Patent Description:
Mass transfer columns are configured to contact at least two fluid streams in order to provide product streams of specific composition and/or temperature. The term "mass transfer column," as used herein is intended to encompass columns in which mass and/or heat transfer is the primary objective. Some mass transfer columns, such as those utilized in multicomponent distillation and absorption applications, contact a gas-phase stream with a liquid-phase stream, while others, such as extraction columns, may be designed to facilitate contact between two liquid phases of different densities. Oftentimes, mass transfer columns are configured to contact an ascending vapor or liquid stream with a descending liquid stream, usually along multiple mass transfer surfaces disposed within the column. Commonly, these transfer surfaces are defined by structures placed in the interior volume of the column that are configured to facilitate intimate contact between the two fluid phases. As a result of these transfer surfaces, the rate and/or degree of mass and heat transferred between the two phases is enhanced.

Structured packing is commonly used to provide heat and/or mass transfer surfaces within a column. Many different types of structured packing exist, and most include a plurality of corrugated structured packing sheets that are positioned in an upright, parallel relationship and are joined together to form a structured packing module with fluid passages formed along the crisscrossing corrugations of adjacent sheets. The structured packing module may itself form a structured packing layer that fills a horizontal internal cross section of the column or the packing module may be in the form of individual bricks that are positioned end-to-end and side-by-side to form the structured packing layer. Multiple structured packing layers are normally stacked on top of each other with the orientation of the sheets in one layer rotated with respect to the sheets in adjacent structured packing layers. Specific examples of structured packings are disclosed in <CIT>, <CIT>, <CIT> and <CIT>. <CIT> is directed to a structured packing element having corrugations with peaks and troughs. Surface texturing and through holes are provided in the element. The through holes are described as being provided in an array across the element and may be in a regular array or may be distributed randomly across the element. A similar structured packing element having corrugations and at least one aperture is described in <CIT>. A sawtooth corrugated packing is disclosed in <CIT>. It is proposed that the surface of the filler sheet of the sawtooth corrugated packing is evenly punched. <CIT> is directed to a packing for heat exchange and mass transfer between a liquid and a gas in a column. The packing comprises a plurality of packing sheets having straight-line kinks which divide the packing sheets into kink areas which have a specific width, measured from kink edge to kink edge. The kink edges form an angle of from <NUM>° to <NUM>° to the column axis. The packing sheets in D8 further comprise passage apertures in the vicinity of the kink edges.

It is generally desirable to maximize mass and energy transfer between the vapor and liquid phases as they flow through the structured packing layer; this is typically achieved by increasing the specific surface area available for mass and energy transfer. However, fluids passing through a structured packing layer having a higher specific surface area will normally experience a higher pressure drop, which is undesirable from an operational standpoint.

A need thus exists for an improved structured packing that is able to achieve a reduction in pressure drop without a significant decrease in mass and energy transfer efficiency. This allows one to either produce a packing with a lower pressure drop and the same efficiency, or to increase the packing's specific surface area, thereby increasing efficiency, without significantly increasing the pressure drop of the packing.

In one aspect, the present invention is directed to a structured packing module with the features of independent claim <NUM>. Amongst others, the structured packing module according to the present invention comprises a plurality of structured packing sheets positioned in an upright, parallel relationship to each other. Each structured packing sheet has corrugations formed of alternating peaks and valleys and corrugation sidewalls that extend between adjacent ones of the peaks and valleys. The structured packing sheets are constructed and arranged such that the corrugations of each one of the structured packing sheets extend at an oblique angle to the corrugations of each adjacent one of the structured packing sheets and a specific surface area of the structured packing sheets in the structured packing module is generally greater than <NUM><NUM>/m<NUM>. The structured packing module also includes a plurality of apertures for allowing passage of fluid through the structured packing sheets. The apertures in each one of the structured packing sheets is open to each adjacent one of the packing sheets and is substantially unimpeded. The apertures are distributed in each one of the structured packing sheets such that the corrugation sidewalls have a greater density of open areas formed by the apertures than any density of any of the open areas that may be present in the peaks and valleys. The apertures are distributed such that a greater density of said open areas is present nearer the center lines of said corrugation sidewalls than any density of any open areas that may be present nearer to said peaks and valleys. Furthermore, the structured packing module includes spacers on said peaks that contact only some of the peaks on the facing side of an adjacent one of the structured packing sheets.

In another aspect, the present invention is directed to a mass transfer column in which the above-described packing module is placed. The mass transfer column has a shell defining an open internal region and at least one of the above-described packing module within said open internal region. The mass transfer column may also be referred to as a heat exchange column.

In the accompanying drawings that form part of the specification and in which like numbers 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 and heat exchange processes is represented generally by the numeral <NUM>. The mass transfer column <NUM> includes an upright, external shell <NUM> that is generally cylindrical in configuration, although other configurations, including polygonal, are possible and are within the scope of the present invention. Shell <NUM> is of any suitable diameter and height and is 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 mass transfer column <NUM>.

The shell <NUM> of the mass transfer column <NUM> defines an open internal region <NUM> in which the desired mass transfer and/or heat exchange between the fluid streams occurs. Normally, the fluid streams comprise one or more ascending vapor streams and one or more descending liquid streams. Alternatively, the fluid streams may comprise both ascending and descending liquid streams. The fluid streams are directed into the mass transfer column <NUM> through any number of feed lines (not shown) positioned at appropriate locations along the height of the mass transfer column <NUM>. One or more vapor streams can also be generated within the mass transfer column <NUM> rather than being introduced into the column <NUM> through the feed lines. The mass transfer column <NUM> will also typically include an overhead line (not shown) for removing a vapor product or byproduct and a bottom stream takeoff line (not shown) for removing a liquid product or byproduct from the mass transfer column <NUM>. Other column components that are typically present, such as feed points, sidedraws, reflux stream lines, reboilers, condensers, vapor horns, liquid distributors, and the like, are not illustrated in the drawings because an illustration of these components is not believed to be necessary for an understanding of the present invention.

One or more structured packing layers <NUM> comprising individual structured packing sheets <NUM> are positioned within the open internal region <NUM> and extend across the horizontal, internal cross section of the mass transfer column <NUM>. In the illustrated embodiment, four structured packing layers <NUM> are placed in vertically-stacked relationship to each other, but it is to be understood that more or fewer structured packing layers <NUM> may be provided. In one embodiment, each one of the structured packing layers <NUM> is formed as a single structured packing module that extends completely across the horizontal, internal cross section of the column <NUM>. In another embodiment, each structured packing layer <NUM> is formed as a plurality of individual structured packing modules (not shown), referred to as bricks, that are positioned in end-to-end and side-to-side relationship to fill the horizontal, internal cross section of the mass transfer column <NUM>.

The structured packing layers <NUM> are each suitably supported within the mass transfer column <NUM>, such as on a support ring (not shown) that is fixed to the shell <NUM>, on an underlying one of the structured packing layers <NUM>, or by a grid or other suitable support structure. In one embodiment, the lowermost structured packing layer <NUM> is supported on a support structure and the overlying structured packing layers <NUM> are stacked one on top of the other and are supported by the lowermost structured packing layer <NUM>. Successive structured packing layers <NUM> are typically rotated relative to each other so that the individual structured packing sheets <NUM> in one of the packing layers <NUM> are positioned in vertical planes that extend at an angle with respect to the vertical planes defined by the individual structured packing sheets <NUM> in the adjacent one(s) of the packing layers <NUM>. This rotation angle is typically <NUM> or <NUM> degrees, but can be other angles if desired. The height of each structured packing element <NUM> may be varied, depending on the particular application. For example, the height is within the range of from about <NUM> to about <NUM>.

The structured packing sheets <NUM> in each structured packing layer <NUM> are positioned in an upright, parallel relationship to each other. Each of the structured packing sheets <NUM> is constructed from a suitably rigid material, such as any of various metals, plastics, or ceramics, having sufficient strength and thickness to withstand the processing conditions experienced within the mass transfer column <NUM>. Each of the structured packing sheets <NUM> presents a front and back surface, of which all, or a portion, may be generally smooth and free of surface texturing, or which may include various types of texturing, embossing, grooves, or dimples. The configuration of the surfaces of the packing sheets <NUM> depends on the particular application in which the packing sheets <NUM> are to be used and may be selected to facilitate spreading and thereby maximize contact between the ascending and descending fluid streams.

Turning additionally to <FIG>, each of the structured packing sheets <NUM> has a plurality of parallel corrugations <NUM> that extend along a portion, or all, of the associated structured packing sheet <NUM>. The corrugations <NUM> are formed of alternating peaks <NUM> and valleys <NUM> and corrugation sidewalls <NUM> that extend between adjacent ones of the peaks <NUM> and valleys <NUM>. The peaks <NUM> on a front side of each structured packing sheet <NUM> form valleys <NUM> on an opposite or back side of the structured packing sheet <NUM>. Likewise, valleys <NUM> on the front sides of each structured packing sheet <NUM> form peaks <NUM> on the back side of the structured packing sheet <NUM>. Additional examples of corrugated packing sheets <NUM> according to various reference embodiments (<FIG> and <FIG>) and according to the present invention (<FIG> and <FIG>) are shown in <FIG>.

In the illustrated packing sheets <NUM>, the corrugations <NUM> of each one of the structured packing sheets <NUM> extend along the entire height and width of the structured packing sheet <NUM> and are generally of a triangular or sinusoidal cross section. Adjacent ones of the structured packing sheets <NUM> in each structured packing layer <NUM> are positioned in facing relationship so that the front side of one of the structured packing sheets <NUM> faces the back side of the adjacent structured packing sheet <NUM>. The adjacent structured packing sheets <NUM> are further arranged so that the corrugations <NUM> in each one of the structured packing sheets <NUM> extends in a crisscrossing, or cross-corrugated, manner to those in the adjacent one(s) of the structured packing sheets <NUM>. As a result of this arrangement, the corrugations <NUM> in each one of the structured packing sheets <NUM> extend at an oblique angle to the corrugations of each adjacent one of the structured packing sheets <NUM>. Some, all or none of the peaks <NUM> of the corrugations <NUM> of the front side of each one of the structured packing sheets <NUM> may be in contact with the peaks <NUM> on the back side of the adjacent one of the structured packing sheets <NUM>.

The corrugations <NUM> are inclined in relation to a vertical axis of the mass transfer column <NUM> at an inclination angle that may be selected for the requirements of particular applications in which the structured packing sheets <NUM> are to be used. Inclination angles of approximately <NUM>°, approximately <NUM>°, and approximately <NUM>° may be used, as well as other inclination angles that are suitable to a particular intended use of the structured packing layer <NUM>.

The peaks <NUM>, valleys <NUM> and corrugation sidewalls <NUM> of the corrugations <NUM> are normally formed in an automated crimping process by feeding a flat sheet, such as shown in <FIG> and <FIG>, into a crimping press. The peaks <NUM> and valleys <NUM> are generally formed as curved arcs that may be defined by an apex radius. In general, as the apex radius increases, the arc of curvature of the peaks <NUM> and valleys <NUM> increases and the length of the corrugation sidewalls <NUM> between the peaks <NUM> and valleys <NUM> conversely decreases, for a given specific surface area. The two corrugation sidewalls <NUM> of each corrugation <NUM> form an apex angle. Apex radius, apex angle, packing crimp height, and peak <NUM> to peak <NUM> length are interrelated, and may be varied to achieve a desired geometry and specific surface area. In general, as crimp height is lowered the number of structured packing sheets <NUM> contained in each structured packing layer <NUM> (or module), and the associated specific surface area, increases.

The apex radius, apex angle, and crimp height may be varied for particular applications. In the present invention they are selected so that the specific surface area of the structured packing layer <NUM> is, in general, greater than <NUM><NUM>/m<NUM>.

Each of the structured packing sheets <NUM> is provided with a plurality of apertures <NUM> that extend through the structured packing sheet <NUM> for facilitating vapor and liquid distribution within the packing layer <NUM>. Each aperture <NUM> provides an open area for permitting the passage of fluid through the associated packing sheet <NUM>. The apertures <NUM> formed in each structured packing sheet <NUM> are substantially unimpeded in that they are open to the adjacent structured packing sheet(s) <NUM> and are not covered or shielded by structural elements carried by the structured packing sheet <NUM> in which the apertures <NUM> are formed that would otherwise restrict or divert the flow of fluid after it passes through the aperture <NUM>. An aperture <NUM> is not open to the adjacent structured packing sheet <NUM> nor is it substantially unimpeded if a louver or other such structure is placed partially or completely over the aperture <NUM>. An aperture <NUM> is open and substantially unimpeded even though minor perimeter ridges or "burrs" are present as a result of a punching operation that may be used to form the apertures <NUM>.

When the apertures <NUM> are open to the adjacent structured packing sheet <NUM> and are substantially unimpeded in the structured packing layers <NUM> that have a specific surface area of, in general, greater than <NUM><NUM>/m<NUM>, it has been unexpectedly found that particular arrangements of the apertures <NUM> significantly reduce the pressure drop between the top and bottom edges of the structured packing layer <NUM>, with improved mass transfer efficiency or little to no adverse impact on the mass transfer efficiency of the structured packing layer <NUM>. This results in an overall decrease in pressure drop per theoretical separation stage and improved performance of the structured packing layer <NUM> during mass transfer processes occurring within the mass transfer column <NUM>.

This beneficial pressure drop and performance result is obtained since the apertures <NUM> are distributed on the structured packing sheets <NUM> such that the corrugation sidewalls <NUM> have a greater density of open areas defined by the apertures <NUM> than any density of the open areas that may be present in the peaks <NUM> and valleys <NUM>. In one embodiment, the apertures <NUM> are only present in the corrugation sidewalls <NUM>. In another embodiment, some of the apertures <NUM> are present in the peaks <NUM> and the valleys <NUM> to interrupt the flow of liquid along the valleys <NUM> and facilitate its distribution across the corrugation sidewalls <NUM> and from one side of the structured packing sheet <NUM> to its opposite side.

Increasing the collective or total open area formed by the apertures <NUM> when they are positioned with a great density in the corrugation sidewalls <NUM> and decreasing the size of the apertures <NUM>, which thereby increases the number of the apertures <NUM>, may further reduce the pressure drop per theoretical stage. Further improvements may be achieved by placing these apertures <NUM> in rows or other patterns that are preferentially aligned in a direction along the longitudinal length of the corrugations <NUM>. Even further improvements may be achieved by increasing the apex radius and/or adjusting the apex angle of the corrugations <NUM>.

To prevent increased liquid accumulation at the contact points between adjacent structured packing sheets <NUM> that would otherwise result due to the larger apex radii in one embodiment of the current invention, such as exemplarily shown in <FIG>, and would be detrimental to mass transfer efficiency, corrugations <NUM> on adjacent ones of the structured packing sheets <NUM> are separated by spacers <NUM> as shown in <FIG> and <FIG>. In one embodiment, these spacers are formed as sections of some or all of the peaks <NUM> on the front and/or back side of the structured packing sheets <NUM> where the larger apex radius modification is not applied and the smaller, unaltered apex radius and corrugation <NUM> height are retained, thereby forming peaks <NUM> with dual apex radii as shown in <FIG> and <FIG>. The spacers <NUM> are positioned at spaced apart locations along some or all of the peaks <NUM> on at least one side of all or some of the structured packing sheets <NUM> and contact the facing peaks <NUM> of the adjacent structured packing sheet <NUM>, thereby preventing contact between adjacent structured packing sheets <NUM> in the regions incorporating the larger apex radius modification. In one embodiment, the spacers <NUM> may be formed by depressing portions of the peaks <NUM>, initially having the original, smaller apex radii as shown in <FIG>, to create the peaks <NUM> having the larger apex radii as shown in <FIG>. The spacers <NUM> are thereby formed by the undepressed sections that retain the unmodified, smaller apex radii and original corrugation <NUM> height.

The apertures <NUM> may be positioned along the corrugation sidewalls <NUM> in various configurations. In one embodiment, the apertures <NUM> may only be present in the corrugation sidewalls <NUM> of the packing sheets <NUM> so that no apertures <NUM> are present in the peaks <NUM> or valleys <NUM>. In another embodiment, a sufficient number of apertures <NUM> may be located on the peaks <NUM> and valleys <NUM> to interrupt the flow of liquid along the peaks <NUM> and valleys <NUM> and permit at least some of that liquid to drain from one side to the other side of the structured packing sheet <NUM>. Additionally, a majority, or all, of apertures <NUM> positioned in the corrugation sidewalls <NUM> may be located closer to the longitudinal center line of the corrugation sidewall <NUM> than to a peak <NUM> or valley <NUM>. As a result of this placement, the density of the open areas defined by apertures <NUM> nearer the center line is greater than the density of the open areas defined by apertures <NUM> nearer the peaks <NUM> or valleys <NUM> on each corrugation sidewall <NUM>. In some applications, it has been found that increasing the density of the open area defined by apertures <NUM> nearer the center line of the corrugation sidewall <NUM> reduces the pressure drop with minimal reduction in overall mass transfer, producing an overall improvement in terms of pressure drop per theoretical stage.

The positioning of the apertures <NUM> along the corrugation sidewall <NUM> may depend, at least in part, on the size, total open area, and overall spacing of the apertures <NUM>. In some applications, these factors can be adjusted for the structured packing sheet <NUM> in such a way as to increase the total open area, while minimizing aperture size, such that the total number of apertures <NUM> per unit area is maximized. This has been found to result in a decrease in the pressure drop per theoretical stage, indicating a desirable improvement in the performance of the structured packing layer <NUM>.

In some applications, the maximum planar dimension of the apertures <NUM> can be in the range of from about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The maximum planar dimension of each aperture <NUM> is measured along the longest line between two sides of the aperture <NUM> that passes through the center of the aperture <NUM>. When the aperture <NUM> has a round shape, the maximum planar dimension is the diameter. Although shown in the drawing figures as having a generally round shape, the apertures <NUM> may have other shapes, such as a triangular shape, an oblong shape, an oval shape, a rectangular shape, or a square shape. These and other shapes are within the scope of the invention.

In some applications, the open area of each of the apertures <NUM> may be minimized such that individual apertures <NUM> have an open area of not more than about <NUM><NUM>, not more than about <NUM><NUM>, or not more than about <NUM><NUM>, but the number of apertures per unit area may be maximized so that the total open area of each of packing sheets <NUM> is in the range of from about <NUM> to about <NUM> percent, about <NUM> to about <NUM> percent, about <NUM> to about <NUM> percent, or about <NUM> to about <NUM> percent, based on the total surface area of the associated packing sheet <NUM>.

The apertures <NUM> may be arranged along each of the corrugation sidewalls <NUM> in one or more spaced apart rows that extend in a direction substantially parallel to the direction of longitudinal extension of the peaks and valleys. As best shown in <FIG> and <FIG>, which depict a packing sheet <NUM> prior to being folded, the rows of apertures <NUM> may be spaced apart from one another and extend in a direction substantially parallel to the direction of extension of the corrugation fold lines <NUM>. As a result, the rows of apertures <NUM> may extend at an oblique angle with respect to the edges of the packing layer. The total number of rows present on each corrugation sidewall can be at least one, at least two, or at least three, with the particular arrangement varying depending on the particular application. Apertures <NUM> should preferably not be arranged in a random pattern with respect to the corrugations <NUM> and may or may not be parallel to the edges of the packing sheet <NUM>.

When apertures <NUM> are arranged in two or more rows along the corrugation sidewalls <NUM>, apertures <NUM> in adjacent rows may be aligned with one another (not shown), or the apertures <NUM> may be staggered from one another in a direction parallel to the direction of extension of the peaks <NUM> and valleys <NUM>, as shown in the reference embodiments of structured packing sheets in <FIG>, <FIG> and <FIG>. In some applications, apertures <NUM> in adjacent rows may be staggered from one another along the center line of the corrugation sidewall <NUM>. The spacing between adjacent apertures <NUM> may vary depending on the application, and can, for example, be in the range of between <NUM> to <NUM>, between <NUM> to <NUM>, or between <NUM> to <NUM>, when measured between consecutive edges of adjacent apertures.

In one embodiment, the packing sheets <NUM> may have an apex angle in the range of <NUM> to <NUM>°. In another embodiment, they may have an apex angle of <NUM> to <NUM>°. In a further embodiment, they may have an apex angle of <NUM>° to <NUM>°. In various embodiments, the apex radius may be in the range of about <NUM> to about <NUM>, or about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

It has been found to be generally desirable to prevent contact between at least some or most of the corrugations <NUM> of each structured packing sheet <NUM> and those on adjacent structured packing sheets <NUM> by a distance greater than or equal to at least the thickness of the liquid film that is intended to flow along the corrugations <NUM> to prevent undesired liquid accumulation at the contact points where the corrugations <NUM> of one structured packing sheet <NUM> contact the corrugations <NUM> of an adjacent one of the structured packing sheets <NUM> that would be exacerbated in structured packing sheets <NUM> having larger apex radii. For example, the distance between the peaks <NUM> on the front side of one structured packing sheet <NUM> and the peaks <NUM> on the back side of the adjacent structured packing sheet <NUM> may be in the range of between <NUM> to <NUM>, between <NUM> to <NUM>, or between <NUM> to <NUM>. This reduction in contact between the larger radius peaks <NUM> of the corrugations <NUM> may be achieved by the spacers <NUM>, such as those formed by the undepressed sections of the peaks <NUM> as shown in <FIG> and <FIG> that are positioned at spaced-apart locations along all or some of the peaks <NUM> of one or both sides of all or alternate ones of the structured packing sheets <NUM>. The length and spacing of the spacers <NUM> are selected so that they contact only some of the facing peaks <NUM> or spacers <NUM> in the adjacent structured packing sheets <NUM> when they are assembled into the structured packing layer <NUM>. In order to facilitate deformation of the flat sheet during formation of the corrugations <NUM> and the spacers <NUM>, some of the apertures <NUM> may be positioned at the transitions between the depressed portions of the peaks <NUM> and the spacers <NUM>, thereby forming peaks <NUM> with dual apex radii and apertures <NUM> at the transition from large to small radii as shown in <FIG>.

In use, one or more of the structured packing layers <NUM> are assembled from the structured packing sheets <NUM> and are positioned within the open internal region <NUM> within the mass transfer column <NUM> for use in facilitating mass transfer and/or heat exchange between fluid streams flowing counter currently within the open internal region <NUM>. As the fluid streams encounter the structured packing sheets <NUM> in the one or more structured packing layers <NUM>, the fluid streams spread over the surfaces of the structured packing sheets <NUM> to increase the area of contact and, thus, the mass transfer and/or heat exchange between the fluid streams. A fluid stream, typically a liquid stream, descends along the inclined surface of the corrugations, while another fluid stream, typically a vapor stream, is likewise able to ascend in the open spacing between the adjacent structured packing sheets <NUM> and contact the descending fluid stream to affect heat and/or mass transfer. The apertures <NUM> in the structured packing sheets <NUM> facilitate vapor distribution within the structured packing layer <NUM> and also act as a liquid distributor for controlling the pattern of liquid to aid liquid distribution as the liquid moves across the structured packing sheets <NUM>, and to facilitate passage of liquid from one side of the packing sheet to the other. The size, shape, and distribution of apertures <NUM> herein may be specifically configured as described above to reduce the pressure drop between top and bottom edges of structured packing layers <NUM> with a surprising increase or only a minimal, if any, reduction in separation efficiency, thereby resulting in an overall enhanced performance of the structured packing layer <NUM> in the mass transfer column <NUM>.

The invention is further illustrated by reference to the following table showing normalized results of computational fluid dynamics simulations for conventional structured packing sheets A-E, reference structured packing sheets <NUM> and <NUM> and inventive structured packing sheets <NUM>-<NUM> that incorporate various features of the present invention. The information presented in the table is provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

Claim 1:
A structured packing module comprising:
a plurality of structured packing sheets (<NUM>) positioned in an upright, parallel relationship to each other, each structured packing sheet (<NUM>) having corrugations (<NUM>) formed of alternating peaks (<NUM>) and valleys (<NUM>) and corrugation sidewalls (<NUM>) that extend between adjacent ones of the peaks (<NUM>) and valleys (<NUM>), the structured packing sheets (<NUM>) being constructed and arranged such that the corrugations (<NUM>) of each one of the structured packing sheets (<NUM>) extend at an oblique angle to the corrugations (<NUM>) of each adjacent one of the structured packing sheets (<NUM>) and a specific surface area of the structured packing sheets (<NUM>) in the structured packing module is greater than <NUM><NUM>/m<NUM>; and
a plurality of apertures (<NUM>) in the structured packing sheets (<NUM>) for allowing passage of fluid through the structured packing sheets (<NUM>), the apertures (<NUM>) in each one of the structured packing sheets (<NUM>) being open to each adjacent one of the structured packing sheets (<NUM>) and being substantially unimpeded, the apertures (<NUM>) being distributed in each one of the structured packing sheets (<NUM>) such that the corrugation sidewalls (<NUM>) have a greater density of open areas formed by the apertures (<NUM>) than any density of any of the open areas that may be present in the peaks (<NUM>) and valleys (<NUM>),
characterized in that said apertures (<NUM>) are distributed such that a greater density of said open areas is present nearer the center lines of said corrugation sidewalls (<NUM>) than any density of any open areas that may be present nearer to said peaks (<NUM>) and valleys (<NUM>)
and in that the structured packing module includes spacers (<NUM>) on said peaks (<NUM>) that contact only some of the peaks (<NUM>) on the facing side of an adjacent one of the structured packing sheets (<NUM>).