An interval-based mixed integer nonlinear program (MINLP) superstructure model for the synthesis of heat exchange networks (HENS) is presented. The intervals of the superstructure are defined by the supply and target temperatures of either the hot or cold set of streams (including utilities). Heat can be exchanged between each hot and cold stream within each interval. This model can simultaneously trade-off energy, heat transfer area and number of units while at the same time generating a close to optimal network structure. Constraints on matches can easily be handled as well as streams with significantly different heat transfer coefficients. This model, unlike other simultaneous HEN synthesis models, avoids the need for the nonlinear mixing equations by mixing streams at equal temperatures. Multiple utilities can also easily be included in the superstructure. The model is applied to five example problems in the literature and it is shown to produce satisfactory results. A special feature of this method is that no particular initialisation procedure is required in order to obtain the optimal solution. (c) 2008 Published by Elsevier B.V. on behalf of The institution of Chemical Engineers.