Design Optimization Of Solar-aided Coal-fired Power Generation System Under Whole Work Conditions

Due to the excessive consumption of fossil fuels and their adverse effects on the environment,more and more countries are increasing the proportion of renewable energy in energy system.Concentrating solar power(CSP)generation technology,which can provide efficient solar energy utilization and large-scale power generation,is currently developing faster than any other type of renewable energy,and is considered as one of the most promising forms of renewable energy and an important technology for future global clean energy supply.However,compared with conventional fossil fuels power generation,CSP still faces the problems of low energy efficiency,unstable power generation and high cost.As a result,solar-aided coal-fired power generation(SAPG)technology came into being,and attracted continuous attention.Solar-aided coal-fired power generation system,by integrating solar energy heat into conventional coal-fired units,produces electricity while saving fuel consumption.It combines the environmental protection of the former,and the stability and high efficiency of the later,embodies the synergistic power generation effect of conventional fossil fuels and renewable energy,and is an advanced power production technology.Based on this background,and relying on the national key basic research and development plan,the research of solar-aided coal-fired power generation system is carried out.In this paper we establish the model of the solar-aided coal-fired power generation system,and conducted research on the energy conversion characteristic of each subsystem,the general integration optimization method,and design optimizaiton under whole work conditions of the integration system.Firstly,the energy conversion processes of heliostat field,receiver and thermal power subsystem are studied,and the efficiency model of each subsystem is established in detail,then the energy conversion characteristics,the different requirements for design parameters,and the consistency and opposition of each subsystem in the system optimization process are revealed.Then the complete solar-aided coal-fired power generation system model is established.In the heliostat field optimization part,several new methods for calculation and optimization of the heliostat field are proposed,which are used for the topographic gradient effect evaluation,spatial optimization,heliostats pedestals height optimization,rationality evaluation of the field layout,and also a special genetic algorithm toolbox is developed used for heliostat field optimization,ultimately the efficient and reasonable heliostat field is obtained.Secondly,considering the diversity and complexity of equipments of solar-aided coal-fired power generation system,a general system integration optimization method is developed,which is used to simulate all schemes of different integration locations and heat distributions,and determine the optimal integration mode under any work condition.Then,based on a real 600 MW supercritical coal-fired power plant,a reheat supercritical SAPG system is built,and based on a real 660 MW ultra-supercritical coal-fired power plant,a double reheat ultra-supercritical SAPG system is built.And then based on the proposed general system integration optimization method,the optimal integration schemes of the SAPG system under 16 typical work conditions are calculated.The optimization results reveal the general rules of the SAPG system integration,i.e.,under the work conditions of relative high heliostat field power,the collected solar heat should be integrated into the highest pressure feedwater heater as a priority.While the optimization results also reveal the special cases,i.e.,under the work conditions of relative low heliostat field power and relative high turbine power,the collected solar heat should be integrated into the first two highest pressure feedwater heaters in a certain proportion,instead of fully integrated into the highest pressure feedwater heater.Finally,based on the complete solar-aided coal-fired power generation system model,and the proposed general system integration optimization method,the SAPG system design optimization under whole work conditions is carried out.The initial investment of solar collection system and net solar electric generation are traded as the two objectives of SAPG system,and optimized by multi-objective optimization algorithm.In a typical day of Delingha,considering the simultaneous variations of meteorological data and steam turbine load,Pareto optimal solution set of design parameters of the collector system is optimized,and the optimal integration modes under all working conditions of the corresponding solution set are obtained,which provide a reference for the design of SAPG system.