Information Technology Reference
In-Depth Information
An overall energy balance, where
h
with a suitable subscript represents the enthalpy
of the feed, liquid, and vapor, respectively, and
Q
represents the heat added, given by
h
F
F
+
Q
−
h
L
L
−
h
V
V
=
0
(7.5)
completes the set of 2
n
+
1 equations.
The Flash2 block permits the specification of two of the four possibilities: flash tem-
perature, flash pressure, heat required, and the fraction of the feed vaporized, except the
combination
Q
and
V/F
. Various permutations of the specifications require other mod-
ifications of the equations and the list of unknowns. For example, if
V/F
is specified,
equation (7.5) is replaced by
V
F
j
=
1
v
j
j
=
1
f
j
=
specified
−
0
(7.6)
If
Q
, the heat added or removed, and the flash pressure are specified, the 2
n
com-
ponent flows and the flash temperature can be calculated. If the flash temperature and
pressure are specified, the sequence of the solution of the equations changes. Equations
(7.1) through (7.4) are solved simultaneously, after which equation (7.5) is solved
for
Q
.
An example of the use of a Flash2 block is given at Chapter Seven Examples/
Flash2Example. An important aspect of the setup, which is applicable to all simula-
tions, is the selection of the data bank from which the activity coefficient or equation
of state parameters were derived. Figure 7.2 shows that the binary interaction Wilson
Figure 7.2
Flash2 example Wilson parameters.
