Heat integration stream splitting

Let s examine another alternative. For example, the first split might be sloppy , meaning that both distillate and bottoms contain a large amount of the intermediate component. This would imply two more splits, in total three simple columns, obviously uneconomical. In consequence, the second column should deliver all three components, including the intermediate as side-stream. This scheme seems unusual, but it may be in fact more economically when the two columns are heat-integrated. 

In the forward heat integration scheme (FHI) the top vapour of the prefractionator is used to heat the reboiler of the main column, and after condensation split in reflux and secondary feed for the main column (Fig. 11.19). The pressure in the prefractionator has to be high enough to ensure a temperature difference of minimum 10 K in the reboiler of the main column. In the reverse heat integration scheme (RHI) displayed in Fig. 11.20, the top vapour from the main column is used to drive the reboiler of the prefractionator. Note that this vapour is practically the pure component A. After condensation this stream is split in top product and reflux of the main column. 

However, the simulation of the performance for a heat exchanger with a known heat transfer surface area will demand an iterative split boundary solution approach, based on a guessed value of the temperature of one of the exit streams, as a starting point for the integration. 

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