3. Thermodynamic and Economic Analysis of a Gas Turbine Set Coupled with a Turboexpander in a Hierarchical Gas–Gas System

Analysing costs of electricity and heat production in hierarchical power plants and gas-steam [1] cogeneration plants (also referred to as Combined Cycle Power Plants) turns out that the capital component is a very significant factor of those costs. Investment outlays on a steam part using the Clausius-Rankine cycle consist approx. 40% of the outlays on gas-steam system, when the gas turbine (both gas and steam turbine have here more general meaning and cover proper turbines and all the necessary auxiliary devices) requires only 30% of those outlays. In addition, installation-construction work making up the remaining 30% of outlays, are mainly (over 2/3) outlays on the steam part-related installation. Consequently, unit (per unit of installed electric power) “turnkey” investment outlays on the so-called simple systems, i.e. power plants and combined heat and power plants using only the Joule-Brayton cycle (the so-called Simple Cycle Power Plants) are more than twice lower as compared to the outlays on combined systems and make up approx, 45% of those outlays [2].