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Control and simulation studies for a multicomponent batch packed distillation column

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2007
Ceylan, Hatice
During the last decades, batch distillation is preferably used with an increasing demand over continuous one, to separate fine chemicals in chemical and petroleum industries, due to its advantages like, flexibility and high product purity. Consequently, packed distillation columns, with newly generated packing materials, are advantageous compared to plate columns because of their smaller holdups, resistivity to corrosive materials and their higher separation efficiencies. Also, in many industrial applications, mathematical models of distillation systems are frequently used in order to design effective control systems, to train operating personnel and to handle fault diagnostics. Thus, the main objective of this study is to develop a mathematical model for a multicomponent batch distillation column, which is used to separate mixtures at low operating pressures, packed with random packing materials. In multicomponent batch packed distillation, operation with optimum reflux ratio profile is important for efficiency to maximize the amount of the distillate with a specified concentration, for a given time. Therefore, it is also aimed to find the optimum reflux ratio profile for the multicomponent batch packed distillation column. A simulation algorithm is written with the aid of MATLAB and FORTRAN programming languages by taking into account pressure drop and variation of physical properties. The selected incremental bed height, Δz, to be used in the simulation program has an effect on the accuracy of the results. This is analyzed and the optimal incremental height is found to be 3.5 cm for a 1.5m bed height. The change in distillate compositions with a given constant reflux ratio is found to be similar with those of previous studies. The simulation code is also used to obtain responses in distillate compositions for different reflux ratios, condenser holdups and reboiler duties and compared with similar studies found from literature and found to be adequate. Finally, experiments are conducted to verify simulation algorithm by using a lab-scale packed distillation column for the separation of a polar mixture of ethanol and water. It is observed that, there is a good agreement between the experimental and simulation results. After the verification of dynamic model, optimum operation policy to maximize product amount is investigated numerically by using capacity factor approach. The column is operated with and without recycling of the holdups of the slop cut tanks, in order to examine the effect of recycling on capacity factor, CAP. It is observed that, recycling of the molar holdups of the slop cut tanks is resulted in a 28% increase in the separation efficiency.