| 摘要: | 本研究利用實驗室規模流體化床氣化爐，以空氣混合蒸氣作為載氣，控制空氣當量比(Equivalence ratio, ER)為0.3及氣化操作溫度為700、800、900℃條件，探討改變蒸氣/生質物比(steam/biomass ratio, S/B)為0、0.75、1.5 (wt.%/wt.%) 之條件下，對乾咖啡渣蒸氣氣化之產能效率。此外，本研究亦嘗試探討自濕空氣氣化之產能效率，實際規劃以模場規模之流體化床氣化爐，以氣化溫度800℃及當量比0.3之條件，評估濕咖啡渣(40%及60%含水率)空氣氣化之產能效率。前述氣化反應之產氣組成、產氣熱值及冷燃氣效率，為本研究評估產能效率之重要指標。
乾咖啡渣蒸氣氣化反應結果顯示，在蒸氣/生質物比為零，氣化溫度從700℃增加至900℃時，產氣平均氫氣濃度從1.95 vol.%提升至6.74 vol.%，一氧化碳平均濃度亦從8.86 vol.%提升至13.0 vol.%。可見提高氣化溫度有助於Boudouard反應、焦油裂化(Cracking)及水氣(Water-gas)反應等吸熱反應作用，有效提升產氣熱值與冷燃氣效率。其中在未通入蒸氣及氣化溫度900℃條件下，產氣熱值及冷燃氣效率分別為3.76 MJ/Nm3及22.47%。當蒸氣/生質物比增加至1.5，氣化溫度從700℃增加至900℃時，產氣平均氫氣濃度從2.04 vol.%提升至8.60 vol.%，一氧化碳平均濃度亦從9.56 vol.%提升至11.8 vol.%，平均產氣熱值從2.23 MJ/Nm3增加至3.89 MJ/Nm3，冷燃氣效率則從11.28%提升至25.08%。根據前述結果可知，蒸氣氣化反應主要以水氣轉移反應(Water-gas shift)為主，產氣組成可達到提升氫氣濃度之效果。
根據咖啡渣自濕氣化實驗結果顯示，當濕咖啡渣乾燥為含水率0%時，平均氫氣濃度為9.05 vol.%，一氧化碳濃度為12.82 vol.%，而當濕咖啡渣之含水率為60%時，平均氫氣濃度提升至13.1 vol.%，一氧化碳則降低為7.89 vol.%，平均產氣熱值則由5.14 MJ/Nm3提升至5.72 MJ/Nm3，對應之冷燃氣效率則分別為52.7%及39.0%。當濕咖啡渣之含水率控制在40%時，冷燃氣效率最高可達55.5%。由此可知，濕咖啡渣之含水率，可提供水蒸氣作為氣化反應物質，並有效促進水氣轉移反應(CO + H2O ? CO2 + H2)之發生，進而提升氫氣濃度，提高產氣熱值以及產氣之冷燃氣效率。
整體而言，本研究成果已成功驗證咖啡渣自濕空氣氣化轉換為合成氣之可行性，同時促進水氣轉移反應提升其產能效率，相關研究結果可提供未來高含水率生質物之熱處理技術應用與選擇之參考。
;In this study, the coffee residues were successfully gasified using a laboratory-scale fluidized bed gasifier with air/steam mixture as the carrier gas at equivalence ratio (ER) 0.3, varied operation temperatures (700, 800, and 900°C), and steam-to-biomass (S/B) ratio (0, 0.75, and 1.5). This research also tried to explore the energy production efficiency of wet coffee residues by air gasification. The experimental conditions included a gasification temperature of 800°C and an equivalence ratio of 0.3 in wet coffee residues (40% and 60% moisture content) using a pilot-scale fluidized bed gasifier. The gas composition, lower heating value (LHV), and cold gas efficiency (CGE) of the gasification reaction are essential indicators for evaluating energy production efficiency in this study.
The experimental results revealed that H2 and CO concentration in the producer gas increases from 1.95-6.74 vol.% and 8.86-13.0 vol.% with an increase in temperature without steam, respectively. It implied that a higher temperature could increase the producer gas LHV and CGE, resulting in endothermic reactions, such as Boudouard, tar cracking, and water-gas. The LHV and the CGE of the producer gas generated at a gasification temperature of 900°C are 3.76 MJ/Nm3 and 22.47%, respectively. When the S/B ratio increases to 1.5 and the gasification temperature increases from 700°C to 900°C, the average producer gas H2 and CO concentration increases from 2.04 vol.% to 8.60 vol.% and from 9.56 vol.% to 11.8 vol.%, respectively. Meanwhile, the average producer gas LHV and CGE increased from 2.23 MJ/Nm3 to 3.89 MJ/Nm3 and from 11.28% to 25.08%, respectively. According to the previous results, the steam gasification reaction takes the water-gas shift reaction as the leading factor, and the gas production composition can increase the H2 concentration.
According to the results of the self-moisture gasification, the average H2 concentration was increased from 9.05 vol.% to 13.1 vol.% with the coffee residue moisture content increased from 0% to 60%. However, the CO concentration was decreased from 12.82 vol.% to 7.89 vol.% with an increase in moisture content. Overall, the average LHV of producer gas increases from 5.14 MJ/Nm3 to 5.72 MJ/Nm3 with the moisture content increasing. The maximum CGE was 55.5% occurred at the moisture content of 40%. It implied that the moisture content of wet coffee residues could provide steam as a gasification reaction medium and effectively promote the water-gas shift reaction (CO + H2O ? CO2 + H2) and increase the H2 concentration, as well the producer gas LHV and the CGE.
This research has successfully verified that steam gasification and self-moisture air gasification were considerable in converting coffee residues to syngas and increasing energy production. The relevant research results can also provide references for future steam gasification and thermal treatment of high moisture content biomass. |
