Evaluation of advanced technologies based on integration techniques - Application on dividing wall column

In order to separate a mixture into high purity products, Dividing Wall Distillation Columns (DWCs) have shown to be, in most cases, more convenient than using conventional distillation column sequence. In fact in DWCs the entire separation task occurs in one thermally coupled column shell hence reducing investement and operationg cost up to 60%. The DWC is a one column shell with a condensor at the top and a reboiler at the bottom. A wall located inside the shell divides a particular region of the column in two. Size and position of the wall among other elements will have an important effect on product purities strongly dependent on the relative volatility of the components. The assembly of the wall inside the shell represents the most critical step of fabrication, two methods for assembling the wall inside the shell are used, by welding or using stacked wall elements. In order to evaluate DWC using pinch analysis, the DWC has to be separated from the rest of the process GCC, plotting the CGCC and mirroring it to the rest of the process GCC which helps then indentify possible heat recovery between the Column and the background process and hence identify the most efficient way of placing intermediate heat exchangers for heat recovery. Modelling a DWC has proven to be a very difficult task. Using sensitivity analysis we were able to identify the key parameters infulencing the composition of our product streams. In the case of our design, the required high purties in the two stream products meaning 99% Butanol purity and 99% 2-Ethyl- Butanol purity have been reached. Unfortunatly specification to reach low purities in some components for both streams presented to be challenging and were not quite reached (less than 0.5% 2-Ethyl-Butanol was required for the Butanol product stream and 0.68% was reached, less than 0.5% of Hexanol in the 2-Ethyl Butanol product was required and 0.76% was reached). Using pinch analysis tthe MER requirement of both the conventional sequence and the DWC was identified. The CGCC and Carnot CGCC was plotted. The MER for the conventional distillation sequence was found to be 2060 [Kw] while for the DWC model 1809 [Kw]. The DWC has hence an MER 12% lower than what is required for the conventional sequence. However exergy losses in DWC (195 [Kw]) have shown to be larger than for the sequential distillation column (192 [Kw]). This is contrary to the results found in the literature, further improvement of the DWC have to be made.