Patent Description:
Mass transfer columns are used for separating fluids into two or more product streams of specific composition and/or temperature. The term "mass transfer column" as used herein is intended to encompass absorbers, separators, distillation columns, divided wall columns, liquid-liquid extractors, scrubbers, and evaporators, which facilitate heat and/or mass transfer between two or more fluid phases. Some mass transfer columns, such as those used in multicomponent absorption and distillation, are configured to contact gas and liquid phases, while other mass transfer columns, like extractors, are configured to contact two liquid phases of differing density.

Mass transfer columns typically have a cylindrically-shaped shell that is constructed from any of various metals or metal alloys and defines an open internal region where the mass transfer processes occur. Various internals, such as trays, structure packing, random packing, or other mass transfer structures, support grids, downcomers, feed inlet devices, fluid collectors, and fluid distributors may be present in the open internal region. These internals are typically supported directly or indirectly by the shell using support rings, bolting bars, and similar devices that are welded to an inner surface of the shell. Larger mass transfer columns will often include beams that support the internals and are mounted on seats that are welded to the inner surface of the shell.

The thickness of the shell must be selected to provide the strength necessary to withstand the various loads exerted on it by the internals, flowing fluids, and the internal operating pressures. As mass transfer columns increase in height and/or diameter, the loads exerted on the shell increase and other ways are needed to bear those loads than simply increasing the thickness of the metal shell. For example, absorbers that are used to separate carbon dioxide from flue gasses generated by fossil fuel-based power plants may be <NUM> to <NUM> meter (<NUM> to <NUM> feet). or larger in diameter. In some instances, the shells in such absorbers have been constructed using metal-reinforced concrete to provide the strength needed to withstand the loads to which they are subjected. While the metal-reinforced concrete can form a high-strength shell, it provides challenges in providing metal surfaces to which support rings, bolting bars, beams seats may be welded. As a result, a need remains for a way to fabricate a shell having suitable strength for use in mass transfer columns, particularly those having large diameters, while allowing for the ready attachment of support structures for internals. An example of a prior art structure is provided in <CIT>.

In one aspect, the present disclosure is directed to a mass transfer column according to claim <NUM>.

In a further aspect, the present disclosure is directed to method for removing carbon dioxide from a flue gas as defined in claim <NUM>.

In the accompanying drawings that form part of the specification and in which like reference numerals are used to indicated 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 a variety of mass transfer, heat exchange, and/or reaction processes is represented generally by the numeral <NUM>. The mass transfer column <NUM> may be located in any suitable type of processing facility including, but not limited to, a fossil-fuel based power plant, a chemical processing plant, a petroleum refinery, a chemical production facility, a light hydrocarbon separation facility, and the like.

The mass transfer column <NUM> may be any type of column for processing fluid streams, usually liquid and vapor streams or two or more liquid streams having different densities, to obtain fractionation products, or to otherwise cause mass transfer and/or heat exchange between the fluid phases. Examples of suitable types of mass transfer columns <NUM> include, but are not limited to, absorber columns, separators, distillation columns, liquid-liquid extraction columns, scrubber columns, and evaporator columns. The mass transfer column <NUM> may be one in which crude atmospheric fractionating, lube or crude vacuum oil fractionation, catalytic or thermal cracking fractionating, coker or visbreaker fractionating, coker or cracking scrubbing, reactor off-gas scrubbing, gas quenching, edible oil deodorization, pollution control scrubbing, reactive distillation, or other types of processes occur.

As one specific example, the mass transfer column <NUM> may be an absorber that is used to remove carbon dioxide from a flue gas generated by a fossil fuel-based power plant. In such an application, the mass transfer column <NUM> may used as part of a system that may include another mass transfer column that receives the flue gas after it has been subjected to a NOx removal process and cools the ascending flue gas by countercurrent flow with descending water through mass transfer structures such as structured packing. The cooled flue gas is then directed as a side stream to the mass transfer column <NUM> that acts an absorber. The ascending cooled flue gas flows in the absorber countercurrently with a descending carbon dioxide absorbing solvent. The rich solvent is removed as a bottoms and directed to one or more other mass transfer columns that act(s) as a stripper to separate the carbon dioxide from the rich solvent stream and to regenerate the solvent.

As shown in <FIG>, the mass transfer column <NUM> includes a shell <NUM> that has a square cross-sectional shape. The shell <NUM> may be either vertically oriented as shown in <FIG> or it may be horizontally oriented (or elongated). Other cross-sectional shapes, such as a rectangular or other polygonal shapes, or a circular shape are possible and may be used in place of the square cross-sectional shape shown in <FIG>. The shell <NUM> may be of any suitable dimensions and is particularly adapted for use in large mass transfer columns <NUM>. For example, in one embodiment, the shell <NUM> may have a width in the range of <NUM> to <NUM> meter (<NUM> to <NUM> feet) and a height in the range of <NUM> to <NUM> meter (<NUM> to <NUM> feet).

The shell <NUM> of the mass transfer column <NUM> defines an open internal region <NUM> in which the desired mass transfer, heat exchange, and/or reaction between the fluid phases takes place. In one embodiment, the fluid phases within the mass transfer column <NUM> may include ascending vapor and descending liquid, such as when the mass transfer column <NUM> is acting as an absorber in a process for separating carbon monoxide from a flue gas. In other embodiments, the fluid phases within the mass transfer column <NUM> may comprise substantially any combination of ascending or descending liquid and ascending or descending vapor. In some embodiments, the fluid phases within the mass transfer column <NUM> may include ascending or descending liquids having different densities. The fluid phases within the mass transfer column <NUM> may move in a co-current manner, such that the vapor and liquid phases, or both liquid phases, move in the same direction along a longitudinal axis of the mass transfer column <NUM>, or the fluid streams within the mass transfer column <NUM> may move in a counter-current manner, such that the vapor or liquid phase moves in the opposite direction as the other phase within the mass transfer column <NUM>.

One or more fluid streams may be introduced into the mass transfer column <NUM> via one or more feed lines, such as through feed line nozzles <NUM> and <NUM> shown in <FIG>. In some embodiments, the mass transfer column <NUM> may include additional feed line nozzles (not shown) for introducing other fluid streams at one or more other locations. When the fluid streams contacted in the mass transfer column <NUM> include a vapor stream or phase, the vapor may be introduced into the mass transfer column <NUM> through the feed line nozzle <NUM> (or another separate feed line nozzle) and/or all or a portion of the vapor phase may be generated within the mass transfer column <NUM> during operation.

As also shown in <FIG>, one or more fluid streams may be withdrawn from the mass transfer column <NUM> through one or more takeoff nozzles, shown as an upper (or overhead) takeoff nozzle <NUM> and a lower (or bottom) takeoff nozzle <NUM>. In some embodiments, a vapor stream may be removed from the mass transfer column <NUM> through the upper takeoff nozzle <NUM>, while a liquid stream may be removed from the mass transfer column <NUM> through the lower takeoff nozzle <NUM>. For example, when the mass transfer column <NUM> is operating as an absorber to remove carbon dioxide from a flue gas, the processed flue gas from which the carbon dioxide has been absorbed is removed through the upper take off nozzle <NUM> and the rich solvent containing the carbon dioxide is removed through the lower takeoff nozzle <NUM>.

The mass transfer column <NUM> may also include typical components such as one or more heat exchangers for heating and/or cooling the fluid streams introduced into and/or withdrawn from the mass transfer column <NUM>, a condenser for cooling the overhead vapor stream withdrawn from the mass transfer column <NUM> via the upper takeoff nozzle <NUM>, and a reboiler for heating the bottom liquid stream withdrawn from the mass transfer column <NUM> via the lower takeoff nozzle <NUM>. These components are not shown because of their conventional nature.

The shell <NUM> of the mass transfer column <NUM> has at least one side wall <NUM>, and a top <NUM> and a bottom <NUM> that are joined to the side wall <NUM>. The number of side walls <NUM> is dependent upon the cross sectional shape desired for the shell <NUM>. For example, when the shell <NUM> has a circular cross section, a single side wall <NUM> may be used. When the shell <NUM> has a square or rectangular cross section, four of the side walls <NUM> are used. The side walls <NUM> each comprise an exoskeleton <NUM> that supports a skin <NUM>. In one embodiment, the exoskeleton <NUM> comprises a plurality of upright trusses <NUM> that are spaced apart from each other and rails <NUM> that join together adjacent ones of the upright trusses <NUM>. The upright trusses <NUM> and the rails <NUM> each have opposed inner and outer faces.

The upright trusses <NUM> may extend vertically and in parallel relationship to each other. The upright trusses <NUM> are each formed by an inner cord <NUM> and an outer cord <NUM> that are spaced apart from each other and are interconnected by web members <NUM>. The inner cord <NUM> and the outer cord <NUM> in each upright truss <NUM> may extend in parallel relationship to each other or, as illustrated in <FIG>, the inner cord <NUM> may extend vertically and the outer cord <NUM> may be angled toward the inner cord <NUM> in the upward direction because the load carried by the upright trusses <NUM> decreases in the upright direction. The web members <NUM> are arranged in a suitable fashion to provide the strength necessary to withstand the loads carried by the upright trusses <NUM>. The web members <NUM> are arranged in a triangular configuration.

The skin <NUM> is supported by the upright trusses <NUM> and rails <NUM> and, together with the top and bottom <NUM> and <NUM> define the open internal region <NUM> that may be pressurized and in which the mass transfer processes occur. The skin <NUM> has opposed inner and outer faces and the side feed line nozzles <NUM> and <NUM> extend through the skin <NUM>. The upper take off nozzle <NUM> and the lower take off nozzle <NUM> normally extend through the top <NUM> and bottom <NUM>, respectively, of the shell <NUM>.

Turning more specifically to <FIG>, a plurality of horizontally extending beams <NUM> span the open internal region <NUM> and may be used to support various internals, such as the illustrated structured packing <NUM>. The horizontally extending beams <NUM> may be trusses, as illustrated, each of which comprise spaced apart upper and lower chords <NUM> and <NUM>, respectively, and interconnecting web members <NUM>. The web members <NUM> are arranged to form the triangular structure or, alternative, they may be arranged to form other geometric structures capable of supporting the intended loads. The horizontally extending beams <NUM> have opposite end segments <NUM> and <NUM> that are supported in one embodiment by seats <NUM> that, in turn, are supported by the shell <NUM> of the mass transfer column <NUM>.

Turning now to <FIG>, different side wall <NUM> constructions are illustrated. In <FIG>, the rails <NUM> are positioned so that their inner faces lie in the same plane as the inner face of the upright truss <NUM>, specifically the inner face of the inner cord <NUM>. The skin <NUM> is applied to the inner faces of the rails <NUM> and upright truss <NUM> and the seats <NUM> are joined to the inner face of the skin <NUM>. The seats <NUM> are arranged so that the horizontally extending beams <NUM> are supported on top surfaces of the seats <NUM> and, in one embodiment, are able to move along the top surfaces of the seats in response to thermal expansion and retraction of the horizontally extending beams <NUM>. The seats <NUM> may be in alignment with the upright trusses <NUM> or the rails <NUM> or they may be positioned so that they are not aligned with either the upright trusses <NUM> or the rails <NUM> to provide greater flexibility in the positioning of the horizontally extending beams <NUM> within the open internal region <NUM>. The rails <NUM> may be joined to the upright trusses <NUM> by bolting, welding or other suitable means. The skin <NUM> likewise may be joined to the upright trusses <NUM> and/or the rails <NUM> and the seats may be joined to the skin <NUM> by welding, bolting or other means.

In <FIG>, the inner faces of the rails <NUM> are positioned inwardly from the inner face of the upright truss <NUM> and the skin <NUM> is applied to the inner faces of the rails <NUM>. The seats <NUM> are joined to the rails <NUM> or the upright truss <NUM>, rather than to the skin <NUM> as shown in <FIG>. Cutouts are provided in the skin <NUM> to accommodate each rail <NUM> and a seal weld is applied around the perimeter of each cutout to join the skin <NUM> to each seat <NUM>.

In <FIG>, the rails <NUM> are applied to the inner faces of the upright trusses <NUM> and may span multiple ones of the upright trusses <NUM>. The skin <NUM> is applied to the inner faces of the rails <NUM> and is spaced from the inner faces of the upright trusses <NUM> by the thickness of the rails <NUM>. A top surface of some or all of the rails <NUM> may act as the seat <NUM> for the horizontally extending beams <NUM> such that the seat <NUM> comprises a portion of the rails <NUM>. In this embodiment, the horizontally extending beams extend through cutouts provided in the skin <NUM>. A suitable means for sealing the skin <NUM> to the horizontally extending beams <NUM> while allowing for thermal expansion and contraction of the horizontally extending beams <NUM> may be provided. In one embodiment, the skin <NUM> is seal welded to the horizontally extending beams <NUM> using more flexible material to accommodate the thermal axial movement of the horizontally extending beams <NUM>.

In <FIG>, the horizontally extending beams <NUM> extend through the skin <NUM> in a manner similar to the arrangement shown in <FIG>, except the end segments of the horizontally extending beams <NUM> overlap and may be joined to the upright trusses <NUM>. The remainder of the construction may be as described with reference to <FIG>.

In <FIG> and <FIG>, one or more support columns <NUM> may be positioned within the open internal region <NUM> to provide support for the horizontally extending beams <NUM>. Seats <NUM> are provided on the support column <NUM> to support adjacent ends of two beam segments 44a and 44b that form the horizontally extending beam <NUM>. The support column <NUM> may be of a modular construction to facilitate insertion within the mass transfer column <NUM>. In one embodiment, the support column <NUM> is formed from segments that are bolted together using bolting flanges <NUM>.

It can thus be seen that the use of the exoskeleton <NUM> in the construction of the side wall(s) <NUM> provides the shell <NUM> with a high strength that is capable of withstanding high loads, which is particularly beneficial when the mass transfer column <NUM> is used in applications where the shell <NUM> has a width in the range of <NUM> to <NUM> meter (<NUM> to <NUM> feet) and a height in the range of <NUM> to <NUM> meter (<NUM> to <NUM> feet). Fabricating the skin <NUM> and the vertical trusses <NUM> and rails <NUM> from metal or metal alloys provides great flexibility for locating and attaching the seats <NUM> for the horizontally extending beams <NUM> in the open internal region <NUM>. Fabricating the horizontally extending beams <NUM> as trusses allows them to span large distances and support the various internals such as structured packing <NUM> that may be used within the mass transfer column <NUM>.

Claim 1:
A mass transfer column (<NUM>) comprising:
a shell (<NUM>) comprising at least one side wall (<NUM>) and a top and a bottom joined to the side wall (<NUM>), the side wall (<NUM>) comprising:
a plurality of upright trusses (<NUM>) that are spaced apart from each other and have opposed inner and outer faces, wherein the upright trusses (<NUM>) are formed by an inner cord (<NUM>) and an outer cord (<NUM>) that are spaced apart from each other and are interconnected by web members (<NUM>), wherein the web members (<NUM>) are arranged in a triangular configuration;
rails (<NUM>) extending between and joined to adjacent ones of the upright trusses (<NUM>) and having opposed inner and outer faces; and
a skin (<NUM>) supported by the upright trusses (<NUM>) and rails (<NUM>) and together with the top and the bottom defining an open internal region (<NUM>) that may be pressurized and in which mass transfer processes may occur, the skin (<NUM>) having an inner face and an outer face;
a plurality of horizontally extending beams (<NUM>) spanning the open internal region (<NUM>), each of the horizontally extending beams (<NUM>) having opposite end segments (<NUM>, <NUM>);
seats (<NUM>) supported by the shell (<NUM>) and supporting the opposite end segments (<NUM>, <NUM>) of the horizontally extending beams (<NUM>), wherein the seats (<NUM>) are joined to the skin (<NUM>) of the shell (<NUM>); and
nozzles (<NUM>, <NUM>, <NUM>, <NUM>) extending through the skin (<NUM>) of the shell (<NUM>) for introducing fluid into the open internal region (<NUM>) and removing fluid from the open internal region (<NUM>).