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  • 學位論文

模擬與優化生質氣化爐及廢熱回收熱電效應

Modeling and Optimization of Biomass Gasifier with Waste Heat Recovery via Thermoelectric Effect

指導教授 : 馬小康

摘要


基於石化燃料在世界上蘊藏量有限,為此世界各國都在研究開發替代能源。其中包含風能、太陽能、氫能、洋流潮汐能,以及本文所要探討的生質燃料能。由於前述幾種能量均需要特殊的設備與大量的資金,唯獨固定床式固態生質燃料氣化爐是簡易及方便組裝。可應用在以農業廢棄物為主之生質燃料的農村地區。本文利用火場動態模擬器(Fire Dynamics Simulator, FDS) 程式模擬氣化爐內生質燃料之氣化過程,並以此設計一具改良之下引式氣化爐。為提昇整體系統的能源利用,故另外設計排氣通道計算其表面各處溫度以評估貼上熱電片模組(Thermoelectric generator,TEG)後的廢熱回收效能。改良之下引式氣化爐在當量比(ER)為0.3時氣化爐有最佳操作狀況,而空氣滲入氣化爐內的量應少於排氣流量的5%。此時熱值可達5.71MJ/m3 且氫氣產生濃度為26.53 vol%。當初始水份含量為11.18%時所測到的產氣效率(cold gas efficiency, CGE)為66.85%,此值亦落在65.07%到70.44%的計算範圍內。另生質燃料之初始水分含量介於10%至20%之間時氣化效果較佳。實驗量測單片熱電模組最佳效率是在144℃溫差、負荷在1Ω 和 5Ω下最大電壓可達1.33V 和 1.83V,單位面積電功率為857W/m2。綜觀整個實驗與計算的結果,FDS程式可有效的模擬和分析氣化爐內的氣化性能,並據此改善與增進氣化爐的氣化效率。

並列摘要


Based on fossil fuels in the world have limited, and usage keeps increase in the present there are quick to shorten its serviceable life. For this tendency, all countries are research and development in alternative energy sources, which includes wind energy, solar energy, hydrogen energy, ocean currents, tides, and the biofuels of this article discussion. Due to the front mention different kinds of alternative energy development would require special equipment and need to spend a great deal of money, but solid biomass fuels fixed-bed gasifier would easy to assemble and construct. It can be promoted the application of biomass fuel of agriculture wastes in local rural area. Computational Fluid Dynamic (CFD) modeling applications of the biomass gasification process help to optimize the gasifier. This study aims to investigate the impact of several physical parameters on the behavior of gasification in a fixed-bed downdraft gasifier. To that end, the study presents a comparison of the results computed using the Fire Dynamics Simulator (FDS) model with the experimental results of biomass gasification. Therefore, different sets of simulations and experiments have been performed to examine the effects of initial moisture content, equivalence ratio, high heating value (HHV), and cold gas efficiency (CGE). At the optimum operation, the equivalence rate is 0.3, the HHV can reach 5.71 MJ/m3, and the produced hydrogen concentration is 26.53 vol%. For an initial moisture content of 11.18%, the measured CGE is 66.85%, which is within the range of 65.07% to 70.44%. In general, the initial moisture content of the rice husks is suggested in between 10% to 20%. Meanwhile FDS is also application on biomass gasifier venting duct temperature distribution for investigated searching the best position of the modules to enhance the system thermal efficiency. The electrical characteristic of TEG modules at temperature difference 140℃, the maximum voltage can reach 1.33V and 1.83V at 1Ω and 5Ω respectively, however the output power attain 1.37W is higher than cooling pump power waste 0.45W, and the TEG power per unit area can reach 857W/m2. The overall results indicate that the FDS model can effectively simulate and analyze gasification performance inside the gasifier, and the performance of an improved downdraft gasifier system (IDGS) is improved by higher cold gas efficiency.

並列關鍵字

Gasification Downdraft gasifier Biomass FDS TEG

參考文獻


91. 行政院農業委員會農糧署,農業統計年報,2012
39. Ma, H. K, Chen, B. R, Chen, S. W., Wang, M. Y, Shen, C. H, and Hsu, H. W. (2010) “Environmental impact study and life cycle assessment of a coal-petroleum coke gasification process,” Poster Session. 33rd International Symposium on Combustion Beijing China, 2-6 August 2010
10. Basu P., (2006) “Combustion and gasification in fluidized beds,” London: Taylor & Francis Group, CRC Press.
13. Vervaeke P, Tack FMG, Navez F, Martin J, Verloo MG, Lust N., (2006) “Fate of heavy metals during fixed bed downdraft gasification of willow wood harvested from contaminated sites,” Biomass Bioenergy; 30, 58–65.
14. Li, X. T., Grace, J. R., Lim, C. J., Watkinson, A. P., Chen, H. P. and Kim, J. R., (2004) “Biomass gasification in a circulating fluidized bed,” Biomass Bioenergy., 26, 171-193.

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