This paper presents an improved mixed integer nonlinear programming (MINLP) model for heat integration of simultaneous synthesis of heat exchanger network with the process. The model can deal with nonconvex nonlinear objective and constraints which can be solved with genetic algorithm for MINLP problems. A heat integration synthesis example of a distillation sequence with a heat exhanger network is given to illustrate the capabilities of the improved simultaneous model which can be more realistically formulated as an MINLP problem.