Experimental analysis of pre-startup, normal operation, and accident conditions for a megawatt-scale molten salt steam generation system

MW-level pilot platform was derived from 100 MW solar thermal project, including preheater, evaporator, superheater and molten salt heater. Experiments were carried out under system pre-start, normal, and accident conditions. Results show that the steam/water side before the superheater must be preheated to operational temperature before introducing molten salt in natural circulation mode, as initial salt introduction causes significant thermal shocks to the tank walls. When the molten salt flow increases from 1 to 2 kg/s and temperature rises from 425 to 480 °C, the thermal efficiency of the heat exchangers decreases due to increased heat loss and worsening boiling conditions. Efficiency ranges for the preheater, evaporator, and superheater are 40–55 %, 80–95 %, and 50–65 %, respectively. Preheater and evaporator exhibit minimal thermal resistance (∼0.0004 °C/W). While 90 % and 70 % of the total thermal resistance of the superheater and preheater are on the steam and molten salt sides, respectively. Failures in the molten salt heater, pump shutdown, and safety valve release significantly impact the superheater but have minimal effect on the preheater and evaporator. After heater failure, the temperature on the molten salt side of the superheater decreases by 1–2 °C/min, while the superheated steam temperature drops by 8–9 °C/min. When combined with pump stoppage, steam pressure decreases by 0.4 MPa/min, with the temperature dropping as fast as 16 °C/min. Overpressure range and prediction model were obtained based on measured data and statistical analysis. Findings will provide a theoretical basis for the design and operation of 100 MW class SGS.