Abstract:
The invention relates to a method producing a portioned column by forming a first segment and a third segment into arcuate segments, and attaching these arcuate segments to a second z-shaped segment to from two contiguous volumes with approximately semi-circular cross-sections that combine to form a partitioned, approximately cylindrical segment.

Description:
This application is a §371 of International PCT Application PCT/EP2009/058816, filed Jul. 10, 2009. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for fabricating divided wall columns. 
     BACKGROUND 
     Distillation columns have, of course, been widely used to perform separations of all types in different industrial applications. Over fifty years ago, it was proposed to replace two distinct distillation columns with a single distillation column having a vertical partition (dividing wall column) within the column. This single, divided wall column could effect the separation of the column feed into three constituent fractions. It was recognized then that a dividing wall column could reduce, or minimize, the size or cost of the equipment needed to produce overhead, bottoms, and sidedraw products. 
     Control systems for dividing wall distillation columns have been known since at least 1980, when U.S. Pat. No. 4,230,533 described a dividing wall distillation column and its control system. In the late 1990&#39;s, control systems for dividing wall distillation columns have been studied in further detail by researchers. 
     Despite the advantages of the dividing wall column and despite much research and study, the processing industry has long felt reluctant to use dividing wall columns in commercial processes. This widespread reluctance has been attributed to various concerns, including control problems, operational problems, complexity, simulation difficulties, and lack of design experience. General guidelines and considerations when substituting a dividing wall column for conventional columns have been established. Nevertheless, there are relatively few documented practical uses of dividing wall columns in commercial plants. 
     It is known, for example, to provide a partition in such a column to thereby subdivide the interior of the column into an inlet region and a discharge region. The partition in this system serves to prevent transverse mixing of liquid and/or vapor streams over a limited height of the column. The apparatus reduces the number of distillation columns required for the separation of multicomponent feed stocks. 
     The partitions can extend between opposite walls of the column and can have heights which, as a rule, can be greater than the column diameter and can be at least equal to the spacing between individual horizontal bottoms of the column. The use of continuous partitions has, however, a number of drawbacks and these drawbacks are the more serious the greater the diameter of the column. 
     The incorporation of a one-piece partition in the column is difficult because of its weight and the need for a close fit of the partition in the column. From a certain size, the dimensions of such partitions ensures that they can only be handled with mechanical assistance which can lead to additional costs. Furthermore, with increasing weight, the partitions can pose a greater danger for the workers who are necessary for installation of the partition. It has been found in practice that the partition can easily become canted during installation in the column and can thereby damage the inner wall of the column or result in poor sealing between the column and the partition. Irregularities in the shape of the column can also limit the sealing effectiveness. Since possible nonsealing regions may then have to be sealed up by additional acts, the costs of the column and the partition can be prohibitive. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to propose fabrication methods adapted to present and future processes involving dividing wall columns for the transfer of gas/liquid material that serve to integrate a plurality of columns in the same shell in order to reduce the fabrication costs. 
     A further object of the present invention is to propose fabrication methods for divided wall columns for the transfer of gas/liquid material that serve to integrate a plurality of columns in the same shell in order to reduce the separation energy required. 
     For this purpose, the invention relates to a method of producing a partitioned column segment, comprising a first sheet metal segment, a second sheet metal segment, and a third sheet metal segment. The first sheet metal segment comprises a first edge, and a second edge. The second sheet metal segment comprises a third edge, and a fourth edge. The third sheet metal segment comprises a fifth edge, and a sixth edge. The second edge is attached to said third edge, and the fourth edge is attached to said fifth edge. The method comprises forming said first segment into a first arcuate bend in a first direction, wherein adjacent to said first edge comprises a first distal region. The method comprises forming said second segment into a z-shaped bend, wherein said z-shape consists of a first proximal region, a central region, and a second proximal region. The method comprises forming said third segment into a second arcuate bend in a second direction, wherein adjacent to said sixth edge comprises a fourth distal region. The method comprises attaching said first distal region to said second proximate region, thereby producing a first approximately cylindrical segment, said first approximately cylindrical segment having an approximately semi-circular cross-section. And the method comprises attaching said second distal region to said first proximate region, thereby producing a second approximately cylindrical segment, said second approximately cylindrical segment having an approximately semi-circular cross-section. 
     In another embodiment, the arcuate bend is produced by rolling. In yet another embodiment, said second edge is attached to said third edge by being fabricated from the same sheet, and said fourth edge is attached to said fifth edge by being fabricated from the same sheet. In another embodiment said second edge is attached to said third edge by welding; and said fourth edge is attached to said fifth edge by welding. In yet another embodiment, at least one weld is a butt-weld. In another embodiment at least one weld is a lap-weld. In another embodiment, said second sheet metal segment comprises a thicker gauge metal than said first sheet metal segment and/or said third sheet metal segment. 
     In another embodiment, said first distal region is attached to said second proximate region by welding, and said second distal region is attached to said first proximate region by welding. In another embodiment, all welds are performed from the exterior of the said partitioned column. In yet another embodiment, said z-shaped bend has an angle α between said first proximal region and said central region, and said z-shaped bend has an angle β between said second proximal region and said central region. In another embodiment wherein said angle α is about 90 degrees, and wherein said angle β is about 90 degrees. In another embodiment said first proximal region has a length of about 30 mm, and said second proximal region has a length of about 30 mm. 
     In another embodiment, said second segment comprises two sheet metal segments attached together by butt-weld. In another embodiment, said second segment comprises two sheet metal segments attached together by lap-weld. In yet another embodiment, said second segment comprises two sheet metal segments that are of equal length. In another embodiment, said two sheet metal segments are separated to form an insulating cavity. In another embodiment, said insulating cavity is filled by an insulating media. In another embodiment, said first approximately cylindrical segment and said second approximately cylindrical segment form an approximately cylindrical shape with a plane forming a common cord formed in part from said second sheet metal segment, and said plane forming a common cord being axially offset from said approximately cylindrical form to avoid weld crossing during the joining of successive partitioned column segments. Another embodiment comprises a method of producing a partitioned column by means of joining successive partitioned columns as discussed herein. Another embodiment comprises a partitioned column as produced by one of the methods discussed herein. 
     In another embodiment the first sheet metal segment, the second sheet metal segment and the third sheet metal segment may be comprised of different materials. The difference may include, but are not limited to, a different metallic composition or material of the same metallic composition but differing in thickness, surface texture or treatment. In another embodiment, the second sheet metal segment may have mechanical strengthening such as ribbing or the equivalent. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other features and advantages of the invention will appear from a reading of the description that follows. Embodiments of the invention are provided as non-limiting examples. 
         FIG. 1  is a schematic representation of one embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view of one embodiment of the present invention. 
         FIG. 3  is a schematic cross-sectional view of one embodiment of the present invention. 
         FIG. 4  is a schematic cross-sectional view of the second sheet metal segment, showing the z-shape profile 
         FIG. 5  is a schematic cross-sectional view showing some of the various embodiments possible for the second sheet metal segment. 
         FIG. 6  is a schematic cross-sectional view showing one embodiment with an insulating cavity. 
         FIG. 7  is a schematic cross-sectional view showing one embodiment with the second sheet metal segment offset from the first sheet metal segment and the third sheet metal segment. 
         FIG. 8  is a schematic view showing how the completed column segments may be joined successively to form a partitioned column. 
         FIG. 9  is a schematic cross-sectional view showing one embodiment of possible assembly and welding. 
         FIG. 10  are schematic details showing other embodiments of possible welding techniques. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The application of dividing wall columns serves to obtain a gain in fabrication cost in processes involving a plurality of columns, particularly in air distillation processes comprising columns operating in parallel: argon columns (mixture and denitrogenation column), Etienne column, or mixture column. In fact, integrating two columns obtains in particular: the economy of a shell, the reduction of the volume of the cold box (in the case of cryogenic distillation), and sometimes, the economy of connecting pipes between the columns. However, the methods for fabricating this type of column are more complex than those for conventional columns. 
     The present invention describes a method for fabricating dividing wall columns mainly allowing: simpler fabrication of the shell (in particular by limiting the number of internal welds), better sealing between the two parts separated by the partition, and operation with a high pressure differential between the two parts. The invention consists of a method for fabricating a dividing wall column by joining a series of main modules. These main modules have the feature of each consisting of a single elementary part bent on itself, in order to form the outer envelope of the shell and the dividing wall. Secondary modules may be added to supplement the dividing wall column (ends, branches, specific stiffeners, etc.), as well as the column internals (packings, trays, distributors, etc.) and any other part or equipment required for its operation. These additions can be made before, during or after the joining of the main modules. 
     One example of the method for fabricating the main module is shown in the  FIGS. 1 ,  2  and  3 . Turning first to  FIG. 1 , the elementary part, consisting of plate metal, is illustrated. This elementary part comprises a first sheet metal segment  101 , a second sheet metal segment  102 , and a third sheet metal segment  103 . For purposes of illustration, these three sheet metal segments  101 ,  102 ,  103  are illustrated as being separate pieces, but in various embodiments of the present invention all three segments may comprise a single, unitary piece of metal. The second sheet metal segment  102  may be of a different gauge metal, preferably a thicker gauge, than the first sheet metal segment  101  and/or the third sheet metal segment  103 . 
     First sheet metal segment  101  further comprises a first edge,  104 , a second edge  105 , and a first distal region  110 . Second sheet metal segment  102  further comprises a third edge,  106 , a fourth edge  107 , a first proximal region, and a second proximal region  113 . Third sheet metal segment  103  further comprises a fifth edge,  108 , a sixth edge  109 , and a second distal region  112 . 
     Turning now to  FIG. 2 , which maintains the above element numbering in the interest of clarity, first sheet metal segment  101  is bent into first arcuate segment  201 , with one end comprising the first distal region  110 . Second sheet metal segment  102  is bent into a z-shaped, or s-shaped, form, with the two arms of the comprising the first proximal region  111  and the second proximal region  113 . Third sheet metal segment  103  is bent into second arcuate segment  203 , with one end comprising the second distal region  112 . the arcuate segments  201 ,  203  may be formed by rolling. The second edge  105  is attached to the third edge  106 . The second edge  105  may be attached to the third edge  106  by welding. This may be a butt weld or a lap weld. The second edge  105  may be attached to the third edge  106  by being fabricated from the same sheet. The fourth edge  107  is attached to the fifth edge  108 . The fourth edge  107  may be attached to the fifth edge  108  by welding. This may be a butt weld or a lap weld. The fourth edge  107  may be attached to the fifth edge  108   b  being fabricated from the same sheet. 
     Turning now to  FIG. 3 , which also maintains the above numbering in the interest of clarity, first distal region  110  of first arcuate segment  201 , is attached to second proximal region  113 , thereby forming a first approximately cylindrical segment  301  having an approximately semi-circular cross-section. The second distal region  112  is likewise attached to first proximal region  111 , thereby forming a second approximately cylindrical segment  302  having an approximately semi-circular cross-section. The first distal region  110  may be attached to the second proximal region  113  by welding. The second distal region  112  may be attached to the first proximal region  111  by welding. It is preferred that all welds are performed from the exterior of the partitioned column. 
     Turning now to  FIGS. 4   a  and  4   b , which also maintain the above numbering in the interest of clarity, the z-shape of the second sheet metal segment  102  comprises the first proximal region  111  bent into a first arm  401 , the second proximal region  113  bent into a second arm  402 , and an unbent central region  114 . In this embodiment, the first arm  401  and second arm  402  are bent in a clockwise orientation, but a counterclockwise orientation is also possible. A combination of bends that incorporate a counterclockwise and a clockwise orientation (i.e. a c-shaped bend) is also possible. The first arm  401  and second arm  402  may be bent in such a manner as to be imparted with a curve of approximately equal radius to that of the overall column (i.e. an s-shaped cross section). First arm  401  and second arm  402  may be bent in such a manner as to maintain a linear z-shaped cross section. 
     The z-shape of the second sheet metal segment  102  may be bent so as to have an angle α between the first arm  401  (the first proximal region  111 ) and the central region  114 . The angle α may have an angle of less than 90°. The angle α may have an angle of about 90°. The angle α may have an angle of more than 90°. The z-shape of the second sheet metal segment  102  may be bent so as to have an angle β between the second arm  402  (the second proximal region  113 ) and the central region  114 . The angle β may have an angle of less than 90 degrees. The angle α may have an angle of about 90 degrees. The angle β may have an angle of more than 90 degrees. The first arm  401  may have a length of about 30 mm. The first arm  401  may have a length approximately equal to the diameter of the roller in the forming apparatus. The second arm  402  may have a length of about 30 mm. The second arm  402  may have a length approximately equal to the diameter of the roller in the forming apparatus. 
     Turning now to  FIGS. 5   a ,  5   b , and  5   c  which also maintain the above numbering in the interest of clarity, the second sheet metal segment  102  may comprise two separate sheets of metal that are subsequently connected together. As indicated in  FIG. 5   a , the two sheets comprising second sheet metal segment  102  may be attached at their edges, by means of a butt-weld. As indicated in  FIG. 5   b , the two sheets comprising second sheet metal segment  102  may be overlapped and connected by means of a lap-weld. The degree of overlap is a design choice, but typically the degree of overlap would be less than ½ of the overall length of the central region  114 , preferably less than ¼ of the overall length of central region  114 . Preferably this overlap would be less than 20 cm, and more preferably this overlap would be less than 10 cm. This technique provides additional structural rigidity by means of the rib created by this overlap butt-weld. 
     As indicated in  FIG. 5   c , the two sheets comprising second sheet metal segment  102  may be fully overlapped, with each overlapping segment spanning approximately the full width of central region  114 . As indicated in  FIG. 6 , these two overlapping segments may be separated by a space to form an insulating cavity  501 . This insulating cavity may be filled with ambient air, it may be evacuated to form a partial vacuum, or it may be filled with an insulating media. 
     Turning now to  FIGS. 7   a  and  7   b , which also maintain the above numbering in the interest of clarity, the second sheet metal segment  102  may be axially offset Y from the first sheet metal segment  101  and third sheet metal segment  103 . As can be seen in  FIG. 7   b , once the first approximately cylindrical segment  301  and the second approximately cylindrical segment  302  form an approximately cylindrical shape, the second sheet metal segment  102  assumes the nature of a plane forming a common cord within this approximately cylindrical shape. This cord may be a diameter. This cord may be a minor cord, with the first approximately cylindrical segment  301  and the second approximately cylindrical segment  302  being of unequal cross-sectional area. The axial offset Y of the second sheet metal segment  102  results in tab  701  at one end and slot  702  at the other end of the resulting approximately cylindrical segment. 
     Turning now to  FIGS. 8   a  and  8   b , as multiple subassemblies that have been fabricated according to this invention are stacked together, tab  701  of the superior unit fits into slot  702  of the inferior unit, thereby allowing welding without cross welding of any joints. A partitioned column may be fabricated by joining successive partitions of the type described above. 
     In one alternative of the invention, the main modules may consist of a plurality of elementary parts. The mechanical joining of these parts has the special feature of being carried out with access via the exterior of the part. This alternative therefore allows an easy assembly of the main modules because of the external access and the ease of shaping of the elementary parts. It also serves to guarantee a good seal of the main module with regard to the exterior, and also a good seal between the parts of the column. 
     The same method can be applied to divide the column into two or more parts. In another alternative, the invention consists in joining the main modules from a single or a plurality of elementary parts, but with at least one mechanical joint made with access from the interior of the elementary part. In another alternative, it is possible to use the method previously described with elementary parts having heterogeneous mechanical characteristics, in particular thicknesses, or heterogeneous materials in the case of metal plates (to better withstand the pressure differentials). 
     Turning now to  FIGS. 9 and 10  ( a - d ), more details on illustrative embodiments of the above discussed welds are disclosed. Note that, as before, the numbering system has been maintained in the interest of clarity.  FIG. 9  illustrates how the unbent central region  114  may have an effectively linear (i.e. effectively non-curved) first proximal region  111  and an effectively linear second proximal region  113 . These linear first proximal region  111  and linear second proximal region  114  may then act as conventional backing strips to allow the first sheet metal segment  101  and second sheet metal segment  102  to be more easily welded together. 
       FIGS. 10  ( a - d ) illustrate alternative embodiments by which the effectively linear first proximal region  111  and the effectively linear second proximal region  113  may serve as conventional backing strips. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.