Column contactor

However, in a countercurrent column contactor as sketched in Figure 8, the holdup of the dispersed phase is considerably less than this, because the dispersed drops travel quite fast through the continuous phase and therefore have a relatively short residence time in the equipment. The holdup is related to the superficial velocities U of each phase, defined as the flow rate per unit cross section of the contactor, and to a sHp velocity U (71,72) ... 

The earliest large-scale continuous industrial extraction equipment consisted of mixer—settlers and open-spray columns. The vertical stacking of a series of mixer—settlers was a feature of a patented column in 1935 (96) in which countercurrent flow occurred because of density difference between the phases, avoiding the necessity for interstage pumping. This was a precursor of the agitated column contactors which have been developed and commercialized since the late 1940s. There are several texts (1,2,6,97—98) and reviews (99—100) available that describe the various types of extractors. 

Caprolactam Extraction. A high degree of purification is necessary for fiber-grade caprolactam, the monomer for nylon-6 (see Polyamides). Cmde aqueous caprolactam is purified by solvent extractions using aromatic hydrocarbons such as toluene as the solvent (233). Many of the well-known types of column contactors have been used a detailed description of the process is available (234). 

Holdup and Flooding At this point it is useful to introduce the concepts of holdup and flooding in column contactors. It is normal practice to select the phase which preferentially wets the internals of the column as the continuous phase. This then allows the dispersed phase to exist as discrete droplets within the column. If the dispersed phase were to preferentially wet the internals, this could cause the dispersion to prematurely coalesce and pass through the column as rivulets or streams which would decrease interfacial area and therefore column efficiency. 

In a countercurrent-type column contactor, stable operation is possible as long as the rate of arrival of droplets in any section does not exceed the coalescence rate at the main interface once this value is exceeded, droplet backup will occur at the interface and slowly build back into the column active area, a condition known as flooding. This is an inoperable condition. 

The concepts of shp velocity and characteristic velocity are useful in defining the Flooding point and operational regions of different types of column contactors. The shp (or relative) velocity is given by the equation ... 

In Fig. 3.52, the column contactor is represented by a series of N nonequilibrium stages, each of which is of height H and volume V. The effective column height, Z, is thus given by Z = N H. 

Agitated column contactors, 10 767 Agitated drying systems, 18 732 Agitated tanks, heat transfer in,... 

Hayashi, J.-I., Ikeda, J., Kusakabe, K., and Shigeharu, M., Decomposition rate of volatile organochlorines by ozone and utilization efficiency of ozone with ultraviolet radiation in a bubble-column contactor, Water Res., 27, 1091-1097, 1993. 

The advantages and disadvantages of membrane based processes and pertraction through various types of liquid membranes are summarized in Table 23.5. HF contactors are supposed in these processes with the exception of pertraction into stable emulsions (ELM) where mixed column contactors or mixer-settlers are used. 

Nickel and cobalt often occur with copper, and must be separated in pure form from hydrometallurgical leach liquors. Organic acid extractants can quite readily separate copper from cobalt and nickel, but the separation of cobalt from nickel is rather difficult. In one Ni/Co separation process, di-2-ethyl hexyl phosphoric acid (D2EHPA) is used as extractant, with strict control of the pH of the aqueous phase to take full advantage of the slightly different equilibrium constants for the Co and Ni reactions. Pulsed column contactors are used rather than mixer-settlers, and nickel impurity is removed from the loaded organic phase by scrubbing it with a cobalt-rich phase. 

Both phases in a continuous form packed columns thin-film contactors wetted-wall columns contactors with flat surface laminar jet absorber disc (sphere) columns... 

There are several other types of apparata used for reactive absorption, though these are less widespread. In mechanically agitated bubble columns it can be assumed that both phases are ideally mixed, whereas in the jet absorber, the gas stream breaks on a liquid surface and is dispersed in the liquid. In spray towers and venturi scrubbers, liquid is sprayed as fine droplets. Thin-jilm contactors, in which liquid film is scrapped from the walls by impellers, are applied for reactive absorption in viscous liquids. Some units, such as wetted-wall columns, contactor, laminar jet absorber and disc (sphere) column are used mainly in laboratory. 

Solvent Extraction Performance in Petroleum Refining Industry (Lube Oil Refining Subcategory) Using Extractor (Spray Column Contactor and Stripping Column) and Solvent (Isobutylene)... 

Unit configuration Column specifications Type of solvent Solvent flow rate Wastewater flow rate Spray column contactor and stripping column 0.0254 m diameter x 0.914 m glass pipe Isobutylene 0.014 m /h 0.003 m3/h... 

Unit configuration Spray column contactor and stripping column... 

Figure 1. Seven-stage agitated column contactor.

Rautenbach and Machhamer [91] developed a correlation for prediction of drop sizes of emulsion globules in stirred column contactors as... 

Fixed Bed Columns. Column contactors allow multiple equilibrium stages to be obtained in a single unit. This contactor provides for reactions to be driven to the desired level of completion in a single pass by adjusting the resin bed depth and the flow conditions. The main components of a column contactor are shown in Fig. 28. At the end of its useful work cycle, the resin is backwashed, regenerated and rinsed for subsequent repetition of the work cycle. Typically, diis nonproductive portion of the cycle is a small fraction of the total operating cycle. 

Column contactors may be operated in cocurrent, countercurrent or fluidized bed modes of operation. The cocurrent mode means that the regenerant solution flows through the column in the same direction as the feed solution. The countercurrent mode has the regenerant flowing in the opposite direction as the feed solution. 

Continuous Column Operations. When the ionic load of the feed solution is such that the regeneration/elution portion of the operating cycle is nearly as great or greater than the working portion, continuous contactors are recommended instead of column contactors. 

Fluidized Column Operations. Column contactors, when operated with the feedstream in a downflow mode, are poorly suited to handle fermentation slurries because of the excellent filtration characteristics of packed resin beds. For such slurries it is preferable to use a fluidized bed of resin such as is shown in Fig. 33 While most of the commercial applications discussed in the literature pertain to slurries of uranium tailings and paper mill effluent, the equipment may be adapted for use in treating fermentation broths. 

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