Dividing wall columns

On the other hand, a large temperature difference between the reboiler and condenser in a DWG, and the heat transfer across the dividing wall, might cause some limitations in DWG application. Furthermore, conventional or other configurations would be better suited to separation of a mixture with non-ideal behavior (Long and Lee, 2012c). 

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Distillation. There is a large inventory of boiling liquid, sometimes under pressure, in a distillation column, both in the base and held up in the column. If a sequence of columns is involved, then, as discussed in Chap. 5, the sequence can be chosen to minimize the inventory of hazardous material. If all materials are equally hazardous, then choosing the sequence that tends to minimize the flow rate of nonkey components also will tend to minimize the inventory. Use of the dividing-wall column shown in Fig. 5.17c will reduce considerably the inventory relative to two simple columns. Dividing-wall columns are inherently safer than conventional arrangements because they lower not only the inventory but also the number of items of equipment and hence lower the potential for leaks. 

Use the divided wall column shown in Fig. 5.17c to reduce the inventory relative to two simple columns, and reduce the number of items of equipment and hence lower the potential for leaks. 

If complex distillation columns are being considered, then these also can bring about significant reductions in capital cost. The dividing-wall column shown in Fig. 5.17 not only requires typically 20 to 30 percent less energy than a conventional arrangement but also can be typically 30 percent lower in capital cost than a conventional two-column arrangement. ... 

Lestak F, Smith R and Dhole VR (1994) Heat Transfer Across the Wall of Dividing Wall Columns, Trans IChemE, 49 3127. 

Shultz MA, Stewart DG, Harris JM, Rosenblum SP, Shakur MS and O Brien DE (2002) Reduce Costs with Dividing-Wall Columns, Chem Eng Prog, May 64... 

M. Serra, A. Espufia, and L. Puigjaner. Control and optimization of the divided wall column. Chem. Eng. Process., 38 549-562, 1999. 

For certain applications, such as the separation of ternary mixtures, divided wall columns may be of interest, [9] which have shown to reduce the energy requirements and increase exergy efficiency. 

THERMALLY COUPLED SYSTEMS AND DIVIDING WALL COLUMNS... 

In recent years there has been significant interest in thermally coupled systems and dividing wall columns for ternary mixtures. In this subsection we discuss such column arrangements, their energy requirements, design and optimization methods, controllability and operability, experimental and industrial experience, and extension to more than three components. 

FIG. 13-69 Dividing wall columns equivalent to a) side rectifier configuration, h) side stripper configuration, (c) thermally coupled system. 

The minimum vapor flow for the entire thermally coupled system is flat over a wide range of P Pp < P < Pr. This is the reason why dividing wall columns usually work well without tight coutrol of the vapor or liquid spht betweeu both sides of the partitiou. The optimally designed fully thermally coupled system should operate with a fractional recovery of B in the top product of the prefractionator placed somewhere between points P and R. The transition spht P is located at one end of the optimal section PR, and it is not a recommended design point for normal operation because process disturbances may move the operating point outside the optimal section PR shown in Fig. 13-70. 

Experimental tests of dividing wall columns were carried out by Mutalib, Zeglam, and Smith [Trans. Inst. Chem. Eng. 76, 319 (1998)]. Today there are about 60 dividing wall columns in operation 42 are owned by BASF (Parkinson, CEP, p. 10, July 2005). 

FIG. 13-73 One possible dividing wall column for separation of a quaternary mixture. 

M.A. Schultz, D.G. Stewart, J.M. Harris, S.P. Rosenblum, M.S. Shakur, D.E. O Brien, 2002, Reduce costs with dividing-wall columns, Chem. Eng. Prog., 98, 64. 

M. Serra, M. Perrier, A. Espuna, L. Puigjaner, 2000, Study of the Divided Wall Column Controlabillity Influenee of the Design and Operation, Comput. Chem. Eng., vol. 24, p. 901 C. Tryantafillou, R. Smith, 1992, The Design and Optimisation of Fully Thermally Coupled Distillation Columns, TransIChemE, part A, Chem. Eng. Res. Des., vol. 70(A5), p. 118... 

The example illustrates the optimization of a divided wall column. In order to avoid increasing the complexities of the model, we rnrnrtnize the heat flow in the reboiler. A divided wall column can be simulated using the thermodynamically equivalent configuration Petlyuk arrangement[6] (see Figure 1)... 

From a simulation point of view, the two thermal couples introduce two recycles.. In this case, recycles introduces two complications 1. Good initial values are needed to converge the flowsheet, and 2. The time to converge the flowsheet considerably increases. It would be possible to decompose the system in individual columns and develop a kriging for each column, but the dimensionality of the kriging model would be larger, because we would have to deal with the recycles explicitly. Therefore, it is better to keep the divided wall column as an entity that can be efficiently substituted by a kriging metamodel. 

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