利用廢熱回收提升進氣溫度對沼氣發電的影響研究

Abstract

本論文在台中台糖養豬場測試小型30kW沼氣發電機，收集資料以供長時間沼氣發電使用。本論文分為三大部分，第一部分，使用73%甲烷濃度的沼氣，測試在不同沼氣供給量與不同過剩空氣比時的發電狀況;第二部分，將此結果與計畫第一年的60%甲烷濃度實驗數據比較，觀察不同甲烷濃度(60%與73%)對發電效能之影響。第三部分，利用廢熱回收系統加熱進氣，測試不同進氣溫度對沼氣發電的影響。實驗結果顯示，使用目前73%之甲烷濃度沼氣，在沼氣供給量為260L/min時，引擎最佳發電量為26.7kW；在沼氣供給量為200L/min時擁有最佳熱效率27%和最佳甲烷使用率96.03%。提升甲烷濃度，發電功率隨著甲烷濃度提升而提升，除了當過剩空氣比λ<0.85時。對熱效能而言，在燃料量較稀的狀況下(λ>0.95)可讓熱效能提升；但在燃料量較濃的狀況下(λ＜0.95)，提升甲烷濃度對熱效能沒有好的影響。提升近氣溫度，在過剩空氣比約大於1.3後有較明顯的影響。

This research used a 30kW-generator in Taiwan Sugar swine farm in Taichung to collect data for the long-term electricity generation. This study is an continous effort of Lin’s work [3], which carried out the electricity generation project by using 60% methane concentration of biogas in a small swine farm in Miaoli. This experimental study, using 73% methane concentration of biogas, consisted of three parts. Firstly, investigate the effect of biogas supply rate together with the different excess air ratios on generator performance. Secondly, make a comparison with Lin’s results. Finally, apply a waste heat recovery system to preheat the inlet gas under different temperatures and analyze the preheating influence on the generator performance. In the present study, the maximum power generation is 26.7kW occurred at biogas flow rate of 260L/min, whereas the maximum thermal efficiency and methane consumption ratio are 27% and 96.03% at biogas flow rate of 200L/min. The power generation in the present work is higher than one in Lin’s one [3], except the region around λ (excess air ratio) < 0.85. However, the thermal efficiency increases with the increasing methane concentration just in the region of λ>0.95, while on the relatively rich side (λ<0.95), there is no benefit. The improvement by preheating inlet gas is obvious when excess air ratio is relatively high, such as λ>1.3.