Title of Invention

"A STRUCTURED PACKING MODULE"

Abstract

A structured packing module for use in a mass and heat transfer column is disclosed. The module comprises a plurality of corrugated metal sheets, said corrugated metal sheets being stacked in a packing module in such a manner that the corrugations of two adjacent metal sheets are oppositely inclined, a plurality of channels formed by the V-shaped corrugations on said metal sheets, the heavier fluid phase flowing down and the lighter fluid phase flowing up through said channels, the intimate contact between the two fluid phases results in transfer of heat and mass between the two phases, the flow channels formed by the oppositely inclined corrugations intersecting each other at a number of points so that at said intersecting points the multiple streams of both the fluid phases merge and get redistributed, said fluid phases facing sudden change in flow direction due to rotation of packing modules stacked inside a column, transit from one module to another, the descending heavier fluid phase tending to accumulate at said transition zones, the lighter fluid phase, flowing through said accumulated heavier fluid phase experiencing higher pressure drop and the hydraulic capacity of packing being greatly reduced and the transition of fluid phases from one module to another being made smother thus, ensuring less accumulation of heavier fluid phase at the inter module transition zones and thereby, lower pressure drop and higher hydraulic capacity.

Full Text

Field of the invention The present invention relates improved structure packing module with improved capacity and pressure drop for mass and heat transfer columns and a method for the manufacture thereof. Structured packing is used in mass and heat transfer columns for carrying out separation of fluid mixture by countercurrent gas-liquid or liquid-liquid contact. Structured packing beds consist of packing modules, which are stacked one above another in a column up to a specified height. Each module consists of multiple corrugated sheets with inclined V-shaped channels, which are extended from one face to the other face of the module. Corrugated sheets are arranged in such a fashion that the channels on adjacent sheets intersect each other at a number of points. The module height is accurately controlled to have such intersections on both the faces of the module and opening of each pair of intersecting channel appears in perfect rhombus shape. Such module has regular openings of equal size on both faces. This invention relates to the method of preparing structured packing modules with regular openings, which offers improved capacity and pressure drop. Prior art Packed columns are used for mass and heat transfer applications for moving industrial processes e.g. distillation, absorption, extraction etc. In a packed column two fluid streams are contacted typically as counter current flow streams and mass and heat transfer between them result in separation of components between them. The rate of heat and mass transfer depends on the effectiveness with which the two fluid streams are contacted and the surface area which is made available for the transfer operation to take place. In view of the above requirement, structured packing is increasingly used in packed columns because of its superiority over the other contacting devices in terms of capacity, pressure drop and mass transfer efficiency. A structured packing bed consists of a numbers of modules. These structured packing modules are of specific height and number of them are stacked one above another depending on the total height required for the packed bed. Each module consists of a number of corrugated metal sheets stacked together side by side. The metal sheets are either plain as having surface texurisation and are formed into corrugated sheets with included V-shaped channels. Two adjacent sheets are so stacked that the channels are placed in opposite directions and intersect each at a number of points. The modules are also stacked one above another in a typical fashion. Usually each module is rotated by 90 deg. from the orientation of the module just below it. In a structured packing bed fluids flow through flow channels formed by corrugated sheets. In counter current operation the heavier fluid phase flows down from top of the bed along the channel well and the lighter fluid phase moves up from bottom to top of the bed through the center of the flow channels. At the intersecting points of the opposing channels in a module the fluid streams mix and gets redistributed and during transition from one module to the other the fluid streams change direction but continuity of flow channels is maintained. All these effects together provide good mass and heat transfer between fluid phases with low pressure drop and high hydraulic capacity. Inventions related to prior art in fabrication of structured packing modules are described in U.S.Pat.No.4,296,050, U.S.Pat.No. 4,356,611, U.S.Pat.No.4,604,247 and Indian Pat.No. 184574. Drawbacks connected with hitherto known process/devices. As mentioned earlier conventionally a structured packing modules, which placed in column, is rotated typically by 90 deg with respect to the packing module placed below it. The modules are rotated to minimize the bypassing of heavier fluid phase in the form of wall-flow but in that process the flow channels in the packed bed become tortuous. Usually packing modules are fabricated with a specific height irrespective of the size and inclination of corrugation channels. On doing so the faces of packing modules do not always have regular openings. Irregular openings not only destroy the continuity of flow channels but also create obstruction to fluid flow. All these result in additional hold up of heavier fluid phase at module-to-module transition zone, increased pressure drop in lighter fluid phase and lowering of operating capacity limits. Solutions or improvements to some of the above noted problems have been provided by the invention described in U.S. Pat. No. 5,632,934. Objects of the invention It is an important object of the present invention to provide a novel method for fabricating structured packing module with regular opening on both faces which offers improved capacity and pressure drop in mass and heat transfer applications. Summary of Invention The present invention relates to a method of preparation/fabrication of sheet metal structured packing module having regulars opening of flow channels on both faces for application in mass and heat transfer columns. This packing module offers improved capacity and pressure drop compared to the packing as explained in prior art. The packing module consists of corrugated metal sheets with a novel surface texturisation. The plain metal sheets are first cut into strips of desired width. The width is decided based on corrugation size and inclination. The selection of width is important because height of final fabricated module depends on it. Oblong slots or apertures are punched on the metal strips in a specified pattern. The metal strips are then subjected to surface texturisation. Surface texturisation is a two-step process, where linear embossing is done at mutually perpendicular directions using a set of rollers. The embossed metal sheets are then corrugated with large V-shaped inclined corrugation, which form the basic packing elements. The packing elements are then stacked side by side with corrugation channels of adjacent sheets arranged in opposite directions to form the packing module. The module is shaped to match the column inside contour either as a single piece or in segments. The height of each module is adjusted to have regular rhombus shaped openings on both faces of the module. The height of each module is controlled by proper selection of width of metal strips at the fabrication stage. The channels of adjacent corrugated sheets in a module intersect each other at a number of points and by adjusting module height such intersecting points can be precisely kept on module faces and thereby achieving regular openings on the faces. This particular feature allows free transition of fluid from one module to the other, reduces local holdup of heavier fluid phase and results in improved pressure drop and hydraulic capacity. Thus, it will be clear that the present invention relates to preparation / fabrication of an improved structured packing for countercurrent mass and heat transfer columns. Structured packing module, fabricated according to this invention consists of a number of corrugated metal sheets. The metal sheets are stacked in a packing module in such a fashion that the corrugations of two adjacent metal sheets are oppositely inclined. The heavier fluid phase flows down and the lighter fluid phase flows up through the channels formed by the V-shaped corrugations on metal sheets. The intimate contact between the two fluid phases results in transfer of heat and mass between the two phases. The flow channels formed by the oppositely inclined corrugations intersect each other at a number of points. At these intersecting points the multiple streams of both the fluid phases merge and get redistributed. As the fluid phases transit from one module to another, they face sudden change in flow direction due to rotation of packing modules stacked inside a column. The descending heavier fluid phase tends to accumulate at these transition zones. The lighter fluid phase, as flows through this accumulated heavier fluid phase experience higher pressure drop and the hydraulic capacity of packing is greatly reduced. The present invention relates to a fabrication procedure for structured packing modules where the transition of fluid phases from one module to another is made smother. The smooth transition of fluid phases ensures less accumulation of heavier fluid phase at the inter module transition zones and thereby, lower pressure drop and higher hydraulic capacity are experienced. In the present invention, the height of packing module is precisely controlled to have regular rhombus shaped openings on both faces of the module. The oppositely inclined flow channels formed by the corrugations of metal sheets, which intersect with each other at a number of points, may or may not intersect on the top and bottom faces of the module. If the flow channels intersect on the faces, the openings are regular and rhombus shaped. If they do not, the openings are irregular and small. Structured packing modules as per prior art have fixed height irrespective of the packing type and therefore, the regular rhombus shaped openings are not ensured. Modules as per present invention have precise height based on packing type, corrugation size and angle of inclination and thereby, regular and larger openings of flow channels on top and bottom faces are always ensured. This in turn provides lower pressure drop and higher hydraulic capacity for the packing during heat and mass transfer operation in a countercurrent column For the preparation of structured packing module, metal sheets of specific dimensions are chosen. One of the novel features of the present invention lies in selection of the width of the metal sheet. According to the fabrication procedure disclosed in the present invention, the original metal sheet goes through a number of steps whereby its original dimensions get altered. The metal sheet experiences shrinkage in its width and length when it is texturised in two-step process of linear embossing along length and width. Further shrinkage of dimensions takes place when V-shaped corrugations are created on the texturised metal sheet. The final width of the metal sheet is the height of the packing module made from these metal sheets. The height of packing module depends on the selection of original width of the metal sheets, which in turn ensures intersections of opposing flow channels on module faces Experimental Verification Performance of structured packing fabricated following the method described in this invention has been evaluated by testing in a countercurrent column operated with water as heavier phase and air as lighter phase. Improvements observed in performance of this packing over the packings disclosed in prior arts may be summarised as follows: - Lower pressure drop - Higher hydraulic capacity - Less hold up of heavier phase - Less fouling at module interface Comparative performance of the packing is given in Figure-1 and Figure-2. Figure-1 shows the comparison of pressure drop (AP) between the packing according to the present invention (circle marked line) and the packing disclosed in Indian patent no. 18574 (triangle marked line). Brief description of the accompanying drawings Figure-1 shows a comparison of pressure drop for structured packing module with regular openings and that with irregular openings. Figure-2 shows the comparison of hydraulic capacity between the structured packing according to the present invention (circle marked line) and the packing disclosed in Indian patent no. 18574 (triangle marked line). Figure-3 shows column configuration where the location of packed bed containing structured packing is shown relative to liquid distributor, vapour distributor and other column internals. Figure-4 shows the stacking arrangement for structured packing modules in packed bed. Figure-5a shows structured packing module comprising of corrugated metal sheets Figure-5b shows the top view of the packing module described in Figure-5a. Figure-5c shows the stacking arrangement of metal sheets in the packing module described in Figure-5a. Figure-6a shows original metal sheet at the first stage of fabrication. Figure-6b shows punching of oblong slots in metal sheet described in Figure-6a at the second stage of fabrication. Figure-6c shows embossing along length of metal sheet described in Figure-6b for texturisation at the third stage of fabrication. Figure-6d shows embossing along width of metal sheet described in Figure-6c for texturisation at the fourth stage of fabrication. Figure-6e shows creation of V-shaped inclined corrugation on texturised metal sheet described in Figure-6d at the final stage of fabrication. Detailed description of the drawings accompanying the complete specification The pressure drop data presented in Figure-1 has been evaluated for a water rate of 24 cubic meter per hour per square meter of column area. The pressure drop (AP) is measured by fixing a water tube manometer across the packing in the test column and is expressed as millimeter of water column per meter of packing height. The pressure drop is plotted against Superficial F-Factor (Fs), which is defined as : Fs = Vg .(pg)0'5, where Vg is the superficial air velocity in the column in meter per second and pg is the air density in kilogram per cubic meter. Figure-1 clearly shows that the pressure drop of structured packing according to the present invention is less than the pressure drop of the packing disclosed in Indian patent no. 18574. Figure-2 shows the comparison of hydraulic capacity between the structured packing according to the present invention (circle marked line) and the packing disclosed in Indian patent no. 18574 (triangle marked line). The hydraulic capacity of packing is expressed as Capacity Factor (CF), which is defined as : CF = Vg . (pg - (pl - pg))0'5 , where Vg is the superficial air velocity in the column in meter per second and pg and pi are air density and water density respectively in kilogram per cubic meter. In Figure-2 CF is plotted against Flow Parameter (FP), where FP is defined as : FP = (L/G) . (pg / pl)°5, where L and G are water mass flow rate and air mass flow rate respectively in kilogram per hour and pg and pi are air density and water density respectively in kilogram per cubic meter. Figure-2 clearly shows that hydraulic capacity of the structured packing according to the present invention is more than the capacity of the packing disclosed in Indian patent no. 18574. Figure-3 shows the relative position of packed bed (2) containing structured packing in a countercurrent mass and heat transfer column (1). The heavier fluid phase enters the column (1) through feed pipe (5). From the feed pipe (5) the fluid enters the distributor (6) and from the distributor (6) it is distributed over the packed bed (2). The heavier fluid phase flows down the packed bed (2) and leaves the column through the nozzle (10). The lighter fluid phase enters the column through the nozzle (9). Through the distributor (7) the fluid is distributed below the packed bed (2). From the distributor (7) the fluid enters the packed bed (2) and flows up through the packed bed (2) and leaves the column through the nozzle (8). In the packed bed (2) the down flowing heavier fluid phase comes in contact with the up flowing lighter phase and the transfer for mass and heat takes place between the two phases. The packed bed (2) contains structured packing and is supported on support grid (4) at the bottom. A retainer grid (3) or bed limiter is provided at the top of the packed bed (2). Figure-4 shows the composition of the packed bed (2) containing structured packing. The structured packing modules such as (11), (12) and (13) are stacked one above another in the column (1). The bottom most module (13) is placed on the support grid (4). The module (12) above it is rotated by 90° relative to the module (13) below it. The module (11) above the module (12) is again rotated by 90° and therefore the module (11) has the same orientation as that of module (13). Figure-5a shows the details of a structured packing module (11) or (12) or (13). The module consists of corrugated metal sheets such as (15) and (16). The metal sheets of specified dimensions are stacked one against another to form the complete module. The dimensions of sheets are so specified that the top and bottom faces of the module have rhombus shaped openings (14). Figure-5b shows the top view of a structured packing module where the top face has been shown in details. Two corrugated metal sheets such as (15) and (16), when stacked one against another, a rhombus shaped opening (14) is formed. The size of the opening (14) depends on the number of metal sheets assembled in packing module of certain specified diameter and the inclination of V-shaped corrugations on the metal sheets. To achieve perfect rhombus shaped openings (14) the height of metal sheets is adjusted. If the height of metal sheets is more or less than a specified dimension the perfect rhombus shape of the openings cannot be achieved. The method of fabrication of corrugated metal sheet to achieve perfect rhombus shaped openings (14) on both faces of a structured packing module such as (11), (12) and (13) is shown in Figure-6. Figure-5c shows the stacking arrangement of two adjacent corrugated metal sheets (15) and (16). The front sheet (15) has V-shaped corrugations inclined at a certain angle with the vertical axis of the column (1). The sheet (16) next to the sheet (15) has V-shaped corrugations inclined at an angle same as that of sheet (15) but inclination is in opposite direction of the vertical axis. Thus, when viewed from either top or bottom the V-shaped corrugations of two adjacent sheets (15) and (16) form a number of rhombus shaped openings (14), aligned in a straight line. Figure-6a shows the original metal sheet (17) for fabrication of texturised and corrugated metal sheet like (15) or (16). The sheet (17) has specified length (19) and width (18). The width (18) of the sheet (17) is specified based on the requirement of height of the final structured packing module. The length (19) depends on diameter of the column (1) and number of pieces to be cut from the metal sheet (17). Figure-6b shows the punching of oblong slots or openings (20) on metal sheet (17). The slots (20) of specified dimensions are punched in a particular pattern. Figure-6c shows linear embossing (22) of the metal sheet (17) along length. This is done using rollers. This step reduces the width of the metal sheet (17) from (18) to (21). Figure-6d shows linear embossing of the metal sheet (17) along width. The embossing along width on the embossing along length forms the final texurisation (24) of the metal sheet (17). This step reduces the length of the metal sheet (17) from (19) to (23). Figure-6e shows the creation of V-shaped corrugation (27) on the textured metal sheet as described in Figure-6d. The V-shaped corrugation has specified dimensions and angle of inclination. This step further alters both length and width of the metal sheet (17). The final length and width become (25) and (26), respectively. The final width (26) is the height of packing module, which ensures the perfect rhombus shape openings (14) on both faces of the packing module. We Claim: 1. A structured packing module (11, 12, 13) for use in a mass and heat transfer column in which heavier and lighter fluid phases flow in opposing directions, said module comprising: a plurality of corrugated metal sheets (15, 16, 17), characterized in that, said corrugated metal sheets are stacked in a packing module in a manner such that the corrugations of two adjacent metal sheets are oppositely inclined to form a plurality of channels by the V- shaped corrugations (27) on said metal sheets (15, 16, 17), the heavier fluid phase flowing down and the lighter fluid phase flowing up through said channels, wherein the intimate contact between the two fluid phases results in transfer of heat and mass between the two phases, the flow channels formed by the oppositely inclined corrugations intersect each other at a number of points so that at said intersecting points the multiple streams of both the fluid phases merge and get redistributed, said fluid phases facing sudden change in flow direction due to rotation of packing modules stacked inside a column transit from one module to another, the descending heavier fluid phase tending to accumulate at said transition zones, the lighter fluid phase, flowing through said accumulated heavier fluid phase experiencing higher pressure drop and the hydraulic capacity of packing being greatly reduced and the transition of fluid phases from one module to another being made smother thus, ensuring less accumulation of heavier fluid phase at the inter module transition zones and thereby, lower pressure drop and higher hydraulic capacity. 2. A structured packing module as claimed in claim 1, wherein said oppositely inclined flow channel formed by the corrugations of metal sheets (15, 16, 17), which intersect with each other at a number of points, intersecting each other top and bottom faces of the module, resulting in said opening being regular and rhombus shaped (14). 3. A structured packing module as claimed in claim 2, wherein said openings are regular and small. 4. A structured packing module(s) (11, 12, 13) as claimed in any preceding claims whenever incorporated in a mass and heat transfer column (1). 5. A structured packing module (11, 12, 13) for use in a mass and heat transfer column (1) substantially as herein before described.

Documents:

191-DEL-2002-Abstract-(26-09-2008).pdf

191-del-2002-abstract.pdf

191-DEL-2002-Claims-(09-01-2009).pdf

191-DEL-2002-Claims-(26-09-2008).pdf

191-del-2002-claims.pdf

191-del-2002-complete specification (granted).pdf

191-del-2002-correspondence others.pdf

191-DEL-2002-Correspondence-Others-(06-11-2008).pdf

191-DEL-2002-Correspondence-Others-(26-09-2008).pdf

191-del-2002-correspondence-po.pdf

191-del-2002-description (complete)-(09-01-2009).pdf

191-DEL-2002-Description (Complete)-(26-09-2008).pdf

191-del-2002-description (complete).pdf

191-del-2002-drawings.pdf

191-DEL-2002-Form-1-(06-11-2008).pdf

191-DEL-2002-Form-1-(26-09-2008).pdf

191-del-2002-form-1.pdf

191-del-2002-form-18.pdf

191-DEL-2002-Form-2-(26-09-2008).pdf

191-del-2002-form-2.pdf

191-DEL-2002-Form-26-(06-11-2008).pdf

191-DEL-2002-Form-3-(26-09-2008).pdf

191-del-2002-form-3.pdf

191-del-2002-form-4.pdf

191-DEL-2002-Form-5-(26-09-2008).pdf

191-del-2002-form-5.pdf

191-DEL-2002-Petition-137-(06-11-2008).pdf