Full-process Optimization of Reheat Desuperheating Spray Water for a 600 MW Ultra-supercritical Unit under Heat-supply Coupling Conditions

Excessive reheat desuperheating spray water leads to effective enthalpy drop loss in reheat steam, reduces cycle efficiency, and increases specific coal consumption. Taking the #5 and #6 units (600 MW ultra-supercritical, single-reheat) of Yueyang Power Plant Phase III as objects, a full-process optimization approach was proposed to address the frequent reheat steam temperature disturbances and high spray water dependency under heat-supply coupling and rapid load variation conditions. The approach comprises four modules: equipment defect rectification, coordinated operating parameter optimization, heat-supply/load coordination, and data-driven closed-loop management. A dual-index evaluation system was established using both the specific reheat spray water consumption (kg/MWh) and the baseline drift rate (kg/(MWh·d)) to characterize the overall spray water level and the slow-varying fouling-induced bias, respectively. Field results showed that the combined decreased from 16.15 kg/MWh to 3.38 kg/MWh (approximately 79%), and decreased from +0.058 to +0.011 kg/(MWh·d) (approximately 81%), corresponding to an estimated specific coal consumption improvement of approximately 0.39 g/kWh. The method is replicable for similar coal-fired units under heat-supply coupling conditions.