In two related papers we define the concept of structural flexlbility and apply it specifically to a class of heat integrated distillation processes. A process ts structurally feasible if the type of equipment it contains and how it is currently configured allow it to meet specified design requirements. It is structurally infeasible if it does not. Size of equipment is not at issue. The first paper develops a simple rnethod to permit an estimate to be made of a structural flexibility index for a heat integrated distillation process with a fixed configuration. Multieffect columns are permitted. This work shows, that processes that differ only in their heat integration can have very different indices for structural flexibility. The second paper presents a synthesis metfiodotogy to discover the heat integrated arrangements which maximize the structural flexibility index for the process, Only the simpler arrangements of such columns are considered where they are placed one above the other and without multieffecting. The papers present algorithms by example. Insights are stressed.