全球約有20%~50%能量以熱能形式排放至環境，其中250℃以下低溫工業餘熱可用能低不易利用，但排放量大且成本低，有機朗肯循環(ORC)系統已可有效利用此熱能發電，而若考量到熱傳性能以及環境影響，超臨界二氧化碳(S-CO2)朗肯循環具有相當高的發展潛力。
　　本研究分析S-CO2朗肯循環與R134a、R245fa ORC在熱源溫度100℃和150℃之下的性能差異。考量壓力對性能和成本影響，以最大系統輸出功作為設計點。S-CO2流體密度高可大幅縮減膨脹機尺寸，且溫度曲線與熱源較相符，能更有效利用熱源能量。儘管S-CO2朗肯循環的高操作壓力使液幫浦耗功大，每單位質量工作流體所能產生的系統輸出功低於ORC，但CO2成本相對低許多，因此可藉由增加CO2質量流率來提升性能，並同時保有機組尺寸優勢。
　　本研究也與漢力能源科技公司之商用ORC機組進行比較，以了解S-CO2朗肯循環與ORC的市場競爭性，根據初步評估結果，S-CO2朗肯循環適用熱源溫度約為90℃~150℃，且在此溫度範圍下溫度越高性能越好，膨脹機入口壓力則限制在140 bar以下，然而若欲將本系統商品化，仍需進行相關實驗做更進一步分析。

About 20% ~ 50% energy is released to environment in the form of waste heat. The waste heat below 250℃ is difficult to recover due to its low thermal energy, but it has large amount and low fuel cost. ORC systems can efficiently convert this low temperature waste heat to electricity. Recently, due to the better heat transfer and low environmental impacts, S-CO2 Rankine cycle has shown pretty good potential in this field.
A comparative study of S-CO2 Rankine cycle with R134a and R245fa ORC under 100℃ and 150℃ heat source is included in this study. Considering the pressure effect on performance and costs, the parameter settings for S-CO2 Rankine cycle are targeted on maximum power output. S-CO2 has better temperature matching with heat source so it can utilize heat source energy more efficiently. Besides, the high fluid density of S-CO2 can greatly reduce power unit size. Despite that the net power output per unit mass of working fluid in S-CO2 Rankine cycle is lower than that in ORCs, we can increase the mass flow rate of CO2 to improve the power output because of the very low fluid cost of CO2 compared to organic fluids.
In order to realize the competence of S-CO2 Rankine cycle in real market, a comparative study with ORCs from Han Power is also included. Heat source temperature between 90℃~150℃ and inlet pressure of expander under 140 bar are recommended for S-CO2 Rankine cycle. But to commercialize S-CO2 Rankine cycle system, further studies and experiments on real equipment cost and component size are required.

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