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variables. The mole fraction specification is an example. If x i represents the specified
mole fraction of component i in product stream j ,when l is the number of components,
then
f i
l k = 1 f k
x i
=
(3.8)
applies. An equation similar to (3.8) which describes the total flow specification is
l k = 1 f k
m = 1 F m
β j
=
(3.9)
where β j is the overall split fraction of stream j to the sum of flows of all p feeds, F m
represents the sum of the flows of all components in feed stream m ,and l represents
the number of components.
Note that the flows of the components may not be known a priori as in the Sep
block; therefore, the solution of a set of simultaneous equations in which the unknowns
are the individual component flows of product streams is required.
Like the Sep block, there is a tab, Outlet Flash, which enables a user to specify the
state of each outlet stream. A flash of each stream establishes the molar enthalpies and
facilitates calculation of the block energy balance.
3.3 SOME MANIPULATOR BLOCKS
Manipulators may be found in the Aspen Plus library under the tab Manipulators
(see Figure 3.7). The only manipulators considered here are the stream duplicator and
stream multiplier blocks.
3.3.1 Dupl Block
An example illustrating the solution of the same problem with both the Sep and Sep2
blocks is shown in Figure 3.8. Upon execution, streams 2 and 3 are identical to stream 1.
A feed of 100 lbmol/hr of methanol, 200 lbmol/hr of water, and 300 lbmol/hr of
ethanol is to be separated into an overhead product of 100 lbmol/hr with composition
0.95 mole fraction methanol and 0.04 mole fraction ethanol. The column, operating at
14.7 psi, is to be simulated twice, once with a Sep block and once with a Sep2 block.
A Duplicator block is to be used to feed both columns. Figures 3.9, 3.10, and 3.11
show the specifications for both separator blocks.
Figure 3.12 shows that identical results using the file Chapter Three Examples/
DuplicatorExample are obtained; however, the use of Sep would not be straightforward
if it were in the middle of a process where the feed was not known a priori.
Figure 3.7 Manipulators.
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