(709b) A Comparison of the Exergetic and Economic Optimization of the Catalytic Distillation, Based On a Rigorous Model. Case Study: ETBE Synthesis

Abstract

With finite natural resources and
high levels of consumption, due to the incredible growing speed of global
population, it is really important to think about sustainable development [1].
One of the highest consumption resources is energy, not in vain it is the main
constraint to reach sustainable development. There are many possible causes of
high energy consumption, perhaps
the most important one is the lack of industrial processes focused on energy
saving [2]. As a result, exergetic
optimization arises as an interesting alternative solution to mitigate this
problem. Exergy is well-known as the potential to
cause change in terms of available work and useful energy [3].

In this work a comparison between
an exergetic and economic optimization, of a
catalytic distillation (CD) process to obtain Ethyl Tert-butyl Ether (ETBE) is
presented. In order to achieve this, a Mixed Integer Non-Linear Programming
(MINLP) problem was formulated, aiming to optimize not only continuous
variables but integer ones too [4]. The strategy of solution was a
combination between the algorithms: Reduced Sequential Quadratic Programming
(r-SQP) and Simulated Annealing (SA). The exergetic
optimization was carried out through the minimization of the exergetic objective function, defined as the second-law
balance around the catalytic distillation column. The main purpose of this exergetic optimization was to reduce the exergy losses by optimizing design and operating variables
of the process [5]. In addition an economic optimization was presented and
reached by the minimization of the economic objective function, aiming to reduce
the costs of the process and increase its profitability.

In order to assure the correct performance of the column, both, exergetic and economic objective functions, were subjected
to a group of constraints, composed by: model constraints, operational
constraints, and hydraulic constraints. The first group of constraints was defined
by mass balances, energy balances, mole fraction summations, and phase
equilibrium (MESH equations); the second was established by the purity of the
product (ETBE) and the third ones avoids entrainment flooding,  down ?flow flooding and weeping ? dumpling problems.
Finally, a comparison between both, the results obtained with an economic optimization
and the results achieved in an exergetic optimization
are presented.

Bibliography

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[2] Gong Mei. Using Exergy and Optimization Models to Improve Industrial Energy
Systems towards Sustainability. Linkoping University.
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The minimum work requirement for distillation processes. Exergy,
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15-23. (2002)

[4] Gómez Jorge, Reneaume Jean-Michel, Roques Michel,Meyer Michel and Meyer Xuan. A ?MINLP? formulation for optimal
design of a catalytic distillation column based on a generic non equilibrium
model. Computer Aided Chemical
Engineering, 20, pages:  925-930 (2005)

[5] Kaiser Victor and Gourlia Jean-Paul. The Ideal-Column concept: applying Exergy to Distillation. Chem. Eng, 19, pages: 41-53 (1985)