Information Technology Reference
In-Depth Information
where
l
is the number of feed streams. If the split fraction of a particular component
i
, in stream
j
,
j
i
, is given, the quantity of component
i
leaving the block in stream
j
,
α
S
i
,isgivenby
S
i
j
i
F
i
= α
(3.7)
Alternatively, the quantity of component
i
leaving the block in stream
j
,
S
i
,canbe
specified directly. These variables in the equations do not depend on each other, and
thus the solution, where not uniquely specified as in equation (3.7), is direct.
3.2.2 Sep2 Block
The Sep2 block is designed to model a simple two-product separator such as a dis-
tillation or extraction process. Like the Sep model, when a Sep2 block is executed,
all the feed streams are mixed and the combined flow rate, composition, and molar
enthalpy is computed. For
n
product streams, the block permits assignment of the
flow rates or componential split fraction of each component in each product stream of
n
−
1 streams, based on the combined feeds. The Sep2 model, however, provides more
flexibility in specification than that of the Sep block. The additional specs allowed are
overall stream split, that is, the ratio of flow of a product stream to the sum of the flows
of the feed streams, and the mole or mass fraction of a component in a product stream.
The composition of the
n
th stream is calculated by the overall material balance. An
example of a Sep2 block is shown in Figure 3.6.
Unlike the Sep block, there is interdependency between some of the block specifica-
tions. Equations (3.6) and (3.7) describe the specifications of the Sep block that apply
to the Sep2 block, but the other Sep2 specifications involve interaction between the
2
SEP2
1
3
Figure 3.6
Sep2 block.
