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.

Hydrodynamic parameters are investigated for a structured packing (analogy of the Mellapak 250.X packing) in a water-air system under atmospheric pressure. Relationships between the hydraulic resistance of the irrigated packing on the hypothetical gas velocity, and also its holding capacity on the Re number are presented for the liquid phase.Regular structured packings (RSP) assembled from corrugated sheets are widely used as contact devices in industrial columns for heat-and mass-exchange processes, for example, absorption, fractionation, cleaning, and drying of gas. The most widely known RSP carries the Mellapak trademark 250.X/250.Y, and can be used over a broad range of conditions under which these processes take place, and was introduced to industry in 1987 by the Sulzer Chemtech Company (Switzerland) [1,2].A characteristic feature of RSP is a large specific surface, which provides for a developed area of contact for the phases (with a free space of 0.9-0.98 m 3 /m 3 ); this makes it possible to use them for processes with heavy gas and light liquid loads. The low pressure gradient over the height of the packing, and high gas-exchange efficiency should be referred to as advantages of RSP. Owing to its ordered structure, the RSP can be used in columns with diameters of up to 20 m, ensuring uniformity of liquid-phase distribution over the entire volume of the vessel.In studying the performance of packings, major interest is focused on the hydrodynamic pattern of the process, and the character of the gas and liquid in the packed layer.The most critical hydrodynamic characteristics of RSP are the amount h t of liquid retained, the pressure gradient ∆p/∆z over the height of the packing, and the range of stable operation, i.e., maximum and minimum allowable gas and liquid loads.Familiar advertizing information on the hydrodynamic characteristics of RSP is intended only for comparative evaluation, and is not recommended for engineering calculations performed by manufacturing companies. Because these calculations are required in practice, we investigated the hydrodynamic parameters of RSP in an air-water system on an experimental plant (Fig. 1) under atmospheric pressure.The packing under investigation (analogy of the Mellapak 250.X packing) was placed in an absorption column formed from acrylic plastic with an effective section of 250 × 250 mm.

Results are presented for hydrodynamic investigations of a model of a new design of vessel. Limits of the most effective operating regimes of the vessel are determined. A criterial equation is derived for determination of the height of the film layer -a quantity characterizing the operational effectiveness of the vessel on the whole.An original design of a combined heat-and-mass exchanger with two zones of phase contact, which is intended for the cleaning and cooling of gas, as well as condensation of viscous impurities contained in the gas, has been developed at the Moscow State University of Engineering Ecology.The combined vessel is shown in a schematic of an experimental plant (Fig. 1). The vessel housing is cylindrical. A flushing fluid is delivered into the upper part of the vessel, and distributed over its entire section, and gas is fed by counterflow into its lower section. Owing to characteristic design features of the vessel, a sufficiently large specific surface area of phase contact is ensured in the gas-liquid system.A flushing fluid delivered to a film sprayer creates a film that effectively separates the gas being delivered from the spray and particles of carbon black that exist in a mixture with resinous components of the liquid. This liquid is discharged under gravity through a lower connecting pipe. A gas is fed into the flushing liquid, which is accumulating in the lower portion of the vessel, and forms a foam layer.A literature search indicated the following. Golovachevskii [1] mentions a method for gas cleaning in which the gas is delivered using a Γ-shape branch pipe, and forms a foam layer in the lower section of the vessel, and a flushing fluid is atomized by nozzles in the upper section of the vessel. He also describes a vessel for heat-and-mass exchange and wet dust entrapment, which has two zones of phase contact -a foam layer, and a bed of a fluidized spherical packing on a perforated tray situated above. The construction of film sprayers is described in [2][3][4][5].Operating regimes and rules governing the operation of a film sprayer [5], and also the upper limit of the gas load, which corresponds to its effective operation as a separator, were determined as a result of analysis of literature sources.It is established that the maximum gas velocity in the tower should not exceed 0.9 m/sec, since when this condition is violated, a transitional operating regime sets in for the film sprayer, and it ceases to function as a separator.It must be noted that a new type of vessel with two stages of phase contact is a complex system, the high operating effectiveness of which is governed by combined processes in two zones of phase contact: a foam layer, and separating film.The mechanism responsible for cleaning of the gas consists of the following. The basic stage of this process takes place in the foam layer, and drops of liquid with contaminant particles settling on them are separated in the film, reducing splash-away and improving the effectiveness of the cleaning.The proposed design for the ...

Results are presented for investigation of the hydrodynamics of regular packings formed from cellular inclined cylinders for heat-and mass-exchange processes. Characteristics of the influence exerted by the angle of incline of the packing elements were investigated, and computational relationships for the coefficient of hydraulic resistance of the packings ascertained during the course of the study. Keywords: regular packing, heat and mass exchange, hydraulic resistance, mesh formed from polymeric material.Polymers have recently come into widespread use as a material for fabrication of packings in heat and mass exchangers. Polymers are acid and wear resistant, and durable [1,2]. Use of polymeric materials, including those in the form of a mesh, also provides for a reduction in the mass of the packing, lightening the load on the support elements of the structures in column vessels and cooling towers [3,4].This paper presents results of investigation of the hydrodynamics of regular packings formed from cellular inclined cylinders for heat-and mass-exchange processes. The present study is a continuation of tests conducted previously at the Moscow State University of Engineering Ecology (MGUIE) [5,6]. The objective of the study was to ascertain laws defining the influence exerted by geometric parameters on the specific resistance of dry and irrigated packings formed from various types of mesh.Tests were conducted on an experimental plant with a rectangular prototype unit having a cross section of 250 × 250 mm. The hydraulic resistance of the packing layer and the flow rate of air through the unit were recorded by two type-MMH micromanometers using a Pitot tube; the flow rate of water was determined with use of an RS-7 rotometer.The dry packing was tested in the air-velocity region w 0 = 0.8-3.8 m/sec in calculating the full section of the empty unit. Moreover, the Reynolds number Re g = w g d e ρ/μ (here, w g = w 0 /ε is the velocity of the gas through the apparatus with the packing, ε is the free volume, d e is the equivalent diameter of the packing, ρ is the density of the gas, and μ is the dynamic viscosity of the air) was varied from 6000 to 24000. The irrigated packing in the gas-liquid counterflow was tested at reflux densities q l = 8-16 m 3 /(m 2 ·h). The packing was constructed in the form of six layers consisting of cylinders 60 mm in diameter, which were mounted at an angle α to the vertical in the unit (Fig. 1). During the course of the experiment, the angle α was set at 5, 10, 15, 20, and 25°. Three types of mesh with cells having dimensions of 2 × 2, 3 × 3, and 4 × 4 mm in the active section were used as packing material. The design of the upper layer, which includes six centrifugal nozzles, permitted uniform irrigation of the packing. The packing was mounted on the support tray fabricated from a polymeric mesh with cell dimensions of 20 × 20 mm. The resistance of the mesh of the support tray was predetermined and calculated from the resistance of the packing.Geometric characteristics of the alternate d...

The paper is devoted to hydrodynamic and mass-exchange investigations of a new type of combined unit. It sheds light upon results garnered from investigation of the structure of the foam layer, and criterial equations are derived for determination of the height of the foam layer, the mass-yield efficiency in the gaseous phase, and the hydraulic resistance of the unit.The Moscow State University of Engineering Ecology (MGUIE) is developing an original design of combined unit with two phase-contact zones (Patent RU 02377050 C1). The unit is being developed for the treatment and cooling of gas, and for condensation of viscous impurities from the gas.The heat and mass exchanger under development ( Fig. 1) has a cylindrical housing. The flushing liquid is fed into the upper portion of the unit, and distributed over the entire section, while the gas is admitted to the lower part as a countercurrent to the liquid. Owing to characteristic features of its design, this unit provides for a high specific gas-liquid contact surface to reduce deposition of contaminating impurities on this surface.Falling onto a film sprinkler, the flushing liquid fed into the unit creates a film, which effectively separates the passing gas from splash-away and contaminating particles. The flushing liquid is discharged via gravity flow through a lower branch pipe.The gas is admitted to the volume of flushing liquid accumulating in the lower portion of the unit, and forms a bubbling layer.The height and structure of the bubbling layer obtained was of primary interest in studying the hydrodynamics of the combined unit. Three operating regimes became apparent based on the structure of the layer. The initial and transitional regimes are of no practical value due to the absence of a stable developed bubbling layer. Continued investigations were therefore conducted on gas velocities over and above 0.5 m/sec in the columns, which stabilized the operating regime within the unit.The upper boundary of the load with respect to the gas velocity in the column should not exceed 0.9 m/sec [1], since when this boundary is surpassed, the transitional operating regime of the film sets in, and it will readjust effectively to function as a separator.