Equilibrium-stage processes

Mass-transfer calculations, such as the analysis or design of separation units, can be solved by two distinctly different methods, based on either the concept of (1) Equilibrium stage processes or (2) Diffusional rate processes. 

The choice of method depends on the kind of equipment in which the operation is carried out. Distillation, leaching and sometimes liquid extraction, are performed in equipment such as mixed-settler trains, diffusional batteries or plate towers, which contain a series of discrete processing units, and problems in these areas are commonly solved by equilibrium stage calculations. Gas absorption and other operations which are carried out in packed towers or similar equipment, are usually handled using the concept of a diffusional process. 

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Smith, B. D., "Design of Equilibrium Stage Processes," McGraw-Hill, New York (1963). 

The results of the analyses for all the various elements commonly encountered in distillation processes are summarized in Table 13-5. Details of the analyses are given by Smith (Design of Equilibrium Stage Processes, McGraw-Hul, New York, 1967) and in a somewhat different form by Henley and Seader (op. cit.). 

FIG. 14-23 Stable operating region, plates. (Smith, Design of Equilibrium Stage Processes, McGraw-Hill, New Yoik, 1963.)... 

For bubble caps, Ki is the drop through the slots and Ko is the drop through the riser, reversal, and annular areas. Equations for evaluating these terms for various bubble-cap designs are given by BoUes (in chap. 14 of Smith, Equilibrium Stage Processes, McGraw-HiU, New York, 1963), or may be found in previous editions of this handbook. 

Figure 8-5. Chloroform (l)-methanol (2) system at 50°C. Azeotrope formed by positive deviations from Raoult s Law (dashed lines). Data of Sesonke, dissertation, University of Delaware, used by permission. Smith, B.D., Design of Equilibrium Stage Processes, McGraw-Hill New York, (1963), all rights reserved.

Figure 8-129. Discharge coefficients for vapor flow, sieve trays. Used by permission, Smith, B. O., Design of Equilibrium Stage Processes, Chapter 15, by J. R. Fair, McGraw-Hill Book Co. (1963) data from I. Liebson, R. E. Kelley, and L. A. Bullington, Petroleum Refiner, V. 36 (2), Feb. (1957) p. 127 V. 36 (3), (1957) pg. 288, all rights reserved.

Smith, B. D. and Brinkley, W. K. (1960) AIChE Jl 6, 446. General short-cut equation for equilibrium stage processes. 

Sherwood, T. K. and Pigford, R. L. Absorption and Extraction (McGraw-Hill Book Co., New York, 1952). Sherwood, T. K., Pigford, R. L. and Wilke, C. R. Mass Transfer (McGraw-Hill Book Co., New York, 1975). Smith, B. D. Design of Equilibrium Stage Processes (McGraw-Hill Book Co., New York, 1963). 

E.J. Henley and J.D. Seader, Equilibrium-Stage Processes in Chemical Engineering, Wiley, New York, 1981. 

In the following, the principles of mass-transfer separation processes will be outlined first. Details of mass-transfer calculations will be introduced next and examples will be given of both equilibrium-stage processes and diffusional rate processes. The chapter will then conclude with a detailed discussion of the two single most applied mass-transfer processes in the chemical industries, namely distillation and absorption. 

In most equilibrium stage processes, the general energy balance can be simplified by neglecting potential energy and kinetic energy. If, in addition, the process is workless and adiabatic, a simple enthalpy balance applies ... 

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