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Figure 31 Demonstration of the conditions for flashing for a binary system.
where T BP , T f ,and T DP are the bubble point of the feed mixture, flash
temperature, and dew point of the feed mixture, respectively; Z i and K i are
feed. The composition and equilibrium constant, respectively, for
component i.
3.9.3 The Flash Equation
The need to discuss flash calculation arises from the fact that it provides a
tool to determine the relative amounts of the separation products V (gas)
and L (oil) and their composition Y i and X i , respectively.
The flash equation is derived by material balance calculations as
presented in Figure 32. Two forms are presented:
Simple form:
Z i
X i ¼ ð29Þ
V
1 ð1 K i Þ
F
For given conditions of P and T, the solution of the equation to find
the value of X i is obtained by trial and error assuming a value for
V/F (take F unity), until the sum of [X i ] ¼ 1 is satisfied.
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.
