Vapor-liquid equilibrium flow diagrams

The McCabe-Thiele approach for a binary mixture can be described as follows. First, we take the vapor-liquid equilibrium diagram y/x plot). Then we draw the operating lines based on the mass balance for the liquid and the vapor phase. There is one operating line for the stripping section and one for the top (rectification or enriching) section. The assumption of (in each case) constant molar flows of liquid and vapor ensures strictly straight operating lines. 

The major difference between the McCabe-Thiele method and the Ponchon-Savarit method is that the liquid and vapor flow rates in the latter method are not assumed constant throughout the column. Because of this, the Ponchon-Savarit method is a more general and accurate method. Since the method is based on enthalpy values of fluid mixtures throughout the column, an enthalpy-concentration diagram is used in conjunction with a vapor-liquid equilibrium plot to determine the number of theoretical plates required for a specific separation. Units based on either moles (and mole fractions) or mass (and mass fractions) are acceptable as long as they are consistent. 

A portion of the McCabe-Thiele diagram for the simulation involving plug flow of vapor and dispersion flow of the liquid is shown in Fig. 13-55. For a nonequilibrium column these diagrams can only be constructed from the results of a computer simulation. Note that the triangles that represent the stages extend beyond the curve that represents the equilibrium line this is so because the efficiencies are greater than 100 percent. 

For binary flash distillation, the simultaneous procedure can be conveniently carried out on an enthalpy-composition diagram First calculate the feed enthalpy, hp, from Eq. t2-81 or Eq. (2=9b) then plot the feed point as shown on Figure 2-9 (see Problem 2-All. In the flash drum the feed separates into liquid and vapor in equilibrium Thus the isotherm through the feed point, which must be the T nun isotherm, gives the correct values for x and y. The flow rates, L and V, can be determined from the mass balances, Eqs. f2-51 and 2-61. or from a graphical mass balance. 

Figure 11.4-19. Partial condenser where the vapor and liquid leave in equilibrium (a) process flow diagram, (b) M cCabe-Thiele plot. 

Since both equilibrium and operating lines are straight, Eq. (17.27) rather than a graphical construction may be used. The material-balance diagram is shown in Fig. 18.23. No reboiler is needed, as the steam enters as a vapor. Also, the liquid flow in... 

Figure 2.2. McCabe-Thiele diagram for (a) ideal and (b) nonideal mixtures. 1, operating line at infinite reflux. 2, operating line at flnite more minimum reflux 3, operating line at minimum reflux 4, equilibrium line 5, composition of liquid and vapor flow that meet on tray 6, composition of liquid and vapor flow that leave from tray Xpi ch, point of tangential pinch.

Schematic of the three situations that are used for the assessment of metal chloride evaporation, (a) Vapor pressure of the gaseous metal chloride above solid or liquid metal chloride in a closed system (value used in Equation 13.23 and for determining T ). (b) Equilibrium partial pressure of pMe Cl in a closed system containing O2 and CI2 as gas phase and Me, Me Oj, and Me,.Cly as solid or liquid phases (value used for the establishment of the "static" quasi-stability diagram), (c) Mej.Cly transport rate in the gas boundary layer (metal consumption rate) as criterion for the amount of chlorine-induced corrosion in an open system with gas flow across the surface (value used for the establishment of the "dynamic" quasi-stability diagram).

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