Modeling of the multicomponent rectification process considering the mobile control actions
Journal Title: Комп’ютерне моделювання: аналіз, управління, оптимізація - Year 2018, Vol 1, Issue 1
Abstract
The mathematical model of a separate rectifying column contact device is presented, which allows to investigate the effectiveness of mobile control actions when controlling static modes of multicomponent rectification processes. The developed mathematical model contains equations of general and component material balances, the heat balance equation and algorithms for calculating phase equilibrium conditions. Changes of the point of exposure – switching or redistribution of the flow or reflux – are accounted for in the model using additional independent variable. In order to ensure the applicability of the model for studies of continuous mobile control actions, a redistribution coefficient showing which part of the total feed stream is fed to the lower feeding plate, is additionally introduced. Flowrates and flow temperatures are chosen as independent variables for the calculation of the process, so that the intensity of the mobile actions is taken into account. The qualitative initial approximations of the unknown quantities are theoretically justified when calculating the column’s contact device from the bottom up, obtained on the basis of the equality of the enthalpies of the liquid flow that enters and leaves the plate. The solution of the system of nonlinear equations is to ensure the convergence of the balance dependencies, for which the interpolation method is chosen. It is proved that the application of this method allows finding a solution after the first iteration. An algorithm for calculating the contact device from the top down is developed. It includes two iteration cycles. The outer cycle is designed to find the value of the steam flow entering the plate by ensuring the convergence of the heat balance; in the internal cycle the material balance and the conditions of vapor-liquid equilibrium are jointly calculated. The distillation columns for separation of a binary methanol-water mixture and a multicomponent mixture – methyl tert-butyl ether (MTBE) products – were studied using the provided algorithmic support. The achievement of high accuracy of calculations by the minimum number of iterations is proved. At the same time, the number of components in the feed does not significantly affect the accuracy and speed of the developed algorithms.
Authors and Affiliations
А. Р. Шейкус, В. Я. Тришкін, І. Л. Левчук
Keywords
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