Optimization Of Thermodynamic System Structure And Parameter Configuration For Coal-fired Power Stations

Thermodynamic system is the core of a coal-fired power station.It plays a decisive role to the thermal efficiency of power plants.Appropriate system structures and optimal system parameters are the keys of reducing energy consumption for coal-fired power stations.In this dissertation,thermodynamic system structure integration and apparatus interface parameters optimization for conventional coal-fired power stations and complementary coupled power stations were researched based on system engineering theories and methods.A modified dynamic adaptive particle swarm optimization was presented for compensating the weaknesses of current thermodynamic system optimization methods.The descriptions of evolution speed factor and aggregation degree factor were improved,and the control strategy of inertia weight was renovated.The modified algorithm was applied in many classical test functions and practical examples.Results show that the convergence rate and solving accuracy of the proposed algorithm are improved significantly.The modified algorithm is simple,universal and suitable for solving the complex problem of thermodynamic system parameter optimization.Taking the double reheat unit as object of study,the optimal arrangement of outer steam coolers and the optimum potential of some vital parameters including feedwater enthalpy rise distribution,feedwater temperature,reheat steam pressure,the number of feedwater heaters and main steam parameters were analyzed.Calculations of some examples show that main steam parameters have a larger influence on thermal efficiency than other parameters.When adding the number of feedwater heaters,low pressure heater is a better choice.Optimum feedwater temperature increases with the increase of main steam pressure.The changes of main steam temperature and reheat steam temperature have opposite effects on optimum feedwater temperature.Outer steam coolers can enhance feedwater temperature and decrease irreversible losses of boiler.That is the main reason that the unit fuel specific consumption decrease.When adding one outer steam cooler,it's better to place the outer steam cooler at the first extraction pipe after the first reheat.When adding two outer steam coolers,it's better to place them in a series at the first extraction pipes after the twice reheats.A new integration schema was designed for coal-fired power plants with post-combustion CO₂ capture.In this schema,the exhaust steam pressure of intermediate pressure cylinder?IP?was reduced to match the carbon capture system,and the waste heat of overhead condenser was recycled to replace the last low pressure heater.After parameters optimization,thermal efficiency of the integration system was greatly improved.A modified thermal system structure including an extraction backpressure turbine named carbon capture turbine?CCT?was presented for the double reheat power plant with post-combustion CO₂ capture.This design can efficiently avoid the excessive exergy losses caused by the extraction steam superheat and the mismatch of IP exhaust and reboiler.The integrated approaches utilizing solar thermal to replace extraction steam were optimized and analysed for solar and coal-fired hybrid power plants.Calculations of examples show that the greater replaced steam flow and energy level,the higher thermal efficiency that the unit can obtain.Several green-field power station thermodynamic system with solar thermal,coal-fired,and CO₂ capture integrated were presented.Through comparisons and analysis,the schema utilizing CCT exhaust to supply CO₂ capture and solar thermal to heat feedwater makes more sense than the schema utilizing solar thermal to supply CO₂ capture.