Liquid level expansion in steam drum during transient operation of molten-salt-steam-generator-system

To balance unstable renewable energies, a molten-salt-energy-storage-system is integrated with a coal-fired power plant (CFPP) to increase its flexibility. In a 350 MW CFPP with an ultra-fast load ramp rate of 6% Pe/min, the molten-salt-steam-generator-system (MSSG) should supply 3% Pe/min independently. The correspondingly thermal load variation rate of the MSSG reaches 23% Pt/min, which impose fast transients on the drum level of the natural circulation steam generator. The transient thermal-hydraulic model of the MSSG is established in ASYST, by which the dynamic characteristics of the MSSG is simulated. It was found that the MSSG demonstrated the capability to meet the objective provided the liquid level expansion problem is solved. The drum level is dominated by the temporal-spatial void fraction distribution in MSSG, which is influenced by the flashing effect and the thermal load. The flashing effect contribution follows parabola evolution, reaching up to 35.6%. The influence of the thermal load is related to the thermal inertia of the natural circulation, in which the driving force always lags behind the thermal load. The proposed equivalent volume method overcomes the limitations of the classical design method, and solved the level expansion problem, providing critical guidelines for design and operation of steam generator.