A gas liquid separator adapted to be inserted into a conduit is disclosed. The gas-liquid separator includes downward sloping vanes and optionally, one or more return channels. The vanes may have an opening along the length thereof, and a bottom lip to channel accumulated liquid to the conduit wall or to sloped return channels. If the conduit is not sloped such that the captured droplets are returned to the originating vessel, sloped return channel/channels are used to return the captured droplets to the vessel from which the gas stream originated. With a central return channel, the vanes can be attached directly to the channel with the resulting assembly having a fishbone shape. When a central return channel is not used, the vanes can be attached to a central plate or spine with the resulting spine-vanes assembly again having a fishbone shape. The separation enhancers can be used in a variety of conduit configurations. Furthermore, a plurality of separation enhancers can be utilized in an exhaust gas conduit to increase the removal efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to Patent Application No. 20050056150, filed Sep. 17, 2003

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to separation of liquid droplets from gas-liquid streams in chemical processes.

2. Background Art

Many chemical processes require take-off of a gas phase from chemical processing equipment such as chemical reactors. In some cases, the nature of the various reactants, products, and by-products facilitate removal of a gas phase substantially free of liquid. However, in other processes, considerable quantities of liquid droplets may be associated with the gas phase, and in the case where the liquid droplets can later solidify, whether due strictly to a phase change or to subsequent reaction, lines and valves may be plugged and require disassembly and cleaning or replacement. Furthermore, in many cases, the liquid droplets may constitute a loss of valuable reactants, intermediate products, or end products. For example, during preparation of polyethylene terephthalate polymers, polymer and oligomer particles may carry over with ethylene glycol and water as the latter are removed from the reactor in a vapor phase.

Many types of devices for liquid removal from gas streams are known, including cyclone separators, chill plates, filters, and the like. Packed columns efficiently remove liquid droplets, for example. However, many of these methods, for instance chill plates, are energy intensive, and others such as packed columns exhibit a severe pressure drop as well as being prone to plugging. In-line filters also suffer from these drawbacks.

Inertial separators or traps make use of the fact that a flowing gas can easily make turns that droplets with large inertia cannot. The droplets that cannot turn with the gas stream because of their inertia strike or impact a target or collecting surface, onto which they are deposited. A simple pipe elbow is an example of such a separator. However, such separators are generally efficient only for droplets of materials with large inertia. Since the inertia of the droplets is measured by its mass, the size and density of the droplets is important in determining the removal efficiency.

In U.S. Pat. No. 5,181,943, liquid removal is effectuated by providing a large number of plate-type baffles across the path of a liquid-gas stream, the baffles being substantially parallel but downward sloping, and alternately extending from opposite sides of the separation device, positioned transverse to the initial direction of flow. This device creates a high surface area serpentine path, and must be quite large if pressure drop is to be low. Since in many cases the separator must be maintained at a specific operating temperature and thus requires considerable external insulation, such devices are relatively capital intensive.

U.S. Pat. No. 5,510,017 discloses a gas-liquid separator involving two sets of concentric, radially arranged vanes, which cause a swirling flow of liquid-containing gas directed there through. The centrifugal forces generated cause liquid droplets to impinge upon the walls of the pipe section containing the separator, from which they are removed as bulk liquid by a series of drains. This device is of rather complex construction, and is believed to be useable only when configured for horizontal flow due to the placement of liquid-trapping baffles and drains. Moreover, conversion of linear flow to a swirling flow necessarily requires energy, which is manifested as a pressure drop.

EP 0 197,060 discloses a gas liquid separator useful in gas desulfurizing, which employs a plurality of groups of obliquely mounted large surface area slats which are sprayed with a rinsing liquid to carry away droplets impinging upon the slats. Use of a rinsing liquid is undesirable in many applications.

U.S. patent application No. 20050056150 discloses a gas-liquid separator that is referred to as a fishbone separator because the construction of it involves a central spine from which emanates a plurality of vanes for collecting liquid droplets. The fishbone construction described in the '150 application is limited in that it is placed in the upstream (inlet) region of an elbow where the centerline of the elbow inlet is substantially vertical. This limitation is significant in that the conduit system carrying the gas exiting polymerization reactors tend to be large and inflexible offering only a limited number of available conduit positions for placing the gas-liquid separator. In some conduit layouts the upstream (inlet) region of an elbow may not be accessible, or an elbow as such may not be present in the conduit system.

Accordingly, there is a need for an improved gas-liquid separator with a simple design and construction that can be positioned at addition positions in a polymerization reactor conduit system, which can be used without rinse liquid, which offers low pressure drop, and which is efficient at separating droplets with relatively small inertia from a gas stream.

SUMMARY OF THE INVENTION

The present invention solves one or more problems of the prior art by providing in one embodiment, a gas liquid separation enhancer that can be placed within a conduit attached to a polymerization reactor. The gas-liquid separation enhancer of the invention advantageously separates liquid, and in particular liquid droplets from a gas stream. In one embodiment, the separation enhancer includes a central return channel and a plurality of longitudinally extending vanes. The longitudinally extending vanes are positioned to direct a portion of any liquid contacting the vanes into the central return channel. The central return channel directs liquid in a downward direction under the force of gravity in an opposite sense to the direction of the stream of gas and liquid droplets.

In another embodiment of the invention, a gas-liquid separation enhancer with a peripheral return channel and without a central return channel is provided. The gas-liquid separation enhancer of this embodiment includes a central spine (instead of a central channel), a plurality of longitudinally extending vanes distributed along the central spine, and a peripheral return channel. Each vane has a first end and a second end wherein the first end of each vane is adjacent to the central spine with each vane positioned to direct a portion of any liquid contacting the vanes to the second end away from the central spine toward the conduit wall and the peripheral return channel. The peripheral return channel directs material from the conduit wall above the return channel in a downward direction under the force of gravity in an opposite sense to the direction of the gas stream containing liquid droplets.

In another embodiment of the invention, a gas-liquid separation enhancer with both a central return channel and a peripheral channel is provided. The gas-liquid separation enhancer of this embodiment includes a plurality of longitudinally extending vanes distributed along the central return channel. Each vane has a first end and a second end wherein the first end of each vane is adjacent to the central return channel with each vane positioned to direct a portion of any liquid contacting the vanes to the second end toward the central return channel. Finally, the central return channel directs liquid from the vanes in a downward direction under the force of gravity in an opposite sense to the direction of the stream of gas and liquid droplets. The peripheral return channel directs material from the conduit wall above the return channel in a downward direction under the force of gravity in an opposite sense to the direction of the stream of gas containing liquid droplets.

In yet another embodiment of the invention, a gas-liquid separation enhancer without return channels (central or peripheral) and positionable in a section of a conduit extending from a process vessel is provided. The gas-liquid separation enhancer of this embodiment includes a central spine and a plurality of longitudinally extending vanes distributed along the spine. Again, each vane has a first end and a second end wherein the first end of each vane is adjacent to the central spine. This embodiment is distinguished from the other separation enhancers in that this embodiment is applicable to conduits which are sloped such that liquid on the spine and conduit wall around it flows back to the reactor from which it originates under the influence of gravity so return channels as such may not be needed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventors.

With reference toFIGS. 1A and 2A, a first embodiment of the gas-liquid separation enhancer (i.e., the gas-liquid separator) of the invention is provided.FIG. 1Aprovides a side-view of the separation enhancer placed within the exit region of an elbow of a reactor conduit.FIG. 2Ais a magnified view of the side-view ofFIG. 1A. Gas-liquid separation enhancer10is positionable in conduit12for separating liquid from a stream having gas and liquid droplets emanating from process vessel14. Typically, conduit12has a circular cross-section although other shapes are possible. The stream flows through conduit12in flow direction16which leads away from process vessel14. In some variations of this embodiment, process vessel14is a polymerization reactor such as a polycondensation polymerization reactor. Accordingly, the liquid droplets typically include at least one of liquid monomers or oligomers.

Still referring toFIGS. 1A and 2A, separation enhancer10may be placed in conduit12in the exit region of conduit elbow20. In a variation of this embodiment, bottom end22of separation enhancer10is attached at position24of conduit12which is at or adjacent to apex position26of conduit elbow20while top end28of separation enhancer10is attached to at position30of conduit12. An inlet end of elbow20is in fluid communication with process vessel14which emanates a stream of gas containing liquid droplets—into elbow20with collected liquid from separation enhancer10being directed back into vessel14. In this variation, most of separation enhancer10will be outside of a line of site for most positions within process vessel14such that at least a portion of separation enhancer10extends in a direction past apex position26of elbow20in a direction downstream of elbow20when conduit12is part of process vessel14.

With reference toFIGS. 2B and 2C, the utilization of the separation enhancer of the invention as used with mitered bends is provided. As used herein, “mitered bend” means that the bend is formed by joining the ends of straight sections of conduit together.FIG. 2Billustrates a simple two-piece 90° bend with a separation enhancer. InFIG. 2Bmitered bend42includes bend sections44,46which are connected along beveled seam48. InFIG. 2Ca mitered bend is shown that is an alternative to the elbow ofFIG. 2A. Mitered bend50is formed from bend sections52,54,56,58,60.

With reference toFIGS. 1B and 2D, a variation of the separation enhancer as used in a conduit that is a side nozzle extending from the reactor is provided.FIG. 1Bprovides a side-view of separation enhancer10placed within side nozzle62that extends from process vessel14.FIG. 2Dis a magnified view of the separation enhancer and side nozzle ofFIG. 1B. In some variations, section63of side nozzle62extends into process vessel14in order to prevent droplets that have contacted the top of process vessel14from entering side nozzle62. In this variation, the stream containing gas and liquid emanates from process vessel14through a side nozzle62. An inlet end of side nozzle62is in fluid communication with process vessel14which emanates a stream of gas containing liquid droplets into side nozzle62with collected liquid being directed back into vessel14from separation enhancer10. Bottom end22of separation enhancer10is attached at position64of side nozzle62while top end28of separation enhancer10is attached to at position66of conduit (side nozzle) side nozzle62. In general, separation enhancer10will be outside the line of site for positions below height68.

With reference toFIG. 3, an illustration of one embodiment of the separation enhancer10is provided. Separation enhancer10includes central return channel70and a plurality of longitudinally extending vanes72distributed in a fishbone pattern along central return channel70. The vanes and central return channel70are constructed from any material that is compatible with the temperature and chemical conditions to which separation enhancer10is exposed. In particular, a metal construction is useful. The central return channel has a width of about one half or less of the internal diameter of the conduit. In general, vanes70have a somewhat hollow construction. Specifically, the vanes have an opening along a length thereof with the opening facing the direction of gas flow. As set forth below, the opening is located such that the hollow vane has a fluid collecting lip located at the bottom thereof. Vanes are positioned to provide a surface to contact the stream having gas and liquid droplets when separation enhancer10is placed within process vessel14. Specifically, each of vanes72are positioned to provide substantially maximal contact with the stream having gas and liquid droplets during operation. Therefore, vanes72are mounted such that an axis through the height of the cross-section is angled from the direction of gas flow from 20° to about 90°. Additional vane designs and methods of attaching vanes are provided in Patent Application No. 20050056150, which is hereby incorporated by reference. In a variation of the inventions, central return channel70includes a plurality of inlet openings74. Each vane of the plurality of longitudinally extending vanes72includes first end80and second end82. Moreover in the embodiment shown, vanes72include top lip84and bottom lip86. Bottom lip86provides a channel for transporting liquid to central return channel70. Vanes72are attached to central return channel70by any technique that results in a structure that can withstand the temperature and chemical environment likely present during operation of the process vessel. Regardless of the mechanism with which vanes72are attached, the plurality of longitudinally extending vanes72are distributed along central return channel70and positioned to direct a portion of any liquid contacting the vanes to first end80and through one of the inlet openings74and into the central return channel70. It should also be appreciated that when separation enhancer10is placed within a conduit, vanes72will be angled relative to a horizontal plane such that liquid collecting in the vanes will flow under the force of gravity into central return channel70. Moreover, separation enhancer10is positionable in a conduit as set forth above such that central return channel70is also at an angle with respect to a horizontal plane. Although any angle is possible so long as central return channel70slopes towards process vessel14when separation enhancer12is positioned in a conduit, typical values for this angle are from about 20° to 80°. When separation enhancer10is placed within conduit12(or side nozzle32) of a functioning process vessel14, liquid droplets emanating with the gas stream from process vessel14impinges on central return channel70and vanes72. At least a portion of the liquid contained in the stream is captured by central return channel70and vanes72. That portion of the liquid captured by vanes72flows toward and then into central channel70. Liquid collected by central return channel70flows in downward direction90under the force of gravity towards process vessel14. Clearly, direction90is in an opposite sense to the flow direction of the stream having gas and liquid droplets. Accordingly, at least a portion of the collected liquid falls back into process vessel14. Optionally, separation enhancer10also includes bottom guard88which further directs the liquid away from separation enhancer10, and to inhibit liquid from bypassing the separation enhancer by flowing away from process vessel14.

With reference toFIGS. 4A-E, alternative constructions for the vanes used in the separation enhancer of the invention are provided. The vanes preferably are constructed “hollow,” with a longitudinal slit, e.g. having a “C” or “J” cross-section, and are of a cross-section such that when in position in the fishbone, a bottom channel is preferably present, to aid in conducting liquid along the vane, and to shield collected liquid from the gas flow, so that liquid does not reenter the gas stream. Circular, elliptical, airfoil, square, rectangular, or other shapes may be used. The shape and oblique angle with respect to gas flow may be calculated by aerodynamic simulations to minimize pressure drop, and/or to maximize fluid collection efficiency. InFIG. 4A, a rectangular vane92is shown, with discontinuous openings. InFIG. 4B, an open “semi-circular” vane94is depicted, with two holes96for attaching the vane by bolts to a mounting strut.FIG. 4Cillustrates a triangular vane98with a completely open portion100along its length, and a liquid collecting lip102.FIG. 4Dshows an airfoil vane104with a discontinuous opening, whileFIG. 4Eshows a vane108having no top lip at its upper end106.

With references toFIGS. 5A and 5B, examples of alternative mechanisms for positioning vanes72about central return channel are provided.FIG. 5Aprovides a perspective view in which the vanes line up which notches in the central return channel. Specifically, return channel70includes a plurality of notches110instead of openings. Vanes72are aligned with notches110. Moreover, opposing vanes72a,72bare optionally attached together at position112for added structural strength.FIG. 5Bprovides a perspective view of another variation in the method of attaching the vanes. In this variation, vanes72overhang central return channel70and are mounted on brackets114.

In another embodiment of the invention, the separation enhancer set forth above includes a peripheral return channel. With reference toFIGS. 6A and 6Bvariations of the utilization of a peripheral return channel are illustrated.FIG. 6Ais a perspective view of the incorporation of a peripheral return channel positioned in front of the vanes. Peripheral channel130is positioned in front of ends132of vanes72. Moreover, peripheral return channel130when placed within a conduit will be adjacent to the interior surface of such a conduit such that liquid does not escape past the periphery of separation enhancer10. Liquid collected by peripheral return channel130flows downward under the force of gravity in a direction that is in an opposite sense to the direction of the stream of gas and liquid droplets. If present, the liquid will then flow over bottom guard88.FIG. 6Bis a perspective view of the incorporation of a peripheral return channel positioned behind the vanes. The peripheral return channel130of this variation functions similarly to the peripheral return channel130ofFIG. 6A.

In another embodiment of the invention, a gas-liquid separation enhancer is provided with a peripheral return channel and a central spine in place of a central return.FIG. 7provides a perspective view of the separation enhancer of this embodiment. Separation enhancer138includes a plurality of longitudinally extending vanes72distributed along central spine140. Each vane of vanes72has first end80and a second end82such that each vane is attached to central spine140at first end80and is positioned to direct a portion of any liquid contacting the vane to second end82. Peripheral return channel142is located behind the periphery of vanes72. The specific details regarding the construction of vanes72are set forth above. Moreover, separation enhancer138may optionally include a central return channel (not shown) positioned behind (i.e., downstream of) central spine140to receive droplets flowing from vanes72when the vanes are sloped such that captured droplets flow towards central spine140.

In another embodiment of the invention, a gas-liquid separation enhancer without return channels (central and peripheral) and positionable in a section of a conduit extending from a process vessel is provided. The location and slope of the section of conduit containing the separation device determines if this is the case. With reference toFIGS. 8 and 9, a separation enhancer positionable within a straight and substantially vertical section of a conduit is illustrated.FIG. 9is a perspective view of the separation enhancer ofFIG. 8. In this embodiment, separation enhancer150is placed within conduit section152that is in fluid communication with process vessel14. Separation enhancer150includes central spine154and a plurality of longitudinally extending vanes72distributed along central spine154. Again, each of vanes72has first end80and second end82such that first end80of each vane is adjacent to the central spine154and each vane is positioned to direct a portion of any liquid contacting vanes72to second end82away from the central spine154. The specific details regarding the construction of vanes72are set forth above. Moreover, separation enhancer150may optionally include a central return channel (not shown) positioned to receive droplets flowing from vanes72when the vanes are sloped such that captured droplets flow towards central spine154.

In still another embodiment of the invention, a plurality of separation enhancers is included in an exhaust gas conduit. With reference toFIG. 10, inclusion of multiple separation enhancers is illustrated. Utilization of multiple separation enhancers always improves the efficiency of liquid droplet removal from a gas stream compared to a single separation enhancer. Conduit156includes separation enhancer150and separation enhancer10each of which is described in detail above. Also included in conduit156is separation enhancer160which is of the designs described in U.S. patent application No. 20050056150 which is already incorporated by reference.

In yet another embodiment of the invention, the separation enhancers set forth above are used in a process for the separation of droplets of liquid from a flowing gas stream. An example of such a process is best appreciated with reference toFIGS. 1A,1B,2A,2B,2C and2D. A stream that includes gas and entrained liquid droplets emerges from process vessel14along direction16. Conduit12directs the stream into separation enhancer10which is of a fishbone construction as set forth above being constructed with vanes emanating from a central return channel or spine. Liquid is subsequently collected by contact of the droplets with separation enhancer10and the walls of elbow20or mitered bend50and42. An exist gas stream depleted of liquid droplets emerges from elbow20. When the conduit containing the separation device is a side nozzle, liquid is collected by contact of the droplets with separation enhancer10and the walls of side nozzle62. The details for separation enhancer10are set forth above. Similarly, with reference toFIGS. 8 and 9, a stream that includes gas and entrained liquid droplets emerges from process vessel14flowing into conduit152. Conduit152directs the stream into separation enhancer150which is of a fishbone construction as set forth above being constructed with vanes emanating from a central spine or a central spine with return channel. Liquid is subsequently collected by contact of the droplets with separation enhancer150.