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A novel cascade energy utilization to improve efficiency of double reheat cycle

Fan, Chenghao, Pei, Dongsheng, Wei, Hongqi
Energy conversion and management 2018 v.171 pp. 1388-1396
air, economic investment, exergy, feasibility studies, flue gas, heat recovery, hemorrhage, income, models, power plants, steam, temperature
Large mean terminal temperature difference of conventional regenerative air heater and high superheat degree of bleeding steams are the bottleneck of conventional steam rankine cycle, which limits the cycle for further efficiency improvement. In this study, a state-of-the-art double reheat power plant is selected as the reference cycle. A novel cycle covering steam, water and air process is invented based on the systematic combination of flue gas heat recovery and bleeding steam cascade energy utilization.Thermodynamic model is developed to analyze the performance improvement and exergy method is applied to validate and identify the cycle thermodynamic efficiency advantage. Simulation result presents novel cycle net heat rate is improved by 104.8 kJ/kWh and cycle net efficiency is increased by 0.61%. Feed water pump turbine inlet steam connection optimization accounts for 14 kJ/kWh net heat rate benefits for the novel cycle. Feasibility study proves it is possible to implement the novel cycle in a newly planned power plant. Based on techno-economic analysis, it is found that the total investment capital of novel cycle is 7.44 million US dollars and net annual revenue is 0.59 million US dollars compared with the reference cycle. Static capital investment paid back period is expected within 15 years in a newly planned power plant.