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h F F + Q h L 1 L 1
h L 2 L 2
h V V
= 0
(7.10)
The Flash3 block permits the specification of two of the four possibilities: flash tem-
perature, flash pressure, heat required, and the fraction of the feed vaporized. Various
permutations of the specifications require other modifications to the equations and the
list of unknowns. For example, if Q , the heat added/removed and the flash pressure
are specified, the 3 n component flows and the flash temperature can be calculated.
When specifying the block it is important to identify the key component in the
bottom takeoff (liquid 2) such that the block conforms with its physical behavior (i.e.,
the heaviest of the solvents should be selected). An example of the use of a Flash3
block is given at Examples/Flash3Example.
7.3 DECANTER BLOCK
Figure 7.8 is a graphical depiction of a Decanter block. The nomenclature used is as
follows: F represents the total feed flow, in moles/time; f i the flow of component i
in the feed, in moles/time; L 1 the total flow of the first liquid phase, in moles/time; l i
the flow of component i in the liquid, in moles/time; L 2 the total flow of the second
liquid phase, in moles/time; and l i the flow of component i in the liquid, in moles/time.
Including the decanter temperature T d and pressure P d results in 2 n + 2 independent
variables, where n is the number of components given the feed state. The variables
consist of the equilibrium temperature and the decanter pressure, the two total flows
L 1 and L 2 ,and2 (n 1 ) componential flows or, alternatively, 2 n componential flows,
excluding the total flows. Mole fractions are calculated from the independent variables
by an equation such as (7.1).
The applicable material balances are n componential equations, such as
f i l i
l i
=
0
(7.11)
Feed, F, f i
First Liquid, L 1 , l i 1
Decanter
Second Liquid, L 2 , l i 2
Figure 7.8
Decant model.
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