Development of Accurate and Computation-Efficient Linearization Techniques for Modeling Absorption with Complex Chemical Reaction
Abstract: Design of
chemical absorption and stripping columns requires a model of interphase transport and
an algorithm for solving the governing algebraic and differential equations. Numerical
methods for calculating reaction-enhanced gas absorption rates are
computation-intensive. Combined with the iterative nature of design calculations for
absorber-stripper systems with countercurrent ... read moreinternal flows, this results in long
computation times. Prior to this work, the open literature included numerous reports of
linearization techniques for solving simple absorption/reaction problems. Few were
designed to treat systems characterized by multiple nonlinear differential equations,
and most made simplifying assumptions about reaction kinetics that limited their
applicability. The primary goals of this project were to substantially reduce
computation times for film theory-based simulations of steady-state absorption with
multiple reversible reactions, and do so without significant loss of accuracy. An added
incentive was to be able to simulate flue gas carbon dioxide capture via absorption in
aqueous solutions of blended amines. The primary goals were accomplished by improving
upon linearization techniques known to yield approximate but accurate closed-form
solutions to the nonlinear ordinary differential equations (ODEs) governing absorption
with one reaction. Closed-form solutions also facilitate elucidation of underlying
physicochemical phenomena. The first part of this thesis assesses the accuracy of two
published linearization schemes for modeling absorption with one reversible reaction.
One scheme, published in 1948 by Van Krevelen and Hoftijzer ("VKH"), is asymptotically
valid for thin liquid films; the other for thick liquid films. The VKH method proved
more accurate and versatile. The second part further validates the VKH linearization
scheme by applying it to simulate carbon dioxide absorption in solutions containing a
weak base or a weak acid, both of which catalyze CO2 hydrolysis. The VKH method proved
highly accurate; generally yielding absorption rates that differed by less than 1% from
exact values obtained via numerical analysis. The same method was then modified to
accurately linearize models of absorption with series and parallel reactions; and
eventually to simulate absorption with the complex reactions that mediate CO2 capture in
solutions of amine blends. The modified thin-film approximation proved easy to apply and
remarkably accurate for simulating industrially relevant operating
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Chemical and Biological Engineering.
Advisor: Jerry Meldon.
Committee: Kenneth Smith, Daniel Ryder, and Christoph Börgers.
Keywords: Chemical engineering, and Applied mathematics.read less
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