An essential component of the utility systems which support the operation of most chemical plants involves steam turbine networks. Their design and operation affects the overall efficiency of the process and the cogeneration potential of the plant. This paper proposes a new conceptual tool for industrial steam turbine networks, which can be used to analyse and optimise their operation and design. Basic concepts are first exploited towards a general representation for the operational region of the entire network. The representation is then partitioned into domains of optimality that provide the optimum operation mode for the network under specific demands. The new tool, termed as Hardware Composites, involves a graphical construction which is explained along with the principles and the rules that underlie the partitioning. The development of the Hardware Composites is illustrated through several example problems with different numbers and types of turbines.;Their use as an analysis and optimisation tool can be extended to large number of applications in coordination with other technologies. Application areas where the Hardware Composites can be involved are presented in Part II where comparisons with alternative technologies in the form of MINLP are included.