A Rapid Wet-Dry State Conversion Method of the Ultra-Supercritical Coal-Fired Power Plant by Optimizing the Recirculation Water Control Strategy

Abstract Switching between wet and dry states occurs frequently when the ultra-supercritical coal-fired power plant operates between 15% and 30% rated load. How to keep wet-state operation stable and switching between wet and dry states rapidly becomes an increasing concern. This study established a detailed dynamic model of a 660MW ultra-supercritical coal-fired power plant, including the boiler recirculation system in low-load. During the state conversion process, the boiler components’ safe operation limitations were also considered as boundary conditions. Based on the developed model, the change trends of the key parameters were simulated when the wet-state operation and the energy distribution characteristics were analyzed during the conversion process. The results show that the temperature of separated recirculation water is greater than that of feedwater before converging, which has great potential to shorten the conversion time. The control scheme of recirculation water was revised by reconstructing the curve between the water level of the separator storage tank and the opening of the recirculation valve. The subcooling degree of feedwater entering the water wall decreased by regulating the recirculation of separated water on time and reasonably. The duration required for saturation decreased considerably with a constant water flow rate. By implementing the optimized control scheme, the operating mode switches from wet to dry in advance, and the corresponding unit load can decrease from 24.5% to 23.1% rated load. Based on the boiler components’ safe operation, the state-conversion time can be shortened by 30% at most. This research will guide the low-load flexibility and safe operation optimization.