Information Technology Reference
In-Depth Information
Figure 5.6
Results of sensitivity study Mixer5s.
fraction of alcohols in stream 4 is tabulated. This example may be found at Examples/
mixer5s.
5.4 DESIGN SPECIFICATION
The features of the design function will be displayed by the modification of the example
mixer5s.bkp and is given at mixer5d.bkp. The Design-Spec is located under the setup
menu Flowsheeting Options, and when selected initiates the Design-Spec Data Browser.
Selection of the New button assigns an identifier to a design spec such as DS-1. The
key to implementing the design specification is to manipulate the feed, stream 2, so that
it can take on the required flow rate to achieve the required stream 4 specification. One
possibility is shown in Figure 5.7. The inclusion of stream 5, which has a larger flow
than what is required to meet the stream 4 specification (the flow rate is determined
from the sensitivity study), is fed to a multiply block. The design spec function will
manipulate the multiplier value, which will place the appropriate value into stream 2 to
satisfy the design specification. The implementation requires the definition of a Fortran
variable, in this case, XETOH, just like the setup in the Sensitivity study; however,
there are two other tabs in the Design-Spec Data Browser, the target value and an
acceptable tolerance, which must be selected and implemented. Figure 5.8 shows the
setup of the function to be solved:
f(factor)
=
xetoh
−
0
.
5
(5.2)
where
factor
is the multiplying factor of the block M1. The function is solved by
Aspen Plus's built-in secant method equation solver within a user-specified tolerance,
in this case 0.001. Results are shown in Figure 5.9.
