Dynamic Characteristics and Control Strategy Optimization of a 1000 MW Lignite-Fired Power Unit Integrated With Primary Air Heater

Abstract Lignite is a kind of low rank coals with abundant reserves, and it is cost-effective for power plants. However, the moisture content is about 30% to 60% for the lignite, and the water carried by the raw lignite is dried in the pulverization system, which will consume much energy. Therefore, high temperature should be maintained for the primary air of the lignite-fired power plants, especially when the power plant operates under low power ratio or with low temperature feed air. In this study, a 1000 MW lignite-fired power system integrated with a primary air heater is proposed and analyzed. In the primary air heater, the low temperature reheated steam is extracted from the boiler to heat the primary air after the air preheater. The integration of primary air heater makes the lignite-fired power system be more complex, which will influence the operational flexibility of the power plant. Therefore, dynamic models of steam turbines and the boiler with waste heat recovery system were developed in this study. The transient characteristics of the unit under load cycling conditions and primary frequency modulation processes were analyzed. Then, control strategy of the primary air heater of turbine and boiler were enhanced based on the simulation results. The results show that the temperature of primary air can be increased by 51–69 °C by the additional air preheater, and the primary frequency modulation capacity can be improved by 8 MW at 50% power load ratio during primary frequency modulation process.