| A new methodology for the synthesis of general separation flowsheet structures is presented. The methodology is based on the identification of the process' characteristic pinch states, and the simultaneous optimization of the mass and energy flows between them. Infinite countercurrent cascades are the chosen stream contacting devices, forming all the mass exchange operations in the possible structures. The use of countercurrent cascades limits the methodology to equilibrium-based separation technologies, such as distillation, absorption, extraction, and adsorption.;The solution of the overall synthesis problem is performed using a decomposition strategy: the master problem is the identification of the pinch state nodes, while the optimization of the mass and energy flows between the nodes is a subproblem. Starting with a standard grid of state nodes, the optimal flows are calculated by solving a cost minimization problem formulated as a linear program. Intermediate solutions of the optimal flows problem, for a fixed set of state nodes, allows for the modification of the grid of state nodes used following a defined heuristic procedure. Alternating solution of the flow optimization subproblem and modification of the grid of state nodes is performed, until defined end criteria are met.;A number of mathematical models of the behavior of pinched countercurrent contactors under different simplification assumptions are formulated. These models are investigated and implemented in the synthesis methodology.;The usefulness of the methodology is illustrated by several case examples. These include ethane purification from a refinery off-gas stream, a simplified Rectisol process, and cryogenic air separation. |
