Phase Flow Absorption

In absorption processes with cocurrent flow, the feed phase flows parallel with the solvent phase through a single absorber or through a series of absorbers. 

Cocurrent absorption is usually carried out in spray or jet scrubbers and film absorbers. Cocurrent absorption is mainly used for the absorption of chemically acting wash liquids and only small residence times are needed to obtain the required absorption yield also at a large throughput. 

5 Countercurrent Phase Flow Absorption, Design of Countercurrent Flow Columns 

During absorption with countercurrent flow, the feed gas phase flows upward into the absorption column. The solvent phase, which is introduced at the top and withdrawn at the bottom, flows against the gas phase. Internals in the column provide stepwise (trays, spray zones, rotating discs) or continuous (random packing, regular packing, etc.) phase contact. 

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In the preceding solvent extraction models, it was assumed that the phase flow rates L and G remained constant, which is consistent with a low degree of solute transfer relative to the total phase flow rate. For the case of gas absorption, normally the liquid flow is fairly constant and Lq is approximately equal to Li but often the gas flow can change quite substantially, such that Gq no longer equals Gj. For highly concentrated gas phase systems, it is therefore often preferable to define flow rates, L and G, on a solute-free mass basis and to express concentrations X and Y as mass ratio concentrations. This system of concentration units is used in the simulation example AMMONAB. 

Ray used high performance liquid chromatography to estimate diloxanide furoate and tinidazole in single and combined dosage forms [39], Tablets were dissolved in the mobile phase, and 20 pL was injected on to a stainless steel column (30 cm x 3.9 mm) of p-Bondapak Cig. 8 3 methanol 0.05 M phosphoric acid (pH 3) was used as the mobile phase (flow rate of 2.5 mL/min), and detection was on the basis of the UV absorption at 254 nm. 

Most of the properties change somewhat from one end to the other of industrial columns for effecting separations, so that the mass transfer coefficients likewise vary. Perhaps the property that has the most effect is the mass rate of flow which appears in the Reynolds number. Certainly it changes when there is a substantial transfer of material between the two phases in absorption or stripping and even under conditions of constant molal overflow in distillation processes, the mass rate of flow changes because of differences of the molecular weights of the substances being separated. As a practical expedient, however, mass transfer coefficients are evaluated at mean conditions in a column. 

H10. Hewitt, G. F., King, I., and Lovegrove, P. C., Brit. Chem. Eng. 8, 311 (1963). Hll. Hewitt, G. F., and Lovegrove, P. C., The application of the light-absorption technique to continuous film thickness recording in annular two-phase flow. At. Energy Res. Eslab. (Gl. Brit.) Harwell AERE-R 3953 (1962). 

Kenig EY, Kholpanov LP, Katysheva LI, Markish IH, Malyusov VA. Calculation of two-phase nonisothermal absorption in a liquid film in downward cocurrent flow. Theor Found Chem Eng 1985 19 97-102. 

The absorption and scattering of the y-rays in the presence of matter between the tracers and the detectors, such as human bones and body tissues in medical application as well as vessel walls and internals of a multi-phase flow system in non-medical application, will introduce... 

Reactive absorption is usually carried out in apparata providing a continuous flow of both contacting phases. Reactive absorption units can be best classified if one considers which of the phases is in a continuous form, and which is in a disperse form. Using this criterion, the classification of the reactive absorption equipment is represented in Tab. 9.2 (see Ref. [1]). 

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. 

F. Absorption, cocurrent downward flow, random packings, Reiss correlation Air-oxygen-water results correlated by k i/i = 0.lZEi5. Extended to other systems. = pressure loss in two-phase flow = lbf/ft2 ft AL [E] Based on oxygen transfer from water to air 77°F. Liquid film resistance controls. (Dwater 77°F = 2.4 x 10 5). Equation is dimensional. Data was for thin-walled polyethylene Raschig rings. Correlation also fit data for spheres. Fit 25%. See [122] for graph. k La = s"1 Dl = cm/s El = ft, lb Us ft3 Vi = superficial liquid velocity, ft/s [122] [130] p. 217... 

In absorption operations, the concentration in the gas phase is larger in comparison to the concentration in the liquid phase. Thus, the flow of mass transfer is from gas to liquid. The reverse is true in the case of stripping, and the direction of mass transfer is from liquid to gas. In other words, the liquid phase is said to be stripped of its solute component, decreasing the concentration of the solute in the liquid phase and increasing the concentration of the solute in the gas phase. In absorption, the solute is absorbed from the gas into the liquid, increasing the concentration of the solute in the liquid phase and, of course, decreasing the concentration of the solute in the gas phase. 

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