Thermo-economic performance analyses and comparison of two turbine layouts for organic Rankine cycles with dual-pressure evaporation

Multi-pressure evaporation organic Rankine cycle involves two or more evaporation processes with different pressures. Compared to the conventional single-pressure evaporation type, the multi-pressure evaporation type can significantly reduce the exergy loss in the endothermic process, and its widely used in the heat-work conversion of low and medium temperature (<350 °C) thermal energy is promising. The turbine layout of the multi-pressure evaporation type has two typical forms: the separate turbine layout and induction turbine layout. Turbines in two layouts may exhibit considerable differences in the geometric and operating parameters. Selecting a suitable turbine layout is crucial to improve the system thermo-economic performance. While, the thermo-economic performance variations and comparison of two turbine layouts remain indeterminate for various operating conditions. This study was based on the one-dimensional efficiency model and purchased equipment cost model of the radial-flow turbine. The thermo-economic performance of two turbine layouts was analyzed and compared for nine pure organic fluids. Effects of two-stage evaporation pressures on the thermo-economic performance of two turbine layouts were also studied. Results show that the total power output of the induction turbine layout can increase by 0.3-5.4%, and its specific investment cost is lower for most of operating conditions and the maximum decrement is 34.2%, compared to the separate turbine layout. The decrement in the specific investment cost decreases as the high-stage evaporation pressure increases, and it generally increases as the low-stage evaporation pressure increases. Moreover, the total power output is larger, the thermo-economic advantage of the induction turbine layout is generally greater.