Enhancing the flexibility and efficiency of a double-reheat coal-fired power unit by optimizing the steam temperature control: From simulation to application

Flexibility enhancement is crucial for thermal power plants to assist the power grid in accommodating the high penetration of intermittent renewable power. In this study, a new scheme for controlling the steam temperatures of a double-reheat coal-fired power unit is proposed. The scheme uses the leading signal correction of the low -temperature reheater for the control loop regulating the dampers fixed in the fuel gas ducts of the boiler. The scheme was tested using a dynamic model and applied to an in-service double-reheat coal-fired power plant. The results show that both flexibility and efficiency were enhanced when the new control scheme was adopted. The quantity of spray water for the secondary reheat steam could be reduced by 10 %-50 % during the peak-shaving transients with a load cycling rate in the range of 1 %-4 % rated power per minute. The average coal consumption rate decreased by 0.8-1.9 g kW(-1)h(-1), which accounted for 0.29 %-0.69 % of the thermal efficiency of the power plant. The variation trends of the reheat steam temperatures became smooth, and the maximal measured metal temperature decreased by 12 ?. The results can guide the control optimization of modern peak -shaving power plants.