Modeling and hierarchical energy storage dispatch control of a pulverized coal buffer unit for flexible operation of coal-fired power plants

With the increasing integration of renewable energy, coal-fired power units require higher operational flexibility. However, the delays caused by raw coal grinding and pulverized coal transport in conventional direct fired pulverizing systems limit rapid load response. To address this issue, this study proposes a pulverizing system equipped with a pulverized coal buffer unit, which extends the fuel supply mode from a single direct fired mode to a combined direct fired and storage based mode, thereby reducing fuel supply delay and improving operational flexibility. A nonlinear dynamic model of a 600 MW coal-fired power units with the pulverized coal buffer unit is established, and a two-level pulverized coal energy storage mechanism is developed, where explicit energy storage is represented by the buffer bin level and implicit energy storage is represented by residual pulverized coal inside the coal mill. Based on this model, a hierarchical model predictive control method is designed for pulverizing system energy storage dispatch. The dispatch layer generates the buffer bin level setpoint and primary air command, a dedicated proportional integral derivative controller regulates the buffer bin level, and the model predictive control coordinates key boiler side and turbine side variables to achieve flexible fuel supply. Simulations are conducted under load change rates of 0.5%Pe/min, 1.5%Pe/min, and 2.5%Pe/min. The results show that, at a load change rate of 2.5%Pe/min, compared with the conventional coordinated control method, the proposed method reduces the overshoot of main steam pressure by 7.66% and shortens the settling time by 543s, effectively improving the load response capability and operational flexibility of the unit.