Method for operating a solar thermal power system with an economizer recirculation line

A method of operating a solar thermal power system, comprising:

• providing a solar receiver;
• with a thermal energy storage arrangement, circulating a thermal energy storage fluid through the solar receiver to store thermal energy;
• operating a multistage steam turbine on variable pressure steam generated from feedwater supplied from a feedwater supply via the thermal energy storage fluid;
• providing a steam generator arrangement comprising an economizer section, an evaporator section and a superheater section that utilizes heat of the thermal energy storage fluid at an entrance of the evaporator section to generate and supply the variable pressure steam to the superheater section and further to the multistage steam turbine;
• providing a recirculation line around the economizer section, the recirculation line having an inlet and an outlet, the inlet of the recirculation line disposed at one of an outlet from the economizer section or the evaporator section, the outlet of the recirculation line disposed at an inlet of the feedwater to the economizer, and the recirculation line configured directly between the inlet and the outlet of the recirculation line such that all heated water directed into the inlet of the recirculation line is discharged at the outlet of the recirculation line;
• adjusting recirculation through the recirculation line to increase efficiency of the thermal power system by:
• increasing flow of heated water through the recirculation line to the economizer white reducing temperature of the feedwater supplied from the feedwater supply to the economizer;
• and
• maintaining temperature of the thermal energy storage fluid leaving the economizer at a lowest level for safe operation above a freezing temperature of the thermal energy storage fluid.