2.3 Steam cycle
The steam pressure and the pinch point play a crucial role in determining the gas–steam tem­perature profiles. The pinch and approach points are selected. Moreover, the exit gas temperature from the economizer cannot be arbitrarily assumed [39]. These temperature profiles serve to evaluate the steam genera­tion since the principle inputs to HRSG are the gas temperature outlet (\(T_{g4}\)) and the mass flow (\({\dot{m}}_{g}\)). With the solar radiation varying during the day, the exhaust gas flow rate/ temperature condi­tions to the steam are evaluated iteratively. A subprogram is used to interpolate between the tabulated values of enthalpy and entropy for water/steam at each point including the steam quality x . The temperature profiles shown in Fig. 2 are determined based on the data given in Table 7 and the definitions of pinch point \({\text{ΔTpp}=T}_{g5^{\prime}}-T_{\text{sat}}\)and approach point \({\text{ΔTap}=T}_{\text{sat}}-T_{w7}\).
Table 7. Pinch and approach points [39]