Patent Application
20180087834
The present invention relates to an exchange column containing structured packing and a method for using the exchange column. Structured packing has particular application in heat and/or mass exchange columns, especially in cryogenic air separation processes, although it may be used in other applications, such as heat exchangers, for example.
The term “column” as used herein means a distillation or fractionation column, i.e. a column wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, such as by contacting of the vapor and liquid phases on packing elements or on a series of vertically-spaced trays or plates mounted within the column.
A divided wall column is a column having at least one dividing wall located in the interior space of the column defining separated volumes within the column that are thermally coupled. Dividing walls are typically oriented vertically. Two different mass transfer separations may occur in the separated volumes on either side of the dividing wall. U.S. Pat. No. 7,357,378 B2, incorporated herein by reference, discloses a divided wall exchange column.
The term “packing” means solid or hollow bodies of predetermined size, shape and configuration used as column internals to provide surface area for the liquid to allow heat and/or mass transfer at the liquid-vapor interface during countercurrent flow of two phases. Two broad classes of packings are “random” and “structured”.
“Random packing” means packing wherein individual members have no specific orientation relative to each other or to the column axis. Random packings are traditionally small, hollow structures with large surface area per unit volume that are loaded into a column in a manner resulting in a random orientation of the packing.
“Structured packing” means packing wherein individual members have specific orientation relative to each other and to the column axis. Structured packings usually are made of thin metal foils stacked in layers.
The term “surface area density” means the surface area of the structured packing per unit volume of the structured packing, and usually is expressed in terms of m2/m3 of the volume occupied by the packing.
In processes such as distillation, it is advantageous to use structured packing to promote heat and/or mass transfer between counterflowing liquid and vapor streams. Structured packing, when compared with random packing or trays, offers the benefits of higher efficiency for heat and/or mass transfer with lower pressure drop. It also has more predictable performance than random packing.
The separation performance of structured packing is often given in terms of height equivalent to a theoretical plate (HETP), which is the height of packing over which a composition change is achieved that is equivalent to the composition change achieved by a theoretical plate. The term “theoretical plate” means a contact process between gaseous and liquid phases such that the existing gaseous and liquid streams are in equilibrium. The smaller the HETP of a particular packing for a particular separation, the more efficient the packing, because the height of the packing bed being used decreases with HETP.
The separation performance of structured packing or packing efficiency may also be described in terms of the height of a transfer unit (HTU) or height of an overall transfer unit, gas concentration basis (HOG), having units of length.
Packing efficiency parameters such as HETP and HOG are common parameters used in the industry and are defined in reference books, for example, Perry's Chemical Engineers' Handbook, 8th Edition, section 14.4.2.
Cryogenic separation of air is carried out by passing liquid and vapor in countercurrent contact through a distillation column. A vapor phase of the mixture ascends with an ever increasing concentration of the more volatile components (e.g., nitrogen) while a liquid phase of the mixture descends with an ever increasing concentration of the less volatile components (e.g., oxygen). Various packings or trays may be used to bring the liquid and gaseous phases of the mixture into contact to accomplish mass transfer between the phases.
There are many processes for the separation of air by cryogenic distillation into its components (i.e. nitrogen, oxygen, argon, etc.). Such processes are described for example, in U.S. Pat. No. 6,357,728 B1, and EP 2 822 683 B1, each incorporated herein by reference.
As described in the prior art, structured packing may be used to provide contact between the liquid and gaseous phases in the exchange column for separating various components, e.g. oxygen, nitrogen, and optionally argon.
The conventional technology for using structured packing has been described in various patents pertaining to structured packing that followed U.S. Pat. No. 4,296,050 (Meier), which describes corrugated structured packing and its applications.
A basic conventional structured packing element 20 is shown in
In addition to being corrugated, the elements or sheets may have a surface texture 30 (e.g., lateral or horizontal striations), perforations, holes or apertures 28, fluting, dimples, grooves, or other features which can enhance the performance of the basic element 20 in order to meet specific requirements for its intended application.
The perforations 28 and the texture 30 formed by elevated/depressed areas aid liquid/vapor spreading on the surface of foil, thus improving the heat and mass transfer efficiency of the packing. Typically, the surface area of the foil occupied by the perforations is from 5% to 20%. Typically, the fluting may be in the form of horizontal striations, or a bidirectional surface texture in the form of fine grooves in crisscrossing relation.
The corrugations, as illustrated in the sectional view of
A typical structured packing employs vertically-oriented corrugated packing sheets or elements 20 such as that in
Using such basic packing elements 20, a “brick” 24 of structured packing is made by assembling the elements (typically about 40 to 50 elements per brick) such that the corrugations of adjacent elements are arranged in a crisscrossing fashion shown in
A distillation column 40 packed with conventional structured packing is shown schematically in
Structured packing bricks 24 typically are assembled into layers (48, 48′) in a section of a distillation column 40 as shown in
Within a layer of structured packing in a column, multiple foils are oriented vertically (that is to say, with the plane of the foil substantially parallel to the axis of the column), with adjacent foils having their corrugations oriented transversely (that is to say, if a first foil has its corrugations running from bottom left to top right, an adjacent foil will be oriented such that its corrugations run from bottom right to top left). Such an arrangement is depicted in FIG. 3 of U.S. Pat. No. 4,296,050 (Meier). It is conventional to rotate successive layers of structured packing, typically by an angle of 90° about the column axis with respect to the underlying layer, in order to improve the flow characteristics. Such an arrangement is shown in FIG. 4 of U.S. Pat. No. 4,296,050 (Meier). However, each rotation increases the pressure drop through the column comprised of the packing.
Structured packing and its features are described, for example, in Distillation Design, Chapter 8, Henry Z. Kister, McGraw-Hill, Inc. 1992, Distillation Operation, Henry Z. Kister, McGraw-Hill, Inc. 1990, and Perry's Chemical Engineer's Handbook, 8th Edition, 2008, Chapter 14.4. EQUIPMENT FOR DISTILLATION AND GAS ADSORPTION: PACKED COLUMNS, each incorporated herein by reference.
In Perry's Chemical Engineer's Handbook, 8th Ed., it states “The corrugations spread gas and liquid flow through a single element in a series of parallel planes. To spread the gas and liquid uniformly in all radial planes, adjacent elements are rotated so that sheets of one element are at a fixed angle to the layer below (
In Distillation Design, § 8.1.8 of Kister, it states “The corrugated sheets are assembled into an element, typically 8 to 12 in tall.” In Distillation Operation, § 10.8 of Kister, it states that “The packing is usually supplied in sections, or “bricks.” Typical brick height is 8 to 12 in.” (i.e. 200 mm to 300 mm). Kister goes on to state that “A brick can be as long as the wall-to-wall distance in smaller columns, but to minimize the possibility of damage it is better to have a number of bricks make up this distance in the central portion of the column.”
While structured packing in exchange columns has been used for many years and improvements made over the years, industry still desires exchange columns having improved separation performance.
The present invention relates to an exchange column with corrugated structured packing, a method for using the exchange column, and a method of making the exchange column.
There are several aspects of the invention as outlined below. In the following, specific aspects of the invention are outlined below. The reference numbers and expressions set in parentheses are referring to an example embodiment explained further below with reference to the figures. The reference numbers and expressions are, however, only illustrative and do not limit the aspect to any specific component or feature of the example embodiment. The aspects can be formulated as claims in which the reference numbers and expressions set in parentheses are omitted or replaced by others as appropriate.
Aspect 1. An exchange column comprising:
Aspect 2. The exchange column according to aspect 1 wherein the angle (i.e. the rotation angle) ranges from 70° to 90°.
Aspect 3. The exchange column according to aspect 1 or aspect 2 wherein the height of the first layer of structure packing (110) and the height of the second layer of structured packing (120) are greater than 350 mm or greater than 400 mm.
Aspect 4. The exchange column according to any one of aspects 1 to 3 wherein the second layer of structured packing (120) comprises the second set of corrugated plates (121) and the second set of corrugated plates (121) have a vertical height greater than 350 mm or greater than 400 mm and wherein the second set of corrugated plates (121) have a vertical height less than 1000 mm.
Aspect 5. The exchange column according to any one of aspects 1 to 3 wherein the second layer of structured packing (120) comprises the second group (220) of two or more sets of corrugated plates (221, 222), and wherein the two or more sets of corrugated plates (221, 222) of the second group (220) have a combined vertical height greater than 350 mm or greater than 400 mm.
Aspect 6. The exchange column according to aspect 5 wherein the combined vertical height of the two or more sets of corrugated plates (221, 222) of the second group (220) is less than 7.5 m, or less than 3.5 m, or less than 2.5 m.
Aspect 7. The exchange column according to any one of aspects 1 to 6 wherein the area of the cross section of the at least one volume is less than 177 m2, or less than 40 m2, or less than 24 m2.
Aspect 8. The exchange column according to any one of aspects 1 to 7 wherein the first layer of structured packing comprises the first set of corrugated plates (111) and wherein the first set of corrugated plates (111) have a vertical height less than 1000 mm.
Aspect 9. The exchange column according to any one of aspects 1 to 7 wherein the first layer of structured packing (110) comprises the first group (210) of two or more sets of corrugated plates (211, 212), wherein the two or more sets of corrugated plates (211, 212) of the first group (210) have a combined vertical height less than 7.5 m, or less than 3.5 m, or less than 2.5 m.
Aspect 10. The exchange column according to any one of aspects 1 to 9 further comprising:
Aspect 11. The exchange column according to aspect 10 wherein the angle of the corrugated plates of the third layer (130) relative to the adjacent corrugated plates of the second layer (120) ranges from 70° to 90°, preferably about 90°, and wherein the angle of the corrugated plates of the fourth layer (140), if present, relative to the adjacent corrugated plates of the third layer (130) ranges from 70° to 90°, preferably about 90°.
Aspect 12. The exchange column according to aspect 10 or aspect 11 wherein the third layer of structured packing (130) comprises the third set of corrugated plates and the third set of corrugated plates have a vertical height greater than 350 mm or greater than 400 mm, and wherein the fourth layer of structured packing (140), if present, comprises the fourth set of corrugated plates and the fourth set of corrugated plates have a vertical height greater than 350 mm or greater than 400 mm.
Aspect 13. The exchange column according to aspect 12 wherein the third set of corrugated plates have a vertical height less than 1000 mm and wherein the fourth set of corrugated plates, if present, have a vertical height less than 1000 mm.
Aspect 14. The exchange column according to aspect 10 or aspect 11 wherein the third layer of structured packing (130) comprises the third group of two or more sets of corrugated plates, and wherein the two or more sets of corrugated plates of the third group (230) have a combined vertical height greater than 350 mm or greater than 400 mm, and wherein the fourth layer of structured packing (140), if present, comprises the fourth group (240) of two or more sets of corrugated plates (241, 242), and wherein the two or more sets of corrugated plates of the fourth group (240) have a combined vertical height greater than 350 mm or greater than 400 mm.
Aspect 15. The exchange column according to aspect 14 wherein the combined vertical height of the two or more sets of corrugated plates of the third group (230) is less than 7.5 m, or less than 3.5 m, or less than 2.5 m, and wherein the combined vertical height of the two or more sets (241, 242) of corrugated plates of the fourth group (240), if present, is less than 7.5 m, or less than 3.5 m, or less than 2.5 m.
Aspect 16. The exchange column according to any one of aspects 1 to 15 wherein the at least one aperture in each corrugated plate of the first set (111) or first group (210) of corrugated plates have an equivalent diameter ranging from 1 to 5 mm, wherein the at least one aperture in each corrugated plate of the second set (121) or second group (220) of corrugated plates have an equivalent diameter ranging from 1 to 5 mm, wherein the at least one aperture in each corrugated plate of the third set (131) or third group (230) of corrugated plates, if present, have an equivalent diameter ranging from 1 to 5 mm, and wherein the at least one aperture in each corrugated plate of the fourth set (141) or fourth group (240) of corrugated plates, if present, have an equivalent diameter ranging from 1 to 5 mm.
Aspect 17. The exchange column according to any one of aspects 1 to 16 wherein the apertures in each corrugated plate of the first set (111) or first group (210) of corrugated plates create an open area in each corrugated plate of the first set (111) or first group (210) of corrugated plates in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate, wherein the apertures in each corrugated plate of the second set (121) or second group (220) of corrugated plates create an open area in each corrugated plate of the second set (121) or second group (220) of corrugated plates in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate, wherein the apertures in each corrugated plate of the third set (131) or third group (230) of corrugated plates, if present, create an open area in each corrugated plate of the third set (131) or third group (230) of corrugated plates in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate, and wherein the apertures in each corrugated plate of the fourth set (141) or fourth group (240) of corrugated plates, if present, create an open area in each corrugated plate of the fourth set (141) or fourth group (240) of corrugated plates in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
Aspect 18. The exchange column according to any of aspects 1 to 17 wherein the first layer of structured packing (110) has a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3, and wherein the second layer of structured packing (120) has a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
Aspect 19. The exchange column according to any one of aspects 10 to 18 wherein the third layer of structured packing (130), if present, has a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3, and wherein the fourth layer of structured packing (140), if present, has a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
Aspect 20. The exchange column according to any one of aspects 1 to 19 wherein at least one corrugated plate in the first layer of structured packing (110) has a surface with a surface texture on at least a portion of its surface.
Aspect 21. The exchange column according to any one of aspects 1 to 20 wherein at least one corrugated plate in the second layer of structured packing (120) has a surface with a surface texture on at least a portion of its surface.
Aspect 22. The exchange column according to any one of aspects 1 to 21 wherein the surface texture on the surface of the at least one corrugated plate in the first layer of structured packing (110) is in the form of horizontal striations and/or dimples.
Aspect 23. The exchange column according to any one of aspects 1 to 22 wherein the surface texture on the surface of the at least one corrugated plate in the second layer of structured packing (120) is in the form of horizontal striations and/or dimples.
Aspect 24. The exchange column according to any one of aspects 10 to 23 wherein at least one corrugated plate in the third layer of structured packing (130), if present, has a surface with a surface texture on at least a portion of its surface, and wherein at least one corrugated plate in the fourth layer of structured packing (140), if present, has a surface with a surface texture on at least a portion of its surface.
Aspect 25. The exchange column according to aspect 24 wherein the surface texture on the surface of the at least one corrugated plate in the third layer of structured packing (130), if present, is in the form of horizontal striations and/or dimples, and wherein the surface texture on the surface of the at least one corrugated plate in the fourth layer of structured packing (140), if present, is in the form of horizontal striations and/or dimples.
Aspect 26. The exchange column according to any one of the preceding aspects wherein the corrugations have a corrugation angle, a, relative to the horizontal ranging from about 35° to about 70° or ranging from about 40° to about 60°, and each corrugation when approximated to be a substantially triangular cross-section, has an included angle, angle, β, ranging from 80° to 110° or ranging from 80° to 95°.
Aspect 27. A method for separating a mixture comprising:
Aspect 28. The method according to aspect 27 wherein the mixture comprises oxygen and nitrogen, and wherein the first product is an oxygen-enriched product and the second product is a nitrogen-enriched product.
Aspect 29. The method according to aspect 27 wherein the mixture comprises oxygen and argon, and wherein the first product is an oxygen-enriched product and the second product is an argon-enriched product.
Aspect 30. The method according to aspect 27 wherein the mixture comprises hydrogen and carbon monoxide, and wherein the first product is a hydrogen-enriched product and the second product is a carbon monoxide-enriched product.
Aspect 31. The method according to aspect 27 wherein the mixture comprises hydrogen and carbon monoxide, and wherein the first product has a H2:CO molar ratio between 0.5:1 and 2.5:1, or between 0.9:1 and 1.5:1, or between 0.9:1 and 1.1:1, and the second product is a hydrogen-enriched product or a carbon monoxide-enriched product.
Aspect 32. A method of making an exchange column, the method comprising:
Aspect 33. The method of making the exchange column according to aspect 32 wherein the height of the first layer of structured packing (110) and the height of the second layer of structured packing (120) are greater than 350 mm or greater than 400 mm.
Aspect 34. The method of making the exchange column according to aspect 32 or aspect 33, the method further comprising:
Aspect 35. The method of making the exchange column according to aspect 34, the method further comprising:
Preferred embodiments of the invention are described with reference to the accompanying figures.
The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of elements without departing from scope of the invention as defined by the claims.
The articles “a” and “an” as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used.
The adjective “any” means one, some, or all indiscriminately of whatever quantity.
The term “and/or” placed between a first entity and a second entity includes any of the meanings of (1) only the first entity, (2) only the second entity, and (3) the first entity and the second entity. The term “and/or” placed between the last two entities of a list of 3 or more entities means at least one of the entities in the list including any specific combination of entities in this list. For example, “A, B and/or C” has the same meaning as “A and/or B and/or C” and comprises the following combinations of A, B and C: (1) only A, (2) only B, (3) only C, (4) A and B and not C, (5) A and C and not B, (6) B and C and not A, and (7) A and B and C.
The phrase “at least one of” preceding a list of features or entities means one or more of the features or entities in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. For example, “at least one of A, B, or C” (or equivalently “at least one of A, B, and C” or equivalently “at least one of A, B, and/or C”) has the same meaning as “A and/or B and/or C” and comprises the following combinations of A, B and C: (1) only A, (2) only B, (3) only C, (4) A and B and not C, (5) A and C and not B, (6) B and C and not A, and (7) A and B and C.
The term “plurality” means “two or more than two.”
The phrase “at least a portion” means “a portion or all.” The at least a portion of a stream may have the same composition with the same concentration of each of the species as the stream from which it is derived. The at least a portion of a stream may have a different concentration of species than that of the stream from which it is derived. The at least a portion of a stream may include only specific species of the stream from which it is derived.
As used herein, “first,” “second,” “third,” etc. are used to distinguish from among a plurality of steps and/or features, and is not indicative of the total number, or relative position in time and/or space unless expressly stated as such.
As used herein, “vertical” has its customary meaning. The vertical direction is aligned with gravity.
The terms “rich” or “enriched” means having a greater mole % concentration of the indicated component than the original stream from which it was formed.
The present invention relates to an exchange column with corrugated structured packing and a method for using the exchange column.
The exchange column with corrugated structured packing is described with reference to
The exchange column comprises one or more walls 105 defining one or more volumes within the one or more walls 105. At least one volume of the one or more volumes has a longitudinal axis 101 and a cross section normal to the longitudinal axis 101 where the cross section has an area greater than 0.636 m2. The present invention is suitable for any exchange column having a cross-sectional area greater than 0.636 m2. The upper limit for the area of the cross section of the exchange column may be limited only by practical limitations of construction and may be, for example, 177 m2, or 40 m2, or 24 m2.
The exchange column has a height dimension, which extends in the same direction as the longitudinal axis.
The exchange column may be a cylindrically-shaped column such as described for example in U.S. Pat. No. 6,357,728 B1, incorporated herein by reference. The exchange column may be a divided wall column as described, for example, in U.S. Pat. No. 7,357,378 B2, incorporated herein by reference. The one or more walls 105 may define the two or more volumes containing packing as found in a divided wall column. The exchange column may be a side-arm column as known in the prior art, for example, U.S. Pat. No. 4,994,098 A, U.S. Pat. No. 4,983,194 A, and U.S. Pat. No. 5,970,743 A, each incorporated herein by reference.
The exchange column comprises a first layer of structured packing 110 disposed within the at least one volume. The first layer of structured packing 110 comprises either (i-a) a first set of corrugated plates 111 or (i-b) a first group 210 of two more sets of corrugated plates 211, 212, where the first group 210 of two or more sets of corrugated plates 211, 212 are oriented to provide the equivalent function as a single set corrugated plates.
The first set of corrugated plates 111 is a set of corrugated plates disposed in vertically parallel relation, each corrugated plate of the first set of corrugated plates 111 having at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The first set of corrugated plates 111 have a vertical height. When the first layer 110 comprises the first set of corrugated plates 111, the height of the first layer 110 is the vertical height of the first set of corrugated plates 111. The vertical height of the first set of corrugated plates 111 may be greater than 350 mm or greater than 400 mm. The height dimension of the corrugated plates corresponds to (aligns with) the height dimension of the exchange column. The upper limit for the vertical height may be limited by practical considerations and may be as high as 1000 mm.
The first set of corrugated plates 111 comprises a plurality of corrugated plates. The first set of corrugated plates 111 may comprise a plurality of from 50 to 5,000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the first set of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The first set of corrugated plates 111 may be part of a “brick.” The first set of corrugated plates may comprise multiple bricks.
The at least one aperture in each corrugated plate of the first set of corrugated plates may have an equivalent diameter ranging from 1 to 5 mm. An equivalent diameter of an aperture is the diameter of a circle having the same open area as the aperture. The apertures in each corrugated plate of the first set of corrugated plates 111 may create an open area in each corrugated plate of the first set of corrugated plates 111 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
The first group 210 of two or more sets of corrugated plates 211, 212 is a group of two or more sets of corrugated plates, where the corrugated plates of each set of the two or more sets 211, 212 disposed in vertically parallel relation. Each corrugated plate of each set have at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The two or more sets of corrugated plates 211, 212 of the first group 210 are positioned vertically relative to one another, where the corrugated plates of the two or more sets of corrugated plates 211, 212 of the first group 210 are aligned or rotated relative to the corrugated plates of an adjacent set of the two or more sets 211, 212 by less than 5°, or less than 2°, or less than 1°. The two or more sets of corrugated plates 211, 212 of the first group 210 have a combined vertical height. When the first layer 110 comprises the two or more sets of corrugated plates 211, 212 of the first group 210, the height of the first layer 110 is the combined vertical height of the two or more sets of corrugated plates 211, 212 of the first group 210. The combined vertical height of the two or more sets of corrugated plates 211, 212 of the first group 210 may be greater than 350 mm or greater than 400 mm. The upper limit for the combined vertical height may be limited by practical considerations and may be as high as 2.5 m, or 3.5 m, or 7.5 m.
The at least one aperture in each corrugated plate of the first group of two or more corrugated plates may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the first group 210 of corrugated plates 211, 212 may create an open area in each corrugated plate of the first group 210 of corrugated plates 211, 212 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
Each set of the two or more sets of corrugated plates of the first group 210 comprises a plurality of corrugated plates. Each set of the two or more sets of corrugated plates of the first group 210 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the first group of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The each set of the two or more sets of corrugated plates of the first group 210 may be part of a brick. The first group 210 may comprise multiple bricks.
A set of corrugated plates above an adjacent set of corrugated plates of the first group may be aligned or rotated such that the two or more sets of corrugated plates provide the equivalent function as a single set of corrugated plates of equivalent height. A set of corrugated plates above an adjacent set of corrugated plates of the first group may be aligned or rotated within 5°, or within 2°, or within 1° clockwise or counterclockwise of a set of corrugated plates below. In this orientation, the two or more sets of corrugated plates provide the equivalent function as a single set of corrugated plates of equivalent height.
The first layer of structured packing may have a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
The exchange column comprises a second layer of structured packing 120 disposed within the at least one volume. The second layer of structured packing 120 is located below and adjacent the first layer of structured packing 110. The second layer of structured packing 120 comprises either (ii-a) a second set of corrugated plates 121 or (ii-b) a second group 220 of two more sets of corrugated plates 221, 222, where the second group 220 of two or more sets of corrugated plates 221, 222 are oriented to provide the equivalent function as a single set corrugated plates.
The second layer 120 may be installed in the exchange column prior to the first layer 110 being installed. When the first layer is installed, the first layer 110 is rotated relative to the second layer. The corrugated plates of the first layer 110 adjacent the corrugated plates of the second layer 120 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the second layer 120, the angle ranging from 20° to 90°, or ranging from 70° to 90°, or about 90°. The corrugated plates of the first layer 110 adjacent the corrugated plates of the second layer 120 may be rotated 20° to 90°, or 70° to 90°, or about 90° clockwise or counterclockwise relative to the adjacent corrugated plates of the second layer 120.
The second set of corrugated plates 121 is a set of corrugated plates disposed in vertically parallel relation, each corrugated plate of the second set of corrugated plates 121 having at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The second set of corrugated plates 121 have a vertical height. When the second layer 120 comprises the second set of corrugated plates 121, the height of the second layer is the height of the second set of corrugated plates 212. The vertical height of the second set of corrugated plates 121 may be greater than 350 mm or greater than 400 mm. The upper limit for the vertical height may be limited only by practical considerations and may be as high as 1000 mm. The height dimension of the second set of corrugated plates corresponds to the height dimension of the exchange column.
The at least one aperture in each corrugated plate of the second set of corrugated plates 121 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the second set of corrugated plates 121 may create an open area in each corrugated plate of the second set of corrugated plates 121 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
The second set of corrugated plates 121 comprises a plurality of corrugated plates. The second set of corrugated plates 121 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the second set of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The second set of corrugated plates 121 may be part of a “brick.” The second set of corrugated plates may comprise multiple bricks.
The second group 220 of two or more sets of corrugated plates 221, 222 is a group of two or more sets of corrugated plates, where the corrugated plates of each set of the two or more sets 221, 222 disposed in vertically parallel relation. Each corrugated plate of each set have at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The two or more sets of corrugated plates 221, 222 of the second group 220 are positioned vertically relative to one another, where the corrugated plates of the two or more sets of corrugated plates 221, 222 of the second group 220 are aligned or rotated relative to the corrugated plates of an adjacent set of the two or more sets 221, 222 by less than 5°, or less than 2°, or less than 1°. The two or more sets of corrugated plates 221, 222 of the second group (220) have a combined vertical height. When the second layer 120 comprises the two or more sets of corrugated plates 221, 222, the height of the second layer 120 is the combined vertical height of the two or more sets of corrugated plates 221, 222 of the second group 220. The combined vertical height of the two or more sets of corrugated plates 221, 222 of the second group 220 may be greater than 350 mm or greater than 400 mm. The upper limit for the combined vertical height may be limited only by practical considerations and may be as high as 2.5 m, or 3.5 m, or 7.5 m.
The at least one aperture in each corrugated plate of the second group 220 of two or more corrugated plates 221, 222 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the second group 220 of corrugated plates 221, 222 may create an open area in each corrugated plate of the second group 220 of corrugated plates 221, 222 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
Each set of the two or more sets of corrugated plates of the second group 220 comprises a plurality of corrugated plates. Each set of the two or more sets of corrugated plates of the second group 220 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the second group of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The each set of the two or more sets of corrugated plates of the second group 220 may be part of a brick. The second group 220 may comprise multiple bricks.
A set of corrugated plates above an adjacent set of corrugated plates of the second group may be aligned or rotated within 1° clockwise or counterclockwise of a set of corrugated plates below. In this orientation, the two or more sets of corrugated plates provide the equivalent function as a single set of corrugated plates of equivalent height.
The second layer of structured packing may have a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
The exchange column is characterized by a first layer of structured packing 110 above and adjacent a second layer of structured packing 120 where the corrugated plates of the first layer 110 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the second layer, the angle ranging from 20° to 90°, and where the height of the first layer 110 and/or the height of second layer 120 is greater than 350 mm or greater than 400 mm.
In contrast, as described in the Background section, the prior art (for example Perry's Chemical Engineer's Handbook, and books by Kister) has limited the vertical height of layers of structured packing to about 300 mm (12 inches). However, the inventors have discovered that for exchange columns having a large cross-sectional area, e.g. having a cross-sectional area greater than about 0.636 m2, vertical heights greater than about 350 mm (13.8 in.) provide improved performance.
The exchange column may optionally comprise a third layer of structured packing 130 disposed within the at least one volume, and may further optionally comprise a fourth layer of structured packing 140 disposed within the at least one volume. The third layer of structured packing 130 and the fourth layer of structured packing 140 are optional. The exchange column may comprise any desired number of additional layers of structured packing.
The third layer of structured packing 130, if present, is located below and adjacent the second layer of structured packing 120. The third layer of structured packing 130 comprises either (iii-a) a third set of corrugated plates 131 or (iii-b) a third group 230 of two more sets of corrugated plates 231, 232, where the third group 230 of two or more sets of corrugated plates 231, 232 are oriented to provide the equivalent function as a single set corrugated plates. The corrugated plates of the third layer 130 adjacent the corrugated plates of the second layer 120 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the second layer 120, the angle ranging from 20° to 90°, or ranging from 70° to 90°, or about 90°. The corrugated plates of the third layer 130 adjacent the corrugated plates of the second layer 120 may have an orientation that is rotated 20° to 90°, or 70° to 90°, or about 90° clockwise or counterclockwise relative to the adjacent corrugated plates of the second layer 120.
The third set of corrugated plates 131 is a set of corrugated plates disposed in vertically parallel relation, each corrugated plate of the third set of corrugated plates 131 having at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The third set of corrugated plates 131 have a vertical height. When the third layer 130 comprises the third set of corrugated plates 131, the height of the third layer is the height of the third set of corrugated plates 131. The vertical height of the third set of corrugated plates 131 may be greater than 350 mm or greater than 400 mm. The upper limit for the vertical height may be limited only by practical considerations and may be as high as 1000 mm. The height dimension of the third set of corrugated plates corresponds to the height dimension of the exchange column.
The at least one aperture in each corrugated plate of the third set of corrugated plates 131 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the third set of corrugated plates 131 may create an open area in each corrugated plate of the third set of corrugated plates 131 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
The third set of corrugated plates 131 comprises a plurality of corrugated plates. The third set of corrugated plates 131 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the third set of corrugated plates 131 may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The third set of corrugated plates 131 may be part of a “brick.” The third set of corrugated plates 131 may comprise multiple bricks.
The third group 230 of two or more sets of corrugated plates 231, 232 is a group of two or more sets of corrugated plates, where the corrugated plates of each set of the two or more sets 231, 232 disposed in vertically parallel relation. Each corrugated plate of each set have at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The two or more sets of corrugated plates 231, 232 of the third group 230 are positioned vertically relative to one another, where the corrugated plates of the two or more sets of corrugated plates 231, 232 of the third group 230 are aligned or rotated relative to the corrugated plates of an adjacent set of the two or more sets 231, 232 by less than 5°, or less than 2°, or less than 1°. The two or more sets of corrugated plates 231, 232 of the third group 230 have a combined vertical height. When the third layer 130 comprises the two or more sets of corrugated plates 231, 232, the height of the third layer 130 is the combined vertical height of the two or more sets of corrugated plates 231, 232 of the third group 230. The combined vertical height of the two or more sets of corrugated plates 231, 232 of the third group 230 may be greater than 350 mm or greater than 400 mm. The upper limit for the combined vertical height may be limited only by practical considerations and may be as high as 2.5 m, or 3.5 m, or 7.5 m.
The at least one aperture in each corrugated plate of the third group 230 of two or more corrugated plates 231, 232 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the third group 230 of corrugated plates 231, 232 may create an open area in each corrugated plate of the third group 230 of corrugated plates 231, 232 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
Each set of the two or more sets of corrugated plates of the third group 230 comprises a plurality of corrugated plates. Each set of the two or more sets of corrugated plates of the third group 230 may comprise a plurality of from 50 to 5,000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the third group of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The each set of the two or more sets of corrugated plates of the third group 230 may be part of a brick. The third group 230 may comprise multiple bricks.
A set of corrugated plates above an adjacent set of corrugated plates of the third group may be aligned or rotated within 1° clockwise or counterclockwise of a set of corrugated plates below. In this orientation, the two or more sets of corrugated plates provide the equivalent function as a single set of corrugated plates of equivalent height.
The third layer of structured packing may have a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
The fourth layer of structured packing 140, if present, is located below and adjacent the third layer of structured packing 130, if present. The fourth layer of structured packing 140 comprises either (iv-a) a fourth set of corrugated plates 141 or (iv-b) a fourth group 240 of two more sets of corrugated plates 241, 242, where the fourth group 240 of two or more sets of corrugated plates 241, 242 are oriented to provide the equivalent function as a single set corrugated plates. The corrugated plates of the fourth layer 140 adjacent the corrugated plates of the third layer 130 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the third layer 130, the angle ranging from 20° to 90°, or ranging from 70° to 90°, or about 90°. The corrugated plates of the fourth layer 140 adjacent the corrugated plates of the third layer 130 may have an orientation that is rotated 20° to 90°, or 70° to 90°, or about 90° clockwise or counterclockwise relative to the adjacent corrugated plates of the third layer 130.
The fourth set of corrugated plates 141 is a set of corrugated plates disposed in vertically parallel relation, each corrugated plate of the fourth set of corrugated plates 141 having at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The fourth set of corrugated plates 141 have a vertical height. When the fourth layer 140 comprises the fourth set of corrugated plates 141, the height of the fourth layer 140 is the height of the fourth set of corrugated plates 141. The vertical height of the fourth set of corrugated plates 141 may be greater than 350 mm or greater than 400 mm. The upper limit for the vertical height may be limited only by practical considerations and may be as high as 1000 mm. The height dimension of the fourth set of corrugated plates correlates to the height dimension of the exchange column.
The at least one aperture in each corrugated plate of the fourth set of corrugated plates 141 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the fourth set of corrugated plates 141 may create an open area in each corrugated plate of the fourth set of corrugated plates 141 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
The fourth set of corrugated plates 141 comprises a plurality of corrugated plates. The fourth set of corrugated plates 141 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the fourth set of corrugated plates 141 may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The fourth set of corrugated plates 141 may be part of a “brick.” The fourth set of corrugated plates 141 may comprise multiple bricks.
The fourth group 240 of two or more sets of corrugated plates 241, 242 is a group of two or more sets of corrugated plates, where the corrugated plates of each set of the two or more sets 241, 242 disposed in vertically parallel relation. Each corrugated plate of each set have at least one aperture and a plurality of regularly spaced corrugations disposed in crisscrossing relation to the corrugations of an adjacent corrugated plate. The two or more sets of corrugated plates 241, 242 of the fourth group 240 are positioned vertically relative to one another, where the corrugated plates of the two or more sets of corrugated plates 241, 242 of the fourth group 240 are aligned or rotated relative to the corrugated plates of an adjacent set of the two or more sets 241, 242 by less than 5°, or less than 2°, or less than 1°. The two or more sets of corrugated plates 241, 242 of the fourth group 240 have a combined vertical height. When the fourth layer 140 comprises the two or more sets of corrugated plates 241, 242, the height of the fourth layer is the combined vertical height of the two or more sets of corrugated plates 241, 242 of the fourth group 240. The combined vertical height of the two or more sets of corrugated plates 241, 242 of the fourth group 240 may be greater than 350 mm or greater than 400 mm. The upper limit for the combined vertical height may be limited only by practical considerations and may be as high as 2.5 m, or 3.5 m, or 7.5 m.
The at least one aperture in each corrugated plate of the fourth group 240 of two or more corrugated plates 241, 242 may have an equivalent diameter ranging from 1 to 5 mm. The apertures in each corrugated plate of the fourth group 240 of corrugated plates 241, 242 may create an open area in each corrugated plate of the fourth group 240 of corrugated plates 241, 242 in the range from 5% to 20%, preferably 8% to 12%, of the total area of each respective corrugated plate.
Each set of the two or more sets of corrugated plates of the fourth group 240 comprises a plurality of corrugated plates. Each set of the two or more sets of corrugated plates of the fourth group 240 may comprise a plurality of from 50 to 5000 corrugated plates or from 75 to 4000 corrugated plates. At least one corrugated plate in the fourth group of corrugated plates may have a surface with a surface texture on at least a portion of its surface. The surface texture on the surface of the at least one corrugated plate may be in the form of horizontal striations and/or dimples, and/or any other surface texture known in the art. The each set of the two or more sets of corrugated plates of the fourth group 240 may be part of a brick. The fourth group 240 may comprise multiple bricks.
A set of corrugated plates above an adjacent set of corrugated plates of the fourth group may be aligned or rotated within 1° clockwise or counterclockwise of a set of corrugated plates below. In this orientation, the two or more sets of corrugated plates provide the equivalent function as a single set of corrugated plates of equivalent height.
The fourth layer of structured packing 140 may have a surface area density ranging from 250 m2/m3 to 800 m2/m3 or ranging from 500 m2/m3 to 675 m2/m3.
The method for separating a mixture comprises introducing the mixture into any exchange column as described above. The exchange column has the required features as described above, and may have any of the optional features.
The method for separating the mixture further comprises contacting the mixture with the first layer of structured packing 110 and the second layer of structured packing 120, withdrawing a first product from the exchange column, and withdrawing a second product from the exchange column.
The mixture may comprise oxygen and nitrogen, for example, a mixture formed from air. The first product may be an oxygen-enriched product and the second product may be a nitrogen-enriched product.
The mixture may comprise oxygen and argon, for example, a mixture formed from air. The first product may be an oxygen-enriched product and the second product may be an argon-enriched product.
The mixture may comprise hydrogen and carbon monoxide, for example a gas mixture from a steam-hydrocarbon reformer or partial oxidation reactor. The first product may be a hydrogen-enriched product and the second product may be a carbon monoxide-enriched product. The exchange column may be used to form an oxo-gas, that is, a mixture containing a desired ratio of hydrogen to carbon monoxide. The first product may have a H2:CO molar ratio between 0.5:1 and 2.5:1, or between 0.9:1 and 1.5:1, or between 0.9:1 and 1.1:1, and the second product may be a hydrogen-enriched product or a carbon monoxide-enriched product.
The present invention also relates to a method of making an exchange column, where the exchange column has the required features as described above and may have any of the optional features.
The method of making the exchange column comprises providing the one or more walls of the exchange column; providing the first layer of structured packing 110 where the first layer of structured packing 110 has any of the features as described above; and providing the second layer of structured packing 120, where the second layer of structured packing 120 has any of the features as described above.
The method of making the exchange column also comprises installing the first and second layers of structured packing 110, 120 within the one or more walls of the exchange column such that the first layer of structured packing 110 is located above and adjacent the second layer of structured packing 120, and such that the corrugated plates of the first layer 110 adjacent the corrugated plates of the second layer 120 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the second layer 120, the angle ranging from from 20° to 90° or ranging from 70° to 90°.
The method of making the exchange column may also comprise providing a third layer of structured packing 130 where the third layer of structured packing 130 has any of the features as described above, and installing the third layer of structured packing within the one or more walls of the exchange column such that the third layer of structure packing 130 is located below and adjacent the second layer of structure packing 120, wherein the corrugated plates of the third layer 130 adjacent the corrugated plates of the second layer 120 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the second layer 120, the angle ranging from 20° to 90° or ranging from 70° to 90°.
The method of making the exchange column may also comprise providing a fourth layer of structured packing 140 where the fourth layer of structured packing 140 has any of the features as described above, and installing the fourth layer of structured packing 140 within the one or more walls of the exchange column such that the fourth layer of structure packing 140 is located below and adjacent the third layer of structure packing 130, wherein the corrugated plates of the fourth layer 140 adjacent the corrugated plates of the third layer 130 have an orientation that is rotated at an angle relative to the adjacent corrugated plates of the third layer 130, the angle ranging from 20° to 90° or ranging from 70° to 90°.
Cryogenic experiments were performed in a laboratory distillation column with an internal diameter of about 200 mm, having a corresponding cross sectional area of 0.0314 m2. Several packing layers with a surface area density of 500 m2/m3 were placed on top of each other to create various packed bed heights in the ranging from 1648 mm to 1854 mm. The individual packing layers had a layer height of 52.5 mm, 103 mm, or 207 mm. In some experiments all layers of packing were rotated at an angle of 90 degrees relative to the layers above and below them. In these cases the effective layer height is the same as the packing layer height.
In some experiments, layers were rotated as a group, two or more at a time, such that the layers within the group were aligned with each other in terms of the orientation of their respective corrugation elements. In these cases, which were done only with the 103 mm high plates in this example, the effective layer height is accordingly 2 or more times the 103 mm plate height depending on the number of layers that are aligned.
The column was operated to perform separation of a binary argon/oxygen mixture at a pressure of about 141 kPa (0.4 barg) and under total internal reflux. This made the liquid to vapor flow ratio within the column, commonly referred to as the L/V ratio, equal to 1. After reaching steady state at a variety of flow conditions, the data were reduced in terms of HTU versus a reduced vapor velocity. Then a characteristic HTU was found for each run at a common vapor velocity that would be representative of the operating conditions in industrial distillation columns. All such values were then normalized by dividing each value by the HTU obtained for the 207 mm layer height packing as this is a very commonly used layer height in the industry.
The results for the 200 mm diameter column are shown in
Several observations can be made.
The optimum layer height of about 100 mm is much smaller than the commonly used layer height of about 200 mm to 250 mm in industrial scale distillation columns. This is the result in this small laboratory column which has a diameter of about 200 mm. It is believed that such an optimum occurs due to a complex interplay of several physical parameters and operational characteristics of the vapor and liquid flow over a packed section. Under uniform flow distribution conditions, structured packing has an inherent mass transfer efficiency along with an associated pressure drop within its individual cells which are formed by the opposing corrugations. But even when liquid and vapor are introduced very uniformly at the top and bottom respectively of a packed bed, maldistribution develops naturally thereby degrading the performance. The effect of such maldistribution is mitigated by any lateral spreading of both vapor and liquid, and this happens more easily within a small diameter column such as 200 mm or less for instance as opposed to a large diameter column of industrial significance such as 900 mm or more.
In addition to the above general effects there are some specific effects which can trade off against each other. A smaller effective layer height which results in more frequent layer rotations leads to better lateral spreading of both liquid and vapor which would be beneficial. There will also be an increase in the vapor phase mass transfer coefficients in the entrance zone where vapor enters each layer and this effect is beneficial. This effect would be more pronounced any time there is also a significant layer rotation such as at 90 degrees in addition to a layer transition. In contrast, any time there is a layer transition, the dripping of liquid from an upper layer to a lower layer would tend to disrupt the liquid distribution near the entrance zone resulting in degradation of the liquid phase mass transfer in this entrance zone. This effect would be deleterious to the overall mass transfer efficiency of the column.
In Example 1 when the effective layer height is 618 mm, there are only three such effective layers in the bed that are rotated relative to each other at 90 degrees. This leads to less lateral spreading of both the vapor and liquid phases thereby resulting in a relatively high relative HTU of about 1.07. As the effective layer height is reduced, the relative HTU improves due to more spreading and more local vapor phase entrance enhancement which dominate over other effects. The optimum value for the relative HTU is about 0.90 which occurs at an effective layer height 103 mm. But when the effective layer height is reduced further to 52.5 mm the relative HTU turns up and increases to a value of 0.92. This occurs due to the presence of too many layer transitions where liquid entrance is disrupted leading to an overall decrease in mass transfer efficiency which now dominates over the other known good effects of more frequent layer rotations.
Another interesting observation from Example 1 is that the relative HTU of a 207 mm layer height packing is slightly worse at 1.0 compared to the value of about 0.95 for the 2×103 layer height packing with its layers rotated in pairs. The only difference between these runs is an extra layer transition without rotation within each 206-207 mm. This implies that the vapor phase mass transfer enhancement at these transitions is more beneficial than the liquid phase degradation that also occurs at these transitions. This is plausible as the liquid phase maldistribution effect in a column which is only 200 mm in diameter would not be too severe to compensate for with other means.
Cryogenic experiments were performed in a laboratory distillation column with an internal diameter of about 900 mm, corresponding to a cross-sectional area of 0.636 m2. Several packing layers with a surface area density of 500 m2/m3 were placed on top of each other to create a packed bed height of about 4550 mm. The individual packing layers had a layer height of 103 mm or 207 mm. Two types of experiments were conducted with each packing. In the first type of experiment, all the layers were rotated at an angle of 90 degrees relative to the layers above and below them. In these cases the effective layer height is the same as the corresponding layer height. In the second type of experiment, layers were rotated in pairs, such that the layers within the pair were aligned with each other in terms of the orientation of their respective corrugation elements. In these cases the effective layer height is 2 times the nominal packing layer height of the individual layers and thus 206 mm for a pair of 103 mm layers and 414 mm for a pair of 207 mm layers. The column was operated to perform separation of a binary argon/oxygen mixture at a pressure of about 141 kPa (0.4 barg) and under total internal reflux in a manner similar to that of Example 1 and the data were also normalized by dividing each value by the HTU obtained for the 207 mm layer height packing as was done for
The results are shown in
The lowest relative HTU occurs for the effective layer height of about 400 mm. Note that this effective layer height is about 4 times the optimum effective layer height for the smaller column while the diameter is larger by a factor of 4.5. A layer height of 400 mm is much greater than suggested in the prior art literature and is outside the band of 8 to 12 inches taught in the books by Kister, noted earlier.
The relative HTU value for the 103 mm layer height packing is about 1.43. In comparison when the 103 mm layers are rotated in pairs the relative HTU increases to about 1.61. While this trend is similar to what is seen in Example 1 the magnitude of this change is much bigger. The underlying operating mechanisms would be similar except for the added challenge of lateral spreading of liquid and vapor in a bigger 900 mm diameter column in the current example as opposed to a smaller 200 mm diameter column in Example 1.
The relative HTU value for the 207 mm layer height packing at 1.0 is very low compared to the relative HTU value of 1.61 for the 2×103 layer height packing. This is very surprising and unlike what was seen in Example 1. The only physical difference between these test conditions is the additional layer transition in the middle of a 206-207 mm layer height. One plausible explanation is that the effect of the disruption to the liquid at this additional layer transition is dominant compared to the vapor phase mass transfer enhancement that also occurs as an entrance effect at this location. The overall effect is different and opposite to that seen in Example 1 and can be explained based on the challenge of lateral spreading of liquid and vapor phases in large diameter columns in comparison to small diameter columns.
When the 207 mm high layers of packing are rotated in pairs resulting in an effective layer height of 414 mm, the relative HTU decreases compared to the single 207 mm layer height packing. This is the opposite of what happens with the 103 mm layer height packing. This implies that the disruption to the liquid phase at interfaces is less significant as the basic layer height itself increases as this entrance effect on the liquid will occupy a progressively smaller proportion of the overall height.
Based on the above it is expected that if full contiguous packing layers of 414 mm are fabricated, the performance would be similar to what is seen with the aligned pairs of layers (2×207 mm) arrangement which shows a relative HTU value of 0.93.
In large scale industrial columns, which may be defined as having a diameter of at least 900 mm, the optimum layer height would be at least 350 mm or at least 400 mm. As the diameter increases the optimum layer height would continue to increase although not linearly and would also be constrained by other factors. In a given packed section, it is preferable to have at least four layers that are rotated relative to each other in order to facilitate lateral spreading of both the liquid and vapor phases. Thus in the smallest of industrial columns with a diameter of 900 mm, the bed height would be at least 4 times the minimum layer height of 350 mm or namely at least 1400 mm or at least 1600 mm for a layer height of 400 mm. The optimum value for layer rotations is 20-90 degrees with a preferred value of 70-90 degrees. The most optimum layer rotation would be at 90 degrees which would facilitate maximum lateral spreading of vapor and liquid.
In a given application the optimum combination of such parameters should be arrived at to maximize the efficiency of the packed column while also minimizing the cost of fabricating the column. The use of larger layer heights than what is known in the prior art will tend to reduce the number of bricks of packing that need to be assembled and installed into a packed column. This will reduce the overall cost although mechanical aid may be necessary when the bricks get too big for manual handling alone.
Lastly, while plausible explanations have been offered for all of the observed data and trends, the current invention is not limited by any of these theorized mechanisms that have been offered. It is possible to offer alternative theorized mechanisms to explain all the observations. The invention is mostly based on the experimental trends observed in the two sets of tests shown in Examples 1 and 2 and anticipated extrapolation to larger diameter columns therefrom.
