Structured metal wire device as packing for process engineering applications

Abstract

Device (1) for improving mass and heat transfer in packed columns (4) under different operating conditions, characterized in that tubular structured metal wire devices (3, 7, 12) are used as packings for operating the column.

Description

[0001] Structured packings have been used for approximately 50 years in chemical and thermal process engineering, wastewater and exhaust air treatment in special heat and mass transfer columns.

[0002] In this technology area, separation processes such as absorption, distillation, rectification, and extraction are frequently used. Internals such as random packings and / or structured packings are positioned to increase the mass and / or heat transfer surfaces between a gas or vapor phase and a liquid or liquid-liquid phase within a separation column. The purpose of these internals is to distribute the phases evenly across the column cross-section and achieve a maximum liquid surface area for mass and heat transfer.

[0003] Packed columns always aim for continuous mass and heat transfer, and they are not equipped with individual trays, as is the case with tray columns, but rather have a continuous layer of packing material extending the entire column height. Depending on the task, the packing material can be formed from a wide variety of geometries, specific surfaces, and materials (metal, ceramic, plastic). Raschig rings, Pall rings, or saddles are primarily used. The primary focus of the process engineering process is always continuous and consistent spraying of the packing surfaces to achieve the longest possible residence times between gas or vapor and liquid.The uniform application across the column cross-section and the distribution of the liquid over the entire column is considered a very demanding requirement, which continues to be the focus of optimization measures in research and development.

[0004] It is known from packed columns that, despite uniform feed, the trickling liquid always flows toward the column wall due to the high degree of voids at the edge, leaving the core of the packing layer unaffected or only partially exposed. As the liquid loading decreases, this adverse effect is even more pronounced. It should be noted that the so-called creeping flows or stream formations caused by edge penetration represent a narrow peripheral zone, but can occupy a large portion of the column cross-section when viewed circumferentially. This phenomenon is also referred to as maldistribution in the field of column technology.

[0005] The effects of edge penetration and channeling, which frequently occur in packings, with subsequent axial and radial maldistribution, often have such drastic negative consequences that the required and guaranteed separation efficiency of a column is not achieved. Almost all known failures of packed columns can be traced back to maldistribution [M. Gann, Chem. Ing. Tech. 64 (1992) 1, pp. 6-16].

[0006] Maldistribution significantly reduces mass transfer in packed columns. Therefore, according to the current state of the art, the packing is interrupted every 2-4 meters, depending on the column size, and the liquid is collected at the edge and redistributed. This redistribution procedure is very complex because additional receiving grates, collection devices, and devices for distributing the liquid are required. These multiple measures significantly increase the height of the packed columns. Furthermore, the costs for the additional receiving, collection, and distribution devices are usually higher than the packing itself.

[0007] Furthermore, it is known that the separation efficiency of packed columns is quite low in the lower loading range. As the column approaches the flooding point, it continuously improves. This is due to the formation of a pronounced turbulent spray and bubbling layer within the packed bed, which positively influences mass transfer. However, improving the separation efficiency by approaching the flooding point can only be achieved by increasing the pressure drop. The disadvantage here is that packings used in columns inherently exhibit high pressure drops due to the unfavorable flow geometry (drag coefficient).

[0008] Within chemical and thermal process engineering, as well as in other demanding technological fields, devices equipped with defined and reproducible contact surfaces have been increasingly used for several decades. These so-called "structured packings" have replaced established random packings in many areas due to their advantageous properties, such as low pressure drop, high efficiency, and high performance. Together with optimized versions of this type, they currently represent the state of the art.

[0009] Due to their low pressure drop, structured packings are ideal for applications involving volatile chemicals. They also allow for higher throughput rates and, as a result, smaller column dimensions than tray or packed columns. Furthermore, there is no risk of fluidized bed formation and material discharge when the flooding point is exceeded.

[0010] However, the production of conventional structured packings is considerably more costly and complex than the production of random packings. The "Prozesstechnik Online" report of December 11, 2015, reports that 10,000 to 20,000 weld points per cubic meter are required for the production of structured packings, depending on the application.

[0011] This is where the invention comes in. It has surprisingly been shown that structured metal wire devices, similar to conventional structured packings, can be successfully used in columns for a variety of purposes. However, they have significant advantages over these, namely that their manufacture is much simpler than that of structured packings. Furthermore, to achieve a large exchange area, the wires can be repeatedly formed into a variety of geometries with almost any diameter, length, gap size, and specific surface area. The wires can be arranged horizontally, vertically, or at specific angular positions within the column. To achieve very long lengths, these tubular metal wire devices can be suspended from one another.In summary, it can be stated that these innovative packing structures, with their versatility, are a suitable means of meeting a wide range of requirements regarding diameter and column length, and are significantly more cost-effective in production and replacement (simply removed from the reactor). Furthermore, they tend to offer a lower pressure drop for the same surface area than comparable packings with similar void ratios and specific surface areas, but a significantly lower pressure drop than random packings.

[0012] Another major advantage and simple measure for avoiding creeping flows and streams in the edge region, which is offered by this innovative packing device, is that it can be flexibly formed with a larger outer diameter than the inner diameter of the column. This creates a compression packing during installation and the wires of the device are compressed in the edge region. The pressure loss is increased locally at the edge and false flows are therefore avoided. A further benefit of this arrangement is the self-locking of the larger diameter within the columns. This eliminates the need for additional holding and distribution devices for the liquid phase and, last but not least, the overall height of the columns is considerably reduced. This means that the otherwise essential holding devices for loose packings and conventional packed columns can be completely dispensed with.It's important to note that the otherwise required support and hold-down grids require very careful pre-selection, as malfunctions can adversely affect fluid dynamics. By avoiding the highly detrimental edge penetration, channel formation, and the elimination of additional fittings, a very uniform liquid distribution within the columns is achieved.

[0013] The aim of the invention is therefore to improve mass and heat transfer within columns used in chemical and thermal process engineering, as well as in exhaust gas purification. This object is achieved by equipping the columns with tubular, structured metal wire devices as packing internals that function as exchange packing.

[0014] These internals ensure that a considerably large surface area can be provided for mass and heat exchange between gaseous or vaporous and liquid phases, while at the same time avoiding maldistribution.

[0015] A special embodiment of the invention is that these structured metal wire packings according to the invention cause a much lower pressure drop compared to other options used in such columns and can therefore be operated at higher velocities and thus with higher loadings. The introduction and distribution of the liquid in the head region of the column can be carried out as usual and proven according to the state of the art, because the uniform design of the structured metal wire column packing ensures a uniform distribution of the individual phases within the column. Continuous collection and distribution of the liquid in the edge region of the column is eliminated because, as already described, edge penetration can be virtually eliminated through design measures.

[0016] From these advantageous geometries of structured metal wire devices, a variety of other structured packing geometries can be derived to carry out process engineering tasks.

[0017] For example, it is possible to produce segments with different diameters, heights, gap sizes, and specific surface areas from the metal wires. These are primarily arranged longitudinally to the flow direction, and the individual wires / cores exhibit corrugation in one or two planes. This corrugation makes the alternative packings resilient at least to their diameter and, in the unloaded state, are manufactured slightly larger than the column diameter. Upon insertion into the column, the alternative packings are slightly compressed, thus forming a tight seal with the column's inner diameter. This compression effectively prevents edge penetration in the outer packing area.

[0018] The alternative packings can also be shaped like metal sponges used for cleaning pots, only considerably larger. These segments can be combined into modules and used within columns, similar to the aforementioned structured metal wire devices, to carry out process engineering operations. Additionally, they can be provided with so-called guide holes to simplify assembly, fastening, and operation.

[0019] However, it is also possible to form tubular packings from metal wire mesh. The parameters regarding material, wire thickness, geometry, and process characteristics (number of gaps, specific surface area) can be freely selected within a wide range.

[0020] A further advantage of this device according to the invention is that due to the significantly lower pressure drop than other comparable structured packings, the Opex content can be kept low. In addition, it is possible to produce significantly higher specific surface areas with small overall dimensions of this equipment, so that comparatively very compact columns can be produced (Capex).

[0021] Furthermore, it is known that all columns require droplet separators at the top of the gas outlet as a safety feature to prevent droplet entrainment, for example, when operating at the limits of their capacity, such as the stagnation point and flooding point. A disadvantage is that, in order to function properly, they require very high specific surface areas and flow velocities, thus causing high, costly pressure drop contributions. Due to the fact that these novel structured metal wire packings according to the invention can be easily manufactured with very high specific surface areas and comparatively low pressure drop values, they are also suitable as droplet separators in columns.

[0022] Optionally, the alternative packing can also actively supply heat in addition to its function as a large phase interface for mass and heat transfer by designing the wires / cores entirely or partially as resistance wire heaters. The defined length and distribution of the corrugated wires / cores ensures uniform heat transfer across the radius and length of the packing, thus maintaining an optimal temperature window for, for example, highly effective desorption.

[0023] A further advantage is the elimination or at least significant reduction of the separate heat exchanger unit otherwise required for fluid heating, for example in the desorber, which is usually heated by low-pressure steam.

[0024] In addition, the heat is supplied precisely where it is needed. The already very large surface area for mass transfer also ensures energy-saving and gentle energy supply using renewable electricity wherever possible.

[0025] The aforementioned optional electrical heating of the alternative packing using resistance wire can also be used to supply heat in catalytic processes. The key design feature here is that no significant additional heat input, for example, using burners, is necessary, and the amount of heat introduced radially across the reactor diameter and along the reactor's longitudinal axis is evenly distributed. Further advantages, details, and features of the invention will become apparent from the following description and the drawings, which show: Fig. 1 a simplified sketch of the structured metal wire packing according to the invention, Fig. 2 a simplified illustration of round structured metal wire segments that can be assembled into a stack and inserted into the columns, Fig. 3 a representation of a tubular packing consisting of metal wire mesh Fig. 4 a simplified sketch of a desorber, with direct electrical resistance heating of the structured metal wire packing according to the invention

[0026] In Fig. Figure 1 shows the structured tubular metal wire packing according to the invention, indicated by (1). The scrubbing solution is introduced into (2), ideally directly above the wires / cores. The corrugated wires / cores are marked (3), and the exchange column is marked (4). This is where the most optimal reaction possible between scrubbing liquid (2) and exhaust gas (5) takes place.

[0027] In Fig. 2, (6 7) is a similar alternative packing as under Fig. 1. Metal sponges are formed into segments (8) and combined into stacks / modules (9). To simplify assembly / disassembly / operation, mounting rods or similar devices with supports (10) can be used.

[0028] In Fig. 3 is another alternative to the description according to Fig. 1. Here, tubular packings (14) made of metal wire mesh (12) are twisted around a guide rod (13). However, it is also possible to use "compressed wire mesh" made of high-strength steel wires, including stainless steel wires, copper wires, nickel wires, and other materials as the starting material and form them into tubular metal wire packings.

[0029] Determining the number and arrangement of the guide and mounting rod(s) is common practice for a technically trained expert and requires no further explanation. Further information can be found, among other sources: EP 1 628 727 B1 & US 4 744 929.

[0030] In Fig.Figure 4 shows a desorber (18). It is known that the absorber and desorber can use the same mass and heat exchange devices (17). Therefore, in addition to the function of the large phase interface for mass and heat exchange, the alternative packing can also actively supply heat by designing the wires / cores (18) entirely or partially as resistance wire pickling (19). The saturated scrubbing liquid is introduced into (15) for regeneration and flows out of the desorber (18) again at (20). The separated absorbate (16) is discharged in the upper region of the desorber. (+) and (-) define the current feed (19) for the conductive heating.

[0031] The parameters regarding material, wire thickness, geometry, and process-related parameters (degree of voids, specific surface area) can be freely selected within a wide range.

[0032] Of course, the described examples can be modified and supplemented in many ways without departing from the basic idea of ​​the invention. These devices can, of course, be used in both absorbers and desorbers. Should the reactions require an external heat input, it is also possible to provide electrical heat via this device according to the invention (conductive / inductive).

[0033] Of course, the invention also relates to the method for optimizing packed columns by using structured metal wire devices as ordered packing for process engineering applications. List of reference symbols 1 Structured metal wire packing (device for exchange columns) 2 washing liquid 3 Wire / core as part of the metal wire package 4 Exchange column (absorber) 5 Exhaust 6 Wire for the alternative structure of a wire packing (metal sponges) 7 Top view of the alternative structure 8 segments consisting of metal sponge wire (1 of 4 shown here) 9 stacks / modules consisting of segments (here 1 stack with 4 segments) 10 mounting rod 11 Direction of the helix for the production of tubular packings 12 Extract Metal wire mesh for tubular spiral production 13 Guide rod 14 Top view of the tubular packing made of metal wire mesh 15 Saturated washing liquid 16 Absorbate 17 metal wire pack 18 desorbers 19 Power supply 20 Regenerated washing liquid QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 1 628 727 B1

[0029] US 4,744,929

[0029] Cited non-patent literature

[0000] M. Gann, Chem. Ing. Tech. 64 (1992) 1, pp. 6-16

[0005]

Claims

[1] Device (1) for improving mass and heat exchange in packed columns (4) under different operating conditions, characterized by that tubular structured metal wire devices (3, 7, 12) are used as packings for operating columns. [2] Device according to claim 1, characterized by that the vertical structures (1) made of wires / cores (3) introduced into the columns (4) are bent / kinked in one or two planes relative to their longitudinal axis. [3] Device according to the preceding claims, characterized by that the elastic metal wire devices (1) with a larger outer diameter than the inner diameter of the column (4) are inserted into the latter. [4] Device according to the preceding claims, characterized by that the outer wires (3) of the metal wire device (1) are compressed within the column (4) and form a press packing with the inner diameter of the column. [5] Device according to the preceding claims, characterized by that the metal wire device (1) is used in a desorber (18) for the regeneration of saturated washing liquid (15). [6] Device according to the preceding claims, characterized by that the wires (17) of the metal wire device (1) in the desorber (18) can be heated electrically (19). [7] Device according to the preceding claims, characterized by that the saturated washing liquid (15) is introduced into the top part of the desorber (18), the expelled absorbate (16) leaves the desorber (18) in the top part and the regenerated washing liquid (20) in the lower part of the desorber is circulated back to the column (4).

Images