Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
1999-10-07
2001-06-26
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C261S114300, C261S114500
Reexamination Certificate
active
06250611
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in vapor-liquid contact apparatus used in chemical processing, and particularly to the type of such apparatus in which a vessel contains a plurality of substantially horizontal trays which support a vapor-liquid mixture; liquid is introduced at the upper end of the vessel and it flows down from tray-to-tray, via downcomers; each downcomer has a floor which form a downwardly facing outlet for releasing liquid from the downcomer to a subsequent tray; and, the trays are apertured to provide bubbling areas through which ascending vapors can rise to contact liquid and/or vapor-liquid mixtures which are supported on and flowing across them.
It has been recognized in the art that the performance of contact tray apparatus can be enhanced if the liquid flow on the tray is uniform in the respect that the flow in the lateral areas of the tray is substantially the same as the flow along the central flow axis thereof. Heretofore, shaped downcomer tips, directional vapor outlets and other means have been utilized for this purpose.
It has also been recognized in the art that, by providing apertured floors in downcomers, the deentrainment of vapors from liquid from the vapor-liquid mixture in downcomers can be improved by providing the downcomers with apertured floors which increase the residence time of the vapor-liquid mixture in the downcomers. Downcomer floor configurations disclosed in this specification serves both to increase the residence time of the vapor-liquid mixture in the downcomer and to provide a more uniform flow of the vapor-liquid mixture in the bubbling area of a tray.
According to the present invention, the flow of fluid into the bubbling area of a tray is made more uniform across the width of the bubbling area by providing a novel shape and location of a downwardly facing liquid outlet opening of a downcomcr which feeds the tray. Utilizing the simple and effective design of the present invention, the apparatus will have increased capacity, higher efficiency, and a greater operating range. The risk of fouling or plugging the downcomer outlet is minimized. By providing adjustability of the components which define the novel downcomer outlet opening, the apparatus can be fine-tuned to achieve optimum performance.
It has been observed experimentally that, when liquid is released through a circular outlet opening (a pour point) in a downcomer floor, and the liquid from the pour point strikes a target area on an unobstructed flat surface, the liquid flows from the pour point in the form of an expanding shallow inner ring which extends radially from the pour point. The liquid depth suddenly increases in an annular area, referred to in this specification as an “hydraulic jump ring” which is concentric with the target area and the pour point.
When two pour points are close enough together that the hydraulic jump rings emanating from their respective target areas interact, an even deeper wave is formed equidistantly from the target areas. By using an elongated downcomer outlet opening or openings in accordance with the present invention, these deeper waves are eliminated or reduced in number.
When the target area of a pour point is near an obstruction such as the inner wall of a vessel, the liquid emanating radially from the target area will strike and rebound from the vessel wall. Due to the concave curvature of the wall of a cylindrical vessel, some of the rebounding liquid will be directed toward the central flow axis of the tray, thus causing a focusing effect which results in a higher flow rate at the central flow axis of the tray than at the sides thereof. This is of particular concern when the outer edge of a downcomer outlet slot is contiguous with the inner wall of the vessel, thus avoiding the undesirable rebound and focusing effect which is associated with prior floored downcomers.
This invention is based in part on the recognition that there are inherent deficiencies in the liquid distribution at the upstream ends of the bubbling areas of the trays in the apparatus described above, particularly due to the configurations and arrangements of the apertures in the downcomer floors. Significant features of the apparatus disclosed in this specification are believed to represent new and beneficial approaches to the design and construction of such apparatus.
SUMMARY OF THE INVENTION
According to one principal feature of the present invention, a vapor-liquid contact apparatus comprises a vessel, and a plurality of vertically spaced horizontal trays in the vessel for supporting a vapor-liquid mixture. Each of the trays has a bubbling area, a liquid infeed area at an upstream end of the bubbling area, and an exit opening at a downstream end of the bubbling area. The bubbling area has a central flow axis which leads from the liquid infeed area to the exit opening, and apertures which permit ascending vapors to flow up through the tray and into a vapor-liquid mixture on the tray. A downcomer is provided for receiving the vapor-liquid mixture from the tray and for carrying liquid to another tray. The downcomer has an upper portion located at the exit opening of the tray, and a lower portion with a cross-section which is surrounded by an inner edge and a convex outer edge. These edges are transverse with respect to the central flow axis. The cross-section of the downcomer has a centerline which is parallel to the central flow axis of the bubbling area. A downcomer floor is provided in the above-mentioned cross-section to control flow of liquid from the downcomer. The downcomer floor forms a downcomer outlet which includes an elongated downcomer outlet slot or series of slots, each of which has a length which is greater than its width, the width being perpendicular to the outer edge of the downcomer and the length being parallel to the outer edge of the downcomer. The slot width at the centerline of the cross-section is no greater than the slot width at locations which are spaced from the centerline.
According to another main feature of the invention, a vapor-liquid contact apparatus comprises a vessel, and a plurality of vertically spaced horizontal trays in the vessel for supporting a vapor-liquid mixture. Each of the trays has a bubbling area, a liquid infeed area at an upstream end of the bubbling area, and an exit opening at a downstream end of the bubbling area. The bubbling area has a central flow axis which leads from the liquid infeed area to the exit opening, and apertures which permit ascending vapors to flow up through the tray and into a vapor-liquid mixture on the tray. A downcomer is provided for receiving the vapor-liquid mixture from the tray and for carrying liquid to another tray. The downcomer has an upper portion located at the exit opening of the tray, and a lower portion with a cross-section which is surrounded by an inner edge and a convex outer edge. These edges are transverse with respect to the central flow axis. The cross-section of the downcomer has a centerline which is parallel to the central flow axis of the bubbling area. A downcomer floor is provided in the above-mentioned cross-section to control flow of liquid from the downcomer. The downcomer floor has a convex outer edge, at least a portion of which is spaced from the outer edge of the cross-section of the downcomer to form a downcomer outlet which includes an elongated downcomer outlet slot.
In connection with the foregoing features, the invention also includes a downcomer outlet which is wider at locations which are spaced from the downcomer centerline than at the downcomer centerline. The downcomer outlet has a total area no greater than 70% of the area of the downcomer cross-section where the downcomer floor is located. A preferred downcomer outlet is a slot with a length which is at least 60% of the length of the cross-section. The outlet slot has an end which is spaced from the downcomer centerline by a distance which is at least 30% of the length of said cross-section. The slot width is preferably no more than about 40% of t
Nutter Dale E.
Pilling Mark W.
Bushey C. Scott
Smith Gambrell & Russell
Sulzer Chemtech USA, Inc.
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