Thermally Coupled Systems and Dividing Wall Columns

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. 

Thermally Coupled Systems and Dividing Wall Columns. 13-60... 

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. 

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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