基于动态透平效率的有机朗肯循环性能分析及优化

PERFORMANCE ANALYSIS AND OPTIMIZATION OF ORGANIC RANKINE CYCLE BASED ON DYNAMIC TURBINE EFFICIENCY

常规有机朗肯循环(ORC)中透平效率多假设为定值,而实际上透平效率因工质种类和运行参数的不同而有较大差异。因此,采用向心透平效率计算模型,将动态透平效率与ORC系统耦合,分析透平效率随蒸发温度与冷凝温度的变化规律,比较固定透平效率与动态透平效率ORC系统热效率的差异。综合考虑热力性与经济性,采用多目标优化算法,对固定透平效率与动态透平效率ORC系统进行工质筛选及参数优化,并对优化结果进行分析比较。结果表明:透平效率随蒸发温度的下降或者冷凝温度升高而增大;不同工质及不同蒸发冷凝温度条件下,透平效率差异较大,最大达0.148。固定透平效率ORC系统与动态透平效率ORC系统的热效率随蒸发温度的变化规律有较大差异,尤其在高蒸发温度区间更为明显。对于固定透平效率ORC系统,R245ca和R236ea为最佳工质;而对于动态透平效率ORC系统,R114为最佳工质。在引入动态透平效率前后,各工质的最佳蒸发温度与最佳冷凝温度也有较大变化。

Turbine efficiency is generally assumed to be a constant value in the conventional organic Rankine cycle(ORC). A turbine efficiency varies with the type of working fluids and the operating parameters. Therefore,a calculation model of the turbine efficiency is presented and the dynamic turbine efficiency is coupled with ORC system. The variation of the turbine efficiency with evaporation temperature and condensation temperature were analyzed,and thermal efficiency of ORC system with constant turbine efficiency and dynamic turbine efficiency were compared. Considering thermodynamic and economic performances,multi-objective algorithm was adopted to select the optimal working fluid and determine the operating parameters for constant turbine efficiency ORC system and dynamic turbine efficiency ORC system,and the optimal results were compared and analyzed. The results show that the turbine efficiency increases with the decrement of evaporation temperature or the increment of condensation temperature. Turbine efficiency is different for different working fluids and operating parameters,the maximum difference value is 0.148. There is significant difference of thermal efficiency between constant turbine efficiency ORC and dynamic turbine efficiency ORC,which is more obvious in high evaporation temperature range. For constant turbine efficiency ORC system,R245 ca and R236 ea are the optimal working fluids,while for dynamic turbine efficiency ORC system,R114 is the optimal working fluid. The optimal evaporation and condensation temperature changed a lot after the introduction of dynamic turbine efficiency.