Trays mass transfer analysis

Use mass transfer analysis to determine tray efficiency of binary systems... 

Example 4.9 Entropy production in separation process Distillation Distillation columns generally operate far from their thermodynamically optimum conditions. In absorption, desorption, membrane separation, and rectification, the major irreversibility is due to mass transfer. The analysis of a sieve tray distillation column reveals that the irreversibility on the tray is mostly due to bubble-liquid interaction on the tray, and mass transfer is the largest contributor to the irreversibility. 

Mora and Bugarel (1976) used the theory of irreversible thermodynamics to analyze interphase mass transfer on a distillation tray. Compare their treatment with the analysis in Chapters 12 and 13 which is more general, theirs or that given in this book Write up your comparison in the form of a paper to Entropie. 

A major assumption made in the column models of Chapters 3 through 13 was the equilibrium stage. Tray hydraulics provides additional information essential for applying mass transfer theories to evaluate the column performance with a rate-based approach. This analysis provides a basis for calculating the tray efficiency associated with an equilibrium stage. The topics of rate-based analysis and tray efficiency are also discussed in this chapter. 

This rate-based analysis of trayed columns gives an estimate of the number of overall gas phase mass transfer units corresponding to a given tray. The practical application of this analysis is to provide a means for estimating the tray Murphree vapor efficiency discussed in Section 14.3. 

Unlike the previous analysis (38), the boundary conditions were properly treated as dependent variables found by taking account of film and bulk reaction balanced with the input and output flows and mass transfer fluxes across a tray. The approach (39) involved perfect backmixing of the liquid, but with provision of the possibility of axial mixing in the gas phase being represented by staging of backmixed zones. In practise though, the authors claimed that a single gas zone was sufficiently accurate. 

Size the Distillation Column. This includes the hydraulic analysis to establish operating ranges, pressure drop, and mass transfer efficiency. The result is a set of dimensions, including column diameter and height, number of actual trays (or height of packed bed), details of internal devices, and profiles of temperature and pressure. 

Liapis, A. 1., Bruttini, R 2008. Exergy analysis of freeze drying of pharmaceuticals in vials on trays. nt. J. Heat Mass Transfer 51(15-16) 3854-3868. 

The alternative to differential extraction is staged extraction. This frequently uses the mixer-settlers shown in Fig. 14.2-l(d), but it can also use column extractors containing the equivalent of sieve trays. In these cases, extraction is analyzed using the same concepts of equilibrium stages used in the analysis of distillation. Such an equilibrium stage analysis depends on mass transfer only tangentially. As a result, we will quickly review the analysis and then discuss how mass transfer is involved. 

Often recovery of the separated molecules is necessary for further analysis or sequencing (chapters 6 and 7). For this, a process called electroblotting is commonly employed. A polymeric membrane is placed over the gel and the molecules are transferred onto this membrane by an applied electric field. Sequencing reactions can be performed directly on the membrane. Furthermore, the membrane can be placed directly onto the sample tray of a MALDI-MS (section 4.1) for mass analysis. 

Force analysis on the ith concentrated mass is shown in Figure 2. Since concentrated mass consists of mass of column and mass of residual medium on plate, some existing literatures only the inertia force (maofyi) generated by mass of column is considered for tray column calculation based on transfer matrix in some existing literatures, but eccentric inertia force (mbco ei) generated by fluidity of medium is also taken into consideration in the Article. 

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