McCabe-Thiele diagrams absorption

Composition and temperature profiles are shown in Figures 14.13 and 14.14. In this example we see that the vapor and liquid temperatures are rather different. This result is quite typical of absorption columns indeed, it is possible for temperature differences to be over the order of 20 K. The McCabe-Thiele diagram is shown in Figure 14.15 and the component efficiencies in Figure 14.16. The efficiencies tend to be lower than in the distillation operations considered above. 

Dissolution of the HCl in water sets free a large amount of heat of absorption (approximately as high as the latent heat of evaporation of water). Hence, the liquid in the absorber reaches boiling temperature and, in turn, some water is evaporated by the absorption of HCl. Hence, the conditions in the absorber are quite similar to those in a distillation column. The equilibrium curve of a boiling HCI/H2O liquid is shown in the McCabe-Thiele diagram of Fig. 11.1-6. The presence of the inert gases only reduces the effective pressine of the HCI/H2O system. 

If the solute mole fraction in the feed yB,N+i very low, then transferring most or even all of the solute to the liquid will have very litde effect on the overall vapor flow rate V or on the overall liquid flow rate L. Thus, we can assume that L and V are both constant, and the operating line on a McCabe-Thiele diagram will be straight. Using the mass balance envelope around the top of the absorption column shown in Figure 12-1. we can write the solute B mass balance for constant L and V. 

Figure 12-3. McCabe-Thiele diagram for absorption. Example 12-1...

Figure 12-16. Co-current irreversible absorption (A) apparatus, (B) McCabe-Thiele diagram...

Figure 3.3.30 McCabe-Thiele diagram of an absorption process (adapted from Cmehling and Brehm, 1996) (Y and X refer to absorbed component A, i.e., to Va arid Xa in the text).

Figure 3.3.33 McCabe-Thiele diagram for absorption of CO2 in cold water (5 °C).

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