利用沼氣發電供應養豬場用電之需求實驗研究

Abstract

本研究以商業套裝軟體CFD-ACE+ 模擬微型氣渦輪機引擎(WREN-MW54)在保持外型結構，但更換原廠預設的液態Jet A1燃料為較低熱值的氣態甲烷混合氣燃料時，其燃燒室的燃燒流場。所得之數值模擬計算結果著重於經燃燒反應後，熱傳效應所造成之襯筒壁高溫與燃燒室出口溫度與實驗數據比較之探討。 本研究模擬不同濃度的氣態甲烷混合氣燃料，並分別在各組的甲烷燃料中混入四種不同二氧化碳質量濃度(10%，20%，30%，40%)來做為稀釋效應的研究。因使用甲烷燃料純度的不同，渦輪機轉速的上限也各有不同。渦輪機轉速的設定範圍在使用90%，80%，70%，與60%甲烷燃料時，分別是40000~50000，40000~65000，40000~80000，40000~90000與轉/分。此外，本研究也比較一步和四步兩種化學反應機制之差異。 由模擬結果可以得知：(1) 燃燒室出口溫度在使用固定燃料濃度時會隨著轉速上升而降低；而在比較不同濃度燃料的相同轉速情況下，溫度則會隨著燃料濃度的上升而降低 (2) 在定轉速的條件下，燃燒室出口均速隨著燃料濃度上升而降低 (3) 使用一步與四步化學反應預測之燃燒室出口溫度與實驗數據相比，四步與實驗結果較相近 (4) 觀察暫態之結果可得知燃燒反應在13秒達到穩定，與穩態之誤差為1.3% (5) 主燃燒區的渦流在3.5秒發展完全，內部流場在13秒達到穩定，燃燒室出口最大流速與穩態之誤差為4.2%。最後也提出幾點建議，可供未來研究工作的改進與延伸。

This study carried out the 30kW-generator experiments on a small biogas plant in a swine farm to collect data to serve as a preliminary study for constructing a 300-KW power plant of a bigger scale biogas plant in the near future. Firstly, the effects of fuel supply rate together with corresponding different excess air ratio on power generation were studied. Secondly, the effect of oxygen-enriched combustion for engine was tested. Finally, a heat exchanger was installed to recover waste heat from the engine exhaust gas to increase the usage of the energy. The economic benefits were also estimated by the data obtained by this research. The experimental results showed that the optimum biogas flow rate to the present engine is around 240 to 260L/min, and the maximum power generation, the corresponding thermal efficiency and the percentage of consumed CH4 is 26.8kW, 28.7% and 95.4%, respectively, at biogas supply rate of 260L/min. With 3% oxygen-enriched air, the maximum power generation, thermal efficiency and the percentage of consumed CH4 are increased up to 28.2kW, 30.2% and 100% approximately for 260 L/min, and the engine can operate normally at a lower limiting fuel supply rate at 220 L/min. The heat exchanger can recover 923kJ/min of heat leading to an overall efficiency of 47.3% at the biogas supply rate of 240 L/min. With the total swine population (around 4.3 million heads) from the farm scale of over 1000 heads of pigs in Taiwan, the estimation based on data from this study shows the economic benefits of using biogas: Per year, electricity generation of 2.67 × 108 kWhe (corresponding to electricity charge saving of 800 million NT$), nature gas charge saving of 260 million and carbon dioxide reduction of 170 thousand tons.