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Title: Algorithm synthesis for modelling cyclic processes : rapid pressure swing adsorption
Author: Choong, T. S. Y.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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In this dissertation, an algorithm for modelling cyclic processes is designed. In principle, the algorithm could be used for any cyclic processes. Air separation using rapid pressure swing adsorption (RPSA) is used as an illustration of the algorithm. The first step in the algorithm is to identify physical phenomena to be included in or omitted from a model. The effect of the external fluid film resistance at the surface of an adsorbent particle is studied in detail using a linear driving force model. A simple method that could be used to determine quickly the importance of film resistance in cyclic processes is developed. For the RPSA cases considered, it transpires that the film resistance could be neglected. The use of concentrations as dependent variables and of Danckwerts boundary conditions (BCs) in an axially dispersed plug flow (ADPF) model for the modelling of RPSA are shown to violate the conservation of mass. To conserve mass in an ADPF model, we recommend adopting mole fractions as dependent variables and using modified BCs. The modified BCs advocated preserve the original argument of Danckwerts and are also physically sound. The RPSA models are then solved numerically using the method of orthogonal collocation. An improved method that calculates accurately quantities involving time integrals, and also minimises the number of decision parameters that need to be made by the users of the computer programs, is introduced. A major achievement of this work is the development of two novel algorithm features for the transient simulation of cyclic processes that exhibit cyclic steady state (CSS). The first feature of the algorithm is an a priori rational stopping criterion to determine the CSS unambiguously. The stopping criterion ensures that neither is the progress towards CSS truncated prematurely nor is computer time wasted by simulating an unnecessarily large number of cycles. The second feature of the algorithm is a reduction of the number of cycles required to reach the CSS while ensuring that the CSS is certainly determined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available