熱力循環於低溫熱源回收之系統分析

Analysis of Thermodynamic Cycle for Low Grade Heat Recovery

李鈺堂(Yu-Tang Lee)

指導教授 ： 劉耀先

國立交通大學/工學院/機械工程系所/碩士(2020年)

摘要

有機朗肯循環(Organic Rankine Cycle, ORC)是國內普遍用於低溫回收廢熱之技術，但因其循環特性限制了系統之取熱量。三邊閃蒸循環(Trilateral Flash Cycle, TFC)因其不變相之熱交換過程使得熱源能被有效的利用，但因變相之膨脹過程導致系統產生體積變化率過大之問題，因此，此循環尚未被商用化。部分蒸發循環(Partially Evaporating Cycle, PEC)因流體部分蒸發使其膨脹機之體積變化率之問題可以得到解決，因實體操作機組之乾度控制難易，此技術之相關研究較少。
　　本文利用熱力學定率分析三種循環用於80、110、140⁰C的低溫熱源條件，在循環系統之取熱元件，利用觀察熱傳-溫度圖中的夾點溫度差(Pinch point temperature difference, PPTD)之方式找尋系統之最佳操作點，在熱功轉換元件之部分，TFC及PEC為雙相流膨脹，使用了經驗公式以反映工作流體之實際狀態，分析R245fa、R134a、R236fa及R1233zd四種工作流體系統之性能表現，其中在110⁰C的熱源條件下，ORC、TFC、PEC三循環的有最高發電量的工作流體皆為R236fa，發電量依序為61.34、86.09、87.56kW。

關鍵字

有機朗肯循環 ； 三邊閃蒸循環 ； 部分蒸發循環 ； 低溫廢熱回收

並列摘要

Organic Rankine Cycle (ORC) is a commonly used technology which has a limitation in heat recovery due to its characteristic. In Trilateral Flash Cycle (TFC), the heat absorption is more effective because the heat transfer process is employed without phase change. However, the two-phase expansion causes greater volume ratio than the conventional cycle. Therefore, TFC has not been commercialized. In the cycle, the fluid is evaporated partially to resolve the high volume ratio problem, and it is referred as Partially Evaporating Cycle (PEC). There are relatively few references since the quality in the practical system is not easy to control.
　In this study, a model is established which is based on the thermodynamic equations to analyze the three cycles under the different heat source conditions of 80,110 and 140⁰C. The Pinch Point Temperature Difference (PPTD) analysis is applied to find the optimal operation point in the heat exchanger. In the thermal energy conversion process, TFC and PEC use variable-phase turbine to model the two-phase expander with the empirical formula to estimate the practical state of the working fluid.
　There are four different working fluids (R245fa、R134a、R236fa and R1233zd) to analyze the system performance. Among these working fluids, R236fa has the highest net power performance in all cycles (ORC, TFC and PEC) under the heat source of 110⁰C. The net power outputs are 61.34, 86.09 and 87.56kW for ORC, TFC and PEC, respectively.

並列關鍵字

Organic Rankine Cycle ； Trilateral Flash Cycle ； Partially Evaporating Cycle ； low grade heat recovery

參考文獻

[1] 李毓仁, "蒸汽壓降節能發電與餘(廢)熱再利用," 2016.

[2] D. Olsen, Y. Abdelouadoud, P. Liem, and B. Wellig, "The role of pinch analysis for industrial ORC integration," Energy Procedia, vol. 129, pp. 74-81, 2017.

[3] I. K. Smith, "Development of the trilateral flash cycle system: Part 1: fundamental considerations," Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power Energy Procedia, vol. 207, no. 3, pp. 179-194, 1993.

[4] S. Lecompte, M. van den Broek, and M. De Paepe, "Thermodynamic analysis of the partially evaporating trilateral cycle," in 2nd International Seminar on ORC Power Systems (ASME Organic Rankine Cycle), 2013.

[5] C. Forman, I. K. Muritala, R. Pardemann, and B. Meyer, "Estimating the global waste heat potential," Renewable Sustainable Energy Reviews, vol. 57, pp. 1568-1579, 2016.