The concept of optimization of operating and design parameters of the regenerative air turbine cogeneration (RATC) system is proposed. To determine the energy efficiency indicators of this system, its thermodynamic analysis was performed. At the same time, it is shown that it is not correct to search for the optimal parameters of such a system only by energy indicators, and modern thermoeconomic methods should be more actively involved in pre-design practice, which allow a comprehensive evaluation of the efficiency and economy of the energy-technological system as a whole and its individual elements. Therefore, on the basis of the data obtained during the thermodynamic analysis, exergy destruction and losses in the main system elements were calculated. Then, using the structural-variant method in combination with the graphical apparatus of C-curves, the pre-project thermoeconomic optimization of the RATC system was performed. This made it possible to choose the optimal operating and design parameters of the system and determine the minimum cost for its creation and operation throughout the entire life cycle, taking into account the thermodynamic perfection of the main system elements. Each variable operating mode parameter of the system serves as a kind of navigator when searching for the option of system parameters that is optimal in terms of energy and economic indicators, which is accompanied by graphic visualization. Therefore, the proposed approach makes the optimization of the system being designed convenient and clear. It can be used in the optimal design of various types of thermal transformers and other energy-technological systems.