Convection-diffusion models for distillation columns : application to estimation and control of cryogenic air separation processes

Abstract : This thesis addresses the problem of modeling the composition profiles dynamics inside cryogenic distillation columns, for control applications. We obtain a non-linear convection-diffusion model from the reduction of a singularly perturbed mass-balances model. In the control theory framework, we consider the stability of the resulting composition profiles and their observability. From the process viewpoint, we express the novelty of our model in terms of operating-conditions dependent packing efficiency. The model is validated against real dynamic plant data for a binary separation case. On a more complex, ternary separation columns cascade, the model shows highly sensitive to reflux rate estimation errors. Result adapted from the field of chromatography allows us to interpret this sensitivity in terms of erroneous coherent composition waves speeds. In parallel, we also propose and test a simple transfer functions model (based on static gains and pure delays only) for small composition dynamics, which explicitly depends on measurable or observable process data.
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Stéphane Dudret. Convection-diffusion models for distillation columns : application to estimation and control of cryogenic air separation processes. General Mathematics [math.GM]. Ecole Nationale Supérieure des Mines de Paris, 2013. English. ⟨NNT : 2013ENMP0018⟩. ⟨pastel-00874677⟩

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