Diameter absorption column

Once packing heights are determined in other sections from HETP (distillation) or Koa (absorption), the height allowances for the internals (from Figure 1) can be added to determine the overall column height. Column diameter is determined in sections on capacity and pressure drop for the selected packing (random dumped or structured). 

Methods for quick sizing trayed fractionation and absorption column diameter have been reduced here to equations to facilitate programming for calculators or computers. Three methods are discussed and it is not a bad idea to compare results with all three. 

Determining the number of theoretical and actual trays in a distillation column is only part of the design necessary to ensure system performance. The interpretation of distillation, absorption, or stripping requirements into a mechanical vessel with internal components (trays or packing, see Chapter 9) to carry out the function requires use of theoretical and empirical data. The costs of this equipment are markedly influenced by the column diameter and the intricacies of the trays, such as caps, risers, weirs, downcomers, perforations, etc. Calcvdated tray efficiencies for determination of actual trays can be lost by any unbalanced and improperly designed tray. 

Yoshida and Akita (Yl) determined volumetric mass-transfer coefficients for the absorption of oxygen by aqueous sodium sulfite solutions in counter-current-ffow bubble-columns. Columns of various diameters (from 7.7 to 60.0 cm) and liquid heights (from 90 to 350 cm) were used in order to examine the effects of equipment size. The volumetric absorption coefficient reportedly increases with increasing gas velocity over the entire range investigated (up to approximately 30 cm/sec nominal velocity), and with increasing column diameter, but is independent of liquid height. These observations are somewhat at variance with those of other workers. 

Absorption column diameter 1 m, vessel overall height 15 m, packed height 12 m, packing 25 mm ceramic intalox saddles, vessel carbon steel, operating pressure 5 bar. 

Absorption column packed column, diameter 0.5 m, height 6.0 m, packing height 4.5 m, packing 25 mm ceramic saddles, design pressure 2 bar, material carbon steel. 

The same issues apply to the height and diameter of an absorption column as for a distillation column the more difficult the separation, the taller the column and the more liquid and vapour flowing inside the column, the wider the column diameter. 

Bubble columns are used very widely for reaction absorption applications. In bubble columns, the gas phase flows in the form of bubbles, either countercurrently or co-currently. Bubble columns provide significant liquid hold-up and sufficient liquid residence time. The column diameter sometimes exceeds 5 m, and its height reaches 10 m or more. 

Gas absorption is a function of the gas and liquid mass transfer coefficients, the interfacial area, and the enhancement due to chemical reaction. The gas-liquid interfacial area is related to the Sauter mean bubble diameter and the gas holdup fraction. The gas holdup fraction has been reported to vary with radial position (7-11) for column internal diameters up to 0.6 m. Koide et al" Tl2), however, found that the radial distribution of gas holdup was nearly constant for a column diameter of 5.5 m. Axial distribution of average gas holdup has been reported by Ueyama et al. (10). The average gas holdup... 

The calculation of column diameter for distillation and absorption columns %h,6 is usually based on the flooding velocity, which, in turn, requires values of the flooding capacity factor, Cf- Fair s flooding-capacity plot for sieve trays [1] correlates the flooding capacity factor with a flow parameter Flv for each tray-spacing value, t, as shown in Figure 2. The flow parameter involves the liquid mass flow, LMi, and vapor mass flow, F v (both in lb/ s), as well as the densities of the two streams. 

The process is visualized by injection of Gd + chelate complexes like Gd(DTPA) as contrast agents on top of the column and using a FLASH sequence for rapid imaging. The unique insight into the separation process gained by NMR ima ng is illustrated in Figure 10.1.4 by a series of FLASH images [Bayl] a parabolic profile arises from faster elution in the core of the column. It is caused by a combination of wall absorption and thermal effects from a temperature distribution across the column diameter. The band... 

Because the gas throughput (mass or volumetric flow) in an absorption process is typically a set design parameter, a variable other than gas flow must be adjusted to maintain an acceptable velocity. The column diameter is the chosen parameter. According to... 

Absorption and stripping are usually conducted in packed columns or in trayed towers. Packed columns are preferred when (1) the required column diameter is less than 60 cm (2) the pressure drop must be low, as for a vacuum service (3) corrosion considerations favor the use of ceramic or polymeric materials and/or (4) low liquid holdup is desirable. Trayed towers are preferred when (1) the liquid/gas ratio is very low, and (2) frequent cleaning is required. If there is no overriding consideration, cost is the major factor to be taken into account when choosing between packed columns and trayed towers for absorption or stripping. 

A gas absorption column to handle 3630 kg/hr of a gas is being designed. Based on pressure drop, entrainment, and foaming consideration, the maximum vapor velocity must not exceed 0.61 m/sec. If the density of the vapor is 0.801 kg/m , what is the column diameter ... 

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