Abstract:
A vapor horn device for use in an elongated, generally upright mass transfer and/or heat exchange column having an internal region comprises an elongated, generally arcuate wall arranged to be located within the internal region and disposed to extend around a longitudinal axis of the column. The arcuate wall includes an inlet area positioned for being contacted by a vapor or mixed phase stream entering the column and causing the stream to flow along an outer surface of the arcuate wall and generally around the axis. The device also includes a primary elongated vane extending outwardly from the outer surface of the arcuate wall. This primary vane has an inner end located adjacent the outer surface of the inner wall and an outer end disposed in spaced relationship relative to the outer surface of the wall. The vane is disposed at a tangential angle relative to the direction of flow of the stream such that the inner end of the vane is further downstream than the outer end thereof whereby any portion of the stream impinging on the primary vane is redirected toward the outer surface of the arcuate wall. The device also desirably includes one or more vanes that extend radially outwardly from the inner wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Priority benefits under 35 U.S.C. §119(e) are claimed in this application from provisional application Ser. No. 60/520,635, filed on Nov. 17, 2003, the entirety of the disclosure of which is hereby specifically incorporated herein by this reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to mass transfer and heat exchange columns and, more particularly, to methods and apparatus to improve vapor distribution in such columns. 
     In mass transfer and heat exchange columns, liquid and vapor streams are brought into contact with each other, normally in countercurrent flow, for mass or heat transfer, fractionation or other operations. Various types of internals, such as trays and random and structured packing, have been developed to facilitate interaction between the liquid and vapor streams within selected contact regions of the column. In order to increase the efficiency of the mass transfer or heat exchange taking place between the vapor and liquid within these contact regions, it is important that the liquid and vapor be uniformly distributed across the horizontal cross section of the column, particularly at the lower vapor-liquid interface where the vapor enters the packing or other contacting or internal device. 
     In columns of the types described above, vapor or mixed phase feed streams are frequently introduced radially or tangentially into the column through a feed nozzle at a location below the contact region. The vapor phase of the feed stream then rises through the contact region and interacts with downwardly flowing liquid. In certain specialized columns, the vapor or mixed phase feed stream is fed at high velocity through the feed nozzle into a flash zone located just above a section where the column transitions to a reduced diameter. The vapor then rises through overlying internals, such as trays, random packing, structured packing, grid packing, open spray chambers or side-to-side shower decks. Examples of such columns include, but are not limited to, virgin crude vacuum columns, virgin crude columns, FCCU main fractionator slurry pumparounds, visbreaker vacuum flashers, heavy oil vacuum towers, heavy oil fractionators, coker main fractionators, visbreaker fractionator, flexicoker main fractionators, and recovered lube oil vacuum towers. 
     Various devices have been developed in an attempt to interrupt the radial or tangential momentum of the feed stream entering columns of the types described above and redirect it so that it is able to rise in a more uniformly distributed manner across the cross section of the column as well as to separate the liquid components present in the feed stream from the vapor phase. An example of such a device is disclosed in U.S. Pat. No. 5,106,544 to Lee et al., where internal vanes are positioned within an annular vapor horn and are oriented to redirect the vapor or mixed phase feed stream downwardly through the open bottom of the vapor horn. The downwardly deflected vapor is then said to rise in a more uniform manner into an overlying packing bed. These internal vanes are also angled toward the external column shell in the direction of fluid flow so that the feed stream is deflected to impact against the inner surface of the column shell to facilitate separation of the liquid from the feed stream. As a result of computational fluid dynamics (“CFD”) modeling, it has been discovered that the internal vanes, when angled toward the column shell in the direction of fluid flow, create a localized high velocity zone of upwardly flowing vapor in the center of the column. This high velocity zone is undesirable because the high velocity and horizontal maldistribution of vapor reduces the efficiency of the mass transfer or other processing occurring in the overlying zones. A need has thus developed for a way to further improve the distribution of the vapor across the column cross section. 
     SUMMARY OF THE INVENTION 
     In accordance with the concepts and principles of the invention, the same provides a vapor horn device for use in an elongated, generally upright mass transfer and/or heat exchange column having an internal region. In accordance with one preferred aspect of the invention, the device includes an elongated, generally arcuate wall arranged to be located within the internal region and the same is disposed to extend around a longitudinal axis of the column. The arcuate wall includes an inlet area positioned for being contacted by a vapor or mixed phase stream entering the column and causing the stream to flow along an outer surface of the arcuate wall and generally around the longitudinal axis of the column. The device also includes a primary elongated vane that extends outwardly from the outer surface of the arcuate wall and the same has an inner end located adjacent the outer surface of the wall and an outer end disposed in spaced relationship relative to the outer surface. This primary vane is thus desirably disposed at a tangential angle relative to the direction of flow of the vapor or mixed phase stream such that the inner end of the vane is further downstream than the outer end thereof whereby any portion of the stream impinging on the primary vane is redirected toward the outer surface of the arcuate wall. 
     Desirably, in accordance with one preferred aspect of the invention, the arcuate wall may be located for being contacted by a radially directed vapor or mixed phase stream. Alternatively, the arcuate wall may be located for being contacted by a tangentially directed vapor or mixed phase stream. In either case, the device may ideally include one or more radially extending elongated vanes which extends outwardly from the outer surface of said arcuate wall 
     The device of the invention may also desirably include a secondary elongated vane that extends outwardly from the outer surface of the arcuate wall. Such secondary vane also has an inner end located adjacent the outer surface of the wall and an outer end disposed in spaced relationship relative to the outer surface of the wall. Such secondary vane is desirably disposed at a tangential angle relative to the direction of flow of the vapor or mixed phase stream such that the inner end of the secondary vane is further upstream than the outer end thereof. With this configuration, any portion of the stream impinging on the secondary vane is redirected away from the outer surface of the arcuate wall. 
     In further accordance with the concepts and principles of the invention, the secondary vanes and/or the radially extending vanes may be located downstream from the primary vane. 
     In a further aspect, the invention is directed to a column having a feed nozzle through which vapor or a mixed phase is fed at a high velocity into a feed zone within the column. The feed zone is preferably located above a portion of the column shell that tapers or transitions to a reduced diameter. In one example, the transitional portion of the column may be an elliptical head having a 2:1 ratio of the major horizontal radius to the height of the head. A feed device such as a vapor horn or vane inlet device is positioned within the column adjacent the feed nozzle to interrupt and redirect the momentum of the feed stream so that the vapor phase is able to rise in a more uniform manner into an overlying contact zone containing internals such as trays, random packing, structured packing, grid packing, open spray chambers or side-to-side shower decks. The feed device includes an at least partially open-bottomed, annular passageway in which a plurality of vertically-staggered internal vanes are positioned to redirect at least a portion of the feed stream downwardly through the bottom of the passageway toward the transitional portion of the column. The internal vanes extend inwardly from the column shell at one or more tangential angles that are selected to facilitate a more uniform horizontal distribution of the vapor as it rises through the open center of the feed device. At least one of the internal vanes is oriented to deflect the feed stream toward an inner annular wall of the feed device rather than toward the column shell. Preferably, at least one of the internal vanes is tangentially angled to deflect the feedstream toward the inner annular wall and at least one of the other internal vanes is radially oriented. One or more, but less than all, of the internal vanes may also be tangentially angled to deflect the feed stream toward the column shell. By varying the orientation of the internal vanes, it has been determined that a substantial reduction in the ascending vapor velocity and a corresponding improvement in horizontal vapor distribution are obtained. 
     In yet another aspect, the invention is directed to a method of distributing a vapor or mixed phase feed stream within a column having a feed zone located above a section of the column that transitions to a reduced diameter. The method includes the steps of directing the feed stream into a feed device having internal vanes extending inwardly at one or more tangential angles from the column shell toward an inner annular wall of the feed device, deflecting portions of the feed stream off of at least one of the internal vanes toward the inner annular wall, and discharging the deflected portions of the feed stream downwardly through an at least partially open bottom of the feed device. By deflecting the feed stream at selected, preferably differing tangential angles, the vapor is more uniformly distributed and has a more uniform velocity profile after it exits through the bottom of the feed device and then ascends through the open region centrally of the feed device into an overlying internal or other contacting device. At least one of the tangential angles is greater than 90° in the direction of flow of the feed stream so that portions of the feed stream are deflected toward an inner annular wall of the feed device rather than toward the column shell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary side elevation view of a portion of a mass transfer or exchange column which transitions from an upper region of a preselected diameter to a lower region having a reduced diameter, and illustrating a feed device constructed according to the present invention; 
         FIG. 2  is a top perspective view of the feed device of the present invention; 
         FIG. 3  is a fragmentary side elevation view of the mass transfer column similar to the view shown in  FIG. 1  but illustrating a liquid shield in the form of an annular wall positioned in a transition region of the column; and 
         FIG. 4  is a schematic top plan view of the feed device of  FIG. 1  but with the top of the feed device removed for clarity and with one of the internal vanes oriented differently. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in greater detail, and initially to  FIGS. 1 and 2 , a mass transfer or heat exchange column is designated generally by the numeral  10 . Column  10  comprises an external shell  12  which defines an open internal region  14  and which has an upper region  16  of a preselected diameter, a lower region  18  of lesser diameter, and a transition region  20  positioned between the upper region  16  and lower region  18 . The transition region  20  tapers from the diameter of the upper region  16  at the top to the diameter of the lower region  18  at the bottom. The primary function of the transition region  20  is to provide a transition between the larger diameter of the upper region  16  and the reduced diameter of the lower region  18 . To achieve this function, the transition region  20  preferably is an elliptical head as illustrated in  FIG. 1 , or it may have planar or multi-segmented sides to form other shapes such as hemispherical or conical. An elliptical head having a 2:1 ratio of the major horizontal radius to the height of the head is one preferred configuration for the transition region  20 . 
     The column  10  includes at least one vapor or mixed phase feed nozzle  22  that is located within the upper region  16 , but may also partially extend into the transition region  20 . The feed nozzle  22  delivers a high velocity vapor or mixed phase feed stream radially (in the direction of the arrow  98  in  FIG. 4 ) into a feed zone  24  located within the upper region  16  of the column  10 . Alternatively, the nozzle  22  may be oriented to deliver the vapor or mixed phase feed stream tangentially as shown in U.S. Pat. No. 5,106,544 mentioned above or at some intermediate orientation into the feed zone  24 . It is to be noted in these latter regards, that the entirety of the disclosure of U.S. Pat. No. 5,106,544 is hereby specifically incorporated herein by this specific reference thereto. 
     More than one nozzle  22  may also be used if desired for particular applications. A feed device  26  is positioned at the outlet of the feed nozzle  22  to interrupt and redirect the momentum of the high speed feed stream so that the vapor phase is able to rise in a more uniform manner into an overlying contact zone  28 . The feed device  26  preferably comprises a vapor horn  30  having an inner annular wall  32  spaced inwardly from the column shell  12  to form an annular flow passage  33  around at least a major portion of the periphery of the shell  12 . The inner annular wall  32  is preferably placed at a constant distance from the shell  12  around its entire circumference. Alternatively, the inner annular wall  32  can be positioned gradually closer to the shell  12  in the direction of flow of the feed stream so that the radial width of the flow passage  33  gradually decreases in the direction of feed stream flow. 
     The vapor horn  30  includes a top  34  that extends horizontally between a top edge of the inner annular wall  32  and the column shell  12  to block upward passage of the feed stream traveling within the vapor horn  30 . An optional floor  35  extends between a lower edge of the inner annular wall  32  and the column shell  12  in the region of the feed nozzle  22 . The floor  35  extends along only a small portion of the circumference of the flow passage  33 . 
     A plurality of internal vanes referred to in the drawings by the reference numerals  36   a ,  36   b  and  36   c  extend upwardly through an open bottom  38  of the vapor horn  30  into the feed stream flow passage  33 . The internal vanes  36   a ,  36   b  and  36   c  are constructed to redirect the vapor or mixed phase feed stream in a downward direction and are positioned at gradually increasing heights in the direction of feed stream flow within the vapor horn  30 . In one embodiment, the internal vanes  36   a ,  36   b  and  36   c  may desirably be planar. In another embodiment, an upper edge of the internal vanes  36   a ,  36   b  and  36   c  may be curved in a direction facing the flow of the feed stream, again as shown in U.S. Pat. No. 5,106,544. Other configurations for the internal vanes  36   a ,  36   b  and  36   c  are also possible and are within the scope of the invention. The internal vanes  36   a ,  36   b  and  36   c  preferably have a horizontal dimension sufficient to span the distance between the column shell  12  and the inner annular wall  32 . If desired, however, one or more of the internal vanes  36   a ,  36   b  and  36   c  may be spaced from either the column shell  12  and/or the inner annular wall  32  so that a flow passage is formed between a vertical edge of the internal vane  36   a ,  36   b  and  36   c  and the shell  12  and/or wall  32 . 
     In accordance with the present invention, the internal vanes  36   a ,  36   b  and  36   c  may desirably extend outwardly from an outer surface  132  of inner wall  32  at one or more tangential angles from the column shell  12 , with at least one of the internal vanes (see the vanes  36   a ) angled toward the inner annular wall  32  to deflect the vapor toward the inner annular wall  32  rather than toward the column shell  12 . That is to say, each vane  36   a  has an inner end  136   a  that is located adjacent surface  132  and an outer end  236   a  that is disposed in spaced relationship to surface  132 . Thus, the vanes  36   a  are disposed at a tangential angle relative to the direction of flow of the feed stream (see arrow  100  in  FIG. 4 ) with the inner end  136   a  thereof disposed further upstream relative to the feed stream flow than the outer end  236   a  thereof. Preferably, therefore, the internal vanes  36   a  are each angled toward the inner annular wall  32 . Preferably, one or more of the internal vanes may be arranged so as to extend radially outwardly from surface  132  (see vanes  36   b  and  36   c  in  FIGS. 1 and 2 ). In addition, one or more, but less than all, of the internal vanes (see vane  36   c ′ in  FIG. 4 ) may desirably be angled in the opposite direction from vanes  36   a  so that the feed stream is directed outwardly toward the column shell  12 . In this latter regard it is to be noted that  FIG. 4  shows a different orientation for the vane  36   c ′ relative to the corresponding vane  36   c  of  FIGS. 1 and 2 . By varying the tangential orientation of the internal vanes  36   a ,  36   b  and  36   c , it has been determined that a substantial reduction in the ascending vapor velocity and a corresponding improvement in horizontal vapor distribution are obtained. 
     Using CFD modeling of a column  10  having a 2:1 elliptical head for the transition region  20  and a radial feed nozzle  22 , it has been determined that positioning the internal vanes  36   a  (which are those that are closest to the feed nozzle  22 ) at a tangential angle α (see  FIG. 4 ) of 120 to 140°, and ideally 130°, in the direction of flow of the feed stream, and positioning the internal vanes  36   b  and  36   c  so as to extend radially (as shown in  FIGS. 1 and 2 ) produces a more uniform vapor distribution and a more uniform velocity profile in a horizontal plane located six inches above the feed device  26  than was obtained by the conventional practice of angling each of the turning vanes  36  toward the column shell  12 . In the preferred CFD model, opposite edges of the vapor horn floor  35  were positioned 22.5° from the centerline of the feed nozzle  22  and the internal vanes  36   a ,  36   b  and  36   c  were positioned in each flow direction at successive 22.5° spacings from the edge of the vapor horn floor  35 . These angles are represented by the angles β, γ and δ in  FIG. 4 . The internal vane  36   a  in each flow direction extends upwardly into the passage  33  a vertical distance of 20 inches and the second and third internal vanes  36   b  and  36   c  extend upwardly 30 and 40 inches, respectively. Positioning the internal vanes  36   a  closer to the edge of the vapor horn floor  35  less than 22.5° provided an even more uniform vapor distribution and velocity profile, but greater spacing was believed necessary to permit efficient liquid deentrainment at the internal vanes  36   a . It will be appreciated that other arrangements of internal vanes  36   a ,  36   b  and  36   c  also provide improved results provided that they are positioned at differing tangential angles with at least one of the internal vanes ( 36   a ) being angled toward the inner annular wall  32 . By using a combination of tangential angles, the vapor is directed out of the feed device  26  in different directions rather than being focused toward the center of the column  10 . As a result, a much more uniform velocity profile can be obtained. 
     The method of the present invention includes the steps of directing the feed stream into the feed device  26  described above, deflecting portions of the feed stream off of at least one of the internal vanes ( 36   a ) toward the inner annular wall  32 , and discharging the deflected portions of the feed stream downwardly through the at least partially open bottom  38  of the feed device  26 . By deflecting the feed stream at selected, preferably differing tangential angles, the vapor is more uniformly distributed and has a more uniform velocity profile after it exits through the bottom  38  of the feed device  26  and then ascends through the open region centrally of the feed device  26  into the overlying internal or other contacting device in the contact zone  28 . At least one of the tangential angles is greater than 90° in the direction of flow of the feed stream so that portions of the feed stream are deflected toward an inner annular wall  32  of the feed device  26  rather than toward the column shell  12 . 
     Numerous modifications can be made to the vapor horn  30 , such as those described in U.S. Pat. No. 5,605,654, which is incorporated herein by reference in its entirety. Alternatively, other types of feed devices  26  known in the prior art can be used. 
     Various internals  40 , such as trays, random packing, structured packing, grid packing, open spray chambers and/or side-to-side shower decks, are located in the contact zone  28 . For example, when the column  10  is a crude vacuum column, the internals  40  will comprise part of a wash zone that is designed to remove entrained residual components from a flash zone vapor stream. The wash zone internals  40  will typically comprise contacting devices, such as trays or packings, and spray nozzles or headers that deliver wash oil to the contacting devices. Other combinations and arrangements of internals  40  are possible and are within the scope of the invention. 
     The transition region  20  includes at least one and preferably a plurality of baffles  42  that are constructed and positioned to prevent or reduce the swirling motion that can be imparted to the high velocity vapor or mixed phase feed stream as it is deflected downwardly into the transition region  20  by the feed device  26 . The baffles  42  may abut the column shell  12  or they may be spaced therefrom to allow a portion of the feed stream to pass between the baffle  42  and shell  12 . The baffles  42  may be planar or curved and may extend along only a portion or the entire longitudinal length of the transition region  20 . The baffles  42  may each be of the same construction, or baffles  42  in one portion of the transition region  20  may be constructed or oriented differently than baffles in other portions of the transition region  20 . The objective of the baffles  42  is to prevent or disrupt some or all of the swirling motion of the feed stream in the transition region  20  to achieve a uniform vapor stream flow pattern with only vertical velocity components. In addition, the baffles  42  reduce the vapor maldistribution that can result as the swirling vapor rises upwardly through the feed zone  24  into the overlying internals  40 . It will be appreciated that many modifications can be made to the baffles  42  to achieve these objectives. In addition, the invention is generally directed to various types of columns  10  that employ a transition region  20  and a high velocity vapor or mixed phase feed, such as virgin crude columns, FCCU main fractionator slurry pumparounds, visbreaker vacuum flashers, heavy oil vacuum towers, heavy oil fractionators, coker main fractionators, visbreaker fractionator, flexicoker main fractionators, and recovered lube oil vacuum towers. 
     In an alternate embodiment shown in  FIG. 3 , the column  10  can include a shield  44  positioned in the transition region  20  to shelter liquid flowing downwardly along the inner face of the column shell  12  from the swirling feed stream that can cause unwanted reentrainment of the liquid. The shield  44  can take many forms and as illustrated is a wall  46  that is spaced inwardly from the transition region  20  of the column shell  12 . Appropriate mounts  48  are used to secure the wall  46  to the shell  12 . The spacing between the shell  12  and the wall  46  forms an annulus  50  that provides a passageway for liquid to flow downwardly through the transition region  20  while being shielded from the swirling feed stream. The shield  44  thus reduces the amount of liquid that is entrained by the vapor. Baffles  42  are preferably used in conjunction with the shield  44 , and they can be mounted to an inner face of the wall  46 . 
     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objectives hereinabove set forth together with other advantages that are inherent to the structure. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the invention. 
     Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.