Design Considerations of a Simplified Multiple Dividing Wall Column Pilot Plant

This contribution elaborates the design considerations of a simplified version of a four-product multiple dividing wall column in pilot plant scale that will be built at Ulm University. This will be the first realization of a multiple dividing wall column worldwide. A detailed simulation approach, starting from the initialization by Vmin-method, is presented to obtain a feasible design of the column, taking into account the constraints of the operation within a university environment. The operating point was found by simulation studies, using the integrated optimization tool of AspenPlus© V10. It is shown that an NQ-curve can be applied on simplified multiple dividing wall columns. Based on the determined operating point, the thermodynamic and the fluid dynamic design of the pilot plant are discussed in detail. It is shown that the designed column can be operated to obtain all products with a purity of at least 98 mol%

Robust Initialization of Rigorous Process Simulations of Multiple Dividing Wall Columns via Vmin Diagrams

Dividing Wall Columns (DWCs) allow the separation of a ternary mixture in one column shell by applying a vertical partition wall, yielding a reduction of operational and capital costs of up to 30%. Multiple DWC (mDWC), the consequent advancement of standard DWC, makes use of more than one partitioning wall, allowing the separation of quaternary or even higher mixtures in one column shell accompanied by a further reduction of energy consumption. Since no dedicated models for these columns are available in commercial process simulators, thermodynamic consistent flowsheets have to be designed and implemented. The thermally fully coupled Petlyuk arrangement is one important example. However, the initial convergence of these substituting flowsheets is demanding, since a large number of meaningful initial guesses have to be provided. A promising method for generating these first estimates are minimum vapor (Vmin) diagrams. All internal flows can be extracted from these diagrams and used for robust initialization of the simulation. The goal of this work is to present the Vmin method in a comprehensive way in order to initialize mDWC simulations to predict the separation of four component mixtures. Additionally, the adaptation of the diagram to configurations different than Petlyuk arrangements for mDWC is evaluated and a systematic procedure to obtain them is presented. In the end, an example of a converging simulation is given, which was obtained with the values from the Vmin diagram

Correction: Ränger, L.-M., et al. Robust Initialization of Rigorous Process Simulations of Multiple Dividing Wall Columns via Vmin Diagrams. <i>ChemEngineering</i> 2018, <i>2</i>, 25

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Investigation of control structures for a four‐product laboratory multiple dividing‐wall column using dynamic simulation

Multiple dividing‐wall columns offer high investment and energy cost savings in distillation. To ensure these savings during operation, robust control structures must be applied. Three basically simple and practical control structures were investigated for a simplified multiple dividing‐wall column. All three control structures allow a robust control of the laboratory column. The dynamic behavior of a multiple dividing‐wall column pilot plant is evaluated by means of dynamic simulation. Three different control structures are developed or adapted from the literature, which are constrained by the actual design features of the pilot plant column. Since in the present case the design of the column was chosen such that very different mixtures can be separated, it cannot be optimally designed for each of these potential mixtures. Rather, the design focused on the flexibility of the plant. All three investigated control structures were tested on feed flow rate and feed composition disturbance and allowed a robust control of the pilot plant, whereby control structure 2 is slightly better than others in terms of steady‐state deviations and less pronounced fluctuations during the dynamic phase. The transferability of control structure 2 to other variants of multiple dividing‐wall columns is easily possible