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Figure 2.6 Material balances, (a) Rectifying section; (b) stripping section; (c) overall.

Figure 2.6 Material balances, (a) Rectifying section; (b) stripping section; (c) overall.

VR + l = K + D (2.5) Similarly, a component balance gives

V.+1y,+1 = + Dxd (2.6) Instead of an energy balance, the McCabe-Thiele method assumes

Figure 2.6 (Continued)

Figure 2.6 (Continued)

constant molar overflow (Sec. 2.2.2). Mathematically, this assumption means

These equations simplify Eq. (2.6) to y„ + l = yXn + -xD (2.9)

A similar derivation for the stripping section (Fig. 2.66) gives

Equations (2.9) and (2.10) are basic building blocks for McCabe-Thiele diagrams. They are discussed further in Sec. 2.2.3. Equations (2.7) and (2.8) also simplify Eq. (2.5) to

V = L + D (2.11) A similar derivation for the stripping section gives

V =L' - B (2.12) An overall column mass balance (Fig. 2.6c) gives

Combining Eqs. (2,11), (2.12), and (2.13) gives a relationship that can also be derived from a feed stage mass balance (Fig. 2.6c)

An overall column component balance gives

The definition of reflux ratio is

Similarly, the stripping ratio is

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