| 摘要: | 近年隨著工業的發展，人類對能源的需求與日俱增，節能裝置以及再生能源的開發已是全世界關注的議題。有機朗肯循環(organic Rankine cycle, ORC)是用於低溫熱源發電的技術，用於工業廢熱回收、太陽能以及地熱發電等等領域。工廠排放的廢熱低於230°C被定義為低階廢熱，因無法有效再次運用於製程通常被排放於環境。本文針對低階廢熱回收之有機朗肯循環系統進行熱力分析，分別使用R134a、R1234yf、R227ea、R245fa、丙烷作為工作流體進行系統最大熱效率及淨輸出功的分析。於三個熱源溫度100°C、150°C、200°C以及四個狹點溫差5°C、10°C、15°C、20°C的條件下以迭代的方式計算熱傳量，分別利用蒸發壓力及蒸發溫度探討其對系統性能的影響並找出最佳參數。結果顯示當熱源溫度200°C時R245fa具有最高的淨輸出功505.5kW以及系統熱效率15%。以硬焊型板式熱交換器作為熱交換器模型，根據上述條件所得之最佳點計算總傳熱面積並計算熱交換器建設成本；結果表明熱源溫度越高所需的建設成本越低，在熱源溫度150°C、200°C時使用丙烷作為工作流體時具有最低的建設成本。;As industry develops, there is an increasing demand on energy. The development of energy-saving devices and renewable energy have been emerging issues around the world. Organic Rankine cycle, ORC, is a technique to generate power from low temperature heat sources. ORC is used in recycling industrial waste heat, solar energy and geothermal power generation. Waste heat below 230°C is called low-grade waste heat. Low-grade waste heat cannot be efficiently reused in process, so it is usually exhausted into the environment. In this research, we perform thermodynamic analysis on low-grade waste heat recycling ORC systems. R134a,R1234yf, R227ea, R245fa, and Propane are used as working fluids and their max system thermal efficiency and net power output is calculated. We discuss the effect of different evaporation pressure and evaporation temperature to the system performance with different conditions of three heat source temperatures, 100°C, 150°C,and 200°C, and four pinch point temperature differences, 5°C,10°C,15°C, and20°C by iteration methods to find the optimum parameters. The result shows that R245fa has the highest net work output of 505.5kW and system thermal efficiency of 15% at heat source temperature of 200°C. In this research, we use brazed plate heat exchangers as example. We use the optimum conditions to calculate the total heat transfer area and evaluate the constructing costs of the heat exchanger. It is found that the higher heat source temperature, the lower cost it needs. When the propane is used as working fluid, the lowest cost can be achieved with heat source temperature at 150°C、200°C. |
