Research On Evaluation Method Of Solar Contribution In Solar-aided Coal-fired Power Generation System

Solar aided(coal fired)power generation(SAPG)is the synergy of solar thermal energy and fossil power plant technologies by using solar thermal energy to replace extraction steam to preheat feed water.SAPG combines environmental benefits of the former and large capacity,high efficiency and reliability of the latter.However,there are no appropriate criteria for evaluating the thermal performance of the system now.In this paper,a new evaluation method of SAPG system is proposed based on the exergy analysis and the characteristics of exergy flows crossing the boundary of the system.In the established evaluation method,a new ideal cycle is constructed in the perspective of external heat sources,and the difference of solar proportion among the exergy input,work output and exergy output in the same subsystem is considered.With the evaluation method,the contribution proportion of solar energy in a SAPG system can be determined.To illustrate applications of the new method,a parabolic trough solar field aided 600 MW coalfired power generation system is discussed as a case study to prove the practicality and rationality of the method.Besides,the difference of solar contribution between this method and other methods has been discussed.The result shows that,the result obtained from the new method is lower,but do not has the difference in magnitude.Finally,this new evaluation method is applied to back-pressure optimizations for both steam turbine net power and solar contribution under different DNI,ambient temperature,and load.The result shows that,to back-pressure optimizations,the effect of DNI is lower that ambient temperature,and the optimum back-pressure under different loads is mainly determined by ambient temperature.Besides,back-pressure optimizations for steam turbine net power is similar to that for solar contribution.The novelty of this paper is:(1)A new ideal cycle is constructed in the perspective of external heat sources.Based on this,the functional relationship between solar work output and steam pressure under both ideal condition and actual systems is deduced.(2)A novel evaluation method of SAPG system is proposed.(3)The difference of solar proportion among exergy input,exergy output and work output of the same subsystem is considered.