The imperfection of the technical processes can be revealed with the help of known methods of thermodynamics. The calculation provides process-specific irreversibility profiles as the basis for a comparative process analysis. Based on this, methods can be found, of how a circuit with the objective of an efficiency increase can be modified (optimization of structure). In the following, the GuD-Prozess (gas and steam process) and the GDT-Prozess (gas-steam-turbine process) (in American writing known as STIG-process) are investigated correspondingly and the causes of a reduced efficiency of the GDT-process are shown.