Patent Description:
As used herein, the term "mass transfer column" refers to a column in which mass transfer and/or heat exchange occur. Examples of mass transfer columns include distillation, absorption, stripping, and extraction columns.

Various types of trays are commonly used in mass transfer columns to promote contact and mass transfer between ascending and downwardly flowing fluid streams. The ascending fluid is typically vapor and the descending fluid is typically liquid, although liquid-liquid and gas-liquid systems are also known. Each tray normally extends horizontally across substantially the entire horizontal cross section of the column and is supported around its perimeter by a ring welded to the inner surface of the circular column wall or shell. A number of trays are positioned in this manner with a uniform vertical spacing between adjacent trays. The trays may be located in only a portion of the column to perform one part of a multi-step process occurring with the column. Alternatively, the trays may fill substantially the entire open area within the column.

Trays of the type described above contain one or more downcomers that are positioned at openings in the tray deck to provide passageways for liquid to descend from one tray to an adjacent lower tray. Prior to entering the downcomer, the liquid on the tray deck interacts with ascending vapor that passes through openings provided in selected portions of the tray deck. Those areas of the tray deck containing vapor openings are commonly referred to as "active" areas because of the vapor and liquid mixing and frothing that occurs above those areas of the tray.

The vapor openings in the tray deck can be simple sieve holes or can be formed as part of fixed or moveable valves. Conventional valves have valve covers supported over the opening in the tray deck by attachment legs. In fixed valves, the valve cover is fixed against vertical movement. In moveable valves, the valve cover is able to move up and down in response to variations in vapor or fluid flow rates through the opening. The valve cover functions to shield the opening in both the fixed and moveable valves against undesirable weeping of fluid downwardly through the opening and to laterally direct the vapor or other fluid that has ascended through the opening for enhanced interaction with the fluid flowing along the tray deck. Documents <CIT> and <CIT> discloses such trays with valves.

While a variety of fixed and moveable valves are known, further improvements in their design and performance are desired.

A contact tray not according to the invention is disclosed and said contact tray comprises a generally planar tray deck and a plurality of valves distributed across the tray deck. Each of the valves comprises an opening that extends through the tray deck to allow for passage of fluid through the tray deck, a weir extending upwardly from the tray deck around a perimeter of the opening, and a valve cover supported by attachment legs above said opening and said weir. The valve cover extends outwardly beyond the entire perimeter of the opening and has a downwardly extending perimeter region.

The present invention is directed to a contact tray for use in a mass transfer column. The contact tray comprises a generally planar tray deck and a plurality of valves distributed across the tray deck. Each of the valves comprises an opening that extends through the tray deck to allow for passage of fluid through the tray deck, a weir extending upwardly from the tray deck around an entire perimeter of the opening, a valve cover supported above said opening and said weir by first and second attachment legs positioned at opposite ends of said valve cover, and a vent opening formed in one of said attachment legs. The valve cover extends outwardly beyond the entire perimeter of the opening and has a downwardly extending perimeter region.

In a preferred embodiment, the contact tray according to the present invention has the following features: The contact tray comprises a generally planar tray deck and a plurality of valves distributed across the tray deck. Each of the valves comprises an opening that extends through the tray deck to allow for passage of fluid through the tray deck, a weir extending upwardly from the tray deck around an entire perimeter of the opening, a valve cover supported above said opening and said weir by first and second attachment legs positioned at opposite ends of said valve cover, and a vent opening formed in one of said attachment legs. The opening in the tray deck is circular and the valve cover is in the form of an isosceles trapezoid. The attachment legs comprise first and second attachment legs respectively connected to opposed parallel first and second ends of the valve cover. The valve cover each extends outwardly beyond the entire perimeter of the opening in the tray deck and the first attachment leg has a width greater than a largest width of the opening. The valve cover has a downwardly extending perimeter region.

In the accompanying drawings that form part of the specification and in which like reference numerals are used to indicate like components in the various views:.

Turning now to the drawings in greater detail and initially to <FIG>, a mass transfer column suitable for use in mass transfer or heat exchange processes is represented generally by the numeral <NUM>. The column <NUM> may include an upright, external shell <NUM> that may be generally cylindrical in configuration, although other configurations, including polygonal, are possible and are within the scope of the present invention. The shell <NUM> may be of any suitable diameter and height and may be constructed from one or more rigid materials that are desirably inert to, or are otherwise compatible with, the fluids and conditions present during operation of the column <NUM>.

The column <NUM> may be of a type used for processing fluid streams, typically liquid or vapor streams, to obtain fractionation products or to otherwise cause mass transfer or heat exchange between the fluid streams. For example, the column <NUM> may be one in which crude atmospheric, lube vacuum, crude vacuum, fluid or thermal cracking fractionating, coker or visbreaker fractionating, coke scrubbing, reactor off-gas scrubbing, gas quenching, edible oil deodorization, pollution control scrubbing, or other processes occur.

The shell <NUM> of the column <NUM> defines an open internal region <NUM> in which the desired mass transfer or heat exchange between the fluid streams occurs. In one implementation, the fluid streams may comprise one or more ascending vapor streams and one or more descending liquid streams. In other implementations, the fluid streams may comprise substantially any combination of ascending or descending liquid streams or ascending or descending vapor streams.

One or more fluid streams may be directed into the column <NUM> through any number of feed lines <NUM>, such as lower feed lines 16a or upper feed lines 16b, positioned at appropriate locations along the height of the column <NUM>. In one implementation, vapor streams may be generated within the column <NUM> rather than being introduced into the column <NUM> through the feed lines 16a, 16b. One or more fluid streams may be directed out of the column <NUM> through any number of takeoff lines <NUM>, such as lower takeoff line 18a and upper takeoff line 18b. In one implementation, liquid may be introduced through upper feed line 16b, descend through the column <NUM>, and be removed through lower takeoff line 18a, while vapor may be introduced through lower feed line 16a, ascend through the column <NUM>, and be removed through upper takeoff line 18b.

Other column components that would typically be present, such as reflux stream lines, reboilers, condensers, vapor horns, liquid distributors, and the like, are not illustrated in the figures because they are conventional in nature and an illustration of these components is not believed to be necessary for an understanding of the present invention.

In accordance with the present invention, a plurality of pairs of fixed-valve contact trays <NUM> and <NUM> is positioned within the open internal region <NUM> of the column <NUM> to facilitate interaction of the fluids flowing within the open internal region <NUM>. The trays <NUM> and <NUM> extend generally horizontally across the entire cross-section of the column <NUM> and are arranged in an alternating fashion such that each tray <NUM> overlies and is vertically adjacent to one of the trays <NUM>. The specific design of each tray <NUM> and <NUM> can be varied while remaining within the scope of the present invention.

In the illustrated embodiment of <FIG>, the trays <NUM> and <NUM> are constructed to form a single-pass fluid flow arrangement in which the descending fluid flows from end-to-end opposite flow directions on each tray <NUM> and <NUM>. Each tray <NUM> has a side downcomer <NUM> that is positioned at one end of a tray deck <NUM> that is normally formed from interconnected tray panels. The side downcomer <NUM> receives and removes the descending fluid from the tray deck <NUM> and delivers it to one end of a tray deck <NUM> of a paired underlying tray <NUM>. The fluid then flows across the tray deck <NUM> in an opposite direction to a side downcomer <NUM> that is positioned at an opposite end of the tray deck <NUM>. The fluid enters the side downcomer <NUM> and is delivered to the tray deck <NUM> of the next underlying tray <NUM>. This flow pattern is repeated on each of the lower pairs of trays <NUM> and <NUM>. Although the trays <NUM> and <NUM> are illustrated as being constructed for single-pass fluid flow, the invention encompasses trays constructed for multi-pass flow.

Fixed valves <NUM> are positioned in a preselected pattern on some portions of the tray decks <NUM> and <NUM> of the trays <NUM> and <NUM> to allow vapor or another fluid to ascend through the tray decks <NUM> and <NUM> and interact with flowing across the upper surface of the tray decks <NUM> and <NUM>. The area of the tray decks <NUM> and <NUM> containing these fixed valves <NUM> is normally referred to as the active area of the trays <NUM> and <NUM>.

The area of the tray deck <NUM> underlying the side downcomer <NUM> of the overlying tray <NUM> comprises an inlet panel <NUM> and is normally imperforate or has shielded flow passages that impede or prevent the descending fluid from passing through the inlet panel <NUM>. Similarly, the area of the tray deck <NUM> underlying the side downcomer <NUM> of the overlying tray <NUM> comprises an inlet panel <NUM> that is imperforate or has shielded flow passages.

The side downcomer <NUM> of each tray <NUM> comprises a wall <NUM> that extends in a chordal fashion across the open internal region <NUM> of the column <NUM>. The upper portion of the wall <NUM>, or a separate piece attached to the wall <NUM>, extends upwardly above the tray deck <NUM> to form an inlet weir <NUM> that causes liquid to accumulate on the tray deck <NUM> before spilling over the weir <NUM> and entering the side downcomer <NUM>. A lower portion of the wall <NUM> is spaced above the underlying tray deck <NUM> or contains flow openings (not shown) to allow fluid to exit the side downcomer <NUM> and flow along the upper surface of the tray deck <NUM> before entering the side downcomer <NUM> at the opposite end of the tray deck <NUM>.

Similarly, the side downcomer <NUM> on each tray <NUM> comprises a chordal wall <NUM> that has a lower portion that is spaced above the underlying tray deck <NUM> or contains flow openings (not shown) to allow fluid the exit the side downcomer <NUM> and flow along the upper surface of the tray deck <NUM>. An upper portion of the wall <NUM>, or a separate piece attached to the wall <NUM>, extends upwardly above the tray deck <NUM> to form an inlet weir <NUM>. While each of walls <NUM> and <NUM> is illustrated as planar and vertically-extending, stepped, sloped or multi-chordal walls or other constructions are within the scope of the invention.

Turning now to <FIG>, each of the fixed valves <NUM> on tray deck <NUM> comprises an opening <NUM> that extends through the tray deck <NUM> to allow for passage of fluid through the tray deck <NUM> and a weir <NUM> extending upwardly from the tray deck <NUM> a preselected distance along an entire perimeter of the opening <NUM>. Each fixed valve <NUM> also includes a valve cover <NUM> supported by first and second attachment legs <NUM> and <NUM> at a fixed, preselected location above the opening <NUM>. While two attachment legs <NUM> and <NUM> are used in the illustrated embodiment to support the valve cover <NUM>, additional attachment legs could be used if desired.

The attachment legs <NUM> and <NUM> in the illustrated embodiment extend upwardly from the tray deck <NUM> and are located at opposite ends of the valve cover <NUM>. The attachment legs <NUM> and <NUM> are shown as extending generally perpendicularly to the tray deck <NUM>, but they may in other embodiments slope toward or away from each other. Each of the attachment legs <NUM> and <NUM> has an upper end that is attached to and is integral with an edge of the valve cover <NUM>.

The attachment legs <NUM> and <NUM> are fixed to the tray deck <NUM> in a suitable fashion. In the illustrated embodiment, the attachment legs <NUM> and <NUM> extend downwardly through parallel slots <NUM> and <NUM> (<FIG>), respectively, positioned on opposite sides of the opening <NUM> in the tray deck <NUM>. Each of the attachment legs <NUM> and <NUM> includes a pair of shoulders <NUM> and <NUM>, respectively, that engage against an upper surface of the tray deck <NUM> and a locking tab <NUM> that has an upper surface spaced a preselected distance below the shoulders <NUM> and <NUM>. The locking tab <NUM> engages against an under surface of said tray deck <NUM>. The distance between the shoulders <NUM> and <NUM> and the upper surface of the tab <NUM> is selected to prevent vertical movement of the attachment legs <NUM> and <NUM>, and valve cover <NUM> carried thereon, when the shoulders <NUM> and <NUM> of the attachment legs <NUM> and <NUM> engage the upper surface of the tray deck <NUM> and the upper surfaces of said locking tabs <NUM> engage against the under surface of the tray deck <NUM>. If desired, the distance between the shoulders <NUM> and <NUM> and the upper surface of the locking tab <NUM> can be increased to allow some vertical movement of the attachment legs <NUM> and <NUM> and valve cover <NUM> in response to variations in upward pressure exerted on the under surface of the valve cover <NUM> by the fluid ascending through the openings <NUM> in the tray deck <NUM>.

The locking tab <NUM> can be of various suitable forms that allow the attachments legs <NUM> and <NUM> to be inserted downwardly through the slots <NUM> and <NUM> before the upper surface of the locking tab <NUM> is positioned to engage against an under surface of the tray deck <NUM>. For example, the locking tab <NUM> can simply be manually bent to bring its upper surface into engagement with the under surface of the tray deck <NUM> following installation of the attachment legs <NUM> and <NUM>. In the illustrated embodiment, the locking tab <NUM> is formed in the associated attachment leg <NUM> or <NUM> by cutting along two sides and an upper edge of the locking tab <NUM> while leaving a lower edge of the locking tab <NUM> attached to the attachment leg <NUM> or <NUM>. The locking tab <NUM> is then bent about the attached lower edge to move the remainder of the locking tab <NUM> out of the plane of the associated attachment leg <NUM> or <NUM>. When the attachment leg <NUM> or <NUM> is inserted downwardly through the associated slot <NUM> or <NUM>, the portions of the tray deck <NUM> surrounding the slot <NUM> or <NUM> cause the locking tab <NUM> to pivot toward the plane of the attachment leg <NUM> or <NUM>. The locking tab <NUM> then springs outwardly once the locking tab <NUM> clears the slot <NUM> or <NUM>.

Attachment leg <NUM> has a width that is greater than a largest corresponding width of the opening <NUM> in the tray deck <NUM> to shield the opening <NUM> against unwanted weeping of fluid downwardly through the opening <NUM>. The fixed valve <NUM> is oriented on the tray deck <NUM> so that the attachment legs <NUM> and <NUM> are aligned in the general direction of fluid flow along the upper surface of the tray deck <NUM>, with the attachment leg <NUM> located at the upstream side of the fixed valve <NUM>. The upstream attachment leg <NUM> in one embodiment is greater than that of the attachment leg <NUM> to facilitate a more streamlined flow of fluid around the opening <NUM>.

The valve cover <NUM>, in one embodiment, is in the form of an isosceles trapezoid with the attachment legs <NUM> and <NUM> connected to opposed parallel first and second ends of the valve cover <NUM>. The valve cover <NUM> may alternatively be formed with other shapes. The valve cover <NUM> is dimensioned to extend outwardly beyond the entire perimeter of the opening <NUM> in the tray deck <NUM> to more effectively shield the opening <NUM> against the detrimental downward weeping of fluid through the opening <NUM> and has a downwardly-extending outer perimeter region <NUM>. The valve cover <NUM> (except at the perimeter region <NUM>) lies in a plane that is parallel to that of the tray deck <NUM>. In other embodiments, the valve cover <NUM> may be inclined, such as in an upward direction in the general direction of fluid flow on the upper surface of the tray deck <NUM>.

The downstream attachment leg <NUM> in each fixed valve <NUM> includes a louvered vent opening <NUM> directed in the downstream fluid-flow direction away from the upstream attachment leg <NUM>. The vent opening <NUM> allows fluid ascending through the opening <NUM> in the fixed valve <NUM> to vent through the attachment leg <NUM> to facilitate intermixing with the fluid flowing along the upper surface of the tray deck <NUM> and to provide a directional push to the flowing fluid. Each of the fixed valves <NUM> on tray deck <NUM> are of the same construction as those described above on the tray deck <NUM>.

It has been found through comparative testing that the fixed valves <NUM> reduce the entrainment of liquid in the vapor ascending through the fixed valves <NUM> and decrease the weeping of liquid downwardly through the fixed valves <NUM> in comparison to conventional PROVALVE™ fixed valves that are of similar construction but lack the downturned perimeter region <NUM> of the valve cover <NUM>, the weir <NUM> surrounding the opening <NUM>, and the vent opening <NUM> formed in the downstream attachment leg <NUM>. The results of the comparative testing are set forth in <FIG>.

Turning to <FIG>, moveable valves <NUM> having many of the same structural features as fixed valves <NUM> are illustrated in a tray deck <NUM>. For ease of reference, the prefix "<NUM>" is used with the reference numerals for components of the moveable valves <NUM> that generally correspond to those of the fixed valves <NUM>. The moveable valves <NUM> each comprise an opening <NUM> that extends through the tray deck <NUM> and a weir <NUM> extending upwardly from the tray deck <NUM> a preselected distance along an entire perimeter of the opening <NUM>.

In each fixed valve <NUM>, a valve cover <NUM> is attached to first and second attachment legs <NUM> and <NUM>. While two attachment legs <NUM> and <NUM> are used in the illustrated embodiment, additional attachment legs could be used if desired.

The attachment legs <NUM> and <NUM> are located at opposite ends of the valve cover <NUM> and extend perpendicularly to the tray deck <NUM>. Each of the attachment legs <NUM> and <NUM> has an upper end that is attached to and is integral with an edge of the valve cover <NUM>. The attachment legs <NUM> and <NUM> extend downwardly through parallel slots <NUM> and <NUM> (<FIG>), respectively, positioned on opposite sides of the opening <NUM> in the tray deck <NUM>. Each of the attachment legs <NUM> and <NUM> includes a locking tab <NUM> that has an upper surface spaced a preselected distance below the valve cover <NUM>. The locking tab <NUM> engages against an under surface of said tray deck <NUM> to fix the upper limit of upward movement of the valve cover <NUM>. Engagement of the under surface of valve cover <NUM> on an upper edge of the weir <NUM> sets the lower limit of downward movement of the valve cover <NUM>. Alternatively, shoulders <NUM> and <NUM> such as shoulders <NUM> and <NUM> used with attachment legs <NUM> and <NUM> described above may be used to set the lower limit of downward movement. The distance between the locking tab <NUM> and the under surface of the valve cover <NUM> is selected to set the range of the vertical distance of movement of the attachment legs <NUM> and <NUM> and the valve cover <NUM> carried thereon in response to variations in upward pressure exerted on the under surface of the valve cover <NUM> by the fluid ascending through the openings <NUM> in the tray deck <NUM>. For illustration purposes, the right-hand moveable valve <NUM> in <FIG> is shown in its fully-open position and the left-hand moveable valve <NUM> in that figure is shown in its closed position.

The locking tab <NUM> can be of various suitable forms that allow the attachments legs <NUM> and <NUM> to be inserted downwardly through the slots <NUM> and <NUM> as described above with reference to locking tab <NUM>.

Attachment leg <NUM> has a width that is greater than a largest corresponding width of the opening <NUM> in the tray deck <NUM> to shield the opening against unwanted weeping of fluid downwardly through the opening <NUM>. The moveable valves <NUM> are oriented on the tray deck <NUM> so that the attachment legs <NUM> and <NUM> are aligned in the general direction of fluid flow along the upper surface of the tray deck <NUM>, with the attachment leg <NUM> located at the upstream side of the moveable valve <NUM>. The upstream attachment leg <NUM> in one embodiment is greater than that of the attachment leg <NUM> to facilitate a more streamlined flow of fluid around the opening <NUM>.

The valve cover <NUM>, in one embodiment, is in the form of an isosceles trapezoid with the attachment legs <NUM> and <NUM> connected to the opposed parallel first and second ends of the valve cover <NUM>. The valve cover <NUM> may alternatively be formed with other shapes. The valve cover <NUM> is dimensioned to extend outwardly beyond the entire perimeter of the opening <NUM> in the tray deck <NUM> to more effectively shield the opening <NUM> against the detrimental downward weeping of fluid through the opening <NUM> and has a downwardly-extending outer perimeter region <NUM>. The valve cover <NUM> (except at the perimeter region <NUM>) lies in a plane that is parallel to that of the tray deck <NUM>. In other embodiments, the valve cover <NUM> may be inclined, such as in an upward direction in the general direction of fluid flow on the upper surface of the tray deck <NUM>.

The downstream attachment leg <NUM> in each moveable valve <NUM> may differ from the downstream attachment leg <NUM> in the fixed valve <NUM> by omitting the louvered vent opening <NUM> or substituting a simple opening in place of the louvered vent opening <NUM>. Alternatively, a louvered vent opening <NUM> may be included, such as in an embodiment in which the shoulders described above are used to set the lower limit of the downward movement of the valve cover <NUM>. In such an embodiment, the louvered vent opening would be positioned above the shoulders so that it does not impede the downward movement of the attachment leg <NUM> in its associated slot <NUM>.

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.

Claim 1:
A contact tray for use in a mass transfer column, said contact tray comprising:
a generally planar tray deck; and
a plurality of valves distributed across the tray deck, each of said valves comprising an opening that extends through the tray deck to allow for passage of fluid through the tray deck, a weir extending upwardly from the tray deck around an entire perimeter of the opening, a valve cover supported above said opening and said weir by first and second attachment legs positioned at opposite ends of said valve cover, and a vent opening formed in one of said attachment legs,
wherein said valve cover extends outwardly beyond the entire perimeter of said opening and has a downwardly extending perimeter region.