螺桿膨脹機有機朗肯循環性能分析與實驗研究

Performance Analyses and Experimental Studies on Screw-Expander ORCs for Low grade Heat to Power

徐菘蔚(Hsu, Sung Wei)

指導教授 ： 蔣小偉

國立清華大學/工學院/動力機械工程學系/博士(2015年)

https://doi.org/10.6843/NTHU.2015.00449

摘要

有機朗肯循環系統(ORC)為中低溫熱能發電技術中最簡單且最具經濟效益的技術。一般建議裝置容量低於300 kW的ORC系統採用螺桿膨脹機最為核心動力元件。本研究針對螺桿ORC進行理論分析與實驗驗證。藉由次臨界與穿臨界系統建立之系統優化模式，本研究針對不同熱源進行工作流體篩選與系統優化，並針對系統中工作流體泵與膨脹機效率進行敏感度分析，研究顯示此二元件之效率對穿臨界ORC系統的影響遠高於對次臨界ORC系統之影響。本研究針對不同熱源溫度範圍開發兩組次臨界ORC系統，分別為應用於60~85°C熱水型熱源的20-kW R134a-ORC系統與應用於90~105°C熱水型熱源的50-kW R245fa-ORC系統，並藉由實驗探討熱源變動與冷源變動對於系統以及關鍵元件效率的影響。實驗證實螺桿型ORC系統具有寬廣的操作範圍與穩定的性能表現，後續系統性能提升除了由動力元件效率提升外，亦可朝降低蒸發器壓損著眼。本研究亦針對螺桿膨脹機之作功模式建立理論分析模式探討系統離點操作對膨脹機性能之影響，包含過膨脹與膨脹不足等離點狀態，以及入口壓力對膨脹機性能的影響。透過實驗，理論推導獲得良好的驗證。

關鍵字

有機朗肯循環 ； 次臨界 ； 穿臨界 ； 螺桿膨脹機 ； 系統優化 ； 過膨脹 ； 膨脹不足 ； 離點性能

並列摘要

To date, ORC is the most efficient and economical approach for the recovery of low-to-medium heat to power. In general, a volumetric-type screw-expander is selected as the ORC’s engine core for power capacity less than 300 kW due to its superior performance and competitive cost. This thesis theoretically and experimentally studies on the system characteristics and performance behaviors of screw-expander ORCs.
Steady-state models of the ORC’s components are theoretically developed and experimentally validated. Then, the model of the ORC system is established to predict its performance. In view of practical and economical applications of an ORC, a trade-offs analysis between cycle efficiency and amount of power output is performed for system optimization under limited heat source for subcritical ORCs and trans-critical ORCs.
Two sets of ORCs are designed and developed, and a series of performance tests are done to explore the characteristics of these two ORC systems. (1)20kW screw-expander ORC: using R134a as working fluid, converted the heat of 60~85°C hot water into power. (2) 50kW screw-expander ORC: using R245fa as working fluid, converted the heat of 90~105°C hot water into power.
A theoretical expansion model of screw expander is developed and compared with experimental data. The achieved performance of these two ORCs are promising, with expander efficiency of 72.5% and cycle efficiencies higher than the typical efficiencies reported for the considered temperature range. The ORCs can be used to exploit the low temperature heat, as low as 60°C, with high performance which predict their wide application and potential energy saving.

並列關鍵字

organic Rankine cycle ； subcritical ； trans-critical ； screw expander ； system optimizatoin ； over-expansion ； under-expansion ； off design performance

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