Effective Designs of Structured Packings for Heat and Mass Exchange Processes

Abstract

Various types of structured packing, such as Pyrapak F, Mellapak 250.Y, Pyrapak G, DAO TsKBN, etc., are examined. Relationships of hydraulic resistance of dry and irrigated structured packings with F-factor of gas flow rate in the column are given for these packings.Structured packings were developed in early 1960s, and in the 1970s they came into wide use in various separation processes as contact devices of industrial columnar apparatuses for implementing heat and mass exchange processes, such as absorption, fractionation, extraction, purification and drying of gas, etc.We propose to define structured packings as regular packings that are comprised of packets assembled from flat or corrugated sheets forming a spatial multichannel structure. Sheet packing components made of metal foil, network, and polymer, ceramic and other materials may lie in the apparatus as a pack of sheets, may be twisted into spirals and cylinders, and assembled into honeycombed or cellular structures. Coaxial channels thus formed, depending on the shape and relative dispositions of individual sheets, have various configurations ranging from simple (round or polygonal cross section) to complex spatial packing periodically changing with height. Thus, the proposed term "structured packings" encompasses a whole multitude of film-type heat-exchanging contact devices (for instance, sprinklers) for cooling towers [1].Most popular in the industry are structured packings of the type that are well adaptable to process conditions and geometric dimensions of the apparatuses. Such packings are distinguished by equally high and stable indices of separation of the components of mixtures in a wide range of diameters of the mass-exchange columns (80 mm-20 m). They are usable in almost all process conditions regardless of pressure in the apparatus, gas flow velocity, and liquid load per unit cross sectional area of the apparatus.In this packing family, the most known are Mellapak 250.X/250.Y pressed into service in the industry in 1987 by the Swiss company Sulzer Chemtech. Almost all major packing companies manufacture modified versions of this packing [2][3][4].A notable feature of the referred structured packings is large specific surface, which ensures developed phase contact surface with a high free volume (0.9-0.98 m 3 /m 3 ). This made them widely applicable in processes occurring with high gas and low liquid loads. Low differential pressure across the packing height and high mass exchange efficiency are among the advantages of the structured packings. For instance, for getting equal separating power using Pall rings, at least four times larger column volume is required than when Sulzer BX cellular structured packings are used [5]. Under the same conditions 1 Moscow State University of Engineering Ecology (MGUIÉ). 2 TsNTU RINVO ZAO.

Совершенствование Насадочных Контактных Устройств Массообменных Аппаратов

“…Перспективные контактные устройства для осуществления различных тепло-и массообменных процессов разрабатывались и исследовались в нашей стране в отраслевых институтах (ГИАП, НИУИФ), ИВЦ «Инжехим» (Казань), Казанском национальном исследовательском технологическом университете (КНИТУ), Санкт-Петербургском государственном университете технологии и дизайна, Ивановском государственном химико-технологическом университете, Московском государственном университете инженерной экологии, вошедшем в состав Московского политехнического университета, и других университетах Российской Федерации [2][3][4][5][6][7][8][9].…”

“…Регулярная насадка, выполненная из четырёх лопастных винтообразных (геликоидных) горизонтальных полимерных элементов, плотно уложенных в пакет с поворотом на 90° от слоя к слою, целиком соответствует предложенному в работе [6] определению структурированных насадок. Вместе с тем, в отличие от регулярных насадок пленочного типа, например известных насадок фирмы «Зульцер», гофрированные листы которой образуют совокупность отдельных замкнутых и не сообщающихся между собой каналов, насадка из геликоидных элементов образует открытую многоканальную ячеистую структуру постоянно сообщающихся между собой по высоте каналов переменного сечения.…”

Comparison of plate and packed contact devices in column vessels

“…This trend is also continuing at the present time, even in those branches (for example, in petroleum chemistry), where PLC had been traditionally used earlier on. In recent years, PC with SP have been introduced all the more increasingly to different branches of industry, especially in processes requiring heavy gas and light liquid loads [8]. The high cost of SP is, however, limiting their broad-scale use.…”

New combination packing for heat-and mass-exchange vessels

“…The sheet components of the packing, which are fashioned from metallic foil, meshes, and polymeric, ceramic, and other materials, may be arranged in a vessel as a set of plates, spirals, cylinders, and may also be assembled into a honeycomb or cellular structure. Coaxial channels, which are formed by the packing elements, may assume different configurations -from simple (a circular or polygonal section) to complex three-dimensional [4].The term structured packings has also been expanded to include film heat-exchange contact assemblies for cooling towers (sprinklers) [5].Despite their high heat-and mass-exchange efficiency, SP have a number of deficiencies, primary among which is nonuniform distribution of the gaseous and liquid flows throughout the cross section of the vessel [1], since the geometric structure of the packing excludes communication between the free channels formed by neighboring sheets. To improve the operating efficiency of SP, it is necessary to ensure uniformity of gas and liquid throughout all channels, even at the inlet to a layer of packing.…”

“…The sheet components of the packing, which are fashioned from metallic foil, meshes, and polymeric, ceramic, and other materials, may be arranged in a vessel as a set of plates, spirals, cylinders, and may also be assembled into a honeycomb or cellular structure. Coaxial channels, which are formed by the packing elements, may assume different configurations -from simple (a circular or polygonal section) to complex three-dimensional [4].…”