Energy consumption characteristics and energy saving potential of thermal power plants under ultra-low power load ratio conditions

The operational flexibility of thermal power plants should be enhanced to accommodate the high penetration of photovoltaic and wind power within the power grid. The energy efficiency deteriorates heavily when thermal power plants operate under ultra-low power load ratio conditions, which will increase the carbon emissions of the low-carbon power system. To achieve the energy saving under ultra-low power load ratio condition, the CFPP's (coal-fired power plant) off-design condition models were developed, and the thermal system regulation with additional losses of the CFPP operates under below 30 % power load ratio condition was simulated. Then, influences of the degradation factors on the energy consumption characteristics under ultra-low power load ratio condition were evaluated. Moreover, the carbon emission rate of power generation considering the renewable power accommodation was evaluated. Results show the degradations of turbines' internal efficiencies are the main source of internal losses, and the degradation of boiler's efficiency and the increase of the auxiliary power ratio are the main source of external losses. The total carbon emission rate of power generation decreases by 21.98 g/(kW h) with the power load ratio of CFPP decreasing from 30 % to 20 % due to the increased accommodation of renewable power. Finally, energy saving potential evaluations under ultra-low power load ratio conditions were conducted. The net coal consumption rate is 298.56 g/(kW h) and 522.39 g/(kW h) when the thermal power plant operates under 100 % and 20 % power load ratio conditions respectively. The maximal energy saving potential of b_net under ultra-low power load condition are 87.25, 29.47, 25.05, 2.33 and 1.05 g/(kW h), for the degradation of isentropic efficiency of turbine, the degradation of boiler's efficiency, the increase of auxiliary power ratio, the additional drainage water of the boiler and the switching action of BFPT's supply steam, respectively.