Research On System Optimization Of 1000MW Double Reheat Coal-fired Power Unit

As day by day energy demand increases and fossil fuels are going to be decreased.Along with that,environmental protection is a serious concern for the survival of human species and nature.Therefore improving energy conservation efficiency of coal fired power units is very urgent to sustain coal fired power generation and at the same time to protect both people and the environment.Compared with a single reheat coal-fired power generation,the double reheat coal-fired power generation shows better thermal and economic performances.However,the large mean terminal temperature difference of conventional air preheater and high superheat degree of extraction steams in double reheat coal-fired power generation systems increase the exergy losses of heat transfer processes and limit the cycle efficiency for further improvement.In order to solve these problems,this study presents two new double reheat systems based on the systematic combination of flue gas heat recovery and extraction steam cascade energy utilization in the first stage and in the second stage optimized system 3 by further optimization of system 1.Based on the first and second laws of thermodynamics,the energy balance model and exergy balance model of coal-fired power unit are established,which would provide the theoretical basis for system optimization.EBSILON Professional software is implemented to perform simulation work and thermal performances of two new double reheat systems are analyzed and compared with reference system.The results show that,the exergy losses of heat transfer processes are significantly reduced and heat rate of the two new systems are improved through the system optimization.The power generation efficiencies of new system 1 and system 2 are improved by 1.08%and 1.04%points respectively,and the standard coal consumption rates are reduced by 5.71 g/kWh and 5.52 g/kWh respectively compared with reference system.The performances of both new systems are better than that of reference system.However,system 1 is superior to system 2.On the basis of system 1,further optimized system 3 is presented,and performance characteristics are analyzed.The power generation efficiency of optimized system 3 is further improved by 0.36%points and the standard coal consumption rate is reduced by 1.86 g/kWh compared with system 1.Thermodynamic analyses under partial load conditions are also presented.The results reveal that the performances of system 1 and system 2 are superior to that of the reference system under low load conditions.The standard coal consumption rates of new systems under different loads are 1.33-5.71 g/kWh lower than that of the reference system,Whereas the standard coal consumption rate of optimized system 3 is further reduced by 1.68-4.34 g/kWh under low load conditions compared with system 1.In order to reveal the actual benefits,lastly,specific techno-economic analysis is conducted.The result shows that the net annual revenues of system 1 and system 2 are increased by 2.04 and 1.94 million USD respectively compared with reference system.However,the net annual revenue of optimized system 3 is further increased by 0.17 million USD compared with system 1,which indicates that system 3 is not only superior in thermodynamic performances but also superior in techno-economic performances to all other systems.This research may provide an effective method for the optimization of double reheat coal-fired power units.