Development of Accurate and Computation-Efficient Linearization Techniques for Modeling Absorption with Complex Chemical Reaction
Fiordalis, Andrew.
2017-04-18T11:38:53.163Z
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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 internal... read moreflows, 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 conditions.
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 - ID:
- 6m312184g
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