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c. Solve the complete process. Take care to place starting values for the tear streams
estimated from the segments.
Workshop 4.5
Search Aspen Plus Help for adding a stream table to your results.
Replace all simple boxes with suitable icons. Place a stream table on your flowsheet
graphic. Place suitable text labels on your flowsheet.
Workshop Notes
Workshop 4.1
a. Since this is a material-balance-only approach, no rigorous blocks are used, and
all internal calculations are by simple blocks, the type of thermodynamics chosen
is arbitrary since it is not used in the simulation. If this problem were solved with
rigorous blocks such as Radfrac and Decant, rigorous thermodynamics would be
required.
b. The Aspen Plus execution does not converge. You may try the following:
Increase the number of iterations. Check the overall material balance.
Check the performance of each block.
Check that no unrealistic specifications were used.
Change the tear streams.
Change the convergence method used.
Workshop 4.2
Four-2.bkp uses 100 Wegstein iterations and it, too, fails to converge.
This looks like a situation where Wegstein may not work or the tear streams Aspen
chose were not suitable. Examining this process from a chemical engineering point of
view, the composition of the streams that are easiest to estimate are those leaving the
decanter: streams C and F.
Workshop 4.3
Streams C and F may be initialized with unconverged results from
Four-2.bkp. As an alternative, the compositions of streams C and F can be estimated
from a phase diagram of the ethanol - water -cyclohexane system.
a. Four-3.bkp using Wegstein's method again fails to converge. This problem is not
suitable for Wegstein convergence, even with 100 iterations.
b. Four-3n.bkp using Newton's method converges easily with only a few iterations.
Workshop 4.4
a. Since Aspen Plus deals mostly with solids in a special way (an advanced appli-
cation) and the states considered are either vapor or liquid, there is no specific
provision for dealing with solids dissolved or suspended in a solution. Further-
more, for a situation in which there are no specific database components for
unidentified by-products of reactions, one must assure that these are accounted
for on a mass basis, and that their behavior in rigorous blocks is accounted for
in some way. For example, it is safe to assume that the unknown vapor pressure
