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Figure 2.5
Example of properties analysis specification PT-1.
analysis to be generated is specified. For example, a vapor-liquid equilibrium prop-
erties specification, labeled PT-1, is shown in Figure 2.5, where points along a flash
curve are chosen in anticipation of preparing a
T
-
x
-
y
diagram. Aspen Plus requires
the specification of composition, even though it is not needed for this example. Note
the appearance of the adjusted variable range display shown in Figure 2.6. Prior to
completing the analysis input, Aspen Plus prompts the user to define which proper-
ties are required. These are defined in a Prop-Set, with an example labeled PS-1, and
displayed in Figure 2.7, where the properties required are the bubble and dew points
at 14.7 psi as a function of composition. It is possible for several property analyses
and property sets to be executed with one Aspen Plus run, and a display is provided
to associate a Prop-Set with an analysis. An example of such an association is shown
in Figure 2.8. The results are the tabular display shown in Figure 2.9, which can be
plotted with Aspen Plus's Plot function, as shown in Figure 2.10.
Another example of a Prop-Set, PT-2, which deals with an analysis of temperature-
dependent properties, is shown in Figure 2.11. The tab Qualifiers is used to define the
components, the phases, and other specifications for which properties are desired with
the associated Prop-Set PS-2. Tabular results are shown in Figure 2.12. A property
analysis example may be found at Chapter Two Examples/property analysis example.
2.3 PROPERTY ESTIMATION
There are many methods for estimating pure component properties such as the critical
pressure. When using Aspen Plus to estimate such values, a user is offered a choice
of methods, most of which are described by Poling et al. (2000), and in some cases,
in an earlier edition of the same topic. As an example, Joback's method for estimating
