Targeting the integration of the utility system in an industrial site, introduces the problem of combined heat and power production and more specifically the optimal integration of the steam network. We present a mathematical tool that allows, using only the definition of the headers of the system, to target the integration of the steam network to satisfy the heat requirements at minimum cost while maximising the combined production of mechanical power. This tool allows to automatically adapt the steam flowrates when the hot utility is changed. It defines the optimal steam flowrates to be considered in the Heat Exchanger Network design of the processes or of the industrial site. Furthermore this technique may be used to compute the optimal configuration of power plants.