Thermoenvironomic optimization of gas turbine cycles with air preheat

In optimization of thermodynamic cycles, it is appropriate for the economic and environmental aspects to be considered simultaneously. The sum of the fuel and investment cost flowrates is known as thermoeconomic objective function. A new objective function, known as a thermoenvironomic objective function, is obtained by integrating the environmental impacts, which should be defined and expressed in terms of cost, and thermoeconomic objective function. The objective of this paper is to study the effect of air preheater (APH) in the thermodynamic cycles by considering environmental impacts. In order to perform this, four simple thermodynamic cycles are selected and economic and environmental aspects are optimized. All considered thermodynamic cycles produce 30 MW of electricity and two of them, which are cogeneration systems, produce 18 kg/s of saturated steam at 20 bar, too. For optimization of these cycles, a code has been developed in MATLAB based on the real coding and optimal solutions have been obtained. The results show that the existence of APH increases exergetic efficiency of the cycles and the environmental impacts cost flowrate but decreases the total cost flowrate. Also, in the cycles without APH, the optimum values of decision variables corresponding to thermoeconomic and thermoenvironomic objective functions do not change considerably, while in the cycles with APH, they change noticeably.