BACKGROUND OF THE INVENTION

field pf the Invention The present invention pertains to chemical process towers and, more particularly, to agitated extraction columns assembled with structured packing.

History of the Prior Art

In the liquid-liquid contact art, it is highly desirable to utilize methods and apparatus that efficiently improve the quantity of mass transfer occurring in process towers. This is generally

accomplished with countercurrent liquid extraction systems. Liquids of such systems flow continuously and countercurrently through one or more chambers which may have specially designed apparatus mounted therein. Apparatus of this type may include agitators for affecting the physical properties (e.g., droplet size) of the liquid and tower packing which serves to obstruct the direct flow of the liquids. Packing also provides better contact between lighter rising liquids and heavier settling liquids, and better contact means higher efficiency.

Liquid-liquid process towers are generally constructed to provide descending heavy liquid flow from an upper portion of the tower and ascending li.ght liquid from a lower portion of the tower. It has been found desirable in the liquid-liquid contact portion of the prior art to provide apparatus and methods affording efficient mass transfer, or liquid-liquid contact, whereby contact of the fluids can be accomplished with a minimum pressure drop through a given zone of minimum dimensions. High efficiency and low pressure drop are important design criteria in liquid-liquid extraction operations. Sufficient surface area for liquid-liquid contact is necessary for the primary function in the

reduction or elimination of heavy liquid entrainment present in the ascending lighter liquid. Most often, it is necessary for the structured packing array in the column or in the calming zone of agitated extraction systems to have sufficient surface area in both its horizontal and vertical plane so that fractions of the heavy constituents are conducted downwardly, and the lighter liquid is permitted to rise upwardly through the packing with minimum resistance. With such apparatus, heavy and light constituents of the feed are recovered at the bottom and top of the tower, respectively.

A passive liquid-liquid tower (no mechanically induced agitation) , generally includes a plurality of stacked layers affording compatible and complemental design. Such a design is set forth, shown and discussed in U.S. Pat. 5,185,106. In such a passive column, each layer utilizes the velocity and kinetic energy of the fluids to perform the dual function of eliminating heavy liquid entrainment in the ascending liquid phase and the thorough contacting of the light and heavy liquids to accomplish sufficient separation or extraction of the fluids into desired components. Oppositely inclined, corrugated lamellae, or plates, have thus been utilized in the prior art for affording multiple light phase

passages through the horizontal and vertical planes of the packing layers to insure the flow of lighter liquid and distribution thereof within the lamellae and to prevent maldistribution, or channeling, of the lighter liquid through certain portions of the layers and not others. Only in this manner is efficient and effective utilization of the column and the energy applied therein effected.

Addressing still the structured packing of such towers, the structural configuration of the inclined, corrugated contact plates of the prior art variety have incorporated holes for liquid passage. Turbulence is created by such holes to insure intimate iighr and heavy phase contact. It is necessary to insure that the ascending light phase performs a dual function of phase contact and liquid disentrainment within close proximity to the vertical location at which the ascending phase approaches or leaves the passage holes. In this manner, maldistribution of the ascending or descending phases is reduced. It is, moreover, a paramount concern of the prior art to provide such methods and apparatus for liquid-liquid contact in a configuration of economical manufacture. Such considerations are necessary for cost effective operation.

Oppositely inclined corrugated plates provide but one method and apparatus for counter-current liquid- liquid interaction. With such packing arrays, the liquid introduced at or near the top of the column and withdrawn at the bottom, is effectively engaged by the separate liquid stream being introduced at or near the bottom of the column and withdrawn at the top. The critical feature in such methods and apparatus is to insure that the first and second liquids achieve the desired degree of contact with each other so that the planned mass or energy transfer occurs at the designed rate. The internal structure may be active or passive depending on whether or not it is power-driven externally. There are, however, established reasons for utilizing active systems.

One prior art perception is that passive, packed columns give poor results compared to active columns. One of the problems is channeling which results in very little contact between liquids. Another problem is the size of the first liquid phase droplets dispersed into a second continuous liquid phase. Through agitator systems, the droplets of a first liquid can become extremely fine and remain dispersed in a second liquid for longer periods of time. One example of an active

extraction column is the Scheibel type extraction apparatus as shown in U.S. Patent No. 2,493,265. One aspect of the invention set forth in this reference comprises a substantially vertical column or chamber provided with a mixing section in which one or more agitators are installed to promote intimate contact between the liquids so as to cause equilibrium contact between them. Above and below the mixing chambers are calming sections where layers of fibrous packing, preferably of the self-supporting type, as for example, a roll of tubular knitted wire mesh, are mounted. As set forth in the Scheibel patent, the packing in the calming sections stops the circular motion of the liquids and permits them to separate. Thus, in the lower layer of packing, the heavier liquid settles out and flows downwardly, countercurrently to and through a rising stream of lighter liquid. Similarly, in the upper layer of packing the rising stream of lighter liquid flows countercurrently to and through a descending stream of heavier liquid. The agitators are mounted on a central shaft extending through the column and the shaft is rotated by any suitable device such as a motor. Other countercurrent contractor designs are set forth and shown in U.S. Patent No. 2,072,382, 3,032,403, and 4,855,113.

A more recent Scheibel patent design is set forth and shown in U.S. Patent No. 2,850,362. In this system, self-supporting wire mesh screen extending vertically through the entire calming section is again set forth and shown.

The concept of agitated extraction columns with structured packing is not new, as seen in the column of L. Steiner and S. Hartland described in £E£ December 1980 (page 60) incorporated herein by reference. However, many problems have surfaced in the development and testing of these designs. One such problem is the "bypassing of liquid" around the packing. For this and other reasons, the commercial applications of such systems have been limited. Liquid liquid contacting systems are distinctly different from gas-liquid contacting systems, although both systems may use structured packing. In gas-liquid contacting systems, the liquid phase wets the packing and mass transfer is afforded from the liquid phase on the packing surface from a continuous gas phase flowing thereover. In agitated extraction columns, a first liquid phase is dispersed into a second continuous phase in the form of droplets. As recited above, the droplets can become extremely fine through agitation and it is

very desirable to have the dispersed phase droplets remain dispersed throughout the entire column. In view of this operation parameter, it is advantageous to have the packing of such liquid-liquid systems not be wetted by the dispersed phase. It is well known that metal surfaces are more efficient for keeping organic phases dispersed than Teflon surfaces which are more effective for keeping aqueous phases dispersed. The function of the packing within agitated-packed systems is mainly to provide a restriction or "roadblock" to increase the number of dispersed phase droplets per unit volume of counter flowing continuous phase. By means of increased dispersed phase holdup, improved mass transfer may be realized. If, however, the holdup is too severe, the flow can be reduced to the point at which the droplets collide one with the other to form a continuous phase. This condition is referred to as flooding. Flooding then becomes the end condition at which point the efficiency of the tower performance drops off and no further increase in flow rates may be achieved. Because of this limitation, it is important to consider the size of the droplets (which is effectively controlled by the agitator design) and the dispersed phase holdup (which is

effectively set by the structured packing, hydraulic diameter design) in agitated-packed system designs.

It would be an advantage, therefore, to provide an advance over the prior art by providing an improved, agitated extraction column with an effective design for and effective placement of structured packing in the calming regions thereof for improving the liquid-liquid extraction efficiency therein. Such methods and an apparatus are provided by the system of the present invention which provides a structured array of corrugated plates positioned in such a configuration so as to effectively present an efficient liquid-liquid extraction assembly in axially alternating transverse calming regions of a liquid-liquid extraction tower. The present invention also provides improvements in the hydraulic diameter effectiveness by utilizing a larger crimp height for the structured packing and number of layered packing elements rotated with respect to one another.

Summary of the Invention The present invention pertains to agitated extraction columns and more particularly one aspect of the present invention pertains to countercurrent, liquid- liquid extraction systems comprising a substantially

vertical column having a central axis therethrough and including a series of axially alternating transverse calming and mixing sections therein. Agitation devices are disposed within each of the mixing sections for exerting a non-vertical thrust to the liquid flowing therein. Structured packing is mounted within the calming sections and between the mixing sections, and the structured packing mounted within the calming sections comprises at least one layer of corrugated contact plates disposed in generally face-to-face relationship for facilitating the flow of liquid therebetween.

In another aspect, the above described invention includes corrugated plates disposed with opposed corrugations inclined oppositely one to the other and at an angle relative to the vertical axis of the column. The corrugated plates disposed within the calming sections have corrugations orientated at an angle on the order of 45° relative to the axis of the column. The corrugations of the plates may be formed with a height on the order of one-half inch and may have a generally smooth surface finish. In one embodiment, the plates are foil-like and are formed from metal. In another embodiment the plates are either formed from or coated

with a class of engineering plastics including Teflon and polypropylen .

In yet another aspect, the above described invention includes at least two axial layers of packing, transversely disposed within each of the calming sections. The packing is preferably arranged with at least a second layer of packing rotated on the order of 90° relative to a first layer of packing to enhance the edge sealing between said packing and said column. In yet another embodiment, a third layer of packing is provided contiguous to the second layer of packing and rotated on the order of 90° relative thereto and so on if there are more than three layers.

In yet another aspect, the present invention relates to a method of counter-current liquid-liquid extraction of the type performed in a substantially vertical column with a series of axially alternating, transverse calming and mixing sections. The method comprises the steps of providing the mixing sections with at least one agitator therein for exerting a non-vertical thrust to the liquid and providing structured packing of the corrugated variety. The structured packing is then mounted within the calming sections and the structured packing with at least one layer of corrugated contact plates disposed in

generally face-to-face relationship within said calming sections. The method may further include the steps of disposing the corrugated metal sheets with opposed corrugations inclined oppositely one to the other and at an angle relative to the vertical axis of the column.

Brief Description of the Drawings For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a diagrammatic elevational schematic of a plant illustrating an agitated extraction system in accordance with the principles of the present invention; Fig. 2 is a side elevational cross-sectional view of a diagrammatic illustration of an agitated-packed column constructed in accordance with the principles of the present invention;

FIG. 3A is a graphical representation illustrating the distribution of acetone between toluene and water with the system of FIG. 1;

Fig. 3B is a graph of theoretical stages per meter versus RPM of the agitator paddles for a first structured packing size with the system of FIG. 1,*

Fig. 4 is a graph of a theoretical stages per meter versus RPM for a second structured packing size with the system of FIG. 1;

Fig. 5 is a Stichlmair-type plot showing maximum theoretical stages per meter for versus total flow for the two different structured packing sizes of Figs. 3 and 4; and

Fig. 6 is a graph of volumetric efficiency verses total flow with mass transfer from the continuous to dispersed phase for the structured packing of Figs. 3 and 4; Fig. 7 is an enlarged fragmentary exploded perspective view of the assembly of the structured packing of Fig. 2 in accordance with the principles of the present invention.

Detailed Description Referring first to Fig. 1, there is shown a diagrammatic schematic of one embodiment of an agitated- packed column system constructed in accordance with the principles of the present invention. The system 10

comprises a column 12 constructed with a plurality of calming sections 14 and mixing sections 16 therein. In combination, the assembly of the column 12 provides a counter-current, liquid-liquid extraction system having a shaft 18 positioned along a central axis 26. The shaft 18 is constructed with paddles 28 disposed within each mixing section 16 for exerting a non-vertical thrust to liquid flowing therein. Each calming section 14 further includes structured packing 20 mounted therein, between the mixing sections 16 with the structured packing comprising at least one layer of corrugated contact plates disposed in generally face-to-face relationship for facilitating the flow of liquid there between as will be described in more detail below. It should be noted that Fig. 1 is a schematic illustration which shows a simple system for illustrating the principles of the present invention. The schematic illustration is itself a diagram of a pilot plant operation, but is equally applicable and convertible to a commercial system by those skilled in the art.

Referring still to Fig. 1 a variable speed drive motor 22 is secured at the top 24 of column 12 for powering mixing sections 16. The drive motor 22 rotates the shaft 18 extending down the axis 26of the column 12.

Paddles 28 are installed in the mixing sections 16 to generate the agitation of the liquids therein from the rotation of the shaft 18 as the liquids pass in countercurrent flow therethrough. The agitation imparted thereto is designed to reduce the size of liquid phase droplets dispersed into another continuous phase liquid. Vertical blades 29 are thus assembled to paddles 28 to create agitation with a non-vertical thrust. Agitation from blades 29 and the like has been shown to produce an extremely fine dispersed droplet configuration in such assemblies.

The first, or heavier, liquid 30 is thus shown to be provided in a reservoir or drum 32 adjacent the column 12 and pumped to the top 24 of said column by a _r pump 34. A flow measurement system 36 is diagrammatically shown for monitoring the liquid flow rates. The liquid 30 is forced from pump 34 through conduit 38 into the top 24 of column 12 while lighter liquid 40 is pumped into the bottom 42 of the column 12. Lighter liquid 40, shown herein in the form of organic solvent, is provided in a drum or reservoir 44 and forced through pump 46 through pipes 48 into the bottom 42 of the column 12. A flow calibration measurement system 49 is likewise shown. When the heavier liquid 30 has descended through the

agitated packed extraction column 12, it is carried from the bottom 42 through discharge line 50 into a reservoir, shown herein as a drum 52. A pump 54 may be utilized to force the liquid 30 into the drum 52, which liquid 30 is generally referred to as aqueous underflow or raffinate 56. Likewise, the lighter, organic solvent 40 passes upwardly through column 12 and is carried away from the top 24 through discharge line 60 past vent 62 into a reservoir, shown herein as a drum 64, where it is accumulated as an organic overflow or extract 66. Mesh pad coalescers (not shown) were used in the pilot plant tests as is conventional in the chemical process tower art.

Referring now to Fig. 2 there is shown the column 12 of Fig. 1 with the variable speed drive motor 22 disposed thereabove. In this particular side elevational, cross- sectional view, the calming sections 14 are shown in more detail. Each section 14 contains structured packing 20 in three distinct layers. The structured packing 20 in each of the calming sections 14 is comprised of a first bottom layer 67 of corrugated packing facing a first direction with a second layer 68 of corrugated packing disposed thereabove and orientated into a second direction. The orientation of layers 67 and 68 are

described in more detail below. A third packing layer 69 is disposed above second layer 68, which third layer 69 is also rotated relative to second layer 68. In this particular illustration, the bottom 42 of the tower 12 is shown to be constructed with a sufficient axial length to provide for an organic solvent distributor 70. The distributor 70 distributes the flow of the lighter fluid 40 upwardly through column 12 while an aqueous feed distributor 72 is disposed in the upper region of the column 12 for distributing the heavier liquid 30 downwardly therein. This particular system design has been utilized in the analysis of the present invention as part of pilot plant tests utilizing a column having a relatively small diameter (on the order of 3 inches) . Other test parameters and results will be set forth below.

Referring still to Fig. 2, one aspect of the present invention is the utilization of corrugated metal packing in the calming sections 14. In a preferred embodiment, the layers 67, 68 and 69 of calming section 14 are rotated 90° relative to each other and are formed of smooth, impervious corrugated metal structured packing. This packing configuration is used in the present invention to replace the mesh packing of the Scheibel

mesh-type extraction apparatus of U.S. Patent 2,493,265. It was found during the test of this assembly that this substitution permitted a six fold increase in processing capacity to be realized at volumetric efficiencies which are comparable, if not higher, than prior art designs.

TESTS UTILIZING THE PRESENT INVENTION

Pilot plant extraction column tests were performed to demonstrate the performance of an agitated-packed extraction column of the type shown in Fig. 2 with a standard acetone-water-toluene system. The two extraction columns evaluated were patterned after the original Scheibel mesh column as shown in U.S. Patent No.

2,493,265 (hereafter the "Scheibel mesh column") with the mesh sections replaced with the above described higher corrugated, capacity structured packing. With both packings described herein, active heights of 30" which contained four (4) actual stages were used in 3" diameter extraction columns. Agitation was provided with standard 4-bladed radial turbines of the type typically used in a 3" diameter Scheibel mesh column. Tests with both acetone mass transfer from the continuous aqueous phase to dispersed organic phase (c-d) and dispersed organic to continuous aqueous phase (d-c) were performed, but a

detailed analysis of only the (c-d) mass transfer data is presented.

The tests were conducted with a smooth surface, unperforated crimp structured packing of 3/8" and " crimp sizes. The smaller crimp size is attributable to the small diameter of the column as compared to commercial columns. With larger, commercial columns, the crimp size would preferably increase to as much as three inches. In the tests with the 3/8" crimp, combined feed and solvent flow rates from 10 to 50 m ³ / (m ² /hr) were considered and agitator speeds from 300 to 1750 rpm were used. The maximum theoretical stages per meter ranged from 3.83 at 10 m ³ (m ² /hr) to a maximum of 5.91 at 20 m ³ /(m ² hr) , with a decrease at higher processing rates to 2.11 stages/meter at a combined throughput of 49.89 m ³ /(m ² hr) . The maximum volumetric efficiency (at optimum rpm) increased from 38.3 HR ^"1 at a combined throughput of 10 m ³ / (m ² hr) to a maximum of 186.8 HR ^-1 at 40 m ³ / (mhr) and then it fell off to 106 HR ^"1 at 49.89 m ³ / (m ² hr) . In the tests with the M" crimp packing, combined throughputs from 10.58 to 41.01 m ³ /(m ² hr) were considered and agitator speeds from 450 to 1700 rpm were used. The maximum theoretical stages per meter ranged from 5.2 at 10.58 m ³ /(m ² hr) to a maximum of 7.14 stages per meter at

20.48 m ³ / (m ² hr) with a decrease a higher processing rates to 2.74 stages/hr at a combined throughput of 49.89 m ³ /(m hr) . The maximum volumetric efficiency increased from 55.5 HR- ¹ at 10.58 m ³ / (m ² hr) to 154.6 HR- ¹ at 30.73 m ³ /(m ² hr) and then it fell off to 112.4 HR- ¹ at 41.01 m ³ /(m ² hr) .

By replacing the mesh in the original Scheibel mesh column with 3/8" and crimp structured packing, combined processing rates increased from 10 m ³ / (m ² hr) to as high as 40 m ³ / (m ² hr) with volumetric efficiencies over

150 HR ^"1 . This data indicates a six-fold increase in capacity with excellent volumetric efficiency

The above tests were performed to (1)evaluate the performance of a 3" diameter agitated-packed column with 3/8" structured packing with the standard acetone water- toluene system at room temperature processing conditions, and (2) .to evaluate the performance of a 3" diameter agitated-packed column with M" crimp structured packing with the standard acetone water-toluene system at room temperature processing conditions.

Referring now to Fig. 3A, the equilibrium distribution of acetone between reagent grade toluene and water (steam condensate) phases at room temperature may be seen. These data were obtained by performing shake

tests with a 1 liter round bottom flask. Compositions of the resulting raffinate and extract phases were determined by gas chromatography.

As stated above, Fig. 1 illustrates a simplified schematic of the extraction pilot plant from which the data was taken that is presented herein. The pilot plant included a 3" diameter agitated column 12 with variable speed paddles 28 installed in mixing sections 16, metered supplies of feed 30 and solvent 40, and collection systems for an organic extract overflow 66 and a raffinate underflow 56. In all cases the organic toluene phase was dispersed in the continuous aqueous phase so the liquid-liquid interface was located at the top of the extraction column. Specific geometries of the agitated column 12 tested may be seen in Figures 3B, 4, 5 and 6. Packing for the 3/8" crimp column was fabricated from structured packing sold under the trademark Gempak ^® which is a registered trademark of Glitsch, Inc. The Gempak elements were constructed in a 4-3/4" thickness with a 3" outside diameter and were drilled with a V hole axially through the center thereof for receipt of the shaft 18 therethrough (See FIG. 7) . Packing for the W crimp Gempak ^® columns was fabricated from plain sheet metal

elements (no lances, perforations or holes) by welding three (3) 1 " thick x 3" diameter discs of the Gempak™ together to form a 4}_" long (high) element. Each disc was rotated 90° to the adjacent disc before welding. Again, a V." diameter hole was drilled axially through the center of each finished element for passage of the agitator shaft 18 therethrough.

Pilot plant test results are shown in Figs. 3B, 4, 5 and 6.Theoretical extraction stages were determined graphically, from operating lines plotted on Figure 3A. Since the mutual solubility of water and toluene is very small in the range studied, an operating line on Figure 3A employing weight ratio units can be assumed to be a straight line. In all tests, the volumetric flow ratio of organic solvent to aqueous feed was 1.5. Therefore, the operating lines for the runs were nearly parallel to the equilibrium line and the resulting extraction factor was close to unity. Under these circumstances, HETS (Height Equivalent of Theoretical Stage) and HTU (Height of Transfer Unit) are essentially equal.

The volumetric efficiency is the product of the total flow in units of m ³ /(m ² hr) and the number of theoretical stages per meter. Thus volumetric efficiency has the units of HR ^"1 and is inversely proportional to

the volume of column required to do a given extraction job.

Theoretical stages per meter versus rpm for the 3/8" and _" crimp agitated-packed columns are shown in Figures 3B and 4, respectively. At a combined processing rate of 10 m ³ /(m ² hr) the optimum rpm is 50 to 70% of the rpm at flooding. At higher processing rates, however, the optimum rpm (highest theoretical stages per meter) is within 5% of the flood point rpm. The maximum theoretical stages per meter versus combined processing rate (total flow) on a Stichlmair type plot is shown in FIG. 5. For both 3/8" and .*_" crimp Agitated Packed (AP) columns, the maximum theoretical stages per meter occurs at approximately 20 m ³ /m ² hr) . Volumetric efficiency versus total flow is shown in FIG. 6. For both 3/8" and M" crimp agitated-packed columns,_ the maximum volumetric efficiency occurs at approximately 40 m / (m hr) .

Referring now to FIG.7, there is shown an enlarged, exploded, perspective view of a preferred embodiment of the structured packing 20 of the present invention disposed within the calming sections 14 of a tower 12 in layers 67, 68 and 69, which correspond to the description in FIG. 2. The individual layers 67, 68 and 69 are

referred to generally as layers 100. For example, the structured packing 20 is provided in an assembly of multiple packing layers 100. Each layer 100 of packing 20 comprises a plurality of corrugated sheets 102, the corrugations of which are disposed at an angle relative to the tower axis 18 and angularly oriented one to the other in face-to-face relationship. A somewhat similar structured packing array is also shown in U.S. Patent No. 4,842,778 assigned to Glitsch, Inc. The plurality of layers are rotationally oriented on the order of 90° one to the other as represented by phantom line 111 for bi¬ directional lateral dispersion and full distribution of the liquids passing therethrough. This rotational c relationship between layers as represented by line 111 affords not only even liquid distribution but also enhances the sealing of the assembly thereof relative to the round walls of column 12. Thiε rotational relationship between layers affords not only even liquid distribution and improved sealing of the assembly relative to the round walls of column 12, but also increases the dispersed phase holdup in the calming sections of said column. For example, a single layer 100 of corrugated sheets 102 seals best against the round inside column walls 104 along its ends 110 which may be

cut more precisely to size. Bypassing of liquid around the packing layers 100 is greatly reduced with improvements in the fit between the packing 20 and the inside column walls 104. By disposing rotated layer 68 of corrugated sheets 102 above layer 67, the area of least sealing of one layer is compensated for by the next layer. As sated above, the enhanced sealing is because the ends 110 of the sheets 102 may be sized more to closely fit against the walls 104 than the sides 113 of the corrugated sheets 102. Because of this better sealing, bypassing of the dispersed phase around the packing 20 is minimized.

Referring still to FIG. 7, the multiple packing layers 100 are each constructed with a central aperture 199 formed therein. The apertures 199 of layers 100 are adapted for receipt of the shaft 18 therethrough for permitting assembly of the paddles 28 in the adjacent mixing section 16 and the rotation thereof. In this manner, agitation may be imparted to the liquids flowing therein, as described above. In one embodiment of the invention the paddles 28, blades 29, shaft 18, packing layers 100 and the side walls 104 of tower 12 are coated with plastic such as polypropylene, Teflon (a trademark of Dupont) or Kymar (a trademark of Pennwalt Corp.) . The

packing layers and other parts, such as paddle blades 29 may actually be formed of such plastics. Such plastic coatings can be applied by dip coating and the like and are most useful when using the present invention to disperse an aqueous liquid into a continuous organic liquid because aqueous liquids coalesce on metals.

The present invention has thus been shown to provide an improved agitated extraction column with enhanced performance characteristics, but specifically, FIGS. 1, 2 and 7 (now referred to in combination) illustrate a countercurrent, liquid-liquid extraction system 10 comprising a substantially vertical column 12 having a central axis 18 therethrough and including a series of axially alternating transverse calming sections 14 and mixing section 16 therein. Agitation means in the form of paddles 28 are disposed within each of the mixing sections 16 for exerting a non-vertical thrust to the liquid flowing therein. At least one layer of structured packing 20 is mounted within each of the calming sections 14 and between the mixing sections 16 and said structured packing mounted within said calming sections comprises at least one layer of corrugated contact plates or sheets 102 disposed in generally face-to-face relationship for facilitating the flow of liquid therebetween.

The corrugated sheets 102 disposed within the calming sections may, as shown, have the corrugations oriented at an angle on the order of 45° relative to the axis 18 of the column 12. The corrugations of the sheets 102 may be formed with a height on the order of one- quarter inch to three inches, depending on the size of the column 12, and may have a generally smooth surface finish as described herein, or the sheets may include apertures. In one embodiment of the invention, the sheets 102 are foil-like and are formed from metal. As described above, the sheets 102 may be formed from plastic or coated therewith. In yet another aspect, the preferred embodiment of the above described invention includes at least two axial layers 100 of packing 20 transversely disposed within each of the calming sections 14. As many as five or more layers are contemplated in certain conventional applications. In this particular embodiment, the packing is rotated 90° relative to a first layer of packing to enhance the edge sealing between said packing and the inside walls 104 of the column 12.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. While the method and

apparatus shown or described has been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the following claims.