Energy, Exergy analysis and optimization of solar thermal power plant with adding heat and water recovery system

Abstract

Water scarcity and environmental impacts of the steam power plants blow down, is one of the growing concerns. During the evaporation of water in the steam cycle of the power plant, most of the impurities of water and vapor do not evaporate and remain in the boiler. By increasing the concentration of these impurities, boiler tubes are corroded. To adjust the concentration of these impurities, some of the water in the cycle is drained, which is called blowdown. Blowdown water has a high exergy content that is going to be wasted. In this study, by recovering a great amount of contained water and heat of power plant blow down, the entering wastewater to the environment is decreased and the total power of power plant is increased. This recovery system includes Evaporator and Vacuum pump. In this system a vacuum is created in the vaccum tank by vacuum pump which causes the water to evaporate and is injected into the steam cycle. The results show that by adding the recovery system, the amount of drained wastewater from the plant to the surrounding environment decreases from 3.118 kg/s to 1.799 kg/s. After Energy and Exergy analysis, it is shown that the output power increases by 0.53%, and the exergy returns from 20.73% to 20.84%. Also, the effect of the Evaporator vacuum on the output power and the amount of recovered water indicates that with the reduction of the Evaporator vaccum pressure, the amount of the output power is reduced, but instead due to further evaporation of the water, the amount of recovered water in the Evaporator will increase. After Energy and Exergy analysis, the results are optimized by the Genetic Algorithm. The inlet temperature of HPT1, inlet pressure of HPT1, outlet pressure from each turbine, and pinch point for the first heat exchanger are considered as decision variables. Optimization results show that by obtaining suitable decisions variable amounts, output power is increased from 34.01 MW to 34.92 MW. For evaluating the results on the power plant operation, SEGS VI power plant in the US (California) is used.