(516a) An Approach Considering Both Operation Stability and System's Hopf Bifurcations to Chemical Process Design

In
order to consider the inherent safety of chemical processes, researchers
proposed many methods and strategies, many quantitative indices have been
developed to describe the potential hazard and dangerous of different reaction
routes and reactants. In authors' previous paper[1] an
integrated quantitative index considering both speed to return to steady state
point and capability of resistance to disturbances is introduced. In the other
hand, oscillation behavior was observed in both experiment and mathematical
simulation in some chemical processes[2-10], in which the concentration of
feedstock and product oscillation occur under certain
operation conditions. In order to design a more stable process, these potential
oscillations should be avoided. And it is reported that the oscillation was
caused by the existence of Hopf bifurcations in systems[2, 11]. Since
all Hopf singularity points can be identified by using mathematic calculation
under given operation condition range, consequently, the Hopf singularity point
range can be determined. This paper proposed a design approach to chemical process design, considering both operation point
stability and systems Hopf singularity points to improve the process stability
and avoid potential oscillation in process. The detailed steps of this approach
are described as follows:

(1)    Solve the steady state solution of the dynamic model of chemical
process.

(2)    Judge the stability of these solutions and divide the solution
curve into parts with different stabilities (stable and unstable).

(3)    Calculate the integrated quantitative stability index of the process
system

(4)    Calculate Hopf points under the possible operation condition
range.

(5)    Formulate
a multi-objective optimization problem for the process design in which the
quantitative stability index together with the economic index are considered as
objectives and the Hopf points ranges are involved as constraints,

(6)    Obtain
the optimal operation conditions.

The proposed
approach is applied to a continuous fermentation process and a multi-objective optimization problem considering
both economic and stability factors were conducted, and the Hopf points
ranges are considered as constraints at the same time in this optimization
problem. After calculation, a Pareto set is obtained.
The optimization results provide information that is very useful
for guiding process design and operation. From this study, conclusions can be
drawn:

(1)      Quantitative
stability index is useful in multi-objective optimization problem when
stability was considered as one of the objectives.

(2)      Hopf
singularity points range can be considered as constraints in optimal process
design problems to avoid the potential oscillation in process.

References:

1.            Wang,
H., et al., An integrated quantitative index of stable steady state points
in chemical process design, in Proceedings of the 11th International
Symposium on Process Systems Engineering, I.A. Karimi and R. Srinivasan,
Editors. 2012, Elsevier B.V.: Singapore

2.           Sridhar,
L.N., Elimination of Oscillations in Fermentation Processes. AIChE
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3.            Paz
Astudillo, I.C. and C.A. Cardona Alzate, Importance of stability study of
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F.W., W.A. Anderson, and M. Moo-Young, Ethanol fermentation technologies
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8.            Sprenger,
G.A., Carbohydrate metabolism in Zymomonas mobilis: a catabolic highway with
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9.            Ghommidh,
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10.          Jöbses,
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11.          Kuznetsov,
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* Corresponding author. Tel.: +86
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E-mail address: dcecbz@tsinghua.edu.cn  (Bingzhen
Chen)