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分别以净发电效率和系统火用效率最大为目标,通过热力学分析,确定了两种不同余热类型发电系统候选工质的选择原则:热流量恒定余热应选择临界温度较高的工质,初温和质量流量恒定的余热应选择临界温度较低的工质。并定义了相应余热类型最佳工质主要评价参数α和β,数值大的工质性能较优。以两级烟气余热发电系统为例,采用Aspen Plus软件模拟计算验证理论分析结论。结果表明,第一级系统不同工质净功、参数α和火用损失随蒸发温度变化的趋势与理论分析结果完全吻合;第二级系统不同工质的净功、参数β和火用效率随蒸发温度变化趋势与理论分析结果也完全吻合。这表明,本研究提出的工质优选原则和方法是正确、可行的。
Based on the goal of net generation efficiency and maximum system exergy efficiency respectively, the principle of selecting working medium for two different types of power generation systems with different waste heat is determined through thermodynamic analysis. For the constant residual heat of heat flux, the working fluid with higher critical temperature should be selected. The constant mass flow of residual heat should be selected low temperature working fluid. And defines the main evaluation parameters α and β of the best working fluid of the corresponding residual heat type, and the working fluid with large value has better performance. Taking two-stage flue gas heat recovery power generation system as an example, the theory analysis conclusion is verified by Aspen Plus software simulation. The results show that the tendency of the net work, the parameter α and the exergy loss with the evaporation temperature of the first-stage system are completely consistent with the theoretical analysis results. The net work, the parameter β and the exergy efficiency of the second-stage system with different working fluids The trend of evaporation temperature is in good agreement with the theoretical analysis. This shows that the principles and methods of working fluid optimization proposed in this study are correct and feasible.