindrical cyclone body, and the lower width dimension was adjacent to the horizontal base closing the bottom of the cyclone body. The conditions of the feed gas flow rate, paniculate level, and average paniculate diameter were maintained within the ranges given in the Comparative Examples. Again, studies were performed using underflow values of 1% and 3% by volume. Also, the same performance parameters were evaluated and are given in Table 2. (Table Removed) [0036] From the above test results, it is evident that the cyclone of the present invention, when compared to the open-bottom " uniflow" cyclone of the prior art, provides greater efficiency of solid particulate removal at both the 1% and 3% underflow conditions. This is illustrated graphically in FIG. 5. Furthermore, the cyclone separator of the present invention is superior for removing particulates of 4-5 microns in diameter, which are relevant for the overall improvement of FCC third stage separator designs. The increased ability of the present invention cyclone separator to separate small particulates, based on its d50 performance parameter, is illustrated in FIG. 6. Lastly, in contrast to the results in the Comparative Examples for cyclone separators of the prior art, the cyclone separator of the present invention consistently achieved a clean (overflow) gas solids contamination level of less than 50 mg/Nm, in compliance with current and even potential future legislation. We Claim: 1. A cyclone separator (100) for use between an upper and a lower tube sheet (102, 104), the cyclone comprising: (a) a vertical cyclone body (106) having a closed bottom end (108) and a top end (110) fixed with respect to the upper tube sheet, the cyclone body having a feed gas inlet (112) at its top end, the feed gas inlet (112) extending above the upper tube sheet for receiving a particle-contaminated gas stream therefrom, the cyclone body having a sidewall of the cyclone body, the sidewall having a plurality of disdiaige openings (114) located between the upper and the lower tube sheets (102,104) for discharging particles and a minor amount of an underflow gas stream; (b) one or more swiri vanes (116) located proximate the gas inlet to induce centripetal acceleration of the particle-contaminated gas stream; (c) a gas outtet tube defining a clean gas inlet end (120) located centrally within the cyclone body for receiving a purified gas stream and having a clean gas outlet located (122) below the lower tube sheet for discharging the purified gas stream, the gas outlet tube extending through the closed bottom end of the cyclone body and extending through the lower tube sheet characterized in that dischaige openmgs are rectangular slots having lengths parallel to the axis of die cyclone body, the slots spaced uniformly about the circumference of the cyclone body and the discharge opoiings have a total open area from 0.05% to 0.5% the surface area of the cyclone body. 2. The cyclone separator as claimed in claim 1, wherein the cyclone body is cylindrical in shape. 3. The cyclone separator as claimed in claim 1, wherein the clean gas inlet (120) is located above the discharge openings. 4. The cyclone separator as claimed in claim 1, wherein the disdiaige openings (114) are inclined from the radial direction to allow the dicharge of gas without change from its tangential direction within the cyclone body. 5. THE cyclone separator as claimed in claim 1, wherein the vertical slot lengths are from 5% to 25% of the length of the cyclone body. 6. The cyclone separator as claimed in claim 5, wherein the lower ends of the rectangular slots arc adjacent to the closed bottom of the cyclone body. 7. The cyclone separator as claimed in claim 5, wherein die lower ends of the rectangular slots extend to the closed bottom of the cyclone body. 8. A cyclone separator as claimed in any of the preceding claims for use in purifying a solid-contaminated gas stream. 9. A cyclone separator for use between an upper and a lower tube sheet, substantially as hereinbefore described with reference to the foregoing description, examples and accompanying drawings.

Full Text

BACKGROUND OF THE INVENTION
[0001] The present invention relates to a novel cyclone separator for removing fine
solid participates from a gas stream. The cyclone is especially applicable in a third stage
separator apparatus, often used to purify the catalyst fines-laden flue gas stream exiting a
refinery fluid catalytic cracking (FCC) catalyst regenerator.
[0002] The emission of particulates in industrial gas streams must be carefully
controlled in light of federal, state, and local regulations designed to curtail pollution. In
the area of oil refinery operations, a major concern regarding paniculate emissions lies in
the flue gas exiting the catalyst regenerator section of fluid catalytic cracking (FCC)
units. Current United States federal regulations limit paniculate levels to 1 kg of solids
per 1000 kgs of coke burned in the catalyst regenerator, or the equivalent of a flue gas
paniculate concentration of approximately 80-110 mg/Nm^. Corresponding European
regulations currently vary considerably, from 80-500 mg/Nm^; however, this value is
expected to decline potentially to 50 mg/Nm^.
[0003] FCC technology, now more than 50 years old, has undergone continuous
improvement and remains the predominant source of gasoline production in many
refineries. This gasoline, as well as lighter products, is formed as the result of cracking
heavier (i.e. higher molecular weight), less valuable hydrocarbon feed stocks such as gas
oil. Although FCC is a large and complex process involving many factors, a general
outline of the technology is presented here in the context of its relation to the present
invention.
[0004] In its most general form, the FCC process comprises a reactor that is closely
coupled with a catalyst regenerator, followed by downstream hydrocarbon product
separation. A major distinguishing feature of the process is the continuous fluidization
and circulation of large amounts of catalyst having an average particle diameter of 50-
100 microns, equivalent in size and appearance to very fine sand. For every ton of
cracked product made, approximately 5 tons of catalyst are needed, hence the
considerable circulation requirements. Coupled with this need for a large inventory and
recycle of a small particle diameter catalyst is the ongoing challenge to prevent this
catalyst from exiting the reactor/regenerator system into effluent streams.
«
[0005] Overall, the use of cyclone separators internal to both the reactor and
regenerator has provided over 99% separation efficiency of solid catalyst. Typically, the
regenerator includes first and second (or primary and secondary) stage separators for the
purpose of preventing catalyst contamination of the regenerator flue gas, which is -
essentially the resulting combustion product of catalyst coke in air. While normal-sized
catalyst particles are effectively removed in the internal regenerator cyclones, fines
material (generally catalyst fragments smaller than 50 microns resulting from attrition
and erosion in the harsh, abrasive reactor/regenerator environment) is substantially more
difficult to separate. As a result, the FCC flue gas will usually contain a particulate
concentration in the range of 200-1000 mg/Nm^. This solids level can present difficulties
related to either the applicable legal emissions standards or the desire to recover power
from the flue gas stream. In the latter case, the solids content in the FCC flue gas may be
sufficient to damage turbine blades of an air blower to the regenerator if such a power
recovery scheme is indeed selected.
[0006] A further reduction in FCC flue gas fines loading is therefore often warranted,
and may be obtained from a third stage separator (TSS) device containing a manifold of
cyclones. Electrostatic precipitators. are known to be effective for this gas/solid
separation but are far more costly than a TSS, which relies on the induction of centripetal
acceleration to a particle-laden gas stream, forcing the higher-density solids to the outer
edges of a spinning vortex. To be efficient, a cyclone separator for an FCC flue gas
effluent will normally contain many, perhaps 100, small individual cylindrical cyclone
bodies installed within a single vessel acting as a manifold. Tube sheets affixing the
upper and lower ends of the cyclones act to distribute contaminated gas to the cyclone
inlets and also to divide the region within the vessel into sections for collecting the
separated gas and solid phases.
[0007] In the area of cyclone design, significant emphasis has been placed on socalled
"reverse flow" types where incoming gas is added around a gas outlet tube
extending from the inlet side of a cylindrical cyclone body. Particle-rich gas can be
withdrawn from openings in the sidewall of the cyclone body, while clean gas essentially
reverses flow from its initial path toward the end of the cyclone body opposite the gas
inlet, badk toward the gas outlet. The gas outlet is a tube normally concentric with, and
located within the cyclone body. These types of cyclones are described in US 5,514,271
Bl and US 5,372,707 Bl, where the inventive subject matter is focused on the shape and
distribution of the sidewall openings in order to minimize turbulent eddy formation that
can re-entrain solids into the clean gas outlet. In US 5,643,537 Bl and parent US
5,538,696 B1, devices are contemplated for use with this fundamental cyclone design to
further extend, or improve the uniformity of, the vortex flow pattern and thereby increase
separation efficiency.
[0008] Unfortunately, the requirement by itself for a gas stream to reverse direction
and exit the cyclone body on the same side as the gas inlet imposes flow disturbances
that are not easily overcome. Cyclones of the type described in US 5,690,709 Bl, termed
"uniflow", eliminate the re-entrainment of solids associated with the reversal of gas
direction. In this case, clean gas moves continually downward and exits the cyclone body
below a lower tube sheet, which serves as the physical boundary between the separated
particles and purified gas. This design, however, also promotes non-uniform flow
patterns, which are here associated with the discharge of particles at essentially right
angles to the particle-laden gas vortex, through the open bottom in the cylindrical
cyclone body. Again, the basic operation of the cyclone in this case involves a change in
direction of gas flow that should ideally be avoided. Furthermore, the open bottom
design provides a relatively large surface area for exiting "dirty" gas to enter the bodies
of adjacent cyclones in an overall arrangement of cyclones, such as in a TSS. This
communication of gas among cyclones reduces separation efficiency.
[0009] Aside from general considerations about cyclone design, such as the induction
of centripetal acceleration and the maintenance of a uniform flow pattern, further
improvements in efficiency associated with any particular cyclone configuration must be
verified through actual testing. Indeed, some proposed designs that were believed in
principle to mitigate uneven flow patterns and localized eddy formation actually
performed quite poorly in laboratory experiments. Even sophisticated computational
fluid dynamics computer software has been found in some cases to be a poor predictor of
TSS separation efficiency. Therefore, through extensive trial and error, coupled with the
overall objective of refining the cyclone internal flow pattern, a significant improvement
in fine particle separation from gas streams has been achieved.
SUMMARY OF THE INVENTION
[0010] The present invention is an improved cyclone for the separation of solid
particulates from a gas stream. Many of these cyclones can be combined in a vessel for
use as a third stage separator in the treatment of solid-contaminated gas streams, and in
particular flue gas from a refinery fluid catalytic cracking unit or other solidcontaminated
gas streams. The cyclone provides a high separation efficiency because a
particulate-laden gas vortex is established and travels through the device with minimal
flow pattern disturbances. The feed gas and exiting clean gas move in the same direction
throughout the separation, and the clean gas, representing the bulk of the feed gas on a
volume basis, is removed from the central portion of the vortex using a gas outlet tube
extending with the cyclone body. Furthermore, solid particles are forced through
openings in the sidewall of the cyclone body to prevent backflow and gas communication
among adjacent cyclones, rather than discharged axially.
[0011] The use of a plate or other structure to close off the bottom of cyclone body
means that particle-laden gas can exit only through openings on the cylinder wall. Thus,
the pressure drop across the area through which the gas discharges is generally higher
than that for open bottom designs. This increase in pressure drop and gas velocity
induces a more forceful ejection of particulates through the cylinder sidewall, thereby
preventing re-entry of solids into the cyclone body or any adjacent cyclones operating
upon the same principal. In effect, the slots through which the ^article-contaminated gas
exits act as a "check valve" to prevent backflow and particle re-entrainment into the
cyclone body.
[0012] The cyclone of the present invention is effective for separating even fine dust
particles as small as 4-5 microns in diameter from the feed gas stream. These solid
contaminants would otherwise render the contaminated gas non-compliant with
environmental regulations or possibly prove detrimental to the proper functioning of
power recovery turbines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a simplified schematic view of an FCC unit of the prior art.
[0014] FIG. 2 is a simplified schematic view of a third stage separator of the prior
art.
[0015] FIG. 3 is a cross sectional view "of the cyclone of the present invention.
[0016] FIG. 4 is a sectional view of FIG. 3 taken along line AA.
[0017] FIG. 5 shows the improved separation performance efficiency of the cyclone
of the present invention, compared to those of the prior art.
[0018] FIG. 6 shows the improvement associated with the present invention in terms
of its d50 value, or measure of the particle diameter for which 50% removal would be
obtained.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention applies to the purification of a broad range of solidcontaminated
gas streams, and especially those containing dust particles in the 1-10 «m
range. A number of commercial gas purification operations meet this description,
including the treatment of effluent streams of solid catalyst fluidized bed processes, coal
fired heaters, and power plants. Several well-known refinery operations rely on fluidized
bed technology, such as a preferred embodiment of the process for converting methanol
to light olefins, as described in US 6,137,022 Bl, using a solid zeolitic catalyst
composition. Another area of particular interest lies in the purification of fluid catalytic
cracking (FCC) effluent streams that contain entrained catalyst particles resulting from
attrition, erosion, and/or abrasion under process conditions within the reactor.
[0020] As mentioned, fluid catalytic cracking (FCC) is a well-known oil refinery
operation relied upon in most cases for gasoline production. Process variables typically,
include a cracking reaction temperature of 400-600°C and a catalyst regeneration
temperature of 500-900°C. Both the cracking and regeneration occur at an absolute
pressure below 5 atmospheres. FIG. 1 represents a typical FCC process unit of the prior
art, where a heavy hydrocarbon feed or raw oil in line 12 is contacted with a newly
regenerated catalyst entering from a regenerated catalyst standpipe 14. This contacting
occurs along a narrow section extending from the bottom of the reactor 10, known as the
reactor riser 16. Heat from the catalyst vaporizes the oil, and the oil is thereafter cracked
in the presence of the catalyst as both are transferred up the reactor riser into the reactor
10 itself, operating at a pressure somewhat lower than that of the riser 16. The cracked
light hydrocarbon products are thereafter separated from the catalyst using first stage 18
and second stage 20 internal reactor cyclones and exit the reactor 10 through line 22 to
subsequent fractionation operations. At this point, some inevitable side reactions
occurring in the reactor riser 16 have left detrimental coke deposits on the catalyst that
lower its activity. The catalyst is therefore referred to as being spent (or at least partially
spent) and requires regeneration for further use. Spent catalyst, after separation from the
hydrocarbon product, falls into a stripping section 24 where steam is injected in line 26
to purge any residual hydrocarbon vapor. After the stripping operation, the spent catalyst
is fed to the catalyst regenerator 30 using a spent catalyst standpipe 32.
[0021] In the catalyst regenerator 30, a stream of air from line 34 is introduced
through an air distributor 28 to contact the spent catalyst, burn coke deposited thereon,
and provide regenerated catalyst. The catalyst regeneration process adds a substantial
amount of heat to the catalyst, providing energy to offset the endothermic cracking
reactions occurring in the reactor riser 16. Some fresh catalyst is added in line 36 to the
base of the regenerator 30 to replenish catalyst exiting the reactor as fines material or
entrained particles. Catalyst and air flow upward together along the combustor riser 38
located within the regenerator 30 and, after regeneration (i.e. coke burn), are initially
separated by discharge through a "T" disengager 40, also within the regenerator 30.
Finer separation of the regenerated catalyst and flue gas exiting the disengager 40 is
achieved using first stage 44 and second stage 46 regenerator cyclone separators within
the catalyst regenerator 30. Regenerated catalyst is recycled back to the cracking reactor
10 through the regenerated catalyst standpipe 14. As a result of the coke burning, the flue
gas vapors exiting at the top of the regenerator in line 42 contain C02 and H,O, along
with smaller amounts of other species. While the first stage 44 and second stage 46
regenerator cyclone separators can remove the vast majority of the regenerated catalyst
from the flue gas in line 42, fine catalyst particles, resulting mostly from attrition,
invariably contaminate this effluent stream. The fines-contaminated flue gas therefore
typically contains 200-1000 mg/Nm^ of particulates, most of which are less than 50
microns in diameter. In view of this contamination level, and considering both
environmental regulations as well as the option to recover power from the flue gas, the
incentive to further purify the flue gas using a third stage separator (TSS) is significant.
[0022] A typical TSS of the prior art, containing numerous individual cyclones, is
shown in FIG. 2. The TSS vessel 50 is normally lined with refractory material 52 to
reduce erosion of the metal surfaces by the entrained catalyst particles. The finescontaminated
flue gas from the FCC regenerator enters the top of the TSS at its inlet 54
above an upper tube sheet 56 that retains the top ends 58 of each cylindrical cyclone
body 62. The contaminated gas stream is then distributed among cyclone feed gas inlets
60 and contacted with one or more swirl vanes 64 proximate these inlets to induce
centripetal acceleration of the particle-contaminated gas. The swirl vanes are structures
within the cyclone body that have the characteristic of restricting the passageway through
which incoming gas can flow, thereby accelerating the flowing gas stream. The swirl
vanes also change the direction of the contaminated gas stream to provide a helical or
spiral formation of gas flow through the length of the cyclone body. This spinning
motion imparted to the gas sends the higher-density solid phase toward the wall of the
cyclone body 62.
[0023] The cyclone design shown in FIG. 2 represents the so-called " uniflow"
apparatus where a bottom end 66 of the cyclone body 62 is open, allowing solid particles
that have been thrown near the wall of this cylinder to fall into the space 68 between the
upper and lower tube sheets. Clean gas, flowing along the centerline of the cyclone body,
passes through an inlet 70 of a gas outlet tube 72 before reaching the bottom end 66 of
the cyclone body 62. The clean gas is then discharged via the gas outlet tube 72 below a
lower tube sheet 74. The combined clean gas stream, representing the bulk of the finescontaminated
flue gas, then exits through a gas outlet 76 at the bottom of the TSS vessel
50. The separated particles and a minor amount (typically less than 10% of the finescontaminated
flue gas) of underflow gas are removed through a separate paniculate and
underflow gas outlet 78 at the bottom of the TSS 50.
[0024] In FIG. 3, an individual cyclone separator 100 of the present invention, also
affixed between an upper tube sheet 102 and a lower tube sheet 104, is shown. The
cyclone 100 comprises an essentially vertical cyclone body 106 having a closed bottom
end 108 with the cyclone body fixed at its top end 110 to the upper tube sheet 102. The
closed bottom end 108 is preferably in the form of a horizontal plate. The cyclone body
defines a feed gas inlet 112 at its top end 110 for receiving a particle-contaminated gas
stream (e.g. a fines-contaminated flue gas stream) from above the upper tube sheet 102.
Also, the cyclone body further defines a plurality of openings 114 for discharging gas.
These openings 114 are between the upper, tube sheet 102 and the lower tube sheet 104,
and are generally located in the lower portion of the cyclone body 106. Preferably, these
openings 114 are proximate the bottom end 108 and extend upward from it. These
openings allow for the discharge of particles along with a minor amount of an underflow
gas, typically less than 10% of the particle-contaminated gas by volume, between the
upper tube sheet 102 and the lower tube sheet 104. Closure of the bottom end 108
induces a high gas velocity and pressure drop through the discharge openings 114 by
providing relatively little surface over which the exiting gas can escape. This leads to an
overall improved separation.
[0025] One or more swirl vanes 116 are located proximate the gas inlet at the top of
the cyclone to induce centripetal acceleration of the particle-contaminated gas stream. A
gas outlet tube 118 is located centrally within the cyclone body 106, extends through the
closed bottom end 108, and further extends upward through the lower tube sheet 104.
The top and bottom ends of this gas outlet tube 118 define, respectively, a clean gas inlet
120 for receiving a purified gas stream from within the cyclone body 106 and near its
centerline, and a clean gas outlet 122 below the lower tube sheet 104 for discharging the
purified gas stream. The clean gas inlet 120 is generally located above the discharge
openings 114. The clean gas outlet 122 can be located anywhere below the bottom end
108. As mentioned, the cyclone body 106 is oriented generally vertically, so that
separation of the solid phase is assisted by gravity. Preferably, the cyclone body is in the
form of a vertical cylinder, however, other shapes are certainly possible, including, for
example, a cone shape.
[0026] As noted previously, the major advantage of this design is that it provides a
very uniform vortex of swirling gas that is essentially undisturbed along its downward
path through the cyclone body and gas outlet tube. A further advantage is related to the
increased pressure drop accompanying the ejection of particulate-rich gas through the
cylinder wall openings. These openings provide a relatively small surface area for gas to
exit, compared to the larger bottom ring-shaped surface between the cyclone body and
the gas outlet tube, used in the aforementioned uniflow cyclone designs. As a result, each
opening provides a type of "check valve" through which backflow of discharged gas, a
cause of reduced separation efficiency, is substantially eliminated.
[0027] The uniformity in gas flow is maintained in part through the use of a plurality
of openings on the cyclone cylinder body for discharge of particles and a small amount
of underflow gas. The openings may be of virtually any shape and located anywhere on
the cyclone cylinder body, although it is preferred that at least some of these openings are
near the closed bottom end of the cyclone to prevent an accumulation of solid particles in
this region. The openings may also be of varying shapes, for example, slots and holes,
and located at various elevations on the cyclone body. Preferably, at least some of the
openings are in the form of rectangular slots with their major dimension (length)
substantially parallel to the axis of the cyclone body, as depicted in FIG. 3. These slots
are normally spaced uniformly about the circumference of the cyclone body. Also, the
vertical slot lengths usually range from 5% to 25% of the length of the cyclone body. In a
preferred embodiment, the lower ends of the rectangular slots are adjacent to the closed
bottom of the cyclone body.
[0028] To further promote flow uniformity and thereby improve overall solid-gas
separation efficiency, that the gas discharge openings are inclined from a radial direction.
This allows gas to exit the cyclone body without a substantial change in its swirling,
tangential flow direction, as established within the cyclone body. An example of this
desired configuration is illustrated in FIG. 4, where the slots 114 also have edges 200 that
are beveled (i.e. not normal to the line tangent to the circular cross section of the cyclone
body 106 where the slots 114 are located). This beveling with respect to the curvature of
the cyclone body 106 has the desired effect of allowing gas to exit the cyclone body 106
with a significant tangential velocity component and minimal change from the direction
of gas flow within the cyclone body. Also, the leading edge along the principal length of
each rectangular slot may be slightly raised from the general curvature of the cyclone
body to divert the gas flow in the desired tangential direction. Alternatively or
concurrently, the trailing edge of the slot may be sunk into the general curvature for a
similar effect.
[0029] Furthermore, it has been determined that good solid/gas separation
efficiencies are obtained when the openings are located below the clean gas inlet, which
is also represented in FIG. 3. The total open area through which spinning gas may be
discharged is preferably from 0.05% to 5% of the surface area of the cyclone body. This
parameter, of course, depends on several factors including solid contaminant
concentration, average particle size, gas flow rate, and pressure. When multiple cyclones
of the present invention are used in the design of a third stage separator (TSS) for an
FCC refinery unit, the separator performance efficiency preferably includes a d50
particle size of below 5 microns. As understood in the art, the d50 value represents the
diameter of a dust particle that is 50% removed in the underflow gas of the TSS.
Accordingly, in a preferred embodiment, the purified gas stream has a concentration of
particles of 5 microns or greater that is less than 50% of the concentration of particles of
5 microns or greater in the catalyst fines-contaminated flue gas stream.
[0030] The performance benefit obtained using the cyclone of the present invention
is further clarified in the following examples, which provide laboratory test data from
experiments designed to simulate conditions found in FCC flue gas effluent streams.
Although the following examples illustrate specific embodiments of the cyclone
separator of the present invention, they are not intended to limit the overall scope of the
invention as set forth in the claims.
COMPARATIVE EXAMPLES 1-7
[0031] The previously mentioned "uniflow" type cyclone separators of the prior art
were compared in performance to various cyclone separators according to the present
invention. Separation of paniculate matter of 40 microns in diameter and smaller from a
flowing gas stream was investigated. The cyclone separator in each test included a 280
mm i.d. cylindrical body with a 130 mm gas outlet tube concentric with the cylinder and
extending from 250 mm above, to well below, the bottom of the cylinder.
[0032] In the comparative tests, except for this gas outlet tube extension, the bottom
of the cylinder was open, although a disk was mounted on the exterior of the gas outlet
tube 130 mm below the cylinder bottom. Separated particulates, having been discharged
at essentially right angles to the spinning feed gas flow, were collected, along with a
minor amount of underflow gas, in a dust hopper surrounding the cylindrical cyclone
body. Both this gas and the clean (overflow) gas exiting through the gas outlet tube were
analyzed for solid contamination levels as well as the particle size distribution of these
contaminants. Likewise, these analyses were performed on the feed gas.
[0033] In each separate experiment, the feed gas inlet flow rate to the cyclone was
maintained at 0.45-0.50 Nm^/sec. This gas contained 300-400 mg/Nm^ of solids with a
median particle diameter of 10-20 microns. After exiting the swirl vanes near the gas
inlet, the gas velocity gas was accelerated due to the flow restriction effected by these
vanes. The gas discharged with the bulk of separated solids, called the underflow gas,
represented either 1% or 3% by volume of the feed gas, depending on the specific test.
After each test, the efficiency of solid paniculate removal was calculated as a weight
percentage of the feed solids that were removed in the underflow gas. The percentage of
solid particles in this stream of less than 10 microns in diameter was also determined,
along with the calculated estimate of the particle diameter for which 50% removal would
be achieved (the d50 value).
[0034] Results for these comparative examples are summarized in Table 1.
(Table Removed) EXAMPLES 8-12
[0035] The cyclone separator of the present invention was tested, by including in the
cyclone design a horizontal base that was used to close the bottom of the cylinder body.
In accordance with the description of the present invention, the solid particulates were in
this case discharged from the spinning feed gas through openings in the cyclone cylinder
sidewall. This was achieved by forming two rectangular slots of 90 mm in length and 10
mm in width. The length was parallel to the axis of the cylindrical cyclone body, and the
lower width dimension was adjacent to the horizontal base closing the bottom of the
cyclone body. The conditions of the feed gas flow rate, paniculate level, and average
paniculate diameter were maintained within the ranges given in the Comparative
Examples. Again, studies were performed using underflow values of 1% and 3% by
volume. Also, the same performance parameters were evaluated and are given in Table 2.
(Table Removed) [0036] From the above test results, it is evident that the cyclone of the present
invention, when compared to the open-bottom " uniflow" cyclone of the prior art,
provides greater efficiency of solid particulate removal at both the 1% and 3% underflow
conditions. This is illustrated graphically in FIG. 5. Furthermore, the cyclone separator of
the present invention is superior for removing particulates of 4-5 microns in diameter,
which are relevant for the overall improvement of FCC third stage separator designs. The
increased ability of the present invention cyclone separator to separate small particulates,
based on its d50 performance parameter, is illustrated in FIG. 6. Lastly, in contrast to the
results in the Comparative Examples for cyclone separators of the prior art, the cyclone
separator of the present invention consistently achieved a clean (overflow) gas solids
contamination level of less than 50 mg/Nm, in compliance with current and even
potential future legislation.

We Claim:
1. A cyclone separator (100) for use between an upper and a lower tube sheet (102, 104), the
cyclone comprising:
(a) a vertical cyclone body (106) having a closed bottom end (108) and a top end (110) fixed with respect to the upper tube sheet, the cyclone body having a feed gas inlet (112) at its top end, the feed gas inlet (112) extending above the upper tube sheet for receiving a particle-contaminated gas stream therefrom, the cyclone body having a sidewall of the cyclone body, the sidewall having a plurality of disdiaige openings (114) located between the upper and the lower tube sheets (102,104) for discharging particles and a minor amount of an underflow gas stream;
(b) one or more swiri vanes (116) located proximate the gas inlet to induce centripetal acceleration of the particle-contaminated gas stream;
(c) a gas outtet tube defining a clean gas inlet end (120) located centrally within the cyclone body for receiving a purified gas stream and having a clean gas outlet located (122) below the lower tube sheet for discharging the purified gas stream, the gas outlet tube extending through the closed bottom end of the cyclone body and extending through the lower tube sheet characterized in that dischaige openmgs are rectangular slots having lengths parallel to the axis of die cyclone body, the slots spaced uniformly about the circumference of the cyclone body and the discharge opoiings have a total open area from 0.05% to 0.5% the surface area of the cyclone body.

2. The cyclone separator as claimed in claim 1, wherein the cyclone body is cylindrical in shape.
3. The cyclone separator as claimed in claim 1, wherein the clean gas inlet (120) is located above the discharge openings.
4. The cyclone separator as claimed in claim 1, wherein the disdiaige openings (114) are inclined from the radial direction to allow the dicharge of gas without change from its tangential direction within the cyclone body.
5. THE cyclone separator as claimed in claim 1, wherein the vertical slot lengths are from 5% to 25% of the length of the cyclone body.
6. The cyclone separator as claimed in claim 5, wherein the lower ends of the rectangular slots arc adjacent to the closed bottom of the cyclone body.
7. The cyclone separator as claimed in claim 5, wherein die lower ends of the rectangular slots extend to the closed bottom of the cyclone body.
8. A cyclone separator as claimed in any of the preceding claims for use in purifying a solid-contaminated gas stream.

9. A cyclone separator for use between an upper and a lower tube sheet, substantially as hereinbefore described with reference to the foregoing description, examples and accompanying drawings.

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Patent Number

233513

Indian Patent Application Number

2414/DELNP/2004

PG Journal Number

14/2009

Publication Date

27-Mar-2009

Grant Date

30-Mar-2009

Date of Filing

18-Aug-2004

Name of Patentee

UOP LLC

Applicant Address

25 EAST ALGONOQUIN ROAD,DES PLAINES,ILLINOIS 60017-5017,U.S.A.

Inventors:

#	Inventor's Name	Inventor's Address
1	SECHRIST,PAUL ALVIN	UOP LLC,25 EAST ALGONQUIN ROAD,DES PLAINES,IL 60017-5017 U.S.A.
2	HEDRICK,BRIAN,WESLEY	UOP LLC,25 EAST ALGONQUIN ROAD,DES PLAINES,IL 60017-5017 U.S.A.

PCT International Classification Number

B04C 3/06

PCT International Application Number

PCT/US02/02232

PCT International Filing date

2002-01-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA