Performance analysis of tower solar aided coal-fired power plant with thermal energy storage

Abstract

• An innovative TSACPG system with thermal energy storage is proposed. • Solar energy is used to heat reheat steam and boiler feed water simultaneously. • Thermal performances of the system under different loads are explored. • Solar contribution and CO 2 reduction in the system are discussed. • Economic evaluation of the system with different configurations are studied. A novel tower solar aided coal-fired power generation (TSACPG) system with thermal energy storage is proposed in this paper. Based on the principle of energy grade matching and cascade utilization, the high-temperature solar energy is used to heat the first and second reheat steam extracted from the boiler and the low-temperature solar energy is used to heat the boiler feed water. The maximum steam extraction mass flow rates of the boiler under different load rates are obtained and the thermal performances are also analyzed. The results show that the maximum steam extraction mass flow rates from the first and second reheat part of boiler are 69.7 kg/s and 37 kg/s in 100 %THA (Turbine Heat Acceptance), 78.7 kg/s and 37 kg/s in 90 %THA, 81 kg/s and 31.4 kg/s in 75 %THA, 76.3 kg/s and 31 kg/s in 60 %THA, 68.2 kg/s and 31.2 kg/s in 50 %THA load, respectively. And the standard coal consumption rates can be reduced by 39.85 g/kWh, 39.47 g/kWh, 38.08 g/kWh, 35.50 g/kWh and 35.25 g/kWh, respectively. Both the boiler thermal efficiency and overall thermal efficiency of the TSACPG system descend sightly and the boiler exergy efficiency ascends. With the decline of the load, the solar-to-electricity efficiency, the power output and the proportion of solar power generation descend gradually. And they can reach up to 28.62%, 120.90 MW and 18.32% in 100 %THA load, respectively. The economic performance analysis of the TSACPG system is carried out. The system configuration and investment corresponding to different typical days, different thermal energy storage hours and capacities are considered. The payback times and the levelized costs of electricity of the solar field in different DNI level regions are analyzed. The results show that these two evaluation indices are the lowest in high level DNI region and they are on the contrary in low level DNI region. As for the environmental protection, the CO 2 emission rates are reduced by 69.26 g/kWh in 100 %THA, 68.61 g/kWh in 90 %THA, 66.19 g/kWh in 75 %THA, 61.69 g/kWh in 60 %THA and 61.26 g/kWh in 50 %THA load, respectively. The maximum annual CO 2 emission can be reduced about 526739.55 tons. The renewable energy and traditional fossil energy are integrated organically in this study and the low-carbon transformation of coal-fired power generation system is further promoted. The study also contributes to the realization of both the carbon peak and the carbon neutralization.