Information Technology Reference
In-Depth Information
Figure 3.4
Separators.
3.2.1 Sep Block
When the Sep model is executed, all the feed streams are mixed and the combined flow
rate, composition, and molar enthalpy is computed. The block permits the assignment
of the flow rates or componential split fraction of each component in each of the
n
−
1
product streams, based on the combined feeds. The composition of the
n
th stream is
calculated by the overall material balance. An example of a Sep block is shown in
Figure 3.5.
As part of the block's input specifications, 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.
Since Sep is a typical sequential modular block, for an
n
-component,
m
-product
stream configuration, with the temperature and pressure of the feeds and products
specified, a degree-of-freedom analysis shows that for a material-balance-only appli-
cation there are
nm
unknowns. If
n(m
−
1
)
products are associated with a specification
such as the fraction of the sum of the feeds of a component, to exit in a particular
stream,
n
unknowns remain to be calculated by a material balance; thus, the com-
position is calculable for all streams. For an energy balance calculation there is one
additional unknown per product stream: the molar enthalpy. Since the composition
temperature and pressure of each stream is known at the conclusion of the material
balance calculations, an adiabatic flash produces the molar enthalpy of all streams, and
an overall energy balance can be performed.
If
f
i
represents the quantity of component
i
in feed stream
k
, the amount of
component
i
entering the block,
F
i
,isgivenby
l
f
i
F
i
=
(3.6)
k
=
1
SEP
2
1
3
4
Figure 3.5
Sep block.
