The issue of energy has emerged as one of the greatest challenges facing the mankind. In the industrial perspective, the development of site utility system (generally CHP systems) for the generation and management of utilities provide a great potential source for energy savings. However, a master/slave relationship usually governs this kind of system; the management of such type of industrial units is carried out in three sequential steps: scheduling of the production plant, estimation of the utility needs and finally scheduling of the CHP based utility system are three tasks performed . To improve the decision-making process, this contribution proposes an integrated approach which carries out simultaneous and consistent scheduling of batch production plant and site utility system. The proposed methodology relies on discrete time modelling and uses Mixed Integer Linear Programming (MILP). Moreover, to permit an efficient and generic formulation of various kinds of industrial problems, an extension of the existing framework RTN is developed: the ERTN (Extended Resource Task Network (ERTN). The results show that the integrated approach leads to better synchronization between production plant and site utility system. Hence, the integrated approach leads to significant reduction in energy costs and decrease in harmful gas emissions.