Abstract The depth-first heuristic search for a process flowsheet proposed earlier by the authors is now extended to generate good (optimal) limiting process flowsheets. A look-back strategy follows the initial look-ahead procedure to eliminate the fragmentation of process tasks. Then an evolutionary search improves the process structure by eliminating the earlier dependence on the order of consideration of individual product goals followed by the implementation of by-product recycling to reduce raw material consumption. In recycling, preference is given either to those by-product streams requiring the smallest changes to the current flowsheet or to those which maximize the mass of recycled streams. Six look-back heuristics and three evolutionary rules are described. Examples of evolutionary structure generation are chosen from the production of multicomponent hydrocarbon mixtures and the production of monochlorodecane.