In this work, process intensification is identified as a process synthesis activity seeking significant improvements over traditional designs. The Infinite-DimEnsionAl State-space (IDEAS) conceptual framework is proposed as a systematic process intensification tool, which can identify intensified process designs, and assess fundamental performance limitations of networks of technologies under consideration. The synthesis of intensified flowsheets, in an energy efficiency sense, is pursued through the simultaneous synthesis of the flowsheet and its heat exchange network. The use, for the first time in process synthesis, of atomic balance, and Gibbs free energy minimization based equilibrium reactor models, enables a broad state-space search for process intensification opportunities, even by low dimensional, feasible, linear programming, IDEAS approximations. Application of the proposed method to natural gas reforming based hydrogen production, identifies intensified process designs featuring hot utility costs that can be lower by over an order of magnitude to those of traditional designs. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.