Research on influence of steam extraction parameters and operation load on operational flexibility of coal-fired power plant

Abstract The operational flexibility of coal-fired power plant is very important for the integration of large-scale renewable energy to the grid. In order to increase the operational flexibility of coal-fired power plant, a 600 MW subcritical coal-fired power plant was selected as research example to analyze the influence of steam extraction parameters and operation load by simulation. A novel main steam extraction system was proposed to adjust the power output under the low load period. The sensible and latent heat of the extracted steam was stored in molten salts and phase change materials, respectively, during the load reduction process. While the stored heat was reused again to heat the feed water and condensate water during the load raising process. The 50% rated load (300.03 MW) of the unit was used as the research benchmark to further adjust the load. The results show that the proposed steam extraction system can improve the operational flexibility of coal-fired power plant. The power output can be reduced to 204.51 MW from 300.03 MW when the main steam extraction mass flow rate is 250 t/h during the load reduction process. The sensible heat storage power factor and the operation load of the unit can affect the power output increment of coal-fired power plant during the load raising process. Under the condition of the maximal sensible heat storage power factor is 0.2462, the power output can be increased to 325.47 MW from 300.03 MW when the bypassed feed water mass flow rate of 251 t/h was heated by the stored heat during the load raising process. Using such operation model, the coal-fired power plant can achieve the maximum deep peak shaving time of 8.4 h/d, and its equivalent thermal efficiency is increased by 2.28%. With the same stored thermal energy to heat the bypassed feed water of 308.65 t/h, the power output can be increased to 394.2 MW from 360.07 MW (60% rated load) at the same sensible heat storage power factor of 0.2462 during the load raising process, and the coal-fired power plant can achieve the maximum deep peak shaving time of 9.86 h/d with its equivalent thermal efficiency increase of 2.55%. The results show that the proposed steam extraction method can make the unit operate in the lowest stable load and provide a wider renewable energy access space below the minimum stable load. The research provides a theoretical guidance for the flexibility design of coal-fired power plant, especially suitable for the large-scale renewable energy access to the grid in China.