The present invention relates generally to cross flow trays used in mass transfer columns in which mass transfer and/or heat exchange processes occur and, more particularly, to apparatus and methods for supporting such cross flow trays.
Cross flow trays are used within mass transfer columns to facilitate interaction between fluid streams flowing in countercurrent relationship within the column. The term mass transfer column as used herein is not intended to be limited to columns in which mass transfer is the primary objective of the processing of the fluid streams within the column, but is also intended to encompass columns in which heat transfer rather than mass transfer is the primary objective of the processing. The fluid streams are typically an ascending vapor stream and a descending liquid stream, in which case the cross flow trays are commonly referred to as vapor-liquid cross flow trays. In some applications, both fluid streams are liquid streams and the cross flow trays are commonly referred to as liquid-liquid cross flow trays. In still other applications, the ascending fluid stream is a gas stream and the descending fluid steam is a liquid stream, in which case the cross flow trays are referred to as gas-liquid cross flow trays.
The cross flow trays are positioned within the column in vertically spaced-apart relationship with each of the tray decks extending horizontally to fill the entire internal cross-section of the column. Each of the cross flow trays has a planar tray deck on and above which interaction between the ascending fluid stream and the descending fluid stream occurs, a plurality of apertures to allow upward passage of the ascending fluid stream through the tray deck and into the descending fluid stream to create a froth or mixture in which the desired mass transfer and/or heat exchange occurs, and at least one downcomer that directs the descending fluid stream from the associated tray deck to a tray deck on an underlying cross flow tray. The portion of the tray deck that receives the descending fluid stream from the downcomer of an overlying cross flow tray typically comprises an inlet panel that is either imperforate or contains bubble promoters or other structures that allow upward passage of the ascending fluid stream but impede the descending fluid stream from weeping through the inlet panel.
Cross flow trays having a single side downcomer located at one end of the tray deck are known as single-pass trays. In other applications, typically those involving higher descending liquid flow rates, multiple downcomers may be used on some or all of the cross flow trays. For example, in two-pass configurations, two side downcomers are positioned at opposite ends of one cross flow tray and a single center downcomer is positioned in the center of the adjacent cross flow trays. In four-pass configurations, one cross flow tray has two side downcomers and a center downcomer and the adjacent contact trays have two off-center downcomers.
The tray decks of cross flow trays are typically secured by clamps to support rings welded to the interior surface of the column shell. The downcomer walls are also normally bolted at their opposite ends to bolting bars that are welded to the interior surface of the column shell. In some applications, such as in larger diameter columns and in columns in which vibratory forces are a concern, it is known to add further support to portions of the tray deck by using a strut that extends upwardly from major beams, lattice trusses or a system of hangers to connect the tray deck of a cross-flow tray to the downcomer walls of a similar tray located directly above, or below. When hangers are utilized, the downcomer walls act as beams to carry a portion of the load of the coupled tray, thereby reducing sagging and bracing against uplift of the tray deck. These hangers and other structures, however, add complexity to the design and increase the cost of fabrication and installation of the cross flow tray.
In other applications, the inlet panel on the tray deck is formed as a structural beam to provide added support to the tray deck. The inlet panel must then be interconnected to the adjacent portions of the tray deck using fasteners of various types, thereby adding to the complexity in the design and the installation of the tray deck. A need has thus arisen for a method of supporting and bracing the tray deck while reducing the disadvantages resulting from the conventional methods of providing additional support in larger diameter columns and in columns in which vibratory forces are present.