Flexibility and efficiency enhancement for double-reheat coal-fired power plants by control optimization considering boiler heat storage

Double reheat is a potential technique to increase the efficiency of coal-fired power plants. Large penetration of renewable power requires coal-fired power plants to operate flexibly. The thermal inertia of a double-reheat boiler is extremely high due to its complicated flow, strong coupling and numerous devices, which seriously restrict the operational flexibility of double-reheat coal-fired power plants. In this study, dynamic simulation models and temperature control systems of a double-reheat boiler are developed via GSE software and then validated to understand the heat storage change law. An improved control model considering heat storage changes is proposed. The flexibility of original and improved control strategies is compared. It turns out that steam temperatures in the boiler system with the original control exceed the allowable ranges when the load cycling rate is 1.5% Pe0 min⁻¹. By contrast, steam temperatures in the boiler system with the improved control remain within the allowable ranges when the load cycling rate is 3.0% Pe0 min⁻¹. The response time with the improved control is shorter than that with the original control. This study is expected to provide a detailed reference for improving the flexibility of double-reheat power plants.