Developing off-design model of Yazd integrated solar combined cycle for analyzing environmental benefits of using solar energy instead of supplementary firing

An integrated solar combined cycle (ISCC) is analyzed at "off-design" operating conditions. Using the principles of thermodynamics heat and mass transfer a computer code is developed in FORTRAN programming language to simulate the system’s hourly performance under steady state conditions. Three scenarios are considered for the study. In the first one, only the combined cycle (CC) is studied. In the second scenario, two solar heat exchangers are added to the system (ISCC) to produce some extra steam fed to the steam turbine for more power production. In the third one, as that of the ISCC scenario, a supplementary firing is used instead of solar heat exchangers to produce the same power. The main performance parameters are calculated for the hourly variation of solar direct normal irradiation intensity (DNI) and ambient air temperature for analyzing environmental benefits of using solar energy instead of supplementary firing. Results show that the contribution of solar energy in the annual produced power by the ISCC scenario is 75.14 GWh, which is 2.1% of the whole. In addition, it is found that using solar energy leads to an annual reduction of 36.13 Kton in the produced CO2 and an annual fuel saving of 3.76 ton.