(168e) Synthesis Of Optimal Distillation Networks | AIChE

(168e) Synthesis Of Optimal Distillation Networks



The synthesis of optimal distillation networks for a given application is a challenging problem in process design. One difficulty is that the space of all possible configurations for a given multicomponent feed is combinatorially large, with a large fraction of these configurations using more columns than necessary, without compensating with better energy consumption. Our prior work in this area classifies and reduces the search space to a set of basic configurations, all of which use (n-1) columns for a given n-component feed. We have shown that most of these basic configurations are more efficient than the sharp-split configurations commonly used in industry, when considered on the basis of first law heat duty alone. A source of design complexity still remains unsolved in that while the overall heat duty can be reduced for a distillation network, more heating or cooling might be needed at temperatures farther removed from ambient temperatures than in the original network, and therefore be more expensive on a second law basis. In this work, we present a framework to deal with the effect of utility temperatures and heat duties on the optimal distillation configuration. We present case studies where a large saving in overall heat duty was achieved, but the new design required significantly more cooling at the lowest temperature, affecting the cost. We show how this can be taken into account both by minimizing a cost function that takes the nature of the utility into account, as well as by calculating the thermodynamic exergy loss. We present ways to maintain the saving in heat duty while reducing the exergy loss.