The article presents a partial synthesis of progress in control thermodynamics by laying out the main results as a sequence of principles. We state and discuss nine general principles (0-8) for finding bounds on the effectiveness of energy conversion in finite-time.
In this paper multiplicity in heterogeneous azeotropic distillation sequences is studied. Two
sequences, suitable for ethanol dehydration, are treated as sample problems and compared. As
a basis the ∞/∞ analysis method (Petlyuk, F. B.; Avet'yan, V. S. Theor.
Found. Chem. Eng.
1971,
5, 499−507; Bekiaris, N.; Meski, G. A.; Morari, M. Ind. Eng. Chem. Res.
1993, 32, 2023−2038),
which assumes infinite reflux rate and infinite number of trays, is extended to and applied on
heterogeneous azeotropic distillation sequences in order to determine steady-state bifurcation
diagrams from thermodynamic considerations. The bifurcation diagrams are very different for
the two sequences despite their similar structures. In particular, it is predicted that output
multiplicity of the single azeotropic column, as recently experimentally verified by Müller and
Marquardt (Ind. Eng. Chem. Res.
1997a, 36, 5410−5418), can induce output multiplicity of one
sequence. It is further predicted that output multiplicity can be avoided by the choice of a
different sequence structure. Furthermore, ∞/∞ analysis predicts state multiplicity in both
heterogeneous azeotropic distillation sequences. This phenomenon in the ∞/∞ case is also
analyzed and it is shown that state multiplicity in heterogeneous distillation sequences can be
induced either by the corresponding single column behavior as reported by Gani and Jørgensen
(Comput. Chem. Eng.
1994, 18, 55) or by closing the sequence. The predicted bifurcation
diagrams and multiplicities are substantiated through rigorous simulation of column sequences
operating at finite reflux and with a finite number of stages. Finally, the implications of the
thermodynamics including the liquid−liquid plait point position are demonstrated to be important
for obtaining reliable predictions.
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