生質燃料與燃煤混燒應用於實廠鍋爐之可行性

Feasibility Study on Application of Co-firing of Biofuel with Coal in Full-scale Boiler

張瑋仁(Wei-Ren Chang)

指導教授 ： 張慶源

國立臺灣大學/工學院/環境工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02682

摘要

隨能源的需求日益增加，導致化石燃料殆盡、溫室效應日漸明顯，燃煤也造成空氣污染等問題，故尋找再生能源以代替傳統的化石燃料應為當務之急。生質能是有利於環境的再生能源，因生質能具有碳中和原理(carbon neutrality)，可有效降低溫室氣體的淨排放量，有利於環境永續發展。
本研究針對稻稈、木料與其焙燒後之生質炭及生活廢棄物中的生質纖維，與煤於實廠連續式鍋爐燃燒系統中進行混燒，探討生質物混燒所產生之氣狀、粒狀污染物及灰分與生質物種類、混燒比例之間之變化趨勢，包含生質物焙燒前後於燃燒行為之差異，並且觀察生質物混燒之燃燒情形與鍋爐之蒸汽流量變化。此外，以實驗室批次式高溫爐進行不同比例之混燒試驗，以提供更多生質燃料應用之資料。實廠連續混燒為固定熱值進料量及固定空氣流量。實驗室批次混燒則為固定熱值，進氣為理論空氣量。
結果顯示木料熱值較高，且灰分量較低為較適合用來作為生質物混燒之燃料。焙燒轉製生質炭可提升生質物熱值，且成分較均質，有助於混燒，此外焙燒可破壞生質物表面羥基而較趨近疏水性，有利於生質物之貯存、運輸。實廠連續式混燒之煙道氣組成中，添加生質纖維造成CO、NOx及SO2排放量(濃度)明顯增加；整體來說，添加其他生質物，會導致CO排放量增加，NOx及SO2排放量減少，且隨生質物添加比例而有CO更增加或NOx及SO2更減少的趨勢。實驗室批次規模混燒受生質物添加比例之影響則趨勢有些差異，NOx排放量於低添加比例(< 20%)時差異不大，而較高添加比例及單獨生質物燃燒時，NOx排放則較明顯增加；SO2排放量則隨添加比例之增加而減少。添加生質物造成排氣中細微顆粒比例增加，尤其是PM2.5比例明顯增加。產生之固體產物中，添加生質物後，飛灰中氯、鉀及鈉含量大幅增加，且灰分殘留有大量之未燃碳。

關鍵字

生質物混燒 ； 實廠鍋爐 ； 煙道氣 ； PM2.5 ； 灰分

並列摘要

Because of increasing demand of energy, fossil fuels are gradually depleted while greenhouse effect rised. Combustion of coal also causes air pollution. Therefore, it is urgent to look for renewable energies as alternatives for substituting traditional fossil fuels. With the characteristics of carbon neutrality, bioenergy can reduce net emissions of greenhouse gases, matching the appeal of environmental sustainability.
In this study, rice straw, wood, their biochars after torrefaction and biofiber extracted from municipal solid waste (MSW) were co-fired separately with coal in a continuous full-scale boiler system, which was conducted at fixed input rate of heating value of solid feed as well as fixed air flow rate. Effects of system parameters on the gaseous and particulate pollutions and ash were examined. These include biomass type, blending ratio of biomass (RBL) for co-firing and combustion conditions. The combustion behavior and the production of steam during biomass co-firing were also elucidated. Furthermore, a batch lab-scale co-firing was conducted to provide more information for the use of biofuel. It was operated with fixed heating value of solid feed while with theoretic air demand.
Results indicated that wood, which posses high heating value while less amount of ash, is suitable for co-firing with coal. Torrefaction can increase the heating value of biomass and homogenize its property, being beneficial to co-firing. Besides, torrefaction can decompose hydroxyl group of biomass, which makes biomass tending to posses hydrophobicity. This in turn helps the storage and transportation of biomass. The addition of biofiber increases the emissions (concentratins) of CO, NOx, and SO2 in full-scale co-firing tests. Generally, adding the other biomass except biofiber with coal would increase the emission of CO, while decrease those of NOx and SO2, with the extent of effect increasing with RBL. Regarding the lab-scale tests which may have combustion characteristics different from those of full-scale tests, the emission of NOx exhibits little variation at lower RBL, while increases with RBL at conditions with higher RBL and sole biomass. As for the emission of SO2 in lab-scale co-firing, it shows the same decreasing tendency with increasing RBL as in full-scale co-firing. The fine particles especially PM2.5 in the flue gases increase with addition of biomass. The addition of biomass also results in the increase of chlorine, potassium and sodium in the fly ash, and of unburned carbon in the bottom ash.

並列關鍵字

Biomass co-firing ； full-scale boiler ； flue gas ； PM2.5 ； ash

參考文獻

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