4. Coupling of AP1000 with fossil-fueled superheater
The thermal efficiency of AP1000, which is about 30.23%, is quite
low compared to the conventional thermal power plants. As
mentioned earlier, this low thermal efficiency can be improved by
using the superheater to increase the generated steam temperature.
There are two schemes considered in this work for such
combination. The first scheme couples the AP1000 Rankine cycle
with a generic gas turbine cycle. In this coupling scheme, the
exhaust gas from a gas turbine is used to superheat the steam. The
gas turbine SGT5-4000 F designed by Siemens is used for this study
as a reference due to considerable experience of its use in CCGT. The
exhaust temperature of this gas turbine is 577 C and its exhaust
gas flow rate is 692 kg/s at full power [10]. The properties of air
needed for the thermodynamic analysis were taken from Lemmon
et al. [11].
The other coupling scheme considered is by using a combustor
fueled by natural gas. In this coupling scheme, the steam can reach
higher temperature than in the scheme which uses the gas turbines
exhaust gas. However, the superheated steam temperature is
limited by the existing steam turbine maximum operating temperature
take as 600 C in this study. The steam cycle flow diagram
of AP1000 with the conventional superheater is displayed in Fig. 2.
The results of the thermodynamic analysis of both coupling
schemes are shown in Table 3. The total cycle efficiency was
calculated from Eq. (9) while the fossil fuel cycle efficiency was
calculated from Eq. (10)